Synthetic Fatty Acids and Detergents
The Wax Oxidation Process
According to Henkel the ideal raw material would consist entirely of straight-chain paraffins. Branched-chain paraffins gave rise to branched-chain fatty acids which were definitely dangerous as constituents of edible fat and gave soaps of poor detergency and unpleasant odour. Lower yields of the desired fatty acids were also obtained. If olefines were present the rate of oxidation was lower, the products were dark in colour, and the yield of the main fraction of fatty acids was less. Naphthenes gave rise to naphthenic acids which gave poor soaps and if aromatics were present there was a danger of producing carcinogenic substances. Iso-paraffins, olefines and cyclics gave excessive amounts of hydroxyl acids, as shown by the hydroxyl number of the distilled acids.
The best available raw material was Fischer-Tropsch gatsch from the normal-pressure cobalt catalyst process. Gatsch from the medium pressure process was less suitable and that from iron catalyst synthesis was the least suitable of the Fischer waxes.
The next best raw material was "T.T.H. - wax" - wax obtained from the product of the low-temperature hydrogenation of brown-coal tar. Most waxes of petroleum origin were less suitable than the above.
Henkel did not consider that it would be economic to attempt to improve an unsuitable wax by refining treatment, and up to the present have had no success in this direction even on the laboratory scale. They doubt whether it is possible to produce suitable oxidation gatch by mild thermal cracking of Ruhrchemie hard wax.
They have not tried the I.G. method for determining the proportion of branched-chain hydrocarbons in waxes, using SbCl5, but doubt its reliability. They believe that while pure normal paraffins do not react with this reagent they do so when mixed with iso-hydrocarbons. They consider that the only reliable test of the suitability of a wax for production of the fatty acids is by means of a test oxidation. The most suitable wax is one giving the maximum yield of C10 - C20 acids of highest melting point and palest colour. They stated, however, that the results of such test oxidations agreed with I.G. figures for the proportion of branched-chains, (the higher the content of iso-paraffins the less suitable the wax). They has not carried out test oxidations with pure branched-chain paraffins.
The following is a short summary of a document prepared by Henkel on the testing of waxes for the oxidation process.
"The suitability of a gatsch as starting material for the preparation of fatty acids is decided by its characteristics and by test oxidations. A good gatsch should have a low iodine number, and should boil mainly (ca. 90%) between 320°C. and 460°C. at 700 mm. as determined by distillation at 15 mm. Oxidation tests are carried out at 105 110°C., with an air rate of ca. 10 litres/100 g.wax/h., to a final saponification number of 135 - 140. Several tests on a 100 g. scale in glass reaction tubes, carried out simultaneously (in the same heating bath), serve to determine the best reaction conditions (time, temperature, amount of catalyst). The colour of the reaction product for a suitable material should not be darker than orange-yellow. A 2 kg. scale test in an electrically heated aluminium tube, 120 cm. long and fitted with a filter candle for distributing the air stream, is then carried out to permit determination of the yield and quality of the products. Working up is similar to the technical scale method but the unsaponifiable material (U.S.M.) is separated by solvent extraction instead of distillation. A second 2 kg. scale test, in which the unsaponifiable material from the first is incorporated in the starting material, is required for a complete estimation of the suitability of a gatsch".
The fatty acid plant of Deutsche Fettsaurewerke Witten used only Fischer-Tropsch wax as raw material, but the I.G. plant at Oppau used a variety of raw material, the principal one being T.T.H. brown-coal tar wax. Dr. Kurzinger, the manager of this plant, gave the following information:- During the war years T.T.H. wax formed 80% of the total wax oxidised, Fischer-Tropsch gatch (from Brabg, Schaffgotsch and Krupp Treibstoffwerk) formed 10% and 'Nerag' gatsch (petroleum wax from the dewaxing of spindle oil) the retaining 10%.
At the time of the visit, the plant was operating on "Espenheim Gatsch", a wax extracted from low-temperature brown-coal tar obtained from the Sachsiche Werke, Espenheim, and refined with liquid SO2. This wax is unsaturated (iodine number ca. 40) and must be hydrogenated before use. It contains some naphthenes and has a high sulphur content and was altogether less satisfactory than T.T.H. wax. They had received a consignment of 1,200 t. of this wax (of which 600 t. had been oxidised at the date of inspection) and when this had been used the plant would have to shut down. The yields of fatty acids obtained by the oxidation of 100 parts of the various waxes were stated to be as given in Table 59.
