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The CO - H₂ Synthesis at I. G. Farben A.G. - 1949

Dr. H. Zorm
Under the appeciation of
Dr. W. F. Faragher

Office of Military Government for Germany (US)

Foreword to

The CO - H₂ Synthesis

    The reports assembled in this publication were compiled by German technicians of the French occupation zone and represent the part played by I. G. Farben A. G. in the field of CO - H2 synthesis (Volume I).  They will supplement the reports on this subject made under the direction of Professor Dr. Friedrich Martin, former president of the Board Ruhrchemie A. G., Oberhausen-Holten-Ruhr, who brought together under his authority technologists of the Ruhrchemie, Lurgi, Brabag, and Rheinpreussen companies.

    In addition to the CO - H2 synthesis studied at Ludwigshafen, there appear in volume II the report of Dr. Winkler on the possibilities for practical application of his gas producer, and in volume III reports on polymerized gasolines.

    The initiative for this project belongs to Dr. W. F. Faragher, European Chief of the Synthetic Fuels and Lubricants Section of the American Field Intelligence Agency, Technical who with the cooperation of "Institut du Petrole de Paris" effected a Franco-American cooperation in collecting documents indispensable to the progress of science.

    The French team wishes to render him thanks for the energy and understanding he showed in the undertaking and prosecution of this vast project.

Jacques Foucher
Military Government of the French Zone
Enseigne de Vaisseau, Administration Branch
for I. G. Farben A. G. Factories at
Ludwigshafen-Oppau/Rhine

Volume I:

CO - H₂ Synthesis

Table of Contents

      A. The researches on CO - H₂ synthesis in the Gasification Section of the BASF Laboratory from 1925 to 1945 (June 6, 1947 by dr. Duftschmidt).

I.  The development of fused-iron catalysts (according to research by Dr. Lincckh and Dr. Klemm).

II.  The oil-circulation process (on the basis of research by Dr. Duftschmidt).

III.  The high-pressure gas-circulation process for the synthesis of ethyl alcohol from waste gases (on the basis of research by Dr. Linckh and Dr. Klemm).

    Appendix: Fused-iron catalysts for the CO- H₂ synthesis. (Report of Dr. Klemm, dated July 1, 1944).

    B.  Hydrocarbon synthesis from carbon monoxide and hydrogen.  Researches of the Ammonia Laboratory from 1935 to 1944 (by Dr. Arno Scheuermann, June 1947).

    C.  Hydrocarbon synthesis from CO - H₂ with iron catalysts.  Gas circulation process and foam process (by Dr. Michael, July 10, 1947).

Volume II

Winkler Generators

    The historic development of the gasification of fine coal according to the process of Dr. Winkler.

October 1947

Volume III

Polymerized Gasoline

Table of Contents

Report of Dr. Franz Duftschmid on the Researches on the CO - H2 Synthesis with Generator Experiments of the BASF from 1925 to 1945

1. The development of fused-iron catalysts (on the basis of researches by Dr. Eduard Linckh and Dr. Richard Klemm).
2. The oil-circulation process (on the basis of researches by Dr. Franz Duftschmid).
3. The high-pressure gas-circulation process for the synthesis of ethyl alcohol from waste gases (on the basis of researches by Dr. Eduard Linckh and Dr. Richard Klemm).

Appendix:  Fused-iron catalysts for CO - H₂ synthesis (report of Dr. Klemm, July 1, 1944).

                                                                                   Oppau, May 30, 1947.

Low Pressure Division, Oppau
Gasification Experiments Section
Dr. Fritz Winkler

Introduction to

Part I     CO - H₂ Experiments

    Research was conducted at the Badische #nilin- und Soda- Fabrik by Dr. Mittasch and Dr. Pier on the conversion of CO - H₂ to methanol (1921-1922) and by Dr. Karl Hochschwender on the conversion to isobutyl alcohol (1924-1925).  Experiments on the production of hydrocarbons only from CO - H₂, and in particular, of C₂H₄, C₃H₆, and C₄H₈ from CO - H₂ were started in January 1926 at the instance of Dr. Fritz Winkler by his collaborator Dr. Eduard Linckh.  A slight conversion of CO - H₂ to C₂H₄ etc, was found to occur with copper catalysts at ordinary pressure and at 100° C.  On April 1, 1926 Franz Fischer published (for the first time) an article in the Zeitschrift für Brennstoffchemie on the production of oils etc. from CO - H₂ at ordinary pressure with iron and cobalt catalysts.  Furthermore, Linckh discovered that silver, gold, and zinc catalysts act like copper catalysts (French patent 635950, English patent 293185), but that the yields were very small.  In the fall of 1926 he turned to the preparation of oils etc. from CO - H₂ under pressure with fused iron-oxide catalysts.  Linckh investigated more than 1000 catalysts, all in the gas phase under a pressure of 100-200 atmospheres.  Special arrangements of the catalyst in the reactor were tested for the purpose of conducting away the large quantities of heat evolved during the conversion of CO - H₂ to oils.  It was extraordinarily difficult, however, to avoid soot formation on the catalyst in the gas phase under pressure.  The solution of this problem was arrived at by Duftschmid: conversion of CO - H₂ with Linckh's catalyst in its own oil.

    Dr. Klemm conducted experiments on the preparation of ethyl alcohol from CO - H₂ under 200 atmospheres pressure in the gas phase.  He was able to avoid the deposition of carbon on the Linckh catalyst by copper plating a part of the catalyst, by arrangement of the catalyst in a thin bed at the tube wall (the reactor consisted of a bundle of tubes); and by using large quantities of circulating gas.

Dr. Fritz Winkler

The Development of Fused-Iron Catalysts for the CO - H₂ Synthesis

(On the basis of researches by dr. E. Linckh and Dr. R. Klemm)

    In 1925 Dr. F. Winkler brought forward the suggestion of making gaesous olefins from coal or water gas.  To this end Dr. Eduard Linokh had begun to conduct experiments in 1926 for the purpose of producing gaseous hydrocarbons with catalysts, in particular ethylene from water gas.

    At this time there already existed long-established BASF patents dealing with the preparation of liquid hydrocarbons along with oxygen-containing compounds with the aid of catalysts under high pressure.  Orlov was supposed to have obtained gaseous olefins with nickel catalysts.  The initiated experiments were conducted with this report in mind, but the information could not be verified.  However, Dr. Linckh soon succeeded in producing noticeable quantities of gaseous olefins under ordinary pressure and at 100° C. with copper catalysts for the first time.  An increased yield, however, could not be achieved.  The experiments were therefore extended to include iron catalysts.  Substantial quantities of gaseous olefins were thereby obtained under high pressure.  Final gases containing 13 per cent by volume of olefins were supposed to have been obtained.  Later, however, interest reverted to the recovery of liquid hydrocarbons.  As a result of these researches Dr. Linckh succeeded in developing serviceable fused-iron catalysts for the synthesis.  The technique of preparing these catalysts depends almost entirely on the production of the conventional ammonia synthesis catalysts.  Carbonyl iron powder was always employed as the starting material for the preparation of a catalysts.  It is intimately mixed with added substances having a promoting action and melted in water-cooled crucibles with a blast of oxygen.  The resulting molten lumps contain the iron in the form of oxides, principally as Fe₃O₄.  The molten cakes are broken up into suitable particle sizes.

    They are treated with hydrogen to prepare them for the synthesis.  This reaction takes place at temperatures ranging from 450 to 650 degrees.  The reduction temperature, however, can be still further lessoned by the use of high pressure.

    In this manner Dr. Linckh investigated more than 1000 assorted catalysts.  Unfortunately, the detailed results of these researches were lost as a result of the war and of the death of Dr. Linckh toward the end of the war.

    The catalysts covered by German patent 708512, November 14, 1935, French patent 812290, English patent 465668 have remained of lasting value for us. The catalyst identified by Expt. No. 997 became the standard catalyst for all our later technical development researches.

This catalyst is produced by admixing

25 grams of silicon powder

25 grams of titanium oxide

50 grams of potassium permanganate

50 grams of water

to 1 kilogram of iron powder.  In place of patassium permanganate the equivalent amount of manganous oxide, pyrolusite (MnO₂), or manganese powder and potassium hydroxide can be used without impairing the effectiveness of the catalyst.  If these catalysts are treated at 650 degrees, the reaction will proceed rapidly and, on completion of reduction and cooling, will be rather insensitive to air.  However, these catalysts are only sufficiently reactive for the synthesis at pressures of 100 atm. gage and over.  On the other hand, if the reaction is conducted at temperatures ranging from 450 to 500 degrees, the catalysts will develop a reactivity favorable for synthesis at medium pressures ranging from 15 to 25 atm. gage.  However, since the catalysts are markedly pyrophoric, special precautionary measures must be applied in this instance to prevent the catalyst from burning in air.  Transference in the synthesis reactors therefore takes place with exclusion of air in the presence of carbon dioxide, or in case of synthesis, in a liquid medium by soaking or dipping in oil.  Reduction at low temperatures possesses the additional disadvantage of a duration of 5 - 6 days.  The hydrogen is recirculated above the catalysts and is dried before admittance into the reaction vessels.  This drying is advantageously accomplished in a silica gel drying installation.

    Dr. Linckh endeavored to develop the iron catalysts to a point where the synthesis could be conducted at ordinary pressure with a good yield.  He believed that this was achieved by the addition of antimony or arsenic to the iron catalysts.  However, as a result of the war, practical tests on these catalysts were no longer carried out.

    Linckh made the interesting proposal that etched metal disks and the like be employed instead of catalysts (German patent 721359, French patent 805696, English patent 458035).

