Sulfur dioxide reduction process

Sulfur dioxide is converted to elemental surfur by reduction with a carbonaceous material in a reaction zone containing a molten salt. Heat is provided by reacting a portion of the carbonaceous material with oxygen. In a preferred embodiment alkali metal sulfates present in the molten salt are reduced to alkali metal sulfides.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a process for the production of elemental 
sulfur from sulfur dioxide. In one of its more particular aspects, this 
invention relates to the reduction of sulfur dioxide to elemental sulfur 
by a carbonaceous material in the presence of a molten salt. In another 
aspect this invention relates to the simultaneous reduction of sulfur 
dioxide to elemental sulfur and an alkali metal sulfate to the 
corresponding alkali metal sulfide. The simultaneous reduction of the 
sulfur dioxide and sulfate is desirable in flue gas desulfurization 
processes wherein some sulfate is unavoidably produced along with the 
sulfite-bisulfite compounds from which the sulfur dioxide is regenerated. 
2. Prior Art 
The need to eliminate sulfur-containing gases from flue gases has resulted 
in many different methods being suggested for this purpose. In some of 
these methods the flue gases are desulfurized without recovering any of 
the sulfur values in usable form. In other words, processes have been 
provided to recover the sulfur values as either hydrogen sulfide or 
elemental sulfur. In those processes recovering the sulfur values as 
hydrogen sulfide, the hydrogen sulfide thereby produced is generally 
utilized either in a sulfuric acid producing plant or a Claus plant for 
the production of sulfur. 
Thus the conversion of sulfur-containing compounds involved in flue gas 
desulfurization to elemental sulfur has achieved some importance as the 
need for environmental clean-up has grown. 
U.S. Pat. No. 3,438,733 describes a process for producing sulfur by 
reducing molten alkali metal sulfite with carbon. The alkali metal sulfite 
is formed by absorption of sulfur dioxide using a molten alkali metal 
carbonate as an absorbent. The process is conducted by trickling the 
molten alkali metal sulfite in admixture with molten alkali metal 
carbonate over a solid carbonaceous bed, with the sulfur thereby produced 
being recovered in the form of gaseous elemental sulfur. Although 
elemental sulfur is produced in this process, it is necessary to operate 
the reactor at relatively high pressures in order to convert the sulfite 
to elemental sulfur and to minimize the formation of alkali metal sulfide. 
U.S. Pat. No. 3,904,387 discloses a process in which sulfur dioxide and 
carbon are heated together to produce a gaseous mixture of carbon monoxide 
and elemental sulfur. The process is carried out in a gasifier into which 
hot carbonaceous matter and a heated stream of concentrated sulfur dioxide 
are introduced. This process thus requires extensive heating of all 
carbonaceous matter and the sulfur dioxide. 
U.S. Pat. No. 4,095,953 describes a modular system for reducing sulfur 
dioxide which consists of a plurality of compartments having coal inlets 
associated with each compartment and a single source of sulfur dioxide. In 
this modular system it is required that burners be situated in each 
compartment in order to heat the reactants to the proper reaction 
temperature, namely one between 1100.degree. and 1550.degree. F. (about 
595.degree. to 845.degree. C.). 
Other processes in which sulfur is formed directly from sulfur dioxide 
utilize hydrogen sulfide as a reactant. 
For example, in U.S. Pat. No. 3,170,766 there is disclosed a process which 
involves the reaction of hydrogen sulfide with sulfur dioxide in an 
organic solvent to produce sulfur as the product of the reaction. 
U.S. Pat. No. 3,441,379 discloses a similar process in which the reaction 
of hydrogen sulfide and sulfur dioxide is carried out in a liquid 
phosphoric acid ester as the reaction medium. 
In U.S. Pat. No. 3,447,903 the reaction of hydrogen sulfide and sulfur 
dioxide is carried out in liquid sulfur in the presence of a catalyst 
comprising a basic nitrogen compound. 
