JPS6318669B2 - - Google Patents

Description

[Detailed description of the invention]

BACKGROUND OF THE INVENTION The present invention is directed to the treatment of alkali metal sulfate values, particularly sodium sulfate or potassium sulfate, contained in used rayon spinning baths using two-chamber and three-chamber electrodialysis water splitting methods, i.e., the same water dissociation method. The present invention relates to a method for converting alkali metal hydroxides and alkali metal sulfates/sulfuric acid. Electrodialytic water splitting of aqueous neutral salts in a two-chamber cell to produce the corresponding acids and bases is C, A...
Vol. 5311070b (1959) (Oda et al.). Electrodialysis water splitting methods for converting sulfate-containing waste streams using two-compartment bipolar membrane cells are disclosed in U.S. Pat. Nos. 4,082,835 and 4,107,015 (Chlanda et al.). The production of rayon is a well-developed technology; for example, in 1969, Intersciences Publishers
Encyclopedia of Polymer published by
Volume 79 No. 810-847 in Science and Technology
It is described in "Rayon" by RLMitch et al., page. Alkali metal sulfate values from used rayon spinning baths, especially Na ₂ SO ₄ or K ₂ SO ₄ /
Regeneration of H ₂ SO ₄ is an energy-intensive process and requires a sulfuric acid purification step and supplementary sulfuric acid. Due to rising energy costs,
It would be advantageous to improve the efficiency of methods for regenerating alkali metal sulfate values from rayon spinning baths. It is therefore an object of the present invention to provide an electrodialysis water split process for converting aqueous alkali metal sulfate values obtained from rayon spinning baths into alkali metal hydroxide and alkali metal sulfate/sulfuric acid. . These and other objects and advantages of the invention will become clearer below. SUMMARY OF THE INVENTION In accordance with the present invention, a two- or three-compartment electrodialysis water splitter is provided.
(a) a liquid consisting of water; (b) supplying a liquid containing at least a portion of the alkali metal sulfate values derived from the spent rayon spinning bath to the base chamber of a two-chamber or three-chamber electrodialysis water splitter; supplying the acid chamber of the dialysis water splitter and the salt chamber of the three-chamber electrodialysis water splitter; (c) supplying the liquid consisting of the other portion of the spent rayon spinning bath solution containing the alkali metal sulfate values to the three-chamber electrodialysis water splitter; (d) passing a direct current through the two-chamber water splitter while maintaining an average temperature of at least 40°C; and (e) supplying the alkali metal sulfate and sulfuric acid to the acid chamber of the splitter; A method is provided comprising recovering a liquid containing from an acid compartment, a liquid containing an alkali metal hydroxide from a base compartment, and a liquid containing a reduced amount of an alkali metal sulfate from a salt compartment. The present invention also provides a two-chamber electrodialysis water splitter comprising alternating acid chambers and base chambers formed by alternating cation membranes and bipolar membranes between two electrodes. A method for converting alkali metal sulfate values derived from used rayon spinning bath liquor into alkali metal hydroxide and alkali metal sulfate/sulfuric acid in: (b) supplying a liquid containing alkali metal sulfate values derived from the spent rayon spinning bath to the base chamber formed by the anion face of the bipolar membrane; (c) increasing the temperature of the water splitter to at least about 40°C;
A direct current is passed through the water splitter to introduce hydrogen ions into the liquid containing alkali metal sulfates in the acid chamber, hydroxide ions are introduced into the liquid containing water in the salt chamber, and the alkali metal cations are (d) recovering a liquid containing an alkali metal hydroxide from the base chamber; (e) recovering a liquid containing an alkali metal sulfate and sulfuric acid from the acid chamber; and (f) A method is provided comprising transferring at least a portion of the alkali metal sulfate and sulfuric acid containing liquid recovered from the acid chamber to a rayon spinning bath. Furthermore, the present invention provides a cation film between two electrodes,
Alkali metal sulfates derived from a spent rayon spinning bath in a three-chamber electrodialysis water splitter consisting of alternating base, acid and salt chambers formed by alternating bipolar and anionic membranes. Valuables are converted into alkali metal hydroxides,
