Treatment of Sodium Dithionite Reaction Mixture

Europaisches Patentamt 211 3 European Patent Office uy Publication number: 0 648 Office europ6en des brevets A2

EUROPEAN PATENT APPLICATION

® Date of filing: 05.08.86

© Priority: 06.08.85 US 762839 © Applicant: VIRGINIA CHEMICALS, INC. 3340 West Norfolk Road © Date of publication of application: Portsmouth Vlrginia(US) 25.02.87 Bulletin 87/09 © Inventor: Wlnslow, Charles E., Jr. © Designated Contracting States: 1308 W.Ocean View Avenue BE DE FR GB IT NL Norfolk Virginia(US) Inventor: Bush, Joseph L. 3722 Cannon Point Drive Chesapeake Virginia(US) Inventor: Dickens, Daniel D. 4009 Maple Drive Chesapeake Virglrria(US)

Treatment of sodium dithionite reaction mixture.

© A method is taught for increasing the yield of reactor. Preferably, it is added concurrently with the anhydrous sodium dithionite by adding an organic third feed and throughout the entire course of the compound that is thiosulfate reactive to a batch reaction, ending with the beginning of the cooling reactor containing a puddle solution of methanol and period. A suitable addition rate is 0.4-0.6 fed with formic acid or an alkali formate as a first' wt.%/minute, preferably 0.5 wt.%/minute. All of the feed, an aqueous alkali compound as a second feed, organic compound is consumed, and at least a por- an aqueous alkali formate solution as a third feed, tion of the thiosulfate ion is destroyed. The organic and a methanolic SO2 solution as a fourth feed. This compound is selected from the group consisting of ^ji organic compound may be added prior to, combined epoxy compounds having the formula ^with, or concurrently with one of the four feeds to the 00 *° R,-CH

© A or halogenated hydrocarbons having the general carbon atoms, a phenyl group, or a substituted mformula R,X or XR2X, R, being hydrogen, an alkyl phenyl group. The compound represented by this group containing from 1 to 8 carbon atoms, a formula includes ethylene oxide, propylene oxide, halogenated alkyl group containing from 1 to 2 butylene oxide, epichlorohydrin, epibromohydrin,

Xerox Copy Centre 0 211 648 and styrene oxide. R2 is a primary or secondary alkyl group containing from 1 to 8 carbon atoms, an aliyl group or a 2-methylallyl or 2-ethyiallyI group, and X is a halogen atom. Suitable compounds include methyl iodide and ailyl chloride. 0 211 648

