CA1043724A - Coal desulfurization process - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Coal is dessulfurized by heating it in comminuted form in the presence of NO2 and other gases to remove part of the sul-fur in the coal. Sulfur still remaining in the coal will be in the form of an inorganic sulfate or sulfite or included in an organic radical, assuming coal has a condensed aromatic ring structure, with two double bonded oxygen atoms attached. This sulfur is for the most part removed by a subsequent additional step of exposing the pre-treated coal to water or to a heated alkali metal hydroxide solution.

Description

3~
1 BACKGROUND OE' T~IE INVENTION
_ 1. Prior Art Among the prior art known to the inventors is United States Patent No. 3,451,769 issued June 2~, 196~, to Kishitaka, et al, which is not concerned with desulfurizing coal, but is nevertheless considered of some pertinency. This patent teaches the concept of oxidation of ferrous ions to ferric ions by employment of NO2 as a catalyst in the presence of oxygen. The invention thereafter achieves a simplification of processing by mixing the oxidized solution with a concentrated amount of un-oxidized solution and subsequently neu-tralizes the mixture with ammonia. This entire process involves the treating of waste pickling liquors. The present invention, on the other hand, -~
involves the use of NO2 to electively oxidize the sulfur in coal in the presence of both carbon and hydrocarbon. Unli~e Kishitaka, in the present invention the sulfur is in a solid (not liquid) phase. Kishitaka has water present and depends upon the solution of NO2 to form nitric acid which is the oxidizinq agent. The use of an alkali metal hydroxide in the present invention method is an added step to remove sulfur not previously removed, while Kishitaka uses ammonia as an integral reagent.
United States Patent No. 3,387,941 issued June 11, 196 to Murphy, involves desulfurizing coal with steam and alkali metal hydroxides at 500-850C. The present invention, on the other hand, operates at lower temperatures of 100-500F and hydroxides are used only to hydrolyze and dissolve previously oxidized organic sulfur compounds. Water is only used to mechan-ically extract previously oxidized iron-sulfur compounds in the coal (iron and sulfites and sulfates).
United States Patent No. 3,607,718 issued September 21, 7~ `
1 1971 to Leaders, also -teaches a sulfur removing method for coal--involving the dissolution and hydrogenation of the coal to remove ash and inorganic and organic sulfur by the use of a ~`
partially hydrogenated hydrocarbon solvent. This is a process -clearly totally different from that of this invention.
United States Patent No. 3,375,188 issued March 26, 1968 to Bloomer, teaches a method for deashing coal by dissolving pulverized coal at 600-850F in a boiling aromatic hydrocarbon mixture. The present invention method is carried out at a lower temperature without hydrocarbons being present, and the coal itsel is not dissolved by the sulfur bearing components are oxi-dized and subsequently leached out.
United States Patent No. 3,723,291 issued to Thakker on March 27, 1973 involves adding an alkali metal ca~bonate to the ~`
coker feed stack prior to coking and then after coking, treating the coke with hydrogen at a temperature of from 1000F to 2000F.
This is a toaally different and much higher temperature process than that of the present invention.
SUMMARY OF THE INVENTION

The pre~ent invention method provides an improved method for desulfurizing coal while producing concentrated sulfuric acid as a commercially useful by-product.
The preferred embodiment of the present invention in- ~;
volves the following steps: Coal is first converted into particu-lates. We prefer to use pulverized coal in which no particulate is lar~er than approximately 1/4" in diameter. Although the process can be made to work on larger particles the sulfur removal ~ `
efficiency is reduced. The pulverized coal is placed into a reaction chamber into which is passed a combination of four gases with the interior of the chamber being maintained at a temperature

-2-~ L3~7~

1 in the range from 100 to 500F, for from 1 to 30 minutes, for continuous reactions or for Erom O.S to 5 hours for batch reaction, at a pressure in the range from 1 to 20 atmospheres. The prccess can be either on a batch or continuous basis as desired.
The yases used are preferably 2 (0-5 to 20 volume %), NO (0.25 to 10 volume ~), NO2 (0.25 to 10 volume ~) and N2 the remainder. The resulting sulfur containing products from this -O

