WO1999038825A1

WO1999038825A1 - Method for producing alkylene glycol

Info

Publication number: WO1999038825A1
Application number: PCT/EP1999/000476
Authority: WO
Inventors: Aktiengesellschaft Basf
Original assignee: Dockner, Toni; Mohr, Jürgen; Frede, Markus
Priority date: 1998-01-30
Filing date: 1999-01-26
Publication date: 1999-08-05
Also published as: DE19803675A1

Abstract

The invention relates to a method for producing alkylene glycol, according to which a reaction mixture containing an alkylene oxide or a mixture of two or more alkylene oxides as well as water and a catalyst triggering dissociation in water is reacted. In this way a product mixture containing alkylene glycol is obtained which is then purified by means of electrodialysis.

Description

Process for the production of alkylene glycol

The present invention relates to a process for the production of alkylene glycol, in which the alkylene glycol-containing product mixture is treated by means of electrodialysis.

Glycols, especially ethylene glycol, are used in a wide range of applications. These include, for example, their use as a polyol component in the synthesis of polymers, in particular polyesters, polyethers and polyurethanes, their use as antifreeze in cooling systems or as a deicing agent in aviation. Furthermore, glycols can be used as difunctional alcohols, in particular in the production of hydroxy esters of mono- or polycarboxylic acids, the production of hydroxy esters of (meth) acrylic acid being particularly emphasized.

Glycols can be prepared by a wide variety of processes, for example the reaction of alkylene oxides with water, optionally under pressure and in the presence of basic catalysts. An alkali metal salt or alkali metal salt mixtures are generally used as catalysts.

For example, GB-A 2 023 601 describes a process for the hydrolysis of alkylene oxides to alkylene glycol, in which alkylene glycols are reacted in the presence of CO ₂ and a basic, halogen-free catalyst. The reaction is carried out at a carbon dioxide pressure of less than 2.41 MPa at a reaction temperature between about 85 ° C and about 400 ° C. The reaction is preferably carried out in the presence of an organic solvent. Potassium carbonate, potassium phosphate, potassium acetate or guanidine carbonate are proposed as catalysts. The use of electrodialysis to clean the resulting product mixture is not mentioned.

Japanese Patent Laid-Open No. S56-71028 relates to a manufacturing process for alkylene glycol. The document describes the reaction of alkylene oxide and water in the presence of carbon dioxide using a catalyst which contains alkali metal carbonate or alkali metal bicarbonate or a mixture thereof. The use of a mixture of various alkali metal bicarbonates and carbonates in a ratio of 1: 1 together with 0.1 mol of carbon dioxide is described by way of example. The use of electrodialysis to clean the resulting product mixture is not mentioned.

EP-B 226 799 relates to a process for the production of ethylene and propylene glycol by aqueous hydrolysis of ethylene oxide or propylene oxide, in which a metal salt, for example an alkali metal salt, of formic acid or a mixture of a carboxylic acid and a carboxylic acid salt is used as the catalyst. The use of electrodialysis to clean the resulting product mixture is not mentioned.

EP-A 089 704 relates to a process for separating glycol from electrolyte-containing, aqueous solutions. The electrolyte-containing, aqueous solutions are, for example, waste water from ethylene oxide production or the mixtures of triethylene glycol which are obtained in the drying of natural gas. The use of electrodialysis in the production of alkylene glycol is not mentioned.

While the processes known from the prior art generally have satisfactory conversions, based on the yield of alkylene glycol in Product mixture, result, subsequent distillative workup of the alkylene-containing product mixture often leads to high losses in yield of alkylene glycol. In many cases, the salt or salt mixture used as catalyst accumulates in the distillation bottoms during distillation, where it often does not precipitate in crystalline form, but instead forms an oily liquid from salt or salts and alkylene glycol. As a rule, the alkylene glycol can no longer be removed by distillation from this oily liquid. Depending on the amount of catalyst used, this can cause high losses of alkylene glycol.

Furthermore, when the alkylene glycol-containing product mixture is worked up, the water must first be largely removed, as a rule this is done by distillation with a high expenditure of energy.

Accordingly, the object of the present invention was to provide an economical process for the purification of product mixtures containing alkylene glycol, with the aid of which an product mixture containing alkylene glycol can be at least largely freed of salt or salts, and which also allows economical process management.

