Return to Table of Contents

IV. HYDROGENATION

A. General

Leuna was the world’s first commercial scale hydrogenation plant and also the first to operate on coal (brown coal). In its present form, the Leuna hydrogenation plant consists of 10 liquid phase coal or heavy oil stalls, 5 vapour phase presaturation units and 3 stalls for splitting hydrogenation of middle oils to gasoline. In 1943 and the first half of 1944, the average rates of consumption of the various feedstocks were:

Production of final liquid products was slightly more than 600,000 T/yr. and according to Dr. Buterfisch,, these products were made up of 40% aviation base gasoline, 20% motor gasoline, and 40 Diesel oil. In addition, some 150,000 Tons/year of by-product hydrocarbon gases were for liquefied gas fuels (propane or propane + butane) and for manufacture of synthetic lube oils (ethane).

In July 1944, Leuna suffered a surprise air attack and because of the absence of facilities for safe emergency draining of the coal hydrogenation converters, the plant was coked up. The coal-paste preparation plant was also badly damaged. At the same time damage to the nearby Brabag hydrogenation plants prevented them from hydrogenating all the available brown coal tar. It was therefore decided to change over Leuna from brown coal to brown coal tar and 5 or 6 coal stalls were modified for hydrogenation of liquid phase heavy oil. During the second half of 1944 it was possible to operate the normal liquid phase and vapour phase process for conversion of brown coal tar to gasoline but production was interrupted more and more by continued air raids and, following sections was obtained from Dr. Schunck, Director and Manager of the hydrogenation section of Leuna, Dr. Becker, his principal assistant and stalls manager, Ing. Cron hydrogenation section engineer, and Dr. Pichler, a costs expert attached to the hydrogenation section.

B. Brown Coal Hydrogenation

(i) Outline of present process

The brown coal hydrogenated at Leuna is obtained from local open workings owned and operated by the I.G. As delivered to the plant, it contains 54% water and 5.5% ash. The ash and moisture free coal substance has the analysis - 71% carbon, 5% hydrogen, 5-6% sulphur, 17-18% oxygen and 1% nitrogen. A high proportion of the ash constituents of the coal is sand with very erosive properties.

The hydrogenation process as applied to brown coal is summarized in the flowsheet shown in Fig. II. The wet coal together with about 4% of its weight of catalyst (Bayermasse obtained as a by product in the manufacture of aluminium) is dried down to 5% water. The product is immediately wetted with part of the recycle pasting oil in order to avoid dust difficulties and explosion risks and is fed to the grinding and pasting mills where it is mixed with the rest of the recycle pasting oil. The resulting “paste” containing some 44% dry coal (49% total solids) is injected into the hydrogenation stall which operates at a pressure of 230 atmospheres. It is heated together with circulating gas (900-1,000 M3 circulating gas/M3 paste) firstly by interchange with outgoing vapour products and finally in a gas-fired tube preheater. The reactants then enter the first of (usually) 4 converters at a temperature of about 430° C. This temperature is quickly raised by the heat of reaction to 490° C and is then controlled at this figure, by introduction of cold circulating gas at suitable points, until the reactants leave the third reactor. Under the latest operating conditions, this average reaction temperature in the last reactor is dropped to 475° C by introduction of more cold circulating gas. The total circulating gas used for temperature control is about 1000 M³/M³ paste fed.

A small amount (100 litres/hour) of reactant is continuously drawn off at the bottom of the first reactor in order to prevent the build up of sand and the formation of “Caviar” i.e. small spheres consisting of coke formed round a central sand particle. This draw off is automatically controlled.

The products leaving the last converter pass to a hot catchpot where liquids and vapours are separated at a temperature of about 440° C. The liquid products are cooled by passage through finned air coolers and are let down to atmospheric pressure. Approximately two thirds of this heavy oil let down (Abschlamm) is diluted with 75% of its weight of distillate heavy oil and the mixture is centrifuged. The “filtrate” is recycled as pasting oil and the “concent rate” is recycled as pasting oil and the “concentrate” mixed with the remaining “Abschlamm” is carbonized in “Schneckenofen” for recovery of its vapourisible oil content. All the ash of the original coal, the unconverted coal and the new formed asphalt is purged as coke from the “Schneckenofen.”

