HYDROGENATION F. S. SINNATT, J. 0. KING, AND ANGUS MACFARLANE Fuel Research Station, Department of Scientific and Industrial Research of Great Britian, London, England
I n 1923 experimental work on hydrogenation was started to ascertain whether British bituminous coals could be readily converted to gasoline. After a study of catalysts, an experimental plant of one ton per day capacity was constructed. The mechanism of coal hydrogenation has been studied especially for the light it sheds on coal constitution. Special attention has been given to the hydrogenation and treatment of low-temperature tars, the properties of which are described. The influences of pressure and temperature upon the hydrogenation and cracking of the aromatic constituents of low-temperature tars are reviewed, especially with reference to naphthalene.
The influence of temperature from 300" to 510" C. and of pressure at 200 and 400 atmospheres on the hydrogenation of tar in a continuous plant has been studied. After hydrogenation above 320" C. the tar loses its black color but remains opaque ; at 450" C. the product is transparent and pale yellow. Deterioration of catalyst increases with increasing temperature of operation. The construction and operation of the semi-technical-scale tar hydrogenation plant now in use is described together with analyses of the raw and treated tars. Temperature conditions in the catalyst chamber and means for dissipating the heat of reaction are described.
T
HE Fuel Research Station has been associated with the development of hydrogenation from the early days. The Director of Fuel Research was in touch with Bergius in 1921, and experimental work started a t the Fuel Research Station in 1923. The object of the early work was to ascertain whether the bituminous coals of Great Britain could be readily converted into gasoline. The investigation soon showed that the yield of oil and the rate of hydrogenation varied with the type of coal used. A search was therefore made for suitable catalysts to hasten the process of hydrogenation. The results were generally satisfactory, and a plant was erected which treated one ton of coal a day. This work continued until 1927 when Imperial Chemical Industries Ltd. started research on a considerable scale, which culminated in the erection of a plant capable of producing about 45 million gallons of gasoline a year. The investigation of the mechanism of the hydrogenation of coal has been continued a t the station, largely for the light it throws upon the constitution of coal. For example, the addition of a small percentage of hydrogen to noncoking coal converts the coal into a product with high coking properties. The proportion of hydrogen required may be as low as 0.5 per cent of the weight of the coal. In addition, a continuously working plant capable of treating 1 kg. of coal an hour is in use as an instrument for measuring the properties of the coals of Great Britain in relation to hydrogenation. It has been an important part of the work of the Fuel Research Coal Survey to discover the characteristics of the seams in relation to hydrogenation and the manner in which the seams vary in this quality. Figure 1 is a diagram of the unit for the hydrogenation of coal. Considerable importance is attached to the results obtained in this plant, since experiments in intermittent converters do not show how different coals may vary in the rates a t which they are hydrogenated. Thus it has been found that coals of similar
carbon content yield approximately the same percentage of oil in an intermittent plant but exhibit marked differences when treated in a continuous plant. Special attention has been paid a t the Fuel Research Station to the treatment of low-temperature tar and distillates from high-temperature tar. Work on this aspect of the problem has been developed largely as a means of increasing the value of the products obtained by the low-temperature carbonization of coal. Burning solid fuel on an open hearth remains one of the favorite means of domestic heating in Great Britain, but to use bituminous coal in this manner is not only wasteful but causes damage to property and danger to health because the smoke intensifies fog. For this and other reasons attention has been paid to the carbonization of coal a t low temperatures to yield a smokeless, free-burning coke which provides a very pleasant fire in an open grate. As a by-product of low-temperature carbonization, tar is produced in quantities up to 20 gallons per ton of coal, so that the commercial disposal of this material is an important factor in the economic success of the process. The Fuel Research Station therefore took up the problem of correlating the conditions for carbonizing the coal and for converting the low-temperature tar into gasoline by hydrogenation.