None of the processes in which hydrogen sulfide is used to convert sulfur 
dioxide to elemental sulfur are particularly desirable for the reduction 
of sulfur dioxide recovered from flue gas streams since each requires a 
source of hydrogen sulfide gas, which is not normally available at the 
site of flue gas desulfurization plants. 
Other processes are known in which the production of sulfur from sulfur 
dioxide requires that the sulfur dioxide be first reduced to hydrogen 
sulfide. For example, U.S. Pat. No. 3,932,586 discloses such a process in 
which sulfur dioxide is absorbed in an aqueous absorption solution 
including potassium carbonate, and the resulting potassium sulfite or 
sulfate is treated to regenerate potassium carbonate with the release of 
hydrogen sulfide, which can then be converted to elemental sulfur by 
processing in a Claus plant or other sulfur recovery unit. This process 
has the disadvantage that several intermediate steps are required to 
produce sulfur from sulfur dioxide. 
OBJECTS OF THE INVENTION 
It is an object of the present invention to provide a process for producing 
elemental sulfur from sulfur dioxide in high yields with a minimum number 
of process steps. 
Another object of this invention is to provide such a process which results 
in a minimum number of byproducts requiring disposal. 
Another object is to provide a means for producing elemental sulfur from 
sulfur dioxide which uses a low cost carbonaceous material as the reducing 
agent in a simple compact reactor. 
Another object of this invention is to provide a means for the simultaneous 
reduction of sulfur dioxide and alkali metal sulfates. 
Another object of this invention is to provide a process which can utilize 
the sulfur dioxide absorbed from flue gases to produce elemental sulfur. 
Another object of this invention is to provide a means for simultaneously 
reducing the sulfur dioxide absorbed from a flue gas to elemental sulfur 
and for regenerating the absorbent used in the absorption of such sulfur 
dioxide. 
Other objects and advantages of the present invention will be apparent in 
the course of the following detailed description. 
SUMMARY OF THE INVENTION 
In accordance with the broad aspects of the present invention, sulfur 
dioxide is reduced to elemental sulfur by reaction with carbonaceous 
material in the presence of a molten salt. Heat is provided for the 
reaction and for the purpose of maintaining the temperature above the 
melting point of the salt by reacting additional carbonaceous material 
with oxygen. The elemental sulfur is condensed from the gaseous product 
stream resulting from reactions between the sulfur dioxide, carbonaceous 
material and oxygen gas in a molten salt reducer which contains the molten 
salt. In a preferred embodiment, the source of the sulfur dioxide feed is 
the regeneration step of a flue gas desulfurization system which uses an 
alkali metal sulfite as the active absorbent. Any alkali metal sulfate 
produced in the flue gas desulfurization system is also reduced in the 
molten salt reducer resulting in regeneration of the absorbent. 
The invention will be more clearly understood by reference to the detailed 
description of certain preferred embodiments which follows, taken in 
connection with the accompanying drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention provides a process for converting gaseous sulfur 
dioxide to elemental sulfur using a molten salt as the reaction medium and 
carbonaceous material as the reactant. The principal overall reaction 
occurring in the molten salt reducer is the following: 
EQU SO.sub.2 +2C.fwdarw.S+2CO (1) 
Hydrogen in the carbonaceous material can also react with the sulfur 
dioxide feed to form additional elemental sulfur or hydrogen sulfide by 
reactions 2 and 3: 
EQU 4H+SO.sub.2 .fwdarw.S+2H.sub.2 O (2) 
EQU 6H+SO.sub.2 .fwdarw.H.sub.2 S+2H.sub.2 O (3) 
In addition, side reactions result in the formation of carbonyl sulfide and 
carbon disulfide. These reactions are illustrated in the following 
equations: 
EQU S+CO.fwdarw.COS (4) 
EQU 2S+C.fwdarw.CS.sub.2 (5) 
The reactions illustrated above occur in a reaction zone containing a 
molten salt, which may consist of an alkali metal sulfide or a mixture of 
salts with an appropriate melting point. A mixture is preferred in order 
that the temperature at which the molten salt reaction zone must be 
maintained to keep the salts in molten condition is lower than the melting 
point of, for example, pure sodium sulfide which melts at about 
1180.degree. C. Particularly preferred is a mixture of sodium and 
potassium sulfides. Use of this mixture permits operation well below the 
freezing point of pure sodium sulfide. The presence of other anions in the 
melt, for example, polysulfides, carbonates, sulfites, sulfates, 
hydroxides and silicates is also effective in lowering the melting point 
and some of these will normally be present due to side reactions and 
impurities in the feed materials. Alternatively, non-reactive salts such 
as sodium chloride may be used to lower the melting point or increase 
fluidity at the reaction temperature. 