The vapours leaving the hot catchpot are cooled by interchange with the incoming coal paste and by passage through a water cooler. Condensed liquids are separated from recycle gas in a cold catchpot and the former are let down in three stages (45 ats., 4 ats. and 1 at.) in order to separate the dissolved gases into “lean” gas for use as fuel and “rich gas” from which butane, propane and ethane are separated. The cold catchpot liquid product is finally distilled together with recovered oils from the “Schenckenofen” (when brown coal tar is hydrogenated simultaneously, this is also introduced at this stage) to give a gasoline + middle oil fraction of 335° C end point as overhead and a heavy oil “bottoms”. The light product is passed on for vapour phase hydrogenation and the bottoms are recycled either directly to coal pasting or indirectly as “Abschlamm” diluent oil via the fugals. Gas from the cold catchpot is boosted back to the inlet of the plant via a gas washing plant in which hydrocarbons and nitrogen are dissolved in oil (heavy middle oil ex cold catchpot liquid product) in order to maintain the required hydrogen partial pressure (170-180 ats).

Under these latest operating conditions this paste throughput is slightly under 1.2 M³/M³ of reaction space/hour corresponding to 0.46 tons ash and moisture free coal/M³ reaction volume/hour. Throughput and reaction temperature are adjusted so that there is no net make of heavy oil. The yield of 0-335° C light product is 49-50% by weight on the ash and moisture free coal fed. Unconverted coal purged in the Schneckenofen coke amounts to 1.5% on the original ash and moisture free coal. (This is not apparent from the flowsheet in Fig. II since no distinction is made between weight of the latter due to chemical reduction during the hydrogenation reaction). Gas make in the hydrogenation of brown coal is 25.75% on the amf. coal. This is made up as follows:

Oil lost in the carbonization of Abschlamm and Abschlamm concentrate amounts to 8.5% by weight on the ash and moisture free coal.

The follow figures show roughly the carbon balance for this process:

Hydrogen consumption is 800 M³/Ton of ash and moisture free coal hydrogenated or 6.6-6.7% by wt.

(ii). Consideration of process improvements made since the war.

The process described above, although much the same as regards yields as that operated before the war, shows a marked improvement in output per stall. Fig. III is a typical Leuna flowsheet for brown coal hydrogenation in a single stall in 1939-1940 and it shows that the coal throughput rate then obtainable was only 0.32 Tons amf. coal/M³ reaction volume/hour or 70% of that achieved in more recent times. The improvement which has been made is actually greater than this, because in addition to a throughput of 0.46 T. of amf. coal, 0.047 T/hr. of tar heavy oil is now hydrogenated in each M³ of reaction space.

With fixed pressure and catalyst conditions the only method for increasing the rate of hydrogenation of a given raw material to a given extent is to increase reaction temperature. The extent to which this can be done is, however, limited because of the following considerations:

1. For a given extent of hydrogenation, (i.e. in this case, complete conversion of coal to petrol and middle oil with only sufficient new formed heavy oil to replace sludge carbonisation losses) increase in temperature increases the yield of gas, asphalt and unconverted oil at the expense of petrol and middle oil. The increase in asphalt make is particularly serious because, in a workable figure all new formed asphalt must be destroyed in sludge carbonization and this results in an appreciable loss of carbon from the hydrogenation system. Further, the carbonization plant it self gets into operating troubles when the asphalt content of the feed is too high.
2. Unless special precautions are taken to cool the products before they enter the hot catchpot, increase in reaction temperature leads to a reduction in the amount and therefore, an increase in the solids content of the Abschlamm. One of the most serious practical difficulties encountered in the brown coal hydrogenation process has been due to coke formation on the hot catchpot walls and this is more difficult to avoid the higher the solids concentration in the liquid product.

The secret of the increase in throughput of the Leuna stalls is that, by attention to a number of process details, the I.G. have been able to get round some of the above limitations and so increase the mean reaction temperature by 20-25° C.

Firstly, automatic controls have been widely adopted. The mixing of Abschlamm and fugal concentrate in the proper proportions fro feeding to carbonization is automatic and this coupled with the provision of a large buffer storage for carbonization feed, has led to much steadier running of the Schneckenofen and has enabled a higher average asphalt content feed to be used than was the case when a margin had to be allowed for possible errors in hand mixing. The hot catchpot level is also automatically controlled; this eliminates the danger of the periodic drying out of the walls of this vessel which greatly encourages coke formation and therefore, allows a higher solids content of Abschlamm to be tolerated.

