Abstract: The present invention relates to a method for preparing dithionite solution with a reaction wherein sodium bisulfite is reduced with sodium borohydride solution to obtain dithionite, wherein the rise of the pH of the solution is prevented by adjusting the pH with carbon dioxide.

Abstract: The invention relates to a process for the preparation of sodium dithionite, comprising the steps (a) provision of a synthesis batch comprising sodium formate, sulfur dioxide and an alkaline sodium compound in aqueous methanolic solution with formation of a sodium dithionite mother liquor, (b) isolation of sodium dithionite from the sodium dithionite mother liquor, a residual mother liquor being obtained, (c) separation of methanol from the residual mother liquor, (d) separation of the residual mother liquor into a thiosulfate-rich first part-stream and a thiosulfate-poor, formate-containing second part-stream by means of nanofiltration, (e) concentration of sodium formate in the second part-stream and (f) recycling of the concentrated second part-stream to process step (a).

Abstract: The invention relates to a process for the preparation of sodium dithionite, comprising the steps (a) provision of a synthesis batch comprising sodium formate, sulfur dioxide and an alkaline sodium compound in aqueous methanolic solution with formation of a sodium dithionite mother liquor, (b) isolation of sodium dithionite from the sodium dithionite mother liquor, a residual mother liquor being obtained, (c) separation of methanol from the residual mother liquor, (d) separation of the residual mother liquor into a thiosulfate-rich first part-stream and a thiosulfate-poor, formate-containing second part-stream by means of nanofiltration, (e) concentration of sodium formate in the second part-stream and (f) recycling of the concentrated second part-stream to process step (a).

Abstract: A method for brightening virgin mechanical pulp. The method comprises combining: (i) an aqueous solution comprising sodium borohydride and sodium hydroxide; and (ii) an aqueous solution comprising sodium bisulfite, in a chemical mixer and adding output of the chemical mixer to an aqueous slurry of virgin mechanical pulp. The ratio of (moles bisulfite?moles hydroxide)/moles borohydride is from 0 to 7.8.

Abstract: The present invention provides an inexpensive process for the preparation of lithium salts of formula LiX having a desired or required level of purity using lithium chloride and lithium sulfate. In the process of the invention, a lithium salt selected from lithium chloride, lithium sulfate, and combinations thereof is reacted with NaX or KX in a aqueous, semiaqueous, or organic solution and the precipitated salts are removed to obtain the LiX solution of desired purity. Preferably, a semiaqueous solution containing water and an organic solvent is used at some point in the reaction. The process of the invention eliminates the use of highly acidic materials and thus reduces the cost of raw materials and the need for specialized equipment.

Abstract: A process for reacting metallic iron with sulfur dioxide (SO.sub.2) gas in the presence of water and bleachable matter, especially iron-contaminated kaolin clay, whereby the kaolin or the like is bleached in situ and the viscosity of the kaolin is less than it would be if bleached in a conventional manner.

Abstract: An improved high yield process and apparatus for producing sodium hydrosulfite by simultaneously contacting a first reaction mixture of sodium borohydride, sodium hydroxide, and water with a second reaction mixture of an acidic sulfur-containing compound or precursors thereof used in producing sodium hydrosulfite from sodium borohydride.

Abstract: A process for stabilizing sodium dithionite is disclosed, whereby a selected additive is used.

Abstract: Aqueous co-product, produced by distillation of reaction filtrate from a batch reaction for manufacturing sodium dithionite by reacting sodium formate, sodium hydroxide, and sulfur dioxide in aqueous methanol solution, is rapidly evaporated to remove about 80% of its water content, so that only the determined quantity of water remains with its determined contents of alkali metal compounds, and is utilized as an admixed component of a succeeding batch.

Abstract: Heavy metal ions react with ferrous dithionite in acidic aqueous solution. They are reduced to metallic particles that are suitable for recycling and reuse when recovered from the acidic water. When chelating agents are present, they are deactivated by bonding to the ferrous ions. Ferrous dithionite, (FeS.sub.2 O.sub.4) is either generated in-situ or ferrous ions and dithionite ions can be provided by other methods.

Abstract: A method of stabilizing sodium dithionite is disclosed which comprises exposing a quantity of sodium dithionite to a quantity of amino material under pressure, wherein the partial pressure of amino material is at least 0.5 atmospheres.

