CA2280535A1 - Process for separating polyfunctional alcohols from water-soluble salts in aqueous systems - Google Patents
Process for separating polyfunctional alcohols from water-soluble salts in aqueous systems Download PDFInfo
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- CA2280535A1 CA2280535A1 CA002280535A CA2280535A CA2280535A1 CA 2280535 A1 CA2280535 A1 CA 2280535A1 CA 002280535 A CA002280535 A CA 002280535A CA 2280535 A CA2280535 A CA 2280535A CA 2280535 A1 CA2280535 A1 CA 2280535A1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
- B01D61/42—Electrodialysis; Electro-osmosis ; Electro-ultrafiltration; Membrane capacitive deionization
- B01D61/44—Ion-selective electrodialysis
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
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- C07C29/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring
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- C07C29/76—Separation; Purification; Use of additives, e.g. for stabilisation by physical treatment
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract
Disclosed is a process for separating polyols from water-soluble salts in aqueous solutions using electrodialysis.
Because no organic solvents are used, the process is environmentally friendly and can be conducted inexpensively.
Desired polyols may be obtained colorless and may be processed directly without further purification.
Because no organic solvents are used, the process is environmentally friendly and can be conducted inexpensively.
Desired polyols may be obtained colorless and may be processed directly without further purification.
Description
PROCESS FOR SEPARATING POLYFUNCTIONAL ALCOHOLS FROM WATER
SOLUBLE SALTS IN AQUEOUS SYSTEMS
The present invention relates to a process for separating polyfunctional alcohols from water-soluble salts in aqueous systems.
Polyfunctional alcohols or polyols are produced in large amounts for a wide variety of applications and are used, for example, as heat transfer media, as viscosity modifiers, as fragrance components, as intermediates for surfactants, as bases for ointments, as antifreezes, as additives for the coatings industry, as mold release agents, as adhesives, as plasticizers, as starting materials in the production of synthetic resins (e. g. polyesters or polyurethanes) and as lubricants. Polymeric polyfunctional alcohols such as polyvinyl alcohol are used, for example, as protective colloids, as suspension stabilizers, as constituents of adhesives, as pigmented binders and as packaging materials (Ullmann's Encyclopedia of Industrial chemistry, 5th.
Ed. (1985/1992), Vol. A1, Vol. A21).
Polyfunctional alcohols can be prepared in various ways, for example by epoxidation reactions with subsequent hydrolysis (e.g. in the preparation of ethanediol), by Cannizzaro reactions (e. g. in the preparation of neopentyl glycol) or by saponification of polymeric precursors with alkalis or by transesterification (e.g. in the preparation of polyvinyl alcohol). In some cases during the preparation, in other cases during the subsequent work-up and use, one obtains a mixture of salts and the polyfunctional alcohol which needs to be separated.
Various methods of extracting the polyfunctional alcohols and also processes for crystallizing out the salts have been proposed in order to separate the water-soluble polyfunctional alcohols from the likewise water-soluble salts.
SOLUBLE SALTS IN AQUEOUS SYSTEMS
The present invention relates to a process for separating polyfunctional alcohols from water-soluble salts in aqueous systems.
Polyfunctional alcohols or polyols are produced in large amounts for a wide variety of applications and are used, for example, as heat transfer media, as viscosity modifiers, as fragrance components, as intermediates for surfactants, as bases for ointments, as antifreezes, as additives for the coatings industry, as mold release agents, as adhesives, as plasticizers, as starting materials in the production of synthetic resins (e. g. polyesters or polyurethanes) and as lubricants. Polymeric polyfunctional alcohols such as polyvinyl alcohol are used, for example, as protective colloids, as suspension stabilizers, as constituents of adhesives, as pigmented binders and as packaging materials (Ullmann's Encyclopedia of Industrial chemistry, 5th.
Ed. (1985/1992), Vol. A1, Vol. A21).
Polyfunctional alcohols can be prepared in various ways, for example by epoxidation reactions with subsequent hydrolysis (e.g. in the preparation of ethanediol), by Cannizzaro reactions (e. g. in the preparation of neopentyl glycol) or by saponification of polymeric precursors with alkalis or by transesterification (e.g. in the preparation of polyvinyl alcohol). In some cases during the preparation, in other cases during the subsequent work-up and use, one obtains a mixture of salts and the polyfunctional alcohol which needs to be separated.
Various methods of extracting the polyfunctional alcohols and also processes for crystallizing out the salts have been proposed in order to separate the water-soluble polyfunctional alcohols from the likewise water-soluble salts.
Extraction using solvents for the polyfunctional alcohols, for example using amyl alcohol, cyclohexanol or various ester, requires large amounts of extractant which subsequently have to be removed again from the desired product, e.g. by distillation.
US-A 2468718 describes a process for separating methylolalkanes from water-soluble salts by extraction of the methylolalkanes using a low-boiling, water-soluble ketone.
Ullmann, Volume 7, 4th edition, p.231 (1974) describes the work-up of the mixture of polyols and salts by extraction with solvents such as amyl alcohol, cyclohexanol or ethyl acetate and subsequent distillation of the polyols. However, these extraction methods require the use of large amounts of extractants which have to be removed afterwards. This gives intensely colored products which contain many by-products and, mainly because of their disadvantageous color, have to be subjected to a further distillation.
The removal of the by-products is important because these would lead to insuperable problems in the subsequent applications. Thus, in the coatings application, colored by-products have an adverse effect on the reproducibility of the coatings. In addition, salt residues adversely affect possible further reactions of the polyfunctional alcohols, e.g. in the preparation of the corresponding esters.
It is likewise possible to concentrate the mixture of polyols and salts and to crystallize the salts (CN-A-1076185).
However, this process also gives colored products. Furthermore, considerable amounts of polyols remain in the crystallized material and can be washed out only with significant losses in yield.
It is an object of the present invention to provide an improved process for separating polyfunctional alcohols from water-soluble salts in aqueous systems which can be carried out inexpensively, i.e. with a low consumption of energy, which makes do without the use of solvents and can thus be carried out in an environmentally friendly manner and which gives colorless polyols which can be further processed directly without further purification steps.
Attempting to achieve this object, the invention provides a process for separating polyols from water-soluble salts in aqueous systems by subjecting aqueous systems to electro dialysis, with the proviso that the polyols do not include trimethylolpropane.
Figure 1 is a diagrammatic view of an electrodialysis view of an electrodialysis apparatus that may be used for carrying out a particularly preferred embodiment of the process according to the present invention; and Figures 2 to 5 are graphs showing the current and voltage curves and conductivity changes in Salt-depletion and Salt-uptake solutions employed in the working examples.
The polyols are water-soluble and may also be called as polyfunctional alcohols hereinunder. However, "poly-functional alcohols" may not be completely accurate since polyphenols are also included.
Those polyols that can be used according to the invention include:
a) diols of the formula HO-R1-OH, where R1 is:
1. a linear saturated aliphatic unit, preferably containing 2 to 10 carbon atoms, such as -C2H4-, -C3H6-, -C4Hg-or -C6H12- (e. g. ethylene glycol, 1,2- or 1,3-propylene glycol and 1,2-, 1,3- or 1,4-butanediol), 2. a linear unsaturated aliphatic unit, preferably containing 4 to 10 carbon atoms, such as -C4H6-, -C4H4- or -C6H10- (e. g. 2,3-butene-1,4-diol, 2,3-butyne-1,4-diol and 2,3-or 3,4-hexene-1,6-diol), 3. a branched saturated aliphatic unit, preferably containing 3 to 10 carbon atoms, such as -C4Hg-, -C5H10- or -C6H12- (e. g. 2-methyl-propane-1,2-diol, 2-methylpropane-1,3-diol, 2,2-dimethylpropane-1,3-diol, 2-methylbutane-1,2-diol, 2-methylbutane-1,3-diol, 2-methylbutane-1,4-diol, 2,3-dimethylbutane-1,2-diol, 2,3-dimethylbutane-1,4-diol, 2,2-dimethylbutane-1,3-diol and 2,2-dimethylbutane-1,4-diol), 4. a branched unsaturated aliphatic unit, preferably containing 5 to 10 carbon atoms, such as -CSHg- or -C6H10- (e. g.
