WO2022189318A1

WO2022189318A1 - Process for purifying cyclic carbonates

Info

Publication number: WO2022189318A1
Application number: PCT/EP2022/055662
Authority: WO
Inventors: Jürgen BAUSA; Michael Traving; Jörg Hofmann; Stefanie Braun
Original assignee: Covestro Deutschland Ag
Priority date: 2021-03-12
Filing date: 2022-03-07
Publication date: 2022-09-15

Abstract

The invention relates to a process for purifying cyclic carbonates, characterized by the steps (A) attaching alkylene oxide and carbon dioxide to a H-functional starter substance in the presence of a catalyst, resulting in a mixture that contains polyether carbonate polyol and cyclic carbonate; (B) separating the mixture resulting from (A) into polyether carbonate polyol and cyclic carbonate that contains impurities; (C) supplying the cyclic carbonate that contains impurities from (B) to a first rectification column, equipped with at least one feature selected from the group consisting of structured packing, packed bed of fillers, or trays, and subsequently separating a part of the impurities from the top of the first rectification column and obtaining a raw mixture that contains cyclic carbonate; (D) supplying the raw mixture containing cyclic carbonate obtained in (C) to a second rectification column, equipped with at least one feature selected from the group consisting of structured packing, packed bed of fillers, or trays, and subsequently separating another part of the impurities as a sump in the second rectification column and obtaining the pure cyclic carbonate product, (D-1) a sump temperature of 130 to 170°C prevailing in (D) and/or (D-2) the pure cyclic carbonate product being removed from the second rectification column via a side draw.

Description

Process for the purification of cyclic carbonates

The present invention relates to the purification of cyclic carbonates from the production of polyether carbonate polyols.

The production of polyether carbonate polyols by catalytic conversion of alkylene oxides (epoxides) and carbon dioxide in the presence of H-functional starter substances ("starters") has been intensively studied for more than 40 years (e.g. Inoue et al., Copolymerization of Carbon Dioxide and Epoxide with Organometallic Compounds; Die Makromolecular Chemie 130, 210-220, 1969). This reaction is shown schematically in Scheme (I), where R is an organic radical such as alkyl, alkylaryl or aryl, each of which may also contain heteroatoms such as O, S, Si, etc., and where e, f and g are a are integers, and the product shown here in scheme (I) for the polyethercarbonate polyol should only be understood in such a way that blocks with the structure shown can in principle be found in the resulting polyethercarbonate polyol, the sequence, number and length of the blocks and the OH However, functionality of the initiator can vary and is not limited to the polyethercarbonate polyol shown in Scheme (I). This reaction (see scheme (I)) is ecologically very advantageous, since this reaction represents the conversion of a greenhouse gas such as CO2 to a polymer and thus replaces, i.e. saves, a corresponding amount of alkylene oxide. The cyclic carbonate shown in scheme (I) is formed as a by-product (for example for R=CH3 propylene carbonate, also referred to below as cPC, or for R=H ethylene carbonate, also referred to below as cEC).

O

Start r-OH + (e+f+g) A + (e+g) C0 ₂ -

R

The separation of cyclic carbonate, which is formed as a by-product in the production of polyether carbonate polyols by addition of alkylene oxide and CO2 onto H-functional starter substances, is described, for example, in WO 2016/001164 A1. In the examples, the cyclic carbonate is removed by a falling-film evaporator coupled to a stripping column. The proportion of the cycl. Carbonate is reduced from 8.4% by weight in the crude polyethercarbonate polyol to at least 55 ppm in the final product. WO 2016/001164 A1 does not give any information on the purity or further purification of the cycl. carbonate made.

US 2010/0130751 A1 describes a process for producing 1,2-alkylene carbonates and subsequent purification of the 1,2-alkylene carbonates. By the reaction of CO2 with 1,2-alkylene oxides in the presence of a carbonization catalyst gives 1,2-alkylene carbonate. After separating the catalyst, only one distillation step is carried out and that

Removed 1.2-alkylene carbonate from the bottom of the distillation apparatus. Furthermore, the impurities to be separated differ from cyclic carbonate, which is obtained from the production of polyether carbonate polyols by addition of CO2 and alkylene oxide to H-functional starter substances.

The object on which the present invention is based was therefore to increase the purity of cyclic carbonate from the production of polyethercarbonate polyols, preferably to values of >99.90%, and to reduce the proportion of low-boiling and high-boiling by-products.

This object was achieved according to the invention by a process for purifying cyclic carbonate, characterized by the steps

(A) Addition of alkylene oxide and carbon dioxide in the presence of a catalyst onto an H-functional starter substance, resulting in a mixture containing polyether carbonate polyol and cyclic carbonate,

(B) separation of the mixture resulting from (A) into polyether carbonate polyol and cyclic carbonate containing impurities,

(C) Feeding the cyclic carbonate containing impurities from (B) into a first rectification column equipped with at least one feature selected from the group consisting of structured packing, random packing or trays, and then separating off part of the impurities overhead in the first rectification column , wherein a crude mixture containing cyclic carbonate is obtained,

(D) Feeding the crude mixture obtained in (C) containing cyclic carbonate into a second rectification column, equipped with at least one feature selected from the group consisting of structured packing, a random packing or trays, and subsequent removal of another part of the impurities as a bottom in the second rectification column, wherein the pure cyclic carbonate product is obtained, wherein

(D-l) in (D) a bottom temperature of 130 to 170°C prevails and/or

(D-2) the pure cyclic carbonate product is removed from the second rectification column through a side draw. It has been found that the process according to the invention increases the purity of the cyclic carbonate obtained from the production of polyether carbonate polyols.

Step (A):

In step (A), polyether carbonate polyol and cyclic carbonate are obtained by the addition reaction of alkylene oxide and carbon dioxide onto an H-functional starter substance in the presence of a catalyst, preferably by a method characterized in that

(a) a subset of H-functional starter substance and/or a suspending agent which has no H-functional groups is placed in a reactor, optionally together with a catalyst,

(ß) optionally, to activate a DMC catalyst, a portion (based on the total amount of alkylene oxide used in the activation and copolymerization) of alkylene oxide is added to the mixture resulting from step (a), this addition of a portion of alkylene oxide optionally can take place in the presence of CO ₂ , and in which case the temperature peak ("hotspot") occurring as a result of the following exothermic chemical reaction and/or a drop in pressure in the reactor is awaited in each case, and in which step (ß) for activation can also take place several times,

(g) an H-functional starter substance, alkylene oxide and, if appropriate, a suspending agent which does not have any H-functional groups, and/or carbon dioxide are metered into the reactor during the reaction,

(d) if appropriate, the reaction mixture continuously removed in step (g) is transferred to an after-reactor in which the content of free alkylene oxide in the reaction mixture is reduced by way of an after-reaction.

The catalyst used in step (A) is at least one compound which catalyzes the addition of alkylene oxide and carbon dioxide, preferably at least one double metal cyanide catalyst or at least one metal complex catalyst based on the metals zinc and/or cobalt, particularly preferably a double metal cyanide catalyst.

To (a):

In the process, a subset of H-functional starter substance and/or a suspending agent which has no H-functional groups can initially be initially taken in the reactor. If appropriate, the amount of catalyst required for the polyaddition is then added to the reactor. The order of addition is not critical. It is also possible to first fill the catalyst and then a portion of H-functional starter substance into the reactor. Alternatively, the catalyst can first be suspended in a portion of H-functional starter substance and the suspension can then be filled into the reactor.

In a preferred embodiment of the invention, in step (a) an H-functional Starter substance is initially introduced into the reactor, if appropriate together with the catalyst, and no suspension medium which does not contain any H-functional groups is initially introduced into the reactor.

