1 Characteristics of Synthetic Crude from Crude Shale O i l Produced by in Situ Combustion Retorting
Downloaded by 117.253.185.157 on October 15, 2015 | http://pubs.acs.org Publication Date: September 1, 1976 | doi: 10.1021/ba-1976-0151.ch001
R. E . POULSON, C. M. FROST, and H. B. JENSEN U.S. Energy Research and Development Administration, Laramie Energy Research Center, Laramie, Wyo. 82071 A synthetic crude prepared by hydrogenating the naphtha, the light oil, and the heavy oil fractions obtained from i n situ crude shale oil by distillation and coking of the 850°F+ residuum was characterized by examining the fractions. The heavy oil had 935 ppm nitrogen of which 40% was pyridine-type nitrogen, and 60% was pyrrole-type nitrogen. The light oil had 79 ppm nitrogen, all of which was pyridine-type nitrogen. The naphtha had less than 1 ppm nitrogen, which was not characterized. The saturate content of the fractions was—naphtha, 87%; light oil, 77%; and heavy oil, 73%. In addition, the heavy oil contained 6% olefins and 2% polar material.
f T ^ h e nitrogen contents of in situ crude shale oils may be somewhat lower than those of crude shale oils produced i n other retorts ( I ) ; however, these in situ oils still contain more than twice as much nitrogen as high nitrogen petroleum crude oils. Because existing refineries would not be able to cope with the high nitrogen content of shale o i l if it were a substantial portion of the refinery feed, the National Petroleum Council ( N P C ) has suggested (2) that crude shale oil be upgraded at the retorting site by a catalytic hydrogénation process to produce a synthetic, premium feedstock called "syncrude." The production of such a syncrude from in situ crude shale, a description of its bulk properties, and a comparison of its properties to those of an N P C - t y p e syncrude have been covered i n Chapter 6 of this volume. This paper reports the compound-type characteristics of that syncrude produced b y Frost (3) by catalytic hydrogénation of in situ crude oil. Special attention has A
1 In Shale Oil, Tar Sands, and Related Fuel Sources; Yen, T.; Advances in Chemistry; American Chemical Society: Washington, DC, 1976.
Downloaded by 117.253.185.157 on October 15, 2015 | http://pubs.acs.org Publication Date: September 1, 1976 | doi: 10.1021/ba-1976-0151.ch001
2
SHALE OIL, T A R SANDS, A N D R E L A T E D F U E L SOURCES
been devoted to the nitrogen-compound types that are likely to be present i n a syncrude because it is these compounds w i t h which a refiner w i l l have to deal if he uses this or a similar syncrude as his refinery feed. In addition to reporting the nitrogen-compound types present i n this syncrude, this paper also reports on the nitrogen types i n intermediate hydrogénation products in order to relate this study to other studies (4, 5, 6, 7, 8) which have shown that the efficacy of nitrogen removal depends upon the nitrogen types in the charge stock. Earlier studies were on pure compounds, or on charge stocks spiked with pure compounds, or on nitrogen-containing stocks and were concerned with nitrogen removals approaching 8 0 % . The syncrude described i n the present work represents a case approaching 9 5 - 9 9 % nitrogen removal. Experimental Preparation of the Samples. The synthetic crude oil (syncrude) (3) used in this study was prepared by hydrogenating the naphtha ( I B P 350°F), the light oil (350°-550°F), and the heavy oil (550°-850°F) fractions that had previously been obtained from i n situ crude shale oil by distillation and coking of the vacuum residuum. The syncrude is the proportioned sum of these hydrogenated products. The heavy oil used in this study was the 5 5 0 ° F + material from the heavy oil hydrogénation. The light oil was the 3 5 0 ° F + material from the hydrogénation of the light oil from the distillation step combined with the 350°-550°F material from the heavy oil hydrogénation. The 175°-350°F heavy naphtha was the 175 ° F + material from the hydrogénation of the combined IBP-350°F naphtha from the distillation and the heavy naphthas from both the heavy oil and the light oil hydrogénations. The C - 1 7 5 ° F light naphtha was the material with that boiling range from each of the three hydrogénations. 5
In addition to using these four fractions i n the syncrude characterization the nitrogen compounds in three intermediate hydrogénation fractions were characterized in order to relate this denitrification study to other such studies. These materials were the light oil from the heavy oil hydrogénation, the 175°-350°F heavy naphtha from the heavy o i l hydrogénation, and the 175°-350°F heavy naphtha from the light oil hydrogénation. The heavy oil, which contained nearly 9 0 % of the nitrogen i n the syncrude, was fractionated by liquid displacement chromatography on Florisil. The nonpolar, nonnitrogen-containing hydrocarbons were washed from the Florisil column with η-heptane, a very weak base con centrate was displaced with benzene, and a weak base concentrate was displaced with benzene—methanol azeotrope.
