Return to Table of Contents

5.  Synthesis of Aromatics and Production of Base stocks.

Since isoparaffins constituted only 10 to 15 percent volume of C-3 gasoline and none of B-4 and since components other than synthetic isoparaffins and base stocks were used only in small quantities in these aviation fuels the base stocks themselves than consisted at least 85 percent of Germany’s total aviation gasoline volume..

Most of these base stocks originated in coal and coal tar hydrogenation plants. Only a very small volume of carefully selected petroleum fraction was blended directly into aviation gasolines. These plants consist of three stages of hydrogenation, the first (sump) phase being the bulk destruction operation to produce an intermediate boiling distillate from the coal or heavy tar, the second being a purifying treatment of the distillate, and the third being a fine hydrogenation step producing directly (as the only product) a gasoline of the required end point. All material boiling above the gasoline end point is recycled back to the third stage feed.

The B-4 aviation gasoline of Germany was this hydrogenated gasoline, stabilized to the specified vapor pressure (refer Table II). The quality varied somewhat, depending upon the raw material to hydrogenation, and individual gasolines needed some quality correction, either with small amounts of isoparaffin or outside base stocks. In general, however, the straight hydrogenation gasolines constituted the total supply of B-4 quality. In Table IV are given a few average data for these gasolines obtained from four (4) different hydrogenation plant feeds, all of which were used in Germany during the war.

TABLE IV
Properties of B-4 Base Stocks from
High pressure Hydrogenation Plants.

Feed to Hydrogenation

Brown
Coal

Stein Coal

Brown Coal Tar

Stein
Coal Tar

B-4 Base Stock

       

Density at 59° F.

0.723

0.730

0.725

0.725

Volume percent Distilled at 212° F.

65

57

58

65

End Point, ° F.

270

308

302

320

Paraffin Content, percent volume

53

40

60

37

Naphthene Content, percent volume

42

52

30

55

Aromatic and Olefin Content, percent volume

5

8

10

8

Octane Number, Motor Method, Unleaded

73

73

69

76

Octane Number, Motor Method, With 4.35 cc Tetraethyl Lead/Gallon

90

91

89

94

The supply of the high quality 85 percent base stock component to C-3 grade aviation gasoline involved additional processing of the hydrogenated gasolines. In order to obtain gasolines that were high in anti knock performance throughout the whole range of air-fuel ratios, aromatizing processes were invoiced.

By applying a particular as of operating conditions to the second stage of hydrogenation, the Ruhröl - Welheim installation produced a high aromatic content base stock directly. Distillate from the sump phase hydrogenation of coal tar pitch was fed to a second stage operating at 700 atmospheres pressure over a new catalyst containing molybdenum, chromium, and lead on an inert carrier. At 930 degrees Fahrenheit and in one step, a 350 degrees Fahrenheit end point gasoline was produced which contained 40 to 45 percent volume aromatics and which was used directly as the base stock ingredient of C-3 gasoline. This base stock had an unleaded octane number of 80, and with 4.35 cc. tetraethyl lead per gallon it was 92. This process of producing directly in hydrogenation plants a highly aromatic aviation gasoline base stock was a new development in Germany and was being widely discussed. It is likely that application to locations other than Welheim would have been made had earlier conditions continued to prevail in Germany

Perhaps the most important aromatizing operation was the “DHD Process”, an operation used on hydrogenated gasoline to increase their aromatic contents. Hydroforming was also used, but on a small scale only. catalytic cracking was studied but no plant was in operation. Also, several processes were in operation synthesizing individual aromatic, but they made a small contribution only to the total gasoline volume. There are discussed below these processes and their contributions to the German aviation gasoline supply.

(a)  The DHD Process.

The DHD process (Dehydrierung unter Druck or dehydrogenation under pressure) was developed by I.G. in Ludwigahafen. It was a catalytic process for increasing the aromatic content of a gasoline catalytic process for increasing the aromatic content of a gasoline, through both naphthene dehydrogenation and paraffin cyclization.

At the end of the war there were four (4) DHD plants in operation Ludwigahafen, leuna, Scholven and Pölitz. The combined intake capacity of these four plants was about 20,000 barrels per day. These plants were fed gasolines produced from both coals and coal tars. There were about ten (10) DHD plants and plant extensions planned which were never completed. It was planned that ultimately nearly all of the hydrogenation plant gasolines and certain crude oil factions as well, would have been processed through DHD plants.