The catalyst is preferably used in an amount such that the content of catalyst in the resulting reaction product is 10 to 10000 ppm, more preferably 20 to 5000 ppm and most preferably 50 to 500 ppm

In a preferred embodiment, inert gas (e.g. argon or nitrogen) an inert gas-carbon dioxide mixture or carbon dioxide is introduced and at the same time a reduced pressure (absolute) of from 10 mbar to 800 mbar, particularly preferably from 50 mbar to 200 mbar, is applied.

In an alternative preferred embodiment, the resulting mixture of (a) a portion of H-functional starter substance and (b) catalyst at a temperature of 90 to 150 ° C, particularly preferably from 100 to 140 ° C at least once, preferably three times with 1, 5 bar to 10 bar (absolute), particularly preferably 3 bar to 6 bar (absolute) of an inert gas (e.g. argon or nitrogen), an inert gas-carbon dioxide mixture or carbon dioxide and the overpressure then increased to approx. 1 bar (absolute) reduced.

The catalyst can be added in solid form or as a suspension in a suspension medium which does not contain any H-functional groups, in H-functional starter substance or in a mixture of the above.

In a further preferred embodiment, in step (a)

(a-I) submitted a portion of H-functional starter substance and

(a-II) the temperature of the subset of H-functional starter substance is brought to 50 to 200° C., preferably 80 to 160° C., particularly preferably 100 to 140° C., and/or the pressure in the reactor to less than 500 mbar, preferably 5 mbar to 100 mbar, with an inert gas stream (for example of argon or nitrogen), an inert gas carbon dioxide stream or a carbon dioxide stream being passed through the reactor, where appropriate, with the catalyst for the subset of H-functional starter substance in step (a-I ) or is added immediately afterwards in step (a-II).

To step (ß):

Step (ß) serves to activate the DMC catalyst. If appropriate, this step can be carried out under an inert gas atmosphere, under an atmosphere of an inert gas/carbon dioxide mixture or under a carbon dioxide atmosphere. Activation for the purposes of this invention is a step in which a portion of alkylene oxide is added to the DMC catalyst suspension at temperatures of 90 to 150° C. and then the addition of the alkylene oxide is interrupted, heat being generated as a result of a subsequent exothermic chemical reaction , which can lead to a temperature peak ("hotspot"), as well as due to the conversion of alkylene oxide and optionally CO2 a pressure drop in the reactor is observed. The process step of activation is the period of time from the addition of the partial amount of alkylene oxide, if appropriate in the presence of CO 2 , to the DMC catalyst until heat is generated. If appropriate, the partial amount of the alkylene oxide can be added to the DMC catalyst in a number of individual steps, if appropriate in the presence of CO2, and the addition of the alkylene oxide can then be interrupted in each case. In this case, the process step of activation comprises the period of time from the addition of the first portion of alkylene oxide, optionally in the presence of CO2, to the DMC catalyst until the occurrence of heat evolution after addition of the last portion of alkylene oxide. In general, the activation step can be preceded by a step for drying the DMC catalyst and, if appropriate, the H-functional starter substance at elevated temperature and/or reduced pressure, if appropriate with passing an inert gas through the reaction mixture.

The alkylene oxide (and optionally the carbon dioxide) can in principle be metered in in different ways. Dosing can be started from the vacuum or with a previously selected pre-pressure. The admission pressure is preferably set by introducing an inert gas (such as nitrogen or argon) or carbon dioxide, the pressure (absolute) being 5 mbar to 100 bar, preferably 10 mbar to 50 bar and preferably 20 mbar to 50 bar.

In a preferred embodiment, the amount of alkylene oxide used in the activation in step (ß) is 0.1 to 25.0% by weight, preferably 1.0 to 20.0% by weight, particularly preferably 2.0 to 16 .0% by weight (based on the amount of egg-functional starter substance used in step (a)). The alkylene oxide can be added in one step or in portions in several portions. After the addition of a portion of the alkylene oxide, the addition of the alkylene oxide is preferably interrupted until heat is generated and only then is the next portion of alkylene oxide added. A two-stage activation (step ß) is also preferred

(ßl) in a first activation stage, the addition of a first subset of alkylene oxide takes place under an inert gas atmosphere and

(ß2) in a second activation stage, the addition of a second subset of alkylene oxide takes place under a carbon dioxide atmosphere.

To step (g):

The metering of egg-functional starter substance, alkylene oxide and, if appropriate, a suspending agent that has no egg-functional groups, and/or carbon dioxide can be done simultaneously or sequentially (in portions), for example, the entire amount of carbon dioxide, the amount of egg-functional starter substance, Suspension agent that has no egg functional groups, and / or in step (g) metered amount of alkylene oxide are added all at once or continuously. As used herein, the term "continuously" can be defined as a mode of addition of a reactant such that a concentration of the reactant effective for copolymerization is maintained, ie, for example, dosing can be carried out at a constant dosing rate, with a varying dosing rate or in portions.

It is possible during the addition of the alkylene oxide, suspending agent not having H-functional groups, and/or H-functional starter substance to gradually or stepwise increase or decrease the CCE pressure or leave it the same. The total pressure is preferably kept constant during the reaction by adding more carbon dioxide. The metering of the alkylene oxide, the suspending agent which has no H-functional groups, and/or H-functional starter substance takes place simultaneously or sequentially with the carbon dioxide metering. It is possible to meter in the alkylene oxide at a constant metering rate, or to increase or decrease the metering rate gradually or stepwise, or to add the alkylene oxide in portions. The alkylene oxide is preferably added to the reaction mixture at a constant metering rate. If several alkylene oxides are used to synthesize the polyether carbonate polyols, the alkylene oxides can be metered in individually or as a mixture. The dosage of the alkylene oxide, the suspending agent that has no H-functional groups, or the H-functional starter substance can be done simultaneously or sequentially via separate dosages (additions) or via one or more dosages, with alkylene oxide, the suspending agent that has no Has H-functional groups, or the H-functional starter substance can be dosed individually or as a mixture. Statistical, alternating, block-like or gradient-like polyether carbonate polyols can be synthesized via the type and/or order of metering of the H-functional starter substance, the alkylene oxide, the suspending agent which has no H-functional groups, and/or the carbon dioxide.

An excess of carbon dioxide is preferably used, based on the calculated amount of carbon dioxide to be incorporated in the polyethercarbonate polyol, since an excess of carbon dioxide is advantageous due to the inertness of carbon dioxide. The amount of carbon dioxide can be determined via the total pressure under the particular reaction conditions. The range from 0.01 to 120 bar, preferably from 0.1 to 110 bar, particularly preferably from 1 to 100 bar, has proven advantageous as the total pressure (absolute) for the copolymerization to prepare the polyethercarbonate polyols. It is possible to supply the carbon dioxide continuously or discontinuously. This depends on how quickly the alkylene oxide is consumed and whether or not the product is intended to contain CCE-free polyether blocks. The amount of carbon dioxide (expressed as pressure) can also vary when adding the alkylene oxide. CO2 can also be added to the reactor as a solid and then, under the selected reaction conditions, convert to the gaseous, dissolved, liquid and/or supercritical state.

It has also been shown for the process according to the invention that the copolymerization (step (g)) for preparing the polyethercarbonate polyols is advantageously at 50 to 150° C., preferably at 60 to 145° C., particularly preferably at 70 to 140° C. and very particularly preferably is carried out at 90 to 130 °C. If temperatures are set below 50 °C, the reaction in generally very slow. At temperatures above 150 °C, the amount of undesired by-products increases sharply.

