CA1140759A - Catalytic coal gasification process - Google Patents
Catalytic coal gasification processInfo
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- CA1140759A CA1140759A CA000331739A CA331739A CA1140759A CA 1140759 A CA1140759 A CA 1140759A CA 000331739 A CA000331739 A CA 000331739A CA 331739 A CA331739 A CA 331739A CA 1140759 A CA1140759 A CA 1140759A
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- sodium
- potassium
- gasification
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- coal
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Abstract
(U.S. 925,644) ABSTRACT OF THE DISCLOSURE
Carbonaceous material is gasified in the presence of an added potassium salt having poor catalytic activity as compared to potassium carbonate and a sodium or lithium compound. The added sodium or lithium compound apparently activates the relatively noncatalytic potassium salt thereby producing a substantial catalytic effect on the gasification reactions. In general, activation of the noncatalytic potassium salt will take place when the sodium or lithium compound in-troduced into the reactor is either a salt of a weak acid or a salt of a strong acid that is converted to a sodium or lithium salt of a weak acid in the reactor at gasification conditions.
Carbonaceous material is gasified in the presence of an added potassium salt having poor catalytic activity as compared to potassium carbonate and a sodium or lithium compound. The added sodium or lithium compound apparently activates the relatively noncatalytic potassium salt thereby producing a substantial catalytic effect on the gasification reactions. In general, activation of the noncatalytic potassium salt will take place when the sodium or lithium compound in-troduced into the reactor is either a salt of a weak acid or a salt of a strong acid that is converted to a sodium or lithium salt of a weak acid in the reactor at gasification conditions.
Description
1 BACKGROUN~.OF THE INVENTION
2 1. Field of the In~ention: This invention re-
3 lated to the gasification of carbonaceous materials such
4 as oils, petroleun residua, coals and the liket and is par-ticularly concerned with catalytic gasification operations 6 carried ou~ in the presènce of alkali metal-containing ca-7 talysts.
8 2. Description of the Prior Art: It has long 9 been recognized that certain alkali metal compounds can be employed to cataLyze the gasification of carbonaceous ma-ll terial such as coal and other carbonaceous solids. Studies 12 have shown that potassium carbonate, sodium carbonate, ces-13 ium carbonate and lithium carbonate will substantially ac-14 celerate the rate at which steam, hydrogen, carbon dioxide, oxygen and the like react with bituminous coal, subbitu-16 minous coal, lignite, petroleum coke, organic waste mater-17 ials and similar carbonaceous solids to form methane, car-18 bon monoxide, hydrogen, carbon dioxide and other gaseous ~9 products~ Other alkali metal salts such as al~ali metal chlorides~ however, have a low catalytic activity when com-21 pared to that of the sorresponding carbonate Because of 22 the relatively high cost of cesium carbonate and the low 23 effectiveness of lithium and sodium carbonates, most of the 24 experimental work in this area which has been carried out in the past has been directed toward the use of potassium 26 carbonate~
27 In addition to utilizing individual alkali metal 28 salts as a catalyst for the gasification of a carbonaceous 29 material, it has been proposed to utilize mixtures of alkali i metal salts. When such mixtures of alkali metal salts are 2 used to promote the gasification of a carbonaceous feed ma-3 terial, it is expected that the mixture will accelerate the 4 gasification reactions less than if an equivalent ~mount of the more active alkali metal compound is used alone and 6 more than if an equivalent amount of the less active alkali 7 metal salt is employed.
8 In gasification processes using alkali metal-con-g taining catalysts, the cost of the catalyst is a signifi-cant factor in determing the overall cost of the product 11 gas. Potassium carbonate is relatively expensive.
12 The costs of other alkali metal compounds such 13 as potassium chloride, potassium sulfate, sodium carbonate, 14 sodium chloride and sodium sulfate are substantially cheaper than potassium carbonate but these compounds exhibit only 16 a ~raction of the catalytic activity exhibited by potassium 17 carbonate. It would be highly desirable if the compounds 18 mentioned above and other more abundant, less expensive po-g tassium and sodium compounds could be effectively used as gasification.catalysts thereby substan~ially decreasing the 21 initial investmen~ required in the catalyst and obviating 22 the need for expensive secondary recovery techniques to de-23 crease the amount of makeup alkali compounds that would 24 otherwise be required to maintain the catalyst inventory at the required level.
27 The present invention provides an improved process 28 for the catalytic gasification of a carbonaceous feed mater-29 ial. In accordance with the invention, it has now been found that catalyst costs incurred during the gasification 31 of oils, petroleum residua, bituminous coat, subbituminous 32 coal, lignite, or~anic waste material, petroleum coke, and 33 other carbonaceous feed materials can be significantly re-34 duced while at the sam~ time obtaining unexpectedly hi~h gasification Iates by employing mixtures of inexpensive po-36 tassium compounds ~nd sodium compounds as the catalyst.
1 Laboratory tests have shown that when mixtures of coal, po-2 tassium chloride or potassium sulfate, and sodium carbonate 3 or sodium sulfate are injected into a reaction zone and the 4 coal is subsequently gasified, surpris~ngly high gasifica-tion rates are obtained. These gasification rates are sub-6 stantially higher than expected based on the low activity 7 of the individual potassium and sodium compounds relative 3 to that of potassium carbonate. This is a significant and 9 unexpected discovery since the observed gasification rates are high enough to enable mixtures of these inexpensive po-11 tassium and sodium salts to be used as gasi~ication catalysts 12 in lieu of the substantially more expensive potassium car-13 bonate. Because of the quantities in which catalysts are re-14 quired in catalytic gasification operations, the overall savings made possible in a large gasification plant by the 16 invention may be quite substantial.
17 In general, unexpectedly high gasification rates 18 will be obtained when a carbonaceous feed material is intro-19 duced into a reaction zone along with a mixture of a potassium compound having a relatively poor catalytic activity as com-21 pared to that of potassium carbonate and a sodium or lithium 22 compound se~ected from the group consisting of a weak acid 23 salt of sodium or lithium and a strong acid salt of sodium or 24 lîthium that is converted to a weak acid salt in the reaction zone at reaction eQnditions, and the carbonaceous material is 26 subsequently gasified. For mixtures of certain relatively 27 noncatalytic potassium and sodium compounds, the gasification 28 rate obtained will be nearly as great as the rate obtained 29 when potassium carbonate alone is introduced into the reaction zone ~ith the feed material in an amount that yields the same 31 alkali metal-to-carbon atomic ratio as that of the mixture.
32 Evidently, the sodium or lithium compound activates the poorly 33 catalytic potassium compound thereby producing a substantial 34 catalytic effect on the gasification rate of the carbonaceous feed material.
36 In accordance with the inven~ion, the use of s~
catalysts containing mixtures of inexpensive potassium and sodium compounds reduces the initial catalyst cost and the cost of makeup catalyst and at the same time permits the attainment of high gasification rates. The use of such mixtures also obviates the need for expensive secondary catalyst recovery procedures. As a result, the invention makes possible substantial savings in gasification operations and permits the generation of product gases at signi-ficantly lower cost than would normally otherwise be the case.
Thus the present invention provides a process for the catalytic gasification of a carbonaceous feed material characterized by the following steps in combination:
(a) introducing said carbonaceous feed material into a reaction zone;
(b) introducing a potassium salt of an organic or inorganic acid having an ionization constant greater than 1 x 10 3 into said reaction zone;
(c) in-troducing into said reaction zone in a sufficient quantity to activate said potassium salt a sodium or lithium compound which is either a weak acid salt of sodium or lithium or a strong acid salt of sodium or lithium that is converted into a weak acid sodium or lithium salt in said reaction zone; and (d~ gasifying said carbonaceous material in said reaction zone.
Preferably, when the potassium salt is potassium .sulphate, the sodium or lithium cormpound is selected from the group consisting of sodium sulfate, sodium carbonate, sodium chloride9 sodium nitrate and lithlum sulfaten Further, when the potassium salt is potassium chloride, the sodium or lithium compounds are preferably present in concentrations sufficient to yield a sodium or lithium to potassium atomic ratio of at least 1Ø
BRIEF DESCRIPTION OF THE`DRAWING
Figure 1 in the drawing is a schematic flow diagram of a process for the gasification of coal carried out in accordance with the invention;
L,. i~ .~ ..
