Cross-Reference to Related Applications

This application claims the benefit of U.S. Provisional Application No. 62/439,516, filed on 28 December 2016, which is incorporated herein by reference.

Field of the Invention

The invention relates to a method of treating an organic carbonate stream to remove contaminants.

Background of the Invention

Alkylene carbonate, such as ethylene carbonate, is an important starting material in the production of acyclic dialkyl carbonate and monoalkylene glycol, by reaction with an alkanol. For example, ethylene carbonate and ethanol may be reacted to form diethyl carbonate and monoethylene glycol. Alkylene carbonates are also widely used as solvents and diluents in industrial processes such as dyes, fibers, plastics, and batteries. In many applications, ethylene and propylene carbonate offer a safe and clean alternative to more hazardous dipolar aprotic solvents. They are also used as raw materials for commercial products such as cosmetics and pharmaceuticals.

Subsequently, acyclic dialkyl carbonate, such as dimethyl carbonate or diethyl carbonate, is an important chemical product. It may, for example, be used as a starting material in the production of diaryl carbonate, by reaction with an aromatic alcohol. For example, diphenyl carbonate may be produced by the reaction of a dialkyl carbonate with phenol.

Diphenyl carbonate is an important starting material in the commercial production of polycarbonates. Diphenyl carbonate may be polymerized with a dihydroxy aromatic compound, for example, bisphenol acetone into a polycarbonate. The diphenyl carbonate must be of sufficient purity before it is reacted with the dihydroxy aromatic compound.

This can be achieved by purifying the diphenyl carbonate or by ensuring that the starting materials used to produce the diphenyl carbonate, for example, ethylene carbonate and diethyl carbonate, are of sufficient purity.

In addition, ensuring that the dialkyl carbonate starting materials are of sufficient purity would also result in fewer side reactions, and therefore a higher yield and/or selectivity for the desired reactions. US6586605 describes a process for contacting an alkylene carbonate with at least two solid adsorbents comprising carbon and inorganic silicon or aluminum oxide.

Summary of the Invention

The invention provides a method of treating an organic carbonate stream comprising passing the organic carbonate stream through a fixed bed to remove contaminants and produce a less contaminated stream wherein the fixed bed comprises alumina or silica.

The invention further provides a method of producing diphenyl carbonate comprising: a) reacting carbon dioxide and ethylene oxide to form ethylene carbonate; b) reacting the ethylene carbonate with ethanol in a transesterification reaction to form diethyl carbonate and mono-ethylene glycol; and c) reacting the diethyl carbonate with phenol in a transesterification; and disproportionation reaction to form diphenyl carbonate wherein one or more of the ethylene carbonate, diethyl carbonate and diphenyl carbonate is passed through a fixed bed comprising alumina or silica to remove contaminants.

Detailed Description of the Invention

The invention provides a method of treating one or more organic carbonate streams. The organic carbonate that is treated may be one or more of an alkylene carbonate, a dialkyl carbonate and/or a carbonate. For example, the treating process can reduce the total halogens to a very low content, i.e., less than 0.3 ppm. With regards to diphenyl carbonate, this compound has a very stringent halogen specification of less than 300 ppbw halogens because halogens are known color bodies that will cause color and other issues in the melt polymerization process to produce polycarbonate. Since the alkylene carbonate and the dialkyl carbonate are precursors used in the formation of the diphenyl carbonate, any of these streams may be subjected to a treating step to reduce the level of

contaminants.