TREATMENT OF SODIUM DITHIONITE REACTION MIXTURE

The severity of these various losses will be deter- BACKGROUND OF THE INVENTION mined by the perfection of the design and opera- tion of the equipment used to carry out each of This invention relates to the manufacture of these functions. anhydrous alkali dithionites by reacting an alkaline 5 A second source of yield deficiency is chemi- formate, an alkali metal agent, and sulfur dioxide in cal decomposition of sodium dithionite after it is an alcohol/water solvent. It particularly relates to made. While several modes of sodium dithionite improving this process by removing troublesome decomposition are possible, the predominating loss impurities from the reaction mixture while the reac- results in the formation of sodium thiosulfate and tion is occurring. 70 other unidentified sulfur compounds which are In the process for the manufacture of alkali found in the reactor throughout the course of the metal dithionites from an alkali metal salt of formic reaction: acid, an alkali metal hydroxide, carbonate, or bicar- bonate, and sulfur dioxide, the pertinent chemistry (5) 2Na,S2O, - Na,S,O3 + Na2S,O5. is believed to be as shown in the following equa- 15 It has also been found that the sodium thiosul- tions, using sodium formate and sodium hydroxide fate forming reaction is auto-catalytic with respect for illustration: to sodium thiosulfate. That is, as the concentration of sodium thiosulfate increases in the reactor, its (1) 2NaOH + 2SO2 - Na2S20, + H2O, rate of formation similarly increases. This increas- 20 ing rate of formation may be owing to thiosulfate (2) 2HC00Na + 2SO2 + H2O - 2HCOOH + itself or to the accompanying sulfur compounds. A Na2S20s, number of factors are known to influence the rate of sodium thiosulfate formation, principally the re- (3) 2HCOOH + 2Na,S2O5 - 2Na2S2O, + 2CO2 + action temperature, the pH, and the water-to-al- 2H2O. 25 cohol ratio in the reaction medium. Despite all According to these equations, and assuming efforts to optimize these various conditions and that an excess of sodium metabisulfite is present, minimize the loss of sodium dithionite, this loss one mol of sodium dithionite should be produced continues to be a principal cost in the manufacture via Equation (3) for each one mol of formic acid of sodium dithionite. generated as shown in Equation (2). 30 Japanese Patent Publication No. 28,397/75 In practice it is found that substantially less teaches a process for manufacturing anhydrous than one mol of sodium dithionite is produced per sodium dithionite in an alcohol/water solvent from mol of formic acid. Empirically it has been estab- sodium formate, an alkali compound, and sulfur lished that approximately 0.8 mol of sodium dioxide, followed by filtering the sodium dithionite dithionite is produced per mol of formic acid. 35 crystals from the mother liquor. The publication One reason for this yield deficiency is that discloses a method for recycling the reaction fil- formic acid in the alcohol reaction medium used for trate with reduced distillation of the filtrate by treat- the process undergoes a certain degree of es- ing the filtrate with 1-to-4-fold excess on a molar terification: basis of ethylene oxide, propylene oxide, or a 40 mixture thereof over the amount of sodium thiosul- (4) HCOOH + CH3OH s* HCOOCH, + H20. fate contained in the reaction filtrate and by allow- The alcohol used for the reaction medium is ing the reaction mixture to stand for several hours recovered for re-use via distillation. The methyl at room temperature. The reaction filtrate is com- formate in the alcohol should be similarly recov- bined with the methanol used in washing the sepa- ered. If the methyl formate recovery were 100% 45 rated crystals of sodium dithionite to form a mix- efficient, no yield loss would be occasioned by the ture of which a part is distilled to recover the chemistry of Reaction (4). In practice, however, it methanol and isolate the addition product, which is has been found that methyl formate losses do discarded, of sodium thiosulfate and ethylene oxide occur, owing principally to its very high volatility. or propylene oxide. This is hereinafter referred to Some loss occurs directly from the reactor, as the 50 as the filtrate purification/recycle method. methyl formate is carried out by the effluen carbon Japanese Patent Disclosure No. 110,407/83 dioxide. Other losses occur in the act of filtering, teaches a method for producing dithionites by washing, and blowing the product filter cake. Still reacting a formic acid compound, an alkali com- more loss is occasioned by the distillation process. pound, and sulfur dioxide in a water-organic solvent mixture and by adding an epoxy compound, a 0 211 648 halogenated hydrocarbon of the general formula R- period of 20 minutes is then started, and simulta- X, or a mixture of two or more compounds of these neously the epoxy compound, the halogenated hy- types to the reaction mixture in the final stage of drocarbon, or a mixture thereof is added within less the reaction. Suitable epoxy compounds include than five minutes. The dithionite crystals are sepa- ethylene oxide, propylene oxide, butylene oxide, 5 rated out by filtration under applied pressure with isobutylene oxide, styrene oxide, cyclohexene ox- carbon dioxide and subsequently washed with ide, epichlorohydrin, and epibromohydrin. In the methanol and then dried under reduced pressure. halogenated hydrocarbon, R is a primary or secon- Both the filtrate and the washing liquid were dem- dary alkyl group having 1-8 carbons, an allyl group, onstrated to be equivalent to distilled methanol as a 2-methylallyl group, or a 2-ethylallyl group, and X 10 the organic solvent for producing sodium dithionite. is a halogen. The filtrate obtained by isolating the This is referred to hereinafter as the mother liquor dithionite crystals, the organic solvent used for cooling/purification method. washing the crystals, or a mixture thereof is re- In European Patent Publication 68,248 and in cycled and reused in the reaction. U.S. Patent No. 4,388,291, a process is disclosed The reaction is conducted according to Patent 15 for producing anhydrous dithionites in which the Disclosure No. 110,407/83 by dissolving sodium washing liquid discharged from the washing step is formate in hot water, adding methanol, and heating sequentially divided into two portions, a first di- at 82°C under an applied pressure of 1.0 kg/cm2 scharge liquid and a second discharge liquid, the gauge while stirring in a reactor equipped with a former being treated to convert undesirable sub- reflux condenser and a deep-cooling condenser. 20 stances inhibiting the production of dithionites into Subsequently, 50% sodium hydroxide solution and substances which do not exert an adverse influ- a methanolic solution containing methyl formate ence on the production of dithionites by adding an and sulfur dioxide are added simultaneously and organic compound selected from the group con- dropwise over a 90-minute period. Stirring is consisting of compounds represented by Formulas I tinued for an additional 150 minutes at the same 25 and II and cyclohexene oxide. Formula I is as temperature and pressure. Cooling to 73° over a follows:

