CA1196876A - Coal hydrogenation process using acid hydrolysis and precipitation of asphaltenes - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A coal hydrogenation process for producing hydrocarbon liquid and gas products, wherein an inorganic acid is added to a coal derived liquid fraction to cause precipitation of asphaltene and preasphaltene materials contained therein and to produce clean fuel oil products. In the process, the acid precipitation step overflow stream is preferably used for coal slurrying oil and is recycled to the reactor for further catalytic reaction. The precipitated material containing asphaltenes and preasphaltenes is further processed to recover desirable product oils. The acid precipitation step occurs at a temperature of about 400°F to about 600°F, and preferably, hydrochloric acid is used.

Description

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COAL HYDROGENAl~ION PROCESS USING ~CID HYDP~OL~'SIS AMD
PRECIPITATION OF ASPHALTENES
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BACKGROU~D OF INVENTIO~I

! Field of Invention ! This invention pertains to a coal hydrogenation process for producing hydrocarbon liquid and gas products, wherein unconverted coal and ash solids are removed from a coal-derived liquid fraction by acid precipitation so as to produce hydro-carbon liquid products which contain low sulfur and ash.
;~ i Description of Prior Art Conventional process steps for coal hydrogenation and liquefaction processes, such as the H-CoalTM Process, usually includes hydroclone devices for liquid-solid separation to pro-duce a relatively low ash ~esidual oil recycle stream used to slurry the coal for feeding it into the reactor. However, the hydroclone devices present problems in that the~ must be ver~
small to be effective for performing their solid-liquid separation function. In a commercial size coal liquefaction plant, undesirably large numbers of individual hydroclone units must be used together with complex associated piping systems.
~urthermore, because of the hydroclones small size, high fluid velocities and the abrasive slurry being handled, they are subject to severe wear and require frequent replacement.
For coal hydrogenation processes such as in the H-Coal process boiler fuel product mode using higher space velocities, the process can also include ~n effective solid-liquid separation system using solvent precipitation to produce a low ash net product containing non-distillable oil, but low enough in sulfur and ash to be a legally burnable fuel for electric utilities. However, solid-liquid separation for coal liquids ~L~8~
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using such solvent precipitation to produce boiler fuels is a still more difficult problem. The solvent precipitation of coal I solids is believed to function via precipitation of asphaltenes !! and preasphaltenes by the addition of a hydrocarbon liquid which is a poor solvent to a heavy coal-derived liquid. The asphaltenes, !~ coalesce around the solid particles of ash and unconverted coal and co-precipitate the solids, producing a highly viscous under-flow material containing most of the solids and an overflow fraction containing most of the high molecular weight oils.
~¦ Such solvent precipitation processes for coal-derived liquids using a solvent oil from an external source are disclosed in U.S. Patents 3,791,956 to Gorin, et al and 3,932,266 to I¦ Sze, et al. However, a problem with this a?proach is that if an !¦ extraneous antisolvent liquid, ie.., not self-generated in the !I coal hydrogenation process is used, a complete separation and recovery of the antisolvent liquid fraction is necessary, which is quite expensive. -I The prior art also teaches treating petroleum distillate .. .
and coal-derived liquids with acid at near ambient temperatures to precipitate out heavy fractions. For example, U.S. Patent

2,068,847 to Davis mentions the coagulation of asphaltic material il in oil by treatment with sulfuric acid and an aromatic material.
U.S. Patent 2,209,123 to Koelbel disclosed mixing coal tar oils with paraffin hydrocarbons and dilute acid to cause precipitation ¦
~of sediments to make clean diesel fuels. Also, U.S. Patent ¦3,084,118 to Overholt, et al, discloses a process for refining coal-derived liquids by adding a hydrocarbon precipitant oil and an acid coasulant such ,-s sulfuric acid at relatively low temperature to provide a supernatant ash~free liquid product ana form a soft sludge containing the acid and carbon residues.
The present invention provides an improvement over the prior ar_ for coal hydrogenation processes and petroleum refining in that an inorganic acid is used to cause precipitation of the pre-asphaltene components of the recycled coal liquid rather than using acid precipitation as a refining step on the product.
The acid precipitatlon step replaces the hydroclone liquid-soli~s l separation system in the usual H-Coal~~ process arra~gement, and i the overflow liquid product is used as recycle oil for slurrying l the coal feed.
Il l ji SUMMARY OF INVENTION