It was a further object of the invention to provide a process which makes it possible to increase the alkylene glycol concentration in the alkylene glycol-containing product mixture without removing a corresponding amount of water by distillation.

It has now been found that the removal of salt or salts and water from product mixtures containing alkylene glycol, such as are obtained in the production of alkylene glycols by hydrolysis of the corresponding alkylene oxides, can be carried out economically by electrodialysis.

Accordingly, the present invention relates to a process for the preparation of alkylene glycol, in which a reaction mixture containing an alkylene oxide or a Mixture of two or more thereof, and water and a catalyst dissociating in water is reacted, an alkylene glycol-containing product mixture being formed, characterized in that the alkylene glycol-containing product mixture is cleaned by means of electrodialysis.

Of course, the alkylene glycol-containing product mixture to be treated may contain other by-products and decomposition products which are produced, as long as these do not have an adverse effect on the implementation of electrodialysis or the cation exchange process.

However, it may also be necessary to remove such components, which can be done, for example, by conventional separation processes, e.g. Filtration can happen.

The alkylene oxides which can be converted by the process according to the invention are preferably alkylene oxides of the general formula I in which R, R, R and R are in each case identical or different and are, independently of one another, hydrogen, C ₁ -io-alkyl, C ₂ -io-alkenyl , C2-ιo-alkynyl, C _3- ι ₀ -cycloalkyl, C3-10- cycloalkenyl, C _6- i2-aryl or heteroaryl, where the alkyl, alkenyl or alkynyl radicals can be linear or branched and in turn still further functional Groups can carry, and the cycloalkyl, aryl and heteroaryl radicals can in turn carry further functional groups or can be substituted with Ci-IO-alkyl, alkenyl, alkynyl or aryl radicals.

Preferred alkylene oxides are, for example, ethylene oxide, propylene oxide, butylene oxide, isobutylene oxide, 1,2-butylene oxide, 2,3-butylene oxide, pentylene oxide and styrene oxide, or mixtures of two or more thereof, ethylene oxide, propylene oxide or 1,2-butylene oxide, or mixtures of two or more of them are preferred.

The alkylene oxide which can be used in the context of the present process, or the mixture of two or more different alkylene oxides, can be obtained from one originate from any source or from various sources, that is to say have been produced by any method. For example, ethylene oxide can be obtained by catalytic oxidation of ethylene, ethylene and a gas containing molecular oxygen, for example air, oxygen-enriched air or pure oxygen, being reacted in the gas phase on a silver-containing catalyst.

The alkylene oxide which can be used in the context of the present invention, or the mixture of two or more different alkylene oxides, is preferably used in pure form. This means that the alkylene oxide or alkylene oxides used are essentially free of impurities and thus essentially contain 100% of the alkylene oxide, or of the mixture of two or more different alkylene oxides. However, it is also possible to use a technical grade of alkylene oxide which still contains venine purifications, such as are usually present before the purification of the alkylene oxide after production, if appropriate with lower yields or lower selectivity, or both.

The water used in the context of the present invention can come from a wide variety of sources and does not have to meet any special conditions with regard to its purity. Suitable are, for example, fresh water, as is generally available from process water treatment plants or, for example, from waterworks, water which has been subjected to an ion exchange process, water vapor condensate, and water of reaction which is usually obtainable in the case of chemical reactions which proceed with the elimination of water.

It has been shown that a weight ratio of water to compounds bearing alkylene oxide groups of about 1 to 20 is generally advantageous for the process according to the invention. It is preferred if the weight ratio of water to compounds carrying alkylene oxide groups is greater than 1 and less than about 10, in particular less than about 7.6, and particularly preferably about 1.1 to about 4.5, for example about 2 or about 3.

Any catalyst which is capable of accelerating the reaction between the alkylene oxide used or the mixture of two or more alkylene oxides and which also contains at least one anion and at least one in the aqueous reaction mixture can be used as catalyst in the process according to the invention a cation dissociates. It can be an acidic catalyst, but a basic catalyst can also be used. It is also possible to use catalysts which have both acidic and basic groups. Low molecular weight catalysts can be used in the context of the present invention, but it is equally possible to use catalysts which are firmly bound to a support. Suitable catalysts of the latter type are, for example, ion exchange resins which preferably have covalently bonded acid groups, basic groups or a mixture of acidic and basic groups. In the context of the process according to the invention, low molecular weight catalysts or catalysts located on supports can be used individually or in a mixture with one another. If low molecular weight catalysts are used, it is a prerequisite in the context of the present invention that they can be removed from the reaction mixture by electrolysis. Catalysts on supports are generally separated from the reaction mixture by mechanical processes, for example by sieving processes.