Because of their high naphthane contents, gasolines from stein coal tars were preferred feeds to DHD. By altering operating conditions to encourage paraffin cyclization as well as naphthene dehydrogenation, gasolines from brown coal and brown coal tars were also greatly increased in aromatic content by this operation.

The feed gasolines to the process had end points of about 360 degrees Fahrenheit. These feeds were first stabilized to remove ca. 15 percent volume overhead which was the non-asphthene containing fraction boiling to about 160 degrees Fahrenheit. The stabilized gasoline was then pumped together with recycled hydrogen gas through a feed-product heat exchanger and a preheater, which raised the temperature to 930 degrees Fahrenheit. The vapor mixture entered the top of the first of a series of five (5) reactors. The operating pressure was 25 atmospheres total of which 10 atmospheres was the hydrogen partial pressure, when the feed gasoline originated from brown coal (or its tar). For stein coal gasolines, the total pressure was 50 atmospheres, of which 35 was hydrogen. (The lower pressure with brown coal materials was used to encourage paraffin cyclization).

The reactors were filled with a catalyst consisting of 10 percent weight MoO3 on Al2O3. The alumina was precipitated and impregnated with molybdemum acide and formed into cubes of about ½ inch on a side. (Catalyst was made from “Tonerdo” (hydrated alumina earth). The earth was first dissolved in caustic and then precipitated at 120° F, with HNO3 at a pH of 5.5 to 6.5. The precipitate was filtered, washed and dried up to an 80 percent Al2O3 concentration, pilled into ½ inch cubes, and calcined at 840° F. The catalyst cubes were then washed with an ammonium molybdate solution of such concentration that the final dried catalyst contained 10 percent wt of MoO3. The catalyst was dried at 400° F. for a short period and than at 750° F. until all amounts liberation ceased. The apparent density of the finished catalyst was about 0.8) Each reactor contained about 280 cubic feet of catalyst. The reactors had steel shells lined with fire brick and an internal liner of N8 steel. The space velocity employed was about 0.5 volumes of liquid feed per volume of total catalyst in the system per hour.

The endothermic heat of reaction caused the temperature to drop from 930 degrees Fahrenheit at the top of the first reactor to 840 degrees Fahrenheit at the bottom exit. A heater was therefore supplied after each of the first four reactors, raising the temperature back to 930 degrees Fahrenheit at the top of the second and third reactors. With the extent of reaction subsiding, the entering temperature in the fourth reactor was raised to 950 degrees Fahrenheit, its exit temperature was ca/ 930 degrees Fahrenheit, and the fifth reactor feed was 970 degrees Fahrenheit with very little temperature drop occurring through it.

A sixth reactor was used for saturation of olefins. After leaving the fifth reactor, the temperature was lowered to about 650 degrees Fahrenheit. The sixth reactor was filled with DHD catalyst except for the bottom fifth which was filled with floride earth.

After 40 hours of operation on brown coal gasoline, or 250 hours with stein coal products, a regeneration for carbon removal was necessary. A 20 to 24 period was required for the complete regeneration. In regeneration, exit gas use recycled to control burning rate and limit the temperature to a section of 1,030 degrees Fahrenheit. The carbon deposition on catalyst was equivalent to abut one percent weight of brown coal gasoline and 0.1 percent weight of stein coal gasoline which corresponded to a coke content on spent catalyst of about 3 percent weight.

The life of the catalyst was at least a year and perhaps would become considerably longer with more operating experience. Sulfur was a definite catalyst poison, but this was a problem in Germany only when operating on crude oil fractions. In general, stocks with the lowest possible sulfur content should be chosen as feeds.

Operating under the above described conditions, the yield of redistilled, stabilized gasoline was 75 to 85 percent by weight of the stabilized gasoline fed to the DHD unit proper. (The higher yield was obtained from stein coal gasolines).

The DHD outturn contained 65 percent volume of aromatics, so that where the original 15 percent of low boiling fraction was reblended the final gasoline contained about 50 percent volume of aromation. The overall might yield based on the original hydrogenated gasoline, was therefore 70 to 87 percent and the corresponding volume yield figures were 75 to 83 percent.

The final product from this DHD operation had the following averaged properties:

Density at 59° F.

0.760

Volume percent distilling at 212° F.

48

End Point, ° F.

