CA1279027C - Two-stage coprocessing of bitumen/coal slurries - Google Patents

Abstract

Abstract A process is described for two-stage coprocessing of coal and a heavy hydrocarbon, such as bitumen from tar sands. A slurry of the bitumen and coal is passed upwardly through a coal dissolving and hydrogenation zone and the top discharge from the coal dissolving zone, containing partially solubilized coal and ash, is passed through a confined hydrocracking zone. The effluent emerging from the hydrocracking zone is sepa-rated into a gaseous stream containing a wide boiling range of material and a liquid stream containing heavy hydrocarbons. This process permits maximum yields from both coal and bitumen, while suppressing coke formation during hydrocracking.

Description

,7'3~)~7 Two-stage coprocessinq of bitumen/coal slurries This invention relates to hydrocracking and, more particularly, to the two-stage coprocessing of coal and a heavy hydrocarbon oil, such as bitumen from tar sands.
Hydrocracking processes for the conversion of heavy hydrocarbon oils to light~ and intermediate naphthas of good quality for reforming feedstock, fuel oil and gas oil are well.known. These heavy hydrocarbon oils can be such materials as petroleum crude oil, atmospheric tar bottoms products, vacuum tar bottoms products, heavy cycle oils, shale oils, coal derived fluids, crude oil residuum, topped crude oils and the heavy bituminous oils extracted : from tar sands. Of particular interest are the oils ex-tracted from tar sands which contain wide boiling range materials from naphtha through kerosene, gas oil, pitch, etc., and which contain a large portion, usually more than S0 weight percent of material boiling above 525C, equivalent atmospheric boiling point.
The heavy hydrocarbon oils of the above type tend to contain nitrogeneous and sulphurous compounds in quite large concentrations. In addition, such heavy hydrocar-bon fractions frequently contain excessive quantities of.
organo-metallic contaminants which tend to be extremely detrimental to various catalytic processes that may subsequently be carried out, such as hydrofining. Of the metallic contaminants, those containing nickel and vanadium are most common, although other metals are often -; , ' - .
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'' ' ~'~,7~ ''7 present. These metallic contaminants, as well as others, are usually present within the bituminous material as organo-metallic compounds of relatively high molecular weight. A considerable quantity of the organo-metallic complexes are linked with asphaltenic material and con-tain sulphur. Of course, in catalytic hydrocracking procedures, the presence of large quantities of asphal-tenic material and organic-metallic compounds interferes considerably with the activity of the catalyst with respect to the destructive removal of nitrogeneous, sul-phurous and oxygenated compounds. A typical Cold Lake bitumen may contain 54.2 wt. % material boiling above 525C, 4.4 wt. % sulphur, 0.41 wt. % nitrogen, 160 ppm vanadium and 55 ppm nickel.
As the reserves of conventional crude oils decline, these heavy oils must be upgraded to meet the demands.
In this upgrading, the heavier material is converted to lighter fractions and most of the sulphur, nitrogen and metals must be removed. This is usually done by a carbon rejection process such as delayed or fluidized coking or by a hydrogen addition process such as thermal or cataly-tic hydrocracking. The distillate yield from the coking process is about 70 weight percent and this process also yields about 23 wt. % coke as by-product which cannot be used as fuel because of low hydrogen:carbon ratio, and high mineral and sulphur content. Depending on operating conditions, hydrogenation processes can give a distillate yield of over 87 wt. %.
It has been shown in Ternan et al., Canadian Patent 1,073,389, issued March 11, 1980 and Ranganathan et al., U.S. Patent 4,214,977, issued July 29, 1980 that the i addition of coal or coal-based catalyst results in a reduction of coke deposition during hydrocracking and a generally improved operation. The coal additive acts as a "getter" Eor coke deposits and prevents accumulation ; of coke. It is also possible that coal mineral matter :

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: ~ -. ~ . - - ` -~,7'3()~7 acts as a coke-preventing catalyst. In these previous procedures the hydrogenation of the coal represented only a secondary consideration.
In the hydroliquefaction of coal, the coal hdrogenation process involves slurrying coal with a coal-derived oil and subsequent reaction with hydrogen at high temperatures and pressures in the presence of Co-Mo/alumina catalyst.
Other processes for converting coal such as SRC (solvent refined coal), EDS (Exxon donor solvent) and Synthoil processes also recycle heavy oil fractions derived from coal as solvents. These processes are described, for instance, by Richardson, F.W. "Oil From Coal", Noyes Data Corporation, Parkridge, New Jersey, 1975, 386 pp.
Not only the bitumen, but also the coal contains heavy asphaltenes and mineral matter which rapidly poison the catalyst. This results in excessive catalyst usage and high operating costs. For both bitumen and coal upgrad-ing processes, the fixed bed catalytic processes are not economical because of bed plugging resulting in costly shut-downs. An ebullated bed of catalyst is more suitable for hydrocracking bitumen or coal. Both the coal hydro-genation and the oil hydrogenation processes use this mode of operation. In the ebullated bed, the upward passage of liquid and gaseous materials maintains the catalyst in a fluidized state. Catalyst can be added and withdrawn con-tinuously so that a constant activity can be maintained.
However, the coal hydrogenation or oil hydrogenation uses an expensive Co-Mo/alumina catalyst which deactivates rapidly at high conversions, resulting in excessive operating costs.
As has been shown in the above patents, the operating costs can be reduced by using cheap throw-away type cata-lysts and, for instance, U.S. Patent 4,214,977 describes the use of coal-iron catalyst which enables operation at lower pressures and at higher conversions. The use of ` coal and Co, Mo and Al on coal catalysts are described ;~