In the process according to the invention, a basic catalyst is preferably used as the catalyst. In particular, these are water-soluble inorganic or optionally organic bases. The inorganic bases include, for example, the hydroxides, carbonates, hydrogen carbonates or oxides of the alkali and alkaline earth metals. In particular, these are the hydroxides, carbonates and hydrogen carbonates of lithium, sodium, potassium, rubidium, cesium, barium and calcium, the hydroxides of sodium and potassium being used with particular preference. In a further embodiment of the process according to the invention, an alkali metal formate or a mixture of two or more alkali metal formates is used as the catalyst, for example. All alkali metals are suitable as alkali metals in the context of the present process, ie lithium, sodium, potassium, rubidium and cesium, sodium and potassium usually being preferred for economic reasons.

If the base strength of the formates used as catalyst is not sufficient to achieve a specific pH value required for carrying out the process according to the invention, a base can be added to the reaction mixture in order to set a specific pH value required. The bases used to adjust the pH are preferably the above-mentioned hydroxides of the alkali metals.

In a preferred embodiment of the present invention, the production of alkylene glycol is carried out in the presence of a formate or a mixture of two or more formates, at a pH of at least about 8.1, in particular at least about 8.5.

In a further embodiment of the present invention, for example an alkali metal bicarbonate or a mixture of two or more alkali metal bicarbonates or an alkali metal carbonate or a mixture of two or more alkali metal carbonates is used as the basic catalyst. However, it is also possible within the scope of the process according to the invention to use a mixture of one or more alkali metal bicarbonates and one or more alkali metal carbonates as catalyst.

In a preferred embodiment of the invention, the method in

In the presence of a basic catalyst, a mixture containing alkali bicarbonate and alkali carbonate is used as the basic catalyst, in which the weight fraction of alkali bicarbonate, based on the Weight fraction of alkali carbonate predominates in the basic catalyst, i.e. is greater than 1. In particular, the weight ratio of alkali bicarbonate to alkali carbonate is from about 1.5 to about 10.

In the context of this embodiment of the present process, all alkali metals are suitable as alkali metals, i. H. Lithium, sodium, potassium, rubidium and cesium, with sodium and potassium usually being preferred for economic reasons.

If a mixture of two or more different alkali metal salts is used as the catalyst, salts of an identical alkali metal can be used, for example. However, it is equally possible that the salts present in the mixture carry different alkali metal ions. A combination of sodium and potassium ions, for example a basic catalyst, containing a mixture of potassium bicarbonate and sodium carbonate is particularly suitable.

The proportion by weight of the catalyst, based on the total mass of water and alkylene oxide or the mixture of two or more different alkylene oxides, is between about 1 and about 50% by weight. The proportion by weight of the basic catalyst in the reaction mixture, based on the mass sum of water and alkylene oxide or the mixture of two or more different alkylene oxides, is preferably more than about 2% by weight, particularly preferably more than about 5% by weight, for example at about 6 wt%, 10 wt%, 15 wt% or 20 wt%, or above.

As a rule, the total salt content of the alkylene glycol-containing product mixture is based on the catalyst content; non-catalytically active salts are usually not present in the alkylene glycol-containing product mixture, or are present only in minor amounts. The salt content of the alkylene glycol-containing product mixture is therefore generally in accordance with that above specified catalyst content up to about 50 wt .-%, preferably less than 45 wt .-% and in particular less than 40 wt .-%. Good results can be achieved with electrodialytic cleaning, for example at a total salt content of about 1% by weight to about 39% by weight, for example at low salt contents of about 2 to about 8% by weight, or for example at medium salt contents of about 10 to about 20% by weight.

The reaction temperature in the production of the alkylene oxides is generally between approximately 50 and approximately 250 ° C., preferably between approximately 80 and approximately 150 ° C., temperatures of, for example, 90 ° C., 100 ° C., 110 ° C. or 120 ° C. being preferred become. The reaction time can be varied over a wide range, for example depending on the reaction temperature and the amount of the basic catalyst used. A lower limit for the reaction time is, for example, about 0.5 h, but a lower limit for the reaction time of about 1 h or 2 h should generally be observed. For procedural reasons, the upper limit should be, for example, a reaction time of about 10 hours, which time can be extended if necessary. Good results can be achieved, for example, with reaction times of between about 3 hours and about 6 hours, in particular about 4 hours to about 5 hours.