    The fused iron catalysts were developed further by Dr. Richard Klemm, to be used for a specific purpose, viz., to attain the greatest possible yields of ethyl alcohol.

    It is no longer necessary to abstract these researches at this point because a relevant original report can be appended (see report of Dr. Klemm, July 1, 1944).

The Oil Circulation Process

1.  General Comments on the Oil Circulation Process

    In the synthesis of hydrocarbons from carbon monoxide and hydrogen, large quantities of heat are evolved which must be conducted away from reaction chamber in a suitable manner.

    This problem had heretofore been technically solved in the Fischer-Tropsch process by dividing the catalyst into relatively thin beds and by charging it into narrow tubes and pockets.  The reaction heat is thereby indirectly conducted away by water under pressure.

    The use of iron instead of cobalt catalysts poses greater problems of heat removal because iron catalysts only react at temperatures higher than those of cobalt catalysts, the danger of spontaneous carbon monoxide decomposition consequently becoming appreciably greater.  In addition, the known iron catalysts react principally at elevated pressures thus further promoting formation of methane and carbon monoxide decomposition.

    These considerations led to the development of oil circulation process.  This process (discovered by F. Duftschmidt, E. Linckh and F. Winkler) and developed by the Fritz Winkler experimental team since 1935 at the I. G. Farbenindustrie at Oppau is differentiated from the Fischer-Tropsch process principally by the fact that the quantities of heat evolved in this markedly exothermic reaction are directly taken up and removed by a liquid medium located in the reaction chamber.

    It should be mentioned at this point that a second process was later developed by the I. G. Farbenindustrie at Ludwigshafen by Dr. Michael in which work was also done in the liquid phase with circulation of oil.  This is the so-called foam process, which is most clearly differentiated from the oil circulation process dealt with here, by the fact that finely divided catalyst suspended in a circulating oil is employed in the foam process.  This process was developed in Ludwigshafen since about 1940.  These two processes embody differing viewpoints in still another respect.  The Oppau oil circulation process employs oil evaporation for the removal of the reaction heat and is therefore characterized as a synthesis in a boiling liquid.  The Ludwigshafen foam process, however, substantially features a non-evaporating liquid medium, thereby representing a further development of the principle already proposed in 1928 by the I. G. Farbenindustrie A. G. (M. Pier) of conducting the synthesis in a high-boiling, non-evaporating liquid medium.

    The I. G. Farbenindustrie interests, and in particular the BASF works, immediately obtained the basic rights and also acquired technical leadership in this field by the development of the two processes.

    The present report deals only with the oil circulation process since the foam process has received separate treatment.

    The oil circulation process operates with a fixed granular catalyst.  As a result of the immediate removal of the heat it is possible to do without division of the catalyst into thin beds.  The synthesis reactor consequently acquired a much simpler shape without the necessity of any built-in installations.  In the indirect heat removal process the quantities of heat conducted through the wall of the catalyst chamber per unit of the time are quite limited.  However, this limitation is largely done away with in the direct heat removal method of the oil circulation process.  As a result a greater capacity can be achieved in the oil circulation process with regard to time and reactor space.  Also, power consumption in operating the oil circulation is slight and posseses hardly any importance in determining production costs.

    In 1936 and 1937 the process was developed to a semi-commercial stage (200 liter reactor), and run under high pressure (100 atm. gage).  In 1938 it was developed into a medium pressure process (15-20 atm. gage) and worked out as a two-stage process similar to the Fischer synthesis.  The first stage of the medium pressure process was tested in a 1.5 m³ reactor for 5 months with an output of 9 ton/month.  The second stage was successfully tried for a period of one month in a makeshift 0.2 m³ reactor (unfortunately a complete two-stage pilot plant was unavailable).

    The process was thus proved to be practical and safe.  The robustness of the catalysts is characteristically indicated by an experiment with the afore-mentioned 1.5 m³ reactor in which the catalysts were used without harm after the reactor had been in disuse for two years, the spent catalyst lying in the oil residue of the reactor during this time.

    Fast experimental results, however, justified plans of a reactor height of about 18 meters for large-scale units.  It was also planned to conduct the synthesis in one stage.

2.  The Principle of Heat Removal by Means of Oil

    The quantity of heat evolved during the conversion is computed according to equations

   2 CO + H₂ -------- CH₂ + CO₂ + 46.9 calories

CO + 3 H₂ --------- CH₄ + H₂O (steam) + 48.9 calories

to roughly 4000 calories per kilogram of liquid hydrocarbon produced if it is assumed that the conversion proceeds to 80 per cent according to the first equation with 20 per cent methane formation, i.e., if about 165-170 grams of liquid hydrocarbons are formed, including liquifiable gas, for every 1 m³ of converted CO - H₂, which is the case in the procedure dealt with here.

    The principle of working in the liquid phase consists in collecting this evolved heat by the oil itself and removing it.  This can be accomplished in various ways; by simply conducting away the heat in the heated oil in the form of sensible heat, or by removing it from the reaction chamber by evaporation of the oil in the form of latent heat of evaporation.

    In the first case the liquid medium consists of oil which is not vaporizable under the reaction conditions; in the second case it consists of oil containing vaporizable consituents under the conditions of the reaction, or containing an oil fraction which is vaporizable under these conditions.

    If the heat is removed only in the form of sensible heat, a rise in temperature within the reaction chamber will be the precondition for removal of the reaction heat.

    The quantity of oil to be put into circulation per kilogram of made products is calculated simply from the equation:

    If the quantity of final gas G - 2.7 m³ and the quantity of the made water W = 0.23 kgs. for 1 kg. of product at 90 per cent conversion are included in the above equations, the amounts of oil to be circulated are calculated as follows:

t	Q = kg 01/kg product
= 5°	1600
= 10°	800
= 25°	320
= 50°	156

    The quantities of circulating oil are appreciably higher in this case as compared to the second case since a part of the circulating oil is evaporated.

    If the quantity of circulating oil is divided into an evaporating portion Q1 and a non-evaporating portion Q2, we get the following equation:

The quantities of circulating oil can be calculated on the basis of this equation, as was done, for example, in the table for various  D t and various portions of vaporizable oil.

    The oil circulation process is carried out by the following procedures:

(Diagrams I and II on page 133o)

    In the procedure according to Diagram I the circulating oil is cooled within temperature range t₂ - t₁ before being returned to the reactor.  This procedure approaches that of the above-mentioned procedure in that the oil medium contains relatively few vaporizable constituents.  The extent to which this precondition is carried out depends on the temperature range  Dt and the quantity of the final gas.  It is evident that the boiling curve of the circulating oil cannot be freely chosen for even if relatively high-boiling circulating oils are employed, the oil will acquire a specific composition by condensation in apparatus K, depending on the working procedure.

    The procedure according to Diagram II, on the other hand, permit cooling in the cooling device K to the extent that hydrocarbons are condensed in a wider boiling range, depending on the selection of temperature t_o.  A lower limit for t_o is substantially conditioned by the fat that high-boiling paraffins are formed during the synthesis which naturally enrich the circulating oil.  It is expedient, in general, not to exceed a temperature of 80 - 100 degrees in order to avoid obstructions in the tube of the cooling device of the steam producer caused by solidifying of these paraffins.  It is also advantageous to cool below the strictly necessary temperature for low-boiling hydrocarbons would otherwise condense which evaporate on being reheated to t₁ before entering the reaction chamber.  The heat exchanger, which is a section of the cooling device and is used to reheat the circulating oil, would then be unnecessarily large.  The Oppau experiments which were conducted in order to develop the oil circulation process were always carried out according to the procedure shown by Diagram II.  However, it was planned to revert to Procedure I for new plant units.  In this connection, provision was to be made for the injection of lighter-boiling fractions, which were removed from the final gas in the form of condensates, into a supplementary circulation in the reaction chamber, as is shown by Diagram III:

(Diagram III on page 134)

3.  Catalysts

    After the granular fixed-bed catalyst was proved to be practicable, the oil circulation process was developed on this basis since this procedure shows considerable simplicity and distinction as compared with the catalyst suspended in oil.

    Certain minimum requirements had to be met by the catalyst with regard to firmness and durability when the oil circulation procedure was adopted.

    These requirements were fulfilled by the iron catalysts developed by Dr. E. Linekh, which were produced by melting iron with promoters in a current of oxygen into ammonia systhesis catalysts in the form of oxides (Fe_sO₄).

    The fused cakes thus obtained are broken up into 6-12 mm. pieces and the catalyst is reduced with hydrogen at 450-500 degrees for the medium pressure synthesis, and up to 650 degrees for the high pressure synthesis.  Deficient reduction of the pieces is to be avoided because a bursting of the nucleus, caused by a splitting off of carbon might occur.  The catalysts are substantially composed of iron, with slight additions of silicon, alkali, manganese, and titanium oxide.  The exact composition of catalyst No. 997, which is most often used as a standard in experimental work, is given in Part I, page 2 of this report.

    The catalyst reduced in a reduction furnace installation apart from the synthesis reactor is charged into the reactor after cooling in the presence of carbon dioxide, or, particularly if the catalyst is reduced at temperatures below 600 degrees and is very pyrophoric, it is discharged from the reduction vessel into oil in the absence of air and is charged into the reactor.

    The following figures are assumed in the plans for a catalyst  reduction installation:

Reduction temperature	470 - 500° C,
Hydrogen current	200 - 300 liter per hour kilogram catalyst
Bulk density of the oxidic catalyst	2.5 kg./liter
Reduction time	6 - 8 days

    The hydrogen is recirculated in the reduction installation.  The hot hydrogen issuing from the reduction vessels is first conduct into a heat exchanger in a countercurrent to the cold hydrogen which recycled to the reduction vessels.  After passing out of the heat exchanger the hydrogen is cooled as far as possible and then, after separation the condensed liquid, passed through a silica gel dryer for complete drying before being returned to the reduction vessels.