Abstract: A process for treating an alkali metal hydrosulfite solution which comprises contacting the alkali metal hydrosulfite solution with aluminum in a reaction mixture, and admixing carbon dioxide gas with the reaction mixture to remove dissolved aluminum as an aluminum-containing precipitate, the alkali metal hydrosulfite solution having a residual alkalinity of from about 0.1 to about 20 grams per liter of hydroxide ion.

Abstract: An improved high yield process and apparatus for producing sodium hydrosulfite by reacting sodium borohydride, sulfur dioxide, sodium hydroxide, and sodium bisulfite is provided. The improved result of the invention is obtained by a feed system that requires the introduction of a first mixture comprising sodium borohydride, sodium hydroxide, and water into a flow stream prior to the introduction of a second mixture comprising water and sulfur dioxide. The improved result can be further enhanced by techniques of intimately mixing the first mixture and the flow stream as well as intimate mixing the second mixture and the flow stream.

Abstract: Vent gas from the condenser-scrubber system of a reactor, in which dithionites are made by reacting a formate, sulfur dioxide, and an alkali in aqueous methanol, is reduced in its ethylene oxide content to less than 10 ppm maintaining the ratio of sulfur dioxide to ethylene oxide entering the scrubber to greater than 1.0, preferably greater than 2.5, and most preferably greater than 3.0 and at a temperature of -20.degree. C. to 0.degree. C.

Abstract: A process for treating an alkali metal hydrosulfite solution which comprises contacting the alkali metal hydrosulfite solution, having a residual alkalinity of from about 1 to about 20 grams per liter of hydroxide ion, with aluminum. The process of the invention can be operated at low temperatures i.e., those which are normally used for storage of the sodium hydrosulfite solution to minimize thermal decomposition.

Abstract: An aqueous solution comprising alkali metal hydrosulfite and hydroxide ions in an amount to provide a residual alkalinity of at least 0.25 moles per liter results in the decomposition of thiosulfate ions present and inhibits their formation during storage. These solutions can be used, for example, in the bleaching of mechanical pulp.

Abstract: There is disclosed a method for the production of dust-free sodium dithionite from the reaction of a alkaline formate sulfur dioxide and an alkaline metal agent in the presence of a thiosulfate reactive compound by introducing a water-soluble polymer having a molecular weight less than 60,000 and delaying the start of the alkaline metal agent until the sodium formate and the sulfur dioxide have begun to be introduced into the reactor.

Abstract: Process for bleaching of materials, at which an aqueous solution of borohydride containing borohydride corresponding to from 15 to 35 percent by weight of sodium borohydride and hydroxylic ions corresponding to not more than 10 percent by weight of NaOH is brought to react with a bisulfite solution, after which the dithionite solution thus obtained is added to the material to be treated. This process gives a simple and economic preparation of dithionite bleaching solution in situ, in connection with the bleaching.

Abstract: Solutions of low viscosity solvents and high viscosity, pasty products, for example water and sodium dithionite formulations, are prepared in a continuous manner in a matter of seconds in static and dynamic mixers connected in series while at the same time the ingress of air is avoided.

Abstract: An improved high yield process and apparatus for producing sodium hydrosulfite by reacting sodium borohydride, sulfur dioxide, sodium hydroxide and sodium bisulfite is disclosed. A continuously recirculating split process stream may be used along with control of pH, temperatures, and concentration parameters to obtain sodium hydrosulfite yields in excess of 85%.

Abstract: A process for producing an anhydrous alkali metal hydrosulfite comprises contacting hydrate crystals of an alkali metal hydrosulfite with an alkaline aqueous solution of a dehydrating agent having a pH of at least about 7. The slurry formed is maintained at or above the transition temperature to covert the hydrate crystals to anhydrous crystals of the alkali metal hydrosulfite. The process permits the conversion of hydrate crystals to produce anhydrous crystals of alkali metal hydrosulfite without substantial dissolving or decomposition of the alkali metal hydrosulfite.

Abstract: An improved high yield process and apparatus for producing sodium hydrosulfite by reacting sodium borohydride, sulfur dioxide, sodium hydroxide and sodium bisulfite is disclosed. A continuously recirculating split process stream may be used along with control of pH, temperatures, and concentration parameters to obtain sodium hydrosulfite yields in excess of 85%.

Abstract: Aqueous sodium dithionite slurries or suspensions, which are nonsettling during shipment thereof and are thereafter pumpable after storage at 32.degree.-40.degree. F. for at least fourteen days, comprise, on a weight basis, about 34% of sodium dithionite, about 0.17% of a xanthan gum, 5.5-6.5% of 50% sodium hydroxide, about 0.26% of a chelate, and about 1.96% of sodium tripolyphosphate which is added after adding the sodium dithionite. Preferably, the sodium tripolyphosphate is added last in making the slurry which is used as a woodpulp bleaching composition.

