CA2280541A1 - Process for separating trimethylolpropane and water soluble salts from a solution - Google Patents
Process for separating trimethylolpropane and water soluble salts from a solution Download PDFInfo
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- CA2280541A1 CA2280541A1 CA 2280541 CA2280541A CA2280541A1 CA 2280541 A1 CA2280541 A1 CA 2280541A1 CA 2280541 CA2280541 CA 2280541 CA 2280541 A CA2280541 A CA 2280541A CA 2280541 A1 CA2280541 A1 CA 2280541A1
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C29/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring
- C07C29/74—Separation; Purification; Use of additives, e.g. for stabilisation
- C07C29/76—Separation; Purification; Use of additives, e.g. for stabilisation by physical treatment
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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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- 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
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A20/00—Water conservation; Efficient water supply; Efficient water use
- Y02A20/124—Water desalination
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Abstract
The invention relates to a process for separating trimethylol-propane and a water-soluble salt from a solution thereof using electrodialysis. The solution is typically a crude product originating from an aldol addition of formaldehyde to butyraldehyde followed by a Cannizzaro reaction in the presence of an alkali metal hydroxide and contains trimethylolpropane, hydroxy functional byproducts and an alkali metal formate. The process does not use an organic solvent and may produce trimethylolpropane that is not colored and can be processed directly without further purification.
Description
Process for separating trimethylolpropane and water-soluble salts from a solution The present invention relates to a process for separating trimethylolpropane and water-soluble salts from a solution.
Trimethyiolpropane- is a commercially available product and is used, for example, as heat-transfer medium, as antifreeze, as starting material in the preparation of synthetic resins (e.g. polyurethanes), in the preparation of additives for the coatings industry, as a plasticizer for plastics and as lubricants.
Trimethylolpropane is prepared industrially, for example, by base-catalyzed reaction (e.g. in the presence of potassium hydroxide solution or sodium hydroxide solution) of butyraldehyde with formaldehyde. This reaction produces stoichiometric amounts of the alkali metal salt of formic acid (e.g.
potassium formate or sodium formate). Since the alkali metal salts and alkaline earth metal salts of the lower homologs of organic acids are generally highly to very highly water soluble, they cannot be separated off simply from the equally highly water-soluble polyol (triol). A further com-plication is the tact that the pure substances also have a more or less high mutual solubility.
Various processes for the extraction of polyols and processes for crystallizing out salts have been proposed to separate off the water-soluble polyols from the likewise water-soluble salts.
In the case of extraction with solvents for the polyols, such as with amyl alcohol, cyclohexanol or various esters, large amounts of extraction medium are necessary which must then 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 with a low-boiling O.Z. 5347 water-soluble ketone.
Ullmann, volume 7, 4th edition, p. 231 (1974) states that the mixture of polyols and salts can be worked up by extraction with solvents, such as amyl alcohol, cyclohexanol or ethyl acetate, and subsequent distillation of the polyols. However, these extraction processes require the use of large amounts of solvents which must be subsequently removed. Tk~ese processes produce intensively colored products which comprise a multiplicity of byproducts and which, chiefly because o~ their adverse color, must be subjected to another distillation.
Separating off the byproducts is therefore of importance, because these byproducts would lead to uncontrollable interferences in the subsequent applications. Thus, colored byproducts, in the coatings application, adversely affect the reproducibility of the coatings. Furthermore, residues of salts interfere in the conversion of trimethylolpropane in subsequent reactions, e.g. in the preparation of trimethylolpropane esters. However, any byproducts which can be reacted in subsequent reactions of trimethylolpropane have an adverse effect on the properties, such as viscosity, of the trimethylolpropane reaction products.
It is likewise possible to concentrate the mixture of polyols and salts and crystallize out the salts (CN-A-1076185). However, colored products are obtained in this process also. In addition there is the fact that considerable amounts of polyols remain in the crystals, which polyois can only. be washed out with marked decreases in yield.
It is an object of the present invention to provide an improved process for separating trimethylolpropane and water-soluble salts from a solution-which can be carried out inexpensively, i.e. with low energy consumption, which succeeds without the use of solvents and can thus be carried out in an environmentally acceptable manner, and which produces a colorless triol which can be further processed directly without further purification pro-cesses. The term "triol" below includes trimethylolpropane (TMP) together O.Z. 5347 with hydrofunctional byproducts, such as di-TMP.
Attempting to achieve this object, the invention provides a process for separating trimethylolpropane and a water-soluble salt from a solution, by subjecting the solution to electro-dialysis.
The use of electrodialysis for seawater desalination, for brine production, for the production of drinking water, to regulate the degree of hardness of water, for desalting whey in the food industry, to prevent sedimentation of tartaric acid in winemaking or in the recovery of valuable substances from electro-chemical wastewaters is known (Rompp Chemie Lexikon [Rompp's Chemical Lexicon], 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 migration of ions through a permeation-selective membrane is accelerated by an applied direct current voltage. During the electro-dialysis, ions are transported through membranes by the action of an electric field. If, in the dialysis apparatus, ion exchange membranes are arranged in such a manner that an anion exchange membrane and a cation exchange membrane are altern-ately situated between a cathode and an anode and divide the cell into narrow chambers, with an appropriate connection, reduced-salt and increased-salt streams are obtained, since, during the passage of current, the cations can only pass through the cation-exchange membranes and the anions can only pass through the anion-exchange membranes. Enrichment occurs against the concentration gradient. That is to say, by con-necting in series a plurality of pairs of anion- and cation-selective ion-exchange membranes, the liquid to be dialysed can be deionized with simultaneous enrichment of ions in the O.Z. 5347 electrode cells.
Figure 1 shows a diagrammatic view of an electrodialysis apparatus which may be used for carrying out a preferred embodiment of the process according to the present invention.
It has now surprisingly been found that electrodialysis can likewise be used to separate an aqueous mixture of tri-methylolpropane and water-soluble salts, even if the salts are present at high concentration (> 50% by weight). High selectivities (S > 250) may be achieved in this process.