    Moreover, the given conditions are dependent on the type catalyst and its ease of reduction.  The reduction temperature can be raised to 650 degrees for conducting the synthesis under high pressure.  A substantial shortening of the reduction time is thereby attained.

4.  Procedure and Equipment

   After granular, fixed-bed catalysts in the reactor proved to be feasible, the oil circulation process was developed on this basis it offers a substantial simplification in contradistinction to the suspended in oil.

    An upright high pressure tube of 200 or 500 mm. internal and a height of 6 meters served as the synthesis reactor.  Apart from central tube for the thermo elements, the reactor had no built-in exchanger.

    The empty reactor chamber was charged with catalyst.  The synthesis gas runs through the reactor (S) from bottom to top along with the circulating oil in a direct current.  The hot oil and gas leaving the reactor surrenders its heat to the cold circulating oil in a heat exchanger (R).  After passing out of the heat exchanger the oil is again cooled in a condenser or a steam generator (K1) to about 120 degrees.  At this temperature the final gas is separated from the oil in a separator (A1).  The made oil excess and if necessary the reaction water is drawn off from the separator (R).  The oil is again conducted to the reactor (S) via the heat exchanger (R) and a supplementary pre-heater (W) by a circulation pump, the oil in the separator in the meantime being maintained at a specific level.  The supplementary pre-heater is merely used for starting.  The final gas is cooled to approximate external temperature in another cooler (K2), gasoline as well as alcohol-containing water being separated in another separator.  If the operation is carried out in two stages, then the final gas is conducted to the second stage which is coordinated with the first stage.  In the second stage the final gas is either depressured and conducted to the activated charcoal plant (AK) or washed with oil without being depressured so that the light gasoline and O₃ - C₄ hydrocarbons still retained in it may be recovered.

(Diagrams on pages 135 and 136)

    The fresh gas is also pre-heated in a suitable manner and admitted to the reactor from below.

5.  The Oil Circulation

    The oil produced in the synthesis itself is employed as circulating oil.  In this procedure, as distinct from similar procedures, the use of high-boiling fractions, which remain almost completely liquid under the reaction conditions, is deliberately given up.  It is desirable for higher performance that vaporizable constituents be present in the circulating oil under the reaction conditions if possible.  The boiling of the liquid in the synthesis reactor creates the conditions, on the one hand, for good contact of the synthesis gas with the catalyst, thus achieving a higher capacity, and, on the other hand, for favorable heat removal and temperature regulation.

    The boiling range of the circulating oil may be regulated as desired by the condensation temperature of the separator (A) placed in the oil circulation.  Two examples are cited as typical for the boiling range of the circulating oil:

        (Table on page 137)

    The reaction can safely be kept at the desired degree of conversion and at the desired temperature by regulation of the quantity of recirculated oil.

    The quantity of circulating oil is increased with the charge rate to the reactor.  In the case of the plant units hitherto operated the quantity of circulating oil was adjusted for 70 - 80 liters per hour per kilogram of made product in the same period.  In the case of larger units, where heat losses are of less importance, the quantity of circulating oil could probably be adjusted to a higher level.  Future plans call for a quantity of circulating oil of 120 - 150 kg./hour per kg. of product.

6.  Evaluation of the Experimental Results of the Plans for a Large Scale Reactor

(Graph on page138)

    It is evident from the two curves representing the temperature course and the distribution of the conversion in the experimental reactor that the procedure is especially more favorable for larger reactor units.  It is clear that the temperature t₁ in the lower part of the 6 meter long experimental reactor was not very much in excess of the temperature at the start of the reaction, and that conversion in the lower part of the reactor therefore sets in very slowly, increasing by degrees with the gradual rise in temperature as a result of the slight conversion.  Thus, the lower sector of the reactor was poorly utilized.  Just as soon as temperature t₂ (sic) is reached, conversion also attains a corresponding increase.  After temperature t_y near the upper end of the catalyst bed is passed, the conversion undergoes a similar rise with rapidly increasing temperature.  This means that the proportion of vaporizable fractions present in the range of temperature is too small to conduct away satisfactorily the best by evaporation.  Since the boiling point distribution of the circulating oil is not subject to any arbitrary influencing, the process has therefore been expanded to this end ^(x) so that vaporizable "cool oil" is fed to t_y in order to check this undesirable temperature rise.

    An experiment with a cold feed of this kind conducted in a 200 mm. reactor achieved the desired success.  Since another oil pump was unavailable, this operation could only be carried out by a makeshift branching off from the main oil circulation with valve regulation.  It was possible by careful attention to arrest the undesired temperature rise in the upper end of the reactor to the desired extent.  However, only an approximate 55 per cent conversion of the gas was attained because of the low (6 meter) height of the experimental reactor.

    In planning a large-scale reactor unit the improvement of the process outlined in Diagram III, page 5 is offered, the temperature cou? being shown in the following chart:

(Chart on page 139)

    The temperature range  D t, which was previously maintained at 50 degrees, and often at 100 degrees, in order to attain a 50 per cent conversion in the 6 meter reactor, can be reduced to 25 degrees to insure the same degree of conversion with a reactor height of 9 meters.  With reactor height of 18 meters it will be possible to carry out the entire 50 per cent conversion in one stage.  It cannot be decided here whether the one-stage or the two-stage process is economically more advantageous for large scale production.  The procedure which was conducted in the ? plant up to 75 per cent conversion only produced a specific yield of 140-150 grams in the second stage as compared with a yield of 165-170 grams in the first stage.  This difference in yield should have decreased as a result of the equalization of the reactor temperature and the low-peak temperature at the reactor exit which could be accomplished because of the better control of the process possible in a large-scale reaction.  An increase in yield can therefore be counted on in large-scale reaction. However, in the following sections only those yield figures are given which were actually obtained in past experiments.

7.  Synthesis Gas

    In general a CO:H₂ ratio of 55:45 or 1:0.8 is necessary for the synthesis.  Gases rich in hydrogen can also be used; however, they cause a shift in the composition of the product with proportionate increase of the hydrocarbons boiling in the gasoline boiling range and the C₃ and C₄ hydrocarbons.

    The following table assembles the results of comparative experiments in which the CO:H₂ ratio was modified, conditions in other respects being the same.  These comparative experiments were carried out in pressures of 15 to 20 atm. gage.

(Table on page 140)

    The table shows the decrease in C₃ and C₄ formation with rising CO content of the synthesis gas and the simultaneous increase in the formation of high-boiling products.

    The gas rich in CO which is necessary for the synthesis can be directly produced by oxygen gasification in Winkler generators.  The desired CO:H₂ ratio can also be attained in the customary cyclic water gas production from coke, if a part of the steam is replaced by CO₂.  A gasification medium consisting of 27 per cent by volume of carbon dioxide and 73 per cent by volume of steam is needed to attain a CO:H₂ ratio of 55:45 or of 1:0.82 according to experiments with Pintsch-Drehrost (rotary grate) generators.  The water gas will then be composed of 12.7 per cent CO₂, 47.7 per cent CO, 39.0 per cent H₂ and 0.2 per cent CH₄.  The synthesis itself produces the CO₂ necessary for gasification if the resdual gas put through a CO₂ scrubber.  This quantity of CO₂ is sufficient to produce the necessary quantity of synthesis gas rich in CO.

    A final gas good for heating purposes is simultaneously obtained with the CO₂ scrubbing of the residual gas of the synthesis.

    A gas rich in CO can also be produced from natural gas by using the carbon dioxide resulting from the synthesis process.  It should be mentioned at this point that most of our experiments were conducted with synthesis gas poor in inert gases (2% N₂).  However, we conducted a number of experiments with gases containing a higher proportion of inert gases (13%).

    In the following example the composition of the final gases the two-stage procedure are given with a synthesis gas free of inert gas.

(Table on page 141)

    The composition of gases when gases containing inert gases are used can easily be calculated from these figures if it is assumed that inert constituents take no part in the conversion.

    The synthesis gas must be purified from inorganic and organic sulfur.  According to our experience the catalysts are not as sensitive as in the Fischer process.  Fine purification to a sulfur content of 4-5 mg/m² should suffice.

8.  Pressure

    The medium pressure synthesis is conducted under 15-25 atm. gage.  The results obtained at this high pressure have been cited in the individual sections of this report in comparison with the results of the medium pressure synthesis.  Apart from the high capacity attainable, however, these results have little commercial significance since the compression costs cannot be compensated for by increased yields or by improvement of the properties of the product.

    Pressures up to 200 atm. gage are briefly referred to at the conclusion of the report.  These were used, however, in the formation of oxygen-containing products.

9.  Performance

    The medium pressure synthesis is capable of a continuous hourly output of 20-25 grams total product per liter catalyst.

    The hourly output of the high pressure process was stepped up to 160 grams total product per liter.

10.  Temperature

    The temperature in the reactor rises from the bottom to the top.  It is conditioned by the oil circulation.  A temperature rise of 50 degrees C. was established in general in the experiments conducted here so that the following temperatures were recorded with maximum reactor charge rate:

(Table on page 142)

        However, as was mentioned before, an extensive temperature equalization is possible by using a more advantageous procedure, a temperature difference of 15 to 20 degrees C. being possible with a reactor unit temperature of 250-255 degrees C. in larger reactor units.

11. Yield and Conversion

    145 - 150 grams of total product per Nm³ CO - H₂ were obtained on medium pressure reactors with a 90 per cent conversion in two stages.