Alkylene carbonate

In one embodiment, the organic carbonate stream that is treated comprises alkylene carbonate. The alkylene carbonate may be prepared by any method known to one of ordinary skill in the art, including by reacting carbon dioxide with an alkylene oxide resulting in a stream containing alkylene carbonate and impurities, and recovering alkylene carbonate from said stream. This reaction may be carried out in the presence of a catalyst. Suitable catalysts include quaternary ammonium halides, quaternary phosphonium halides and metal halides. Additional catalysts are described in US 7,674,919. In one embodiment, the alkylene carbonate may be prepared according to the description provided in US 7,674,919, which is herein incorporated by reference. This patent describes a process for the preparation of an alkylene carbonate, comprising contacting the corresponding alkylene oxide with carbon dioxide in the presence of water, wherein the amount of water is at least 0.05 mol/mol alkylene oxide, and in the presence of a catalytic composition comprising an organic base neutralized with a hydrogen halide, wherein the organic base comprises a carbon-based compound comprising one or more nitrogen atoms with at least one free electron pair and/or one or more phosphorous atoms with at least one free electron pair and wherein the organic base has a pKa greater than 8.

In another embodiment, the alkylene carbonate may be prepared according to the description provided in US 7,488,835, which is herein incorporated by reference. This patent describes a process for the catalytic carboxylation of alkylene oxides with carbon dioxide, in the presence of a catalytic composition and water, wherein the catalyst composition comprises an alkali metal halide and a macrocyclic chelating compound.

In another embodiment, the alkylene carbonate may be prepared according to the description provided in US 7,501,531, which is herein incorporated by reference. This patent describes a process for the preparation of an alkylene carbonate, said process comprising contacting the corresponding alkylene oxide with carbon dioxide in the presence of a metal salt immobilised on a solid support, wherein the metal salt comprises a cation of a metal selected from those in the third period and group 2, the fourth period and groups 2 and 4 to 12, the fifth period and groups 2, 4 to 7, 12 and 14, and the sixth period and groups 2 and 4 to 6 of the periodic table, according to IUPAC nomenclature, and an anion selected from anions of inorganic acids and organic acids, and wherein the solid support contains a quaternary ammonium, a quaternary phosphonium, a quaternary arsenonium, a quaternary stibonium, or a ternary sulfonium cation.

Ethylene carbonate is infinitely soluble in water. Propylene carbonate is soluble in water up to 25.0 g of propylene carbonate per 100 g of water at 25 °C.

Dialkyl carbonate

In another embodiment, the organic carbonate stream that is treated comprises dialkyl carbonate. The dialkyl carbonate may be prepared by any method known to one of ordinary skill in the art, including by reacting an alkanol (for example ethanol) and an alkylene carbonate (for example ethylene carbonate) using a catalyst to produce the dialkyl carbonate (for example diethyl carbonate) and a monoalkylene glycol (for example monoethylene glycol).

In one embodiment, the dialkyl carbonate may be prepared according to the process described in US 8,975,432, which is herein incorporated by reference. This patent describes a process for the preparation of an alkanediol and a dialkyl carbonate comprising: (a) reacting an alkylene carbonate and an alkanol in the presence of a transesterification catalyst to obtain a reaction mixture comprising dialkyl carbonate, unconverted alkanol, alkanediol, unconverted alkylene carbonate and an alkoxy alkanol impurity; (b) subjecting the reaction mixture to distillation in a first distillation column to obtain a top stream comprising dialkyl carbonate, alkanol and alkoxy alkanol impurity and a bottom stream comprising alkanediol and alkylene carbonate; (c) subjecting the bottom stream from the first distillation column to distillation in a second distillation column to obtain a top stream comprising alkanediol and a bottom stream comprising alkylene carbonate; (d) subjecting the top stream from the first distillation column to distillation in a third distillation column in the presence of a catalyst to effect reaction of the alkoxy alkanol impurity with the dialkyl carbonate into a carbonate ether impurity, to obtain a top stream comprising alkanol and a bottom stream comprising dialkyl carbonate and carbonate ether impurity; and (e) subjecting the bottom stream from the third distillation column to distillation in a fourth distillation column to obtain a top stream comprising dialkyl carbonate and a bottom stream comprising dialkyl carbonate and carbonate ether impurity; and (f) recycling the bottom stream from the fourth distillation column to the first distillation column.

