Title of Invention	"A PROCESS FOR DEMINERALIZATION AND DESULPHURIZATION OF COAL USING SODIUM CARBONATE AND ACID SOLUTIONS"
Abstract	The present invention provides a process for demineralization and desulphurization of coal. The process of demineralization and desulphurization of coal is carried out by using aqueous sodium carbonate and acid solutions, at atmospheric pressure and at relatively low temperature. The process for demineralization and desulphurization of high sulphur sub bituminous coal using aqueous sodium carbonate solution (2-16% w/v) is less corrosive in comparison to other alkalies like sodium hydroxide, potassium hydroxide etc. used by previous workers.

Title of Invention

"A PROCESS FOR DEMINERALIZATION AND DESULPHURIZATION OF COAL USING SODIUM CARBONATE AND ACID SOLUTIONS"

Abstract

The present invention provides a process for demineralization and desulphurization of coal. The process of demineralization and desulphurization of coal is carried out by using aqueous sodium carbonate and acid solutions, at atmospheric pressure and at relatively low temperature. The process for demineralization and desulphurization of high sulphur sub bituminous coal using aqueous sodium carbonate solution (2-16% w/v) is less corrosive in comparison to other alkalies like sodium hydroxide, potassium hydroxide etc. used by previous workers.

Full Text	Field of the invention This invention relates to a process for demineralization and desulphurization of coal using sodium carbonate and acid solutions. More particularly, this invention relates to a process for beneficiation and upgradation of coal using sodium carbonate and acid solutions. Background of the invention Coal contains a number of ash forming constituents. The most predominant are Quartz, chert, sandstone etc. forms of silica, kaolinite, illite etc. clay minerals, sulphide minerals like pyrite, calcium, iron etc. sulphates, carbonates like siderite, ankerites etc. The mineral matters have detrimental effects on utilization of coal for combustion, gasification, carbonization, liquefaction, reduction etc purposes. Combustion of high sulphur coal produces sulphur dioxide which is corrosive and toxic. It leads to acid rain, which corrodes boiler and other metal structures of the surroundings. Some of the mineral matters in coal lower the fusion temperature of the ash forming constituents, resulting in loss of heat due to melting. Ash fusion leads to high maintenance cost of boiler including down time loss. Combustion of high ash coal increases the amount of generated fly ash, bottom ash and consequently intensifies the ash disposal problems. The ash leads to environmental pollution and ecological problem. Ash handling involves dirty and cumbersome operations and is also expensive. Coke produced from high ash coal is not suitable for use in extraction of metal. It lowers the productivity and increases the slag rate of the furnace used for extraction of the metal. Coal/coke containing sulphur more than a certain level is also unsuitable for metallurgical purposes. Therefore there is a growing necessity for removal of ash and sulphur from a coal prior to its utilization. Demineralization of coal may be achieved by both physical and chemical methods. The physical methods are based on the differences between the physical properties of the mineral matters and the carbonaceous part of the coal. The chemical methods are based on solubilization of the inorganic constituents or their converted forms in various solvents. The physical methods are not effective in removal of the finely dispersed minerals and those bound to the coal structure. Chemical methods are effective for removing the mineral matter, which are finely dispersed and bound to the coal structure. Demineralization and desulphurization of coal by treatment with alkali and acid solutions has been studied since long. Molten caustic leaching (MCL) process as reported in Fuel 1965, Vol. 44, p-269, Symp. on Removal of Heteroatoms from Fuel, ACS Meeting, Houston, TX, March 23-28, 1980, Proc. Resources from coal, coal wastes, and Ash workshop, Reston, VA, June 10-11, 1982, pp 66-75 etc. has proved effective in reducing significant amount of ash-forming minerals, pyritic and organic sulphur present in coal. Norton et al. in the report, Processing and Utilization of High sulphur coals-ll, Chugh YP, Caudle RD, eds., Elsevier, New York, NY, 1987, pp 213-223 reported removal of 60-90 % ash and sulphur from some bituminous coals from New Zealand using fused caustic. Markuszewski et al. in the publication, Am. Chem. Soc. Div. Fuel Chem. preprints, 1985, Vol. 30, p-41 reported removal of 80-90 % of the ash and 70-80 % of the total sulphur from several bituminous coals by treatment with molten mixtures of NaOH + KOH at 350-370 °C temperature. Many workers reported removal of both ash and sulphur from low rank coal by treating with alkali solution at a relatively low temperature and pressure. Arya et al. in the publication, Fuel 1981, Vol. 60, p-1127 reported reduction of 29 wt. % ash and 30 wt. % total sulphur from a subbituminous coal from Chile by treatment with 10 % sodium hydroxide solution at 80 °C. Demineralization and desulphurization of the coal was reported to increase with increase of reaction time, temperature, alkali concentration and decrease of particle size. Kara and Ceylan in the publication, Fuel 1988, Vol. 67, p-170 reported removal of 60 wt % total sulphur and 65 % ash from some lignite samples of Turkey by treatment with 20 % sodium hydroxide solution at 70 °C. Bolat et al. in the publication, Fuel Processing Technology 1988, Vol. 57, p-93 reported about 46 % demineralization of a high ash-low sulphur bituminous coal from Turkey by treatment with 2 % aqueous alkali followed by 10 % acid under mild condition. Mukherjee and Borthakur in the publication, Fuel, Vol. 80, Year 2001, pp. 2037-2040 reported removal of significant amount of mineral matter and sulphur by successively treating subbituminous coal from Assam, North Eastern Region, and India with aqueous sodium hydroxide solution followed by hydrochloric acid treatment. Demineralization and dsulphurization were reported to increase with alkali concentration. Reports