Carbon dioxide can be added when carrying out the process according to the invention, but is generally not necessary. In a preferred embodiment of the invention, no external addition of carbon dioxide is used. In a further preferred embodiment of the invention, the presence of carbon dioxide is largely excluded, i. that is, the proportion of carbon dioxide in the entire reaction mixture is less than 0.1 mmol / mol alkylene oxide groups, preferably less than 0.01 mmol / mol alkylene oxide groups.

The reaction can be carried out isothermally, but it is also possible in the context of the process according to the invention to carry out an adiabatic reaction. Here, the reaction temperature in the course of the reaction pass through a gradient, with a reaction temperature of between approximately 80 and approximately 120 ° C. initially and a reaction temperature of approximately 160 to approximately 210 ° C. at the end of the reaction.

The pressure prevailing during the reaction can also vary within wide limits. It is possible to carry out the reaction at ambient pressure, i.e. generally at about 1 bar, provided that the boiling points of the reaction participants in the reaction mixture allow this. As a rule, however, the reaction will be carried out under increased pressure, ie at a pressure of more than about 1 bar up to about 10 bar, for example at about 2, about 4, about 6 or about 8 bar .

The process according to the invention is usually carried out either in a batch process or in a continuous procedure.

The batch process is carried out in a closed apparatus, water and the basic catalyst being introduced in any order and then, if appropriate after the water / catalyst mixture has been brought to the reaction temperature, the alkylene oxide or the mixture of two or more different alkylene oxides , is added. Gaseous alkylene oxides are generally added by a corresponding gas supply, so that the reaction mixture may be under pressure during the reaction. If liquid or solid alkylene oxides are to be reacted in the sense of the present invention, the addition to the reaction mixture is usually carried out together with the water and the basic catalyst, the order of addition not being important. The course of the reaction can be carried out isothermally in compliance with the temperature limits indicated above, that is to say that the temperature of the reaction mixture is kept at least largely constant throughout the course of the reaction. However, it is also possible to make the reaction process adiabatic or isobaric, so that the pressure in the reaction vessel remains essentially constant and the temperature of the reaction mixture changes within the limits specified above during the course of the reaction. In the case of adiabatic reaction control in a batch process, an initial reaction temperature of more than approximately 80 ° C. is advantageously maintained, the reaction temperature being able to rise to a temperature of approximately 160 ° C. in the course of the reaction.

If the process according to the invention is carried out in a continuous manner, this is expediently done in a tubular reactor. The reaction can also take place isothermally or isobarically or adiabatically.

The alkylene glycol-containing product mixture is treated according to the invention by means of electrodialysis.

The primary effect of this electrodialysis is cleaning, i.e. in the removal of ionic components, e.g. of the catalyst, or of catalyst components, from the product mixture.

In the context of the present text, the cleaning of the alkylene glycol-containing product mixture means in particular the removal of salts, in particular the removal of salts which were used as a catalyst or at least as a component of the catalyst in the preparation of the alkylene glycol or the mixture of two or more alkylene glycols.

The conventional two-circuit electro-dialysis used in the context of the present invention primarily for cleaning the alkylene glycol-containing product mixture is known per se and is used, among other things. in EP-B-0 381 134, the content of which is fully incorporated into the present application with regard to conventional two-circuit electrodialysis.

The drawing shows a basic sketch of the electrodialysis. 1 shows a schematic diagram of an electrodialysis apparatus, the material and ion flows being incorporated into the representation. Here 1 means an anode, 2 a cathode, 3 a cation exchange membrane, 4 an anion exchange membrane, 5 a diluate circuit, 6 a concentrate circuit, M ⁺ a cation, X ^" an anion and A alkylene glycol.

In an electrodialysis variant preferred in the context of the present invention, an apparatus is used which has a positive (anode (1)) and a negative (cathode (2)) large-area electrode. The space between these electrodes is divided by a large number of alternately arranged cations (3) and anions (4) exchange membranes into a large number of narrow chambers separated by the membranes, which are also referred to as diluate circuits (5) and concentrate circuits (6) , divided up. Chambers which have an anion-exchange membrane on the cathode side and a cation-exchange membrane on the anode side represent the so-called concentrate chambers or concentrate circles, while chambers which have the anion-exchange membrane on the anode side and the cation-exchange membrane on the cathode side form the diluate chambers or the diluate circuit.