If appropriate, catalyst can likewise be metered in in step (g). The metering of the alkylene oxide, H-functional starter substance, the suspending agent, which has no H-functional groups, and the catalyst can take place via separate or common metering points. In a preferred embodiment, alkylene oxide, H-functional starter substance and, if appropriate, suspension medium which has no H-functional groups are fed continuously to the reaction mixture via separate metering points. This addition of H-functional starter substance and the suspending agent, which has no H-functional groups, can take place as continuous metering into the reactor or in portions.

Steps (a), (β) and (g) can be carried out in the same reactor or each separately in different reactors. Particularly preferred reactor types are: tubular reactors, stirred tanks, loop reactors.

Polyethercarbonate polyols can be prepared in a stirred tank, the stirred tank being cooled, depending on the embodiment and mode of operation, via the reactor jacket, internal cooling surfaces and/or cooling surfaces located in a pumped circuit. Both in the semi-batch application, in which the product is removed only after the end of the reaction, and in the continuous application, in which the product is removed continuously, particular attention must be paid to the metering rate of the alkylene oxide. It is to be set in such a way that, despite the inhibiting effect of the carbon dioxide, the alkylene oxide reacts sufficiently quickly. The concentration of free alkylene oxide in the reaction mixture during the activation step (step ß) is preferably >0 to 100% by weight, more preferably >0 to 50% by weight, most preferably >0 to 20% by weight (each based on the weight of the reaction mixture). The concentration of free alkylene oxide in the reaction mixture during the reaction (step g) is preferably >0 to 40% by weight, more preferably >0 to 25% by weight, most preferably >0 to 15% by weight (each based on on the weight of the reaction mixture).

In a preferred embodiment, the activated DMC catalyst-containing mixture resulting from steps (a) and (β) is further reacted in the same reactor with alkylene oxide, H-functional starter substance, optionally suspension medium which has no H-functional groups, and carbon dioxide. In a further preferred embodiment, the mixture containing the activated DMC catalyst resulting from steps (a) and (ß) is further treated in another reaction vessel (e.g. a stirred tank, tubular reactor or loop reactor) with alkylene oxide, H-functional starter substance, optionally suspension agent, that has no H-functional groups, and implemented carbon dioxide.

When the reaction is carried out in a tubular reactor, the activated DMC catalyst-containing mixture resulting from steps (a) and (ß), H-functional starter substance, alkylene oxide, if appropriate suspension medium which has no H-functional groups, and carbon dioxide continuously pumped through a tube. The molar ratios of the reactants vary depending on the polymer desired. In a preferred embodiment, carbon dioxide is metered in in its liquid or supercritical form in order to enable optimum miscibility of the components. Advantageously, mixing elements are installed for better mixing of the reactants, such as those sold by Ehrfeld Mikrotechnik BTS GmbH, for example, or mixer-heat exchanger elements, which at the same time improve mixing and heat dissipation.

Loop reactors can also be used to produce polyethercarbonate polyols. These generally include reactors with material recycling, such as a jet loop reactor, which can also be operated continuously, or a loop-shaped tubular reactor with suitable devices for circulating the reaction mixture, or a loop of a plurality of tubular reactors connected in series. The use of a loop reactor is particularly advantageous because backmixing can be implemented here, so that the concentration of free alkylene oxide in the reaction mixture is in the optimum range, preferably in the range >0 to 40% by weight, particularly preferably >0 to 25% by weight % by weight, most preferably >0 to 15% by weight (in each case based on the weight of the reaction mixture).

The polyether carbonate polyols are preferably produced in a continuous process which comprises both continuous copolymerization and continuous addition of H-functional starter substance and, if appropriate, suspension agent which has no H-functional groups.

The invention therefore also relates to a process in which, in step (g), H-functional starter substance, alkylene oxide, any suspension agent which has no H-functional groups, and DMC catalyst in the presence of carbon dioxide (“copolymerization”) are continuously introduced into the reactor are metered in and the resulting reaction mixture (comprising polyether carbonate polyol and cyclic carbonate) is continuously removed from the reactor. In step (g), the DMC catalyst suspended in H-functional starter substance is preferably added continuously.

For example, a DMC catalyst-containing mixture is prepared for the continuous process for preparing the polyethercarbonate polyols, then according to step (g)

(gΐ) in each case a subset of H-functional starter substance, alkylene oxide and carbon dioxide metered in to initiate the copolymerization, and

(g2) as the copolymerization progresses, the remaining amount of DMC catalyst, H-functional starter substance, any suspension agent that has no H-functional groups, and alkylene oxide are metered in continuously in the presence of carbon dioxide, with the resulting reaction mixture being simultaneously discharged continuously from the reactor Will get removed. In step (g), the catalyst is preferably added suspended in H-functional starter substance, the amount preferably being chosen such that the content of catalyst in the resulting reaction product is 10 to 10000 ppm, particularly preferably 20 to 5000 ppm and most preferably 50 to 500 ppm.

Preferably, steps (a) and (β) are carried out in a first reactor and the resulting reaction mixture is then transferred to a second reactor for the copolymerization of step (g). However, it is also possible to carry out steps (a), (β) and (g) in one reactor. As used herein, the term "continuously" can be defined as a mode of addition of a relevant catalyst or reactant such that a substantially continuously effective concentration of the catalyst or reactant is maintained. The catalyst feed can be truly continuous or in relatively closely spaced increments. Likewise, continuous addition of H-functional initiator and continuous addition of suspending agent not having H-functional groups can be truly continuous or incremental. It would not depart from the present method to incrementally add a catalyst or reactant such that the concentration of the materials being added falls to essentially zero for some time prior to the next incremental addition. However, it is preferred that the catalyst concentration is maintained at substantially the same concentration during the majority of the course of the continuous reaction and that H-functional initiator substance is present during the majority of the copolymerization process. Incremental addition of catalyst and/or reactant that does not substantially affect the nature of the product is still "continuous" as the term is used herein. For example, it is feasible to provide a recycle loop in which a portion of the reacting mixture is recycled to a previous point in the process, thereby smoothing out discontinuities caused by incremental additions.

step (d)

If appropriate, in a step (d) the reaction mixture in step (g) can be transferred to an after-reactor in which the content of free alkylene oxide in the reaction mixture is reduced by way of an after-reaction. A tubular reactor, a loop reactor or a stirred tank, for example, can serve as the after-reactor.

The pressure in this after-reactor is preferably the same as in the reaction apparatus in which reaction step (g) is carried out. However, the pressure in the downstream reactor can also be selected to be higher or lower. In a further preferred embodiment, all or part of the carbon dioxide is released after reaction step (g) and the downstream reactor is operated at normal pressure or at a slight excess pressure. The temperature in the downstream reactor is preferably from 50 to 150.degree. C. and particularly preferably from 80 to 140.degree. The polyether carbonate polyols obtained have, for example, a functionality of at least 1, preferably from 1 to 8, particularly preferably from 1 to 6 and very particularly preferably from 2 to 4. The molecular weight is preferably 400 to 10000 g/mol and particularly preferably 500 to 6000 g/mol.

alkylene oxide

In general, alkylene oxides (epoxides) having 2-24 carbon atoms can be used for the process. The alkylene oxides having 2-24 carbon atoms are, for example, one or more compounds selected from the group consisting of ethylene oxide, propylene oxide, 1-butene oxide, 2,3-butene oxide, 2-methyl-1,2-propene oxide (isobutene oxide), 1-pentene oxide, 2,3-pentene oxide, 2-methyl-1,2-butene oxide, 3-methyl-1,2-butene oxide, 1-hexene oxide, 2,3-hexene oxide, 3,4-hexene oxide, 2-methyl- l,2-pentene oxide, 4-methyl-l,2-pentene oxide, 2-ethyl-1,2-butene oxide, 1-heptene oxide, 1-octene oxide, 1-nonene oxide, 1-decene oxide, 1-undecene oxide, 1-dodecene oxide, 4-Methyl-1,2-pentene oxide, butadiene monoxide, isoprene monoxide, cyclopentene oxide, cyclohexene oxide, cycloheptene oxide, cyclooctene oxide, styrene oxide, methyl styrene oxide, pinene oxide, mono- or polyepoxidized fats as mono-, di- and triglycerides, epoxidized fatty acids, Ci-C24- Esters of epoxidized fatty acids, epichlorohydrin, glycidol, and derivatives of glycidol such as methyl glycidyl ether, ethyl glycidyl ether, 2-ethylhexyl glycidyl ether, allyl glycidyl ether, Gly cidyl methacrylate and epoxy-functional alkoxysilanes such as 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropyltriethoxysilane, 3-glycidyloxypropyltripropoxysilane, 3-glycidyloxypropylmethyldimethoxysilane, 3-glycidyloxypropylethyldiethoxysilane, 3-glycidyloxypropyltriisopropoxysilane. The alkylene oxide used is preferably ethylene oxide and/or propylene oxide, in particular propylene oxide. A mixture of alkylene oxides can also be used as the alkylene oxide in the process according to the invention.