step will typically be Fe SO4, SO3 or SO2 gas and R~ - R2 and Rl - S - R2. Fe SO4 is removed by water extraction as *his salt is soluble in water. The SO3 is converted into concentrated H2SO~ by being passed into a condenser containing a solution of H2SO4. The SO2 is recycled to the reactor where it is subsequent-ly oxidized to S03. It is within the scope of our invention to convert the SO2 or other sulfur containing compounds to SO3 by exposure of the SO2 to oxygen within the reactor by further reacting the reactOr effluent gas before contacting the gas with sulfuric acid. It is also within the scope of our invention to react the SO3 gas with compounds such as calcium oxide or sodium hydroxide t form calcium sulfate or sodium sulfate instead of sul~uric acid. These latter two variations are not discussed in dètail herein. In addition to calcium oxide or sodium hydroxide, any other alkali metal or alkaline earth oxide or hydroxide may he employed. If it is deslred to remove the sulfur from the above two indicated hydrocarbon sulfur containing radicals, a subsequent exposure thereof to sodium hydroxide heated to a temperature of from 200-220F at a pressure of from 1 to 20 atmosphere for 1 to ~;
30 minutes is required. `~
: .
It is therefore an object of the present invention to ;

provide an improved and simplified method for the desulfurization of coal.

:

:
. . ':

7~4 . `
1 Another object of the present invention is to provide an improved coal desulfurizing method which provides ~2SO~ acid as a by-product at a cost which renders the same commercially saleable.
These and other objects o~ this invention may be had by referring to the following description taken in conjunction with the accompanying drawings.
DESCRIPTION OF THE DRA~INGS
In the drawings: `
FIGURE 1 is a block diagram representing the process for removing sulfur from coal in accordance with the presently preferred embodiment of ~he invention;
FIGURE 2 is a diagrammatical illustration, in section, ;~
of the condenser of FIGURE l;
FIGU~E 3 is a diagrammatical illustration, in section, o~ the reactor of FIGURE 1, suitable for continuous processing;
and ` FIGURE 4 is a diagrammatical view,;in section, of a reactor for the present invention suited for batch processing. `~
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the drawings and more particularly to FIGURE 1, there is shown a representative continuous process arrangement for carrying out the present inventinn. A batch processing arrangement is also understood to be within the scope of this inventinn.
Coal in crushed or raw form is initially fed into a pulverizer 10 which serves to convert the raw coal into particles `
to be processed, the size of which will range from 200 mesh to as large as 1/4" in diameter. Pulverizers for accomplishing this commutation are well known and are commercially available, and thus pulverizer 10 will not be described in detail.

' _4_ , : :
; :

~ t7Z~
1 The converted coal is then fed into a reactor 18.
Reactor 18 will be more fully described hereinafter in combination with FIGURE 2. Reactor 18 receives the coal particles from pulverizer 10, together with a predetermined quantity of a combin-ation of the following four gases in the below listed relative quantities.
2 ~ 0-5 to 20 volume %
NO - 0.25 to 10 volume ~
NO2 ~ 0.25 to 10 volume %
N2 balance The chemical reaction which occurs both in reactor 18 and in subsequent steps in accordance with this invention will be described hereinafter. The physical steps only will first be considered. Upon being heated for a period of time of from 1 to 30 minutes at a pressure in the range from 1 to 20 atmospheres at a temperature of from 100 to 500F in reactor 18, the output from reactor 18 will typically be a combinatlon of materials, some solid, some gaseous, including Fe SO4, desulfurized coal and some additional hydrocarbons containing some sulfur. The solid portion of the output from the reactor 18 is directed to an extractor 26.
Water is added to the reactor products in extractor 26 and the inorganic sulfur present as sulfates or sulfites dissolves and passes to separa~or 24 with the liquid stream. This soluble portion includes the sulfur initially present as iron pyrites which is converted to sulfates and sulfites in the reactor. To aid in the removal of the sulfates and sulfites in the extractor, a soluble caustic such as sodium hydroxide may be added to the water in extractor 26. The water may also be kept warm to facilitate solubility.

',.: , . ' ' : ,-: ' . ' ': :' ' ' ., :'........ : . .

37~
1 The liquid phase, as men-tioned above, passes to separ-ator 24 where it is cooled to precipate the inorganic sulfates and sulfites, which are then removed by filtration. The water is then heated and recycled through extractor 26.
The solid phase product of extractor 26 is then passed to dryer 28 where it is dried. The drier is a standard commercial product, known to the art, and need not be described in detail.
The dried output of drier 28 is coal having a substantially lower sul~ur content than that entering the process.