Dr. Kurzinger said that if the dehydration of the hydroxy-acids in the pipe still treatment has been complete, the properties of the main fractions of acids are similar in all cases (ester number 5 - 10, U.S.N. 2 - 4%) apart from the iodine number, which is higher, the higher the proportion of hydroxy-acids formed. Thus the iodine number of the main fraction was about 20 for Espenheim gatsch and about 5 for Fischer-Tropsch gatsch.
The total weight of gatsch oxidised and weights of acids obtained during the war years at Oppau are given in Table 60.
Although the process and plant used, both at Witten and Oppau, have been described in previuos reports, the following account of the oxidation of a good batch of T.T.H. gatsch at Oppau includes details not previously reported, and, at the risk of some duplication, appears worthy of inclusion in this report.
To a mixture of 40 t. fresh wax and 60 t. U.S.M. from a previous oxidation, 0.12 t. KMnO4 in aqueous solution is added and the whole heated to 140°C. The mixture is then pumped into the oxidation vessels, and as soon as the reaction has started, the temperature is reduced to 105 to 115°C. (usually 105 - 110°C.) Air at 40 - 50% cu.m./t. charge/hour is blown through until the acid number reaches 70 (sap. number 120 - 140). The normal period of time is 20 to 30 hours. The amount of catalyst used depends on the quality of the gatsch and may range from 0.12 to 0.20%. Increase in the sulphur content and olefine content of the gatsch increases the amount of catalyst required. From 0.05 to 0.20% of sodium or potassium carbonate can also be added with advantage.
The oxidised product amount to rather more than 100 t. is then washed with water at 70 - 80°C. and formic and acetic acids and manganese salts removed. The washed product 99 t. or more is then saponified with the addition of 10 t. NaOH and 24 t. water, and the 133 t. of mixture transferred to an autoclave and maintained at 110 to 150°C. under the prevailing steam pressure (about 10 atm.) for about 2 hours. The U.S.M.-I (44 t.) rises to the top of the mixture and is removed for addition to later oxidation batches.
The remaining 89 t. soap solution is then passed through a pipe still maintained at 280 - 330°C. under a pressure of 80 - 120 atm. The time of contact is about 45 - 60 mins. The pressure is then released and the solution passed through a second pipie still at 300 - 36°C. (Usually 350°C.) at atmospheric pressure, and thence into a vessel where then molten soap collects and U.S.M.-II is carried off in the steam. Amount of U.S.M.-II returned to oxidation is 16 t. The molten soap is then run into twice its weight of water and split by the addition of 95% H2SO4. The liberated crude fatty acids amount to 28 - 32 t. The vacuum distillation of the raw acids has been adequately described in previous reports.
The air leaving the oxidation vessels passes through water-cooled condensers and an oily condensate know as "condenser oil" and an aqueous condensate known as "condenser water", recovered. At Oppau the condenser oil was worked up together with the main oxidised charge, but at Witten it was disposed of, without further treatment, as a by-product. The air, after leavin g the condensers, still contains volatile organic matter which is lost, and other quite appreciable losses occur at later stages in the process. The nature and extent of these losses is shown in the following weight balance, given in Table 61, based on data supplied by Dr. Helm, manager of the Witten oxidation plant.
Some data for the wax throughput, and yields and production costs for fatty acids at the Witten plant are given in Table 62. In 1943 the wax throughput reached a maximum (actually rather more than the related throughput of 40,000 t.) and this was the best year of operation the plant had experienced. Full details were also obtained for the process costs but as these have already been reported by J.W. Vincent (BIOS Final Rreport No. 805) they have been omitted from this report.
The wax oxidation pant of the I.G. at Magdeburg, which never came into operation, was to operate the Hubbe and Farenholtz process. Some information was obtained concerning this process from the Lurgi Company who had built the plant. The process used oxidation with air at 25 atm. pressure and a temperature of 120 - 140°C. Under these conditions, no catalyst was required and the reaction time was reduced to 6 h. As the exit gases were under pressure the recovery of the volatile products was simplified, and the losses were less than those of Deutsche Fettsaurewerke, who claimed, however, that their own overall efficiency was higher.
