7 Upgrading Primary Coal Liquids by Hydrotreatment A. J. DEROSSET, GIM TAN, and J. G. GATSIS
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Corporate Research Center, UOP Inc., Des Plaines, IL 60016 Primary coal liquefaction products from three processes— solvent-refined coal, Synthoil, and Η-Coal—were hydro -treated. Upgrading was measured in terms of the decrease in heptane and benzene insolubles, the decrease in sulfur, nitrogen, and oxygen, and the increase in hydrogen content. Hydrotreating substantially eliminated benzene insolubles and sulfur. An 85% conversion of heptane insolubles and an 80% conversion of nitrogen was obtained. Catalyst stability was affected by metals andparticulatesin the feedstocks. " O r i m a r y coal liquids are high-viscosity black oils or pitches. Compared with petroleum crudes, they are deficient i n hydrogen, only partially soluble i n benzene, and contain relatively high levels of oxygen and nitrogen. They contain a variable amount of ash and unconverted coal, depending on the efficiency of the mechanical removal of solids achieved i n each process. These coal liquids originally were intended to serve as boiler fuels. The sulfur content may be sufficiently low to qaulify them as replacement for high-sulfur coal, and bring sulfur dioxide emissions within acceptable limits. However, for large boilers, such as major base load power plants, pollution control via coal hydroliquefaction probably is not competitive with stack gas scrubbing ( J ) . In other fuel markets, coal liquids can be more competitive. Indus trial boilers presently are not amenable to stack gas scrubbing. The same is true of smaller utility plants. I n particular, peak load units require a clean, storable liquid fuel as an alternative to natural gas. However, the high viscosity of primary coal liquefaction products is undesirable for many of these applications. Also, their residual sulfur and nitrogen contents may be excessive as emission standards become more stringent. 0-8412-0456-X/79/33-179-109$05.00/1 © 1979 American Chemical Society Gorbaty and Harney; Refining of Synthetic Crudes Advances in Chemistry; American Chemical Society: Washington, DC, 1979.
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110
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O F SYNTHETIC
CRUDES
If there is a petroleum shortage i n the future the problem w i l l be to provide a portion of the demand for transportation fuels from coal. Transportation fuels—jet, diesel, and gasoline—are distillates boiling below 650°F. However, the quantity of such distillates i n primary coal liquids is small. Primary coal liquids must be upgraded i n order to serve these markets. A logical route is to use current black oil conversion technology as practiced i n the petroleum industry ( 2 ) . A n applicable U O P process is R C D Unibon ( 3 ) . This comprises the direct processing of petroleum residues to reduce the sulfur and nitrogen content of heavy fuel o i l or to combine desulfurization with conversion of residue to lighter, more valuable products. This chapter reports results of applying a catalytic hydrorefining process to four coal liquids: solvent-refined coal ( S R C ) process filter feed, S R C extract product, Synthoil, and H - C o a l process hydroclone underflow. The achieved upgrading is evaluated in terms of reduction i n benzene and heptane insolubles, reduction i n sulfur, nitrogen, and oxygen, an increase i n hydrogen content, and a yield of lower boiling products. Hydrotreatment was carried out over a commercial U O P black oil conversion catalyst i n bench-scale units of 200-800 m L catalyst capacity. Temperature range was 375°-450°C and the pressure range was 20003000 psig. Weight hourly space velocity ( W H S V ) varied from 0.1 to 1.0 depending on the heptane-insoluble content of the feed. A flow diagram of a typical plant is shown i n Figure 1. The stripper bottoms usually
GAS. PROD. AND H
OIL FEED
2
H
STRIPPER GAS
t
2
ài
TRICKLE-BED REACTOR
SCRUBBER
LIGHT PRODUCT (AND H 0)
STRIPPER
r
HIGH PRESSURE SEPARATOR
HYDROTREATED LIQUID PRODUCT (STRIP. BOTTS.)
H 0 2
Figure 1.
Hydrotreatment plant
Gorbaty and Harney; Refining of Synthetic Crudes Advances in Chemistry; American Chemical Society: Washington, DC, 1979.
2
7.
DBROSSET
E T
A L .
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Upgrading Primary Coal Liquids
comprised over 9 0 % of the exit streams. It was the only portion analyzed i n detail and is referred to as product. The first stock run was S R C filter feed obtained from the Pittsburg and M i d w a y C o a l Company S R C pilot plant at F t . Lewis, Washington. This contains all of the recycle process solvent, ash, and unconverted coal. The stock was filtered prior to hydrotreating. (Table I compares inspections of the filter feed and filtrate.) Filtration upgraded the o i l portion of the stock.
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Table I.
Inspection of SRC Stocks SRC Filter Feed
°API @ 6 0 ° F Distillation ( A S T M D-1160) IBP (°F) 10% 30% 50% 70% SRC (850°F+) (Vol%) Heptane insoluble ( W t % ) Benzene insoluble (Wt %) D M F / x y l e n e insoluble (Wt %) » Ash (ASTM) ( W t % )
-11.8 400 579 654 729 925 30.3" 29.7* 16.7* 6.7 4.0
UOP Filtrate
SRC
-5.8
-13.7
400 550 620 685 825 29.0 26.9 9.4
648 905
0.01
93.0 89.4 34.7 0.15 0.11
" Corrected to "ash plus unconverted coal" free basis. * Assumed to be "ash plus unconverted coal."
The dimethylformamide ( D M F ) / x y l e n e insolubles, assumed to repre sent ash and unconverted coal, were eliminated substantially. The ben zene and heptane insolubles i n the feed, adjusted to an "ash plus unconverted coal" free basis, were reduced substantially and the A S T M ash dropped from 4 % to 0.1%. The S R C content of the filtrate, defined as percentage 850°F* bottoms was 29%, as compared w i t h 30.3% i n the feed after correction to an "ash plus unconverted coal" basis. Hydrotreating the filtrate resulted i n the upgrading shown i n Table II. Generally the degree of upgrading corresponded to the severity of the operation. F o r example, Product Β was obtained at a space velocity twice that used to make Product A . Similarly, within the limits of the range of experimental conditions used, upgrading improved with increas ing temperature and pressure. N o substantial decline i n performance was observed over 144 hr of operation.
Gorbaty and Harney; Refining of Synthetic Crudes Advances in Chemistry; American Chemical Society: Washington, DC, 1979.
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Table II.
O F SYNTHETIC
CRUDES
Upgrading Primary
SRC Filter Feed* Feed Heptane insoluble (Wt %) Benzene insoluble (Wt %) Sulfur ( W t % ) Nitrogen (Wt %) Oxygen ( W t % ) Hydrogen (Wt %) β
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b
26.9 9.4 0.72 1.28 3.81 6.90
Product A
Product B
0.5 0.03