The gaseous products from reactor 18 flow through trap 12 which removes volatile fuels and entrained coal particles which are carried in the gas stream. Suitable traps are commer-cially available and commonly known.
The clean gas from trap 12 which contains sulfur dioxide .
and sulfur trioxide given up by the coal in reactor 18 is bubbled ;~
through a sulfuric acid solution in condenser 14 dissolving sulfur trioxide ln the acid solution. As previously mentioned, it is also within the scope of our invention to react with the ;
S03 to form other compounds instead of sulfuric acid ~i.e. with ammonium hydroxide to form ammonium sul~ate, with sodiu~ hydroxide to form sodium sulfate, with calcium oxide to make calcium su~fatej.
These compounds could also be made by reacting the sulfuric acid with ~he appropriate basic compound.
A cross-sectional representation of the condenser 14 is shown in greater detail in FIGURE 2. Fed into inlet pipe 25 ~are the outlet gases from reactor 18, including 2' N2~ N0, N02, ~ ~
S2 and S03. It should be noted that two other gases may also be ``
generated in reactor 18; these are C0 and C02. The la~ter two gases will be produced, if at all, from an unavoidable minimal

3~ oxidation of some of the coal particles in the reactor in the .

:
.

~ 37~ :

1 pre~ence of oxygen. Any C0 produced will merely pass on through the system without affecting the present invention process as C0 is basically inert. Any generated C02 on the other hand, should be removed, and this is accomplished at a later stage in the present invention method in a manner hereafter to be explained~
The incoming gases to condenser 14 are treated as ~ollows: The gases containing S03 are bubbled up under some pressure through a porous disk 27 ~ituated within and near the lower end of the condenser. This disk 27 permits the gases to pass up therethrough while preventing liquid H2S04 previously included within the condenser 14 from leaking through. Any sulfur trioxide in the gas will dissolve in the acid covering ~ ;
porous disk 27. The acid with dissolved sulfur trioxide is passed into tank 29 where water is added to make more sul~uric acid.
The withdrawal of concentrated acid from the vessel and its re-placement by water keeps the acid concentration in the tank approx- -~
imately constant during operation.
The gas passing through condenser 14l having its acid soluble sulfur compounds removed, consists primarily ~ 2~ N0, 20 N02, C0 and C02, N2 and acid insoluble sulfur compounds This ~ ~
gas is passed through purifier 16 where the C02 is removed. A - -: -~.. :: -, ~raction of the gas leaving purifier 16 (about 0.1 to 1%~ is ~ ~ -vented through scrubber 22 (which removes the noxious componenta).
This is necessary since the reactant gases are consumed by the process, causing a buildup in the inert gas in the gas stream.
By venting a portion of the gas and providing makeup gas, as indicated by gas mixer 20, the active gas proportions can be - -maintained. ~ -Since N0, 2 and N02 exist in an equilibrium at any temperature, only N0 and 2 need be supplied, the required N02 being formed from the mixture.

.
. , . ~ .. . .
. :, :~':. . , ' : . ~ . ,-, -3~

1 As shown in FIGU~E 1, the reconstituted gas mixture is then recycled through reactor 18.
While most of the processing equipment required to practice the invented process is standard equipment, the reactor itself is not and therefore detailed descriptions of suitable reactors for both continuous and batch processing follows:
Re~erring now to FIGURE 3 which illustrates a continuous process reactor utilizing a so-called fluidized bed for the handling of the coal.

The reactor comprises an outer casing 30 and an inner shell 31 spaced there~rom. The inner shell ,must be capable of withstanding the process pressure and temperature contemplated! `~
and the outer casing is preferably theremally insulated. Heating ,D
fluid, for example steam or hot oil, is introduced into the space between casing 30 and shell 31 throu~h inlet pipe 32. After ~ -passing through the annular space 34 between the casing 30 and . . .
shell 31, thereby heating shell 31 and its contents, the heating fluid flows out of outlet 33. An inlet 37 is provided at the '- ~' bottom of shell 31 for the purpose of introducing the oxidizing gas into the reactor. As will be presently di,scussed, the oxidizing gas is blown through the recctor at high velocity. It will therefore be desirable that the~gas be preheated to prevent the gas from cooling the contents o~ the reactor.
. ~ :
Coal is conveniently introduced into the reactor at ~ , the bottom o~ the reac~or and from the side at inlet 36. A , ~
porous disk 35 below the coal inlet spreads the inlet gas across ~ ' the area of the reactor so that its vertical velocity is relatively uniform over the entire area.

The gas stream flowing upward through the particles of coal causes the particles to be agitated and thus the coal in the ':
,~

.. : " -. . : ~- .
', .. .. ~ . :. : .
: .. : ... . , .. - .. . ..