The composition of the molten salt may in certain circumstances be affected 
by the composition of salts used in the stages preceding the molten salt 
reducer, that is, the stages resulting in the provision of a sulfur 
dioxide stream. For example, where sodium sulfite is used to absorb sulfur 
dioxide from flue gases, sodium sulfite, sodium thiosulfate, sodium 
bisulfite and sodium sulfate are among the compounds which may be present 
in the spent absorbent or the regenerated absorbent, in those cases in 
which the absorbent is regenerated. Use of these salts as feed to the 
molten salt reactor generally provides the necessary environment for the 
occurrence of the desired reduction reactions. In an especially preferred 
embodiment sodium sulfate is continuously fed to the molten salt reducer 
during operation in order to provide the requisite salt mixture. 
The temperature of the molten salt reaction zone is maintained above the 
melting point of the salts present. In particular, temperatures in the 
range of about 850.degree. to 1250.degree. C. have been found desirable, 
with temperatures in the range of about 900.degree. to 1100.degree. C. 
being preferred. 
The temperature of the molten salt reaction zone is maintained by oxidizing 
a portion of the carbonaceous material feed. The oxidation of carbon to 
carbon monoxide and carbon dioxide is illustrated in Equations 6 and 7. 
EQU 2C+O.sub.2 .fwdarw.2CO (6) 
EQU C+O.sub.2 .fwdarw.CO.sub.2 (7) 
These reactions are highly exothermic and can readily be utilized to 
provide the requisite heat to maintain the temperature of the molten salt 
reaction zone. 
The sulfur dioxide to be reduced in the molten salt reducer may be provided 
from any number of gas streams containing sulfur dioxide, principally, 
concentrated sulfur dioxide streams. One of the most common sources of 
sulfur dioxide is from flue gas desulfurization processes in which gaseous 
sulfur dioxide is absorbed from a flue gas by means of a suitable 
absorbent. In subsequent processing the resultant absorbate containing the 
sulfur dioxide values in the form, for example, of an alkali metal 
bisulfite, is treated to provide a concentrated sulfur dioxide stream and 
regenerated alkali metal sulfite. The sulfur dioxide stream is fed to the 
molten salt reducer in gaseous form. 
An oxidizing gas, for example, air, oxygen or oxygen enriched air is also 
fed to the reducer in gaseous form. The function of the oxidizing gas, as 
pointed out above, is to oxidize a portion of the carbonaceous material 
which serves as the reductant for the sulfur dioxide in order to provide 
sufficient heat to sustain the reaction and maintain the salts in molten 
form. 
The principal reduction for the sulfur dioxide is carbon. It may be 
provided in the form of a carbonaceous material which is preferably fed as 
a dry solid with the sulfur dioxide or the oxidizing gas. Petroleum coke 
is preferred for this purpose. Other forms of carbonaceous materials which 
may be used include coal, petroleum products, lignite or wood. 