This invention discloses a coal hydrogenation process for producing hydrocarbon liquid and gas products, wherein an inorganic acid i5 added to a coal-derived liquid fraction to cause precipitation of preasphaltenes, unconverted coal and ash solids, and to produce clean oil products. Because preasphaltenes contained in the heavy liquid fraction are salts of nitrogen bases and phenolic acids, lt is found that these salts can be dis associated and the basic moiety precipitated by adding a strong inorganic acid, such as hydrochloric acid, to the heavy coal-derived liquid. The supernatant overflow material is recycled tc the catalytic reaction zone for further reaction, from which the precipitated material is withdrawn for further ~rocessins to increase liquid product yields.
More specifically, in a coal liquefaction process such as the H-Coal~ Process ma~ing use of this invention, the heavy coal- I
derived liquid fraction normally boiling above about 800F and 1, containing oils, asphaltenes, preasphaltenes unreacted coal and ash solids is treated with an inorganic acid such as hydrochloric acid. The acid is added to the slurry liquid fraction of the coal liquefaction ?rocess at temperature within the range of 400-600F, and disassociation of the preasphaltenes occurs. The basic ortion of the heavy molecules precipitates, leaving behind a . . , ¦ coal tar acid liquid overhead 5tream having relatively 10W
nitrogen. Destruction of the preasphaltenes reduces the viscosityl ! f the remaining liquid. Preclpitation of the basic constituent co-precipitates the solid ash and unconverted coal, similarly as ¦ for solvent ?recipitation. The overflow liquid stream is low in solids, low in nitrogen due to removal of the nitrogen bases, and i has low viscosity. This material provides a much more desirable recycle stream to the reaction zone than is produced by a hydro-clone liquid-solids separation system, and produces more desirable¦
product yields from the reactor. Thus, the usual hydroclone sub- ¦
Isystem ~or solids removal from liquid recycled to the reactor is ¦replaced by an acid treating and settling step.
il The preferred process arrangement is to recycle this over- ¦
flow liquid stream from the acid precipitation step for use in ,slurrying the coal feed. The composition of the recycle liquid 'Istream can be adjusted by varying the pressure at which the feed i to the acid precipitator is flashed to recycle more or lesser amounts of distiliate oil. The precipitator bottoms material is ' withdrawn and can be passed to a ~Jacuum distillation step, coker l or solid separation system provided downstream from the acid ; precipitation step to recover additional clean hydrocarbon liquid I?roduct. Also, if desired the precipitator bottom material can ,ibe used either as feed to a hydrogen-producing plant, as feed to ,la gasification plant, or as boiler fuel with on-site stac~ gas ' scrubbing.
Acids useful in this invention must be -strong inorganic ~acids and include both Bronsted acids such as hydrochloric (HRI), phosphoric (H3P04) and sulfuric ~H2S04) acids, and Lewis acids suc~
as boron trifluoride (BF3) and aluminum chloride (AlC13).
'ISufficient acid is added to the liquid to cause precipitation or Ithe preasphaltenes materials. The acid may be added either in liquid form, or as a gas bubbled up through the coal-deri-Jed liqui , The advantages oE this acid precipitation-senaration step are that it is a potentially simple and ineY.pensiVe process step having low u-tilities requirements that replaces both hydroclones and solvent precipitation solid-liquid separation equipment. Also, it provides a hydrocarbon liquid product having reduced viscositv and low sulfur, and which is a more desirable fuel product.
DESCRIPTION OF DRAWING
FIG. 1 is a schematic drawing illustrating a coal hydrogenation process utilizing an acid precipitation step to remove preasphaltenes and coal solids according to the present invention.
DESCRIPTION OF PREFERRED EMBODIMENT
This invention will be described as used in a coal hydrogenation process having an ebullated catalyst bed type reactor as illustrated by FIG. 1. As is shown, a bituminous or semi-bituminous coal is provided at 10, and is first passed through a preparation unit generally indicated at 12. In such unit the coal is dried of substantially all surface moisture, ground to a desired size range, and screened for uniformity.
For our purposes, it is preferable that the coal have a particle size of about 50 to 375 mesh (U.S. Sieve Series).
The coal fines are removed through conduit 13 and pass to slurry tank 14, where the coal is blended with a slurrying oil at 15 which is made in the process. To provide an effectively transportable coal-oil slurry, the ground coal should be mixed with at least about an equal weight of the slurrying oil. The resulting coal-oil slurry is pressurized by pump 16 to superatmospheric pressure, such as 30 500-5000 psi, and i5 then passed through heater 18 for heating the slurry to a temperature in the range of ! ;1~L~
I li 600F to 800~F. The heated coal-oil slurry along with recycle hydrogen at 17, is then passed into reactor feed line 19, where it is sup~lied with fresh makeup hydrogen as needed at 33a.