The selectivity of separation between the originally salt-containing and subsequently desalted solution and the con-centrated solution with respect to the neutral component polyol is defined as with other membrane processes:
S = ( [polyol] conc (salt] conc) ~ ( LPolyol] dil Lsalt] dil) where: dil: is the salt-releasing solution conc: is the salt-accepting solution [polyol]: is the content by weight of polyol in the solution [salt]: is the content by weight of salts in the solution The selectivity of salt transport is described by current efficiency, i.e. the amount of salt actually transported (Nmeasured in moles) relative to the maximum amount possible due to the electrical charge transport (electrical current) (Ntheoretical) according to the following equation:
Nmeasured~Ntheoretical O.Z. 5347 When the triol solution is desalted, despite the high salt content, a current efficiency of above 95% can be achieved.
The electrodialysis apparatus used in the process according to the invention may be any commercially available electro-dialysis modules fitted with likewise commercially available anion- and cation-exchange membranes. Preferably, in this case, the anion-exchange membrane may be selected according to the criteria: a) low resistance, b) high selectivity relative to the anion and c) low solvent flow.
The electrodialysis apparatus may include a salt-releasing or salt-deletion circuit (solid line) 14 and a salt-accepting (or salt-uptake) circuit (dotted line) 15, as shown in Figure 1, each connected to a narrow chamber of the cell. In the electrodialysis apparatus shown in Figure 1, three cation-exchange membranes (K) and two anion-exchange membranes (A) are placed alternately in the cell to form narrow chambers each connected to the salt-releasing circuit 14 or the salt-accepting circuit 15.
The mixture of polyol and salts, as is formed, for example, as crude product from the base-catalyzed aldol addition of butyraldehyde to formaldehyde and subsequent Cannizzaro reaction in the presence of stoichiometric amounts of base (e.g. alkali metal hydroxide), can be fed directly to the salt-releasing circuit of an electrodialysis apparatus according to Figure 1. It is unimportant here how high the concentration of the individual components in the mixture is, provided that the mixture is pumpable. Certainly in general, the higher the concentration, the higher the separation cost.
Preferably, the mixture has a concentration of all the components of from about 20 to about 85% more. Preferably, from about 55 to about 80% by weight. In a typical crude O.Z. 5347 product of the aldol addition - Cannizzaro reactions, the concentration of polyol is from about 25 to 50% and that of salts is from about 20 to 40% by weight. The pH of the salt-releasing solution is adjusted to be approximately neutral with an acid, preferably with formic acid, or a base, pre-ferably with the same base which was used in the preparation of the triol, e.g. alkali metal hydroxide. Acidic or alkaline pHs are possible, provided that the stability of the membranes is not impaired by this. Preference is given to pHs in the range from 4 to 10.
The upper temperature limit of the salt-releasing solution is determined by the stability of the ion-exchange membranes; the lower temperature limit is determined by the viscosity or pumpability of the medium. However, the temperature is pre-ferably set to a value in the range from 10 to 50°C.
Consideration must be paid here to the fact that the salt-releasing solution heats up during the separation process.
The salt-accepting solution in the salt-accepting circuit of the electrodialysis apparatus preferably consists of water or an aqueous salt solution. The pH of the salt-accepting solution is preferably adjusted 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 also, the upper concentration limit of the medium is determined by the pump-ability of the solution. It is also of importance that the solubility product of the membrane-permeating anions and cations in the salt-accepting solution is not exceeded. Salt sediments in the salt-accepting circuit can lead to irreversible damage to the entire apparatus, in particular to the membranes.
The current density in the electrodialysis is preferably in the range from 50 to 750 A/m2, particularly preferably in the O.Z. 5347 _ 7 _ range from 150 to 250 A/m2, Under optimum process conditions, the current efficiency can be more than 95%. The limiting current density must be matched to the salt concentration in the mixture to be desalted and can readily be determined by those skilled in the art. The limiting current density as a function of concentration thus determines the control of the current density during the separation process.
In the electrodialysis apparatus used according to the invention, an electrode rinse solution 11 is preferably used, as shown in Figure 1 through an electrode rinse circuit 16.
The electrode rinse solution ensures that the electrodes do not react with substances in the solution, that gases produced in the electrode reaction can be discharged, and that, owing to high conductivity, electrical resistance is decreased and thus energy consumption of the electrode reaction is minimized. The electrode rinse solution should preferably contain the same cations as the other salt solutions, in order to prevent penetration of other cations into the process. As the electrode rinse solution, use may be made of an aqueous solution of an inorganic salt.
The course of the separation process can be followed via the conductivity of the salt-releasing 12 and salt-accepting solutions 13. The conductivity is correlated to the analytically determined contents of triol or salt, i.e. at a given conductivity, using other analytical methods (e. g. high-performance liquid chromatography, HPLC, gas chromatography, GC), the actual concentration of trimethylolpropane, by-products and salt may be determined. It is generally sufficient to carry out the electrodialysis until the conductivity of the salt-releasing solution has fallen to about 2 ~S/cm. At this stage, the salts have been sub-stantially, entirely accumulated in the salt-accepting solution and the salt-releasing solution has become an aqueous O.Z. 5347 _ g _ solution of substantially solely triol. The cleaning of the entire electrodialysis module depends on the separation task.
To clean the system, it is, for example, sufficient to rinse the module with warm deionized water for about 2 hours every two weeks.
In the case of the base-catalyzed reaction (e. g. with potassium hydroxide solution or sodium hydroxide solution) of butyraldehyde with formaldehyde, trimethylolpropane is produced, not as a pure substance, but, depending on the process procedure, as a mixture with small amounts of di-DMP
and other hydroxyfunctional compounds in addition to the corresponding formate salt from the Cannizzaro reaction. If this crude product is desalted by electrodialysis, an aqueous colorless solution of the polyol mixture remains which can be subjected, as such or in concentrated form without further purification processes, to other reactions, e.g. condensation reactions, such as esterifications with carboxylic acids such as oleic acid, for example, for the preparation of lubricants, or with acrylic acid for the preparation of coating additives.