To carry out the process according to the invention, the diluate circles are filled with the alkylene glycol-containing product mixture to be purified, the concentrate circles, on the other hand, are filled with an aqueous electrolyte, and the chambers in which the electrodes are located and, if appropriate, the adjacent chambers directly adjacent to them are filled with an electrode rinsing solution in the Rule of a sodium sulfate solution.

Under the influence of the voltage applied to the electrodes, ions (M ⁺ , X ^" ) migrate through the membrane that is permeable to them from the diluate circuit (5) into the concentrate circuit (6). Through the following membrane (3, 4), further migration is not possible and the ion thus remains in the concentrate circuit (6) .The liquids in the diluate, concentrate and Electrode circuits are pumped around in separate circuits, possibly with the help of reservoirs.

In the present process, salts present in the alkylene glycol-containing product mixture, for example the catalyst, thus accumulate in the concentrate circuit during electrodialysis. Thus, for example, an aqueous solution of a catalyst dissociating in water is formed, the content of alkylene glycol (A) of which is lower than the alkylene glycol content of the alkylene glycol-containing product mixture. The aqueous solution then generally contains only water, the catalyst dissociating in water and optionally a small amount of alkylene glycol. In a preferred embodiment of the invention, therefore, a catalyst contained in the aqueous solution is used again for the production of alkylene glycol, preferably it is returned to the process for the production of alkylene glycol following the purification of the alkylene glycol-containing product mixture.

This recycling can take place, for example, in that the catalyst is obtained from the aqueous solution and is used again in concentrated form, for example in solid form or in concentrated aqueous solution. However, it is also possible to recycle the catalyst in the form of the aqueous solution present after the electrodialysis in the process for the production of alkylene glycol.

The product mixture to be treated in the process according to the invention generally has an alkylene glycol content of about 5 to about 80% by weight, preferably about 20 to about 60% by weight and particularly preferably about 30% by weight to about 50% by weight. Particularly advantageous results can be achieved if the total amount of salts and alkylene glycol is more than about 8% by weight, in particular more than about 10 or 15% by weight.

The electrodialysis used in the process according to the invention is preferably carried out in a 2-circuit electrodialysis module with an alternating arrangement of cation and anion exchange membranes. In principle, any membranes usually used in the context of electrodialysis processes can be used to carry out the process according to the invention. In the electrodialysis carried out as part of the present method, commercially available ion exchange membranes are preferably used. These membranes preferably consist of organic polymers that have ion-active side chains. Cation exchange membranes contain sulfo or carboxyl groups in the polymer matrix, anion exchange membranes have tertiary or quaternary amino groups as substituents on the polymeric base material. Copolymers of styrene and divinylbenzene are particularly suitable as polymeric base material for the ion exchange membranes. In a preferred embodiment, membranes are used which, in addition to the polymeric base material, have a further base material which has hydrophobic properties, for example PVC.

In the context of the present invention, ion exchange membranes with an ion exchange capacity of 0.8 to 5, preferably 1.2 to 3.5 milliequivalents per g (meq / g) are used. Preferred ranges for the ion exchange capacity are, for example, about 1.3 to about 3.2 meq / g, about 1.5 to about 2.5 meq / g or about 1.6 to about 2.2 meq / g.

In a preferred embodiment, membranes are used, the thickness of which is approximately 0.05 to less than approximately 0.5 mm, preferably approximately 0.1 to approximately 0.3 mm. Membranes with a thickness of approximately 0.13 to approximately 0.2 mm, for example 0.14 to approximately 0.19 or 0.16 to approximately 0.18 mm, or thicknesses between these values, for example 0.15, are particularly preferred , 0.16 or 0.17 mm.

The membranes that can be used in the context of the present invention have in the

- Regulate an electrical resistance of about 0.2 to about 13 ü * cm. The resistance is preferably about 0.4 to about 4.5 Ω * cm. In a In a preferred embodiment, the electrical resistance is approximately 2.5 to approximately 3.5 Ω * cm, but it is also possible to carry out the method according to the invention with membranes which have an electrical resistance of approximately 0.4 to approximately 1.5 Ω * cm or about 1.2 or about 1.3 to about 2.0 or about 3.0.

