Note: Descriptions are shown in the official language in which they were submitted.
~2tj~ ~ZV
METHOD FOR REMOVING PYRITIC, ORGANIC
AND ELEMENTAL SULFUR FROM COAL
FIF.LD OF THE INVENTION
The present invention relates to a method for
reducing the sulfur and ash content of coal or other
carbonaceous materials. More particularly, the
present invention relates to a chlorinolysis method
for extracting pyritic, organic and elemental sulfur
as well as ash from coal or other carbonaceous
materials. In one embodiment of the present inven-
tion, the pyritic, organic and elemental sulfur may be
largely removed in the form of sulfate sulfur. In a
second embodiment of the present invention, sulfur is
first removed which can be recovered as elemental
sulfur, and then, a large proportion of the remaining
sulfur is removed as sulfate sulfur. The present
invention is particularly useful for removing organic
sulfur from coal or other carbonaceous materials.
BACKGROUND OF THE INVENTION
Processes for desulfurizing coal are well known
in the art. Most of these processes are useful for
reducing the pyritic content of coal, but have little
or no effect on reducing the organic or elemental
sulfur in coal.
One process is set forth in U.S. Patent 3,960,513
which discloses a process for reducing the amount of
sulfur in coal by subjecting an aqueous slurry of coal
to pressure oxygen leacning. In one embodiment, the
aqueous solution may be acidic. However, this treat-
ment removes mainly pyritic sulfur. Removal of
organic sulfur requires an additional step of treating
the coal with oxygen and a solvent such as ammonium
hydroxide. Further, removal of the elemental sulfur
requires a separate extraction with a solvent such as
kerosene or toluene.
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Removal of pyritic sulfur by means of an acid
leach solution or an oxygen-containing gas is also
disclosed in U.S. ~atent 4,083,696.
Another approach to removal of pyritic sulfur
s from coal is set forth in U.S. Patents 3,926,575
and 3,768,988. This process comprises reacting finely
divided coal with sulfuric acid and, optionally,
hydrochloric acid to form ferric chloride which pre-
sumably reacts with the pyrite in the coal to generate
free sulfur. In addition to an acid leach, a final
solvent extraction step may be included to remove
further free sulfur in the coal. If the solvent is
para cresol, apparently a portion of organic sulfur
compounds contained in the coal can also be removed.
U.S. Patent 4,305,726 relates to a method for
removing pyritic sulfur and ash from coal. The method
involves treating coal with spent pickle liquor and
reacting in the presence of hydrochloric acid, hypo-
chorous acid and oxygen gas formed by adding the
coal/pickle liquor mixture to a reactor with water and
chlorine gas. After reaction, the ash is removed by
mechanical means, for examp~e by use of a weir.
In addition to the above-described desulfuriza-
tion methods, methods are known which employ metal
chloride salts. For example, U.S. Patent 3,909,213
discloses a process for desulfurization of coal which
comprises digesting coal with a Group IA or IIA metal
oxide and a fused metal chloride salt such as zinc or
ferric chloride. The medium is apparently capable of
dissolving sulfur-containing organic compounds present
in the coal. Anhydrous hydrogen chloride is passed
through the digestion zone. U.S. Patent 4,127,390
discloses a process employing an aqueous solution of
sodium chloride for extracting pyritic sulfur from
coal.
In addition to the numerous examples of processes
set forth above, it is also known that organic
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sulfates can be extracted from coal by the use of
solvents such as combustible sulfur solvents (U.S.
Patent 4,203,727) and chlorinated organic solvents
(U.s. Patent 4,081,250).
Despite the numerous above-described processes
for desulfurizing coal, it is apparent that there
still remains room for improvement. In particular, a
more efficient, more economical method of desulfuriz-
ing coal and other carbonaceous materials would be
desirable.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention
is to provide a process for removing sulfur and ash
from coal and other carbonaceous materials which
removes not only pyritic sulfur, but also organic
sulfur and elemental sulfur.
A further object of the present invention is to
provide a process for removing sulfur and ash from
coal which utilizes readily available, inexpensive
chemical components.
A further object of the present invention is to
provide a process for removing sulfur and ash from
coal which will in a short period of time successfully
remove large amounts of organic, sulfate and pyritic
sulfur impurities from coal without chlorinating the
coal and without losses of large amounts of the coal
during the treatment process.
A further object of the present invention is to
provide a process for removing pyritic sulfur, organic
sulfur, elemental sulfur and ash from raw coal.
An even further object of the present invention
is to provide a method for removing sulfur and ash
from coal wherein the ash is removed in solution.
These and other objects have been achieved by
providing a process for removing sulfur and ash from
coal and other carbonaceous materials which contain
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pyritic sulfur, sulfides, elemental sulfur, organic
sulfur and/or sulfate sulfur which comprises the steps
of:
(I) treating an aqueous slurry of the coal or
other carbonaceous materials at an elevated tempera-
ture below the oxidation temperature of the coal or
other carbonaceous materials and in the presence of an
oxidizing agent capable of reducing pyritic sulfides
to a soluble state with
(A) a formulation comprising:
(1) one or more alkaline earth
metal chlorides, one or more alkali
metal chlorides or a mixture of the
chlorides, and
(2) a treating agent comprising:
(a) a catalyst comprising: (i) one or
more deliquescent halogen salts, barium
chloride, potassium chloride or mix-
tures thereof, and (ii~ one or more
reducing oxides, one or more chromate
salts, or mixtures thereof, (iii) pro-
vided that if potassium chloride is not
present in the slurry containing
formulation (A), potassium fluoride or
tannic acid is also present in the
catalyst; and (b) an inorganic acid
selected from the group consisting of:
(i) hydrochloric acid, (ii) nitric
acid, (iii) hydrochloric acid and
nitric acid, (iv) hydrochloric acid and
ferric chloride, and (v) nitric acid
and ferric chloride,
(3) provided that if iron is not
present in the coal or other carbona-
ceous material, then ferric chloride is
present in the slurry containing
formulation (A), or
.