1~4~5~
Figure 2 is a plot illustrating that unexpectedly high ga$ification rates are obtained by using a mixture of potassium sulfate and sodium carbonate which is equimolar in potassium and sodium to catalyze the gasification of a carbon-aceous material;
Figure 3 is a plot illustrating that unexpectedly high gasification rates are obtained by using a mixture of potassium sulfate and sodium sulfate which is equimolar in potassium and sodium to catalyze ~he gasification of a carbon-aceous material;
Figure 4 is a plot illustrating that unexpectedly high gasiEication rates are obtained by using a mixture of potassium sulfate and sodium chloride which is equimolar in potassium and sodium to catalyze the gasification of a carbon-aceous material;
Figure S is a plot illustrating that unexpectedly high gasification rates are obtained by using a mixture of potassium sulfate and sodium nitrate which is equimolar in potassium and sodium to catalyze the gasification of a carbon-aceous material;
Figure 6 is a plot illustrating that unexpectedly high gasification rates are obtained by using a mixture of potassium chloride and sodium carbonate which is equimolar - 4a -
8 2. Description of the Prior Art: It has long 9 been recognized that certain alkali metal compounds can be employed to cataLyze the gasification of carbonaceous ma-ll terial such as coal and other carbonaceous solids. Studies 12 have shown that potassium carbonate, sodium carbonate, ces-13 ium carbonate and lithium carbonate will substantially ac-14 celerate the rate at which steam, hydrogen, carbon dioxide, oxygen and the like react with bituminous coal, subbitu-16 minous coal, lignite, petroleum coke, organic waste mater-17 ials and similar carbonaceous solids to form methane, car-18 bon monoxide, hydrogen, carbon dioxide and other gaseous ~9 products~ Other alkali metal salts such as al~ali metal chlorides~ however, have a low catalytic activity when com-21 pared to that of the sorresponding carbonate Because of 22 the relatively high cost of cesium carbonate and the low 23 effectiveness of lithium and sodium carbonates, most of the 24 experimental work in this area which has been carried out in the past has been directed toward the use of potassium 26 carbonate~
27 In addition to utilizing individual alkali metal 28 salts as a catalyst for the gasification of a carbonaceous 29 material, it has been proposed to utilize mixtures of alkali i metal salts. When such mixtures of alkali metal salts are 2 used to promote the gasification of a carbonaceous feed ma-3 terial, it is expected that the mixture will accelerate the 4 gasification reactions less than if an equivalent ~mount of the more active alkali metal compound is used alone and 6 more than if an equivalent amount of the less active alkali 7 metal salt is employed.
8 In gasification processes using alkali metal-con-g taining catalysts, the cost of the catalyst is a signifi-cant factor in determing the overall cost of the product 11 gas. Potassium carbonate is relatively expensive.
12 The costs of other alkali metal compounds such 13 as potassium chloride, potassium sulfate, sodium carbonate, 14 sodium chloride and sodium sulfate are substantially cheaper than potassium carbonate but these compounds exhibit only 16 a ~raction of the catalytic activity exhibited by potassium 17 carbonate. It would be highly desirable if the compounds 18 mentioned above and other more abundant, less expensive po-g tassium and sodium compounds could be effectively used as gasification.catalysts thereby substan~ially decreasing the 21 initial investmen~ required in the catalyst and obviating 22 the need for expensive secondary recovery techniques to de-23 crease the amount of makeup alkali compounds that would 24 otherwise be required to maintain the catalyst inventory at the required level.
27 The present invention provides an improved process 28 for the catalytic gasification of a carbonaceous feed mater-29 ial. In accordance with the invention, it has now been found that catalyst costs incurred during the gasification 31 of oils, petroleum residua, bituminous coat, subbituminous 32 coal, lignite, or~anic waste material, petroleum coke, and 33 other carbonaceous feed materials can be significantly re-34 duced while at the sam~ time obtaining unexpectedly hi~h gasification Iates by employing mixtures of inexpensive po-36 tassium compounds ~nd sodium compounds as the catalyst.
1 Laboratory tests have shown that when mixtures of coal, po-2 tassium chloride or potassium sulfate, and sodium carbonate 3 or sodium sulfate are injected into a reaction zone and the 4 coal is subsequently gasified, surpris~ngly high gasifica-tion rates are obtained. These gasification rates are sub-6 stantially higher than expected based on the low activity 7 of the individual potassium and sodium compounds relative 3 to that of potassium carbonate. This is a significant and 9 unexpected discovery since the observed gasification rates are high enough to enable mixtures of these inexpensive po-11 tassium and sodium salts to be used as gasi~ication catalysts 12 in lieu of the substantially more expensive potassium car-13 bonate. Because of the quantities in which catalysts are re-14 quired in catalytic gasification operations, the overall savings made possible in a large gasification plant by the 16 invention may be quite substantial.
17 In general, unexpectedly high gasification rates 18 will be obtained when a carbonaceous feed material is intro-19 duced into a reaction zone along with a mixture of a potassium compound having a relatively poor catalytic activity as com-21 pared to that of potassium carbonate and a sodium or lithium 22 compound se~ected from the group consisting of a weak acid 23 salt of sodium or lithium and a strong acid salt of sodium or 24 lîthium that is converted to a weak acid salt in the reaction zone at reaction eQnditions, and the carbonaceous material is 26 subsequently gasified. For mixtures of certain relatively 27 noncatalytic potassium and sodium compounds, the gasification 28 rate obtained will be nearly as great as the rate obtained 29 when potassium carbonate alone is introduced into the reaction zone ~ith the feed material in an amount that yields the same 31 alkali metal-to-carbon atomic ratio as that of the mixture.
32 Evidently, the sodium or lithium compound activates the poorly 33 catalytic potassium compound thereby producing a substantial 34 catalytic effect on the gasification rate of the carbonaceous feed material.
36 In accordance with the inven~ion, the use of s~
catalysts containing mixtures of inexpensive potassium and sodium compounds reduces the initial catalyst cost and the cost of makeup catalyst and at the same time permits the attainment of high gasification rates. The use of such mixtures also obviates the need for expensive secondary catalyst recovery procedures. As a result, the invention makes possible substantial savings in gasification operations and permits the generation of product gases at signi-ficantly lower cost than would normally otherwise be the case.
Thus the present invention provides a process for the catalytic gasification of a carbonaceous feed material characterized by the following steps in combination:
(a) introducing said carbonaceous feed material into a reaction zone;
(b) introducing a potassium salt of an organic or inorganic acid having an ionization constant greater than 1 x 10 3 into said reaction zone;
(c) in-troducing into said reaction zone in a sufficient quantity to activate said potassium salt a sodium or lithium compound which is either a weak acid salt of sodium or lithium or a strong acid salt of sodium or lithium that is converted into a weak acid sodium or lithium salt in said reaction zone; and (d~ gasifying said carbonaceous material in said reaction zone.
Preferably, when the potassium salt is potassium .sulphate, the sodium or lithium cormpound is selected from the group consisting of sodium sulfate, sodium carbonate, sodium chloride9 sodium nitrate and lithlum sulfaten Further, when the potassium salt is potassium chloride, the sodium or lithium compounds are preferably present in concentrations sufficient to yield a sodium or lithium to potassium atomic ratio of at least 1Ø
BRIEF DESCRIPTION OF THE`DRAWING
Figure 1 in the drawing is a schematic flow diagram of a process for the gasification of coal carried out in accordance with the invention;
L,. i~ .~ ..
1~4~5~
Figure 2 is a plot illustrating that unexpectedly high ga$ification rates are obtained by using a mixture of potassium sulfate and sodium carbonate which is equimolar in potassium and sodium to catalyze the gasification of a carbon-aceous material;
Figure 3 is a plot illustrating that unexpectedly high gasification rates are obtained by using a mixture of potassium sulfate and sodium sulfate which is equimolar in potassium and sodium to catalyze ~he gasification of a carbon-aceous material;
Figure 4 is a plot illustrating that unexpectedly high gasiEication rates are obtained by using a mixture of potassium sulfate and sodium chloride which is equimolar in potassium and sodium to catalyze the gasification of a carbon-aceous material;
Figure S is a plot illustrating that unexpectedly high gasification rates are obtained by using a mixture of potassium sulfate and sodium nitrate which is equimolar in potassium and sodium to catalyze the gasification of a carbon-aceous material;
Figure 6 is a plot illustrating that unexpectedly high gasification rates are obtained by using a mixture of potassium chloride and sodium carbonate which is equimolar - 4a -
5~
1 in potassium and sodium to cataly~e the gasi~ication of a 2 carbonaceous material;
3 Figure 7 is a plot illustrating that unexpectedly 4 high gasification rates are obtained by using a mixture of po~
tassium chloride and sodium sulfate which is equimolar in po-
1 in potassium and sodium to cataly~e the gasi~ication of a 2 carbonaceous material;
3 Figure 7 is a plot illustrating that unexpectedly 4 high gasification rates are obtained by using a mixture of po~
tassium chloride and sodium sulfate which is equimolar in po-
6 tassium and sodium to catalyze the gasification of a carbonace-
7 ous material;
8 Figure 8 is a plo~ illustrating that unexpectedly
9 high gasification rates are obtained by using a mixture of po-tassi~m and lithium to catalyze the gasification of a carbonace-ll ous material;
12 Figure 9 is a plot illustrating that the addition of 13 small amounts of various sodium salts will activate relatively 14 nonca~alytic potassium sulfate thereby rapidly increasing the gasification ra~e o~ a carbonaceous material; and 16 Figure 10 is a plot illustrating that the catalytic 17 gasification acitiv~y of relatively noncatalytic potassium chlo-18 ride can be substantially increased by adding sodium carbonate 19 in an amount sufficient to yield a sodium-to-potassium mole ratio of 1.0 or greater.
22 The process depicted in Figure 1 is one for the gasi-23 fication of bituminous coal, subbituminous coal, lignite, organic 24 waste materials or similar carbonaceous solids in the presence of added sodium and potassium compounds. It will be understood 26 that the in~ention is not restricted to this particular gasifi-27 cation process and instead may be employed in any of a wide var-28 iety of fixed bed, moving bed and fluidi~ed bed gasification 29 o~erations in whick alkali metal compounds are used to promote the reaction of st~am, hydrogen, carbon dioxide, or a similar 31 gasification agent with carbonaceous feed materials and a char, 32 coke or other solid product containing alkali metal residues is 33 recovered. Many such operations have been described in the 34 technical litera~ure and will be familiar to those skilled in 35 the art.
