FOR THE PRODUCTION OF ARYL CARBONATES

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of European Patent Application Serial No. 15382136 filed March 23, 2015. The related application is incorporated herein by reference in its entirety.

BACKGROUND

[0002] The present disclosure relates generally to a method and an apparatus for the production of aryl carbonates such as alkyl aryl carbonates and diaryl carbonates, and especially to a method and an apparatus for the production of aryl carbonates.

[0003] Diaryl carbonates such as diphenyl carbonate (DPC) are important reactants in the production of polycarbonates. Polycarbonates can be manufactured by polymerization of an aromatic dihydroxy compound such as bisphenol A (BPA), with a diaryl carbonate such as DPC. Polycarbonates are useful materials valued for their physical and optical properties. As the uses for polycarbonates have increased, the efficient production of diaryl carbonates has become of greater significance. A phosgene-free process involves first reacting a dialkyl carbonate such as dimethyl carbonate (DMC) with an aromatic alcohol such as phenol in the presence of a transesterification catalyst, to produce an alkyl aryl carbonate (e.g., phenyl methyl carbonate (PMC)) and an aliphatic monohydric alcohol (alkanol) (e.g., methanol or ethanol). In the second step, two molecules of the alkyl aryl carbonate undergo a disproportionation reaction to produce one molecule of diaryl carbonate (e.g., DPC) and one molecule of the starting material dialkyl carbonate (e.g., DMC).

[0004] Phosgene-free industrial processes for producing the dialkyl carbonate starting material include oxidative carbonylation of an alkanol, alkyl nitrate carbonylation, direct synthesis from CO2, and epoxide carbonylation of an alcohol. In the epoxide carbonylation process, an alkylene oxide (e.g., ethylene oxide) is reacted with carbon dioxide in the presence of a catalyst to produce an alkylene carbonate (e.g., ethylene carbonate or propylene carbonate), which is then transesterified with an alkanol (e.g., methanol or ethanol) to produce the dialkyl carbonate (e.g., dimethyl carbonate) and an alkylene glycol (e.g., ethylene glycol), which itself can be a valuable by-product. [0005] Despite intensive work to develop and improve these phosgene-free industrial processes, there remains a continued need for methods and apparatuses for the production of diaryl carbonates that have reduced energy consumption while still producing high quality diaryl carbonates, particularly DPC. It would be a further advantage if the methods and apparatuses could be adopted with lower investment costs.

BRIEF DESCRIPTION

[0006] Disclosed herein is an integrated method and apparatus for the production of aryl carbonates.

[0007] In an embodiment, a method for producing an alkyl aryl carbonate, comprises reacting an alkylene carbonate and an alkanol in the presence of a first transesterification catalyst in a dialkyl carbonate reactor to produce a dialkyl carbonate azeotrope stream comprising a dialkyl carbonate and an unreacted alkanol, and an alkylene glycol product stream comprising an alkylene glycol and an unreacted alkanol; purifying the dialkyl carbonate azeotrope stream in a dialkyl carbonate purification section comprising a distillation column and a pervaporation unit to provide a first purified dialkyl carbonate stream and a first purified alkanol stream; reacting the first purified dialkyl carbonate stream and an aromatic alcohol in the presence of a second transesterification catalyst in an alkyl aryl carbonate reactor to produce an alkanol product stream comprising an alkanol product and an unreacted dialkyl carbonate, and an alkyl aryl carbonate product stream comprising the alkyl aryl carbonate and an unreacted aromatic alcohol; and purifying the alkanol product stream in the dialkyl carbonate purification section.

[0008] In another embodiment, a method for producing an alkyl aryl carbonate, comprises: reacting a carbon monoxide, an oxygen, and an alkanol in the presence of a catalyst in a reactor to produce a raw dialkyl carbonate stream comprising a dialkyl carbonate and a water, and an dialkyl carbonate azeotrope stream comprising the dialkyl carbonate and an unreacted alkanol; recovering from the raw dialkyl carbonate stream a water stream comprising water and a second purified dialkyl carbonate stream comprising the dialkyl carbonate in a recovery section; purifying the dialkyl carbonate azeotrope stream in a dialkyl carbonate purification section comprising a distillation column and a pervaporation unit to provide a first purified dialkyl carbonate stream and a first purified alkanol stream; reacting the first purified dialkyl carbonate stream, the second purified dialkyl carbonate stream, or a combination comprising at least one of the foregoing, and an aromatic alcohol in the presence of a transesterification catalyst in an alkyl aryl carbonate reactor to produce an alkanol product stream comprising an alkanol product and an unreacted dialkyl carbonate, and an alkyl aryl carbonate product stream comprising the alkyl aryl carbonate and an unreacted aromatic alcohol; and purifying the alkanol product stream in the dialkyl carbonate purification section.

[0009] In another embodiment, an apparatus for production of an alkyl aryl carbonate comprises: a dialkyl carbonate reactor, an dialkyl carbonate purification section, an alkyl aryl carbonate reactive distillation column. The dialkyl carbonate reactor comprises a reactant inlet, and a dialkyl carbonate azeotrope outlet in fluid communication with a dialkyl carbonate azeotrope inlet of a dialkyl carbonate purification section. The dialkyl carbonate purification section comprises a distillation column in fluid communication with a pervaporation unit, the dialkyl carbonate azeotrope inlet, a first purified dialkyl carbonate outlet, and a first purified alkanol outlet. The alkyl aryl carbonate reactive distillation column comprises an aromatic alcohol inlet, a first purified dialkyl carbonate inlet in fluid communication with the first purified dialkyl carbonate outlet of the dialkyl carbonate purification section, an alkanol product outlet in fluid communication with an inlet of the dialkyl carbonate purification section, and an alkyl aryl carbonate outlet.

[0010] The above described and other features are exemplified by the following figures and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The following is a brief description of the drawings wherein like elements are numbered alike and which are presented for the purposes of illustrating the exemplary embodiments disclosed herein and not for the purposes of limiting the same.

[0012] FIG. 1 is an illustration of an embodiment of an epoxide carbonylation and transesterification process;

[0013] FIG. 2 is an illustration of an embodiment of an alkanol carbonylation process;

[0014] FIG. 3 is an illustration of an embodiment of a diaryl production process utilizing an alkylene carbonate transesterification process for the production of dialkyl carbonate; and

[0015] FIG. 4 is an illustration of an embodiment of a diaryl production process utilizing an alkanol carbonylation process for the production of dialkyl carbonate. DETAILED DESCRIPTION

[0016] In the process of producing aryl alkyl carbonate, high pressure distillation methods are generally relied on to separate the unreacted alkanol prior to diaryl production, as described, for example, in US Patent 8,049,028. For example, high pressure distillation methods are generally used to separate an alkanol (such as methanol and ethanol) and dimethyl carbonate as they form an azeotrope at 63°C and 1 bar(abs) or 100 kiloPascal kPa(abs), where the abbreviation "abs" refers to absolute pressure or pressure zero-referenced to a perfect vacuum. However, high pressure distillation can be an energy intensive, inefficient process, e.g., reliant on high quality steam, which can result in high operational costs. As disclosed herein, processes and apparatuses for the production of alkyl aryl carbonates were discovered that can improve the overall efficiency of the process, including reducing energy consumption and initial capital costs that includes a separation process of unreacted alkanol from a dialkyl carbonate via purification section comprising a distillation column and a pervaporation unit. Furthermore, the present process can provide for integration of the dialkyl carbonate and alkyl aryl carbonate production processes by merging the recovery of unreacted alkanol from the dialkyl carbonate process and the alkyl aryl carbonate process into a single recovery system. In other words, streams from a dialkyl carbonate production reactor and from an alkyl aryl carbonate production reactor can be sent to a single dialkyl carbonate purification section. Outputs obtained from this unit can be a dialkyl carbonate -rich stream that can be directly used in the production of the alkyl aryl carbonate and a purified alkanol. The purity of the alkanol can be adjusted by adjusting the operating conditions of the dialkyl carbonate purification section. The number of separation units needed to separate the products and recycle the unreacted reactants can therefore be reduced. When used in the production of aryl carbonates, the overall process can be more efficient, and can have reduced cost (e.g., capital cost, operating cost, maintenance cost, and the like).