(B) a formulation comprising:
(1) a hypochlorite or a mixture
of hypochlorites, and
(2) a treating agent comprising
one member selected from the group
consisting of (a) a catalyst com-
prising: (i) one or more deliquescent
halogen salts, barium chloride,
potassium chloride or mixtures thereof,
and (ii) one or more reducing oxides,
one or more chromate salts or a mixture
thereof, (iii) provided that if potas-
sium chloride is not present in the
slurry containing formulation (B),
potassium fluoride or tannic acid is
also present in the catalyst, and (b) a
mixture of (a) and an inorganic acid
selected from the group consisting of
(i) hydrochloric acid, (ii) nitric
acid, (iii) hydrochloric acid and
nitric acid, (iv) hydrochloric acid and
ferric chloride, and (v) nitric acid
and ferric chloride,
(3) provided that if iron is not
present in the coal or other carbon-
aceous materials, ferric chloride is
present in the slurry containing
formulation (B),
whereby substantially all the sulfur extracted from
said coal or other carbonaceous materials is converted
to sulfate sulfur or other water soluble sulfates;
(II) separating the coal or other carbonaceous
materials from solution; and
(III) washing the separated coal or other carbon-
aceous materials.
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In another embodiment, the present invention also
provides a process for removing sulfur and ash from
coal and other carbonaceous materials whlch contaln
pyritic sulfur, sulfides, elemental sulfur, organic
sulfur and/or sulfate sulfur which comprises the steps
of:
(I) treating an aqueous slurry of the coal or
other carbonaceous materials at an ele~ated tempera-
ture below the oxidation temperature of the coal or
other carbonaceous materials with a formulation com-
prising one or more alkaline earth metal chlorides,
one or more alkali metal chlorides or a mixture of
said chlorides and nitric acid, provided that if iron
is not present in said coal or other carbonaceous
materials, ferric chloride is also present, whereby
substantially all the sulfur extracted from the coal
or other carbonaceous materials can be removed as
elemental sulfur;
(II) separating the coal or other carbonaceous
materials from solution;
(III) agitating the separated coal or other car-
bonaceous materials at anlelevated temperature below
the oxidation temperature of the coal or other carbon-
aceous materials and in the presence of an oxidizing
agent capable of reducing pyritic sulfides to a
soluble state in an aqueous mixture containing:
(A) a formulation comprising
(1) one or more .alkaline earth
metal chlorides, one or more alkali
metal chlorides or a mixture of the
chlorides, and
(2) a treating agent comprising
one member selected from the group con-
sisting of: (a) an inorganic acid se-
lected from the group consisting of:
(i) hydrochloric acid, (ii) nitric
ZO
acid, (iii) hydrochloric acid and
nitric acid, (iv) hydrochloric acid and
ferric chloride, and (v) nltric acid
and ferric chloride, and (b) mixtures
of (a) and a catalyst comprising:
(i) one member selected from the group
consisting of one or more deliquescent
halogen salts, barium chloride, potas-
sium chloride and mixtures thereof, and
(ii) one or more reducing oxides, one
or more chromate salts or mixtures
thereof, (iii) provided that if
potassium chloride is not present in
the slurry containing formulation (A),
potassium fluoride or tannic acid is
also present in the catalyst,
(3) provided that if iron is not
present in the coal or other carbon-
aceous material, then ferric chloride
is present in the slurry containing
formulation (A); or
tB) a formulatioln comprising:
(1) a hypochlorite or mixtures of
hypochlorites, and
(2) a treating agent comprising
one member selected from the group
consisting of: (a) a catalyst
comprising: (i) one or more
deliquescent halogen salts, barium
chloride, potassium chloride or
mixtures thereof, and (ii) one or more
reducing oxides, one or more chromate
salts or mixtures thereof,
(iii) provided that if potassium
chloride is not present in the
formulation (B), potassium fluoride
or tannic acid is also pr.esent.in the
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lZ~V~20
catalyst, and (b) a mixture of (a) and
an inorganic acid selected from the
group consisting of (i) hydrochloric
acid, (ii) nitric acid, (iii) hydro-
chloric acid and nitric acid,
(iv) hydrochloric acid and ferric
chloride, and (v). nitric acid and
ferric chloride,
(3) provided that if iron is not
present in the coal or other carbon-
aceous materials, ferric chloride is
present in the slurry containing
formulation (B),
whereby substantially all the sulfur extracted from
the separated coal or carbonaceous materials is con-
verted to sulfate sulfur or other water soluble
sulfurs;
(IV) again separating the coal or other carbona-
ceous materials from solution; and
(V) washing the again separated coal or other
carbonaceous materials.
In a further embodiment, elemental sulfur may be
recovered at an intermediate stage in the latter
described process by addition of a sulfur precipitant
to the solution of step (II).
BRIEF DESCRIPTION OF T~lE DRAWINGS
Fig. 1 is a schematic diagram of one embodiment
of the present invention wherein sulfur compounds, in-
cluding pyritic sulfur, organic sulfur and elemental
sulfur, in the coal are converted to sulfate or other
water soluble sulEur compounds.
Fig. 2 is a second embodiment of the present
invention wherein a portion of the sulfur compounds in
the coal is recovered as elemental sulfur before
treatment to form sulfate or other water soluble
sulfur compounds.
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DE;TAILE;D DESCRI TION OF THE INVENTION
According to the present invention, coal or other
carbonaceou~ materials can be de~ulfurized and the ash
solubilized. Examples of other carbonaceous materials
include lignites, peats, shales, sands and solid coal
derivative~, including bituminous, subbituminou~ and
anthracitic. However, coal is preferred and raw coal,
is even more preferred.
As u~ed herein, raw coal is coal from which only
the rock, dirt and sand have been removed.