2-methyl-2,3-butene-1,4-diol and 2,2-dimethyl-3,4-pentene-1,5-diol), 5. a cylic saturated aliphatic or alicyclic unit, preferably containing 3 to 10 carbon atoms such as -C5H10-, -C6H12- or -C~H14- (e. g. 1,2-cyclopentane-diol, 1,3-cyclopentanediol, 1,2-cyclohexanediol, 1,3-cyclohexanediol and 1-methyl-1,2-cyclopent-anediol), 6. a cyclic unsaturated aliphatic or alicyclic unit, preferably having 5 to 10 carbon atoms, such as -CSHg-, -C6H10-or -C~H12- (e. g. 1,2-cyclopentene-3,4-diol, 1,2-cyclopentene-3,5-diol, 1,2-cyclo-hexene-3,4-diol, 1,2-cyclohexene-3,5-diol, 1,2-cyclohexene-4,5-diol, 1,2-cyclohexene-3,6-diol, 1,2,3,4-cyclohexadiene-5,6-diol and 1-methyl-1,2-cyclopentenediol), 7. an aromatic carbocyclic unit, preferably a phenylene unit optionally substituted by a lower alkyl group, such as -C6H4- or -C6H3(CH3)- (e. g. 1,2-dihydroxybenzene, 1,3-dihydroxybenzene, 1,2-dihydroxy-3-methylbenzene and 1,3-dihydroxy-2-methylbenzene), where further substituents may also be present on the aromatic ring system or on alicyclic side chains, 8. an aromatic heterocyclic unit, preferably a pyridine unit, such as -C5H3N- (e.g. 2,4-dihydroxypyridine), or 9. a unit comprising a combination of the above-mentioned units (a) 1-8;
b) monoglycerides of the formula: CH20Rr-CHORs-CH20Rt, where two of the groups Rr, Rs and Rt are each hydrogen and the other group is a saturated or unsaturated monocarboxylic acid residue having from 1 to 22 carbon atoms, e.g. CH20H-CHOH-CH20-CO-5 C17H35%
c) oligomeric and polymeric ether diols of the formula:
HO-[(CR2R3)n-0]m-H, where n >_ 2 and m >_ 2, preferably n is 2, 3 or 4 and m is 2-100, where R2 and R3 are each, independently of one another, hydrogen or an aliphatic group such as -CH3 or -C2H5 (preferably, (CR2R3)n is -CH2CH2- or -CH2CH(CH3)-);
examples include HO-CH2-CH2-O-CH2-CH2-OH (diethylene glycol), HO[CH2CH20]3pH (polyethylene glycol having a mean molecular weight of 1338) and HO [CH2CH (CH3) 0] 3pH (polypropylene glycol having a mean molecular weight of 1758);
d) triols and higher-functional polyols of the formula:
R4(OH)x where x >_ 3, preferably x is 3-6, and R4 is:
1. a linear saturated aliphatic unit, preferably having 3-10 carbon atoms, such as -C3H5-, -C4H7-, -C5H9- or -CSHg-(e.g. glycerol, 1,2,3-butanetriol, 1,2,4-butanetriol and 1,2,3-pentanetriol), 2. a linear unsaturated aliphatic unit, preferably having 5-10 carbon atoms, such as -C5H7-, -C6H9- or -C6Hg (e.g. 1-pentene-3,4,5-triol, 1-hexene-3,4,5-triol, 2-hexene-1,4,5-triol and 3-hexene-1,2,5,6-tetrol), 3. a branched saturated aliphatic unit, preferably having 4 to 10 carbon atoms, such as -C4H7- or -CSHg-(e. g. 2-methyl-1,2,3-propanetriol and pentaerythritol), 4. a branched unsaturated aliphatic unit, preferably having 5 to 10 carbon atoms, such as -C5H7- or -C6H9-(e.g. 2-methylol-2-butene-1,4-diol and 2-methylol-2-pentene-1,5-diol), 5. a saturated alicyclic or cyclic aliphatic unit, preferably having 5 to 10 carbon atoms, such as -C5H7-, -C6Hg-, -C6H8- or -C7H11- (e. g. 1,2,3-cyclopentanetriol, 1,2,3-cyclohexanetriol, 1,2,3,4-cyclohexanetetrol, 6-methyl-1,2,3-cyclohexanetriol and 6-methylol-1,3-cyclohexanediol), 6. an unsaturated alicyclic or cyclic aliphatic unit, preferably having 5 to 10 carbon atoms, such as -C5H5- or -C6H7-(e. g. cyclopentene-3,4,5-triol and cyclohexene-3,4,5-triol), 7. an aromatic carbocyclic unit, preferably a benzene unit optionally substituted by a lower alkyl group, such as -C6H3- or -C6H2(CH3)- (e. g. 1,2,3-trihydroxybenzene and 2,3,4-trihydroxytoluene), 8. an aromatic heterocyclic unit, preferably a pyridine unit, such as -C5H2N-(e.g. 2,3,4- trihydroxypyridine), or 9. a unit comprising a combination of the above-mentioned units (d) 1-8; and e) polymeric polyfunctional alcohols such as polyvinyl alcohol, polysaccharides and branched or dendrimer-like polyether polyols having, for example, the following structure:
HO-[CHz-CH2-O]d CH2\ / CHZ [O-CH2-CH2] a OH
C
2 0 HO-[CHz-CH2-O] f CH2 ~ CH2 [O-CH2-CH2]g OH
where d, e, f and g are, independently of one another, an integer >_ 1, preferably 1-10.
The use of electrodialysis for desalination of sea water, for brine recovery, for obtaining drinking water, for regulating the hardness of water, for desalination of whey in the food industry, for preventing cream of tartar deposits in wine production or for recovering valuable materials from waste solutions from electrolytic processes is known (Rompp Chemie Lexikon, Volume 2, 10th edition, pp. 1113-1114 (1997)).
However, these applications, always involve aqueous systems having a relatively low salt content (< 5% by weight).
Electrodialysis is a separation process in which the migration of ions through a permeation-selective membrane is accelerated by application of a direct current (DC) voltage. In electrodialysis, ions are transported through a membrane under the action of an electric field. If ion exchange membranes are installed in the dialysis apparatus in such a way that anion exchange membranes and cation exchange membranes are arranged alternately between a cathode and an anode and divide a cell into narrow chambers, appropriate connection of the chambers gives streams which are depleted in salt and enriched in salt, since when current is passed through the apparatus, the cations can only pass through the cation exchange membranes and the anions can only pass through the anion exchange membranes. The enrichment occurs against the concentration gradient. This means that connection of a plurality of anion- and cation-selective ion exchange membranes in series makes it possible to deionize the liquid to be dialysed while simultaneously increasing the concentration of the ions in the concentrate chambers.
In contrast to the other known membrane processes such as membrane filtration, reverse osmosis or gas permeation, in which the fluids are separated as a result of pressure or concentration differences, electrodialysis enables a separating force acting in a targeted way to be applied by means of the electric current. In this way, charged constituents can be moved selectively in the solution. The ion exchange membranes used for the separation are organic polymer membranes having functional, charge-bearing groups and act similarly to an electrical rectifier. Ion exchange membranes allow passage of only one type of ion, while the oppositely charged ions are prevented from passing through. The construction of an electrodialysis module corresponds approximately to that of a chamber filter press, i.e. two or three solutions are fed separately into the module frame via internal feed channels and then flow, separated from one another by the ion exchange membranes, through the respective hollow spaces in the frame.
Under the action of the applied electric potential, ions are transported from the individual chambers through the ion exchange membranes. Appropriate connection in series of anion exchange membranes (A) and ration exchange membranes (K), i.e.
membranes which allow either only anions or only rations to pass through, makes it possible for solutions to be reduced in salt content or concentrated or for undesired ions to be replaced by others.
An example of an apparatus which can be used according to the invention for separating polyfunctional alcohols from water-soluble salts is shown in Figure 1. The apparatus consists of an electrodialysis module having three separate circuits (a salt-depletion or salt-releasing circuit 14, a salt-uptake or salt-accepting circuit 15 and an electrode-flushing or electrode-rinse circuit 16) and the associated reservoirs 17, 18 and 19. In order to achieve a large membrane surface, five successive cell units were installed.
In Figure 1:
M or M+ = metal ions, X or X - anions, Polyol - poly-functional alcohol, K = ration exchange membrane and A = anion exchange membrane.
To remove the reaction gases formed at the electrodes, an Electrode-flushing solution may preferably be passed through the end chambers. This electrode-flushing solution, if used, should be inert toward the electrodes, have a low electrical resistance and release no extraneous ions into the salt-uptake and salt-depletion circuits.
It has now surprisingly been found that electrodialysis can likewise be used for separating a mixture of water-soluble polyols and water-soluble salts dissolved therein, even if the salts are present in high concentration (> 50°s by weight). High selectivities (S > 250) can be achieved in such a process.
The selectivity of the separation between the originally salt-containing and then salt-depleted solution and the concentrated solution in respect of the neutral component polyfunctional alcohol is defined as for other membrane processes:
S = ( [polyol] conc [salt] conc) ~ ( [polyol] dil [salt] dil) where: dil: salt-depletion solution conc: salt-uptake solution [polyol]: proportion by weight of polyol in the solution [salt]: proportion by weight of the salts in the solution.
