crudes now, being utilized are of relatively high sulfui content. Hydrogenation is a n ideal means of removing this sulfur since it can be accomplished with little or no loss in yield. Another application for the hydrogen produced from catalytic reforming operations is to improve the properties of cpcle gas oil from catalytic cracking for use in further cracking. The cycle stocks from catalytic cracking are aromatic in character and do not give as good yields on subsequent catalytic cracking as the virgin feed stock. By hydrogenation it is possible to convert the aromatic materials into naphthenic-type materials that can readily be cracked over catalyst with high yields. By such hydrogenation the cycle gas oil can be made equivalent to or better than the original virgin feed from a cracking standpoint. Reduced Fuel Oil Yield. Under present price levels for various petroleum products the production of residual fuel oil in the United States is definitely unattractive. Most processes that will reduce fuel oil yields show a high return. Those processes that give major reduction in fuel oil yield, above that which can be accomplished by distillation and viscosity breaking, are deasphalting with light hydrocarbons, coking, and direct catalytic cracking of reduced crude. I n the case of deasphalting, fuel oil yield is greatly reduced and in the case of coking or direct catalytic cracking fuel oil can be eliminated as a product. Domestic cue1 oil production now amounts to around 1,300,000 barrels per day, so the financial gains that would result from converting the fuel oil into higher value products would, because of the large volume, be very wbstantial-over $600,000,000 per year Heavy Crude Bottoms. The hydrogenation of heavy crude bottoms for conversion t o lighter products has been frequently considered in the past but has not proved economic because of the large investment and operating costs associated FTith hydrogen production and with the hydrogenation equipment itself +ks catalvtic reforming is more extensively applied, it would appear that there will be hydrogen in excess of that which can be utilized in the various finishing and desulfurization operations discussed. The volume of hydrogen left over will probably not be great enough to hydrogenate all heavy crude bottoms to lighter products but it could supply the hydrogen needed for so converting a substantial portion of these heavy crude bottoms. For this reason it is likely there will be revived interest in the hydrogenation of heavy crude bottoms to produce lighter products and an improved hydrogenation operation would certainly be most attractive. To be successful an operation must be developed that is considerably less expensive from the standpoint of investment and operating costs than those that have been used for hydrogenating heavy crude bottoms in the past. Catalysts are needed that will enable operation to be carried on a t lower piessures in cheaper forms of equipment.
Theoretical Advances
It is v-ell known that the octane number requirements of the engine of a new car increase subEtantially in the first 3000 to 6000 miles of use. This increase is believed due a t least in part to carbonaceous deposits formed in the combustion chambers of the engine. These deposits frequently cause preignition. The development of a catalyst to be added to the fuel or motor oil that would prevent these deposits from accumulating could be of very real benefit. The production of catalysts for a given catalytic operation is at the present time mainly a trial and error procedure. Different catalyst compositions are made up and tested and there is little theoretical background that can be applied in determining how to produce an optimum catalyst for a given operation. Much more needs to be knonrn about the mechanism by which catalysts work, and such information should give a clearer insight to the preparation of a catalyst for a given service. I t is expected that in the future considerable strides will be made in obtaining a better picture of how catalysts perform and this will be of great help in making improved catalysts. Sum ma ry The discussion in this paper has touched on some of the present applications of catalysts in the petroleum industry and on what some of the future trends may be. In summary, continued extension and advancement of catalytic processes in the petroleum industry may be expected. Catalytic cracking Rill likely continue to be the largest application but a rapid growth in catalytic reforming will occur. Because of this, many improvements in catalytic reforming should be realized. both from the standpoint of catalysts that will give more favorable yield-octane relationships and from the standpoint of catalysts that will allow the octane level that can economically be obtained to be increased. Along with improved catalysts, more efficient e uipment for applying catalytic reforming may be expected, wi% the result that the operation may be installed a t a loTver cost. Catalytic reforming when extensively applied will produce large quantitieE of hydrogen, and it is expected this hydrogen 71 ill find many uses for the refining of petroleum products and fractions. There is considerable economic incentive for conversion of heavy crude residues to lighter products and this may involve catalysis. In the field of product application there is need for a catalyst that can be so applied that it will continuously prevent the accumulation of the bulk of the deposits in the combustion chambers of automotive engines. Research now going on and to be carried out in the future on how catalysts perform should be most helpful in improving all types of catalytic operatione. literature Cited (1) Storch, H.
