Effect of Solvent Properties in Thermal Decomposition of Oil Shale

Effect of Solvent Properties in Thermal Decomposition of Oil Shale Kerogen To gain information on the chemical constitution of kerogen and the mechanism of its decomposition to shale oil, under conditions of minimum cracking of the resulting fragments, finely ground shale was subjected to thermal solution at 200° C. and autogenous pressure, in the presence of selected associating and nonassociating solvents. Total yield of product oils was found to be a function of the molecular volume of the solvent. Their carbon-hydrogen ratio and the percentage of original organic nitrogen and sulfur solubilized were found to be functions of the internal pressure of the solvent and its associating characteristics. The carbon-hydrogen ratio of the product oils was lower in almost all cases than that of Fischer assay shale oil. Nitrogen and sulfur contents were considerably less than that of pure kerogen or of an average assay oil. It is postulated that two forms of kerogen exist.

M

WERNER D. SCHNACKENBERG

AND

CHARLES H. PRIEN

University of Denver, Denver, Colo.

A

MONG the sources now under investigation in the United States for the production of synthetic fuels, it appears that oil shale has the greatest possibility of economic development in the near future. In the light of this fact it is surprising that, in spite of many years of research, much still remains to be known about the oil-producing substance “kerogen,” from which shale oil is derived. Indeed, only recently has kerogen even been isolated in anything approaching a pure state. It was therefore with the dual objectives of furnishing possible additional evidence on the chemical constitution of kerogen and of studying the mechanism of its decomposition to shale oil that the research reported below was undertaken. No attempt is made to suggest that the objectives have been attained in this preliminary program. It is hoped, however, that the data obtained, together with those being accumulated in subsequent phases of this research now in progress, may lend greater understanding as to the nature of kerogen and its mode of pyrolysis, and may eventually permit a more scientific approach to the design of retorts for the pyrolysis of oil shale to produce shale oil. NATURE OF OIL SHALE

“r

iu

Oil shale is usually defined as a wide variety of laminated, solidified mixtures of argillaceous sediments and organic matter having the common property of yielding oil upon destructive distillation, yet being but slightly susceptible to the action of common petroleum solvents. It is this last property, insolubility in petroleum solvents under ordinary temperatures and pressures, which distinguishes a true oil shale from such closely related materials as tar sands, torbanites, and “kerosene shales.” Although several different theories of the geologic origin of oil shale have been postulated, it is now generally accepted that organic matter, principally of vegetable origin and indigenous to the area, was laid down in successive layers by the repeated evaporation and refilling of extensive shallow lakes. The deposited layers of organic matter, interspersed with layers of silt and mud, in time lithified, and are found today as the extensive, stratified type of oil shale deposits, of which the Green River formation in western Colorado is an excellent example. An alternative theory of geologic origin, postulated some 20 years ago by Craig ( 6 ) ,is of possible interest in the light of certain results of the present research. Craig proposed that the kerogen, as a degraded vegetable substance, was transported from external sources into its present inorganic matrix, after which selective

February 1953

adsorption of heavy hydrocarbon molecules occurred, followed by inspissation (evaporation). As supporting evidence he shows how closely the average composition of the inorganic matrix resembles the highly adsorptive substance fuller’s earth. This is certainly true of the highly alkaline, so-called calcareous shales of western Colarsdo, the ash of which has an average analysis (68)of 46.5Y0 silica, 11.8y0 alumina, 5.2% ferric oxide, 19.4% calcium oxide, 8.2% magnesia, 6.4y0 sodium oxide plus potassium oxide, and 2.570 sulfur trioxide. I n addition, this inorganic matter, when free of all organic constituents, is found to be in an extremely finely divided state-Le., to have the large surface area which would aid in imparting high adsorptive capacity. Carlson agrees with the above adsorption theory, but suggests further (6) that actual loose chemical combination may exist between organic-inorganic constituents, probably as an acid-susceptible bond. Himus (18) disagrees with the bond theory, but concedes that perhaps at least the iron of oil shale is chemically bound.to the kerogen. These opposing postulates have not been resolved to date. The organic portion of oil shale, called kerogen, is composed of carbon, hydrogen, nitrogen, sulfur, and oxygen. An average analysis for this material, in the case of Colorado shale (26), is 76.45y0 carbon, Q.97y0hydrogen, 2.87y0 nitrogen, 1.2%, sulfur, 9.51% oxygen. The carbon-hydrogen weight ratio is thus seen to be 7.7. Kerogen is present in raw shales in concentrations ranging from 4 to over 30% by weight, corresponding to from 10.5 to over 75.0 gallons of derived shale oil per ton of shale. I t has not been isolated in pure form to date, although enriched samples containing less than 5% inorganic matter have been prepared. The chemical structure of kerogen still remains to be determined, and probably varies with the geographical location of the shales in the world. Among the postulates which have been advanced are the following: 1. Kerogen is a polymerized product of montan wax (1). 2. Kerogen has a benzenoid structure (8). 3. Kerogen resembles long-chain fatty acids, chemically bonded to or physically adsorbed on an inorganic base (6). 4. Torbanite kerogen is a decarboxylated polymer of unsatumany of its rated fatty acids, such as eleostearic acid, CI,H~,O~, physical properties closely resembling those of plastic polymeis (3). 5. Colorado kerogen is largely a material of high molecular weight (B), consisting essentially of a loosely interconnected

INDUSTRIAL AND ENGINEERING CHEMISTRY

313

structure of partly unsaturated, polyisoprenoid, resinlike chains and rings. This material is nonbenzenoid in character. Interconnected in this structure are oxygen-containing and oxygenheterocyclic fragments condensed with some benzenoid and pyridine ring structures. MECHANlSlM O F THERMAL DECOMPOSlTION

When dry oil shale is heated, thermal decomposition of the kerogen begins to take place immediately. The rate of pyrolysis does not become of practical significance, however, until temperatures of 300" t o 400" C. are reached. The process occurs in several stages, which might be summarized as follows: Step 1. Under gentle heating the kerogen softens to a rubberlike material, showing elastic and swelling properties. Some carbon dioxide and hydrogen sulfide gases are given off, but this "rubberoid" is still relatively insoluble. Step 2. With further heating the rubberoid cracks to form a ver viscous, though soluble, bitumen with liberation of more hy%ogen sulfide, and also carbon dioxide and water. Step 3. More heating produces a liquid, oily product Step 4. At high temperatures the oil is cracked and vaporized leaving a residue of coke. The first step is thought t o be partially a depolymerization, similar to that occurring in rubber ( 4 ) ,accompanied by rupture of cross linkages and reduction of the original macromolecule essentially to a simple elastomer. The succeeding stages are true thermal cracking reactions, accompanied by loss of fixed gases and the production of a residue of increased carbon-hydrogen ratio. These reactions are of course accompanied by increased solvent solubility. The presence of paraffin waxes in the final "shale oil" resulting may be due to the presence of long side chains attached t o polycyclic nuclei in the original macromolecule, or to the opening of heterocyclic ring structures. The primary over-all decomposition, a t least to the soluble bitumen stage, is a first-order reaction, with an activation energy of 40 to 50 kcal. per gram-mole (see Table I). I n the case of Colorado shale values of 41,500 t o 54,600 calories per gram-mole appear to be an acceptable figure, in the range 355" to 440" C., from published rate studies in the literature ( 4 , 22, 28). For dry decomposition the rate appears to be essentially independent of the original ratio of inorganic matter to organic matter in the raw shale.