In a method of converting into a stream of alkali metal sulfate and/or sulfuric acid: (a) supplying a liquid consisting of water to a base chamber formed by the face of the cationic membrane and the anionic face of the bipolar membrane; (b ) supplying a liquid comprising at least a portion of a used rayon spinning bath solution containing an alkali metal sulfate value to the acid chamber formed by the face of the anionic membrane and the cationic face of the bipolar membrane; (c) supplying a liquid containing an alkali metal sulfate value derived from another portion of the spent rayon spinning bath solution to the salt chamber formed by the respective faces of the anionic and cationic membranes; (d) the water; Direct current is passed through the splitter to add hydrogen ions to the liquid containing alkali metal sulfate valuables in the acid chamber, hydroxide ions to the liquid consisting of water in the base chamber, and alkali metal cations from the salt chamber. (e) recovering the liquid containing the alkali metal hydroxide from the base chamber; (f) transferring the liquid containing the alkali metal sulfate and sulfuric acid to the acid chamber; (g) transferring at least a portion of the liquid containing the alkali metal sulfate and sulfuric acid recovered from the acid chamber to a rayon spinning bath; and (h) recovering the alkali metal sulfate value (supplied A method is provided comprising the step of withdrawing a liquid from a salt chamber containing a reduced amount of liquid (compared to a liquid that has been removed). DETAILED DESCRIPTION OF THE INVENTION The present invention converts alkali metal sulfate values obtained from spent rayon spinning baths into aqueous alkali metal hydroxide and alkali metal sulfate/sulfuric acid by operating in a two- or three-chamber cell. Provides an electrodialysis water split method. The spent rayon spinning bath liquor from rayon production, e.g. the viscose process, usually contains at least 5% by weight up to saturation amounts of alkali metal sulfates, primarily sodium or potassium sulfate, and spin additions to increase the spinning speed. Contains organic impurities and divalent metal cation impurities used as agents or modifiers. The present invention purifies the used rayon bath fluid by methods such as neutralization and filtration to remove organic impurities and Although the aim is to obtain an alkali metal sulfate substantially free of valence metal cation impurities, the used rayon spinning bath solution containing organic impurities and divalent metal impurities can be processed in a three-chamber electric bath without purification or pretreatment. It is a special feature of the invention that it can be fed to a dialysis water splitter. Another feature of the invention is to maintain the average temperature of the two-compartment electrodialysis water splitter at least 40°C, preferably at least 45°C, and more preferably at least 45°C in each compartment. This means that the two-chamber electrodialysis water splitter will be able to operate with improved current efficiency. It was found that there is no upper temperature limit other than the decomposition temperature of the membrane or the boiling point of the solution. Surprisingly, the improvement in current efficiency of two-chamber and three-chamber electrodialysis water splitters maintained at at least 40° C. is significant for aqueous alkali metal sulfate streams. Similar operating conditions, e.g. current density,
When water-splitting aqueous alkali metal chlorides by a two-chamber electrodialysis water splitter under a specific membrane, the improvement in current efficiency was small as the temperature of the water splitter increased from 30°C to 45°C. (See Figure 6). The three-chamber water splitter used in the method of the invention includes a plurality of cationic, ambipolar and anionic membranes arranged alternately between two electrodes, so that the base, acid and salt compartments are alternately arranged. are arranged to form an electrodialysis stacked structure. The two-chamber water splitter used in the method of the present invention may be any of the devices disclosed in Ohlanda et al., U.S. Pat. Something can happen. The two-compartment water splitter includes a plurality of cation exchange membranes and bipolar ion exchange membranes arranged alternately between two electrodes to form an electrodialysis stack. The configuration of electrodialysis stacked structures is well known; for example, the unit is manufactured by Asahi Glass Co., Ltd.;
Masachi Yusettsu, Watertown's Ionics,
Inc. and other companies. In general, stacked structures suitable for concentrating electrolytes, such as the Asahi model CU-IV, can be used in water splitters. However, the membrane used must be of a type that is compatible with the water split. Two-chamber and three-chamber water splitters are, for example,
As disclosed in U.S. Pat. No. 2,829,095 (generally referring to water splits), or U.S. Pat. or other types of suitable bipolar membranes that effectively convert water to hydrogen and hydroxide ions. The operation of the two-chamber water splitter is covered by a U.S. patent.
The procedure is similar to that described in 4082835 and 4107015, but the composition of the feed solution is changed as described below. (Figure 2a). For the operation of the three-chamber water splitter, see Section 2b.