If, nevertheless, the trimethylolpropane is to be isolated as pure substance from the mixture, methods for separation by distillation are available.
The following examples illustrate the invention.
Example 1:
Triol synthesis, KOH route, continuous A nitrogen-flushed 100 ml jacketed flask 1 is cooled to +10°C.
This flask is fitted with 3 feeds and one outlet to a further 500 ml vacuum flask 2. The outlet of flask 1 is mounted in such a manner that a liquid level of 40 ml can be maintained.
Over a period of 150 minutes, 80 g of freshly distilled O.Z. 5347 butyraldehyde, 275.68 g of formalin solution (38.34% by weight) and 130.87 g of KOH solution (48.99% by weight) are then metered in simultaneously. In the course of this, after approximately 15 minutes the liquid level reaches 40 ml in flask 1, so that when a low vacuum is applied, the reaction medium is continuously drawn into flask 2. During the process, the cooling is set in such a manner that the temperature of the reaction medium in flask 1 can be kept at approximately 32°C.
l0 Post-treatment of the entire contents of flask 2 over a period of 2.5 hours at 85°C, after addition of 3.6 g of hydrogen peroxide and subsequent neutralization with 2.4 g of KOH, gives trimethylolpropane (TMP) in a yield of 90% and potassium formate in a yield of 100%. In addition to the TMP, still higher-condensed alcohols are identified, of which the majority, 9%, arises as di-TMP.
O.Z. 5347 Example 2:
Triol synthesis, NaOH route, continuous A nitrogen-flushed-100 ml jacketed flask 1 is cooled to +10°C. This flask is fitted with 3 feeds and one outlet to a further 500 ml vacuum flask 2. The outlet of flask 1 is mounted in-such a manner that a liquid levea of 40 ml can be maintained. Over a period of 150 minutes, 80 g of freshly distilled butyraldehyde, 276.33 g of formalin solution (38.34% by weight) and 92.02 g of NaOH solution (49.67% by weight) are then added simultaneously. During this operation, after approximately 15 minutes, the liquid level reaches 40 ml in flask 1, so that when a low vacuum is applied, the reaction medium is continuously drawn into flask 2. During the process, the cooling is adjusted in such a manner that the temperature of the reaction medium in flask 1 can be kept at approximately 32 ° C.
Post-treatment of the entire contents of flask 2 over a period of 2.5 hours at 85°C, after addition of 3.6 g of hydrogen peroxide and subsequent neutrali-zation with 2.51 g of NaOH, gives trimethyfolpropane (TMP) in a yield of 90%
and sodium formate in a yield of 100%. In addition to the TMP, still higher-condensed alcohols are identified. of which the majority, 9%, arises as 2 0 di-TMP.
Example 3:
Separation of the crude solution from Example 1 In a laboratory module having an effective membrane area of 100 cmz, the reaction solution, which had been prepared in accordance with Example 1, consisting of 26.7% by weight potassium formate, 33.9% by weight of (tri-methylolpropane + more highly condensed alcohols) and water, was desalted by electrodialysis. The experimental setup consisted of five cell units and the O.Z. 5347 anode and cathode chambers. In the concentrate, a slightly dilute, purely aqueous potassium formate solution was introduced. In the anode circuit was situated a potassium carbonate solution. As membranes, use was made of Neosepta*AHA2 and C66 10F from Tokuyama Soda. .
During the experiment, owing to the decreasing conductivity in the desalting circuit, the cun-ent would fall from 2.73 A-to 0:3 A. Therefore, to maintain the current, the applied voltage was increased from 29 V (at the start of the experiment) to greater than 80 V (at the end of the experiment).
After an experimental period of 11 hours, the diluate circuit comprised 65.0%
by weight triol and 0.03% by weight potassium formate, and the concentrate circuit comprised 0.2% by weight triol and 27.4% by weight potassium formate.
Example 4:
Separation of a test solution In a further experiment, in the laboratory, in a larger test module having an effective membrane area of 375 cmz, a synthetic mixture of 33% by weight potassium formate, 44% by weight TMP and the remainder water was desalted. The stack stnacture consisted of three cell units and the anode and cathode chambers. During the experiment, the current, owing to the decrea-sing conductivity in the desalting circuit, would fall from 8 A to 1 A.
Therefore, to maintain the current, the applied voltage was increased from 10 V (at the beginning of the experiment) to 80 V (at the end of the experiment). For the separation, Neosepta AHA2 and C66 10F membranes from Tokuyama Soda were used; in the concentrate circuit, a dilute potassium formate solution was introduced and a potassium carbonate solution in the anode circuit.
In this experiment also, virtually all the potassium formate was separated off from the desalting circuit (from 32.3% by weight to 0.022% by weight). The current efficiency in this desalting was 89.1 %.
Trade-mark O.Z. 5347 In the course of the experiment, in addition, approximately 10 g of TMP were co-transported as neutral particles across the membranes. This means a TMP loss of approximately 1.95% by weight, based on the starting quantity.
The exact concentrations can be taken from the tables below.
Table 1: Electrodialysis data for_Example 4:
Salt=releaser -Salt-acce ptor Start End Start End Potassium g 401.6 0.15 0.3 398.9 formate 32.2 0.022 0.02 21.5 TMP g 527.2 487.39 0.08 10.3 42.3 69.453 0.006 0.5 H20 g 315.6 214.21 1383.7 1444.9 25.3 30.525 99.9 77.9 Total g 1244.4 436.98 1384.1 1698.8 Example 5:
Trios synthesis, KOH route, continuous, pilot scale 46 liters of softened drinking water are introduced into a circulation reactor having a circulation/discharge ratio of 10:1. Three separate feed streams of butyraldehyde at 6.0 kg/hour, formaldehyde solution (37.6% by weight) at 21.0 kg/hour and potassium hydroxide solution (50% by weight) at 9.3 kg/hour are then started simultaneously. By means of a water cooling device, the start temperature is kept between 17 ° C and 19 ° C
and the reac-tion temperature during the 4.5 hour reaction is kept at < 29°C. 192 kg of the ZO triol thus produced are heated to 70°C to 75°C under nitrogen and with stirring and stirred for a further 2.5 hours at this temperature. After addition of 20 kg of hydrogen peroxide (40% by weight), the reaction mixture was _ O. Z. 5347 cooled overnight, the pH being neutral (7.2).
