Organic carbonate production process

Abstract

The present invention relates to a process for preparing organic carbonates which comprises contacting carbon dioxide with an alcohol in the presence of water and a catalyst in a reaction zone to result in the production of the organic carbonate, wherein the organic carbonate is continuously removed from the reaction zone.

Description

Technical Field

[0001] The present invention relates to a process for preparing organic carbonates.

Background Art

[0002] Organic carbonates such as dialkyl carbonates, diaryl carbonates, and alkylene carbonates have found wide applications in the chemical industry. Organic carbonates have come to be widely used as solvents due to their low toxicity, as monomers for the preparation of polymers, and in several other applications. The use of carbonates as monomers for forming polymers has been expanding and may cause a significant increase in their demand in the world market. Organic carbonates are important precursors for the production of polycarbonates, polyesters, polyurethanes, and polyamides. Furthermore, organic carbonates can be used as fuel oxygenate additives, or solvents or entrainers, or high dielectric constant components for lithium batteries, or intermediates for chemical alcohol purification, or for medical or cosmetic applications.

[0003] Current and conventional synthetic techniques use phosgene, which is prohibited in several countries, as a constituent, so the development of new synthetic methodologies for organic carbonates has attracted great attention worldwide. The phosgene-free synthesis of organic carbonates such as dimethyl carbonate (DMC) and diethyl carbonate (DEC) has been highly regarded. There is a continuing need to develop improved processes for producing organic carbonates. The object of the present invention is to provide a technically advantageous, efficient, and cost-effective process for producing organic carbonates.

Summary of the Invention

[0004] Surprisingly, it has been found that the above organic carbonate production process can be provided as a process in which carbon dioxide is contacted with an alcohol in the presence of water and a catalyst in a reaction zone to result in the production of an organic carbonate, which is continuously removed from the reaction zone.

[0005] The present invention thus relates to a process for preparing an organic carbonate which comprises contacting carbon dioxide with an alcohol in the presence of water and a catalyst in a reaction zone to effect the production of the organic carbonate, wherein the organic carbonate is continuously removed from the reaction zone.

[0006] It is known to produce organic carbonates from the reaction of alcohols with carbon dioxide in the presence of a catalyst, thereby producing organic carbonates and water. A literature overview of this type of reaction is given in "Studies in Surface Science and Catalysis", volume 178, 2019, Elsevier BV, by T. Tabanelli et al., entitled "Conversion of CO 2 The overview is provided in Chapter 7, Section 3.2 of the "Research to Valuable Chemicals: Organic Carbonate as Green Candidates for the Replacement of Noxious Reactants" in which the CO reaction of alcohols and diols is 2 It is recognized that the direct condensation reaction suffers from several bottlenecks related to the unfavorable thermodynamic equilibrium of the reaction. The overview states that continuous removal of water from the reaction medium will shift the unfavorable equilibrium towards the product. The solution according to the overview is the use of an effective dehydrating agent. However, the continuous removal of the organic carbonate product required in the present invention is not disclosed or suggested in the overview. [Brief description of the drawings]

[0007]

Figure 1

Embodiments for Carrying Out the Invention

[0008] The processes of the present invention and the streams or compositions used in such processes are each described with the terms "comprising", "containing", or "including" one or more various described steps and components, but they can also "consist essentially of" or "consist of" each of the one or more various described steps and components.

[0009] In the context of the present invention, when a stream or composition contains two or more components, these components should be selected in an overall amount not exceeding 100%.

[0010] Furthermore, when upper and lower limits of a property are cited, the range of values defined by any combination of any upper limit and any lower limit is also included.

[0011] In the following examples and figures, the locations of the different feed streams to the distillation column and the product streams from the distillation column are selected such that the components are directed to the locations required by their relative volatilities. This means that different alcohol reactants and different organic carbonate products can result in different feed locations to drive the chemical and separation processes.

[0012] In the present invention, in the presence of water and a catalyst in the reaction zone, carbon dioxide is contacted with an alcohol, thereby producing an organic carbonate. Referring to dimethyl carbonate as the organic carbonate of interest, the overall reaction is shown below.

Number

[0013] The carboxylation of such alcohols has thermodynamic limitations. It has an unfavorable equilibrium with respect to the product organic carbonate and water. However, in the present invention, since the organic carbonate is continuously removed from the reaction zone, the thermodynamic equilibrium advantageously shifts towards the product. In addition, in the present invention, water needs to be present in addition to the catalyst, and the water can be supplied as will be further described below. Therefore, in the present invention, dehydrating agents such as molecular sieves or sodium sulfate or magnesium sulfate as outlined in the above documents are not used.