Prior to being subjected to the process of the
invention, raw coal is washed to remove shale, dirt and
other gangue and is crushed to a standard ball mill
feed size, i.e. to particles approximately three-
fourth~ to one-half inch minu~ in size.
The particles are then fed into a ball mill and
wet ground for reduction to about 100-300 mesh parti-
cles. Fine grinding of the coal is desired because it
facilitates rapid interaction between sulfur compounds
contained in the coal matrix and components in the
extraction mixture.
If de~ired, comminuted Icoal can be sink floated
before being combined with the extraction mixture.
Sink floating removes sulfur-rich heavy particles from
comminuted coal by utilizing a hydrocarbon solvent and
other chemicals.
As used herein, the term extraction mixture
refers to an aqueous solution containing, either
separately or in combination, the following components
of the present invention: one or more alkaline earth
metals or alkali metal salts or mixture~ thereof; one
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.~,., ~ . ,
or more hypochloritesi one or more inorganic aclds;
one or more catalysts or catalyst components; an
oxidizing agent; oxygen, oxygen enriched air, or air;
and ferric chloride.
Further, unless otherwise specified, all concen-
trated solutions of hydrochloric acid are reagent
grade concentrated hydrochloric acid, i.e., about 38%
by weight; all concentrated solutions of nitric acid
are approximately 68% by weight; all concentrated
solutions of ferric chloride are 30% by weight; all
concentrated solutions of sulfuric acid are approxi-
mately 98% by weight; and all concentrated solutions
of acetic acid are approximately 100% by weight. All
concentrated solutions of acids not specifically men-
tioned above are, unless otherwise specified, the com-
mericially available reagent grade concentrated
solutions.
In one embodiment of the present invention, an
aqueous slurry of coal or other carbonaceous material
containing pyritic sulfur, sulfites, elemental sulfur,
organic sulfur and/or sulfate sulfur is treated with
one or more alkaline earth metal chlorides, one or
more alkali metal chlorides or a mixture of the chlor-
ides and a treating agent comprising a catalyst and an
inorganic acid at an elevated temperature in the
presence of an oxidizing agent capable of reducing
pyritic sulfides to a soluble state, provided that if
iron is not present in the coal or other carbonaceous
materials, ferric chloride is also present in the
aqueous slurry containing the extraction mixture.
Alternatively, the aqueous slurry is treated with a
formulation comprising a hypochlorite or a mixture of
hypochlorites and a catalyst or a catalyst and an
inorganic acid at an elevated temperature in the
presence of an oxidizing agerlt capable of reducing
pyritic sulfides to a soluble state, provided that if
iron is not present in the coal or other carbonaceous
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materials, ferric chloride is also present in the
a~ueous slurry containing the extraction mixture. In
this embodiment, sulfur is removed as sulfate or other
water soluble sulfurs~
Of the alkaline earth metal chlorides such as
barium chloride, magnesium chloride and calcium
chloride, calcium chloride is preferred. Of the
alkali metal chlorides, sodium chloride, potassium
chloride and mixtures thereof are preferred.
The alkaline earth metal and/or alkali metal
chlorides are used in an amount of about 7 to ~
chlorine molecules for each sulfur molecule contained
in the coal.
The catalyst of the present invention comprises
one or more deliquescent halogen salts, barium chlo-
ride, potassium chloride or mixtures thereof, and one
or more reducing oxides, one or more chromate salts or
mixtures thereof, provided that if potassium chloride
is not present in the aqueous slurry containing the
extraction mixture, potassium fluoride or tannic acid
is also present in the catalyst.
Examples of deliquescent halogen salts especially
useful in the present invention include calcium chlo-
ride, magnesium chloride and mixtures thereof.
Examples of reducing oxides include chromic
oxide, magnanese dioxide and iron (III) oxide.
Examples of chromate salts include potassium
dichromate and sodium chromate.
The components of the catalyst are generally
present in the following amounts: deliquescent
halogen salt(s), barium chloride, potassium chloride
or mixtures thereof (about 90 to 95% by weight of the
catalyst mixture); reducing oxide(s), chromate salt(s)
or mixtures thereof (about 6 to 10% by weight of the
catalyst mixture); if present, potassium fluoride or
tannic acid (about 3 to 5% by weight of the catalyst
mixture).
420
An especially preferred catalyst composition
comprises, by total weight of the catalyst mixture,
calcium chloride, magnesium chloride and/or potassium
chloride in an amount of about 90 to 95% by weight;
chromic oxide or chromate salts in an amount of about 3 to
5% by weight; manganese dioxide in an amount of about 3 to
5% by weight; and potassium fluoride in an amount of about
3 to 5% by weight lc potassium chloride i5 not present in
the aqueous slurry containing the extraction mixture.
Examples of compositions, but not necessarily
amounts, of suitable ca~alysts are disclosed in U.S.
Patent 2,369,024 and U.S. Patent 2,089,599. These patents
teach spraying of catalyst components on the coal prior to
burning, which concentrates sulfur dioxide from the
pyrites when the coal burns. Thus, it is indeed
unexpected that such catalyst components would be useful
in an aqueous slurry of coal or other carbonaceous
materials in order to desulfurize the material
particularly because the desulfurization process of the
present invention alleviates sulfur dioxide emissions
rather than concentrates these emissions.
The catalyst is used in an amount of about 1 to
10% by weight of the total sullfur in the solids, i.e.,
coal or other carbonaceous materials, and preferably in an
amount of about 2 to 10% by weight of the total sulfur in
the solids. The amount of total sulfur present in the
solids can be determined using routine chemical analysis.
The inorganic acid can be hydrochloric acid,
nitric acid, hydrochloric acid and nitric acid,
hydrochloric acid and ferric chloride, or nitric acid and
ferric chloride. Nitric acid and a mixture of
hydrochloric acid and ferric chloride are preferred.