Example 6:
Separation of the crude solution from Example 5 In a 4-chamber electrodiaiysis module (4 x 100 I) having a cathode circuit (dilute potassium formate solution) and an anode circuit. (potassium sulfate solution) as well as diluate and concentrate circuits, . a volume of crude solution or water was introduced in accordance with the- #ollowing table.
When the pump circuits were opened; care was taken to ensure that the pressure difference either side of the membranes (Neosepta AHA2 and C66 10F membranes from Tokuyama Soda) was no more than 0.2 bar. All circuits were operated at a pressure of 0.7 to 0.8 bar and a flow rate of 400 I/hour. The maximum voltage was 40 V. The temperature increased to a maximum of 45°C. In the course of 20 hours, operations were carried out up to a conductivity in the diluate of 2 mS/cm.
Table 2: Electrodialysis data for Example 6:
Salt-releaser Salt-acce ptor Start End Start End Potassium kg 11.91 0.077 0.03 10.84 formate 17.0 0.19 0.075 16.2 TMP kg 7.84 7.84 0.008 0.528 11.2 19.6 0.02 0.8 H20 kg 45.92 30.53 39.96 55.0 65.6 75.95 99.9 82.3 Total kg 70.0 40.2 40.0 66.8 Trade-mark O.Z. 5347 Example 7:
Esterification with oleic acid of the triol from Example 6 612 g of triol from Example 6 (120 g dry) are first dehydrated via a film evaporator under reduced pressure at a maximum bottom temperature of 90°C. The remaining colorless viscous substance is admixed with 658.8 g of rapeseed oil acid (MW 280 ) and heated in an N2 stream. After 2 hours, at a bottom temperature of 210°C, 37.4 g of distillate are collected, after 3.5 hours at a bottom temperature of 270°C, 45.3 g of distillate are collected and after a further 0.5 hours at a bottom temperature of 280°C and a vacuum of 30 mbar, in total 49.8 g-of distillate are collected. 726.9 g of oleic acid triol ester are present in the reaction vessel as a clear light brown liquid.
Example 8:
Esterification with acrylic acid of the triol from Example 6 1224 g of triol from Example 6 (240 g dry) are dehydrated as in Example 7.
The remaining triol is dissolved with- 373 g of acrylic acid and 0.414 g of hydroquinone monomethyl ether in 207.2 g of toluene. After addition of 8.3 g of toluenesulfonic acid monohydrate and passing through air and heating, water is distilled off azeotropically. After 8 hours, 86.5 g of distillate water were produced. The crude product of the triester is washed twice alkaline and twice neutral as a toluene solution and then the toluene phase is freed from the solvent by distillation. 591 g of trio) triacrylate were obtained.
O.Z. 5347
Trimethyiolpropane- is a commercially available product and is used, for example, as heat-transfer medium, as antifreeze, as starting material in the preparation of synthetic resins (e.g. polyurethanes), in the preparation of additives for the coatings industry, as a plasticizer for plastics and as lubricants.
Trimethylolpropane is prepared industrially, for example, by base-catalyzed reaction (e.g. in the presence of potassium hydroxide solution or sodium hydroxide solution) of butyraldehyde with formaldehyde. This reaction produces stoichiometric amounts of the alkali metal salt of formic acid (e.g.
potassium formate or sodium formate). Since the alkali metal salts and alkaline earth metal salts of the lower homologs of organic acids are generally highly to very highly water soluble, they cannot be separated off simply from the equally highly water-soluble polyol (triol). A further com-plication is the tact that the pure substances also have a more or less high mutual solubility.
Various processes for the extraction of polyols and processes for crystallizing out salts have been proposed to separate off the water-soluble polyols from the likewise water-soluble salts.
In the case of extraction with solvents for the polyols, such as with amyl alcohol, cyclohexanol or various esters, large amounts of extraction medium are necessary which must then 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 with a low-boiling O.Z. 5347 water-soluble ketone.
Ullmann, volume 7, 4th edition, p. 231 (1974) states that the mixture of polyols and salts can be worked up by extraction with solvents, such as amyl alcohol, cyclohexanol or ethyl acetate, and subsequent distillation of the polyols. However, these extraction processes require the use of large amounts of solvents which must be subsequently removed. Tk~ese processes produce intensively colored products which comprise a multiplicity of byproducts and which, chiefly because o~ their adverse color, must be subjected to another distillation.
Separating off the byproducts is therefore of importance, because these byproducts would lead to uncontrollable interferences in the subsequent applications. Thus, colored byproducts, in the coatings application, adversely affect the reproducibility of the coatings. Furthermore, residues of salts interfere in the conversion of trimethylolpropane in subsequent reactions, e.g. in the preparation of trimethylolpropane esters. However, any byproducts which can be reacted in subsequent reactions of trimethylolpropane have an adverse effect on the properties, such as viscosity, of the trimethylolpropane reaction products.
It is likewise possible to concentrate the mixture of polyols and salts and crystallize out the salts (CN-A-1076185). However, colored products are obtained in this process also. In addition there is the fact that considerable amounts of polyols remain in the crystals, which polyois can only. be washed out with marked decreases in yield.
It is an object of the present invention to provide an improved process for separating trimethylolpropane and water-soluble salts from a solution-which can be carried out inexpensively, i.e. with low energy consumption, which succeeds without the use of solvents and can thus be carried out in an environmentally acceptable manner, and which produces a colorless triol which can be further processed directly without further purification pro-cesses. The term "triol" below includes trimethylolpropane (TMP) together O.Z. 5347 with hydrofunctional byproducts, such as di-TMP.
