US3165378A - Conversion of sodium sulfide to sodium sulfite - Google Patents

Description

Jan. 12, 1965 I J. E. GREENAWALT 3,165,373

CONVERSION OF SODIUM SULFIDE T0 SODIUM SULFITE Filed June 26. 1961 2 Shasta-Sheet 1 Jan. 12, 1965 J. E. GREENAWALT 3,165,378

CONVERSION OF SODIUM SULFIDE TO SODIUM SULFITE Filed June 26. 1961 2 Sheets-Sheet 2 26 2+ l I 2| v 25 2| United States Patent 3,165,378 CONVERSION OF SQDIUM SULFIDE T0 SGDHJM SULFITE John Eckert Greenawait, Bronxville, N.Y.; Joy S. Greenawait, executrix of said John E. Greenawait, deceased Filed June 26, 1961, Ser. No. 119,445

7 Claims. (Cl. 23129) the particular digester or cooking process that is used for freeing the cellulose fibers from encrusting matter. For example, a solution of caustic soda and sodium sulfide is used as the active chemicals in the sulfate or kraft'process; caustic soda is used in the soda process; and in the sulfite process, an acid sulfite solution, sometimes referred to as bisulfite of lime liquor is used. Sodium sulfite also is used. In all these processes the problem is to dissolve and remove the resinous or encrusting matter to free the cellulose fibers contained in wood, or rags, or straw, etc., used for the production of paper. The dissolving agents most commonly used are very active and they act not only upon the encrusting and non-cellulose constituents but also to a greater or lesser extent upon the pulp-making fibers themselves and may destroy or injure a considerable portion of the valuable fibers which are intended to be used for the production of paper. The yield with the various more active chemicals varies with the character of the wood treatedand is usually from 38% to 55% of the dry weight of the wood treated. By the use of substantially neutral sodium sulfite solution which is considered to be a milder acting chemical, the yield of desirable fibers may be increased 25% to due to the milder solvent action of the solvent. Sodium sulfite (Na SO is used as the active chemical in a dilute solution of approximately 12% in the semi-chemical process; but to realize the full benefits of the use of sodium sulfite cooking liquor it is desirable to use a 30% to solution.

Such a highly concentrated solution is uneconomical and impractical to use without a successful and economirecovery and regenerating process which will permit the use and-reuse of the sodium sulfite for cooking the wood in the digesters. I

. It is an object of this invention to provide such a process by which to recover the spent sodium sulfite liquor and regenerate the chemicals therein to the initial sodium sulfite form so that the chemical may be used again, then recovered,-.regenerated, and reused repeatedly. To 'accomplish this desirable end the invention, in one way of stating it, provides a method for converting sodium sulfide (Na s) to sodium sulfite (Na SO In further explanation of the foregoing statement, it is mentioned here that the spent liquor, from the wood digesters in the chemical process of producing pulp, contains carbonaceous and ligneous matter in addition to the spent chemicals. Processes are known for separating the carbonaceous and ligneous matter contained in the spent liquor from the chemicals, by burning or otherwise. Some of these processes produce a smelt in which. the chemical is in the form of sodium sulfide. Or sodium sulfide may be produced by smelting sodium sulfate (salt cake) in a reducing atmosphere. Or it may be provided from other sources. While the process of conversion of sodium sulfide to sodium sulfite according to the invention is applicable whether the sodium sulfide is produced from black liquor which comes from pulp digesters or whether it comes from other sources, the invention is particularlysuited to the recovery of chemicals and regeneration of the chemicals in pulp-producing processes employing sodium sulfite in the cooking liquor.