The oxidation vessels had to be made of stainless steel (instead of aluminium as at Witten and Oppau), and the capital cost of the plant was very high, viz., 60 million RM. for a plant of 50 t. wax per about 55% and the yield of residual acids was somewhat higher than at Witten.
The soap prepared from the HUbbe and Farenholtz acids was claimed to have a less unpleasant odour than the Witten product.
The Smell Caused by Synthesis Soaps
The main fraction of fatty acids was used primarily for soap manufacture, but an objection to their use for this purpose is the unpleasant odour which develops on the skin after washing with soap containing these acids.
According to Henkel et Cie, this property is due to the presence of branched-chain fatty acids. When the soap is used for toilet purposes, the soap is absorbed by the skin and the free fatty acids gradually liberated by the stronger acids of the sweat. Enzymes in the skin decompose the branched-chain fatty acids to lower acids which give rise to the objectionable odour. Whether or not this mechanism is correct, the production of the odour is undoubtedly associated with the human skin, and varies from individual to individual. Some people can use the soap without any unpleasantness at all - others develop the odour with soap containing only 10% of synthetic fatty acids. One of Henkels employees was exceptionally sensitive and was used by the Company for testing soap samples. For the majority of people, soap containing 20 - 25% of synthetic acids can be used without unpleasant after effects. Henkel would not, however, recommended the use of the acids in good quality toilet soap. The soap is perfectly satisfactory for laundry purposes. No odour is left on textiles even with soap made entirely from the synthetic acids. They can also be used in soap powders because of the stabilizing effect of the excess alkali present. Repeated recrcystallisation of the main fraction of fatty acids removed the property causing unpleasant small but Henkel did not consider this to be of more than academic interest.
The views of Dr. Kurzinger of I.G. Farben, Oppau, on this subject were sought. He considered that the odour of synthetic soap was due to three causes:-
The first two are a function of the oxidation and purification processes, and the third, a function of the raw material. Dr. Weiss (who unfortunately was not available for interrogation) of the Ammonia Laboratory had prepared a number of pure branched-chain fatty acids, some of which had unpleasant odours. He definitely proved that branched-chain paraffins give rise to branched-chain acids on oxidation.
Dr. Kurzinger had oxidised a synthetic C20 straight-chain paraffin. The main fraction of acids with 3% unsaponifiable matter and an ester number of 20 - 30 gave a soap which had an unpleasant odour but not so pronounced as the technical synthetic acids of ester number 5 - 10, U.S.M. 2 - 4%. After further refining, the ester number was reducd to 5 and the U.S.M. to 1% and the resulting soap was completely without odour. Dr. Kurzinger also oxidised two fractions of a Fischer gatsch which by distillation and solvent extraction had been split into straight-chain and branched-chain concentrates. The soap prepared from the straight-chain concentrate had much less odour than that from the branched-chain material, although both samples of acids had the same ester number.
In Dr. Kurzinger ??? the odour which arises immediately ?? an washing with these soaps is due to the presence of unsaponifiable matter and lactones. Soap substantially free from these impurities gives no immediate odour. The smell which develops on the skin after washing is due to the branched-chain fatty acids set free by the acids of the sweat. He did not postulate the enzyme action referred to by Henkel and, indeed, ad certain free synthetic acids themselves have an objectionable odour this does not appear to be necessary to the argument.
Dr. Rossow, cheif chemist of Deutsche Fettsaurewerke, did not consider that branched-chain acids were responsible for the odour phenomenon exhibited by synthetic soaps, but believed it was due to the lactones of hydroxy-acids. His evidence was as follows.
If a sample of the main C10 - C20 fraction of fatty acids is steam distilled in vacuum in the presence of excess caustic soda, an oily distillate of foul odour is obtained. This material is neutral but has a high saponification value. The residual soap after this treatment has very much less value. The residual soap after this treatment has very much less odour. He considers that, in the soap solution, lactones are present as unstable salts which are broken down in the steam treatment and the free lactones distil off. He stated that it was known that lactones have a strong affinity for the skin and pointed out that large-ring ketones usually have strong odours.