[0017] An epoxide carbonylation and transesterification process 10, to produce a purified dialkyl carbonate stream 46, is schematically shown in FIG. 1. In the process 10, an alkylene oxide stream 12 can be reacted with carbon dioxide stream 14 in a reactor section 20 in the presence of a catalyst to produce an alkylene carbonate stream 22. The alkylene carbonate stream 22 can then be transesterified in a second reactor section 30 in the presence of a transesterification catalyst with an alkanol stream 24 to produce a raw dialkyl carbonate stream 32 containing a dialkyl carbonate, an alkylene glycol and unreacted alkanol. Because the yield of the transesterification reaction can be limited by the equilibrium conversion, a molar excess of the alkanol stream 24 can be used to overcome this thermodynamic limitation. Unreacted alkanol, present in the raw dialkyl carbonate stream 32, can be recovered as a unreacted alkanol stream 42 from a separation section 40 and can be recycled back to the dialkyl carbonate production process. Optionally, the alkylene glycol present in the raw dialkyl carbonate stream 32 can be recovered in an alkylene glycol stream 44 to provide a purified dialkyl carbonate stream 46 to a diaryl carbonate production process.

[0018] An alkanol carbonylation process 50, to produce a purified dialkyl carbonate stream 76, is schematically shown in FIG 2. In an alkanol carbonylation process 50 a carbon monoxide stream 52 can be reacted with an alkanol stream 54 and a stream containing oxygen 56 in the presence of a catalyst, e.g., copper chloride, in a reactor section 60 to produce a raw dialkyl carbonate stream 62 containing dialkyl carbonate, unreacted alkanol, and water. Following the alkanol carbonylation process 50, unreacted alkanol present in the raw dialkyl carbonate stream 62, can be recovered in a separation section 70 as an unreacted alkanol stream 72 and can be recycled back to the dialkyl carbonate production process. Optionally, water present in the raw dialkyl carbonate stream 62 can be recovered in a water stream 74 from the separation section 70 to provide a purified dialkyl carbonate stream 76 to a diaryl carbonate production process.

[0019] The dialkyl carbonate produced by either of these methods can then be converted to a diaryl carbonate in a diaryl carbonate production process. In the diaryl carbonate production process the dialkyl carbonate can be reacted with an aromatic alcohol in the presence of a transesterification catalyst to produce an alkyl aryl carbonate and an alkanol. Disproportionation of the alkyl aryl carbonate can produce the diaryl carbonate. In the transesterification of the dialkyl carbonate an azeotropic mixture of alkanol and dialkyl carbonate also arises.

[0020] A more complete understanding of the components, processes, and apparatuses disclosed herein can be obtained by reference to FIG. 3-4, which are schematic representations based on convenience and the ease of demonstrating the present disclosure, and are, therefore, is not intended to indicate relative size and dimensions of the devices or components thereof and/or to define or limit the scope of the exemplary embodiments.

[0021] Although specific terms are used in the following description for the sake of clarity, these terms are intended to refer only to the particular structure of the embodiments selected for illustration in the drawings, and are not intended to define or limit the scope of the disclosure. Various feed, product, and recycle streams are shown in the attached figures. It is further noted that it will be appreciated by persons skilled in the art that the positioning of the various streams/lines as described herein as being, e.g., in the "top", "middle", "bottom", or "side" of a particular column is relative because the actual position at which material is to be introduced or recovered is dependent on the conditions being maintained in the particular column. For example, a stream entering the "bottom" of a column can actually enter several stages above the sump including the reboiler of the column, and a line/stream exiting the "top" of the column can actually exit several stages below the top stage including the condenser of the column. Thus, such terms herein are included for ease of reference to describe a general orientation regarding various columns and lines/streams and such terms are not meant to be limiting to one exact location. Also, although for illustrative purposes, the figures and their description can depict singular vessels, such as reaction vessels or mixing vessels, it is understood that multiple vessels in series or parallel can be used where suitable. The direction of flow for each line is indicated in each figure. Various valves, heaters, pumps, heat exchangers, fittings and the like can optionally be included with the feed/recycle lines shown in adapting the design to a particular installation.

[0022] The reactors and units of the figures can be interconnected by a series of feed/recycle lines, which serve to transport streams comprising reactants and/or products. It is appreciated that the conditions in the reactors and units shown of the Figures, such as temperature, pressure and molar ratio of reactant feeds can be selected and optimized to reduce or otherwise control the concentration of the products without undue experimentation. The apparatus depicted in the figures can be used in accordance with a method to produce diaryl carbonate, for example, DPC, according to embodiments disclosed herein. Although the description of the processes is directed to a continuous process, any one or more of the steps can be conducted batch-wise.

[0023] FIG. 3 schematically depicts a system 200 utilizing an alkylene carbonate transesterification process for the production of dialkyl carbonate. The system 200 comprises three reactors 210, 240, and 280, a dialkyl carbonate purification section 260 for purification of two separate azeotropic streams, and an optional alkylene glycol purification unit 230.

[0024] FIG. 4 schematically depicts a system 300 utilizing an alkanol carbonylation process for the production of dialkyl carbonate. The system 300 comprises two reactors 340 and 380, a dialkyl carbonate purification section 360 for purification of two separate azeotropic streams, and an optional water recovery section 330. [0025] Advantageously, the dialkyl carbonate purification section (260,360) can recover alkanol from a dialkyl carbonate production facility and an alkyl aryl carbonate or diaryl carbonate production facility. It is noted that the reactors 210, 240, 280, 340, and 380 can each comprise one or more reactive distillation columns, each comprising a rectification section and a reaction section in which a chemical reaction can occur. In general, the reaction section of a column can be furnished with packings or fixed internals ("internals" referring herein to the part in the distillation column where gas and liquid are actually brought into contact with one another) to provide at least one reactive distillation stage. For example, the reaction section of a column can provide greater than or equal to 5, such as 5 to 60, reactive stages, specifically, greater than or equal to 10, such as 10 to 40, distillation stages. Known dumped packings and/or arranged packings can be employed. Specifically, packings having a large surface area, good wetting and residence time of the liquid phase, such as, for example, Novolax rings, CY packings, can be used. Fixed internals, such as tray columns also can be employed, and specific examples include sieve trays, valve trays, and bubble -cap trays.

[0026] The alkylene glycol purification unit 230 can include a high-pressure distillation column. The water recovery section 330 can include one or more distillation columns. Such columns can carry out a separation of materials based upon boiling point, without driving a concurrent chemical reaction.

[0027] The dialkyl carbonate purification section (260,360) can include a distillation column (270,370) and a pervaporation unit (290,390). The distillation column (270,370) can nominally operate at ambient pressure and can provide a feed stream to the pervaporation unit (290,390) which can separate species of the feed mixture based on their mass transport differences through a mass transport selective barrier device (e.g., a membrane).

[0028] In the operation of the system 200 an alkylene carbonate stream 202 comprises an alkylene carbonate (e.g., ethylene carbonate, propylene carbonate, and the like) and an alkanol stream 204 comprises an alkanol (e.g., methanol, ethanol, and the like) which can be fresh, recycled, or a combination thereof. The alkylene carbonate stream 202 and the alkanol stream 204 can be fed continuously to a dialkyl carbonate reactor 210, which can be a reactive distillation column. Transesterification can be carried out in the presence of a catalyst to produce an alkylene glycol (e.g., ethylene glycol), and a dialkyl carbonate (e.g., dimethyl carbonate). When the catalyst is homogeneous, the catalyst can be fed with the alkylene carbonate or the alkanol, or can be fed at a position different from both. When the catalyst is heterogeneous, the catalyst can be packed in a desired amount at a desired position of the dialkyl carbonate reactor 210. In an embodiment, the catalyst is a heterogeneous catalyst immobilized on a catalyst bed.

[0029] A reaction mixture having a high boiling point temperature, alkylene glycol product stream 212 containing a diol, can be continuously withdrawn from a lower portion of the dialkyl carbonate reactor 210 in a liquid form, and a low boiling point reaction mixture, dialkyl carbonate azeotrope stream 206 containing the dialkyl carbonate product and unreacted alkanol can be continuously withdrawn from an upper portion of the dialkyl carbonate reactor 210 in a gaseous form.