Secondly, the I.G. staff have found that, when the hydrogenation process is operated in the normal way using a gradual upward temperature gradient in the reactor system, much of the asphalt make is produced in the last converter where temperature is at a maximum and hydrogen partial pressure is at its lowest. Dropping the temperature in the last converter materially reduces the asphalt make and it also helps to reduce the solids content of Abschlamm and therefore, the hot catchpot coking danger.

At Leuna, this reduction of temperature in the last converter can be practiced only in conjunction with high feed rates resulting in a high rate of heat evolution perstall. At lower throughputs, the loss of recoverable heat by cooling the last converter introduces a preheater capacity limitation.

The Leuna staff feel that still greater throughputs would be possible if it were not for two other limiting factors, (1) erosion of preheater tubes and (2) the capacity of the existing Schneckenofen. With the present high rates preheaters have to be shut down for examination every 120-150 days and this shut-down takes 6 days. Incidentally, the general maintenance shut-down of a brown coal stall takes 25 days and occurs, normally, every 15 months. Kugel ovens are considered to be superior to Schneckenofen and several were on order for installation on the Leuna plant.

(iii) Details of Plant Equipment

Paste Mills. These are simply horizontal rotating ball mills fed from each end with the appropriate quantities of dried coal and pasting oil, measurement of both being automatically controlled. The paste leaves the mill via slots cut in the side and passes through a 1 mm. screen for removal of nibs of coal, tramp iron, etc.

Paste Injectors. These are ram pumps, the power for both injection and suction strokes being hydraulically supplied. Injection rate varied by controlling the rate of entry of water into the hydraulic cylinder.

The gland packing for these injectors had latterly been lead alloyed with 0.1% Cadmium and this had been satisfactory. Before the war, tin packings were used.

The I.G. had ceased to use nitrided rams because of the wide variation in quality which had been experienced. Ordinary case hardened rams of 400 B.H. were being used.

Paste Interchangers consist of a bundle of 199 tubes in a forging 600 mm. diameter and 18 M long. Formerly 241 tubes were used but trouble was experienced with chokes. The tubes are zinc treated.

With a paste feed rate of 30 M3/hour and a gas rate of 20,000 M3/hour the K value is 250-200. Units for K value: Kg. cals/M2/°C/hr. Interchange are stripped every two years.

Paste Preheaters. These are gas-fired convection type heaters of the standard I.G. rectangular design. The tube hairpins are 15.5 m long, 120 mm. bore and 171 mm. external diameter. They are fitted with fins 4 mm. thick and 10 mm. apart and which give the tubes an internal/external arearatio of 1:20. 6-7 hairpins are used in a normal preheater the average overall K value of which is 180-150. With high feed rates erosion of the hairpin bends is appreciable and the average life of a bend had fallen to 18 months. It was proposed to change to tubes of 160 mm. bore and 229 mm. external diameter with fins 4 mm. apart. The hairpins were to have been made with a pitching of 500 mm. instead of the standard 400 mm.

Brown coal stall Converters. Leuna used converter forgings of a variety of sizes varying from 800-1200 mm. diam. and from 11-18 M. in length. A stall had four converters and the size was usually such that the total stall reaction volume was roughly 27 M3.

Hot Catchpot. Several designs have been tried in an attempt to reduce coking. The type most commonly adopted is shown in Fig. IV A. It is fitted with gas cooling coils between the forging and inner catchpot wall and the inlet pipe for reactants is outside the inner vessel. The idea of the cooling tubes at the top of the catchpot is to ensure sufficient condensation that the walls never dry out. Another type (Fig. IV B) has no cooling coils but cold gas is introduced at the bottom of the vessel via a ring distributor. It is claimed that the stirring provided by this method helps to reduce coke formation.

Let down valves. These are fitted with “Wildia” inserts but even so they have a life of only 200-400 hours.

Sludge carbonization kilns. Leuna has 26 Schnecenofen arranged in sets of two. Each kiln comprises two horizontal steel tubes 2 ft. in diameter and 30 ft. long, arranged one above the other and sitting inside a brickwork gas-fired furnace. Each tube is fitted with paddles, fixed with a slight pitch on to a central rotating shaft, and these scrape the inner wall of the tube free From adhering coke. Loose iron bars are attached to the paddles in such away that, as the peddle rotates, the bars are lifted to fall later with sufficient force to dislodge coke deposited on the paddle.