    This total product consisted of

        13 - 15% liquifiable gaseous hydrocarbons

        32 - 35% gasoline fraction, boiling range to 175° C.

        18 - 20% middle oil fraction, boiling range to 175 - 320°

        10 - 12% soft paraffin fraction, boiling range 320 - 400°

        16 - 18% hard paraffin

        5 - 6% water-soluble alcohols

    The following page shows a chart giving conversions for two-stage conversion.  The results are converted to an oxygen-free synthesis gas (ideal gas).

(Chart on page 143)

12.  Properties of the Product

    The products have a marked olefinic character.  The olefin content drops with increasing molecular size, as is shown by the table:

(Table at top of page 144)

    The oils also contain oxygen-containing constituents (alcohol esters).  The oxygen content of the low-boiling gasoline fractions up 1? 100 degrees runs to about 1.5 - 2.0 per cent.  However, it can exceed 1? amount if the water-soluble alcohols produced are separated out in a concentrated form with the gasoline fraction, for the gasoline partially dissolves these water-soluble alcohols (C₂H₅-OH).  However, these water-soluble alcohols can be removed from the gasoline by treatment with water.  The oxygen content declines with rising boiling point to 0.5 per cent in the fractions ranging from 200 - 400 degrees C.

    The primary gasoline has an octane number of 68 (research) which is increased to 85 by addition of 0.1 per cent lead.  After hydrogenation the octane number suffers a considerable drop.

    The middle oil fraction yields Diesel oil directly.  The cetane number is 75 - 78.  A middle oil test gave the following values:

        The hard paraffin has a melting point in excess of 90° C. and can be used for all practical purposes (emulsifying wax and the like).  The hydrocarbon products are branched to a certain extent.

(Tables on pages 145 and 146)

13.  Results of Experiments with Synthesis Gases Having an Appreciable Excess of Hydrogen

    The influence of an appreciable excess of hydrogen on the carbon monoxide has already been mentioned in the previous section on "Synthesis gas".  The results of the experiments will be dealt with here in greater detail.  Circulating depressured gases of the methanol or isobutyl alcohol synthesis were used as the synthesis gas.

(Table follows on page 147)

    The carbon monoxide is extensively converted when these hydrogen rich gases are used; however, the greater part of the hydrogen remains the final gas.

    The working up of such hydrogen-rich gases frequently obtain as residual gases of other syntheses under pressure might very well considerable commercial interest although the yields with respect to ? of fresh gas would be relatively low.  However, since only the CO are portion of the H₂ is withdrawn from the synthesis gas, the CH₄ conte? the final gas being increased, commercial application of the synthesis be assured in many instances if the residual gas is worked up in a ? decomposition plant and again made available for other syntheses (N₂ ? synthesis).  The yields in the above table are given as specific yields m³ of converted CO - H₂, in order to facilitate comparative evaluation.

    It can be seen that water-soluble alcohols, consisting of  ?% ethyl alcohol, are principally formed under high pressures addition, the formation of C₃ and C₄ hydrocarbons is very great.

    The formation of ethylene is not included in the yields c? above although ethylene formation in individual experiments has reached a point where it can no longer be neglected.

    In the following the example of Experiment 35a is subject to more intense consideration:

Procedure according to Experiment 35a

    In the large-scale experiment conducted under a working p? of 15 atm. gage (one-stage conversion), 1000 cbm. of isobutyl recycle gas, containing 200 m³ of CO and 640 m³ of H₂, resulted in conversion of 130 m³ of CO and 165 m³ of H₂, with 770 m³ of residual gas containing 70 m³ of CO and 475 m³ of H₂.

        The composition was

        12.5 % CO₂

        1.9 % CnH₂n

        9.1 % CO

        61.4 % H₂

        9.0 % CnH₂n+2

        6.1 % N₂

        From this 56.1 kgs. of product were obtained, composed of

        7.8 % ethylene

        12.9 % propylene

        6.8 % butylene

        19.5 % propane and butane

        15.0 % light gasoline

        30.0 % gasoline and oil

        5.6 % ethanol

        2.4 % methanol

    The synthesis was carried out in one stage under medium pressure of 15 atm. gage in such a manner that for 5000 m³/hour of isobutyl recycle gas a reactor unit with 12 m³ of catalyst space was used.

    Catalyst life was estimated at one year.  Not the slightest evidence of catalyst fatigue was observed in an experimental period lasting one and one-half months, using hydrogen-rich synthesis gas under a pressure of 20 atm. gage.

    If 5000 m³/hour = 43.2 million m³/year of isobutyl recycle gas is passed through a synthesis installation of this kind, then 3840 m³/h = 33.15 million m³/year of residual gas will again be available after the synthesis and removal of the products in an activated charcoal plant.  This can again be worked up for the NH₃ synthesis according to the decomposition process of Dr. Sachse.

    From the conversion of the 1475 m³/hour CO-H₂ withdrawn from the isobutyl recycle gas, 2400 tons/year of the above-mentioned composition are obtained.

Procedure according to Experiment 25c

    Experiment 25c can be treated similarly to the example of Experiment 25a.  A working pressure of 150 atm. gage was used, the other working conditions remaining the same.  If 1000 m³ gas containing 922 m³CO-H₂ are converted according to the oil circulation process, 777 m³ of residual gas are obtained.

        The analysis follows:

        12.9 % CO₂

        0.9 % CnH₂n

        6.2 % CO

        72.3 % H₂

        4.7 % CnH₂n+2

        3.0 % N₂

A product of 43.7 kg. was obtained, consisting of 17.70 kg. water-soluble alcohols (of which 12 kg. are ethyl alcohol 11.05 kg. C₃ and C₄ hydrocarbons (about 40 per cent olefinic) 14.95 kg. oxygen-containing oils Moreover 0.6 per cent by volume, i.e., 5.8 kg. of ethylene are contained in the residual gas which is not counted in the yield.

      383 tons of product per year would be obtained if 1000 m³ of synthesis recycle gas were worked up hourly.  777 m³ of residual gas of the above-mentioned composition would be delivered hourly to the synthesis decomposition plant for working up.

14.  Experiments in the Production of Oxygen-Containing Products

    The experiments described in the above section lead to the formation of oxygen-containing products.

    When the researches of Ruhrchemie on the Oxo reaction became known at the start of the war, the question was universally raised whether such products could not also be obtained in the CO - H₂ synthesis in one operation.

    In 1940 we received the assignment from Dr. Müller-Contadi of investigating the preparation of higher-molecular weight alcohols by the oil circulation process.

    At the same time investigations were initiated in the Leuna Works which lead to the discovery of the Synol synthesis.  The actual circumstance that led to the Synol synthesis was the fact that a method of treatment of fused iron catalysts was discovered which permitted lowering of the synthesis temperature to 195-215 degrees.  In this connection it was shown that the low synthesis temperature was the decisive factor in obtaining higher-molecular weight alcohols.

    The experiments which we were conducting at Oppau at that time assumed that elevated pressure and an excess of hydrogen in the synthesis gas was the most important factor in guiding the synthesis toward the formation of oxygen-containing products.

    The experiments dealt with in the preceding section confirm the conception to the extent that increasing yields of water-soluble alcohol are obtained with hydrogen-rich synthesis gas and rising pressure.  Both factors, however, forced the synthesis into the formation of low-molecular products.

    We have already reported in the previous section that we obtained products relatively poor in oxygen when synthesis gas rich in carbon monoxide was used.  These were the conditions under which we initially developed the hydrocarbon synthesis according to the oil circulation process at 1? atm. gage in 1935.  We had already turned to experimentation with the o? circulation process at 200 atm. gage in a pilot plant at Leuna.  The re? of this pressure rise to 200 atm. gage was only a further shifting of the products toward the short chain lengths and an increase in methane formation.  Besides, a very rapid catalyst fatigue was observed at high pressure.  In 19 (illegible) we made the observation that we actually arrived at ?ed oxygen-containing compounds with gas rich in carbon monoxide under high pressure if we reduced the fused iron catalysts at 450 - 500 degrees C. instead of the previous 650 degrees for the high pressure procedure, as was already done in the medium pressure synthesis.

    The following considerations were adopted in our experiments in the production of higher-molecular alcohols:

1.  The reduction of the fused iron catalysts was to occur at the lowest possible temperature.

2.  Conversion in the synthesis should be divided into more than two systems.

3.  The catalyst space velocity should be kept as low as possible.

4.  Overheating in the oil circulation must be avoided to protect any higher-molecular weight alcohols from decomposition.

    All of these four considerations attempt to lower the synthesis temperature as much as possible in order to counteract the tendency toward formation of lower-molecular weight compounds as the result of high pressure.

    The application of these conditions had the desired effect, to some extent, as is shown by the appended experimental date.  It is beyond doubt, however that our results have been surpassed by the Leuna Synol process and our experiments outstripped.  The progress of the Launa process is based on the fact that, with catalysts which can be used at 200 degrees C. and middle pressure, the molecule-reducing use of high pressure can be avoided, since the formation of oxygen-containing compounds can also be attained at these low synthesis temperatures without excessive increase in pressure.

    The application of this Leuna know-how to the oil circulation process was obvious.  An experiment was also conducted in which our fused iron catalysts were reduced with a great excess of hydrogen according to the experience of the Synol synthesis.  However, it was found out that an excess of hydrogen is not effective in catalyst reduction if the particle size exceeds 2-3 mm.  In any case an experiment conducted with a particle size of 8 mm. did not have the desired effect of lowering the synthesis temperature to about 200 degrees.  It was not possible to conduct further experiments because of the progress of the war.

    In this connection we present the results of one of the many experiments in the preparation of higher-molecular weight alcohols according to the oil circulation process.  In this experiment the same catalyst was used that was employed in most of the earlier experiments in the production of hydrocarbons.