Properties of Low-Temperature Tar A typical tar, formed by the carbonization of bituminous coal a t 650" C. in narrow brick retorts which have been designed and developed a t the Fuel Research Station, contains 0.5 per cent of water and has a specific gravity of 1.058 a t 15' C.; 57.8 per cent of the dry tar distills below 360" C., and analysis shows that 19.3 per cent consists of tar acids, 1.2 per cent of tar bases, and 37.3 per cent of neutral oil. The detailed results of the fractionation of the tar acids and the neutral oil are given in Table I. Some 41.7 per cent of the 133
INDUSTRIAL AND ENGINEERING CHEMISTRY
134
VOL. 29, N O . 2
rJ En
NOM-RLTURN
,
Burr HwPm
""L
tar remains as pitch which does not distill below 360" C. In order to convert this material into gasoline, it is necessary to eliminate the sulfur and to reduce the acids and bases to hydrocarbons. The boiling point of the neutral oils, which are predominantly aromatic in character, must be reduced below 200" C., and the volatility of the product must be suitably distributed over the lower temperature range. For this reason, cracking plays as important a part in the production of gasoline as hydrogenation. Indeed the secret of the process seems to consist in promoting the suitable balance of reactions of the two types. It has therefore been of the first importance to establish the effect upon them of the variable factors, of which the most important are pressure, temperature, and catalysts.
Influence of Pressure When, on the basis of Haber's classical researches, the synthesis of ammonia was realized in industrial practice, the necessity of operating a t high pressures followed unequivocally from thermodynamic principle. In such a process as the conversion of tar into gasoline by hydrogenation, the influence of pressure is more complicated. Its separate effect on each of the reactions involved may be more readily
disentangled, if some consideration is first given to the reasons why high pressures have been introduced in other reactions. Besides the direct advantage that pressure favors reactions which take place with a reduction in the number of molecules, it may have the additional advantage of controlling which of alternative paths the process is to follow. The synthesis of methanol from carbon monoxide and hydrogen is an example; the importance of pressure is not only that less alcohol would be formed without it, but that with it the production of methane can be avoided in the presence of a suitable catalyst. TABLEI.
ON
FRACTIONATION O F TARACIDSAND NEUTRAL OIL
Fractionation of Neutral Oil B. p. range Dry tar
c.
% b y wt.
0-170 170-200 200-230 230-270 270-310 310-360 Residue Loss
3.6 3 7 4 5 7 7 7.7 6 6 3 2
0.3 ~
37.3
Fractionation of Tar Aoids B. p. range Dry tar c. % by wt. 0-220 9.4 220-230 1.3 230-260 2.0 250-290 1.1 290-330 3.6 1.6 Residue Loss 0.3 ~
19.3
FEBRUARY, 1937
INDUSTKIAI, L\IYD ENGINEEI1IR;G CHEMISTRY
135
The practical merits of working at high pressure are that by Hall (3) are of particular interest in this connection. It has been established that the primary reaction is the formation greater yields may be obtained from a given quantity of catalyst and that higher throughputs can be maintained, or of Tetralin: a smaller plant be used to give the same output. A striking instance of the saving caused by improvements in technic, even since the early days of pressure plant, was given recently (1) by Keith and Montgomery (4). They pointed out that a modern cracking unit erected on the site of the first Burton battery produced gasoline a t four hundred seventy times the rate of the original still. At first sight the use of Hydrogenation may be carried further with the formation pressure when cracking would seem to be definitely disadof Decalin: vantageous, since the reaction must result in an increase in the number of molecules. High pressure, however, is used to control that increase, for it reduces the loss through further I (2) breakdown of the products of reaction to form gaseous hydrocarbons. On the other hand, when oil is hydrogenated \CH%ACH/ to form lubricants of quality by working under pressure with catalysts of great activity, the reaction can be carried out or the reduced ring in Tetralin may open with the formation a t temperatures low enough to avoid loss through cracking. of n,-butylbenzene: In the conversion of tar into gasoline, partial hydrogenation of the complex aromatic material is a necessary preliminary to its breakdown by cracking to simpler hydrocarbons, and these two reactions are differently affected by a high pressure of hydrogen. A delicate balance must t e maintained between the extent of cracking and hydrogenation, for reduction of benzene homologs to naphthenes A cracking of the side chain of this hydrocarbon niay then lowers the antiknock value of the product and increases the occur, the prevalent course of which can be represented conamount of hydrogen used. The danger that this