GB1595612A - Recovery of alkali metal compounds for reuse in a catalytic coal conversion process - Google Patents

Description

(54) RECOVERY OF ALKALI METAL COMPOUNDS FOR REUSE IN A CATALYTIC COAL CONVERSION PROCESS (71) We, EXXON RESEARCH AND ENGINEERING COMPANY, a Corporation duly organised and existing under the laws of the State of Delaware, United States of America, of Linden, New Jersey, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to the conversion of coal and similar carbonaceous solids in the presence of alkali metal-containing catalysts and is particularly concerned with the recovery of alkali metal constituents from spent solids produced during coal gasification and similar operations and their reuse as constituents of the alkali metalcontaining catalysts.

Potassium carbonate, cesium carbonate and other alkali metal compounds have been recognized as useful catalysts for the gasification of coal and similar carbonaceous solids. The use of such compounds in coal liquefaction, coal carbonization, coal combustion and related processes has also been proposed. To secure the higher reaction rates made possible by the presence of the alkali metal compounds it has been suggested that bituminous coal, subbituminous coal, lignite, petroleum coke, oil shale, organic wastes and similar carbonaceous materials be mixed or impregnated with potassium, cesium, sodium or lithium compounds, alone or in combination with other metallic constituents, before such materials are reacted with steam, hydrogen, oxygen or other agents at elevated temperatures to produce gaseous and/or liquid effluents.

Studies have shown that a wide variety of different alkali metal compositions can be used for this purpose, including both organic and inorganic salts, oxides and hydroxides.

In general the above-described studies indicate that cesium compounds are the most effective gasification catalysts followed by potassium, sodium and lithium compounds, in that order. Because of the relatively high cost of cesium compounds and the low effectiveness of lithium compounds, most of the experimental work in this area that has been carried out in the past has been directed toward the use of compounds of potassium and sodium. This work has shown that the potassium compounds are substantially more effective than the corresponding sodium compounds.

Attention has therefore been focused on the use of potassium carbonate.

Coal gasification processes and similar operations carried out in the presence of alkali metal compounds at high temperatures generally result in the formation of chars and alkali metal residues. The chars normally include unconverted carbonaceous constituents of the coal or other feed material and various inorganic constituents generally referred to as ash. It is generally advisable to withdraw a portion of the char from the reaction zone during gasification and similar operations in order to eliminate the ash and keep it from building up within the reaction zone or other vessels in the system. Elutriation methods and other techniques for separating char particles of relatively high ash content and returning particles of relatively low ash content to the reaction zone in order to improve the utilization of carbon in such processes have been suggested.

In gasification and other processes referred to above that utilize alkali metalcontaining catalysts, the cost of the alkali metal constituents is a significant factor in determining the overall cost of the process.

In order to maintain catalyst cost at reasonable levels, it is essential that the alkali metal constituents be recovered and reused. There have been proposals for the recovery of alkali metal constituents by leaching as they are withdrawn from the reaction zone with char during operations of the type referred to above. Studies indicate that these constituents are generally present in part as carbonates and other water soluble compounds which can be recovered by water washing. Experience has shown that only a portion of the potassium carbonate or other alkali metal constituents is normally recovered and that substantial quantities of makeup alkali metal compounds are therefore required.

This adds appreciably to the cost of such operations.

The present invention provides an improved process for the recovery of alkali metal constituents from particles produced during coal gasification and other conversion processes carried out in the presence of an alkali metal-containing catalyst. In accordance with the invention, a process for the conversion of a solid carbonaceous feed material in the presence of an alkali-metal containing catalyst into liquids and/or gases wherein particles containing alkali metal residues are produced, comprises: (a) mixing the particles containing alkali metal residues with calcium oxide or a solid calcium-containing compound that decomposes upon heating to form calcium oxide, to form a mixture of solids; (b) heating the resultant mixture of solids to a temperature sufficiently high to cause calcium oxide to react with water insoluble alkali metal aluminosilicates in the alkali metal residues to produce reaction products containing water insoluble calcium silicates and water soluble alkali metal aluminates; (c) contacting the reaction products with water, thereby forming an aqueous solution containing said soluble alkali metal aluminates; (d) lowering the pH of the resultant aqueous solution containing the water soluble alkali metal aluminates to cause aluminium hydroxide to precipitate, thereby forming a solution containing water soluble alkali metal constituents substantially free of aluminium; and using said alkali metal constituents from said aqueous solution formed in step (d) as at least a portion of the alkali metal constituents which comprise the alkali metal-containing catalyst. Preferably, such use is achieved by recycling the solution directly to the conversion process. If desired, however, the alkali metal constituents may first be recovered from the solution and then used in the conversion process.