The selectivity of the salt transport is described by the current yield, i.e. the actual amount of salt transported (N
measured in mole) divided by the maximum possible amount (Ntheoretical) which can be transported by means of the electric charge transport (electric current).
Nmeasured~Ntheoretical In the salt removal from the alcoholic solution, a current yield of over 95% can be achieved despite the high salt content.
The electrodialysis apparatus used in the process of the invention may employ commercially available electrodialysis modules fitted with likewise commercially available anion and cation exchange membranes. Here, the anion exchange membrane may have to be selected according to the criteria: a) low resistance, b) high selectivity in respect of the anion and c) low solvent flux.
The electrodialysis apparatus preferably has a Salt-depletion circuit 14 and a salt-uptake circuit 15, as shown in Figure 1.
The mixture (which is typically an aqueous solution) 5 of polyfunctional alcohols and salts, as is formed, for example, as crude product from the base-catalyzed aldol addition of a relatively long chain aliphatic aldehyde and a shorter-chain aliphatic aldehyde and subsequent Cannizzaro reaction in the presence of stoichiometric amounts of base (e. g. alkali metal 10 hydroxide), can be fed directly to the salt-depletion circuit of an electrodialysis apparatus as shown in Figure 1. The concentration of the individual components in the mixture is immaterial, as long as the mixture is pumpable. It is preferable, however, that the concentration of the polyfunctional alcohols is from about 5 to 80, more preferably 30 to 60% by weight and the concentration of the salt is from about 2 to 40, more preferably 5 to 20% by weight. An overall concentration is preferably 10-90% by weight.
The pH of the solution to be depleted in salt may be adjusted to an approximately neutral value by means of an acid or a base (preferably the same base which has been used for the preparation of the polyols). Acidic or alkaline pH values are possible as long as this does not affect the stability of the membranes. Preference is given to pH values in the range from 4 to 10.
The upper temperature limit for the solution to the depleted in salt is determined by the stability of the ion exchange membranes; the lower temperature limit is determined by the viscosity or the pumpability of the medium. However, the temperature is preferably set to a value in the range from 10 to 50°C. Account needs to be taken of the fact that the salt-depletion solution heats up during the separation process.
US-A 2468718 describes a process for separating methylolalkanes from water-soluble salts by extraction of the methylolalkanes using a low-boiling, water-soluble ketone.
Ullmann, Volume 7, 4th edition, p.231 (1974) describes the work-up of the mixture of polyols and salts by extraction with solvents such as amyl alcohol, cyclohexanol or ethyl acetate and subsequent distillation of the polyols. However, these extraction methods require the use of large amounts of extractants which have to be removed afterwards. This gives intensely colored products which contain many by-products and, mainly because of their disadvantageous color, have to be subjected to a further distillation.
The removal of the by-products is important because these would lead to insuperable problems in the subsequent applications. Thus, in the coatings application, colored by-products have an adverse effect on the reproducibility of the coatings. In addition, salt residues adversely affect possible further reactions of the polyfunctional alcohols, e.g. in the preparation of the corresponding esters.
It is likewise possible to concentrate the mixture of polyols and salts and to crystallize the salts (CN-A-1076185).
However, this process also gives colored products. Furthermore, considerable amounts of polyols remain in the crystallized material and can be washed out only with significant losses in yield.
It is an object of the present invention to provide an improved process for separating polyfunctional alcohols from water-soluble salts in aqueous systems which can be carried out inexpensively, i.e. with a low consumption of energy, which makes do without the use of solvents and can thus be carried out in an environmentally friendly manner and which gives colorless polyols which can be further processed directly without further purification steps.
Attempting to achieve this object, the invention provides a process for separating polyols from water-soluble salts in aqueous systems by subjecting aqueous systems to electro dialysis, with the proviso that the polyols do not include trimethylolpropane.
Figure 1 is a diagrammatic view of an electrodialysis view of an electrodialysis apparatus that may be used for carrying out a particularly preferred embodiment of the process according to the present invention; and Figures 2 to 5 are graphs showing the current and voltage curves and conductivity changes in Salt-depletion and Salt-uptake solutions employed in the working examples.
The polyols are water-soluble and may also be called as polyfunctional alcohols hereinunder. However, "poly-functional alcohols" may not be completely accurate since polyphenols are also included.
Those polyols that can be used according to the invention include:
a) diols of the formula HO-R1-OH, where R1 is:
1. a linear saturated aliphatic unit, preferably containing 2 to 10 carbon atoms, such as -C2H4-, -C3H6-, -C4Hg-or -C6H12- (e. g. ethylene glycol, 1,2- or 1,3-propylene glycol and 1,2-, 1,3- or 1,4-butanediol), 2. a linear unsaturated aliphatic unit, preferably containing 4 to 10 carbon atoms, such as -C4H6-, -C4H4- or -C6H10- (e. g. 2,3-butene-1,4-diol, 2,3-butyne-1,4-diol and 2,3-or 3,4-hexene-1,6-diol), 3. a branched saturated aliphatic unit, preferably containing 3 to 10 carbon atoms, such as -C4Hg-, -C5H10- or -C6H12- (e. g. 2-methyl-propane-1,2-diol, 2-methylpropane-1,3-diol, 2,2-dimethylpropane-1,3-diol, 2-methylbutane-1,2-diol, 2-methylbutane-1,3-diol, 2-methylbutane-1,4-diol, 2,3-dimethylbutane-1,2-diol, 2,3-dimethylbutane-1,4-diol, 2,2-dimethylbutane-1,3-diol and 2,2-dimethylbutane-1,4-diol), 4. a branched unsaturated aliphatic unit, preferably containing 5 to 10 carbon atoms, such as -CSHg- or -C6H10- (e. g.
2-methyl-2,3-butene-1,4-diol and 2,2-dimethyl-3,4-pentene-1,5-diol), 5. a cylic saturated aliphatic or alicyclic unit, preferably containing 3 to 10 carbon atoms such as -C5H10-, -C6H12- or -C~H14- (e. g. 1,2-cyclopentane-diol, 1,3-cyclopentanediol, 1,2-cyclohexanediol, 1,3-cyclohexanediol and 1-methyl-1,2-cyclopent-anediol), 6. a cyclic unsaturated aliphatic or alicyclic unit, preferably having 5 to 10 carbon atoms, such as -CSHg-, -C6H10-or -C~H12- (e. g. 1,2-cyclopentene-3,4-diol, 1,2-cyclopentene-3,5-diol, 1,2-cyclo-hexene-3,4-diol, 1,2-cyclohexene-3,5-diol, 1,2-cyclohexene-4,5-diol, 1,2-cyclohexene-3,6-diol, 1,2,3,4-cyclohexadiene-5,6-diol and 1-methyl-1,2-cyclopentenediol), 7. an aromatic carbocyclic unit, preferably a phenylene unit optionally substituted by a lower alkyl group, such as -C6H4- or -C6H3(CH3)- (e. g. 1,2-dihydroxybenzene, 1,3-dihydroxybenzene, 1,2-dihydroxy-3-methylbenzene and 1,3-dihydroxy-2-methylbenzene), where further substituents may also be present on the aromatic ring system or on alicyclic side chains, 8. an aromatic heterocyclic unit, preferably a pyridine unit, such as -C5H3N- (e.g. 2,4-dihydroxypyridine), or 9. a unit comprising a combination of the above-mentioned units (a) 1-8;
b) monoglycerides of the formula: CH20Rr-CHORs-CH20Rt, where two of the groups Rr, Rs and Rt are each hydrogen and the other group is a saturated or unsaturated monocarboxylic acid residue having from 1 to 22 carbon atoms, e.g. CH20H-CHOH-CH20-CO-5 C17H35%
c) oligomeric and polymeric ether diols of the formula:
HO-[(CR2R3)n-0]m-H, where n >_ 2 and m >_ 2, preferably n is 2, 3 or 4 and m is 2-100, where R2 and R3 are each, independently of one another, hydrogen or an aliphatic group such as -CH3 or -C2H5 (preferably, (CR2R3)n is -CH2CH2- or -CH2CH(CH3)-);
examples include HO-CH2-CH2-O-CH2-CH2-OH (diethylene glycol), HO[CH2CH20]3pH (polyethylene glycol having a mean molecular weight of 1338) and HO [CH2CH (CH3) 0] 3pH (polypropylene glycol having a mean molecular weight of 1758);
d) triols and higher-functional polyols of the formula:
R4(OH)x where x >_ 3, preferably x is 3-6, and R4 is:
1. a linear saturated aliphatic unit, preferably having 3-10 carbon atoms, such as -C3H5-, -C4H7-, -C5H9- or -CSHg-(e.g. glycerol, 1,2,3-butanetriol, 1,2,4-butanetriol and 1,2,3-pentanetriol), 2. a linear unsaturated aliphatic unit, preferably having 5-10 carbon atoms, such as -C5H7-, -C6H9- or -C6Hg (e.g. 1-pentene-3,4,5-triol, 1-hexene-3,4,5-triol, 2-hexene-1,4,5-triol and 3-hexene-1,2,5,6-tetrol), 3. a branched saturated aliphatic unit, preferably having 4 to 10 carbon atoms, such as -C4H7- or -CSHg-(e. g. 2-methyl-1,2,3-propanetriol and pentaerythritol), 4. a branched unsaturated aliphatic unit, preferably having 5 to 10 carbon atoms, such as -C5H7- or -C6H9-(e.g. 2-methylol-2-butene-1,4-diol and 2-methylol-2-pentene-1,5-diol), 5. a saturated alicyclic or cyclic aliphatic unit, preferably having 5 to 10 carbon atoms, such as -C5H7-, -C6Hg-, -C6H8- or -C7H11- (e. g. 1,2,3-cyclopentanetriol, 1,2,3-cyclohexanetriol, 1,2,3,4-cyclohexanetetrol, 6-methyl-1,2,3-cyclohexanetriol and 6-methylol-1,3-cyclohexanediol), 6. an unsaturated alicyclic or cyclic aliphatic unit, preferably having 5 to 10 carbon atoms, such as -C5H5- or -C6H7-(e. g. cyclopentene-3,4,5-triol and cyclohexene-3,4,5-triol), 7. an aromatic carbocyclic unit, preferably a benzene unit optionally substituted by a lower alkyl group, such as -C6H3- or -C6H2(CH3)- (e. g. 1,2,3-trihydroxybenzene and 2,3,4-trihydroxytoluene), 8. an aromatic heterocyclic unit, preferably a pyridine unit, such as -C5H2N-(e.g. 2,3,4- trihydroxypyridine), or 9. a unit comprising a combination of the above-mentioned units (d) 1-8; and e) polymeric polyfunctional alcohols such as polyvinyl alcohol, polysaccharides and branched or dendrimer-like polyether polyols having, for example, the following structure:
HO-[CHz-CH2-O]d CH2\ / CHZ [O-CH2-CH2] a OH
C
2 0 HO-[CHz-CH2-O] f CH2 ~ CH2 [O-CH2-CH2]g OH
where d, e, f and g are, independently of one another, an integer >_ 1, preferably 1-10.