The average feed rate is 2.5-3.0 M³/hour falling to 1.8 M³/hour after 50 days when the unit is taken off line for cleaning.

Gas Circulators. The coal and heavy oil hydrogenation system at Leuna normally employs 5 or 6 circulators each of 80-85,000 M³/hour capacity. The machines throw a maximum pressure of 30 ats. They are operated at constant speed and circulation rate is varied by controlled bypass. Stall pressure is hand controlled and it was stated that swings of up to 20 ats. are observed.

Gas washing. Purification of the circulating gas is carried out in 9 towers each 1300 mm. diamteter.  Wash oil (a heavy cut of liquid phase hydrogenation middle oil) is injected partly with three throw pumps and on the saturated wash oil. The wash oil feed rate was controlled automatically in order to maintain a constant hydrogen content o circulating gas.

Automatic Controls. Full details of the various automatic controls were obtained but these are amongst the documents (2nd Leuna visit) which have not yet reached London.

C. Brown Coal Tar Hydrogenation

The Leuna flowsheet for hydrogenation of Central German brown coal tar is shown in Fig. V. The crude tar which contains 1% water, 0.5% solid and 1-3% asphalts, is fugalled to remove slightly over 2% of its weight of sludge which is sent to carbonization for oil recovery. The cleaned tar is mixed with “Leuchtöl”, i.e. recovered oil from brown coal carbonization gases (the crude tar + Leuchtöl mix usually contains 45% by weight of heavy oil boiling above 325° C, 35-40% distilling between 180 and325° C and 15-20% boiling below 180° C) and with the crude product from the liquid phase hydrogenation of heavy oils. This mixture is distilled to give a 0-325° C fraction as overhead and a heavy oil bottoms which is the feed to the hydrogenation stalls.

The plant employed is substantially the same as in the case of coal hydrogenation with the exception that a special pump is installed for hot recycle of liquid from the hot catchpot to the inlet of the preheater.

Hydrogenation conditions for heavy oil are:

The catalyst (10927) is made by impregnation of the coke obtained from Winkler generators with the necessary amount of ferrous sulphate and caustic soda solutions in stoichiometric proportions. The impregnated coke is dried and ground so that not more than 2% remained a 10,000 mesh screen. There is no washing step in the preparation of this catalyst. Make up catalyst is introduced as a suspension in part of the heavy oil feed usually injected into the hot liquid recycle system. Catalyst consumption is roughtly 1% by weight on the fresh >325°° C heavy oil feed.

The main purpose of the hot liquid recycle from the hot catchpot to the preheater is to increase the velocity of liquid in the former and so reduce the coke formation. The rate of recycle necessary depends on the hot catchpot design. With the later types, hot recycle can be eliminated and it was stated that Brux operated in this way.

In order to purge spent catalyst and non hydrogenable material in the tar, there is a small let down from the hot catchpot. Part of this product is recycled direct and the remainder treated in fugals to give a concentrate which is carbonized for oil recovery.

The yield of petrol and middle oil obtained by liquid phase hydrogenation of brown coal tar heavy oil is just over 80% by weight. Hydrogen consumption is 3.9 to 4.0% by weight. It is interesting to note that the petrol + middle oil production “leistung” per M/³ reaction volume is lower from brown coal tar heavy oil than from brown coal. The figures are 0.25-0.26 Tons/M³/hour for tar heavy oil and 0.29-00.30 for coal.

D. Vapour Phase Hydrogenation of Middle Oils

(i). Process conditions and yields

Leuna operates the two-stage process, i.e. straight through presaturation to convert nitrogen compounds to ammonia and to hydrogenate the greater part of the oxygenated components followed by splitting hydrogenation with recycle of unconverted middle oil.

For each stage the plant consists simply of a preheater, two interchangers, three or four converters, a cooler and a cold catchpot. Reaction volume per stall is usually about 25 M³. for the first stage, Leuna, in common with most other German hydrogenation plants, have changed from 5058 (tungsten sulphide) in the form of 10 mm. pellets, to 8376 (25% tungsten sulphide + 3% nickel sulphide on alumina) catalyst used in the form of cubes. This was found to be as good as 5058 for reduction of phenols and superior to 5058 in that it gave less splitting to comparatively low quality petrol. It was not as good as 5058, however, for destruction of nitrogen compounds which is the most important function of the presaturation stage.