The invention is based in part upon studies of the reactions that catalysts containing alkali metal constituents undergo during coal gasification and similar operations. Coal and other carbonaceous solids used in such operations normally contain mineral constituents that are converted to ash during the gasification process. Although the composition of ash varies, the principal constituents, expressed as oxides, are generally silica, alumina and ferric oxide. The alumina is usually present in the ash in the form of aluminosilicates.

Studies have indicted that at least a portion of the alkali metal compounds, such as potassium carbonate, that are used as gasification catalyst constituents react with the alumino-silicates and other ash constituents to form alkali metal residues containing water soluble alkali metal compounds such as carbonates, sulfates, sulfides, sulfites and the like and water insoluble, catalytically inactive materials such as potassium aluminosilicates and other alkali metal aluminosilicates. Unless the alkali metal constituents in these insoluble aluminosilicates can be recovered, they are lost from the process and must be replaced by makeup alkali metal compounds. The process of this invention allows recovery of these alkali metal constituents and thereby decreases the costs incurred by utilizing large amounts of makeup alkali metal compounds. As a result, the invention makes possible substantial savings in gasification and other conversion operations carried out in the presence of alkali metal-containing catalysts and permits the generation of product gases and/or liquids at significantly lower cost than would otherwise be the case.

The accompanying drawing is a schematic flow diagram of a catalytic coal gasification process in which alkali metal constituents of the catalyst are recovered and reused in the process.

The process depicted in the drawing is one for the production of methane by the gasification of bituminous coal, subbituminous coal, lignite or similar carbonaceous solids with steam at high temperatures in the presence of a carbonalkali metal catalyst prepared by impregnating the feed solids with a solution of an alkali metal compound or a mixture of such compounds and thereafter heating the impregnated material to a temperature sufficient to produce an interaction between the alkali metal and the carbon present. It will be understood that the alkali metal recovery system disclosed is not restricted to this particular gasification process and that it can be employed in conjunction with any of a variety of other conversion processes in which alkali metal compounds or carbon-alkali metal catalysts are used to promote the reaction of steam, hydrogen, oxygen or the like with carbonaceous feed materials to produce a char, coke or similar solid product containing alkali metal residues from which alkali metal compounds are recovered for reuse as the catalyst or a constituent of the catalyst. It can be employed, for example, for the recovery of alkali metal compounds from various processes for the gasification of coal, petroleum coke, lignite, organic waste materials and similar solids feed streams which produce spent carbonaceous solids at temperatures below the ash fusion point. Other conversion processes with which it may be used include operations for the carbonization of coal and similar feed solids, for the liquefaction of coal and related carbonaceous feed materials, for the retorting of oil shale and for the partial combustion of carbonaceous feed materials. Such processes have been disclosed in the literature and will be familiar to those skilled in the art.

In the process depicted in the drawing, a solid carbonaceous feed material, such as bituminous coal, sub bituminous coal or lignite, that has been crushed to a particle size of about 8 mesh our smaller on the U.S.

Sieve Series Scale is passed into line 10 from a feed preparation plant or storage facility that is not shown in the drawing. The solids introduced into line 10 are fed into a hopper or similar vessel 11 from which they are passed through line 12 into feed preparation zone 14. This zone contains a screw conveyor or similar device 15 that is powered by a motor 16, a series of spray nozzles or similar devices 17 for the spraying of alkali metal-containing solution supplied through line 18 onto the solids as they are moved through the preparation zone by the conveyor, and a similar set of nozzles or the like 19 for the introduction of steam into the preparation zone. The steam, supplied through line 20, serves to heat the impregnated solids and drive off the moisture. Steam is withdrawn from zone 14 through line 21 and passed to a condenser not shown, from which it may be recovered for use as makeup water or the like. The majority of the alkali metal-containing sblution is recycled through line 79 from the alkali metal recovery section of the process, which is described in detail hereafter. Any makeup solution required may be introduced into line 79 via line 13.