~v~
1 reactor acts as a fluid. Coal en-tering at inlet 36 flows upward through the reactor and eventually out of the top of the reactor through outlet 38. Coarse pieces of coal which are too large to flow upward under the influence of the oxidizing gas and other particles of coal flow out of the coarse coal outlet 39.
Oxidized coal flowiny out of outlet 38 is separated from the oxidizing gas by a cyclone separator 40, a standard item, well known in the art.
As previously described, the coal output is fed to the extractor while the gas is fed to a condenser through a trap.
The batch type reactor illustrated in FIGURE 4 includes 5 an outer casing 50 and inner shell 51 similar to the casing 30 and shell 31 of FIGURE 3, except that in the case of casing 50 ~ ~
and shell 51, removable tops 50' and 51' are provided to allow ~ -charging of the shell with coal. Alternatively, hatches could - ~-be provided for this purpose. -, ~
.i ~ :. .
The heating jacket 54 is supplied with heating f1Uid ~-through inlet 52, the outlet being indicated as 53.
A porous disk 55 spxeads the flow o~ gas entering through inlet 57 in a manner identical to that previously described ~or the continuous process reactor. Gas outlet 58 directs the spent oxidizing gas to the trap and condenser.
In operation, the batch reactor is disassembled, re-moving casing cover 50' and shell cover 51', and a charge of pulverized coal is loaded into the reactor. The reactor is then covered, heating fluid is started heating up the vessel and oxidizing gas is blown through the charge. After sufficient time to oxidize the sulfur compounds in the coal has passed, the fluid and gas flows are stopped, the reactor disassembled, and the charge removed and placed in the extractor for the next step in the process.

_g_ 3~

1 ~ representative empirical formula for coal is ClooH80NS
which also includes FeS and FeS0~. This coal may, when including these typical sulfur compounds, be depicted by the formula C10OH80NS FeS FeS04. of these three S's in this highly empirical and genralized ~ormula, the sulfur content will typically divide as follows:
FeS04 - 5%
FeS - 47-l/2~
Rl-S-R2 - 47-l/2%

The S in the Rl-S-R2 formula is considered as the organic sulfur included in the coal while FeS (Pyrites) and FeS04 is the inorganic iron bearing sulfur. The R would in turn refer-ence the ClooH80 of the above noted general formula.
- The chemical reaction steps of the presently invented method may generally be explained as follows:
N02 gas reacts in the coal reac-tor 18 with FeS contained ~;
in accordance with this equation.
(A) Fe S + 4 N02~ FeS04 + 4 N0 ~ ~ -The organic sulfur on the other hand reacts as follows with the N02 gas, also within reactor 18 in accordance with the following equation: 0 1 Rl ~ S - R2 + N2-~ R1 - S - R2 + N0 The partially oxidized organic sulfur compound again reacts with the N02 gas in the reactor, thusly:

(B2) Rl - S - R2 + N02 Rl ~ 11 ~ R2 + N0 The organic sulfur compound which now contains two doubling bonded oxygen atoms further reacts with N02 gas within the reactor 18 as follows:
O
ll (C) 1 ~ R2 + N02 ~ l + R2 ~ S03 ~ or So --1 0 ~

:~V'~3~
1 The reactions represented by equa-tions (A), (Bl) and (B2) all result in the production of NO gas. This NO combines with oxygen as indicated by equation (D) to produce N02; this N02 is used again in equations (A), (Bl), (s2) and (C). - ~
(D) NO + 1/2 2~ ~ 2 : :
Thus without water, without hydrogen, without a hydrogenated organic solvent and without an alkali soak, most of r the organic sulfur is freed from the coal.
The reactor products produced by the reactor as depicted ~ : :
in equation (Bl) and (B2) to the extent that they do not react further with N02 to totaIly free the organic sulfur, may further be treated in accordance with an additional process as-follows~
~- ~
Each of these reaction products may be exposed in the extractor 26 to NaOH or some other alkali metal hydroxide, thus the following will occur~

O
11 . ' Rl S R2 Ol - :

20 . 1 I R2 ;~

H2- + NaOH --- ~Rl + R2 + Na2S03 in solutio~
or Na2S04 in solution.
The above-described reaction which is intended to remove additional.organic sulfur not totally removed in reactor 18 is carried out in the extractor 26.

It will be understood that in lieu of sodium hydroxide, there may be used potassium hydroxide or any other alkali metal hydroxide for the indicated purpose. This step when employed is ; ~- ;
preferably ~arried out at from 1 to 10 atmospheres, at a tempera~
ture in the range of from 180F to 230F.

~LV437 ~1Lii 1 It will be observed that in the above reac-tions, the active gas which reacts with the sulfur compounds present in the coal is N02. Neither NO nor 2 is directly invalved in the re-action, however, both NO and 2 are unavoidably present since NO, 2 and N02 react in an equilibrium reaction as follows:
NO ~ 1/2 2~ N02 Thus as N02 is consumed by the reaction with sulfur, additional N02 is formed by the equilibrium reaction. Similarly, N02 is formed as NO and 2 are supplied in the make-up gas.