The use of electrodialysis for desalination of sea water, for brine recovery, for obtaining drinking water, for regulating the hardness of water, for desalination of whey in the food industry, for preventing cream of tartar deposits in wine production or for recovering valuable materials from waste solutions from electrolytic processes is known (Rompp Chemie Lexikon, Volume 2, 10th edition, pp. 1113-1114 (1997)).
However, these applications, always involve aqueous systems having a relatively low salt content (< 5% by weight).
Electrodialysis is a separation process in which the migration of ions through a permeation-selective membrane is accelerated by application of a direct current (DC) voltage. In electrodialysis, ions are transported through a membrane under the action of an electric field. If ion exchange membranes are installed in the dialysis apparatus in such a way that anion exchange membranes and cation exchange membranes are arranged alternately between a cathode and an anode and divide a cell into narrow chambers, appropriate connection of the chambers gives streams which are depleted in salt and enriched in salt, since when current is passed through the apparatus, the cations can only pass through the cation exchange membranes and the anions can only pass through the anion exchange membranes. The enrichment occurs against the concentration gradient. This means that connection of a plurality of anion- and cation-selective ion exchange membranes in series makes it possible to deionize the liquid to be dialysed while simultaneously increasing the concentration of the ions in the concentrate chambers.
In contrast to the other known membrane processes such as membrane filtration, reverse osmosis or gas permeation, in which the fluids are separated as a result of pressure or concentration differences, electrodialysis enables a separating force acting in a targeted way to be applied by means of the electric current. In this way, charged constituents can be moved selectively in the solution. The ion exchange membranes used for the separation are organic polymer membranes having functional, charge-bearing groups and act similarly to an electrical rectifier. Ion exchange membranes allow passage of only one type of ion, while the oppositely charged ions are prevented from passing through. The construction of an electrodialysis module corresponds approximately to that of a chamber filter press, i.e. two or three solutions are fed separately into the module frame via internal feed channels and then flow, separated from one another by the ion exchange membranes, through the respective hollow spaces in the frame.
Under the action of the applied electric potential, ions are transported from the individual chambers through the ion exchange membranes. Appropriate connection in series of anion exchange membranes (A) and ration exchange membranes (K), i.e.
membranes which allow either only anions or only rations to pass through, makes it possible for solutions to be reduced in salt content or concentrated or for undesired ions to be replaced by others.
An example of an apparatus which can be used according to the invention for separating polyfunctional alcohols from water-soluble salts is shown in Figure 1. The apparatus consists of an electrodialysis module having three separate circuits (a salt-depletion or salt-releasing circuit 14, a salt-uptake or salt-accepting circuit 15 and an electrode-flushing or electrode-rinse circuit 16) and the associated reservoirs 17, 18 and 19. In order to achieve a large membrane surface, five successive cell units were installed.
In Figure 1:
M or M+ = metal ions, X or X - anions, Polyol - poly-functional alcohol, K = ration exchange membrane and A = anion exchange membrane.
To remove the reaction gases formed at the electrodes, an Electrode-flushing solution may preferably be passed through the end chambers. This electrode-flushing solution, if used, should be inert toward the electrodes, have a low electrical resistance and release no extraneous ions into the salt-uptake and salt-depletion circuits.
It has now surprisingly been found that electrodialysis can likewise be used for separating a mixture of water-soluble polyols and water-soluble salts dissolved therein, even if the salts are present in high concentration (> 50°s by weight). High selectivities (S > 250) can be achieved in such a process.
The selectivity of the separation between the originally salt-containing and then salt-depleted solution and the concentrated solution in respect of the neutral component polyfunctional alcohol is defined as for other membrane processes:
S = ( [polyol] conc [salt] conc) ~ ( [polyol] dil [salt] dil) where: dil: salt-depletion solution conc: salt-uptake solution [polyol]: proportion by weight of polyol in the solution [salt]: proportion by weight of the salts in the solution.
The selectivity of the salt transport is described by the current yield, i.e. the actual amount of salt transported (N
measured in mole) divided by the maximum possible amount (Ntheoretical) which can be transported by means of the electric charge transport (electric current).
Nmeasured~Ntheoretical In the salt removal from the alcoholic solution, a current yield of over 95% can be achieved despite the high salt content.
The electrodialysis apparatus used in the process of the invention may employ commercially available electrodialysis modules fitted with likewise commercially available anion and cation exchange membranes. Here, the anion exchange membrane may have to be selected according to the criteria: a) low resistance, b) high selectivity in respect of the anion and c) low solvent flux.
The electrodialysis apparatus preferably has a Salt-depletion circuit 14 and a salt-uptake circuit 15, as shown in Figure 1.
The mixture (which is typically an aqueous solution) 5 of polyfunctional alcohols and salts, as is formed, for example, as crude product from the base-catalyzed aldol addition of a relatively long chain aliphatic aldehyde and a shorter-chain aliphatic aldehyde and subsequent Cannizzaro reaction in the presence of stoichiometric amounts of base (e. g. alkali metal 10 hydroxide), can be fed directly to the salt-depletion circuit of an electrodialysis apparatus as shown in Figure 1. The concentration of the individual components in the mixture is immaterial, as long as the mixture is pumpable. It is preferable, however, that the concentration of the polyfunctional alcohols is from about 5 to 80, more preferably 30 to 60% by weight and the concentration of the salt is from about 2 to 40, more preferably 5 to 20% by weight. An overall concentration is preferably 10-90% by weight.
The pH of the solution to be depleted in salt may be adjusted to an approximately neutral value by means of an acid or a base (preferably the same base which has been used for the preparation of the polyols). Acidic or alkaline pH values are possible as long as this does not affect the stability of the membranes. Preference is given to pH values in the range from 4 to 10.
The upper temperature limit for the solution to the depleted in salt is determined by the stability of the ion exchange membranes; the lower temperature limit is determined by the viscosity or the pumpability of the medium. However, the temperature is preferably set to a value in the range from 10 to 50°C. Account needs to be taken of the fact that the salt-depletion solution heats up during the separation process.
The solution to be depleted in salt is introduced into an electrodialysis cell. When the apparatus of Figure 1 is used, the solution is introduced into the salt-depletion circuit.
