TW202128606A - Process for removing an ether alkanol impurity from an organic carbonate stream - Google Patents

Abstract

The invention relates to a process for removing an ether alkanol impurity from a stream containing an organic carbonate and the ether alkanol impurity, comprising contacting the stream with an extraction solvent and separating the extraction solvent phase comprising the ether alkanol impurity from the organic carbonate phase, wherein the extraction solvent comprises an alkanol containing 2 or more hydroxyl groups. The invention also relates to processes for the preparation of a dialkyl carbonate and an alkanediol, wherein a stream containing the dialkyl carbonate and an ether alkanol impurity is subjected to the above-described extraction process. Further, the invention relates to a process for making a diaryl carbonate, comprising reacting an aryl alcohol with a stream containing a dialkyl carbonate from which stream an ether alkanol impurity has been removed in accordance with the above-described extraction process.

Description

Method for removing ether alkanol impurities from organic carbonate stream

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

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

Dialkyl carbonate can be produced by reacting alkylene carbonate with alkanol. In the case where alkylene carbonate (such as ethylene carbonate) is reacted with alkanol (such as ethanol), the products are dialkyl carbonate (such as diethyl carbonate) and alkanediol (such as monoethylene glycol). Such methods are well known and examples thereof are disclosed in US5359118. This document discloses a method in which carbonate bis(C ₁ -C ₄ alkyl) alkanediol is prepared by transesterification of alkylene carbonate and C ₁ -C ₄ alkanol.

At different points in the overall process of preparing dialkyl carbonate from alkylene oxide through alkylene carbonate, organic carbonate streams containing one or more ether alkanol (ie, alkoxy alkanol) impurities may be generated. For example, in a reactor where ethanol and ethylene carbonate react to produce diethyl carbonate and monoethylene glycol, ethanol and ethylene oxide may occur (due to the reverse reaction of ethylene carbonate to ethylene oxide And carbon dioxide) to produce 2-ethoxyethanol (ethyl oxitol or ethylene glycol monoethyl ether). In addition, the side reaction of ethanol and ethylene carbonate can release carbon dioxide and produce ethylene glycol ether to form ethylene glycol ether. Furthermore, side reactions may occur between ethanol and monoethylene glycol, producing ethyl glycol ether and water. Furthermore, ethylene glycol ethyl ether can be formed by the decarboxylation reaction of hydroxyethyl ethyl carbonate.

Therefore, the product stream from the reactor for the reaction of ethanol and ethylene carbonate to produce diethyl carbonate and monoethylene glycol may include unconverted ethanol, unconverted ethylene carbonate, diethyl carbonate, and monoethylene glycol. And the ethylene glycol ether impurities mentioned above. The presence of this alkoxyalkanol impurity may be unfavorable for any subsequent production process. For example, the alkoxyalkanol impurity can finally enter the dialkyl carbonate, and the dialkyl carbonate is used as a starting material to synthesize diphenyl carbonate from the dialkyl carbonate and phenol. For example, in the case where the dialkyl carbonate is diethyl carbonate and the alkoxy alkanol impurity is ethylene glycol ethyl ether, the ethylene glycol ethyl ether can be combined with the phenol starting material and/or with the diphenyl carbonate product reaction.

The direct reaction of phenol with ethylene glycol ether may lead to the production of phenyl 2-ethoxy ether, thus leading to the loss of valuable phenol reactants. In addition, this type of reaction leads to the introduction of undesired chemicals into the process, thus causing separation problems.

The reaction of diphenyl carbonate with ethylene glycol ether resulted in product loss due to the production of 2-ethoxyethyl phenyl carbonate. In addition, in any subsequent polymerization of diphenyl carbonate to polycarbonate material, the latter product acts as a "poison". For example, when diphenyl carbonate reacts with bisphenol A (BPA), polycarbonate and phenol are formed. Diphenyl carbonate can react with BPA because phenol is a relatively good leaving group. However, dialkyl carbonates (such as diethyl carbonate) cannot be used to produce polycarbonates by reaction with BPA because alkanols are not good leaving groups. Alkoxy alkanols (such as ethylene glycol ether) are not good leaving groups. Therefore, in the case where phenyl carbonate 2-ethoxyethyl is present in the diphenyl carbonate feed to be reacted with BPA, phenol will be easily separated from the phenyl carbonate 2-ethoxyethyl, but not easily separated. Ethylene glycol ether, so the polymerization process is terminated at one end of the chain. Therefore, the 2-ethoxyethyl phenyl carbonate must be removed from the diphenyl carbonate before the diphenyl carbonate is brought into contact with BPA.

The above exemplified that in the case of forming an organic carbonate stream containing ether alkanol impurities, the ether alkanol impurities need to be removed before any subsequent processes in which the organic carbonate is converted into valuable end products. For example, it is necessary to remove any ethylene glycol ether impurities from the diethyl carbonate stream containing the impurities before proceeding with the reaction of diethyl carbonate and phenol.

Referring to the above example where ethanol and ethylene carbonate have reacted to form diethyl carbonate and monoethylene glycol, the product stream that also contains unconverted ethanol, ethylene carbonate and by-products of ethylene glycol ether can be separated by distillation . The boiling points of the various components in this product stream are mentioned in the table below. Boiling point (℃) Ethanol 78.4 Diethyl carbonate 126-128 Ethylene glycol ether 135 Monoethylene glycol 197.3 Ethylene carbonate 260.4

The distillation as mentioned above can produce an overhead stream containing diethyl carbonate and unconverted ethanol and a bottom stream containing monoethylene glycol and unconverted ethylene carbonate. Most likely, all ethylene glycol ether will eventually enter the top stream. However, depending on the specific conditions of the distillation, part of the ethyl glycol ether may eventually enter the bottom stream. Subsequently, the overhead stream can be further separated by distillation into an overhead stream containing unconverted ethanol (which can be recycled to the reactor producing diethyl carbonate and monoethylene glycol) and containing diethyl carbonate and ethylene Bottom stream of glycol ether impurities.

As discussed above, before the organic carbonate is converted into a valuable end product in any subsequent process, the ether alkanol impurity must be removed from it, because the ether alkanol impurity may interfere with the subsequent process and/or any other process . For the above example, this means that the ethylene glycol ether impurities should be removed from the bottom stream containing diethyl carbonate and the ethylene glycol ether impurities. In principle, ethylene glycol ethyl ether and diethyl carbonate can be separated by a further distillation step. However, due to the small difference in boiling point between diethyl carbonate and ethylene glycol ether (see the above table), this type of separation is very complicated and requires multiple distillation steps and stages.

Similarly, in the case where ethanol and propylene carbonate have reacted to form diethyl carbonate and monopropylene glycol, ethyl proxitol may be formed as an impurity of ether alkanol. Propylene glycol ethyl ether (propylene glycol monoethyl ether) contains 1-ethoxy-2-propanol and/or 2-ethoxy-1-propanol. In this case, diethyl carbonate (126°C to 128°C) and ether alkanol impurities (1-ethoxy-2-propanol: 132°C; 2-ethoxy-1-propanol: 138°C) The boiling point difference between them is also small, making the distillation separation very complicated.

Therefore, there is a need to find a simple method to remove such ether alkanol impurities from organic carbonate streams containing ether alkanol impurities. WO2010063694 discloses a method for removing ether alkanol impurities from a stream containing organic carbonate and ether alkanol impurities, which comprises contacting the stream with an extraction solvent and separating the extraction solvent phase from the organic carbonate phase. In addition, according to WO2010063694, the extraction solvent can be 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. Optimally, according to WO2010063694, the extraction solvent is water.