According to the process of this invention, sodium sulfite is oxidized in an atmosphere of saturated steam and oxidizing gases, such as air or oxygen containing gases under controlled pressure materially greater than atmospheric and under controlled conditions of temperature. The conversion is believed to be accomplished by direct oxidation of the sodium sulfide according to the following reaction: 7

It is important in my process that the temperature be carefully controlled within a narrow range and preferably at a constant temperature, in the zone where the oxidation reaction takes place. If the temperature is permitted to go too high, the oxidation of the sodium sulfide proceeds to the-formation of unwanted sulfate, and this reaction is believed to proceed as follows:

But this unwanted oxidation may be practically substantially avoided by not permitting the temperature in the reaction zone to rise above 350 F, provided the reaction is carried out in the presence of saturated steam. However, the temperature should not be permitted to go below 310 F. because the desired oxidation of the sulfide to sulfite will not then proceed in satisfactory manner. I have obtained satisfactory results when the temperature in the reaction zone was maintained between 310" F. and 350 F. Not only is it important in my process to control and maintain the temperature within a limited range but it is imporant that the zone in which the oxidation reaction takes place be maintained at a pressure substantially greater than atmospheric. In my process the pressure in the reaction zone, wherein are present the saturated steam, air (or oxygen) and the solution containing the reacting sulfur compounds, should be within the range of eighty to one hundred twenty-five pounds per square inch (gauge), and preferably about one hundred twenty-five, although in some instances a pressure as low as sixty pounds may sufiice.

If the source of the sodium sulfide is the concentrated or smelted product from black liquor or if it otherwise comes from spent liquor in apulp digesting or paper making process other sulfur compounds such as, sodium thiosulfate, or caustic soda or both, may be present in the charge in small amounts or formed during the course of the process. But this is not a serious drawback in my process for the thiosulfate and the caustic soda will react to form sodium sulfite according to the following:

tion of pulp, is concentrated. The spent liquor, containing the spent sulfite chemicals and the dissolved resinous and ligneous matter, is evaporated in a known way to contain about fifty percent, or more, of solids. This concentrated liquor is then burned in a known way in a smelting furnace under reducing conditions so as to convert the sulfur compounds into sodium sulfideform. The sodium sulfide smelt is discharged from the smelting furnace as amolten stream and this may contain other sulfur compounds, such as thiosulfate in small amount'and caustic soda along with sodium sulfide. The smelt is then dissolved in water and this solution constitutes the charge or solution which is then treated according to my process for conversion of the sodium sulfide to sodium sulfite suitable for reuse as a cooking liquor in the wood pulp digesters. if sodium carbonate is present in the liquor, the smelt will contain sodium carbonate. t

The following analysesof solutions, for example, show results obtainedby my process operated at .80 pounds steam pressure; there being a certainaniount of concentration of'the solutions due to the driving otfof some steam duringthe treatment.

In the regenerated solution the important thing is the conversion of the sodium sulfide to sodium sulfite. The thiosulfate may be useful in the cooking operation but preferably should be kept at a minimum as a large amount has ,a tendency to darken the color of the pulpv being treated. The small amount of sodium sulfate is not harmful as it is inactive during the cooking process and will be converted to sodium sulfide in the furnace operation during a succeeding cycle. Sodium carbonate is preferred in some operations and aids in maintaining the alkalinity of the solution. 7