[0014] Furthermore, advantageously, the present invention enables the direct synthesis of organic carbonates starting from carbon dioxide (e.g., taken from flue gas) and (bio)ethanol which can be derived from, for example, fermentation and an alcohol feed stream that usually contains water. In any case, since water is required in the present invention, advantageously, it is not necessary to separate the water from the alcohol before using it in the present invention.

[0015] Therefore, in the present invention, the organic carbonate is continuously removed from the reaction zone. This process is preferably a continuous process. Preferably, such continuous removal of the organic carbonate is achieved by carrying out the reaction in a distillation column. As used herein, a "distillation column" refers to a column in which distillation is carried out, which is a process of separating components from a liquid mixture of components by using selective boiling and condensation, and a part of the condensed liquid may or may not be recycled (refluxed) to the column.

[0016] In this way, advantageously, the production and separation of the organic carbonate are carried out simultaneously in the distillation column, thereby shifting the thermodynamic equilibrium towards the product and resulting in the production of more organic carbonate. Therefore, the reaction zone is part of the distillation column, and it is preferred that the organic carbonate is continuously removed from the distillation column. Such a distillation column is also referred to as a "reactive distillation column".

[0017] In the present invention, it is preferable that carbon dioxide, alcohol, and water are supplied to the reaction zone. They can be supplied separately and / or together. For example, alcohol and water can be supplied to the reaction zone together. The amount of water supplied to the reaction zone can be 1 to 99% by weight, preferably 5 to 95% by weight, more preferably 10 to 80% by weight, and most preferably 20 to 50% by weight based on the total amount of water and alcohol supplied to the reaction zone. The presence of water in this process can have various advantages. First, water is a polar reaction medium suitable for the intended reaction that can dissolve carbon dioxide, as will be further described below. Second, water can be useful for further optional purification of the stream containing carbon dioxide, water, alcohol, and organic carbonate, as will be further described below. Third, water may be required to activate and stabilize the catalyst used in this process, as will be further described below.

[0018] It is preferable that an amount of carbon dioxide such that the aqueous liquid phase present in the reaction zone is saturated with dissolved carbon dioxide is supplied to the reaction zone. Such dissolved carbon dioxide is sometimes referred to as "liquid" carbon dioxide.

[0019] In the present invention, in the reaction zone of the first distillation column, it is preferable to bring carbon dioxide into contact with alcohol in the presence of water and a catalyst to result in a mixture containing carbon dioxide, water, alcohol, and organic carbonate. The organic carbonate is continuously withdrawn from the bottom stream from the first distillation column from the first distillation column, and the upper stream from the first distillation column contains carbon dioxide, water, alcohol, and optionally organic carbonate. Since the organic carbonate can form an azeotrope with water, it can be present in the upper stream. For example, dialkyl carbonate forms an azeotrope with water, while alkylene carbonate is known not to. Thus, when the organic carbonate is dialkyl carbonate, it will ultimately be in both the bottom stream and the upper stream.

[0020] In this specification, the "upper stream" or "bottom stream" from the column refers to the flow that exits the column at a position of 0% to 30%, more preferably 0% to 20%, and even more preferably 0% to 10% based on the total length of the column, from the upper part or the bottom part of the column, respectively.

[0021] Fresh water is preferably supplied to the first distillation column at a position above the position where fresh alcohol is supplied, preferably at the upper part of the reaction zone or a position above it. Further, fresh alcohol is preferably supplied to the first distillation column at a position below the position where fresh water is supplied, preferably at the bottom of the reaction zone or a position below it. The reaction zone can be a zone within the first distillation column containing packing with a heterogeneous catalyst, such as structured packing. "Fresh water" or alcohol refers to water or alcohol that has not been recycled. Alternatively, or additionally, fresh water and fresh alcohol can be simultaneously supplied as part of an aqueous alcohol stream, preferably at the bottom of the reaction zone or a position below it. Still further, carbon dioxide is preferably supplied at a position below the position where fresh alcohol is supplied. An inert gas such as nitrogen can be simultaneously supplied together with carbon dioxide. Further, carbon dioxide can be simultaneously supplied together with water. Advantageously, since water is required in some way in this process, especially for dissolving carbon dioxide as described above, there is no need to remove water from a feed stream containing both carbon dioxide and water. In the present invention, a stream containing 5 to 100% by weight of carbon dioxide and the balance containing an inert gas and / or water can be supplied.