This will be further described below with reference to the figures. The aqueous alkali metal sulfate solution supplied to the chambers of two-chamber and three-chamber water splitters preferably contains sulfuric acid, sodium or potassium sulfate, more preferably sodium sulfate, but lithium sulfate or other alkali metal sulfates. Or it may be a mixture thereof. A particularly useful solution for the acid chamber of a three-compartment cell is a spent spin bath solution obtained directly from a rayon spin bath without any pretreatment to remove organic and divalent metal cation impurities and containing 2% by weight. Contains up to saturated amounts of sodium or potassium sulfate, at least 5% by weight sulfuric acid, and organic impurities and divalent metal ion impurities. The pH of the solution fed to the acid chamber of two-chamber and three-chamber water splitters is advantageously below 7, preferably between 1 and 4, although the exact pH of the solution fed is not a critical condition. However, if more than 5% by weight of sulfuric acid is present in the alkali metal sulfate solution, it is preferred to utilize a three-chamber water split. Typical concentrations of alkali metal sulfates in the spent rayon spinning bath solution fed to the acid chamber of a three-compartment water splitter can range from concentrations as low as 5% by weight to saturating amounts of alkali metal sulfates; and may contain 0-15% by weight sulfuric acid; preferably the feed solution has a saturated concentration of 10% by weight (more preferably 25% by weight) and alkali metal sulfate (32% by weight for sodium sulfate). It is between. The acidified salt solution produced in the acid chamber of the three-compartment cell and recycled to the rayon spinning bath contains alkali metal sulfate and the solution fed to the acid chamber of the three-compartment cell, typically alkali metal sulfate 5 ~22% by weight, containing a concentrated amount of sulfuric acid compared to solutions that are 6-8% by weight H ₂ SO ₄ . Typically, the solution recovered from the acid chamber is
The concentration of H ₂ SO ₄ is 8-14, preferably 9-12% by weight. The solution fed to the salt compartment of the three-chamber water splitter contains alkali metal sulfate values derived from spent rayon spinning baths and purified by conventional methods to remove organic and divalent metal impurities. Preferably it is sodium or potassium sulfate, more preferably sodium sulfate, but also lithium sulfate or other alkali metal sulfates or mixtures thereof. A particularly advantageous feedstock fed to the salt chamber of a three-compartment cell is crystallized glauber salt, obtained as a by-product from spent rayon spinning baths, i.e. glauber's salt (Na ₂ SO ₄ 10H ₂ O ). Preferably, the feed solution to the salt chamber moves through a cation membrane;
and/or organic impurities and divalent metal cations (e.g. Ca ⁺² ,
Mg ⁺² , Zn ^+2, etc.) are processed so as to be substantially free of them. The pH of the feed solution is not critical, but is preferably 7. The concentration of alkali metal sulfate in the solution fed to the salt chamber of the three-compartment cell can be between concentrations as low as 5% by weight to a saturation amount of alkali metal sulfate. Preferably, 15 to 32 (saturated) weight percent alkali metal sulfate is fed to the salt compartment. The solution fed to the acid chamber of the two-chamber water splitter is derived from the spent rayon spinning bath solution.
Advantageously, it has an alkali metal sulfate value concentration of 32% by weight. Typically, a 30 wt% sodium sulfate solution containing 0 to 5 wt% sulfuric acid and pretreated to form an aqueous solution of Glauber's salt derived from spent rayon spinning baths is prepared in a two-chamber system. Supplied to the acid chamber of the cell. The liquid supplied to the base chamber of three-compartment and three-compartment water splitters may be water alone or water containing various electrolytes.
Preferably, this liquid is in a neutral or basic chamber (PH7-
14) and more preferably at a concentration of 1 to 50% by weight
(more preferably between 5 and 25% by weight) sodium hydroxide aqueous solution. This concentration (actual feed to the base chamber) can be achieved by recirculation, staging, or a combination thereof, as described in more detail below, and can range from 5 to 50% by weight. of aqueous sodium hydroxide. The current normally applied to a water splitter is direct current at a voltage specified by design and performance characteristics that will be apparent to those skilled in the art and/or determined by routine experimentation. Generally, current densities in the range of 50-150 mamp/ ^cm2 are convenient for use. 100～
A current density of 150 mamp/cm ² is particularly advantageous. Cation membranes useful in the methods of the invention can be weakly acidic or weakly acidic cation permselective membranes. A particularly useful cation membrane is Dupont's Nafion
Acidic fluorocarbon membranes, especially Nafion
110, 901 and 324 are utilized, although other commercially available cationic membranes may also be used. Anionic membranes useful in the three-chamber cells used in the present invention are available from Ionics Inc. of Watertown, Massachusetts.
Ionics204-UZL-386 sold by or SelemionAMV or ASV from Asahi Glass Co., Ltd.
strong, moderate or weakly basic anion permselective membranes, such as those sold under the trade name , but other commercially available anion permselective membranes may also be utilized. The invention will be better understood by referring to the accompanying drawings. FIG. 3 schematically shows a preferred embodiment of the process of the invention when carried out in a two-chamber electrodialysis water splitter. An aqueous alkali sulfate value solution is removed from the rayon spinning bath 100 via line 102. Typically, the spent rayon spinning bath solution in line 102 has a composition of sodium sulfate concentration from 2 wt% to the saturation point, sulfuric acid concentration of 0 to 15 wt%, and contains organic and inorganic impurities, typically ( (such as spin bath additives) divalent metal cations. Although sodium sulfate is used in the following description, it should be understood that other alkali metal cations such as potassium or lithium or mixtures thereof may also be used and are within the scope of the invention. The pH of the used rayon spinning bath in line 102 is not important; it is neutral,
It may be either an acidic or basic chamber. At least a portion of the sodium sulfate value in line 102 is transferred via line 104 to evaporator 108 to remove water. Water is removed via line 110 and concentrated sodium sulfate/sulfuric acid, typically containing 10-32% by weight sodium sulfate and 0-12% by weight sulfuric acid, is removed from evaporator 108 via line 112. is transferred to the purification zone 114 to remove organic impurities and 2
Valent metal cations are removed. The purification step may be PH adjustment and filtration or ion exchange, but typically purification involves the formation of a mother liquor rich in mirabilite (Na ₂ SO ₄ 10H ₂ O) and sulfuric acid and depleted in sodium sulfate. including evaporative crystallization. Here, mirabilite is line 1
16, while the mother liquor is removed from the refining zone 114 via line 140 and into the spinning bath 100 via line 140 and line 142.