As mentioned above in WO2010063694, the disadvantage of using water as the extraction solvent is that after such etheralkanol impurities have been extracted from the organic carbonate stream containing etheralkanol impurities, water and etheralkanol impurities (such as ethylenedioxide) Alcohol ether) will form an azeotrope, which complicates the further separation of ether alkanol impurities from the water extraction solvent. Another disadvantage of using water as the extraction solvent is that water can also react with organic carbonates that can be dialkyl carbonate and/or alkylene carbonate without a catalyst, which results in the loss of valuable organic carbonates. After adding water, the dialkyl carbonate can be hydrolyzed into the corresponding alkanol and carbonic acid (H ₂ CO ₃ ), which can be converted into water and carbon dioxide. Similarly, alkylene carbonate can be hydrolyzed to the corresponding alkanediol and the carbonic acid. Furthermore, the density of water (1.00 g/ml at 25°C) can be similar to the density of the organic carbonate from which ether alkanol impurities are extracted (for example, at 25°C, the density of diethyl carbonate is 0.98 g/ml). This complicates the formation of the separated extractant (water) phase and organic carbonate phase. In addition, it may be necessary to distill the resulting extractant (water) phase containing the ether alkanol impurities in order to remove the ether alkanol impurities therefrom, which may disadvantageously result in the need to separate the water as the overhead stream instead of the relatively lighter evaporation The ether alkanol impurity to separate it from the extractant.

The object of the present invention is to provide a simple, effective and efficient method for removing such impurities from organic carbonate streams containing ether alkanol impurities, which can be used to prepare dioxane carbonate from alkylene oxide through alkylene carbonate. Formed during the process of ester and alkanediol, the removal method preferably does not have one or more of the above-mentioned disadvantages. In addition, the removal method preferably results in energy and/or capital savings.

Surprisingly, it has been found that such a method as described above can be achieved by using an alkanol containing 2 or more hydroxyl groups as the extraction solvent to remove such impurities from an organic carbonate stream containing ether alkanol impurities .

Therefore, the present invention relates to a method for removing the ether alkanol impurities from a stream containing organic carbonate and ether alkanol impurities, which comprises contacting the stream with an extraction solvent and contacting the extraction solvent containing the ether alkanol impurities The phase is separated from the organic carbonate. The method involves liquid-liquid extraction, where the extraction solvent contains an alkanol containing 2 or more hydroxyl groups.

The present invention also relates to a method for preparing dialkyl carbonate and alkanediol, wherein a stream containing the dialkyl carbonate and ether alkanol impurities is subjected to the above-described extraction method.

In addition, the present invention relates to a method for preparing diaryl carbonate, which comprises reacting an aryl alcohol with a stream containing dialkyl carbonate, and the ether alkanol impurities in the stream have been removed according to the above-mentioned extraction method.

In the case where a method including two or more steps is disclosed in this specification, the method may include one or more intermediate steps between subsequent steps. Furthermore, the method may include one or more additional steps before the first step and/or after the last step.

Although in this specification, a method and the mixture or stream or catalyst used or produced in the method are respectively referred to by the terms "comprising", "containing" or "including" one or more of the various steps and components. Description, but it can also be "essentially composed of the one or more of the various steps and components" or "composed of the one or more of the various steps and components" respectively.

In the context of the present invention, where the mixture, stream or catalyst contains two or more components, these components are selected in a total amount not exceeding 100%.

In addition, when the upper limit and the lower limit are quoted for a characteristic, the value range defined by the combination of any upper limit and any lower limit is also implied.

Unless otherwise indicated, when the boiling point is mentioned in this specification, this means the boiling point at a pressure of 760 mm Hg (101.3 kPa).

In the present invention, the ether alkanol impurities are removed from the stream containing organic carbonate and ether alkanol impurities. Ether alkanols are the same as alkoxy alkanols, and these two terms are used interchangeably in this specification.

The extraction method of the present invention is characterized by contacting a stream containing organic carbonate and ether alkanol impurities with an extraction solvent, which is an alkanol containing 2 or more hydroxyl groups, thereby producing impurities containing ether alkanol and The extraction solvent phase of the organic carbonate phase, and the extraction solvent phase is separated from the organic carbonate phase. In this specification, contacting a stream containing organic carbonate and ether alkanol impurities with an extraction solvent means contacting the previous stream with another stream containing the extraction solvent. In the present invention, the extraction method is a method involving liquid-liquid extraction. In addition, the organic carbonate phase (or raffinate phase) may be the upper phase and the extraction solvent phase (or extraction phase) may be the lower phase.

In the method of the present invention for removing the ether alkanol impurities from a stream containing organic carbonate and ether alkanol impurities, the organic carbonate may be dialkyl carbonate, diaryl carbonate, alkyl aryl carbonate, alkylene carbonate The ester or a mixture of such organic carbonates is preferably dialkyl carbonate and/or alkylene carbonate. The diaryl carbonate may be diphenyl carbonate. The alkyl aryl carbonate may be alkyl phenyl carbonate, where the alkyl group may be as defined below for dialkyl carbonate. The alkylene carbonate may be C ₂ -C ₆ alkylene carbonate, more preferably C ₂ -C ₄ alkylene carbonate, and most preferably C ₂ -C ₃ alkylene carbonate. Specifically, the alkylene carbonate may be ethylene carbonate or propylene carbonate.

Preferably, in the invention, mentioned above, and the organic carbonate is a dialkyl carbonate, which may be a di (C ₁ -C ₄ alkyl) esters, more suitably from di (C ₁ -C _{The 3-} alkyl) ester is most preferably bis(C ₂ -C ₃ alkyl) carbonate. In addition, preferably, the dialkyl carbonate is dimethyl carbonate, diethyl carbonate or diisopropyl carbonate, more preferably diethyl carbonate or diisopropyl carbonate, and most preferably diethyl carbonate.

In addition, in the method of the present invention for removing the ether alkanol impurity from a stream containing organic carbonate and ether alkanol impurities, the ether alkanol impurity is an alkoxy alkanol, which is an alkanol of formula R ₁ OH, Wherein R ₁ is an alkoxyalkyl group. The alkoxy moiety in the alkoxyalkyl group is preferably methoxy, ethoxy or isopropoxy, more preferably ethoxy or isopropoxy, most preferably ethoxy. In addition, the alkyl part of the alkoxyalkyl group is preferably ethyl or propyl, most preferably ethyl. The ether alkanol impurity can be, for example, 2-ethoxyethanol or 1-ethoxy-2-propanol and/or 2-ethoxy-1-propanol.

Furthermore, in the method of the present invention for removing the ether alkanol impurities from a stream containing organic carbonate and ether alkanol impurities, the amount of the ether alkanol impurities in the latter stream may be contained within 10 parts per million by weight Parts (ppmw) to 10 wt.%, specifically, 100 ppmw to 9 wt.%, more specifically, 0.1 to 8 wt.%, more specifically, 0.3 to 7 wt.%, more specifically In other words, 0.5 to 6 wt.% and most specifically, 0.5 to 5 wt.%.

The stream containing organic carbonate and ether alkanol impurities to be treated according to the extraction method of the present invention may contain alkanols containing 2 or more hydroxyl groups, for example alkanediols, such as monoethylene glycol. Such alkanediol can be advantageously used as an additional extraction solvent. Therefore, in the case that the stream containing organic carbonate and ether alkanol impurities is derived from the process of preparing dialkyl carbonate and alkanediol by reacting alkylene carbonate with alkanol, the advantage is that the alkanediol extraction solvent ( Such as monoethylene glycol) is a component that has been formed in the entire process, so that in order to remove the ether alkanol impurities from the stream containing organic carbonate, ether alkanol impurities and the alkane glycol, less extraction solvent needs to be added .

In the extraction method of the present invention, the extraction solvent contains 2 or more hydroxyl groups, preferably 3 or more hydroxyl groups, preferably 2 to 5 hydroxyl groups, more preferably 2 to 4 hydroxyl groups, more preferably Alkanols with 2 to 3 hydroxyl groups, preferably 3 hydroxyl groups. In addition, the alkanol may contain 2 to 9 carbon atoms, preferably 2 to 7 carbon atoms, more preferably 2 to 5 carbon atoms, and most preferably 2 to 3 carbon atoms. Preferably, the alkanol contains at least 2 carbon atoms and at least 2 hydroxyl groups, wherein each hydroxyl group of the alkanol is bonded to a different carbon atom. Suitable examples of the alkanol are monoethylene glycol, monopropylene glycol, glycerol, erythritol, xylitol and sorbitol, more preferably monoethylene glycol, monopropylene glycol and glycerol. More preferably, the alkanol is monoethylene glycol or glycerin, most preferably glycerin.