wherein R, is hydrogen, an alkyl group containing the sodium dithionite product were substantially from 1 to 8 carbon atoms, a halogenated alkyl identical to those obtained with pure methanol. This 35 group containing from 1 to 2 carbon atoms, a is hereinafter referred to as the washing liquid phenyl group, or a substituted phenyl group. The purification/recycle method. compound represented by this formula includes The use of a thiosulfate-reactive compound for ethylene oxide, propylene oxide, butylene oxide, destroying thiosulfate ions in the mother liquor, the epichlorohydrin, epibromohydrin, and styrene ox- reactor filtrate, or the washing liquid before re-use 40 ide. Formula II is as follows: R2-X, of the methanol therein, as respectively taught in Japanese 110,407/83, Japanese 28,397/75, and Eu- wherein R2 is a primary or secondary alkyl group ropean No. 68,248, enables the initial reaction mix- containing from 1 to 8 carbon atoms, an allyl group ture of the next run to be substantially free of or a 2-methylallyl or 2-ethylallyl and X is a thiosulfate ions, but it does nothing to diminish the group, 45 halogen atom. Suitable compounds include methyl formation of thiosulfate ions during the dithionite- iodide and allyl chloride. forming reaction. The use of such a thiosulfate- In the examples, the reaction of the first di- reactive compound in the final (i.e., cooling) stage scharge liquid (48 parts) with the treatment com- of the formate/SO2 reaction, as taught in Japanese pounds (0.07-0.13 parts) occurred at 25-45°C for 1- 110,407, similarly enables the reaction filtrate or 50 24 hours after filtration at 73 °C. A portion of the the washing liquid to be utilized for making sodium treated first discharge liquid was mixed with nearly dithionite at yields and purities equal to results twice as much of the untreated second discharge from manufacture with distilled methanol. Again, liquid and used to prepare sodium dithionite after however, such protection for the next batch pro- adjusting for the amount of water in the discharge vides no help for the current batch. 55 liquid mixture. The resulting purities and yields for Accordingly, there is clearly a need for destroying thiosulfate ions as they are being formed within the reaction vessel in order to minimize destruction of the sodium dithionite product. More- 0 211 648 over, if the thiosulfate ions could be at least par- The organic compound can also be pumped tially destroyed in the current batch, the treatment into the reactor throughout the course of the so- needed for the mother liquor during the cooling dium dithionite producing process to obtain a simi- period, for the filtrate, or for the wash liquid accord- lar effect. Preferably, the organic compound is ing to prior art methods could also be decreased 5 pumped into the pressurized reactor throughout the before each recycle of filtrate and/or wash liquid to course of the entire reaction, beginning when the the next batch. Similarly, an in situ treatment to reactor contents have been heated to about 50 °C diminish the harmful effects of thiosulfate and other and ending wtih the start of the cooling period. The deleterious sulfur compounds would allow the use pumping rate is suitably 0.4-0.6 wt.%/minute and of raw materials containing these contaminants in 70 preferably about 0.5 wt.%/minute. the manufacture of sodium dithionite. These organic compounds that are capable of reacting with or complexing sodium thiosulfate include the epoxy compounds such as ethylene ox- SUMMARY OF THE INVENTION ide, propylene oxide, butyl and isobutyl oxide, epi- 75 chlorohydrin, and epibromohydrin. These organic It has surprisingly been discovered that the compounds also include halogenated hydrocarbons auto-catalytic action of sodium thiosulfate and ac- of the general formula R2X, or XR2X, where Ra is an companying sulfur compounds can be negated or alkyl group of carbon number 1 to 8, or an allyl, at least minimized by adding an organic compound methallyl, or ethallyl group, and X is a halogen. In to the reactor prior to starting the sodium dithionite 20 the case of ethylene oxide, propylene oxide, and producing process so that the sodium thiosulfate is the like, the result of the reaction is a Bunte salt: consumed as soon as it is produced.