The amount of acid used is the amount necessary
to raise the pH of the beginning solution to about 2-5.
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Further, if iron is not preserlt in the coal or
other carbonaceous materials, then ferric chloride
must be present in the aqueous slurry containing the
extraction mixture. The ferric chloride can be added
as such or formed ln situ. The amount of iron is
suitably about O.S to 3.0 lbs for each lO0 lbs of coal
or other carbonaceous materials being processed.
In the alternative embodiment, the hypochlorite
can be calcium hypochlorite or sodium hypochlorite,
preferably sodium hypochlorite.
Hypochlorite is used in an amount of about lO0 gm
of hypochlorite to 400 gm of water and 200 gm of coal
or other carbonaceous material.
Further, in the alternative embodiment when hypo-
chlorite is ~mployed, the catalyst is the same as that
described above. The amount of the catalyst used is
about l to 10% by weight of the total sulfur in the
solids, preferably about 2-10% by weight of the total
sulfur in the solids. If inorganic acid is used along
with the catalyst, the inorganic acid is used in an
amount of about 1-5% by volume of a solution of the
acid(s) to the final vollume of the aqueous slurry
containing the extration mixture.
As with the above embodiment, if iron is not
present in the coal or other carbonaceous materials,
then ferric chloride must be present in the extraction
mixture in an amount of about 0.5 to 3.0 lbs for each
lO0 lbs of coal or other carbonaceous materials being
processed.
The above-described formulations of metal chlo-
. ride, catalyst and acid or hypochlorite and catalyst
~or catalyst and acid) are contacted with the coal or
other carbonaceous materials for a period of approxi-
mately lO to 45 minutes, preferably about 30 minutes,
with the addition of an oxidizing agent capable of
reducing pyritic sulfides to a soluble state, such as
oxygen gas, sulfur dioxide gas, oxygen enriched air,
;()420
sulfur dioxide enriched air, or air. A suitable
amount of the above described oxidizing agents is
about 1-5 liters per minute, preferably about
1-2 liters per minute. The coal or other carbonaceous
material is agitated with the extraction mixture at
an elevated temperature below the oxidation tempera-
ture of the coal or other carbonaceous materials. A
suitable temperature range is about 80 to 130C.
Further, it is preferred that the agitation be carried
out at about atmospheric pressure. However, the
pressure can range from about atmospheric pressure to
over 500 psi, if no degradation of the carbonaceous
material is encountered.
When the agitation is carried out at about
atmospheric pressure, the temperature is preferably
about 85 to 95C.
Further, according to the present invention, the
point at which the coal or other carbonaceous material
is treated with the above-described formulations can
be varied as follows: (1) the coal or other carbon-
aceous material may be wet ground and then transferred
to a second reaction zo~e wherein the cosnminuted
material is heat reacted with agitation in the
presence of the alkaline earth metal and/or alkali
metal chloride and catalyst and acid or the hypochlor-
ite and catalyst (or catalyst and acid); (2) the coal
or other carbonaceous materials may be wet ground in
the presence of the alkaline earth metal and/or alkali
metal chloride or the hypochlorite and then this
aqueous solution transferred to an agitator wherein
the slurry is heat reacted in the presence of the
catalyst and acid or the catalyst (or catalyst and
acid), respectively; and (3) the wet grinding and heat
reaction with agitation may be accomplished simultane-
ously in the preseslce of the alkaline earth metal
and/or alkali metal chloride and catalyst and acid or
the hypochlorite and catalyst (or catalyst and acid),
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respectively. The oxidizing agent is added at the
heat reacting step. If ferric chloride is added to
the extraction mixture, the ferric chloride is prefer-
ably added at the heat reacting step but can be added
at the wet grinding step.
of the three above-described embodiments the
second and third are preferred because grinding the
~ coal or other carbonaceous material in the mixture
markedly increases the amount of sulfur removed from
the coal. Lhis is believed to be due to the catalytic
action of the acids and heat generated in the grinding
zone which act to release the sulfur by conversion of
some of the sulfides.
By following the above-described procedure, all
lS types of sulfur found in the coal appear to become
water soluble and susceptible to removal with hot
water washing, a hot dilute acid wash or a hot alka-
line wash. A hot dilute acid wash or a hot alkaline
wash are preferred.
According to the present invention, the dilute
acid wash can be any inorganic or organic acid.
Examples of suitable inorganic acids include nitric
acid, sulfuric acid and hydrochloric acid. Examples
of suitable organic acids include paraacetic and
acetic acid. Preferred acids are nitric acid and
sulfuric acid. Nitric acid is particularly preferred.
Nitric acid, even in dilute hot solutions, strongly
oxidizes any sulfur films occluded to the solids and
will also complete the dissolution of any sulfides
that have started to break down in the processing, as
well as aid in the removal of some organics that
remain in a dissolution state.
A suitable acid concentration is about 5 to 10%
by volume of a corlcentrated solution of the acid to
the final volume of the wash solution.
Suitable alkaline washes include a solution of
about 0.1 to 3 molar of ammonium hydroxide, sodium
16
hydroxide or potassium hydroxide. ~ soLution of about
0.1 molar to 0.2 molar is preferred. The concentra-
tion of the alkaline solution is limited however by
the point at which the volatiles, or soluble carbon
compounds start to break down which can be easily
determined by one skilled in the art.
The temperature of the water, dilute acid or
alkaline wash is about 90-100C, preferably just below
boiling at atmospheric pressure. The wash is carried
out for a period of time which can readily be deter-
mined by one skilled in the art. A suitable time is
about 5 to 30 minutes, preferably about 15 minutes.