    A report on experiments with other fused iron catalysts which according to the results of the investigators, is especially favorably the formation of oxygen-containing products, is unnecessary since the results of the experiment are basically the same.

Procedure according to Experiment 25

    A specific yield of 195 grams of product per 1 Nm³ of conve? product was obtained, using synthesis gas (CO=H₂ = 1.16), an hourly output of 40 grams of product/1 catalyst and a degree of conversion of 3? per cent of CO - H₂ in the first stage.  Temperature 236 - 260 degrees pressure 180 atm. gage.  The product consisted of

24.0 % C₃ and C₄ hydrocarbons

21.6 % oil boiling to 150 degrees

12.7 % oil boiling at 150-250 degrees

9.0 % oil boiling above 250 degrees

32.7 % water-soluble oxygen compounds (C₂H₅OH).

        A detailed investigation conducted by Dr. Leithe led to the following approximate composition of the total product:

8.5 % methanol

21.0 % ethanol

10.0 % propanol

6.5 % alcohols C₁ - C₁₂

2.5 % alcohols C₁₂ - C₂₀

11.5 % water-soluble fatty acids

5.0 % fatty acids C₅ - C₁₁

1.5 % fatty acids C₁₂ - C₂₀

26.5 % hydrocarbons to 200 degrees

3.5 % hydrocarbons 200 - 300 degrees)   about half olefinic

3.5 % hydrocarbons over 300 degrees)

List of Patents for the Oil Circulation Process

    Diagrams I and II (referenced from page 15)

The High Pressure Gas Circulation Process for the Synthesis of Ethyl Alcohol from CO - H₂ - containing Waste Gases

    The experiments of Dr. Eduard Linkh in the prepararation of hydrocarbons from CO - H₂ under elevated pressure with fused iron catalyst furnished the groundwork for this process.  In this connection appreciated quantities of reaction water were formed containing water-soluble alcohol especially ethyl alcohol.  The experiments were continued by Dr. Klemm in order to increase the proportion of alcohols.  At the same time Dr. Klemm initiated experiments for the study of fused iron catalysts and to de? new catalyst compositions which would especially favor the formation water-soluble alcohols.

The Gas Circulation Process

    The conversion of carbon monoxide-hydrogen mixtures with fu? iron catalysts under pressure necessitates special preparations in order to avoid an excessive reaction in the direction of methane or soot formation.  If such measures are not taken, the reaction will be concentrated into catalyst layer situated near the gas entry to the accompaniment of ma? heating.  As a result of the high reaction heat the reaction continue to proceed rapidly in the narrowest space and spontaneously leads to carbon monoxide decomposition and to loss of control of the reaction temperature.

    After several experiments the following measures were taken to control the reaction:

    1. The catalyst is arranged annularly in a thin bed inside of a tube.  The outside of the tube is jacketed with water under pressure in order to surrender a portion of the reaction heat to the water through the tube.

    2. The synthesis gas is recirculated so that the carbon monoxide concentration in the circulated gas does not exceed 10 per cent by volume.

    3.  The catalyst at the gas entry side is copper plated in order to diminish the danger of soot formation.

    4.  The recirculated synthesis gas is conducted throughout the entire length of the catalyst bed but mainly passes the space free of catalyst in the middle of the tube so that it only sweeps along the annular catalyst, partially penetrating it.

    The ration of the quantity of circulating gas to the fresh gas was 3 : 1.

    20 - 25 per cent of the fresh gas was constantly released from circulation as final gas.

    In general, the circulating depressured gas of the isobutyl alcohol synthesis was used as fresh gas; however, other gas mixtures were experimented with.  The experiments were conducted at a pressure of 180 atm. gage and a temperature of 290-320 degrees.

Equipment

    The reactor consisted of a high pressure tube of 120 mm. internal diameter with a built-in seamless boiling tube of 82 mm. internal diameter.  Water, activated by a thermosyphon, was circulated in the outer annular space between both tubes.  The inner boiling tube contains a central wire net hose which keeps the middle of the tube free from catalyst for the catalyst is charged into the annular space between the boiling tube and the hose.  The diameter of the bed was 10 - 12 mm.

    The synthesis gas enters the top of the reactor, passes from top to bottom of the central boiling tube containing the catalyst and conducted to a hot separator via a small separator, a heat exchanger and a hot cooler.  It then passes through a "cold cooler", the cold separates and is washed by oil.  The circulating gas is returned to the reactor by means of a gas circulating pump after depressuring a part of the circulated gas and adding make-up gas.  Before entry into the reactor the circulating gas passes through a pre-heater and finally the heat exchanger where it is heated to the reactor entry temperature by the hot circulating gas.  The depressured gases of the compressed oil wash, as well as the circulated depressured oil, were led through an activated charcoal plant in order to recover highly volatile hydrocarbons.

Catalysts

    Fused iron catalysts that were obtained by melting the following mixture in a current of oxygen were used in the pilot plant:

89.5 % iron powder

2.24 % titanium dioxide

2.24 % silicon powder

2.24 % manganous oxide

2.03 % copper powder

1.80 % KOH dissolved in some water

    If the mixture is carefully added to the melt the copper will burn well and will enter the melt.  On the other hand, when copper o? was employed it was reduced to metal and separated out in the form of molten metallic globules.

Reduction of the Catalysts

    The oxidic fused catalyst cakes were crushed to a particle size of (sic) mm. and then reduced with hydrogen at 650 degrees C. for 3 days.  A hydrogen quantity of 500 - 700 liters is used hourly for every liter of catalyst.

    The reduction temperature of 650 degrees is the most favorable.  Higher temperature markedly impairs catalyst activity.  A lower temperature during reduction means greater activity and shows that the synthesis takes place at low temperatures.  In this connection, however, the formation of water-soluble alcohols diminishes, and the formation of oil increases.

Copper Plating of the Catalyst

    It was observed over and over again when working in the gas phase that more or less marked formation of soot readily occurred at the side of the catalyst charge turned to the gas entrance.  To correct this trouble, which causes catalyst decomposition, copper-plated catalyst was charged into the upper sixth of the reactor.  Copper-plating of the catalyst is accomplished by treatment with a weak (5%) nitric acid copper nitrate solution.

    In this manner soot deposition was avoided without impairment of activity.

Synthesis Gas

    a. Type of Gas   

        Three different types of fresh gas were used in the various experiments.

    1.    A mixture of 20 per cent pure CO and 80 per cent zero (Nullgas) gas (2 per cent N₂).

    2.  Butyl residue gas enriched to about 45 per cent with pure CO; rediluted to 20 - 22 per cent CO by addition of zero gas (2 per cent N₂).

    3.  Pure butyl residue gas (6 - 6.5 per cent CO₂, 0.5 - 1 per cent HnH₂n, 20 - 22 per cent CO, 57 - 64 per cent H2, 5 - 6 per cent CnH₂n+2, 5 - 6 per cent N₂.

    In these investigations an approximately constant proportion 20 per cent CO was maintained so that differences in result could not attributed to divergencies in this constituent.  The hydrogen proportion showed appreciably greater differences.  In the mixture of CO with zero gas it was 80 per cent.  In the case of the butyl (Tanol) residue, gas treated according to 2., it was 70 per cent, and in the case of pure butyl (Tanol) residue gas, it was 60 per cent.  This gives a ratio of CO : H ? = 1 : 4, 1 : 3.5, 1 : 3.

    The third important difference lies in the "inert gas content" particularly with saturated and unsaturated hydrocarbons.  In this instance the butyl residus gas clearly has the greatest proportion.

    According to the experimental results there is no noticeable difference if the mixed gas consisting of CO - H₂ or the rediluted, er? Tanol residue gas is used.  However, the use of pure Tanol residue gas immediately resulted in appreciably better yields.  This was shown with ?cular clarity in an experiment in which rediluted gas was used in the period, iso-gas in the second, and rediluted gas again in the third.  The first period yielded 64.35 grams/m³ fresh gas product, the second 82.4 grams/m³, the third 60.75 grams/m³.  This increase in yield which occurred in several experiments is explained by the proportion of low-molecular carbons and similar compounds which were then synthesized or built up larger molecules.  It is not clear to what extent  the CO² and methane participate in the conversion.  It can be said in general that the use of 1? Tanol residue gas is most advantageous.  In addition, there is the omition  of compression since the gas can be used with the obtained pressure.

    b. Space Velocity

    The throughput of fresh gas is of further importance in increasing the yield.  This is shown by several experiments.  Calculations are for a space velocity of m³ per liter of catalyst per hour.  Three  experiments were conducted with a special catalyst arrangement ("lower bed installation" with 50 cups") with Tanol flue gas under similar conditions.  The use of 0.65 m³/liter catalyst resulted in 93.3 grams/m³ fresh gas; 0.75 m³/liter gave 62.28 grams.  Another experiment, conducted with mixed gas consisting of CO-zero gas (Nullgas), resulted in 58.25 g/m³, using 2.15 m³/liter of catalyst in the first period; a space velocity of 3.4 m³/liter in the second period gave only 41.54 grams.  Experimental conditions were almost the same.

    c.  Pressure

    Increase in pressure acts in two directions.  Under similar conditions the yield increases with rising pressure and the tendency toward formation of hydrogen-containing products simultaneously increases.  An experiment with a bundle of tubes with circulation of water, using a space velocity of 3.4 m³/hour, gave 41.94 grams/m³ at 100 atm. gage, and using a space velocity of 3.7 m³/hour gave 44.08 grams/m³ at 180 atm. gage.  In the first case the yield consisted of 30.59 per cent of alcohol; in the second case it consisted of 84.5 per cent of alcohol.

    d.  Circulating Gas

    The quantity of circulating gas is kept as high as necessary, to insure that the entrance gas does not exceed 10 per cent of CO on an average by dilution with fresh gas.  Larger quantities of circulating gas are too large to pass through and produce yields that are too little.  As a result of increasing enrichment of the CO in the incoming gas the conversion is altered in favor of the oil content, and finally the reactor tends to get out of control.

