JP5579737B2 - Method for removing alkanol impurities from organic carbonate streams - Google Patents

Description

  The present invention relates to a method for removing alkanol impurities from a stream containing organic carbonate and alkanol impurities.

  Examples of organic carbonates include cyclic alkylene carbonates (such as ethylene carbonate) and acyclic dialkyl carbonates (such as diethyl carbonate). It is well known to synthesize cyclic alkylene carbonates by reacting alkylene oxide (such as ethylene oxide) with carbon dioxide in the presence of a suitable catalyst. Such a method is described, for example, in US4508927 and US5508442.

Dialkyl carbonates can be produced by reacting alkylene carbonates with alkanols. When an alkylene carbonate (such as ethylene carbonate) reacts with an alkanol (such as ethanol), the product is a dialkyl carbonate (such as diethyl carbonate) and an alkanediol (such as monoethylene glycol). Such methods are well known and examples of this are disclosed in US Pat. No. 5,359,118. This document discloses a process for preparing di (C ₁ -C ₄ alkyl) carbonate alkanediols by performing a transesterification reaction with an alkylene carbonate and a C ₁ -C ₄ alkanol.

  At various points throughout the process for producing a dialkyl carbonate from an alkylene oxide via an alkylene carbonate, an organic carbonate stream containing one or more alkanol impurities can occur. Examples of such alkanol impurities are ether alkanols such as alkoxyalkanols. For example, in a reactor in which ethanol and ethylene carbonate are reacted into diethyl carbonate and monoethylene glycol, a side reaction between ethanol and ethylene oxide (resulting from the reverse reaction of ethylene carbonate into ethylene oxide and carbon dioxide). Can produce 2-ethoxyethanol (ethyl oxitol). In addition, ethyloxitol can be produced by side reactions of ethanol and ethylene carbonate in such a way that carbon dioxide is released to produce ethyloxitol. Furthermore, side reactions between ethanol and monoethylene glycol can occur to produce ethyl oxitol and water. Still further, ethyl oxytol may be generated by decarboxylation of hydroxyethyl ethyl carbonate.

  Thus, the product stream from the reactor that reacts ethanol and ethylene carbonate to diethyl carbonate and monoethylene glycol is unconverted ethanol, unconverted ethylene carbonate, diethyl carbonate, monoethylene glycol, and the above Of ethyl oxytol impurities. The presence of the alkoxyalkanol impurity can be detrimental in any subsequent production method. The alkoxyalkanol impurity may end up in, for example, a dialkyl carbonate, which is used as a starting material for synthesizing diphenyl carbonate from the dialkyl carbonate and phenol. For example, if the dialkyl carbonate is diethyl carbonate and the alkoxyalkanol impurity is ethyl oxitol, the ethyl oxytol may react with the phenol starting material and / or with the diphenyl carbonate product.

  Direct reaction of phenol with ethyl oxytol can result in the formation of phenyl 2-ethoxyethyl ether, and thus can lead to a reduction in beneficial phenol reactants. Furthermore, such reactions can lead to undesirable chemical species in the process, and can therefore cause separation problems.

  Reaction of diphenyl carbonate with ethyl oxitol results in product loss in the form of phenyl 2-ethoxyethyl carbonate. In addition, phenyl 2-ethoxyethyl carbonate acts as a “poison” in any subsequent polymerization reaction that makes diphenyl carbonate a polycarbonate material. For example, reacting diphenyl carbonate with bis-phenol A (BPA) yields polycarbonate and phenol. Diphenyl carbonate can react with BPA because phenol is a relatively good leaving group. However, because alkanols are not good leaving groups, dialkyl carbonates (such as diethyl carbonate) cannot be used to produce polycarbonate by reaction with BPA. Alkoxyalkanols (such as ethyl oxitol) are also not good leaving groups. Therefore, when phenyl 2-ethoxyethyl carbonate is present in diphenyl carbonate supplied to be reacted with BPA, phenol is easily released from the phenyl 2-ethoxyethyl carbonate, but from ethyl oxytol. That is not the case, and as a result, the polymerization process stops at one end of the chain. For this reason, the phenyl 2-ethoxyethyl carbonate must be removed from the diphenyl carbonate before the diphenyl carbonate is reacted with BPA.