H., IND.ENQ.CHEM., 45, 1444 (1953).
(2) Taylor, H.
S.,Ibid., 45, 1440 (1953).
RECEIVED for reviex December 3, 1952.
ACCEPTED March 11, 1953.
Synthetic Liquid Fuel Processes HENRY H. STORCH Fuels-Technology Division, Bureau o f Mines, Brucefon, Pa.
HE chief raw materials other than petroleum for the manufacture of liquid fuels are oil shale and coal. The quantity of liquid fuel recoverable from our richest oil shale deposits (in Colorado, and Utah) is about billion barrels; that from our coal deposits is of the order of trillion barrele. A~~~~( 2 ) estimates that commercial scale plants producing liquid fuels from oil shale and coal will be operating by 1960 and by 1970, respectively, The time available for completion of development of processes (to an operable level) for manufacture of liquid fuels from oil shale is a t most 5 years and from coal about 15 years.
T
1444
liquid Fuel from Oil Shale
Development work on the mining and retorting of oil shale is well advanced and involves no special problems in catalysis. The refining of crude shale oil for the production of chiefly liquid fuel for use in internal combustion engines involves special catalytic processing. The crude shale oil contains relatively large fractions of nitrogen and sulfur compounds, which must be converted to hydrocarbons. The processes developed thus far are: 1. Coking distillation of the crude shale oil, followed by hydrogenation of the coker distillate a t 100 atmospheres on a cobalt
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 45, No. 7
A
brief review is presented of some problems in the catalytic steps of processes for the conversion of oil shale and coal to liquid fuels. More efficient and selective catalysts for the hydrosplitting of shale oil and of middle oils from hydrogenation of coal are needed. The changes in selectivity and activity of iron Fischer-Tropsch catalysts resulting from nitriding after reduction; the desirability of similar research on iron catalysts containing boron or silicon as interstitial elements, and the homogeneous catalyses of hydroformulation and hydrogenation reactions by cobalt carbonyl are discussed.
molybdate-alumina catalyst. Part of the product is suitable for direct use as a jet fuel or as feed for catalytic reforming t o produce gasoline. The remainder is a satisfactory Diesel fuel. 2. Direct catalytic hydrogenation of the crude shale oil a t pressures above 200 atmospheres. The first procedure has been developed t o an operable state (5,4). It is desirable that a more selective catalyst be developed t o decrease the frequency of catalyst regeneration cycles (now every 100 to 300 hours). There is need for additional (6, 8) development of catalysts for the direct high pressure (200 to 700 atmospheres) hydrogenation of crude shale oil. Because of the high nitrogen and sulfur content of this oil,, it is probable that use of activated charcoal either per se or with small amounts of more active hydrogenation catalysts, such as molybdic acid, will result in extensive nitrogen and sulfur elimination and a large reduction in molecular weight. The product from this hydrogenolysis may be a suitable feedstock for standard petroleum refining operations-Le., catalytic cracking, hydroforming, etc.
250 atmospheres) hydrogen. The preheat temperature usually is 430' C. Because of the exothermic character of the reaction, the temperature increases rapidly in the reactor t o about 480" C. For the lower rank coals (such as German brown coal), about 4% of red-mud and for bituminous coals, about 0.1% of tin oxalate plus 1%of ammonium chloride are used as catalyst. Despite extensive laboratory and pilot plant experiments since about 1927, the great importance of the manner of mixing the catalyst with the coal was discovered only recently (10-19). Table I ( 8 ) shows the enhanced catalysis achieved by impregnating the powdered coal with an aqueous solution of the cttalyst as compared with mixing the dry powdered catalyst with the coal. The coal was a high volatile C bituminous coal from Rock Springs, Wyo. No vehicle or pasting oil was used in the tests. The apparatus was a glass-lined rotary autoclave of 1-liter capacity, the temperature was 450" C., pressure (initial, in the autoclave a t room temperature) was 70 atmospheres, and the reaction time 1 hour.