He claimed, further, that they had oxidised a wax, obtained from Dr. Pichler of the K.W.I, Mulheim, which was guaranteed to consist only of straight-chain paraffins, and that this had given evil-smelling acids. He agreed, however, that the matter was for from settled and regretted that he had not had sufficient time to make a more complete study of it.
The matter is complicated by the fact that it is not always clear precisely what odour was being referred to by the persons interrogated - the odour of the free acids, the odour of the dry soap, the odour which arises when washing or the odour which gradually develops on the skin after washing. The questions put by the authors of this report related to the last of these, which in their view of perfume in the soap.
Dr. Herbert, of Lurgi, said that one could wash with soap containing synthetic fatty acids from the first two weeks without undue discomfort but that after that, with continued use of the soap, the smell on the skin became intolerable.
The Iodine Number of Synthetic Fatty Acids
Questions were put concerning the cause of the increase in the iodine number of synthetic fatty acids with increase in time of contact between iodine solution and the acids, whereas so such increase takes place under similar conditions with the natural fatty acids. Henkel considered that it was probably due to the substitution in the side chains of the iso-fatty acids and stated that the phenomenon was more marked with products obtained from the oxidation of petroleum gatsch than with those from Fischer gatsch. Dr. Rossow of Witten considered that when ?? solution is used, the strong acetic acid may cause dehydration of hydroxy-acids to form olefines and hence cause increased iodine absorption.
The impression was gained that neither organisation had paid much attention or attached much significance to the phenomenon.
To make toilet soap last longer, Deutsche Fettsaurewerke produced their air-blown "floating soap" which had been described in previous reports. The I.G. at Ludwigshafen - Oppau had devised another method for effecting soap economy, based on the use of a urea-formaldehyde condensation product as a "diluting" medium. Tablets of soap were produced which lathered in a satisfactory manner and yet contained only 15% of fatty acids.
The "Soap Base H.F." was prepared as follows:- 100kg. of 30% formalin and 100 kg. of urea are heated to 45°C. for 30 minutes, caustic soda being added to maintain pH = 8 throughout this period. Then 0.4% of sodium phosphate is added as s stabilizer and to maintain the Ph at 8, and the product evaporated in vacuo to sp. gr. = 1.25 at 50°C. The clear solution is then cooled with constant stirring and whn cold forms a translucent paste.
To prepare the soap, the 'base' is heated to 80 - 90°C. until it becomes cloudy (10 - 15 minutes). The fatty acids and equivalent amount of caustic soda are then added with stirring and the mobile solution poured into moulds and allowed to cool.
Synthetic Edible Fat
Contrary to statements which have been made elsewhere, Deutsche Fettsaurewerke used only natural glycerine derived from inedible fat for the production of glycerides from their synthetic fatty acids. The synthetic glycerine manufacture by I.G. at Heydebreck was not considered pure enough for the purpose.
The Sesterification process has been described in previous reports but the following additional details were obtained. The acids are esterified with the theoretical amount of glycerine using 1 to 1.5 parts of zinc dust per 1,000 parts of fatty acids. The temperature is 210 - 220°C. and the pressure initially 100mm. The pressure is then reduced to 20 mm., and in the last two hours, to 15 mm. The total time for a charge of 3,00 to 7,00 kg. is 8 to 10 hours. The products, with acid number 3 to 3.5, are cooled and discharged into a tank and treated with 20% sulphuric acid to dissolve the zinc. The product is then neutralised with caustic soda solution, and agitated with a mixture of active carbon and bleaching earth at 110°C. The main object of this treatment is to remove traces of soap. After filtration, the fat is heated to 250°C. under a vacuum of 2 to 3 mm. and steam, preheated to 300 - 360°C., blown through it for 13 to 18 hours. It is essential to maintain a good vacuum during this deodorising process, which was stated to be vital for obtaining good-quality fat. The fat is then cooled and again filtered.
Information concerning the suitability of these fats for human consumption was sought.
Dr. Rossow supplied a copy of a minute (16) from an official of the German Health Department to State Secretary Keppler, dated 1039, which stated that more than a thousand experiments on animals had shown that the fat made by Deutsche Fettsaurewerke was non-toxic and non-irritant and was digested, absorbed and utilised in a perfectly satisfactory manner. Experiments on 6,000 human subjects (in concentration camps) had shown that the synthetic fat was in every way a satisfactory substitute for the natural product. The German Health Department therefore approved of its use for human consumption.