  In the above example where an organic carbonate stream containing an alkanol impurity is formed, it is desirable to remove this alkanol impurity prior to performing any subsequent method of converting the organic carbonate to a valuable end product. For example, prior to the reaction of diethyl carbonate with phenol, it is sought to remove this impurity from a diethyl carbonate stream containing any ethyl oxitol impurity.

  Referring to the above example where ethanol and ethylene carbonate reacted to diethyl carbonate and monoethylene glycol, a product stream that also contains unconverted ethanol, unconverted ethylene carbonate, and ethyl oxitol by-product Can be separated by distillation. The boiling points of the various components in the product stream are listed in the table below.

上記に記載されるとおりの蒸留は、ジエチルカーボナートおよび未変換エタノールを含有する頂部流、ならびにモノエチレングリコールおよび未変換エチレンカーボナートを含有する底部流をもたらすことができる。ほとんどの場合、エチルオキシトールは全て、最終的に頂部流に行き着く。しかしながら、蒸留を行なう特定の条件に依存して、エチルオキシトールの一部が底部流に行き着く可能性もある。その後、前記頂部流をさらに蒸留して、未変換エタノールを含有する頂部流（これはジエチルカーボナートおよびモノエチレングリコールを生成する反応器に戻して再利用できる。）、およびジエチルカーボナートとエチルオキシトール不純物とを含有する底部流に分離することができる。

Distillation as described above can result in a top stream containing diethyl carbonate and unconverted ethanol, and a bottom stream containing monoethylene glycol and unconverted ethylene carbonate. In most cases, all ethyl oxitol eventually ends up in the top stream. However, depending on the specific conditions under which the distillation is carried out, some of the ethyloxitol may end up in the bottom stream. The top stream is then further distilled to a top stream containing unconverted ethanol (which can be recycled back to the reactor to produce diethyl carbonate and monoethylene glycol), and diethyl carbonate and ethyloxy It can be separated into a bottom stream containing toll impurities.

U.S. Pat. No. 4,508,927 US Pat. No. 5,508,442 US Pat. No. 5,359,118

  As noted above, alkanol impurities can be adversely affected in any subsequent method and / or any further method of converting organic carbonates to beneficial end products, so prior to such methods, Must be removed from there. For the example above, this means that ethyloxitol impurities should be removed from the bottom stream containing diethyl carbonate and ethyloxitol impurities. In principle, ethyl oxytol and diethyl carbonate can be separated in a further distillation step. However, since the difference in boiling point between diethyl carbonate and ethyl oxitol is small (see table above), such separation is very cumbersome and requires multiple distillation steps and steps. Accordingly, there is a need for the discovery of a simple method for removing such alkanol impurities from organic carbonate streams containing alkanol impurities.

  Surprisingly, it was found that by contacting the organic carbonate stream with the extraction solvent and separating the extraction solvent layer from the organic carbonate layer, such alkanol impurities are extracted into the extraction solvent layer and removed from the organic carbonate stream. It was done.

  Accordingly, the present invention relates to a method for removing alkanol impurities from a stream containing organic carbonate and alkanol impurities, the method comprising contacting the stream with an extraction solvent and separating the extraction solvent layer from the organic carbonate layer. including.

Organic carbonates contained in the stream from which alkanol impurities should be removed according to the present invention are di (C ₁ -C ₅ ) alkyl carbonates such as methyl, ethyl, propyl (alkyl groups contained therein (straight, branched) And / or cyclic) may be the same or different.); Or di (C ₅ -C ₇ ) aryl carbonates such as phenyl (the aryl groups contained therein are the same or different) Or (C ₁ -C ₅ ) alkyl (C ₅ -C ₇ ) aryl carbonate (the alkyl and aryl groups contained therein are as defined above); or ethylene, propylene, butadiene or cyclic, such as styrene carbonate _(C 1 _{-C 10)} alkylene carbonate; or such organic mosquito Mixtures of Bonato are possible. Specifically, the organic carbonate is a dialkyl carbonate, and more specifically diethyl carbonate.

  The alkanol impurity to be removed from the stream containing the organic carbonate and the alkanol impurity according to the present invention can be an ether alkanol, more specifically an alkoxy alkanol, and even more specifically 2-ethoxyethanol, as described above. .

  The amount of alkanol impurities in the stream containing the organic carbonate and said alkanol impurities is 0.1 to 10% by weight, specifically 0.3 to 8% by weight, more specifically 0.5 to 6% by weight. %, Even more specifically in the range of 0.5 to 5% by weight.