Liquid Fuel from Coal Coal Gasification. All procedures for producing liquid fuel from coal include the manufacture of hydrogen or mixtures of hydrogen and carbon monoxide. In fact, of the total cost of synthetic liquid fuel, 40 to 50% is expended for compressed hydrogen in the coal hydrogenation process and about 60% for synthesis gas (hydrogen-carbon monoxide mixture) in the Fischer-Tropsch process. Although underground gasification of coal with air and steam offers some chance of cheap power production by driving turbines with hot gas of relatively low B.t.u., the possibility of the production of synthesis gas by underground gasification of coal with oxygen and steam is more remote. For purposes of direct hydrogenation of coal at high pressures (200 to 700 atmospheres), experiments should be made on the rate of reaction of the primary hydrogenation product with high pressure steam in the temperature range 480' t o 550" C. It is possible that the asphaltenes made by mild hydrogenation of coal are sufficiently reactive with steam to provide enough hydrogen for the conversion of the remaining asphaltenes t o oil. Catalysts which accelerate the asphaltene-steam reaction should be developed. In the complete gasification of coal with oxygen and steam in those types of converter; where the reaction temperature is not above about 1000"C., the slow step is of a chemical nature, and a more intensive study of catalysts may be profitable. I n converters where the reaction temperature is above about 1100" C., the slow step is a diffusion of rractants to or products away from the carbon surface, and for such processes catalysts are not of importance. Liquid Phase Hydrogenation of Coal. The first step in the Bergius-I.G. Farben process for hydrogenation of coal consists in mixing 1 part (by weight) of pulverized (minus 80 mesh) coal with 1.0 to 1.5 parts of a recycle heavy oil and 0.1 to several per cent of the weight of the coal of catalysts such as stannous oxalate, ammonium molybdate, ferrous sulfate, or luxmasse (also known as red-mud, a by-product from the purification of bauxite for aluminum production). This mixture is then pumped through a preheater into a pressure vessel along with compressed (about July 1953
Table I. Effect of Catalyst Distribution on Coal Hydrogenation
Catalyst
(Rock Springs coal, no vehicle) Moisture and Ash Mode of Catalyst ConAsphalDistribution version'" teneb 26.5 Powder added 82.3 19.9 Impregnated 88.3 44.2 Powder added 6.8 15.5 88.3 Impregnated 6.9 38.9 Powder added 84.9 38.9 Impregnated 33.7 1.0 Powder added 27.2 Impregnated 92.7 2.8 33.4
...
Free Goa= OilC 29.2 41.4 13.2 45.3 8.1 21.7 13.8 41.1 10.4
Gaseous hydrocarbons 14.5 15.5 13.4 18.0 13.1 15.0 8.1 13.6 9.0
Converted to gaseous products, water, and liquid products soluble in benzene. b Liquid products soluble in benzene but insoluble in n-hexane. Liquid products soluble in n-hexane. a
As shown in Table I1 (11), when applied as aqueous solutions in which the powdered coal was dispersed and the slurry then evaporated to dryness (104' C.), the sulfates of iron and cobalt are more effective catalysts than the chlorides, and the chlorides of nickel and tin are more effective than the sulfates for the hydrogenation of Rock Springs coal. The degree of hydration of the cation and the effect of the hydrogen ion concentration on such hydration may correlate with these facts, which are otherwise difficult to interpret. Further research is needed on the application of aqueous solutions of these catalysts t o coal a t carefully controlled hydrogen ion concentrations. Use of solvents other than water also should be more extensively studied. The mechanism by which metal sulfates and chlorides catalyze the primary hydrogenolysis of coal is unknown. Indeed, in view of the fact that at least 1 atmosphere of hydrogen sulfide is present in all coal hydrogenation tests, the metal sulfates or chlorides probably are rapidly converted to the sulfides which are stable even a t high hydrogen pressures. However, the rate of conversion to sulfides may be reduced if the cation is combined with a polar group attached to the coal molecule. Assuming that such a
INDUSTRIAL AND ENGINEERING CHEMISTRY
1445
combination exists, and that it can function as a hydrogen carrier by reason of the existence of more than one valence state of the cation, a conceivable mechanism can be postulated. Recent application of catalyst impregnation techniques a t the Bruceton, Pa., laboratories of the Bureau of Mines has shown the possibility of a one-step coal-to-gasoline process, at 500’ t o 525” C., and a pressure of 10,000 pounds per square inch. The gasoline contains about 35% (volume) of aromatics, 35% naphthenes, and 30% paraffins. The yield is about 50% (weight) of the dry. ash-free coal. No asphaltenes are produced.