Although the above-described process of contac-
ting comminuted coal with alkaline earth metal and/or
alkali metal salts, catalyst and an acid or hypochlor-
ite and a catalyst (or catalyst and acid) removes con-
siderable amounts of the sulfur compounds from the
coal, the coal must still be washed with a dilute acid
wash or hot alkaline wash in order to obtain sulfur
reduction sufficient to meet the EPA standards for
burning coal, i.e., 1.2 lbs SO2 emmissions per million
BTU. I
In a second embodiment of the present invention,
removal of sulfur in the form of sulfate or other
water soluble sulfur is preceded by a step in which an
aqueous slurry of coal or other carbonaceous materials
is treated at an elevated temperature below the oxida-
tion temperature of said coal or other carbonaceous
materials with a formulation comprising one or more
alkaline earth metals and/or alkali metal chlorides or
a mixture of the chlorides and nitric acid provided
that if iron is not present in the coal or other
carbonaceous material, ferric chloride is also present
in the aqueous slurry containing the extraction
mixture, whereby substantially all the sulfur
extracted from the coal or other carbonaceous
materials can be removed as elemental sulfur.
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A suitable alkaline earth metal chloride is an
alkaline earth metal chloride as described above with
calcium chloride being preferred. Suitable alkali
metal chlorldes include, ~or example, sodium chloride
and potassium chloride. A mixture of sodlum chloride
and potassium chloride is preferred and even more pre-
ferred is a mixture of equal parts by weight of sodium
chloride and potassium chloride.
The alkaline earth metal and/or alkali metal
chloride(s) can be added in a concentration of about
0.5-15% by weight of the aqueous solution. A con-
centration of about 15% by weight of the aqueous
solution is preferred.
The nitric acid is varied between about 0.5 to
10% by volume of a concentrated solution of the acid
to the final volume of the aqueous slurry depending
upon the amount of total sulfur in the coal or other
carbonaceous material. The particular amount of
nitric acid within the range that can be used can
readily be determined by one skilled in the art by
monitoring the sulfur removal.
The coal or other Icarbonaceous material is
reacted with the above-described components at an ele-
vated temperature below the oxidation temperature of
the coal or other carbonaceous materials. A suitable
temperature range is about 80-130C.
The reaction pressure can range from about
atmospheric pressure to over 500 psi if no degrada-
tion of the carbonaceous material is encountered.
However about atmospheric pressure is preferred.
When the reaction is carried out at atmospheric
pressure, the mixture is preferably reacted at a tem-
perature of about 85-130~C, and more preferably about
85-90C.
The reaction is carried out for a period of about
10-30 minutes preferably about 15 minutes without the
use of added oxygen, oxygen enriched air, or air.
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;VI}A,O
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The reaction may also be carried out in the pres-
ence of added oxygen, oxygen enriched air, or air in
an amount of about 1-2 liters per minute, for a period
of about 15-30 minutes. The oxygen, oxygen enriched
air or air is used in the presence of the nitric acid.
As with the first embodiment, if ferric chloride
is added to the reaction mixture, the ferric chloride
is added in an amount of about 0.5 to 3.0 lbs iron for
each 100 lbs of coal being processed.
After reaction, the solids can be separated from
the liquid while hot and elemental sulfur recovered
from the liquid by known means such as, for example,
by using a sulfur precipitant. Examples of suitable
sulfur precipitants include sodium citrate (as
described in United States Bureau of Mines report of
investigations - 1981, RI 8540 by W.N. Marchant, et
al) and acidic solutions, such as an aqueous solution
of hydrochloric acid. Since chlorine is present in
the circuit with sulfur, elemental sulfur can also be
precipitated with hydrogen iodide or an aqueous solu-
tion of hydrogen iodide, i.e., hydriodic acid (HI).
As much as 85% of the sulfur can possibly be recovered
by this intermediate step.
This intermediate treatment for recovering ele-
mental sulfur can be performed in three embodiments
just as the steps for recovering sulfate and other
soluble sulfurs. That is, the following combinations
are possible: (1) the coal or other carbonaceous
material can be wet ground and then heat reacted in
the presence of alkaline earth and/or alkali metal
chloride(s) and nitric acid; (2) the coal or other
carbonaceous material can be wet ground in the
presence of the alkaline earth and/or alkali metal
chloride(s) and this solution heat reacted with nitric
acid; and (3) the wet grinding and heat reacting can
be carried out simultaneously in the presence of the
alkaline earth and/or alkali metal chloride(s) and
1~6042V
nitric acid. As with the first embodiment, if ferric
chloride is added to the extraction mixture, the
ferric chloride is preferably added at the heat
reacting step but can be added at the agitation step.
The solids separated from the extraction mixture
are desirably washed with hot water, hot dilute acid
or a hot alkaline solution as described above. A hot
acid or alkaline solution is preferred and a hot acid
solution is especially preferred.
1~ After carrying out the intermediate steps, the
solids are then reagitated with a new solution
containing alkaline earth and/or alkali metal
chloride(s) and an inorganic acid or with a solution
containing one of the above-described formulations of
(a) alkaline earth metal and/or alkali metal
chloride(s) and acid and catalyst or (b) hypochlor-
ite(s) and catalyst (or catalyst and acid), at a
temperature below the oxidation temperature of the
coal or other carbonaceous material and in the
presence of an oxidizing agent capable of reducing
pyritic sulfides to a soluble state, such as oxygen
gas, sulfur dioxide gas, oxygen enriched air, sulfur
dioxide enriched air or air, as described above, to
remove further sulur as sulfate before the coal is
finally washed with hot water, hot dilute acid or a
hot alkaline solution and burned. If iron is not
present in the coal or other carbonaceous material,
then ferric chloride must be present in the reagita-
tion extraction mixture in the same amount as
described above.
When the solids are reagitated with an alkaline
earth metal and/or alkali metal chloride and an
inorganic acid, the alkaline earth and/or alkali metal
chloride can be the same as those descrit?ed in the
second embodiment for treating the coal or other
carbonaceous materials to extract sulfur as elemental
sulfur. The inorganic acid can be the same as those
described in the first embodiment for treating the
coal or otller carbonaceous materials to extract sulfur
as sulfate or other water soluble sulfurs. However,
nitric acid is preferred.