[0030] The dialkyl carbonate azeotrope stream 206 can be fed to the dialkyl carbonate purification section 260 to an inlet of the distillation column 270, an inlet of the

pervaporation unit 290, or a combination comprising at least one of the foregoing. The dialkyl carbonate purification section 260 can include a distillation column 270 and pervaporation unit 290 as described in more detail below. The dialkyl carbonate purification section 260 can separate the azeotropic streams (alkanol product stream 224 and dialkyl carbonate azeotrope stream 206) into a first purified alkanol stream 291 containing the alkanol as a main component and a first purified dialkyl carbonate stream 234 containing the dialkyl carbonate as a main component. The first purified alkanol stream 291 can optionally be recycled to the dialkyl carbonate reactor 210. The system 200 can optionally include a second purified dialkyl carbonate stream 242 which can provide a source of additional dialkyl carbonate to the alkyl aryl carbonate reactor 240. The second purified dialkyl carbonate stream 242 can be combined with the first purified dialkyl carbonate stream 234 or can be fed separately to the alkyl aryl carbonate reactor 240.

[0031] In the operation of the system 300 the dialkyl carbonate reactor section 310 can be used in an alkanol carbonylation process to provide a dialkyl carbonate azeotrope stream 306 and a raw dialkyl carbonate stream 304. The dialkyl carbonate reactor section can comprise one or more reactors and one or more separation units, for example, the dialkyl carbonate reactor section 310 can comprise a dialkyl carbonate reactor 312 and two separation columns 314 and 315. One or more streams can enter the dialkyl carbonate reactor, where Fig. 4 illustrates stream 302 entering the dialkyl carbonate reactor 312.

Reactant stream 302 can comprise carbon monoxide, an alkanol, and oxygen. Likewise, the carbon monoxide, the alkanol, and the oxygen can enter the dialkyl carbonate reactor 312 as separate streams. The dialkyl carbonate azeotrope stream 306 can be fed to the dialkyl carbonate purification section 360 to an inlet of the distillation column 370, an inlet of the pervaporation unit 390, or a combination comprising at least one of the foregoing. The dialkyl carbonate purification section 360 can separate the azeotropic streams (alkanol product stream 324 and dialkyl carbonate azeotrope stream 306) into a first purified alkanol stream 391 containing the alkanol as a main component and a first purified dialkyl carbonate stream 334 containing the dialkyl carbonate as a main component. The first purified alkanol stream 391 can optionally be recycled to a dialkyl carbonate reactor section 310.

[0032] The reaction to produce an alkyl aryl carbonate (e.g., methyl phenyl carbonate) can be carried out in alkyl aryl carbonate reactor (240,340), for example, which can be an alkyl aryl reactive distillation column. An aromatic alcohol feed stream (222,322) can comprise a transesterification catalyst and an aromatic alcohol (e.g., phenol) that can be fresh, recycled, or a combination thereof. For example, an aromatic alcohol product stream (236,336) containing an aromatic alcohol can be recycled from a diaryl carbonate reactor (280,380) in addition to or in place of a fresh aromatic alcohol feed. Another starting material for the production of alkyl aryl carbonate, dialkyl carbonate, can be provided in the first purified dialkyl carbonate stream (234,334) which can be recycled from the dialkyl carbonate purification section (260,360).

[0033] The first purified dialkyl carbonate stream (234,334) can be fed to, for example, the bottom of alkyl aryl carbonate reactor (240,340) including being fed directly to a reboiler. The first purified dialkyl carbonate stream (234,334) can be a liquid, vapor or two-phase (e.g., liquid and vapor). The aromatic alcohol feed stream (222,322) can be fed as a liquid into, e.g., the middle section of the alkyl aryl carbonate reactor (240,340), or at a location at or near the top of the reactive distillation section. The feed rate of the aromatic alcohol feed stream (222,322) and the first purified dialkyl carbonate stream (234,334) can be such that the molar ratio of dialkyl carbonate to aromatic alcohol introduced into the alkyl aryl carbonate reactor (240,340) can be 0.1 and 10, specifically, 0.5 and 5, and more specifically, 0.5 and 3. Dialkyl carbonate can be provided in excess through the first purified dialkyl carbonate stream (234,334) because the dialkyl carbonate can serve as both a reactant and as a stripping agent, which facilitates removal of alkanol produced in the

transesterification reaction. This removal can increase the rate of production of the alkyl aryl carbonate in the alkyl aryl carbonate reactor (240,340).

[0034] The transesterification reaction can be carried out in the alkyl aryl carbonate reactor (240,340) at, for example, a temperature greater than or equal to 100 degrees Celsius (°C), for example, greater than or equal to 130°C, or, greater than or equal to 140°C, or, 100°C to 300°C, or, 110°C to 270°C, or 120°C to 250°C. The operating pressure at the top of alkyl aryl carbonate reactor 240 can be greater than or equal to 0.5 bar(g) (50 kPa(g)), for example, greater than or equal to 2 bar(g) (200 kPa(g)), or, greater than or equal to 3 bar(g) (300 kPa(g)), where the abbreviation "g" refers to gauge pressure or pressure zero-referenced to ambient air pressure at sea level. Reaction products and unreacted starting materials can be removed from the alkyl aryl carbonate reactor (240,340) in a continuous manner through an alkanol product stream (224, 324) and an alkyl aryl carbonate product stream (226,326). The alkanol product stream (224,324) can be drawn from the top of alkyl aryl carbonate reactor (240,340). The alkanol product stream (224,324) can comprise unreacted dialkyl carbonate and the alkanol produced in the transesterification reaction, as well as other reactants and by-products, such as the aromatic alcohol.

[0035] The alkyl aryl carbonate reactor (240,340) can have a rectification section and a reaction section. The rectification section is an upper section of the alkyl aryl carbonate reactor (240,340) above the feeding point of at least one of the reactants, and can comprise, for example, packing or trays. A chemical reaction is generally thought not to occur in the rectification section. The presence of a rectification section can affect the amounts the aromatic alcohol in the alkanol product stream (224,324). Alternatively, the alkanol product stream (224,324) can optionally pass first to an optional rectification column (not shown) for processing and recovery.

[0036] The rectification section and the optional rectification column also can be furnished with packings or fixed internals to provide, for example, greater than or equal to 3, specifically, greater than or equal to 5, more specifically, 5 to 50 distillation stages. For example, known dumped packings and/or arranged packings can be employed.

[0037] The temperature profile of the optional rectification column (not shown) can be greater than or equal to 10°C, for example, greater than or equal to 50°C, or, 10°C to 200°C, or, 50°C to 110°C. The operating pressure in the optional rectification column can be greater than or equal to 0.1 bar(g) (10 kPa(g)), for example, greater than or equal to 0.5 bar(g) (50 kPa(g)), or 0.1 bar(g) to 10 bar(g) (10 kPa(g) to 1000 kPa(g)), or 0.5 bar(g) to 3 bar(g) (50 kPa(g) to 300 kPa(g)).

[0038] The alkanol product stream (224,324) can comprise an azeotropic mixture of dialkyl carbonate and the alkanol produced in the transesterification process, as well as aromatic alcohol in trace or greater amounts. The alkanol product stream (224,324) can be fed to the dialkyl carbonate purification section (260,360) where the alkanol can be recovered in the first purified alkanol stream (291,391) and the dialkyl carbonate can be recovered in the first purified dialkyl carbonate stream (234,334).

[0039] The alkyl aryl carbonate product stream (226,326), which can be drawn from, e.g., the bottom of the alkyl aryl carbonate reactor (240,340), such as from a reboiler when the alkyl aryl carbonate reactor (240,340) comprises an alkyl aryl reactive distillation column, can comprise the alkyl aryl carbonate produced in the alkyl aryl carbonate reactor (240,340) in combination with one or more of unreacted starting materials, alkyl aryl ether, and catalyst. The alkyl aryl carbonate product stream (226,326) can be suitable for use in the production of diaryl carbonates. However, it is to be understood that alkyl aryl carbonates produced as described herein can be used for other purposes, for example, as a solvent or in the manufacture of other compounds or polymers.