OF ACTIVATION OF PYROLYSIS REACTIONS OF TABLE I. ENERGY VARIOUS ~IATERIALS~

E Csl./GrLm-Mole 48,500 41,500 49,956 59,500 53,400

a

XIaterial Torbanite U. S. A. shale Kukersite Paraffin wax Crude oil

Temperature Range, C . 350-400 300-325 390-440 425-450 430-700

From data of (4)

When thermal decomposition is made to occur by heating the ground raw shale in the presence of a suitable solvent (thermal solution), two deviations from dry pyrolysis are noted. I n the first place, the rate of decomposition is slightly loxer, as denoted by an activation energy (for Colorado shale) of 61,800 calories per gram-mole, in the range 355" to 440' C. Secondly, leaner shales (greater inorganic matter content) are found to decompose more rapidly than the richer shales (28). The rates of decomposition, however, whether determined in the dry state or in solution, are many times more rapid than might be assumed from the long residence times required in large scale commercial shale retorts, where rate of heat transfer, not rate of decomposition, is the controlling phenomenon. THERMAL SOLUTION OF 0 1 L SHALE

The kerogen of a true oil shale is only soluble to the extent of 2% or less in such common solvents as benzene, acetone, carbon 314

tetrachloride, carbon disulfide, chloroform, ethyl alcohol, ethyl ether, acetic acid, and cyclohexanol a t atmospheric pressure and the normal boiling point of the solvent in each case. This is not true, of course, as the extraction temperature is raised. D'yakova ( 1 1 , 12), after studying seven different U.S.S.R. ' of organic matter extracted a t shales, reported yields of 72 to 96 % temperatures of 385" to 420" C. and 30 to 40 atmospheres' pressure, with a contact time of 5 to 20 minutes. Solvents used were Tetralin, anthracene oil, petroleum fuel oil, Diesel fuel, hydrogenated shale tars, and shale oil distillate (boiling range 220" to 370" C.). Using lZustralian torbanite (which is a geologic progenitor of true oil shale kerogen) as his raw material, Dulhunty (B, 10) conducted extensive work in the 300" to 400" C. temperature range. His x-ork included preheating the torbanite a t successively higher temperatures, and extracting with benzene a t 270" C. and 560 pounds per square inch absolute after each preheat. Although no detailed quantitative values of yield were given, he described his results qualitatively by stating that the bulk of the extraction product was obtained after preheating in the 360" t o 380" C. range, with little product obtained either below or above this temperature range. Additional extractions were made with solvents at their normal boiling point, using torbanite samples which had been preheated 4 hours at 380" C., but yield data are again lacking. Solvents used were benzene, chloroform, carbon tetrachloride, Tetralin, toluene, torbanite crude oil distillate, and coal tar naphtha. The general conclusion was drawn that aromatics were better than aliphatics as solvents. The Estonian shale called kukersite was extracted with benzene under pressure a t 240' to 250" C. by Klever ( 2 2 ) and a yield of 1.86% of the total organic matter was reported. The U. S. Bureau of Mines (28) has recently conducted a series of thermal solution tests on both a 26- and a 52-gallon-per-ton Colorado shale. Both petroleum oil and shale oil were used as solvents. Extraction temperatures ranged from 357" to 454" C. with pressures of up to 21 atmospheres. Yields of up to 96y0 of total organic matter were obtained. From the investigations reported above only the most generalized inferences can be drawn. Even if complete yield data were available for all of these tests, no valid correlations could be made, because the shales investigated varied both in total organic content and in over-all composition. Furthermore, the test conditions differed with each investigator. OBJECTIVES OF PRESENT RESEARCH

Under dry distillation or retorting processes the kerogen of shale is heated t o temperatures of 350' to 500" C. and the products of thermal cracking are condensed. The thermal decomposition thus proceeds through all four steps of the pyrolysis previously described. Some repolymerization occurs during condensation. The resulting crude, viscous shale oil has a carbon-hydrogen ratio, in the case of Colorado shales, of 7.2 to 7.5 (compared to 7.7 for nearly pure kerogen), which is considerably greater than that for crude petroleums (6 to 7 ) . The ratio of organic carbon to hydrogen in the spent shale ranges from 7 (for lean shales) to 19 (for rich shales), with an average value of approximately 13. The value for the 35-gallons-per-ton shale used in the present research is 13.0. These high spent shale carbon-hydrogen ratios are, of course, the result of repolymerization to heavy oil residues during pyrolysis. When shale is depolymerized in the presence of a solvent, in the same temperature range as employed for dry retorting, conversions of kerogen to shale oil are slightly higher, and the rate of pyrolysis is increased. I t is thought that this latter fact is due primarily to the more favorable heat transfer rates which exist. The character of the solvent itself may also influence the process, although no basic data have been obtained t o date in this regard


Vol. 45, No. 2

Unit Prooesses

*I

'

except for the rough product analyses previously reported. It is known that greater quantities of heavy oils are produced than are yielded by dry retorting. A t the temperature ranges employed to date pyrolysis proceeds completely through all four of the stages previously mentioned. The higher reaction rates and more uniform conditions of heating possible in thermal solution appeared to offer an ideal medium for studying the kerogen decomposition process. If the temperature were lowered considerably below the cracking range, using this process, it was postulated that intermediates characteristic of step 2 or 3 in the decomposition process could be obtained under conditions before extensive thermal cracking took place. Finally, by selection of solvents of varying physical and/or chemical properties some insight could be gained as to the nature of these intermediates and their mechanism of formation. After examination of.some 20 solvents a group of 11 was selected as representing the range of physical and chemical p r o p erties desired. A temperature of 200' C. was selected as being below the critical temperature of any member of the group, thus ensuring a liquid-phase extraction in all cases. The process oonsisted in charging a mixture of finely divided raw oil shale (100% minus ?@mesh, 45.60/, minus 200-mesh) and solvent to a rockingtype autoclave, cooling and removing the charge after a predetermined interval, separating solvent, product oil, and spent shale by centrifuging and distillation, and determining the ultimate analyses of the spent shale and product oils. Correlations were then attempted between the yields and analyses obtained, and the properties of the solvents employed. SELECTION O F SOLVENTS