In addition, in the extraction method of the present invention, any mixture of two or more of the above-mentioned extraction solvents can be used. The weight ratio of the two or more extraction solvents can vary within a wide range. In the case of two extraction solvents, the weight ratio can be 0.1:10 to 10:1, preferably 0.5:1 to 5:1. If the stream containing organic carbonate and ether alkanol impurities to be treated according to the extraction method of the present invention contains an alkanol containing 2 or more hydroxyl groups, such as an alkanediol, such as monoethylene glycol, the alkanol It is regarded as an extraction solvent and should therefore be included in the weight ratio of the two or more extraction solvents mentioned above. A preferable mixture of the extraction solvent is a mixture of an alkanol containing 2 hydroxyl groups (for example, such as alkanediol, monoethylene glycol) and an alkanol containing 3 hydroxyl groups (for example, glycerol).

Preferably, in the extraction method of the present invention, the density of the lower phase is higher than the density of the upper phase by at least 0.05 g/ml, more preferably at least 0.10 g/ml, even more preferably at least 0.15 g/ml, most preferably at least 0.20 g/ml ml. When needed, such density differences can also be achieved by adding additives that change the density of a phase. Such additives include salts.

Advantageously, in the method of the present invention, the contact of the stream containing organic carbonate and ether alkanol impurities with the extraction solvent causes the formation of an extraction solvent phase containing the ether alkanol impurities and the organic carbonate phase, thereby making the ether alkanol impurities and organic Carbonate separation.

In the method of the present invention, the time for contacting the stream containing organic carbonate and ether alkanol impurities with the extraction solvent should be sufficient to complete the extraction process. The contact time can be about 10 seconds to 5 hours, for example, 10 seconds to 2 hours.

The temperature for performing the extraction method of the present invention, that is, the temperature of the two-phase mixture of the extraction solvent and the organic carbonate, may be included in the range of 0°C to 150°C, for example, 10°C to 100°C. Advantageously, the feed in the extraction method of the present invention is obtained by reacting alkylene carbonate with alkanol and contains unconverted alkylene carbonate, unconverted alkanol, dialkyl carbonate, and alkanediol. In the case of product mixtures with ether alkanol impurities, the feed does not have to be cooled before it is sent to the extraction method of the present invention.

A suitable weight ratio of the extraction solvent to the stream containing organic carbonate and ether alkanol impurities is included in the range of 10:1 to 1:10, for example, 5:1 to 1:5. If the stream containing organic carbonate and ether alkanol impurities to be treated according to the extraction method of the present invention contains an alkanol containing 2 or more hydroxyl groups, for example an alkanediol, such as monoethylene glycol, the alkanol It is regarded as an extraction solvent and should therefore only be used as an "extraction solvent" to include the above-mentioned weight ratio of the extraction solvent to the stream containing organic carbonate and ether alkanol impurities.

The pressure for performing the extraction method of the present invention can be sub-atmospheric pressure, atmospheric pressure or super-atmospheric pressure, preferably atmospheric pressure or super-atmospheric pressure.

After this extraction, the extraction solvent phase should be separated from the organic carbonate phase according to the present invention in order to retain the organic carbonate-containing stream from which the ether alkanol impurities have been removed. In the method of the present invention, anyone skilled in the art can find a suitable method for separating the extraction solvent phase from the organic carbonate phase.

In the case where the stream containing organic carbonate and ether alkanol impurities is a stream containing dialkyl carbonate that has been produced by reacting alkanol with alkylene carbonate, in addition to the ether alkanol impurities, the stream is usually Also contains unconverted alkanol reactant. Refer to the introduction in this specification, which describes the formation of such organic carbonate streams.

In the case that the stream containing organic carbonate and ether alkanol impurities is a stream containing dialkyl carbonate, unconverted alkanol and ether alkanol impurities, the stream is contacted with an extraction solvent to extract and remove the impurities according to the present invention. The ether alkanol impurities can be carried out after the step of separating the dialkyl carbonate from the unconverted alkanol.

The separation of dialkyl carbonate and unconverted alkanol can be achieved by distillation. In the case where the unconverted alkanol has reacted with alkylene carbonate in the previous step to produce dialkyl carbonate and alkanediol, such distillation produces an overhead stream containing unconverted alkanol (such as ethanol) and containing carbonic acid The bottom stream of dialkyl esters (such as diethyl carbonate).

Therefore, the present invention advantageously removes the ether alkanol impurities in the organic carbonate stream. If the ether alkanol impurities have not been removed, the ether alkanol impurities may interfere with any subsequent processes using the organic carbonate.

Therefore, the present invention relates to a method for preparing dialkyl carbonate and alkanediol, which comprises: (A) Reacting alkylene carbonate with alkanol to obtain a product mixture containing unconverted alkylene carbonate, unconverted alkanol, dialkyl carbonate, alkanediol and ether alkanol impurities; (B) Separating the unconverted alkylene carbonate and alkanediol from the product mixture to obtain an overhead stream containing unconverted alkanol, dialkyl carbonate and the ether alkanol impurities; (C) Recover the alkanediol; (D) Separating unconverted alkanol from the top stream obtained in step (b) to obtain a bottom stream containing dialkyl carbonate and the ether alkanol impurities; and (E) contacting the bottom stream obtained in step (d) with an extraction solvent, and separating the extraction solvent phase containing the ether alkanol impurities from the dialkyl carbonate phase, wherein the extraction solvent contains 2 or more Hydroxy alkanol; and (F) removing the ether alkanol impurities from the extraction solvent phase obtained in step (e), and recycling the extraction solvent to step (e).

Step (a) of the above-mentioned method for preparing dialkyl carbonate and alkanediol includes reacting alkylene carbonate with alkanol to obtain unconverted alkanol containing unconverted alkylene carbonate , Dialkyl carbonate, alkanediol and ether alkanol impurity product mixture.

Therefore, step (a) involves the reaction of alkylene carbonate and alkanol. The alkylene carbonate may be C ₂ -C ₆ alkylene carbonate, more preferably C ₂ -C ₄ alkylene carbonate, and most preferably C ₂ -C ₃ alkylene carbonate. The alkylene carbonate is preferably ethylene carbonate or propylene carbonate, most preferably ethylene carbonate. The properties of alkylene carbonate determine the properties of the alkanediol product: for example, the reaction of ethylene carbonate and alkanol produces monoethylene glycol, which is 1,2-ethylene glycol (alkanediol).

In addition, the alkanol is a C ₁ -C ₄ alkanol, more preferably a C ₁ -C ₃ alkanol, and most preferably a C ₂ -C ₃ alkanol. The alkanol preferably contains 1 or 2 hydroxyl groups, most preferably 1 hydroxyl group. In addition, the alkanol is preferably methanol, ethanol or isopropanol, more preferably ethanol or isopropanol, and most preferably ethanol. The nature of the alkanol determines the nature of the dialkyl carbonate product: for example, the reaction of alkylene carbonate and ethanol produces diethyl carbonate (dialkyl carbonate).

The product mixture obtained in step (a) contains ether alkanol impurities. As mentioned above, ether alkanols are the same as alkoxy alkanols. Alkoxyalkanols are alkanols of the formula R ₁ OH, wherein R ₁ is an alkoxyalkyl group. The alkoxy moiety in the alkoxyalkyl group is directly or indirectly derived from the alkanol used in step (a), and the alkyl moiety in the alkoxyalkyl group is directly or indirectly derived from the use in step (a) The alkylene carbonate. Therefore, the same preferred solution as discussed above with reference to the alkanol and alkylene carbonate used in step (a) applies. For example, the alkoxy moiety in the alkoxyalkyl group is preferably methoxy, ethoxy or isopropoxy, more preferably ethoxy or isopropoxy, most preferably ethoxy . In addition, for example, the alkyl moiety in the alkoxyalkyl group is preferably an ethyl group or a propyl group, and most preferably an ethyl group. The ether alkanol impurity can be, for example, 2-ethoxyethanol or 1-ethoxy-2-propanol and/or 2-ethoxy-1-propanol.