[0022] When the overhead stream from the first distillation column contains carbon dioxide, water, alcohol, and organic carbonate, the overhead stream is preferably at least partially condensed and separated into a gas stream containing carbon dioxide, a first liquid stream containing organic carbonate and alcohol, and a second liquid stream containing alcohol and water. The latter separation can be effected by using a decanter. The separated stream containing carbon dioxide can be removed from the process or recycled to the first distillation column. The separated stream containing organic carbonate and alcohol can be recycled to the first distillation column such that further organic carbonate can be recovered and the alcohol can be recycled to the reaction zone. The stream is preferably fed to the first distillation column at a position below the bottom of the reaction zone and below the position where fresh alcohol is fed. The separated stream containing alcohol and water can be fed to a second distillation column where separation into a stream containing alcohol and a stream containing water is effected. The separated stream containing alcohol from the second distillation column can be recycled to the first distillation column. The stream can be fed separately or co-fed to the first distillation column together with fresh alcohol. The separated stream containing water from the second distillation column can be removed from the process.

[0023] Preferably, the temperature in the reaction zone is a temperature of 50 to 200 °C, more preferably 60 to 160 °C, and most preferably 70 to 140 °C. Further, preferably, the pressure in the reaction zone is a pressure of 5 mbar to 10 bar, more preferably 10 mbar to 5 bar. The pressure can be selected and set such that the desired boiling point is achieved in the reaction zone.

[0024] In the present invention, the alcohol is an aromatic C 5 -C 9 alcohol and / or an aliphatic C 1 -C 30 alcohol. The aromatic C 5 -C 9 alcohol can be phenol. Preferably, in the present invention, the alcohol is an aliphatic C 1 -C30 is an alcohol. Preferably, an aliphatic C 1 -C 30 alcohol has 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms, and most preferably 1 to 3 carbon atoms. Further, preferably, an aliphatic C 1 -C 30 alcohol is selected from methanol, ethanol, and isopropanol, more preferably methanol and ethanol, and most preferably ethanol.

[0025] Furthermore, in the present invention, the alcohol may contain one hydroxyl group (monohydric alcohol) or two or more hydroxyl groups (polyhydric alcohol). In the case of a monohydric alcohol, a linear organic carbonate is formed, which can be a dialkyl carbonate (when the starting alcohol is aliphatic) or a diaryl carbonate (when the starting alcohol is aromatic). In the case of a polyhydric alcohol, two of the hydroxyl groups, particularly two hydroxyl groups separated from each other by two or three carbon atoms, can react with carbon dioxide to form a cyclic organic carbonate. Examples of such polyhydric alcohols are monoalkylene glycols, such as monoethylene glycol or monopropylene glycol, which, when reacted with carbon dioxide, result in the formation of alkylene carbonates, such as ethylene carbonate and propylene carbonate. Another example of such a polyhydric alcohol is glycerol, which results in the formation of glycerol carbonate when reacted with carbon dioxide.

[0026] As described above, in the present process, aromatic C 5 -C 9 alcohol and aliphatic C 1 -C 30Both alcohols can be supplied. This has the advantage that an alkyl aryl carbonate can be formed which can disproportionate to a dialkyl carbonate and a diaryl carbonate. For example, in this process, when a mixture of methanol and phenol is used, dimethyl carbonate and methyl phenyl carbonate can be formed. The disproportionation of methyl phenyl carbonate will then result in diphenyl carbonate and further dimethyl carbonate.

[0027] In the present invention, a catalyst should be used. Any catalyst that catalyzes the formation of an organic carbonate from carbon dioxide and an alcohol can be used.

[0028] The catalyst is preferably an acidic catalyst. Further, there may be cases where the catalyst is preferably a basic catalyst. Generally, a catalyst having both acidic and basic properties can be used. Thus, in the present invention, the catalyst can be acidic or basic, or can have acidic and basic properties. Further, preferably, the catalyst is a heterogeneous catalyst. Further, preferably, the heterogeneous catalyst is an immobilized catalyst, which implies that it cannot leave the reaction zone. Immobilization of the heterogeneous catalyst can be achieved, for example, by incorporating the catalyst into the packing in the reaction zone.

[0029] The above-mentioned acidic catalyst can be an acidic resin, specifically an acidic ion exchange resin. The acidic resin can be any acidic resin capable of protonating water and / or alcohol as present in this process. The proton of the acidic functional group of such an acidic resin can advantageously activate the alcohol to undergo the desired reaction. When such an acidic resin is used, water as present in this process can be advantageously used both in the activation and stabilization of such an acidic resin. In the case of an acidic resin, it may swell significantly upon contact with water. When dried, the carrier polymer matrix may become brittle, and any fragments may escape from the cage held in the reaction zone by the packing. This implies both the stabilization and activation of the catalytic acidic resin. Further, water keeps the pores of the resin open and makes the acidic functional groups accessible.