of different investigators have indicated that the extent of ash and sulphur removal by caustic soda (sodium hydroxide) solution alone or followed by acid treatment varies from coal to coal. Sodium hydroxide employed in the process is a strong base and is highly caustic in character i.e. burns or corrodes organic tissues. Report on removal of ash and sulphur from coal using sodium carbonate, a salt of caustic soda, which is a mild base and relatively less corrosive chemical, has also been reported by several investigators. Markusewski et al. in the publication, Proc. of Symp. on coal to Achieve Energy and Environmental Goals, Sept. 1978, Vol. II, pp1039-63 reported complete removal of inorganic sulphur and 70 wt % reduction in organic sulphur by treating coal with dilute solutions of sodium carbonate. But the methods work at a considerably high temperature of around 120 to 150 °C and at pressures above the atmospheric pressure. Chuang et al. in the article, Desulphurization of coal by oxidation in alkaline solutions, published in Fuel Processing Technology, Vol. 7, 1993, pp. 43-57 reported a method which removed almost the entire inorganic sulphur and a significant amount of the organic sulphur from a high volatile bituminous coal using sodium carbonate and acid solutions. But the method involves oxidation with dissolved oxygen, which works under pressure. Objectives of the invention The objective of the present investigation is to provide an effective process for demineralization and desulphurization of high sulphur subbituminous coal using aqueous sodium carbonate solution at atmospheric pressure and at relatively low temperature. Summary of the invention Accordingly, the present invention describes the process for demineralization and desulphurization of coal using sodium carbonate and acid solutions, the said process comprising the steps of: a) pulverizing the coal to about 212um fineness, b) suspending the pulverized coal obtained in step (a) in a solution of aqueous sodium carbonate ranging from 1-16% (w/v), followed by heating, at a temperature of 50-95°C for 1-8 hours under stirring, and removing the residual materials known methods, c) washing the residual coal obtained from step (b) with deionized water and treating it with about 1-10% dilute solution of mineral acid, under reflux with stirring , for a period of 15 minutes to 16 hours, d) separating the resultant residue from the reaction mixture obtained in step (c) by known method, followed by washing with deionized water and finally drying it to recover the desired product. In an embodiment of the present invention, the concentration of aqueous sodium carbonate used is preferably in the range of 4-16 % by wt. In another embodiment of the present invention, the mineral acid used is selected from the group consisting of hydrochloric acid, nitric acid and sulfuric acid. In another embodiment of the present invention, the mineral acid used is preferably sulfuric acid and nitric acid. In yet embodiment of the present invention, the concentration of mineral acid used is about 10 % by volume In yet embodiment of the present invention, the maximum percentage of sulphur removed from coal obtained is 49% when nitric acid is used as mineral acid. In still embodiment of the present invention, the maximum percentage of ash removed from coal is 48% when nitric acid is used as mineral acid. The novelty lies in the use of aqueous Sodium Carbonate in place of Sodium Hydroxide. Sodium hydroxide is a strong base (alkali). It is highly corrosive. It burns or corrodes organic tissues (skin). Therefore, extreme precaution is required in handling of sodium hydroxide, both solid and liquid (in solution). It is highly hygroscopic and becomes liquid when placed in the atmosphere. Sodium carbonate on the other hand, is a salt of sodium hydroxide and carbonic acid, a mild acid. It dissolves in water giving alkaline solution due to hydrolysis. During hydrolysis along with hydroxyl ion, bi-carbonate and carbonic acid ions are also produced. Therefore, use of sodium carbonate is not associated with the disadvantage (corrosiveness) as found with sodium hydroxide. Detailed description of the invention The present invention provides a process for removal of ash forming constituents and sulphur from coal which consists of pulverization of a coal, suspending, the pulverized coal in a solution of sodium carbonate, heating the mixture under stirring condition for a period ranging from few minutes to several hours, followed by removing the dissolved materials by filtration, centrifugation, decantation or the like methods, washing the recovered coal with deionized water followed by removing the adhered moisture by air drying to obtain the product or optionally treating the recovered coal with dilute solution of a mineral acid like hydrochloric, nitric, sulphuric and heating the mixture for few minutes to few hours, separating the solid by filtration, centrifugation, sedimentation or the like methods, washing with deionized water followed by drying in air at ambient condition or in an air oven to recover the final product. Another feature of the present investigation is the powdered coal sample is suspended in a aqueous sodium carbonate solution containing 2-16 % sodium carbonate and maintaining coal: liquid ratio at 1:3 to 1:5, heating the resultant mixture under stirring condition at 50-90 °C for a period ranging from 15 minutes to 16 hours, followed by separation of the solid by filtration, washing with water till free from adhered CO32~, drying the same under atmospheric condition or in an air oven. Yet another feature is the aqueous sodium carbonate treated coal sample obtained as above is further suspended in a 1 to 10 % solution of an acid like hydrochloric, nitric, sulphuric followed by warming the mixture at 50-90 °C for a period ranging from few minutes to several hours, separating the coal from the liquid by adopting procedures like decantation, filtration, centrifugation, washing it with demineralized water followed by drying at air at ambient condition or in an air oven. The invention is illustrated with the following examples, which should not be construed to limit the scope of the