36 In the process shown, a solid carbonaceous feed 1 material such as bituminous coal~ subbituminous coal, lignite 2 or the like, which has been crushed and screened to a parti-3 cle size of about 8 mesh or smaller on the U.S. Sieve Series 4 Scale is fed into the system through line 10 from a coal pre^
paration plant or storage facility which is not shown in the 6 drawing. The solids introduced through line 10 are fed into 7 a hopper or similar vessel 12 from which they are passed 8 through line 13 into a feed preparation zone 14. The feed 9 preparation zone shown includes a screw conveyor or similar device, not shown in the drawing, which is powered by a motor 11 16, a series of spray nozzles or the like 17 for the spraying 12 of a solution of soluble alkali metal compounds introduced 13 through line 18 onto the solids as they are moved through the 14 preparation zone by the conveyor, and nozzles or the like 19 for the introduction o steam from line 20 into the prepara-16 tion zone to heat the solids and drive off moisture. The al-17 kali metal solution fed through line 18 is prepared by intro-18 ducing soluble sodium and potassium salts or other sodium and 19 potassium compounds into mixing vessel 21 as indicated by lines 22 and 23, respectively and dissolving these in water 21 or other suitable solvent solution admitted through line 24.
22 Alkali metal solution recycled from the catalyst recovery 23 zone through line 25 as described hereafter may also be used.
24 Steam is withdrawn from the preparation zone 14 through line 28 and will normally be passed to a condenser or heat ex-26 changer not shown for the recovery of heat and condensate 27 which can be used as makeup water or the like.
28 The potassium compound introduced into mixing ves-29 sel 21 through line 23 will normally be an inexpensive com-pound which has a relatively poor catalytic activity as com-31 pared to that of potassium carbonate. "Relatively poor ca^
32 talytic activity as compared to that of potassium carbonate"
33 as used herein refers to a gasification rate obtained from 34 gasifying a carbonaceous ma~erial in the presence of a suffi-cient amount of potassium compound to yield an atomic ratio 36 of potassium cations-to-carbon atoms of about .03 or greater 7S~
1 that is about one-half or less ~hat of the rate obtainable 2 by gasifying the same material in the presence of an equi-3 vale~t amount of potassium carbonate. Examples of such po-4 tassium compounds include potassium chloride, potassium sul-S fa~e, and similar potassium salts of a strong acid. "Strong 6 acid" as used herein refers to an organic or inorganic acid 7 having an ioni~a~ion constant greater than about lxlO 3 at 8 25C.
9 The sodium compound introduced into mixing vessel 21 through line 22 will normally be either a sodium salt of 11 a weak acid or a sodium salt of a s~rong acid that is con-12 verted, either temporarily or permanently, in~o a weak acid13 salt of sodium when subjected to gasification conditions in 14 the presence of the potassium compound. "Weak acid" as used herein refers to an organic or inorganic acid having an ioni-16 zation constant less than about 1 x 10 3 at 25~C. Examples 17 of suitable sodium compounds that are salts of weak acids in-18 clude sodium hydroxide, sodium carbonate, sodium bicarbonate 19 sodium sul~ide, sodium oxalate, sodium acetate, and the like.
Examples of sodium salts of strong acids that may be used in 21 conjunction with potassium sulfate because they are temporar-22 ily or permanently converted to weak acid salts include sodium 23 chloride, sodium sulfate and sodium nitrate. The actual so-24 dium compound used will normally depend upon its availability,25 cost, degree of solubility and the potassium compound uti-26 lized.
27 It ~as been surprisingly found that when mixtures of28 the potassium and sodium compounds referred to above are in-29 jected into a catalytic gasification zone with a carbonaceous feed material which is subsequently gasified in the zone~ gas-31 ification rates are obtained that are much hi~her than those 32 that would normally be expected by one of ordinary skill in 33 the art. Apparently, the poorly catalytic potassium compound 34 activated by the sodium compound thereby producing a substan-tial catalytic effect on the gasification rate of the carbon-36 aceous feed material. Normally a concentration of the sodium l~V759 1 compound sufficient to yield a sodium-to-potassium mole ratio 2 of 1.0 will completely activate the potassium compound. In 3 some mixtures, however, lesser amounts of the sodium compound 4 may be used to activate the potassium compound without mNch activity loss.
6 The actual mechanism by which the sodium compound 7 activates the potassium compound in the presence of the car-8 bonaceous feed material and under gasification conditions is 9 not fully understood. It is believed, however, that certain interactions between the compounds take place which eventually 11 result in transforming the poorly catalytic strong acid salt 12 of potassium into a catalytically active weak acid salt. For 13 example, the following equations are believed to represent 14 the reactions that take place when the potasslum compound lS utilized is potassium sul~ate and the sodium compound utili-16 zed is sodium carbonate.
17 K2S4 + Na2C03 ~ Na2S04 + K2C03 (1) 18 K2 o4 Na~ ~ K2S + Na2S04 (2) ~ . I
19 As can be seen in equations (1) and (2), the anion associated with the potassium compound and the anion associated with the 21 sodium compound exchange with one another to produce ~C03 22 and Na2SO4, which is reduced in the presence of carbon, hydro-23 gen ~r carbon monoxide under gasification conditions to Na2S.
24 The Na2S then undergoes an anion exchange with the K2S04 to produce K2S and additional Na2SO4, which also is reduced to 26 Na2S. The net results of these reactions is the conversion 27 of the poorly catalytic K2SO4, a strong acid salt of potassium 28 into catalytically active K2CO3 and K2S, weak acid salts of 29 potassium. The Na2s that is formed is also catalytically ac-tive and is believed to add to the overall resultant catalytic 31 activity ~f the original combination. I~ is believed that the 32 wea~ acid salts, K2C03, K2S and Na2S, react with the acidic 33 carbonaceous solids to form an alkali metal-char "salt", 34 which is believed to be the active si~e in gasification. Thus, 5~ ' 1 in the case where the potassium compound is K2SO~ and the 2 sodium compound is Na2CO3y both the potassium and sodium ca-3 tions end up catalyzing the gasification of the carbonaceous 4 solids.
If the potassium compound is potassium sulfate and 6 the sodium compound is sodium sulfate, the following equations 7 are believed to represent the reactions that take place.
8 K2SQ4 + Na2S04 (3) 9 K2SO4 + Na2S + Na2SO4 (4) In the above-illustrated case, an anion exchange cannot take ll place between ~SO4 and Na2SO4 since the anions are identical.
12 It is theorized, however, that the strong acid salt Na2SO4 13 is reduced in the presence of carbon, carbon monoxide or hy-14 drogen under gasification conditions to the weak acid salt Na2S, which then undergoes an anion exchange with the K2S04 16 to produce K2S and Na2SO4. The Na2SO4 thus formed is also 17 reduced in the presence o~ carbon, carbon monoxide or hydro-18 gen to Na2S. The net result of these reactions is the forma-19 tion of catalytically active K2S and Na2S and therefore, like the example illustrated in equations (l) and (2~ above, both 21 the potassium and sodium cations end up catalyzing the gasi-22 fication of the carbonaceous solids.
23 It is believed that equations (5) and (6) set forth 24 below represent the mechanism by which potassium sulfate is activated by sodium chloride.
26 K2S04 + 2NaCl -~ 2KCl + Na2SO4 (5) 27 2KCl ~ Na~S -~ K2S ~ 2NaCl (6) 28 As can be seen~ the potassium and sodium compounds exchange 29 anions thereby forming CKl and Na2SO4. The Na2SO4 is then reduced under gasification conditions and in the presence of 31 carbon, hydrogen or carbon monoxide to Na2S~ which undergoes 32 an anion exchange with KCl to yield catalytically active K2S
7~
12 Figure 9 is a plot illustrating that the addition of 13 small amounts of various sodium salts will activate relatively 14 nonca~alytic potassium sulfate thereby rapidly increasing the gasification ra~e o~ a carbonaceous material; and 16 Figure 10 is a plot illustrating that the catalytic 17 gasification acitiv~y of relatively noncatalytic potassium chlo-18 ride can be substantially increased by adding sodium carbonate 19 in an amount sufficient to yield a sodium-to-potassium mole ratio of 1.0 or greater.
22 The process depicted in Figure 1 is one for the gasi-23 fication of bituminous coal, subbituminous coal, lignite, organic 24 waste materials or similar carbonaceous solids in the presence of added sodium and potassium compounds. It will be understood 26 that the in~ention is not restricted to this particular gasifi-27 cation process and instead may be employed in any of a wide var-28 iety of fixed bed, moving bed and fluidi~ed bed gasification 29 o~erations in whick alkali metal compounds are used to promote the reaction of st~am, hydrogen, carbon dioxide, or a similar 31 gasification agent with carbonaceous feed materials and a char, 32 coke or other solid product containing alkali metal residues is 33 recovered. Many such operations have been described in the 34 technical litera~ure and will be familiar to those skilled in 35 the art.