conversion ventionally by the equation: will take place is lessened by working at high temperatures where equilibrium lies on the side of the dehydrogenated hydrocarbons, but such conditions may favor the production of excessive amounts of gas and lead to the formation of coke. On the other hand, since benzene boils at 80' C., the formation of naphthenes and their subsequent cracking must be allowed to proceed to a sufficient extent to provide the more volatile fractions required in a well-balanced gasoline. The separate influence of pressure on the hydrogenation In Hall's investigations 175 grams of naphthalene mere and cracking reactions can be seen more readily from a study heated in a 2-liter autoclave with 10 per cent of a supported of individual hydrocarbons than of such a complex material molybdenum catalyst to 450' C. and maintained a t that as tar. The hydrogenation cracking of many pure subtemperature for 2 hours. The initial pressure of hydrogen stances has been investigated a t the Fuel Research Station ; was varied in a series of experithe results of some experiments from 60 to 120 atinosCONTINUOUS LIQUID-PHASE PLANT FOR C O A L ments on naphthalene made HYDROGENATION, F U E L RESEARCH STATION
n
INDUSTRIAL AND ENGINEERING CHEMISTRY
136
pheres. Under these conditions, reaction 1 proceeds rapidly enough for equilibrium to be reached during the period of heating, but the subsequent changes take place relatively slowly. The liquid products of reaction were examined by fractional distillation, and the quantities of naphthalene
VOL. 29, NO. 2
should also increase with the hydrogen pressure. But the yield of hydrocarbons boiling below 160' C. is virtually unaffected by increase of pressure from 80 to 120 atmospheres, although the concentration of n-butylbenzene increases as well as that of hydrogen. It therefore seems probable that the cracking of the n-butyl side chain is to be represented as a monomolecular reaction of the type
80
00
70
This step determines the rate a t which n-butylbenzene is decomposed and is followed, no doubt, by the rapid reduction of the unsaturated molecule. The zero order of the reaction suggests that hydrogen acts as a negative catalyst; whether this occurs heterogeneously is now being investigated. The opening of reduced aromatic rings and the subsequent cracking of the aliphatic side chains seem, therefore, to take place by two distinct mechanisms; increasing the hydrogen pressure seems to accelerate the first and to retard the second reaction.
40
30 20
IO 0 80
80
100
110
INITIAL HYDROGEN PRESSUREIN ATMOSPHERES
{
184 Z I M U M PRESSURE
228
!
ATTAINEDIN ATMOSPHERES 259
FIGURE 2. INFLUENCE OF HYDROGEN PRESSURE ON REACTION 2
unchanged and of Decalin formed were determined separately. The liquid boiling below 160' C. may be considered to measure the extent to which reaction 4 has taken place. The weight of the fraction boiling between 160' and 195'C., minus the quantity of Decalin it contains, represents the n-butylbenzene produced by reaction 3, although these figures must be regarded with some caution owing to the difficulty of separating n-butylbenzene from Tetralin by fractionation. The yield of any fraction cannot be regarded as proportional to the rate of the reaction by which it is formed, since the concentrations of the consecutive reactants are continuously changing during the experiment. The variation in these yields with pressure can, however, be used to test the mechanisms by which the reactions take place. Curve A in Figure 2 gives the percentage of naphthalene converted during each experiment and, as is to be expected, the conversion increases with the hydrogen pressure. The formation of Decalin by reaction 2 takes place (curve B ) only to a minor extent with this catalyst, but the percentage of the naphthalene completely reduced definitely increases as the pressure is raised. The influence of hydrogen pressure on reactions 3 and 4 can be followed from curves C and D,Figure 3. The percentage of naphthalene converted can be considered as a measure of the Tetralin available for further reaction during the course of the experiment. It is therefore interesting to notice that curve C continues to rise a t pressures of 100 and 120 atmospheres where curve A is flattening out, showing the separate influence of an increased concentration of hydrogen and suggesting that the mechanism of the opening of the reduced ring to give n-butylbenzene is, in fact, the bimolecular reaction 3. The results a t the higher pressures (Figure 3) are the mean of several experiments; the radii of the circles around thq points represent the average deviation from the mean. If the cracking of 8:butylbenzene to form ethylbenzene took place according to @quation 4, the rate of this reaction