In Shale Oil, Tar Sands, and Related Fuel Sources; Yen, T.; Advances in Chemistry; American Chemical Society: Washington, DC, 1976.
Downloaded by 117.253.185.157 on October 15, 2015 | http://pubs.acs.org Publication Date: September 1, 1976 | doi: 10.1021/ba-1976-0151.ch001
1.
POULSON E T A L .
3
Characteristics of Synthetic Crude
Analytical Methods. Total nitrogen values were determined w i t h a reductive, hydrogen-nickel pyrolysis tube and an ammonia microcoulometer. Nonaqueous potentiometric titration (6, 9, 10, 11) was used to classify the nitrogen compounds into weak base (pK* + 2 — f - 8 ) , very weak base ( p K a —2—1-2), and neutral types. Infrared spectrometry (10,11,12) was used to determine the concentration of pyrrolic nitrogen (nonhydrogen-bonded N - H ) . Colorimetry (JO, 13, 14) was used to determine pyrroles and indoles with unsubstituted a or β positions. These methods classified the nitrogen compounds into weak bases such as pyridines (including quinolines, 5,6,7,8-tetrahydroquinolines, and acridines) and as arylamines (including 1,2,3,4-tetrahydroquinolines, 2,3dihydroindoles, and anilines ) ; into very weak base pyrroles and indoles with an α or β position unsubstituted; and into neutral carbazoles without N-substitution. L o w voltage mass spectrometry and high resolution mass spectrometry allowed classification of the remaining nitrogen compounds into either pyrrole types with a and β positions substituted or carbazoles with N-substitution. Hydrocarbon types were estimated using the substractive method of Poulson ( 15,16) for the fractions boiling above 175°F. The hydrocarbon compound composition of the C -175°F naphtha was determined by gas chromatography. Paraffin and naphthene contents of the 175°-350°F naphtha and of the 350°-550°F light oil were calculated from mass spectra. L i q u i d displacement chromatography on Florisil was used to determine the amount of polar material in the 550°-850°F heavy oil. 5
Results and
Discussion
Hydrocarbon-type Characterization. Table I lists the four fractions, their wt % of the syncrude, and their hydrocarbon-type compositions. The values for polar material for the two naphthas and the light oil are estimates based on their nitrogen contents. The polar material value for the heavy oil is based on the recovered weights from the Florisil separaTable I.
Hydrocarbon Types in Syncrude Fractions Wt%
Boiling Range
Name
C -175°F light naphtha 175°-350°F heavy naphtha 350°^550°F light oil 555°-850°F heavy oil 5
Hydrocarbon Type (Wt% of Fraction)
of Par- Naph- Ole- AroCrude affins thenes fins matics 3 21 49 27
71.8 20.5 42.8 43.4 51.5 25.0 72.7 *
0.0 0.0 0.0 6.0
7.7 13.8 23.5 19.2
•Includes naphthenes.
In Shale Oil, Tar Sands, and Related Fuel Sources; Yen, T.; Advances in Chemistry; American Chemical Society: Washington, DC, 1976.
Polar Material