H-functional starter substance

As a suitable H-functional starter substance ("starter"), compounds with active H atoms for the alkoxylation can be used which have a molar mass of 18 to 4500 g/mol, preferably 62 to 500 g/mol and particularly preferably 62 to 182 g/mol.

Groups with active H atoms which are active for the alkoxylation are, for example, -OH, -NH2 (primary amines), -NH- (secondary amines), -SH and -CO2H, -OH and -NH2 are preferred, and -OH is particularly preferred. As an H-functional starter substance, for example, one or more compounds are selected from the group consisting of monohydric or polyhydric alcohols, polyhydric amines, polyhydric thiols, amino alcohols, thioalcohols, hydroxy esters, polyether polyols, polyester polyols, polyester ether polyols, polyether carbonate polyols, polycarbonate polyols, polycarbonates, polyethylene imines, polyether amines , polytetrahydrofurans (e.g. PolyTHF ^® from BASF), polytetrahydrofuranamines, polyetherthiols, polyacrylate polyols, castor oil, the mono- or diglyceride of ricinoleic acid, monoglycerides of fatty acids, chemically modified mono-, di- and/or triglycerides of fatty acids, and C1- C24 alkyl fatty acid esters containing an average of at least 2 OH groups per molecule are used. Examples are the C1-C24 alkyl fatty acid esters contain an average of at least 2 OH groups per molecule in order to obtain commercial products such as Lupranol ^Balance® (BASF AG), ^Merginol® types (Hobum Oleochemicals GmbH), ^Sovermol® types (Cognis Deutschland GmbH & Co. KG ) and Soyol ^® TM grades (USSC Co.).

Alcohols, amines, thiols and carboxylic acids can be used as monofunctional starter substances. The following can be used as monofunctional alcohols: methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, tert. -Butanol, 3-buten-l-ol, 3-butyn-l-ol, 2-methyl-3-buten-2-ol, 2-methyl-3-butyn-2-ol, propagyl alcohol, 2-methyl-2 -propanol, l-tert-butoxy-2-propanol, 1-pentanol, 2-pentanol, 3-pentanol, 1-hexanol, 2-hexanol, 3-hexanol, 1-heptanol, 2-heptanol, 3-heptanol, 1 - Octanol, 2-octanol, 3-octanol, 4-octanol, phenol, 2-hydroxybiphenyl, 3-hydroxybiphenyl, 4-hydroxybiphenyl, 2-hydroxypyridine, 3-hydroxypyridine, 4-hydroxypyridine. Suitable monofunctional amines are: butylamine, tert-butylamine, pentylamine, hexylamine, aniline, aziridine, pyrrolidine, piperidine, morpholine. The following can be used as monofunctional thiols: ethanethiol, 1-propanethiol, 2-propanethiol, 1-butanethiol, 3-methyl-1-butanethiol, 2-butene-1-thiol, thiophenol. The following may be mentioned as monofunctional carboxylic acids: formic acid, acetic acid, propionic acid, butyric acid, fatty acids such as stearic acid, palmitic acid, oleic acid, linoleic acid, linolenic acid, benzoic acid, acrylic acid.

Polyhydric alcohols suitable as H-functional starter substance are, for example, dihydric alcohols (such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,4-butenediol , 1,4-butynediol, neopentyl glycol, 1,5-pentanediol, methylpentanediols (such as 3-methyl-1,5-pentanediol), 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, 1, 12-dodecanediol, bis(hydroxymethyl)cyclohexanes (such as 1,4-bis(hydroxymethyl)cyclohexane), triethylene glycol, tetraethylene glycol, polyethylene glycols, dipropylene glycol, tripropylene glycol, polypropylene glycols, dibutylene glycol and polybutylene glycols); trihydric alcohols (such as trimethylolpropane, glycerin, trishydroxyethyl isocyanurate, castor oil); tetrahydric alcohols (such as pentaerythritol); Polyalcohols (such as sorbitol, hexitol, sucrose, starch, starch hydrolysates, cellulose, cellulose hydrolysates, hydroxy-functionalized fats and oils, especially castor oil), and all modification products of these aforementioned alcohols with varying amounts of e-caprolactone.

The H-functional starter substance can also be selected from the substance class of polyether polyols, which have a molecular weight M _n in the range from 18 to 4500 g/mol and a functionality of 2 to 3. Preference is given to polyether polyols which are built up from repeating ethylene oxide and propylene oxide units, preferably with a proportion of 35 to 100% propylene oxide units, particularly preferably with a proportion of 50 to 100% propylene oxide units. These can be random copolymers, gradient copolymers, alternating or block copolymers of ethylene oxide and propylene oxide.

The H-functional starter substance can also be selected from the substance class of polyester polyols. At least difunctional polyesters are used as polyester polyols. Preferably pass Polyester polyols made from alternating acid and alcohol units. As acid components z. B. succinic acid, maleic acid, maleic anhydride, adipic acid, phthalic anhydride, phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride or mixtures of the acids and / or anhydrides mentioned. As alcohol components z. B. ethanediol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,4- Bis-(hydroxymethyl)-cyclohexane, diethylene glycol, dipropylene glycol, trimethylolpropane, glycerol, pentaerythritol or mixtures of the alcohols mentioned are used. If dihydric or polyhydric polyether polyols are used as the alcohol component, polyester ether polyols are obtained which can also serve as starter substances for the production of the polyether carbonate polyols.

Furthermore, polycarbonate diols can be used as H-functional starter substance, which are produced, for example, by reacting phosgene, dimethyl carbonate, diethyl carbonate or diphenyl carbonate and difunctional alcohols or polyester polyols or polyether polyols. Examples of polycarbonates can be found e.g. B. in EP-A 1359177.

In a further embodiment of the invention, polyether carbonate polyols can be used as the H-functional starter substance. In particular, polyether carbonate polyols which can be obtained by the process according to the invention described here are used. These polyether carbonate polyols used as H-functional starter substance are prepared beforehand for this purpose in a separate reaction step.

The H-functional starter substance generally has a functionality (i.e. number of H atoms active for the polymerization per molecule) of 1 to 8, preferably 2 or 3. The H-functional starter substance is used either individually or as a mixture of at least two H-functional starter substances.

The H-functional starter substance is particularly preferably at least one compound selected from the group consisting of ethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 2 -Methylpropane-1,3-diol, neopentyl glycol, 1,6-hexanediol, 1,8-octanediol, diethylene glycol, dipropylene glycol, glycerol, trimethylolpropane, pentaerythritol, sorbitol, polyether carbonate polyols with a molecular weight M _n in the range from 150 to 8000 g/mol with a functionality of 2 to 3 and polyether polyols with a molecular weight M _n in the range of 150 to 8000 g/mol and a functionality of 2 to 3.

