WO2020021364A1 - Disubstituted oxalate and disubstituted carbonate production from an oxalate salt and alcohol - Google Patents

Abstract

Processes for producing a disubstituted oxalate and/or disubstituted carbonate are disclosed. The processes use a water removal agent to tune the amount of disubstituted oxalate and/or disubstituted carbonate in the product mixture. One process includes contacting a cesium salt with one or more alcohols in the presence of an effective amount of a water removal agent under a carbon dioxide (CO2) atmosphere and reaction conditions sufficient to produce a composition that includes a disubstituted oxalate. Methanol can be used to produce dimethyl oxalate.

Description

DISUBSTITUTED OXALATE AND DISUBSTITUTED CARBONATE

PRODUCTION FROM AN OXALATE SALT AND ALCOHOL

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Provisional Patent Application No. 62/711,004 filed July 27, 2018, which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

A. Field of the Invention

[0002] The invention generally concerns a process for preparing a disubstituted oxalate or disubstituted carbonate. In particular, the process includes contacting an oxalate salt with one or more alcohols and carbon dioxide (CO2) in the presence of a water removal agent under reaction conditions sufficient to produce a disubstituted oxalate and/or a disubstituted carbonate. Modifying the amount of the water removal agent present during the reaction can tune the amount of disubstituted oxalate and/or disubstituted carbonate produced such that product streams comprising primarily disubstituted carbonate is produced, primarily disubstituted oxalate is produced, and/or primarily a mixture of disubstituted oxalate and disubstituted carbonate are produced.

B. Description of Related Art

[0003] Dimethyl oxalate (DMO) is the dimethyl ester of oxalic acid. DMO is used in various industrial processes, such as in pharmaceutical products, for the production of oxalic acid and ethylene glycol, or as a solvent or plasticizer. Commercially, DMO can be prepared by the high pressure oxidative coupling of carbon monoxide and an alkyl nitrite in the presence of a palladium catalyst. Most processes used to prepare DMO require carbon monoxide (CO) as a feedstock. Carbon monoxide is typically produced from the gasification of coal. Due to depleting global fossil fuels reserves, there is a foreseeable demand for new processes that require alternate feedstocks for DMO production.

[0004] Dimethyl carbonate (DMC) is another chemical raw material that can be used in a variety of downstream processes. For example, DMC can be used as a carbonylating and methylating agent. It can also be used as a solvent in the polycarbonate industry. DMC can be prepared by the reaction of phosgene and chloroformate.

[0005] These types of processes for producing DMO and DMC can use expensive starting materials and/or catalysts and feedstocks that can pose environmental and safety concerns. SUMMARY OF THU INVENTION

[0006] A discovery has been made that provides an alternate feedstock for the production of disubstituted oxalates ( e.g ., dimethyl oxalate) and/or disubstituted carbonates (e.g, dimethyl carbonate). The discovery is premised on the selective removal of water during the conversion of an oxalate salt (e.g, cesium oxalate) in the presence of an alcohol and CCk to a disubstituted oxalate. The selective removal of water can be performed using a water removal agent. It was unexpectedly discovered that under reaction conditions to produce disubstituted oxalates from oxalate salts, the water generated during the reaction facilitated the formation of disubstituted carbonates. A water removal agent was added to the reaction mixture, which resulted in the formation of disubstituted oxalates. Tuning the amount of water removal agent can allow for production of a disubstituted oxalate (e.g, DMO), a mixture of disubstituted oxalates and disubstituted carbonates (e.g, DMO and DMC), or a disubstituted carbonate (e.g, DMC). If only disubstituted carbonates are desired, the water removal agent does not have to be used. The process of the current invention provides an elegant alternative to conventional methods of making DMO from CO and alkyl nitrites using expensive noble metal catalysts or DMC from phosgene and chloroformate. The process of the present invention also provides for a way to produce mixtures of DMO and DMC from the same reaction feed. In one embodiment of the current invention, a process for producing a disubstituted oxalate is described. The process includes contacting a cesium salt (e.g, cesium oxalate) with one or more alcohols with a water removal agent under reaction conditions sufficient to produce a composition containing a disubstituted oxalate having the general structure of:

where R¹ and R² are each independently an alkyl group, a substituted alkyl group, an aromatic group, a substituted aromatic group, or a combination thereof. In particular instances, R¹ and R² can include 1 to 20 carbon atoms, 1 to 10 carbon atoms, 1 to 5 carbon atoms, preferably 1 carbon atom. More specifically, R¹ and R² can be a methyl group, an ethyl group, a propyl group, an isopropyl group, a «-butyl group, a sec-butyl group, a /e/7-butyl group, a pentyl group, a neopentyl, or a hexyl group, or combinations thereof. In some aspects of the current invention, R¹ and R² are each methyl groups. In still other aspects, the process can include reacting the disubstituted oxalate under conditions sufficient to form oxalic acid or reacting the disubstituted oxalate under conditions sufficient to form glycol. In some aspects, the reaction is performed under a carbon dioxide (CO2) atmosphere. In one aspect, the reaction conditions can include a temperature of 115 °C to 200 °C, 120 °C to 150 °C, or preferably about 130 °C and/or a pressure of 2 MPa to 5 MPa, 3 MPa to 4 MPa, or preferably about 3.5 MPa. The cesium salt used in the process can be a cesium salt/inert material composition. The inert material can be a metal oxide, an aluminate, a zeolite, or a mixture thereof, preferably a metal oxide, more preferably gamma alumina. The water removal agent can be a material or compound that has the ability to adsorb, absorb, or breakdown water. In some preferred instances, the water removal agent can be an inorganic compound ( e.g ., a molecular sieve, preferably a 4 angstrom (A) molecular sieve), an organic compounds (e.g., a quinone), or a mixture of thereof. Non-limiting examples of a quinone compound include benzoquinone, hydroquinone, naphthoquinone, anthraquinone, or mixtures thereof. In some aspects, a quinone and a 4 A molecular sieve are used together. A total weight percent of water scavenger to volume percent of solvent can be 1 to 50 wt.%/vol.%, preferably 10 to 40 wt./vol.%, more preferably 15 to 30 wt./vol.%, or about 20 wt./vol.%. The amount of water removal agent can be adjusted to produce a product stream that includes (1) a disubstituted carbonate and a disubstituted oxalate (e.g, DMC and DMO) in desired amounts (e.g, more DMC than DMO by mol. %, more DMO than DMC by mol. %, or equal amounts of DMO and DMC, by mol. %), (2) a disubstituted carbonate (e.g, DMC) and substantially no or no disubstituted oxalate (e.g, DMO), or (3) a disubstituted oxalate (e.g, DMO) and substantially no or no disubstituted carbonate (e.g, DMC).

[0007] In another aspect of the present invention a process for producing a disubstituted carbonate (e.g, dimethyl carbonate) is described. The process can include contacting an oxalate salt (e.g, cesium oxalate) in the presence of an alcohol and carbon dioxide (e.g, under a carbon dioxide atmosphere) under reaction conditions sufficient to produce a composition comprising a disubstituted carbonate having the general structure of:

where R³ and R⁴ are each independently alkyl group, a substituted alkyl group, an aromatic group, a substituted aromatic group, or a combination thereof. In a preferred embodiment, the alcohol is methanol and the carbonate is dimethyl carbonate. In particular instances, R³ and R⁴ can include 1 to 20 carbon atoms, 1 to 10 carbon atoms, 1 to 5 carbon atoms, preferably 1 carbon atom. More specifically, R³ and R⁴ can be a methyl group, an ethyl group, a propyl group, an isopropyl group, a «-butyl group, a sec-butyl group, a /e/7-butyl group, a pentyl group, a neopentyl, or a hexyl group, or combinations thereof. In some aspects of the current invention, R³ and R⁴ are each methyl groups. In some aspects, R³ and R⁴ are the same as R¹ and R².