investigation. Proximate and Ultimate analysis along with the distribution of sulphur of a few typical coal samples used in the investigation are shown in Table 1. The chemical analysis of the coal ash samples are shown in Table 2. Table 1 Proximate and Ultimate analysis and distribution of sulphur of some coal samples (Table Remove) Table 2 Chemical analysis of coal ash (Table Remove) Example-1 25 gm of a coal sample having 8.80 % ash, 4.27 % total sulphur, pulverized to -212 urn fineness was mixed with 100 ml 2 % aqueous sodium carbonate solution in a three necked round bottom flask kept over a heating mantle and fitted with a condenser and a stirrer. The mixture was heated to 95 °C and kept at the temperature for 30 minutes. The mixture was stirred during heating. The mixture was then cooled, filtered and the residue was washed with deionized water till free of alkali and dried. The ash and total sulphur of the washed coal are 7.64 and 3.94 % respectively. This indicates that the treatment has removed 13.18 % ash and 7.73 % total sulphur from the coal. Example-2 25 gm of another coal samples having 10.98 % ash, 4.31 % total sulphur was pulverized and treated with the same volume and concentration of aqueous sodium carbonate in the same manner as outlined in Example-1. The treated coal has 8.99 % ash, 4.10 % total sulphur. This indicates that the treatment has removed 18.12 % ash and 4.87 % total sulphur from the coal. Example-3 The same experiment as outlined in Example-1 was conducted with the same coal and in the same manner but the treatment time was increased from 30 minutes to 1 hour. The treated coal has 7.78 % ash, 3.84 % total sulphur. The treatment has removed 11.59 % ash and 10.07 % total sulphur from the coal. Example-4 The same experiment as outlined in Example-2 was conducted with the same coal and in the same manner but the treatment time was increased from 30 minutes to 1 hour. The treated coal has 9.11 % ash, 4.02 % total sulphur. The treatment has removed 17.03 % ash and 6.73 % total sulphur from the coal. Example-5 The same experiment as outlined in Example-1 was conducted with the same coal and in the same manner but the treatment time was increased from 1 hour to 8 hour. The treated coal has 8.17 % ash, 3.55 % total sulphur. The treatment has removed 7.16 % ash and 16.86 % total sulphur from the coal. Example-6 The same experiment as outlined in Example-2 was conducted with the same coal and in the same manner but the treatment time was increased from 1hour to 8 hour. The treated coal has 9.61 % ash, 3.71 % total sulphur. The treatment has removed 12.48 % ash and 13.92 % total sulphur from the coal. Example-7 The same experiment as outlined in Example-1 was conducted with the same coal and in the same manner but using 4 % aqueous sodium carbonate solution. The treated coal has 7.76 % ash, 3.87 % total sulphur. The treatment has removed 11.82 % ash and 9.37 % total sulphur from the coal. Example-8 The same experiment as outlined in Example-2 was conducted with the same coal and in the same manner but using 4 % aqueous sodium carbonate solution. The treated coal has 9.05 % ash, 4.04 % total sulphur. The treatment has removed 17.58 % ash and 6.26 % total sulphur from the coal. Example-9 The same experiment as outlined in Example-7 was conducted with the same coal and in the same manner but the treatment time was increased from 30 minutes to 1 hour. The treated coal has 7.84 % ash, 3.75 % total sulphur. The treatment has removed 10.91 % ash and 12.18 % total sulphur from the coal. Example-10 The same experiment as outlined in Example-8 was conducted with the same coal and in the same manner but the treatment time was increased from 30 minutes to 1 hour. The treated coal has 9.20 % ash, 3.88 % total sulphur. The treatment has removed 16.21 % ash and 9.98 % total sulphur from the coal. Example-11 The same experiment as outlined in Example-7 was conducted with the same coal and in the same manner but the treatment time was increased from 1 hour to 8 hour. The treated coal has 8.22 % ash, 3.44 % total sulphur. The treatment has removed 6.59 % ash and 19.44 % total sulphur from the coal. Example-12 The same experiment as outlined in Example-8 was conducted with the same coal and in the same manner but the treatment time was increased from 1 hour to 8 hour. The treated coal has 9.74 % ash, 3.62 % total sulphur. The treatment has removed 11.29 % ash and 16.01 % total sulphur from the coal. Example-13 The same experiment as outlined in Example-7 was conducted with the same coal and in the same manner but using 16 % aqueous sodium carbonate solution in place of 4 %. The treated coal has 7.87 % ash, 3.71 % total sulphur. The treatment has removed 10.57 % ash and 13.11 % total sulphur from the coal. Example-14 The same experiment as outlined in Example-8 was conducted with the same coal and in the same manner but using 16 % aqueous sodium carbonate solution in place of 4 %. The treated coal has 9.18 % ash, 3.80 % total sulphur. The treatment has removed 16.39 % ash and 11.83 % total sulphur from the coal. Example-15 The same experiment as outlined in Example-13 was conducted with the same coal and in the same manner but the coal was treated with aqueous sodium carbonate for 1 hour in place of 30 minutes. The treated coal has 8.04 % ash, 3.63 % total sulphur. The treatment has removed 8.64 % ash and 14.99 % total sulphur from the coal. Example-16 The same experiment as outlined in Example-14 was conducted with the same coal and in the same manner but the treatment time was increased from 30 minutes to 1 hour. The treated coal has 9.35 % ash, 3.75 % total sulphur. The treatment has removed 14.84 % ash and 12.99 % total sulphur from the coal. Example-17 10 gm of the treated coal sample as obtained in Example-1 was mixed with 50 ml 10 % hydrochloric acid. The mixture was stirred under reflux for 8 hours at 95 °C. The treated coal samples was separated by filtration and washed with distilled water till neutral to litmus paper and dried. The ash and total sulphur content of the sample are 5.62 and 3.28 % respectively. The treatment with 2 % aqueous sodium carbonate solution followed by 10 % hydrochloric acid remove 36.14 % ash and 23.18 % total