US3926575A - Removal of pyritic sulfur from coal - Google Patents
Removal of pyritic sulfur from coal Download PDFInfo
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- US3926575A US3926575A US164006A US16400671A US3926575A US 3926575 A US3926575 A US 3926575A US 164006 A US164006 A US 164006A US 16400671 A US16400671 A US 16400671A US 3926575 A US3926575 A US 3926575A
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- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
- C10L9/00—Treating solid fuels to improve their combustion
- C10L9/02—Treating solid fuels to improve their combustion by chemical means
Definitions
- ABSTRACT Finely divided coal or coal derivatives, containing pyrite, are reacted with sulfurous acid (the oxidizing agent); if desired, HCl may also be used to improve the reaction efficiency to remove pyritic sulfur from coal as shown by the following equations:
- This invention relates to the removal of pyritic sulfur from coal and solid coal derivatives and, more specifically, to the solvent extraction of sulfur from pyrites in coal using a solution containing sulfurous acid.
- coal in the United States is primarily for the purpose of conversion into electrical energy and thermal generating plants.
- One of the principal drawbacks in the use of United States mined coal is due to their high sulfur contents which can range up to 5 percent.
- the solution containing mainly free sulfur, ferrous chloride and any unconsumed ferric chlorideand sulfurous acid is removed from the coal by filtration.
- the coal is then washed and dried, preferably by heating in a vacuum; this results in most of the free sulfur being volatized. If desired, a further wash, filtration and heating will remove additional sulfur and more ferrous ion.
- Regeneration of the unused ferric chloride and ferrous chloride solution may be accomplished by first evaporating most of the water to concentrate the solution. Cooling the concentrated solution precipitates the ferrous chloride from the ferric chloride, the latter still remaining in solution. The ferrous chloride precipitate is air oxidized to ferric chloride and iron oxide; finally, the ferric chloride is recycled or sold as a byproduct and the iron oxide recovered.
- Typical pyrite extraction temperatures may vary from C to C. Reflux times are typically /2 2 hours and higher. Typical coal particle sizes may vary from 200 mesh to /2 inch particles. Atmospheric pressure may be employed, but higher pressures can also be used.
- the effective amount of the sulfurous acid employed for extraction depends on the amount of treated coal and its pyritic sulfur content, the amount of sulfur desired to be extracted, extraction times, extraction temperatures, concentration of the sulfurous acid, etc.
- Coals which may be employed in this invention include those which are considered as coals in the popular or commercial sense, such as anthracites, charcoal, coke, bituminous coals, lignites, etc.
- solvent refined coals such as hydrocracked coal, and middlings are all capable of being refined by the extraction process of this invention.
- the procedure employed was to reflux an aqueous solution of sulfur dioxide and hydrochloric acid with pulverized coal. This converted the ferrous persulfide (pyrite) to ferric chloride and produced free sulfur. Additional pyrite is removed by interaction with ferric chloride. The resultant solution of ferrous chloride was then separated from the coal by filtering. Following a water wash, the coal was then heated to dryness under vacuum thereby vaporizing some of the free sulfur. Most of the remaining free sulfur in the coal was extracted with a suitable solvent such as benzene, kerosene, gas oil, or para cresol. In addition, the para cresol removes a portion of organic sulfur compounds contained in the coal. If desired, the solution containing ferrous ion can be recycled for subsequent reuse and/or oxidized to iron oxide; these products may be recovered as noted previously.
- Typical coals which may be employed in the process include Lower Freeport, Bevier, Indiana No. V, and Pittsburgh. These coals contain pyritic sulfur as shown in Table 1.
- a process for reducing the pyrite sulfur content in coal which comprises:
- sulfurous acid but not HNO reacting the coal containing FeS with an effective H 0 or HOC
- Table 2 in the following example indiform free sulfur in the coal matrix; cates that generally use of HCl when combined with filtering the solution from the coal; sulfurous acid improves the removal of pyritic sulfur washing the coal; and compared to the use of sulfurous acid alone. extracting the free sulfur from the coal with an or- Also, effective pyrite removal can be achieved at ganic solvent for sulfur. 100C reaction temperature in as little time as two 3. The process of claim 2 in which the sulfur solvent hours.
- aqueous sulfurous acid (10 times ric acid at about 100C to 140C to form free sulfur stoichiometric excess over pyrite content of coal), hyin the coal matrix; drochloric acid (where designated), and pulverized filtering the solution from the coal; coal were introduced into a glass aerosol stirred bomb. washing the coal; and The mixture was heated for the temperature and time heat drying the coal to volatize the free sulfur shown; this caused a pressure rise to about 20-30 psig. therein. The mixture was then cooled. The coal was then fil- 6.
- a process for reducing the pyrite sulfur content in tered from the aqueous phase and washed with hot coal which comprises: water to remove residual acid.
- Some of the samples reacting the coal with an effective amount of an were slurried with benzene for 20 mins. and then filaqueous solution of sulfurous acid and hydrochlotered again. All samples were dried in a vacuum oven at ric acid to form free sulfur in the coal matrix; 160C/30 min. to constant wt. (ca 24 hrs). Elemental filtering the solution from the coal; sulfur was distilled out and collected on the oven winwashing the coal; dow and in the pump trap and lines. extracting the free sulfur from the coal with an or- Table 2 shows the effect on l4 mesh Indiana No. V ganic solvent for sulfur and containing pyrite, after treatment with a sulfurous acid heat drying the coal to remove the free sulfur consolution. tained therein.
Abstract
Finely divided coal or coal derivatives, containing pyrite, are reacted with sulfurous acid (the oxidizing agent); if desired, HCl may also be used to improve the reaction efficiency to remove pyritic sulfur from coal as shown by the following equations: Primary: Oxidation - reduction 4 FeS2 (pyrite) +3SO2 + 12 HCl -> 4 FeCl3 + 11S + 6 H2O Secondary: Oxidation - reduction 4 FeCl3 + FeS2 (Pyrite) -> 6 FeCl2 + 4S Overall reaction 6 FeS2 + 3SO2 + 12 HCl -> 6 FeCl2 + 15S + 6 H2O The solution containing ferrous chloride and unreacted sulfurous acid is then filtered from the coal which is then washed and heat dried under low pressure. Most of the free sulfur is volatized from the coal due to the heat drying; additional free sulfur can be removed by additional washing and heat drying and/or solvent extraction techniques. If desired, the ferrous chloride can be oxidized to ferric oxide and hydrochloric acid. The hydrochloric acid may be recycled and the iron oxide used for production of steel or discarded.
Description
United States Patent 1191 Meyers 1451 Dec. 16, 1975 REMOVAL OF PYRITIC SULFUR FROM COAL [75] Inventor: Robert A. Meyers, Encino, Calif.
[73] Assignee: TRW Inc., Redondo Beach, Calif.
[22] Filed: July 19, 1971 [21] Appl. No.: 164,006
52 US. Cl 44/1 R; 201/17; 208/8,
[51] Int. Cl. C10L 9/00; C10B 17/00; C10B 57/00 [58] Field of Search 44/1 R, l B; 23/224, 226, 23/225 R, 209.9; 208/8; 201/17 [56] References Cited UNITED STATES PATENTS 2,057,486 10/1936 Higgins 201/17 X 2,739,105 3/1956 Ford et al. 201/17 X Primary Examiner-Carl F. Dees Attorney, Agent, or Firm-Willie Krawitz; Daniel T. Anderson; Alan D. Akers [57] ABSTRACT Finely divided coal or coal derivatives, containing pyrite, are reacted with sulfurous acid (the oxidizing agent); if desired, HCl may also be used to improve the reaction efficiency to remove pyritic sulfur from coal as shown by the following equations:
Primary: Oxidation reduction 4 FeS (pyrite) +380 12 HCl 4 FeCl 118 6 H O Secondary: Oxidation reduction 4 FeC1 FeS (Pyrite) 6 FeCl 48 Overall reaction 6 FeS 380 +12 HCl 6 FeCl +15S 6 The solution containing ferrous chloride and unreacted sulfurous acid is then filtered from the coal which is then washed and heat dried under low pressure. Most of the free sulfur is volatized from the coal due to the heat drying; additional free sulfur can be removed by additional washing and heat drying and/or solvent extraction techniques. If desired, the ferrous chloride can be oxidized to ferric oxide and hydrochloric acid. The hydrochloric acid may be recycled and the iron oxide used for production of steel or discarded.
6 Claims, No Drawings REMOVAL OF PYRITIC SULFUR FROM COAL BACKGROUND OF THE INVENTION This invention relates to the removal of pyritic sulfur from coal and solid coal derivatives and, more specifically, to the solvent extraction of sulfur from pyrites in coal using a solution containing sulfurous acid.
The present use of coal in the United States is primarily for the purpose of conversion into electrical energy and thermal generating plants. One of the principal drawbacks in the use of United States mined coal is due to their high sulfur contents which can range up to 5 percent.
Based on a 4 percent sulfur content, a one million kilowatt plant burns about 8,500 tons per day of coal and consequently emits 6 tons per day of sulfur dioxide. If this sulfur could be removed and converted, it would produce 900 tons of H SO daily.
It has long been recognized that S in the atmosphere will either retard growth or kill vegetation. In addition, the potential hazard to humans appears about the same as for the vegetable kingdom.
While it is possible to remove pyritic sulfur from coal by froth flotation or washing processes, the selectivity is poor; hence, a large portion of the coal is discarded along with ash and pyrite. Consequently, the solution so far has been to simply burn coal having a low sulfur content. However, many pollution control districts now prohibit the use of coal having an excess of 1 percent sulfur. The result has been to severely restrict the use of many United States coals, 90 percent of which average about 2.5 percent contained sulfur. This has led to the importation of low sulfur content fuel oils for domestic and industrial use.
It is, therefore, an object of this invention to provide a process for the reduction of sulfur, particularly pyritic sulfur in coal.
Another object'is to provide a process for the recovery from coal of iron oxide, sulfur and sulfur compounds.
Other objects of this invention will become apparent from the description to follow.
According to the invention, it has been found that it is possible to react the pyrite contained in the coal with a solution containing an effective amount of sulfurous acid. A typical reaction proceeds substantially as follows:
Primary: Oxidation reduction 4 FeS (pyrite) 380 12 HCl- 4 FeCl +1 1ST +6 H O Secondary: Oxidation reduction 4 FeCl 2 FeS (pyrite) 6 FeCl 4ST Overall reaction 6 FeS- 380 12 I-ICl 6 FeCl +lS+6 H O In addition to these major reactions, it is to be assumed that a small part of the free sulfur formed initially may be further oxidized to sulfite, sulfate, thiosulfate, etc. Formation of the secondary products can be further lessened by minimizing reaction times, acid concentration and temperature.
The solution containing mainly free sulfur, ferrous chloride and any unconsumed ferric chlorideand sulfurous acid is removed from the coal by filtration. The coal is then washed and dried, preferably by heating in a vacuum; this results in most of the free sulfur being volatized. If desired, a further wash, filtration and heating will remove additional sulfur and more ferrous ion.
' Finally, one or more extractions with a suitable organic sulfur solvent such as benzene, kerosene, gas oil, or para cresol at temperature of 50C up to solvent reflux is employed to further reduce "the sulfur content of the coal.
Regeneration of the unused ferric chloride and ferrous chloride solution may be accomplished by first evaporating most of the water to concentrate the solution. Cooling the concentrated solution precipitates the ferrous chloride from the ferric chloride, the latter still remaining in solution. The ferrous chloride precipitate is air oxidized to ferric chloride and iron oxide; finally, the ferric chloride is recycled or sold as a byproduct and the iron oxide recovered.
Typical pyrite extraction temperatures may vary from C to C. Reflux times are typically /2 2 hours and higher. Typical coal particle sizes may vary from 200 mesh to /2 inch particles. Atmospheric pressure may be employed, but higher pressures can also be used.
The effective amount of the sulfurous acid employed for extraction depends on the amount of treated coal and its pyritic sulfur content, the amount of sulfur desired to be extracted, extraction times, extraction temperatures, concentration of the sulfurous acid, etc.
Coals which may be employed in this invention include those which are considered as coals in the popular or commercial sense, such as anthracites, charcoal, coke, bituminous coals, lignites, etc. In addition, solvent refined coals such as hydrocracked coal, and middlings are all capable of being refined by the extraction process of this invention.
In general, the procedure employed was to reflux an aqueous solution of sulfur dioxide and hydrochloric acid with pulverized coal. This converted the ferrous persulfide (pyrite) to ferric chloride and produced free sulfur. Additional pyrite is removed by interaction with ferric chloride. The resultant solution of ferrous chloride was then separated from the coal by filtering. Following a water wash, the coal was then heated to dryness under vacuum thereby vaporizing some of the free sulfur. Most of the remaining free sulfur in the coal was extracted with a suitable solvent such as benzene, kerosene, gas oil, or para cresol. In addition, the para cresol removes a portion of organic sulfur compounds contained in the coal. If desired, the solution containing ferrous ion can be recycled for subsequent reuse and/or oxidized to iron oxide; these products may be recovered as noted previously.
Typical coals which may be employed in the process include Lower Freeport, Bevier, Indiana No. V, and Pittsburgh. These coals contain pyritic sulfur as shown in Table 1.
TABLE 1 Lower Indiana Freeport No. V Bevier Pittsburgh Pyritic S 2.2-3.8 l 5-l.8 1.7-2.3 0.5-1.7 Organic S 0.4-0.8 1.5-1.8 1.7-2.3 0.5-0.7 Total S 3.0-4.2 3.0-3.5 3.5-4 5 2-22 3 since it well might be expected that the free sulfur would recombine either with iron or with the coal upon heating. It is also well known that iron pyrites may be oxidatively dissolved from the coal matrix with strong 1. A process for reducing the pyrite sulfur content in coal which comprises:
reacting the coal containing FeS with an effective amount of an aqueous solution of sulfurous acid at aqueous oxidizing agents such as HNO H or HOCl. 5 about 100C to 140C and hydrochloric acid to This will convert the sulfur content to sulfate but not to form free sulfur in the coal matrix; free sulfur. This is the basis for chemical analysis of the filtering the solution from the coal; pyritic sulfur content of coal; however, such strong washing the coal; and oxidizing agents also extensively oxidize the organic removing the free sulfur from the coal. coal matrix. By contrast, sulfur dioxide is almost totally 2. A process for reducing the pyrite sulfur content in selective in the sense that the organic coal matrix is coal which comprises: undisturbed. Hence, sulfurous acid, but not HNO reacting the coal containing FeS with an effective H 0 or HOC], provides an economical route to the amount of an aqueous solution of sulfurous acid removal of pyrites from coal. and hydrochloric acid at about 100C to 140C to The data in Table 2 in the following example indiform free sulfur in the coal matrix; cates that generally use of HCl when combined with filtering the solution from the coal; sulfurous acid improves the removal of pyritic sulfur washing the coal; and compared to the use of sulfurous acid alone. extracting the free sulfur from the coal with an or- Also, effective pyrite removal can be achieved at ganic solvent for sulfur. 100C reaction temperature in as little time as two 3. The process of claim 2 in which the sulfur solvent hours. is selected from the class consisting of benzene, kero- Hence, the present process is selective for removal of sene, gas oil, and paracresol. pyrite from coal without adversely affecting the BTU 4. The process of claim 2 in which the extraction content of the coal. Also, the sulfur and iron values temperature varies from 50C up to solvent reflux. may be recovered from the treatment process if de- 5. A process for reducing the pyrite sulfur content in sired. coal which comprises:
reacting the coal with an effective amount of an EXAMPLE aqueous solution of sulfurous acid and hydrochlo- In a typical case, aqueous sulfurous acid (10 times ric acid at about 100C to 140C to form free sulfur stoichiometric excess over pyrite content of coal), hyin the coal matrix; drochloric acid (where designated), and pulverized filtering the solution from the coal; coal were introduced into a glass aerosol stirred bomb. washing the coal; and The mixture was heated for the temperature and time heat drying the coal to volatize the free sulfur shown; this caused a pressure rise to about 20-30 psig. therein. The mixture was then cooled. The coal was then fil- 6. A process for reducing the pyrite sulfur content in tered from the aqueous phase and washed with hot coal which comprises: water to remove residual acid. Some of the samples reacting the coal with an effective amount of an were slurried with benzene for 20 mins. and then filaqueous solution of sulfurous acid and hydrochlotered again. All samples were dried in a vacuum oven at ric acid to form free sulfur in the coal matrix; 160C/30 min. to constant wt. (ca 24 hrs). Elemental filtering the solution from the coal; sulfur was distilled out and collected on the oven winwashing the coal; dow and in the pump trap and lines. extracting the free sulfur from the coal with an or- Table 2 shows the effect on l4 mesh Indiana No. V ganic solvent for sulfur and containing pyrite, after treatment with a sulfurous acid heat drying the coal to remove the free sulfur consolution. tained therein.
TABLE 2 REMOVAL OF SULFUR FRoM -14 MESH INDIANA No. v COAL WITH SULFUROUS ACID Experi- Conc Conc fib ri Benzene Total Pyritic ment Temp of HCl H2503 Time Post Sulfur Ash btu Sulfur Sulfur Ash btu No. "C M M Hrs Treatment 70 Content Removed Removed Removed Change 1 140 3.6 0.9 20 N0 3.06 7.4 13000 15 30 37 +4 2 1.00 3.6 0.9 20 NO 2.76 7.8 12600 23 46 33 +1 3 100 3.6 0.9 20 Yes 2.69 7.5 13000 26 52 36 +4 4 100 3.6 0.9 2 N0 2.69 8.2 1 1900 26 52 30 5 5 100 0 0.9 2 N0 2.82 8.7 12800 22 44 26 +2 6 100 0 0.9 20 Yes 3.19 8.9 12950 12 25 24 +4 7 100 0 0.9 20 NO 3.53 8.9 12800 2 4 25 +2 Starting Indiana No. V: 3.62% total sulfur; 0.03% sulfate; 1.79% organic sulfur; 1.80% pyrite sulfur; ash content 1 1.8%, heat content 12500 btu.
1 claim:
Claims (6)
1. A PROCESS FOR REDUCING THE PYRITE SULFUR CONTENT IN COAL WHICH COMPRISES: REACTING THE TOTAL CONTAINING FES2 WITH AN EFFECTIVE AMOUNT OF AN AQUEOUS SOLUTION OF SULFUROUS ACID AT ABOUT 100*C TO 140*C AND HYDROCHLORIC ACID TO FORM FREE SULFUR IN THE COAL MATRIX, FILTERING THE SOLUTION FROM THE COAL; WASHING THE COAL; AND REMOVING THE FREE SULFUR FROM THE COAL.
2. A process for reducing the pyrite sulfur content in coal which comprises: reacting the coal containing FeS2 with an effective amount of an aqueous solution of sulfurous acid and hydrochloric acid at about 100*C to 140*C to form free sulfur in the coal matrix; filtering the solution from the coal; washing the coal; and extracting the free sulfur from the coal with an organic solvent for sulfur.
3. The process of claim 2 in which the sulfur solvent is selected from the class consisting of benzene, kerosene, gas oil, and paracresol.
4. The process of claim 2 in which the extraction temperature varies from 50*C up to solvent reflux.
5. A process for reducing the pyrite sulfur content in coal which comprises: reacting the coal with an effective amount of an aqueous solution of sulfurous acid and hydrochloric acid at about 100*C to 140*C to form free sulfur in the coal matrix; filtering the solution from the coal; washing the coal; and heat drying the coal to volatize the free sulfur therein.
6. A process for reducing the pyrite sulfur content in coal which comprises: reacting the coal with an effective amount of an aqueous solution of sulfurous acid and hydrochloric acid to form free sulfur in the coal matrix; filtering the solution from the coal; washing the coal; extracting the free sulfur from the coal with an organic solvent for sulfur and heat drying the coal to remove the free sulfur contained therein.
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| US4022588A (en) * | 1976-03-05 | 1977-05-10 | Mobil Oil Corporation | Oxidative chemical removal of pyritic sulfur from coal by manganese, vanadium, and cerium oxidants |
| US4071328A (en) * | 1976-01-22 | 1978-01-31 | The Dow Chemical Company | Method of removing sulfur from coal |
| US4083696A (en) * | 1975-02-24 | 1978-04-11 | Texaco Inc. | Process for desulfurizing pipelined coal |
| US4092235A (en) * | 1975-11-26 | 1978-05-30 | Exxon Research & Engineering Co. | Treatment of coal by alkylation or acylation to increase liquid products from coal liquefaction |
| US4198291A (en) * | 1977-04-12 | 1980-04-15 | Atlantic Richfield Company | Float-sink separation of coal with liquid SO2 |
| US4203727A (en) * | 1978-11-29 | 1980-05-20 | Simpson Charles H | Process for reducing the sulfur content of coal |
| US4233034A (en) * | 1979-05-03 | 1980-11-11 | Union Oil Company Of California | Desulfurization of coal |
| US4257869A (en) * | 1979-08-17 | 1981-03-24 | Electric Power Research Institute | Liquefaction of acid treated coal |
| US4260471A (en) * | 1979-07-05 | 1981-04-07 | Union Oil Company Of California | Process for desulfurizing coal and producing synthetic fuels |
| US4297108A (en) * | 1978-05-10 | 1981-10-27 | Polymer Research Corp. Of America | Desulfurization of coal |
| US4305726A (en) * | 1979-12-21 | 1981-12-15 | Brown Jr George E | Method of treating coal to remove sulfur and ash |
| US4351716A (en) * | 1979-03-15 | 1982-09-28 | Exxon Research & Engineering Co. | Liquefaction process |
| EP0230500A1 (en) * | 1986-01-31 | 1987-08-05 | Charles H. Simpson | Method for removing pyritic, organic, and elemental sulfur from coal |
| US4695290A (en) * | 1983-07-26 | 1987-09-22 | Integrated Carbons Corporation | Integrated coal cleaning process with mixed acid regeneration |
| US4743271A (en) * | 1983-02-17 | 1988-05-10 | Williams Technologies, Inc. | Process for producing a clean hydrocarbon fuel |
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Cited By (61)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4083696A (en) * | 1975-02-24 | 1978-04-11 | Texaco Inc. | Process for desulfurizing pipelined coal |
| US4092235A (en) * | 1975-11-26 | 1978-05-30 | Exxon Research & Engineering Co. | Treatment of coal by alkylation or acylation to increase liquid products from coal liquefaction |
| US4071328A (en) * | 1976-01-22 | 1978-01-31 | The Dow Chemical Company | Method of removing sulfur from coal |
| US4022588A (en) * | 1976-03-05 | 1977-05-10 | Mobil Oil Corporation | Oxidative chemical removal of pyritic sulfur from coal by manganese, vanadium, and cerium oxidants |
| US4198291A (en) * | 1977-04-12 | 1980-04-15 | Atlantic Richfield Company | Float-sink separation of coal with liquid SO2 |
| US4297108A (en) * | 1978-05-10 | 1981-10-27 | Polymer Research Corp. Of America | Desulfurization of coal |
| US4203727A (en) * | 1978-11-29 | 1980-05-20 | Simpson Charles H | Process for reducing the sulfur content of coal |
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