Coal Science

2 Oxygen Functional Groups in Green River Oil-Shale Kerogen and Trona Acids J. I. FESTER* and W. E. ROBINSON

Downloaded by UNIV LAVAL on September 12, 2016 | http://pubs.acs.org Publication Date: January 1, 1966 | doi: 10.1021/ba-1966-0055.ch002

Laramie Petroleum Research Center, Bureau of Mines, U.S. Department of the Interior, Laramie, Wyo.

Carboxyl, ester, amide, hydroxyl, aldehyde, and ketone groups were estimated for oil-shale kerogen and kerogen-derived trona acids from the Green River Formation. Ether groups were estimated by difference. Carboxyl, ester, and ether groups were found to account for the major portion of the oxygen in both the kerogen and trona acid samples. Minor amounts of amide, hydroxyl, aldehyde, and ketone groups were indicated. The reactive oxygen groups, carboxyl and ester, account for about one-half of the total oxygen in kerogen and two-thirds of the total oxygen in trona acids while the unreactive ether group accounts for the other half of the total oxygen in kerogen and one-third of the total oxygen in trona acids.

y h e production of carbon monoxide, carbon dioxide, and water during low temperature heating of o i l shale indicates the presence of oxygen functional groups i n kerogen. Evolution of carbon dioxide begins at about 2 0 0 ° C . (2) and reaches a maximum at about 2 6 0 ° C . About 3 0 - 6 0 % (5, 7) of the total kerogen oxygen appears i n the pyrolytic gases from heating kerogen at 3 5 0 ° C . Nearly all of the kerogen oxygen appears in the gases when kerogen is retorted at 5 0 0 ° C . T h e oxygenated gases may be derived from carboxyl (acids a n d acid salts), aldehyde, ketone, ester, ether, hydroxyl, and amide groups. Little quantitative data are available in the literature about the oxygen functional groups i n kerogen. A recent report (3) describes a modified method for determining the carboxyl groups present i n kerogen by utilizing steam distillation i n the Fuchs calcium acetate exchange method (4). * Deceased

22

Given; Coal Science Advances in Chemistry; American Chemical Society: Washington, DC, 1966.

2.

FESTER AND ROBINSON

Oxygen Functional Groups

23

T h e present report gives the methods used a n d the data obtained for acid, ester, aldehyde, ketone, amide, hydroxyl, a n d ether functional groups i n kerogen a n d trona acids. These methods may be applicable also i n studying coals and other carbonaceous materials.


Experimental Sample Preparation. A kerogen concentrate was prepared from Green River o i l shale from the Mahogany zone of the Bureau of Mines oil-shale mine near Rifle, Colo. T h e untreated o i l shale contained 3 5 % organic material. T h e concentration procedure consisted of benzene extraction of the crushed shale (100 mesh) to remove benzene soluble organic material, dilute hydrochloric acid leaching to remove mineral carbonates, and attrition grinding (8) i n the presence of water and cetane to remove much of the remaining mineral matter. The resulting kerogen concentrate contained 8 6 % organic material and 1 4 % mineral matter consisting of quartz, feldspar, a n d pyrite. In a l l of the functional group tests of kerogen, the inorganic material removed from the o i l shale by attrition grinding was used as a mineral blank. Because pyrite was concentrated with the kerogen a n d was not separated w i t h the mineral, pyrite equivalent to that present in the kerogen concentrate was added to the mineral blank. The trona acids used i n this study are alkali soluble organic acids that have been leached or degraded from the oil shale of the Green River Formation subsequent to deposition by the action of a sodium carbonate-sodium bicarbonate brine, referred to as trona. In certain locations, such as near Rock Springs, W y o . where the sample was obtained, trona brine containing the organic acids can be pumped from wells drilled into the Green River Formation. In preparing the sample, the brine was acidified with mineral acid which precipitated the organic trona acids out of solution. After water washing, the precipitated trona acids contained 0 . 8 % mineral matter. These trona acids were used as a comparison sample i n this study because they contain structures similar to those present i n Green River kerogen a n d are essentially free of mineral matter. A n a l y t i c a l Methods. T h e carboxyl group was determined by a modified Fuchs calcium exchange method ( 3 ) . T h e modified procedure consisted of exchanging the carboxyl groups of the samples with calcium acetate, removing the liberated acetic acid b y steam distillation, and determining both the amount of acetic acid liberated and the amount of calcium exchanged. In the procedure, 1 gram of sample was added to a 500-ml. reaction flask to which is added 40 m l . of carbon dioxide-free distilled water and 10 m l . of I N calcium acetate solution. T h e reaction mixture was steam distilled at an approximate rate of 250 m l . of distillate per hour for 24 hours and titrated with 0 . 0 2 N sodium hydroxide to a cresolphthalein end point. W h e n steam distillation was completed, the sample was filtered and washed with dilute ( p H 8-9) sodium hydroxide to remove excess calcium acetate. T h e sample was dried, and calcium was determined by chemical methods. T h e ester function was determined by alkaline hydrolysis followed by precipitating the liberated acids as calcium salts. In the present work, samples of 1-1.5 grams were added to 50 m l . of 0 . 2 N aqueous sodium hydroxide a n d refluxed with continuous stirring under nitrogen for 18-24 hours. After hydrolysis the samples were titrated to a p H of 9 with hydrochloric acid. Then 15 m l . of I N calcium acetate was added, and the sample was stirred rapidly under a stream of nitrogen for 1 hour. T h e suspension of calcium salt was filtered, washed with dilute base until free of excess calcium acetate as determined by titration with ethylenediaminetetraacetic acid ( E D T A ) , and dried under a stream of nitrogen. Calcium was determined on the dried product.