[0040] In the manufacture of a diaryl carbonate (e.g., DPC) the alkyl aryl carbonate product stream (226,326) can be fed to an inlet of the diaryl carbonate reactor (280,380) which can be a reactive distillation column, to produce a diaryl carbonate (e.g., diphenyl carbonate) by disproportionation of the alkyl aryl carbonate. Diaryl carbonate reactor (280,380) can be operated under conditions effective to further drive the reaction toward a desired diaryl carbonate product, while separating other materials from the product, which can be recycled. A diaryl carbonate product stream (238,338), comprising diaryl carbonate produced together with residual catalyst, unreacted alkyl aryl carbonate, and high-boiling point temperature by-products, can be removed from the bottom of the diaryl carbonate reactor (280,380). The diaryl carbonate product stream (238,338) can optionally be further purified if additional purification is desired. Moreover, because the reactions in the process are carried out using starting materials and catalyst not containing a halogen, the dialkyl carbonate produced in the process can be manufactured to not contain halogen. For example, the diaryl carbonate product stream (238,338) can have a concentration of greater than or equal to 97 wt , or greater than or equal to 99 wt , or greater than or equal to 99.9 wt , with a halogen content of 0.5 parts per million by weight (ppm) or less, or 0.1 ppm or less, or 1 part per billion by weight (ppb) or less.

[0041] An aromatic alcohol product stream (236,336), comprising unreacted aromatic alcohol starting material, dialkyl carbonate, and by-product alkyl aryl ether, can be removed from the top of the diaryl carbonate reactor (280,380). In an embodiment, the aromatic alcohol product stream (236,336) can be recycled to the alkyl aryl carbonate reactor

(240,340) separately, or combined with the aromatic alcohol feed stream (222,322).

[0042] The diaryl carbonate reactor (280,380) can be operated at a temperature greater than or equal to 90°C, for example, greater than or equal to 100°C, or, greater than or equal to 110°C, or 100°C to 140°C, or 120°C to 250°C, or 110°C to 240°C. The operating pressure of the diaryl carbonate reactor (280,380) can be greater than or equal to 10 millibar(g) (mbar(g)) (1 kPa(g)), for example, greater than or equal to 50 mbar(g) (5 kPa(g)), or, greater than or equal to 100 mbar(g) (10 kPa(g)), or 50 mbar(g) to 3 bar(g) (5 kPa(g) to 300 kPa(g)), or 50 mbar(g) to 1 bar(g) (5 kPa(g) to 100 kPa(g)), or 200 mbar(g) to 900 mbar(g) (20 kPa(g) to 90 kPa(g)).

[0043] As described above in FIG. 3, both of the dialkyl carbonate azeotrope stream 206 from the dialkyl carbonate reactor 210 and the alkanol product stream 224 from the alkyl aryl carbonate reactor 240 can be directed to the same purification process, in particular dialkyl carbonate purification section 260, that separates the dialkyl carbonate and the alkanol into the first purified alkanol stream 291 and the first purified dialkyl carbonate stream 234. Optionally, in system 200, the alkylene glycol product stream 212 can be fed to an alkylene glycol purification unit 230, which can be a high pressure distillation column, where unreacted alkanol can be separated from a purified alkylene glycol stream 212 and recycled in a second purified alkanol stream 208, for example, to the dialkyl carbonate reactor 210.

[0044] As described above in FIG. 2, because water is produced in the alkanol carbonylation process, the raw dialkyl carbonate stream 304 can include the dialkyl carbonate, unreacted alkanol, and water. Fig. 4 illustrates that water can optionally be recovered in a water stream 316 by passing the raw dialkyl carbonate stream 304 through an optional water recovery section 330. The water recovery section 330 can include separation devices, e.g., distillation column 320 and distillation column 350, and can provide a second purified dialkyl carbonate stream 342 to an alkyl aryl production reactor 340 and the water stream 316.

[0045] In addition to optionally recovering water from the raw dialkyl carbonate azeotrope stream 304, the water recovery section 330 can optionally receive a portion, or all, of the first purified dialkyl carbonate stream 334 from a dialkyl purification section 360 (shown in FIG. 4 by a dotted line) and can remove water from this additional stream. In this way, the water recovery section 330 can be used to remove water from one or more streams containing dialkyl carbonate and water and can feed the alkyl aryl production column 340 with the second purified dialkyl carbonate stream 342.

[0046] The alkanol carbonylation process can result in a dialkyl carbonate azeotrope stream 306 which can include the dialkyl carbonate and the alkanol. This stream can be subjected to a separation process to recover the alkanol and purify the dialkyl carbonate. The dialkyl carbonate azeotrope stream 306 can be sent to a dialkyl carbonate purification section 360 where it can be separated into the first purified alkanol stream 391 and the first purified dialkyl carbonate stream 334. The first purified dialkyl carbonate stream 334 can be fed directly to the alkyl aryl carbonate reactor 340, recycled the water recovery section 330, combined with the raw dialkyl carbonate stream 304, or a combination including at least one of the foregoing. When recycled to the water recovery section 330, as a separate stream or as a combined stream with the raw dialkyl carbonate stream 304, water that may be present in the stream can be removed prior to feeding the dialkyl carbonate to the alkyl aryl carbonate reactor 340, which can improve the alkyl aryl carbonate conversion.

[0047] In an embodiment, dialkyl carbonate purification section (260,360) can include a distillation column (270,370) and a pervaporation unit (290,390). The distillation column (270,370) can include a continuous multi-stage distillation column comprising a stripping section and an enrichment section. The continuous multi-stage distillation column can comprise trays or packings as the internal (i.e., the part in the distillation column where gas and liquid are actually brought into contact with one another) in each of the stripping section and the enrichment sections. Examples of the trays include a bubble-cap tray, a sieve tray, a ripple tray, a ballast tray, a valve tray, a counterflow tray, a Unifrax tray, a Superfrac tray, a Maxfrac tray, a dual flow tray, a grid plate tray, a turbogrid plate tray, a Kittel tray, or the like. Examples of the packings include random packings such as a Raschig ring, a Lessing ring, a Pall ring, a Berl saddle, an Intalox saddle, a Dixon packing, a McMahon packing or Heli-Pak, or structured packings such as Mellapak, Gempak, Techno-pack, Flexipac, a Sulzer packing, a Goodroll packing or Glitschgrid. A multi-stage distillation column having both a tray portion and a portion packed with packings can also be used. The internal in both the stripping section and the enrichment section of the continuous multi-stage distillation column can be a tray. Sieve trays each having a sieve portion and a downcomer portion can be used, for example, a sieve tray having 150 to 1200 holes per meter squared (holes/m ) in the sieve portion, or 200 to 1100 holes/m 2 , or 250 to 1000 holes/m 2 in the sieve portion, where the cross-sectional area per hole of each sieve tray is 0.5 to 5 centimeters squared (cm ), or 0.7 to 4 cm , or 0.9 to 3 cm . The distillation column 260 can operate at ambient pressure, or near ambient pressure, such as operating at 0.8 bar(abs) to 1.2 bar(abs).

[0048] The pervaporation unit (290,390) can include a membrane or similar mass transport selective barrier device. The selective barrier can be arranged in any shape, e.g., flat, conical, cylindrical, tubular, spiraled, and the like. The selective barrier can include undulations, corrugations, pleats, other features to increase the mass transfer surface area of the selective barrier, or a combination including at least one of the foregoing. The selective barrier can be arranged as an inline filter forming a retentate cavity and a permeate cavity which are separated by the selective barrier. In an embodiment, the selective barrier can be arranged in spiral wound sheets which can further include spacer layers for spacing the selective barrier apart and allowing permeate and/or retentate flow between adjacent layers of the wound selective barrier. In an embodiment, the selective barrier can be arranged as a tube wall where the tube can have a porous core allowing for mass transport of permeate through the tube wall (e.g. permeate can pass into the porous core, while retentate remains outside the core, or vice versa).