is recirculated to Additionally, when supplemental sulfuric acid is required, sulfuric acid can be added via line 141 to the aqueous sodium sulfate/sulfuric acid solution in line 142. At least a portion of the spent rayon spin bath liquor in line 102 is transferred via line 106 to reduce the sodium sulfate concentration and combine with the sulfuric acid-rich mother liquor removed from purification zone 114. Sufficient water is added to the Glauber's Salt (Na ₂ SO ₄ .10H ₂ O) in line 116 via line 118 to form an aqueous solution typically containing from 2 wt% sodium sulfate to the point of saturation. In the case of a solution containing 5 wt % or more of sulfuric acid, water splitting using a three-chamber water splitter illustrated and explained in FIG. 4 below is preferred. The aqueous sodium sulfate solution in line 116 is composed of an alternating base chamber and The water is supplied to the acid chamber A of a two-chamber electrodialysis water splitter 120 consisting of a plurality of unit cells forming an acid chamber. When a direct current is applied, the sodium sulfate in the acid chamber A becomes bipolar membrane 122b.
The sulfuric acid is concentrated by the hydrogen ions generated on the cation surface. Sodium cations and a small amount of hydrogen ions move from acid compartment A to base compartment B through cation permselective membrane 124. A sulfuric acid-enriched sodium sulfate solution, typically from 5 wt % sodium sulfate to saturation point, with a sulfuric acid concentration of 5 to 15 wt %, is removed from chamber A via line 126 and transferred to purification zone 114 for further processing. Glauber's salt (Na ₂ SO ₄ .10H ₂ O) is removed or transferred to the spinning bath 100 via line 140 .
The water in line 128 is a two-chamber water splitter 120.
The base is supplied to the base chamber B. The hydroxide ions generated on the anion surface of the bipolar membrane 122a combine with sodium ions moving from the acid chamber to the base chamber via the cation membrane 124 in the base chamber B to form sodium hydroxide, typically 10~ Forms 20wt% sodium hydroxide. This sodium hydroxide is removed from base compartment B via line 130. At least a portion of the sodium hydroxide in line 130 may be recycled to line 128 via line 132. Another portion of the sodium hydroxide in line 130 is fed to evaporator 134 40
It is concentrated to ~50 wt% and taken out via line 138. Typically, the composition of sodium hydroxide in line 130 may be any concentration suitable for dissolving the cellulose used in rayon manufacture. FIG. 4 shows another preferred embodiment of the invention that can be implemented in a three-chamber electrodialysis water splitter.
The used rayon spinning bath solution is removed from the rayon spinning bath 200 via line 202. Typically, the composition of the spent rayon spinning bath in line 202 consists of 15 wt% to saturation sodium sulfate and 0 to 15 wt%, preferably 2 to 10 wt% sulfuric acid, and is free of organic impurities and divalent metals. Contains cationic impurities. At least a portion of the used rayon spinning bath in line 202 is routed through line 204 to a three-chamber electrodialysis water splitter 22.
0 acid chamber. This water splitter 22
0 is a bipolar membrane 222a and an anion permselective membrane 22 positioned and alternately arranged between two electrodes.
6 and a cation permselective membrane 224a, thus forming an acid chamber A, a salt chamber S and a base chamber B which are arranged alternately. In the acid chamber A, under the influence of the applied direct current, sulfate ions move from the salt chamber S to the acid chamber A via the anion permselective membrane 226, where they are combined with the hydrogen ions generated on the cation face of the bipolar membrane 222a. Join. An aqueous solution of sodium sulfate in which sulfuric acid is concentrated is taken out from acid chamber A through line 206 and transferred to the evaporator.
The water is removed via line 210. If there is no need to adjust the water balance in the system, the evaporation step can be omitted. If evaporator 208 is used, a more concentrated sodium sulfate/sulfuric acid solution is removed via line 212 and transferred to rayon spinning bath 200. The remainder of the spent rayon spinning bath containing sodium sulfate and sulfuric acid in line 202 is not fed to the acid chamber and is removed from the purification zone 2.
14 to remove organic impurities and divalent metal cation impurities. Although conventional purification steps such as PH adjustment and filtration may be used, evaporative recrystallization is typically employed in purification zone 214 to produce mirabilite (Na ₂ SO ₄ .10H ₂ O),
and sulfuric acid are condensed to form a mother liquor with reduced sodium sulfate concentration. Glauber's Salt is Line 21
6, while the mother liquor is removed from the refining zone via line 218 and transferred to line 212 and then to the rayon spinning bath 200. line 21
6. Glauber's salt (Na ₂ SO ₄ 10H ₂ O) is stored in the salt chamber recirculation tank 230 in the form of solid, slurry or aqueous solution.
will be forwarded to. An alkali metal base, typically soda ash or sodium hydroxide, is added to the salt room recirculation tank 230 via line 232 and removed from the salt room S to form a sodium sulfate solution which may optionally contain sulfuric acid. at least part of line 23
6 and added to the salt compartment recirculation tank 230.