36 In the process shown, a solid carbonaceous feed 1 material such as bituminous coal~ subbituminous coal, lignite 2 or the like, which has been crushed and screened to a parti-3 cle size of about 8 mesh or smaller on the U.S. Sieve Series 4 Scale is fed into the system through line 10 from a coal pre^
paration plant or storage facility which is not shown in the 6 drawing. The solids introduced through line 10 are fed into 7 a hopper or similar vessel 12 from which they are passed 8 through line 13 into a feed preparation zone 14. The feed 9 preparation zone shown includes a screw conveyor or similar device, not shown in the drawing, which is powered by a motor 11 16, a series of spray nozzles or the like 17 for the spraying 12 of a solution of soluble alkali metal compounds introduced 13 through line 18 onto the solids as they are moved through the 14 preparation zone by the conveyor, and nozzles or the like 19 for the introduction o steam from line 20 into the prepara-16 tion zone to heat the solids and drive off moisture. The al-17 kali metal solution fed through line 18 is prepared by intro-18 ducing soluble sodium and potassium salts or other sodium and 19 potassium compounds into mixing vessel 21 as indicated by lines 22 and 23, respectively and dissolving these in water 21 or other suitable solvent solution admitted through line 24.
22 Alkali metal solution recycled from the catalyst recovery 23 zone through line 25 as described hereafter may also be used.
24 Steam is withdrawn from the preparation zone 14 through line 28 and will normally be passed to a condenser or heat ex-26 changer not shown for the recovery of heat and condensate 27 which can be used as makeup water or the like.
28 The potassium compound introduced into mixing ves-29 sel 21 through line 23 will normally be an inexpensive com-pound which has a relatively poor catalytic activity as com-31 pared to that of potassium carbonate. "Relatively poor ca^
32 talytic activity as compared to that of potassium carbonate"
33 as used herein refers to a gasification rate obtained from 34 gasifying a carbonaceous ma~erial in the presence of a suffi-cient amount of potassium compound to yield an atomic ratio 36 of potassium cations-to-carbon atoms of about .03 or greater 7S~
1 that is about one-half or less ~hat of the rate obtainable 2 by gasifying the same material in the presence of an equi-3 vale~t amount of potassium carbonate. Examples of such po-4 tassium compounds include potassium chloride, potassium sul-S fa~e, and similar potassium salts of a strong acid. "Strong 6 acid" as used herein refers to an organic or inorganic acid 7 having an ioni~a~ion constant greater than about lxlO 3 at 8 25C.
9 The sodium compound introduced into mixing vessel 21 through line 22 will normally be either a sodium salt of 11 a weak acid or a sodium salt of a s~rong acid that is con-12 verted, either temporarily or permanently, in~o a weak acid13 salt of sodium when subjected to gasification conditions in 14 the presence of the potassium compound. "Weak acid" as used herein refers to an organic or inorganic acid having an ioni-16 zation constant less than about 1 x 10 3 at 25~C. Examples 17 of suitable sodium compounds that are salts of weak acids in-18 clude sodium hydroxide, sodium carbonate, sodium bicarbonate 19 sodium sul~ide, sodium oxalate, sodium acetate, and the like.
Examples of sodium salts of strong acids that may be used in 21 conjunction with potassium sulfate because they are temporar-22 ily or permanently converted to weak acid salts include sodium 23 chloride, sodium sulfate and sodium nitrate. The actual so-24 dium compound used will normally depend upon its availability,25 cost, degree of solubility and the potassium compound uti-26 lized.
27 It ~as been surprisingly found that when mixtures of28 the potassium and sodium compounds referred to above are in-29 jected into a catalytic gasification zone with a carbonaceous feed material which is subsequently gasified in the zone~ gas-31 ification rates are obtained that are much hi~her than those 32 that would normally be expected by one of ordinary skill in 33 the art. Apparently, the poorly catalytic potassium compound 34 activated by the sodium compound thereby producing a substan-tial catalytic effect on the gasification rate of the carbon-36 aceous feed material. Normally a concentration of the sodium l~V759 1 compound sufficient to yield a sodium-to-potassium mole ratio 2 of 1.0 will completely activate the potassium compound. In 3 some mixtures, however, lesser amounts of the sodium compound 4 may be used to activate the potassium compound without mNch activity loss.
6 The actual mechanism by which the sodium compound 7 activates the potassium compound in the presence of the car-8 bonaceous feed material and under gasification conditions is 9 not fully understood. It is believed, however, that certain interactions between the compounds take place which eventually 11 result in transforming the poorly catalytic strong acid salt 12 of potassium into a catalytically active weak acid salt. For 13 example, the following equations are believed to represent 14 the reactions that take place when the potasslum compound lS utilized is potassium sul~ate and the sodium compound utili-16 zed is sodium carbonate.
17 K2S4 + Na2C03 ~ Na2S04 + K2C03 (1) 18 K2 o4 Na~ ~ K2S + Na2S04 (2) ~ . I
19 As can be seen in equations (1) and (2), the anion associated with the potassium compound and the anion associated with the 21 sodium compound exchange with one another to produce ~C03 22 and Na2SO4, which is reduced in the presence of carbon, hydro-23 gen ~r carbon monoxide under gasification conditions to Na2S.
24 The Na2S then undergoes an anion exchange with the K2S04 to produce K2S and additional Na2SO4, which also is reduced to 26 Na2S. The net results of these reactions is the conversion 27 of the poorly catalytic K2SO4, a strong acid salt of potassium 28 into catalytically active K2CO3 and K2S, weak acid salts of 29 potassium. The Na2s that is formed is also catalytically ac-tive and is believed to add to the overall resultant catalytic 31 activity ~f the original combination. I~ is believed that the 32 wea~ acid salts, K2C03, K2S and Na2S, react with the acidic 33 carbonaceous solids to form an alkali metal-char "salt", 34 which is believed to be the active si~e in gasification. Thus, 5~ ' 1 in the case where the potassium compound is K2SO~ and the 2 sodium compound is Na2CO3y both the potassium and sodium ca-3 tions end up catalyzing the gasification of the carbonaceous 4 solids.
If the potassium compound is potassium sulfate and 6 the sodium compound is sodium sulfate, the following equations 7 are believed to represent the reactions that take place.
8 K2SQ4 + Na2S04 (3) 9 K2SO4 + Na2S + Na2SO4 (4) In the above-illustrated case, an anion exchange cannot take ll place between ~SO4 and Na2SO4 since the anions are identical.
12 It is theorized, however, that the strong acid salt Na2SO4 13 is reduced in the presence of carbon, carbon monoxide or hy-14 drogen under gasification conditions to the weak acid salt Na2S, which then undergoes an anion exchange with the K2S04 16 to produce K2S and Na2SO4. The Na2SO4 thus formed is also 17 reduced in the presence o~ carbon, carbon monoxide or hydro-18 gen to Na2S. The net result of these reactions is the forma-19 tion of catalytically active K2S and Na2S and therefore, like the example illustrated in equations (l) and (2~ above, both 21 the potassium and sodium cations end up catalyzing the gasi-22 fication of the carbonaceous solids.
23 It is believed that equations (5) and (6) set forth 24 below represent the mechanism by which potassium sulfate is activated by sodium chloride.
26 K2S04 + 2NaCl -~ 2KCl + Na2SO4 (5) 27 2KCl ~ Na~S -~ K2S ~ 2NaCl (6) 28 As can be seen~ the potassium and sodium compounds exchange 29 anions thereby forming CKl and Na2SO4. The Na2SO4 is then reduced under gasification conditions and in the presence of 31 carbon, hydrogen or carbon monoxide to Na2S~ which undergoes 32 an anion exchange with KCl to yield catalytically active K2S
7~
- 10 1 and catalytically ina~tive NaCl, one of the original reac-2 tants. Thus, unlike the examples illustrated in equations 3 (1) through (4) above, only the potassium cations end up 4 ca~alyzing the gasification reactions.
As stated previously, any weak acid salt o~ sodium 6 may be used to activate the relatively noncatalytic potassium 7 compound, however, only certain strong acid sodium salts will 8 be effective for this pur~ose. In general, only strong acid 9 salts of sodium that are either temporarily or permanently converted to weak acid sodium salts under gasification condi-
As stated previously, any weak acid salt o~ sodium 6 may be used to activate the relatively noncatalytic potassium 7 compound, however, only certain strong acid sodium salts will 8 be effective for this pur~ose. In general, only strong acid 9 salts of sodium that are either temporarily or permanently converted to weak acid sodium salts under gasification condi-
11 tions and in the presence of the potassium compound to be
12 activated can be utilized. The examples illustrated by equa-
13 tions (3) through (6) above represent two cases in which re-
14 latively noncatalytic K2SO4 is activated by a strong acid sodium salt that is converted into a weak acid salt. In the 16 example illustrated by equations (3) and (4), the strong acid 17 sodium salt Na2SO4 undergoes reduction and is thereby perman-18 ently converted to the weak acid salt Na2S. In the example 19 illustrated by equations ~5) and (6), the strong acid salt NaCl is converted to the weak acid salt Na2S in a two-step 21 process. First the NaCl participates in an anion exchange 22 with the K2S04 to form the strong acid salt Na2S04 which then 23 undergoes reduction to Na2S. The Na2S, however, then ex-24 changes anions with RCl to reform the strong acid salt NaCl.
This example, therefore, represents a case where a strong acid 26 sodium salt is only temporarily converted to a weak acid salt.
27 An example of a strong acid salt or sodium which is neither 28 temporarily nor permanently con~erted to a weak acid sodium 29 sal~ under gasification conditions in the presence of K2S04 and therefore will not activate K2S04 is Na3PO4.
31 The total quanity of the sodium and potassium com-32 pounds used should normally be sufficien~ to provide a com-33 bined added alkali metal-to-carbon atomic ratio in excess of 34 about .03:1. Generally speaking, from about %5 to about 50%
by weight of sodium and potassium compounds, based on the coal 3~ or o~her ~arbonaceous feed material will be employed. From 37 about 10~/O to about 35% by weight is generally preferred.