The alkaline earth and/or alkali metal chloride is
used in an amount of about 0.5 to 5% by weight final
concentration, preferably about 0.5 to 2% by weight
final concentration.
The acid is used in an amount of about 1.25% to
5% of a concentrated solution to the final aqueous
volume, preferably about 1.25% to 3%.
The amount of oxidizing agent, the temperature
and pressure conditions, and time parameters are the
same as those described in the first embodiment for
extracting sulfur as sulfate or other water soluble
sulfurs.
After reagitation, the separated solids are
washed with hot water, hot dilute acid or a hot
alkaline solution as described above for the first
embodiment.
As a further desirable step in all of the
above-described embodiments, there can be a last
washing with a dilute solution of potassium chromates
or potassium fluoride in order to reduce corrosion and
slagging when the coal is burned. This is not an
essential step but is preferred. A suitable amount of
potassium chromate or potassium fluoride is 1% weight
to volume.
As earlier described, fine grinding of the solids
facilitates a rapid and complete reaction between
sulfur impurities in the solids and chemicals in the
extraction mixture. The solids-extraction mixture
reactions are exothermic and raise the temperature of
the extraction mixture slurry from ambient temperature
to a temperature as high as 50C. Thus, the only
additional heat necessary while the extraction mixture
is maintained in contact with comminuted solids is a
l~V ~V
quantity of heat which will raise the temperature of
the extraction mixture slurry from about 50C to 80C.
Further, the rapid, almost instantaneous reaction
between the solids and the extraction mixture
chemicals causes violent foaming and, therefore, it is
desirable to include an emulsifier in the extraction
mixture slurry in order to increase efficiency of the
process. A suitable commercially available emulsifier
useful in the present invention is DB-llOA manufac-
tured by Dow-Corning which is a non-ionic emulsifier.
The emulsifier is used in an amount of 2 to 5 gms of a
2% solution of emulsifier to one liter of aqueous coal
slurry.
The coal and extraction mixture are preferably
combined and agitated in a closed reaction vessel both
to retain heat generated by the exothermic chemical
reactions which occur and to reduce the quantity of
chemical reagents which escape into the air during the
agitation of the extraction mixture slurry. Since
anly a portion of each chemical component in the ex-
traction mixture is normally consumed during treatment
of a quantity of coal, the extraction mixture can be
separated from the desulfurized, treated solids,
replenished with the necessary amount of each
extraction chemical and then recycled for treatment of
another quantity of solids. The extraction mixture
301ution is periodically processed to remove sulfur or
sulfates and is then replenished or .recycled or is
simply discarded. Carrying out agitation of the coal
and extraction mixture in a closed reactor vessel con-
serves reaction chemicals and decreases the amount of
new chemicals which must be added to recycled extrac-
tion mixtures.
Sulfate and other soluble sulfur compounds are
removed from the spent extraction mixture solution by
- known means, such as by precipitation with calcium
salts or barrium chloride.
.
.iZ~
22
When the comminuted solids and the extraction
mixture are initially combined, the pH of the liquid
component of the extraction mixture solution is
approximately 2 to 5. After the extraction mixture
solution has contacted the solids for approximately
15 minutes, the pH of the solution is appro~imately
0.1. After comminuted solids are separated from the
extraction mixture solution by any conventional means,
the solids are washed with hot water, a hot alkaline
solution or a dilute acid, as described above. The
water, alkaline or acid wash removes soluble sulfur
compounds and sulfates along with organic sulfur com-
pounds which adhere to the solids during the separa-
tion of the solids from the extraction mixture
solution. Washed solids are dried using any conven-
tional means, for example, under vacuum or with steam
to remove moisture or occluded acids carried by the
solids. Since the solids have been finely ground,
care must be taken not to expose the solids to a
source of oxygen while the solids are hot.
Washed, dried solids can be fed directly into a
boiler for combustion, may be moved as slurry by pipe-
line to another plant, or may be pelletized or
briquetted for shipment, storage and subsequent sale
and use.
Further, although the invention has been
described as a continuous process, a modified batch
process, i.e., a semicontinuous circuit, can also be
used.
The overall integrated process for producing
sulfur-purified coal on site at open pit or under-
ground coal-mining operations will now be described by
reference to the Figures.
Fig. 1 illustrates one embodiment of the present
invention wherein all the extracted sulfur is extrac-
ted as sulfate or other soluble sulfur compounds.
Crushed raw coal 1 is wet ground 2 in combination with
i~iV~20
23
water 3 and a mixture 4 of potassium chloride and
sodium chloride. The ground coal slurry 5 is then
agitated in a heat reactor 6 with the addition of oxy-
gen gas or air 7, catalyst 8, and nitric acid 9 to
produce sulfate and other soluble sulfur compounds.
The coal may be agitated in the heat reactor at any
desired pressure. The temperature of the mixture in
the heat reactor may be increased by supplying heat
which is a by-product of a plan~ which manufactures
any of the components used in the present process.
After agitating for about 15 minutes, the reacted coal
slurry 10 is separated 11 into a liquid component 16
and a solid component 12. The solid component 12 is
washed _ in hot water, dilute acid or an alkaline
solution to produce desulfurized coal 14. The wash
solution may be recycled 15.
Sulfate 19 is periodically recovered 17 from the
liquid 16 from the coal liguid separation. The
liquid 16 or 11 may be recycled for use in the
agitated heat reactor 6. When extraction mixtures
are recycled, fresh chemicals are added to bring the
strength of each chemicall in the solution up to an
acceptable level within the ranges hereinbefore
described.
Fig. 2 illustrates a second embodiment of the
present invention wherein elemental sulfur is
recovered midway through the extraction process.