The entire mixture of coal-oil slurry and hydrogen then enters reactor 20 containlng catalyst bed 22, passing uniformly ! upwardly from the bottom through flow distributor 21 at a flow rate and at a temperature and pressure to accomplish the desired 1 hydrogenation. The catalyst in bed 22 would be from the class of cobalt, iron, molybdenum, nickel, tin or other hydrocarbon ~ hydrogenation catalyst metals known in the art, deposited on a i! base selected from the class of alumina, magnesla, silica, or similar materials. In addition, particulate hydrogenation catalyst may be added to reactor 20 at connection 23 in the ratiol of about 0.1 to 2.0 pounds of catalyst per ton of coal processed.!
By concurrently flowing liquid and gasiform materials upwardly through the reactor containing a bed of solid particles of a contact material, whi~h may be a specific catalyst as indicated above, and e~panding the bed of solid particles by at least 10~ and usually by 20 - 100% over its stationary volume, ! the solid particles are placed in random ebullated motion within ¦ the reactor by the upflowing streams. The characteristics of I the ebullated bed at a particular degree of volume ex.pansion can ~
Il be such that finer, lighter particulate solids will pass upwardly;
¦I through the catalyst bed, so that the contact particles con-¦ stituting the ebullated bed are retained in the reactor and the finer, lighter material may pass from the reactor. The catalyst ¦ bed upper level 22a, above which few if any contact particles ascend, is the upper level of ebullation.
Il In general, the gross density of the stationary mass of ! contact material will be between about 25 to 200 pounds per cubic I foot, the flow rate of the liquid will be between about 5 and 120 gallons per minute per square foot of horizontal cross-section area of the reactor, and the expanded volume of the ebullated bed usually will be not more than double the volume of the settled mass. To maintain the desired superficial upward liquid velocity in the reactor, a portion of the liquid slurry is usually recycled to the reactor, such as a liquid stream which is removed from above the upper level of ebullation 22a and recycled via downcomer conduit 24 and pump 25 to the bottom of the reactor 20, and upwardly through distributor 21. Alternatively, this rPcycle liquid stream and pump may be located external to the reactor. Spent catalyst may be removed by drawoff at connection 26 to main-tain the desired catalytic activity within the reaction zone.
Reactor operating conditions are maintained in the ranges of 700-930F temperature and 1000-5000 psi partial pressure of hydrogen and preferably 750-900F and 1000-4000 psi hydrogen partial pressure. Coal throughput or space velocity is at the rate of 15 to l50 pounds coal per hour per cubic foot of reactor volume, so that thP yield of unconverted coal as char is between about 5 and 15 W % of the moisture and ash-free coal feed. The relative size of the coal and catalyst particles and conditions of ebullation is such that catalyst is retained in the reactor, while the ash and unreacted char particles are carried out with the liquid reaction products.
From reaction zone 20, an effluent stream 27, which is virtually free of solid particles of contact material or catalyst is withdrawn, cooled at 28, and then passed to phase separator 30. From separator 30, a light gas stream is removed at 31 and passed to hydrogen purificiation step 32.
A medium-purity hydrogen stream 33 is recovered from purification step 32, warmed at heat exchanger 28, if desired, and recycled through heater :L8 to reactor 20 to provide most of the hydrogen requirements therein as heated hydrogen stream 17.
From separator 30 a li~uid stream 34 is withdrawn, pressure-reduced at 35 and is passed to phase separator 3~.
This separator operates at near atmospheric pressure and 500-650F temperature, and permits removal of a light liquid stream at 39 and a heavy hydrocarbon li~uid stream at 44.
Stream 39 contains naphtha and light distillate fractions and is passed to fractionation step 40, from which hydrocarbon gas products are withdrawn at 41 and light distillate product at 42. A hydrogenated coal liquid fraction, usually having a normal boiling range of 500 to 1050F containing oil, asphaltenes, preasphaltenes, unconverted coal and ash solids, is withdrawn at 44 and is mixed with an acid at 45, and passed to acid precipitation step 46. If desired, acid stream 45 can be added directly into precipitation step 46. It has been found that the ratio of acid stream 45 to the asphaltenes in stream 44 should be between about 3 and 5 W % of the preasphaltenes therein. Stream 44 will usually contain 12 to 40 W % preasphaltenes. The resulting mixed stream is maintained at a temperature between about 400 600F and at pressure conditions sufficient to avoid vaporization of the precipitating acid~ generally about 50 psig and usually not exceeding about 200 psig. An overflow liquid stream contain-ing reduced concentration of solids is removed at 47, and is recycled usually as coal slurrying oil 15 to reactor 20 to control the solids concentration in the reactor and to achieve further conversion to increased yields of low-boiling hydrocarbon products. An underflow liquid stream, containing acid and an increased concentration of preasphaltenes and coal i~9~