Table
II.
Comparison of Impregnated Metal Sulfates and Chlorides
(Rock Springs coal, 450’ C., 1 hour, 1000 lb./sq. inch gage initial hydrogen pressure) Moisture and Ash Free Coal, % Gaseous Catalyst Conversion Asphaltene Oil hydrocarbons FeSOd (1% Fe) 84.9 21.7 15.0 38.9 15.2 FeClz (1% Fe) 12.2 4.8 44.8 cos04 (1% CO) 22.5 14.9 36.5 83.6 11.2 COClZ (1% CO) 16.3 8.3 58.0 NiSOa (1% iVi) 33.0 10 0 14.8 78.9 NiClz (1% hi) 15,5 18.0 45.3 88.3 SnSOa (1% Sn) 12,3 12.9 46.3 7.9 19.9 41.4 SnCI? (1% Sn) 15.5 88.3
Hydrorelining of Coal Hydrogenation Middle Oil. The second or vapor-phase stage of the coal hydrogenation process is the hydrogenolysis of the middle oil (or gas oil) produced in the first or liquid phase stage. Usually the second stage involves two steps. In the first or “saturation” step, the oil is vaporized in a stream of hydrogen a t a pressure of about 280 atmospheres and passed through a bed of catalyst granules maintained a t about 410 O C. The catalyst is pellets of either pure tungsten disulfide or 25% tungsten disulfide plus 3% nickel sulfideonactivated alumina. The bulk of the nitrogen and sulfur content of the feed is removed as ammonia and hydrogen sulfide, and some hydrogen is added t o the aromatics and olefins during the saturation step. Little or no reduction in molecular Ti-eight occurs. In the second or “splitting” step of the vapor-phase hydrogenation, the products of the saturation step are passed through a bed of catalyst granules, which are usually 90% hydrofluoric acid-treated clay plus 10% of a hydrogenating component such as ferrous, tungsten, or molybdenum sulfide. The temperature in the splitting step is in the range 425 O to 450’ C. and the pressure is about 250 atmospheres. When the vapor-phase stage of coal hydrogenation is operated a t 700 atmospheres, the saturation and splitting steps can be achieved in one reactor. Recent developments in hydroforming of gasoline from petroleum, such as platforming and Houdriforming, have shown that control of the cracking activity of the silica-alumina base by regulated sintering makes skeletal isomerization possible, without appreciable formation of gaseous hydrocarbons or of carbon. This procedure should be applicable t o the high pressure hydrogenolysis of middle oils, and development of more selective catalysts is possible. Such selectivity already has been partially achieved by the use of smaller amounts of the hydrogenation element in the I.G. Farben catalysts K-534 and K-536 [acidtreated clay plus about 0.7% molybdenum oxide, 5% zinc oxide, 3% chromium oxide, and 2.5% sulfur ( I t ? ) ] . Hydrogenation of Carbon Monoxide
Fischer-Tropsch and Related Processes. A review of the development of catalysts for the hydrogenation of carbon monoxide to produce chiefly liquid aliphatic hydrocarbons, alcohols, and smaller amounts of aldehydes, fatty acids, and ketones is avail1446
able (9). Marked changes in selectivity and activity of iron catalysts for Fischer-Tropsch processes have resulted from nitriding the fully reduced catalysts. The nitrided catalysts yield a much higher fraction of oxygenated organic compounds in the condensed liquid product and a large reduction in the amount of wax (1, 6 , 7 ) . They are much more active and durable than the unnitrided catalysts. It is expected that the introduction of boron or of silicon atoms into the lattice of reduced magnetite also should yield outstanding changes in selectivity, activity, and durability. These elements should be introduced by the reaction of a gas containing boron or silicon with the reduced magnetite. In this fashion the original lattice structure of the magnetite should be preserved with minor changes in spacing. These changes in spacing of the iron atoms and the effect of the interstitial atoms (carbon in carbides, nitrogen in nitrides, etc.) on the electron distribution are sufficient, however, to cause marked changes in performance of the catalyst. In the course of research on the Fischer-Tropsch process, the hydroformylation (addition of hydrogen and carbon monoxide) of olefins or “oxo” synthesis was discovered by 0. Roelen of Ruhrchemie A.G. in Germany and patented by him