Any FeS04 contained within the coal in the reactor 18 (or produced as a result of reaction (A)), will not further react therein as it is already fully oxidized. It will later be precipitated out in the extractor 26 where water is added to the coal. Thus, the FeS04 is removed baslcally by mechanical as opposed to chemical means.
It will, of course, be apparent from an examinatio~ of the chamical reactions occurring in reactor 18 that the oxidized sulfur compounds there formed, if they are further to be reduced are soluble in caustic and not in waker -- thus encouraging use 2~ of the additional but not necessary step previously described.
A further note regarding the oxidation step in reactor 18 for the removal of sulfur in the organic form is considered significant. The oxidation reaction product ..
Rl - R2 in equation (Bl) combined with additional N02 at step (B2) resulting in a further oxidized state of the sulfur in the organic radical, permitting the substantial removal of the organic sulfur at step (C) by the still further ;
exposure of the radical O

.

3~
1 to N02 gas freein~ the Rl and R2 (coal) radicals from the organic sulfur without the employment of the caustic step previously described.
While both of the reactor products of the organic sulfur containing radicals will react with caustic as employed above, it -should further be noted that only the reaction product producea by --equation (B2) will react with NO2 to free the sulfer [equation ~C)].

A further study of equations (A), (Bl) and (B2) indicate the formation of NO whichis required for equation D to go forward and the reaction product of equation D is NO2 which is required for the reaction of (A), (Bl), (B2) and (C) to occur.
The gases which are introduced into reactor 18 are as followS :, N0 - lJ4 to 10~ by vclume 2 ~ 1/4 to 20% by volume NO2 ~ 1/4 to 10% by volume N2 ~ remainder.
While N2 is preferred, another inert gas or gases may be substitutea in whole or in part therefor. The inert N2 gas is required primarily for safety purposes (i~e., to prevent an explosion) in the otherwise highly volatile atmosphere which would be present in reactor 18, especially under conditions of elevated temperature and pressure. The inert N2 is also present in the selective reaction of the sulfur in the coal as opposed to the combustion thereof.
~ -of course some of the 2 and N0 is consumed during the reactions which occur as above described in the reactor 18, which must be replenished. NO2 exists in equilibrium with N0 and 2 at any temperature, and thus is spontaneously formed from a mixture of N0 and 2 and need not be individually supplied.

.
- : . ::
,,.. , '`: ' . ' ' ' ,. ' :"'`' ` ' ` ` '., " ' ' ' ~ 3t~
1 The following are examples of the sulfur reduction which has been obtained by utilizing the process o this inven-tion in accordance wi-th the batch process which takes place in a period from 1 to 4 hours. The continuous process on the other hand, will typically occur in from 1 to 30 minutes.
EXAMPLES
EX~PLE 1 .
Using the batch reactor process a sample of Lower Kittanning coal previously pulverized and segreg~ted as to size was treated. Coal of -14 t +28 ~esh-particle size was loaded into the reactor, the reactor assembled and heated to 20QF. For 3 hours a ~as mixture consisting of air with 9 per cent nitrogen oxide added was passed through the reactor and the bed of coal at one atmosphere pressure. The flow rate was such that about 10 times the stoichiometric quantity of oxygen required to oxidize the sulfur to sulfate forms was passed through the reactor.
The coal had an initial sulfur content of 4.3 per cent (3.6~ pyritic, 0.7~ organic, a trace of sulfate). After treatment, the coal was removed from the reactor, washed with water and 20 dried. The total sulfur content was 1.58 percent (i.e., 63% of the sul~ur was removed). The coal was then washed with 10 per cent aqueous sodium hydroxide ~ollowed by water and then dried. -The total sulfur content was 0.47 per cent (i.e. 87~ of the sulfur was removed).

Using the batch reactor process a sample of Lower Kittanning coal previously pulverized and segregated as to size was treated. Coal of -14 to +28 mesh size was loaded into the reactor, the reactor assembled and heated to 200~F. For 3 houxs a gas mixture consisting of air with 4.5 per cent nitrogen oxide ;

~: , . . . .

:1 134~ 7~

1 added was passed through the reactor and the bed of coal at one atmosphere pressure. The flow rate was such that about 10 times the stoichiometric quantity of oxygen required to oxidize the sulfur to sul~ate form was passed through the reactor. -The coal had an initial sulfur content of 4.3 per cent.After treatment, the coal was removed from the reactor, washed with water and dried. The total sulfur content was 2.5 per cent (i e., 43 per cent of the sulfur was removed). The coal was then washed with 10 per cent aqueous sodium hydroxide followed by -lQ water and then dried. The total sulfur was 2.1 per cent (i.e~, S0 per cent of the sulfur was removed). Approximately 95 per cent of the initial coal sample was recovered after treatment and before extraction.