If makeup water is needed, it is added to tank 230 via line 234. For further purification, soda ash is added via line 232, for example to remove divalent metal cations such as zinc, magnesium or calcium that would interfere with the operation of the cation permselective membrane adjacent to the salt chamber S. Ru. An aqueous solution of sodium sulfate containing from 10 wt% to saturation, typically from 25 wt% to saturation, and insolubles is removed from recirculation tank 230 via line 240 through a filter (not shown). , transferred to salt room S. In the salt chamber S, sodium cations move from the salt chamber S to the base chamber B through the anion permselective membrane 224a. Sulfate ions move from the salt chamber S to the acid chamber A through the anion permselective membrane 226. An aqueous solution of sodium sulfate containing a reduced amount of sodium sulfate is removed from the salt compartment S via line 241.
The pH of the sodium sulfate solution in line 241 is acidic.
Basic or neutral. If the sodium sulfate solution in line 241 is acidic, at least a portion of it
The sodium sulfate solution fed to acid compartment A via line 204 can be transferred via line 238. The remainder of the acidic sodium sulfate solution in line 241 is passed through line 236 to recirculation tank 230.
can be transferred to. Water in line 244 is supplied to base chamber B. In base chamber B, sodium ions moving from the salt chamber through cation permselective membrane 224a combine with hydroxide ions introduced at the anion face of bipolar membrane 222b to form sodium hydroxide, typically 10 Forms ~20wt% sodium hydroxide. This sodium hydroxide is removed from base compartment B via line 246. The composition of the sodium hydroxide solution in line 246 is not critical and any concentration suitable for dissolving the cellulosic materials used in rayon manufacture may be used.
At least a portion of the sodium hydroxide solution in line 246 is added via line 248 to line 244 for recirculation, further via line 236 to a recirculation tank, and the remainder is transferred via line 246 to evaporator 250. , water is removed via line 252 and a 40-50 wt% sodium hydroxide solution is removed from the evaporator via line 254. The present invention may be advantageously operated with two-chamber or three-chamber electrodialysis water splitters. If a three chamber electrodialysis water splitter is used, at least a portion, and optionally all, of the output of the salt chamber is introduced into the acid chamber shown in FIG. If a two-chamber electrodialysis water splitter is used, one of the two-chamber electrodialysis water splitters shown in Figures 2a, 2c or 5 may be used. The two-chamber electrodialysis water splitter shown in Figure 2a is used under normal conditions, i.e.
% or less, for example, 1 mol Na ₂ SO ₄ sulfate is converted to 0.25% or less.
It is sufficient under conditions to convert to 0.50 mol NaHSO ₄ /0.75-0.50 mol Na ₂ SO ₄ and under conditions to achieve higher conversions, i.e. 25-50% or more, Figures 2c and 5. It is advisable to use one of the embodiments of the two-compartment electrodialysis water splitter illustrated in the figure. 3 acid stage/2 shown in Figure 2c
The chamber electrodialysis water splitter includes one bipolar membrane 32a and two substantially non-porous water-swollen cationic or neutral membranes 34a, 34, respectively.
b and a cation permselective membrane 34c, whereby a first acid chamber A ₁ , a second acid chamber A ₂ , a third acid chamber A ₃ and a base chamber B are located between the two electrodes anode 31 and cathode 33 . arranged alternately,
It includes a plurality of unit cells formed by forming a plurality of unit cells. The operation of the three acid stage/two chamber electrodialysis water splitter shown in Figure 2c is essentially as follows:
Direct current is passed from anode 31 to cathode 33. An aqueous solution of alkali metal sulfate derived from the spent rayon spinning bath liquor in line 35 and containing, for example, sodium sulfate is fed to the third acid compartment _A3 . Hydrogen ions introduced at the cationic surface of the bipolar membrane 32a move to the base chamber B through the membranes 34a, 34b and 34c, and at the same time enter the acid chamber.
Alkali metal cations such as sodium in A ₃ move to the base chamber B through the cation membrane 34c and head toward the cathode 33. The aqueous solution of sodium sulfate from A ₃ , which may be acidic, neutral or basic, preferably acidic, is removed via line 37a to the second
Transferred to acid room A ₂ . The hydrogen ions and sodium cations of _A1 are transferred to the cation membrane or neutral membrane 24a.
It moves to the second acid chamber A ₂ through. neutral or acidic,
An aqueous sodium sulfate solution, which may preferably be acidic, is removed from A ₂ via line 37b to the acid chamber.
A ₁ is supplied. The hydrogen ions generated in the bipolar membrane 32a are added to the sodium aqueous solution of _A1 ,
The acidified aqueous solution of sodium sulfate and sulfuric acid is then withdrawn from A ₁ via line 39a.