In the process of the present invention, contact of the stream containing the organic carbonate and alkanol impurities with the extraction solvent results in the formation of the extraction solvent phase and the organic carbonate phase. In order for the extraction solvent phase to contain the alkanol impurity, the alcohol impurity should be more soluble in the extraction solvent than the organic carbonate. Preferably, the extraction solvent is a polar extraction solvent. More preferably, the extraction solvent is selected from the group consisting of water, C ₁ -C ₄ aliphatic ketones, C ₁ -C ₄ aliphatic alcohols, and C ₁ -C ₄ aliphatic carboxylic acids. More preferably, the extraction solvent is water or a C ₁ -C ₄ aliphatic carboxylic acids (formic acid, acetic acid, propionic acid or butyric acid). Even more preferably, the extraction solvent is water.

  In the process of the present invention, the contact time between the stream containing the organic carbonate and alkanol impurities and the extraction solvent should be sufficient to complete the extraction process. The contact time may be in the order of 1 minute to 24 hours, for example 3 minutes to 12 hours.

  The temperature at which the present invention is carried out, ie the temperature of the two-phase mixture of extraction solvent and organic carbonate, can be in the range of -50 to 100 ° C. Surprisingly, it has been found that in the process of the invention, alcohol impurities are extracted to the maximum extent in the extraction solvent at relatively low temperatures. This is demonstrated in the examples below. Accordingly, in the present invention, the temperature is preferably in the range of 0 to 40 ° C, more preferably 1 to 30 ° C, more preferably 2 to 25 ° C, and even more preferably 2 to 10 ° C. In accordance with the present invention, this temperature is preferably at least 0 ° C, more preferably at least 1 ° C, more preferably at least 2 ° C, and even more preferably at least 3 ° C. Furthermore, according to the invention, this temperature is preferably at most 40 ° C., more preferably at most 35 ° C., more preferably at most 30 ° C., more preferably at most 25 ° C., more preferably at most 20 ° C, more preferably at most 15 ° C, and even more preferably at most 10 ° C.

  A suitable weight ratio of extraction solvent to stream containing organic carbonate and alkanol impurities is in the range of 10: 1 to 1:10. Preferably, the weight ratio is in the range of 5: 1 to 1: 5, more preferably 3: 1 to 1: 3, and even more preferably 2: 1 to 1: 2. Even more preferably, this weight ratio will be 1: 1.

  The pressure at which the method of the present invention is performed may be lower than atmospheric pressure, atmospheric pressure, or higher than atmospheric pressure. Preferably, the pressure is atmospheric pressure.

  After this extraction, the extraction solvent phase should be separated from the organic carbonate phase in accordance with the present invention so that an organic carbonate-containing stream from which alcohol impurities have been removed remains. If water is the extraction solvent, the aqueous phase must be separated from the organic phase. Anyone skilled in the art can find a suitable method for separating the extraction solvent phase from the organic carbonate phase in the process of the present invention.

  If the stream containing the organic carbonate and alkanol impurities is a stream containing a dialkyl carbonate formed from the reaction of an alkanol and an alkylene carbonate, this stream usually contains unconverted alkanol reactants in addition to the alkanol impurities. contains. The present specification describing the formation of such organic carbonate streams is incorporated by reference. If the stream containing organic carbonate and alkanol impurities is a stream containing dialkyl carbonate, unconverted alkanol, and alkanol impurities, the stream is contacted with an extraction solvent in accordance with the present invention to extract and remove alkanol impurities. Is preferably carried out after the step of separating the dialkyl carbonate from the unconverted alkanol.

  Separation of dialkyl carbonate from unconverted alkanol can be accomplished by distillation. Such distillation is a top stream containing unconverted alkanol (such as ethanol), and dialkyl carbonate, if the unconverted alkanol reacts with alkylene carbonate in the preceding step to form a dialkyl carbonate and alkanediol. This produces a bottoms stream containing natto (such as diethyl carbonate).

  The present invention advantageously results in the removal of alkanol impurities in the organic carbonate stream. This alkanol impurity may have had an adverse effect if the alkanol impurity has not been removed in any subsequent method using organic carbonate.