Although the process of my invention may becarried out in'variousforms of apparatus, I have shown in the drawings, for illustrative purposes, one form of apparatus in which the process of my, invention may be practiced. And although the novel features which are believed to be characteristic of my invention are pointed out ,in the c, d, e, f, g, It, i, j, k, l, in, 21, 0, 17, q, r, s, t connected inseries by nipples 15a to s inclusive. This serpentine conduit made by connecting the elbowsin series constitutes in efiect a reaction chamber 1%) defining a reaction zone ltd, andproviding a meandering course or path of travel for the charge solution, as describedlater on.- The serpentine chamber ill provided by the elbows is mounted vertically'within a housing or casing 15, which, as shown, is a suitable length of-twenty-four inch steel pipe. The lower end of the casing 16 has welded thereto an annular flange It: and'the upper end has a corresponding flange The casing 16 is closed at both ends; by a blind flange 9. at it'slower end, and a blind flange 2% at its upper end." It will be observed that the upper casing flange Edissuitably secured't'o the closure-flangem and the lower casing flange 17 .to the closure flange 19; which may be by bolts 21. The lower closure flange 1") has a downwardly extending hollow boss 22 through which extends an outlet nipple ZSconnectedtO elbow 14a. The 'upper closure flange hasa corresponding upwardly extending hollow. boss ZFrthrough which extends an'inlet nipple 2-4 connected to elbow Mt. Nipples 23 1 and 24- are mounted in the. hollow bosses and suitably sealed on their exteriors by packing materialzlfi in a manner that provides top closureZil. This pipe 26 has a valve Zea and'is annexed claims, the invention itself as to its objects and advantages and the manner in which it may be carried out may be better understood by reference to thefollowing more detailed description taken in connection with the accompanying drawings forming a part hereof, in which: FIG. 1 is a view in elevation partly in section,'partly broken away, and largely diagrammatic, showing one form of apparatus for carrying out the method of my invention;

FIG. 2 is a view in elevation partly in section and largely diagrammatic of the reaction chamber or tower and to. larger scale;

FIG. 3 is a plan view of the reaction tower shown in FIG. 2.

Referring now to the drawings in which like reference characters indicate like parts-throughout the several views, the apparatus as shown comprises a reaction chamber 10, a pro-heater 11, a receiver tank 12 and a cooling and settling chamber 13. r The reaction zone 14, as shown, is

. provided by mounting a series of six inch elbows 14a, b,

connected toa suitable source of steam (not shown) preferably under sufficient pressure tornaintain, if desired, a pressure higher than 8 poundsv per squareinch gauge within the housing chamber127. The bottom closure 19 is provided with an outlet pipe ZS-With' valve 28a for withdrawing condensed water that may be formed in chamber 27. The steam line 26 may be: connected with appropriate valves to the same steam supply line as the reaction zone so the pressure-will always be the same.

The preheater. ill, aslshown, comp-rises a casing 31 closed at both ends by closure members 32, 33. Mounted within the casing 31 is a pipe conduit' 34 made up ofsuitable lengths of 'pipesfifi connected in series by=return bends 36. The inlet end of preheater conduit 34 is connected to a T 37 towhich is connected an air inlet pipe 38 for introducing air and a raw'solution pipe 39 for introducting the. charge solution. The raw or charge solu.tion, as explained later, is an aqueous solution containing sodium sulfide which it is desired to convert to sodium sulfite and,as described hereiis the sodium sulfide smelt described hereinbefore .Which I has been recovered from the burning of black liquor in a reducing atmosphere; However, itjwill bef-understood that the methodis applicable to any of the alkali metal sulfides whichrnay be converted intothe corresponding sulfite.

A stearn'pipe 49, connected to a suitable sourceof steam leads into the preheater housing 31 and an outlet steam pipe 41' having a regulating valve-42h connected to the opposite end of thepreheater housing. As indi-- placed a pressure regulatin valve 26. A pressure gauge 47 in line 45 serves to indicate the pressure within the reaction Zone 14. A pressure gauge 61 connected to' housing chamber 16 serves to'indicate the" steam pressure in the housing. I i

The discharge conduit 45 leads into a treated solutionreceiving tank 12, havinga draw-off pipe tdiand valve 49 for drawing off treated-solution. The receiving tank E2 has connected thereto at'its upper sidea vapor and drain-back conduit 5%, which leads in'to the bottom of a cooling and settling chamber 13 which, as shown, isa with the upper end 3,1 east/ s length of large size pipe 51 closed at its upper end by a closure 52 and at its base end by a closure 53. The cooling chamber 51 is mounted on a suitable foundation and base 62. Mounted within the cooling chamber housing 51 is a cooling coil 54 having an inlet 55 connected to a suitable source of cooling water (not shown) and an outlet 56. The cooling chamber 13 is provided at its upper end with a vent pipe 57 for discharge to atmosphere of residual gases and uncondensed vapors. The vent pipe 57 is provided with a blow o or pressure regulator valve 57a, which may be set to maintain any desired pressure within the chamber 13 so as to maintain, in turn, the desired pressure and temperature within the reaction zone 14. By maintaining the pressure the same as the rest of the equipment the efficiency may be enhanced.