An attempt was made to select solvents which could be grouped on the basis of chemical structure-i.e., aliphatic, naphthenic, aromatic, saturated and unsaturated, monocyclic, polycyclicand/or solvent properties-i.e., internal pressure, hydrogenbonding characteristics, molar volume. The more important of these physical properties are shown in Tables I1 and 111.

~~~~~~~

~

TABLE 111. MISCELLANEOUS PROPERTIES OF SOLVESTS Normal Boiling Point, ' C. 207.4 190.0 83.0 68.74 80.74 182.24 80.10 281.4 56.13 64.46 100.00

Tetralin Decalin Cyolohexene *-Hexane gg~yxane Benzene Dimethylsulfolane Acetone Methanol Water

Ir

PROPERTIES O F

SOLVENTS AT 200

Molar Vapor Latent Speciflo Liquid Pressure, Lbs., Solvent Vapor- Vaporiz,aaHeat of Molar Density, Sq. Inch k e d a , tion, Volume, G./MI. Abs. % Cal. Liters Tetralin 0.83 12.3 0.57 9,190 0.159 0.173 0.76 8,410 17.9 Decalin 0 80 Cyclohexene 0.63 168 4 2.96 5,010 o.I3O 0.197 7.18 3,340 260.9 n-Hexane 0.436 Cyclohexane 0.577 192.8 3.65 4,950 0.146 0.47 10,720 0.100 0.94 23.1 Phenol Benzene 0.660 203.5 3.04 5,270 0.118 Dimethylsulfolane 1.00 2.2 0.37 12,680 0.148 404.6 5 92 3,960 Acetone 0.514 0.113 Methanol 0.553 567.1 4.53 4,820 0.058 0.021 0.58 8,380 0.865 225.6 Water a

c. Internal Pressme, Atm. 2,140 1,780

l*$!g

1,130 4,030 1,520 3,280 1,100

2,760 14,750

Sugden Parachor 335.0 368.0 229.1 268.2 240.1 227.1 207.1 327.8 160.2 93.2 54.2

200" C. were arrived at by using compressibility factors, and were in excellent agreement with experimental values published for several of the solvents. Liquid specific volumes a t 200' C. were obtained by graphical means using the known volumes a t 20' C., normal boiling point, and critical point as prime reference points, and interpolating for the desired volume after careful comparison with the complete temperature us. liquid volume curves for six of the solvents under consideration. Values for the van der Waals constants a and b were derived from the critical temperature and pressure by the generalized equations discussed by Dodge (7). The internal pressures of the liquids at both 20' and 200' C. were calculated from two of the several possible correlations discussed by Glasstone ( I @ , the final values used being those based on the temperature-sensitive internal latent heat of vaporization rather than on the van der Waals "constant" a. I n addition, each of the solvents listed was classified into one of the five groups of compounds with respect to hydrogen bonding ability, as proposed by Ewell, Harrison, and Berg (19). Of all the properties listed for each solvent it was felt that the internal pressure was the most fundamental with respect to solubility. Hydrogen bonding was a factor known to increase the internal uressure of liauids. but its individual contribution thereto could not be quantitatively evaluated. These two properties then were considered as the basis for choosing the solvents to be studied. From a listing of the internal pressures of the solvents at the extraction temperature of 200' C., seven solvenb-vir., nhexane, cyclohexene, carbon tetrachloride (see Results), Tetralin, acetone, dimethylsulfolane, and methanol-were initially chosen (see Table 111). Five further solvents-decahydronaphthalene (high molar liquid volume), water (high internal pressure and association), cyclohexane, benzene, and phenol-were later added to the list t o help confirm the trends brought out in the results of the initial runs. All solvents were subjected to a preliminary fractionation and purification. -

TABLE 11.

Critical Critical Critical Molar Temp., Pressure, Volumes, ' K. Atm. Liters 33.5 0.470 744 692.1 28.0 0.522 39.8 0.305 568 507.9 29.6 0.364 553.1 39.8 0.320 692.1 0.303 60.5 563.1 47.9 0.273 39.3 0.457 848 47.0 0.176 508.1 513.1 0.121 78.7 647.3 218.2 0.056

I

% solvent in vapor state in bomb used, a t 200' C. EXPERIMENTAL PROCEDURES

B~~~~~~of the absence of many of the required data in the literature it was often necessary to employ fundamental theoretical and/or empirical correlations to calculate the properties and constants required. Thus, critical constants were obtained through the Sugden parachors (87) by means of the Meissner and Redding correlations (38). Seglin's method (26) was used to supply values for the latent heat of vaporization a t the normal boiling point, using water as the reference and the tables of Keenan and Keyes tl@* The and Watson ('4) method was found, from among the several tried, to give the best values for the latent heat of vaporization a t the reference temperature of 200 C , vaporpressures at 2000c. were alsoobtained from ~ ~ ~ correlations (%), but for calculation of the latent heat of vaporization a t XNl" c. the fundamental ClaPeyron-Clausius equation waa employed. The specific volumes of the solvent vapors at February 1953

Raw oil shale, roughly 0.25-inch size, was ground in a laboratory pebble mill to minus 30-mesh for use in this research. A total of 15 pounds of ground shale was prepared, thoroughly mixed by means of a sample splitter of the type and *tored in glass containers under an atmosphere of nitrogen. A screen analysis of the ground shale showed: Minus Minus Minus Minus

30 mesh 40 mesh 60 mesh 100 mesh Minus 200 mesh

10010%

The specific gravity of the ground shale was found to be 0.75 gram per cc. Determinations of the oil content of the raw shale, usin the U.S.B.M. modified Fischer assay retorting method, yielfed a value of 12.0% oil by weight (approximately 35 gallons lof oil i per ~ ton ' ~of raw shale). Similar assay testa were conducted on the oversize discard from the pebble mill grinding operation, resultin in the same oil contentvalue, and on this basis it was assume2 that the finely ground material was truly representative of the original shale.


'

315

Moisture determinations on the ''as received" raw shale showed a moisture content of only 0.259& An Aminco high pressure, shaking autoclave of the 43/s-inch diameter series was used for the extractions. The 1750-ml. capacity stainless steel bomb of the autoclave wm fitted with an internal, double hairpin cooling coil for rapid water cooling of the char e on completion of the desired reaction cycle, and the electricay heating jacket was provided with air blast ports to facilitate rapid cooling of the bomb exterior. The shaking mechanism was driven through a gear motor t o oscillate at 58 cycles per minute. Reactor temperature was controlled semiautomatically by means of a Wheelco Rheotrol. Two Chromel-Alumel thermocouples were installed, one indicating the temperature of the charge inside the reactor, the other located in the annular space between the heating jacket and the bomb wall. A series of seven preliminary runs mas made to determine the optimum ratio of raw shale to solvent and the run duration, using acetone as solvent. A charge of 350 grams of ground shale was selected on the basis of a net internal volume of the bomb of 1600 ml. (after correction for displacement of cooling coils), and an allowance of 30 to 40y0 free space t o assure adequate mixing from the rocking action of the shaker. A charge ratio of approximately 1 volume of shale t o 0.5 volume of solvent was found t o be too dry t o process. Thereupon, a 1 t o 1 ratio was used, and this was subsequently increased to a ratio of 1 to 1.5. On this basis, the solvent charge was standardized at approximately 675 ml. for all subsequent runs, the resulting free volume in the bomb being about 29%. Became a decrease in reaction time to 0.5 hour brought only an insignificant decrease in yield, and an increase in reaction time showed no corresponding increase in yield, the run duration was standardized a t 0.5 hour. Choice of maximum operating temperature was governed by the fact that one of the solvents (dimethylsuAfolane) would begin to decompose at temperatures above 220 C., and that the critical temperatures of several others of the solvents lay in the range from 230" t o 240" C. For these reasons i t was decided that the average extraction temperature should be 200" C., and in no case should the temperature exceed 220" C. Under these conditione, as shown in Table 11. no more than 7% of the original charge of even the most volatile solvent was present in the vapor state during the run. Operating procedure for the extraction runs was as follows:

'