The invention therefore also relates to a process for the preparation of dialkyl carbonates and alkanediols, the process comprising:
(A) reacting an alkylene carbonate with an alkanol in the presence of a transesterification catalyst to obtain a mixed product containing unconverted alkylene carbonate, unconverted alkanol, dialkyl carbonate, alkanediol, and alkanol impurities; And
(B) separating unconverted alkylene carbonate and alkanediol from the mixed product to obtain a top stream containing unconverted alkanol, dialkyl carbonate, and alkanol impurities;
(C) recovering the alkanediol; and (d) separating the unconverted alkanol from the top stream obtained in step (b) containing unconverted alkanol, dialkyl carbonate, and alkanol impurities to obtain a dialkyl Obtaining a bottom stream containing carbonate and alkanol impurities;
And (e) contacting the bottom stream obtained in step (d) containing dialkyl carbonate and alkanol impurities with an extraction solvent to separate the extraction solvent phase from the organic carbonate phase. To do.

  The above general method for removing alkanol impurities from a stream containing organic carbonate and alkanol impurities comprising contacting a stream containing organic carbonate and alkanol impurities with an extraction solvent and separating the extraction solvent phase from the organic carbonate phase All of the above-mentioned embodiments and preferred in relation to are applied respectively to the specific methods described above for preparing dialkyl carbonates and alkanediols, particularly in step (e) of this method.

  The transesterification catalyst used in step (a) of the above process can be one of a number of suitable homogeneous and heterogeneous transesterification catalysts known in the prior art.

  For example, suitable homogeneous transesterification catalysts are described in US Pat. No. 5,359,118, hydrides, oxides, hydroxides, alkanolates, amides of alkali metals, ie lithium, sodium, potassium, rubidium and cesium, Or a salt is mentioned. Suitable homogeneous transesterification catalysts are potassium or sodium hydroxides or alkanolates. Other suitable homogeneous transesterification catalysts are alkali metal salts such as acetate, propionate, butyrate or carbonate. Suitable catalysts are described in US Pat. No. 5,359,118 and references described therein (such as EP 274953A, US 3803201, EP 1082A, and EP 180387A).

  Examples of the heterogeneous transesterification catalyst suitable for use in step (a) of the above method include an ion exchange resin having a functional group. Suitable functional groups include tertiary amine groups and quaternary ammonium groups, as well as sulfonic acid groups and carboxylic acid groups. Further suitable catalysts include alkali metal and alkaline earth metal silicates. Suitable catalysts are described in US4062884 and US4691041. The heterogeneous catalyst can be selected from an ion exchange resin comprising a polystyrene matrix and a tertiary amine functional group.

  An example is Amberlyst A-21 (eg, Rohm & Haas) that includes a polystyrene matrix to which N, N-dimethylamine groups are attached. Eight classes of transesterification catalysts, including ion exchange resins having amine and quaternary ammonium groups, are described in JF Knifton et al. , J .; MoI. Catal, 67 (1991) 389ff.

  Additional transesterification conditions for step (a) of the above method are known in the art and suitably include a temperature of 40 to 200 ° C. and a pressure of 50 to 5000 kPa (0.5 to 50 bar).

  Furthermore, the present invention relates to a method for producing a diaryl carbonate comprising a dialkyl carbonate from which an aryl alcohol has been removed in accordance with any one of the above methods in the presence of a transesterification catalyst. Including contacting with a stream.

  Still further, the present invention relates to a process for producing a diaryl carbonate, the process comprising contacting a stream containing a dialkyl carbonate and an alkanol impurity with an extraction solvent and an organic carbonate according to any one of the above processes. Separating the extraction solvent phase from the phase, and then contacting the aryl alcohol with the dialkyl carbonate-containing stream in the presence of a transesterification catalyst.

  Preferably, the diaryl carbonate is diphenyl carbonate and the aryl alcohol is phenol.

  In addition, the above ester transfer reaction catalyst and other ester transfer reaction conditions are equally applicable to the above-mentioned method for producing diaryl carbonate.

  The invention is further illustrated by the following examples.

  An aliquot of Solution A containing 99.16 wt% diethyl carbonate (DEC), 0.76 wt% ethyl oxitol (EtOx; 2-ethoxyethanol), and 0.04 wt% ethanol (EtOH) is placed in a glass vial. It was. A constant amount of deionized water (extraction solvent) was then added to the vial. The following table shows the temperature, the amount of solution A, the amount of water added, and the ratio of the amount of water added to the amount of solution A added in Examples 1-5.

  The vial was then closed and shaken for 5 minutes to homogenize and allowed to stand at the above temperature for 1 day to separate the phases. During the day, the contents of the vial were homogenized again three times. At the end of the experiment, the aqueous phase was separated from the organic phase and the composition of the sample was analyzed by gas chromatography. The results are shown in the table below.