Influence of Temperature Raising the temperature affects both the kinetics and thermodynamics of the process; it will be expected to increase the rates a t which both hydrogenation and cracking reactions proceed, but it will also reduce the possible extent of hydrogenation. Free energy data of any reliability are available only for the simplest reactions of this type. Parks and Huffman (6) calculated that, for the equilibrium between benzene, hydrogen, and cyclohexane,
the free energy change in the vapor phase is given in calories per gram molecule by the equation: AF" = -43,800
+ 18.2 T log. T - 0.008Ta- 30.0 T
It follows that A F becomes zero a t 544' K. (271' C . ) under standard conditions, but that, if the hydrogen pressure is raised to 200 atmospheres, AF is reduced to about -17,000 calories per gram molecule a t this temperature, and does not reach zero until around 800' K. (527' C.). Hall's experiments with naphthalene show clearly the tendency towards dehydrogenation a t higher temperatures. In his experiments in 2-liter bombs, charged with 100 atmospheres of hydrogen a t room temperature, the percentage of naphthalene converted was found to reach a maximum a t 425' C. and to decrease steadily as the temperature was raised to 500' C. (curve A , Figure 4). The acceleration of the cracking reactions by increasing the temperature is strikingly shown by this series of experiments. Although over 90 per cent of the naphthalene is converted into Tetralin a t 400' C., it is only when the reaction temperature is raised to 450' C. that large quantities of the n-butylbenzene fraction are formed (curve B, Figure 4). Further cracking to yield a lower boiling fraction (curve C) and gaseous hydrocarbons requires an even higher temperature, but a t 500" C . it proceeds so rapidly that the yield
FEBRUARY, 1937
INDUSTRIAL AND ENGINEERING CHEMISTRY
of n-butylbenzene has passed through a maximum, and very little is recovered. Cawley (1) studied under the same conditions the reduction of phenol to benzene and cyclohexane:
0
HZ
-
ck
CL,
\CH/
Phenol is stable a t temperatures up to 300" C. but a t 450" C. is completely converted into hydrocarbons. These results may be compared with the reduction of the tar acids in lowtemperature tar, when carried out under 200 atmospheres pressure in a continuous plant: Temp., O C. Phenol unconverted Tar acids unoonverie? %
300
100 99
350 76 100
390
400 430 ... 22 ... 39 ... 6
pressing cracking becomes appreciable, and a t 510" C. the difference in the quantity of spirit produced under 400 and under 200 atmospheres pressure amounts to as much as 10 per cent by weight of the tar treated.
Deterioration of Catalyst in Low-Temperature Tar Processing
CdCH2&H,
+ H2-0
450 0
0
Influence of Variables on Tar Hydrogenation in a Continuous Plant The effect of temperature on the conversion of low-temperature tar into gasoline was examined in a continuous plant a t temperatures from 300" to 510" C. and under pressures of 200 and 400 atmospheres. Reaction seems to begin a t about 320" C., when the complex material of which the pitch is composed is the first to be attacked and is converted into oil that is soluble in petroleum ether of low boiling point. After treatment a t 370" C. the tar loses its black appearance and turns brown, although it remains opaque. If the reaction temperature is raised to 410" C., the color changes to dark orange and a t 450" C. to lemon; with the normal running temperature of 480" C. the crude product from the plant is transparent and pale yellow in color. The yields of gasoline boiling below 200" C . , expressed as percentages by weight of the tar treated, are plotted in Figure 5 . At a pressure of 200 atmospheres the yield increases approximately linearly with temperature up to 475' C. This curve shows a slight concavity towards the temperature axis, which becomes more marked a t the upper end. This is probably due to an increase in cracking to gaseous hydrocarbons, At 450" C. the optimum pressure is 200 atmospheres, since the yield is appreciably reduced a t lower pressures and is only slightly increased a t 400 atmospheres. Above 470" C., however, the influence of hydrogen in re80
00 80
80 70
70
The inference that the working conditions chosen to obtain the greatest economic output of gasoline from a plant should be the maximum temperature and pressure attainable is not, however, correct. At a high temperature there is a smaller residue of oil of high boiling point to be recycled, and a higher throughput of fresh tar can therefore be maintained, but a t the same time the catalyst deteriorates more rapidly and must be more frequently revivified. The deterioration of the catalyst results in a progressive decrease in the yield of gasoline and an increase in the specific gravity of the product. When the throughput of raw material was maintained a t 10 volumes of tar per volume of catalyst per day, the average daily rate of deterioration of a molybdenum catalyst during the first 6 days of its life was found to vary with temperature as follows: Temp., O C. Daily increase in sp. gr. a t 1 5 O C. Daily decrease in gasoline yield, %
UJ
B
P
5
30 20
L?