[0008] The cesium salt can be cesium oxalate and/or a cesium oxalate/inert material composition. The cesium oxalate can be obtained by contacting a mixture of CO2 and carbon monoxide (CO) under reaction conditions sufficient to form a composition containing the cesium oxalate. In some instances, the cesium oxalate can be obtained by contacting a mixture of CO2 and hydrogen (H2), or a mixture of O2 and CO with cesium carbonate (CS2CO3), under reaction conditions sufficient to form a composition containing the cesium oxalate. The inert material can be added to the cesium carbonate. Particularly, the reaction conditions for obtaining the cesium oxalate can include a temperature of 200 °C to 400 °C, 250 °C to 350 °C, preferably 290 °C to 335 °C, or most preferably 300 °C to 325 °C. In some instances, the reaction conditions for obtaining the cesium oxalate can include providing carbon dioxide at a pressure of 2.0 MPa to 3.0 MPa, preferably about 2.5 MPa, and providing carbon monoxide at a pressure of 1.0 MPa to 3 MPa, preferably about 2.0 MPa. In other instances, the reaction conditions for obtaining the cesium oxalate can include providing carbon dioxide at a pressure of 2.0 MPa to 4.0 MPa, preferably about 3.5 MPa, and providing H2 at a pressure of 0.05 MPa to 0.5 MPa, preferably about 0.1 MPa. In yet another instance, the reaction conditions for obtaining the cesium oxalate can include providing carbon monoxide at a pressure of 2.0 MPa to 4.0 MPa, preferably about 3.5 MPa, and providing O2 at a pressure of 0.05 MPa to 4 MPa, 0.1 to 1.5 MPa, or about 0.1 MPa. The process can further include contacting the cesium carbonate with the carbon dioxide at a reaction temperature of 200 °C to 400 °C, 250 °C to 350 °C, preferably 290 °C to 335 °C, or most preferably 300 °C to 325 °C, for at least 1 hour to form a cesium carbonate/carbon dioxide reaction mixture and then contacting the cesium carbonate/carbon dioxide reaction mixture with hydrogen. Such a controlled addition of the carbon dioxide and hydrogen can inhibit the formation of sodium formate. In a particular instance, the process can further include isolating the cesium oxalate salt from the product stream prior to converting it to the disubstituted oxalate. Alternatively, the process can be a one-pot synthesis such that it is performed in a single reactor such that cesium oxalate is generated in situ and then contacted with the one or more alcohols and additional CO2 to produce the disubstituted oxalate. [0009] The following includes definitions of various terms and phrases used throughout this specification.

[0010] The term“alkyl group” can be a straight or branched chain alkyl having 1 to 20 carbon atoms. Examples include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, secondary butyl, tertiary butyl, pentyl, isopentyl, neopentyl, hexyl, benzyl, heptyl, octyl, 2-ethylhexyl, l,l,3,3-tetramethylbutyl, nonyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, and/or eicosyl.

[0011] The term“substituted alkyl group” can include any of the aforementioned alkyl groups that are additionally substituted with one or more heteroatom, such as a halogen (F, Cl, Br, I), boron, oxygen, nitrogen, sulfur, silicon, etc. Without limitation, a substituted alkyl group can include alkoxy or alkylamine groups where the alkyl group attached to the heteroatom can also be a substituted alkyl group.

[0012] The term“aromatic group” can be any aromatic hydrocarbon group having 5 to 20 carbon atoms of the monocyclic, polycyclic or condensed polycyclic type. Examples include phenyl, biphenyl, naphthyl, and the like. Without limitation, an aromatic group also includes heteroaromatic groups, for example, pyridyl, indolyl, indazolyl, quinolinyl, isoquinolinyl, and the like.

[0013] The term“substituted aromatic group” can include any of the aforementioned aromatic groups that are additionally substituted with one or more atom, such as a halogen (F, Cl, Br, I), carbon, boron, oxygen, nitrogen, sulfur, silicon, etc. Without limitation, a substituted aromatic group can be substituted with alkyl or substituted alkyl groups including alkoxy or alkylamine groups.

[0014] The term“inert” is defined as a material or chemical that undergo a chemical reaction with the starting materials or product during the course of the reaction.

[0015] The terms“about” or“approximately” are defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment, the terms are defined to be within 10%, preferably, within 5%, more preferably, within 1%, and most preferably, within 0.5%.

[0016] The terms“wt.%,”“vol.%,” or“mol.%” refers to a weight, volume, or molar percentage of a component, respectively, based on the total weight, the total volume, or the total moles of material that includes the component. In a non-limiting example, 10 moles of component in 100 moles of the material is 10 mol.% of component. [0017] The term“substantially” and its variations are defined to include ranges within 10%, within 5%, within 1%, or within 0.5%.

[0018] The terms“inhibiting” or“reducing” or“preventing” or“avoiding” or any variation of these terms, when used in the claims and/or the specification, includes any measurable decrease or complete inhibition to achieve a desired result.

[0019] The term“effective,” as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result.

[0020] The use of the words“a” or“an” when used in conjunction with any of the terms “comprising,”“including,”“containing,” or“having” in the claims or the specification may mean“one,” but it is also consistent with the meaning of“one or more,”“at least one,” and “one or more than one.”

[0021] The words“comprising” (and any form of comprising, such as“comprise” and “comprises”),“having” (and any form of having, such as“have” and“has”),“including” (and any form of including, such as“includes” and“include”), or“containing” (and any form of containing, such as“contains” and“contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0022] The process of the present invention can“comprise,”“consist essentially of,” or “consist of’ particular ingredients, components, compositions, etc ., disclosed throughout the specification. With respect to the transitional phase“consisting essentially of,” in one non limiting aspect, a basic and novel characteristic of the process of the present invention is the ability to produce a disubstituted oxalate or a mixture of a disubstituted oxalate and a disubstituted carbonate from an alcohol and a water removal agent under a CO2 atmosphere. In another aspect, a basic and novel characteristic of the process of the present invention is the ability to produce a disubstituted carbonate from an alcohol under a CO2 atmosphere without the use of a water removal agent.

[0023] In the context of the present invention, at least 20 embodiments are now described. Embodiment 1 is a process for producing a disubstituted oxalate. The process includes the steps of contacting an oxalate salt with an alcohol in the presence of a water removal agent and carbon dioxide under reaction conditions sufficient to produce a composition comprising a disubstituted oxalate having the general structure of:

[0024] where R¹ and R² are each independently alkyl group, a substituted alkyl group, an aromatic group, a substituted aromatic group, or a combination thereof. Embodiment 2 is the process of embodiment 1, wherein contacting is performed under a carbon dioxide (CO2) atmosphere. Embodiment 3 is the process of embodiment 1, wherein the water removal agent is an inorganic compound, an organic compound, or both. Embodiment 4 is the process of embodiment 3, wherein the inorganic compound is a molecular sieve, preferably a 4 angstrom (A) molecular sieve. Embodiment 5 is the process of any one of embodiments 3 to 4, wherein the organic compound is a quinone. Embodiment 6 is the process of embodiment 5, wherein the quinone is benzoquinone, hydroquinone, naphthoquinone, anthraquinone, or mixtures thereof. Embodiment 7 is the process of any one of embodiments 1 to 6, wherein the water removal agent is a quinone compound and a 4 A molecular sieve. Embodiment 8 is the process of any one of embodiments 1 to 7, wherein the total weight percentage of water removal agent to volume percentage of solvent is 1 to 50 wt./vol.%, preferably 20 wt./vol.%. Embodiment 9 is the process of any one of embodiments 1 to 8, wherein the reaction conditions comprise a temperature of 115 °C to 200 °C, 120 °C to 150 °C, or preferably about 130 °C, a pressure of 2 MPa to 5 MPa, 3 MPa to 4 MPa, or preferably about 3.5 MPa, or both. Embodiment 10 is the process of any one of embodiments 1 to 9, wherein the oxalate salt is cesium oxalate (CS2C2O4). Embodiment 11 is the process of embodiment 10, wherein the reaction conditions for obtaining the cesium oxalate comprise a temperature of 200 °C to 400 °C, 250 °C to 350 °C, preferably 290 °C to 335 °C, or most preferably 300 °C to 325 °C, a pressure of 2.0 MPa to 3.0 MPa, preferably about 2.5 MPa, and providing carbon monoxide at a pressure of 1.0 MPa to 3 MPa, preferably about 2.0 MPa, or both. Embodiment 12 is the process of any one of embodiments 10 to 11, wherein the mixture further comprises a metal oxide, an aluminate, a zeolite, or a mixture thereof, preferably a metal oxide, more preferably gamma alumina. Embodiment 13 is the process of any one of embodiments 1 to 12, wherein R¹ and R² comprise 1 to 20 carbon atoms, 1 to 10 carbon atoms, 1 to 5 carbon atoms, preferably 1 carbon atom. Embodiment 14 is the process of embodiment 13, wherein R¹ and R² are a methyl group, an ethyl group, a propyl group, an isopropyl group, a n-butyl group, a sec-butyl group, atert-butyl group, a pentyl group, a neopentyl, or a hexyl group, or combinations thereof. Embodiment 15 is the process of embodiment 14, wherein R¹ and R² are each methyl groups. Embodiment 16 is the process of any one of embodiments 1 to 15, further including the step of adjusting the amount of water removal agent such that the product stream further includes disubstituted carbonate, preferably dimethyl carbonate.

[0025] Embodiment 17 is a process for producing dimethyl carbonate. The process includes the steps of contacting an oxalate salt in the presence of an alcohol under a carbon dioxide atmosphere under reaction conditions sufficient to produce a composition containing a dicarbonate having the general structure of:

[0026] where R¹ and R² are each independently alkyl group, a substituted alkyl group, an aromatic group, a substituted aromatic group, or a combination thereof. Embodiment 18 is the process of embodiment 17, wherein the alcohol is methanol and the carbonate is dimethyl carbonate. Embodiment 19 is the process of embodiment 18, wherein the oxalate salt is cesium oxalate. Embodiment 20 is the process of any one of embodiments 17 to 19, reaction conditions comprise a temperature of 115 °C to 200 °C, 120 °C to 150 °C, or preferably about 130 °C, a pressure of 2 MPa to 5 MPa, 3 MPa to 4 MPa, or preferably about 3.5 MPa, or both.