)7~
-- 1~
1 The higher the mineral content of the feed material, the 2 more sodium and potassium compounds tha~ should normally be 3 used.
4 Referring again to Figure 1, the feed solids which are impregnated with sodium and potassium compounds in feed 6 preparation zone 14 are withdrawn through line 30 and passed 7 to a feed hopper or similar vessel 31. From here they are 8 discharged through a star wheel ~eeder or a similar device 32 9 in line 33 at an elevated pressure sufficient to permit theLr entrainment in a stream of steam, recycle product gas~ inert 11 gas or other carrier gas introduced into the system through 12 line 34. The carrier gas and entrained solids are passed 13 through line 35 into manifold 36 and fed through miltiple 14 feed lines 37 and nozzles, not shown in the drawing, into gasifier 38. In lieu of or in addition to hopper 31 and star 16 wheel feeder 32~ the feed system employed may include parallel 17 lock hoppers9 pressurized hoppers~ aerated standpipes operated 18 in series, or other apparatus for raising the i~put feed solid 19 stream to the required pressure level.
Gasifier 38 comprises a refractory-lined vessel 21 contain~g afluidized bed of carbonaceous solids extending up-22 ward within the vessel above an internal grid or similar dis-23 tribution device not shown in the drawing. The solids are 24 maintained in the fluidized state within the gasifier by means25 of a mixture of steam ant oxygen injected through bottom in-26 let line 39 and multiple nozzles 40 connected to manifold 41.27 Sufficient oxygen is added to the steam through line 42 to 28 maintain the fluidized bed at a tempe~ature within the range 29 between about 1200F and about 2000F. The gasifier pressure will normally be between about 100 psig and about 2000 psig.
31 Under these conditions, the added sodiium and potassium com-32 pounds result in the production of an unexpected and substan-33 tial catalytic effect on -the steam gasification reaction 34 thereby resulting in the production of a gas composed primar-ily of hydrogen, carbon monoxide and carbon dioxide. Other 36 reactions will also take place and some methane will normally 1 be formed depending on the gasification conditions 2 The gas leaving the fluidized bed in ~asifier 38 3 passes ~hrough ~he upper section of the gasifier, which ser-4 ve5 as a disengagement zone where particles too heavy to be entrained by the gas leaving the vessell are returned to the 6 bed. If desired, this disengagement zone may include on or 7 more cyclone separators or the like for removing relatively 8 large particles from the gas. The gas withdrawn from the 9 upper part of the gasifier through line 43 is passed to cy-clone separator or similar de~ice 44 for removal of larger 1~ fines. The overhead gas then passes through line 46 into a 12 second separator 47 where smaller particles are removed. The 13 gas from which the solids have been separated is taken over-14 head from separator 47 through line 48 and the fines are dis-charged downward through dip legs 45 and 49. These fines may 16 be returned to the gasifier or passed to the catalyst reco-17 very section of the process as discussed hereafter. After 18 entrained solids have been separated from the raw product 19 gas, the gas stream may be passed through suitable heat ex-change equipment for the recovery of heat and subsequently 21 passed downstream for further processing.
22 Char particles containing carbonaceous m~terial, 23 ash and alkali metal residues are continuously withdrawn 24 through line 50 from the bottom of the fluidized bed ;n gasi-fier 38. The particles flow downward through line 50 counter-26 current to a stream of steam or other elutriating gas intro-27 duced through line 51. Here a preliminary separation of so-28 lids based on differences in size and density takes place.
29 The lighter particles containing a relatively large amount of carbonaceous material tend to be returned to the gasifier 31 and the heavier particles having a relatively high content 32 of ash and alkali metal residues continue downward through 33 line 52 into fluidized bed withdrawal zone 53. Steam or other 34 fluidizing gas is introduced into the bottom of the withdrawal zone through line 54 to maintain the bed in the fluidized 36 state. Water may be introduced through llne 55 in order to 75~
1 cool the particles and facilitate their further processing.
2 The withdrawal rate is controlled by regulating the pressure 3 within zone 53 by means of throttle valve 56 in overhead line 4 57. The gases from line 57 may be returned to the gasifier through line 58 or vented through val~e 59. From vessel 53 6 the solid particles are passed through line 60 containing 7 valve 61 into hopper 62. The char fines recovered from the 8 raw product gas through dip legs 45 and 49 may be combined 9 with the char particles withdrawn from the gasifier by passing the fines through line 63 into hopper 62.
11 The particles in hopper 62 will contain sodium and 12 potassium residues composed of water-soluble and water-in-13 soluble sodium and potassium compounds. These particles are 14 passed from hopper 62 through line 64 into catalyst recovery unit 65. The catalyst recovery unit will normally compr~se 16 a multistage countercurrent extractio~ system in which the 17 particles containing the sodium and potassium residues are 18 countercurrently contacted with water introduced through line 19 66. An aqueous solution of sodium and potassium compounds is recovered from the unit and may be recycled through lines 67 21 and 25 to the catalyst preparation unit or mixing vessel 21.
22 Particle~ from whi~h substantially all of the soluble sodium 23 and potassium constituents have been extracted are withdrawn 24 from ~he catalyst recovery unit ~hrough line 68. These solids will normally contain su~stantial quantities of sodium and 26 potassium present in the form of sodium and potassium alumino-27 silicates and other water-insoluble compounds. These com-28 pounds are formed in part by the reaction with the ash in the 29 coal and other feed material of sodium and potassium compounds added to catalyze the gasification reaction. In general, from 31 about 15% to as much as 50% of the added alkali metal consti-32 tuents will be converted into alkali metal aluminosilicates 33 and other water-insoluble compounds. By employing a mixture 34 of inexpensive potassium and sodium compounds in accordance with the process of the invention in lieu of the more expen-36 sive potassium carbonate and other previously known catalysts, 3t7~
1 the need to recover and reuse the sodium and potassium com-2 pounds tied up as water-insoluble alkali metal residues by 3 expensive and sophisticated secondary recovery methods is 4 obviated.
In the embodiment of the invention described above, 6 the feed solids are impregnated with a solution containing a 7 mixture of sodium and potassium compounds prior to their in-8 troduction into the gasifier 38. It will be understood that 9 other methods of introducing the sodi~m and potassium com-pounds into the gasification zone may be utilized. For ex 11 ample, the compounds may be mixed in the solid state with the 12 carbonaceous feed particles and the mixture may be subse-~13 quently passed into the gasifier. In some cases it may be 14 desirable to introduce the feed solids, the sodium compound and the potassium compound through separate lines into gasi-16 fier 38. Other methods for separate introduction of the so-17 dium and potassium compounds into this system will be appa-18 rent to those skilled in the art.
19 The nature and objects of the invention are further20 illustrated by the results of laboratory gasification studies 21 which show that unexpectedly high gasification rates are ob-22 tained by utilizing certain combinations o~ sodium and potass-23 ium compounds, and lithium and potassium compo~mds as catal-24 ysts. In all of the tests, about 2 grams of Illinois No. 625 coal crushed to between about 30 and about 100 mesh on the 26 U.S. Sieve Series Scale was mixed with varying amounts if 27 finely divided alkali metal compounds and combinations of 28 such compounds. The resultant mixture was then dampened with 29 about one milliliter of distilled water and pyrolyzed for about 15 minutes at about 1400F in a retort under an inert 31 nitrogen atmosphere. A portion of the resultant char, con-32 taining between about 0.2 and about 0.5 grams of carbon, was 33 then steam-gasified at a temperature of about 1300F and es-34 sentially atmospheric pressure in a laboratory bench scale gasification unit. The gasification rate obtained for each 36 char sample was determined. The char not gasified was ashed
This example, therefore, represents a case where a strong acid 26 sodium salt is only temporarily converted to a weak acid salt.
27 An example of a strong acid salt or sodium which is neither 28 temporarily nor permanently con~erted to a weak acid sodium 29 sal~ under gasification conditions in the presence of K2S04 and therefore will not activate K2S04 is Na3PO4.
31 The total quanity of the sodium and potassium com-32 pounds used should normally be sufficien~ to provide a com-33 bined added alkali metal-to-carbon atomic ratio in excess of 34 about .03:1. Generally speaking, from about %5 to about 50%
by weight of sodium and potassium compounds, based on the coal 3~ or o~her ~arbonaceous feed material will be employed. From 37 about 10~/O to about 35% by weight is generally preferred.
)7~
-- 1~
1 The higher the mineral content of the feed material, the 2 more sodium and potassium compounds tha~ should normally be 3 used.
4 Referring again to Figure 1, the feed solids which are impregnated with sodium and potassium compounds in feed 6 preparation zone 14 are withdrawn through line 30 and passed 7 to a feed hopper or similar vessel 31. From here they are 8 discharged through a star wheel ~eeder or a similar device 32 9 in line 33 at an elevated pressure sufficient to permit theLr entrainment in a stream of steam, recycle product gas~ inert 11 gas or other carrier gas introduced into the system through 12 line 34. The carrier gas and entrained solids are passed 13 through line 35 into manifold 36 and fed through miltiple 14 feed lines 37 and nozzles, not shown in the drawing, into gasifier 38. In lieu of or in addition to hopper 31 and star 16 wheel feeder 32~ the feed system employed may include parallel 17 lock hoppers9 pressurized hoppers~ aerated standpipes operated 18 in series, or other apparatus for raising the i~put feed solid 19 stream to the required pressure level.