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C O A L GEOCHEMISTRY

Since it was possible that a portion of the amide structure, if present, w o u l d react as ester structure i n the above hydrolysis, a separate reaction was carried out to estimate the amount of amide present. Since amides are gen erally more difficult to hydrolyze than esters, the following procedure was used: 2-gram samples were weighed into Kjeldahl flasks, a n d 200 m l . of 1 0 % sodium hydroxide were added. T h e mixture was refluxed for 3 hours, and the ammonia was trapped i n boric acid solution and determined b y titration. T h e hydrolyzed kerogen concentrate was filtered, washed thoroughly w i t h distilled water, a n d dried. Because the trona acids are alkali soluble, it was necessary to neutralize the excess base w i t h 5N hydrochloric acid; 5 m l . were added i n excess. T h e acids that precipitated out of the solution were filtered, washed thoroughly w i t h water, and dried. T h e residue from hydrolysis of kerogen a n d trona acids was suspended i n 100 m l . of ether, washed for 1 hour w i t h rapid stirring, filtered, and the resulting residue was dried. T h e trace of ether soluble material was examined b y infrared techniques for primary a n d secondary amines. T h e ether-insoluble residues from kerogen concentrate and trona acids then were subjected to Kjeldahl nitrogen determinations to check for decrease i n nitrogen owing to loss of ammonia a n d primary a n d secondary amines cleaved from amide structure. T h e hydroxylamine reaction was used to estimate ketone a n d aldehyde groups. T h e method used was similar to one described b y Kaverzneva and Salova ( 6 ) . A 25-ml. solution of 5 % aqueous hydroxylamine hydrochloride (previously adjusted to a p H 7.5-8 w i t h sodium hydroxide) was added to 1.5 grams of sample a n d allowed to react for 1 8 - 2 4 hours at room temperature. The mixture was filtered, washed w i t h water, a n d dried. T h e residue was analyzed for nitrogen, a n d the amount of aldehyde a n d ketone structure was calculated from the nitrogen increase. Attempts were made to reduce any aldehyde a n d ketone function w i t h sodium borohydride. A 1.5-gram sample was weighed into a 100-ml. reaction flask and suspended i n 10 m l . of methanol. A solution of 0.3 gram of sodium borohydride i n 25 m l . of 0.1 Ν sodium hydroxide was added to the sample over a period of 15 minutes. T h e mixture was refluxed under nitrogen for 6 hours, filtered, and washed thoroughly w i t h water. T h e amount of aldehyde a n d ketone was estimated b y the decrease i n the 5.8 micron peak i n the infrared spectrum of the treated sample as compared w i t h the untreated sample. H y d r o x y l groups were determined b y the acetylation method described by B l o m et al. ( I ) . T h e procedure consisted of treating 1-gram samples w i t h acetic anhydride-pyridine reagent. T h e acetylated sample was recovered b y filtration and thoroughly washed. T h e amount of hydroxyl function was then determined b y hydrolyzing the sample w i t h 0.2N sodium hydroxide and measuring the amount of acetic acid liberated when the hydrolyzate was neutralized w i t h sulfuric acid and steam distilled. T h e x-ray scattering intensities for kerogen and trona acids were obtained w i t h an X R D - 5 diffractometer using zirconium-filtered M o Κ alpha radiation. T h e experimental x-ray intensities were corrected for air scattering, polariza tion, and absorption a n d then converted, using data from chemical analysis, to express the scattering per carbon atom. C a l c i u m was determined b y an E D T A method; carbon and hydrogen by the combustion method; total nitrogen b y the Kjeldahl method; sulfur b y the Eschka method; infrared spectra b y the potassium bromide pellet technique. Results and Discussion T h e similarity of kerogen a n d trona acids is indicated b y their elemental compositions shown i n Table I. I n both materials the carbon to oxygen ratio indicates the presence of considerable quantities of oxygen functional groups.


2.

FESTER AND ROBINSON Table I.