In another embodiment, the dialkyl carbonate may be prepared according to the process described in US 8,618,322, which is herein incorporated by reference. This patent describes a process for the preparation of an alkanediol and a dialkyl carbonate comprising: (a) reacting an alkylene carbonate and an alkanol in the presence of a transesterification catalyst to obtain a reaction mixture comprising dialkyl carbonate, unconverted alkanol, alkanediol and unconverted alkylene carbonate; (b) subjecting the reaction mixture to distillation in a first distillation column to obtain a top stream comprising dialkyl carbonate and alkanol and a bottom stream comprising dialkyl carbonate, alkanol, alkanediol and alkylene carbonate; (c) subjecting the bottom stream from the first distillation column to distillation in a second distillation column to obtain a top stream comprising dialkyl carbonate and alkanol and a bottom stream comprising alkanediol and alkylene carbonate; (d) recovering alkanediol from the bottom stream from the second distillation column; and (e) subjecting the top streams from the first and second distillation columns to distillation in a third distillation column to obtain a top stream comprising alkanol and a bottom stream comprising dialkyl carbonate.

In the dialkyl carbonate, the alkyl groups and may be the same or different, preferably the same. Further, preferably, the alkyl groups and in such dialkyl carbonates, which groups may be straight, branched and/or cyclic, are Cl-8 alkyl groups, more preferably Cl-6 alkyl groups, such as isopropyl, ethyl and methyl, suitably ethyl.

Preferably, the dialkyl carbonate is dimethyl carbonate or diethyl carbonate, more preferably diethyl carbonate.

The industrially important dialkyl carbonates, such as dimethyl-, diethyl-, dipropyl-

, di-n-butyl carbonates are all colorless liquids, and most of them have a pleasant odor.

Dimethyl carbonate and diethyl carbonate are sparingly soluble in water.

The dialkyl carbonate feed to be treated in the present process may comprise a dialkyl carbonate feed which does not meet specifications regarding the maximum amount of impurities.

Diaryl carbonate

In another embodiment, the organic carbonate stream that is treated comprises diaryl carbonate. The diaryl carbonate may be prepared by any method known to one of ordinary skill in the art, including by reacting a dialkyl carbonate with an aryl alcohol (for example, phenol) to produce alkyl aryl carbonate and the corresponding alkanol, followed by disproportionation of the alkyl aryl carbonate to produce diaryl carbonate and dialkyl carbonate. Further transesterification of the alkyl aryl carbonate with aryl alcohol yielding diaryl carbonate and alkyl alcohol may also take place.

The above-mentioned diaryl carbonate may be a carbonate of the following formula:

R ¹ 0(CO)OR ²

wherein both R ¹ and R ² are aryl groups. Preferably, the aryl group is a phenyl group and the diaryl carbonate is diphenyl carbonate (DPC).

In one embodiment, the diaryl carbonate also may have been subjected to conventional purification and recovery techniques before it is treated. If the diaryl carbonate is produced from an aryl alcohol and a dialkyl carbonate, such purification and recovery techniques typically involve the removal of unreacted aryl alcohol, dialkyl carbonate, co-product alkyl alcohol, and the reaction intermediate alkylaryl carbonate. Preferably, the diaryl carbonate treated in the process of the present invention is for use as raw material in making a polycarbonate.

In one embodiment, the diaryl carbonate may be prepared according to the process described in US 8, 110,698, which is herein incorporated by reference. This patent describes a process for the production of diaryl carbonate, the process including: feeding an aromatic hydroxy compound and a dialkyl carbonate to a first reaction zone comprising a solid transesterification catalyst; and feeding a soluble organometallic compound to the first reaction zone, wherein the solid transesterification catalyst and the soluble organometallic compound each independently comprise a Group II to Group VI element.