sulphur from the coal. Example-18 10 gm of the sodium carbonate treated coal sample as obtained by adopting procedure described in Example-2 was further treated with hydrochloric acid in the same manner as outlined in Example-17. The treated coal has 7.65 % ash, 3.52 % total sulphur. The treatment therefore removed 30.33 % ash and 18.33 % total sulphur from the coal. Example-19 The same experiment as outlined in Example-17 was conducted with the same coal in the same manner but 10 % sulphuric acid was used in place of hydrochloric. The treated coal has 5.55 % ash, 3.37 % total sulphur. The treatment therefore removed 36.93 % ash and 21.20 % total sulphur from the coal. Example-20 The same experiment as outlined in Example-18 was conducted with the same coal in the same manner but 10 % sulphuric acid was used in place of hydrochloric. The treated coal has 8.22 % ash, 3.60 % total sulphur. The treatment has removed 25.14 % ash and 16.47 % total sulphur from the coal. Example-21 The same experiment as outlined in Example-19 was conducted with the same coal in the same manner but 10 % nitric acid was used in place of sulphuric. The treated coal has 5.28 % ash, 2.75 % total sulphur. The treatment has removed 40.00 % ash and 35.60 % total sulphur from the coal. Example-22 The same experiment as outlined in Example-20 was conducted with the same coal in the same manner but 10 % nitric acid was used in place of sulphuric. The treated coal has 7.28 % ash, 3.23 % total sulphur. The treatment has removed 33.70 % ash and 25.06 % total sulphur from the coal. Example-23 The same experiment as outlined in Example-17 was conducted with the same coal in the same manner but the concentration of aqueous sodium carbonate solution was changed to 16 %. The treated coal has 5.09 % ash, 2.96 % total sulphur. The treatment has removed 42.16 % ash and 30.68 % total sulphur from the coal. Example-24 The same experiment as outlined in Example-18 was conducted with the same coal in the same manner but the concentration of aqueous sodium carbonate solution was changed to 16 %. The treated coal has 7.05 % ash, 3.33 % total sulphur. The treatment has removed 35.79 % ash and 22.74 % total sulphur from the coal. Example-25 The same experiment as outlined in Example-19 was conducted with the same coal in the same manner but the concentration of aqueous sodium carbonate solution was changed to 16 %. The treated coal has 5.15 % ash, 3.08 % total sulphur. The treatment has removed 41.48 % ash and 27.87 % total sulphur from the coal. Example-26 The same experiment as outlined in Example-20 was conducted with the same coal in the same manner but the concentration of aqueous sodium carbonate solution was changed to 16 %. The treated coal has 7.66 % ash, 3.40 % total sulphur. The treatment has removed 30.24 % ash and 21.11 % total sulphur from the coal. Example-27 The same experiment as outlined in Example-21 was conducted with the same coal in the same manner but the concentration of aqueous sodium carbonate solution was changed to 16 %. The treated coal has 4.66 % ash, 2.22 % total sulphur. The treatment has removed 47.04 % ash and 48.01 % total sulphur from the coal. Example-28 The same experiment as outlined in Example-22 was conducted with the same coal in the same manner but the concentration of aqueous sodium carbonate solution was changed to 16 %. The treated coal has 6.58 % ash, 2.77 % total sulphur. The treatment has removed 40.07 % ash and 35.73 % total sulphur from the coal. Advantages 1. The process for demineralization and desulphurization of high sulphur subbituminous coal using aqueous sodium carbonate solution (2-16% w/v) is less corrosive in comparision to other alkalies like sodium hydroxide, potassium hydroxide etc. used by previous workers. 2. Demineralization and desulphurization of high sulphur subbituminous coal in the present process have been carried out at atmospheric pressure using sodium carbonate solution in the temperature range of 50-95 °C in comparision to reported high temperature and high pressure. 3. Demineralization and desulphurization of high sulphur subbituminous coal in the present investigation have been carried out in the presence of sodium carbonate solution alone followed by acid treatment at low concentration (1-10%v/v) in comparison to reported demineralization and desulphurization of coal using sodium carbonate in presence of oxidizing agent/ dissolved oxygen followed by treating with acid at high concentration. 4. Demineralization and desulphurization of high sulphur subbituminous coal in the present inventigation have been carried out in the time period of half an hour to 16 hours in comparision to reported long duration of 24-48 hours by previous workers. We claim 1. A process for demineralization and desulphurization of coal using sodium carbonate and acid solutions, the said process comprising the steps of: a) pulverizing the coal to about 212um fineness, b) suspending the pulverized coal obtained in step (a) in a solution of aqueous sodium carbonate ranging from 1-16% (w/v), followed by heating, at a temperature of 50-95°C for 1-8 hours under stirring, and removing the residual materials known methods, c) washing the residual coal obtained from step (b) with deionized water and treating it with about 1-10% dilute solution of mineral acid, under reflux with stirring , for a period of 15 minutes to 16 hours, d) separating the resultant residue from the reaction mixture obtained in step (c) by known method, followed by washing with deionized water and finally drying it to recover the desired product. 2. A process as claimed in claim 1, wherein the coal used in step (a) has following ingredients: (Table Removed) 3. A process as claimed in claim 1, wherein, the concentration of aqueous sodium carbonate used is preferably in the range of 4-16 % by wt. 4. A process as claimed in claim 1, wherein the mineral acid used is selected from the group consisting of hydrochloric acid, nitric acid and sulfuric acid. 5. A process as claimed in claim 1, wherein the mineral acid used is preferably sulfuric acid and nitric acid. 6. A process as claimed in claim 1, wherein, the concentration of mineral acid used is about 10 % by volume