The physiological experiments on synthetic fats carried out for the Reichsgesundheitsant were under the direction of Prof. Elossner, who is now at Hemendorf, near Hannover, and is engaged in writing a comprehensive account of this work.
A rather different picture was obtained from Henkel. They considered that the presence of branched-chain fatty acids made it extremely dangerous to use the synthetic fats as human food because acids of this type could be definitely toxic (e.g. phtirionic acid - a product of the tuberculosis bacillus) and they consider that permission to use the fat should have never been given. They referred to the work of Prof. Jantzen, of Friburg, who had carried out extensive feeding trials with rats. Rats which had previously been fed on natural fat were starved for a period and then re-fed (a) with natural fats (b) with various samples of Witten fat (c) with fat prepared from pure branched-chain acids. In case (a) the rats rapidly regained their former weight. In case (b) the weight increased much more slowly and never regained the original value. In case (c) the weight continued to fall and the rats died.
Prof. Thomas, formerly of Leipzig, had shown (Deutsche Medizinische Wechenschrift, 1946, May 10th, p.18) by tests on human subjects that the toleration limit for the synthetic fat was much lower than for the natural fats and that excessive amounts of dibasic acids appeared in the urine leading to kidney disorders and ultimately to decalcification of the bone structure. (A photostst copy of this paper and also of a paper dealing with synthetic fats by Kaufman, Fette and Seifen, 1944, p.215, were obtained (7), (6).
Henkel considered it significant that the work of Profs. Jantzen and Thomas had been suppressed by the Government whereas Prof. Flossner had been allowed to publish his work (Die Ernahrung, 1943, 8, 89). They also attach some significance to the fact that dogs would not eat the synthetic fat!
Dr. Kurzinger, of I.G. Farben, Oppau, stated that the fats synthesised from pure normal paraffins were quite satisfactory but those containing branched-acids were less satisfactory than natural fats. Dr. Schiller, of I.G. Farben, Ludwigshafen, Oppau, had established this by feeding tests with rats and his results were in agreeement with those of Prof. Thomas, with whom he had discussed the whole problem. Dr, Kurzinger considered that the acceptance of the Witten fat by the Reichgesundheitsamt was a political move.
By-products of the Oxidation Process.
An excellent survey of the actual and possible uses of the lower- and higher-boiling fatty acids and other by-products was published by Dr. Ludwig Mannes, of Menkel, in Die Chemie, 1944, 57 and the main object of the visit to Henkel was to obtain further information on points arising from this paper. It transpired, however, that Mannes was at the Henkel factory in the Russian Zone with all his papers and patent applications dealing with the by-product side. The staff at Dusseldorf, therefore, were not able to add much to what has been published by Mannes.
Up to the present, the foul-smelling waste air from the oxidation process has been injected into the boiler furnaces to satisfy the local authorities. They had tried scrubbing it with active carbon, but the oxygen content (11%) was sufficient to fire the carbon.
By azeotropic distillation of the aqueous condensate from the air coolers, an acid concentrate containing 79.5% formic and 8.7% acetic acids had been obtained which it was intended to use for preserving cattle food.
Although a number of uses were developed for the C4 - C9 acids, the main application was as modifiers in the manufacture of glyptal resins. Dicarboxylic acids produced by oxidation of these acids with nitric acid in the presence of vanadium pentoxide were found to be suitable for the preparation of nylon polymers, but the yields of acids so far obtained were not high enough to make the process practicable for industrial purposes. Dr. Kurzinger, of Oppau, stated that the C4 - C9 acids were being used for manufacture of plasticizers either as the acid component of esters with higher alcohols, or by hydrogenation to the corresponding alcohols and esterification with phthalic acid.
One of the main uses of the C18 - C22 acids ("after runnings") was in the preparation of greases and wire drawing lubricants.
The main use of the residue from the ditillation of fatty acids was in the lacquer industry. Although heating the residue to a high temperature in vacuo produced a hard, brittle resin or gum-like product, lacquer manufactures preferred the untreated distillation residue. If the residue is dissolved or dispersed in methyl alcohol and then neutralised with caustic soda a dark coloured colloidal solution is obtained which found use as a binder for pigments in camouflage paints and was sold for this purpose to Herberts of Wuppertal.