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Elemental Composition of Kerogen and Trona Acids Weight Percent Kerogen Trona Acids 77.7 75.7 10.1 9.8 2.6 1.9 1.1 1.6 8.5 11.0 1

C H Ν S Ο' Total

100.0

100.0


Atomic Ratio H/C C/N C/S C/O

1.56 34.8 190.4 12.2

1.56 46.4 126.2 9.2

Mineral free basis * Determined by difference 1

Figure 1 shows x-ray scattering intensities per carbon atom of the kerogen and trona acid samples. These materials have nearly identical peaks, indicating the presence of similar structures. Similarly, the infrared spectra of kerogen and trona acids (Figure 2) show a structural correlation between the two materials. Particularly significant are the similarities i n absorbance i n the 3 . 4 micron region attributed to the C - H aliphatic stretch; the 5.83 micron region attributed to the C = 0 stretching vibration; the 6.85 micron region attributed 1

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X-ray scattering intensities per carbon atom of trona acids kerogen from Green River oil shale


and

1 0.6

COAL GEOCHEMISTRY


26

Figure 2.

Infrared spectra of trona acids and kerogen

concentrate

to aliphatic C - H deformation vibrations; the 7.25 micron region w h i c h is associated with the presence of C H 3 groups. T h e strong absorption of the kerogen sample i n the 9-10 micron region is probably caused by the silicate minerals w h i c h are still present. Because absorption i n the 2.85 micron region is normally observed for all potassium bromide pellets, no significance is attached to the presence of this peak i n the spectra. T h e results of the calcium exchange method using steam distillation for determining the carboxyl function are shown i n Table II. Triplicate determinations were i n good agreement and accounted for 15.8% of the kerogen oxygen and 38.9% of the trona acids as carboxyl oxygen. T o test the agreement between the amount of acetic acid liberated and the amount of calcium added, Table II.

Carboxyl Content of Kerogen and Trona Acids Based on Amount of Acetic Acid Formed

Kerogen '

Average Trona acids

Average 1

Based on Amount of Calcium Exchanged

Meq. COOH pet gram

Percent of total oxygen

Meq. COOH per gram


0.41 0.43 0.42

15.3 16.2 15.8

0.41 0.40 0.40

15.3 15.1 15.1

0.42

15.8

0.40

15.2

1.34 1.32 1.35

39.1 38.2 39.5

1.36 1.32 1.34

40.0 38.2 39.1

1.34

38.9

1.34

39.1

Mineral free basis



2.

FESTER AND

ROBINSON


27

the amount of calcium i n the exchanged product was determined. The results of these determinations, calculated on the basis of two carboxyl groups per atom of calcium, also are shown i n Table II. These results also agreed closely and accounted for 15.2% of the kerogen oxygen and 3 9 . 1 % of the trona acid oxygen as carboxyl oxygen. The results of the ester determinations are shown i n Table III. T h e calcium-exchanged kerogen before hydrolysis contained an equivalent of 8.4 m g . of calcium per gram of sample. After hydrolysis the exchanged kerogen contained 21.5 mg. of calcium per gram of sample. This increase of 13.1 m g . of calcium was equal to the hydrolysis of 0.65 meq. of ester groups per gram of sample and represented 24.7% of the total kerogen oxygen. Similarly, the increase i n the calcium exchange owing to hydrolysis of the trona acids was Table III.

Ester Content of Kerogen and Trona Acids Based on Hydrolysis and Calcium Exchange Ester Content

Cakium, mg. per gram

Kerogen *

Average Trona acids

Average

1

Before hydrolysis

After hydrolysis

Meq. ester per gram


8.4 8.4 8.4

22.1 21.0 21.5

0.68 0.63 0.65

25.9 23.5 24.7

8.4

21.5

0.65

24.7

27.3 26.4 26.7

41.9 41.3 41.6

0.73 0.75 0.75

20.9 21.8 21.8

26.8

41.6

0.74

21.5

* Calculations based upon two ester groups per calcium atom * Mineral free basis

equal to the hydrolysis of 0.74 meq. of ester groups per gram of sample and represented 2 1 . 5 % of the total trona acid oxygen. Infrared spectra (Figure 3) of the kerogen concentrate, trona acids, and salts of the treated materials show the relative changes i n the 5.5-6.5 micron region w i t h a particular treatment. Spectra A and Β are of the starting materials. Spectra C and D show a de crease i n absorption i n the 5.8 micron region and a corresponding increase i n absorption i n the 6.3 region caused by calcium exchange and formation of the carboxylate ion. Spectra Ε and F show additional shifts of absorption to the 6.3 micron region attributed to hydrolysis of ester groups to acid groups and formation of additional carboxylate ion by the exchange with calcium. Spectra Ε and F show remaining absorption i n the 5.8 micron region. Reducing alde hyde and ketone groups w i t h sodium borohydride showed no major decrease i n the intensity of the 5.8 micron band. This indicates that groupings other than carbonyl groups may account for some of the absorption i n the 5.8 micron region. T h e results of the amide determination are shown i n Table I V . Hydrolysis of the kerogen produced ammonia equal to 0.052 mg. equivalents of amide


COAL GEOCHEMISTRY


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60

6 5 45 50 WAVELENGTH, microns

Figure 3. Infrared spectra in the 5.5-6.5 micron region of trona acids and kerogen concentrates and derivatives of these materiah Table IV.

Amide Content of Kerogen and Trona Acids Meq. amide per gram


0.043 0.059

0.5 0.7

0.052

0.6

Trona acids

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