In a particularly preferred embodiment of the method for preparing dialkyl carbonate and alkanediol mentioned above, the alkylene carbonate is ethylene carbonate, the alkanol is ethanol, and the dialkyl carbonate is carbonic acid. Diethyl, alkanediol is monoethylene glycol and the ether alkanol impurity is 2-ethoxyethanol. 2-Ethoxyethanol can also be called ethylene glycol ether.

In another particularly preferred embodiment of the method for preparing dialkyl carbonate and alkanediol mentioned above, the alkylene carbonate is propylene carbonate, the alkanol is ethanol, and the dialkyl carbonate is Diethyl carbonate, the alkanediol is monopropylene glycol and the ether alkanol impurity is propylene glycol ethyl ether (propylene glycol monoethyl ether), the propylene glycol ethyl ether contains 1-ethoxy-2-propanol and/or 2-ethoxy-1 -Propanol.

Preferably, in the step (a) for preparing dialkyl carbonate and alkanediol, a catalyst, more specifically a transesterification catalyst, is used.

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

For example, suitable homogeneous transesterification catalysts have been described in US5359118 and include alkali metal (ie lithium, sodium, potassium, rubidium and cesium) hydrides, oxides, hydroxides, alkanolates, amines Compounds or salts. The preferred 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 US5359118 and references mentioned therein, such as EP274953A, US3803201, EP1082A and EP180387A.

As mentioned above, it is also possible to use heterogeneous transesterification catalysts. Among the methods mentioned above, it is preferable to use a heterogeneous transesterification catalyst in step (a). Suitable heterogeneous catalysts include ion exchange resins containing functional groups. Suitable functional groups include tertiary amine and quaternary ammonium groups, as well as sulfonic acid and carboxylic acid groups. Other suitable catalysts include alkali metal and alkaline earth metal silicates. Suitable catalysts are disclosed in US4062884 and US4691041. The heterogeneous catalyst can be selected from ion exchange resins containing a polystyrene matrix and tertiary amine functional groups. An example is Amberlyst A-21 (from Rohm & Haas), which contains a polystyrene matrix to which N,N-dimethylamine groups have been attached. Eight types of transesterification catalysts (including ion exchange resins with tertiary amine and quaternary ammonium groups) are disclosed in JF Knifton et al., "Journal of Molecular Catalysis (J. Mol. Catal)", 67 (1991) 389 and below middle.

A suitable heterogeneous transesterification catalyst may be a catalyst comprising: Group 4 (such as titanium), Group 5 (such as vanadium), Group 6 (such as chromium or molybdenum), or Group 12 ( Elements such as zinc; or tin or lead; or a combination of such elements, such as a combination of zinc and chromium (for example, zinc chromite). These elements may be present in the catalyst in the form of oxides, such as zinc oxide. Preferably, in step (a), a heterogeneous catalyst containing zinc is used.

The conditions in step (a) include a temperature of 10 to 200°C and a pressure of 0.5 to 50 absolute bar (5×10 ⁴ to 5×10 ⁶ N/m ² ). Preferably, especially in parallel flow operation, the pressure is in the range of 1 to 20 bar, more preferably 1.5 to 20 bar, most preferably 2 to 15 bar, and the temperature is 30 to 200° C., more preferably 40 to 170 ℃, preferably in the range of 50 to 150℃.

In addition, it is preferable to use an excess amount of alkanol relative to alkylene carbonate in step (a). In step (a), the molar ratio of alkanol to alkylene carbonate is preferably 1.01:1 to 25:1, preferably 2:1 to 20:1, more preferably 3:1 to 15:1, most Preferably, it is 3:1 to 13:1.

Further, the step of weight hourly space velocity (WHSV) (a) may suitably be in the 0.1 to 100 kg / kg _cat .hr ( "kg _cat" refers to the amount of catalyst), more suitably 0.5 to 50 kg / kg _cat. hr, more suitably 1 to 20 kg/kg _cat .hr, more suitably 1 to 10 kg/kg _cat .hr.

As described in US5359118, step (a) can be carried out in a reactive distillation column. This will allow the reaction to proceed countercurrently. The distillation column may contain trays with bubble caps, sieve trays or Raschig rings. Those familiar with this technology will realize that several types of catalyst packing and several tray configurations will be possible. Suitable towers have been described, for example, in "Ullmann's Encyclopedia of Industrial Chemistry", 5th edition, volume B4, page 321 et seq., 1992.

Alkylene carbonate will generally have a higher boiling point than alkanols. In the case of ethylene carbonate and propylene carbonate, the atmospheric pressure boiling point is higher than 240°C. Therefore, in general, alkylene carbonate will be fed in the upper part of the reactive distillation column, and alkanol will be fed in the lower part of this column. The alkylene carbonate will flow downwards and the alkanol will flow upwards.

Preferably, step (a) is performed in a parallel flow mode. A suitable mode of operation is to perform the reaction in a trickle mode, in which the part of the reactant in the gas phase and the part in the liquid phase are dropped on the catalyst. A better way to operate step (a) is to perform in a reactor with only liquid. A suitable reaction zone of this type is a tubular reaction zone, in which the reaction is carried out in a plug flow mode. For example, step (a) can be carried out in one plug flow reactor or in a series of two or more plug flow reactors. This will allow the reaction to approach equilibrium.

Another possibility is to perform step (a) in a continuous stirred tank reactor (CSTR). In the latter case, the effluent from the CSTR is preferably post-reacted in a plug flow reactor so that the reaction can approach equilibrium.

Step (a) is preferably carried out continuously. In addition, it is preferable to recycle unconverted alkylene carbonate and alkanol.

Step (b) of the above-mentioned method for preparing dialkyl carbonate and alkanediol includes separating unconverted alkylene carbonate and alkanediol from the product mixture obtained in step (a) to obtain An overhead stream containing unconverted alkanol, dialkyl carbonate and ether alkanol impurities. This step (b) can be achieved by distillation. The bottom stream obtained in step (b) contains unconverted alkylene carbonate and alkanediol.

Step (c) of the above-mentioned method for preparing dialkyl carbonate and alkanediol includes recovering alkanediol. This step (c) can be achieved by distillation. The alkanediol can be recovered by separating the bottom stream containing unconverted alkylene carbonate and alkanediol obtained in step (b) to obtain a top stream containing alkanediol and a bottom stream containing unconverted alkylene carbonate Bottom logistics. The unconverted alkylene carbonate in the bottom stream can be recycled to step (a).

Step (d) of the above-mentioned method for preparing dialkyl carbonate and alkanediol includes separating unconverted alkanol from the top stream obtained in step (b) to obtain dialkyl carbonate and The bottom stream of ether alkanol impurities. This step (d) can be achieved by distillation. The top stream obtained in step (d) contains unconverted alkanol. The unconverted alkanol in the top stream can be recycled to step (a).

The separation and recovery of products in step (b), step (c), step (d) and step (f) can be achieved in any known manner. For example, regarding steps (b), (c) and (d), they can be recovered by applying the method disclosed in WO2011039113, the disclosure of which is incorporated herein by reference.

The amount of ether alkanol impurity in the bottom stream obtained in step (d) and containing dialkyl carbonate and the impurity may be contained within 10 parts per million by weight (ppmw) to 10 wt.%, specifically 100 ppmw To 9 wt.%, more specifically 0.1 to 8 wt.%, more specifically 0.3 to 7 wt.%, more specifically 0.5 to 6 wt.%, and most specifically 0.5 to 5 wt.% Within range.

Step (e) of the above-mentioned method for preparing dialkyl carbonate and alkanediol includes contacting the bottom stream obtained in step (d) with an extraction solvent to produce impurities containing ether alkanol and dialkyl carbonate And separating the extraction solvent phase from the dialkyl carbonate phase, wherein the extraction solvent contains an alkanol containing 2 or more hydroxyl groups. In this specification, contacting the bottom stream obtained in step (d) with the extraction solvent means contacting the previous stream with another stream containing the extraction solvent.