Attempting to achieve this object, the invention provides a process for separating trimethylolpropane and a water-soluble salt from a solution, by subjecting the solution to electro-dialysis.
The use of electrodialysis for seawater desalination, for brine production, for the production of drinking water, to regulate the degree of hardness of water, for desalting whey in the food industry, to prevent sedimentation of tartaric acid in winemaking or in the recovery of valuable substances from electro-chemical wastewaters is known (Rompp Chemie Lexikon [Rompp's Chemical Lexicon], 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 migration of ions through a permeation-selective membrane is accelerated by an applied direct current voltage. During the electro-dialysis, ions are transported through membranes by the action of an electric field. If, in the dialysis apparatus, ion exchange membranes are arranged in such a manner that an anion exchange membrane and a cation exchange membrane are altern-ately situated between a cathode and an anode and divide the cell into narrow chambers, with an appropriate connection, reduced-salt and increased-salt streams are obtained, since, during the passage of current, the cations can only pass through the cation-exchange membranes and the anions can only pass through the anion-exchange membranes. Enrichment occurs against the concentration gradient. That is to say, by con-necting in series a plurality of pairs of anion- and cation-selective ion-exchange membranes, the liquid to be dialysed can be deionized with simultaneous enrichment of ions in the O.Z. 5347 electrode cells.
Figure 1 shows a diagrammatic view of an electrodialysis apparatus which may be used for carrying out a preferred embodiment of the process according to the present invention.
It has now surprisingly been found that electrodialysis can likewise be used to separate an aqueous mixture of tri-methylolpropane and water-soluble salts, even if the salts are present at high concentration (> 50% by weight). High selectivities (S > 250) may be achieved in this process.
The selectivity of separation between the originally salt-containing and subsequently desalted solution and the con-centrated solution with respect to the neutral component polyol is defined as with other membrane processes:
S = ( [polyol] conc (salt] conc) ~ ( LPolyol] dil Lsalt] dil) where: dil: is the salt-releasing solution conc: is the salt-accepting solution [polyol]: is the content by weight of polyol in the solution [salt]: is the content by weight of salts in the solution The selectivity of salt transport is described by current efficiency, i.e. the amount of salt actually transported (Nmeasured in moles) relative to the maximum amount possible due to the electrical charge transport (electrical current) (Ntheoretical) according to the following equation:
Nmeasured~Ntheoretical O.Z. 5347 When the triol solution is desalted, despite the high salt content, a current efficiency of above 95% can be achieved.
The electrodialysis apparatus used in the process according to the invention may be any commercially available electro-dialysis modules fitted with likewise commercially available anion- and cation-exchange membranes. Preferably, in this case, the anion-exchange membrane may be selected according to the criteria: a) low resistance, b) high selectivity relative to the anion and c) low solvent flow.
The electrodialysis apparatus may include a salt-releasing or salt-deletion circuit (solid line) 14 and a salt-accepting (or salt-uptake) circuit (dotted line) 15, as shown in Figure 1, each connected to a narrow chamber of the cell. In the electrodialysis apparatus shown in Figure 1, three cation-exchange membranes (K) and two anion-exchange membranes (A) are placed alternately in the cell to form narrow chambers each connected to the salt-releasing circuit 14 or the salt-accepting circuit 15.
The mixture of polyol and salts, as is formed, for example, as crude product from the base-catalyzed aldol addition of butyraldehyde to formaldehyde and subsequent Cannizzaro reaction in the presence of stoichiometric amounts of base (e.g. alkali metal hydroxide), can be fed directly to the salt-releasing circuit of an electrodialysis apparatus according to Figure 1. It is unimportant here how high the concentration of the individual components in the mixture is, provided that the mixture is pumpable. Certainly in general, the higher the concentration, the higher the separation cost.
Preferably, the mixture has a concentration of all the components of from about 20 to about 85% more. Preferably, from about 55 to about 80% by weight. In a typical crude O.Z. 5347 product of the aldol addition - Cannizzaro reactions, the concentration of polyol is from about 25 to 50% and that of salts is from about 20 to 40% by weight. The pH of the salt-releasing solution is adjusted to be approximately neutral with an acid, preferably with formic acid, or a base, pre-ferably with the same base which was used in the preparation of the triol, e.g. alkali metal hydroxide. Acidic or alkaline pHs are possible, provided that the stability of the membranes is not impaired by this. Preference is given to pHs in the range from 4 to 10.
The upper temperature limit of the salt-releasing solution is determined by the stability of the ion-exchange membranes; the lower temperature limit is determined by the viscosity or pumpability of the medium. However, the temperature is pre-ferably set to a value in the range from 10 to 50°C.
Consideration must be paid here to the fact that the salt-releasing solution heats up during the separation process.
The salt-accepting solution in the salt-accepting circuit of the electrodialysis apparatus preferably consists of water or an aqueous salt solution. The pH of the salt-accepting solution is preferably adjusted 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 also, the upper concentration limit of the medium is determined by the pump-ability of the solution. It is also of importance that the solubility product of the membrane-permeating anions and cations in the salt-accepting solution is not exceeded. Salt sediments in the salt-accepting circuit can lead to irreversible damage to the entire apparatus, in particular to the membranes.
The current density in the electrodialysis is preferably in the range from 50 to 750 A/m2, particularly preferably in the O.Z. 5347 _ 7 _ range from 150 to 250 A/m2, Under optimum process conditions, the current efficiency can be more than 95%. The limiting current density must be matched to the salt concentration in the mixture to be desalted and can readily be determined by those skilled in the art. The limiting current density as a function of concentration thus determines the control of the current density during the separation process.
In the electrodialysis apparatus used according to the invention, an electrode rinse solution 11 is preferably used, as shown in Figure 1 through an electrode rinse circuit 16.