340

Paraffin, percent volume

30

Naphthene, percent volume

20

Aromatic, percent volume

50

Olefins, percent volume less than

0.5

Octane Number, Motor Method, Unleaded

80

Octane Number, Motor Method, With 4.35 cc Tetraethyl Lead/Gallon

92

Octane Number, Motor Method, unleaded, of Residual Oil after Aromatic Extraction

70

There appears on the following page a photostat of an I.G. tabulation showing the properties of DHD gasolines made from various raw materials.

A copy of a speech by Dr. Pier of I.G. in 1941 was transmitted to the Bureau of Ships. This paper gives some of the background of German aviation gasoline developments leading up to the manufacturing position exiting at the end of the war.

XIII. Uber Flisgerbensine und ihre Herstellung.
(I.G. Ludwigshafen-speech by Dr. Pier on 21 November 1941)

There was also transmitted the following document describing the DHD process.

XIV.Technischer Entwicklung des DHDVerfahrena
(I.G. - Ludwigshafen-Report of 15 October 1942)

(b) Hydroforming.

There were (2) hydroforming plants in operation in German territory. Both were located in the Moosbierbaun refiery near Vienna. A straight run petroleum gasoline boiling from 140 to 330 degrees Fahrenheit was hydroformed in conventional discontinuous units. (The process and design data were obtained from America.) Both Roumanian and Austrian crudes were processed at this refinery.

The operation was carried out at 15 to 30 atmospheres pressure of which the hydrogen partial pressure was 65 to 70 percent. The reaction temperature was 930 degrees Fahrenheit and the space velocity was 0.5 volume of all per volume of catalyst per hour. The catalyst was 5 to 10 percent weight MoO3 on alumina.

The operating cycle was from 17 to 30 hours with 9 hours required for regeneration.

The hydroformed product was used in the same manner as was DHD gasolines, i.e., as the base stock for C-3 grade aviation gasoline.

In table V are given some yield and analytical data for the average Moosbierbaun operation.

TABLE V

Yield and Analytical data on Moosbierbaun Hydroforming of Straight Run Gasoline

Yield Data

Feed

Product

Gasoline, percent wt.

100.0

79.0

Redistillation Residue, percent wt

-----

3.5

Coke, percent wt

-----

1.1

Hydrogen, percent wt

-----

1.4

C1 plus C2 plus C3, percent wt.

-----

11.0

Isobutane, percent wt.

-----

1.3

Normal Butane percent wt

-----

2.7

Total

100.0

100.0

     

Analytical Data

   

Density 68° F.

0.725

0.776

Distillation °F. I.B.P.

144

112

Distillation °F. end point

330

330

Distillation at 212° F. percent volume

18

36

Distillation at 320° F. percent volume

95

94

Olefin content, percent volume

0.5

1.5

Aromatic content, percent volume

14

54

Naphthene content, percent volume

44

8

Reid Vapor Pressure, lbs.

5.3

5.1

Octane Number motor Method, unleaded

58

80

Octane Number Motor Method, with 4.35 cc. Tetraethyl lead/gallon

79

91

XV: HF-Verfahren und Anlage Moosbierbaum. (I.G. - Leuna - report by Dr. Kaufmann of 9 December 1941).

XVI. Das HF-Verfahren. und Anlage Moosbierbaum. (I.G.-Leuna-report by Dr. Welz of 12 February 1943).

(c) Synthetic Alkyl/Aromatics

The only important commercial synthesis of alkyl aromatics in Germany was of diethyl benzene. The chemical plants of I.G. at Hüls and Schopau produced together about 300 barrels per day of this material, named “Kybol”, as a by-product in the manufacture of styrene. Benzene was alkylated with ethylene and the product, containing some diethyl benzene, was fractionated to separate into one fraction all of the diethyl compound together with a small amount of higher boiling alkylated bezenes. This fraction boiled from 325 to 350 degrees Fahrenheit.

No cumene (isopropyl benzene) was being made, but one installation was being considered for producing a mixture of alkyl benzenes which would have contained cumene. Propane was to have been cracked thermally, yielding ethylene and propylene, and the olefins would then have been selectively absorbed with a copper nitrate-ethanol amine solution. The mixed olefins were to be used to alkylate benzene, obtaining thereby a mixture of mono- and di-ethyl and isopropyl benzenes.