The above-mentioned features, preferred solutions and examples of the extraction method of the present invention are also applicable to step (e) of the method for preparing dialkyl carbonate and alkanediol mentioned above.

Step (f) of the above-mentioned method for preparing dialkyl carbonate and alkanediol includes removing ether alkanol impurities from the extraction solvent phase obtained in step (e) and recycling the extraction solvent to step (E).

Step (f) can be achieved by separating the extraction solvent phase containing ether alkanol impurities obtained in step (e) to obtain a top stream containing ether alkanol impurities and a bottom stream containing the extraction solvent. This separation can be achieved by distillation. At least a portion of the ether alkanol impurities can be advantageously recovered as a high-purity ether alkanol product. Then the extraction solvent in the bottom stream is recycled to step (e). A part of the bottom stream containing the extraction solvent obtained in step (e) and/or step (f) (preferably step (e)) can be removed as an effluent to prevent the accumulation of any heavy objects. In the case of this effluent, it is necessary to feed the make-up stream containing the extraction solvent to step (e).

Optionally, the dialkyl carbonate phase obtained in step (e) additionally contains an extraction solvent. In this case, the above-mentioned method for preparing dialkyl carbonate and alkanediol may include step (g), and the step (g) includes the dialkyl carbonate phase obtained from step (e) The extraction solvent is removed from, and the extraction solvent is recycled to step (e). Optionally, step (g) can be achieved by separating the dialkyl carbonate phase containing the extraction solvent obtained in step (e) to obtain a top stream containing dialkyl carbonate and a bottom stream containing the extraction solvent. This separation can be achieved by distillation. Then the extraction solvent in the bottom stream is recycled to step (e).

In addition, the present invention relates to a method for preparing dialkyl carbonate and alkanediol, which comprises: (I) Reacting alkylene carbonate with alkanol to obtain a product mixture containing unconverted alkylene carbonate, unconverted alkanol, dialkyl carbonate, alkanediol and ether alkanol impurities; (Ii) Contact the product mixture obtained in step (i) with an extraction solvent, and separate the unconverted alkanol and alkanediol from the organic carbonate phase containing unconverted alkylene carbonate and dialkyl carbonate And an extraction solvent phase of ether alkanol impurities, wherein the extraction solvent comprises an alkanol containing 2 or more hydroxyl groups; (Iii) Recover the dialkyl carbonate; (Iv) separating the extraction solvent obtained in step (ii) into a top stream containing unconverted alkanol and the ether alkanol impurities and a bottom stream containing extraction solvent and alkanediol; and (V) Recycling the extraction solvent from the bottom stream obtained in step (iv) to step (ii).

Compared with another method for preparing dialkyl carbonate and alkanediol as described above involving steps (a) to (f), the above-mentioned methods involving steps (i) to (v) The advantage of the method for preparing dialkyl carbonate and alkanediol is to avoid the formation of azeotrope of alkanediol (for example, ethylene glycol) and unconverted alkylene carbonate (for example, ethylene carbonate), because In the extraction step (ii), the unconverted alkylene carbonate finally enters the organic carbonate phase and the alkanediol finally enters the extraction solvent phase. On the other hand, step (c) of another method includes the recovery of alkanediol by means of distillation to obtain a top stream containing alkanediol and a bottom stream containing unconverted alkylene carbonate. In this distillation step The formation of this azeotrope may cause problems because it can produce an overhead stream containing alkanediol and otherwise unconverted alkylene carbonate and a bottom stream containing unconverted alkylene carbonate. WO2008090108 solves this problem by a further purification procedure, which involves first converting the alkylene carbonate in the latter top stream into alkanediol and carbon dioxide by hydrolysis after adding water, and further separating the resulting stream to obtain a purified The alkanediol. However, the disadvantage is that this additional purification procedure involving hydrolysis and further separation is cumbersome, and the amount of unconverted alkylene carbonate recycled to the reactor is lower, resulting in a lower overall yield of the desired dialkyl carbonate product. Low. The advantage of the method for preparing dialkyl carbonate and alkanediol mentioned above involving steps (i) to (v) is that it advantageously avoids problems involving hydrolysis and further separation as disclosed in this WO2008090108 A cumbersome additional purification procedure because the alkanediol and alkylene carbonate have been separated from each other by extraction in the extraction step (ii). Therefore, it is not necessary to hydrolyze part of the unconverted alkylene carbonate as disclosed in the WO2008090108, so that more alkylene carbonate can be recycled to the reaction step, thereby increasing the overall yield of the desired dialkyl carbonate product.

Compared with another method for preparing dialkyl carbonate and alkanediol as described above involving steps (a) to (f), the above-mentioned methods involving steps (i) to (v) An additional advantage of the method for preparing dialkyl carbonate and alkanediol is that in the case that any polyalkylene glycol (polyethylene glycol) such as diethylene glycol is formed as a by-product, these substances eventually enter The bottom stream including the extraction solvent and alkanediol obtained in step (iv) of the method of the present invention. The problem solved in WO2008090108 mentioned above is that such polyethylene glycol may be formed when dialkyl carbonate and alkanol are prepared from alkylene carbonate and alkanol. In the separation scheme as disclosed in this WO2008090108, such polyethylene glycol finally enters the aforementioned bottoms stream containing unconverted alkylene carbonate. By recycling the latter bottom stream to the reactor, these higher boiling point polyethylene glycol by-products can accumulate. In the invention of WO2008090108, a part of this (bottom) stream containing alkylene carbonate and polyethylene glycol is subjected to the above-mentioned hydrolysis step to obtain alkylene glycol (alkylene glycol), To prevent this accumulation. However, the disadvantage is that only part of the unconverted alkylene carbonate can be recycled to the reactor and the other part is converted into alkylene glycol, thereby further reducing the overall yield of the desired dialkyl carbonate product. Because in the present invention, any unconverted alkylene carbonate from the bottom stream containing the extraction solvent and alkanediol obtained in step (iv) does not need to be recycled to the reaction step (i), there is no polyethylene glycol Any recycling of reaction step (i) is advantageous. Therefore, in the present invention, there is no need to separate the stream containing unconverted alkylene carbonate and polyethylene glycol, as in the method of WO2008090108 mentioned above, one part of which is recycled to the reactor and the other part hydrolysis. In contrast, in the present invention, if polyethylene glycol is formed, it can be transported to the extraction step (ii) together with the extraction solvent from the bottom stream obtained in step (iv) in step (v), in the extraction step ( In ii), such polyethylene glycol containing 2 hydroxyl groups can advantageously serve as an additional extraction solvent. In addition, advantageously, by not having to separate the stream containing unconverted alkylene carbonate and polyethylene glycol and then hydrolyzing a portion as taught in this WO2008090108, even more alkylene carbonate can be recycled to The reaction step, thereby increasing the overall yield of the desired dialkyl carbonate product.

Step (i) of the above-mentioned method for preparing dialkyl carbonate and alkanediol includes reacting alkylene carbonate with alkanol to obtain unconverted alkanol containing unconverted alkylene carbonate , Dialkyl carbonate, alkanediol and ether alkanol impurity product mixture.

This step (i) can be performed in the same way as the above step (a). The above-mentioned features, preferred solutions and examples related to step (a) of the method for preparing dialkyl carbonate and alkanediol mentioned above are also applicable to this step (i).

Step (ii) of the above-mentioned method for preparing dialkyl carbonate and alkanediol includes contacting the product mixture obtained in step (i) with an extraction solvent and contacting the unconverted alkanol and alkanediol The extraction solvent phase containing the ether alkanol impurities is separated from the organic carbonate phase containing unconverted alkylene carbonate and dialkyl carbonate, wherein the extraction solvent contains an alkanol containing 2 or more hydroxyl groups. In this specification, contacting the product mixture obtained in step (i) with an extraction solvent means contacting a stream containing the product mixture obtained in step (i) with another stream containing the extraction solvent.