Examples of anion exchange membranes that can be used are: Tokuyama AMI, AM2, AM3, AMX, AMH, AFN, Asahi Glass AMV. Tokuyama CM1, CM2, CMX, CMH and Asahi Glass CMV are examples of cation exchange membranes.

In a modification of the conventional 2-circuit electrodialysis known from EP-B 0 381 134, a membrane arrangement using bipolar membranes can also be used. Bipolar membranes are laminates made from anion and cation exchange membranes. Compared to monopolar anion or cation exchange membranes, they are characterized by the fact that they catalyze efficient water splitting in the electrical field of electrodialysis and thus serve to simultaneously provide H and OH ^" equivalents.

A 3-circuit (chamber) arrangement (3-circuit bipolar electrodialysis) is used, consisting of diluate (1), acid (2) and base (3) circuits. The 3-circuit arrangement is achieved by alternating the respective ion exchange membrane:

.KM BK BM SK AM DK KM.

KM = cation exchange membrane; BM = bipolar membrane;

AM = anion exchange membrane

BK = base circle; SK = acid circle; DK = diluate circle

The electrodialysis is preferably carried out at approximately 10 to approximately 80 ° C., in particular between approximately 20 and approximately 60 ° C. The current density at the conventional 2-circuit electrodialysis varies between about 1 and about 700

2 2

A / m, preferably between about 50 and about 500 A / m. In 3-circuit bipolar electrodialysis, the current density varies between approximately 1 and approximately 1,500 A / m, preferably between approximately 200 and approximately 1,200 A / m.

In the process according to the invention, electrodialysis is carried out up to a final conductivity of the diluate of at most about 2 mS / cm, in particular about 1 mS / cm and below, for example up to about 0.8, up to about 0.5 or up to about 0 , 1 mS / cm, or less.

The diluate discharge is generally subjected to a further work-up step to obtain the corresponding alkylene glycol or the mixture of two or more alkylene glycols. The further workup is usually carried out by distillation. As a rule, the water is first removed from the diluate in one or more distillation stages and then the essentially anhydrous alkylene glycol or the mixture of two or more alkylene glycols thus obtained is subjected to a final distillation to finally obtain the desired alkylene glycol or alkylene glycols .

In a preferred embodiment of the invention, formic acid or a formate or a mixture of two or more formates or a mixture of formic acid and one or more formates is added to the alkylene glycol-containing product mixture after the electrodialysis at any time before the final distillation in order to determine the content of carbonyl compounds in the alkylene glycol obtainable after the final distillation.

In principle, all salts of formic acid are suitable as formates, but the alkali formates, for example the formates of lithium, are particularly suitable,

Sodium or potassium, or the ammonium formates, such as those made from Formic acid and ammonia or organic amines are available.

The formic acid or the formate or a mixture of two or more formates or a mixture of formic acid and one or more formates is generally distilled in an amount of from about 0.01 to about 10% by weight of the diluate to be distilled or added to the already largely anhydrous alkylene glycol or the mixture of two or more alkylene glycols. In preferred embodiments of the invention, for example, amounts of about 0.05 to about 8% by weight, for example about 0.1 to about 6% by weight or about 0.5 to about 3% by weight, are used. Quantities from about 1 to about 2% by weight are also suitable, for example.

The alkylene glycol to be finally distilled or the mixture of two or more alkylene glycols advantageously has a water content of less than about 500 ppm, preferably less than about 200 ppm.

The distillation bottoms obtained in the course of the various distillation steps can either be sent to a combustion plant or, for further increases in yield, can be returned to electrodialysis. It is also possible to further desalt the distillation bottoms by other methods, for example by ion exchange, and thus to make it possible to utilize any residual alkylene glycol content that may still be present.

The invention also relates to the use of electrodialysis to remove a catalyst from an alkylene glycol-containing product mixture. The use according to the invention relates in particular to catalysts as described in the context of the present text. These are preferably catalysts which were used in the production of alkylene glycol from an alkylene oxide.

The invention is illustrated below by examples, but the scope not limit the invention.

Examples:

1. General conditions:

The conventional electrodialysis was carried out in a two-circuit electronic dialysis module with an alternating arrangement of cation and anion exchange membranes, the types AM3 or AMX being used as the anion exchange membranes and the types CM2 or CMX, each Tokuyama, being used as the cation exchange membranes. The membranes were spaced 0.5 mm apart.