[0049] The selective barrier can be arranged with any flow configuration, for example, cross-flow, dead-end flow, counter-flow, co-flow, or a combination comprising at least one of the foregoing. For example, in a cross-flow configuration the feed flow can be tangential to the surface of the selective barrier (e.g., spiral wound membrane forming a cylinder and feed flow axially through the cylinder across the surface of the membrane). In another flow configuration the direction of the feed flow can be normal to the surface of the selective barrier. The selective barrier can be adjacent to a spacer layer disposed on a side of the selective barrier which can increase the cross-sectional flow area of a flow passage (e.g., permeate flow passage, retentate flow passage, or both) which can allow for continuous flow through the purification unit. The spacer layer can include a porous substrate which can provide mechanical support to the selective barrier and open volume to provide a flow passage through the spacer layer. The selective barrier can include a selective layer having a thickness (as measured along its shortest dimension) of less than 0.5 micrometers (μπι), for example, 0.01 μπι to 0.4 μπι, or 0.05 μπι to 0.15 μπι.

[0050] The pervaporation unit can separate constituents of the feed stream by allowing them to permeate through the selective barrier and evaporate. Advantageously, a pervaporation unit can separate the feed stream based on the difference in mass transport rates of the individual constituents through the selective barrier rather than relying on differences in their volatility (e.g., distillation). The transport rates of the individual constituents of the feed stream can be a function of difference in the chemical potential of a species in the liquid feed and vapor permeate on either side of the selective barrier.

[0051] The selective barrier can include any material capable of separating an azeotropic alkanol and dialkyl carbonate mixture. For example, the selective barrier can include ceramic material, polymeric material, hydrophobic material, hydrophilic material, nano-porous materials (e.g., having pore size of less than or equal to 100 nanometers), or a combination including at least one of the foregoing. The selective barrier can comprise a polyacrylonitrile support layer, where the polyacrylonitrile can have a number average molecular weight of 5,000 to 100,000 Daltons, specifically, 20,000 to 60,000 Daltons. The support layer can have a thickness of 40 to 80 micrometers. The support layer can have a pore size of less than 500 Angstroms.

[0052] The selective barrier can comprise a selective layer comprising one or both of poly( vinyl alcohol) (PVA) and poly( acrylic acid) (PAA) (such as a poly(meth acrylic acid)). The PVA can have a number average molecular (Mn) weight of 20,000 to 200,000 Daltons, specifically, 96,000 to 115,000 Daltons based on polystyrene or polycarbonate standards. The PAA can have an Mn of 90,000 to 300,000, specifically, 90,000-250,000 Daltons based on polystyrene or polycarbonate standards. The weight ratio of PVA to PAA can be 0.1-10:1. The selective layer can be cross-linked with an aliphatic dialdehyde, a diacid, a dihalogen compound, epichlorohydrin, an olefinic aldehydes, boric acid, a sulfonamideoaldehye, or a combination comprising one or more of the foregoing. The selective barrier can comprise an organophilic (methanol-philic) membrane such as PERVAP™ 1137 membranes

(commercially available from Sulzer Chemtech Ltd., Switzerland). The separating layer can have a thickness of 1 to 80 micrometers.

[0053] The pervaporation unit (290,390) can be constructed out of any suitable material, including ceramic, metal and the like. The pervaporation unit (290,390) can include internal features, such as a retention ring, clip, holder, tube sheet, porous spacer, baffles and the like. Internal features can support the selective barrier. Internal features can control the flow direction through the pervaporation unit (290,390). Use of the pervaporation unit (290,390) can reduce the need for thermal energy in separating an azeotropic alkanol and dialkyl carbonate mixture, and can accordingly reduce the capital and/or operating cost of the alkyl aryl carbonate production facility. For example, a pervaporation unit (290,390) can separate the azeotropic alkanol and dialkyl carbonate mixture into an alkanol rich stream and a dialkyl carbonate rich stream without the use of steam.

[0054] Effective conditions for operation of the pervaporation unit (290,390) can vary depending on the form of the internal features in the unit, the form of the membrane, the type of selective barrier, composition and flow rate of the pervaporation feed stream (228,328), the purity of the dialkyl carbonate and/or alkanol to be obtained through the separation, and so on. For example, the temperature of the pervaporation unit (290,390) can be 150°C to 250°C, or 170°C to 230°C, or 180°C to 220°C. The pressure of the pervaporation unit (290,390) can vary depending on the composition in the unit and the temperature of the pervaporation unit 290. The vapor phase section (e.g., permeate cavity or permeate exit) of the pervaporation unit (290,390) can be operated under vacuum to increase the mass transport rate of species through the selective barrier, for example, the permeate cavity, the permeate exit, or a combination including at least one of the foregoing can be maintained at 0.01 bar(abs) to 1 bar(abs) (1 kPa(abs) to 100 kPa(abs)), or, 0.01 bar(abs) to 0.25 bar(abs) (1 kPa(abs) to 25 kPa(abs)). The liquid phase portion of the pervaporation unit (290,390) can contain dialkyl carbonate which can be selectively retained in the retentate cavity of the pervaporation unit (290,390) and can be returned to the distillation column (270,370) through the retentate outlet stream (232,332).

[0055] When feeding the dialkyl carbonate azeotrope stream 206 and the alkanol product stream 224 (Fig. 3) or dialkyl carbonate azeotrope stream 306 and alkanol product stream 324 (Fig. 4) to dialkyl carbonate purification section (260,360), the streams can be fed separately, or combined before entering the unit. Any of the feed streams can be fed in a gaseous form, in a liquid form, or in two-phase form. In an embodiment, the feed(s) are heated or cooled to a temperature close to the liquid temperature in the vicinity of the feeding inlet of the dialkyl carbonate purification section (260,360), for example, within 1 to 10°C. The position at which the feed(s) are introduced to the distillation column (270,370) can be between a stripping section and an enrichment section. The alkyl aryl carbonate reactor (240,340) can be equipped with a reboiler for heating the distillate, and a refluxing apparatus.

[0056] The concentration of the alkanol in the first purified alkanol stream (291,391), exiting dialkyl carbonate purification section (260,360), can greater than or equal to 80 wt , or greater than or equal to 85 wt , greater than or equal to 90 wt . The concentration of the dialkyl carbonate in the first purified dialkyl carbonate stream (234,334), exiting the dialkyl carbonate purification section (260,360), can be greater than or equal to 9 7wt , or greater than or equal to 99 wt , or greater than or equal to 99.9 wt%. The content of unreacted alkanol in the first purified dialkyl carbonate stream (234,334) can be less than or equal to 3 wt , or less than or equal to 1 wt , or less than or equal to 0.1 wt%.

[0057] The above-described methods and processes can be used for the production of variety of dialkyl carbonates and diaryl carbonates from an alkylene carbonate, an alkanol, and an aromatic alcohol starting materials.

[0058] Examples of the alkylene carbonate include ethylene carbonate, propylene carbonate, l,3-dioxacyclohexa-2-one, l,3-dioxacyclohepta-2-one, and combination comprising at least one of the foregoing. Ethylene carbonate or propylene carbonate can be particularly advantageous due to ease of procurement, and ethylene carbonate is preferred.

[0059] The alkanols that can be used include all isomers of linear and branched d_i2 aliphatic alcohols and C ₄ _g cycloaliphatic alcohols, each of which can be unsubstituted or substituted with 1 to 3 halogen, Cj_6 alkoxy, cyano, Q_6 alkoxycarbonyl, C _6- i2

aryloxycarbonyl, Cj_6 acyloxy, or nitro groups, provided that the valence of any substituted carbon is not exceeded. Examples of alkanols include methanol, ethanol, 1 -propanol, 2- propanol, allyl alcohol, 1-butanol, 2-butanol, 3-buten-l-ol, amyl alcohol, 1-hexanol, 2- hexanol, 3-hexanol, 1-heptanol, 2-heptanol, 3-heptanol, and 4-heptanol, cyclopentanol, cyclohexanol, cycloheptanol, cyclooctanol, 3-methylcyclopentanol, 3-ethylcyclopentanol, 3- methylcyclohexanol, 2-ethylcyclohexanol (isomers), 2,3-dimethylcyclohexanol, 1,3- diethylcyclohexanol, 3-phenylcyclohexanol, benzyl alcohol, 2-phenethyl alcohol, and 3- phenylpropanol. In a specific embodiment, the alkanol is methanol, ethanol, 1 -propanol, 2- propanol, 1-butanol, 2-butanol, or 3-butanol. Ethanol or methanol can be used, but methanol is preferred.