By adding intermediate acid chambers A ₁ , A ₂ and A ₃ connected in series, the third acid chamber A ₃ closest to the anion face of the bipolar membrane 32b contains the lowest concentration of acid; On the other hand, the first acid chamber _A1 , which is closest to the cationic side of the bipolar membrane 32a, contains the highest concentration of acid, thereby providing an advantage over prior art two-chamber electrodialysis water splitters such as that shown in FIG. 2a. Improve acid production efficiency. By reducing the amount of hydrogen ions transferred to the base chamber, the efficiency of producing aqueous hydrogen ions and hydroxide ions is improved. A liquid consisting of water, preferably also containing dilute alkali metal hydroxide, is supplied via line 36 to base chamber B, into which hydroxide ions generated on the anionic side of bipolar membrane 32b are introduced. A concentrated aqueous solution of alkali metal hydroxide is removed from B via line 38. The flow rates from the different chambers may be the same or
or may be different, and in particular the flow rate or net flow rate after recirculation from the base chamber is such that the hydroxyl ion concentration of the product recovered from chamber B is the same as that of the aqueous acidified salt solution recovered from _A1 . The flow rate from the acid chamber can be much slower than the acid concentration so that it is substantially higher than the acid concentration. The flow rate can also be adjusted such that the acid concentration of the product aqueous salt recovered from A ₁ is higher than the hydroxyl ion concentration of the product recovered from base compartment B. The cation surface of the bipolar film 32a and the cation film 34
Additional membranes 34a and 34b disposed between the faces of c and forming at least two acid chambers are arranged such that these additional membranes are substantially non-porous (with respect to water) and swellable with water. It can be a cation permselective membrane or a neutral membrane as long as it is possible. The term "substantially non-porous (with respect to water)" as used herein for membranes means a water or hydraulic permeability of less than or equal to 1 ml/dm ² membrane area of water per hour at 1 meter of water pressure. means a membrane with Lower water permeability, e.g. 1× at 1 m water pressure
A water permeability of 10 ⁻¹ ml/dm ² /h is preferred. However, it is contemplated by the present invention that there is no lower limit to water permeability as long as the additional substantially non-porous water-swollen cationic or neutral membrane allows water molecules to pass along with the ions under the application of a direct current. It was found that this was not important for the operation of Water permeability value for 1 hour, water pressure
The use of membranes with a density higher than 1 ml/dm ² should be avoided. The term "water-swollen" as used herein for membranes refers to membranes that are water-insoluble and water-absorbing. The membranes 34a and 34b dividing A ₁ /A ₂ and A ₂ /A ₃ are made of a low-resistance, substantially non-porous, weakly, moderately acidic or weakly acidic membrane as described in connection with Figures 1, 2a and 2b. It may be a water-swollen cationic membrane, or it may be an uncharged membrane. These uncharged or neutral membranes are non-
Ion selective but anion and cation-
A permeable, substantially non-porous, water-swellable membrane. Suitable uncharged membranes can be prepared by copolymerizing, or interpolymerizing, a difunctional vinyl monomer, such as divinylbenzene, with a non-ionic hydrophilic monomer, such as acrylamine. Examples of uncharged membranes include cross-linked polyvinyl alcohol and cellulose-based membranes. Another aspect of the invention shown in FIG. 2c is
The method includes an acid stage by placing a substantially non-porous, water-swollen cationic or neutral membrane in an acid chamber. FIG. 5 shows an embodiment including a two-stage or diacid chamber by placing a single substantially non-porous, water-swollen cationic or neutral membrane in the acid chamber. The number of stages that can be placed in the acid chamber is not a critical condition, as the solution with the lowest acidity enters the acid chamber closest to the cathode and flows successively to the acid chamber closest to the anode, where the solution with the highest acidity enters the acid chamber closest to the anode. can be varied in a range of at least 2 to 10 stages as long as it is manufactured. In the case of a single stage, the water splitter is a conventional two-chamber water splitter as shown in Figure 2a. FIG. 5 illustrates another preferred embodiment of the invention using a two acid stage/two chamber electrodialysis water splitter in producing acidified aqueous sodium sulfate. Aqueous sodium sulfate is line 33
1 to tank 330, and then to line 3
32 and the acid chamber A ₂ formed by the surface of the substantially non-porous water-swollen cationic or neutral membrane 320b and the surface of the cation permselective membrane 320c.
is supplied to Anode 321 and cathode 3
Under the influence of a direct current through 23, hydrogen ions and sodium ions pass through the cation permselective membrane 32.