[0027] Other objects, features and advantages of the present invention will become apparent from the following figures, detailed description, and examples. It should be understood, however, that the figures, detailed description, and examples, while indicating specific embodiments of the invention, are given by way of illustration only and are not meant to be limiting. Additionally, it is contemplated that changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. In further embodiments, features from specific embodiments may be combined with features from other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specific embodiments described herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Advantages of the present invention may become apparent to those skilled in the art with the benefit of the following detailed description and upon reference to the accompanying drawings.

[0029] FIG. 1 is the CO to CO2 transformation energies.

[0030] FIG. 2 is the CS2CO3 to Cs2(C20₄) transformation energies.

[0031] FIG. 3 is the Cs₂C₂04 to DMO transformation energies.

[0032] FIG. 4 is the CS2CO3 regeneration from CsOH transformation energies.

[0033] FIG. 5 is a schematic of a one reactor system to produce disubstituted oxalates and/or disubstituted carbonates of the present invention.

[0034] FIG. 6 is a schematic of a two reactor system to produce disubstituted oxalates and/or disubstituted carbonates of the present invention.

[0035] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings. The drawings may not be to scale.

DETATEED DESCRIPTION OF THE INVENTION

[0036] A discovery has been made that provides an elegant solution to the problem of diminishing carbon monoxide (CO) feedstocks that are used for producing disubstituted oxalates such as dimethyl oxalate and/or disubstituted carbonates such as dimethyl carbonate. The discovery is premised on addition of an effective amount of a water removal agent in a reaction mixture for producing disubstituted oxalates. The reaction mixture, which includes an alcohol, carbon dioxide (CO2), and the water removal agent (WRA), can be contacted with a cesium salt ( e.g ., cesium oxalate) under reaction conditions sufficient to produce a disubstituted oxalate (e.g., dimethyl oxalate) containing composition as shown in overall general reaction equation (1). In the absence of the water removal agent, disubstituted carbonates can be formed as shown in reaction equation (2). In reaction (2), dimethyl oxalate and water can be formed. In the presence of water, the disubstituted oxalate can be converted to a disubstituted carbonate. Although not shown, water can also be formed in reaction (1), but the WRA can be used to adsorb or absorb the water, which can help reduce or prevent the conversion of the disubstituted oxalate to the disubstituted carbonate. Tuning the amount of water removal agent can produce a mixture of both products.

where X is a counter anion to the cesium metal cation and R¹, R², R³, and R⁴ are defined as above. In a preferred embodiment, R'OH, R²OH, R³OH, and R⁴OH are methanol and the disubstituted oxalate is dimethyl oxalate and the disubstituted carbonate is dimethyl carbonate. In some instances, the cesium salt (CsX) is cesium oxalate. These and other non-limiting aspects of the present invention are discussed in further detail in the following sections with reference to the Figures.

A. Materials

1. Cesium Salts and Cesium Oxalate

[0037] Cesium salts ( e.g ., carbonate (CS2CO3)) may be purchased in various grades from commercial sources. Preferably, the cesium salt (CS2CO3) is highly pure and substantially devoid of water. A non-limited commercial source of the cesium salts for use in the present invention includes SigmaMillipore (USA). In some embodiments, CS2CO3 is mixed with an inert material. Non-limiting examples of inert materials include alumina (acidic, basic or neutral), silica, zirconia, ceria, zeolites, lanthanum oxides, or mixtures thereof. In preferred embodiments, the CS2CO3 is mixed with alumina or silica using solid-solid mixing. Providing the CS2CO3 as a Cs2C03/inert material mixture can inhibit the cesium oxalate from forming a melt that requires further processing (e.g., grinding, powdering, etc.) prior to reaction with alcohol to form the disubstituted oxalate of the present invention.

[0038] In particular embodiments, the process of the present invention provides temperature efficient and alternative processes for the formation of cesium oxalate. Cesium carbonate can be selectively converted to cesium oxalate though the reaction with CO2 and CO. The cesium carbonate can be supported (e.g, alumina or silica support) or be used in an unsupported form (i.e., bulk catalyst). Alternative processes to produce cesium carbonate include the reaction of CO2 and Fh, or the reaction of CO and O2, under sufficient temperature and pressures to produce cesium oxalate. In a non-limiting aspect, the formed cesium oxalate can be further reacted in situ or separately to form further synthesis products (e.g., disubstituted oxalate). Cesium oxalate production can be produced in the context of the present invention by contacting a mixture of inert material and a cesium salt (e.g, CS2CO3 and/or CsHCCb) with an oxygen source and a carbon source under reaction conditions sufficient to form a composition that includes CS2C2O4. The composition can also include cesium formate (HCC Cs) or cesium bicarbonate (CsHCCb). Formation of a cesium oxalate in presence of an inert material can inhibit the cesium oxalate from forming a melt that requires further processing (e.g, grinding, powdering, etc.) prior to reaction with other reagents to form various products (e.g, disubstituted oxalates, oxalic acids, oxamides, or ethylene glycol), especially when the cesium oxalate is generated in situ. The inert material can be any material that does not promote reactions between the gaseous carbon source and the gaseous oxygen source. In some embodiments, the inert material can include at least one metal oxide, charcoal, or a mixture thereof. Non-limiting examples of metal oxides include alumina (acidic, basic, gamma, or neutral), ceria, silica, zirconia, lanthanum oxides, zeolites, or mixtures thereof. In one non limiting embodiment, alumina and/or silica is used as the inert material. In one particular embodiment, gamma alumina is used as the inert material. In another embodiment, alumina and/or silica is combined with charcoal, and the mixture is used as the inert material. The a mass ratio of charcoal to metal oxide can be 0.1 : 10 to 10:0.1, or 0.2:8, 1 :5, 1 : 1, 2: 1, or 3 :0.2, preferably 1 : 1. A mass ratio of inert material to the cesium salt can be 0.1 : 10 to 10:0.1, or 0.2:8, 0.5:5, 1 : 1, 2: 1, 5:0.2, or 8:0.5. In one non-limiting embodiment, the mass ratio of inert material to the cesium salt can be 1 : 1, or 0.5: 1. In some embodiments, the inert material (e.g, gamma alumina) is added to the cesium carbonate or bicarbonate in the presence of water and mixed under agitation to form a dispersion, slurry, mull, or wet powder of inert material and cesium salt. The water can be removed under vacuum and the resulting powder dried under vacuum at a temperature of 250 to 325 °C for 10 minutes to 5 hours, or 15 minutes to 2 hours.

[0039] Conventionally, cesium oxalate is generated by the reaction of cesium carbonate with carbon monoxide and carbon dioxide as shown in reaction equation (3).

Cs₂C0₃ + CO + co₂ ^ Cs₂(C₂0₄)

(3)_·

[0040] In one alternative process, the cesium oxalate can be generated by the reaction of cesium carbonate with carbon dioxide and H2 as shown in reaction equation (4) as described in more detail below and in the Examples section.

Cs₂C0₃ + H₂ + C0₂ -► Cs₂(C₂0₄)

(4). In some embodiments, the carbon dioxide and H2 are added in a sequential manner as shown in reaction equation (5). The sequential addition of carbon dioxide then hydrogen can inhibit or substantially inhibit the formation of cesium formate (HCO2CS). Limiting the formation of cesium formate, limits the formation of alkyl formate in subsequent reactions with alcohols. In some instances, cesium formate is not formed in the production of cesium oxalate.

(5)·

[0041] In yet another alternative process, the cesium oxalate can be generated by the reaction of cesium carbonate with carbon monoxide and O2 as shown in reaction equation (6) as described in more detail below.

Cs₂C0₃ + 0₂ + CO -► Cs₂(C₂0₄)

(6).

While the above reactions show CS2CO3, the reactions are the same when an inert material is used. With respect to reaction equation (6), and without wishing to be bound by theory, it is believed that the use of molecular oxygen will require lower heat requirements when compared to other processes as the reaction between CO and O2 is exothermic (free energy change of - 61.4 kcal/mol as determined through density functional theory (DFT)). FIG. 1 depicts the carbon monoxide to carbon dioxide transformation energetics. The CO2 can bind with cesium carbonate to form a CO2-CS2CO3 adduct, which has an enthalpy of fusion at a molecular level. This enthalpy of fusion can be compensated by the CO + 0.5 O2 to CO2 energy of 122.8 kcal/mol. The remaining carbon monoxide can then transform the CO2-CS2CO3 adduct into cesium oxalate. FIG. 2 shows the overall CS2CO3 to CS2C2O4 transformation energies. Thus, the overall reaction is exothermic with a calculated free energy (DFT) change of -23.4 kcal/mol making the reaction favorable for low heating requirements.