The above-mentioned features, preferred solutions and examples of the extraction method of the present invention are also applicable to step (ii) of the above-mentioned method for preparing dialkyl carbonate and alkanediol. The product mixture obtained in step (i) to be processed according to the extraction step (ii) of the above-mentioned method also contains an alkanediol containing 2 hydroxyl groups, such as monoethylene glycol. Such alkanediol can be advantageously used as an additional extraction solvent. Therefore, the advantage is that in the reaction step (i), the alkanediol extraction solvent (such as monoethylene glycol) is a component that has been formed in the entire process, so that less extraction solvent needs to be added in the extraction step (ii).

The total amount of unconverted alkanol and ether alkanol impurities in the product mixture of the above-mentioned extraction step (ii) can be contained in 10 parts per million by weight (ppmw) to 10 wt.%, specific 100 ppmw to 9 wt.%, more specifically 0.1 to 8 wt.%, more specifically 0.3 to 7 wt.%, more specifically 0.5 to 6 wt.%, and most specifically 0.5 to 5 Within the range of wt.%.

For example, in the case where there is a relatively large amount of unconverted alkanol in the product mixture obtained in step (i), the unconverted alkanol is first removed from the product mixture before being subjected to the extraction step (ii) mentioned above. The converted alkanol may be preferred. In this case, preferably 10% to 80%, more preferably 20% to 70% of unconverted alkanol can be removed from the product mixture obtained in step (i). This removal of unconverted alkanol can be achieved in any known manner, for example by distillation including gas-liquid flash evaporation.

Step (iii) of the above-mentioned method for preparing dialkyl carbonate and alkanediol includes recovering dialkyl carbonate. This step (iii) can be achieved by distillation. Dialkyl carbonate can be obtained by separating the organic carbonate phase containing unconverted alkylene carbonate and dialkyl carbonate obtained in step (ii) to obtain an overhead stream containing dialkyl carbonate and unconverted alkylene carbonate. The bottom stream of the ester is recovered. The unconverted alkylene carbonate in the bottom stream can be recycled to step (i). In the case where the organic carbonate phase obtained in step (ii) additionally contains an alkanediol and/or an extraction solvent, the bottom stream additionally contains an alkanediol and/or an extraction solvent. In the latter case, preferably, the bottoms stream contains less than 15 wt.% of alkanediol.

In the case where the organic carbonate phase obtained in step (ii) additionally contains the alkanediol and/or extraction solvent as mentioned above and/or the bottoms stream containing unconverted alkylene carbonate as mentioned above When combined with the alkanediol and extraction solvent from the stream derived from the extraction solvent phase obtained in step (ii), the bottom stream may contain unconverted alkylene carbonate and additionally include alkanediol and/or extraction solvent The combined stream can be separated into a top stream containing unconverted alkylene carbonate and a bottom stream containing alkanediol and/or extraction solvent. The unconverted alkylene carbonate in the top stream can be recycled to step (i). The alkanediol and/or extraction solvent in the bottom stream can be recycled to step (ii). In the case where step (iii) produces a bottom stream containing unconverted alkylene carbonate and additionally containing alkanediol and/or extraction solvent, the bottom stream can be separated into two streams. A separated stream can then be recycled to step (ii). As described above, another separated stream can be separated into a top stream containing unconverted alkylene carbonate and a bottom stream containing alkanediol and/or extraction solvent. If necessary, the other separated stream can be separated from the top stream containing unconverted alkylene carbonate. (V) After the separated streams produced and containing alkanediol and extraction solvent are combined, as described below. These separations can be achieved by distillation.

Step (iv) of the above-mentioned method for preparing dialkyl carbonate and alkanediol includes separating the extraction solvent obtained in step (ii) into a top portion containing unconverted alkanol and ether alkanol impurities Stream and bottom stream containing extraction solvent and alkanediol. In the case where the extraction solvent phase additionally contains unconverted alkylene carbonate, the bottoms stream additionally contains unconverted alkylene carbonate. In the latter case, preferably, the bottoms stream contains less than 50 wt.% of unconverted alkylene carbonate. In addition, the top stream containing unconverted alkanol and ether alkanol impurities can be separated into a top stream containing unconverted alkanol (the unconverted alkanol can be recycled to step (i)) and a bottom containing ether alkanol impurities logistics. These separations can be achieved by distillation.

Step (v) of the above-mentioned method for preparing dialkyl carbonate and alkanediol includes recycling the extraction solvent from the bottom stream (including extraction solvent and alkanediol) obtained from step (iv) to In step (ii). Step (v) may include separating the bottom stream obtained in step (iv) into an overhead stream containing alkanediol (thereby recovering alkanediol as one of the products) and a solvent containing extraction solvent that can be recycled to step (ii) Bottom logistics. Alternatively, for example, in the above-mentioned case where the organic carbonate phase obtained in step (ii) additionally contains alkanediol and/or extraction solvent and/or the bottom stream obtained in step (iv) additionally contains unconverted carbonic acid In the case of alkylene esters, the bottom stream obtained in step (iv) can be separated into two streams. As described above, a separated stream can then be separated into a top stream containing alkanediol (thereby recovering alkanediol as one of the products) and a bottom stream containing the extraction solvent that can be recycled to step (ii). Another separated stream can be combined with the bottoms stream obtained in step (iii), which bottoms stream contains unconverted alkylene carbonate and additionally contains alkanediol and/or extraction solvent, and is then separated in the manner described above . This separation can be achieved by means of distillation.

The separation and recovery of the products in steps (iii), (iv) and (v) can be achieved in any known manner.

In addition, the present invention relates to a method for preparing diaryl carbonate, which comprises reacting an aryl alcohol with a stream containing dialkyl carbonate, and the ether alkanol impurities in the stream have been made according to any of the above methods. Remove.

Therefore, the present invention relates to a method for preparing diaryl carbonate, which comprises contacting an aryl alcohol with a dialkyl carbonate-containing stream in the presence of a transesterification catalyst. The ether alkanol impurities in the stream have been determined according to Remove any of the above methods.

In addition, the present invention also relates to a method for preparing diaryl carbonate, which comprises removing ether alkanol impurities from a stream containing dialkyl carbonate and ether alkanol impurities according to any of the above methods, and then The aryl alcohol is contacted with a stream containing dialkyl carbonate in the presence of a transesterification catalyst.

Preferably, in the above method for preparing diaryl carbonate, the diaryl carbonate is diphenyl carbonate and the aryl alcohol is phenol.

In addition, as described in step (a), the above-mentioned transesterification catalyst and other transesterification conditions are also applicable to these methods for preparing diaryl carbonate.

Figure 1 shows the above-mentioned method for preparing dialkyl carbonate and alkanediol involving steps (a) to (f), including the extraction method of the present invention as one of the steps.

In Figure 1, ethanol enters reactor 2 via line 1. Reactor 2 may suitably be a continuous stirred tank reactor. Via line 3, ethylene carbonate is also fed into reactor 2. The transesterification catalyst may be present or may be continuously fed to the reactor. The catalyst can be mixed with one of the reactants or fed into the reactor via a separate line (not shown). The unconverted ethylene carbonate, unconverted ethanol, diethyl carbonate, ethylene glycol (alkane glycol) and 2-ethoxyethanol (ether alkanol impurity; ethyl alcohol) are extracted from the reactor 2 via line 4 Glycol ether) product mixture. Via line 4, the mixture is sent to distillation column 5, where the product is separated into an overhead stream containing diethyl carbonate, unconverted ethanol and ethylene glycol ether (which is extracted via line 7) and containing ethylene glycol And the bottom stream of unconverted ethylene carbonate (which is withdrawn via line 6). The bottom stream in line 6 is distilled in distillation column 8 to produce a top stream containing ethylene glycol (which is recovered via line 10) and a bottom stream containing unconverted ethylene carbonate (which is recycled via lines 9 and 3) Circulate to reactor 2).