.
Using the batch reactor process a sample of Illinois #5 coal previously pulverized and seyregated as to size was treated. Coal of -14 to +28 mesh size was loaded in~o the reactor, the reactor assembled and heated to 200F. For 3 hours a gas mixture consisting of air with 4.5 per cent nitrogen oxide adaed was passed through the reactor and the bed of coal. The flow rate was such that about 12 times the stoichiometric quantity of ` ~ -oxygen required to oxidize the sulfur to sulfate forms was passed `
through the reactor.
The coal had an initial sulfur content of 3.5 per cent (1.6% pyritic, 1.9% organic, a trace of sulfate). After treatment, -the coal was removed from the reactor, washed with water and dried. The total sulfur content was 1.9 per cent (i.e., 3~% of the sulfur was removed). The coal was then washed with 10 per cent aqueous sodium hydroxide followed by water and then dried.

The total sulfur content was 1.2 per cent (i.e., 60 per cent of r;:
the sulfate was removed).
.'' `~ ~''.

-15- ~

,'`- ':'' , ~

3~

Vsing the batch reac-tor process, a sample of Illinois #5 coal previously pulverized and segregated as to size was treated. Coal of -14 to ~28 mesh ~article size was loaded into the reactor, the reac-tor assembled and heated to 200F. For 3 hours a gas mixture consistiny of air with 10% nitrogen oxide added was passed through the reactor and the bed of coal at one atmos-phere pressure. The flow rate was such that about 12 times the stoichiometric quantity o~ oxygen required to oxidize the sulfur to sulfate forms was passed thorugh the reactor.

The coal had an initial sulfur content of 3.5% (1.6%
pyritic, 1.9~ organic, a trace of sulfate). After treatment, the coal was removed from the reactor, washed with water and dried.
The total sulfur content was 1.9% ~i.e., 46~ of the sulfur was removed). The coal was then washed with 10~ aqueous sodium hydroxide followed by water and then dried. The total sulfur content was 1.0 per cent (i.e., 71% of the sulfur was removed).

Using the batch reactor process, a sample of Lower ~O Kittanning coal previously pulverized and segregated as to size was treated. Coal of -80 to +100 mesh particle size was loaded into the reactor, the reactor assembled and heated to 200F For 3 hours a gas mixture consisting of air with 5~ nitrogen oxide added was passed through the reactor and the bed of coal at one atmosphere pressure. The flow rate was such that about 10 times ~
the stoichiometric quantity of oxygen required to oxidize the ~ ;
sulfur to sulfate forms was passed through the reactor.
The coal had an initial sulfur content of 4.3~ (3.6%
pyritic, 0.7% organic, a trace of sulfate). After treatment, the coal was removed from the ~eactor, washed with water, and dried.

~7~4 1 The total sulfur content was 2.9~ (i.e., 33~ of the sulfur was removed). The coal was then washed with 10% aqueous sodium hydroxide followed by water and then dried. The total sulfur content was 1.9% (i.e., 56% of the sulfur was removed).

Using the ba-tch reactor process, a sample of Lower Kittanning coal previously pulverized and segregated as to size was treated. Coal of -14 to ~28 mesh particle ~ize was loaded i~nto the reactor, the reactor assembled and heated to 200F. For 1.5 hours a gas mixture consisting of air with 10~ nitrogen oxide added was passed through the reactor and the bed of coal at one atmosphere pressure. The flow rate was such that about 5 times the stoichiometric quantity of oxygen required to oxidize the sulfur to sulfate forms was passed through the reactor.
The coal had an initial sulfur content of 4.3% ~3.6%
pyritic, 0.7~ organic, a trace of sulfate~. The coal was then washed with 10~ aqueous sodium hydroxide followed by water and then dried. l'he total sulfur content was 1.4% (i.e., 67% of the sulfur was removed). ;

. .. .
Using the batch reaction process, a sample of Lower Kittanning coal was treated as described above. The coal was -14 -~
to ~28 mesh size reacted ~or 5 hours at 200F using air with S
per cent nitrogen added. An excess of oxygen of 16 times was passed through the reactor.
- The coal had an initial sulfur content of 4.3~. After ~-oxidating and without any extraction (washing), the coal had a ~ -sulfur content of 3.3% ~i.e., 23% of the sulfur was removed by the oxidation treatment). ~-There thus has been described a new and improved process for desulfurizing coal and producing sulfuric acid in commerical ~ . . .
quantities as a valuable by-product. `~

-i7-

Claims (50)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for desulfurizing coal which includes the steps of:
a) heating coal particles to a temperature of from 100° to 500°F; and b) subjecting said heated coal particles to an oxidizing gas having NO2 as one of its constituents, said NO2 selectively oxidizing sulfur-containing compounds in said coal particles, said other constituents of said oxidizing gas being substantially non-reactive with said coal, whereby oxidized sulfur-containing compounds and gaseous sulfur compounds are formed which are readily separable from said coal particles.