[0042] In another embodiment, the oxalate salt ( e.g ., cesium oxalate) can be produced from oxalic acid and a metal hydroxide (e.g., cesium hydroxide). By way of example, oxalic acid can be mixed with water or another solvent until dissolved. Two molar equivalents of cesium hydroxide can be added to the acidic solution of oxalic acid until full neutralization is achieved (e.g, pH of 6.8 to 7.2). Either the amount of the acid or the base can be in slight excess to ensure completion of neutralization. After the completion of the neutralization, the reaction solution can be concentrated (e.g, vacuum distilled, evaporated) to remove the solvent (e.g, water) and collect the product that includes cesium oxalate. In some embodiments, the solution can be concentrated to remove a majority of the solvent ( e.g ., about 90 to 95 vol.% of the water) and the solution can be cooled to promote crystallization of the cesium oxalate from the solvent. The cesium oxalate can then be isolated (e.g., filtered, centrifuged) and washed thoroughly with ethanol.

2. Water Removal Agents

[0043] Water removal agents can be any inorganic or organic compound capable of removing water formed during the reaction of the cesium oxalate, alcohol and carbon dioxide. To produce a mixture of disubstituted oxalates and disubstituted carbonates, an effective amount of water removal agent can be at least, equal to, or between any two of 0.1 wt./vol.%, 0.5 wt./vol.%, and 10 wt./vol.%. Non-limiting examples of inorganic water removal agents include molecular sieves. All types of molecular sieves which are suitable for drying gaseous or liquid mixtures can be employed. These sieves may in particular include zeolites. Non limiting examples of zeolites includes zeolites A and X, zeolites formed with the aid of a binder which may be a clay (kaolinite, bentonite, montmorillonite, attapulgite etc), an alumina (alumina gel or alumina produced by the rapid dehydration of aluminum hydroxides or oxyhydroxides), an amorphous mixture of silica and alumina, a silica gel or titanium oxide. The molecular sieve pore size is chosen to exclude CO2, but capture H2O under the reaction conditions. In a preferred embodiment, the molecular sieve has a 3 A or 4 A pore size. Molecular sieves are commercially available from various manufacturers. A non-limiting example of a commercial manufacture is Zeochem AG (Switzerland). Organic compounds that can be used as water removal agents include quinone compounds. Non-limiting examples of a quinone include l,4-benzoquinone, hydroquinone, naphthoquinone, anthraquinone, or mixtures thereof. In some embodiments, a mixture of inorganic and organic water removal agents can be used. The total weight/vol. percentage of organic water removal agent to solvent can be at least, equal to, or between any two of 1 wt./vol.%, 10 wt./vol.%, 15 wt./vol.%, 20 wt./vol.%, 30 wt./vol.%, and 50 wt./vol.%. In a preferred embodiment, 5 to 40 wt./vol.% or about 15 to 25 wt./vol.% or about 20 wt./vol% is used. The amount of a single water removal agent in the alcohol reaction mixture can range from 0 wt./vol.% to 20 wt./vol.%, or at least, equal to, or between any two of 0 wt./vol.%, 1 wt./vol.%, 2 wt./vol.%, 3 wt./vol.%, 4 wt./vol.%, 5 wt./vol.%, 6 wt./vol.%, 7 wt./vol.%, 8 wt./vol.%, 9 wt./vol.%, 10 wt./vol.%, 15 wt./vol.%, or 20 wt./vol.%. In a preferred embodiment, 1 to 20 wt./vol.% or about 2 to 20 wt./vol.% of a single water removal agent is used. 3. Alcohols

[0044] Alcohols may be purchased in various grades from commercial sources. Preferably the alcohol is devoid of, or includes a minimal amount, of water. Non-limiting examples of the alcohol that can be used in the process of the current invention to form a disubstituted oxalate can include methanol, ethanol, «-propanol, isopropanol, «-butanol, isobutanol, sec- butanol, fert-butanol, 1-pentanol, 2-pentanoi, 3-pentanol, 3 -methyl -1 -butanol, 2-methyl- 1- butanol, 2,2-dimethyi-l-propanol, 3 -methyl -2-butanol, 2-methyl -2-butanol, 1-hexanol, 2- hexanol, 3-hexanoi, 1-heptanol, 2-heptanol, 3-heptanol, 4-heptanol, 1-octanol, 2-octanol, 3- octanol, 4-octanol, cyclohexanol, cyclopentanol, phenol, benzyl alcohol, ethylene glycol, propylene glycol, or butylene glycol or any combination thereof. In certain embodiments, the alcohol includes a mixture of stereoisomers, such as enantiomers and diastereomers. Preferably, the alcohol is methanol, ethanol, «-propanol, isopropanol, «-butanol, isobutanol, sec-butanol, fert-butanol, 1-pentanol, 2,2-dimethyl- 1 -propanol (neopentanol), hexanol, or combinations thereof.

4. Gases

[0045] CO2 gas, CO gas, O2 gas, and H2 gas can be obtained from various sources. In one non-limiting instance, the CO2 can be obtained from a waste or recycle gas stream ( e.g ., from a plant on the same site such as from ammonia synthesis, or a reverse water gas shift reaction) and/or after recovering the carbon dioxide from a gas stream. A benefit of recycling carbon dioxide as a starting material in the process of the invention is that it can reduce the amount of carbon dioxide emitted to the atmosphere (e.g., from a chemical production site). The CO can be obtained from various sources, including streams coming from other chemical processes, like partial oxidation of carbon-containing compounds, iron smelting, photochemical process, syngas production, reforming reactions, and/or various forms of combustion. O2 can come from various sources, including streams from water-splitting reactions and/or cryogenic separation systems. The hydrogen may be from various sources, including streams coming from other chemical processes, like water splitting (e.g., photocatalysis, electrolysis, or the like), syngas production, ethane cracking, methanol synthesis, and/or conversion of methane to aromatics. In some embodiments, the gases are obtained from commercial gas suppliers. When a mixture of gases is used such as a mixture of CO2 and CO or H2, or CO and O2, the gas can be premixed or mixed when added separately to the reactor. When the reactor contains a mixture of CO2 and CO, the pressure ratio of C02:CO in the reactor can be greater than 0.1. In some embodiments, the C02:CO pressure ratio can be from 0.2: 1 to 5: 1, from 0.5: 1 to 2: 1, or 1 : 1 to 1.5: 1. Preferably, the CO2.CO pressure ratio is about 1.25. The partial pressure at room temperature ratio of C02:CO in the reactor can range from 40: 10 or from 45: 15. When the reactor contains a mixture of CO2 and H2, the pressure ratio of C02:H2 in the reactor can be greater than 0.1. In some embodiments, the C02:H2 ratio can be from 5: 1 to 80: 1, from 10: 1 to 60: 1, 20: 1 to 50: 1, or 30: 1 to 40: 1, or 35: 1. Preferably, the C02:H2 pressure ratio is about 35: 1. The partial pressure at room temperature of C02:H2 in the reactor can range from 4.5 MPa to 1 MPa, or from 1 MPa to 0.1 MPa. When the reactor contains a mixture of CO and O2, the pressure ratio of COO2 in the reactor can be greater than 0.1. In some embodiments, the COO2 pressure ratio can be from 5: 1 to 80: 1, from 10: 1 to 60: 1, 20: 1 to 50: 1, or 30: 1 to 40: 1, or 35: 1. In another example, cesium carbonate is contacted with CO and 02 to form cesium oxalate. The pressure ratio of CO and O2 to cesium carbonate can be 1 :0.5 to 3 : 1 and all ranges and values there between ( e.g ., 1 :0.5, 1 : 1.2, 1 : 1.3, 1 : 1.4, 1 : 1.5, 1 : 1.6, 1 : 1.7, 1 : 1.8, 1 : 1.9, 1 :2, 1 :2.1, 1 :2.2, 1 :2.3, 1 :2.4, 1 :2.5, 1 :2.6, 1 :2.6, 1 :2.7, 1 :2.8, or 1 :2.9) Preferably the ratio is 2: 1. In some examples, the remainder of the reactant gas can include another gas or gases provided the gas or gases are inert, such as argon (Ar) and/or nitrogen (N2), further provided that they do not negatively affect the reaction. Preferably, the reactant mixture is highly pure and substantially devoid of water. In some embodiments, the gases can be dried prior to use (e.g., pass through a drying media) or contain a minimal amount of water or no water at all. Water can be removed from the reactant gases with any suitable method known in the art (e.g., condensation, liquid/gas separation, etc.).

B. Disubstituted Oxalates and Disubstituted Carbonates

[0046] The produced cesium oxalate product from Section A can then be reacted with the desired alcohol in the presence of the water removal agent (WRA) and carbon dioxide (e.g, a CO2 atmosphere), to produce the desired disubstituted oxalate. In some instances, the produced cesium oxalate product is first purified before being converted to a disubstituted oxalate. Such purification can help with reducing or avoiding the formation of undesired by-products during disubstituted oxalate production. Reaction equations (7) through (9) show the overall reaction starting with cesium salt under a conventional CO/CO2 atmosphere (reaction equation (7)), and the alternative processes using H2/CO2 (reaction equation (8)), or CO/O2 (reaction equation (9)). Reaction conditions are described in more detail below and in the Examples Section. As shown, reactions (7)-(9) the optional inert material is not shown.