[0030] A preferred example of the acidic resin is an acidic resin based on sulfonated polystyrene. The latter acidic resin contains sulfonic acid (-SO 3 H) groups. Such an acidic resin can be macroporous. Preferred commercially available examples of acidic ion exchange resins based on sulfonated polystyrene are Amberlyst 15 and Amberlyst 48.

[0031] Typically, a wide variety of catalysts can be used in the present invention. The nature of the catalyst is not essential for the present invention. For example, one or more of the catalysts described in the following references [1] to [9] can be used in the present invention. The disclosures of the references are incorporated herein by reference.

[0032] As disclosed in reference [1], MgO-CeO 2 can be used as a catalyst in the present invention.

[0033] As disclosed in reference [2], an organotin material, for example, n-Bu 2 Sn(OCH 3 ) 2 can be used as a catalyst in the present invention.

[0034] As disclosed in Reference [3], an organocopper material, for example, Cu-AC [AC = activated carbon], can be used as a catalyst in the present invention.

[0035] As disclosed in Reference [4], CeO 2 can be used as a catalyst in the present invention.

[0036] Reference [5] discloses the following. For the direct synthesis of DMC (dimethyl carbonate) containing organometallic-alkoxy compounds, metal oxides, metal-supported catalysts, and ionic liquids, various catalysts have already been tested. In general, it has been proposed that balanced acidic and basic properties play an important role in methanol activation in DMC synthesis. Most of the research on metal oxides has dealt with ceria or zirconia. The discussion about the influence of crystal structure and morphology on activity is still ongoing. Ceria catalysts showing morphologies such as nanorods, nanocubes, octahedra, and spindles exhibit different activities. In general, the observed trend is that mixed oxides often exhibit better performance than pure oxides. Therefore, the authors are exploring modified ceria and zirconia such as H 3 PO 4 -functionalized ZrO 2 、Al 2 O 3 、Fe 2 O 3 doped ceria, as well as mixed oxides of ceria-zirconia. As disclosed in Reference [5], one or more of these catalysts can be used as a catalyst in the present invention. The CeO 2 can be used in combination with one or more of Al, Zn, Fe, La, Y, Gd, Sm, Zr, Nd, Nb, Ti.

[0037] As disclosed in Reference [6], yttrium oxide, Y 2 O 3 can be used as a catalyst in the present invention.

[0038] As disclosed in Reference [7], metal / activated carbon materials, such as Cu-Ni / AC and Ru-Fe / AC [AC = activated carbon], can be used as catalysts in the present invention.

[0039] Reference [8] discloses the following. ZnO-CeO combined with 2-cyanopyridine 2 can be used to remove water formed during the reaction. Excellent catalytic activity is the combined effect of the crystal size of CeO 2 and the presence of an optimal number of acidic and basic sites. As disclosed in Reference [8], the ZnO-CeO 2 catalyst can be used as a catalyst in the present invention.

[0040] Reference [9] discloses the following. In DMC synthesis, different types of catalysts have been reported, such as organotin, copper-based catalysts, homogeneous and heterogeneous catalysts, organometallic complexes, phosphines, organic bases, metal oxides, acid-base bifunctional systems, zeolite-smectite catalysts, and supported organic base catalysts. As disclosed in Reference [9], one or more of these catalysts can be used as catalysts in the present invention.