It is preferred that sufficient alkali metalcontaining solution be introduced into feed preparation zone 14 to provide from about 1 to about 50 weight percent of the alkali metal compound or mixture of such compounds on the coal or other carbonaceous solids. From about 1 to about 15 weight percent is generally adequate.

The dried impregnated solid particles prepared in zone 14 are withdrawn through line 24 and passed to a closed hopper or similar vessel 25. From here they are discharged through a star wheel feeder or equivalent device 26 in line 27 at an elevated pressure sufficient to permit their entrainment into a stream of high pressure steam, recycle product gas, inert gas or other carrier gas introduced into line 29 via line 28. The carrier gas and entrained solids are passed through line 29 into manifold 30 and fed from the manifold through feed lines 31 and nozzles, not shown in the drawing, into gasifier 32. In lieu of or in addition to hopper 25 and star wheel feeder 26, the feed system may employ parallel lock hoppers, pressurized hoppers, aerated standpipes operated in series, or other apparatus to raise the input feed solids stream to the required pressure level.

It is generally preferred to operate the gasifier 32 at a pressure between about 500 and about 2000 psig. The carrier gas and entrained solids will normally be introduced at a pressure somewhat in excess of the gasifier operatic pressure. The carrier gas may be preheated to a temperature in excess of about 300"F. but below the initial softening point of the coal or other feed material employed. Feed particles may be suspended in the carrier gas in a concentration between about 0.2 and about 5.0 pounds of solid feed material per pound of carrier gas. The optimum ratio for a particular system will depend in part upon the feed particle size and density, the molecular weight of the gas employed, the temperature of the solid feed material and input gas stream, the amount of alkali metal compound employed and other factors. In general, ratios between about 0.5 and about 4.0 pounds of solid feed material per pound of carrier gas are preferred.

Gasifier 32 comprises a refractory-lined vessel containing a fluidized bed of carbonaceous solids extending upward within the vessel above an internal grid or similar distribution device not shown in the drawing. The bed is maintained in the fluidized state by means of steam introduced through line 33, manifold 34 and peripherally spaced injection lines and nozzles 35 and by means of recycle hydrogen and carbon monoxide introduced through bottom inlet line 36. The particular injection system shown in the drawing is not critical and hence other methods for injecting the steam and recycle hydrogen and carbon monoxide may be employed. In some instances, for example, it may be preferred to introduce both the steam and recycle gases through multiple nozzles to obtain more uniform distribution of the injected fluid and reduce the possibility of channeling and related problems. The space velocity of the rising gases within the fluidized bed will normally be between about 300 and about 3000 volumes of steam and recycle hydrogen and carbon monoxide per hour per volume of fluidized solids.

The injected steam reacts with carbon in the feed material in the fluidized bed in gasifier 32 at a temperature within the range between about 800"F. and about 1600"F.

and at a pressure between about 500 and about 2000 psig. Due to the equilibrium condition existing in the bed as a result of the presence of the carbon-alkali metal catalyst and the recycle hydrogen and carbon monoxide injected near the lower end of the bed, the reaction products will normally consist essentially of methane and carbon dioxide. Competing reactions, which in the absence of the catalyst and the recycle gases would ordinarily tend to produce additional hydrogen and carbon monoxide, are suppressed. The ratio of methane to carbon dioxide in the raw product gas thus formed will preferably range from about 1 to about 1.4 moles per mole, depending upon the amount of hydrogen and oxygen in the feed coal or other carbonaceous solids. The coal employed may be considered as an oxygenated hydrocarbon for purposes of describing the reaction. Wyodak coal, for example, may be considered as having the approximate formula CHo84Oo 20 based on the ultimate analysis of moisture and ashfree coal and neglecting nitrogen and sulfur.

The reaction of this coal with steam to produce methane and carbon dioxide is as follows: 1.24 H2O(g)+1.8 CHo84Oo2o ,0.8 CO2+CH4 Under the same gasification conditions, coals of higher oxygen content will normally produce lower methane to carbon dioxide ratios and those of lower oxygen content will yield higher methane to carbon dioxide ratios.