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It is the object of the present invention to take - advantage of the solvent and hydrogen donor action of a bitumen feedstock as well as the catalytic action of coal S mineral matter so as to provide a novel coal plus heavy oil upgrading process showing improved economics.
Summarv of the Invention In accordance with the present invention, there is described a two-stage coprocessing of coal and heavy hydrocarbon oil, a substantial portion of which boils above 525C, which comprises:
a) passing a slurry of said heavy hydrocarbon oil and from about 2-50 wt. % coal in the presence of hydro-gen through a confined coal dissolving and hydrogenation zone at a space velocity of 1.5-15 volumes of slurry per hour per volume of coal dissolving zone capacity, said coal dissolving/hydrogenation zone being maintained at a temperature between about 375 and 450C, b) passing the discharge from the coal dissolving/hydrogenation zone through a confined hydro-- cracking zone, said hydrocracking zone being maintained at a temperature between about 400 and 470C, a pressure of at least 1.4 MPa and a space velocity between about 0.5 and 4 volumes of discharge slurry per hour per volume of hydrocracking zone capacity, c) removing from said hydrocracking zone a mixed effluent containing a gaseous phase comprising hydrogen and vaporous hydrocarbons and a slurry phase comprising heavy hydrocarbons and ash, and d) separating said effluent into a gaseous stream containing hydrogen and vaporous hydrocarbons and a slurry stream containing heavy hydrocarbons and ash.
This process provides a simultaneous hydrocracking or coprocessing of the heavy oil and coal, with the heavy 35 oil acting as a good solvent vehicle and the coal acting as a catalyst, preventing coke formation reactions. The :

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~ -: - . . -~,7~0;~7 two-stage coprocessing produces lighter distillates than a single stage operation at a given pitch conversion and also improves the system operability.
While the process of this invention is particularly well suited for the treatment of topped bitumen or pitch, it is also very well suited for the treatment of bitumen.
The system can be operated at quite moderate pressures, e.g. in the range of 1.4 to 24 MPa, without coke formation.
Preferably the coal dissolver is operated at about the same pressure as the hydrocracker.
The hydrocracking portion of this invention can be carried out in a variety of known reactors with either up or down flow. Thus, the hydrocracking reactor zone can be an empty tubular reactor, an ebullated bed reactor ; 15 or a fluidized bed reactor. The empty tubular reactor has been found to be particularly convenient with the effluent from the top being separated in a hot separator and the - gaseous stream from the hot separator being fed to a low temperature-high pressure separator where it is separated into a gaseous stream containing hydrogen and lesser amounts of gaseous hydrocarbons and a liquid product stream containing light oil products. The coal solubili-zation vessel may also conveniently be a single tubular reactor.
Any type of coal, such as lignite, sub-bituminous, bituminous, etc., can be used as the coal portion of the charge slurry. The coal may be coated with up to about 10 wt. % of metal salts such as iron, cobalt, molybdenum,-zinc, tin, tungsten, nickel or other catalytically active salts. The use of the catalytic materials improve the conversion of coal and bitumen as well as the operability of the process, but the metal loading must depend on the cost of materials, tolerable ash content and optimum catalyst activity.
35 ~ The catalyst can be coated on the coal by spraying the aqueous solution of the metal salt on all or part . . .: . : .