20
U
10
n 2 IO
0 100
120
228
{ ~EIMUM PRESSURE ATTAINED 184
I N ATMOSPHERES
0
350
4m
510 0.0050 1.0
From the experience gathered during continuous experiments on a small scale, fortified by the knowledge gained by the study of the behavior of pure substances, it has been pomible to design a plant of semi-technical size for the hydrogenation of low-temperature tar. The general outline of this plant, which was first operated in March, 1935, is shown in Figure 6; a more detailed description has been given by King and Shaw (6).
40
BO
480 0.0028 0.7
Development of a Semi-technical Plant
30
BO
400 0.0010 0.45
On the other hand, when the pressure was raised from 200 to 400 atmospheres a t 480' C., the average daily increase in specific gravity was reduced from 0.0028 to 0.0010 and the decrease in gasoline yield from 0.7 to 0.1 per cent a day. This beneficial effect of the higher pressure must, however, be balanced against the greater costs of compression, the need of using a larger proportion of hydrogen to tar if the maximum yield of spirit is to be obtained, and the danger, already mentioned, that the antiknock value of the product will be lowered by the conversion of aromatic hydrocarbons into naphthenes. The systematic search for active hydrogenation catalysts and details of the preparation and properties of the molybdenum compounds that have been most satisfactory has already been described (6).
40
INITIAL HYOROOEN PRESSURE IN ATMOSPHERES
137
450
500
TEMPERATUREDEGREESCENTIGRADE
4. INFLUENCE OF TEMPERAFIGURE3. INFLUENCE OF HYDROGEN FIGURE TURE PRESSURE ON REACTIONS 3 AND 4
460
TARHYDROGENATION
PLANT .4T THE
FUELRESEARCH STATION
Above, control room ; below, converter room
Low-temperature tar from storage is fed into a tank, where it is mixed with recycle oil, and thence to a tar pump which compresses the mixture to 200 atmospheres. Hydrogen is forced into the high pressure line and passes with the tar through a heat interchanger and a preheater into the converter, where the reaction is carried out a t 480" C. The heat interchanger consists of two 90-foot (27.5-meter) lengths of piping, welded together and bent to form a coil, through which the materials entering and leaving the converter flow in countercurrent to each other. The preheater is a coil 170 feet (52 meters) long and is heated by gas. The converter measures 13 feet (4 meters) long and 16 inches (40.6 cm.) across internally, and the reaction chamber is 11 feet (3.4 meters) long and 8 inches (20.3 cm.) in diameter. The throughput of raw material can be varied from 1000 to 2000 kg. a day. For each kilogram, 1 to 3 cubic meters of hydrogen are compressed; about 0.6 cubic meter is used in the reaction and the remainder is recirculated. The products of reaction pass from the converter through the preheater to the high-pressure separator, where the liquids are collected while the residual gas passes on. The liquid products are released to a low-pressure separator, in which the gas dissolved under pressure is evolved and thence to a still where the gasoline boiling below 200" C. is removed
and tlie residue returned as recycle oil to the converter. When steady conditions are maintained in the converter a t 480" C., the yield of gasoline is approxiniately 50 per cent hy volume of the total material fed in, or 100 per cent by volume of the fresh tar treated. The residual gas from the high-pressure separator contains 90 per cent of hydrogen; it is scrubbed with a countercurrent flow of oil to remove gaseous hydrocarbons and is then returned to the converter. The hydrocarbon gases are recovered by releasing the pressure, and the oil is then returned to the scrubber. Together with that from the lowpressure separator, this gas amounts to 140 liters per kg. of material treated, or 7 per cent by weight of the gasoline produced, and contains 40 per cent of hydrocarbons. The chief problem in operating this plant has been to control the temperature and to maintain it constant throughout the interior of the converter. The process of hydrogenation is highly exothermic, the heat evolved amounting to about 270 calories per gram of tar. To maintain stable ronditions, the products must be removed from the converter a t a higher temperature than that a t which the reactants enter, with the consequent disadvantage that a part of the catalyst bed serves mainly as a preheater. If tar is mixed with recycle oil, the conversion of which into gasoline is less exothermic, the heat released in the converter a t a given throughput can be reduced, so that a higher feed temperature can be used and more of the catalyst can be maintained a t the temperature of reaction. Any tendency for the temperature to rise unduly rapidly can be controlled by feeding cold hydrogen into the top or the center of the converter. With the high ratio of hydrogen to raw material (2.8 cubic meters per kg.) employed, however, the rate at which heat is removed can he closely regulated by increasing or diminishing the flow of gas. Fluctuations in temperature are so far reduced in this way that it is rarely necessary to employ cold hydrogen. As the activity of the catalyst slowly falls off, the rate a t which heat is evolved gradually diminishes during the course of an experiment. The correct conditions for reaction are maintained by raising the temperature a t which the reactants enter the converter by increasing the throughput or the proportion of tar in the raw material. A heat flow diagram of the plant is shown in Figure 7. During this experiment
ANALYSESOF RAWMATERIAL AND TABLE11. ULTIMATE TYPICAL PRODUCTS Analysis
Tar
S and errors 0
85.1 7.8 0.8 0.8 5.5
C H
N
H/C atomic ratio Q
Reoyole
Raw Oil Materiala Product Per cent bg weight---89.1 87.1 88.6 9.3 11.3 10.7 0.0 0.4 0.0 0.04 0.4 0.04 0.06 2.8 0.06
Oil
0.97
1.44
1.21
1.53
GWoline to 200' C. 87.0 12.8 0.0 0.03 0.17 1.77
50% tar and 50% recycle oil.