The process and apparatus may be operated as follows: Raw solution is introduced through pipe 39 into preheater coil 34 together with compressed air which is introduced from a suitable source, through pipe 38. The raw solution is an aqueous solution of sodium sulfide from a suitable source. The amount of air introduced is sufficient to provide an excess of oxygen necessary to convert the sulfide to sulfite. This raw solution, for example, may be an equeous solution made up from the sodium sulfide smelt resulting from the burning of concentrated spent black liquor from the pulp digesters in which sodium sulfite solution has been used for cooking the wood chips.

As the mixture of air and raw solution (this mixture is herein called the charge mixture) passes through the preheater coil 34 in the preheater 11, it is heated by steam introduced into the housing 31 through'pipe 40. It will be understood, of course, that the charge mixture is introduced under sufficient pressure to pass through the system. Suflicient heat is applied in the preheater to bring the temperature of the charge of raw solution and air as it enters the upper end of the reaction chamber to the neighborhood of the temperature at which the reaction zone is maintained. A suitable temperature for introducing the charge solution into the reaction zone is in the neighborhood of 300 F. This temperature may go even as high as 350 F., but inasmuch as it is desired to maintain the temperature Within the reaction zone 14 within the range of 310 to 350 F., and the reaction to oxidize the sulfide to sulfite is an exothermic reaction, the temperature of the charge mixture entering the reaction zone should be maintained so that the temperature in the reaction zone is maintained within the desired range. This may be done by regulating the pressure in the reaction zone. The temperature in the preheater coil, as will be seen, may be adjusted by adjusting the steam introduced in the preheater and according to the temperature and amount of solution and air introduced into the preheater. It is desirable, but not necessary, tohave the temperature of the solution being treated as it leaves the preheater the same as the temperature in the reacting zone as the efiiciency of the reacting zone is thereby increased. The concentration of the sodium sulfide in the raw solution may vary but preferably should be such that the concentration of sodium sulfite in the treated solution received in the receiving tank 12 would be suitable as a sodium sulfite cooking liquor. But even this may vary and the treated solution may be adjusted for use in the paper-making process.

The charge moves downwardly in the serpentine reaction chamber 10 in the presence of the oxidizing air and saturated steam and it will be noted that the reaction chamber is filled with steel balls ilwhich provide more surface area over which the solution is spread as it descends, thus the stream of liquor being treated is broken up into very thin layers and each ball is completely covered with film so that morev surface film of solution is exposed for reaction with the oxygen of the air introduced with the charge. As the liquid charge descends it is caused to follow a tortuous path as the elbows cause turns in direction of flow and a mild turbulence to insure intimate contact between the chemical reagents dissolved in the solution and the reactive oxygen or other reacting agents intermediately formed as the reaction proceeds. As mentioned hereinbefore, the temperature in the reaction zone is preferably maintained within the range of 310 F. to 350 F.