In the distillation column 11, the overhead stream containing diethyl carbonate, unconverted ethanol, and ethylene glycol ether from the distillation tower 5 is distilled to produce an overhead stream including unconverted ethanol (which passes through lines 13 and 1 again). Recycle to reactor 2) and the bottom stream containing diethyl carbonate, ethylene glycol ether and unconverted ethanol. The latter bottom stream is fed to the lower part of the extraction column 14 via the line 12. In this column, glycerol is used as an extraction solvent to perform liquid-liquid extraction of a stream containing diethyl carbonate, ethylene glycol ethyl ether and unconverted ethanol, and the extraction solvent is fed to the upper part of the column. The resulting overhead stream from extraction column 14 contains diethyl carbonate. The resulting bottom stream in line 15 contains unconverted ethanol, ethyl glycol ether and glycerol and is separated into two substreams 15a and 15b. The substream 15a (the "rich" extractant stream) is recycled to the upper part of the extraction column 14. The substream 15b is sent to the distillation column 17 to produce a top stream (in line 19) containing unconverted ethanol and ethylene glycol ether and a bottom stream (in line 18) containing glycerol. The latter bottom stream 18 (the "lean" extractant stream) may contain some ethylene glycol ether and is recycled to the extraction column 14 at a position higher than the substream 15a is fed to the column. The stream containing unconverted ethanol and ethylene glycol ether in line 19 is sent to distillation column 20 to produce an overhead stream containing unconverted ethanol (which is recycled to reactor 2 via lines 22 and 1) and containing ethylene glycol ether The bottom stream (in line 21).

Figure 2 shows the above-mentioned method for preparing dialkyl carbonate and alkanediol involving steps (i) to (v), including the extraction method of the present invention as one of the steps.

In Figure 2, ethanol enters reactor 2 via line 1. Reactor 2 may suitably be a continuous stirred tank reactor. Via line 3, ethylene carbonate is also fed into reactor 2. The transesterification catalyst may be present or may be continuously fed to the reactor. The catalyst can be mixed with one of the reactants or fed into the reactor via a separate line (not shown). The unconverted ethylene carbonate, unconverted ethanol, diethyl carbonate, ethylene glycol (alkane glycol) and 2-ethoxyethanol (ether alkanol impurity; ethyl alcohol) are extracted from the reactor 2 via line 4 Glycol ether) product mixture. The mixture enters the lower part of the extraction column 5 via the line 4. In the column, the product mixture is subjected to liquid-liquid extraction using glycerol as the extraction solvent, and the extraction solvent is fed to the upper part of the column.

The top stream obtained from extraction tower 5 in line 7 contains diethyl carbonate, unconverted ethylene carbonate, ethylene glycol and glycerin, and is distilled in distillation tower 8 to produce an overhead stream containing diethyl carbonate (It is recovered via line 9) and a bottom stream (in line 10) containing unconverted ethylene carbonate, ethylene glycol and glycerol. Stream 10 is separated into two sub-streams 10a and 10b. The substream 10a is recycled to the extraction tower 5.

The bottom stream obtained from extraction column 5 in line 6 contains unconverted ethanol, ethylene glycol ether, ethylene glycol and glycerin. Optionally, the bottom stream can be separated (not shown in Figure 2, but shown in relation to stream 15 in Figure 1), one of the substreams is recycled to the upper part of the extraction column 5, and the other substream is sent to the distillation column 11. Stream 6 (unseparated) is distilled in distillation column 11 to produce an overhead stream (in line 12) containing unconverted ethanol and ethylene glycol ether, and a bottom stream (in line 13) containing ethylene glycol and glycerin. The stream in line 12 is distilled in distillation column 14 to produce an overhead stream containing unconverted ethanol (which is recycled to reactor 2 via lines 15 and 1) and a bottom stream containing glycol ether (in line 16). The stream in the pipeline 13 is separated into two sub-streams 13a and 13b as appropriate. Substream 13b (with separation) or stream 13 (without separation) is distilled in distillation column 17 to produce an overhead stream containing ethylene glycol (which is recovered via line 18) and a bottom stream containing glycerol (which is sent to Extraction tower 5).

Optionally, the substream 10b containing unconverted ethylene carbonate, ethylene glycol and glycerin combined with the substream 13a is distilled in the distillation column 20 to produce an overhead stream containing unconverted ethylene carbonate (which passes through line 21 and 3 Recycle to reactor 2) and the bottom stream containing ethylene glycol and glycerol (which is sent to extraction column 5 via line 22).

The following examples further illustrate the extraction method of the present invention. Instance

Liquid-liquid equilibrium (LLE) data measurement is carried out in a stirred and temperature-adjusted glass cell. After equilibrium and phase settling, samples were taken from the two phases and analyzed by gas chromatography. Determine the molar concentration of each component in each of the two phases.

For the five-element system 2-ethoxyethanol (ethylene glycol ethyl ether or EE) + diethyl carbonate (DEC) + ethylene carbonate (EC) + monoethylene glycol (MEG) + glycerol (GLY), in the environment The LLE data was measured under pressure and at a temperature of 50°C. The concentration of the 2-ethoxyethanol feed was changed (1, 3, 5, and 7.5 wt.%). The weight ratio of DEC:EC:MEG:GLY in the feed is kept constant at 1:1:1:1.

In addition, for the five-element system ethanol (EtOH)+DEC+EC+MEG+GLY, the LLE data is also measured in the same way, except that the ethanol feed concentration is 1, 3, 5, and 6 wt.%, respectively.

For each component in each of the above two five-element systems, determine its molar fraction in each of the two phases. The molar fraction of the components in the upper phase (the raffinate phase) is called x (component) in Tables 1 and 2 below, for example x (DEC). The molar fraction of the components in the lower phase (extract phase) is referred to as y (component) in Tables 1 and 2 below, for example y (DEC). These molar fraction data can be transformed into a distribution coefficient (K value), where for a certain component (such as K (DEC)), K (component) is equal to the molar fraction of the upper phase divided by the molar fraction of the lower phase. Ear fraction. The relative selectivity α (component/ethylene glycol ether or EtOH) can be defined as the ratio of DEC to the K value of ethylene glycol ether (EE) or ethanol (EtOH), for example, in a five-element system containing glycol ether It is K(DEC)/K(EE) and K(DEC)/K(EtOH) in a five-element system containing ethanol. When the relative selectivity is 1, there is no difference in selectivity between the component and ethylene glycol ether or EtOH relative to the two phases. The efficiency of solvent-enhanced separation of ethyl glycol ether and/or EtOH from organic carbonates (such as DEC and EC) can be evaluated by monitoring the change in the relative selectivity α when the solvent is added.

Table 1 below shows the LLE data of the five-element system containing ethylene glycol ether, including the derived K value and relative selectivity (compared to ethylene glycol ether). Table 1 below shows the LLE data of the five-element system containing ethanol, including the derived k value and relative selectivity (compared to ethanol). The alpha value (relative selectivity) higher than 1 means that in the liquid-liquid extraction column, the first component will eventually enter the upper (raffinate) phase, while the second component (ethylene glycol ether or EtOH) will eventually enter the lower (Extract) phase.