The gas leaving the fluidized bed in gasifier 32 passes through the upper section of the gasifier, which serves as a disengagement zone where particles too heavy to be entrained by the gas leaving the vessel are returned to the bed. If desired, this disengagenent zone may include one or more cyclone separators or the like for removing relatively large particles from the gas. The gas withdrawn from the upper part of the gasifier through line 37 will normally contain methane and carbon dioxide produced by reaction of the steam with carbon, hydrogen and carbon monoxide introduced into the gasifier as recycle gas, unreacted steam, hydrogen sulfide, ammonia and other contaminants formed from the sulfur and nitrogen contained in the feed material, and entrained fines. This gas is introduced into cyclone separator or similar device 38 for removal of the larger fines. The overhead gas then passes through line 39 into a second separator 41 where smaller particles are removed. The gas from which the solids have been separated is taken overhead from separator 41 through line 42 and the fines are discharged downward through dip legs 40 and 43. These fines may be returned to the gasifier or passed to the alkali metal recovery section of the process as discussed hereafter.

After entrained solids have been separated from the raw product gas as described above, the gas stream may be passed through suitable heat exchange equipment for the recovery of heat and then processed for the removal of acid gases.

Once this has been accomplished, the remaining gas, consisting primarily of methane, hydrogen and carbon monoxide, may be cryogenically separated into a product methane stream and a recycle stream of hydrogen and carbon monoxide, which is returned to the gasifier through line 36. Conventional gas processing equipment can be used. Since a detailed description of this downstream gas processing portion of the process is not necessary for an understanding of the invention, it has been omitted.

The fluidized bed in gasifier 32 is comprised of char particles formed as the solid carbonaceous feed material undergoes gasification. The composition of the char particles will depend upon the amount of mineral matter present in the carbonaceous material fed to the gasifier, the amount of the alkali metal compound or mixture of such compounds impregnated onto the feed material, and the degree of gasification that the char particles undergo while in the fluidized bed. The lighter char particles, which will have a relatively high content of carbonaceous material, will tend to remain in the upper portion of the fluidized bed. The heavier char particles, which will contain a relatively small amount of carbonaceous material and a relatively large amount of ash and alkali metal residues will tend to migrate toward the bottom of the fluidized bed. A portion of the heavier char particles are normally withdrawn from the bottom portion of the fluidized bed in order to eliminate ash and thereby prevent it from building up within the gasifier and other vessels in the system.

Since the cost of the alkali metal constituents comprising the gasification catalyst is a significant factor in determining the overall cost of the gasification process, it is particularly important that these constituents be recovered and reused. It has been proposed to recover these alkali metal constituents as they are withdrawn from the gasifier with the char particles by leaching them out with water. Studies have indicated that these alkali metal constituents are generally present in part as carbonates, sulfates, sulfides, sulfites and other water soluble compounds that can be recovered by water washing. Experience has shown, however, that only a portion of the alkali metal carbonates or other alkali metal constituents is normally recovered and that a substantial quantity of makeup alkali metal compounds is therefore required.

The process of this invention is based in part upon studies of the reactions that catalysts containing alkali metal constituents undergo during coal gasification and similar operations. Coal and other carbonaceous solids used in such operations normally contain mineral constituents that are converted to ash during the gasification process. Although the composition of the ash varies, the principle constituents, expressed as oxides, are generally silica, alumina and ferric oxide. The alumina is usually present in the ash in the form of aluminosilicates. Studies have indicated that at least a portion of the alkali metal compounds, such as potassium carbonate, sodium carbonate and the like, that are used as gasification catalyst constituents react with the aluminosilicates and other ash constituents to form alkali metal residues containing water soluble alkali metal compounds such as carbonates, sulfates, sulfides, sulfites and the like and water insoluble, catalytically inactive materials such as potassium aluminosilicates and other alkali metal aluminosilicates.

It has been found that from about 10 to about 50 percent by weight of the potassium carbonate or other alkali metal compound employed to impregnate coal or similar feed material prior to gasification will react with the aluminosilicates in the ash during gasification to form water insoluble alkali metal aluminosilicates, which cannot normally be recovered from the ash by water washing. Preliminary studies tend to indicate that when potassium carbonate is utilized to impregnate the coal, the major constituent of the water insoluble potassium aluminosilicates produced is a synthetic kaliophilite, which has the chemical formula KAISiO4.