In a particularly preferred embodiment, the subset of H-functional starter substance in step (a) is selected from at least one compound from the group consisting of polyether carbonate polyols with a molecular weight M _n in the range from 150 to 8000 g/mol with a functionality of 2 to 3 and polyether polyols with a molecular weight M _n in the range from 150 to 8000 g/mol and a functionality from 2 to 3. In another particularly preferred embodiment, the H-functional starter substance in step (g) is selected from at least one compound from the group consisting of ethylene glycol, Propylene Glycol, 1,3-Propanediol, 1,3-Butanediol, 1,4-butanediol, 1,5-pentanediol, 2-methylpropane-1,3-diol, neopentyl glycol, 1,6-hexanediol, 1,8-octanediol, diethylene glycol, dipropylene glycol, glycerine, trimethylolpropane, pentaerythritol and sorbitol.

The polyether carbonate polyols are produced by catalytic addition of carbon dioxide and alkylene oxide onto H-functional starter substance. For the purposes of the invention, “H-functional” means the number of H atoms active for the alkoxylation per molecule of the starter substance.

suspending agent

The suspending agent used, if any, does not contain any H-functional groups. All polar-aprotic, weakly polar-aprotic and non-polar-aprotic solvents which do not contain any H-functional groups are suitable as suspension medium which does not have any H-functional groups. A mixture of two or more of these suspending agents can also be used as the suspending agent which does not have any H-functional groups. The following polar aprotic solvents may be mentioned here as examples: 4-methyl-2-oxo-l,3-dioxolane (also referred to below as cyclic propylene carbonate or cPC), l,3-dioxolan-2-one (also referred to below as referred to as cyclic ethylene carbonate or cEC), acetone, methyl ethyl ketone, acetonitrile, nitromethane, dimethyl sulfoxide, sulfolane, dimethylformamide, dimethylacetamide and N-methylpyrrolidone. The group of non-polar and weakly polar aprotic solvents includes, for example, ethers such as dioxane, diethyl ether, methyl tert-butyl ether and tetrahydrofuran, esters such as ethyl acetate and butyl acetate, hydrocarbons such as pentane, n-hexane, benzene and alkylated benzene derivatives (e.g. toluene, xylene, ethylbenzene) and chlorinated hydrocarbons such as chloroform, chlorobenzene, dichlorobenzene and carbon tetrachloride. 4-Methyl-2-oxo-1,3-dioxolane, 1,3-dioxolan-2-one, toluene, xylene, ethylbenzene, chlorobenzene and dichlorobenzene and mixtures of two or several of these suspending agents are used, particular preference being given to 4-methyl-2-oxo-1,3-dioxolane and 1,3-dioxolan-2-one or a mixture of 4-methyl-2-oxo-1,3-dioxolane and 1 ,3-dioxolan-2-one.

In step (g), preference is given to 2% by weight to 20% by weight, particularly preferably 5% by weight to 15% by weight and particularly preferably 7% by weight to 11% by weight of the suspending agent has no H-functional groups, based on the sum of the components metered in step (g).

DMC catalysts

DMC catalysts for use in the homopolymerization of alkylene oxides are known in principle from the prior art (see, for example, US-A 3,404,109, US-A 3,829,505, US-A 3,941,849 and US-A 5,158,922) . DMC catalysts described, for example, in US-A 5,470,813, EP-A 700,949, EP-A 743,093, EP-A 761,708, WO 97/40086, WO 98/16310 and WO 00/47649 a very high activity and allow the production of polyether carbonate polyols at very low catalyst concentrations, so that a separation of the catalyst from the finished product ia is no longer required. A typical example are the highly active DMC catalysts described in EP-A 700 949, which, in addition to a double metal cyanide compound (eg zinc hexacyanocobaltate(III)) and an organic complex ligand (eg tert-butanol), also contain a polyether with a number-average molecular weight greater than 500 g/mol.

The DMC catalysts are preferably obtained by

(i) in the first step, an aqueous solution of a metal salt is reacted with the aqueous solution of a metal cyanide salt in the presence of one or more organic complex ligands, e.g. an ether or alcohol,

(ii) wherein in the second step the solid is separated from the suspension obtained from (i) by known techniques (such as centrifugation or filtration),

(iii) where, in a third step, if appropriate, the isolated solid is washed with an aqueous solution of an organic complex ligand (e.g. by resuspending and subsequent renewed isolation by filtration or centrifugation),

(iv) the resulting solid then being dried, optionally after pulverization, at temperatures of generally 20-120° C. and at pressures of generally 0.1 mbar to atmospheric pressure (1013 mbar), and in the first step or immediately thereafter the precipitation of the double metal cyanide compound (second step) one or more organic complex ligands, preferably in excess (based on the double metal cyanide compound) and optionally further complexing components are added.

The double metal cyanide compounds contained in the DMC catalysts are the reaction products of water-soluble metal salts and water-soluble metal cyanide salts.

For example, an aqueous solution of zinc chloride (preferably in excess relative to the metal cyanide salt such as potassium hexacyanocobaltate) and potassium hexacyanocobaltate are mixed and then dimethoxyethane (glyme) or tert-butanol (preferably in excess relative to zinc hexacyanocobaltate) is added to the suspension formed.

Metal salts suitable for preparing the double metal cyanide compounds preferably have the general formula (II),

M(X)n (II) where

M is selected from the metal cations Zn ²⁺ , Fe ²⁺ , Ni ²⁺ , Mn ²⁺ , Co ²⁺ , Sr ² . Sn ²⁺ , Pb ²⁺ and, Cu ²⁺ , preferably M is Zn ²⁺ , Fe ²⁺ , Co ²⁺ or Ni ²⁺ ,

X is one or more (ie different) anions, preferably an anion selected from the group consisting of halides (ie fluoride, chloride, bromide, iodide), hydroxide, sulfate, carbonate, cyanate, thiocyanate, isocyanate, isothiocyanate, carboxylate, oxalate and nitrate ; n is 1 when X = sulfate, carbonate or oxalate and n is 2 when X = halide, hydroxide, carboxylate, cyanate, thiocyanate, isocyanate, isothiocyanate or is nitrate, or suitable metal salts have the general formula (III),

M _r (X) ₃ (III) where

M is selected from the metal cations Fe ³⁺ , Al ³⁺ , Co ³⁺ and Cr ³⁺ ,

X is one or more (i.e. different) anions, preferably an anion selected from the group consisting of halides (i.e. fluoride, chloride, bromide, iodide), hydroxide, sulfate, carbonate, cyanate, thiocyanate, isocyanate, isothiocyanate, carboxylate, oxalate and nitrate ; r is 2 when X = sulfate, carbonate or oxalate and r is 1 when X = halide, hydroxide, carboxylate, cyanate, thiocyanate, isocyanate, isothiocyanate or nitrate, or suitable metal salts have the general formula (IV),

M(X) _S (IV) where

M is selected from the metal cations Mo ⁴⁺ , V ⁴⁺ and W ⁴⁺

X is one or more (i.e. different) anions, preferably an anion selected from the group consisting of halides (i.e. fluoride, chloride, bromide, iodide), hydroxide, sulfate, carbonate, cyanate, thiocyanate, isocyanate, isothiocyanate, carboxylate, oxalate and nitrate ; s is 2 when X = sulfate, carbonate or oxalate and s is 4 when X = halide, hydroxide, carboxylate, cyanate, thiocyanate, isocyanate, isothiocyanate or nitrate, or suitable metal salts have the general formula (V),

M(X), (V) where

M is selected from the metal cations Mo ⁶⁺ and W ⁶⁺

X is one or more (i.e. different) anions, preferably an anion selected from the group consisting of halides (i.e. fluoride, chloride, bromide, iodide), hydroxide, sulfate, carbonate, cyanate, thiocyanate, isocyanate, isothiocyanate, carboxylate, oxalate and nitrate ; t is 3 when X = sulfate, carbonate or oxalate and t is 6 when X = halide, hydroxide, carboxylate, cyanate, thiocyanate, isocyanate, isothiocyanate or nitrate,

Examples of suitable metal salts are zinc chloride, zinc bromide, zinc iodide, zinc acetate, zinc acetylacetonate, zinc benzoate, zinc nitrate, iron(II) sulfate, iron(II) bromide, iron(II) chloride, iron(III) chloride, cobalt(II) chloride, cobalt(II) thiocyanate, nickel(II) chloride and nickel(II) nitrate. Mixtures of different metal salts can also be used.

