6 Feedstocks from Paraho Shale Oil
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C. G. RUDERSHAUSEN and J. B. THOMPSON Experimental Station, Ε. I. du Pont de Nemours & Co., Inc., Wilmington, DE 19898 Shale oil from internally fired retorting to 482°C was con verted in 36% yield to BTX and C -C olefins. In a scouting program with bench-scale equipment and without recycle, the process entailed (1) distillation, (2) hydrocracking, (3) hydrotreating to further reduce heteroatoms, (4) reforming, and (5) steam pyrolysis. Established and readily available catalysts were used for steps 2, 3, and 4. The yield to chemi cal feedstocks could probably be improved significantly by using state-of-the-art catalysts with well-optimized process conditions, by reducing nitrogen in reformer feed, and by increasing severity in steam pyrolysis to favor olefins. 2
4
T7or about 50 years, petroleum and natural gas have replaced conventional coal tar derivatives as the essential sources of large-scale organic chemicals in the United States. The present petrochemical industry has evolved to convert these raw materials to commodity-scale products such as benzene, toluene, ethylene, butadiene, and propylene, together with methane-based ammonia and methanol. A large and diverse chemical industry has grown up relying on these petrochemicals as feed stocks. More recently, the chemical industry has seen the need to look beyond petroleum to processes for converting nonpetroleum materials to feedstocks (1, 15). These processes, all fuel-oriented but having feed stock potential in varying degrees, usually deal with coal-derived liquids, shale oil, and biomass. Shale oil is of special interest here because of its comparatively high hydrogen content, similar to that for petroleum and about twice that in coal. This feature is especially attractive for conversion to fuels and feedstocks. A short but comprehensive review of the huge oil shale potential in the United States is given in Réf. 1; it notes some of the 0-8412-0468-3/79/33-183-091$05.00/0 © 1979 American Chemical Society
Oblad et al.; Thermal Hydrocarbon Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1979.
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THERMAL HYDROCARBON CHEMISTRY
processes recently under development for oil recovery. Oil shale was studied in the fifties as a source of chemicals; in a review article by Thome (2), by-product chemicals and liquid fuels potential were specifically noted. High temperature retorting—actually a steam cracking operation—yielded up to 90 pounds of C - C olefins per ton of high quality shale (30 gal oil/ton). But conventional retorting gave a heavy oil very high in nitrogen and therefore undesirable for a petroleum refiner. A recent view on oil shale development is presented comprehensively in Ref. 3 which notes that widely ranging uncertainties ( especially concerning mining techniques, environmental problems, and water supplies) continue to restrain the pace of oil shale development despite the abundance of high quality shale in the United States. Nevertheless, some predictions suggest the availability of as much shale oil as 0.8 million bbl/day by 1990 ( 17); mostly, if not all, would be from the Green River formation. During a recent three-year test program funded by private companies, 10,000 bbl of shale oil was refined into fuels for specific testing (18). 2
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Objectives The potential for converting synthetic crudes to chemical feedstocks has been judged in a manner roughly analogous to that tried by the Bureau of Mines (4) and others for refining shale oil to fuels, including gasoline. One of our long-term goals was to find correlations between process results and simple analytical tests of the raw crude. For petroleum, much progress has been made, and refiners can predict rather closely the value of a given crude for a given product mix from analytical tests alone. In this chapter we will describe some of our initial evaluation work on Paraho shale oil. This initial evaluation was not performed in depth; rather, this first step consisted of chemical characterizations and high-spot, bench-scale processing of oil shale and several other syncrudes for direct comparisons of chemical feedstocks potential. Conventional analytical and petroleum processing techniques were used in the expectation that these would provide reference data on which to base specifically adapted techniques for evaluations of individual syncrudes. The results represent only our first attempts and except for occasional comparisons, are only for Paraho shale oil. Analytical Characterization The sample used for the present work was produced by Paraho on October 23,1975 by using the direct mode (Figure 1), that is, by internal firing using the heat of combustion from coke formed on the rock in a
Oblad et al.; Thermal Hydrocarbon Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1979.