The C10 - C14 fraction of acids was used by the I.G. as an emulsifier in the manufacture of Buna rubber.
The unsaponifiable matter which is separated upon the oxidation product and normally is returned to the oxidation vessels, contains alcohols. Henkel had not succeeded in recovering these alcohols, but had converted then into the corresponding fatty acids by heating the crude U.S.M. with 5 - 10% excess of NaOH (based on hydroxyl number) in a close vessel to 200 - 250°C. The product was then distilled in vacuum and the soaps obtained as a residue. It was stated that this might give better yields of soap acids than returning the material to the oxidation vessels.
At Oppau, the "U.S.M.-II" recovered from the crude soap was distilled, and the fraction distilling below 280°C., which contain 50% of alcohols and ketones was hydrogenated under pressure to convert the ketones to alcohols. The product was then esterfied with phthalic acid and used as a plasticizer without separating the paraffinic material. This had been carried out on a large scale, using batches of 50 - 100 t.
The oxidation of Hard Wax
An emulsifier for use in the paint industry, sold under the trade name 'Parestol', was manufactured by Rheinpreussen at Moers-Meerbeck by the oxidation of crude wax, m.p. 75 - 80°., extracted from the Fischer-Tropsch catalyst. The precess was as follows:-
The wax is filtered to remove catalyst dust and then heated to 160°C. by steam coils in an aluminium vessel 2.5 m. high by 1.5 m. diameter. Air is then blown through distributors fitted in the bottom of the vessel at a rate of 100/cu.m./h./100 kg.wax. No catalyst is used, and after 1 to 2 hours induction, the reaction starts (indicated by a rise in temperature) and the steam is cut off. The oxidation then proceeds at a temperature of 120°C. with a constant rise in acid number. After 10 - 12 hours the acid number reaches 60 and after 15 hours, 75. This is the normal end point for preparing emulsifiers for use in the paint industry, but the acid number can be increased, if desired, to 120. At the specified air rate, no steam is required to maintain the temperature but at lower air rates, some steam heating must be used. from 100 kg. of wax, 105 kg. of product, acid no. ?, sap. no, 140, softening point 40 - 50°C., are obtained. The crude product was sold, without further treatment, to Herberts of Wuppertal and Wiegand of Oberhausen for the manufacture of oil-bound distempers and cheap camouflage paints. It can be used for the preparation of ointment bases and other pharmaceutical products. The cost of production is given as 35 Rpfg./kg. based on a cost of 30 Rpfg./kg. for the catalyst wax used as raw material. The annual production was 1,200 t.
The blow-off gases were cooled and low-boiling acids (below C11) were recovered and sold for use in the leather industry.
According to Dr. Sauter, the catalyst wax obtained from the Brabag (Ruhland - Schwarzheide) plant was oxidised in aluminum vessels by blowing with air at 110°C. in the absence of catalysts on a scale of 5 t. per day. There was no noticeable induction period and an acid number of 50 - 60 was reached in 36 hours. The crude product was marketed under the name "Emulgierwachs P.S." by the Paraffin Verwertungsgesellschaft (a company founded by I.G. Farben and Brabag) for use, after saponification, as a textile impregnate and constituent of ointment bases and lubricating greases. An excellent emulsion for sulphonamide ointments was obtained was obtained by blending equal parts of the saponified products, water, and the ointment base described on page 147.
This product (Emulgierwachs P.S.) must have been almost identical with the Parestol made by Rheinpreussen.
The "O.P." Process
As reported in early CIOS Reports, Ruhrchemie had developed to the pilot-plant stage a process for obtaining emulsifiers (similar in general properties and utility to Parestol and Emulgierwachs P.S.), in which their Hartwachs was oxidised with nitrosyl sulphuric acid. The products were designated "O.P.3", "O.P.32" etc. This work was carried out by Dr. Velde, who is no longer employed by Ruhrchemie, but a survey of his work has been prepared by Dr. Clar of Ruhrchemie and this constitutes the best account of the process yet obtained.(1)
Velde has always claimed that the fatty acids present in these products were similar length to the original wax, but Dr. Buchner, head of the analytical laboratory, stated that the Velde based this claim on the acid number etc., of the product after extracting unsaponifiable matter with heptane, but since the latter does not remove the higher hydrocarbons, his low acid number was not due to long-chain fatty acids but to hydrocarbon impurities. Buchner claims that by extraction of the crude "O.P.3" with 80% ethyl alcohol at the boiling point he removed 80% of the fatty acids present and was able to prove that these were all in the range C10 - C18. Ruhrchemie therefore believe that the O.P. process if the most efficient way of producing soap acids by wax oxidation, as very few by-products are formed. They claim that oxidation of the hard wax by notrosyl sulpuric acid gives a higher proportion of short-chain acids than oxidation of the "block wax", m.p. 50 - 52°C.