Metal cyanide salts suitable for preparing the double metal cyanide compounds preferably have the general formula (VI) (Y)a M'(CN) _b (A), (VI) where

M' is selected from one or more metal cations from the group consisting of Fe(II), Fe(III), Co(II), Co(III), Cr(II), Cr(III), Mn(II), Mn( III), Ir(III), Ni(II), Rh(III), Ru(II), V(IV) and V(V), preferably M' is one or more metal cations from the group consisting of Co(II), Co(III), Fe(II), Fe(III), Cr(III), Ir(III) and Ni(II),

Y is selected from one or more metal cations from the group consisting of alkali metal (ie Li ⁺ , Na ⁺ , K ⁺ , Rb>nd alkaline earth metal (ie Be ²⁺ , Mg ²⁺ , Ca ²⁺ , Sr ² . Ba ²⁺ ),

A is selected from one or more anions from the group consisting of halides (i.e. fluoride, chloride, bromide, iodide), hydroxide, sulfate, carbonate, cyanate, thiocyanate, isocyanate, isothiocyanate, carboxylate, azide, oxalate or nitrate and a, b and c are integers, the values for a, b and c being chosen such that the metal cyanide salt is electroneutral; a is preferably 1, 2, 3 or 4; b is preferably 4, 5 or 6; c preferably has the value 0.

Examples of suitable metal cyanide salts are sodium hexacyanocobaltate(III), potassium hexacyanocobaltate(III), potassium hexacyanoferrate(II), potassium hexacyanoferrate(III), calcium hexacyanocobaltate(III) and lithium hexacyanocobaltate(III).

Preferred double metal cyanide compounds contained in the DMC catalysts are compounds of the general formula (VII)

M _x [M' _x ,(CN) _y ] _z (VII) wherein M is as defined in formula (II) to (V) and M' is as defined in formula (VI), and x, x', y and z are integer and chosen so that the electron neutrality of the double metal cyanide compound is given.

Preferably x = 3, x' = 1, y = 6 and z = 2,

M = Zn(II), Fe(II), Co(II) or Ni(II) and M' = Co(III), Fe(III), Cr(III) or Ir(III).

Examples of suitable double metal cyanide compounds a) are zinc hexacyanocobaltate(III), zinc hexacyanoiridate(III), zinc hexacyanoferrate(III) and cobalt(II) hexacyanocobaltate(III). Further examples of suitable double metal cyanide compounds can be found, for example, in US 5,158,922 (column 8, lines 29-66). Zinc hexacyanocobaltate(III) is particularly preferably used.

The organic complex ligands added in the preparation of the DMC catalysts are described, for example, in US Pat. No. 5,158,922 (see in particular column 6, lines 9 to 65), US Pat. No. 3,404,109, US Pat. No. 3,829,505, US Pat , EP-A 761 708, JP 4 145 123, US 5 470 813, EP-A 743 093 and WO-A 97/40086). For example, water-soluble, organic compounds with heteroatoms, such as oxygen, nitrogen, phosphorus or sulfur, are used as organic complex ligands able to form complexes with the double metal cyanide compound. Preferred organic complex ligands are alcohols, aldehydes, ketones, ethers, esters, amides, ureas, nitriles, sulfides and mixtures thereof. Particularly preferred organic complex ligands are aliphatic ethers (such as dimethoxyethane), water-soluble aliphatic alcohols (such as ethanol, isopropanol, n-butanol, isobutanol, sec.-butanol, tert-butanol, 2-methyl-3-buten-2-ol and 2-methyl-3-butyn-2-ol), compounds containing both aliphatic or cycloaliphatic ether groups and aliphatic hydroxyl groups (such as ethylene glycol mono-tert-butyl ether, diethylene glycol mono-tert-butyl ether, tripropylene glycol mono -methyl ether and 3-methyl-3-oxetane-methanol). Highly preferred organic complex ligands are selected from one or more compounds from the group consisting of dimethoxyethane, tert-butanol, 2-methyl-3-buten-2-ol, 2-methyl-3-butyn-2-ol, ethylene glycol mono-tert. -butyl ether and 3-methyl-3-oxetane-methanol.

In the production of the DMC catalysts, one or more complex-forming component(s) from the compound classes of polyethers, polyesters, polycarbonates, polyalkylene glycol sorbitan esters, polyalkylene glycol glycidyl ethers, polyacrylamide, poly(acrylamide-co-acrylic acid), polyacrylic acid, poly(acrylic acid-co -maleic acid), polyacrylonitrile, polyalkyl acrylates, polyalkyl methacrylates, polyvinyl methyl ether, polyvinyl ethyl ether, polyvinyl acetate, polyvinyl alcohol, poly-N-vinylpyrrolidone, poly(N-vinylpyrrolidone-co-acrylic acid), polyvinyl methyl ketone, poly(4-vinylphenol), poly(acrylic acid-co- styrene), oxazoline polymers, polyalkylenimines, maleic acid and maleic anhydride copolymers, hydroxyethyl cellulose and polyacetals, or glycidyl ethers, glycosides, carboxylic acid esters of polyhydric alcohols, bile acids or their salts, esters or amides, cyclodextrins, phosphorus compounds, a,b-unsaturated carboxylic acid esters or ionic surfaces - Or surface-active compounds used currently

When preparing the DMC catalysts, preference is given in the first step to using the aqueous solutions of the metal salt (e.g. zinc chloride), used in a stoichiometric excess (at least 50 mol %) based on the metal cyanide salt (i.e. at least a molar ratio of metal salt to metal cyanide salt of 2.25 to 1.00) and the metal cyanide salt (e.g. potassium hexacyanocobaltate) in the presence of the organic complex ligand (e.g. tert-butanol) to form a suspension containing the double metal cyanide compound (e.g. zinc hexacyanocobaltate), water, excess metal salt, and the organic Contains complex ligands.

The organic complex ligand can be present in the aqueous solution of the metal salt and/or the metal cyanide salt, or it is added directly to the suspension obtained after the double metal cyanide compound has been filled out. It has proven advantageous to mix the aqueous solutions of the metal salt and the metal cyanide salt and the organic complex ligand with vigorous stirring. Optionally, the suspension formed in the first step is then treated with another complex-forming component. The complex-forming component is preferably used in a mixture with water and organic complex ligands. A preferred method of performing the first step (i.e. the Preparation of the suspension) takes place using a mixing nozzle, particularly preferably using a jet disperser as described in WO-A 01/39883.

In the second step, the solid (i.e. the precursor of the catalyst) is isolated from the suspension by known techniques such as centrifugation or filtration.

In a preferred embodiment, the isolated solid is then washed in a third process step with an aqueous solution of the organic complex ligand (e.g. by resuspending and subsequent renewed isolation by filtration or centrifugation). In this way, for example, water-soluble by-products such as potassium chloride can be removed from the catalyst. The amount of the organic complex ligand in the aqueous washing solution is preferably between 40 and 80% by weight, based on the total solution.