1. The bomb was charged with the finely ground shale and solvent, sealed, inserted in the heating jacket, and flushed with helium t o eliminate air oxldation reactions during pyrolysis. The shaking mechanism was started and the bomb contents were brought up t o the desired temperature (75 minutes to attain 200" C.). 2 . The temperature was held constant for the duration of the reaction time, a t the end of which the air blast and cooling water were turned on until room temperature was regained. (The absence of any residual pressure a t this point indicated that no fixed gases were evolved by thernml cracking during the solvation process.) 3. The bomb was opened, emptied of the resulting black slurry, and rinsed with fresh solvent to assure complete removal of thk charge. 4. The slurry was transferred to 250-ml. capacity centrifuge bottles and centrifuged at 3000 r.p.m. for 10 minutes. The liquid was decanted and the residual spent shale was successively washed with fresh solvent and centrifuged until the resulting extract was clear. 5. The combined product oil and solvent were fractionally distilled (under vacuum for the higher boiling solvents) until the solvent had been completely stripped off, as, indicated by boiling point. (Hot water washes and steam distillation were also employed in several cases, as noted below.) The product oil was then carefully weighed. 6. The spent shale remaining was either air-dried (for low boiling solvents) or further extracted with suitable low boiling solvents to remove the original solvent, before air drying to an odor-free dry powder. 7. The complete removal of solvent from both the product oil and the spent shale was checked by means of the satisfactory closing of an over-all carbon and hydrogen material balance.

Some difficulty was experienced in separating the high boiling solvents dimethylsulfolane, phenol, Tetralin, and Decalin from the extracted product oils. -4s dimethylsulfolane was over 50% soluble in water a t a temperature of 85" C., hot water extraction of both product oil and spent shale was used t o remove the excess 316

solvent. Subsequent analysis of the products, however, showed this method t o have been not completely successful. In the case of phenol, steam distillation was used t o achieve lower stripping temperatures. The spent shale from the phenol run was extracted repeatedly with hot water until the characteristic aromatic odor was no longer noted. With Tetralin and Decalin there were no such selective secondary solvents. Although n-hexane was used in the spent shale washing process to reduce the total amount of high boiling solvent t o be stripped, the initial solvent charged with the shale still had to be removed by fractional distillation. Vacuum distillation \w,s used (approximately 50 mm. of mercury absolute pressure) to reduce possible cracking of the product oil; however, there is no assurance that some low boiling fragments of the partially depolymerized kerogen were not removed along with the solvent. Examination of boiling point tabulations shows that organic compounds having boiling points below those of Decalin and Tetralin include: straight- and branched-chain compounds having up to ten carbon atoms, most naphthenes, benzene nuclei with side chains of up to three carbon atoms, and many of the common heterocyclic compounds. Thus, with the degree of actual depolymerization of kerogen under the imposed test condition unknown, the question of losses at this point remains unresolved. The apparent loss of hydrogen reflected in the high carbon-hydrogen ratio of particularly the Tetralin product, coupled with some difficulty in closing the hydrogen material balance for this run, might indicate that such a loss did occur. ASALYTICAL PROCEDURES

Elemental analyses of both the extracted oils and the residual spent shales were made. These included quantitative determinations of the carbon, hydrogen, nitrogen, and sulfur content of the oils; the oxygen content was obtained by difference. For the spent shales the same determinations were made with the addition of the ash content and a determination of the carbon present in the form of inorganic carbonates. Thp latter value when subtracted from the total carbon content results in a figure for the net organic carbon present in the shale.

For the determination of carbon and hydrogen a standard combustion train was employed, using an apparatus patterned after that described by Tunnicliff and coworkers (19). Because of the high nitrogen content of the samples, a special combustion tube filling of lead peroxide replaced the usual copper oxide-lead chromate filling. The analytical procedure followed was that described by ,Tunnicliff, with modifications of temperatures and combustion times as required to assure complete combustion of the organic material in the oil shales. Product oil samples were run a t the standard temperatures of 700" C. in the sample furnace and 775 O C. in the main furnace. The temperatures were increased to 850" C. in both furnace sections for the solid shale samplee. Both oils and shales were held a t the combustion temperatures for 1.5 t o 2 hours. Reproducibility of results averaged 0.2% for hydrogen and o.5Y0 for carbon. The carbonate carbon in raw and spent shales was determined employing the apparatus and method used by the U. S. Bureau of Mines Oil Shale Experiment Station a t Laramie, Wyoming ( 3 ) . The procedure consisted in the liberation of the carbonate carbon as carbon dioxide, through reaction with dilute hydrochloric acid, the carbon dioxide being determined volumetrically in a standard gas-measuring buret. Interfering sulfides were precipitated as mercuric sulfide by addition of mercuric chloride to the solution. By correcting the total carbon value for the carbon present as inorganic carbonates, the net organic carbon content of the shales was obtained. Nitrogen determinations on both the oils and the shales were made by the standard macro-Kjeldahl method, using seleniumcoated Hengar granules as catalyst. The Eschka method for sulfur analysis, as modified by Harding (16) for oil shales, was employed for bdth the raw and spent shales. The sulfur content of the shale oils was obtained by the standard Parr oxygen bomb method. Attempts t o chromatograph the product oils on silica gel, in order to identify specific hydrocarbon types, were not successful,


Vol. 45, No. 2

Unit Processes I-

?

5.0

-I ‘n

2I

4.0

e Y

d

30

u)

6‘

2.0

U I

d

E

10

I-

Y

8

O.04

06 0-3 .IO .I2 .I4 16 SOLVENT. LIQUID MOLAR VOLUME AT ZOO*C,

.IS

20

Lirms

Figure 1. Yield vs. Molecular Volume

+

owing to their viscous, semisolid nature and the small quantities of sample available. A hot water jacket on the column and sample dilution with pure solvent did not solve the difficulties. It waa therefore decided to postpone such analyses until the operational difficulties could be overcome. RESULTS

*

value of 2.5% is well within the extraction yield reproducibility of 5% and confirms the accuracy of the analytical techniques and methods employed. Similar balances for sulfur and nitrogen were initially considered, but proved to be of little value, because of the relatively large quantity of both raw and spent shales with very low nitrogen and sulfur contents, coupled with the small oil yields with equally low nitrogen and sulfur contents. Carbon tetrachloride is not included as a solvent in the tabulated results. This is due to the fact that considerable solvent decomposition occurred during the runs in which carbon tetrachloride was employed, as denoted by the presence of considerable hydrogen chloride as residual bomb gases upon cooling, and the formation of a porous, cokelike solid residue upon removal of solvent. During distillation of the residual solvent, white crystals of hexachloromethane were found to form in the flask and condenser, indicating that the reaction 2 CCla +CzCla Clzhad undoubtedly occurred during solvation. The chlorine so produced would, of course, halogenate any hydrocarbons present, with liberation of hydrochloric acid. An examination of the literature indicated that carbon tetrachloride decomposes to hexachloroethane and chlorine, under even lower temperatures than prevailed in these tests, in the presence of finely divided metallic and other inorganic catalysts. It seems reasonable, then, to assume that the finely divided shale with its aluminum and iron content provided sufficient catalytic action to promote this decomposition.