To improve the economics of the catalytic gasification process described above and other catalytic conversion processes where water insoluble alkali metal residues are formed, it is desirable to recover as much as possible of the alkali metal constituents from the insoluble residues and reuse them as catalyst constituents in the conversion process, thereby decreasing the amount of costly makeup alkali metal compounds needed. It has been found that a substantial amount of the alkali metal constituents in the water insoluble alkali metal residues withdrawn with the char and ash from the gasifier of the above described process or the reaction zone of other conversion processes can be recovered for reuse in the conversion process by mixing the particles withdrawn from the reaction zone with calcium oxide or a solid calcium-containing compound that decomposes upon heating to form calcium oxide, and heating the resultant mixture of solids to a temperature sufficiently high to cause calcium oxide to react with water insoluble alkali metal aluminosilicates in the alkali metal residues to produce reaction products containing water soluble alkali metal aluminates and water insoluble calcium silicates. The reaction products are contacted with water, which leaches the alkali metal aluminates and other water soluble alkali metal constituents from the solids. The pH of the resultant aqueous solution containing the water soluble alkali metal aluminates is sufficiently lowered to cause aluminum hydroxide to precipitate, thereby forming a solution containing alkali metal constituents substantially free of aluminum. These alkali metal constituents are then used in the conversion process as at least a portion of the alkali metal constituents which comprise the alkali metal-containing catalyst. Preferably, such use is achieved by recycling the solution directly to the conversion process. If desired, however, the alkali metal constituents may first be recovered from the solution and then used in the conversion process.

Referring again to the drawing, char particles containing carbonaceous material, ash and alkali metal residues are continuously withdrawn through line 44 from the bottom of the fluidized bed in gasifier 32. The particles flow downward through line 44 countercurrent to a stream of steam or other elutriating gas introduced through line 45. Here a preliminary separation of solids based on differences in size and density takes place. The lighter particles having a relatively large amount of carbonaceous material tend to be returned to the gasifier and the heavier particles having a relatively high content of ash and alkali metal residues continues downward through line 46 containing valve 55 into hopper 56. Char fines recovered from the raw product gas through dip legs 40 and 43, and line 57 may also be fed into the hopper.

The solid particles in hopper 56, which contain both water soluble and water insoluble alkali metal residues, are passed into line 58 where they are mixed with a calcium-containing compound introduced into line 58 from hopper 59 via line 60. The solid calcium-containing compound may be calcium oxide or any calcium compound that decomposes to form calcium oxide when subjected to relatively high temperatures. The calcium-containing compound may be inorganic or organic and may, for example, be calcium hydroxide, calcium acetate, calcium oxalate, calcium formate, calcium carbonate and dolomite.

The actual calcium-containing compound used will depend primarily upon its availability and cost. The amount of the calcium-containing compound required will depend in part on the amount of silicates in the particulate matter with which it is mixed. If desired, a mixture of two or more calcium-containing compounds may be used in lieu of a single compound.

The mixtures of char particles containing the alkali metal residues and the calciumcontaining compound is passed through line 61 into rotary kiln or similar heating device 62 where it is subjected to temperatures sufficiently high to cause the alkali metal aluminosilicates in the residues to react with calcium oxide, which is formed by the thermal decomposition of the calciumcontaining compound unless that compound is calcium oxide itself. The reaction converts the water insoluble alkali metal aluminosilicates into reaction products containing water insoluble calcium silicates and water soluble alkali metal aluminates. The reaction products are subsequently treated, as described whereafter, to recover alkali metal constituents that are recycled to the gasification process where they serve as at least a portion of the alkali metal constituents which comprise the alkali metal-containing catalyst.

The mixture of solids introduced into the rotary kiln will normally be subjected to a temperature ranging from about 1600"F. to about 26000 F. Preferably, the mixture is heated to the sintering temperature, which causes the surface of the particles to soften thereby increasing the tendency of the particles to agglomerate or stick together.

Sintering imparts mobility to the calcium ions present and apparently enables them to easily saturate the atomic structure of the alkali metal aluminosilicates and displace alkali metal constituents and alumina to form water insoluble calcium silicates.