Full Text

Field of the invention
This invention relates to a process for demineralization and desulphurization of coal using sodium carbonate and acid solutions. More particularly, this invention relates to a process for beneficiation and upgradation of coal using sodium carbonate and acid solutions.
Background of the invention
Coal contains a number of ash forming constituents. The most predominant are Quartz, chert, sandstone etc. forms of silica, kaolinite, illite etc. clay minerals, sulphide minerals like pyrite, calcium, iron etc. sulphates, carbonates like siderite, ankerites etc. The mineral matters have detrimental effects on utilization of coal for combustion, gasification, carbonization, liquefaction, reduction etc purposes. Combustion of high sulphur coal produces sulphur dioxide which is corrosive and toxic. It leads to acid rain, which corrodes boiler and other metal structures of the surroundings. Some of the mineral matters in coal lower the fusion temperature of the ash forming constituents, resulting in loss of heat due to melting. Ash fusion leads to high maintenance cost of boiler including down time loss. Combustion of high ash coal increases the amount of generated fly ash, bottom ash and consequently intensifies the ash disposal problems. The ash leads to environmental pollution and ecological problem. Ash handling involves dirty and cumbersome operations and is also expensive. Coke produced from high ash coal is not suitable for use in extraction of metal. It lowers the productivity and increases the slag rate of the furnace used for extraction of the metal. Coal/coke containing sulphur more than a certain level is also unsuitable for metallurgical purposes. Therefore there is a growing necessity for removal of ash and sulphur from a coal prior to its utilization.
Demineralization of coal may be achieved by both physical and chemical methods. The physical methods are based on the differences between the physical properties of the mineral matters and the carbonaceous part of the coal. The chemical methods are based on solubilization of the inorganic constituents or their converted forms in various solvents. The physical methods are not effective in removal of the finely dispersed minerals and those bound to the coal
structure. Chemical methods are effective for removing the mineral matter, which are finely dispersed and bound to the coal structure.
Demineralization and desulphurization of coal by treatment with alkali and acid solutions has been studied since long. Molten caustic leaching (MCL) process as reported in Fuel 1965, Vol. 44, p-269, Symp. on Removal of Heteroatoms from Fuel, ACS Meeting, Houston, TX, March 23-28, 1980, Proc. Resources from coal, coal wastes, and Ash workshop, Reston, VA, June 10-11, 1982, pp 66-75 etc. has proved effective in reducing significant amount of ash-forming minerals, pyritic and organic sulphur present in coal. Norton et al. in the report, Processing and Utilization of High sulphur coals-ll, Chugh YP, Caudle RD, eds., Elsevier, New York, NY, 1987, pp 213-223 reported removal of 60-90 % ash and sulphur from some bituminous coals from New Zealand using fused caustic. Markuszewski et al. in the publication, Am. Chem. Soc. Div. Fuel Chem. preprints, 1985, Vol. 30, p-41 reported removal of 80-90 % of the ash and 70-80 % of the total sulphur from several bituminous coals by treatment with molten mixtures of NaOH + KOH at 350-370 °C temperature.
Many workers reported removal of both ash and sulphur from low rank coal by treating with alkali solution at a relatively low temperature and pressure. Arya et al. in the publication, Fuel 1981, Vol. 60, p-1127 reported reduction of 29 wt. % ash and 30 wt. % total sulphur from a subbituminous coal from Chile by treatment with 10 % sodium hydroxide solution at 80 °C. Demineralization and desulphurization of the coal was reported to increase with increase of reaction time, temperature, alkali concentration and decrease of particle size. Kara and Ceylan in the publication, Fuel 1988, Vol. 67, p-170 reported removal of 60 wt % total sulphur and 65 % ash from some lignite samples of Turkey by treatment with 20 % sodium hydroxide solution at 70 °C. Bolat et al. in the publication, Fuel Processing Technology 1988, Vol. 57, p-93 reported about 46 % demineralization of a high ash-low sulphur bituminous coal from Turkey by treatment with 2 % aqueous alkali followed by 10 % acid under mild condition. Mukherjee and Borthakur in the publication, Fuel, Vol. 80, Year 2001, pp. 2037-2040 reported removal of significant amount of mineral matter and sulphur by successively treating subbituminous coal from Assam, North Eastern Region,
and India with aqueous sodium hydroxide solution followed by hydrochloric acid treatment. Demineralization and dsulphurization were reported to increase with alkali concentration. Reports of different investigators have indicated that the extent of ash and sulphur removal by caustic soda (sodium hydroxide) solution alone or followed by acid treatment varies from coal to coal. Sodium hydroxide employed in the process is a strong base and is highly caustic in character i.e. burns or corrodes organic tissues.
Report on removal of ash and sulphur from coal using sodium carbonate, a salt of caustic soda, which is a mild base and relatively less corrosive chemical, has also been reported by several investigators. Markusewski et al. in the publication, Proc. of Symp. on coal to Achieve Energy and Environmental Goals, Sept. 1978, Vol. II, pp1039-63 reported complete removal of inorganic sulphur and 70 wt % reduction in organic sulphur by treating coal with dilute solutions of sodium carbonate. But the methods work at a considerably high temperature of around 120 to 150 °C and at pressures above the atmospheric pressure. Chuang et al. in the article, Desulphurization of coal by oxidation in alkaline solutions, published in Fuel Processing Technology, Vol. 7, 1993, pp. 43-57 reported a method which removed almost the entire inorganic sulphur and a significant amount of the organic sulphur from a high volatile bituminous coal using sodium carbonate and acid solutions. But the method involves oxidation with dissolved oxygen, which works under pressure.
Objectives of the invention
The objective of the present investigation is to provide an effective process for demineralization and desulphurization of high sulphur subbituminous coal using aqueous sodium carbonate solution at atmospheric pressure and at relatively low temperature.
Summary of the invention
Accordingly, the present invention describes the process for demineralization and desulphurization of coal using sodium carbonate and acid solutions, the said process comprising the steps of:
a) pulverizing the coal to about 212um fineness,
b) suspending the pulverized coal obtained in step (a) in a solution of
aqueous sodium carbonate ranging from 1-16% (w/v), followed by heating,
at a temperature of 50-95°C for 1-8 hours under stirring, and removing the
residual materials known methods,
c) washing the residual coal obtained from step (b) with deionized water and
treating it with about 1-10% dilute solution of mineral acid, under reflux
with stirring , for a period of 15 minutes to 16 hours,
d) separating the resultant residue from the reaction mixture obtained in step
(c) by known method, followed by washing with deionized water and
finally drying it to recover the desired product.
In an embodiment of the present invention, the concentration of aqueous sodium carbonate used is preferably in the range of 4-16 % by wt.
In another embodiment of the present invention, the mineral acid used is selected from the group consisting of hydrochloric acid, nitric acid and sulfuric acid.
In another embodiment of the present invention, the mineral acid used is preferably sulfuric acid and nitric acid.
In yet embodiment of the present invention, the concentration of mineral acid used is about 10 % by volume
In yet embodiment of the present invention, the maximum percentage of sulphur removed from coal obtained is 49% when nitric acid is used as mineral acid.
In still embodiment of the present invention, the maximum percentage of ash removed from coal is 48% when nitric acid is used as mineral acid.
The novelty lies in the use of aqueous Sodium Carbonate in place of Sodium Hydroxide. Sodium hydroxide is a strong base (alkali). It is highly corrosive. It burns or corrodes organic tissues (skin). Therefore, extreme precaution is required in handling of sodium hydroxide, both solid and liquid (in solution). It is highly hygroscopic and becomes liquid when placed in the atmosphere. Sodium carbonate on the other hand, is a salt of sodium hydroxide and carbonic acid, a mild acid. It dissolves in water giving alkaline solution due to hydrolysis. During hydrolysis along with hydroxyl ion, bi-carbonate and carbonic acid ions are also produced. Therefore, use of sodium carbonate is not associated with the disadvantage (corrosiveness) as found with sodium hydroxide.
Detailed description of the invention
The present invention provides a process for removal of ash forming constituents and sulphur from coal which consists of pulverization of a coal, suspending, the pulverized coal in a solution of sodium carbonate, heating the mixture under stirring condition for a period ranging from few minutes to several hours, followed by removing the dissolved materials by filtration, centrifugation, decantation or the like methods, washing the recovered coal with deionized water followed by removing the adhered moisture by air drying to obtain the product or optionally treating the recovered coal with dilute solution of a mineral acid like hydrochloric, nitric, sulphuric and heating the mixture for few minutes to few hours, separating the solid by filtration, centrifugation, sedimentation or the like methods, washing with deionized water followed by drying in air at ambient condition or in an air oven to recover the final product.
Another feature of the present investigation is the powdered coal sample is suspended in a aqueous sodium carbonate solution containing 2-16 % sodium carbonate and maintaining coal: liquid ratio at 1:3 to 1:5, heating the resultant mixture under stirring condition at 50-90 °C for a period ranging from 15 minutes to 16 hours, followed by separation of the solid by filtration, washing with water till
free from adhered CO32~, drying the same under atmospheric condition or in an air oven.
Yet another feature is the aqueous sodium carbonate treated coal sample obtained as above is further suspended in a 1 to 10 % solution of an acid like hydrochloric, nitric, sulphuric followed by warming the mixture at 50-90 °C for a period ranging from few minutes to several hours, separating the coal from the liquid by adopting procedures like decantation, filtration, centrifugation, washing it with demineralized water followed by drying at air at ambient condition or in an air oven.
The invention is illustrated with the following examples, which should not be construed to limit the scope of the investigation.
Proximate and Ultimate analysis along with the distribution of sulphur of a few typical coal samples used in the investigation are shown in Table 1. The chemical analysis of the coal ash samples are shown in Table 2.
Table 1
Proximate and Ultimate analysis and distribution of sulphur of some coal samples