Gasifier 38 comprises a refractory-lined vessel 21 contain~g afluidized bed of carbonaceous solids extending up-22 ward within the vessel above an internal grid or similar dis-23 tribution device not shown in the drawing. The solids are 24 maintained in the fluidized state within the gasifier by means25 of a mixture of steam ant oxygen injected through bottom in-26 let line 39 and multiple nozzles 40 connected to manifold 41.27 Sufficient oxygen is added to the steam through line 42 to 28 maintain the fluidized bed at a tempe~ature within the range 29 between about 1200F and about 2000F. The gasifier pressure will normally be between about 100 psig and about 2000 psig.
31 Under these conditions, the added sodiium and potassium com-32 pounds result in the production of an unexpected and substan-33 tial catalytic effect on -the steam gasification reaction 34 thereby resulting in the production of a gas composed primar-ily of hydrogen, carbon monoxide and carbon dioxide. Other 36 reactions will also take place and some methane will normally 1 be formed depending on the gasification conditions 2 The gas leaving the fluidized bed in ~asifier 38 3 passes ~hrough ~he upper section of the gasifier, which ser-4 ve5 as a disengagement zone where particles too heavy to be entrained by the gas leaving the vessell are returned to the 6 bed. If desired, this disengagement zone may include on or 7 more cyclone separators or the like for removing relatively 8 large particles from the gas. The gas withdrawn from the 9 upper part of the gasifier through line 43 is passed to cy-clone separator or similar de~ice 44 for removal of larger 1~ fines. The overhead gas then passes through line 46 into a 12 second separator 47 where smaller particles are removed. The 13 gas from which the solids have been separated is taken over-14 head from separator 47 through line 48 and the fines are dis-charged downward through dip legs 45 and 49. These fines may 16 be returned to the gasifier or passed to the catalyst reco-17 very section of the process as discussed hereafter. After 18 entrained solids have been separated from the raw product 19 gas, the gas stream may be passed through suitable heat ex-change equipment for the recovery of heat and subsequently 21 passed downstream for further processing.
22 Char particles containing carbonaceous m~terial, 23 ash and alkali metal residues are continuously withdrawn 24 through line 50 from the bottom of the fluidized bed ;n gasi-fier 38. The particles flow downward through line 50 counter-26 current to a stream of steam or other elutriating gas intro-27 duced through line 51. Here a preliminary separation of so-28 lids based on differences in size and density takes place.
29 The lighter particles containing a relatively large amount of carbonaceous material tend to be returned to the gasifier 31 and the heavier particles having a relatively high content 32 of ash and alkali metal residues continue downward through 33 line 52 into fluidized bed withdrawal zone 53. Steam or other 34 fluidizing gas is introduced into the bottom of the withdrawal zone through line 54 to maintain the bed in the fluidized 36 state. Water may be introduced through llne 55 in order to 75~
1 cool the particles and facilitate their further processing.
2 The withdrawal rate is controlled by regulating the pressure 3 within zone 53 by means of throttle valve 56 in overhead line 4 57. The gases from line 57 may be returned to the gasifier through line 58 or vented through val~e 59. From vessel 53 6 the solid particles are passed through line 60 containing 7 valve 61 into hopper 62. The char fines recovered from the 8 raw product gas through dip legs 45 and 49 may be combined 9 with the char particles withdrawn from the gasifier by passing the fines through line 63 into hopper 62.
11 The particles in hopper 62 will contain sodium and 12 potassium residues composed of water-soluble and water-in-13 soluble sodium and potassium compounds. These particles are 14 passed from hopper 62 through line 64 into catalyst recovery unit 65. The catalyst recovery unit will normally compr~se 16 a multistage countercurrent extractio~ system in which the 17 particles containing the sodium and potassium residues are 18 countercurrently contacted with water introduced through line 19 66. An aqueous solution of sodium and potassium compounds is recovered from the unit and may be recycled through lines 67 21 and 25 to the catalyst preparation unit or mixing vessel 21.
22 Particle~ from whi~h substantially all of the soluble sodium 23 and potassium constituents have been extracted are withdrawn 24 from ~he catalyst recovery unit ~hrough line 68. These solids will normally contain su~stantial quantities of sodium and 26 potassium present in the form of sodium and potassium alumino-27 silicates and other water-insoluble compounds. These com-28 pounds are formed in part by the reaction with the ash in the 29 coal and other feed material of sodium and potassium compounds added to catalyze the gasification reaction. In general, from 31 about 15% to as much as 50% of the added alkali metal consti-32 tuents will be converted into alkali metal aluminosilicates 33 and other water-insoluble compounds. By employing a mixture 34 of inexpensive potassium and sodium compounds in accordance with the process of the invention in lieu of the more expen-36 sive potassium carbonate and other previously known catalysts, 3t7~
1 the need to recover and reuse the sodium and potassium com-2 pounds tied up as water-insoluble alkali metal residues by 3 expensive and sophisticated secondary recovery methods is 4 obviated.
In the embodiment of the invention described above, 6 the feed solids are impregnated with a solution containing a 7 mixture of sodium and potassium compounds prior to their in-8 troduction into the gasifier 38. It will be understood that 9 other methods of introducing the sodi~m and potassium com-pounds into the gasification zone may be utilized. For ex 11 ample, the compounds may be mixed in the solid state with the 12 carbonaceous feed particles and the mixture may be subse-~13 quently passed into the gasifier. In some cases it may be 14 desirable to introduce the feed solids, the sodium compound and the potassium compound through separate lines into gasi-16 fier 38. Other methods for separate introduction of the so-17 dium and potassium compounds into this system will be appa-18 rent to those skilled in the art.
19 The nature and objects of the invention are further20 illustrated by the results of laboratory gasification studies 21 which show that unexpectedly high gasification rates are ob-22 tained by utilizing certain combinations o~ sodium and potass-23 ium compounds, and lithium and potassium compo~mds as catal-24 ysts. In all of the tests, about 2 grams of Illinois No. 625 coal crushed to between about 30 and about 100 mesh on the 26 U.S. Sieve Series Scale was mixed with varying amounts if 27 finely divided alkali metal compounds and combinations of 28 such compounds. The resultant mixture was then dampened with 29 about one milliliter of distilled water and pyrolyzed for about 15 minutes at about 1400F in a retort under an inert 31 nitrogen atmosphere. A portion of the resultant char, con-32 taining between about 0.2 and about 0.5 grams of carbon, was 33 then steam-gasified at a temperature of about 1300F and es-34 sentially atmospheric pressure in a laboratory bench scale gasification unit. The gasification rate obtained for each 36 char sample was determined. The char not gasified was ashed
- 15 -1 to determine the amount of carbon present and the alkali 2 metal cation-to-carbon atomic ratio was then calculated. The 3 results of these tes~s are set forth in Figures 2 through 10.
4 In all cases the gasification rate is expressed as the conver-sion weighted average rate in percent of carbon present per 6 hour over the interval of 0-90% carbon conversion.
7 Figure 2 sets forth the steam gasification rate 8 data obtained from char impregnated with various concentra~
9 tions of potassium carbonate, potassium sulfate, sodium car-bonate and a mixture of potassium sulfate and sodium carbon-11 ate. It can be seen in Figure 2 that the relatively expensive 12 potassium carbonate yielded much greater gasification rates 13 than did the less expensive potassium sulfate and sodium car-14 bonate and is therefore a much more active gasification ca-talyst than either of the latter two compounds.
4 In all cases the gasification rate is expressed as the conver-sion weighted average rate in percent of carbon present per 6 hour over the interval of 0-90% carbon conversion.
7 Figure 2 sets forth the steam gasification rate 8 data obtained from char impregnated with various concentra~
9 tions of potassium carbonate, potassium sulfate, sodium car-bonate and a mixture of potassium sulfate and sodium carbon-11 ate. It can be seen in Figure 2 that the relatively expensive 12 potassium carbonate yielded much greater gasification rates 13 than did the less expensive potassium sulfate and sodium car-14 bonate and is therefore a much more active gasification ca-talyst than either of the latter two compounds.
16 The dashed line in Figure2 represents the gasifica-
17 tion rates that one of ordinary skill in the art wou1d expect
18 ~o ~bserve if a mixture of sodium carbonate and potassium sul-
19 fate which is equimolar in sodium and potassium (moles Na/K=
1.0) was used as a catalyst. The expected gasification rate 21 for such a mixture that yields an atomic ratio of .066 alkali 22 metal cations per carbon atom was calculated as follows. The 23 observed rate of about 51% carbon per hour for a concentration 24 of sodium carbonate that yielded an atomic ratio o .066 so-dium cations per carbon atom was added to the observed rate 26 of about 9.0% carbon per hour for a concentration of potassium27 sulfate that yielded an atomic ratio of .066 potassium cations 28 per carbon atom and the resultant value of 6~% carbon per hour 29 was divided by 2 to yield the expected rate of 30% carbon per hour. This rate was then plotted against the atomic ratio of 31 .066 cations per car~on atom where .033 of the cations were 32 potassium cations and the other .033 were sodium cations. The 33 expected gasification rates for mixtures of sodium carbonate 34 ~ and potassium sulfa~e that are equimolar in sodium and potas-sium but yield alkali metal cation-to-carbon atomic ratios of 36 other values were calculated in a manner similar to that des-37 cribed above.