solids :is withdrawn at 48.
To facilitate the withdrawal of underflow liquid stream 48 from acid precipitation step 46 rotary device 49 or equivalent mixing means can be used to provide sufficient mixing and continuous agitation to prevent premature solidificat.ion of the precipitated solids component. Because of the effectiveness of - 8a -l~

~ the combination of the acid and coal-derived liquids to produce j~ precipitation of solids, the residence time in the settler to I achieve signlficant solids settling i5 usually less ~han about l 45 minutes and is preferably 15-30 mlnutes.

.j From settler 46, overflow liquid 47 is continuously with- !
! drawn and contains less than abou~ 2.0 W ~ solids comprising fine particles of unconverted coal and ash. This overflow liquid¦
47 contains only a minor amount of acid, and is recycled to reactor 20, preferably as coal slurrying oil 15 for further ! reaction therein. The underflow liquid stream 48, containing an increased solids concentration, is removed from settler 46 by I pumping and with the aid of internal rotary rake 49, can be ¦ reduced in pressure by passage to flash drum 50 which is main-¦ tained at a pressure of at least about 5 psig and a temperature ¦ of 550F for vaporization of acid, and ~assed to vacuum dis-i tillation at 52. The resulting overhead liquid 53 from the vacuum still may be joine~ with stream 43 to provide a heavy distillate product stream 54. The heavy bottoms streams 55 from ! ~Jacuum still 52 containing some asphaltenes and unconverted coal ! and ash solids may be further processed by coking to recover oil products or by gasification to produce the makeup hydrogen needed . in the process. I
. Although this invention has been descxibed with reference j to certain embodiments thereof, it will be understood that modifications and variations to the process can be made within ¦ the spirit and scope of the invention, which is defined by the following cl~ims.

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Claims (12)

I CLAIM:

1. A coal hydrogenation process for producing clean hydrocarbon liquid and gas products, comprising:
(a) slurrying coal with a process-derived oil and feeding the coal-oil slurry with hydrogen to a catalytic hydrogenation reaction zone maintained at elevated temperature and pressure conditions for hydrogenating the coal;
(b) withdrawing a reacted hydrocarbon effluent material and phase separating it to provide gaseous and liquid fractions;
(c) adding acid to the resulting separated bottoms liquid fraction and precipitating asphaltenes and coal solids;
(d) withdrawing from the acid precipitation step an over-head liquid stream containing reduced concentration of preasphaltenes and solids, and recycling said stream to the reaction zone for further hydrogenation therein;
(e) withdrawing a heavy hydrocarbon bottom stream contain-ing precipitated preasphaltenes and coal solids for further processing; and (f) withdrawing a hydrocarbon liquid product stream con-taining low sulfur and ash.

2. The process of claim 1, wherein the hydrogenation reaction conditions are within the ranges of 700-930°F tempera-ture and 1000-5000 psig hydrogen partial pressure.

3. The process of claim 1, wherein the acid precipitation step temperature is between about 400 to 600°F.

4. The process of claim 1, wherein the acid precipitation step pressure ranges from about 50 to about 500 psig.

5. The process of claim 1, wherein the acid added to the coal-derived liquid fraction is from about 3 to about 5 W % of the preasphaltene material contained in the liquid fraction.

6. The process of claim 1, wherein the acid added to the liquid fraction is HC1, H2SO4, H3PO4, BF3 or A1C13.

7. The process of claim 1, wherein the acid added to the liquid fraction is HC1.

8. The process of claim 1, wherein the acid added to the liquid fraction is A1C13.

9. The process of claim 1, wherein the precipitated bottoms material from the acid precipitation step is vacuum distilled to recover additional clean hydrocarbon liquid product.

10. The process of claim 1, wherein the overhead material from the phase separation step is fractionated to provide gas and distillate liquid products.

11. The process of claim 1, wherein the acid added to the solids precipitation step is recovered for reuse.

12. A coal hydrogenation process for producing clean hydrocarbon liquid and gas products, comprising:
(a) slurrying coal with a process-derived oil and feeding the coal-oil slurry with hydrogen to a catalytic hydrogenation reaction zone maintained at 700-930°F temperature and 1000-5000 psig hydrogen partial pressure conditions for hydrogenating the coal;
(b) withdrawing a reacted hydrocarbon effluent material and phase separating it to provide gaseous and liquid fractions;
(c) adding acid to the resulting separated bottoms liquid fraction at temperature between about 400 and 600°F and precipitating asphaltenes and coal solids;
(d) withdrawing from the acid precipitation step an overhead liquid stream containing reduced preasphaltenes and solids, and recycling said stream to the reaction zone for further hydrogenation;
(e) withdrawing a heavy hydrocarbon bottom stream containing precipitated preasphaltenes and coal solids for further processing; and (f) withdrawing a hydrocarbon liquid product stream containing low sulfur and ash.