Abstract: A process for producing an anhydrous dithionite which comprises reacting formic acid or a formate, an alkaline compound and sulfur dioxide in the presence of water and an organic solvent, filtering the resulting dithionite crystal from the mother liquor, washing the dithionite crystal with an organic solvent and drying the dithionite crystal, characterized in that in the washing step, the washings first discharged are distilled by a convention method for recovery of the organic solvent, the washings discharged subsequently being used as the reaction solvent without distillation.

Abstract: There is provided a method for producing compositions which can be used for preparing sodium dithionite, in which sulphur dioxide is brought into contact with a recirculating aqueous solution of sodium hydroxide and previously absorbed sulphur dioxide to a ratio of sulphur dioxide and the sum of sulphur dioxide and sodium oxide of 0.61-0.66, whereafter the resultant mixture is pressurized and liquid sulphur dioxide introduced therein to a ratio between sulphur dioxide and the sum of sulphur dioxide and sodium oxide of 0.75-0.81, and the water content is adjusted to a concentration of sulphur dioxide+sodium oxide of 10-13 percent by weight. The invention also relates to the use of the prepared composition for the manufacture of dithionite.

Abstract: Stabilized water-containing sodium dithionite formulations which have been rendered alkaline have the consistency of a pumpable paste. They additionally contain readily soluble sodium salts and/or potassium salts which are inert to sodium dithionite and whose water-solubility at 20.degree. C. exceeds 500 g/l. These salts are present in the aqueous phase in an amount of not less than 200 g/l. The pastes are useful reducing agents.

Abstract: A method is taught for increasing the yield of anhydrous sodium dithionite by adding an organic compound that is thiosulfate reactive to a batch reactor containing a puddle solution of methanol and fed with formic acid or an alkali formate as a first feed, an aqueous alkali compound as a second feed, an aqueous alkali formate solution as a third feed, and a methanolic SO.sub.2 solution as a fourth feed. This organic compound may be added prior to, combined with, or concurrently with one of the four feeds to the reactor. Preferably, it is added concurrently with the third feed and throughout the entire course of the reaction, ending with the beginning of the cooling period. A suitable addition rate is 0.4-0.6 wt. %/minute, preferably 0.5 wt. %/minute. All of the organic compound is consumed, and at least a portion of the thiosulfate ion is destroyed.

Abstract: Sodium dithionite formulations containing inert organic liquids have the consistency of a pumpable paste.

Abstract: High purity solutions of alkali metal hydrosulfites having low concentrations of alkali metal thiosulfates are produced in a process which comprises feeding an alcohol-free aqueous solution of an alkali metal hydrosulfite containing an alkali metal thiosulfate as an impurity to a crystallizing zone. Produced in the crystallizing zone is a slurry of alkali metal hydrosulfite crystals which is conveyed from the crystallizing zone to a separating zone. The separating zone, employing a non-gravitational separation means, recovers a slurry of alkali metal hydrosulfite crystals from a first mother liquor. A portion of the slurry of alkali metal hydrosulfite crystals is conveyed to a concentrating zone to recover a cake of alkali metal hydrosulfite crystals from a second mother liquor.

Abstract: Guar and xanthan gums are used as additives to sodium dithionite aqueous solutions for enhancing the stability of such solutions when in contact with air and used for vat dyeing of textiles and bleaching. The gums are added at levels of 0.1-0.2% by wt. and preferably at 0.15% by wt. of the solution. The stability of these polymeric-containing bleaching solutions is enhanced by more than 100-200%.

Abstract: Aqueous sodium dithionite slurries, which are non-settling during shipment thereof and are thereafter pumpable, and a method for their manufacture are provided. The slurries contain at least 25% by weight of crystalline pure sodium dithionite and at least about 0.13% by weight of a xanthan gum. As textile bleaching compositions, the slurries comprise, on a weight basis, at least about 36% of commercial sodium dithionite, at least about 3% of sodium hydroxide, at least about 0.25% of a chelate, and at least about 0.25% of a xanthan gum. As woodpulp bleaching compositions, the slurries comprise, on a weight basis, about 28% of commercial sodium dithionite, at least about 2% of sodium carbonate, at least about 2% of sodium tripolyphosphate, and at least about 0.13% of a xanthan gum.