Make-up salt for the molten salt reaction zone is also preferably fed as a 
dry material. For example, dry alkali metal sulfates or thiosulfates may 
be used for this purpose. Under the conditions of operation of the molten 
salt reactor in the process of this invention, the sulfates or 
thiosulfates are converted to sulfides as illustrated in Equations 8, 9, 
10 and 11 
EQU M.sub.2 SO.sub.4 +2C.fwdarw.M.sub.2 S+2CO.sub.2 (8) 
EQU M.sub.2 SO.sub.4 +4C.fwdarw.M.sub.2 S+4CO (9) 
EQU 2M.sub.2 S.sub.2 O.sub.3 +3C.fwdarw.2M.sub.2 S+2S+3CO.sub.2 (10) 
EQU M.sub.2 S.sub.2 O.sub.3 +3C.fwdarw.M.sub.2 S+3CO+S (11) 
where M is an alkali metal ion. 
In cases where the process is used only to treat sulfur dioxide and not to 
reduce alkali metal sulfate at the same time, little or no salt make-up is 
required, and the molten salt mixture composition is determined by the 
composition of the make-up used. If alkali metal carbonates are used as 
make-up these are converted to the sulfides by such reactions as 
illustrated in Equation 12: 
EQU 2M.sub.2 CO.sub.3 +2SO.sub.2 +3C.fwdarw.2M.sub.2 S+5CO.sub.2 (12) 
If, on the other hand, relatively inert salts such as alkali metal 
chlorides are used as make-up, these remain in the molten salt reaction 
zone in relatively unchanged chemical form. 
The advantage of using the salts in dry solid form is that thereby the 
necessity of drying an aqueous solution of the salt or salts is obviated, 
which reduces the amount of heat energy which must be expended in the 
molten salt reducer, thereby reducing the amount of carbonaceous material 
in excess of that required for reaction with the sulfur dioxide which must 
be fed to the molten salt reducer. If, however, it is desired to use an 
aqueous solution of the salt as feed, then it is simply necessary to use a 
larger excess of carbonaceous material than would otherwise be required, 
in order to vaporize the water from the aqueous solution fed to the molten 
salt reducer. 
The carbonaceous material is fed to the molten salt reducer in excess of 
the amount required to reduce the sulfur dioxide in order to provide 
sufficient fuel for oxidation by the oxygen containing gas for the 
production of heat to keep the molten salt reducer at the desired 
temperature, as indicated above. 
The oxygen containing gas is used in an amount sufficient to oxidize the 
excess carbonaceous material. 
The make-up salt is introduced into the molten salt reducer in an amount 
sufficient to maintain the desired salt inventory in the molten salt 
reducer, allowing for any molten salt which may be drained from the system 
for use in various stages of the sulfur dioxide absorption process, for 
example, and to make up the loss of any salts which may be entrained in 
the gases produced in the reactions occurring in the molten salt reducer. 
Reaction between the carbonaceous material and sulfur dioxide fed to the 
molten salt reaction zone results in gaseous products. Other reactions 
occurring between the components of the feed materials may result in other 
gaseous products or products which remain in the molten salt. The gaseous 
products escape from the surface of the molten salt and are further 
processed in order to recover elemental sulfur in liquid form. These 
gaseous products, in addition to gaseous sulfur, include carbon monoxide, 
carbon dioxide, nitrogen, if air is used as the oxidizing gas, carbonyl 
sulfide, and carbon disulfide. If, as is typically the case, the 
carbonaceous feed contains some hydrogen, or moisture is present in any of 
the feed streams, the product gas stream will also contain hydrogen 
containing compounds such as hydrogen sulfide, water and hydrogen. The 
gaseous products exit the molten salt reducer as a hot gas which is 
processed to recover sulfur therefrom. 