Sintering may be effectively accomplished in a countercurrent rotary kiln in which the fuel is passed through the kiln in a direction opposite to that in which the mixture of solids is passed. In lieu of the rotary kiln any furnace or similar heating device may be used as long as the required temperatures are obtainable. If desirable, the temperature in the heating device may be raised above the sintering temperature to convert the mixture of solids into a liquid mass in which the desired reactions will take place more rapidly. This procedure, however, may not be advantageous since the liquid upon cooling will form a glass-like solid from which it may be difficult to water leach soluble alkali metal constituents.

An example of one reaction that is believed to take place in rotary kiln 62 is set forth below. The symbol "M" is used to represent any alkali metal cation. The actual alkali metal present will depend on the type of alkali metal compound utilized as a constituent of the alkali metalcontaining gasification catalyst.

MAlSiO4+2CaOMAlO2+Ca2SiO4 As can be seen from the above equation, an alkali metal aluminosilicate reacts with calcium oxide to produce an alkali metal aluminate and dicalcium silicate. it will be understood that the above equation repesents only one reaction that may occur in the rotary kiln. Other reactions involving more complicated aluminosilicates and other insoluble constituents of the alkali metal residues may also take place.

The sintered mixture of solids from rotary kiln 62 is cooled and passed through line 63 to ball mill or similar crushing device 64 where the solids are pulverized, ground, or otherwise crushed to a size suitable for water leaching. It is desirable to produce relatively small particles since they will provide a high surface area for more effective water leaching. The actual size is determined in part by balancing the cost of crushing with the effectiveness of the water leaching. Preferably, the particles will be crushed to a size smaller than about 60 mesh on the U.S. Sieve Series Scale.

The crushed solids are removed from ball mill 64 and passed through line 65 to water wash zone 66, which will normally comprise a multistage countercurrent extraction system in which the solids are countercurrently contacted with water introduced through line 67. The water leaches alkali metal aluminates and other water solub may subsequently be used in the manufacture of cement.

The aqueous solution containing alkali metal aluminates and other water soluble alkali metal constituents removed from water wash zone 66 via line 68 is passed through line 70 to contactor or similar vessel 71. Here the pH of the solution is lowered to a value in the range between about 10.0 and about 4.0, preferably between about 9.0 and about 5.0, by contacting it with a carbon dioxidecontaining gas. The aqueous solution is passed downward through the contacting zone in contactor 71 where it comes in contact with an upflowing gas that contains carbon dioxide. The carbon dioxidecontaining gas is injected into the bottom of the contactor through line 72. As the carbon dioxide gas rises upward through the downflowing aqueous solution, the carbon dioxide in the gas reacts with the alkali metal aluminaes in the solution to form alkali metal carbonates and water insoluble aluminium hydroxide. If the partical pressure of carbon dioxide is sufficiently high and the temperature in the contactor is low, alkali metal bicarbonates may also form.

A gas depleted in carbon dioxide is withdrawn overhead of contactor 71 through line 73 and either vented to the atmosphere, further processed for the recovery and reuse of carbon dioxide, or otherwise disposed of. Any carbon dioxidecontaining gas, including pure carbon dioxide and air, may be used. It is preferred, however, to utilize the flue gas produced from the fuel combustion taking place in rotary kiln 62. The contacting vessel utilized does not necessarily have to be of the type shown in the drawing but may be any type of vessel that allows for fairly good contacting between the carbon dioxidecontaining gas and the aqueous solution containing alkali metal aluminates. A tank in which the carbon dioxide-containing gas is bubbled through the aqueous solution may be sufficient for purposes of the invention.

The purpose of the above-described step of the alkali metal recovery process is to lower the pH of the aqueous solution containing the alkali metal aluminates so that substantially all of the aluminium is removed from the solution in the form of a water insoluble precipitate of aluminium hydroxide, thereby leaving in solution aluminium free alkali metal constituents that are subsequently recovered and used as constituents of the gasification catalyst.

Removal of aluminium from the alkali metal constituents before their use in the gasification catalyst is desirable to help avoid the possible formation of additional alkali metal aluminosilicates in the gasifier by the reaction of the aluminium with silica in the feed material and alkali metal constituents of the catalyst. It will be understood that for purposes of the invention any method of lowering pH may be used. For example, instead of contacting the aqueous effluent from water wash zone 66 with a carbon dioxide-containing gas, the effluent may be mixed with sufficient quantities of sulfuric acid, nitric acid or the like to lower the pH to the desired value.