The net product oil yield, calculated per mole of solvent on the basis of 675 ml. of solvent charge, is shown for each of the materials employed, in Table IV. Also shown in each case is the yield calculated as per cent of Fischer assay. The latter was determined by dividing the net oil yield extracted from 350 grams of shale by the 42.0 grams of oil obtained by retorting the same quantity of shale in the modified Fischer retort of the U. S. Bureau of Mines. ’ As noted in Table 11, the quantity of solvent in the vapor state at extraction temperature never exceeded approximately 7 %, even for the more volatile materials. The effect of vaporization on yield per mole of solvent was therefore ignored in the data. The ultimate analyses of raw shale, all spent shales, and all product oils, as determined by the procedures previously described, were calculated. These data for the product oils are shown in Table V. As a check on these determinations and on the experimental techniques in general, carbon and hydrogen msLterial balances were made for each run. These balances were closed with a deviation of less than 2.5y0 in all cases, wieh the exception of the Tetralin run, which showed a hydrogen loss (unaccounted for) of roughly 10%. This latter fact is probably due to the relatively severe distillation conditions required for stripping the solvent from the product oil. The average deviation

50

a LO

d

2

‘n

1.0

0

s’ *? 1.0

8

050

100

1%

Figure 2.

200 250 SUCDEH PARACHOR

Yield

vs.

300

360

400

Sugden Parachor

The bleed-down gases from one run were absorbed in standard base and titrated, from which it was possible to ascertain that 9.7% of the carbon tetrachloride charged had reacted in the above manner. DISCUSSION OF RESULTS

w

TABLE IV.

INTERNAL PRESSURE AND

DimethylsulfoPhenol lane 3280 Internal pressure, atm. , 4 0 3 0 Yield, g. oil/mole sol1.30 1.04 vent Yield, of Fischer assay 23.8 12.6

TABLE V.

Methanol 2760

Tetralin 2140

YIELD

Deoalin 1780

O F PRODUCT OILS

Benzene 1520

Cyclohexane 1130

Acetone 1100

n-Hexane 500

0.34

4.20

3.70

1.22

1.53

1.31

0.59

1.39

13.6

49.5

38.1

22.1

24.3

19.5

12.9

17.1

ULTIMATE ANALYSES OF PRODUCT OILS

TetraDecCyolo- n-Hex- C y d o lin alin hexene ane hexane Phenol 81.2 81.6 79.8 82.8 80.5 Carbon, % 52.0 9.8 10.7 11.3 12.4 11.8 7.9 Hydrogen, % 0.6 0.6 0.6 0.8 0.6 1.3 Nitrogen, % Sulfur, % 0.8 0.5 0.9 1.0 1.0 1.1 Oxygena, % 7.6 6.6 7.2 3.2 6.1 37.7 Oxygen values obtained b y difference.

February 1953

Cyolohexene 1300

DiBen- methylMethzene sulfolane Acetone anol 80.8 69.3 67 0 54.0 11.6 9.0 11.0 ’ 8 . 9 0.8 1.1 0.7 0.9 1.1 1.1 1.0 0.9 5.7 19.5 20.3 35.3


The net carbon-hydrogen values reported for the product oils are the ratio of organic carbon to organic hydrogen. I n the case of the raw and spent shales the total carbon present has been corrected for the presence of mineral carbonates only. As has been pointed out by a number of previous i n v e s t i g a t o r s (M), this still does not result in a true carbon-hydrogen ratio for the organic matter p r e s e n t . The net c a r b o n - h y d r o g e n ratios on the spent shales must therefore still be considered subject to some error. They

317

are fortunately of no direct significance in the correlation of results in the present study. Nitrogen values reported are assumed to be organic nitrogen, im no evidence has been found to date of the existence of nitrogen in inorganic form in the Colorado shales. Sulfur values in raw and spent shales include both organic and inorganic forms. It is estimated that approximately one third of all sulfur in raw shales is organic in character, the remaining two thirds being present as pyrites and, to a small extent, as sulfates. Oxygen values, having been determined by difference in all cases, must be regarded with some skepticism, since they include the cumulative errors of all other elemental determinations.

I

I

I

I

*yc6

MOLECULAR

Figure 3.

WEIGHT,

I

~

,

~

~

GRAMS

Yield us. Molecular Weight

The carbon-hydrogen ratio of all product oils, with the exception of those from the Tetralin and dimethylsulfolane extractions, are seen to be less than that previously reported for pure kerogen, thus indicating that solution in solvent has apparently occurred through a thermal decomposition process involving hydrogenation or selective solution of hydrogen-rich fragments of the original macromolecule. The usual thermal cracking occurring in dry pyrolysis apparently did not take place, however, as noted by the absence of carbon dioxide or any other residual gases in the extraction bomb. This might be interpreted as additional evidence of the fact, which has often been expressed previously, that kerogen coexists in a t least two different forms, which have different rates of thermal decomposition and perhaps produce bitumens of different chemical nature, one of which was preferentially solubilized in the present study. It is probably more proper, however, t o regard one given kerogen macromolecule as being capable of initial decomposition to two or more unlike fragments, with varying susceptibility to solution as a result of molecular size and/or chemical structure. With the exceptions noted above, the carbon-hydrogen ratio of the product oils was lower in all cases than that of standard “shale oil” produced by thermal cracking in t,he modified Fischer assay retort. This is not surprising, however, when it is recalled that considerable quantities of “assay gases,” with an approximately average low carbon-hydrogen ratio of 4.8 are produced (66) during retorting, thus raising the carbon-hydrogen value of the oil which remains. Such gases were not evolved in this study. The nitrogen content of the product oils was considerably less in all cases than that in either pure kerogen (2.8%) or an average assay shale oil (1.96) (66). The carbon-nitrogen weight ratio of the product oils is 1.5 to 5 times as great as an average value (21.5) for relatively pure kerogen. It appears, therefore, that in the initial mild decomposition of kerogen occurring during thermal solution a t 200” C. the nitrogen heterocyclic structures which are believed to be present in the macromolecule are preferentially converted to soluble fragments to only a very limited extent. Even in the case of the associating solvents, which tended to solubilize more nitrogen-containing structures than the nonassoci-

318

ating solvents, the carbon-nitrogen ratio was still 1.5 to 3.5 that in kerogen itself. It would therefore appear that few if any of the usual nitrogen compound types (pyrroles, methylpyridines, quinoline) produced by thermal cracking a t retorting temperatures were among the molecular fragments made soluble in the present study. This is true, as the carbon-nitrogen ratios of these materials lie in the range 3.4 to 7.7, and hence would result in a value of carbon-nitrogen in product oils containing them of less than that in kerogen. The sulfur content of the product oils was less in all cases than that in pure kerogen (1.2%). The carbon-sulfur weight ratio of the product oils ranged from 47 to 163, as compared to values for kerogen (enriched shale), as reported in the literature (as), of 48 to 82. I n the case of the associating solvents the carbon-sulfur values for the oils varied from 47 to 67, which is within the kerogen range. Conclusions as t o the role of sulfur during solution are necessarily less clear-cut than for nitrogen, because the enriched shale which must be used as a basis for kerogen analysis may still also contain small quantities of insoluble inorganic sulfur. In addition, the forms in which organic sulfur occurs in oil are less completely understood, but it would appear from literature data that a t least the thiophenes, and perhaps also the mercaptans and disulfides, found among the products of high temperature thermal cracking, are not present as such in the original kerogen. This latter fact may be confirmed by the present study, when it is noted that the above-mentioned sulfur degradation products have carbon-sulfur ratios in the range of 1.1 to 3.0 while the product oils in this study ranged from 47 to 163. It would appear from the present research that associating solvents have a greater tendency to remove sulfur-containing fragments of the original kerogen than do the nonassociating solvents, and that the sulfur-containing fragments so solubilized have nearly the same chemical form as is found in the original kerogen. 9