(6) CH- - CH- + Na2S2O3 + H2O -*■ CH2 - CH2 + NaOH,

S-SO3Na

In the case of the alkyl halides, the reaction is: compound of choice, however, owing to its lower molecular weight and lower cost. The data and 35 (7) R,X + Na,SsO3 - Rs-S-SO,Na + NaX. calculated results are shown in the Table accom- When carrying out repetitive batches on a large panying Example 9. scale, it becomes critically important that every detail of the operational procedure be carried out exactly as scheduled. Such an operational proce- EXAMPLE I 40 dure is typically developed, after numerous tech- nical studies and operational trials, in unending A series of thirteen base line runs was made efforts to maximize product purity and yield. Even while adding no propylene oxide to the reactor. small fractional improvements are greatly valued. These runs were begun by adding to a 100-gallon Accordingly, any destruction of thiosulfate ions and reactor, as a first feed, 150 lbs of distilled recov- 45 other harmful sulfur compounds during the course ered methanol containing 3.67% methyl formate of the dithionite-producing reaction that could mini- and 0.96% sulfur dioxide. Next, as a second feed, mize product losses and increase yield would be a solution of 7 lbs of 96% sodium formate dis- an important improvement over known batch pro- solved in 5 lbs of water was added. The reactor duction methods. contents were heated to 50 °C with agitation, at 50 which time the third and fourth feeds were started simultaneously. The third feed consisted of 69 lbs DESCRIPTION OF PREFERRED EMBODIMENTS of 99% sodium hydroxide, 135 lbs of 96% sodium formate, and 109 lbs of water. Its feed rate was A series of pilot plant experiments was con- controlled so that it was fed in its entirety in 65 55 ducted to demonstrate this process. The organic minutes. The fourth feed consisted of 310 lbs of compound was chosen to be propylene oxide distilled recovered methanol of the same composi- owing to its lesser hazard and ease of handling. tion as the first feed and containing additional sul- Ethylene oxide would be the commercial epoxy fur dioxide of a quantity such that between the first 0 211 648 and fourth feeds a total of 201 lbs of sulfur dioxide EXAMPLE 3 would enter the reactor. The feed rate of the fourth feed was controlled so that 80% of its total amount A series of five runs was made by adding 6 lbs was fed to the reactor in 65 minutes. of propylene oxide to the first feed. All other quan- Owing to the exothermic nature of the reaction 5 tities and conditions were identical to Example 1 between the third and fourth feeds, the contents of except that the distilled recovered methanol used the reactor self-heated to 84° C over a fifteen- for feeds one and four contained 3.00% methyl minute time period. Temperature control was then formate. The five runs made in this manner averag- initiated to maintain 84° C throughout the entire ed a titer of 1.6 at the end of the first 65 minute remaining course of the reaction. Owing to the w period, 2.4 at the end of the second 65 minute evolution of carbon dioxide, the reactor pressure period, and 4.5 at the end of the third 65 minute increased to 40 psig in this same 15-minute period. period. The product averaged 240 lbs in weight at Pressure control was then initiated to maintain 40 an assay of 93.35%, or a yield of 1.287 mols of psig throughout the entire remaining course of the sodium dithionite. reaction. The vented carbon dioxide exited the re- 75 actor through condensers and a scrubber that was fed with essentially pure recovered methanol at a EXAMPLE 4 rate of 0.364 Ib per minute. When the third feed was terminated at 65 minutes, the rate of feed of A series of five runs was made by adding 8 lbs the fourth feed was reduced so that the remaining 20 of propylene oxide to the first feed. All other quan- 20% was fed over an additional 65 minutes. At the tities and conditions were identical to Example 1 conclusion of this feed, an additional 65-minute except that the distilled recovered methanol used period at 84° C and 40 psig was allowed for the for feeds one and four contained 2.71% methyl reaction to go to completion. The sodium thiosul- formate. The five runs made in this manner averag- fate concentration was monitored via sampling the 25 ed a titer of 1.5 at the end of the first 65 minute reactor contents at the end of each of the above 65 period, 2.3 at the end of the second 65 minute minute periods. The concentration is expressed as period, and 4.7 at the end of the third 65 minute the sodium thiosulfate titer of a standard iodine period. The product averaged 246 lbs in weight at solution. At the conclusion of this third 65-minute an assay of 91.17%, or a yield of 1.288 mols of period, the reactor contents were cooled to 73°C so sodium dithionite. and discharged to the filtering apparatus. After methanol washing, the filter cake was vacuum dried to produce the sodium dithionite product. The thir- EXAMPLE 5 teen runs made in this manner averaged a titer of 3.9 at the end of the first 65 minute period, 4.3 at 35 A series of four runs was made by pumping 6 the end of the second 65 minute period, and 7.0 at lbs of propylene oxide into the reactor at a rate of the end of the third 65 minute period. The product 0.031 Ib per minute over the 195 minute reaction averaged 237 lbs in weight at an assay of 91.57%, duration. All other quantities and conditions were or a yield of 1 .246 mols of sodium dithionite. identical to Example 1 except that the distilled 40 recovered methanol used for feeds one and four contained 2.58% methyl formate. The four runs EXAMPLE 2 made in this manner averaged a titer of 1 .5 at the end of the first 65 minute period, 1 .3 at the end of A series of five runs was made by adding 4 lbs the second 65 minute period, and 1 .2 at the end of of propylene oxide to the first feed. All other quan- 45 the third 65 minute period. The product averaged tities and conditions were identical to Example 1 247 lbs in weight at an assay of 90.03%, or a yield except that the distilled recovered methanol used of 1 .277 mols of sodium dithionite. for feeds one and four contained 3.56% methyl It will be noted that according to Equation (6), formate. The five runs made in this manner averag- sodium hydroxide is produced along with the Bunte ed a titer of 1.9 at the end of the first 65 minute so salt when propylene oxide reacts with sodium period, 2.5 at the end of the second 65 minute thiosulfate. In that sodium hydroxide is a raw ma- period, and 4.6 at the end of the third 65 minute terial in the production of sodium dithionite, it period. The product averaged 245 lbs in weight at should be possible to remove a quantity of sodium an assay of 91.64%, or a yield of 1.289 mols of hydroxide from the third feed. sodium dithionite. 55 0 211 648 10