The data in Table 1 and Table 2 first show that by adding monoethylene glycol and glycerin, in the entire range of the evaluated composition (in the case of a change in the concentration of ethylene glycol ether or EtOH in the feed), The relative selectivity of organic carbonates (such as DEC and EE) to ethylene glycol ether or EtOH is higher than 1, and therefore there is a choice between organic carbonates and ethylene glycol ether or EtOH relative to the two phases The rate difference, and secondly, the organic carbonate moves upward in the liquid-liquid extraction tower, while the ethyl glycol ether or EtOH moves downward together with the monoethylene glycol and glycerol. Therefore, advantageously, monoethylene glycol and glycerol are good extraction solvents for separating ethylene glycol ether and/or EtOH from organic carbonates (such as DEC and EE) in a liquid-liquid extraction process. Surprisingly, monoethylene glycol and glycerin are better solvents for dissolving ethylene glycol ether and/or EtOH and to a lesser extent organic carbonates such as DEC and ethylene carbonate. In another step, ethylene glycol ethyl ether and/or EtOH can be easily separated from monoethylene glycol and glycerol (for example, by distillation), and then it can be advantageous to use monoethylene glycol and glycerol as extraction solvents to contain The mixture of organic carbonate and ethylene glycol ether and/or EtOH is subjected to liquid-liquid extraction. Table 1: Liquid-liquid extraction data of 2-ethoxyethanol (EE) EE (wt.%) x (EE) x (DEC) x (EC) x (MEG) x (GLY) 1 0.0106 0.4850 0.3174 0.1364 0.0507 3 0.0307 0.4480 0.2980 0.1590 0.0643 5 0.0569 0.4231 0.2686 0.1866 0.0648 7.5 0.0763 0.3650 0.2345 0.2261 0.0980 y (EE) y (DEC) y (EC) y (MEG) y (GLY) 1 0.0102 0.0594 0.1018 0.5148 0.3138 3 0.0259 0.0622 0.0881 0.5301 0.2938 5 0.0471 0.0768 0.0889 0.5020 0.2852 7.5 0.0611 0.0972 0.0987 0.4475 0.2955 K (EE) K (DEC) K (EC) K (MEG) K (GLY) 1 1.039 8.165 3.118 0.265 0.162 3 1.185 7.203 3.383 0.300 0.219 5 1.208 5.509 3.021 0.372 0.227 7.5 1.249 3.755 2.376 0.505 0.332 K(EE)/K(EE) K(DEC)/K(EE) K(EC)/K(EE) K(MEG)/K(EE) K(GLY)/K(EE) 1 1 7.857 3.000 0.255 0.155 3 1 6.076 2.854 0.253 0.185 5 1 4.560 2.501 0.308 0.188 7.5 1 3.007 1.903 0.405 0.266 Table 2: Liquid-liquid extraction data of ethanol (EtOH) EtOH (wt.%) x (EtOH) x (DEC) x (EC) x (MEG) x (GLY) 1 0.0231 0.4872 0.2552 0.1548 0.0798 3 0.0544 0.4396 0.2538 0.1794 0.0727 5 0.0932 0.3825 0.2240 0.2272 0.0731 6 0.1087 0.3622 0.2241 0.2145 0.0905 y (EtOH) y (DEC) y (EC) y (MEG) y (GLY) 1 0.0273 0.0650 0.0925 0.5440 0.2712 3 0.0579 0.0807 0.0901 0.4906 0.2808 5 0.0984 0.1003 0.0965 0.4598 0.2449 6 0.1121 0.1232 0.1051 0.4305 0.2291 K (EtOH) K (DEC) K (EC) K (MEG) K (GLY) 1 0.846 7.495 2.759 0.285 0.294 3 0.940 5.447 2.817 0.366 0.259 5 0.947 3.814 2.321 0.494 0.298 6 0.970 2.940 2.132 0.498 0.395 K(EtOH)/K(EtOH) K (DEC)/K (EtOH) K(EC)/K(EtOH) K (MEG)/K (EtOH) K (GLY)/K (EtOH) 1 1 8.858 3.261 0.336 0.348 3 1 5.798 2.998 0.389 0.276 5 1 4.026 2.451 0.522 0.315 6 1 3.032 2.199 0.514 0.407

1: pipeline 2: reactor 3: pipeline 4: pipeline 5: Distillation tower; extraction tower 6: pipeline; logistics 7: pipeline 8: Distillation tower 9: pipeline 10: pipeline; logistics 10a: Sub-logistics 10b: Sub-logistics 11: Distillation tower 12: pipeline 13: pipeline; logistics 13a: Sub-logistics 13b: Sub-logistics 14: Extraction tower; distillation tower 15: pipeline; logistics 15a: Sub-logistics 15b: Sub-logistics 16: pipeline 17: Distillation tower 18: Pipeline; bottom logistics 19: pipeline 20: Distillation tower 21: pipeline 22: pipeline

[Figure 1 and Figure 2] shows a method for preparing dialkyl carbonate and alkanediol, which involves the extraction method of the present invention as one of the steps.

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Claims (9)

A method for removing the ether alkanol impurities from a stream containing organic carbonate and ether alkanol impurities, which comprises contacting the stream with an extraction solvent and making an extraction solvent phase containing the ether alkanol impurities and an organic carbonate phase For separation, the method involves liquid-liquid extraction, wherein the extraction solvent contains an alkanol containing 2 or more hydroxyl groups. The method of claim 1, wherein the organic carbonate is dialkyl carbonate, diaryl carbonate, alkylaryl carbonate, alkylene carbonate, or a mixture of such organic carbonates, preferably dialkyl carbonate and / Or alkylene carbonate. The method of claim 1 or 2, wherein the extraction solvent contains an alkanol containing 2 to 5 hydroxyl groups, preferably 2 to 4 hydroxyl groups, more preferably 2 to 3 hydroxyl groups, and most preferably 3 hydroxyl groups. The method of claim 3, wherein the extraction solvent comprises monoethylene glycol, monopropylene glycol, glycerol, erythritol, xylitol or sorbitol, preferably monoethylene glycol, monopropylene glycol or glycerol, more preferably It is monoethylene glycol or glycerin, preferably glycerin. A method for preparing dialkyl carbonate and alkanediol, which comprises: (A) reacting alkylene carbonate with alkanol to obtain a product mixture containing unconverted alkylene carbonate, unconverted alkanol, dialkyl carbonate, alkylene glycol and ether alkanol impurities; (B) separating unconverted alkylene carbonate and alkane glycol from the product mixture to obtain an overhead stream containing unconverted alkanol, dialkyl carbonate and the ether alkanol impurities; (C) Recover the alkanediol; (D) separating unconverted alkanol from the top stream obtained in step (b) to obtain a bottom stream containing dialkyl carbonate and the ether alkanol impurities; and (E) According to the method according to any one of claims 1 to 4, the bottoms stream obtained in step (d) is contacted with an extraction solvent, and the extraction solvent phase containing the ether alkanol impurities and the dialkyl carbonate phase Separation, wherein the extraction solvent comprises an alkanol containing 2 or more hydroxyl groups; and (F) removing the ether alkanol impurities from the extraction solvent phase obtained in step (e), and recycling the extraction solvent to step (e). A method for preparing dialkyl carbonate and alkanediol, which comprises: (I) reacting alkylene carbonate with alkanol to obtain a product mixture containing unconverted alkylene carbonate, unconverted alkanol, dialkyl carbonate, alkylene glycol and ether alkanol impurities; (Ii) According to the method according to any one of claims 1 to 4, the product mixture obtained in step (i) is brought into contact with an extraction solvent and an impurity containing unconverted alkanol, alkanediol and the ether alkanol The extraction solvent phase is separated from the organic carbonate phase containing unconverted alkylene carbonate and dialkyl carbonate, wherein the extraction solvent contains an alkanol containing 2 or more hydroxyl groups; (Iii) Recover the dialkyl carbonate; (Iv) separating the extraction solvent obtained in step (ii) into an overhead stream containing unconverted alkanol and the ether alkanol impurities and a bottom stream containing extraction solvent and alkanediol; and (V) Recycling the extraction solvent from the bottom stream obtained in step (iv) to step (ii). According to the method of claim 5 or 6, wherein in step (a) or (i), the alkylene carbonate is C ₂ -C ₆ alkylene carbonate, preferably C ₂ -C ₄ alkylene carbonate, and more It is preferably a C ₂ -C ₃ alkylene carbonate, and the alkanol is a C ₁ -C ₄ alkanol, preferably a C ₁ -C ₃ alkanol, and more preferably a C ₂ -C ₃ alkanol. The method of claim 7, wherein in step (a) or (i), the alkylene carbonate is ethylene carbonate or propylene carbonate, the alkanol is ethanol, and the dialkyl carbonate is diethyl carbonate ester. A method for preparing diaryl carbonate, which comprises removing the ether alkanol impurities from a stream containing dialkyl carbonate and ether alkanol impurities according to the method according to any one of claims 1 to 8, and then The aryl alcohol is contacted with the stream containing the dialkyl carbonate in the presence of a transesterification catalyst.

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