Leuna achieved an oil throughput of 0.6-0.8 Tons/M³ catalyst/hour in the presaturation stage, for which an average temperature of 410° C and a hydrogen partial pressure of 210-220 ats. was employed. Circulating gas to oil ratio was 2,500 M3/Ton. The high hydrogen partial pressure in the vapour phase stalls is achieved by introducing all the make up hydrogen for liquid and vapour phase systems into the vapour phase circulating gas. A purge from this system is used as make up to the liquid phase.

Gas made in the presaturation step is the equivalent of 3% of the carbon in the feed. Roughly half this gas (by weight) is butane, a third propane and the remainder ethane and methane in approximately equal proportions. The yield of butane-free product depends of course on the oxygen, nitrogen and sulphur content of the feed. In the case of total 0-325° C product from brown coal tar it is 95% and hydrogen consumption is 3.9% by weight. Using petrol + middle oil from brown coal hydrogenation as feed, the yield of saturated product is 97% and hydrogen consumption 307-308%.

The saturated product from both brown coal and brown coal tar contains an appreciable of material boiling in the petrol range. this fraction has a comparatively poor knock rating and it is desirable to keep it separate from the better quality product obtained by splitting hydrogenation. It is, therefore, usual to distil the saturation product, taking overhead 0-150 or 160° C cut if motor gasoline is the desired end product or a 0-120° C fraction if aviation base petrol is being made. It was stated that 0-120° C saturation stage petrol ex brown coal hydrogenation has a motor method octane number of 70-71 while the rating of the corresponding product from brown coal tar was only 68-70. Presaturation stage petrol is frequently used as feed for the D.H.D as a diesel fuel and has a Cetane number of 40-42 a. process.

The middle oil from the presaturation stage contains 2-3 mgs. nitrogen per litre. It can be used direct and a pour point of -15 ° C. The pour point can be lowered to -40° C by cutting 15% from the higher boiling end but this reduces the Cetane number to 38.

Splitting hydrogenation of saturated middle oil is carried out over a tungsten sulphide on Terrana earth catalyst (6434). Other process conditions are:

Circulating gas is water washed before entering the stall to reduce nitrogen to less than 0.1 mgrm/litre oil feed. Motor gasoline is cut to an end point of 190° C and has a volatility of about 30-35% at 100° C and has an end point of 150° C.

When making motor gasoline, 15% of the carbon in the 150-325° C saturated middle oil feed is converted into hydrocarbon gas consisting of 83% by weight of butane, 15% butane 1% ethane and 1% methane. It is possible however, to include 40-50% of the butane in the final petrol so that the net weight yield of motor gasoline is 91-92% on the feed.

20% of the carbon in the 120-325° C feed is converted into hydrocarbon gas of the same composition as given above when making aviation base petrol. It is not possible to include butane in the liquid product and the net yield is thus only 81% by weight.

Figs. VI and VIII show diagrammatically the conversion to two grades of petrol + middle oil from liquid phase hydrogenation of brown coal tar (including Leuchtöl) and brown coal respectively. They show that the following overall yields are obtained:

Overall hydrogen consumption figures are:

(1) Brown coal tar (including Leuchtöl to Motor gasoline

6.9 - 7.0% by weight on tar or .083-0.84 Tons Hydrogen per Ton Motor gasoline.

(2) Same feed to Aviation petrol -

7.3 on tar or .1 Tons H₂/Ton petrol.

(3) Brown coal to Motor gasoline -

9.4% wt. on ahs and moisture free or .203 Tons H₂/Ton motor

(4) Brown coal to Aviation base -

9.6 - 9.7 wt. on a.m.f. coal or .24 Tons H₂/Ton aviation base.

The final blend of motor gasoline from brown coal tar has a C.F.R. motor method octane number of 62-64, while aviation base from the same raw material has a rating of 68. Corresponding ratings for petrols ex brown coal hydrogenation are about two octane numbers higher.

(ii) Details of Plant

Injectors. Normal three throw pumps are used with electric drives. S.E.A. rings for gland packing had not been very satisfactory and the I.G. had used ACACIA wood packing with considerable success. These new packings had a life of about 1,800 hours.