2. The method of Claim 1 wherein said particles of coal have a diameter of no more than 1/4 inch.

3. The method of Claim 1 wherein said particles of coal has a particle size of from -14 to +28 mesh.

4. The method of Claim 1 wherein said coal particles are contacted with said oxidizing gas for 1 to 4 hours in a batch operation.

5. The method of Claim 4 wherein said oxidizing gas is at least 0.25% by volume NO2.

6. The method of Claim 4 and further including the step of leaching oxidized sulfur compounds from said particles of coal after said oxidizing step.

7. The method of Claim 1 wherein said reaction takes place at a temperature of 100° to 500°F and a pressure of 1 to 20 atmospheres over a period of 1 to 30 minutes.

8. The method of Claim 1 wherein said oxidizing gas in-cludes an inert gas in addition to said NO2, said oxidizing gas being at least 0.25% by volume NO2.

9. The method of Claim 8 wherein said oxidizing gas further includes O2 and NO, said O2 being less than 20% by volume of said oxidizing gas and said NO being less than 10% by volume of said oxidizing gas.

10. The method of Claim 9 wherein said O2, said NO and said NO2 exist in approximately equilibrium proportions.

11. The method of Claim 8 wherein said inert gas is nitrogen.

12. The method of Claim 10 wherein said oxidizing gas further includes O2 and NO, Said O2 being less than 20% by volume of said oxidizing gas and said NO being less than 10% by volume of said oxidizing gas.

13. The method of Claim 12 wherein said O2, said NO, and said NO2 exist in approximately equilibrium proportions.

14. The method of Claim l wherein said particles are oxidized and thereafter further including the step of leaching oxidized sulfur compounds from said particles of coal after said reacting step.

15. The method of Claim 14 wherein said leaching is done by water.

16. The method of Claim 14 wherein said leaching is done by a solution of water and caustic.

17. The method of Claim 14 wherein said oxidizing gas is comprised of an inert gas.

18. The method of Claim 14 wherein said oxidizing reaction takes place at a temperature of 100° to 500°F, at a pressure of 1 to 20 atmospheres, over a period of 1 to 30 minutes.

19. The method of Claim 16, wherein said caustic is NaOH.

20. The method of desulfurizing coal and producing salts of sulfuric acid which includes the steps of:
a) placing particles of coal having a diameter of no more than 1/4 inch in a reactor vessel, said vessel being main-tained at a temperature of 100° to 500°F and a pressure between 1 and 20 atmospheres;
b) circulating oxidizing gas through said reactor, said oxidizing gas having NO2 as one of its constituents, said NO2 selectively oxidizing sulfur-containing compounds on said coal particles, said other constituents of said oxidizing gas being substantially non reactive with said coal; and c) removing gaseous sulfur compounds from said oxidizing gas after it has passed through said reactor by contacting said gas with a compound selected from the group consisting of: NH40H, alkali metal oxides, alkali metal hydroxides, alkaline metal oxides, and alkaline metal hydroxides, whereby said gaseous sulfur compounds form salts of sulfuric acid.

21. The method of Claim 20, wherein said oxidizing gas comprises an inert gas.

22. The method of Claim 20 further including the step o*
leaching oxidized sulfur compounds in said coal after said coal has been reacted with said oxidizing gas.

23. The method of Claim 22, wherein said leaching is done by water.

24. The method of Claim 22, wherein said leaching is done by a solution of water and caustic.

25. The method of Claim 24, wherein said caustic is NaOH.

26. The method of Claim 20, wherein said oxidizing gas is contacted with NH40H, and said salt of sulfuric acid formed is ammonium sulfate.

27. The method of Claim 20, wherein said oxidizing gas is contacted with calcium oxide, and said salt of sulfuric acid formed is calcium sulfate.

28. The method of Claim 20, wherein said oxidizing gas is contacted with sodium hydroxide, and said salt of sulfuric acid formed is sodium sulfate.

29. The method of Claim 21 and further including the steps of leaching oxidized sulfur compounds from said particles of coal after said reacting step.