5~
1 As can be seen in Figure 2, the actual gasification 2 rates observed using mixtures of potassium sulfate and sodium 3 carbonate were much greater than the expected rates represen 4 ted by the dashed line an~ approached the rates obtainable with equivalent concentrations of potassium carbonate. The 6 actual observed gasification rate for an atomic ratio of .066 7 potassium and sodium cations per carbon atom was 83% carbon 8 per hour as compared to the 30% carbon p~-; hour that was ex-9 pected. Furthermore, the actual observed rate of 83% carbon per hour for the mixture at an atomic ratio of .066 potassium 11 and sodium cations per carbon atom is much greater than the 12 9.0% per hour obtained for potassium sulfate at an atomic 13 ratio of .066 potassium cations per carbon atom and is also 14 greater than the 51% carbon per hour obtained for sodium car-bonate at an atomic ratio of .066 sodium cations per carbon ï~ ~tom. In view of the foregoing, the gasification rates obtain-17 ed using mixtures of potassium sulfate and sodium carbonate as 18 a catalyst are surprising and unexpected.
lg The data s~t forth in Figures 3 through 5 indicate that surprisingly high gasification rates can also be obtained 21 by utilizing potassium sulfate in combination with various 22 sodium salts other than sodium carbonate. Figure 3 shows 23 ~hat unexpectedly high rates are obtained using mixtures o 24 potassium sulfate and sodium sulfate that are equimolar in potassium and sodium as a gasification catalyst. Figure 5 26 makes a similar showing for mixtures of ~ tassium sulfate 27 and sodium nitrate that are equimolar in potassium and sodi~m.
28 In both Figures the rates one of ordinary skill in the art 29 would expect are represented by dashed lines and were c~lcu-lated as discussed previously in reference to Figure 2. Fi-31 gure 4 shows that surprisingly high gasification rates are 32 obtained using mixtures of potassium sulfate and sodium chlor-33 ide that are equimolar in potassium and sodium. In Figure 4 34 the gasification rates for potassium sulfate alone and for sodium chloride alone fall on the same line. This line, 36 therefore, also represents the gasification rates that would 75~
1 be e~pected for mixtures of the two salts that are equimolar 2 in potassium and sodium.
3 Figures 6 and 7 illustrate that catalysts comprised 4 of a mixture of potassium chloride and one of various inex-pensive sodium salts will yîeld higher than expected gasifi-6 cation rates when the catalyst concentration is above a cer-7 tain value. Figu~e 6 shows that surprisingly high rates are 8 obtained when a mixture of potassium chloride and sodium car-9 bonate that is e~uimolar in potassium and sodium is employed in sufficient concentrations to yield an atomic ratio greater 11 than about .08 alkali metal cations per carbon atom. Figure 7 12 makes a similar showing for a mixture of potassium chloride 13 and sodium sulfate that is equimolar in potassium and sodium.
14 As in previous Figures, the expected gasification rates are represented by a dashed line and were calculated as described 16 in reference to Figure 2.
17 Figure 8 illustrates that a catalyst comprised o 18 a mixture of a relatively noncatalytic potassium salt and a 19 lithium salt -- in lieu of a sodium salt -- will also ~ield unexpectedly high gasification rates. It can be seen in 21 Figure 8 that surprisingly high gasification rates are obtain-22 ed when char is gasified in the presence of a mixture of po-23 tassium sulfate and lithium sulfate tha~ is equimolar in po-24 tassium and lithium. As in prior Figures, the dashed line represents the gasification rate tha~ would be expected by one 26 of ordinary skill in the art.
27 Figure 9 shows the gasification rates obtained when 28 Illinois No. 6 coal char was gasified in the presence of ca-29 talysts comprised of mixtures of potassium sulfate and vary-ing amounts of either sodium carbonate, sodium sulfate or 31 sodium chloride. In all cases the potassium sulfate was pre-32 sent in quan~ities such that the atomic ratio of potassium 33 cations-to-carbon atoms ranged between about .051 and about 34 .057. The amount of the par~icular sodium sal~ present was varied over a range such that the ratio of sodium cations to 36 potassium cations present per carbon atoms ranged from .25 to s~
1 1.O. This ratio (Na/K) is indicated next to each point plQ~-2 ted in ~he Figure. For comparison purposes, the ra~e of 8%
3 carbon per hour obtained for the use of potassium sulfate 4 alone (Na/K = 0) is also shown in the Figure. It can be seen from the plotted data that for each combination of potassium 6 sulfate and one of the three sodium salts, the presence of 7 only a small amount of the sodium salt (Na/K - .25) resulted 8 in a sharp increase in the gasification rate over tha~ for a 9 zero concentration of the sodium salt. The gasification rate continued to increase as the amount o ~he sodium sal~ in 11 the mixture was increased up to a sodium-to-potassium atomic 12 ratio of 1Ø
13 Figure 10 is a plot similar to that of Figure 9 ex-14 cept that the gasification rates plotted are for a catalyst comprnsed of a mixture of potassium chloride and varying a-16 mounts of sodium carbonate. For comparison purposes, the 17 rate of 18% carbon per hour for the use of potassium chloride 18 alone (Na/K - 0) is also shown in the Figure. As can be seen 19 in the Figure, small amounts of the sodium carbonate (Na/K =
.26 to .49) do not substantially increase the gasification 21 rate. It is only when the amount of sodium carbonate in the 22 mixture is sufficient to provide a sodium-to-potassium atomic 23 ratio of 1.0 or greater that ~he gasification rate rises ra-24 pidly. In view of the data set forth in Figures 9 and 10, it can be concluded that small amounts of certain sodium compounds26 will catalytically activate porrly catalytic potassium sul~ate;
27 whereas greater amounts are necessary to activate poorly catal-28 ytic potassium chloride.
29 It will be appar~nt from the foregoing that the in-vention provides a process for gasifying a carbonaceous ma-31 terial which makes it possible to employ mixtures of inexpen-32 sive alkali metal salts as catalysts and at the same time at-33 tain gasification rates nearly as high as those obtainab]e by 34 the use of expensive po~assium carbonate. As a result, the overall cost of the product gas may be substantially reduced.
1.0) was used as a catalyst. The expected gasification rate 21 for such a mixture that yields an atomic ratio of .066 alkali 22 metal cations per carbon atom was calculated as follows. The 23 observed rate of about 51% carbon per hour for a concentration 24 of sodium carbonate that yielded an atomic ratio o .066 so-dium cations per carbon atom was added to the observed rate 26 of about 9.0% carbon per hour for a concentration of potassium27 sulfate that yielded an atomic ratio of .066 potassium cations 28 per carbon atom and the resultant value of 6~% carbon per hour 29 was divided by 2 to yield the expected rate of 30% carbon per hour. This rate was then plotted against the atomic ratio of 31 .066 cations per car~on atom where .033 of the cations were 32 potassium cations and the other .033 were sodium cations. The 33 expected gasification rates for mixtures of sodium carbonate 34 ~ and potassium sulfa~e that are equimolar in sodium and potas-sium but yield alkali metal cation-to-carbon atomic ratios of 36 other values were calculated in a manner similar to that des-37 cribed above.
5~
1 As can be seen in Figure 2, the actual gasification 2 rates observed using mixtures of potassium sulfate and sodium 3 carbonate were much greater than the expected rates represen 4 ted by the dashed line an~ approached the rates obtainable with equivalent concentrations of potassium carbonate. The 6 actual observed gasification rate for an atomic ratio of .066 7 potassium and sodium cations per carbon atom was 83% carbon 8 per hour as compared to the 30% carbon p~-; hour that was ex-9 pected. Furthermore, the actual observed rate of 83% carbon per hour for the mixture at an atomic ratio of .066 potassium 11 and sodium cations per carbon atom is much greater than the 12 9.0% per hour obtained for potassium sulfate at an atomic 13 ratio of .066 potassium cations per carbon atom and is also 14 greater than the 51% carbon per hour obtained for sodium car-bonate at an atomic ratio of .066 sodium cations per carbon ï~ ~tom. In view of the foregoing, the gasification rates obtain-17 ed using mixtures of potassium sulfate and sodium carbonate as 18 a catalyst are surprising and unexpected.
lg The data s~t forth in Figures 3 through 5 indicate that surprisingly high gasification rates can also be obtained 21 by utilizing potassium sulfate in combination with various 22 sodium salts other than sodium carbonate. Figure 3 shows 23 ~hat unexpectedly high rates are obtained using mixtures o 24 potassium sulfate and sodium sulfate that are equimolar in potassium and sodium as a gasification catalyst. Figure 5 26 makes a similar showing for mixtures of ~ tassium sulfate 27 and sodium nitrate that are equimolar in potassium and sodi~m.
28 In both Figures the rates one of ordinary skill in the art 29 would expect are represented by dashed lines and were c~lcu-lated as discussed previously in reference to Figure 2. Fi-31 gure 4 shows that surprisingly high gasification rates are 32 obtained using mixtures of potassium sulfate and sodium chlor-33 ide that are equimolar in potassium and sodium. In Figure 4 34 the gasification rates for potassium sulfate alone and for sodium chloride alone fall on the same line. This line, 36 therefore, also represents the gasification rates that would 75~
1 be e~pected for mixtures of the two salts that are equimolar 2 in potassium and sodium.