The electrode rinse solution ensures that the electrodes do not react with substances in the solution, that gases produced in the electrode reaction can be discharged, and that, owing to high conductivity, electrical resistance is decreased and thus energy consumption of the electrode reaction is minimized. The electrode rinse solution should preferably contain the same cations as the other salt solutions, in order to prevent penetration of other cations into the process. As the electrode rinse solution, use may be made of an aqueous solution of an inorganic salt.
The course of the separation process can be followed via the conductivity of the salt-releasing 12 and salt-accepting solutions 13. The conductivity is correlated to the analytically determined contents of triol or salt, i.e. at a given conductivity, using other analytical methods (e. g. high-performance liquid chromatography, HPLC, gas chromatography, GC), the actual concentration of trimethylolpropane, by-products and salt may be determined. It is generally sufficient to carry out the electrodialysis until the conductivity of the salt-releasing solution has fallen to about 2 ~S/cm. At this stage, the salts have been sub-stantially, entirely accumulated in the salt-accepting solution and the salt-releasing solution has become an aqueous O.Z. 5347 _ g _ solution of substantially solely triol. The cleaning of the entire electrodialysis module depends on the separation task.
To clean the system, it is, for example, sufficient to rinse the module with warm deionized water for about 2 hours every two weeks.
In the case of the base-catalyzed reaction (e. g. with potassium hydroxide solution or sodium hydroxide solution) of butyraldehyde with formaldehyde, trimethylolpropane is produced, not as a pure substance, but, depending on the process procedure, as a mixture with small amounts of di-DMP
and other hydroxyfunctional compounds in addition to the corresponding formate salt from the Cannizzaro reaction. If this crude product is desalted by electrodialysis, an aqueous colorless solution of the polyol mixture remains which can be subjected, as such or in concentrated form without further purification processes, to other reactions, e.g. condensation reactions, such as esterifications with carboxylic acids such as oleic acid, for example, for the preparation of lubricants, or with acrylic acid for the preparation of coating additives.
If, nevertheless, the trimethylolpropane is to be isolated as pure substance from the mixture, methods for separation by distillation are available.
The following examples illustrate the invention.
Example 1:
Triol synthesis, KOH route, continuous A nitrogen-flushed 100 ml jacketed flask 1 is cooled to +10°C.
This flask is fitted with 3 feeds and one outlet to a further 500 ml vacuum flask 2. The outlet of flask 1 is mounted in such a manner that a liquid level of 40 ml can be maintained.
Over a period of 150 minutes, 80 g of freshly distilled O.Z. 5347 butyraldehyde, 275.68 g of formalin solution (38.34% by weight) and 130.87 g of KOH solution (48.99% by weight) are then metered in simultaneously. In the course of this, after approximately 15 minutes the liquid level reaches 40 ml in flask 1, so that when a low vacuum is applied, the reaction medium is continuously drawn into flask 2. During the process, the cooling is set in such a manner that the temperature of the reaction medium in flask 1 can be kept at approximately 32°C.
l0 Post-treatment of the entire contents of flask 2 over a period of 2.5 hours at 85°C, after addition of 3.6 g of hydrogen peroxide and subsequent neutralization with 2.4 g of KOH, gives trimethylolpropane (TMP) in a yield of 90% and potassium formate in a yield of 100%. In addition to the TMP, still higher-condensed alcohols are identified, of which the majority, 9%, arises as di-TMP.
O.Z. 5347 Example 2:
Triol synthesis, NaOH route, continuous A nitrogen-flushed-100 ml jacketed flask 1 is cooled to +10°C. This flask is fitted with 3 feeds and one outlet to a further 500 ml vacuum flask 2. The outlet of flask 1 is mounted in-such a manner that a liquid levea of 40 ml can be maintained. Over a period of 150 minutes, 80 g of freshly distilled butyraldehyde, 276.33 g of formalin solution (38.34% by weight) and 92.02 g of NaOH solution (49.67% by weight) are then added simultaneously. During this operation, after approximately 15 minutes, the liquid level reaches 40 ml in flask 1, so that when a low vacuum is applied, the reaction medium is continuously drawn into flask 2. During the process, the cooling is adjusted in such a manner that the temperature of the reaction medium in flask 1 can be kept at approximately 32 ° C.
Post-treatment of the entire contents of flask 2 over a period of 2.5 hours at 85°C, after addition of 3.6 g of hydrogen peroxide and subsequent neutrali-zation with 2.51 g of NaOH, gives trimethyfolpropane (TMP) in a yield of 90%
and sodium formate in a yield of 100%. In addition to the TMP, still higher-condensed alcohols are identified. of which the majority, 9%, arises as 2 0 di-TMP.
Example 3:
Separation of the crude solution from Example 1 In a laboratory module having an effective membrane area of 100 cmz, the reaction solution, which had been prepared in accordance with Example 1, consisting of 26.7% by weight potassium formate, 33.9% by weight of (tri-methylolpropane + more highly condensed alcohols) and water, was desalted by electrodialysis. The experimental setup consisted of five cell units and the O.Z. 5347 anode and cathode chambers. In the concentrate, a slightly dilute, purely aqueous potassium formate solution was introduced. In the anode circuit was situated a potassium carbonate solution. As membranes, use was made of Neosepta*AHA2 and C66 10F from Tokuyama Soda. .
During the experiment, owing to the decreasing conductivity in the desalting circuit, the cun-ent would fall from 2.73 A-to 0:3 A. Therefore, to maintain the current, the applied voltage was increased from 29 V (at the start of the experiment) to greater than 80 V (at the end of the experiment).
After an experimental period of 11 hours, the diluate circuit comprised 65.0%
by weight triol and 0.03% by weight potassium formate, and the concentrate circuit comprised 0.2% by weight triol and 27.4% by weight potassium formate.
Example 4:
Separation of a test solution In a further experiment, in the laboratory, in a larger test module having an effective membrane area of 375 cmz, a synthetic mixture of 33% by weight potassium formate, 44% by weight TMP and the remainder water was desalted. The stack stnacture consisted of three cell units and the anode and cathode chambers. During the experiment, the current, owing to the decrea-sing conductivity in the desalting circuit, would fall from 8 A to 1 A.