The salt-uptake solution in the salt-uptake circuit of the electrodialysis apparatus shown in Figure 1 is preferably water or an aqueous salt solution. The pH of the salt-uptake solution is preferably set to a value in the range from 4 to 10 and the temperature of the solution is preferably in the range from 10 to 50°C. In this case too, the upper concentration limit for the medium is determined by the pumpability of the solution.
It is also important that the solubility product of the anions and cations which permeate through the membranes is not exceeded in the salt-uptake solution. Salt deposits in the salt-uptake circuit can lead to irreversible damage to the entire apparatus, in particular to the membranes.
The current density during electrodialysis is preferably in the range from 50 to 750 A/m2, particularly preferably in the range from 150 to 250 A/m2. The current yield can be over 95% under optimum process conditions. The limiting current density must be matched to the salt concentration in the mixture from which salts are to be removed and can easily be determined by a person skilled in the art. The limiting current density as a function of concentration thus determines the regulation of the current density during the separation process.
Electrode-flushing solutions are preferably used in the electrodialysis apparatus used according to the invention, as shown in Figure 1. The electrode-flushing solutions ensure that no reaction of the electrodes with the materials in the solution takes place, that gases formed in the electrode reaction can be removed and that the electrical resistance is reduced by a high conductivity and the energy consumption of the electrode reaction is thus minimized. The electrode-flushing solution should, if possible, comprise the same cations as the other salt solutions in order to avoid introduction of further rations into the process. Aqueous solutions of inorganic salts can be used as electrode-flushing solutions.
The course of the separation process can be followed via the conductivity of the salt-depletion and salt-uptake solutions. The conductivity has to be correlated with the analytically determined contents of polyol or salt, i.e. for a given conductivity, the actual concentration of polyol. By-products and salt may be determined by means of other analytical methods (e.g. high performance liquid chromatography (HPLC), gas chromatography (GC)). In general, it is sufficient to carry out electrodialysis until the conductivity of the salt-depletion solution has dropped to about 2 uS/cm. The result is an aqueous solution of the polyfunctional alcohols substantially free of the salts. The cleaning of the overall electrodialysis module depends on the separation task. For example, flushing the module with warm deionized water for about 2 hours every two weeks may be sufficient for cleaning the system.
In the base-catalyzed reaction (e. g. using potassium hydroxide or sodium hydroxide) of relatively long-chain aliphatic aldehydes (e. g. butyraldehyde) with shorter-chain aliphatic aldehydes (e.g. formaldehyde), the polyols are not obtained as pure substances, but, depending on the process conditions, as a mixture of the respective target product with the dimers of the target product and further OH-functional compounds as well as the corresponding salt of the acid from the Cannizzaro reaction. if this crude product is desalted by means of electrodialysis, there remains an aqueous, colorless solution of the polyol mixture which can be subjected as such or in concentrated form, without further purification processes, to further reactions, for example condensation reactions such as esterifications with, for example, oleic acid for producing lubricants or with acrylic acid for producing coating additives.
The salt-uptake solution in the salt-uptake circuit of the electrodialysis apparatus shown in Figure 1 is preferably water or an aqueous salt solution. The pH of the salt-uptake solution is preferably set to a value in the range from 4 to 10 and the temperature of the solution is preferably in the range from 10 to 50°C. In this case too, the upper concentration limit for the medium is determined by the pumpability of the solution.
It is also important that the solubility product of the anions and cations which permeate through the membranes is not exceeded in the salt-uptake solution. Salt deposits in the salt-uptake circuit can lead to irreversible damage to the entire apparatus, in particular to the membranes.
The current density during electrodialysis is preferably in the range from 50 to 750 A/m2, particularly preferably in the range from 150 to 250 A/m2. The current yield can be over 95% under optimum process conditions. The limiting current density must be matched to the salt concentration in the mixture from which salts are to be removed and can easily be determined by a person skilled in the art. The limiting current density as a function of concentration thus determines the regulation of the current density during the separation process.
Electrode-flushing solutions are preferably used in the electrodialysis apparatus used according to the invention, as shown in Figure 1. The electrode-flushing solutions ensure that no reaction of the electrodes with the materials in the solution takes place, that gases formed in the electrode reaction can be removed and that the electrical resistance is reduced by a high conductivity and the energy consumption of the electrode reaction is thus minimized. The electrode-flushing solution should, if possible, comprise the same cations as the other salt solutions in order to avoid introduction of further rations into the process. Aqueous solutions of inorganic salts can be used as electrode-flushing solutions.
The course of the separation process can be followed via the conductivity of the salt-depletion and salt-uptake solutions. The conductivity has to be correlated with the analytically determined contents of polyol or salt, i.e. for a given conductivity, the actual concentration of polyol. By-products and salt may be determined by means of other analytical methods (e.g. high performance liquid chromatography (HPLC), gas chromatography (GC)). In general, it is sufficient to carry out electrodialysis until the conductivity of the salt-depletion solution has dropped to about 2 uS/cm. The result is an aqueous solution of the polyfunctional alcohols substantially free of the salts. The cleaning of the overall electrodialysis module depends on the separation task. For example, flushing the module with warm deionized water for about 2 hours every two weeks may be sufficient for cleaning the system.
In the base-catalyzed reaction (e. g. using potassium hydroxide or sodium hydroxide) of relatively long-chain aliphatic aldehydes (e. g. butyraldehyde) with shorter-chain aliphatic aldehydes (e.g. formaldehyde), the polyols are not obtained as pure substances, but, depending on the process conditions, as a mixture of the respective target product with the dimers of the target product and further OH-functional compounds as well as the corresponding salt of the acid from the Cannizzaro reaction. if this crude product is desalted by means of electrodialysis, there remains an aqueous, colorless solution of the polyol mixture which can be subjected as such or in concentrated form, without further purification processes, to further reactions, for example condensation reactions such as esterifications with, for example, oleic acid for producing lubricants or with acrylic acid for producing coating additives.
If the polyfunctional alcohols are nevertheless to be isolated from the mixture as pure substances, distillative separation methods can be used.
The following examples illustrate the invention.
Examples Various highly concentrated, aqueous solutions of polyfunctional alcohols having a correspondingly high salt content were worked up. A mixture of alcohol, salt and water was placed in the salt-depletion circuit. The uptake phase initially contained a small amount of the salt to be separated off in order to produce a certain minimum conductivity. The electrode-flushing solutions were selected for the respective application according to the above-described criteria. In general, they were intermediate-concentration solutions of the same salts which were to be removed from the aqueous alcohol solution.
The alcohols used were diols: (ethanediol (ethylene glycol), 1,4-butane-diol, diethylene glycol), . triols: (glycerol, neopentyl glycol, pentaerythritol) and also two polyalcohols (polyvinyl alcohol, polyethylene alcohol) having a mean molecular weight of about 1500 g/mol.
Apart from these aliphatic alcohols, 1,3-dihydroxybenzene (resorcinol) was additionally studied as an example of a polyhydric aromatic alcohol.
In each case, a 40% strength solution was prepared, provided that the solubility of the alcohol in water permitted this. Only in the case of pentaerythritol was it only possible to make a 65 strength solution. The salt content varied from 5 to 20%, the remainder was then water. The salts were inorganic salts such as NaCl and Na2S04 or sodium and potassium salts of short-chain and relatively long-chain organic acids (potassium acetate, sodium formate and also the sodium salt of 2-ethyl-caproic acid).
Table 1 Alcohols Salts Name Abbreviation Name Abbreviation Ethanediol A1 Sodium S1 chloride 1,4-Butanediol A2 Potassium S2 acetate Diethylene A3 Sodium S3 glycol sulfate Glycerol A4 Sodium S4 formate Neopentyl A5 Sodium salt S5 glycol of 2-ethyl-caproic acid Pentaerythritol A6 1,3-Dihydroxy- A~
benzene Polyethylene A$
glycol Polyvinyl A9 alcohol The apparatus shown in Figure l~comprised an 5 electrodialysis module from Stantech provided with three separate circuits and the associated reservoirs. Five successive cell units were installed in the module which had an effective membrane area of 100 cm2. The membranes used, namely C66-10F* and AHA-2*, came from tokuyama Soda.
10 The precise proportions by weight together with the corresponding combinations of alcohol, salt and water are shown in Table 2.