(Table Remove)
Table 2
Chemical analysis of coal ash

(Table Remove)
Example-1
25 gm of a coal sample having 8.80 % ash, 4.27 % total sulphur, pulverized to -212 urn fineness was mixed with 100 ml 2 % aqueous sodium carbonate solution in a three necked round bottom flask kept over a heating mantle and fitted with a condenser and a stirrer. The mixture was heated to 95 °C and kept at the temperature for 30 minutes. The mixture was stirred during heating. The mixture was then cooled, filtered and the residue was washed with deionized water till free of alkali and dried. The ash and total sulphur of the washed coal are 7.64 and 3.94 % respectively. This indicates that the treatment has removed 13.18 % ash and 7.73 % total sulphur from the coal.
Example-2
25 gm of another coal samples having 10.98 % ash, 4.31 % total sulphur was pulverized and treated with the same volume and concentration of aqueous sodium carbonate in the same manner as outlined in Example-1. The treated coal has 8.99 % ash, 4.10 % total sulphur. This indicates that the treatment has removed 18.12 % ash and 4.87 % total sulphur from the coal.
Example-3
The same experiment as outlined in Example-1 was conducted with the same coal and in the same manner but the treatment time was increased from 30 minutes to 1 hour. The treated coal has 7.78 % ash, 3.84 % total sulphur. The treatment has removed 11.59 % ash and 10.07 % total sulphur from the coal.
Example-4
The same experiment as outlined in Example-2 was conducted with the same coal and in the same manner but the treatment time was increased from 30 minutes to 1 hour. The treated coal has 9.11 % ash, 4.02 % total sulphur. The treatment has removed 17.03 % ash and 6.73 % total sulphur from the coal.
Example-5
The same experiment as outlined in Example-1 was conducted with the same coal and in the same manner but the treatment time was increased from 1 hour to 8 hour. The treated coal has 8.17 % ash, 3.55 % total sulphur. The treatment has removed 7.16 % ash and 16.86 % total sulphur from the coal.
Example-6
The same experiment as outlined in Example-2 was conducted with the same coal and in the same manner but the treatment time was increased from 1hour to 8 hour. The treated coal has 9.61 % ash, 3.71 % total sulphur. The treatment has removed 12.48 % ash and 13.92 % total sulphur from the coal.
Example-7
The same experiment as outlined in Example-1 was conducted with the same coal and in the same manner but using 4 % aqueous sodium carbonate solution. The treated coal has 7.76 % ash, 3.87 % total sulphur. The treatment has removed 11.82 % ash and 9.37 % total sulphur from the coal.
Example-8
The same experiment as outlined in Example-2 was conducted with the same coal and in the same manner but using 4 % aqueous sodium carbonate
solution. The treated coal has 9.05 % ash, 4.04 % total sulphur. The treatment has removed 17.58 % ash and 6.26 % total sulphur from the coal.
Example-9
The same experiment as outlined in Example-7 was conducted with the same coal and in the same manner but the treatment time was increased from 30 minutes to 1 hour. The treated coal has 7.84 % ash, 3.75 % total sulphur. The treatment has removed 10.91 % ash and 12.18 % total sulphur from the coal.
Example-10
The same experiment as outlined in Example-8 was conducted with the same coal and in the same manner but the treatment time was increased from 30 minutes to 1 hour. The treated coal has 9.20 % ash, 3.88 % total sulphur. The treatment has removed 16.21 % ash and 9.98 % total sulphur from the coal.
Example-11
The same experiment as outlined in Example-7 was conducted with the same coal and in the same manner but the treatment time was increased from 1 hour to 8 hour. The treated coal has 8.22 % ash, 3.44 % total sulphur. The treatment has removed 6.59 % ash and 19.44 % total sulphur from the coal.
Example-12
The same experiment as outlined in Example-8 was conducted with the same coal and in the same manner but the treatment time was increased from 1 hour to 8 hour. The treated coal has 9.74 % ash, 3.62 % total sulphur. The treatment has removed 11.29 % ash and 16.01 % total sulphur from the coal.
Example-13
The same experiment as outlined in Example-7 was conducted with the same coal and in the same manner but using 16 % aqueous sodium carbonate solution in place of 4 %. The treated coal has 7.87 % ash, 3.71 % total sulphur. The treatment has removed 10.57 % ash and 13.11 % total sulphur from the coal.
Example-14
The same experiment as outlined in Example-8 was conducted with the same coal and in the same manner but using 16 % aqueous sodium carbonate solution in place of 4 %. The treated coal has 9.18 % ash, 3.80 % total sulphur. The treatment has removed 16.39 % ash and 11.83 % total sulphur from the coal.
Example-15
The same experiment as outlined in Example-13 was conducted with the same coal and in the same manner but the coal was treated with aqueous sodium carbonate for 1 hour in place of 30 minutes. The treated coal has 8.04 % ash, 3.63 % total sulphur. The treatment has removed 8.64 % ash and 14.99 % total sulphur from the coal.
Example-16
The same experiment as outlined in Example-14 was conducted with the same coal and in the same manner but the treatment time was increased from 30 minutes to 1 hour. The treated coal has 9.35 % ash, 3.75 % total sulphur. The treatment has removed 14.84 % ash and 12.99 % total sulphur from the coal.