6.
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Shale Oil Feedstocks
RUDERSHAUSEN AND THOMPSON
SHALE PRODUCT GAS
CONDENSER
OIL
RETORT
\-AIR
SOLID WASTE Figure 1.
Paraho Process (gas combustion mode)
retort whose temperature profile was 318°-482°C. The Green River shale (Rifle, Colorado) contained 28 gal oil/ton. Some further background on the Paraho and other shale oil processes is given in Ref. 5. The importance of specific retorting temperature is emphasized in Figure 2 by Thorne (2), showing a sharp increase in aromatics as retorting temperature is 100 90 80 AROMATICS
£70 LU
£ 60 Lu CL LU 50 Έ 3 40 ο
>
.OLEFINS 30
SATURATES
20 10 1000
1100
1200 1300 RETORT TEMPERATURE/
1400
1500
Hydrocarbon Process. Pet. Refiner
Figure 2.
Hydrocarbon type distribution in naphthas from entrainedsolids retort crudes (Vè)
Oblad et al.; Thermal Hydrocarbon Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1979.
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THERMAL
HYDROCARBON
CHEMISTRY
increased to 650°C. Another qualification of the present shale oil is that indirect retorting (external firing) may produce a higher-quality oil. The whole crude as well as the fractions used for subsequent processing studies were analyzed, as summarized in Table I.
Table I. Whole Crude C (%) H(%) N(%) 0 (%) S (%) Total Sediment" Mol wt C/H API gravity*
17S°S45°C 31.0 (wt %)
345°-lfi0°i 87.6 (wt %)
83.53 11.76 1.86 1.54 0.69 99.38
84.85 10.20 1.87 1.15 0.57 98.64
0.2 265 0.621 21.3
149 0.556
215 0.592
336 0.693
.
—
1.4637
— —0.8895
Viscosity (CS) 30° 90° 110°
—6.61
β
175°C 5.1 (wt %) 82.56 12.37 1.30 1.51 0.73 98.47
Density 20° 30° 90° 110°
SARA Nonpolar aromatics (%) saturates (%) Polar 1 2 3 Asphaltenes Benzene insol.
460
5.1 31.0 37.6 26.6 (balance)
For three narrow fractions with midcut boiling points of 235°-325°C, the Bureau of Mines Correlation Index (BMCI) is 42-45, respectively. Processing Conventional refinery techniques, supplemented with steam pyrolysis, were used in bench-scale continuous flow equipment which, however, was not integrated. Important liquid recycles were simulated; gases were not recycled. The processing sequence is depicted in Figure 3 and is sum marized as: (1) distillation of crude into four fractions, (2) hydrocracking of gas oils to naphtha, (3) naphtha hydrotreating for further heteroatom removal, (4) naphtha reforming to aromatics, and (5) steam pyrolysis of gas oils to olefins. Conventional and readily obtainable petroleum refinery catalysts were used (Table II). This includes a simple and earlier form of reforming catalyst (platinum only) in deference to its apparently greater resistance to sulfur and nitrogen poisoning. Distillation of crude provided the gas oils that were used in subse quent processing and also that are described in Table I. Note that the total that was distilled-off represents 73.7 wt % . Less effort was applied to the heavy gas oil ( > 4 6 0 ° C ) and to the residuum, and none to the coking where this fraction might be directed for recovery of coke and lighter gas oils.
Oblad et al.; Thermal Hydrocarbon Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1979.
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THERMAL HYDROCARBON CHEMISTRY
SHALE NAPHTHA (TO HYDROTREATING)
OIL
DISTILLATION
I GAS
OILS
HYDR0CRACKIN6
~
HEAVY GAS OIL AND BOTTOMS (TO DELAYED COKING)
GAS OILS
COKE
1
_ _ ^ N H , H S, H 0 3
2
2