*Trade-mark Table 2 Alcohol M(alcohol) w(alcohol) Salt M(salt) w(salt) Water g/mol % g/mol 0 0 A1 62 40.0 S1 58.5 12 48.00 A2 90 40.0 S2 98.0 20 40.00 A3 106 38.6 S3 146.0 5 56.37 A8 1500 40.0 Sl 58.5 12 48.00 A5 104 40.0 S4 68.0 14 46.00 A4 92 40.0 S5 167.0 5 55.00 A6 136 6.0 S4 68.0 14 80.00 A7 110 36.6 S3 146.0 16.5 46.90 -A9 20,000 5.0 S1 58.5 5 90.00 Initial concentrations in percent by weight and molar masses of the alcohol/salt solutions studied.
The concentrations of the electrode-flushing solutions were loo for the Na2S04 solution and 20s for the K2C03 and Na2C03 solutions. They are indicated in Table 3 together with the corresponding alcohols and salts in the solution from which salt is to be removed. In place of chlorides which would be reduced to elemental chlorine in the electrode reaction, carbonates were used in the flushing solutions.
Table 3 Depletion Anode Cathode Circuit Alcohol Salt Salt o Salt s A1 Sl Na2C03 20 Na2C03 20 A3 S3 Na2COq 10 Na2SOq 10 A8 S1 Na2C03 20 Na2C03 20 A5 S4 Na2C03 20 Na2C03 20 A4 S5 Na2C03 20 Na2C03 20 A6 S4 Na2C03 20 Na2C03 20 A7 S3 Na2SOg 10 Na2SOq 10 A9 S1 Na2C03 20 Na2C03 20 Composition and concentration of the electrode-flushing solutions together with the alcohols and salts in the depletion circuit.
Figures 2 to 5 show, by way of example, the current and voltage curves and the conductivity changes in the salt-depletion and salt-uptake solutions for the removal of Sl from A8.
The concentrated salt/alcohol solution is in the depletion circuit and the dilute salt solution is in the uptake circuit. As soon as a voltage is applied to the electrodes, an electric current flows as a result of ion conduction.
At a constant voltage, the current steadily decreases as a result of the decrease in conductivity of the depletion circuit. The increase in the conductivity of the uptake circuit has no influence of the current, since when resistances are connected in series it is the greatest resistance which effectively determines the overall behavior.
Since the mass transport is proportional to the electric transport, the decrease in the conductivity in the depletion circuit also becomes smaller as a result of the decreasing current. The experiment is continued until virtually no change occurs in the conductivity, i.e. all salts have been transported from the depletion circuit to the uptake circuit.
The jump in the conductivity in the uptake circuit results from the temperature fluctuations when the experiment was interrupted overnight.
The changes in the salt concentrations in the two circuits are shown in Table 4 for all experiments. Apart from the desalting of A7, all solutions tested could be desalted very well. The lowest concentration achievable at the end is thus only a question of time, i.e. how long the current has to flow.
Table 4 Alcohol Concentrate Depletion Solution Initial Final Initial Final Salt o o Salt o $
A1 S1 1.00 10.17 S1 12.0 0.0100 A2 S2 0.98 19.09 S2 20.0 0.9200 A3 S3 1.50 4.57 S3 5.0 0.0010 A8 Sl 1.00 9.9 S1 12.0 0.1270 A5 S4 0.68 13.3 S4 14.0 0.0650 A4 S5 2.00 6.82 S5 5.0 0.0720 A6 S4 0.68 8.57 S4 14.0 0.0206 A7 S3 1.50 4.25 S3 16.5 15.2300 A9 Sl 1.00 5.59 S1 5.0 0.0380 Initial and final concentrations in the salt-depletion circuit and the salt-uptake circuit The selectivity of the salt transport is described by the current yield ~, i.e. the actual amount of salt transported (Nmeasured in mol) divided by the maximum possible amount (Ntheoretical) which can be transported by means of the electric charge transport (electric current):
~ = Nmeasured~Ntheoretical The current yield can be calculated from the measured concentrations and the amounts employed and the charge which has passed through (integral of current x time) by accurate balancing. With the exception of A7 which has already been mentioned, it is from 0.8 to almost 1Ø In the desalting of A3 and A5, values of only about 0.6 were achieved.
Chemicals used Ethanediol (ethylene Technical 99.9% HUls glycol) grade 1,4-Butanediol Technical Huls Grade Diethylene glycol >99.9% Riedel-de Haen PEO (MW about 1500 Pure Fluka g/mol Neopentyl glycol Pure >98.Oo Fluka Glycerol AR 99.5% Anhydrous Pentaerythritol Pure >97.Oo Fluka 1,3-Dihydroxybenzene Pure >98.Oo Fluka (resorcinol) Polyvinyl alcohol Wacker Polyviol NaCl AR Merck Potassium acetate AR Fluka Na2S04 Technical >99.9o Riedel-de Haen Sodium salt of 2-ethyl-caproic acid (Fluka);
the sodium salt was prepared in situ by neutralization of the acid with NaOH
Sodium formate AR Fluka Fluka Chemie AG, Industriestr. 25, CH-9471 Buchs Riedel-de Haen Laborchemikalien GmbH & Co. KG, D-30918 Seelze Merck KGaA, Frankfurter Str. 250, D-64293 Darmstadt blacker-Chemie GmbH, Hanns-Seidel-Platz 4, D-81737 Munich
The following examples illustrate the invention.
Examples Various highly concentrated, aqueous solutions of polyfunctional alcohols having a correspondingly high salt content were worked up. A mixture of alcohol, salt and water was placed in the salt-depletion circuit. The uptake phase initially contained a small amount of the salt to be separated off in order to produce a certain minimum conductivity. The electrode-flushing solutions were selected for the respective application according to the above-described criteria. In general, they were intermediate-concentration solutions of the same salts which were to be removed from the aqueous alcohol solution.
The alcohols used were diols: (ethanediol (ethylene glycol), 1,4-butane-diol, diethylene glycol), . triols: (glycerol, neopentyl glycol, pentaerythritol) and also two polyalcohols (polyvinyl alcohol, polyethylene alcohol) having a mean molecular weight of about 1500 g/mol.
Apart from these aliphatic alcohols, 1,3-dihydroxybenzene (resorcinol) was additionally studied as an example of a polyhydric aromatic alcohol.
In each case, a 40% strength solution was prepared, provided that the solubility of the alcohol in water permitted this. Only in the case of pentaerythritol was it only possible to make a 65 strength solution. The salt content varied from 5 to 20%, the remainder was then water. The salts were inorganic salts such as NaCl and Na2S04 or sodium and potassium salts of short-chain and relatively long-chain organic acids (potassium acetate, sodium formate and also the sodium salt of 2-ethyl-caproic acid).
Table 1 Alcohols Salts Name Abbreviation Name Abbreviation Ethanediol A1 Sodium S1 chloride 1,4-Butanediol A2 Potassium S2 acetate Diethylene A3 Sodium S3 glycol sulfate Glycerol A4 Sodium S4 formate Neopentyl A5 Sodium salt S5 glycol of 2-ethyl-caproic acid Pentaerythritol A6 1,3-Dihydroxy- A~
benzene Polyethylene A$
glycol Polyvinyl A9 alcohol The apparatus shown in Figure l~comprised an 5 electrodialysis module from Stantech provided with three separate circuits and the associated reservoirs. Five successive cell units were installed in the module which had an effective membrane area of 100 cm2. The membranes used, namely C66-10F* and AHA-2*, came from tokuyama Soda.
10 The precise proportions by weight together with the corresponding combinations of alcohol, salt and water are shown in Table 2.
*Trade-mark Table 2 Alcohol M(alcohol) w(alcohol) Salt M(salt) w(salt) Water g/mol % g/mol 0 0 A1 62 40.0 S1 58.5 12 48.00 A2 90 40.0 S2 98.0 20 40.00 A3 106 38.6 S3 146.0 5 56.37 A8 1500 40.0 Sl 58.5 12 48.00 A5 104 40.0 S4 68.0 14 46.00 A4 92 40.0 S5 167.0 5 55.00 A6 136 6.0 S4 68.0 14 80.00 A7 110 36.6 S3 146.0 16.5 46.90 -A9 20,000 5.0 S1 58.5 5 90.00 Initial concentrations in percent by weight and molar masses of the alcohol/salt solutions studied.
The concentrations of the electrode-flushing solutions were loo for the Na2S04 solution and 20s for the K2C03 and Na2C03 solutions. They are indicated in Table 3 together with the corresponding alcohols and salts in the solution from which salt is to be removed. In place of chlorides which would be reduced to elemental chlorine in the electrode reaction, carbonates were used in the flushing solutions.
Table 3 Depletion Anode Cathode Circuit Alcohol Salt Salt o Salt s A1 Sl Na2C03 20 Na2C03 20 A3 S3 Na2COq 10 Na2SOq 10 A8 S1 Na2C03 20 Na2C03 20 A5 S4 Na2C03 20 Na2C03 20 A4 S5 Na2C03 20 Na2C03 20 A6 S4 Na2C03 20 Na2C03 20 A7 S3 Na2SOg 10 Na2SOq 10 A9 S1 Na2C03 20 Na2C03 20 Composition and concentration of the electrode-flushing solutions together with the alcohols and salts in the depletion circuit.