In the third step, further complex-forming components are optionally added to the aqueous washing solution, preferably in the range between 0.5 and 5% by weight, based on the total solution. In addition, it is advantageous to wash the isolated solid more than once. In a first washing step (iii-1), it is preferable to wash with an aqueous solution of the organic complex ligand (e.g. by resuspending and then re-isolating by filtration or centrifugation) in order to remove water-soluble by-products, such as potassium chloride, from the catalyst, for example . The amount of the organic complex ligand in the aqueous washing solution is particularly preferably between 40 and 80% by weight, based on the total solution of the first washing step. In the further washing steps (iii-2), either the first washing step is repeated once or several times, preferably once to three times, or preferably a non-aqueous solution, such as a mixture or solution of organic complex ligands and other complex-forming components (preferably in the range between 0.5 and 5 wt. The isolated and optionally washed solid is then dried, optionally after pulverization, at temperatures of generally 20-100° C. and at pressures of generally 0.1 mbar to normal pressure (1013 mbar).

A preferred process for isolating the DMC catalysts from the suspension by filtration, filter cake washing and drying is described in WO-A 01/80994.

In addition to the preferably used DMC catalysts based on zinc hexacyanocobaltate (Zrh|Co(CN), | ₂ ), other metal complex catalysts known to those skilled in the art for the copolymerization of epoxides and carbon dioxide and based on the metals zinc can also be used for the process according to the invention and/or cobalt can be used. This includes in particular so-called zinc glutarate catalysts (described, for example, in MH Chisholm et al., Macromolecules 2002, 35, 6494), so-called zinc diiminate catalysts (described, for example, in SD Allen, J. Am. Chem. Soc. 2002, 124, 14284), so-called cobalt-salen catalysts (described, for example, in US Pat. No. 7,304,172 B2, US 2012/0165549 A1) and bimetallic zinc complexes macrocyclic ligands (described eg in MR Kember et al., Angew. Chem., Int. Ed., 2009, 48, 931).

As shown in scheme (I), polyether carbonate polyol and, corresponding to the alkylene oxide used in step (A), cyclic carbonate are obtained from step (A). The cyclic carbonate is preferably selected from at least one compound from the group consisting of cyclic propylene carbonate and cyclic ethylene carbonate.

Step (B):

The mixture resulting from step (A) is separated in step (B) into polyether carbonate polyol and into cyclic carbonate containing impurities. As impurities, for example, residues of starter substances from step (A) such as propylene glycol, dimers or oligomers of starter substances from step (A) such as dipropylene glycol or pentapropylene glycol, or other by-products that arise during step (A), such as dimethyldioxane, in the cyclic contain carbonate. The cyclic carbonate containing impurities can be removed by methods known to those skilled in the art. Thermal processes such as distillation or rectification are preferably used. The cyclic carbonate is particularly preferably separated off from the mixture resulting from step (A) by an evaporation device, such as, for example, a thin-film evaporator or falling-film evaporator, a stripping column or a combination of the above. The cyclic carbonate can be removed by a single-stage or multi-stage process, preference being given to a two-stage process. The cyclic carbonate is most preferably removed in a two-stage process using a thin-film evaporator or a falling-film evaporator in combination with a stripping column. If an evaporation device is used in step (B), it can be operated at a pressure of 100 mbar or below, preferably at 1 to 100 mbar, particularly preferably at 1 to 50 mbar, particularly preferably at 2 to 25 mbar, the temperature of the mixture resulting from step (A) in step (B) is preferably 120 to 180°C, particularly preferably 150 to 170°C. If a stripping column is used, it can be operated under normal pressure or under vacuum, for example at a pressure of 1 to 150 mbar, preferably 50 to 120 mbar, with the stripping column being operated at a temperature of 120 to 180° C., preferably 150 to 170° C can be operated.

An apparatus for separating cyclic carbonate from a mixture containing polyether carbonate polyol is disclosed, for example, in the application EP 3 164443 A1.

It is also possible after the separation of the cyclic carbonate from the mixture resulting from step (A) containing impurities in the cyclic carbonate to separate any residues of the catalyst present from the cyclic carbonate containing impurities. This can be achieved, for example, by filtration. Step (CI:

The cyclic carbonate containing impurities from step (B) is transferred to a first rectification column in order to separate primarily more volatile by-products (“low boilers”) such as water, dimethyldioxane (DMD), monopropylene glycol (MPG), dipropylene glycol (DPG), Spiro orthocarbonate. The first rectification column is equipped with at least one feature selected from the group consisting of structured packing, random packing or trays. The first rectification column is designed in such a way that part of the cyclic carbonate impurity is removed overhead as a distillate stream and a crude mixture containing cyclic carbonate is obtained. A schematic representation of an exemplary first rectification column is shown in FIG. 1 shown. The first rectification column 1 is equipped with a feed line 2 for the cyclic carbonate containing impurities from step (B), a bottom 3, an evaporator 4, a bottom outlet 5 containing the crude mixture containing cycl. Carbonate, a head 6 with a vapor line 7 to the condenser 8 and a distillate removal for the impurities.

The rectification column can be operated at a pressure of 1000 mbar or below, preferably at 5 to 500 mbar, preferably at 50 to 250 mbar, particularly preferably at 120 to 200 mbar, the cycl. Carbonate containing impurities is heated to a temperature of, for example, 120 to 180 °C, preferably 160 to 180 °C.

In a particularly preferred embodiment, the first rectification column is operated at a top pressure of from 100 to 200 mbar and a bottom temperature of from 155 to 185.degree.

In the first rectification column, part of the impurities in the cyclic carbonate is converted into the gas phase and removed via the distillate. The separated part of the impurities can either be removed from the condenser as a gas phase or, after the condensation of the entire gas stream, can be removed from the condensate stream obtained. In both cases, the remaining condensate is returned to the column.

Step (D):

The raw mixture containing cyclic carbonate removed from the first rectification column is transferred to a second rectification column in order to separate off primarily less volatile by-products ("high boilers") such as tripropylene glycol (TriPG), tetrapropylene glycol (TetPG), pentapropylene glycol, hexapropylene glycol and heptapropylene glycol (summary as PentaPG+). or at least only slightly imitate further low-volatile by-products. The second rectification column is equipped with at least one feature selected from the group consisting of structured packing, random packing or trays and can be structurally identical to the first rectification column

(Dl) in (D) a bottom temperature of 130 to 170°C prevails and or

(D-2) the pure cyclic carbonate product is removed from the second rectification column through a side draw.

Step (D-2) is preferably used.

Step (D-l)

In step (D-1), the rectification column can be operated at a pressure of 1000 mbar or below, preferably at 5 to 500 mbar, preferably at 10 to 250 mbar, particularly preferably at 25 to 120 mbar.

In a preferred embodiment, the second rectification column is operated at a top pressure of from 5 to 80 mbar and a bottom temperature of from 140 to 160.degree.

It should be noted here that in step (D-1) the pure product is preferably removed directly from the second rectification column, ie without a side draw.

Step (D-2)

In a further preferred embodiment of process (D-2) according to the invention, in step (D) the pure product is cycl. Carbonate removed through a side draw from the second rectification column. A schematic representation of an exemplary second rectification column with side draw is shown in FIG. 2 shown. The second rectification column 10 comprises a feed line 11 for the crude mixture containing cyclic carbonate from step (C), a bottom containing the impurities 12, an evaporator 13, a bottom outlet 14, an outlet for the pure product cycl separated off as a side stream. carbonate 15, and a head 16 with a vapor line 17 to the condenser 18 and a distillate extraction 19. The gas phase removed at the head 16 of the second rectification column is converted back into the liquid phase and partly introduced again into the second rectification column, while the remaining proportion of the condensate is removed as a distillate in order to remove secondary components.