Example-17
10 gm of the treated coal sample as obtained in Example-1 was mixed with 50 ml 10 % hydrochloric acid. The mixture was stirred under reflux for 8 hours at 95 °C. The treated coal samples was separated by filtration and washed with distilled water till neutral to litmus paper and dried. The ash and total sulphur content of the sample are 5.62 and 3.28 % respectively. The treatment with 2 % aqueous sodium carbonate solution followed by 10 % hydrochloric acid remove 36.14 % ash and 23.18 % total sulphur from the coal.
Example-18
10 gm of the sodium carbonate treated coal sample as obtained by adopting procedure described in Example-2 was further treated with hydrochloric acid in the same manner as outlined in Example-17. The treated coal has 7.65 % ash, 3.52 % total sulphur. The treatment therefore removed 30.33 % ash and 18.33 % total sulphur from the coal.
Example-19
The same experiment as outlined in Example-17 was conducted with the same coal in the same manner but 10 % sulphuric acid was used in place of hydrochloric. The treated coal has 5.55 % ash, 3.37 % total sulphur. The treatment therefore removed 36.93 % ash and 21.20 % total sulphur from the coal.
Example-20
The same experiment as outlined in Example-18 was conducted with the same coal in the same manner but 10 % sulphuric acid was used in place of hydrochloric. The treated coal has 8.22 % ash, 3.60 % total sulphur. The treatment has removed 25.14 % ash and 16.47 % total sulphur from the coal.
Example-21
The same experiment as outlined in Example-19 was conducted with the same coal in the same manner but 10 % nitric acid was used in place of sulphuric. The treated coal has 5.28 % ash, 2.75 % total sulphur. The treatment has removed 40.00 % ash and 35.60 % total sulphur from the coal.
Example-22
The same experiment as outlined in Example-20 was conducted with the same coal in the same manner but 10 % nitric acid was used in place of sulphuric. The treated coal has 7.28 % ash, 3.23 % total sulphur. The treatment has removed 33.70 % ash and 25.06 % total sulphur from the coal.
Example-23
The same experiment as outlined in Example-17 was conducted with the same coal in the same manner but the concentration of aqueous sodium carbonate solution was changed to 16 %. The treated coal has 5.09 % ash, 2.96 % total sulphur. The treatment has removed 42.16 % ash and 30.68 % total sulphur from the coal.
Example-24
The same experiment as outlined in Example-18 was conducted with the same coal in the same manner but the concentration of aqueous sodium
carbonate solution was changed to 16 %. The treated coal has 7.05 % ash, 3.33 % total sulphur. The treatment has removed 35.79 % ash and 22.74 % total sulphur from the coal.
Example-25
The same experiment as outlined in Example-19 was conducted with the same coal in the same manner but the concentration of aqueous sodium carbonate solution was changed to 16 %. The treated coal has 5.15 % ash, 3.08 % total sulphur. The treatment has removed 41.48 % ash and 27.87 % total sulphur from the coal.
Example-26
The same experiment as outlined in Example-20 was conducted with the same coal in the same manner but the concentration of aqueous sodium carbonate solution was changed to 16 %. The treated coal has 7.66 % ash, 3.40 % total sulphur. The treatment has removed 30.24 % ash and 21.11 % total sulphur from the coal.
Example-27
The same experiment as outlined in Example-21 was conducted with the same coal in the same manner but the concentration of aqueous sodium carbonate solution was changed to 16 %. The treated coal has 4.66 % ash, 2.22 % total sulphur. The treatment has removed 47.04 % ash and 48.01 % total sulphur from the coal.
Example-28
The same experiment as outlined in Example-22 was conducted with the same coal in the same manner but the concentration of aqueous sodium carbonate solution was changed to 16 %. The treated coal has 6.58 % ash, 2.77 % total sulphur. The treatment has removed 40.07 % ash and 35.73 % total sulphur from the coal.
Advantages
1. The process for demineralization and desulphurization of high sulphur
subbituminous coal using aqueous sodium carbonate solution (2-16% w/v)
is less corrosive in comparision to other alkalies like sodium hydroxide,
potassium hydroxide etc. used by previous workers.
2. Demineralization and desulphurization of high sulphur subbituminous coal
in the present process have been carried out at atmospheric pressure
using sodium carbonate solution in the temperature range of 50-95 °C in
comparision to reported high temperature and high pressure.
3. Demineralization and desulphurization of high sulphur subbituminous coal
in the present investigation have been carried out in the presence of
sodium carbonate solution alone followed by acid treatment at low
concentration (1-10%v/v) in comparison to reported demineralization and
desulphurization of coal using sodium carbonate in presence of oxidizing
agent/ dissolved oxygen followed by treating with acid at high
concentration.
4. Demineralization and desulphurization of high sulphur subbituminous coal
in the present inventigation have been carried out in the time period of half
an hour to 16 hours in comparision to reported long duration of 24-48
hours by previous workers.