in 1938. This synthesis occurs in the presence of a reactive cobalt compound or finely dispersed metallic cobalt in the temperature range 115” to 200” C. and pressure range 150 to 300 atmospheres. Recent work on the mechanism of this and similar reactions has disclosed two reactions which may be of critical importance in the development of synthetic liquid fuel processes. These are: 1. Alcohols which cannot yield olefins as intermediates, such as methanol and benzyl alcohol, react with hydrogen and carbon monoxide yielding the homologous alcohol with one more carbon atom. Thus, methanol ( I S ) is largely converted t o ethanol, and benzyl alcohol ( 1 5 ) yields about 26% of phenylethyl alcohol; the bulk of the remainder of the product is toluene. The rate of this homologation reaction is low for all of the primary and secondary alcohols (except methanol, for which it is greater than for the higher normal alcohols) and fairly fast for tertiary alcohols. 2. The rate of hydroformylation of olefins and alcohols is accelerated by cobalt carbonyl and cobalt hydrocarbonyl. This is a homogeneous catalysis, being unaffected by sulfur compounds and independent of the origin of the cobalt carbonyl. Thus, any reactive cobalt compound, or preformed cobalt carbonyl or cobalt hydrocarbonyl, catalyzes the reaction.
This homogeneous catalysis involves the addition of molecular hydrogen to the aldehyde formed by hydroformylation. -4 separate series of studies on this homogeneous catalysis of hydrogen addition is in progress ( 1 4 , 16, 1 7 ) . The hydrogenation of butyraldehyde ( 17 ) illustrates very R ell the homogeneous character of the catalysis. With finely divided cobalt metal and a t 185” C. and 2000 pounds per q u a r e inch of hydrogen pressure, heterogeneous hydrogenation to butyl alcohol occurred. In a second experiment, the same ieactants and conditions viere used except that carbon monoxide a t a partial pressure of 300 pounds per square inch was added. No hydrogenation of the butyraldehyde occurred. I n a third experiment, identical with the second except that the partial pressure of carbon monoxide was increased t o 1000 pounds per square inch, the aldehyde was largely converted to 1-butanol. I n the second experiment it is probable that the cobalt catalyst was poisoned by carbon monoxide for the heterogeneous hydrodrogenation. In the third experiment the partial pressure of the carbon monoxide was high enough to form cobalt carbonyl and/or cobalt hydrocarbonyl, which functioned as a homogeneous catalyst for the hydrogenation of the butyraldehyde. The importance of these two obfiervations for synthetic liquid fuel processes is in the conceivable design of a process starting with C, to Cd olefins or alcohols and hydroformylation of these to produce material boiling chiefly in the gasoline and Diesel range, cracking the residuum boiling above 320” C. to regenerate the C, to CCfeed. The product boiling Lelov 320” C. could be con-
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol, 45, No. 7
verted t o internally bonded olefins by passage through a bed of bauxite at a suitable temperature. Undoubtedly it will be very to obtain the desired product distribudifficult, if at all tion at an adequate rate. However, such a homogeneous catalysis would not require any purification of the synthesis gas or the preparation of special contact catalysts.
literature Cited (1) Anderson, R. B., Advances in Catalysis, 5 , in press. (2) Ayres, E., Petroleum Processing, 7, 41-4 (January 1952). 0
*
(3) Berg, C., Bradley, W. E., Stirton, R. I., Fairfield, R. G., Leffert, C. B., and Ballard, J. H., Chem. Eng. Progr,, 43, 1-12 (1947). (4) Clark, E. L., Hiteshue, R. W., Kandiner, H. J., and Morris, B , IND. ENG.CHEM.,43, 2183-8 (1951). (5) Hoog, H., Koome, J., and Weeda, K. A., presented a t the Second oil Shale and C h n e l Coal Conference, Glasgow, Scotland, July 1950. (6) Shultz, J. F., Seligman, B., Lecky, J. A., and Anderson, R. B., J . Am. Chem. SOC.,74, 637 (1952). (7) Shultz, J. F., Seligman, B., Shaw, L., and Anderson, R. B., IND. ENG.CHEW,44, 397 (1952).
( 8 ) Smith, W. M., Landrum, T. C., and Phillips, G. E 586-9 (1952).