Typically, the gas processing includes steps to remove entrained particles 
of melt, recover useful heat, condense elemental sulfur by cooling, reheat 
the gas to an appropriate catalytic reactor feed temperature, and generate 
additional elemental sulfur from gaseous components by catalysis. These 
steps may be repeated several times in order to ensure the removal of as 
much of the sulfur-containing by-products of the reduction reaction as 
possible as well as to increase the recovery of elemental sulfur. It is 
preferred to continue the processing until the gas contains less than 
about 15% of the sulfur contained in the original sulfur dioxide feed. The 
technologies involved after the removal of entrained particles of melt are 
generally similar to those employed in Claus process plants which convert 
hydrogen sulfide to elemental sulfur. Typical reactions which occur in the 
catalytic reactors are: 
EQU COS+H.sub.2 O.fwdarw.CO.sub.2 +H.sub.2 S (13) 
EQU CS.sub.2 +2H.sub.2 O.fwdarw.CO.sub.2 +2H.sub.2 S (14) 
EQU 2H.sub.2 S+SO.sub.2 .fwdarw.3S+2H.sub.2 O (15) 
The carbonyl sulfide and carbon disulfide hydrolysis reactions, illustrated 
in Equations 13 and 14, proceed more rapidly at elevated temperatures, for 
example, at tempertures in the range of about 300.degree. to 450.degree. 
C., while the elemental sulfur formation reaction illustrated in Equation 
15 proceeds quite rapidly at all practical catalyst temperatures and is 
favored by decreasing temperatures. It is therefore desirable to operate 
the first catalyst bed at high temperature, for example, above about 
350.degree. C. to assure the destruction of carbonyl sulfide and carbon 
disulfide and subsequent beds at temperatures which are as low as possible 
without condensing sulfur on the beds, for example, temperatures in the 
range of about 200.degree. to 300.degree. C. 
Following the processing steps to recover sulfur, the remaining gases are 
removed by way of a stack, incinerator or absorber or further processed 
depending upon whether the carbon monoxide, carbon dioxide and nitrogen 
are to be recovered or disposed of as waste gases. 
The other products of the reactions remain in the molten salt. These 
include sulfides, polysulfides, carbonates, sulfites and hydroxides, among 
others. Unreduced sulfates may also be present. Useful products may be 
separated from a stream drawn off from the molten salt reducer, if 
desired. Particularly, the molten alkali metal sulfide produced in the 
reduction reaction may be recovered by quenching and suitable processing 
and converted to a useful absorbent for removing sulfur dioxide from flue 
gas streams. 
The invention will now be described with respect to one of its preferred 
embodiments by reference to the drawing. 
A flue gas from which sulfur dioxide is to be absorbed is fed into an 
absorber 10 via a conduit 12. A suitable absorbent solution is also fed to 
absorber 10 via a conduit 14. Purified flue gas exits absorber 10 via a 
conduit 16 and the absorbate solution containing the absorbed sulfur 
dioxide exits absorber 10 via a conduit 18. The absorbate solution is then 
fed to a regenerator 20 via a conduit 22. In regenerator 20 the sulfur 
dioxide absorbed from the flue gas in absorber 10 is regenerated from the 
resulting absorbate. The regenerated sulfur dioxide is then fed to a 
molten salt reducer 24 via a conduit 26. The absorbate from which the 
sulfur dioxide has been regenerated in regenerator 20 exits regenerator 20 
via a conduit 28. From conduit 28, the solution from which sulfur dioxide 
has been regenerated is divided into two streams, one of which is 
conducted back to the absorber via conduit 14 and the other to a dryer 32 
via a conduit 34. The dried salts from dryer 32 are conducted to a feeder 
36 via a conduit 38. Petroleum coke is added to feeder 36 via a conduit 
40. The mixture of coke and salt from feeder 36 is fed to molten salt 
reducer 24 via a conduit 42. Air is heated in a heat exchanger 44 prior to 
being introduced into molten salt reducer 24 via a conduit 46. The air 