[0060] A ratio between the amounts of the alkylene carbonate and the alkanol can be varied according to the type and amount of the transesterification catalyst and the reaction conditions. To increase the alkylene carbonate conversion, the alkanol can be used in an excess of 2 times the number of moles of the alkylene carbonate, for example, the molar ratio of the alkanol to the alkylene carbonate can be 2 to 20, specifically, 3 to 15, more specifically, 5 to 12.

[0061] The transesterification can be carried out in the presence of a homogeneous or heterogeneous catalyst. Examples of the catalyst include alkali metals and alkaline earth metals such as lithium, sodium, potassium, magnesium, calcium, and barium; basic compounds of alkali metals and alkaline earth metals such as hydrides, hydroxides, alkoxides, aryloxides, and amides; basic compounds of alkali metals and alkaline earth metals such as carbonates, bicarbonates, and organic acid salts; tertiary amines such as

triethylamine, tributylamine, trihexylamine, and benzyldiethylamine; nitrogen-containing heteroaromatic compounds such as N-alkylpyrroles, N-alkylindoles, oxazoles, N- alkylimidazoles, N-alkylpyrazoles, oxadiazoles, pyridines, quinolines, isoquinolines, acridines, phenanthrolines, pyrimidines, pyrazine, and triazines; cyclic amidines such as diazobicycloundecene (DBU) and diazobicyclononene (DBN); tin compounds such as tributylmethoxytin, dibutyldiethoxytin, dibutylphenoxytin, diphenylmethoxytin, dibutyltin acetate, tributyltin chloride, and tin 2-ethylhexanoate; zinc compounds such as

dimethoxyzinc, diethoxyzinc, ethylenedioxyzinc, and dibutoxyzinc; aluminum compounds such as aluminum trimethoxide, aluminum triisopropoxide, and aluminum tributoxide;

titanium compounds such as tetramethoxytitanium, tetraethoxytitanium, tetrabutoxytitanium, dichlorodimethoxy titanium, tetraisopropoxytitanium, titanium acetate, and titanium acetylacetonate; phosphorus compounds such as trimethylphosphine, triethylphosphine, tributylphosphine, triphenylphosphine, tributylmethylphosphonium halides,

trioctylbutylphosphonium halides, and triphenylmethylphosphonium halides; zirconium compounds such as zirconium halides, zirconium acetylacetonate, zirconium alkoxides, and zirconium acetate; and lead and lead-containing compounds, for example, lead oxides such as PbO, Pb0 ₂ , and Pb ₃ 0 ₄ , lead sulfides such as PbS, Pb2S ₃ , and PbS2, and lead hydroxides such as Pb(OH) ₂ , Pb ₃ 0 ₂ (OH) ₂ , Pb ₂ [Pb0 ₂ (OH) ₂ ], and Pb ₂ 0(OH) ₂ . Specifically, mentioned catalysts include titanium compounds such as titanium tetraphenoxide, titanium isopropylate, titanium tetrachloride, organotin compounds, and compounds of copper, lead, zinc, iron, and zirconium, and combinations comprising at least one of the foregoing. An amount of the catalyst used can be 0.005 to 20 wt , specifically, 0.01 to 10 wt based on the total weight of the alkylene carbonate and the alkanol.

[0062] Aromatic alcohols for transesterification of the alkyl aryl carbonate include C(,. i2 aromatic alcohols which can be unsubstituted or substituted with 1 to 3 halogen, Ci_6 alkoxy, cyano, Ci_6 alkoxycarbonyl, C -n aryloxycarbonyl, Ci_6 acyloxy, or nitro groups, provided that the valence of any substituted carbon is not exceeded. Examples include phenol o-, m- or p-cresol, o-, m- or p-chlorophenol, o-, m- or p-methoxyphenol, 2,6- dimethylphenol, 2,4-dimethylphenol, 3,4-dimethylphenol, 1-naphthol and 2-naphthol.

Phenol can be specifically, mentioned. The catalysts used in this transesterification include those described above in the process to prepare the dialkyl carbonate. Specifically, mentioned catalysts include titanium compounds such as titanium tetraphenoxide, titanium isopropylate, titanium tetrachloride, organotin compounds, and compounds of copper, lead, zinc, iron, and zirconium, and combinations comprising at least one of the foregoing.

[0063] In an embodiment, the alkylene carbonate is ethylene carbonate or propylene carbonate, the alkanol is methanol or ethanol, and the aromatic alcohol is phenol.

[0064] The diaryl carbonate produced can be used to manufacture a polycarbonate. In an embodiment, a dihydroxy compound can be used as a reactant with a diaryl carbonate such as diphenol carbonate as a carbonate source.

[0065] Generally, in the melt polymerization process, polycarbonates can be prepared by co-reacting, in a molten state, a dihydroxy reactant and a diaryl carbonate in the presence of a transesterification catalyst. The reaction can be carried out in typical polymerization equipment, such as a continuously stirred reactor (CSTR), plug flow reactor, wire wetting fall polymerizers, free fall polymerizers, wiped film polymerizers, BANBURY mixers, single or twin screw extruders, or a combination of the foregoing. Volatile monohydric phenol is removed from the molten reactants by distillation and the polymer is isolated as a molten residue. Melt polymerization can be conducted as a batch process or as a continuous process. In either case, the melt polymerization conditions used can comprise two or more distinct reaction stages, for example, a first reaction stage in which the starting dihydroxy aromatic compound and diaryl carbonate are converted into an oligomeric polycarbonate and a second reaction stage wherein the oligomeric polycarbonate formed in the first reaction stage is converted to high molecular weight polycarbonate. Such "staged" polymerization reaction conditions are especially suitable for use in continuous polymerization systems wherein the starting monomers are oligomerized in a first reaction vessel and the oligomeric

polycarbonate formed therein is continuously transferred to one or more downstream reactors in which the oligomeric polycarbonate is converted to high molecular weight polycarbonate. Typically, in the oligomerization stage the oligomeric polycarbonate produced has a number average molecular weight of 1,000 to 7,500 Daltons. In one or more subsequent

polymerization stages the number average molecular weight (Mn) of the polycarbonate is increased to 8,000 and 25,000 Daltons (using polycarbonate standard). Typically, solvents are not used in the process, and the reactants dihydroxy aromatic compound and the diaryl carbonate are in a molten state. The reaction temperature can be 100°C to 350°C, specifically, 180°C to 310°C. The pressure can be at atmospheric pressure, supra- atmospheric pressure, or a range of pressures from atmospheric pressure to 15 torr in the initial stages of the reaction, and at a reduced pressure at later stages, for example, 0.2 to 15 torr. The reaction time is generally 0.1 hours to 10 hours.

[0066] A transesterification catalyst(s) can be employed in the melt polymerization. Transesterification catalysts used in the melt transesterification polymerization production of polycarbonates can include one or both of a first catalyst and a second catalyst, wherein the first catalyst comprises a source of at least one of alkali ions and alkaline earth ions, and wherein the second catalyst comprising a quaternary ammonium compound, a quaternary phosphonium compound, or a combination comprising at least one of the foregoing. The second catalyst can have a reduced metal salt concentration. As used herein, the terms first catalyst and second catalyst are not used to denote an order of addition and are merely used in order to differentiate between the two catalysts.