Therefore, to maintain the current, the applied voltage was increased from 10 V (at the beginning of the experiment) to 80 V (at the end of the experiment). For the separation, Neosepta AHA2 and C66 10F membranes from Tokuyama Soda were used; in the concentrate circuit, a dilute potassium formate solution was introduced and a potassium carbonate solution in the anode circuit.
In this experiment also, virtually all the potassium formate was separated off from the desalting circuit (from 32.3% by weight to 0.022% by weight). The current efficiency in this desalting was 89.1 %.
Trade-mark O.Z. 5347 In the course of the experiment, in addition, approximately 10 g of TMP were co-transported as neutral particles across the membranes. This means a TMP loss of approximately 1.95% by weight, based on the starting quantity.
The exact concentrations can be taken from the tables below.
Table 1: Electrodialysis data for_Example 4:
Salt=releaser -Salt-acce ptor Start End Start End Potassium g 401.6 0.15 0.3 398.9 formate 32.2 0.022 0.02 21.5 TMP g 527.2 487.39 0.08 10.3 42.3 69.453 0.006 0.5 H20 g 315.6 214.21 1383.7 1444.9 25.3 30.525 99.9 77.9 Total g 1244.4 436.98 1384.1 1698.8 Example 5:
Trios synthesis, KOH route, continuous, pilot scale 46 liters of softened drinking water are introduced into a circulation reactor having a circulation/discharge ratio of 10:1. Three separate feed streams of butyraldehyde at 6.0 kg/hour, formaldehyde solution (37.6% by weight) at 21.0 kg/hour and potassium hydroxide solution (50% by weight) at 9.3 kg/hour are then started simultaneously. By means of a water cooling device, the start temperature is kept between 17 ° C and 19 ° C
and the reac-tion temperature during the 4.5 hour reaction is kept at < 29°C. 192 kg of the ZO triol thus produced are heated to 70°C to 75°C under nitrogen and with stirring and stirred for a further 2.5 hours at this temperature. After addition of 20 kg of hydrogen peroxide (40% by weight), the reaction mixture was _ O. Z. 5347 cooled overnight, the pH being neutral (7.2).
Example 6:
Separation of the crude solution from Example 5 In a 4-chamber electrodiaiysis module (4 x 100 I) having a cathode circuit (dilute potassium formate solution) and an anode circuit. (potassium sulfate solution) as well as diluate and concentrate circuits, . a volume of crude solution or water was introduced in accordance with the- #ollowing table.
When the pump circuits were opened; care was taken to ensure that the pressure difference either side of the membranes (Neosepta AHA2 and C66 10F membranes from Tokuyama Soda) was no more than 0.2 bar. All circuits were operated at a pressure of 0.7 to 0.8 bar and a flow rate of 400 I/hour. The maximum voltage was 40 V. The temperature increased to a maximum of 45°C. In the course of 20 hours, operations were carried out up to a conductivity in the diluate of 2 mS/cm.
Table 2: Electrodialysis data for Example 6:
Salt-releaser Salt-acce ptor Start End Start End Potassium kg 11.91 0.077 0.03 10.84 formate 17.0 0.19 0.075 16.2 TMP kg 7.84 7.84 0.008 0.528 11.2 19.6 0.02 0.8 H20 kg 45.92 30.53 39.96 55.0 65.6 75.95 99.9 82.3 Total kg 70.0 40.2 40.0 66.8 Trade-mark O.Z. 5347 Example 7:
Esterification with oleic acid of the triol from Example 6 612 g of triol from Example 6 (120 g dry) are first dehydrated via a film evaporator under reduced pressure at a maximum bottom temperature of 90°C. The remaining colorless viscous substance is admixed with 658.8 g of rapeseed oil acid (MW 280 ) and heated in an N2 stream. After 2 hours, at a bottom temperature of 210°C, 37.4 g of distillate are collected, after 3.5 hours at a bottom temperature of 270°C, 45.3 g of distillate are collected and after a further 0.5 hours at a bottom temperature of 280°C and a vacuum of 30 mbar, in total 49.8 g-of distillate are collected. 726.9 g of oleic acid triol ester are present in the reaction vessel as a clear light brown liquid.
Example 8:
Esterification with acrylic acid of the triol from Example 6 1224 g of triol from Example 6 (240 g dry) are dehydrated as in Example 7.
The remaining triol is dissolved with- 373 g of acrylic acid and 0.414 g of hydroquinone monomethyl ether in 207.2 g of toluene. After addition of 8.3 g of toluenesulfonic acid monohydrate and passing through air and heating, water is distilled off azeotropically. After 8 hours, 86.5 g of distillate water were produced. The crude product of the triester is washed twice alkaline and twice neutral as a toluene solution and then the toluene phase is freed from the solvent by distillation. 591 g of trio) triacrylate were obtained.
O.Z. 5347
Claims (12)
1. A process for separating trimethylolpropane and a water-soluble salt from an aqueous solution thereof which comprises subjecting the aqueous solution to electrodialysis.
2. The process as claimed in claim 1, wherein the aqueous solution of trimethylolpropane and the water-soluble salt is a crude product originating from a reaction of butyraldehyde, formaldehyde and an alkali metal hydroxide and is accompanied by other hydrofunctional byproducts.
3. The process as claimed in claim 1 or 2, wherein the electrodialysis is carried out at a temperature of from 10°C
to 50°C.
to 50°C.
4. The process as claimed in claim 1, 2 or 3 wherein the electrodialysis is carried out at a pH of from 4 to 10.
5. The process as claimed in claim 4, wherein the electrodialysis process is carried out at a pH of about 7.
6. The process as claimed in any one of claims 1 to 5, wherein the electrodialysis is carried out at a current density of from 50 to 750 A/m2.