Catalysts were definately harmful in the oxidation of the waxes but might be of value in the oxidation of the Diesel oil. Presence of olefines was detrimental to the process.
Ruhrchemie definitely considered that the nitrosyl sulphuric acid process was superior to the chromic acid process which they had also studied. They claimed that this opinion was not biased by the fact that they were owners of a nitric acid plant.
Dr. Kolbel, Rheinpreussen, had prepared in experimental quantities a product designated as "P.C.F." which was claimed to be a high grade high-pressure bearing grease. It was compounded according to the following:-
For hard greases, wax with a low chlorine content was used and for soft greases on of higher chlorine content.
Fatty Acids via the OXO Process
Ruhrchemie had investigated several methods of preparing fatty acids suitable for soap manufacture from the C10 - C17 Fischer-Tropsch olefines via the OXO reaction. They tried out the process of oxidizing OXO-aldehydes by air on a semi-technical scale. A batch of 80 kg. of crude OXO aldehydes is stirred in a 100 litre mixer with 20 - 25 kg. Na2CO3 in aqueous solution and air blown through the mixture for 8 hours. The product is a stiff paste containing the paraffins from the original raw material used in the OXO reaction, soap and sodium carbonate solution. It is then treated with dilute ethyl alcohol and maintained at 60 - 80°C. and pH = 9.1, when the paraffins can be separated off, the soap salted out and the fatty acids recovered by splitting with mineral acid. A cheaper process is to heat the paste in a mixer to 170°C. and distil off the paraffins and water, leaving a dry mixture of soap and soda which can be used directly as a soap powder.
They also tried the fusion of aldehydes, alcohols and esters with alkalis. The crude aldehydes are mixed with the theoretical amount of caustic soda and heated in an autoclave under 5 atm. nitrogen pressure to 320°C. The pressure rises to 50 atm. due to evolution of hydrogen. The crude soap is obtained by distilling off the hydrocarbons, but as it contains traces of catalyst from the OXO reaction, it must must be split with mineral acid and the free fatty acids recovered. The yield is 80 - 85% of theory. Alkali fusion of alcohols is carried out in a similar manner but the product is inferior to that obtained from the aldehydes. The best product, however, is obtained by alkali fusion of the esters, obtained by the Cannizzaro reaction from the aldehydes, because they can be readily purified before carrying out the fusion process.
Soap can be produced by direct alkali-fusion of the high boiling fractions of primary products, obtained by synthesis with iron catalysts, as these products contain a large proportion of oxygen compounds.
The final soap in all cases is deodorized by heating the dry material in a stream of air.
The method of analysis of olefines involving oxidation with nitric acid, sp. gr. 1.25 - 1.30, devised by Dr. Rottig of Ruhrchemie, can also be applied to the preparation of fatty acids in the soap-making range. It is advisable for this purpose to use 50 - 100% excess of HNO3 which, however, can be recovered.
To obtain suitable olefines for this process a method of dehydrogenation of paraffins was developed which gave a predominance of olefines with the double-bond in a mid-chain position. The method is as follows:-
Paraffins in the range C20 - C40 are melted and mixed in a heated feed hopper with bromine (one mole/mole paraffin) and passed into a reaction tube containing activated alumina or aluminium silicate. The upper part of the tube, maintained to 200 - 400°C., acts mainly as a preheating zone and the lower part (at 350 - 450°C.) as the reaction zone. The reaction consists of bromination followed by de-bromination and shift of the resulting double-bond towards the centre of the chain. The throughput used is 10 - 20 volumes liquid feed per volume of catalyst per hour and an absolute pressure of 100 - 360 mm. mercury or even lower is necessary.