Move from 0c to base room B. The acidic aqueous solution of sodium sulfate produced in acid room A ₂ is transferred to line 334.
is returned to the tank 330. At least a portion of the acidic aqueous solution of sodium sulfate from A ₂ is removed via line 336 to line 338 and connected to the cationic face of bipolar membrane 322a and the substantially non-porous water-swollen cationic or neutral membrane. 320b
is transferred to the first acid chamber A ₁ formed by the plane of. An acidic solution of sodium sulfate generated by hydrogen ions formed on the cationic surface of the bipolar membrane 322a is taken out from the first acid chamber _A1 through a line 340 and transferred to a tank 342. At least a portion of the acidic aqueous solution of sodium sulfate is present in line 34.
4 and is removed from the tank 342. The operation of the base chamber of FIG. 5 is similar to that of the base chambers of FIGS. 2a and 3. The average temperature of the two-compartment cell may be maintained at least 40°C, preferably at least 45°C, by conventional means contemplated in the art. Preferably, the temperature of the solution in each chamber of the two-compartment water splitter is maintained at at least 40°C, more preferably at least 45°C. The temperature maintained in the three-chamber cell is not critical for the operation of the present invention, but is typically between 35° and 55°C.
and temperatures above 40° C. are particularly advantageous. Experimental Overview The method for determining efficiency is best explained with reference to Figure 1, which describes the laboratory equipment used.
Figure 2b schematically illustrates the major transport processes occurring in a three-chamber electrodialysis water splitter cell. In FIG. 1, the device consists of a cylindrical cell constructed from a fluorocarbon polymer. The cell is provided with platinum electrodes 7 and 8 at each end connected to a DC power source. Five chambers separated by membranes were included in the cell. These chambers are anolyte (anolyte) chamber 1, base chamber 2, acid chamber 3,
There were 4 salt compartments and 5 catholyte compartments. These chambers were divided by an ion exchange membrane with an exposed area of 11 cm ² as follows; 8 and 11 were Dupont
It was a Nafion 110 made by the company. 9 was a bipolar membrane made in US Pat. No. 4,116,889. The anion exchange membrane 10 was a commercially available anionic membrane 204-UZL-386 manufactured by Ionics Inc. 15,1
7 and 16 were pumps for circulating the solution through cell 12. 12 is 0.5M before the experiment
It was an anolyte/catholyte reservoir filled with Na ₂ SO ₄ 1. This solution was circulated to the anolyte chamber as stream 26 and returned to its sump as stream 30, to the catholyte chamber as stream 27, and returned to its sump as stream 30. Base compartment 2 and salt compartment 4 have streams 35 and 3.
6 from reservoir 14, the solution was returned to that reservoir by streams 24 and 25. A solution was circulated in the acid chamber 3 by a pump 17. There were no reservoirs in the acid flow system, and the circulating fluid consisted only of the solution contained in the acid chamber, pump, and attached tubes. At the top of the acid loop,
An overflow tube 20 was provided.
During the experiment, solution was introduced into the acid loop from reservoir 13 at a constant rate by metering pump 18. Introduction of solution and mass transport through the membrane in this manner caused overflow from the acid chamber. This overflow liquid was collected. As shown in Figure 2b, when a direct current was passed through the cell, H ⁺ and OH ^- ions were produced by the bipolar membrane. OH ^- ions are introduced into the base chamber,
Then H ⁺ ions were introduced into the acid chamber. Sulfate ions passed through the anion membrane and entered the acid chamber to form net sulfuric acid in the acid chamber. Since the anion membrane is not completely selective for anions, some of the H ⁺ produced in the acid was lost by moving into the salt chamber, especially when the acid concentration was high. Since the outputs from the salt and base chambers are combined in the experimental setup, the net production of H ⁺ can be monitored by observing the net production of OH ^- produced in the base/salt stream. . Acid production can be monitored by analyzing the flow rate and composition of the overflow from the cell and the solution metered and transported to the cell. Example 1 The cell shown in Figure 1 containing the membrane described in the Experimental Summary was used. 0.5M Na ₂ SO ₄ 1 in electrolyte reservoir 12
The base/salt reservoir 14 was filled with 1.8 of 1M Na ₂ SO ₄ , respectively. A heater, PH probe and thermometer were placed in the base/salt reservoir. The base/salt solution was warmed with a heater and maintained at approximately 33° C. throughout the experiment. 35 g of a 2.0% H ₂ SO ₄ solution (X) was introduced into the acid loop.