7. A process for producing trimethylolpropane (TMP) from an aqueous solution which is obtained by an aldol addition of formaldehyde to butyraldehyde and using a stoichiometric amount of an alkali metal hydroxide as a catalyst and which contains TMP, an alkali metal formate and hydroxyfunctional byproducts in a total concentration of 20 to 85% by weight, which process comprises:
providing an electrodialysis 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-releasing circuit which is connected to the chamber and in which a salt-releasing solution is to be circulated and (f) a salt-accepting circuit which is connected to the chamber other than the one to which the salt-releasing circuit is connected and in which a salt-accepting solution is to be circulated;
introducing the aqueous solution into the cell through the salt-releasing circuit, as a starting salt-releasing solution having a pH of from 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 ions through the membranes, while circulating the salt-releasing solution in the salt-releasing circuit and circulating the salt-accepting solution in the salt-accepting circuit, wherein the salt-accepting solution is water or an aqueous salt solution and has a pH in the range of 4 to to and a temperature of 10 to 50°C, until the alkali metal formate is accumulated substantially entirely in the salt-accepting solution and the salt-releasing solution becomes an aqueous solution of substantially solely TMP and the hydroxyfunctional byproducts.
providing an electrodialysis 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-releasing circuit which is connected to the chamber and in which a salt-releasing solution is to be circulated and (f) a salt-accepting circuit which is connected to the chamber other than the one to which the salt-releasing circuit is connected and in which a salt-accepting solution is to be circulated;
introducing the aqueous solution into the cell through the salt-releasing circuit, as a starting salt-releasing solution having a pH of from 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 ions through the membranes, while circulating the salt-releasing solution in the salt-releasing circuit and circulating the salt-accepting solution in the salt-accepting circuit, wherein the salt-accepting solution is water or an aqueous salt solution and has a pH in the range of 4 to to and a temperature of 10 to 50°C, until the alkali metal formate is accumulated substantially entirely in the salt-accepting solution and the salt-releasing solution becomes an aqueous solution of substantially solely TMP and the hydroxyfunctional byproducts.
8. The process as claimed in claim 7, wherein the aqueous solution introduced into the cell as the starting salt-releasing solution has a concentration of TMP and the hydroxyfunctional byproducts of 25 to 50% by weight, a concentration of the alkali metal formate of 20 to 40% by weight and an overall concentration of 55 to 80% by weight.
9. The process as claimed in claim 7 or 8, wherein the direct current voltage is within the range of from 50 to 750 A/m2 and is increased as the electrodialysis progresses.
10. A process for producing an ester of trimethylol-propane, which comprises reacting a carboxylic acid with trimethylolpropane obtained by the process of any one of claims 1 to 6 without further purification.
11. A process for producing an ester of trimethylol-propane, which comprises reacting a carboxylic acid with trimethylolpropane obtained by evaporating water from the aqueous solution resulting from the salt-releasing solution obtained by the process of claim 7, 8 or 9 without further purification.
12. A process as claimed in claim 10 or 11, wherein the carboxylic acid is oleic acid or acrylic acid.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE1998138426 DE19838426A1 (en) | 1998-08-24 | 1998-08-24 | Process for separating trimethylolpropane from water-soluble salts from a solution |
| DE19838426.2 | 1998-08-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2280541A1 true CA2280541A1 (en) | 2000-02-24 |
Family
ID=7878545
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2280541 Abandoned CA2280541A1 (en) | 1998-08-24 | 1999-08-20 | Process for separating trimethylolpropane and water soluble salts from a solution |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0982284A3 (en) |
| JP (1) | JP2000093755A (en) |
| BR (1) | BR9903889A (en) |
| CA (1) | CA2280541A1 (en) |
| DE (1) | DE19838426A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| TWI473782B (en) * | 2012-09-17 | 2015-02-21 | Oxea Bishop Llc | Recovery of alcohols from purification residue |
| CN114230441A (en) * | 2021-11-26 | 2022-03-25 | 南通百川新材料有限公司 | Electrodialysis membrane separation method for sodium formate in trimethylolpropane |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE10156116A1 (en) * | 2001-11-15 | 2003-06-26 | Basf Ag | Process for the preparation of (meth) acrylic esters of polyhydric alcohols |
| KR100837523B1 (en) * | 2006-03-07 | 2008-06-12 | 주식회사 엘지화학 | Method for Preparing Trimethylolpropane |
| CN104722209A (en) * | 2013-12-18 | 2015-06-24 | 江南大学 | Ampholytic surfactant electrodialysis desalination purification method |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5453683A (en) * | 1977-10-06 | 1979-04-27 | Tokuyama Soda Co Ltd | Neutralizing method for organic compound solution |
| SE8601772L (en) * | 1986-04-18 | 1987-10-19 | Perstorp Ab | SET FOR MANUFACTURING A POLYAL ALCOHOL |
| GB9519975D0 (en) * | 1995-09-28 | 1995-11-29 | Davy Process Techn Ltd | Process |
-
1998
- 1998-08-24 DE DE1998138426 patent/DE19838426A1/en not_active Withdrawn
-
1999
- 1999-08-13 EP EP19990115961 patent/EP0982284A3/en not_active Withdrawn
- 1999-08-20 CA CA 2280541 patent/CA2280541A1/en not_active Abandoned
- 1999-08-23 BR BR9903889A patent/BR9903889A/en not_active Application Discontinuation
- 1999-08-23 JP JP23604799A patent/JP2000093755A/en active Pending
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| TWI473782B (en) * | 2012-09-17 | 2015-02-21 | Oxea Bishop Llc | Recovery of alcohols from purification residue |
| CN114230441A (en) * | 2021-11-26 | 2022-03-25 | 南通百川新材料有限公司 | Electrodialysis membrane separation method for sodium formate in trimethylolpropane |
Also Published As
| Publication number | Publication date |
|---|---|
| EP0982284A3 (en) | 2000-05-24 |
| JP2000093755A (en) | 2000-04-04 |
| EP0982284A2 (en) | 2000-03-01 |
| DE19838426A1 (en) | 2000-03-02 |
| BR9903889A (en) | 2000-09-19 |
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