heated in heat exchanger 44 is furnished via a conduit 48, a blower 50 and 
a conduit 52. The air is heated in heat exchanger 44 by exchange of heat 
with the hot gaseous product stream from molten salt reducer 24 exiting 
via a conduit 54. The hot product gas stream is partially cooled and 
entrained melt particles are removed in heat exchanger 44. The product gas 
stream is then conducted to a condenser 56 via a conduit 58. In condenser 
58 liquid sulfur is condensed from the product gas stream by means of 
cooling with water, which may become steam in the process, and is removed 
from condenser 56 via a conduit 60. The product gas stream from which 
liquid sulfur has been condensed is then conducted to a burner 62 via a 
conduit 64 for reheating from the temperature of sulfur condensation to 
the preferred temperature for catalytic reactions. Hydrogen sulfide is 
introduced into burner 62 via a conduit 66 and air is introduced into 
burner 62 via a conduit 68. In burner 62 the burning of the hydrogen 
sulfide by means of the air results in the generation of heat and the 
formation of sulfur dioxide is illustrated in Equation 16: 
EQU 2H.sub.2 S+3O.sub.2 .fwdarw.2SO.sub.2 +2H.sub.2 O (16) 
The reheated gaseous stream exits burner 62 via a conduit 70. Steam is 
introduced via a conduit 72 in order to provide a source of water, if 
required, for the hydrolysis of carbonyl sulfide to hydrogen sulfide as 
shown in Equation 13. The hydrogen sulfide reacts with sulfur dioxide 
present in the gas stream to form elemental sulfur as shown in Equation 
15. Additional sulfur may be formed by the direct reaction of carbonyl 
sulfide with sulfur dioxide as illustrated in Equation 17: 
EQU 2COS+SO.sub.2 .fwdarw.3S+2CO.sub.2 (17) 
Carbon disulfide may be similarly hydrolyzed or reacted with sulfur dioxide 
as illustrated in Equations 14 and 18, respectively: 
EQU CS.sub.2 +SO.sub.2 .fwdarw.3S+CO.sub.2 (18) 
These reactions take place in a catalytic converter 74 into which the 
gaseous product stream containing the product gas stream from which sulfur 
has been separated in condenser 56 as well as the products of combustion 
from burner 62 are conducted via a conduit 76. Converter 74 is operated at 
a temperature in the range of about 300.degree. to 450.degree. C. and 
preferably a temperature in the range of about 325.degree. and 400.degree. 
C. The product stream from converter 74 which has been enriched with 
sulfur is conducted to a condenser 78 via a conduit 80. Liquid sulfur is 
condensed and removed via a conduit 82. The gas stream from which the 
additional sulfur has been condensed is then conducted to a burner 84 via 
a conduit 86 and the previous steps are repeated in order to recover 
additional liquid sulfur product. Hydrogen sulfide is introduced into 
burner 84 via a conduit 88 and air is introduced into burner 84 via a 
conduit 90. The gas stream from burner 84 which is enriched in sulfur 
dioxide is conducted to a second converter 92 via a conduit 94. The 
product of converter 92 is removed to a condenser 96 via a conduit 98. 
Product liquid sulfur is removed from condenser 96 via a conduit 100. 
Product gases exit via a conduit 102 which leads to a stack, incinerator 
or absorber, depending upon the use to which the product gases are to be 
put. 
A part of the molten salt from molten salt reducer 24 is periodically or 
continuously drawn off and introduced into a quench tank 104 via a conduit 
106. Water or dilute solution for use in quench tank 104 is introduced via 
a conduit 108. Soluble salts including alkali metal sulfides in the melt 
dissolve in the quench tank liquid to form an aqueous solution which is 
then conducted to a stripper 110 via a conduit 112. Stripper 110 functions 
to strip hydrogen sulfide from the aqueous solution by contacting it with 
sulfur dioxide introduced via a conduit 114. The sulfur dioxide serves 
primarily to convert alkali metal sulfides to alkali metal sulfites and 
hydrogen sulfide as illustrated in Equation 19 
EQU M.sub.2 S+SO.sub.2 +H.sub.2 O.fwdarw.M.sub.2 SO.sub.3 +H.sub.2 S (19) 
where M is an alkali metal ion. 