    In addition to removing a part of the heat of reaction the circulating gas should also act as a safety gas.  It is assumed that the first stage of the conversion produces oxygen-containing compounds, in particular alcohols.  These compounds, which call for speedy removal, are safeguarded by dilution with non-reactive or slightly reactive compound.  A decrease in the quantity of circulating gas led to an increase in hydro-carbons and similar compounds.

    With respect to the formation of alcohols, it was shown to be advantageous to free the circulating gas of volatile compounds by the ? wash under pressure before returning to the reactor since these compounds again participate in the formation of hydrocarbons and other similar substances during the reaction.  The total yield was higher if it was not ?

    e.  Final Gas

    The final gas carries with itself a greater or lesser amount highly volatile hydrocarbons, particularly liquefiable hydrocarbons, depending on pre-treatment.  It is therefore purified with charcoal, consisting afterwards essentially of hydrogen, methane and nitrogen, along with a percentage of CO₂ and some non-condensable hydrocarbons.  The remainder of the unconverted CO is also contained in it.  It is available for further working up for fuel purposes.  The remainder is about 30 - 40 per cent the volume of the fresh gas.  The quantity of substances which can be removed by active charcoal ranges between rather wide limits, between about 20 grams/m³ to about 80 grams/m³, depending on conditions.

    5.  Products

    The following products are obtained by the synthesis in the gas phase:

    a.  Oils from the cold separator.

    b.  Light oils as distillates from the wash oil.

    c. Activated charcoal gasoline.

    d.  Liquefiable gas.

    e.  Alcohols from the cold and hot separator.

    A total yield of 53.31 grams/m³ of the following composition was found as means value in the 7 large-scale experiments:

Oils from the cold separator	-    12.61	g/m3	-    23.28 %
Light oils from the wash oil	-    3.14	"	-    5.62 %
Activated charcoal gasolines	-    6.56	"	-    12.64 %
Liquefiable gases	-    4.2	"	-    8.49 %
Alcohols	-    25.58	"	-    49.47 %
	58.31	g/m3	- 100%

        In this connection fluctuating small quantities of semi-solid, paraffin-containing products, which may contain up to 40 per cent of higher alcohols, are obtained from the hot separator.  Because of their small quantity they are calculated as part of the oils from the cold separator.

    These fresh, light-colored oils range from colorless to light yellow.  They turn brown if kept in the presence of air.  They have a pungent odor similar to esters of alcohols.  Mean density 0.771.  Flakes of small amounts of higher hydrocarbons often float in it.  Boiling begins at about 45-50 degrees.  90 - 95 per cent is distilled at 300 degrees, the residue consisting of dark brown, semi-solid paraffinoid masses.  The acid number is 10-12; saponification number 30-35; OH number 120-140.  The oils still contain appreciable quantities of water-soluble alcohols which can be scrubbed out in quantities of 18-25 per cent by stirring with water.  ? per cent of the oil is evaporated at 90 degrees during distillation.  ? distillate is divided into two parts.  The lower layer (8-10 per cent ) with a density of 0.896 contains about 75 per cent alcohol in water. ? upper layer with a density of 0.720 contains about 23-25 per cent of alcohol (water-soluble).  The residue of 48-50 per cent of the crude is dark brown and contains about 5-6 per cent water-soluble alcohol. ? was possible by careful distrillation to recover the bulk of the alcohol, especially on adding slight quantities of water.  The light distillation corresponds substantially to activated charcoal gasoline.  The remainder consist principally of fractions corresponding to illuminating oil and ? oil.  The residue consists principally of paraffins with a V.S. of 16?.  Together with oils of similar origin the oils can be worked up to gas illuminating oils and liquefiable gas.

    B.  Light Oils from Wash Oil

    A light colorless distillate (d = 0.680 - 0.702) is obtained from the wash oil of the oil scrubber.  The distillate stands between oil from the cold separator and the activated charcoal gasoline, but resembles the latter a great deal.  It is therefore mixed into that tar?.  Boiling starts at 30-35 degrees.  This fraction which contains about ? per cent of the yield can be worked up with activated charcoal gasoline.

    c.  Activated charcoal gasoline

    A condensate with a density of 0.660-0.680 and composed of 85-95 per cent of low-boiling, paraffinic and olefinic hydrocarbons if obtained when the activated charcoal towers are purged with superheated steam.  This amounts to 10-15 per cent of the yield.  Boiling starts 30-35 degrees and 40 per cent is evaporated at 45 degrees.  This distillate forms two layers: the lower layer with a density of 0.962 is composed of 55-60 per cent alcohols and amounts to about 1 per cent of the gasoline; the upper layer (38 per cent) with a density of 0.670 is composed of 16 per cent of alcohols and the distillation residue (d=0.722) another 13-14 per cent of alcohols.  The crude gasoline contains roughly 17 per cent alcohol.  After preliminary hydrogenation this product can be worked up with other gasolines.

    d.  Liquefiable Gases

    The liquefiable gases, the C₃ - C₅ hydrocarbons, are driven off along with the activated carbon gasoline.  They form 8-10 per cent of the yield and, according to current analyses, contain about 90-95 per cent olefinic hydrocarbons.  Since no compression is available, they have heretofore not been recovered but their presence merely determined in a part of the residue gases.  The bulk of the liquefiable gas (about 90 per cent) is contained in the let down gases of the pressure scrubber along with a large part of the activated charcoal gasoline.  In a large plant provision could be made for continuous fractional distillation of the wash oil with fractionated depressuring.  The final gasolines and the liquefied gas could be continuously obtained under pressure in a liquified form.  It is planned to return the liquefiable gases to the process by injection.

    e. Alcohols

    The product alcohol is obtained in amounts of 45 - 55 per cent of the yield, in individual cases up to 60 per cent.  The bulk is contained in the water from the cold separator which consists of 45-50 per cent alcohol.  A solution of 3-10 % alcohol is obtained from the hot separator.  The alcohols are pre-concentrated to a concentrate of 90 per cent.  The crude alcohol contains about 10 per cent water.

Acetaldehyde                2 - 3 %

Acetone                        3 - 5 %

Methanol                        10 - 15 %

Ethanol                            60 - 70 %

Higher alcohols                10 - 15 %

    Since the separation of aldehyde and acetone from the alcohol, especially ethyl alcohol, by distillation is incomplete, these imp? should be converted to the corresponding alcohols by a previous ca? hydrogenation.  Experiments show that the aldehyde and ketone reaction thereby completely disappears.

Literature:

French patent 833302	)
English patent 478318	)Discovered by Dr. Ed. Linckh, Dr. Fr. Winkler
American patent 2148099	)
German patent 76490, December 23, 1943	)Discovered by Dr. R. Klemm, Dr. E. Linckh, Dr. Fr. Winkler

Oppau, June 6, 1947                                                            Duftschmidt

Ammonia Laboratory                                                                                        June 1947

Dr. Arno Scheuermann

The Hydrocarbon Synthesis from Carbon Monoxide and Hydrogen

Researches of the Ammonia Laboratory from 1935 - 1944

Researches of the Oppau Ammonia Laboratory in the Fischer-Tropsch Synthesis

I.  Investigations with Cobalt Catalysts

    a.    Experiments at Atomospheric Pressure

    The Ammonia laboratory started its investigations in the f? of pressureless hydrocarbon synthesis according to Fischer-Tropsch i? by setting itself the task of reexamining the relevant material in the literature.  Dr. Lorenz was able to prove by numerous experiments that when the cobalt-thorium-kieselgur and nickel-manganese-aluminum-kieselgur catalysts proposed by Fischer were used, the values checked in respect to performance and life of the catalysts, type of product, and susceptibility of the synthesis to temperature and catalyst poisons.  He further decided that there was little choice in the individual products so that a single adaptation to the market conditions, i.e., a purposeful shifting in the ?position of the product, was not possible.  It was possible, for example to roughly triple the paraffin proportion only by a substantial increase of the contact time of the gas with the catalyst to about 6-7 times the technically conventional period at a synthesis temperature kept down to 160-170 degrees.  This was only possible at the expense of the catalyst life.  But even this short-lived success was dependent on the type of kieselgur used, for other types, even under these extreme conditions did not give these high paraffin yields without some restrictions on the Kieselgur.  When the kieselgur was replaced with silica gel, the formation of higher-boiling products was greatly impaired.  The reproducibility of the catalysts remained unsatisfactory despite expenditure time and effort.  Statements on the influence of experiment variation cannot be made with any certainty until this indispensable condition is met.

    The author, together with Dr. Meisenheimer, in October 1936 undertook to continue the investigations at this juncture.  In this connection it seemed advantageous to examine the part played by the individual components of this catalyst by temporarily restricting ourselves to catalysts containing cobalt as the basic metal.  In order to proceed gradually a cobalt catalyst was produced at first without additions in order to check on the influence of various precipitation conditions, reduction temperature, and alkali content.  The result of the initial investigations, whose success is attributable to our close collaboration with the X-ray laboratory, can be summed up as follows:

    1.    Pure cobalt metal produced under specific precautionary measures, with a catalyst space velocity of 1 liter gas/1 gram Co hourly, yields approximately 110 grams/Ncbn synthesis gas as compared to 25 grams/Nm³ in the gasoline synthesis.  This is the value given in the literature.  The lower the reduction temperature the better the catalytic activity of these catalysts without promoters or carriers.  Catalytic activity does not occur at high reaction temperatures due to premature sintering.