In another embodiment, the diaryl carbonate may be produced by a process for production of diaryl carbonate, including: reacting an epoxide and carbon dioxide in a first reaction zone to form first reaction product comprising a cyclic carbonate; transesterifying the cyclic carbonate with ethanol in the presence of a first transesterification catalyst in a second reaction zone to form a second reaction product comprising diethyl carbonate and glycol; separating the second reaction product to recover a first diethyl carbonate fraction and a first glycol fraction; transesterifying at least a portion of the first diethyl carbonate fraction with an aryl hydroxy compound in the presence of a second transesterification catalyst in a third reaction zone to form a third reaction product comprising ethyl aryl carbonate and ethanol; separating the third reaction product to recover an ethyl aryl carbonate fraction and a first ethanol fraction; disproportionating at least a portion of the ethyl aryl carbonate fraction in the presence of a disproportionation catalyst in a fourth reaction zone to form a fourth reaction product comprising diaryl carbonate and diethyl carbonate; separating the fourth reaction product to recover a diaryl carbonate fraction and a second diethyl carbonate fraction; recycling at least a portion of the first ethanol fraction to the second reaction zone; and recycling at least a portion of the second diethyl carbonate fraction to the third reaction zone.

In a further embodiment, the diaryl carbonate may be produced by a process for producing diaryl carbonate, including: reacting ammonia and carbon dioxide in a first reaction zone to form first reaction product comprising a urea; transesterifying the urea with ethanol in the presence of a first transesterification catalyst in a second reaction zone to form a second reaction product comprising diethyl carbonate and ammonia; separating the second reaction product to recover a first diethyl carbonate fraction and a first ammonia fraction; transesterifying at least a portion of the first diethyl carbonate fraction with an aryl hydroxy compound in the presence of a second transesterification catalyst in a third reaction zone to form a third reaction product comprising ethyl aryl carbonate and ethanol; separating the third reaction product to recover an ethyl aryl carbonate fraction and an ethanol fraction; disproportionating at least a portion of the ethyl aryl carbonate fraction in the presence of a disproportionation catalyst in a fourth reaction zone to form a fourth reaction product comprising diaryl carbonate and diethyl carbonate; separating the fourth reaction product to recover a diaryl carbonate fraction and a second diethyl carbonate fraction; recycling at least a portion of the ethanol fraction to the second reaction zone; and recycling at least a portion of the second diethyl carbonate fraction to the third reaction zone.

In a still further embodiment, the diaryl carbonate may be prepared according to the process described in WO 2008/090107, which is herein incorporated by reference. This published patent application describes a process for the preparation of diaryl carbonate by reaction of an aromatic alcohol with a dialkyl carbonate, which dialkyl carbonate has been prepared by the reaction of an alkanol and an alkylene carbonate, which process comprises the following steps: (a) passing an aromatic alcohol and a dialkyl carbonate into a first transesterification zone to obtain a first product stream containing diaryl carbonate, alkanol, unconverted dialkyl carbonate and unconverted aromatic alcohol; (b) separating the first product stream into a diaryl carbonate-rich product stream, an aromatic alcohol- rich recycle stream and a second recycle stream comprising alkanol, dialkyl carbonate and aromatic alcohol; (c) feeding alkanol and alkylene carbonate into a second

transesterification zone to obtain a second product stream comprising alkanediol and unconverted alkanol and unconverted dialkyl carbonate; (d) separating alkanediol from the second product stream to yield an alkanediol product stream and a mixture of dialkyl carbonate and unconverted alkanol; (e) subjecting the mixture of dialkyl carbonate and unconverted alkanol and the second recycle stream comprising alkanol, dialkyl carbonate and aromatic alcohol to the same distillation to obtain an alkanol stream as the lower- boiling fraction and a contaminated stream comprising dialkyl carbonate and aromatic alcohol as the higher-boiling fraction; (f) recycling the alkanol stream of step e) to the second transesterification zone; and (g) passing the contaminated stream comprising dialkyl carbonate and aromatic alcohol, and the aromatic alcohol- rich recycle stream to the first transesterification zone. Diaryl carbonates are solid at ambient conditions. They are soluble in many organic solvents, particularly polar solvents, such as esters, ketones, ethers, alcohols and aromatic hydrocarbons.