For equi-molar proportions of bromine and hydrocarbon the yield of olefines is 50 - 60% of theory. Using 1.5 moles bromine/mole hydrocarbon the yield rises to 70 - 80%. Unchanged paraffin and undecomposed bromo-compounds (about 5%) can be recycled and the HBr can be reconverted to bromine by oxidation with air over a tungsten catalyst. The losses of hydrocarbon material are of the order of 3 - 5%. For C35 - C40 paraffins the composition of the olefines obtained was:-
The relative merits of the various methods of preparing detergents from the primary products of the Fischer-Tropsch process were discussed with the chemists of Ruhrchemie and Henkel and with Dr, Schwen of I.G. Farben., Ludwigshafen.
The sulphation of olefines was considered first, and Dr. Rottig of Ruhrchemie described the process he had used as follows. A C12 - C18 fraction, containing a high proportion of a-olefines, is treated with fuming sulphuric acid with intensive stirring at a temperature maintained between -5° and +5°C. The acid contains 5 - 10% excess SO3, and a 10 - 20% excess of acid, excess of acid, calculated on the olefine content of the hydrocarbons, is used.
After 30 to 60 minutes, the temperature is allowed to rise to the room level and the mixture is neutralised with caustic soda (30 - 40%) to pH 10 to 10.6 taking care to maintain the temperature below 50°C. The unattached paraffins are then extracted with hexane. Very little polymerisation takes place, if the temperature during the sulphation has been kept low, and the yield of sulphate ester should be 90 - 95% of theory .
Henkel, however, stated that the yield in this process was only 70% of theory and that the separation of the paraffins from the esters was a difficult and expensive process.
The products are esters of secondary alcohols and although their detergent properties are very good they cannot be obtained as dry, free-flowing powders, and Henkel found that they could not handle them in their filling machines for soap powders. Dr. Schwen, however, considered direct sulphation of olefines the best method detergents from Fischer-Tropsch oils, and that by the use of suitable machinery there was no difficulty in incorporating the products in soap powders.
Ruhrchemie considered that a disadvantage of the sulphated olefines was the high pH (10) at which they must be used.
OXO alcohol sulphates are also excellent detergents. The OXO alcohols are primary ones and give sulphate esters which are obtainable as dry powders and can be used at pH 7 and are therefore suitable for the washing of delicate fabrics. Ruhrchemie consider that the OXO product was superior to that derived from natural alcohols due to the greater range of chain length. Primary alcohol sulphates are more stable to heating than the secondary alcohol product, but should not be used at temperatures much in excess of 60°C. Both Ruhrchemie and Henkel considered that, starting from olefines, the production of alcohols by the OXO process and their conversion to sulphates was a more economic process than the direct sulphation of the olefines, in view of the greater value of the product.
The hydrocabon sulphonates prepared by the Mersol process were inferior washing agents to the alcohol sulphates, were not obtainable as dry powders and work only in alkaline solution. They are, however, stable at 100°C. and can therefore be used in boiling solutions are are cheap to produce. The latest type (ersol H), prepared by stopping the sulpho-chlorination after 30 - 40% conversion, is an improvement over the early types whose washing efficiency was impaired by presence of di- and poly-sulphonates. Even with the improved product, the washing efficiency is low compared with other sulphonate detergents such as Igepals, because the So3H group occurs at random along the chain and is not restricted to the desired terminal position.
In general, Dr. Schwen stated that none of these detergent could be used in tablet soap and although they could be used satisfactorily for many purposes in laundry work they were unsuitable for washing cotton goods. Repeated use of any of these products, even the sulphonated primary alcohols, caused a grey colour to develop on cotton due to the absence of colloidal matter to "float-off" the dirt/ This could be partly, but entirely, overcome by adding 2% of Tylose to the washing powder.
Finally a diagram prepared by Ruhrchemie, which summarises the various methods of preparing fatty acids and detergents from the primary products of the Fischer-Tropsch process, is reproduced in Fig. 9.
Summarizing Flow-Sheet of the Rheinpreussen Works
In conclusion, as an example of how the synthesis may be conducted and the primary products worked up to readily marketable secondary products, the complete flowsheet for the Rheinpreussen synthesis works is given in Figure 10.