T A B L111. ~
TYPICAL GASOLtNE FROM HYDROLOW-TEMPERATURE TAR
PROPERTIES OF GENATION OF
Sp. gr. at 15' C. Potential gum, mg./i00 1111. Ootane No. Mannng analysis. % : Aromatics Unsaturates Saturates
Initial h. P., C. Final b. p., ' C.
Engler distn.. % by vol.: 48-75" 76100" 100-125; 126-150 25.4 150-175O 2.1 175-200' 72.6 200P-final h. p. 48 Residue Loss 206
0.806 2 70
2.0
18.5 48.5 70.0 84.5 96.0 98.8 1.1 0.4
.
. * .
INDUSTHIAL A N D EIL~GINEEKIKG CHEMISTRI
FEBRUARY, 1937
139
I
t
FONVERTER
r 1
L FIGURE6.
F L O W DIAGR.Gvf OF SEMI-TECHNICAL-SCALE
the throughput was slightly below normal, and amounted to 128 cubic meters of hydrogen and 48 kg. of a mixture of equal parts of low-temperature tar and recycle oil each hour. Under these conditions 6400 kilocalories must be supplied each hour to the reactants as they pass through the preheater. The heat of reaction exceeds the heat loss from the converter by 3780 kilocalories an hour; it not only assists, therefore, in the maintenance of the temperature in the catalyst bed but also contributes to the sensible heat communicated in the heat interchanger t o the incoming raw material. When the throughput is raised, this contribution may be expected to increase in proportion to the external heat required in the preheater. The plant has been run satisfactorily for periods of 28 days. During one such experiment 3374 gallons of tar and 2194 gallons of recycle oil were used as raw material and converted into 1864 gallons of gasoline and 3975 gallons of recycle oil. The ultimate analyses of the raw m a t e r i a l and Of typical prodFIGURE 7. HEATF L O ~ ucts are compared in D I A G R AOMF F I N A L Table 11, and the propS T A G EP L . 4 N T W H E X erties of the hydro9 GALLONS OF RAWMATERIAL AND genation spirit are sum4500 cnBIc F~~~ OF marized in Table 111. HYDROGEK PER HOUR
HYDROGENATION PLANT
CONDENSER
(23.C) TAR A N 0 HYDROGE
-- - - - - -(24,700)
- - -- - - - - -(59,000) (278%) - -- --- -- - -(60,200)(283'C)
(84,400)
(23'C) (122%)
(95.500) (405'cl
TI
(388%)---- - - - -
k C
QUANTITIESIN B.TH.U.PERHOUR.
INDUSTRIAL AND ENGINEERING CHEMISTRY
140
The advantage of this plant is that it is constructed on a large enough scale for judgment to be made of the economic possibilities of hydrogenation. Now that the technical difficulties of the process have been largely overcome, it will be possible to test some of the deductions that have been drawn from experiments in smaller plants. For example, there is evidence to show that the percentage yield of the gasoline fraction is not proportionately lowered by reducing the time of contact, suggesting that it may prove more economical to work on the large scale a t considerably higher throughputs than is the present practice. It is also hoped to extend the range of raw material that can be treated to include high-temperature tar. It would no doubt have been simpler, technically, to divide the process into stages, but it can now be reasonably claimed that the problem of converting low-temperature tar into gasoline by hydrogenation in a single and economically more advantageous operation is far on its way to complete solution.