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The coal particles used should be quite small, e.g.
less than 60 mesh (Canadian Standard Sieve) and it is particularly preferred to use a material which will pass through a 100 mesh sieve. The coal should be mixed with the bitumen in such a manner as to avoid formation of lumps and, if desired, additional homogeneous or hetero-geneous catalysts may be mixed with the coal-bitumen slurry.
The process produces pitch which contains asphaltenes, ash and residues from both bitumen and coal. Depending on the type of coal used, and the eedstock, the pitch properties vary. For example, low sulphur, high ash sub-bituminous coals obtained from Western Canada produce a low-sulphue pitch. This reduces the cost of stack gas cleanup. The high ash content of the coal feedstock results in the high ash content of the pitch.
The presence of the large amounts of coal in the slurry, as stated above, suppresses coke formation dur-ing hydrocracking. The result is that the simultaneous coal-bitumen hydrocracking can be performed at quite low pressures. Nevertheless, in certain situations it is desirable to operate at higher pressures so as to maximize liquid yields as well as product quality.
According to a preferred embodiment, the bitumen and coal are mixed in a feed tank and pumped with hydrogen through a vertical empty tube reactor. The top discharge from the reactor, containing partially solubilized coal and ash, is fed into the bottom of a vertical hydro-cracking zone. The slurry-gas mixture from the top of the hydrocracking zone is separated in a hot separator maintained at an elevated temperature and at the pres-sure of the hydrocracking zone.
The gaseous stream from the hot separator containing ., ~
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:: ' ' - . . , , , ' - ' ' ~ - , ` -7~ 7 a mixture of hydrocarbon gases and hydrogen is further cooled and separated in a low temperature-high pressure separator. By using this type of separator, the outlet gaseous stream obtained contains mostly hydrogen with some impurities such as hydrogen sulphide and light hy-drocarbon gases. This gaseous stream is passed through a scrubber and the scrubbed hydrogen is recycled as part of the hydrogen feed to the coprocessing. The recycled hydrogen gas purity is maintained by adjusting scrubbing conditions and by adding make-up hydrogen.
The liquid stream from the low temperature-high pres-sure separator represents the light hydrocarbon product of the present process and can be sent for secondary treatment.
Some of the coal may be carried over with the heavy oil product from the hot separator and found in the 525C+
pitch fraction. This coal can conveniently be burned or gasified with the pitch.
For a better understanding of the invention, refer-ence is made to the accompanying drawings in which:
Figure 1 illustrates diagrammatically a preferred process embodiment;
Figure 2 is a plot of change in solvent insolubles vs. temperature; and, Figure 3 is a plot of solvent insolubles yields vs.
residence time.
Heavy hydrocarbon oil feed and coal are mixed together in a feed tank 10 to form a slurry. This slurry is pumped via feed pump 11 through inlet line 12 into the bottom of an empty tower 13. Recycled hydrogen and make up hydro-gen from line 31 is simultaneously fed into the tower 13 through line 12. A slurry containing partially solubilized coal and ash is withdrawn from the top of tower 13 via line 32 and is fed into the bottom of hydrocracking tower 33.
; 35 A gas-slurry mixture is withdrawn from the top of the tower 33 through line 14 and introduced into a hot separator 15.

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'7 In the hot separator the e~luent from tower 33 is separated into a gaseous stream 18 and a slurry stream 16. The slurry stream 16 consists of unconverted coal, ash and heavy oil which is collected at 17.
The gaseous stream from hot separator 15 is carried by way of line 18 into a high pressure-low temperature separator 19. Within this separator the product is separated into a gaseous stream rich in hydrogen which is drawn off through line 22 and an oil product which is drawn off through line 20 and collected at 21.
The hydrogen rich stream 22 is passed through a pack-ed scrubbing tower 23 where it is scrubbed by means of a scrubbing liquid 24 which is cycled through the tower by means of pump 25 and recycle loop 26. The scrubbed hy-drogen rich stream emerges from the scrubber via line 27 and is combined with fresh make up hydrogen added through line 28 and recycled through recycle gas pump 29, recycle gas furnace 30 and line 31 back to tower 13.
Certain preferred embodiments of this invention will now be further illustrated by the following non-limitative examples.
Example 1 A sub-bituminous coal was obtained from the Forestburg area of Alberta and this coal had the following properties:
Calorific Value*, kJ/kg 20640 Carbon*, wt. % 64.04 Hydrogen*, wt. % 3.87 Sulphur*, wt. % 0.53 ; Nitrogen*, wt. % 1.6S
Ash*, wt. % 9 5 Oxygen*, wt. % (by difference) 20.41 Moisture (as received~, wt. %19.17 Iron, ppm 2379 Nickel, ppm 18 Vanadium trace * Properties o~ coal on dry basis.

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7~ 7 g The above coal was crushed and screened to provide a -200 mesh material.
The bitumen used was a Cold Lake vacuum bottoms having the following properties:
Specific Gravity, 15/15C1.038 Sulphur, wt. % 5.5 Nitrogen, wt. % 0.6 Ash, wt. ~ trace Viscosity at 100C, poise 249 Conradson Carbon Residue, wt. ~ 17.1 Pentane insolubles, wt. %23.5 Benzene insolubles, wt. % 0.2 Nickel, ppm (wt.) 93 Vanadium, ppm (wt.) 235 Pitch content, wt. % 83.25 A blended slurry of the bitumen and 30% by weight of the coal (dry ash free) was prepared and this slurry was used as the feedstock to a bench scale unit. The unit used the coprocessing reaction sequence shown in Figure 1 and was operated first as a single stage hydrocracker without the coal dissolver column and then as a two-stage operation as shown in the drawing. The operating condi-tions used are shown in Table 1 below.