Abstract: An improvement in the process for producing anhydrous dithionites by reacting formic acid or a formate with an alkali compound and sulfurous acid anhydride in a mixture of water and organic solvent; filtering dithionite crystals from the mother liquor; and washing the dithionite crystals with an organic solvent as a washing liquid and then drying the dithionite crystals. The improvement comprises dividing the washing liquid into two portions which are discharged as the washing liquid first discharged and the washing liquid discharged subsequently from the washing operation and treating the washing liquid first discharged to convert substances contained therein which inhibit the production of dithionite into harmless substances and recycling both the treated washing liquid first discharged and the washing liquid discharged subsequently which does not require treatment as a reaction solvent.

Abstract: A bleaching composition comprises sodium hydrosulfite, hexamethylenetetramine and a water soluble sulfite such as sodium sulfite or ammonium sulfite, or further a polyphosphate such as a pyrophosphate or a tripolyphosphate and is used in bleaching pulp with a good bleaching effect with no substantial hydrogen sulfide generation.

Abstract: Substantially stable slurries containing 30-35% by weight of sodium dithionite are manufactured by evaporating sodium dithionite solutions while maintaining the heating medium at 220.degree.-250.degree. F. and the solution and slurry at 110.degree.-155.degree. F. under a vacuum of at least 25 inches Hg and by promptly cooling the resultant slurry while agitating it. The vacuum is preferably 26.5-27.5 in. Hg. At 4-5% by weight of the sodium dithionite and preferably at 4.3% by weight, NaOH is preferably added to the solution or alternatively to the slurry, immediately after evaporation. A chelator is preferably added to the solution to prevent metal contamination thereof. Zinc-derived sodiation liquor is the preferred sodium dithionite solution.

Abstract: In a process for the manufacture of sodium dithionite by reacting sulfur dioxide with sodium formate and aqueous sodium hydroxide solution in the presence of methanol, an aqueous methanolic solution of sodium formate is first produced by reacting carbon monoxide with sodium hydroxide solution in an aqueous medium, containing from 1 to 50% by weight of methanol, based on the amount of water, at from 80 to 120.degree. C. under a pressure of from 10 to 40 bars. The resulting aqueous methanolic solution can be reacted directly, in the conventional manner, with sulfur dioxide and aqueous sodium hydroxide solution to give sodium dithionite.

Abstract: A batch process, in which a sodium bisulfite compound is the alkaline agent, is described for producing anhydrous sodium dithionite at high productivity by reduction of sulfur dioxide with the formate radical in concentrated aqueous methanolic solution. Minimum amounts of water, in which sodium formate is dissolved, and of methanol, in which sulfur dioxide is dissolved, are used. The process provides the optimum productivity of U.S. Pat. No. 3,887,695 while obviating the hazards and freeze-up difficulties that are inherent in forming and transferring a sodium hydroxide solution at 160.degree. C. and also minimizes the amount of methyl formate formed at equilibrium after a large number of methanol recyclings.

Abstract: An oxygen absorbent composition consisting essentially of (a) an oxygen absorbent comprising a dithonite as a main component and (b) a fiber material in an amount of from about 1 to about 50 parts by weight per 100 parts by weight of the oxygen absorbent and a process for producing the same are disclosed.

Abstract: Dithionites are produced by reacting hydroquinones with bisulfites, pyrosulfites, alkyl sulfites, or aryl sulfites, substances capable of forming these salts upon reacting with sulfur dioxide or sulfurous acid, and sulfur dioxide or sulfurous acid.

Abstract: Aluminum metal is activated with hydrochloric acid and then reacted with an aqueous solution of sulfur dioxide to produce an aluminum hydrosulfite (dithionite) liquor useful for bleaching materials such as clay. The aluminum hydrosulfite can be converted to a sodium hydrosulfite liquor by precipitating aluminum with a sodium base.

Abstract: A convenient batch process for producing anhydrous sodium dithionite at high productivity by reduction of sulfur dioxide with formate ion in aqueous methanolic solution is described in which sodium carbonate, in the form of a dry powder, is the source of alkali. Minimum amounts of water, in which sodium formate is dissolved, and of methanol, in which sulfur dioxide is dissolved, are used. In one aspect, SO.sub.2 -methanol solution, aqueous sodium formate solution, and powdered sodium carbonate are added to a methanol puddle solution, obtained from a preceding run which contains methyl formate in an equilibrium amount which is usually 4-8%, according to specific schedules which are proportioned to the rate of solution of sodium carbonate in the aqueous methanolic solvent and to the rates of reaction of sulfur dioxide with sodium carbonate and with sodium formate to form sodium metabisulfite.