I

I

~

I

INTERNAL

Figure 4.

PRESSURE

AT

200. C., ATMOSPHERCS

Carbon-Hydrogen Ratio of Product Oils

The above conclusions must be qualified by realization that simultaneous solubilization of carbon, hydrogen, nitrogen, and sulfur is taking place during thermal solution, with consequent possible masking or emphasis of one type of molecular fragmentation by another. I t has also been assumed that, under the mild pyrolytic conditions employed, the original hetero skeleton structures tended to split out of the macromolecule with the minimum amount of rearrangement. I n spite of these facts, however, the conclusions appear to be warranted, in view of the large magnitude of the effects noted. Correlation of results with various fundamental solvent properties is shown in Figures 1 to 8. These properties include the molecular volume of the solvent, the Sugden parachor (a measure


Vol. 45, No. 2

Unit Processes of molecular volume at unit surface tension), the internal pressure of the solvent, and the associating or nonassociating character of solvent. If it is recalled that kerogen is not a simple polymer or even copolymer, and that its decomposition products in solution can be predicted to be of widely diversified chemical character, some tolerance can be expected in the mathematical regularity of the relationships obtained, as denoted by the approximate curves which were necessary in some cases.

1000

zoo0

3000

I

4000

INTERNAL PRESSURE AT 200eC., ATMOSPHERES

Figure 5.

x

4.

Extent of Pyrolysis of Kerogen

The total product yield in all cases corresponds to the maximum solubilitg-Le., saturation-of kerogen or its decomposition products a t 200" C. When expressed on an equivalent basis-i.e., per mole of solvent-it was found that this yield was apparently a function of the molecular volume a t 200' C. (Figures 1 and 2) of the solvent, irrespective of the chemical nature or the associating tendencies thereof. The two solvents, n-hexane and dimethylsulfolane, were seen to be exceptions. The former of these also exhibited regularity, however, when yield was plotted against molecular weight (Figure 3). The last-mentioned correlation could be expected to occur, if it is noted that (n-hexane excepted) molecular volume and molecular weight are approximately directly proportional for the solvents used. No significant relationship was found to exist between internal pressure and product yield, although the associating and nonassociating solvents each showed separate trends toward higher product yields with higher internal pressures. All associating solvents indicated markedly lower yields than the nonassociating solvents. When the carbon-hydrogen ratio of the product oils was plotted against internal pressure, on the other hand, as shown in Figure 4, two definite and distinct correlations were obtained for the nonassociating and the associating solvents. I n each case, the highest carbon-hydrogen ratios were obtained with the solvents having the highest internal pressure. The associating solvents all produced oils with lower carbon-hydrogen values than the nonassociating solvents. I n an effort to determine the degree of thermal cracking which had occurred, the decrease in carbon-hydrogen ratio for each oil was calculated, by subtraction from 7.7, the carbon-hydrogen ratio for pure kerogen. The resulting difference, designated as "extent of pyrolysis," was then plotted against internal pressure. As shown in Figure 5, the least amount of pyrolysis (smallest decrease in carbon-hydrogen) was obtained with solvents having the highest internal pressure. In order to aid in understanding the role of nitrogen and sulfur during the solution process, the percentage of original nitrogen and sulfur in the kerogen which had been made soluble was calculated and plotted against internal pressure of the solvent. In the case of nitrogen (Figure 6) the same separation into two distinct curves was obtained for the nonassociating and the associat-

February 1953

ing solvents, with a greater fraction of original nitrogen solubilized by the former type. Solvents of high internal pressure were shown to solubilize more nitrogen for both types. A similar trend was found in the case of sulfur, although the correlation with internal pressure (Figure 7 ) for the associating solvents was poor. I n an attempt t o learn more about the types of nitrogen a n d . sulfur compounds which had been produced by the thermal solution process the carbon-nitrogen and carbon-sulfur weight ratios of the product, oils were plotted against the internal pressure of the various solvents. No regular correlation was found for the nonassociating solvents. I n the case of the associating solvents, however, as shown in Figure 8, a marked decrease in carbonnitrogen ratio with increasing internal pressure was found, and a slight decrease in carbon-sulfur ratio. Since Tetralin had proven to be the most effective solvent for kerogen, in terms of yield, it was decided to conduct a preliminary investigation of the effect of temperature on its ability to decompose kerogen thermally. Two additional runs were accordingly made a t 300' and 400' C., respectively, and oil yields of 64.3 and 76.7% of Fischer assay obtained (Figure 9). Slight dehydrogenation of the solvent or cracking of kerogen to gaseous "end fragments" was noted at these higher temperatures, as evidenced by a small residual hydrogen gas pressure in the bomb, upon cooling. This decomposition had not occurred a t 200' C. Indeed, as was previously shown by Wagner-Jauregg (SO),neither Decalin nor Tetralin can be dehydrogenated a t temperatures in the range of 185" C., even with a nickel-CIarite catalyst.

I0.OY

2.01 0

Figure 6.

I

I

I

I

3000

4000

J

I

I

I

1000 INTERNAL

2000 PRESSURE A T POO'C.,

ATMOSPHERCS

1

Per Cent Organic Nitrogen Solubilized

The data from the Tetralin runs were plotted on the usual log

K va. 1/T plot, in order to evaluate the heat change which had occurred. Assuming that a saturated solution had been obtained in each case, the value of K, defined as the fraction of kerogen decomposed divided by the fraction undecomposed, becomes the equilibrium constant for the solution process. From the relationship d= I n-K -

dT

AH

RT2

and the slope of the curves obtained (Figure lo), the value of AH, the enthalphy change of the solution process, was determined. The data indicated a value of 3300 calories per mole of kerogen in the range 200' to 300' C., and a value of 4700 calories per mole of kerogen in the range 300" to 400' C. The higher, when converted to a per-gram-of-oil basis, is found to be of the same order for the net heat of dry retorting in the as previously reported ($38) same temperature range.


319

CONCLUSIOXS

The dependence of the solubility of kerogen or its degradation products, when expressed as grams dissolved per mole of solvent, upon the molecular volume of the solvent is not completely understood. It has been theoretically shown, however, in the case of a . homogeneous polymer (17) that the fraction of a given polymer which is soluble in a solvent is directly proportional to the total volume of the solution phases, providing that the volume of polymer under consideration is constant. For a constant weight

INTERNAL

PRESSUe

A T ZW'C.,ATMOSPHERES

Figure 7. Per Cent Sulfur Solubilized