[0067] The first catalyst comprises a source of one or both of alkali ions and alkaline earth ions. The sources of these ions include alkaline earth hydroxides such as magnesium hydroxide and calcium hydroxide. Sources of alkali metal ions can include the alkali metal hydroxides such as illustrated by lithium hydroxide, sodium hydroxide, potassium hydroxide, and combinations comprising at least one of the foregoing. Examples of alkaline earth metal hydroxides are calcium hydroxide, magnesium hydroxide, and combinations comprising at least one of the foregoing. Other possible sources of alkaline earth and alkali metal ions include salts of carboxylic acids, derivatives of ethylene diamine tetraacetic acid, salt(s) of a non-volatile inorganic acid. Alternatively, or in addition, the first transesterification catalyst can comprise mixed alkali metal salt(s) of phosphoric acid, such as NaKHP0 ₄ , CsNaHPC>4, CSKHPO4, and combinations comprising at least one of the foregoing. The first catalyst can comprise KNaHPC>4, wherein a molar ratio of Na to K is 0.5 to 2. The first catalyst typically will be used in an amount sufficient to provide 1 x 10 - ^" 2 to 1 x 10 - ^" 8 moles, specifically, 1 x 10 -4 to 1 x 10 ^"7 moles of metal hydroxide per mole of the dihydroxy compounds employed.

[0068] The second catalyst comprises a quaternary ammonium compound, a quaternary phosphonium compound, or a combination comprising at least one of the foregoing. The quaternary ammonium compound can be organic ammonium compound(s) having structure, (R ⁴ )4N ⁺ X ^" , wherein each R ⁴ is the same or different, and is a Ci_2o alkyl, a C4_2o cycloalkyl, or a C4_2o aryl; and X ^" is an organic or inorganic anion, for example, a hydroxide, halide, carboxylate, sulfonate, sulfate, formate, carbonate, or bicarbonate. The quaternary phosphonium compound can be of organic phosphonium compounds having structure, (R ⁵ )4P ⁺ X ^" , wherein each R ⁵ is the same or different, and is a Ci_2o alkyl, a C4_2o cycloalkyl, or a C ₄ _2o aryl; and X ^" is an organic or inorganic anion, for example, a hydroxide, phenoxide, halide, carboxylate such as acetate or formate, sulfonate, sulfate, formate, carbonate, or bicarbonate. Where X ^" is a polyvalent anion such as carbonate or sulfate, it is understood that the positive and negative charges in the quaternary ammonium and phosphonium structures are properly balanced. For example, where each R ⁵ independently methyl groups and X ^" is carbonate, it is understood that X - ^" represents 2(C(¾ - ^~ 2 ). The amount of second catalyst (e.g., organic ammonium or phosphonium salts) employed typically will be 1 x 10 ^~2 to 1 x 10 ^~5 , specifically, 1 x 10 ^~3 to 1 x 10 ^~4 moles per total mole of the dihydroxy compounds in the reaction mixture.

[0069] The process and apparatus described above, in accordance with embodiments, are further illustrated by the following non-limiting Example. It is noted that the Example below is based, in part, on computer simulation for a production facility as shown, e.g., in FIG. 3.

EXAMPLE

[0070] In this example and with reference to FIG. 3 described above, 5.77 ton/h of ethylene carbonate (EC) is fed by the alkylene carbonate stream 202 to dialkyl carbonate reactor 210, which can be a reactive or catalytic distillation column, at an intermediate position, while 3.78 tons per hour (ton/h) of a methanol-rich stream are fed to a lower section of the column by alkanol stream 204. Alkanol stream 204 is a combined stream of fresh methanol and methanol recycled through the first purified alkanol stream 291 comprising methanol and DMC. Alkanol stream 204 comprises 83.7 wt% methanol and 16.2 wt% DMC. The reaction between ethylene carbonate and methanol is performed in the presence of potassium hydroxide. Yielding a 5.74 ton/h alkylene glycol product stream 212 (70.8 wt% ethylene glycol, 29.1 wt% methanol) which is withdrawn from the bottom of the column and sent to the alkylene glycol purification unit 230 to recover ethylene glycol and unreacted methanol.

[0071] Next, 55.7 ton/h of a phenol-rich stream (75.4 wt% phenol, 19.2 wt% DMC, 1.3 wt% anisole, aromatic alcohol feed stream 222) is fed to alkyl aryl carbonate reactor 240, which can be a reactive or catalytic distillation column, at an intermediate position. Along with 47.7 ton/h of a DMC-rich stream (97.1 wt% DMC, 2.9 wt% anisole, first purified dialkyl carbonate stream 234) which is fed to the alkyl aryl carbonate reactor 240 at a position below the feed point for the aromatic alcohol feed stream 222. Transesterification of DMC and phenol is carried out in this reactive column in the presence of a suitable catalyst.

[0072] Recovered is 57.4 ton/h of bottom product (alkyl aryl carbonate product stream 226) from alkyl aryl carbonate reactor 240 containing 29.0 wt% PMC and 4.3 wt% DPC, 51.9 wt% phenol, 10.1 wt% DMC, 1.3 wt% anisole, and catalyst. The alkyl aryl carbonate product stream 226 is fed to diaryl carbonate reactor 280, which can be a reactive or catalytic distillation column. At a bottom section of diaryl carbonate reactor 280, the PMC disproportionation reaction takes place. A phenol-rich stream is obtained from its overheads (aromatic alcohol product stream 236) and recycled to alkyl aryl carbonate reactor 240, while DPC -rich product (diaryl carbonate product stream 238) is sent to a purification process.

[0073] Distillate streams from dialkyl carbonate reactor 210 (dialkyl carbonate stream 206) and alkyl aryl carbonate reactor 240 (alkanol product stream 224) are treated in a single dialkyl carbonate purification section 260. The pervaporation unit 290 recovers a 4.35 ton/h stream as top product comprising 83.1 wt% methanol (the balance being DMC) from its permeate outlet (first purified alkanol stream 291), which can be recycled back to dialkyl carbonate reactor 210. First purified dialkyl carbonate stream 234 from the dialkyl carbonate purification section 260 is sent back to the alkyl aryl carbonate reactor 240 as the DMC -rich feed stream. The pervaporation unit 290 can be operated at a permeate exit pressure of 0.1 bar(abs) to 0.25 bar(abs) (1 kPa(abs) to 25 kPa(abs)) at the permeate exit and 90°C to 220°C at the retentate exit.

[0074] Set forth below are some embodiments of the present methods of making an alkyl aryl carbonate and a system for making the same.

[0075] Embodiment 1 : A method for producing an alkyl aryl carbonate, comprising: reacting an alkylene carbonate and an alkanol in the presence of a first transesterification catalyst in a dialkyl carbonate reactor to produce a dialkyl carbonate azeotrope stream comprising a dialkyl carbonate and an unreacted alkanol, and an alkylene glycol product stream comprising an alkylene glycol and an unreacted alkanol; purifying the dialkyl carbonate azeotrope stream in a dialkyl carbonate purification section comprising a distillation column and a pervaporation unit to provide a first purified dialkyl carbonate stream and a first purified alkanol stream; reacting the first purified dialkyl carbonate stream and an aromatic alcohol in the presence of a second transesterification catalyst in an alkyl aryl carbonate reactor to produce an alkanol product stream comprising an alkanol product and an unreacted dialkyl carbonate, and an alkyl aryl carbonate product stream comprising the alkyl aryl carbonate and an unreacted aromatic alcohol; and purifying the alkanol product stream in the dialkyl carbonate purification section.

[0076] Embodiment 2: The method of Embodiment 1, further comprising recycling the first purified alkanol stream to the dialkyl carbonate reactor.

[0077] Embodiment 3: The method of any of the preceding Embodiments, further comprising purifying the alkylene glycol product stream in an alkylene glycol purification unit to provide a purified alkylene glycol stream and a second purified alkanol stream.

[0078] Embodiment 4: The method of Embodiment 3, further comprising recycling the second purified alkanol stream to the dialkyl carbonate reactor.

[0079] Embodiment 5: A method for producing an alkyl aryl carbonate, comprising: reacting a carbon monoxide, an oxygen, and an alkanol in the presence of a catalyst in a reactor to produce a raw dialkyl carbonate stream comprising a dialkyl carbonate and a water, and an dialkyl carbonate azeotrope stream comprising the dialkyl carbonate and an unreacted alkanol; recovering from the raw dialkyl carbonate stream a water stream comprising water and a second purified dialkyl carbonate stream comprising the dialkyl carbonate in a recovery section; purifying the dialkyl carbonate azeotrope stream in a dialkyl carbonate purification section comprising a distillation column and a pervaporation unit to provide a first purified dialkyl carbonate stream and a first purified alkanol stream; reacting the first purified dialkyl carbonate stream, the second purified dialkyl carbonate stream, or a combination comprising at least one of the foregoing, and an aromatic alcohol in the presence of a transesterification catalyst in an alkyl aryl carbonate reactor to produce an alkanol product stream comprising an alkanol product and an unreacted dialkyl carbonate, and an alkyl aryl carbonate product stream comprising the alkyl aryl carbonate and an unreacted aromatic alcohol; and purifying the alkanol product stream in the dialkyl carbonate purification section.