    2.    However, if the finished catalyst contains noticeable quantities of Co₃O₄ along with basic carbonate before reduction, it will be substantially less susceptible to the reaction temperature as a result of the difficulty of reducing this oxide, which acts as a stabilizer.   

Red. Temp	grams yield/m3
	without Co3O4	with
350	0	30
300	1	-
270	15	108
225	39	135

    3.    The following was proved to be reliable as a catalyst production recipe:

    Cobalt nitrate containing water of crystallization is dissolved in water and, with a little more than the calculated quantity of potassium carbonate, subjected to a cold drop by drop precipitation within 40-50 hours.  The precipitation is washed out by a suction filter until there was no longer any evidence of nitrate in the filtrate.  The moist catalyst is dried for 24 hours at 110 degrees and, in order to attain a sufficient content of Co₃O₄ by the oxidation of CoO, again moistened and again dried at 110 degrees for 10 hours.  The catalyst is reduced at 225 degrees.  Time about 10 hours.

    4.    The recrystallation which rapidly set in caused a short for this unstabilized catalyst.

    5.    Carbide formation in the spent catalysts could not be obtained with X-rays.

    At the time that this information was discovered a new prob? was added, namely, the increase of the paraffin yield.  This task was closely connected with the work being done at Oppau in the field of paraffin oxidation to soap-stock fatty acids, or wax.  As a result of this we were forced to pursue our activities in several directions which frequently intersected.

    The simplest manner of stabilizing cobalt obtained in an a? form was deposition on carriers. For this purpose we initially used kieselgur, the extreme case simultaneously occurring in which we for once used a Fischer catalyst with a thorium content of 0.  This resulted in a catalyst which naturally did not quite approach the standard Fischer catalyst with its 18 per cent thorium in respect to activity, but when displayed an excellent life.  It was used about 4 months without being regenerated.  This was attributed to the fact that it only formed paraffin at the start; later, after about 14 days, practically no more paraffin was formed.  This direction, however, did not conform to our wishes, but a least is showed us the part played by one of the three components, the thorium oxide.    

    It accomplishes two functions in the catalyst combination:

1.    Stabilization of the catalyst in an active form, which is only possible otherwise by a special drop by drop precipitation.  2.  Guiding the synthesis into the production of long-chain products.  This information led us to investigate catalysts with a high content of thorium oxide for the purpose of an increased paraffin yield.  As was to be expected, an increased percentage of paraffin was obtained.  However, since the total yield in conjunction with the greater thorium content, at first drops slowly, then more rapidly, the actual increased yield of paraffin may be ignored.  However, the combination of a thorium-rich and a normal catalyst in a two-stage operation proved to be good.  The use of this catalyst resulted in a paraffin yield of 35 grams/Ncbm of a total yield of 130 grams/Ncbm.  The experiment lasted 2 months, hydrogen regeneration at 220 degrees occurring after each 14 days.  The experiment was discontinued after two months without any visible falling off of activity.  Further efforts were made to increase the paraffin contents by the pressureless procedure.  Alkalization of the catalyst or modification of the gas composition (increasing CO content) were tried.  It was shown that each individual measure or a combination of both tended towards increased paraffin formation.  However, this increase only reached moderate proportions and does not compare with the increase attained by raising the thorium content.  Since a decrease in the total yield is tied up with these measures, the increase in the percentage of paraffin is no yardstick for the actual formation of paraffin.

    However, all these efforts to achieve an increased yield of paraffin are outstripped by another measure, namely, the application of pressure.  It is therefore not necessary to go into the above experiments in greater detail.  However, before turning to these pressure experiments we should like to report briefly on our efforts to find other promoters and carriers for the promotion and stabilization of the cobalt.

    At first magnesium oxide seemed to us to be a suitable promoter addition since it forms a spinel with cobalt oxide (Co₂o₃), and forms an unbroken series of mixed crystals with CoO.  Because of the attainable homogeneity this appears to us to be a favorable precondition for catalytic activity after the reduction.  It was determined as a result that addition ? of 2-15 per cent MgO without addition of kieselgur were approximately equivalent among each other, but gave a total yield of only about 80 grams.  This type of catalyst is very dense and, since it possesses a higher metal content, with respect to the same quantity of metal, it occupies a substantially smaller volume than the kieselgur catalyst; for example, 4 grams of cobalt are contained in 10 c.c., it would otherwise require about 40 c.c.  This results in a four-fold volume space velocity since the catalyst charge rate is referred to the gram quantity of cobalt (1 liter/1 gram Co/hour).  However, if it is desired to employ the usual volume charge with the catalyst then four times as much catalyst metal is needed and a yield of 100 grams/1? is  obtained after two months without regeneration.  This corresponds to the life of the usual cobalt-thorium-kieselgur catalysts.

    The attempt to deposit the cobalt-magnesium catalyst combination on kieselgur resulted in a catalyst with a yield about 10 per cent poorer than the standard catalyst with a similar paraffin yield.

    Further investigations on the replacement of magnesium oxide by manganese, ceric or lanthanic oxide resulted at best in equivalent but not better catalysts than those proposed by Fischer.

    The cobalt-nickel-manganese-uranium-kieselgur catalyst proposed by the Japanese, with the same yield as the standard catalyst, is quite noteworthy because of the marked direction of its reaction towards paraffin (28 grams paraffin/Ncbm in over four weeks).  On the basis of our own experiments we attribute this condensing property to the influence of the uranium.

    Although we do not ignore the good catalytic properties of the standard catalyst we received the impression during our investigations that the kieselgur might easily lead to trouble.  The fault lies in the undefined character of the material since we have not reached a point where we can exactly analyze its make-up.  Its physical structure is doubtless of importance along with its chemical composition so that, in the end, only catalytic experimentation can decide upon its utility.  We therefore spent a great deal of time in looking for another material to replace kiesslgur, such as aluminum oxide, kaolin, magnesium oxide, silica gel, talc, porcelain, etc.  Our experiments showed that kaolin and aluminum oxide, after a pre-treatment with temperatures of 400-600 degrees or 800-1000 degrees, yield a catalyst practically equivalent to the kieselgur catalyst (life four months), all other carriers reacting unfavorably.  Nevertheless, the fact that we retained the kieselgur in general is explained by the observation that a less favorable type (4 S) was substantially improved by igniting in a current of air at temperatures of 500-700 degrees.  It even outstripped type 20, the type generally employed by Fischer which was supplied by the German Kieslgur-Werks, Hanover after treatment by ignition.  The treatment at Hanover, however, does not occur at a specific temperature, many particles therefore being overburned.  A further observation was made to the effect that if slight additions of magnesium oxide are added to the kieselgur to the extent of 1-2 per cent with respect to the cobalt metal, fluctuations in the behavior of the various kieselgurs could be practically eliminated.  Nevertheless, experiments undertaken from time to time with the aim of replacing kieselgur with silica gel finally achieved success by the observation that a silica gel preheated for about five hours in a current of air at 800 degrees to avoid silicate formation can completely replace kieselgur if a fine-pored gel is employed.

    We can summarize the results of our numerous experiments by stating that we cannot propose a more serviceable catalyst than the cobalt-thorium-kieslegur catalyst.  We consider of equal value for synthesis performance the slowly precipitated thorium-free Co catalyst with about 1 per cent Ag on fine-pored silica gel which offers the advantages of a saving of thorium, of reproducibility in the synthesis reactor, and of better catalyst life.  The weaknesses of the thorium-free containing standard catalyst lie in the fact that it contains kieselgur with its unpredictable qualities and that its reproducibility is still somewhat uncertain.  The flactuations in the kieselgur, however, can be equalized by the addition of slight quantities of magnesium oxide and by heat pre-treatment at a specific temperature that is not too high.  Reduction in receptacles other than synthesis reactors is also technically objectionable.  Transporting the reduced catalyst under carbon dioxide causes the most active spots to be lost as a result of surface oxidation.  Therefore we consider the addition of about 1 per cent of silver to the cobalt catalyst to be one of the advantages of our procedure.  The reduction temperature is thereby lowered so far that we can reduce directly in the synthesis reactor without the necessity of taking a decrease in the yield as is the case with copper.  In conclusion, the following experiences gleaned in catalyst preparation may be mentioned:

    Potassium bicarbonate was proved to be better than potassium carbonate as the precipitating agent for the Fischer catalyst that was quickly precipitated and subsequently boiled since the catalysts become more active and more readily reproducible.  On the other hand, potassium carbonate must be used for the thorium-free catalysts since these catalysts are slowly precipitated without subsequent heating.  Under these circumstances a complete precipitation cannot be achieved with bicarbonate.

    Furthermore, washing with a minimum quantity of wash water was proved to be necessary for otherwise, despite freedom from alkali, less active catalysts would be obtained.

    We know from experience that the size of the excess of precipitating agent is of negligeable importance.  A direct relationship of catalyst efficiency with the PH of the precipitation was not noticeable.  The type of drying, whether in the air at 110 degrees, in a current of carbon dioxide, or in a vacuum, is equally unimportant.

    b.  Experiments with Medium Pressure

    As was already mentioned, the synthesis conducted under a slightly increased pressure brought about a substantial improvement in the paraffin yield.  Nevertheless, more than a year's work was necessary before the technical development of the laboratory apparatus had reached a point where we could obtain with certainty a total yield of 130-140 grams/Ncbm with a paraffin proportion (boiling point above 320 degrees) of upwards of 60 per cent.