Figures 2 to 5 show, by way of example, the current and voltage curves and the conductivity changes in the salt-depletion and salt-uptake solutions for the removal of Sl from A8.
The concentrated salt/alcohol solution is in the depletion circuit and the dilute salt solution is in the uptake circuit. As soon as a voltage is applied to the electrodes, an electric current flows as a result of ion conduction.
At a constant voltage, the current steadily decreases as a result of the decrease in conductivity of the depletion circuit. The increase in the conductivity of the uptake circuit has no influence of the current, since when resistances are connected in series it is the greatest resistance which effectively determines the overall behavior.
Since the mass transport is proportional to the electric transport, the decrease in the conductivity in the depletion circuit also becomes smaller as a result of the decreasing current. The experiment is continued until virtually no change occurs in the conductivity, i.e. all salts have been transported from the depletion circuit to the uptake circuit.
The jump in the conductivity in the uptake circuit results from the temperature fluctuations when the experiment was interrupted overnight.
The changes in the salt concentrations in the two circuits are shown in Table 4 for all experiments. Apart from the desalting of A7, all solutions tested could be desalted very well. The lowest concentration achievable at the end is thus only a question of time, i.e. how long the current has to flow.
Table 4 Alcohol Concentrate Depletion Solution Initial Final Initial Final Salt o o Salt o $
A1 S1 1.00 10.17 S1 12.0 0.0100 A2 S2 0.98 19.09 S2 20.0 0.9200 A3 S3 1.50 4.57 S3 5.0 0.0010 A8 Sl 1.00 9.9 S1 12.0 0.1270 A5 S4 0.68 13.3 S4 14.0 0.0650 A4 S5 2.00 6.82 S5 5.0 0.0720 A6 S4 0.68 8.57 S4 14.0 0.0206 A7 S3 1.50 4.25 S3 16.5 15.2300 A9 Sl 1.00 5.59 S1 5.0 0.0380 Initial and final concentrations in the salt-depletion circuit and the salt-uptake circuit The selectivity of the salt transport is described by the current yield ~, i.e. the actual amount of salt transported (Nmeasured in mol) divided by the maximum possible amount (Ntheoretical) which can be transported by means of the electric charge transport (electric current):
~ = Nmeasured~Ntheoretical The current yield can be calculated from the measured concentrations and the amounts employed and the charge which has passed through (integral of current x time) by accurate balancing. With the exception of A7 which has already been mentioned, it is from 0.8 to almost 1Ø In the desalting of A3 and A5, values of only about 0.6 were achieved.
Chemicals used Ethanediol (ethylene Technical 99.9% HUls glycol) grade 1,4-Butanediol Technical Huls Grade Diethylene glycol >99.9% Riedel-de Haen PEO (MW about 1500 Pure Fluka g/mol Neopentyl glycol Pure >98.Oo Fluka Glycerol AR 99.5% Anhydrous Pentaerythritol Pure >97.Oo Fluka 1,3-Dihydroxybenzene Pure >98.Oo Fluka (resorcinol) Polyvinyl alcohol Wacker Polyviol NaCl AR Merck Potassium acetate AR Fluka Na2S04 Technical >99.9o Riedel-de Haen Sodium salt of 2-ethyl-caproic acid (Fluka);
the sodium salt was prepared in situ by neutralization of the acid with NaOH
Sodium formate AR Fluka Fluka Chemie AG, Industriestr. 25, CH-9471 Buchs Riedel-de Haen Laborchemikalien GmbH & Co. KG, D-30918 Seelze Merck KGaA, Frankfurter Str. 250, D-64293 Darmstadt blacker-Chemie GmbH, Hanns-Seidel-Platz 4, D-81737 Munich
Claims (18)
1. A process for separating a water-soluble polyol from a water-soluble salt in an aqueous solution thereof, which comprises subjecting the aqueous solution to electrodialysis, with the proviso that the polyol does not include trimethylolpropane.
2. The process as claimed in claim 1, wherein the polyol is selected from the group consisting of diols, oligomeric or polymeric ether diols, triols and higher-functional alcohols and poymeric polyfunctional alcohols.
3. The process as claimed in claim 1, wherein the polyol is a diol represented by the following formula:
(where R1 is a linear saturated aliphatic unit, a linear unsaturated aliphatic unit, a branched saturated aliphatic unit, a branched unsaturated aliphatic unit, a saturated cyclic aliphatic unit, an unsaturated cyclic aliphatic unit, an aromatic carbocyclic unit, an aromatic heterocyclic unit or a combination of these units).
(where R1 is a linear saturated aliphatic unit, a linear unsaturated aliphatic unit, a branched saturated aliphatic unit, a branched unsaturated aliphatic unit, a saturated cyclic aliphatic unit, an unsaturated cyclic aliphatic unit, an aromatic carbocyclic unit, an aromatic heterocyclic unit or a combination of these units).
4. The process as claimed in claim 1, wherein the polyol is monoglyceride having the following formula:
CH2OR r-CHOR s-CH2OR t (where two of R r, R s and R t are a hydrogen atom and the other is a saturated or unsaturated monocarboxylic acid residue having 1 to 22 carbon atoms).
CH2OR r-CHOR s-CH2OR t (where two of R r, R s and R t are a hydrogen atom and the other is a saturated or unsaturated monocarboxylic acid residue having 1 to 22 carbon atoms).
5. The process as claimed in claim 1, wherein the polyol is an oligomeric or polymeric ether diol represented by the following formula:
HO-[(CR2R3)n-O]m-H
(where n ~ 2 and m ~ 2, and R2 and R3 are each, independently of one another, a hydrogen atom or an aliphatic group).
HO-[(CR2R3)n-O]m-H
(where n ~ 2 and m ~ 2, and R2 and R3 are each, independently of one another, a hydrogen atom or an aliphatic group).
6. The process as claimed in claim 5, wherein (CR2R3)n is CH2CH2 or CH2CH(CH3).
7. The process as claimed in claim 1, wherein the polyol is a triol or higher-functional polyol represented by the following formula:
R4 (OH) x (where x ~ 3, and R4 is a linear saturated aliphatic unit, a linear unsaturated aliphatic unit, a branched saturated aliphatic unit, a branched unsaturated aliphatic unit, a saturated cyclic aliphatic unit, an unsaturated cyclic aliphatic unit, an aromatic carbocyclic unit, a heterocyclic aromatic unit or a combination of these units).
R4 (OH) x (where x ~ 3, and R4 is a linear saturated aliphatic unit, a linear unsaturated aliphatic unit, a branched saturated aliphatic unit, a branched unsaturated aliphatic unit, a saturated cyclic aliphatic unit, an unsaturated cyclic aliphatic unit, an aromatic carbocyclic unit, a heterocyclic aromatic unit or a combination of these units).
8. The process as claimed in claim 1, wherein the polyol a is polymeric polyfunctional alcohol selected from the group consisting of polyvinyl alcohol, polysaccharides and poyether polyols of the following formula:
(wherein d, e, f and g are, independently of one another, an integer ~ 1).
(wherein d, e, f and g are, independently of one another, an integer ~ 1).
9. The process as claimed in any one of claims 1 to 8, wherein the salt and the polyol are present in an amount up to their respective saturation concentration in the aqueous solution.
10. The process as claimed in any one of claims 1 to 9, wherein the electrodialysis is carried out at a temperature in the range from 10 to 50°C.
11. The process as claimed in any one of claims 1 to 10, wherein the electrodialysis is carried out at a pH in the range from 4 to 10.
12. The process as claimed in claim 11, wherein the electrodialysis is carried out at a pH of about 7.
13. The process as claimed in any one of claims 1 to 12, wherein the electrodialysis is carried out at a current density in the range from 50 to 750 A/m2.
14. The process as claimed in claim 13, wherein the electrodialysis is carried out a current density in the range from 150 to 250 A/m2.
15. The process as claimed in any one of claims 1 to 14, wherein the aqueous solution used for the separation by means of electrodialysis is subjected to filtration beforehand.