charge of shale the grams of shale dissolved is proportional to the fraction of kerogen dissolved, and because this weight is expressed per mole of solvent, the "total volume of the solution phase" becomes the molecular volume, assuming that the volume change accompanying solution is small. The latter might be expected to be true for the low solubilities encountered in the present research. It follows from the above, therefore, that grams of oil per mole of solvent is proportional to molecular volume, as shown in Figure 1. The analysis suffers from the fact that ( a ) kerogen is not a simple homogeneous polymer, or perhaps not a polymer a t all, and (21) the substance in solution is not original kerogen, but the degradation products thereof. The apparent applicability of the above analysis suggests, however, that these degradation products may still be of considerable molecular size in solutions a t 200" C. T h e same conclusion would apply to the parachor correlation (Figure 2). KO obvious theoretical explanation for the molecular weight correlation (Figure 3) could be found, except for the rough proportionality between molecular weight and molecular volume of the solvents previously noted. Before proceeding to the correlations with internal pressure which follow, it is pertinent to review, briefly, the significance of this solvent property upon solubility. For a nonassociating liquid internal pressure is a measure of the strength of the intermolecular van der Waals forces present. I n such systems liquids with internal pressures of the same order of magnitude tend to be completely miscible. Partial miscibility and eventually complete immiscibility result as the differences between the internal pressures of the species present become sufficiently large. I n the case of associating solvents the van der Waals forces, while still present, tend t o be overshadowed by the hydrogen bonding effects (association), which act to control solubility through the formation and/or breaking of 0-H-0, 0-H-X, N-H-N, etc., bonds, one of the bonds in each group shown being the hydrogen bond. Oxygen, nitrogen, and sulfur atoms are the principal donor (of electrons) atoms in the effect, the strength t h e of resulting hydrogen bond with each being of approximately decreasing order, as shown ( 1 7 ) . For solvents which are not themselves internally hydrogenbonded, but which have donor atoms capable of bonding m-ith

320

active hydrogen in the solute (in this case kerogen degradation products), solubility is enhanced by the resulting hydrogen bonds formed. Acetone and dimethylsulfolane fall in this classification in the present research. If hydrogen bonds already exist in the pure solvent, solubility will depend on the strength and amount of hydrogen bonds broken in that solvent upon entry of solute molecules, and upon the amount and strength of new solventsolute hydrogen bonds formed. Methanol and phenol are solvents of this type, as is also water. If no new bonds are formed, immiscibility tends to result, and if strong H-bonds are broken and weak H-bonds only are formed, partial immiscibility is likely. Internal pressure is defined as the internal latent heat of vaporization divided by the molecular volume. Since this latent heat is the sum of the energy necessary to break any H-bonds in thc solvent itself plus that to overcome van der Waals attraction, it follows that the internal pressure is a rough measure of the total strength of both intermolecular forces present, providing that molecular volume is not appreciably affected by any internal H-bonding. The internal pressure of methanol and phenol might so be characterized. In the case of acetone and dimethylsulfolane, however, as no internal H-bonds exist, the internal pressure measures only the van der Waals forces, but does not account for the fact that these solvents can exhibit high solubilizing powers by forming H-bonds, as previously noted. This is important in explaining the results to follow. Because kerogen contains oxygen, nitrogen, and sulfur atoms, which can be "donors" and possibly also active acceptor hydrogen atoms, the thought has been expressed by Prien (34) that a systematic solvation study employing various associating and nonassociating solvents at constant temperature might present a clue as to the chemical nature of kerogen. The present study has resulted.

50 U

E

;

40

I

3

30

- - - -- - - -

20

Figure 8.

C/N

RATIO

FO

KEROGEN

C6HsOH

-- - - -_ __

1000 zwo 3000 INTERNAL PRCSSURL A T ?.W*C.,ATU~~PI.~KRES

4000

Carbon-Nitrogen and Carbon-Sulfur Ratios of Product Oils

The carbon-hydrogen ratios of all product oils obtained from thermal solution with nonassociating solvents were greater than those from the associating solvents (Figure 4). These nonassociating solvents also dissolved more organic nitrogen (Figure 6) and sulfur (Figure 7 ) , in general, from original kerogen than did the associating solvents. The carbon-nitrogen and carbonsulfur ratios of the product oils, however, were greater in all cases from the nonassociating solvents than from the associating type. It might be reasoned from this that the higher carbon-hydrogen fragments produced by pyrolysis are obtained by fission at points in the original macromolecule where these hetero atoms exist, and that the resulting fission products which are soluble include such nitrogen and sulfur hetero structures. From the high carbonnitrogen and carbon-sulfur ratios for these oils (greater in all


Vol. 45, No. 2

Unit Processes

U

cases than for kerogen itself) it is obvious that the fragments are dominantly hydrocarbon in character, and probably (as noted from carbon-hydrogen ratio) cyclic saturated and unsaturated pol ynaphthenes. From the above discussion it would appear that these fragments, to be soluble, must have internal pressures a t the various carbon-hydrogen ratios, corresponding to those on the upper curve in Figure 4. Since nonassociating substances of high internal pressure tend to have high molecular weight, and these higher molecular weight substances would probably have higher carbon-hydrogen ratios, the increasing trend in carbon-hydrogen ratio of product oils (fragments) with internal pressure might be expected. A similar trend has been previously found in the case of coal (20).

300

200 EXTRACTION

400

TEMPERATURE ,'C

Figure 9. Thermal Decomposition in Tetralin as Function of Temperature

*

v

The associating solvents produced oils of lower carbon-hydrogen ratio, lower carbon-nitrogen, and lower carbon-sulfur ratios than the nonassociating solvents. The percentage of origins1 kerogen nitrogen solubilized was also generally lower, except for phenol, and the percentage of original sulfur solubilized was lower in every case. It might be reasoned that the hydrogen-rich, and hence low molecular weight portions of the original macromolecule solubilized by the associating solvents were produced by fission a t heteropoints-i.e., a t nitrogen, sulfur, and perhaps oxygen atomsin the molecule, and dissolved as a result of hydrogen bonding effects. Because hetero atoms were also involved in the fragments dissolved by the nonassociating solvents, it would appear that some credence is given t o the postulate, previously expressed, that kerogen exists in a t least two different forms, one of which is rich in hetero atoms and tends to produce polar groups, attached to low carbon-hydrogen carbon skeletons, upon thermal decomposition. It is this latter form which is solubilized by associating solvents. It might be estimated that 3 to 10% of all organic nitrogen and 10 to 20y0of all organic sulfur in kerogen are present in this form. As noted from Figure 8, the sulfur-containing carbon skeleton is apparently solubilized essentially unchanged from its structure in the original kerogen. I n the case of nitrogen, however, loss of nitrogen atoms with respect to carbon atoms has occurred. The remaining form (or portion of the macromolecule) is predominantly hydrocarbonlike, and poor in hetero atoms in relation to carbon. It is this part (or form) of kerogen which has the greater proportion of the organic nitrogen and sulfur, however. The fact that only the associating solvents showed any regular correlation between carbon-nitrogen and carbon-sulfur ratio and internal pressure (Figure 8) could be interpreted as additional evidence for this '(two form" theory. Correlations between various product oil properties and internal

February 1953

pressure were poor for all associating solvents, except for the percentage nitrogen solubilized. This is to be expected since, m noted previously, it is the hydrogen-bonding effects and not the van der Waals forces which are controlling solubility. The high percentages of aitrogen and sulfur solubilized by phenol particularly, might be interpreted on the basis of its ability to form strong H-bonds with donor nitrogen, sulfur, or oxygen atoms in fragmentized kerogen structures. Bonds formed with methanol, which also contains donor and acceptor atoms both, would tend to be weaker than those with phenol. Solubility of nitrogen and sulfur would hence be less. Similarly, the low values with acetone may be due to the fact that it could hydrogen bond only if active hydrogen atoms were present in the depolymerized kerogen fragments. This is also true of dimethylsulfolane. The difference in solvent power for these two solvents is therefore more a reflection of the relative strength of the van der Waals forces present. No theoretical explanation is immediately obvious for the regular increase in per cent nitrogen solubilized with internal pressure, for the associating solvents. The correlation may be merely fortuitous. It would therefore appear that kerogen contains few active hydrogen atoms in its chemical structure, capable of hydrogen bonding with donor atoms in a solvent.