[0041] References [1] to [9] [1] Pawar et al., “Understanding the synergy between MgO-CeO 2 as an effective promoter and ionic liquids for high dimethyl carbonate production from CO 2 and methanol”, 2020, Chemical Engineering Journal 395, 124970. [2]Ballivet-Tkatchenko et al., “Direct synthesis of dimethyl carbonate with supercritical carbon dioxide: characterization of a key organotin oxide intermediate”, Catal. Today., 115, 2006, pages 80-87. [3]Merza et al., “The synthesis of dimethyl carbonate by the oxicarbonylation of methanol over Cu supported on carbon norit”, Catal. Lett., 145, 2015, pages 881-892. [4]Tomishige et al., “Catalytic function of CeO 2 in non-reductive conversion of CO 2 with alcohols”, 2020, Materials Today Sustainability, 9, 100035. [5]Daniel et al., “Discovery of very active catalysts for methanol carboxylation into DMC by screening of a large and diverse catalyst library”, 2020, New Journal of Chemistry, 44(16), pages 6312-6320. [6]Sun et al., “Study of thermodynamics and experiment on direct synthesis of dimethyl carbonate from carbon dioxide and methanol over yttrium oxide”, 2020, Industrial and Engineering Chemistry Research, 59(10), pages 4281-4290. [7]Arbelaez et al., “Transformation of carbon dioxide into linear carbonates and methane over Cu-Ni and Ru-Fe supported on pellets activated carbon”, 2020, Chemical Engineering Transactions, 79, pages 109-114. [8]Challa et al., “Coupling of CH 3 OH and CO 2 with 2-cyanopyridine for enhanced yields of dimethyl carbonate over ZnO-CeO 2 catalyst”, 2019, Journal of Chemical Sciences 131(8), 86. [9]Pawar et al., “Greener synthesis of dimethyl carbonate from carbon dioxide and methanol using a tunable ionic liquid catalyst”, 2020, Open Chemistry, 17(1), pages 1252-1265.

[0042] The present invention is further shown in Figure 1.

[0043] In the process shown in Figure 1, a liquid feed stream (1) containing water, a liquid feed stream (2) containing ethanol, and a gas feed stream (3) containing carbon dioxide are sent to a reactive distillation column (4) at different positions. As shown in Figure 1, water is fed at the highest position and carbon dioxide is fed at the lowest position. The reactive distillation column (4) contains a reaction zone (5) containing a heterogeneous catalyst capable of catalyzing the formation of organic carbonates (e.g., diethyl carbonate) from carbon dioxide and an alcohol (e.g., ethanol).

[0044] The bottom stream (7) from the reactive distillation column (4) contains the desired product, namely diethyl carbonate. The top stream (6) from the reactive distillation column (4) contains diethyl carbonate, water, ethanol, and carbon dioxide and is sent to a decanter (8) via a partial condensation step. The gaseous carbon dioxide is discharged from the decanter (8) through its top. In the decanter (8), two liquid phases are separated, and the upper phase containing diethyl carbonate and ethanol is recycled to the reactive distillation column (4) as the first liquid stream (10), and the bottom phase containing ethanol and water is sent to a distillation column (12) as the second liquid stream (11). In the distillation column (12), the stream (11) is combined with the ethanol feed stream (2) and separated into an upper stream (13) containing ethanol that is recycled to the reactive distillation column (4) and a bottom stream (14) containing water that is removed from the process.

Claims

**Claim 1** A process for preparing an organic carbonate, comprising contacting carbon dioxide with an alcohol in the presence of water and a catalyst in a reaction zone which is part of a distillation column, thereby resulting in the formation of said organic carbonate, wherein said organic carbonate is continuously withdrawn from said distillation column. **Claim 2** wherein said alcohol is an aromatic C ５ -C ９ alcohol and / or an aliphatic C １ -C ３０ alcohol, the process according to claim 1. **Claim 3** The process according to claim 1 or 2, wherein the temperature is a temperature of 50 to 200 °C. **Claim 4** The process according to claim 1, wherein the pressure is a pressure of 5 mbar to 10 bar. **Claim 5** Contacting carbon dioxide with an alcohol in the presence of water and a catalyst in a reaction zone of a first distillation column, thereby resulting in a mixture comprising carbon dioxide, water, alcohol, and an organic carbonate, wherein the organic carbonate is continuously withdrawn from said first distillation column as a bottom stream from said first distillation column, and the overhead stream from said first distillation column comprises carbon dioxide, water, alcohol, and optionally an organic carbonate, the process according to claim 1. **Claim 6** The overhead stream from said first distillation column comprises carbon dioxide, water, alcohol, and an organic carbonate, said overhead stream is at least partially condensed and separated into a gas stream comprising carbon dioxide, a first liquid stream comprising an organic carbonate and an alcohol, and a second liquid stream comprising an alcohol and water, said separated first liquid stream comprising an organic carbonate and an alcohol is recycled to said first distillation column, said separated second liquid stream comprising an alcohol and water is fed to a second distillation column, and separation into a stream comprising an alcohol and a stream comprising water is carried out, said separated stream comprising an alcohol from said second distillation column is recycled to said first distillation column, the process according to claim 5. **Claim 7** The process according to claim 1, wherein the catalyst is an acidic catalyst. **Claim 8** The process according to claim 7, wherein the acidic catalyst is an acidic resin. **Claim 9** The process according to claim 1, wherein the catalyst is an immobilized heterogeneous catalyst.

Images