Referring again to the drawing, the effluent from contacting vessel 71, which contains alkali metal carbonates and other water soluble alkali metal constituents, and aluminium hydroxide, is withdrawn from the bottom of the vessel through line 74 and passed to rotary filter or similar liquidssolids separation device 75 where the solid aluminium hydroxide is separated from the aqueous solution and then passed through line 76 to rotary kiln or similar heating device 77 where it is calcined at high temperatures to produce alumina, which is recovered via line 78 and may be sold as a byproduct. The sale of this material may produce an additional return from the process and thus reduce the overall cost of the product gas.

A solids-free aqueous solution containing alkali metal carbonates and other water soluble alkali metal compounds is removed from filter 75 through line 79 and recycled to feed preparation zone 14 via line 18 where the coal or similar carbonaceous feed material is impregnated with the alkali metal compounds in the solution. If the concentration of alkali metal compounds in the recycle solution is undesirably low, the solution may be concentrated by removing excess water before it is returned to the feed preparation zone. It will be understood that the exact alkali metal compound or compounds present in the recycled solution will depend on the substance used to lower the pH of the aqueous effluent from water wash zone 66. For example, if nitric acid is used in lieu of a carbon dioxide-containing gas, the recycled solution will contain alkali metal nitrates instead of carbonates.

The embodiment of the invention shown in the drawing and discussed above is one that allows for the recovery of alumina as a byproduct of the alkali metal recovery process. If recovery of alumina is undesirable for any reason, the embodiment of the invention depicted in the drawing may be simplified by eliminating water wash zone 66 and rotary kiln 81 and replacing contactor 71 with a series of stirred tanks through which water and the crushed solids from ball mill 64 are passed countercurrently to the carbon dioxide-containing gas. The slurry effluent from the series of stirred tanks is then passed to rotary filter 75 where the solids are separated from the aqueous solution, which is recycled to the feed preparation zone. The solids, which will contain, among other substances, ash, calcium silicates and aluminium hydroxide, may be used as landfill or otherwise disposed of.

It will be apparent from the foregoing that the process of the invention provides an improved alkali metal recovery system, which makes it possible to significantly increase the amount of alkali metal constituents that are recovered from alkali metal residues produced during catalytic gasification and similar high temperature catalytic conversion processes. As a result, the need for costly makeup alkali metal compounds is reduced, thereby lowering the overall cost of the conversion process.

WHAT WE CLAIM IS: 1. A process for the conversion of a solid carbonaceous feed material in the presence of an alkali metal-containing catalyst into liquids and/or gases wherein particles containing alkali metal residues are produced, which process comprises: (a) mixing said particles containing alkali metal residues with a solid calciumcontaining compound to form a mixture of solids, said calcium-containing compound being selected from calcium oxide and a compound that decomposes upon heating to yield calcium oxide; (b) heating said mixture of solids to a temperature sufficiently high to cause calcium oxide to react with alkali metal aluminosilicates in said alkali metal residues to produce reaction products containing water soluble alkali metal aluminates and water insoluble calcium silicates; (c) contacting said reaction products with water, thereby forming an aqueous solution containing said soluble alkali metal aluminates; (d) lowering the pH of said aqueous solution sufficiently to cause aluminium hydroxide to precipitate, thereby forming an aqueous solution containing water soluble alkali metal constituents substantially free of aluminium; and (e) using said alkali metal constituents from said aqueous solution formed in step (d) in said conversion process as at least a portion of the alkali metal constituents comprising said alkali metal-containing catalyst. ~~~~~~~~~~~~~~~~~~~~~~~ 2. A process according to claim 1, wherein the said conversion process comprises gasification.

3. A process according to claim 1, wherein the said conversion process comprises liquefaction.

4. A process according to any one of claims 1--3, wherein at least a portion ot said alkali metal-containing catalyst comprises potassium carbonate.

5. A process according to any one of claims 14, wherein the said calciumcontaining compound comprises calcium hydroxide.

6. A process according to any one of claims 14, wherein the said calciumcontaining compound comprises calcium carbonate.

7. A process according to any one of claims 1--6, wherein the said mixture of solids is heated to a temperature between 16000 F, and 26000 F.

8. A process according to any one of claims 1--7, including the additional step of converting said reaction products into solid particles of a predetermined size before contacting said reaction products with water.