( )

Without wishing to be bound by theory, it is believed that the conversion of cesium oxalate to disubstituted oxalates ( e.g ., dimethyl oxalate (DMO)) is endothermic with an overall calculated free energy (DFT) change of about 91 kcal/mol. For example, FIG. 3 shows Cs2C20₄to DMO transformation energies. Thus, the exothermic formation of cesium oxalate from cesium carbon monoxide and oxygen can provide energy for this step, thereby requiring less overall energy (e.g., heat input).

[0047] In some embodiments, the WRA is not used and disubstituted carbonates are formed. Reaction schemes (10) through (12) show the formation of a dicarbonate in the presence water and the absence of the WRA.

o

CsX + CO + o₂ Cs₂(C₂0₄) co_2, H₂o

L + 2CSHC0₃

R³OH, R⁴OH R³O OR

(12)

In reaction equations (7) through (12), R¹, R², R³, and R⁴ are each independently alkyl group, a substituted alkyl group, an aromatic group, a substituted aromatic group, or a combination thereof. In a preferred embodiment, the alcohol is methanol and the oxalate dimethyl oxalate and the carbonate is dimethyl carbonate. In particular instances, R¹, R², R³, and R⁴ can include 1 to 20 carbon atoms, 1 to 10 carbon atoms, 1 to 5 carbon atoms, or 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20 carbon atoms, preferably 1 carbon atom. More specifically, R¹, R², R³, and R⁴ can each be a methyl group, an ethyl group, a propyl group, an isopropyl group, a «-butyl group, a sec-butyl group, a /e/7-butyl group, a pentyl group, a neopentyl, or a hexyl group, or combinations thereof. In some aspects, R¹ and R² are the same as R³ and R⁴.

C. Sustainability

[0048] Under certain conditions, cesium hydroxide (CsOH), unreacted cesium oxalate, and/or the cesium bicarbonate can be formed. These products can be separated or further processed. By way of example cesium hydroxide can be isolated and converted into cesium carbonate, thereby regenerating the cesium catalyst. At the molecular level this reaction is exothermic with a calculated free energy (DFT) change of about 35 kcal/mol. FIG. 4 shows CS2CO3 regeneration from CsOH transformation energies. The overall sustainable process is showed in the schematic below. As discussed above and throughout this specification, the combination of“reactant 1” and“reactant 2” in the schematic can be a combination of CO2 + CO, CO2 + H2, or CO + O2. Step 2 can include the WRA (not shown) if there is a desire to produce a disubstituted oxalate or a mixture of a disubstituted oxalate and a disubstituted carbonate. In the absence of the WRA, the disubstituted carbonate is primarily produced, although some disubstituted oxalate can also be produced.

D. System and Processes to Prepare Cesium Oxalate and Disubstituted Oxalate

1. Single Reactor

[0049] Any of the processes of the present invention can be performed in a single reactor or multiple reactors. Referring to FIG. 5, a method and system to prepare disubstituted oxalates is described using a single reactor. In system 100, cesium salt precursor ( e.g ., cesium carbonate (CS2CO3)) and optional inert material can be provided to a reactor unit 102 via solids inlet 104. CO, CO2, O2, or H2, or any combination thereof can be provided to reactor 102 via gas inlets 106 and 108. By way of example, CO2 can be provided to reactor 102 via gas inlet 108 and CO or H2, can be provided to the reactor via gas inlet 106. CO can be provided to reactor 102 via gas inlet 106 and O2 can be provided to the reactor via gas inlet 108. In embodiments when carbon monoxide is used, the CO can be provided to reactor 102 at a pressure ranging from 1 MPa to 3 MPa and all ranges and pressures there between ( e.g ., 1.1 MPa, 1.2 MPa, 1.3 MPa,

1.4 MPa, 1.5 MPa, 1.6 MPa, 1.7 MPa, 1.8 MPa, 1.9 MPa, 2 MPa, 2.1 MPa, 2.2 MPa, 2.3 MPa,

2.4 MPa, 2.5 MPa, 2.6 MPa, 2.7 MPa, 2.8 MPa, or 2.9 MPa). Preferably, the CO pressure is about 2 MPa. In other embodiments when H2 is used, the H2 can be provided to reactor 102 at a pressure ranging from 0.05 MPa to 0.5 MPa, 0.05 to 0.4 MPa, 0.05 to 0.3 MPa, 0.05 to 0.2 MPa, or 0.05 to 0.1 and all ranges and pressures there between (e.g., 0.05 MPa, 0.06 MPa, 0.07 MPa, 0.08 MPa, 0.09 MPa, 0.1 MPa, 0.11 MPa, 0.12 MPa, 0.13 MPa, 0.14 MPa, 0.15 MPa, 0.16 MPa, 0.17 MPa, 0.18 MPa, 0.19 MPa, 0.20 MPa, 0.21 MPa, 0.22 MPa, 0.23 MPa, 0.24 MPa, 0.25 MPa, 0.26 MPa, 0.27 MPa, 0.28 MPa, 0.29 MPa, 0.30 MPa, 0.31 MPa, 0.32 MPa, 0.33 MPa, 0.34 MPa, 0.35 MPa, 0.36 MPa, 0.37 MPa, 0.38 MPa, 0.39 MPa, 0.40 MPa, 0.41 MPa, 0.42 MPa, 0.43 MPa, 0.44 MPa, 0.45 MPa, 0.46 MPa, 0.47 MPa, 0.48 MPa, 0.49 MPa, or 0.50 MPa). Preferably, the H2 pressure is about 0.1 MPa. In other embodiments when O2 is used, the O2 can be provided to reactor 102 at a pressure ranging from 0.05 MPa to 4 MPa, 0.1 to 1.5 MPa, or about 0.1 MPa. CO2 can be provided to reactor 102 at a pressure ranging from 1 MPa to 4 MPa and all ranges and pressures there between (e.g, 1.1 MPa, 1.2 MPa, 1.3 MPa,

1.4 MPa, 1.5 MPa, 1.6 MPa, 1.7 MPa, 1.8 MPa, 1.9 MPa, 2 MPa, 2.1 MPa, 2.2 MPa, 2.3 MPa,

2.4 MPa, 2.5 MPa, 2.6 MPa, 2.7 MPa, 2.8 MPa, 2.9 MPa, 3.0 MPa, 3.1 MPa, 3.2 MPa, 3.3 MPa, 3.4 MPa, 3.5 MPa, 3.6 MPa, 3.7 MPa, 3.8 MPa, 3.9 MPa, or 4 MPa). Preferably, the CO2 pressure is about 2.5 MPa to 3.5 MPa. The upper limit on pressure can be determined by the type and size of reactor used. Although not shown, in some embodiments, CO2 CO, O2, or H2, and can be provided to reactor unit 102 via the same inlet. In certain embodiments, mixtures of CO2, CO, O2, and H2 are used. By way of example, CO2 can be used with CO, CO2 can be used with H2, CO, or CO and H2, and CO can be used with O2. Reactor 102 can be pressurized either through the addition of the gases and/or with an inert gas. The average pressure of reactor unit 102 ranges from 2.0 to 4 MPa (e.g, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9 MPa) after charging the CO2. Reactor 102 can be heated to a temperature sufficient to promote the reaction of cesium carbonate with the carbon dioxide and carbon monoxide or H2 to produce a product composition that includes cesium oxalate. The temperature range of the reactor 102 can be 200 °C to 400 °C, 250 °C to 350 °C, and all ranges and temperatures there between ( e.g ., 205 °C, 210 °C, 215 °C, 220 °C,

225 °C, 230 °C, 235 °C, 240 °C, 245 °C, 250 °C, 255 °C, 260 °C, 265 °C, 270 °C, 275 °C,

280 °C, 285 °C, 290 °C, 295 °C, 300 °C, 305 °C, 310 °C, 315 °C, 320 °C, 325 °C, 330 °C,

335 °C, 340 °C, 345 °C, 350 °C, 355 °C, 360 °C, 365 °C, 370 °C, 375 °C, 380 °C, 385 °C,

390 °C, or 395 °C). Preferably, the reaction temperature is 290 °C to 335 °C, or most preferably 300 °C to 325 °C. The reactants can be heated for a time sufficient to react all or a substantially all of the cesium carbonate. By way of example, the reaction time range can be at least 1 hour, 1 to 5 hours, 1 hours to 4 hours, 1 hour to 3 hours, and all ranges and times there between (e.g., 1.25 hours, 1.5 hours, 1.75 hours, 2 hour, 2.25 hours, 2.5 hours, 2.75 hours, 3 hours, 3.25 hours, 3.5 hours, 3.75 hours, 4 hours, 4.25 hours, 4.5 hours, 4.75 hours, 5 hours). When CO is used, the reaction time can be about 2 hours. When Th is used, the cesium carbonate can be reacted with the carbon dioxide for 1 to 3 hours, (e.g, 1, 1.5, 2, 2.5, 3 hours), and then with Th for an additional 1 to 3 hours, (e.g, 1, 1.5, 2, 2.5, 3 hours). In some embodiments, the oxalate salt (e.g, cesium oxalate) is made by reaction oxalic acid with a metal hydroxide as described above in Section A(l) to produce the oxalate salt.