Of technical interest is a new German process, developed but never applied on large commercial scale to dealkylate high boiling aromatics and reduce their boiling points down into the gasoline range. The process known as the “Arobin Verfahren” was considered for application on high aromatic content hydroforming and DHD residues boiling from 340 to perhaps 600 degrees Fahrenheit (50 percent points of ca. 380 degrees Fahrenheit). A catalyst of synthetic aluminum silicate containing one percent weight of MoO3 was used at a temperature of 750 to 780 degrees Fahrenheit and under a hydrogen pressure of 200 atmospheres. At a space velocity of one volume total liquid feed (of which 50 percent is recycle) per volume catalyst per hour an 85 to87 percent weight yield of 330 degrees Fahrenheit and point product containing 70 percent volume aromation was obtained. A hydrogen consumption equal to 3 percent weight of the product gasoline was incurred. Through the use of the high hydrogen pressure coke deposition on the catalyst was very low and long operating cycles (i.e. several hundred hours) were predicted. In Table VI are given some typical yield and analytical data for this operation.

The following documents, transmitted to the Bureau of Ships, relate this subject:

XVII. Das Arobin - Verfahren. (I.G. - Leuna - report by Dr. Welz of 22 October 1943).

XVIII. Arobin-Anlage. (I.G.-Leuna-material flow diagram of 13 July 1943).

XIX. Bericht über die erste Fahrperiode des Arobinofens. I.G. -Leuna-memorandum of 27 March 1944).

TABLE VI

Yield and Analytical Data on Feed and Products of Arobin Process

Yield, Percent Wt.

Feed

Product

Gasoline

100.0

85.7 to 87

Methane

-----

0.2 to 0.3

Propane

-----

1.7 to 2.0

Isobutane

-----

3.8 to 4.2

Normal Butane

------

2.4 to 2.6

Analytical Data

   

Density at 68° F.

0.91

0.807

Distillation °F, I.B.P.

340

120

Distillation ° F. 50 percent

380

260

Distillation °F. E.P.

600

330

Aromatic Content, percent volume

95

65

Naphthene Content, percent volume

-----

27

Paraffin Content, percent volume

-----

8

Bromine Number

ca. 8

0.8

Octane number, Motor Method, unleaded

-----

86

Octane Number Motor Method, with 4.35 cc. Tetraethyl Lead/Gallon

-----

93.5

(d) Catalytic Cracking

There were no commercial scale catalytic cracking units in operation German areas. One was planned for operation at Moosbierbaum in Austria, a plant to carry out an operation referred to as catalytic cracking was being processed for Rucrchemie at Holten, and a large underground refinery planned for Niedersachswerfen (near Nordhausen) was to have a catalytic unit.

The Moosbierbaum and Niedersachswerfen units were to process crude oil fractions to produce aviation gasoline base stocks. The development work on the process was done by I.G. at Leuna, and a large pilot plant had been built at Deuben (South of Leuna).

The catalytic cracking process that was developed for plant application was quite similar to the TCC process in use in America. A silica alumina catalyst , in the form of small spheres was to be used at a temperature of 840 degrees Fahrenheit and atmospheric pressure to crack straight run gas oil boiling up to about 750 degrees Fahrenheit. The silica-alumina catalyst was made as follows: (A caustic aluminate solution was acidified at 220° F., with nitric acid to a pH of 6.5. The Al2O3 precipitate was washed free of sodium and dried at 210° F., to a water content of 25 and 30 percent wt. The dried Al2O3 was then mixed with 15 percent of its weight of SiO2 (Kieselguhr). The mixed oxides were then ground until 90 percent passed through a screen containing10,000 openings per meter. The powder was moistened with water acidified with nitric acid, well mixed, and then heated to 150° F., for 24 hours. It was extruded into cylindrical pellets, and put between two counter revolving plates which rolled the cylinders into small spheres of ca. 0.2 inches diameter. The spheres then were heated at 750 to 840° F., for 8 to 12 hours.). The main yield was to be a 340 degrees Fahrenheit end point distillate for use directly, without repassing or other treatment in C-3 quality aviation gasoline. A 30 percent weight yield of this fraction a 3 percent weight yield of hydrogen plus methane plus ethane-thylene, and a coke yield of 4 percent wt., all based on feed, were anticipated. A conversion of 50 percent volume i.e., a disappearance of one-half (½) of the feed from its initial boiling range, was expected while employing a space velocity of 0.6 volumes of liquid feed per volume of catalyst (in reactor) per hour.