, Ibid., 44,
(9) Starch, H. H.9 Golumbio, N.. and Anderson, R. B.9 “FischerTropsch and Related Syntheses,” New York, John Wiley & Sons, 1951. (10) weller, S.,Clark, E. L., and Pelipete, M. G., IND. ENG.CHEM., 42, 334 (1950). (11) Weller, S., and Pelipete, M. G., WorEd Petroleum Congr., Proc., $rd Congr., Hague, 1951, Sect. 4. (12) Weller, S.,Pelipetz, M. G , Friedman, S., and Storch, H. H., IND. ENG.CREM.,42, 330 (1950). (13) Wender, I., Friedel, R. A., and Orchin, M., Science, 113, 206-7 (1951). (14) Wender, I., Greenfield, H., and Orchin, M., J . Am. Chem. Soc., 73, 2656-8 (1951). (15) Wender, I., Levine, R., and Orchin, M., Ibid., 71, 4160 (1949). (16) Ibid., 72, 4375-8 (1950). (17) Wender, I., Orchin, M., and Starch, H. H., Ibid., 72, 4842 (1950). (18) Wolfson, M. w,, pelipetz, M. G., ~ ~ ~A. D., i ~ and kClark, , E. L., IND. ENQ.CHEW,43, 536-40 (1951). RECEIVED for review October 8, 1952.
ACCEPTEDJanuary 21, 1953.
Reactions of Hydrocarbons IONIC MECHANISMS LOUIS SCHMERLING Research and Development laborafories, Universal Oil Producfs Co., Riverside, 111.
The hydrocarbon reactions catalyzed by the large class of substances that may be called acid-type catalysts can best b e explained as occurring by way of carbonium ion, usually chain, mechanisms. These acid-type catalysts include acids, the Friedel-Crafts halides, and oxides. All presumably owe their activity to ability to cause the formation of carbonium ions under the reaction conditions. The carbonium ions behave according to certain rather gener-
ally accepted principles, resulting in the formation of the observed products. These principles have been applied to some typical petroleum hydrocarbon reactions, including the polymerization and isomerization of olefins, the alkylation of isoparaffins and of aromatic hydrocarbons, and cracking. It i s probable that the alkylation of aromatic hydrocarbons occurs not only by an electrophilic mechanism but also by a nucleophilic displacement mechanism.
T
lysts have acidic surfaces and that their activity is destroyed when the acid is neutralized by the adsorption of basic compounde (la, 96,30,46,47). It has been postulated (46) that the active constituent is (HAlSiO&. With aluminum chloride and other Friedel-Crafts-type catalysts, the carbonium ion may be formed from olefins in a number of ways. I n the presence of hydrogen chloride promoter, the carbonium ion is formed by the addition of the proton from the promoter to the olefin:
HE hydrocarbon reactions that are catalyEed by acid-type
c
catalysts can best be explained as occurring by way of carbonium ion, usually chain, mechanisms. These catalysts include acids, such as sulfuric acid and hydrogen fluoride, the Friedel-Crafts halides, such as aluminum chloride and boron fluoride, and oxides, such as silica-alumina. These all probably owe their activity to the ability to cause the formation of carbonium ions under the conditions of the reaction. The carbonium ions behave according to certain rather generally accepted principles, which result in the formation of the observed products.
Formation of Carbonium Ions From Olefins. The acid catalysts convert olefins to carbonium ions by addition of protons from the acids t o the extra electron pair in the double bond (the pi electrons):
H&: :C:CHa CHs
+ H+OSOsH-
HaC:$.:CHs
+ OSOBH-
CH3
The activity of silica-alumina catalysts is due t o the presence of hyclrogen ions. Several workers have shown that these cataJuly 1953
HzC=CHz
+ HC1 + AIC13 + CHsCHz+ + AlCId-
I n the presence of water as promoter, the proton may be derived from the complex formed from the promoter and the catalyst: AlCls
+ HzO & HzO: AICIs
$H
+[HOAICla]-
This complex may decompose to yield hydroxyaluminum dichloride and hydrogen chloride, which are also sources of protons: HzO: AICla Ft HCl
+ HOAICl,
Complexes with boron fluoride (BF3.H20 and BF3.2Hz0), on the other hand, %restable active catalysts.
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
1447