VOL. 29, NO. 2
Literature Cited (1) Cawley, Fuel, 11, 217 (1932). Dept. Sci. Ind. Research Gr. Brit., Fuel Research Tech. Papers 40 and 41 (1935). (3) Hall, Fuel, 12,76(1933). (4) Keith and Montgomery, IND.ENQ.CHEM.,26,916 (1934). (5) King and Shaw, Chem. Eng. Congr. of World Power Conf., London, 1936,Paper G1. (6) Parks and Huffman, "Free Energies of Some Organic Compounds," p. 94, American Chemical Society Monograph 60, New York, Chemical Catalog Go., 1932. (2)
x
RECNIVED September 28, 1936. P Rented before the Division of Caa and Fuel Cheinistry at the 92nd Meeti f the Amerioan Chemical Society, The illustrations in this paper Pittsburgh, Pa., September 7 to 11, are the copyright of the Crown and are reproduced by permission of the Controller of H. M. Stationery Office. The photographs and Figures 2, 3, 6, and 7 are reproduced from the Reports of the Fuel Research Board for the years endel March 31, 1835, and Maroh 31, 1936.
COAL HYDROGENATION A Comparison of Hydrogenation Products of Coal and Oil M. PIER I. 0. Farbenindustrie A. G., Ludwigshafen o n Rhine, Germany
T
HE production of gasoline by thermal cracking of petroleum oil is a major industry in the United States. Thermal decomposition of coal is also carried on throughout the world on a large scale, though chiefly for the production of coke and gas. By-products of this operation are tar and benzene; the latter is now an important motor fuel. However, in comparison to the high yield of low-boiling products from petroleum, usually only a small amount of liquid material may be produced from coal. This is obviously due to the fact that petroleum contains twice as much hydrogen as coal and also that, in the decomposition of coal, hydrogen also is consumed, to some extent unintentionally, by the abundance of foreign elements such as oxygen, nitrogen, and sulfur. Therefore in the thermal treatment of coal, the lower boiling products (with a higher hydrogen content) can be formed only to an insignificant extent, with the result that sufficient demand and use for the major product, coke, is necessary in order to make the carbonization of coal economically feasible. Countries with no or only small petroleum reserves, but with large coal deposits, thus have a raw material suitable for the production of oils. Thermal decomposition alone, however, is not sufficient to satisfy the present large demand. A process giving better yields is needed.
Catalytic Destructive Hydrogenation For the production of motor fuels and oil, the process of catalytic destructive hydrogenation at elevated pressure has been developed in Germany. This process makes it possible to convert the raw material almost completely into lowboiling final products by adding the deficient hydrogen,
By use of catalytic destructive hydrogenation, fuels such as coal tar, petroleum, and shale oil give high yields of products usually obtained from mineral oils. Practically the only by-product is a certain amount of gaseous hydrocarbons which, however, may be utilized in the process by conversion to hydrogen. Catalytic hydrogenation makes possible the production from the same raw material of different final products such as fuel oil, lubricating oil, Diesel oil, illuminating oil, or gasoline, according to the market demand. without the necessity of forming a t the same time a large amount of high-boiling or even solid condensation products. Besides the direct hydrogenation of coal, the hydrogenation of tars is important for motor fuel production. I n Germany, for instance, tar from the carbonization of high-bitumen lignites (with a tar yield of about 15 per cent) is now converted by catalytic destructive hydrogenation into motor fuels, whereby a large percentage of the carbonization coke may be used in the hydrogenation plant, especially for the production of hydrogen. Several papers have been published (4, 6) on the fundamentals and the operation of the catalytic destructive hydrogenation. Raw materials such as petroleum, shale oil, tar, or coal can be treated equally well for maximum yields of motor fuels; .gas is practically the only by-product. This gas may be easily reconverted into hydrogen. The process is not dependent on the salability of by-products and avoids waste of raw material. It is also possible to regulate to a great extent the type of final product desired, with the result that an equally great variety of final products can be produced from the large variety of raw materials.