Possible contaminants

The contaminants may comprise halogens or ethyl oxitol. The contaminants may comprise organic chlorides, for example, 2-chloroethanol. The contaminants may also comprise organic bromides, for example, 2-bromoethanol and l-bromo-2-propanol. These contaminants may originate from the catalyst or catalysts used in the preparation of the organic carbonates described above or from one of the reactants used in that preparation.

In addition, monoethylene glycol and diethylene glycol may be considered contaminants in ethylene carbonate streams.

Treating of one or more of these streams to remove contaminants

One or more of the above described organic carbonate streams and/or mixtures thereof may be treated to remove these contaminants or other impurities present in the organic carbonate stream. This treatment comprises contacting the organic carbonate stream with a fixed bed comprising alumina or silica.

The alumina or silica may have a surface area of from 200 to 700 m ² /g. The alumina or silica may be present in the form of spheres, pellets, cylinders, trilobes or quadralobes.

The process preferably removes at least 50% of the contaminants in the organic carbonate stream. In certain embodiments the starting organic carbonate stream may be fairly pure, for example, the organic carbonate stream to be treated may contain less than 0.01 wt.% impurities. For example, the organic carbonate stream to be treated may comprise less than 0.01 wt.% halogens.

The fixed bed may be regenerated to remove accumulated impurities that have been absorbed on the fixed bed. Further, more than one fixed bed may be used to allow for regeneration of one bed at the same time that another bed is used for treating the organic carbonate stream. In another embodiment, more than two fixed bed may be used such that there is an additional fixed bed that can be used as a backup or otherwise used to ensure that the organic carbonate stream can always be treated regardless of required regeneration and/or other downtime.

In one embodiment, an alkylene carbonate (ethylene carbonate) may be prepared by reacting carbon dioxide with an alkylene oxide (ethylene oxide). The ethylene carbonate may be reacted with an alkanol (ethanol) to produce dialkyl carbonate (diethyl carbonate) and a monoalkylene glycol (monoethylene glycol). The diethyl carbonate is reacted with phenol to produce ethyl phenyl carbonate and ethanol. The ethyl phenyl carbonate and ethanol disproportionate to produce diphenyl carbonate and diethyl carbonate. In addition, transesterification of the ethyl phenyl carbonate with phenol yields diphenyl carbonate and ethanol. The resulting diphenyl carbonate contains contaminants from the reaction steps carried out to produce the diphenyl carbonate. The contaminants may include catalyst components and/or side products formed during the reaction steps.

The diphenyl carbonate is treated by contacting the diphenyl carbonate with a fixed bed comprising alumina or silica. The diphenyl carbonate may be further purified by passing the treated diphenyl carbonate through a distillation step to remove additional contaminants.

Examples

Example 1

In this example, a diethyl carbonate (DEC) solution comprising 2-bromoethanol, 2- chloroethanol and l-bromo-2-propanol with a bromine concentration of 1000 ppm was treated by passing it through a fixed bed of alumina. The alumina was a 1.3 mm trilobe shaped alumina extrudate with a surface area of 300 m ² /g. In a separate experiment, the same DEC was treated by passing it through a fixed bed of silica. In both experiments, more than 85% of the bromine was absorbed onto the solid absorbents with very little contact time (LHSV of 0.05 hr ¹ ) at low temperature (ambient).

Example 2

An ethylene carbonate stream that has less than 0.3 wt.% MEG or DEG (dissolved in diethyl carbonate in a 1 : 1 ratio) was treated by passing it through a fixed bed of alumina. The alumina was a 1.3 mm trilobe shaped alumina extrudate with a surface area of 300 m ² /g. Almost all of the MEG or DEG was absorbed onto the alumina.