Crushed raw coal 1 is wet ground 2 in the presence of
sodium chloride and potassium chloride salts 20 and
water 3. The ground coal slurry 5 is then agitated in
a heat reactor 21 in the presence of nitric acid 22.
The reacted coal slurry 23 is separated 24 into a
solid component 25 and a pregnant sulfur liquid com-
ponent 26. The coal solids 25 are washed 3l with hot
water, dilute acid or alkaline solution and the washed
coal solids 32 are again agitated in a second heat
2~
2~
reactor 6 in the presence of sodium chloride and po-
tassium chloride salts 4, nitric acid 8, and oxygen
gas or air 7. The reacted coal slurry 10 is then sub-
jected to further process steps, the same as described
in Fig. 1.
For elemental sulfur recovery 27, a sulfur preci-
pitant 28 is contacted with the pregnant sulfur
liquid 26 to produce elemental sulfur 29. The
liquid 30 having elemental sulfur removed can be
cycled to the agitated heat reactor 6, and this is
especially desirable if an acid process has been used
to recover the elemental sulfur.
The present invention is a significant improve-
ment over the prior art. To accomplish the invention,
it is preferred to locate the processing facilities
near or adjacent to the power producing plants. This
gives a source of inexpensive energey which is now
being wasted and a source of water, particularly that
used in the cooling towers of most large power plants.
These waters in many cases may contain chemicals that
can be used ~o advantage in practicing the present
invention, especially chrqmates or chromium which is
added to the cooling towers to prevent scaling, and is
lost unless a system is installed to recover the
metals from the cooling waters. The cooling waters
can contain as much as 800 ppm chromates. These chro-
mates can be utilized in the invention.
Further, since natural brine or sea water
contains many of the components of the extraction
mixture of the present invention, natural brine or sea
water could possibly be used in the extraction mixture
and, therefore, the present invention is also par-
ticulary desirable when the desulfurization facilities
are located near brine deposits and sea water.
In view of the present invention, it is also ap-
parent that the coal desulfurization plants should be
located near ~he burning plants. In this way, another
~..... .
i2~ 0
noxious product could be utilized to reduce the cost
of processing and the cause of pollution. This
material is known as NOX or nitrous oxide. Nitrous
oxide isolated from coal emissions by several known
means, for example, magnet hydrodynamics, can be
converted to nitric acid for use with the extraction
mixture of the present invention.
The present invention will now be described by
~eference to the following specific examples which are
not intended to be limiting.
EXAMPLE I
A sample of Ohio #6 seam, raw coal, crushed to
100 mesh, was analyzed. The results are shown in
Table A. Unless otherwise indicated, all parts,
percents, ratios and the like are by weight.
TABLE A
Ohio #6 - Seam Raw Coal
As Received DryMoisture &
ComponentBasis BasisAsh Free
Moisture 9.79 -_ __
Ash 24.l69 27.37 --
Sulfur 3.71 4.11 --
Heating Value,
BTU/lb. 9,079 10,06413,857
Grindinq And Extraction
200 gms of the above Ohio #6 coal were ground to
100 mesh, and then mixed in a stirred reaction vessel
at 85-99C for 30 minutes in the presence of 1000 ml
water, 15 gm of a mixture of NaCl and KCl, 15 ml con-
centrated, i.e., about 37% wt./wt., hydrochloric
acid, 10 ml ferric chloride (30% wt./wt. solution),
and 5 gm catalyst comprising 90% MgCl, 5% maganese
dioxide and 5% chromic oxide. The salt mixture of
15% by wt of the solution was 7.5% NaCl and 7.5% KCl.
.,
26
Coal recovered from the extraction mixture was
washed with hot dilute nitric acid (50 ml of 69% to
71% nitric acid to 1000 ml of solution) for 15 minutes
with agitation.
The coal was then separated from the wash liquid
and the coal analyzed for sulfur content. The results
are shown in Table B below.
TABLE B
Ohio #6 ~ Treated Raw Coal
As Treated Dry
Component Basi 5 Basis
Moisture, % 2.11 --
Ash, % 11.62 11.87
Volatile Matter, % 35.30 36.08
Fixed Carbon, % 50.97 52.05
Total Sulfur, % 0.99 1.01
Organic Sulfur, % 0.73 0.74
Pyritic Sulfur, % 0.26 0.27
Sulfate Sulur, % < 0.01 < 0.01
Gross Calorific Value, BTU/lb.10,760 10,997
The results indicatelthat there was about a 76%
reduction in total sulfur on both an as treated basis
and dry basis.
EXAMPLES II-III
A sample of washed, i.e., sink floated, Ohio #6
coal was analyzed. The results are shown below in
Table C.
TABLE C
Sink Floated Ohio #6 Coal
As Received Dry Moisture and
ComponentBasis Basis Ash Free
Moisture 14.66
Ash 11.04 12.94 --
Sulfur 3.46 4.05 --
Heating Value,
BTU/lb. l0,574 12,390 14,232
.
27
Grindillg And Extraction
Sample lA
200 gms of the above Ohio #6 sink floated coal
was heated with agitation for 30 minutes at a temper-
ature of 80-85C in the presence of 600 ml water,
15 gm NaCl, 15 ml concentrated, i.e., about 37%
wt./wt., hydrochloric acid, and 10 ml of a 100%
wt./wt. solution of catalyst comprising 90% calcium
chloride, 5% chromic oxide and 5% mangnese dioxide.
Air was bubbled into the solution at a rate of 1 liter
per minute.
The separated coal was analyzed for sulfur con-
tent and the results are shown in Table D.