It is a feature of my process that the pressure at which the reaction is carried out be maintained substantially higher than atmospheric and preferably under at least four atmospheres. The temperature in reaction chamber is positively controlled by the pressure of the steam with its oxidizing gases and the boiling point of the solution being treated, which depends upon its density or specific gravity since the boiling point will be higher, the greater density of the solution. However, with the same solution continuously flowing through the system, as is the case in this instance, the temperature may be maintained constant by maintaining a constant pressure in the system, notwithstanding that heat is released by the oxidation of the chemicals in the solution. The utilization of this principle is highly important to the success of my process because if there should be an increase in temperature in the reaction zone which would be conducive to the formation of unwanted compounds, such, for example, as sodium sulfate, the excess heat is immediately dissipated for the reason that the increase in pressure brought about by increase in temperature is immediately released with concomitant using up of the excess heat as latent heat of vaporization. Hence, in my process the desired temperature of reaction is maintained constant. That is, if at a given increase in temperature, the oxidation of sodium sulfide (Na s) will proceed beyond the sulfite (Na SO and the compound take up another atom of oxygen and form unwanted sodium sulfate m son, this unwanted increase in temperature is easily and readily avoided by my process.

At the temperature at which the reaction zone is maintained, that is, at a temperature within the range of 310 F. to 350 F., some of the water in the charge is converted into steam. That is, the condition of the solution in the reaction chamber is such that saturated steam and liquid water prevails under the pressure maintained which preferably is within the range of 80 to 125 pounds per square inch gauge pressure. in order to maintain this desired pressure constant, the pressure regulator valve 46 may be set accordingly, so that if the pressure within the reaction zone exceeds a predetermined amount (say 80 p.s.i., for example) the regulator valve'46 will automatically release the excess and maintain the reaction zone pressure constant. Or, the pressure in the system may be controlled by adjusting the blow oft pressure of valve 57a in the vent pipe 57; the important consideration being to control the temperature in the reaction zone. This type of regulation has a further advantage in that for any given pressure within the reaction zone (indicated on gauge 47) the saturated steam in the reaction zone will have a fixed temperature, thus the arrangement provides a simple and effective way of controlling both pressure and temperature within the reaction zone.

I prefer to mount the reaction chamber 14 within a housing 16 equipped with a steam inlet such as inlet 25, and a steam outlet, such as steam outlet 23. If desired, the valve 28;; may be of the blow off type. This has the advantage of providing positive temperature control in the housing 16. The housing chamber 16 is supplied with The reaction which takes place in the reaction zone converts the sodium sulfide in the solution to sodium sulfite and the treated solution is passed into receiving tank 12. This treated solution is accompanied by steam vapors, and spent air, which will pass into the pipe 59 and thence into cooling chamber 13 which is maintained at cooling temperature by circulation of cooling water through coil 54. This causes the-steam and entrained chemical reagent to collect as liquidsolution in the condenser and the condensed solution gravitates back througi the pipe 59 into the receiving tank 12. Uncondensed gases and vapors minus all entrained or Volatiiized chemicals pass through vent 57 as waste to atmosphere. The-treated solution 58 in which the sodium sulfide has been converted to sodium sulfite may be drawn off through pipe ddfor reuse in the digesters of the pulp plant. 7

The examples set forth in the following Table I' will serve further to illustrate the process of my invention.

' The raw solution was made by dissolving a smelt in water,

the smelt having been produced in. a process of recovering the chemicals from black liquor from the digesters of a pulp plant. The raw solution contained the compounds as shown in the table under the columns labelled .Before Treatment. The raw solution together with air in an amount to provide an. excess of oxygen to convert the sodium sulfide to sodium sulfite was passed through the reaction zone as described above. The temperatures and pressures indicated in the table were maintained in the reaction zone. The results of the treatment are shown in the steamwithin said chamber within the range of sixty m 0;) range of 310 F. to 350 F. at which said sodium sulfide isoxidized in an exothermic reaction, to sodium sulfite,

controlling said pressure in said zone at said constant pressure whereby any excess heat produced by the exothermic oxidation of the sodium sulfide to sodium sulfite which would cause the'ternperature in said zone to rise above said given temperature is taken up as latent heat of vaporization inthe conversion of water 'into'steam, thereby to maintain the. temperature in said zone substantially constant. I

2. A process for converting sodium sulfide to sodium sulfite which comprises passing'a charge containing an' and one hundred twenty-five pounds per square inch.

3 A process of converting sodium sulfide into sodium sulfite which comprises passing a stream of aqueous solution of the sodium sulfide in an atmosphere of saturated steam and air through 'a'reaction chamber, subdividing the stream being treated into thin" surface films-thereby to expose the sulfide to the oxygen in the auto promote oxidation of the sulfide while maintaining the pressure'in sulfite which comprises passing an aqueous solution containing sodium sulfide through a reaction zone in an at mosphere of saturated steam and air under substantially constant pressure within therange of 60 to 125 poundspe'r'square inch and at a given temperature within the the columns labelled After Treatment. It may be noted said chamber between sixty and one hundred twenty-five that there is a small amount of evaporation of the water pounds per square inch gauge and the temperature within in the charge as a result of'the treatment. the range of 3l0 F. to 350 F. and controlling and Table I i 7 Run A Bun B Run Q Run D Pressure in Reaction Zone 80 p.s.i. 60 psi. 80 p.s.i. 125 psi. Temperature in Reaction Zone 321 F. 300 F. 324 F. 350 F.

Solution, Solution, Solution, Solution,

g.p.1. 1 g.p.l. g.p.l. Percent By Wt.

Compound Before After Before After Before After Before After Treat- Treat- 'Ireat- Treat- Treat- Treat- Treat- Treatment ment merit meni: merit merit ment ment 1 Sodium Sulfide N3JS 28.36 0.2 28.36 3.22. 21.70 0.5 12.51 .02 Sodium Thiosulfate 2.03 4.0 2.08 7.66 1.10 4.04 .41 .92

NazSzOa. Sodium Sulfite N21280:)" 1.01 32 1.01 14.11 .95 20.52 .10 14.31 Sodium Sulfate NazSO4 2. 4. s 2. 55 5.05 a 2. 01 2. 39 1. 02 1.49 Sodium Carbonate 23.90 21.70 13; 99 15:03

N34003- Sodium Hydroxide .13 .24 Trace Trace NaOH.

1 Grams per liter. 2 Percent by weight. g v

It is contemplated that in some instances in practicing maintaining the temperature in said reaction zone by my method, modified air or similar gaseous oxidizing maintaining the steam therein at a constantpressure beagent might be used, such, for example, atmospheric air tween sixty and one-hundred twenty-five pounds 5 per to which is added additional oxygen. It will be undersquare inch. r v

' stood that the term air as used in the annexedclaims 4. A process for oxidizing sodium sulfide. to sodium is intended to include a gaseous oxidizing agent containsulfite which comprises treating an. aqueous solution coning a substantial portion of oxygen. taining the sodiumsulfide in an atmosphere of saturated The terms and expressions which have been employed steam and air in a reaction zone in Whichsaid sodium herein are used as terms of description and not of limitasulfide is oxidized to. sodium sulfite' in an exothermic tion, and there is no intention, in theuse otsuch terms reaction and maintaining a predetermined constant presand expressions, ofexcluding any equivalents of the tea-I sure in said zone within the range of80 pounds per tures shown and described'or portions thereof, but it is square inch andone hundred twenty-five pounds i per recognized that various modifications are possible Within square inch and maintaining the temperature in said zone the scope of the invention claimed. at a predetermined constant temperature between 310? F.

What is claimed is: v V and 350 F. by controlling the steam pressure 1n said 1. A process for converting sodium sulfide to sodium zone sothat any heat generated in said zone as a result of the exothermic oxidizing reaction which is enough to cause the'temperaturein said zone to rise above said constant temperature is dissipated as latent heat of vapori Zillion whereby said reaction is controlled to avoid OXlda: qu'of the Sulfide tosulfate form,

5. A process for converting sodium sulfide to sodium sulfite which comprises treating an aqueous solution containing the sodium sulfide in an atmosphere of saturated steam and air in a reaction zone wherein said sulfide is oxidized in an exothermic reaction, maintaining the pressure in said zone within the range of 80 to 125 pounds per square inch and maintaining the temperature in said zone at a substantially constant temperature within the range of 310 F. to 350 F. by controlling the pressure in said zone whereby any heat generated in said zone as a result of the exothermic oxidizing reaction which is in excess of that which causes the temperature in said zone to rise above said constant temperature is dissipated as latent heat of vaporization.