Abstract: A process for preparing stable anhydrous sodium dithionite which comprises reacting formic acid or sodium formate, sodium hydroxide, and sulfurous acid anhydride in hydrous methanol, wherein an aqueous solution of sodium carbonate or sodium hydroxide is added to the slurry after the reaction, and stabilized anhydrous sodium dithionite is separated from the slurry.

Abstract: Anhydrous metal dithionite compositions are stabilized by 0.1 to 5% by weight of the composition of one or more of vanillin, ethyl vanillin and benzoin.

Abstract: An effective oxygen-consuming composition for packages, containers, or other closed spaces, especially containing an article susceptible to oxidative deterioration, comprises a dithionite for reacting with oxygen, sufficient alkaline material to at least partially neutralize sulfur dioxide released as a by-product of the oxygen consuming reaction, and porous filler particles in sufficient amount to promote contact with the ambient atmosphere, all in homogeneous mixture.

Abstract: Aqueous solutions containing mixtures of sodium dithionite and sodium sulfite having concentrations of greater than 13 percent by weight of Na.sub.2 S.sub.2 O.sub.4 are stabilized by adding potassium hydroxide in an amount which is sufficient to provide a residual of from about 1 to about 12 grams per liter of solution. These solutions can be stored at temperatures of from about 0.degree. to about 15.degree. C. without crystallization taking place.

Abstract: A process for continuously producing anhydrous sodium dithionite in the form of large granules which comprises reacting formic acid, sodium formate, sodium hydroxide and sulfurous acid anhydride in hydrous methanol using a multi-stage reaction apparatus, wherein all the required amounts of the formic acid or sodium formate, sodium hydroxide, methanol and water, and at least 60%, based on the required amount, of sulfurous acid anhydride are introduced into a first reactor, and the residence time in the first reactor is adjusted so that the conversion of the sulfurous acid anhydride to anhydrous sodium dithionite is within the range of 25 to 50%; the remainder of the sulfurous acid anhydride is introduced into a second reactor; and the reaction temperature in any given reactor is maintained at a point not lower than the reaction temperature in the immediately preceding reactor.

Abstract: An improved method for producing iron hydrosulfite liquor by reduction of sulfur dioxide with metallic iron is disclosed. Also disclosed are improvements in the conversion of the iron hydrosulfite liquor to produce sodium hydrosulfite bleach liquors.

Abstract: In the production of anhydrous sodium dithionite by reacting sodium formate, an alkaline sodium compound and sulfurous acid anhydride in hydrous methanol, a process for treating the mother liquor, which comprises adding an alkali to the mother liquor left after the separation of the resulting anhydrous sodium dithionite to adjust its pH to at least 8, separating the solids precipitated, and oxidizing the filtrate with an oxidizing agent.

Abstract: In the production of anhydrous sodium dithionite by reacting sodium formate, an alkaline sodium compound and sulfurous acid anhydride in hydrous methanol, a process for treating the mother liquor, which comprises cooling the mother liquor left after the separation of the resulting anhydrous sodium dithionite to a temperature in the range of +5.degree. to -30.degree. C, and separating the precipitated sodium thiosulfate by filtration.

Abstract: For the preparation of anhydrous sodium dithionite by the reaction of sulfur dioxide with sodium formate and caustic soda in the presence of organic solvents, sulfur dioxide is passed, together with the formate, into a liquid containing all of the caustic soda required for the reaction. This initial liquid may contain, in addition to the caustic soda, a portion of the sulfur dioxide or formate required for the reaction.

Abstract: Sodium dithionite bleaching solutions for groundwood pulps which require no additional chemicals for pH adjustment prior to direct application to the pulps, based on zinc-derived or formate-derived sodium dithionite and containing small percentages of at least four additives selected from the following: a chelating agent, zinc dithionite, zinc sulfate, sodium carbonate, sodium hydroxide, sodium tripolyphosphate, sodium phosphate, and sodium metaborate. Tested chelating agents are nitrilotriacetic acid (NTA) trisodium salt and ethylenediaminetetraacetic acid (EDTA) tetrasodium salt. The solutions are cool-stable (50.degree.F. or 10.degree.C) for at least 5 days with less than 5% decomposition of the sodium dithionite, and several exhibit similar stability at storage temperatures of 70.degree.-75.degree.F. (21.degree.-24.degree.C.) A method of preparation of the solutions is also provided.