EXAMPLE 6 in this manner averaged a titer of 2.0 at the end of the first 65 minute period, 1.3 at the end of the A series of six runs was made by pumping 6 second 65 minute period, and 1 .2 at the end of the lbs of propylene oxide into the reactor at a rate of third 65 minute period. The product averaged 243 0.031 Ib/minute over the 195-minute reaction dura- 5 lbs in weight at an assay of 92.83%, or a yield of tion. All other quantities and conditions were iden- 1 .295 mols of sodium dithionite. tical to Example 1 with two exceptions; the distilled recovered methanol used for feeds one and four contained 2.63% methyl formate, and the sodium EXAMPLE 9 hydroxide content of the third feed was 66 lbs. The w six runs made in this manner averaged a titer of A series of two runs was made by pumping 4 1.7 at the end of the first 65 minute period 1.9 at lbs of 1-2 dichloroethane to the reactor at a rate of the end of the second 65 minute period, and 1 .8 at 0.021 Ib/minute over the 195 minute reaction dura- the end of the third 65 minute period. The product tion. All other quantities and conditions were iden- averaged 242 lbs in weight at an assay of 92.63%, 75 tical to Example 1 except that the distilled recov- or a yield of 1 .287 mols of sodium dithionite. ered methanol used for feeds one and four contained 3.00% methyl formate. The three runs made in this manner averaged a titer of 3.4 at the end of EXAMPLE 7 the first 65 minute period, 5.3 at the end of the 20 second 65 minute period, and 7.8 at the end of the A series of two runs was made by pumping 1 0 third 65 minute period. The product averaged 237 lbs of propylene oxide into the reactor at a rate of lbs in weight at an assay of 92.19%, or a yield of 0.051 Ib/minute over the 1 95-minute reaction dura- 1 .255 mols of sodium dithionite. tion. All other quantities and conditions were iden- All of these examples demonstrate an en- tical to Example 1 with two exceptions; the distilled 25 hanced yield of sodium dithionite achieved by the recovered methanol used for feeds one and four addition of the named chemical. The results be- contained 3.00% methyl formate, and the sodium come even more coherent if correction is made to hydroxide content of the third feed was 65 lbs. The the yield for the variable methyl formate content of two runs made in this manner averaged a titer of the alcohol entering the reactor. According to 1.5 at the end of the first 65 minute period, 1.9 at 30 Equation (4), any deficiency in methyl formate will the end of the second 65 minute period, and 1 .2 at be made up at the expense of the formic acid the end of the third 65 minute period. The product needed to produce sodium dithionite via Equation - averaged 244 lbs in weight at an assay of 92.15%, (3). It was established in earlier work that the or a yield of 1 .291 mols of sodium dithionite. approach to an equilibrium concentration of methyl 35 formate in one pass through the reactor was only 70%. As was noted earlier, the net efficiency of EXAMPLE 8 formic • acid utilization in producing sodium dithionite is 80%. Therefore, each one mol defi- A series of three runs was made by pumping 8 ciency in methyl formate in the methanol entering lbs of ally! chloride into the reactor at a rate of 40 the reactor will result in a sodium dithionite yield 0.041 Ib/minute over the 195-minute reaction dura- deficiency of 0.56 mol. When this correction (to tion. All other quantities and conditions were iden- 3.00% methyl formate) was applied to the reported tical to Example 1 except that the distilled recov- yields of Examples 1-9, corrected yields were ob- ered methanol used for feeds one and four contained as shown in the Table. tained 3.00% methyl formate. The three runs made 46

55 11 0 211 648 12

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These corrected yields clearly indicate that the 50 improvement when the quantity of sodium hydrox- yield increase was proportional to the quantity of ide in the third feed is adjusted to compensate for propylene oxide added to the reactor up to 8 lbs. the sodium hydroxide generated in situ owing to At the 10 lbs level, a yield decrease was noted as the use of propylene oxide. compared to the identical procedure utilizing 6 lbs "Titer" is a measure of sodium thiosulfate con- of propylene oxide. They also show an improved 55 tent of the solution at the indicated time and is result when the propylene oxide is pumped in therefore an indication of the extent of decomposi- continuously, as opposed to adding it all at the tion of dithionite. It is obtained by mixing a 10 ml. beginning of the reaction, and they show a further 13 0 211 648 14 sample of reactor filtrate with a neutral formal- yield increase was noted or claimed, that none was dehyde solution (to tie up bisulfite), adjusting the observed. To demonstrate this point, the experi- pH to 4.0, and then titrating the sample with 0.1 N ments described in Example 1 0 were performed. standard iodine solution. In the base case Example 1, no organic com- 5 pound added, the titer affords a measure of the EXAMPLE 10 total thiosulfate content of the reaction filtrate but not including the thiosulfate existing as a solid As a comparative example, a series of four within the product. In Examples 2-9, the titer mea- runs was made by adding 6 lbs of propylene oxide sures only the thiosulfate in the filtrate that has not ro to the reactor at the end of the 195-minute reaction reacted or complexed with the organic compound period and simultaneously with cooling the reactor added. No analytical methods are known to deter- contents to 73 °C, a process requiring approximate- mine the quantity of thiosulfate present in the solid ly 15 minutes. All other quantities and conditions product within the reactor or present as a reaction were identical to Example 1 except that the distilled product resulting from the organic compound addi- 75 recovered methanol used for feeds one and four tion. The titer may or may not indicate the quantity contained 3.00% methyl formate. The four runs of the various unidentified sulfur compounds made in this manner averaged a titer of 2.9 at the present in the filtrate depending on the structure of end of the first 65 minute period, 6.8 at the end of those compounds. the second 65 minute period, and 12.6 at the end Because of the shortcomings noted above, a 20 of the third 65 minute period. The product averag- rigorous correlation between the dithionite yield ed 241 lbs in weight at an assay of 88.57% or a increase achieved and the measured titer would yield of 1 .226 mols of sodium dithionite. not be expected. However, it can be said that an This yield, 1 .226 mols, is a slight improvement increased dithionite yield was accompanied by a (0.74%) as compared to the base line (0 Ib pro- decrease in the titer measurement, with the mag- 25 pylene oxide) runs of Example 1. The small yield nitude of the decrease being a function of the way increase is probably owing to a decreased sodium in which the organic compound was added to the dithionite decomposition during both the .slurry reactor. cooling period and the filtration and cake wash In the previously discussed Japanese patents periods. A filtrate sample taken after the propylene describing the use of the various organic chemicals 30 oxide addition resulted in a titer of 2.7. to eliminate the sodium thiosulfate in the filtrate, no Example 10 uses the process taught in Japan examples are given for the production of sodium 110,407/83. In both this procedure and in the pro- dithionite in the absence of the various organic cedure of Examples 2-9, analysis of the filtrate chemicals. It is not possible, therefore, to dem- shows no residual unreacted propylene oxide. That onstrate a yield change owing to the use of these 35 which does not react with the sodium thiosulfate organics. It is assumed, however, that since no reacts with either water or methanol as shown in the following equations:

(8) + - CH,CH-CH,OH CH,-CH-CH,3 2 H,02 2 \l 3! O OH

(9) CH,-CH-CH- + CH,0H - CH,-CH-CHo-0-CH, 3 2 3 3 2 3 \l I O OH

The of both of these reactions were EXAMPLE 1 1 products so found in the filtrate. In the process taught in Japan 28397/75, the organic chemical was added to the cooled filtrate after the product sodium dithionite was removed. When this procedure was followed, immediate ana- 55 lysis confirmed the presence of the added propylene oxide, 1.1%. After 5 hours, the concentration had decreased to 0.71%, and after 16 hours to 15 0 211 648 16

0.62%. Still following the instructions of Japan Claims 28397/75, appropriate amounts of both sodium hydroxide and sodium formate were added to the 1 . In a process for preparing anhydrous sodium filtrate. A sample then showed 0.45% propylene dithionite by reaction of formate ions, sodium ions, oxide. When heated to 70 °C, again as in Japan 5 hydroxyl ions, and sulfur dioxide in an aqueous 28397/75, a sample showed the propylene oxide to methanolic solution as a reaction mixture, wherein be totally consumed, with the same reaction pro- sodium thiosulfate is formed as a byproduct of said ducts noted previously in Equations (8) and (9). reaction, the improvement comprising the addition The mother liquor purification/cooling method, to said reaction mixture of a thiosulfate-reactive the filtrate purification/recycle method, and the w compound selected from the group comprising ep- washing liquid purification/recycle method of the oxy compounds and halogenated hydrocarbons for prior art may be classified as the cooling period reacting with said sodium thiosulfate and other treatment and filtrate/wash liquid treatment meth- sulfur compounds before said sodium thiosulfate ods of the prior art for destroying thiosulfate ions and other sulfur compounds promote decomposi- for recycle purposes. These methods and the reac- 75 tion of said sodium dithionite. tion mixture treatment method of this invention 2. The process of claim 1, wherein said addi- totally consume the added organic chemical com- tion is made continuously during said reaction to pound prior to commencing the subsequent syn- form said sodium dithionite. thesis of the next batch of sodium dithionite. These 3. The process of claim 1, wherein said com- methods also appear to destroy at least a portion zo pound is added to methanol which forms a puddle of the thiosulfate ions. It consequently follows that solution within a batch reactor for receiving aque- the filtrate and/or the wash liquid produced by ous sodium formate, aqueous sodium hydroxide, following the method of this invention can be em- and methanolic sulfur dioxide. ployed in the cooling period or filtrate/wash liquid 4. The process of claim 1, wherein said com- treatment methods of the prior art, by recycling 25 pound is added continuously to said reaction mix- these liquids as the methanol source for the next ture. batch reaction or as the feed methanol for a con- 5. The process of claim 1, wherein said epoxy tinuous reaction, with reduced usage of an epoxy compounds are represented by the formula: compound or a halogenated hydrocarbon for treat- ing the filtrate and/or the wash liquid. 30 What is regarded as the invention and is de- sired to be protected is defined in the accompanying claims.