    The pressure used by us in the laboratory pressure experiments ran from 12 atmospheres to a maximum of 20 atmospheres; no difference in paraffin production was found within this pressure range.  The charge velocity was the same as in the pressureless experiments: 1 liter gas/? 1 gram metallic cobalt/hour.  Experience shows that our procedure for attaining the highest possible paraffin yields with cobalt-kieselgur catalysts free of additions, which almost stopped producing paraffin after several days without pressure, turned out to be more reliable than the thorium-rich catalysts which are good paraffin producers without pressure.  Catalyst life was also satisfactory; after ten weeks of operation the catalyst still retained more than 90 per cent of its maximum activity.  The explanation for the inferiority of the thorium-containing catalysts under pressure to the catalysts free of thorium is based on the fact that former forms very high-molecular weight paraffin which leaves the catalyst to a lesser degree and therefore leads to the block of the active spots.

    The most important innovation in the experiments was the instillation for the first time of pressure flow manometers which permit exact measurement under pressure of the even flow of the smallest quantities of gas (e.g., 12 liters of depressured gas/hour = 1 liter gas/hour at 12 atmospheres).  The requisite pressure capillaries with fused manometer le? were made from special Jena glass.  The connection to the high-pressure piping was accomplished by means of stuffing boxes fitted with special soft rubber packing.  The pressure flow manometers constructed in this manner withstood a test pressure of 20 atmospheres, the glass and metal joints being found sufficiently tight.  The pressure capillaries were tested by putting the entire apparatus under pressure after installation before the start of the experiment.  Then through an analysis valve behind the synthesis reactor a constant volume of gas, e.g., 12 meters/hour, was let down through a flow manometer.  After a little while the proper manometer level could be read off on the pressure flow manometer.  The constancy of the result was tested by repeated readings over a period of time.  Varied volumes of inlet gas under pressure can be accurately gaged by adjusting the quantity of exit gas.  The corresponding quantity of let down gas is then stated to be the inlet gas volume.  Comparison of the inlet gas volume calculated by m    of the oxygen balance with the inlet gas volume measured by flow capillaries demonstrated that measurement of the inlet gas volume under pressure was far superior in most instances to calculation of the inlet gas volume.  An additional advantage lies in the fact that a more uniform operation of the reactors can be attained by keeping the inlet gas volume constant with the pressure capillaries.

    Later operation showed that a by-pass in the inlet gas capillaries was advantageous.  By cutting off the narrow capillary path it enables the product to be forced out of the pressure separator without risk, and makes possible an easy interchange of capillaries without interrupting the inlet gas feed.  This was very convenient when the pressure capillaries were gaged during operation.

    A brief survey of the performance of cobalt-kieselgur-catalyst employed by us, which was prepared by slow drop by drop precipitation of a cobalt nitrate solution in the cold with potassium carbonate, will be given in the following in order to facilitate a comparison with the iron catalysts developed by us at a later date for the carbon monoxide-hydrogen synthesis.  In general the precipitation lasted for more than 24 hours.  Catalyst life lasts for several months so that regeneration with hydrogen seldom comes into question.  

    In the following we give several values obtained by various methods of preparing our catalyst:

Expt. no.

Cat. no.

Temp. °C.

CO consum.

in exit % CO2

gas %CH4

%k2O/grams cat. for 100 Co

Yield solid + liquid product Nm3

% Par. >320

% Straight chain

(Table on page 148)

186°	71	1.0	7.7	=  0.324 kg/liter	Kt/day
appear as mean values				135        61       98
Division of the primary product into boiling ranges

(Table on page 148)

    Mean values

    If a lower yield is desired, especially if only one synthesis reactor is available (technically the process is run in two stages) then it is possible to manage with lower temperatures:

    Experiments with a lower CO conversion (charge velocity as usual 1 liter/1 gram Co)

Expt. no.

Cat. no.

Temp.

CO consum.

in the  % CO2

exit gas %CH4

%K2O in catalyst 100 Co

grams yield solid + liquid product Ncbm

(Table on page 149)

Mean values:

    It can be seen that the methane content is still proportionately high even with this slight CO conversion.  This is attributed to the good hydrogenation power of the cobalt.  One would think therefore that the catalyst could be adjusted to another cobalt concentration by kieselgur, thereby possibly checking the hydrogenating influence of the cobalt.  However, this was not successful, as is shown by the following table:

Cat. no. Expt. Content no. %K2O %Co

Temp.

CO consump.

%CO2 %CH4 in the exit gas

grams yield of solid plus liquid prod. Ncbm

% par. > 320°

% straight-chain

(Table on page 149)

    There are no regular great differences, in particular the methane content shows no progression of values.  There is a progression in the case of paraffin production which increases with rising Co content, whilst, as is evidenced by the boiling point figures, the proportion of hard paraffin rises.

(Table on page 149)

    The following series of experiments answers the question: what effect does alkali in the catalyst have on methane formation?

Expt. no.

Cat. no.

%K2O/cat..

Temp.

CO consumption

%CO2 %CH4 in the exit gas

g. yield solid plus liquid pr. Ncbm

%Par. 320°

% straight-chain

(Table on page 150)

      It is evident that with a rising proportion of alkali the synthetic temperature must be markedly increased to produce the same CO conversion.  This, however, assists in the formation of methane, as can be seen from the corresponding values.  At the same time it diminishes paraffin formation.  This remains even with a decreased CO conversion:

(Table on page 150)

    In conclusion, let us offer one more comparison; the behavior of a cobalt catalyst with a CO:H₂ - 1:1 synthesis gas.  All other experiments were conducted with a CO:H₂ = 1:2 synthesis gas:

(Table on page 151)

    The table shows: at 1:1 there is a smaller yield of primary product, a higher proportion of olefin and alcohol in the primary product, less straightchanedness of the paraffin, and also less methane formation.  In the case of synthesis gas 1:2, methane content diminishes in the course of time if the catalyst is kept at the same temperature.  This being the case, it is important in evaluating the methane value to know at what time the sample was taken:

(Table on page 151)

    II.    Investigations with Iron Catalysts

    a.    Experiments at Atmospheric Pressure

    As a result of the external circumstances caused by the start of the war in 1939 the experiments which were being conducted to synthesize hydrocarbons from carbon monoxide and hydrogen with iron catalysts, which heretofore had been of subordinate interest and had been undertaken in a modest way in connection with cobalt catalysts, became of major interest.  Since subsequent investigations were conducted exclusively under medium pressure, the experiments which were conducted previously at one atmosphere will be briefly presented here.

    Since we were dealing with what amounted to a new field of activity, the experiments must be evaluated in the light of an initial exploration in the field of catalysts, especially in view of the fact that many questions still remained unanswered.  However, this field did not appear urgent enough to devote more work to it.  It became  quite clear to us even in the early part of our work that it would not be possible, without intensive and systematic work, to develop an iron catalyst capable of completely replacing the cobalt catalyst in the atmospheric pressure process.

    The catalysts investigated for the most part consisted largely of mixtures of the following constituents: iron-copper-alkali with magnesium oxide or with aluminum oxide.

    Since the copper, according to our viewpoint at that time (future data on the role of the copper will be given later) served solely to facilitate the reduction of the iron, i.e., to lower the reduction temperature, it was present in all catalysts in the constant ratio of Fe:Cu = 4:1.

    Both catalyst combinations were investigated for the most favorable combination of alkali and metallic oxide, as well as their behavior with respect to variation of the CO:H₂ ratio in the synthetic gas and response to the reduction temperature.  It was found that, even under the most favorable conditions of composition and experiment con? at best yields of 60 grams of solid and liquid products/Ncbm synthesized gas were obtained over several weeks.  Contrasted with this were yield of about 130 grams/Mcbm with the cobalt standard catalyst (with thor?) Of the remaining investigated catalyst combinations only two more ser? will be stressed. The first aimed at progressive replacement of the cobalt by iron in the cobalt-kieselgur catalyst customarily employed by us.  In the second series, several iron-nickel (1:1) - aluminum oxide catalysts with assorted methods of preparation were the object of our investigations.

    The first series demonstrated that cobalt-kieselgur catalyst containing up to 40 per cent iron, with respect to the cobalt, evidenced good effectiveness, the yields, however, decreasing as the proportion or iron rose.  At the same time the optimum synthesis temperature rose. The content of cobalt was controlling in the reaction.  This is inferred by the fact that only water was formed as a by-product during the reaction whereas iron catalysts give carbon dioxide for the most part.

    The catalysts of the second series, iron-nickel catalysts, promoted with 5-15 per cent aluminum oxide, gave yields of about 80 gms of solid and liquid products, falling far short of the normal cobalt catalysts.  The type of precipitation for these catalysts is of little importance with respect to the total yield; however, it is possible to obtain catalysts by slow reverse precipitation (letting the nitrate solution of the metals drop into the potassium carbonate solution) in the cold which are characterized by an extraodinarily small bulk weight as compared with catalysts produced by other means (0.2 and 1.1).  Great economies of metal can be effected with the same catalyst space without influencing the yield.  In addition to the economies in metal there is still another advantage, namely, that they are easy to use because of their slight sensitivity to temperature.  With such catalysts the reaction proceeds mainly in the direction of water formation.  In essence this points to action on the part of the nickel which is neutralized by the addition of the iron.

    The catalysts with high and low bulk weights are clearly differentiated from each other with respect to their external characteristics.  The heavy catalysts are compact, vitreous, dark-brown; the light ones, on the other hand, are light-brown particles which display a tendency toward decomposition as a result of their soft, loose structure.

    So much for the experiments with iron catalysts in synthesis at atmospheric pressure.

    b.    Experiments with Iron Ca