We claim
1. A process for demineralization and desulphurization of coal using sodium
carbonate and acid solutions, the said process comprising the steps of:
a) pulverizing the coal to about 212um fineness,
b) suspending the pulverized coal obtained in step (a) in a solution of aqueous sodium carbonate ranging from 1-16% (w/v), followed by heating, at a temperature of 50-95°C for 1-8 hours under stirring, and removing the residual materials known methods,
c) washing the residual coal obtained from step (b) with deionized water and treating it with about 1-10% dilute solution of mineral acid, under reflux with stirring , for a period of 15 minutes to 16 hours,
d) separating the resultant residue from the reaction mixture obtained in step (c) by known method, followed by washing with deionized water and finally drying it to recover the desired product.
2. A process as claimed in claim 1, wherein the coal used in step (a) has
following ingredients:
(Table Removed)
3. A process as claimed in claim 1, wherein, the concentration of aqueous
sodium carbonate used is preferably in the range of 4-16 % by wt.

4. A process as claimed in claim 1, wherein the mineral acid used is selected from the group consisting of hydrochloric acid, nitric acid and sulfuric acid.
5. A process as claimed in claim 1, wherein the mineral acid used is preferably sulfuric acid and nitric acid.
6. A process as claimed in claim 1, wherein, the concentration of mineral acid used is about 10 % by volume

Documents:

2470-del-2006-abstract.pdf

2470-del-2006-Claims-(15-10-2012).pdf

2470-del-2006-claims.pdf

2470-del-2006-correspondence-other.pdf

2470-del-2006-Correspondence-Others-(15-10-2012).pdf

2470-del-2006-description (complete).pdf

2470-DEL-2006-Form-1.pdf

2470-del-2006-form-2.pdf

2470-del-2006-form-3.pdf

2470-del-2006-form-5.pdf

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Patent Number

255788

Indian Patent Application Number

2470/DEL/2006

PG Journal Number

13/2013

Publication Date

29-Mar-2013

Grant Date

22-Mar-2013

Date of Filing

16-Nov-2006

Name of Patentee

COUNCIL OF SCIENTIFIC &INDUSTRIAL RESEARCH

Applicant Address

ANUSANDHAN BHAWAN RAFI MARG NEW DELHI-110 001 INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	BORTHAKUR PC.	REGIONAL RESERCH LABORATORY JORHAT
2	MUKHERJEE S,	REGIONAL RESERCH LABORATORY JORHAT
3	SENGUPTA P	REGIONAL RESERCH LABORATORY JORHAT
4	MAHIUDDIN S.	REGIONAL RESERCH LABORATORY JORHAT
5	BARUAH BP.	REGIONAL RESERCH LABORATORY JORHAT
6	BORDOLOI D,	REGIONAL RESERCH LABORATORY JORHAT
7	BARUAH AC	REGIONAL RESERCH LABORATORY JORHAT
8	SAIKIA PC.	REGIONAL RESEARCH LABORATORY, JORHAT

PCT International Classification Number

A61N1/04

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA