US3768988A

US3768988A - Removal of pyritic sulfur from coal using solutions containing ferric ions

Info

Publication number: US3768988A
Application number: US00163893A
Authority: US
Inventors: R Meyers
Original assignee: TRW Inc
Current assignee: Northrop Grumman Space and Mission Systems Corp
Priority date: 1971-07-19
Filing date: 1971-07-19
Publication date: 1973-10-30
Anticipated expiration: 1990-10-30
Also published as: GB1328053A

Abstract

Finely divided coal or solid coal derivatives containing pyrite are reacted with a ferric ion solution; FeCl3 is particularly suitable. The ferric ion is reduced to ferrous ion and free sulfur is formed. The solution 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. At least 60 percent of the pyrite sulfur and pyrite iron is removed using the process of this invention. If desired, the ferrous chloride can be regenerated; this permits iron oxide to be recovered as a byproduct.

Description

Unite Statesv Meyers atent 1 REMOVAL OF PYRITIC SULFUR FROM COAL USING SOLUTIONS CONTAINING FERRIC IONS [21] Appl. No.: 163,893

Related US. Application Data Continuation-impart of Ser. No. 116,262, Feb. 17, 1971, abandoned.

[ 1 Oct. 30, 1973 3,652,219 3/1972 Peters et al. 23/200 3,640,016 2/1972 Lee 44]] R 2,592,580 4/1952 Loevensteim. 23/200 1,980,809 11/1934 Levy 23/226 Primary ExaminerC. F. Dees AttorneyDaniel T. Anderson et al.

[57] ABSTRACT Finely divided coal or solid coal derivatives containing pyrite are reacted with a ferric ion solution; FeCl is particularly suitable. The ferric ion is reduced to ferrous ion and free sulfur is formed. The solution is then [52] Egg/ 2 47 filtered from the coal which is then washed and heat [51] Int Cl b 9/00 dried under low pressure. Most of the free sulfur is [58] Fe. 44,4 6 volatized from the coal due to the heat drying; addi gg z gg' 'a 7 3 tional free sulfur can be removed by additional washing and heat drying and/or solvent extraction techniques. At least 60 percent of the pyrite sulfur and pyrite iron is removed using the process of this inven- [56] References cued tion. If desired, the ferrous chloride can be regener- UNITED STATES PATENTS ated; this permits iron oxide to be recovered as a by- 2,204,148 6/1940 Nelms 44/4 X product. 2,895,796 7/1959 Hill 23/224 3,252,769 5/1966 Nagelvourt 44/1 R 19 Claims, 2 Drawing Figures H2O Q H20 1 T f l 2 F90 FeCl SOLUTION .neclmn 0 WATER filmy av coourLe fiaklzmosi A 212F 02 212F 2 l 2 1 3518mm "20 Q F 1 ATM 5316:1014

Fe o

PYRITE o Flcla MAKE-UP COM 1 AT COAL FILTRATION I PATENIEnum 30 ms SHEET 1 [IF 2 H2O Q H 0 2| T T 20 T I9) 'a FeCl WATER Y SOLUTION PREC PITATION REHEAT Y COQUNG YKPTORIZATION i v 21m 2I2F I55F 22 I 23 R0 2 -H QXI ATION .c All ATM SOL ION ll wane J10 Y REACTION FeCl -MAKE UP I AM 4 COAL COAL m FILTRAYTION 0.5 HR

' Fig. I.

I N VEN TOR.

AGENT PATENIEU 0m 30 ms SHEET 2 OF 2 I4 15 FOUR smse COAL WASHING SULFUR COOLING CONDENSATION 225F MEDIA- l7 E Q G SULFUR N VAPORIZATION v 1 'AYM 1 ATM COAL 2I2F 450% Fig- 2 Robert A. Meyers INVENTOR.

AGENT REMOVAL OF PYRITIC SULFUR FROM COAL USING SOLUTIONS CONTAINING FERRIC IONS This application is a continuation-in-part of application Ser. No. 116,262 filed Feb. 17, 1971, now abandoned.

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 a ferric ion.

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 sulfur contents which can range up to percent.

Based on a 4 percent surface content, a 1,000,000 Kilowatt plant burns about 8,500 tons per day of coal and consequently emits 680 tons per day of sulfur dioxide. If this sulfur could be removed and converted, it would produce 900 tons of H 80, daily.

It has long been recognized that S0 in the atmosphere will either retard growth or kill vegetation. In addition, the potential hazard to humans appears about the same as for thevegetable kingdom.

While it is possible to remove pyritic sulfur from coal by froth flotation or washing processes; these are not selective so that a large portion of the coal is discarded along with ash and pyrite. Hence, 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 lead to the importation of low sulfur content fuel oils for domestic and industrial use. The crude oil reserves, which are the source of the residue, are expected to run out in 20 30 years while coal reserves are sufficient for several hundred years at a minimum.

It is, therefore, an object of this invention to provide a process for the reduction of sulfur, particularly pyritic sulfur in coal. I

Another object is to provide a process for the recovery from coal of sulfur and sulfur compounds.

Another object is to provide a process for the recovery of iron values from coal containing pyrite.

Other objects of this invention will become apparent from the description and the diagram 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 ferric ion to obtain a high yield of free sulfur. Fe ion particularly as F eCl is preferred; other ferric salts such as acetate, sulfate, citrate, oxide, ferric ammonium sulfate, etc., may be employed. A typical reaction proceeds as follows:

2 FeCl FeS 3FeCl 25.

The solution containing some free sulfur, ferrous chloride and any unc'onsumed ferric chloride is removed from the coal by filtration.

The coal is then washed and dried, preferably by heating in a vacuum; this results in the major portion of free surfur being volatized as follows: S.Coal S coal. If desired, a further wash, filtration and heating will remove more of the sulfur and any residual ferrous ion. One or more extractions'with a suitable organic sulfur'solvent such as benzene, kerosene or para cresol may be 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 concentrating the solution by evaporating most of the water. The concentrated solution is cooled, thereby precipitating the ferrous chloride from the ferric chloride, most of the latter still remaining in solution. The precipitated ferrous chloride is air oxidized to ferric chloride and iron oxide and finally the ferric chloride is recycled and the iron oxide recovered.

Typical treatment temperatures may vary from 50 C C. Reflux times are typically one-half 2 hours and higher. Typical coal particle sizes may vary from 200 mesh to one-half-inch pieces. Atmospheric pressure may be employed, but higher pressures can also be used.

The effective amount the ferric ion solution employed for extraction depends on the amount of coal treated and its pyritic sulfur content, the amount of sulfur desired to be extracted, extraction times, extraction temperatures, concentration of the ferric ion in the solution, etc.

The reaction of ferric chloride and ferrous persulfide to produce free sulfur is known. However, it was unexpected that the reaction with ferric ion (e.g., FeCl and pyrite could be carried out in a coal medium since pyrite is dispersed very finely throughout the coal matrix, and penetration of such an organic matrix with water is known to be difficult. Furthermore, the volatization of sulfur from coal is unusual 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 aqueous oxidizing agents such as HNO H 0 or HOCl. This will convert the sulfur content to sulfate, but not to free sulfur. This is the basis for chemical analysis of the pyritic sulfur content of coal; however, such strong oxidizing agents also extensively oxidize the organic coal matrix. By contrast, ferric salts are almost totally selective in the sense that the organic coal matrix is undisturbed.-

Hence, ferric salts, but not I-INO H 0 or l-IOCI, provide an economical route to the removal of pyrites from coal.

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, chars from hydrocracked coals and middlings are all capable of being refined by the extraction process of this invention.

The invention will be understood by reference to FIGS. 1 and 2 in which ferric chloride make-up solution and coal are fed into a pyrite reactor 10 maintained at atmospheric pressure and about 212 F. Pyrite (FeS is extracted from the coal, and the slurry containing unreacted ferric chloride, ferrous chloride, sulfur, ferrous persulfide, and the treated coal are fed to a coal filtration unit 11. Vacuum disk filters in the coal filtration unit are used to separate the bulk of the iron chloride solution from the treated coal.

In the

coal washing sections

12, 13, 14, and 15, four stages of countercurrent washing with intermediate filtration steps are used to reduce the residual chloride content of the coal to less than about 100 ppm. A suitable residence time of the coal in each of the washing stages is about l5 minutes; rotary vacuum disk filters FeCl 3/2 4FeCl Fe O The reaction employs air and is carried out at atmospheric pressure at about 480 F. The oxidized precipitate (ferric chloride and iron oxare used to ,separate the coal and wash the Solunon ide) is then transferred to a solution-filtration unit 23 tween washmg where the soluble ferric chloride is then separated from The washed coal then fed to a coal drymg m 16 the insoluble iron oxide by dissolving in water. The ferwhere steam tube dryers are employed E ric chloride solution is recycled to the ferric'chloride the ljesldual ,water from the washe d coal thls make-up solution for use in reactor 10. The iron oxide erauon being earned out at atmosPhenc pressure and is filtered from the ferric chloride solution and may be about 212 F. The heated dry coal is then forwarded to g.ecovemd as a byproduct of the process a sulfur vaporization unit 17 where freesulfur, which Typical coals which may be employed in the process was produced in the extraction reaction in reactor 10, include Missouri Lower Freeport, Bevier, Indiana No is vaporized at atmospheric pressure and a temperature V, and Pittsburgh. These coals contain sulfur forms as of about 2 F under reducfgd (30 min) shown in Table l when freshly mined. As they stand exand i 250 9 The vaponzed sulfur 1s removed posed to air, small amounts of sulfate sulfur are formed by nitrogen gas into a sulfur condensation unit 18 and from the pyrite content. cooled to about 225 F causing it to condense. The sulfur vapor is then passed to a recovery unit as bright sul- TABLE 1 fur. The treated coal with reduced pyrite content is SULFUR COMPOUNDS IN COAL then forwarded for use.

in the ferric chloride regeneration stage, the filtrate Bevier gig Indiana No v Pittsburgh from the coal filtratlon unit 11 15 passed to a thickener p i unit 19 where water is vaporized from the solution at 12-33 0.5-L7 atmospheric pressure and about 212 F. The concen- LL23 L543 trated solution is then passed to a precipitation unit 20 Total where ferrous chloride is precipitated by cooling the solution to 155 F at atmospheric pressure. Unreacted Table 2 shows the original pyritic sulfur content of ferric chloride solution from the precipitation unit 20 the Missouri and Lower Freeport coals and the reducis heated in a reheater 21 and then combined with fer- 3 tion in sulfur content due to treatment of FeCl;,. ric chloride make-up for feeding to the reactor 10. It will be observed that a marked reduction in pyritic The ferrous chloride precipitate, which has been sepsulfur occurs after only a single treatment with FeCl arated by filtration from the ferric chloride solution in followed by a water washing and drying. reactor 20, is transferred to an air oxidation furnace 22 Table 3 shows the effect of employing an organic solwhere it is reoxidized back to ferric chloride and iron vent to remove the free sulfur which remains following oxide, the reaction equation being the FeCl and water washing treatment.

TABLE 2 FeCls extraction data Wt. loss after Reflux washing Pyritic 2 Fe 3 (90 C.) and dry- Sulfur Wt pcrsulfur Sample Wt. Vol. Molarity, pyritic time ing, wt. Eschka, wt. eent Fe removed,

Coal number coal, g. 3 FeOh FeCl; Fe (hrs.) percent 5 percent. in coal 2 percent Missouri untreated (mesh size -200) 4. 75 1. 65

Missouri (mesh size 200) 1 200 0.5 3.9/1 16 0.22

Missouri (mesh size 200) 2 500 0.3 5/1 2 -9.1 4.18 0.86

Missouri (mesh size 200) 3 30 500 0.5 13/1 20 +2.0 3.2; 0.19

Lower Freeport U. (Mesh size -14) 54 16 Lower Ireeport (mesh size -14) 4 50 730 0.5 6/1 3 2 4 l4. 1 1. 99 1.10

1 ASTM D271.

2 Bureau of Mines procedure and Standard Methods of Chemical Analysis, Furman, volume 1, page 542. 3 Remarks: Residue removed from condenser was analysed by electron microprobe as follows: Fe, S, Si, O, C were maior constituents; Ca, 01, A1

were trace.

Yellow crystals formed; Hg spot test for free S was positive.

6 Sample 2 was washed once with 250 cc. hot water and dried 24 hours in a hot water and dried 72 hours at 90 in a vacuum oven.

0. vacuum oven. Samples 3 and 4 were washed twice with 250 cc.

TABLE 3 Solvent extraction data following FeCla treatment and water wash Sulfur concentration Percent Wt. loss, extrac- Sample number Solvent Extraction procedure gain Esehka tion 1 Benzene, 5-10 min 3 hot (80 C.) cc. washings 8L 2 -.do -.do o i g: 60 3a -410 "do +2 2 3g so 3b p-Cresol, 510 min. M111. (200 C.) reflux 13.6%{ 4 Benzene, 5-10 min. 3 hot (80 C.) 100 cc. washings g 74 From the data in Table 3, it appears that the organic solvent treatment causes a major portion of the pyritic sulfur to be extracted; also, use of para cresol appears to result in extraction of organic as well as pyritic bound sulfur. While the efficiencies shown range from 60 percent to at least 89 percent, this efficiency range can be changed by altering such factors as wash times, particle size, amounts and concentrations of FeCl;, and solvents, ferric salt treatment, reflux temperature, etc.

Table 4 shows the effect of FeCl;, extraction on various coals employing reaction conditions similar to Table 2. The table shows that 72 93 percent of the pyritic sulfur content may be removed in 2 hours by 0.5 M rec], solution from a wide variety of coals. Further, the process was applicable to all the coals, and in the case of Indiana No. V, the extraction efficiency was excellent.

TABLE 4 PYRITIC SULFUR REMOVAL DATA Pyritic Total Total Total Sulfur Sulfur Sulfur Sulfur Coal Removed Removed Before After Lower Freeport. 48 75 3.87 2.0l Lower Freeport 64 72 3.40 1.2 3 Bevier 36 72 4.60 2.94 Indiana No. V 51 93 3.28 1.67 Pittsburgh 39 78 L81 l. l0

All coals were 14 mesh except Bevier which was 200 mesh The process of this invention is extremely efficient in that at least 60 percent of the pyrite sulfur is extracted and the iron employed for extraction is easily recovered (about 85-90 percent) and may be reused. Furthermore, iron removal is facilitated since the iron contained in the FeCl extraction solution and the iron in the pyrite are indistinguishable; hence, no special techniques are required to separate different metals from the wash-extraction operation if metal recycling isdesired.

in addition, the process is simple in that no high temperatures, pressures or catalysts are required.

Finally, the extraction with FeCl does not produce an interaction with the organic coal matrix; this permits substantially all of the coal to be utilized as low sulfur fuel.

What is claimed is 1. A process for reducing the pyritic sulfur content of 7 coal which comprises reacting the coal with an effective amount of an aqueous solution containing F e ion and removing from the coal sulfur formed by the pyrite reaction.

2. A process for reducing the pyritic sulfur content of coal which comprises reacting the coal with an effective amount of an aqueous solution containing Fe ion selected from the class consisting of FeCl:, and ferric sulfate, and removing from the coal sulfur formed by the pyrite reaction.

3. A process for reducing the pyritic sulfur content of coal which comprises:

reacting the coal with an effective amount of an aqueous solution containing Fe ion;

removing from the coal sulfur formed by the pyrite' reaction using the following steps:

separating the said solution from the treated coal;

washing the coal and separating the wash solution from the treated coal; and

drying the coal to volatize the free sulfur contained therein.

4. The process of claim 3 in which free sulfur from the volatization step is extracted with an organic solvent for sulfur selected from the class consisting of benzene, kerosene a'nd p-cresol.

5. The process of claim 3 in which the aqueous solution employed is selected from the class consisting of FeCl;; and ferric sulfate.

6. The process of claim 3 in which the aqueous F e ion solution is selected from the class consisting of ferric acetate, ferric citrate, ferric oxide and ferric ammonium sulfate.

7. A process for reducing a pyritic sulfur content in coal which comprises:

reacting the coal with an effective amount of an aqueous solution containing Fe ion and removing from the coal sulfur formed by the pyrite reaction using the following steps:

separating the said solution from the treated coal;

washing the coal and separating the wash solution from the coal; and

extracting free sulfur from the treated coal with an organic solvent for sulfur selected from the class consisting of benzene, kerosene and p-cresol.

8. The process of claim 7 in which the aqueous solution employed is selected from the class consisting of FeCl and ferric sulfate.

9. The process of claim 7 in which the aqueous Fe ion solution is selected from the class consisting of ferric acetate, ferric citrate, ferric oxide and ferric ammonium sulfate.

10. A process for reducing the pyritic sulfur content in coal which comprises:

reacting the coal with an effective amount of ,an

aqueous solution of Fe ion, and removing from the coal sulfur formed by the pyrite reaction using the following steps:

separating the said solution from the treated coal;

washing the coal and separating the wash solution from the treated coal;

drying the coal to volatize the free sulfur contained therein; and

oxidizing the separated solution to ferric ion.

11. The process of claim 10 in which the oxidizing step is carried out with a gas selected from the class consisting of air and oxygen.

12. The process of claim 10 in which the aqueous solution employed is selected from the class consisting of FeCl;, and ferric sulfate.

13. The process of claim 10 in which the aqueous Fe ion solution is selected from the class consisting of ferric acetate, ferric citrate, ferric oxide and ferric ammonium sulfate.

14. A process for reducing the pyritic sulfur content in coal which comprises:

reacting the coal with an effective amount of an aqueous solution Fe ion, and removing from the coal sulfur formed by the pyrite reaction employing the following steps:

separating the said solution from the treated coal;

washing the coal and separating the wash solution from the treated coal;

drying the coal to volatize the free sulfur contained therein;

extracting additional free sulfur from the treated coal with an organic solvent for sulfur selected from the class consisting of benzene, kerosene and p-cresol;

concentrating the ferrous ion solution by evaporating some of the water;

cooling the solution thereby precipitating ferrous ion;

separating the ferrous ion precipitate from the solution containing ferric ion;

oxidizing the ferrous ion precipitate to ferric ion and iron oxide;

dissolving the ferric ion in water; and

separating the iron oxide from the aqueous solution containing ferric ion.

15. The process of claim 14 in which the aqueous solution employed is selected from the class consisting of FeCl;, and ferric sulfate.

16. The process of claim 14 in which the aqueous Fe ion solution is selected from the class consisting of ferric acetate, ferric citrate, ferric oxide and ferric ammonium sulfate.

17. A process for reducing the pyritic sulfur content in coal which comprises:

reacting the coal with an effective amount of an aqueous solution of Fe ion and removing from the coal sulfur formed by the pyrite reaction using the following steps:

separating the said solution from the treated coal;

lution employed is selected from the class consisting of FeCl and ferric sulfate.

19. The process of claim 17 in which the aqueous Fe ion solution is selected from the class consisting of ferric acetate, ferric citrate, ferric oxide, and ferric ammonium sulfate.

Claims

2. A process for reducing the pyritic sulfur content of coal which comprises reacting the coal with an effective amount of an aqueous solution containing Fe 3 ion selected from the class consisting of FeCl3 and ferric sulfate, and removing from the coal sulfur formed by the pyrite reaction.
3. A process for reducing the pyritic sulfur content of coal which comprises: reacting the coal with an effective amount of an aqueous solution containing Fe 3 ion; removing from the coal sulfur formed by the pyrite reaction using the following steps: separating the said solution from the treated coal; washing the coal and separating the wash solution from the treated coal; and drying the coal to volatize the free sulfur contained therein.
4. The process of claim 3 in which free sulfur from the volatization step is extracted with an organic solvent for sulfur selected from the class consisting of benzene, keRosene and p-cresol.
5. The process of claim 3 in which the aqueous solution employed is selected from the class consisting of FeCl3 and ferric sulfate.
6. The process of claim 3 in which the aqueous Fe 3 ion solution is selected from the class consisting of ferric acetate, ferric citrate and ferric ammonium sulfate.
7. A process for reducing a pyritic sulfur content in coal which comprises: reacting the coal with an effective amount of an aqueous solution containing Fe 3 ion and removing from the coal sulfur formed by the pyrite reaction using the following steps: separating the said solution from the treated coal; washing the coal and separating the wash solution from the coal; and extracting free sulfur from the treated coal with an organic solvent for sulfur selected from the class consisting of benzene, kerosene and p-cresol.
8. The process of claim 7 in which the aqueous solution employed is selected from the class consisting of FeCl3 and ferric sulfate.
9. The process of claim 7 in which the aqueous Fe 3 ion solution is selected from the class consisting of ferric acetate, ferric citrate and ferric ammonium sulfate.
10. A process for reducing the pyritic sulfur content in coal which comprises: reacting the coal with an effective amount of an aqueous solution of Fe 3 ion, and removing from the coal sulfur formed by the pyrite reaction using the following steps: separating the said solution from the treated coal; washing the coal and separating the wash solution from the treated coal; drying the coal to volatize the free sulfur contained therein; and oxidizing the separated solution to ferric ion.
11. The process of claim 10 in which the oxidizing step is carried out with a gas selected from the class consisting of air and oxygen.
12. The process of claim 10 in which the aqueous solution employed is selected from the class consisting of FeCl3 and ferric sulfate.
13. The process of claim 10 in which the aqueous Fe 3 ion solution is selected from the class consisting of ferric acetate, ferric citrate and ferric ammonium sulfate.
14. A process for reducing the pyritic sulfur content in coal which comprises: reacting the coal with an effective amount of an aqueous solution Fe 3 ion, and removing from the coal sulfur formed by the pyrite reaction employing the following steps: separating the said solution from the treated coal; washing the coal and separating the wash solution from the treated coal; drying the coal to volatize the free sulfur contained therein; extracting additional free sulfur from the treated coal with an organic solvent for sulfur selected from the class consisting of benzene, kerosene and p-cresol; concentrating the ferrous ion solution by evaporating some of the water; cooling the solution thereby precipitating ferrous ion; separating the ferrous ion precipitate from the solution containing ferric ion; oxidizing the ferrous ion precipitate to ferric ion and iron oxide; dissolving the ferric ion in water; and separating the iron oxide from the aqueous solution containing ferric ion.
15. The process of claim 14 in which the aqueous solution employed is selected from the class consisting of FeCl3 and ferric sulfate.
16. The process of claim 14 in which the aqueous Fe 3 ion solution is selected from the class consisting of ferric acetate, ferric citrate and ferric ammonium sulfate.
17. A process for reducing the pyritic sulfur content in coal which comprises: reacting the coal with an effective amount of an aqueous solution of Fe 3 ion and removing from the coal sulfur formed by the pyrite reaction using the following steps: separating the said solution from the treated coal; washing the coal and separating the wash solution from the treated coal; dRying the coal to volatize the free sulfur contained therein; concentrating ferrous ion solution by evaporating some of the water; cooling the solution therein by precipitating the ferrous ion; separating the ferrous ion precipitate from the solution containing ferric ion; air oxidizing the separated solution to ferric ion and iron oxide; dissolving the ferric ion in water; and separating the iron oxide from the aqueous solution containing ferric ion.
18. The process of claim 17 in which the aqueous solution employed is selected from the class consisting of FeCl3 and ferric sulfate.
19. The process of claim 17 in which the aqueous Fe 3 ion solution is selected from the class consisting of ferric acetate, ferric citrate and ferric ammonium sulfate.