[0080] Embodiment 6: The method of Embodiment 5, further comprising combining the first purified dialkyl carbonate stream with the raw dialkyl carbonate stream to form a combined stream and recovering the water stream from the combined stream in the water recovery section to produce the second purified dialkyl carbonate stream.

[0081] Embodiment 7: The method of any of the preceding Embodiments, further comprising reacting the alkyl aryl carbonate product stream in a diaryl carbonate reactor to produce a diaryl carbonate product stream comprising a diaryl carbonate, and an aromatic alcohol product stream comprising the aromatic alcohol and the dialkyl carbonate by disproportionation. [0082] Embodiment 8: The method of Embodiment 7, further comprising polymerizing an aromatic dihydroxy compound and the diaryl carbonate in the presence of a catalyst to produce a polycarbonate.

[0083] Embodiment 9: The method of any one of the preceding Embodiments, further comprising recycling the aromatic alcohol product stream to the alkyl aryl carbonate reactor.

[0084] Embodiment 10: The method of any one of the preceding Embodiments, wherein the pervaporation unit comprises a permeate exit pressure of 1 to 100 kPa (abs).

[0085] Embodiment 11 : The method of any one of the preceding Embodiments, wherein the dialkyl carbonate reactor, the alkyl aryl carbonate reactor, the diaryl carbonate reactor, or a combination comprising at least one of the foregoing is a reactive distillation column.

[0086] Embodiment 12: The method of any one of Embodiments 1 to 4, wherein the dialkyl carbonate reactor is a first reactive distillation column maintained at a first temperature of 65°C to 150°C, and a first pressure at a first top of the first reactive distillation column of 50 to 300 kPa(g), and the alkyl aryl carbonate reactor is a second reactive distillation column maintained at a second temperature of 120°C to 270°C, and a second pressure at a second top of the second reactive distillation column of 200 to 700 kPa(g).

[0087] Embodiment 13: The method of any one of Embodiments 1 - 12, wherein the alkylene carbonate is ethylene carbonate or propylene carbonate, the alkanol is methanol or ethanol, the dialkyl carbonate is dimethyl carbonate or diethyl carbonate, the aromatic alcohol is phenol, and the alkyl aryl carbonate is methyl phenyl carbonate or ethyl phenyl carbonate.

[0088] Embodiment 14: The method of any of Embodiments 7 - 8, wherein the diaryl carbonate comprising a metal compound, wherein the metal compound comprises less than or equal to 500 ppb of molybdenum; less than or equal to 33 ppb of vanadium; less than or equal to 33 ppb of chromium; less than or equal to 75 ppb of titanium; less than or equal to 375 ppb of niobium; less than or equal to 33 ppb of nickel; less than or equal to 10 ppb of zirconium; and less or equal to 10 ppb iron; all based on the total weight of the diaryl carbonate and the metal compound.

[0089] Embodiment 14: An apparatus for production of an alkyl aryl carbonate comprises: a dialkyl carbonate reactor, an dialkyl carbonate purification section, an alkyl aryl carbonate reactive distillation column. The dialkyl carbonate reactor comprises a reactant inlet, and a dialkyl carbonate azeotrope outlet in fluid communication with a dialkyl carbonate azeotrope inlet of a dialkyl carbonate purification section. The dialkyl carbonate purification section comprises a distillation column in fluid communication with a pervaporation unit, the dialkyl carbonate azeotrope inlet, a first purified dialkyl carbonate outlet, and a first purified alkanol outlet. The alkyl aryl carbonate reactive distillation column comprises an aromatic alcohol inlet, a first purified dialkyl carbonate inlet in fluid communication with the first purified dialkyl carbonate outlet of the dialkyl carbonate purification section, an alkanol product outlet in fluid communication with an inlet of the dialkyl carbonate purification section, and an alkyl aryl carbonate outlet.

[0090] Embodiment 15: The apparatus of Embodiment 14, wherein the dialkyl carbonate reactor comprises an alkylene carbonate transesterification reactor and comprises one or more inlets for the conveyance of an alkylene carbonate and an alkanol.

[0091] Embodiment 16: The apparatus of Embodiment 14, wherein the dialkyl carbonate reactor comprises a alkanol carbonylation reactor and comprises one or more inlets for the conveyance of an oxygen, a carbon monoxide, and an alkanol.

[0092] Embodiment 17: The apparatus of any of Embodiments 14 -16, further comprising a diaryl carbonate reactive distillation column comprising an alkyl aryl carbonate inlet in fluid communication with the alkyl aryl carbonate outlet, an aromatic alcohol carbonate outlet, and a diaryl carbonate outlet.

[0093] Embodiment 18: The apparatus of any of Embodiments 14 - 17, wherein the aromatic alcohol outlet is in fluid communication with an inlet of the alkyl aryl carbonate reactive distillation column.

[0094] Embodiment 19: The apparatus of any of Embodiments 14 - 18, wherein the first purified alkanol outlet is in fluid communication with an inlet of the dialkyl carbonate reactor.

[0095] Embodiment 20: The method or apparatus of any of the preceding embodiments, wherein the pervaporation unit comprises a selective barrier comprising a selective layer (also referred to as a membrane) separating a permeate and a retentate cavity.

[0096] Embodiment 21 : The apparatus of Embodiment 20, wherein the membrane comprises a polymer, a ceramic, or a combination comprising at least one of the foregoing.

[0097] Embodiment 22: The method or apparatus of Embodiment 20 or 21, wherein the selective layer comprises one or both of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PA A). The PVA can have a Mn of 20,000 to 200,000 Daltons, or 96,000 to 115,000 Daltons. The PAA can have an Mn of 90,000 to 300,000, or 90,000-250,000 Daltons. The weight ratio of PVA to PAA can be 0.1-10: 1.

[0098] Embodiment 23: The method or apparatus of any of Embodiments 20-

22, wherein the selective layer is cross-linked with an aliphatic dialdehyde, a diacid, a dihalogen compound, epichlorohydrin, an olefinic aldehydes, boric acid, a

sulfonamideoaldehye, or a combination comprising one or more of the foregoing.

[0099] Embodiment 24: The method or apparatus of any of Embodiments 20-

23, wherein the selective layer comprises an organophilic (methanol-philic) membrane.

[0100] Embodiment 25: The method or apparatus of any of Embodiments 20-24, wherein the separating layer has a thickness of 1 to 80 micrometers.

[0101] In general, embodiments can alternatively comprise (e.g., include), consist of, or consist essentially of, any appropriate components herein disclosed. The embodiments can additionally, or alternatively, be formulated so as to be devoid, or substantially free, of any components, materials, ingredients, adjuvants or species used in the prior art compositions or that are otherwise not necessary to the achievement of the function and/or objectives of the embodiments.

[0102] As used herein, a trace amount is an amount of less than 0.01 wt% based upon a total weight of the product. All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other (e.g., ranges of "up to 25 wt , or, more specifically, 5 wt% to 20 wt ", is inclusive of the endpoints and all intermediate values of the ranges of "5 wt% to 25 wt ," etc.). "Combination" is inclusive of blends, mixtures, alloys, reaction products, and the like. Furthermore, the terms "first," "second," and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The terms "a" and "an" and "the" herein do not denote a limitation of quantity, and are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. "Or" means "and/or" unless clearly indicated otherwise. The suffix "(s)" as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including one or more of that term (e.g., the film(s) includes one or more films). Reference throughout the specification to "one embodiment", "another embodiment", "an embodiment", and so forth, means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various embodiments.

[0103] While particular embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are or can be presently unforeseen can arise to applicants or others skilled in the art. Accordingly, the appended claims as filed and as they may be amended are intended to embrace all such alternatives, modifications variations, improvements, and substantial equivalents.