In step (D-2), a pressure of 1000 mbar or below can be applied to the rectification column, preferably at 5 to 500 mbar, preferably at 10 to 250 mbar, particularly preferably at 25 to 120 mbar, the crude mixture fed in containing cycl. Carbonate is heated to a bottom temperature of, for example, 120 to 180 ° C, preferably from 130 to 170 ° C. The second rectification column using a side draw, ie step (D-2), can be operated at higher temperatures than in a second rectification column without using a side draw, ie step (D1), since more low-boiling secondary components are present due to the higher temperature compared to D1 are reproduced, but these are largely separated from the product stream removed via a side offtake with the aid of the low-boiling discharge via the distillate. In a preferred embodiment of the process according to the invention, the pressure in (D-2) is from 5 to 80 mbar and the bottom temperature is from 140 to 160.degree.

In a particular embodiment of (D1), steps (C) and (D) are carried out in a rectification column with a side column. A schematic representation of an exemplary rectification column with a side column is shown in FIG. 3 shown. The main column 20 has a feed 21, a bottom 22, an evaporator 23, a bottom withdrawal 24, a column top 25, a vapor line 26, a top condenser 27, a distillate withdrawal 28, a side column 29 with associated top condenser 30 and a top withdrawal for the pure cyclic product Carbonate 31. In a further particular embodiment of (D1), steps (C) and (D) are carried out in a dividing wall column. A schematic representation of an exemplary dividing wall column is shown in FIG. 4 shown. The dividing wall column 32 is equipped with a feed 33, a bottom 34, an evaporator 35, a bottom draw 36, a column top 37, a vapor line 38, a top condenser 39, a distillate draw 40, a partition 41 and a side draw for the pure product cyclic carbonate 42 .

examples

The cPC containing impurities used in the examples was obtained from the production of a polyether carbonate polyol by addition of carbon dioxide and propylene oxide to glycerol in the presence of a DMC catalyst (step (A)). The cPC containing impurities was separated from the polyether carbonate polyol by a falling film evaporator and a stripping column.

method description

The educt and product compositions were determined using gas chromatography

All experimental investigations were accompanied by simulation calculations so that the model used could be confirmed on the basis of experimental test results. For this purpose, a stationary simulation model was used that was implemented using the ASPEN PLUS software.

In Example 4, the results were generated using the validated model. For this purpose, a RadFrac unit with 58 theoretical stages and an integrated total condenser and kettle evaporator was implemented in ASPEN PLUS. From a feed stream at stage 41 of 68.7 kg/h, 2% by mass are discharged at the bottom and 2.9% by mass at the top. The remaining amount leaves the column via a liquid side stream at stage 9. The column is operated at a top pressure of 100 mbar and a pressure drop of 12 mbar.

Example 1 (Step (C))

The cPC containing impurities is fed to a packed column which is operated at a top pressure of 140 mbar. With a reflux ratio R/D (reflux amount/distillate amount) of 24, about 2% of the feed amount is removed overhead, while the crude mixture containing cPC leaves the column as bottom product. This resulted in a top temperature of 145° C. and a bottom temperature of 170° C.

Example 2 (Step (D))

The crude mixture containing cPC obtained in Example 1 is fed to a further packed column which is operated at a top pressure of 100 mbar. About 3% of the feed volume is taken off at the bottom, while the pure product cPC leaves the column as the top product at a reflux ratio R/D of 4. This resulted in a head temperature of 160° C. and a bottom temperature of 172° C.

Example 3 (Step (D))

Example 3 was carried out according to the procedure for Example 2, with the described Separation was carried out at a head pressure of 45 mbar instead of 100 mbar. This resulted in a top temperature of 138° C. and a bottom temperature of 150° C.

Example 4 (Step (D))

In this variant, the pure product cPC is drawn off via a liquid side draw in the reinforcement section. A small stream of distillate is produced at the top with a high reflux ratio

Impurities removed. The results for this variant were generated using the simulation model described above. They show that in this configuration, even when operating at 100 mbar, a higher product purity than in example 3 can be achieved. Table 1: Overview of Examples 1 to 4

* Comparative example, nb not determinable, ^# UK. unknown components

The results in table 1, columns 1-3 were determined with GC analysis, the results in column 4 are calculation results of the ASPEN PLUS model.

A comparison of Examples 1 to 4 shows that an additional step (D) (Examples 2 to 4) significantly reduces the proportion of impurities in the cyclic carbonate compared with a process using only step (C) (Example 1). A particularly high purity of the cyclic carbonate is obtained by embodiment D-1 or D-2 according to Examples 3 or 4.

Claims

patent claims

1. A method for purifying cyclic carbonate, characterized by the steps

(B) separation of the mixture resulting from (A) into polyether carbonate polyol and into cyclic carbonate containing impurities,

(D) Feeding the crude mixture obtained in (C) containing cyclic carbonate into a second rectification column, equipped with at least one feature selected from the group consisting of structured packing, a random packing or trays, and subsequent removal of another part of the impurities as a bottom in the second rectification column, wherein the pure product cyclic carbonate is obtained

(D-l) in (D) a bottom temperature of 130 to 170°C prevails and/or

2. The method according to claim 1, wherein a bottom temperature of 155 to 180 ° C prevails in (C).

3. The method according to claim 1 or 2, wherein a pressure of 5 to 500 mbar prevails in (C).

4. The method according to any one of claims 1 to 3, wherein in (D-l) a pressure of 5 to 80 mbar and a bottom temperature of 140 to 160 ° C prevails.

5. The method according to any one of claims 1 to 5, wherein step (D-2) is carried out.

6. The process according to claim 5, wherein in (D-2) the bottom temperature is from 120 to 180°C, preferably from 130 to 170°C.

7. The method according to claim 5 or 6, wherein in (D-2) at a pressure of 1000 mbar or below, preferably from 5 to 500 mbar, preferably from 10 to 250 mbar, particularly preferably from 25 to 120 mbar prevails.

8. The method according to any one of claims 1 to 7, wherein in (D-2) a pressure of 5 to 80 mbar and a bottom temperature of 140 to 160 ° C prevails.

9. The method according to any one of claims 1 to 8, wherein in (A)

(ß) optionally, to activate a DMC catalyst, a portion (based on the total amount of alkylene oxide used in the activation and copolymerization) of alkylene oxide is added to the mixture resulting from step (a), this addition of a portion of alkylene oxide optionally can take place in the presence of CO2, and in which case the temperature peak ("hotspot") occurring as a result of the following exothermic chemical reaction and/or a drop in pressure in the reactor is awaited in each case, and in which step (ß) for activation can also take place several times,

(g) an H-functional starter substance, alkylene oxide and, if appropriate, a suspending agent which has no H-functional groups, and/or carbon dioxide are metered into the reactor during the reaction,

10. The method according to any one of claims 1 to 9, wherein in (B) the cyclic carbonate containing impurities is separated by a thin film evaporator, falling film evaporator, stripping column or a combination of these from the mixture resulting from (A).

11. The method according to any one of claims 1 to 10, wherein the cyclic carbonate is cyclic propylene carbonate, cyclic ethylene carbonate or a mixture of the two mentioned.

12. The method according to any one of claims 1 to 4 and 9 to 11, wherein steps (C) and (D) is carried out in a main column with a side rectification column, each equipped with structured packing, a random packing or trays, the purified cyclic carbonate is removed from the top of the side column.

13. The method according to any one of claims 1 to 4 and 9 to 11, wherein steps (C) and (D) is carried out in a dividing wall column equipped with structured packing, a random packing or trays, the purified cyclic carbonate being removed via a side draw is removed.