{

4 O 03

0 -

-0.1'

1

I

I

I

I

RECIPROCAL

Figure 10.

I

I

I?)

1.7

I.5

TEMPERATURE,

I/

r,

I

2.1 x 10.3

'

IPK.

Heats of Kerogen Decomposition

Brief examination was given to the heats of solution obtained from the Tetralin runs a t various temperatures (Figures 9 and 10). Considering the three reactions noted below: AH

Kerogen (in solvent) + kerogen (in shale) Kerogen (pure)

+ kerogen

Kerogen (pure)

--L

(in solvent)

kerogen (in shale)

( - ) 3.3 to

(I)

4.7 kcal. /mole Zero or (2) positive (+) Negative (3) (-), if an adsorption process

In the case of Reaction 2, involving solution in a nonassociating solvent, the reaction as shown must involve zero or positive enthalpy change. This is theoretically predictable if (17)the system of Tetralin and kerogen degradation products involves no specific interactions (such as association) between molecules-i.e., if it is random. The sum of-Equations 1 and 2-i.e., Equation 3-is the equation for the combination of kerogen with the inorganic matrix as raw oil shale. If the kerogen is physically adsorbed on the inorganic, a theory mentioned earlier in this paper as one of several postulates, Equation 3 must involve a negative enthalpy change, as is true of most adsorption processes. I n order for Equation 3 to be negative, Equation 2 cannot be more endothermic than


32 1


322

Equation 1. The latter could be the case, and hence the adsorption theory could be true for Colorado shales. The same arguments, it is believed, would apply if kerogen were regarded as chemically loosely combined with part of the inorganic matter, as has also been proposed. Because any decision rests upon the determination of the heat of decomposition of pure kerogen in the presence of Tetralin, a t 200’ to 400’ C., such experiments are now being undertaken. ACKNOWLEDGMENT

Funds for the research reported above were furnished in part by a Frederick Cottrell grant from the Research Corp., New York, N. Y., and by the Institute of Industrial Research, University of Denver. The shale used was supplied under cooperative agreement with the U. S. Bureau of Mines, Rifle, Colo. The authors are also indebted to Robert Hurley, University of Denver, for advice on certain of the physicochemical phenomena, and to Lora Keck and Felix Vandewiele for aid in preparing the manuscript. LITERATURE CITED

(1) Blackburn, C. O., Colo. School M i n e s Quart., 19, No. 2 (1924). (2) Bur. Mines, Petroleum and Oil Shale Experiment Station,

(3) (4)

(5) (6) (7) (8) (9)

“Analytical Methods for Use on Oil Shale and Shale Oil,” Laramie, Wyo., -4ugust 1949. Can’e, R. F., J. Soc. Chem. I n d . ( L o n d o n ) , 65, 412 (1946). Cane, R. F., “Oil Shale and Cannel Coal,” Vol. 11, p. 592, London, Institute of Petroleum, 1951. Carlson, A. J., Univ. Calif. (Berkeley) P u b . Eng., 3, 295 (1937). Craig, E. H. C., Proc. World Eng. Congr., Tokyo, 32, 1 (1929). Dodge, B. F., “Chemical Engineering Thermodynamics,” New York, McGraw-Hill Book Co., 1944. Down, A. L., and Himus, G. W., J . I n s t . Petroleum, 27, 426-45 (1941). Dulhunty, J. A., J . Proc. R o y . SOC.N.S. W a l e s , 76, 268-74 (1943).

Vol. 45, No. 2

Dulhunty, J. A., Proc. L i n n e a n SOC.N . S . Wales, 67, 238-48 (1942). D’yakova, M. K., Bull. acad. sci. U.R.S.S. Classe sei. tech., 1944, 258-74. Ibid., pp. 498-505. Ewell, R. H., et al., IND. ENQ.CHEM.,36, 871 (1944). Gamson, B. W., and Watson, K. M., Nutl. Petroleum News, Tech. Sect., 36, (May 3, 1944). Glasstone, S., “Textbook of Physical Chemistry,” 2nd ed., New York, D. Van Nostrand Co., 1946. Harding, E. P., IND. ENQ.CHEM.,18, 731 (1926). Hildebrand, J. H., and Scott, R. L., “The Solubility of Nonelectrolytes,” 3rd ed., A.C.S. Monograph 17, New York, Reinhold Publishing Corp., 1950. Himus, G. W., Petroleum (London), 4, 9-13 (May 1941). Keenan, J. H., and Keyes, F. G., “Thermodynamic Properties of Steam,” New York, John Wiley & Sons, 1936. Kiebler, M. W., IND. ENQ.CHEM.,32, 1389-94 (1940); Gas J., 232, 433-6 (1940). Klever, W. H., and Mauch, K., “‘i;’ber den estlnndischen Olsschiefer Kukersit,” Halle, W.Knapp, 1927. hlaier, C. G., and Zimmerly, S. R., Bull. U I L L U Utah, . 14, No. 7, 62 (1924). Meissner, H. P., and Redding, E. M., IND.ENO.CHEX.,34, 521 (1942). Prien, C. H., “Oil Shale and Cannel Coal,” Vol. 11, p. 76, London, Institute of Petroleum, 1951. Seglin, L., IND. EXG.CHEX.,38, 402 (1946). Stanfield, K. E., et al., U . S . Bur. Mines, R e p t s Invest. 4825 (1951). Sugden, S . , “The Parachor and Valency,” London, Rutledge and Sons, 1930. Thorne, H. M.,et al., “Oil Shale and Cannel Coal,” Vol. 11, p. 301, London, Institute of Petroleum, 1951. Tunnicliff, D. D., et al., IXD.ENG.CHEJI.,ANAL.E D , 18, 710 (1946). Wagner-Jauregg, T., et al., Chem. Ber., 80, 553-7 (1947). RECEIVED for review September 15, 1952. ACCEPTED December 1, 1952. Abstracted from a thesis presented b y W. D. Sohnaokenberg in partial f u l fillment of the requirements for t h e M.S. (Ch.E.) degree, University of Denver.

(END OF SYMPOSIUM)

Future Trends in the Chemical Industry d

FRANK J. SODAY The C h e m s t r a n d Corp., Decatur, Ala.

T

H E future of the chemical industry is predicated on its ability to change the essential nature of things andto produce from available raw materials the many items required by man in his daily life on this planet. While i t has been said that “man wants but little here below,” a survey made sometime ago in this country showed t h a t the average American family owns some 10,000 different objects. The provision of these items is the main responsibility of American industry. I n contrast with the last century, which was almost wholly preoccupied with the development and perfection of mechanical devices t o improve our way of life, the present century has been designated by many as the chemical age. This has not been universally recognized, as chemical developments have been recent and largely unnoticed by the public. On surveying our industrial economy, however, one soon realizes t h a t the chemical industry is so large and has become such an intimate part of our great industrial machine t h a t accurate statistics cannot be had. It is the only industry serving all the72 basic industrial groups recognized by the U. S. Chamber of Commerce. The best estimate concerning chemistry’s present position is that i t accounts for at least 2001, of all industrial production in the United States. Less than 100 years ago, substantially all materials used by man were obtained directly from natural sources-that is, from

the plant, animal, or mineral kingdoms. As these proved t o be inadequate to meet man’s ever-expanding needs, he turned increasingly to chemistry for assistance. The first major industry t o be transformed by chemistry was that of dye manufacturing. Dyes had been obtained from natural sources since the earliest times, and the production, transportation, and sale of dyestuffs played a very important part in industry. Large areas of land were devoted to the production of certain vegetable dyes, such as indigo. Madder, from which indigo was obtained, was cultivated in many areas throughout the world, such as France and India. I n this country, it was grown extensively in many of the southern states, and for many years it was the principal agricultural product of Mississippi. But the rapidly growing world population was making increasing demands on the soil for foodstuffs, and man turned to chemistry for the provision of dyestuffs from nonagricultural sources. The brilliant researches of Sir Henry Perkins in England in the middle of the last century led to the development of a whole spectrum of dyestuffs from coal tar, thus freeing man from his dependence on the soil for dyes and revolutionizing the industry. The cultivation of madder and other dye-producing plants disappeared almost overnight. Today, 99% of all dyes used in this country are produced synthetically.

Effect of Solvent Properties in Thermal Decomposition of Oil Shale

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