16. The process as claimed in any one of claims 1 to 9, wherein the electodialysis is carried out by:
using an apparatus, having (a) a cell, (b) a cathode, (c) an anode, (d) at least one pair of anion-exchange and cation-exchange membranes which divide the cell into chambers, (e) a salt-depletion circuit which is connected to the chamber and in which a salt-depletion solution is to be circulated and (f) a salt-uptake circuit which is connected to the chamber other than the one to which the salt-depletion circuit is connected and in which a salt-uptake solution is to be circulated;
introducing the aqueous solution of the water-soluble polyol and the water-soluble salt into the cell through the salt-depletion circuit as an initial salt-depletion solution having a pH of 4 to 10 and a temperature of 10 to 50°C; and applying a direct current voltage to the cathode and the anode so as to accelerate migration of the ions through the anion-exchange and cation-exchange membranes, while circulating the salt-depletion solution in the salt-depletion circuit and circulating the salt-uptake solution in the salt-uptake circuit, wherein the salt-uptake solution is originally water or an aqueous salt solution having a pH of from 4 to 10 and a temperature of 10 to 50°C, until conductivity of the salt-depletion solution has dropped to 2 µS/cm, whereby obtaining an aqueous solution of the polyol substantially free of the salt.
using an apparatus, having (a) a cell, (b) a cathode, (c) an anode, (d) at least one pair of anion-exchange and cation-exchange membranes which divide the cell into chambers, (e) a salt-depletion circuit which is connected to the chamber and in which a salt-depletion solution is to be circulated and (f) a salt-uptake circuit which is connected to the chamber other than the one to which the salt-depletion circuit is connected and in which a salt-uptake solution is to be circulated;
introducing the aqueous solution of the water-soluble polyol and the water-soluble salt into the cell through the salt-depletion circuit as an initial salt-depletion solution having a pH of 4 to 10 and a temperature of 10 to 50°C; and applying a direct current voltage to the cathode and the anode so as to accelerate migration of the ions through the anion-exchange and cation-exchange membranes, while circulating the salt-depletion solution in the salt-depletion circuit and circulating the salt-uptake solution in the salt-uptake circuit, wherein the salt-uptake solution is originally water or an aqueous salt solution having a pH of from 4 to 10 and a temperature of 10 to 50°C, until conductivity of the salt-depletion solution has dropped to 2 µS/cm, whereby obtaining an aqueous solution of the polyol substantially free of the salt.
17. The process as claimed in claim 16, wherein the aqueous solution of the water-soluble polyol and the water-soluble salt has a concentration of the polyol of 5 to 80% by weight and a concentration of the salt of 2 to 40% by weight, provided that an overall concentration is 10 to 90% by weight.
18. The process as claimed in claim 16 or 17, wherein the water soluble salt is an inorganic salt or a sodium or potassium salt of an organic acid.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19838425A DE19838425A1 (en) | 1998-08-24 | 1998-08-24 | Process for the separation of polyfunctional alcohols from water-soluble salts from aqueous systems |
| DE19838425.4 | 1998-08-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2280535A1 true CA2280535A1 (en) | 2000-02-24 |
Family
ID=7878544
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002280535A Abandoned CA2280535A1 (en) | 1998-08-24 | 1999-08-20 | Process for separating polyfunctional alcohols from water-soluble salts in aqueous systems |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0982283A3 (en) |
| JP (1) | JP2000086558A (en) |
| BR (1) | BR9903888A (en) |
| CA (1) | CA2280535A1 (en) |
| DE (1) | DE19838425A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2198947A1 (en) * | 2008-12-22 | 2010-06-23 | Aquafuel Research Limited | Purification of alcohols |
| WO2012084926A1 (en) * | 2010-12-21 | 2012-06-28 | Ge Healthcare As | Desalination of a composition comprising a contrast agent |
Families Citing this family (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3671917B2 (en) * | 2002-02-08 | 2005-07-13 | 日産自動車株式会社 | Fuel cell system |
| JP2005279433A (en) * | 2004-03-29 | 2005-10-13 | Kurita Water Ind Ltd | Adhesive-containing wastewater treatment method |
| GB2437516A (en) * | 2006-04-26 | 2007-10-31 | Bai Leng | Method and apparatus for purifying glycerine using filter membranes and a deionisation means |
| FR2913974A1 (en) * | 2007-03-19 | 2008-09-26 | Arkema France | GLYCEROL VAPORIZATION PROCESS |
| CN101249385B (en) * | 2007-11-27 | 2010-07-21 | 江南大学 | Method for purifying ampholytic surface active agent with electric dialyze desalination |
| DE102008060888A1 (en) * | 2008-12-09 | 2010-06-10 | Evonik Stockhausen Gmbh | A process for producing acrolein comprising the processing of a crude glycerol phase |
| US9132387B2 (en) | 2011-12-13 | 2015-09-15 | Basf Se | Process for working-up a reaction mixture comprising polyether polyol |
| JP2015500383A (en) * | 2011-12-13 | 2015-01-05 | ビーエーエスエフ ソシエタス・ヨーロピアＢａｓｆ Ｓｅ | Post-treatment method of reaction mixture containing polyether polyol |
| CN105062124B (en) * | 2014-08-10 | 2017-01-25 | 海门江海建设投资有限公司 | System for rapidly extracting pigments from rhododendron simsii planch flowers |
| CN106147290B (en) * | 2014-08-10 | 2017-11-24 | 嵊州北航投星空众创科技有限公司 | A kind of equipment for rapid extraction azalea pigment |
| CN105001667B (en) * | 2014-08-10 | 2016-10-26 | 重庆雅香美源生态农业科技有限公司 | The system of rapid extraction natural plant pigment |
| CN107857693A (en) * | 2017-10-26 | 2018-03-30 | 仇春松 | Saliferous mixes the refinement recovery system and method for alcohol |
| CN113307722B (en) * | 2021-06-15 | 2022-08-16 | 青岛科技大学 | Method for separating neopentyl glycol and sodium formate by continuous method |
| CN114920626B (en) * | 2022-06-07 | 2023-11-28 | 上海师范大学 | Efficient separation method of phenol hydroxylation reaction liquid |
Family Cites Families (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2865822A (en) * | 1956-04-30 | 1958-12-23 | Warren Petroleum Corp Inc | Method for deionizing aqueous pentaerythritol solutions |
| JPS519016B1 (en) * | 1971-06-07 | 1976-03-23 | ||
| US3779883A (en) * | 1972-11-03 | 1973-12-18 | Sybron Corp | Pentaerythritol purification process |
| JPS5453683A (en) * | 1977-10-06 | 1979-04-27 | Tokuyama Soda Co Ltd | Neutralizing method for organic compound solution |
| US4427507A (en) * | 1982-03-22 | 1984-01-24 | Shell Oil Company | Process for the separation of glycol from an electrolyte-containing aqueous solution |
| JPS60149595A (en) * | 1984-01-14 | 1985-08-07 | Taito Kk | High-temperature desalting of saccharide solution by electrodialysis using polyvinyl alcohol diaphragm |
| US4599178A (en) * | 1984-07-16 | 1986-07-08 | Shell Oil Company | Recovery of glycerine from saline waters |
| SE8601772L (en) * | 1986-04-18 | 1987-10-19 | Perstorp Ab | SET FOR MANUFACTURING A POLYAL ALCOHOL |
| DE3721474A1 (en) * | 1987-06-30 | 1989-01-12 | Huels Chemische Werke Ag | METHOD FOR PRODUCING HEXADIINE (2,4) -DIOL-1,6 |
| JPH08143659A (en) * | 1994-11-24 | 1996-06-04 | Mitsui Toatsu Chem Inc | Production of polyoxyalkylene polyol |
| GB9519975D0 (en) * | 1995-09-28 | 1995-11-29 | Davy Process Techn Ltd | Process |
-
1998
- 1998-08-24 DE DE19838425A patent/DE19838425A1/en not_active Withdrawn
-
1999
- 1999-08-13 EP EP99115960A patent/EP0982283A3/en not_active Withdrawn
- 1999-08-20 CA CA002280535A patent/CA2280535A1/en not_active Abandoned
- 1999-08-23 JP JP11236134A patent/JP2000086558A/en active Pending
- 1999-08-23 BR BR9903888-9A patent/BR9903888A/en not_active Application Discontinuation
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2198947A1 (en) * | 2008-12-22 | 2010-06-23 | Aquafuel Research Limited | Purification of alcohols |
| WO2012084926A1 (en) * | 2010-12-21 | 2012-06-28 | Ge Healthcare As | Desalination of a composition comprising a contrast agent |
| US9474808B2 (en) | 2010-12-21 | 2016-10-25 | Ge Healthcare As | Desalination of a composition comprising a contrast agent |
Also Published As
| Publication number | Publication date |
|---|---|
| EP0982283A2 (en) | 2000-03-01 |
| BR9903888A (en) | 2000-09-19 |
| DE19838425A1 (en) | 2000-03-02 |
| EP0982283A3 (en) | 2000-05-24 |
| JP2000086558A (en) | 2000-03-28 |
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