[0050] The desired alcohol and the water removal agent can be added to reactor 102. In embodiments when the oxalate salt is made from a carbonate, reactor 102 can be cooled and/or depressurized. By way of example, reactor 102 can be cooled to a temperature range of 50 °C to 160 °C, or 130 °C to 150 °C, or about 130 °C at a pressure of 0.101 MPa to 1 MPa. In embodiments, when the oxalate salt is made from an acid-base reaction, reactor 102 is at a desired temperature or can be heated to above 5 °C. In some embodiments, commercially available oxalate salt is added to reactor 102. The desired alcohol (e.g, methanol) can be added to reactor 102 via liquid inlet 110 to form a composition that includes a cesium salt (e.g, cesium oxalate, and optionally, cesium carbonate and/or cesium bicarbonate), an alcohol, carbon dioxide, and, optionally, carbon monoxide. The reactor can be pressurized with carbon dioxide and/or an inert gas to a pressure ranging from 2 MPa to 5 MPa, 3 MPa to 4 MPa, and all ranges and pressures there between (e.g, 2.1 MPa, 2.2 MPa, 2.3 MPa, 2.4 MPa, 2.5 MPa, 2.6 MPa,

2.7 MPa, 2.8 MPa, 2.9 MPa, 3 MPa, 3.1 MPa, 3.2 MPa, 3.3 MPa, 3.4 MPa, 3.5 MPa, 3.6 MPa,

3.7 MPa, 3.8 MPa, 3.9 MPa, 4.0 MPa, 4.1 MPa, 4.2 MPa, 4.3 MPa, 4.4 MPa, 4.5 MPa, 4.6 MPa, 4.7 MPa, 4.8 MPa, or 4.9 MPa). In some embodiments, carbon dioxide is present in sufficient amounts that additional CO2 is not necessary. [0051] After the addition of the alcohol, water removal agent, and, optionally CO2, the reactor can be heated to a reaction temperature sufficient to promote the cesium oxalate salt to react with the alcohol under the carbon dioxide atmosphere to produce a disubstituted oxalate containing composition. In other embodiments, sufficient carbon dioxide remains in reactor 102. The reaction temperature can be 115 °C to 200 °C, 130 °C to 180 °C, or at least, equal to, or between any two of 115 °C, 120 °C, 125 °C, 130 °C, 135 °C, 140 °C, 145 °C, 150 °C, 155 °C, 160 °C, 165 °C, 170 °C, 175 °C, 180 °C, 185 °C, 190 °C, 195 °C and 200 °C. Preferably, the reaction temperature is about 130 °C. Reactor 102 can be heated for a time sufficient to react all or substantially all of the cesium salt ( e.g ., cesium oxalate). By way of example, the reaction time range can be at least 1 hour, 1 hours to 18 hours, 10 hour to 14 hours, 1 to 6 hours or 1 to 2 hours, and all ranges and times there between (e.g., 2 hours, 5 hours, 8 hours, 10 hours, 15 hours, or 17 hours). Preferably, the reaction time is 1 to 18 hours, or 15 hours. The upper limit on temperature, pressure, and/or time can be determined by the reactor used. The reaction temperature can be varied depending on the type of catalyst used. In some embodiments, when gamma alumina and cesium bicarbonate is used to form the cesium intermediate, the subsequent carbonate reaction temperature can be 215 to 225 °C or about 220 °C. When gamma alumina and cesium carbonate is used to form the cesium intermediate, the subsequent dicarbonate reaction temperature can be 220 to 230 °C or about 325 °C. The disubstituted oxalate reaction conditions can be further varied based on the type of the reactor used.

[0052] Reactor 102 can be cooled and depressurized to a temperature and pressure sufficient (e.g, below 50 °C at 0.101 MPa) to allow removal of the product composition containing disubstituted oxalate via product outlet 112. The product composition can be collected for further use. In some instances, the product composition can include cesium bicarbonate (CsHCCb).

2. Two Reactors

[0053] Reactor 102 can be depressurized and cooled to a temperature sufficient to crystallize the cesium oxalate or allow handling of the cesium oxalate containing product composition. The cesium oxalate containing product composition can be removed from the reactor via product outlet 112. The product composition can be further treated (e.g, washed) to remove any unreacted products. In one embodiment, the product composition is used without purification. The cesium oxalate can then be transferred to a second reactor unit to produce disubstituted oxalates. Referring to FIG. 6, a schematic of system 200 having two reactor units is depicted. The cesium salt precursor ( e.g ., cesium carbonate) can be provided to reactor 102 via inlet 104 and contacted with carbon dioxide in combination with carbon monoxide and/or H₂ or the combination of carbon monoxide and oxygen as described above (See, FIG. 1) to generate the cesium oxalate.

[0054] The cesium oxalate can exit reactor 102 via product outlet 112 and enter reactor 202 via cesium oxalate inlet 204. The desired alcohol and water removal agent can be provided to reactor 202 via alcohol inlet 206. Carbon dioxide can be provided to reactor 202 via carbon dioxide inlet 208. Reactor 202 can be pressurized to a pressure of 2.0 to 5 MPa (e.g., 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0 MPa) either by the addition of the carbon dioxide or using an inert gas. Once reactor 202 has been pressurized, heat can be applied to the reactor using known methods (e.g, electrical heaters, heat transfer medium, or the like) to a temperature sufficient to promote the reaction of cesium oxalate and the alcohol. The reaction temperature can be 115 °C to 200 °C, 130 °C to 180 °C, or at least, equal to, or between any two of 115 °C, 120 °C, 125 °C, 130 °C, 135 °C, 140 °C, 145 °C, 150 °C, 155 °C, 160 °C, 165 °C, 170 °C, 175 °C, 180 °C, 185 °C, 190 °C, 195 °C and 200 °C. Preferably, the reaction temperature is about 130 °C. Reactor 202 can be heated for a time sufficient to react all or substantially all of the cesium salt (e.g, cesium oxalate). By way of example, the reaction time range can be at least 1 hour, or 1 to 18 hours, 1 hour to 16 hours, 10 hour to 14 hours, and all ranges and times there between as previously described. Preferably, the reaction time is about 1 hour to 18 hours, or about 15 hours. The upper limit on temperature, pressure, and/or time can be determined by the reactor used. The disubstituted oxalate reaction conditions may be further varied based on the type of the reactor used.

[0055] Reactor 202 can be cooled and depressurized to a temperature and pressure sufficient (e.g, below 50 °C at 0.101 MPa) to allow removal of the product composition containing disubstituted oxalate and/or disubstituted carbonate via product outlet 210. The product composition can be collected for further use or sale.

[0056] Reactors 102 and 202 and associated equipment (e.g, piping) can be made of materials that are corrosion and/or oxidation resistant. By way of example, the reactor can be lined with, or made from, Inconel. The design and size of the reactor is sufficient to withstand the temperatures and pressures of the reaction. The systems can include various automated and/or manual controllers, valves, heat exchangers, gauges, etc., for the operation of the reactor, inlets, and outlets. The reactor can have insulation and/or heat exchangers to heat or cool the reactor as desired. Non-limiting examples of a heating/cooling source can be a temperature controlled furnace or an external, electrical heating block, heating coils, or a heat exchanger. The reaction can be performed under inert conditions such that the concentration of oxygen (O2) gas in the reaction is low or virtually absent in the reaction such that O2 has a negligible effect on reaction performance (i.e., conversion, yield, efficiency, etc.).

E. System and Processes to Prepare Cesium Oxalate and Disubstituted Carbonates

1. Single Reactor

[0057] Any of the processes of the present invention can be performed in a single reactor. Referring to FIG. 5, a method and system to prepare disubstituted carbonates using the processes described in Section D above for disubstituted oxalates. The preparation of the oxalate salt is performed in the same manner as described in section D.