（＊）除去されたＥｔＯｘの％＝｛（［溶液Ａ中のＥｔＯｘの重量％］−［有機相中のＥｔＯｘの重量％］）／［溶液Ａ中のＥｔＯｘの重量％］｝×１００％

(*)% EtOx removed = {([% by weight of EtOx in solution A] − [% by weight of EtOx in organic phase]) / [% by weight of EtOx in solution A]} × 100%

  From the results in the table above, extracting this ethyl oxytol from a mixture containing diethyl carbonate and ethyl oxitol using water as the extraction solvent at a relatively low temperature removes alcohol impurities from the organic carbonate. It seems to be an effective means to do.

Claims (14)

A method of removing alkanol impurity from a stream containing an organic carbonate and the alkanol impurity, contacting the extraction solvent with the flow, and viewed including separating the extraction solvent phase from the organic carbonate phase, the organic carbonates are di (C ₁ -C ₅ ) alkyl carbonate, the alkanol impurity is an alkoxy alkanol, the amount of alkanol impurity in the stream containing the organic carbonate and alkanol impurity is in the range of 0.1 to 10% by weight, and the organic The stream containing carbonate and alkanol impurities is the stream resulting from the reaction of the alkanol and alkylene carbonate, and contacting the stream with the extraction solvent is performed after the step of separating the dialkyl carbonate from the unconverted alkanol by distillation. Be called ,Method. The method of claim 1, wherein the di (C ₁ -C ₅ ) alkyl carbonate is diethyl carbonate . The method according to any one of claims 1 to 2, wherein the alkanol impurity is 2 -ethoxyethanol.   4. The method of claim 3, wherein the organic carbonate is diethyl carbonate and the alkanol impurity is 2-ethoxyethanol. Extraction solvent, _water, C 1 -C ₄ aliphatic _ketones, C 1 -C ₄ aliphatic alcohols, and _C 1 -C ₄ are selected from the group consisting of aliphatic carboxylic acids, any of claims 1 to 4 The method according to one item. The method according to any one of claims 1 to 5, wherein the temperature is in the range of 0 to 40 ° C. The method of claim 6, wherein the temperature is in the range of 1 to 30 ° C. The method of claim 7, wherein the temperature is in the range of 2 to 25 ° C. The method of claim 8, wherein the temperature is in the range of 2 to 10 ° C. The stream containing organic carbonate and alkanol impurities is:
(A) reacting an alkylene carbonate with an alkanol in the presence of a transesterification catalyst to obtain a mixed product containing unconverted alkylene carbonate, unconverted alkanol, dialkyl carbonate, alkanediol, and alkanol impurities; When,
(B) separating unconverted alkylene carbonate and alkanediol from the mixed product to obtain a top stream containing unconverted alkanol, dialkyl carbonate, and alkanol impurities;
(C) recovering the alkanediol, and (d) separating the unconverted alkanol from the top stream obtained in step (b) containing unconverted alkanol, dialkyl carbonate, and alkanol impurities, Obtaining a bottom stream containing dialkyl carbonate and alkanol impurities,
Obtained by the preparation method of dialkyl carbonate and alkanediol,
further,
(E) contacting the bottom stream obtained in step (d) containing dialkyl carbonate and alkanol impurities with an extraction solvent, and separating the extraction solvent phase from the organic carbonate phase;
including,
The method according to any one of claims 1 to 9. The alkylene carbonate is ethylene carbonate, the unconverted alkanol is ethanol, the dialkyl carbonate is diethyl carbonate, the alkanediol is monoethylene glycol, and the alkanol impurity is 2-ethoxyethanol. 10. The method according to 10 . The presence of a transesterification catalyst, an aryl alcohol, comprising contacting a dialkyl carbonate containing stream alkanol impurity are removed according to the method of any one of claims 1 to 11, a manufacturing method of the diaryl carbonate. Contacting a stream containing dialkyl carbonate and alkanol impurities with an extraction solvent and separating the extraction solvent phase from the organic carbonate phase according to the method of any one of claims 1 to 11 , and then transesterification A process for producing a diaryl carbonate comprising contacting an aryl alcohol with a dialkyl carbonate-containing stream in the presence of a catalyst. 14. A process according to claim 12 or 13 , wherein the diaryl carbonate is diphenyl carbonate and the aryl alcohol is phenol.