The electronic dialysis module consisted of 5 diluate and concentrate chambers, which corresponded to an effective total membrane area of 3.78 dm. Platinized titanium electrodes were used as anode and cathode material. The maximum nominal current density betmg 7.9 A / dm, the maximum voltage drop per cell (a pairing of diluate and concentrate chamber) was limited to 3 V. The electrodialysis temperature is 50 ° C.

A KHCO ₃ -containing mixture of water / monoethylene glycol (MEG) was placed in the diluate circuit and electrodialyzed to a conductivity of <1 mS / cm.

The exemplary results, varying the membrane pairing and the relative proportions of MEG / KHCO ₃ and H ₂ O, can be found in the following Examples 1-3.

2. Individual examples example 1

Membrane pairing: CM2 / AM3 runtime: 4 h current efficiency: 92.5%

KHC03 depletion diluate → concentrate: 96.6%

Example 2

Membrane pairing: CM2 / AM3 runtime: 8 h current efficiency: 95.2% KHCθ3 depletion diluate → concentrate: 94.3%

Example 3

Membrane pairing: CMX / AMX runtime: 6 h current efficiency: 93.9%

KHCO ₃ depletion diluate → concentrate: 99.4%

Claims

claims

1. A process for the preparation of alkylene glycol, in which a reaction mixture comprising an alkylene oxide or a mixture of two or more thereof, and water and a catalyst dissociating in water, is brought to reaction, an alkylene glycol-containing product mixture being formed, characterized in that the The alkylene glycol-containing product mixture is cleaned by means of electrodialysis.

2. The method according spoke 1, characterized in that an alkylene oxide of the general formula I as alkylene oxide

wherein R, R, R and R are each the same or different and independently of one another for hydrogen, Cι-alkyl, C2-10 alkenyl, C2-10 alkynyl, C3-ιo-cycloalkyl, C3-ιo-cycloalkenyl, Cό -12-Aryl or heteroaryl, where the alkyl, alkenyl or alkynyl radicals can be linear or optionally branched and in turn can carry further functional groups, and the cycloalkyl, aryl and heteroaryl radicals can in turn carry further functional groups or with ci 1 ₀ - alkyl, alkenyl, alkynyl or aryl radicals can be substituted,

or a mixture of two or more of them is used.

3. The method according spoke 1 or 2, characterized in that a catalyst selected from the group consisting of alkali metal salts, alkaline earth metal salts or ammonium salts or a mixture of two or more thereof is contained as a catalyst.

4. The method according to any one of claims 1 to 3, characterized in that a catalyst selected from the group consisting of hydroxides, carbonates, hydrogen carbonates, formates or acetates, or a mixture of two or more thereof is contained as a catalyst.

5. The method according to any one of claims 1 to 4, characterized in that the catalyst is a potassium salt or a mixture of two or more potassium salts or a sodium salt or a mixture of two or more sodium salts or a mixture of one or more potassium salts and one or more Sodium salts is used.

6. The method according to any one of claims 1 to 5, characterized in that the proportion of the catalyst in the alkylene glycol-containing product mixture is 0.1 to 50 wt .-%.

7. The method according to any one of claims 1 to 6, characterized in that the alkylene glycol-containing product mixture has an alkylene glycol content of 5 to 80 wt .-%.

8. The method according to any one of claims 1 to 7, characterized in that the electrodialysis is carried out as a conventional 2-circuit electrodialysis or as a 3-circuit bipolar electrodialysis.

9. The method according to any one of claims 1 to 8, characterized in that the electrodialysis is carried out at a temperature of 10 to 60 ° C.

10. The method according to any one of claims 1 to 9, characterized in that the current density when using the 2-circuit electrodialysis between 1 and 700 A / m and when using the 3-circuit bipolar electrodialysis varies between 1 and 1500 A / m.

5

11. The method according to any one of claims 1 to 10, characterized in that ion exchange membranes with a capacity of 0.8 to 5 meq / g are used as membranes.

10. The method according to any one of claims 1 to 11, characterized in that when cleaning the alkylene glycol-containing product mixture at least one aqueous solution of a water-dissociating catalyst is formed, the content of alkylene glycol is less than the alkylene glycol content of the alkylene glycol-containing product mixture, the in the contained aqueous solution

15 catalyst is used again for the production of alkylene glycol.

13. Use of electrodialysis to remove a catalyst from an alkylene glycol-containing product mixture.