[0058] Reactor 102 can be cooled and/or depressurized to a temperature and pressure sufficient to add the desired alcohol. By way of example, reactor 102 can be cooled to a temperature range of 50 °C to 160 °C, or 130 °C to 150 °C, or about 120 °C at a pressure of 0.101 MPa to 1 MPa. In some embodiments, the reactor is depressurized, but not cooled. The desired alcohol ( e.g ., methanol) can be added to reactor 102 via liquid inlet 110 to form a composition that includes a cesium salt (e.g., cesium oxalate, and optionally, cesium carbonate and/or cesium bicarbonate) or cesium salt/inert material, an alcohol, carbon dioxide, and, optionally, carbon monoxide. The reactor can be pressurized with carbon dioxide and/or an inert gas to a pressure ranging from 2 MPa to 5 MPa, 3 MPa to 4 MPa, and all ranges and pressures there between (e.g, 2.1 MPa, 2.2 MPa, 2.3 MPa, 2.4 MPa, 2.5 MPa, 2.6 MPa, 2.7 MPa, 2.8 MPa, 2.9 MPa, 3 MPa, 3.1 MPa, 3.2 MPa, 3.3 MPa, 3.4 MPa, 3.5 MPa, 3.6 MPa, 3.7 MPa, 3.8 MPa, 3.9 MPa, 4.0 MPa, 4.1 MPa, 4.2 MPa, 4.3 MPa, 4.4 MPa, 4.5 MPa, 4.6 MPa, 4.7 MPa, 4.8 MPa, or 4.9 MPa). In some embodiments, carbon dioxide is present in sufficient amounts that additional CO2 is not necessary.

[0059] After the addition of the alcohol, and, optionally, CO2, the reactor mixture can be heated to a reaction temperature sufficient to promote the cesium oxalate salt to react with the alcohol under the carbon dioxide atmosphere to produce a disubstituted oxalate containing composition. In other embodiments, sufficient carbon dioxide remains in reactor 102. The reaction temperature can be can be 115 °C to 200 °C, 130 °C to 180 °C, or at least, equal to, or between any two of l l5 °C, 120 °C, 125 °C, 130 °C, 135 °C, 140 °C, 145 °C, 150 °C, 155 °C, 160 °C, 165 °C, 170 °C, 175 °C, 180 °C, 185 °C, 190 °C, 195 °C and 200 °C. Preferably, the reaction temperature is about 130 °C. The reaction temperature can be varied depending on the type of catalyst used. In some embodiments, when gamma alumina and cesium bicarbonate is used to form the cesium intermediate, the subsequent carbonate reaction temperature can be 215 to 225 °C or about 220 °C. When gamma alumina and cesium carbonate is used to form the cesium intermediate, the subsequent dicarbonate reaction temperature can be 220 to 230 °C or about 325 °C. Reactor 102 can be heated for a time sufficient to react all or substantially all of the cesium salt ( e.g ., cesium oxalate). By way of example, the reaction time range can be less than 1 hour, 1 hours to 18 hours, 10 hour to 14 hours, 1 to 6 hours or 1 to 2 hours, and all ranges and times there between (e.g., 2 hours, 5 hours, 10 hours, 12 hours, 15 hours, or 17 hours). Preferably, the reaction time is 1 to 18 hours, or 15 hours. The upper limit on temperature, pressure, and/or time can be determined by the reactor used. The disubstituted carbonate reaction conditions can be further varied based on the type of the reactor used.

[0060] Reactor 102 can be cooled and depressurized to a temperature and pressure sufficient (e.g, below 50 °C at 0.101 MPa) to allow removal of the product composition containing disubstituted carbonate via product outlet 112. In some instances, disubstituted oxalate(s) can also be produced in relatively small amounts (e.g, 10 mol. % or less of the product stream can include disubstituted oxalate(s)). The product composition can be collected for further use. In some instances, the product composition can include cesium bicarbonate (CsHCCb), cesium carbonate, or mixtures thereof.

2. Two Reactors

[0061] Reactor 102 can be depressurized and cooled to a temperature sufficient to crystallize the cesium oxalate or allow handling of the cesium oxalate containing product composition. The cesium oxalate containing product composition can be removed from the reactor via product outlet 112. The product composition can be further treated (e.g, washed) to remove any unreacted products. In one embodiment, the product composition is used without purification. The cesium oxalate can then be transferred to a second reactor unit to produce disubstituted carbonates. Referring to FIG. 6, a schematic of system 200 having two reactor units is depicted. The cesium salt precursor (e.g, cesium carbonate) can be provided to reactor 102 via inlet 104 and contacted with CO2 in combination with CO, CO2 in combination with Fh, or CO in combination with O2 as described above (See, FIG. 1) to generate the cesium oxalate.

[0062] The cesium oxalate can exit reactor 102 via product outlet 112 and enter reactor 202 via cesium oxalate inlet 204. The desired alcohol can be provided to reactor 202 via alcohol inlet 206. Carbon dioxide can be provided to reactor 208 via carbon dioxide inlet 208. Reactor 202 can be pressurized to a pressure of 2.0 to 5 MPa ( e.g ., 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0 MPa) either by the addition of the carbon dioxide or using an inert gas. Once reactor 202 has been pressurized, heat can be applied to the reactor using known methods (e.g., electrical heaters, heat transfer medium, or the like) to a temperature sufficient to promote the reaction of cesium oxalate and the alcohol. The reaction temperature can be 125 °C to 350 °C, 130 °C to 325 °C, and all ranges and temperatures there between (e.g, 130 °C, 135 °C, 140 °C, 145 °C, 150 °C, 155 °C, 160 °C, 165 °C, 170 °C, 175 °C, 180 °C, 185 °C, 190 °C, or 195 °C). Preferably, the reaction temperature is about 150 °C. Reactor 202 can be heated for a time sufficient to react all or substantially all of the cesium salt (e.g, cesium oxalate). By way of example, the reaction time range can be at least 1 hour, or 1 to 18 hours, 1 hour to 16 hours, 10 hour to 14 hours, and all ranges and times there between as previously described. Preferably, the reaction time is about 1 hour to 18 hours, or 15 hours. The upper limit on temperature, pressure, and/or time can be determined by the reactor used. The disubstituted carbonate reaction conditions may be further varied based on the type of the reactor used.

[0063] Reactor 202 can be cooled and depressurized to a temperature and pressure sufficient (e.g, below 50 °C at 0.101 MPa) to allow removal of the product composition containing disubstituted carbonate (e.g, DMC) via product outlet 210. In some instances, disubstituted oxalate(s) can also be produced in relatively small amounts (e.g, 10 mol. % or less of the product stream can include disubstituted oxalate(s)). The product composition can be collected for further use or commercial sale.

E. Reactants and Products

[0064] The process of the present invention can produce a product stream that includes a composition containing a disubstituted oxalate, a disubstituted carbonate, or a mixture thereof, and optionally cesium bicarbonate (CSHCO3) that can be suitable as an intermediate or as feed material in a subsequent synthesis reactions to form a chemical product or a plurality of chemical products (e.g., such as in pharmaceutical products, for the production of oxalic acid and ethylene glycol, or as a solvent or plasticizer). In some instances, the composition containing a disubstituted oxalate and/or a disubstituted carbonate can be directly reacted under conditions sufficient to form oxalic acid or ethylene glycol. The product composition includes at least 50 wt.%, at least 60 wt.%, at least 70 wt.%, at least 80 wt.%, at least 90 wt.% or 100 wt.% disubstituted oxalate, with the balance being cesium bicarbonate. The product composition can be purified using known organic purification methods (e.g, extraction, crystallization, distillation washing, etc) depending on the phase of the production composition (e.g, solid or liquid). In a preferred embodiment, the disubstituted oxalate can be recrystallized from hot alcohol (e.g, methanol) solution. DMO can be purified by distillation (boiling point of 166 °C) or crystallization (melting point 54 °C).

[0065] The disubstituted oxalate produced by the process of the present invention can have the general structure of:

where R¹ and R² can be each independently alkyl group, a substituted alkyl group, an aromatic group, a substituted aromatic group, or a combination thereof. R¹ and R² can include 1 to 20 carbon atoms, 1 to 10 carbon atoms, 1 to 5 carbon atoms, preferably 1 carbon atom. Non limiting examples of R¹ and R² include methyl, ethyl, «-propyl, isopropyl, «-butyl, isobutyl, sec-butyl, tert-hutyl, 1 -pentyl, 2-pentyl, 3 -pentyl, 3 -methyl- 1 -butyl, 2-methyl- 1 -butyl, 2,2- dimethyl- 1 -propyl, 3-methyl-2-butyl, 2-methyl-2-butyl, 1-hexyl, 2-hexyl, 3-hexyl, 1-heptyl, 2- heptyl, 3-heptyl, 4-heptyl, 1-octyl, 2-octyl, 3-octyl, 4-octyl, cyclohexyl, cyclopentyl, phenyl, or benzyl. Preferably, R¹ and R² are a methyl group, an ethyl group, a propyl group, an isopropyl group, a «-butyl group, a sec-butyl group, a /er/-butyl group, a pentyl group, a neopentyl, a hexyl group, or combinations thereof. In certain embodiments, R¹ and R² can include a mixture of stereoisomers, such as enantiomers and diastereomers. In a specific embodiment, the disubstituted oxalate is a dialkyl oxalate, such as dimethyl oxalate (DMO) where R¹ and R² are each methyl groups.