R^CH CH. \/

40 wherein R, is hydrogen, an alkyl group containing feed consisting of an alkali compound, and (iii) a from 1 to 8 carbon atoms, a halogenated alkyl third feed consisting of sulfurous acid anhydride in group containing from 1 to 2 carbon atoms, a a mixed reaction solvent of water and an organic phenyl group, or a substituted phenyl group. solvent within a reaction vessel to form dithionite 6. The process of claim 1 , wherein said haloge- 45 crystals in a mother liquor, filtering said dithionite nated hydrocarbons are represented by the for- crystals from the mother liquor, washing the mula: dithionite crystals with an organic solvent as a washing liquid under conditions which do not cause FVX, or XR2X a slurry to form, and drying the dithionite crystals; 50 wherein R2 is a primary or secondary alkyl group the improvement comprising adding to said reac- containing from 1 to 8 carbon atoms, an allyl tion vessel, while, prior to, combined with, or con- group, or a 2-methylallyl or 2-ethylallyl group, and currently with at least one said feed, at least one X is a halogen atom. compound selected from the group consisting of 7. In the process for producing anhydrous .55 the compounds represented by formula I and II; dithionites which comprises reacting (i) a first feed wherein Formula I is consisting of formic acid or a formate, (ii) a second

10 17 0 211 648 18

wherein R, is hydrogen, an alkyl group containing 9. The process of claim 8, wherein said formic from 1 to 8 carbon atoms, a halogenated alkyl acid or formate is sodium formate and wherein said containing from 1 to 2 carbon atoms, phenyl anhydrous dithionite is sodium dithionite. group 70 group or a substituted phenyl group; and Formula II 10. The process of claim 7, wherein said or- is ganic solvent is selected from the group consisting of methanol, ethanol, n-propanol, isopropanol, and R,-X or XR2X, acetone. 11. The process of claim 10, wherein said 75 wherein R, is a primary or secondary alkyl group organic solvent is methanol. containing from 1 to 8 carbon atoms, an ally! 12. The process of claim 11, wherein said group, or a 2-methylallyl or 2-ethylallyl group, and formic acid or a formate is sodium formate and X is halogen, to convert said thiosulfate and other wherein said anhydrous dithionite is sodium sulfur compounds into substances which do not dithionite. 20 exert an adverse influence on the production of 13. The process of claim 7, wherein said formic dithionites. acid or formate is selected from the group consist- 8. The process of claim 7, wherein said at least ing of formic acid, sodium formate, potassium for- one compound is selected from the group consist- mate, zinc formate, and methyl formate. ing of ethylene oxide, propylene oxide, butylene 14. The process of claim 13 wherein said for- 25 oxide, epichlorohydrin, epibromohydrin, styrene ox- mic acid or formate is sodium formate and wherein ide, methyl iodide, allyl chloride, and cyclohexene said anhydrous dithionite is sodium dithionite. oxide.