3 Figures 6 and 7 illustrate that catalysts comprised 4 of a mixture of potassium chloride and one of various inex-pensive sodium salts will yîeld higher than expected gasifi-6 cation rates when the catalyst concentration is above a cer-7 tain value. Figu~e 6 shows that surprisingly high rates are 8 obtained when a mixture of potassium chloride and sodium car-9 bonate that is e~uimolar in potassium and sodium is employed in sufficient concentrations to yield an atomic ratio greater 11 than about .08 alkali metal cations per carbon atom. Figure 7 12 makes a similar showing for a mixture of potassium chloride 13 and sodium sulfate that is equimolar in potassium and sodium.
14 As in previous Figures, the expected gasification rates are represented by a dashed line and were calculated as described 16 in reference to Figure 2.
17 Figure 8 illustrates that a catalyst comprised o 18 a mixture of a relatively noncatalytic potassium salt and a 19 lithium salt -- in lieu of a sodium salt -- will also ~ield unexpectedly high gasification rates. It can be seen in 21 Figure 8 that surprisingly high gasification rates are obtain-22 ed when char is gasified in the presence of a mixture of po-23 tassium sulfate and lithium sulfate tha~ is equimolar in po-24 tassium and lithium. As in prior Figures, the dashed line represents the gasification rate tha~ would be expected by one 26 of ordinary skill in the art.
27 Figure 9 shows the gasification rates obtained when 28 Illinois No. 6 coal char was gasified in the presence of ca-29 talysts comprised of mixtures of potassium sulfate and vary-ing amounts of either sodium carbonate, sodium sulfate or 31 sodium chloride. In all cases the potassium sulfate was pre-32 sent in quan~ities such that the atomic ratio of potassium 33 cations-to-carbon atoms ranged between about .051 and about 34 .057. The amount of the par~icular sodium sal~ present was varied over a range such that the ratio of sodium cations to 36 potassium cations present per carbon atoms ranged from .25 to s~
1 1.O. This ratio (Na/K) is indicated next to each point plQ~-2 ted in ~he Figure. For comparison purposes, the ra~e of 8%
3 carbon per hour obtained for the use of potassium sulfate 4 alone (Na/K = 0) is also shown in the Figure. It can be seen from the plotted data that for each combination of potassium 6 sulfate and one of the three sodium salts, the presence of 7 only a small amount of the sodium salt (Na/K - .25) resulted 8 in a sharp increase in the gasification rate over tha~ for a 9 zero concentration of the sodium salt. The gasification rate continued to increase as the amount o ~he sodium sal~ in 11 the mixture was increased up to a sodium-to-potassium atomic 12 ratio of 1Ø
13 Figure 10 is a plot similar to that of Figure 9 ex-14 cept that the gasification rates plotted are for a catalyst comprnsed of a mixture of potassium chloride and varying a-16 mounts of sodium carbonate. For comparison purposes, the 17 rate of 18% carbon per hour for the use of potassium chloride 18 alone (Na/K - 0) is also shown in the Figure. As can be seen 19 in the Figure, small amounts of the sodium carbonate (Na/K =
.26 to .49) do not substantially increase the gasification 21 rate. It is only when the amount of sodium carbonate in the 22 mixture is sufficient to provide a sodium-to-potassium atomic 23 ratio of 1.0 or greater that ~he gasification rate rises ra-24 pidly. In view of the data set forth in Figures 9 and 10, it can be concluded that small amounts of certain sodium compounds26 will catalytically activate porrly catalytic potassium sul~ate;
27 whereas greater amounts are necessary to activate poorly catal-28 ytic potassium chloride.
29 It will be appar~nt from the foregoing that the in-vention provides a process for gasifying a carbonaceous ma-31 terial which makes it possible to employ mixtures of inexpen-32 sive alkali metal salts as catalysts and at the same time at-33 tain gasification rates nearly as high as those obtainab]e by 34 the use of expensive po~assium carbonate. As a result, the overall cost of the product gas may be substantially reduced.
Claims (11)
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for the catalytic gasification of a carbonaceous feed mater-ial characterized by the following steps in combination:
(a) introducing said carbonaceous feed material into a reaction zone;
(b) introducing a potassium salt of an organic or inorganic acid having an ionization constant greater than 1 x 10-3 into said reaction zone;
(c) introducing into said reaction zone in a sufficient quantity to activate said potassium salt a sodium or lithium compound which is either a weak acid salt of sodium or lithium or a strong acid salt of sodium or lithium that is converted into a weak acid sodium or lithium salt in said reaction zone; and (d) gasifying said carbonaceous material in said reaction zone.
(a) introducing said carbonaceous feed material into a reaction zone;
(b) introducing a potassium salt of an organic or inorganic acid having an ionization constant greater than 1 x 10-3 into said reaction zone;
(c) introducing into said reaction zone in a sufficient quantity to activate said potassium salt a sodium or lithium compound which is either a weak acid salt of sodium or lithium or a strong acid salt of sodium or lithium that is converted into a weak acid sodium or lithium salt in said reaction zone; and (d) gasifying said carbonaceous material in said reaction zone.
2. A process according to claim 1 wherein said potassium salt is select-ed from the group consisting of potassium sulfate, potassium chloride, and mixtures thereof.
3. A process according to claim 2 wherein said potassium salt is mixed with a sodium compound selected from the group consisting of sodium carbonate, sodium bicarbonate, sodium sulfate, sodium sulfide, sodium hydroxide, sodium nitrate and mixtures thereof.
4. A process according to claim 1 wherein the potassium salt is potassium sulphate and the sodium or lithium compound is selected from the group con-sisting of sodium sulfate, sodium carbonate, sodium chloride, sodium nitrate and lithium sulfate.
5. A process according to claim 4 wherein the potassium salt is potassium chloride and the sodium or lithium compounds are present in concentrations sufficient to yield a sodium or lithium to potassium atomic ratio of at least 1Ø
6. A process according to claims 1, 2 or 3 wherein said carbonaceous feed material comprises coal.
7. A process according to claims 1, 2 or 3 wherein said carbonaceous feed material is impregnated with an aqeous solution of said potassium salt and said sodium or lithium compound prior to the introduction of said carbonaceous feed material into said reaction zone.
8. A process for the catalytic gasification of coal which comprises con-tacting said coal with a catalyst under gasification conditions, said catalyst comprising a mixture of potassium salt selected from the group consisting of potassium sulfate, potassium chloride and mixtures thereof and a sodium com-pound selected from the group consisting of sodium carbonate, sodium chloride, sodium nitrate, sodium sulfate, sodium sulfide, sodium bicarbonate, sodium hydroxide and mixtures thereof, said sodium compound being present in a quantity sufficient to yield a sodium-to-potassium atomic ratio of at least about 0.25.
9. A process according to claims 1 or 3 wherein said gasification is carried out in the presence of steam and said carbonaceous feed material com-prises coal.
10. A process according to claims 1 or 3 wherein said gasification is carried out in the presence of hydrogen and said carbonaceous feed material comprises coal.
11. A process for the catalytic gasification of coal which comprises:
(a) introducing said coal into a reaction zone;
(b) introducing potassium chloride into said reaction zone;
(c) introducing sodium carbonate or sodium sulfate into said reaction zone in a sufficient quantity to yield a sodium-to-potassium atomic ratio of at least about 1.0; and (d) gasifying said coal in said reaction zone thereby obtaining a gasification rate that is greater than the weighted average of the separate rates obtained by gasifying said coal in the presence of said potassium chloride only and in the presence of said sodium carbonate or sodium sulfate only, said weighted average based upon the concentration of said potassium chloride and said sodium carbonate or sodium sulfate expressed respectively in potassium-to-carbon and sodium-to-carbon atomic ratios.
(a) introducing said coal into a reaction zone;
(b) introducing potassium chloride into said reaction zone;
(c) introducing sodium carbonate or sodium sulfate into said reaction zone in a sufficient quantity to yield a sodium-to-potassium atomic ratio of at least about 1.0; and (d) gasifying said coal in said reaction zone thereby obtaining a gasification rate that is greater than the weighted average of the separate rates obtained by gasifying said coal in the presence of said potassium chloride only and in the presence of said sodium carbonate or sodium sulfate only, said weighted average based upon the concentration of said potassium chloride and said sodium carbonate or sodium sulfate expressed respectively in potassium-to-carbon and sodium-to-carbon atomic ratios.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US92466478A | 1978-07-14 | 1978-07-14 | |
| US924,664 | 1978-07-17 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1140759A true CA1140759A (en) | 1983-02-08 |
Family
ID=25450509
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000331739A Expired CA1140759A (en) | 1978-07-14 | 1979-07-13 | Catalytic coal gasification process |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1140759A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5611963A (en) * | 1993-04-08 | 1997-03-18 | Shell Oil Company | Method of reducing halides in synthesis gas |
| CN114042464A (en) * | 2021-11-03 | 2022-02-15 | 新奥科技发展有限公司 | Salt-containing wastewater catalyst and method for catalyzing coal gasification reaction by using same |
-
1979
- 1979-07-13 CA CA000331739A patent/CA1140759A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5611963A (en) * | 1993-04-08 | 1997-03-18 | Shell Oil Company | Method of reducing halides in synthesis gas |
| CN114042464A (en) * | 2021-11-03 | 2022-02-15 | 新奥科技发展有限公司 | Salt-containing wastewater catalyst and method for catalyzing coal gasification reaction by using same |
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