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The results obtained are shown in Table 2. Runs 1 and 2 were obtained using a single reactor under very similar conditions. Runs 6 and 7 were obtained using two reactors in series under similar conditions, except in Run 7 recycle gas flow rate was approximately one half the rate used in Run 6. Pitch conversions for all four of the above runs are approximately 77 wt. % and the distillate yields are approximately 68 wt. ~ of the slurry feed ~dry, ash free basis).
As seen in Table 2, the yield of HGO 2 fraction in Runs 1 and 2 was approximately 29 wt. % while that in Runs 6 and 7 was approximately 21 wt. ~. The difference between these runs was upgraded to naphtha (IBP-205C), LGO (205-345C) and HGO 1(345-415C) fractions. Thus, ~- 15 two-stage coprocessing produces more lighter distillates than single stage operation at a given pitch conversion level.
In terms of the system operability, a critical factor is operating severity. In general the higher the operat-ing severity, the higher the coal and pitch conversions.
However when the severity is too high, the polymerization of heavy compounds such as asphaltenes and preasphaltenes produce coke and semi-coke, which tend to deposit on the inside of the coprocessing reactors.
Runs 3 and 4 were carried out under similar conditions to Runs 1 and 2 except in Runs 3 and 4 the slurry feed rates were slightly reduced to increase processing time which resulted in coking in the reactor. The temperature in the reactor decreased as coking proceeded.
Runs 6 and 7 were two-stage runs where the operating ~- temperature and pressure in the second stage were the same as Runs 3 and 4. There were no operational problems encountered when two-stage operation was employed (i.e.
no coking) showing that two-stage operation can improve process operability.
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The results of these tests are shown in Figures 2 and 3. For example, Figure 2 shows that at 400C and 15 minutes residence time, 30~ of coal, expressed as THF
insolubles (daf~, dissolves into bitumen. In terms of a severity function *as defined by Whitehurst, the severity at 400C and 15 minutes residence time is only 5% of the severity at 450C and 60 minutes residence time which is a typical set of operating conditions for the second stage.
As it was shown earlier in Runs 6 and 7, such mild pre-processing was sufficient to make two-stage operation effective.

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Claims (9)

1. A two-stage process for the coprocessing of coal and a heavy hydrocarbon, a substantial proportion of which boils above 525°C, which comprises:
(a) passing a slurry of said heavy hydrocarbon oil and from about 2-50 wt. % coal in the presence of hydrogen through a confined coal dissolving/hydrogenation zone at a space velocity between 1.5 and 15 volumes of slurry per hour per volume of coal dissolving/hydrogenation zone capacity, said zone being maintained at a temperature between about 375 and 450°C, (b) passing the discharge from the coal dissolving/hydrogenation zone, containing partially solu-bilized coal and ash, through a confined hydrocracking zone, said hydrocracking zone being maintained at a tem-perature between about 400 and 470°C, a pressure of at least 1.4 MPa and a space velocity between about 0.5 and 4 volumes of hydrocracking zone capacity, (c) removing from said hydrocracking zone a mixed effluent containing a gaseous phase comprising hydrogen and vaporous hydrocarbons and a slurry phase comprising heavy hydrocarbons and ash, and (d) separating said effluent into a gaseous stream containing hydrogen and vaporous hydrocarbons and a slurry stream containing heavy hydrocarbons and ash.

2. A process according to claim 1, characterized in that the coal is -60 mesh (Canadian Sieve).

3. The process according to claim 2, characterized in that the coal is selected from sub-bituminous, bitu-minous, and lignite coal.

4. A process according to claim 1, characterized in that the feed slurry is moved upwardly through a tubular reactor.

5. A process according to claim 1, characterized in that the coal is coated with up to about 10 wt. % of a metal salt catalyst.

6. A process according to claim 5, characterized in that the metal salt is a salt of iron, cobalt, molybdenum, zinc, tin, nickel or tungsten.

7. A process according to claim 1, characterized in that the coal solubilization and hydrocracking are conducted at a pressure in the range of 1.4 - 24 MPa.

8. A process according to claim 1, characterized in that the mixed effluent is separated in a hot separator.

9. A process according to claim 8, characterized in that the gaseous stream from the hot separator is cool-ed and separated in a low temperature separator into a gaseous stream containing hydrogen and lesser amounts of gaseous hydrocarbons and a liquid product stream containing light oil products.