Water was metered into the acid loop at a flow rate of 7.0 g/1000 seconds. The base/salt reservoir was adjusted to pH 4 by adding a small amount of 1.015NH ₂ SO ₄ and
1.20amp galvanized. The pH of the base/salt reservoir is OH ^-
increased as it was introduced. When the pH reached 7, a timer was started and a tared container was placed to collect the overflow from the acid chamber. This vessel was replaced with a new vessel at 1000 second intervals, and the vessel contents were analyzed for sulfuric acid by titration with standard 1N NaOH. 300 since the timer started
After seconds 5.0 ml of 1.015N N ₂ SO ₄ was added to the base/salt reservoir. This lowered the pH to 4. As the experiment continued, the PH increased due to the formation of OH ^- . The time when the pH reached 7 was recorded. Efficiency for base (i.e. acid production) is calculated from successive PH reading intervals and a known amount of acid added during that interval by the following formula: Current efficiency = ml added x N ×96.5(co
ul/meq)/Current (amps) Current (amps)/Time interval (sec) Change acid collection cup every 1000 seconds and aliquot 5.0 ml of 1.067NH ₂ SO ₄ 300 seconds after pH reaches 7
was added to the base/salt reservoir and the experiment continued for 6000 seconds. The results are shown in the table. Current efficiency was calculated based on the change in acid concentration over the interval, weight collected, and concentration. Based on these results, the current efficiency was 0.77 at 1000 seconds, 0.69 at 3000 seconds, and 0.68 at 5000 seconds. These efficiencies are in good agreement with base efficiencies determined by time intervals in view of the difficulty in determining acid loop flow, concentration, and volume. The efficiency is reported in Table.

【table】

[Table] Example 2 The same method as in Example 1 was adopted except that the average temperature was 43°C, which was 10°C higher than in Example 1. The results are shown in the table. By comparing Examples 1 and 2, 10
It can be seen that the difference in temperature in degrees Celsius has an advantageous effect on current efficiency.

【table】

[Table] Example 3 Fill the base/salt reservoir with 400ml of 0.5M Na ₂ SO ₄ and
Example 3 was carried out in the same manner and cell as described in Example 1, except that the bath liquid from reservoirs 13 and 14 was recycled (instead of metered into and collected from the cell). The temperature was increased during the experiment. The results obtained are shown in the table and in FIG.

[Table] Example 4 Sulfate solutions of acids, bases and salts were prepared separately.
Example 4 was carried out in the same manner as described in Example 3 except that 2.9 wt% HCl and 1M NaCl were substituted and 1000N HCl was added to the base salt reservoir.
The results obtained are summarized in the table and illustrated in FIG. In Figure 6 - ○†a Osamu

Claims (1)

[Claims] 1. A method for converting alkali metal sulfate values into alkali metal hydroxide and alkali metal sulfate/sulfuric acid; (a) providing an electrodialysis water splitter comprising at least one unit cell; (b) supplying a liquid consisting of water to the base chamber of each unit cell of said electrodialysis water splitter; (c) supplying a liquid consisting of water to the acid chamber of each unit cell of said electrodialysis water splitter containing an alkali metal sulfate value; (d) passing an electric current through the electrodialysis water splitter to supply a reaction solution containing alkali metal sulfate/sulfuric acid in the acid chamber of each unit cell; The method described above, comprising the steps of: generating a reaction solution containing an alkali metal hydroxide in the base chamber of the cell. 2. The electrodialysis water splitter is a two-chamber electrodialysis water splitter, each unit cell of which consists of an acid chamber and a base chamber, and is formed by alternately arranging cation membranes and bipolar membranes. A method according to claim 1. 3 At least about 40℃ in the electrodialysis water splitter
2. A method according to claim 1, wherein the average temperature of . 4. The electrodialysis water splitter is a three-chamber electrodialysis water splitter, each unit cell of which has a base chamber,
The base chamber, the acid chamber, and the salt chamber are formed by alternately arranging cation membranes, bipolar membranes, and anion membranes, according to claim 1. the method of. 5. The method according to claim 1, wherein the liquid supplied to the acid chamber is an untreated used rayon spinning bath solution. 6. Claim 4, wherein the liquid supplied to the salt chamber is a pretreated used rayon spinning bath solution.
The method described in section. 7 Pre-treatment of a used rayon spinning bath comprises: (a) neutralizing the used rayon spinning bath; and (b) straining the used rayon spinning bath to substantially free organic and inorganic impurities. do not have,
7. The method of claim 6, comprising: obtaining an aqueous solution having an alkali metal sulfate concentration of about 10 to about 32% by weight. 8. The pretreatment of the used rayon spinning bath comprises: (a) treating the used rayon spinning bath to produce crystallized Glauber's salt; and (b) reducing the alkali metal sulfate concentration from about 15 to about 32% by weight.
7. The method of claim 6, comprising: forming an aqueous solution of Glauber's salt. 9 Claim 1 in which the acid chamber is a multistage acid chamber
The method described in section. 10 A multi-stage acid chamber is formed by having an acid chamber defined by the cation face of the bipolar membrane and a cation permselective membrane, and disposing at least one non-porous water-swollen membrane between the two membranes. 10. The method of claim 9, wherein at least two secondary acid chambers are defined. 11. The method of claim 10, wherein a liquid consisting of a used rayon spinning bath solution is supplied to an auxiliary acid chamber adjacent to the base chamber of the unit cell. 12: (d) moving the liquid from the sub-acid compartment adjacent to the base compartment through all remaining sub-acid compartments in sequence; and (e) from the sub-acid compartment furthest from the base compartment of the unit cell; 12. The method according to claim 11, further comprising the step of: removing the reaction solution containing alkali metal sulfate/H ₂ SO ₄ .