The stripped solution exits stripper 110 via a conduit 116 and is fed via 
conduit 22 to regenerator 20 for return to the sulfur dioxide absorption 
system. Hydrogen sulfide gas is removed from stipper 110 via a conduit 
118. 
The invention will be better understood by reference to the following 
examples which illustrate embodiments of the processes of this invention 
and should not be construed as limiting the scope thereof. 
EXAMPLE 1 
Petroleum coke of the composition given in Table 1 was fed continuously at 
the rate of 164 lb./hr. to a molten salt bath in an insulated reactor 
maintained at a temperature of 1011.degree. C. Sulfur dioxide gas was 
introduced at a rate of 659 lb./hr., sodium sulfate crystals at a rate of 
176 lb./hr. and oxygen gas at a rate of 50 lb./hr. The product gas, which 
had the composition shown in Table 2A, was released from the reactor at a 
rate of 920 lb./hr. The melt, which had the composition shown in Table 3A, 
was formed at the rate of 129 lb./hr. 
EXAMPLE 2 
The procedure of Example 1 was followed except that air was fed instead of 
oxygen gas at a feed rate of 334 lb./hr., the feed rate for petroleum coke 
was 178 lb./hr. and the temperature was 1018.degree. C. Product gas having 
the composition shown in Table 2B was released at a rate of 1235 lb./hr. 
and the melt, which had the composition shown in Table 3B, was formed at 
the rate of 112 lb./hr. 
TABLE 1 
______________________________________ 
PETROLEUM COKE COMPOSITION 
Percent by Weight 
______________________________________ 
Carbon 87.9 
Hydrogen 3.9 
Nitrogen 2.2 
Sulfur 2.1 
Oxygen 1.3 
Ash 1.6 
Moisture 1.0 
100.0 
______________________________________ 
TABLE 2 
______________________________________ 
PRODUCT GAS COMPOSITIONS 
Volume (%) 
Component A (Example 1) 
B (Example 2) 
______________________________________ 
CO 5.3 3.9 
COS 1.0 0.6 
CO.sub.2 52.4 37.4 
H.sub.2 0.7 0.6 
H.sub.2 O 11.4 9.1 
H.sub.2 S 3.9 2.4 
N.sub.2 0.6 28.9 
SO.sub.2 4.3 3.6 
S.sub.2 20.0 13.1 
A 0.0 0.4 
100.0 100.0 
______________________________________ 
TABLE 3 
______________________________________ 
MELT COMPOSITIONS 
Percent by Weight 
Component A (Example 1) 
B (Example 2) 
______________________________________ 
Na.sub.2 SO.sub.4 
52.0 26.7 
Na.sub.2 S 44.5 69.0 
Compounds 
derived from 
the ash 3.5 4.3 
______________________________________ 
It can be seen that the present invention provides a process in which a 
major fraction of the sulfur in the sulfur dioxide feed is converted to 
elemental sulfur, S.sub.2, which leaves with the product gas. It can also 
be seen that a substantial fraction of the melt is converted from sodium 
sulfate to sodium sulfide during the course of the reduction process. 
It will, of course, be realized that various modifications can be made in 
the design and operation of the present invention without departing from 
the spirit thereof. For example, the various feeds for the molten salt 
reducer may be derived from other process streams than those specifically 
illustrated, a different type of molten salt reducer other than the bath 
type illustrated may be used, the elemental sulfur produced in the molten 
salt reducer may be processed otherwise than as specifically described 
above, or the melt withdrawn from the molten salt reducer may be 
regenerated by means of carbon dioxide following quenching. Thus, while 
the principle, preferred design, and mode of operation of the invention 
have been explained and what is now considered to represent its best 
embodiment has been illustrated and described, it should be understood 
that, within the scope of the appended claims, the invention can be 
practiced otherwise than as specifically illustrated and described.