Interchangers were similar to those in use in liquid phase stalls except that those in use in saturation stalls had 241 tubes. K value for both was 300-200.

Preheaters. On the saturation stalls the preheater consisted of 4 or 5 elements of 90 mm. bore, 127 mm. external diameter tube heated electrically. Normal gas-fired preheaters were used in splitting stalls-each contained about 25 elements of 90 mm. bore tube and had a K value of 200-180.

Reactors. The feature of vapour phase hydrogenation reactors is the arrangement of the catalyst in beds with intermediate mixing chambers temperature control. The Leuna engineers do not appear to have been very progressive as regards improvements in design of these bed converters and they are capable of much smaller throughputs than those in use, for example, at Billingham.

The forging body was formerly lined with stamped cement asbestos. During the war, Leuna has used fired bricks of “Schammote stein” with apparent success.

Coolers. The K value of vapour phase hydrogenation stall coolers was stated to be 400-500 kg. cals/°C/M²/hour.

E. Vapour Phase Splitting Hydrogenation at 700 Atmospheres Pressure

This was not practiced at Leuna but the research for the Dutzkendorf plant of the Wintershalle A. G. was done in the Leuna laboratories. Dr. Becker supplied comparative data for 300 ats. direct treatment over 6434 when using bituminous coal tar middle oil (Creosote middle oil) as feed. These data are given in Fig. VII.

It will be seen that the weight yield of petrol of 30% volatility at 100° C is substantially the same in the two processes but that the high pressure method gives a product higher in anti-knock rating by 5-10 octane numbers. Dr. Becker was unable to give figures for hydrogen consumption greater concentration of aromatics in the final product. Incidently this aromatic content and also the octane number of the petrol could be increased still further using a “diluted” catalyst such as is employed at Welheim instead of 6434.

In the 700 ats. process overall petrol production leistung is 0.37-0.38 kgs./litre catalyst/hour. This compares with 0.29 kgs./litre 5058 + 6434 catalyst/hour for the 300 ats. two stage method. since 700 ats. converters have only 75% of the catalyst capacity of vessels of weight used for 300 ats., there is no saving in reaction vessels using the higher pressure process. because the conversion/pass using 700 ats. and nonsaturated feed is low - 43%, the amount of distillation involved is rather higher than is the case in the normal two stage 300 ats. process. If it is essential to produce petrol of high aromatic content and an octane number of 75-79, there is clearly an advantage in using the 700 ats. method (possibly with a less saturating catalyst than 6434) instead of the conventional two-stage method followed by D.H.D. treatment of the saturation stage naphtha.

F. Hydrogenation Costs

On the instructions of the Ministry of Fuel & Power a special effort was made to get detailed information on the economics of the hydrogenation activities at Leuna. During our visit, Dr. Pichler went through the whole of the available records and made the following summary of brown coal hydrogenation costs.

Figs. VIII , IX, X, XI present the basic flowsheet data for hydrogenation of put conditions. They are typical of the Leuna operations during 1943 and early 1944.

Table I gives an analysis of the cost of production of motor and aviation petrols according to these flowsheets in terms of raw material costs, operating costs and capital charges, credits for hydrocarbon gases being taken into account.

Table II shows a breakdown of the operating costs in terms of operating labour, labour and materials for repairs, electric power, fuel gas, steam etc. “Overhead charges” and obsolescence are shown as part of the operating cost. Labour is given in man/hours and consumptions of the various utilities apply to British or American conditions.

Table III gives a still more detailed breakdown of operating costs for production of motor petrol by providing a detailed analysis of the costs in each section of the plant, e.g. coal drying, coal pasting, liquid phase coal hydrogenation, presaturation, splitting hydrogenation, etc.

Table IV shows the costs additional to those set out in Table III which are incurred when aviation based petrol is made.

These cost data will be analysed in a later report

It is interesting to note that although the full cost of production of aviation base petrol was only 200 RM/Ton, the Leuna realization was stated to have been 340 RM for this grade and 310 RM for motor gasoline. On the basis of these figures, the I.G. had a profit margin of about 80 x106 RM/year in respect of Leuna hydrogenation activities alone. Dr. Pichler said that this very high return was allowed in order to compensate the I.G. for its heavy expenditure in developing the hydrogenation process.

Return to Table of Contents