TABLE D
Ohio #6 - Sink Floated lA Coal
As Treated Dry
Component Basis Basis
Moisture, % 1.81 --
Ash, % 12.72 12.94
Volatile Matter, % 34.56 35.20
Fixed Carbon, % 50.91 51.86
Total Sulfur, % 1.33 1.35
Organic Sulfur, % 0.30 0.31
Pyritic Sulfur, % 1.03 1.04
Sulfate Sulfur, % < 0.01 < 0.01
GroRs Calorific Value, B'rU/lb. 12,160 12,379
The results indicate that about 60% of the sulfur
on an as treated basis was removed and about 67% of
the sulfur on a dry basis was removed.
Sample lB
200 gms of the above Ohio #6 washed coal
(Table C), ground to 100 mesh was reacted for 30 min-
utes at 80-85C in the presence of 800 ml water, 15 gm
NaCl, 20 ml concentrated, i.e., about 37% wt./wt.,
hydrochloric acid and 5 ml of a 100% wt.~wt. solution
.
,
28
of catalyst comprising 45% MgCl, 45% CaCl, 5~ MgO2,
and 5% chromic oxide. Air was bubbled into the solu-
tion at a rate of 1 liter per minute.
The separated coal was analyzed for sulfur con-
tent and the results are shown in Table E below.
TABLE E
Ohio #6 - Sink Floated lB Coal
As Treated Dry
Component Basis Basis
Moisture, % 1.12 --
Ash, % 11.67 11.80
Volatile Matter, % 34.38 34.77
Fixed Carbon, % 52.83 53.43
lS Total Sulfur, % 2.07 2.09
Organic Sulfur, % 1.07 1.08
Pyritic Sulfur, % 0.96 0.97
Sulfate Sulfur, % 0.04 0.04
Gross Calorific Value, BTU/lb. 12,160 12,294
The results indicate that about 40% of the sulfur
on an as treated basis was removed and about 48% of
the sulfur on a dry basis was removed.
EXAMPLE IV
100 gms of the above Ohio #6 washed coal (Table
C), ground to 100 mesh was reacted with agitation at
approximately 90C for 30 minutes with 500 ml water,
15 gm NaCl/KCl mix (50/50 by weight), and 500 ml 10%
nitric acid (prepared by mixing 10 volumes of 69 to
71% nitric acid to 90 volumes of water), in the
absence of added air or oxygen. The slurry was
filtered and the coal washed with 500 ml of 10% nitric
acid (prepared as above). rhe separated acid washed
coal was analyzed for sulfur content and the results
are shown in Table F below:
29
TABLE F
Ohio #6 - Sink Floated 2 Coal
As Treated Dry
Component Basis Basis
Moisture, % 0.97 --
Ash, % 11.80 ll.91
Volatile Matter, % 34.16 34.50
Fixed Carbon, % 53.07 53.57
Total Sulfur, % 1.22 1.23
Organic Sulfur, % - 0.01 _ 0.01
Pyritic Sulfur, % 1.18 1.19
Sulfate Sulfur, % 0.04 0.04
Gross Calorific Value, BTU/lb. 11,983 12,106
The results indicate that about 65% of the total
sulfur was removed from the coal on an as treated
basis and about 70% of the total sulfur was removed
from the coal on a dry basis. Further, 100% of the
organic sulfur was removed from the coal on an as
treated, as well as a dry basis.
EXAMPLE V
A sample of Ohio #6 raw coal (Table A) was
extracted as in Example I above and the coal recovered
from the extraction mixture was subjected to various
washes to determine the nature and amounts of sulfur,
total solids at 180C, non-volatile solids at 550C,
i.e., and iron being removed. The results are shown
in Table C below.
4~
TABLE G
Samples Total Total Solids Non-Volatile Weight of
Mark~d Sulf~r @180C Solids @550C Iron Precip.
Ohio 6:
Acid Wa~h 0.15 g/L 1.79 g/L 1.32 g/L -~-- ----
Water Wash 0.04 0.29 0.22 ---- ----
Alkaline
Wash
(2.4%) 0.93 7.58 6.38 0.73 g/L --~-
Alkaline
Wash
(5%) 1.24 172.3 168.5 ---- ----
Special 0.03 ---- ---- ---- 0.32 8
The acid wash was a wash with 10% nitric acid
(prepared by mixing 10 volumes of 69-71% nitric acid
with 90 volumes of water) at about 85C for 15
minutes. The analysis of the spent acid wash solution
indicates that sulfur was washed from the coal in
soluble form and that ash is carried along with the
wash solution. A small lamount of volatiles was
removed. This could be organic sulfur.
The water wash was a wash of the acid washed coal
with water at about 85C for 15 minutes. The analysis
of the spent water wash indicates that only a small
amount of occluded solids, which include sulfur and
ash, remained on the coal after the acid wash sug-
gesting the acid wash was highly efficient at removing
any occluded solids left after extraction.
The 2.4% alkaline wash was a wash of the
extracted coal with 2.4% ammonium hydroxide at about
85C for 15 minutes. The analysis of the spent 2.4%
alkaline wash solution indicates that the alkaline
wash was superior to the acid wash for removing sulfur
and ash. ~owever, the alkallne wash removed more
,- : .
. .~
0
:31
total solids than the acid wastl indicating that more
volatiles may have been removed which would result i~
a concomitant decrease in the gross caloric value of
the coal.
S The 5,' alkaline wash was a wash of the extracted
coal with 5% ammonium hydroxide at about 85C for lS
minutes. The analysis of the spent 5% alkaline wash
solution indicates that extraction of a very high
amount of sulfur, ash, and total solids occurred. The
large amount o total solids removed could be due to
removal of volatiles which would result in a
concomitant decrease in the gross caloric value of the
coal.
The special sample was extraction liquid after
lS extraction had been carried out for ten minutes. The
analysis of the extrac~ion liquid indicates that at
least some sulfur was already removed after reaction
with the extraction mixture for only ten minutes.
While the invention has been described in detail,
and with reference to specific embodiments thereof, it
will be apparent to one skilled in the art that vari-
ous changes and modifications can be made therein
without departing from the ~pirit and scope thereof.