[0066] The dicarbonate of the present invention can have the general structure of:

where R³ and R⁴ are each independently alkyl group, a substituted alkyl group, an aromatic group, a substituted aromatic group, or a combination thereof. In a preferred embodiment, the alcohol is methanol and the carbonate is dimethyl carbonate. In particular instances, R³ and R⁴ can include 1 to 20 carbon atoms, 1 to 10 carbon atoms, 1 to 5 carbon atoms, preferably 1 carbon atom. More specifically, R³ and R⁴ can be a methyl group, an ethyl group, a propyl group, an isopropyl group, a «-butyl group, a sec-butyl group, a /e/7-butyl group, a pentyl group, a neopentyl, or a hexyl group, or combinations thereof. In some aspects of the current invention, R³ and R⁴ are each methyl groups. In some aspects, the carbonate is obtained from the DMO so R³ and R⁴ are the same as R¹ and R².

EXAMPLES

[0067] The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters, which can be changed or modified to yield essentially the same results.

[0068] Cesium carbonate (CS2CO3) was obtained from SigmaMillipore (U.S.A) in powder form and 99.9% purity. Cesium oxalate was prepared by the below method or obtained from SigmaMillipore (U.S.A.) and used as such. Methanol was obtained from Fisher Scientific (HPLC grade, U.S.A.) in 99.99% purity. ¹³C NMR was performed on a 400 MHz Bruker instrument (Bruker, U.S.A). The Parr reactor used was obtained from Parr Instrument Company, USA. Identification and quantitative analysis of reaction products were carried out by a GC-MS spectrometer of Agilent (U.S.A.) 7890 C -5977D MSD and a gas chromatograph equipped with a flame detector (FID). A CP-Sil 5CB CAPILLARY column was used to separate products for GC.

Example 1A

(Preparation of Cesium Oxalate)

[0069] CS2CO3 (500 mg, 0.15 mmol) was added to a 100 mL Parr reactor in a glove box. CO2 (25 bar) and CO (20 bar) gases were then charged and the mixture was stirred for 1-2 hour at 300 °C and cooled to room temperature by circulating air around the reactor. The reactor was depressurized. The product obtained was a solid and a portion was removed from the reactor as a soft (molten) solid. ¹³C NMR analysis was performed on the salt, and confirmed that the salt was primarily cesium oxalate.

Example IB

(Preparation of Cesium Oxalate)

[0070] Oxalic acid dihydrate (4.32 g) was dissolved in water (100 mL). To the acidic solution cesium hydroxide monohydrate (11.52 g) was added slowly ( e.g dropwise) to control the temperature of the acid base reaction. After the completion of the neutralization, the reaction solution was placed in a rotary evaporator to remove the water and collect the product, cesium oxalate. The cesium oxalate was then filtered and washed thoroughly with ethanol.

Example 2

(Preparation of DMO using Molecular Sieves and 1,4-Benzoquinone)

[0071] Equimolar amount of cesium oxalate (0.250 g, 0.00112 mole) from Example 1 A or 1B and methanol (20 mL) was added into the reactor vessel. Molecular sieves (4 A, 0.6 g) and l,4-benzoquinone (0.6 g), which acted as water removal agents, were added to the reactor. The reaction vessel was then tightly closed and pressurized with carbon dioxide (4.5 MPa (45 bar)). The vessel was heated up to 130 °C and stabilized at that temperature for two hours with stirring. The reactor was cooled down to room temperature after the end of the reaction. A small sample of the product is been taken out and was analyzed by GC. The product is confirmed to be DMO.

Example 3

(Preparation of DMO using Molecular Sieves)

[0072] Equimolar amount of cesium oxalate (0.250 g, 0.00112 mole) from Example 1 and methanol (20 mL) was added into the reactor vessel. Molecular sieves (4 A, 0.6 g), which acted as water removal agents, were added to the reactor. The reaction vessel was then tightly closed and pressurized with carbon dioxide (4.5 MPa (45 bar)). The vessel was heated up to 130 °C and stabilized at that temperature for two hours with stirring. The reactor was cooled down to room temperature after the end of the reaction. A small sample of the product is been taken out and was analyzed by GC. The product is confirmed to be DMO.

Example 4

(Preparation of Dimethyl Oxalate with 1,4-Benzoquinone)

[0073] Equimolar amount of cesium oxalate (0.250 g, 0.00112 mole) from Example 1 A or 1B and methanol (20 mL) was added into the reactor vessel. l,4-Benzoquinone (0.6 g), which acted as a water removal agent, was added to the reactor. The reaction vessel was then tightly closed and pressurized with carbon dioxide (4.5 MPa (45 bar)). The vessel was heated up to 130 °C and stabilized at that temperature for two hours with stirring. The reactor was cooled down to room temperature after the end of the reaction. A small sample of the product is been taken out and was analyzed by GC. The product is confirmed to be DMO. Example 5

(Preparation of Dimethyl Carbonate)

[0074] Cesium oxalate (0.250 g, 0.00112 mole, Example 1 A or 1B) and methanol (20 mL) in the molar ratio of 1: 1, was added into the reactor vessel. The reaction vessel was tightly closed and pressurized with carbon dioxide (4.5 MPa (45 bar)). The vessel was heated up to 130 °C and stabilized at that temperature for two hours with stirring. The reactor was cooled down to room temperature after the end of the reaction. A small sample of the product is been taken out and is analyzed by GC and NMR. The product is confirmed to be DMC.

Claims

A process for producing a disubstituted oxalate, the process comprising contacting an oxalate salt with an alcohol in the presence of a water removal agent and carbon dioxide under reaction conditions sufficient to produce a composition comprising a disubstituted oxalate having the general structure of:

where Ri and R2 are each independently alkyl group, a substituted alkyl group, an aromatic group, a substituted aromatic group, or a combination thereof.

2 The process of claim 1, wherein contacting is performed under a carbon dioxide (CO2) atmosphere.

3. The process of claim 1, wherein the water removal agent is an inorganic compound, an organic compound, or both.

4. The process of claim 3, wherein the inorganic compound is a molecular sieve, preferably a 4 angstrom (A) molecular sieve.

5. The process of any one of claims 3 to 4, wherein the organic compound is a quinone.

6 The process of claim 5, wherein the quinone is benzoquinone, hydroquinone, naphthoquinone, anthraquinone, or mixtures thereof.

7. The process of any one of claims 1 to 6, wherein the water removal agent is a quinone compound and a 4 A molecular sieve.

8 The process of any one of claims 1 to 7, wherein the total weight percentage of water removal agent to volume percentage of solvent is 1 to 50 wt./vol.%, preferably 20 wt./vol.%.

9. The process of any one of claims 1 to 8, wherein the reaction conditions comprise a temperature of 115 °C to 200 °C, 120 °C to 150 °C, or preferably about 130 °C, a pressure of 2 MPa to 5 MPa, 3 MPa to 4 MPa, or preferably about 3.5 MPa, or both.

10 The process of any one of claims 1 to 9, wherein the oxalate salt is cesium oxalate (CS2C2O4).

1 1 The process of claim 10, wherein the reaction conditions for obtaining the cesium oxalate comprise a temperature of 200 °C to 400 °C, 250 °C to 350 °C, preferably 290 °C to 335 °C, or most preferably 300 °C to 325 °C, a pressure of 2.0 MPa to 3.0 MPa, preferably about 2.5 MPa, and providing carbon monoxide at a pressure of 1.0 MPa to 3 MPa, preferably about 2.0 MPa, or both.

12 The process of any one of claims 10 to 11, wherein the mixture further comprises a metal oxide, an aluminate, a zeolite, or a mixture thereof, preferably a metal oxide, more preferably gamma alumina.

13. The process of any one of claims 1 to 12, wherein Ri and R2 comprise 1 to 20 carbon atoms, 1 to 10 carbon atoms, 1 to 5 carbon atoms, preferably 1 carbon atom.

14. The process of claim 13, wherein Ri and R2 are a methyl group, an ethyl group, a propyl group, an isopropyl group, a «-butyl group, a sec-butyl group, a /e/7-butyl group, a pentyl group, a neopentyl, or a hexyl group, or combinations thereof.

15. The process of claim 14, wherein Ri and R2 are each methyl groups.

16. The process of any one of claims 1 to 15, further comprising adjusting the amount of water removal agent such that the product stream further comprises disubstituted carbonate, preferably dimethyl carbonate.

17. A process for producing dimethyl carbonate, the process comprising contacting an oxalate salt in the presence of an alcohol under a carbon dioxide atmosphere under reaction conditions sufficient to produce a composition comprising a dicarbonate having the general structure of:

where Ri and R2 are each independently alkyl group, a substituted alkyl group, an aromatic group, a substituted aromatic group, or a combination thereof.

18. The process of claim 17, wherein the alcohol is methanol and the carbonate is dimethyl carbonate.

19. The process of claim 18, wherein the oxalate salt is cesium oxalate.

0 The process of any one of claims 17 to 19, reaction conditions comprise a temperature of 115 °C to 200 °C, 120 °C to 150 °C, or preferably about 130 °C, a pressure of 2 MPa to 5 MPa, 3 MPa to 4 MPa, or preferably about 3.5 MPa, or both.