Catalyst regeneration was to be carried out at a temperature not exceeding 1020 degrees Fahrenheit.

The plant design was to employ one catalyst elevator only. The regenerator would be mounted directly above the reactor, and regenerated catalyst would be dropped directly through control valves into the top of the reactor. Spent catalyst from the bottom of the reactor would then be elevated to the top of the regenerator.

A set of test data was reported for the catalytic cracking of 355 to 670 degrees Fahrenheit fraction from a mixed base crude using a 0.5 space velocity and 790 degrees Fahrenheit reactor temperature. A 36 percent weight yield of 330 degrees Fahrenheit end point gasoline was obtained which contained 20 percent weight aromatics and 4 percent weight olefins. The untouched octane number was 75, add with 4.35 cubic centimeters tetraethyl lead per gallon it was 94. The yield of low boiling components through butanes was 6.7 percent weight of which 3.1 percent was isobutene.

It was the opinion of most German technical people interrogated that catalytic cracking of the above type or of the above type or of the other types employed in America, could have only limited application in Europe. The process was being considered during the war only because it represented a method of making aviation gasoline directly from crude oil fractions. (The hydrogenation of such fractions of crude oil does not give high quality gasolines). Catalytic cracking is not considered applicable to coal tars directly because of high carbon deposition on catalyst, and the process has no obvious application in high pressure hydrogenation systems.

The following documents transmitted to the Bureau of Ships, pertain to this process of catalytic cracking:

XX Flugbenzin durch Katalytisches Kracken. I.G.-Leuna-report by Dr. Kaufmann of July 1942).

XXI. Flow Diagram of I.G. Experimental Catalytic Cracking Unit.

The Ruhrechemie process referred to as catalytic cracking was an operation designed initially to crack the normal paraffin residue of intermediate to Fischer-Tropsch fractions used for various olefin-consuming chemical syntheses. A plant was being constructed at Holten on the basis of development work carried out there.

The reaction was designed to obtain the maximum yield of low boiling olefins for synthesis of high octane aviation gasoline ingredients. It had been concluded that the normal paraffins did not respond adequately to conventional catalytic cracking that their isomerization was not a promising possibility and hence that destruction to low boiling molecules (synthesis raw materials) over a catalyst was the most attractive method of converting them to high performance fuels.

The operation was to be at low (atmospheric) pressure and 930 degrees Fahrenheit over a synthetic silica-alumina catalyst of 0.7 apparent density. A liquid space velocity of ca. 0.1 was to be employed in order to obtain a 40 percent conversion per pass (disappearance from the original boiling range) of a 340 to 660 degrees Fahrenheit Fischer-Tropsch fraction. Of the converted feed material, 75 percent appeared as C3, C4, and C5 fractions, of which about 90 percent were olefins. Gasoline was only 15 percent of the converted yield.

By employing a recycle, a 75 percent weight ultimate yield of usable materials could be realized.

The process was to be discontinuous, with catalyst regeneration after operating cycles of 20 to 25 minutes. The carbon yield was estimated to be 1.5 percent weight of reactor feed.

In Table VII is given a set of yield and product composition data characteristic of this operation. A copy of a report by Ruhrchemie, which describes quite completely the development of the process and its planned application was forwarded to the Bureau of Ships:

XXII. Herstellung von Isogasolen und Flugbenzin aus Synthese-produkten. (Ruhrchemie report by Dr. Kolling in January 1943.)

TABLE VII
Yield and Product composition Data - Ruhrchemie Catalytic Cracking
Feed to process is Fischer-Tropsch fraction of 340 to 660 degrees Fahrenheit boiling range.

Yields of Components,
Percent wt. of Feed

 

Total Conversion

40 percent wt. of feed

Gasoline (C6 to ca. 320° F.)

6-8

C5 Fraction

7.6-9.6

C4 Fraction

10-12

C3 Fraction

8-10

C2 Fraction

2-2.8

Methane & Hydrogen

0.4-0.8

Coke

1.2-1.6

Olefin Contents, percent volume

 

C5 Fraction

85-90

C4 Fraction

90-95

C3 Fraction

90-95

C2 Fraction

60-65

Iso-Contents, percent volume

 

C5 Paraffins

60-65

C5 Olefins

45-50

C4 Paraffins

60-65

C4 Olefins

38-43

Return to Table of Contents