30. The method of desulfurizing coal containing sulfur in the form of iron pyrites which includes the steps of:
a) oxidizing said iron pyrites by reaction with NO2 gas, said coal being in the form of particles no larger than about 1/4 inch in diameter, said oxidation step being of 1 to 30 minutes duration at a temperature of 100° to 500°F and at a pressure of 1 to 20 atmospheres, whereby said iron pyrites are oxidized to form sulfates and sulfites; and b) leaching said sulfates and sulfites out of said particles of coal.

31. The method of Claim 30 wherein the leaching is done by water.

32. The method of desulfurizing coal containing sulfur in the form of an organic compound which includes the steps of:
a) oxidizing said organic sulfur compound by reaction with NO2 gas, said coal being in the form of particles no larger than about 1/4 inch in diameter, said oxidation step being of 1 to 30 minutes in duration, at a temperature of 100° to 500°F and at a pressure of 1 to 20 atmospheres, whereby said organic compounds are oxidized to form sulfates and sulfites; and b) leaching said sulfates and sulfites out of said particles of coal.

33. The method of Claim 32 wherein said leaching is done by water.

34. The method of Claim 32 wherein said leaching is done by a solution of water and caustic.

35. The method of Claim 32 wherein said oxidation step does not convert all of said organic sulfur compounds to sulfates and sulfites and wherein said leaching is done by a solution of water and caustic, said caustic converting said organic sulfur compounds to sulfates soluble in said caustic solution.
36. The method of desulfurizing coal containing sulfur in the form of an organic compound which includes the steps of:
a) oxidizing said organic sulfur compound by reaction with NO2 gas, said coal being in the form of particles no larger than about 1/4 inch in diamter, said oxidation step being of 1 to 30 minutes in duration, at a temperature of 100° to 500°F and at a pressure of 1 to 20 atmospheres; and b) hydrolyzing said oxidized organic sulfur compounds and leaching the products of said hydrolyzation reaction by

Claim 36 continued contacting said coal containing said oxidized organic compounds with a caustic solution, whereby said oxidized organic compounds are converted to sulfates and said sulfates are dissolved in said caustic solution.

37. The method of desulfurizing coal and producing sulfuric acid which includes the steps of:
a) placing particles of coal having a diameter of no more than 1/4 inch in a reactor vessel, said vessel being maintained at a temperature of 100°F to 500°F and a pressure between 1 and 20 atmospheres;
b) circulating oxidizing gas through said reactor, said oxidizing gas having NO2 as one of its constituents, said NO2 selectively oxidizing sulfur-containing compounds in said coal particles, said other constituents of said oxidizing gas being substantially non-reactive with said coal; and c) removing gaseous sulfur compounds from said oxidizing gas after it has passed through said reactor by contacting said gas with water whereby said gaseous sulfur compounds are dissolved in said water and sulfuric acid is formed.

38. The method of Claim 37 wherein said oxidizing gas comprises an inert gas.

39. The method of Claim 37 and further including the step of leaching oxidized sulfur compounds in said coal with a leaching agent after said coal has been reacted with said oxidizing gas.

40. The method of Claim 39 wherein said leaching is done by water.

41. The method of Claim 39 wherein said leaching is done by a solution of water and caustic.

42. The method of Claim 41 wherein said caustic is NaOH.

43. The method of Claim 34 wherein said caustic is NaOH.

44. The method of Claim 38 and further including the step of leaching oxidized sulfur from said coal with a leaching agent after said coal has been reacted with said oxidizing gas.

45. The method of Claim 44 wherein said leaching is done by water.

46. The method of Claim 44 and further including the step of removing said leached sulfur compounds from said leaching agent by reducing the temperature of said leaching agent whereby the solubility of said sulfur compounds in said leaching agent is reduced.

47. The method of Claim 46 wherein said oxidizing gas comprises the following gases:
NO - 0.25 to 10% by volume NO2 - 0.25 to 10% by volume O2 - 0.5 to 20% by volume N2 - balance.

48. The method of desulfurizing coal which includes the steps of:
a) heating particles of coal between -14 and +28 mesh.
size to 200°F;
b) flowing a gas mixture comprised of air with 10% NO
by volume, thus forming NO2 in situ; said mixture being added

Claim 48 continued through said coal particles at one atmosphere for a period of 3 hours;
c) washing said coal particles with water;
d) washing said coal particles with a 10% aqueous solution of NaOH; and e) washing said coal particles with water, whereby said sulfur is extracted from said coal particles.

49. The method of Claim 48 with the amount of NO added to said air in the range from 0.25 to 10% by volume.

50. The method of claim 48 with the usual amount of NO
added to said air increased to 10% and the time said gas is passed through said coal particles is reduced to 1.5 hours.