9: A process according to any one of claims 1--8, wherein the said carbonaceous feed material comprises coal.

10. A process according to any one of claims 1--9, wherein the said aqueous solution formed in step (d) is recycled to said conversion process where said alkali metal constituents substantially free of aluminium are used as at least a portion of said alkali metal constituents comprising said alkali metal-containing catalyst.

11. A process according to any one of claims 1--10, wherein the pH of said aqueous solution containing said water soluble alkali metal aluminates is lowered by contacting said solution with a carbon dioxide-containing gas, thereby forming a water insoluble precipitate containing aluminium hydroxide and an aqueous solution containing water soluble alkali metal carbonates, and using said alkali metal carbonates as at least a portion of said alkali metal constituents comprising said alkali metal-containing catalyst.

12. A process for the conversion of solid carbonaceous feed material substantially as hereinbefore described with particular reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. where the solids are separated from the aqueous solution, which is recycled to the feed preparation zone. The solids, which will contain, among other substances, ash, calcium silicates and aluminium hydroxide, may be used as landfill or otherwise disposed of. It will be apparent from the foregoing that the process of the invention provides an improved alkali metal recovery system, which makes it possible to significantly increase the amount of alkali metal constituents that are recovered from alkali metal residues produced during catalytic gasification and similar high temperature catalytic conversion processes. As a result, the need for costly makeup alkali metal compounds is reduced, thereby lowering the overall cost of the conversion process. WHAT WE CLAIM IS:

1. A process for the conversion of a solid carbonaceous feed material in the presence of an alkali metal-containing catalyst into liquids and/or gases wherein particles containing alkali metal residues are produced, which process comprises: (a) mixing said particles containing alkali metal residues with a solid calciumcontaining compound to form a mixture of solids, said calcium-containing compound being selected from calcium oxide and a compound that decomposes upon heating to yield calcium oxide; (b) heating said mixture of solids to a temperature sufficiently high to cause calcium oxide to react with alkali metal aluminosilicates in said alkali metal residues to produce reaction products containing water soluble alkali metal aluminates and water insoluble calcium silicates; (c) contacting said reaction products with water, thereby forming an aqueous solution containing said soluble alkali metal aluminates; (d) lowering the pH of said aqueous solution sufficiently to cause aluminium hydroxide to precipitate, thereby forming an aqueous solution containing water soluble alkali metal constituents substantially free of aluminium; and (e) using said alkali metal constituents from said aqueous solution formed in step (d) in said conversion process as at least a portion of the alkali metal constituents comprising said alkali metal-containing catalyst. ~~~~~~~~~~~~~~~~~~~~~~~

2. A process according to claim 1, wherein the said conversion process comprises gasification.

3. A process according to claim 1, wherein the said conversion process comprises liquefaction.

4. A process according to any one of claims 1--3, wherein at least a portion ot said alkali metal-containing catalyst comprises potassium carbonate.

5. A process according to any one of claims 14, wherein the said calciumcontaining compound comprises calcium hydroxide.

6. A process according to any one of claims 14, wherein the said calciumcontaining compound comprises calcium carbonate.

7. A process according to any one of claims 1--6, wherein the said mixture of solids is heated to a temperature between 16000 F, and 26000 F.

8. A process according to any one of claims 1--7, including the additional step of converting said reaction products into solid particles of a predetermined size before contacting said reaction products with water.

9: A process according to any one of claims 1--8, wherein the said carbonaceous feed material comprises coal.

10. A process according to any one of claims 1--9, wherein the said aqueous solution formed in step (d) is recycled to said conversion process where said alkali metal constituents substantially free of aluminium are used as at least a portion of said alkali metal constituents comprising said alkali metal-containing catalyst.

11. A process according to any one of claims 1--10, wherein the pH of said aqueous solution containing said water soluble alkali metal aluminates is lowered by contacting said solution with a carbon dioxide-containing gas, thereby forming a water insoluble precipitate containing aluminium hydroxide and an aqueous solution containing water soluble alkali metal carbonates, and using said alkali metal carbonates as at least a portion of said alkali metal constituents comprising said alkali metal-containing catalyst.

12. A process for the conversion of solid carbonaceous feed material substantially as hereinbefore described with particular reference to the accompanying drawing.