6. A process for converting sodium sulfide to sodium sulfite which comprises passing an aqueous solution containing sodium sulfide together with air and saturated steam under pressure of at least 60 pounds per square inch through a reaction chamber While maintaining a given temperature within the range of 310. F. to 350 F. in said chamber at whichsaid sodium sulfide is oxidized to sodium sulfite; controlling and maintaining'a constant pressure in said reaction chamber so that any excess heat produced by the oxidation of the sodium sulfide to sodium sulfite which would cause the temperature in said chamher to rise above said given temperature is taken up as latent heat of vaporization by the conversion of water into steam, and thereby maintaining the temperature in said chamber substantially constant at said given temperature; passing the treated solution containing the sodium sulfite, steam and air, from said reaction chamber into a collecting chamber, and then passing any uncondensed steam with the residual air into a condenser chamber maintained at a temperature to condense the steam to recover entrained sodium compounds, and then discharging residual uncondensed aqueous vapor and residual air from said condenser chamber,

7. A process for converting sodium sulfide to sodium sulfite which comprises passing an aqueous solution containing sodium sulfide together with air and saturated steam under pressure higher than atmospheric pressure through a reaction chamber while maintaining a given temperature within the range of 310 F. to 350 F. in said chamber at which said sodium sulfide is oxidized to sodium sulfite and oxidation to sodium sulfate is avoided; controlling the pressure in said zone at a given pressure within the range of 80 to 125 pounds per square inch so that any excess heat produced by the oxidation of the sodium sulfide to sodium sulfite which would cause the temperature in said chamber to rise above said given temperature is taken up as latent heat of vaporization by the conversion of water into steam, and thereby maintaining the temperature in said chamber substantially constant at said given temperature to avoid formation of sodium sulfate; passing the treated solution containing the sodium sulfite, steam and air, from said reaction chamber into a collecting chamber, and then passing any uncondensed steam with the residual air into a condenser chamber maintained at a temperature to condense the steam and to recover entrained sodium compounds, and then discharging residual uncondensed aqueous vapor and residual air from said condenser chamber.

References Cited by the Examiner UNITED STATES PATENTS Ross et a1 23-283 X MAURICE A. BRINDISI, Primary Examiner.

Claims (1)

1. A PROCESS FOR CONVERTING SODIUM SULFIDE TO SODIUM SULFITE WHICH COMPRISES PASSING AN AQUEOUS SOLUTION CONTAINING SODIUM SULFIDE THROUGH A REACTION ZONE N AN ATMOSPHERE OF SATURATED STEAM AND AIR UNDER SUBSTANTIALLY CONSTANT PRESSURE WITHIN THE RANGE OF 60 TO 125 POUNDS PER SQUARE INCH AND AT A GIVEN TEMPERATUER WITHIN THE RANGE OF 310*F. TO 350*F. AT WHICH SAID SODIUM SULFIDE IS OXIDIZED IN AN EXOTHERMIC REACTION, TO SODIUM SULFITE, CONTROLLING SAID PRESSURE IN SAID ZONE AT SAID CONSTANT PRESSURE WHEREBY ANY EXCESS HEAT PRODUCED BY THE EXOTHERMIC OXIDATION OF THE SODIUM SULFIDE TO SODIUM SULFITE WHICH WOULD CAUSE THE TEMPERATURE IN SAID ZONE TO RISE ABOVE SAID GIVEN TEMPERATURE IS TAKEN UP AS LATENT HEAT

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