Patent Publication Number: US-2021171431-A1

Title: Conversion of cesium carbonate to cesium oxalate

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority of U.S. Provisional Patent Application No. 62/451,985 filed Jan. 30, 2017, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     A. Field of the Invention 
     The invention generally concerns a process for preparing cesium oxalate (Cs 2 C 2 O 4 ). In particular, the process includes contacting cesium carbonate (Cs 2 CO 3 ) with a mixture of carbon dioxide (CO 2 ) and hydrogen (H 2 ), or carbon monoxide (CO) and oxygen (O 2 ) under reaction conditions sufficient to produce Cs 2 C 2 O 4 . The produced Cs 2 C 2 O 4  can then be converted into dimethyl oxalate (DMO), oxalic acids, oxamides, or ethylene glycol. 
     B. Description of Related Art 
     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. These types of processes need relatively large amounts of carbon monoxide as a feedstock. Carbon monoxide is generally 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. 
     SUMMARY OF THE INVENTION 
     A discovery has been made that provides alternate feedstocks for the production of disubstituted oxalates (e.g., DMO). The discovery is premised on selectively converting Cs 2 CO 3  to Cs 2 C 2 O 4  via feed stock mixtures that can include a combination of CO 2  and H 2 , or CO and O 2 . The produced Cs 2 C 2 O 4  can then be selectively converted to DMO when contacted with a methanol (CH 3 OH) and CO 2 . At least three of the following benefits can be obtained by this synthesis process: (1) the reliance on CO as a feed stock to produce DMO can be reduced or avoided all together; (2) the overall production of DMO from Cs 2 CO 3  can be performed in a step-wise manner or in a single-pot fashion where Cs 2 C 2 O 4  is generated in situ and then converted to DMO; and/or (3) the use of expensive noble metal catalysts such as palladium-based catalysts can be reduced or avoided all together. 
     In one aspect of the present invention, there is disclosed a process for preparing cesium oxalate (Cs 2 C 2 O 4 ). The process can include contacting CO 2  and hydrogen (H 2 ) with Cs 2 CO 3  under reaction conditions sufficient to form a composition comprising Cs 2 C 2 O 4 . In yet another embodiment, the process can include contacting CO and O 2  with Cs 2 CO 3  under reaction conditions sufficient to form a composition comprising Cs 2 C 2 O 4 . In still another embodiment, the process can include contacting CO 2  and H 2  with Cs 2 CO 3  under reaction conditions sufficient to form a composition comprising Cs 2 C 2 O 4 . The reaction conditions for each embodiment can include temperature and/or pressure. The reaction temperature can be 250° C. to 400° C., preferably 300° C. to 375° C., more preferably 310° C. to 335° C., or most preferably 320° C. to 330° C. The reaction pressure can be 1 MPa to 6 MPa, preferably 2 MPa to 5 MPa, or more preferably 3 MPa to 4 MPa. In certain instances, cesium bicarbonate (CsHCO 3 ) can also be formed along with Cs 2 C 2 O 4 . 
     In one particular instance, the process includes contacting CO 2  and H 2  with Cs 2 CO 3  under reaction conditions that include providing CO 2  at a pressure of 3.0 MPa to 4.0 MPa, preferably about 3.5 MPa, and H 2  at a pressure of 0.05 MPa to 0.5 MPa, preferably about 0.1 MPa, to produce Cs 2 C 2 O 4 . The mole ratio of CO 2  and H 2  to Cs 2 CO 3  can be 100:1 to 300:1, preferably about 150:1 to 25:1, or more preferably about 200:1. In a particularly preferred instance, a reaction mixture having a H 2  partial pressure 0.5 MPa of H 2  and CO 2  partial pressure of 3.5 MPa can be reacted with Cs 2 CO 3  to produce Cs 2 C 2 O 4 . In some instances, cesium formate (HCO 2 Cs) can also be formed during this process. In one aspect, the process can include first contacting CO 2  with Cs 2 CO 3  at a reaction temperature of 200° C. to 400° C., preferably 250° C. to 350° C., more preferably 290° C. to 335° C., or most preferably 300° C. to 325° C., for at least 1 hour to obtain a Cs 2 CO 3 /CO 2  reaction mixture, and then contacting the Cs 2 CO 3 /CO 2  reaction mixture with the H 2 /CO 2  mixture to produce Cs 2 C 2 O 4 ; this can reduce or inhibit HCO 2 Cs formation. 
     In another particular aspect, the process includes contacting CO and O 2  with Cs 2 CO 3  under reaction conditions comprising providing CO at a pressure of 2 MPa to 6 MPa, preferably about 4.5 MPa, and providing O 2  at a pressure of 0.05 MPa to 4 MPa, or about 0.05, or 1.5 MPa. The mole ratio of CO and O 2  to Cs 2 CO 3  is 1:1 to 3:1 or preferably about 2:1. 
     The produced product stream or composition that includes the Cs 2 C 2 O 4  can be stored for later use in producing a disubstituted oxalate, an oxalic acid, or ethylene glycol. In some instances, the Cs 2 C 2 O 4  can be isolated/purified. In other instances, the produced Cs 2 C 2 O 4  can be directly converted into a disubstituted oxalate, an oxalic acid, or ethylene glycol in the same reaction procedure such as in a one-pot reaction scheme. The reaction conditions for converting the produced Cs 2 C 2 O 4  into a disubstituted oxalate can include contacting Cs 2 C 2 O 4  with one or more alcohols and additional CO 2  under conditions sufficient to produce a disubstituted oxalate, preferably, DMO. Such conditions can include: (a) a reaction temperature of 100° C. to 200° C., preferably 125° C. to 175° C., or more preferably about 150° C.; and/or (b) a pressure of 2 MPa to 5 MPa, preferably 3 MPa to 4 MPa, or more preferably about 3.5 MPa. In some aspect, the alcohol can be methanol, ethanol, propanol, etc. When DMO is produced, the preferred alcohol is methanol. The process of converting the Cs 2 C 2 O 4  into DMO can also result in the production of cesium hydroxide. The cesium hydroxide can be converted into Cs 2 CO 3 , which can be recycled with any one of the processes of the present invention to produce additional Cs 2 C 2 O 4 . 
     The following includes definitions of various terms and phrases used throughout this specification. 
     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, 1,1,3,3-tetramethylbutyl, nonyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, and/or eicosyl. 
     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. 
     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. 
     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. 
     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%. 
     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. 
     The term “substantially” and its variations are defined to include ranges within 10%, within 5%, within 1%, or within 0.5%. 
     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. 
     The term “effective,” as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result. 
     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.” 
     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. 
     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 Cs 2 C 2 O 4  by contacting Cs 2 CO 3  with (i) CO 2  and H 2  or (ii) CO and O 2 . In some particular instances of the present invention, the produced Cs 2 C 2 O 4  can then be converted to DMO in the presence of methanol. 
     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 
       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. 
         FIG. 1  is the CO to CO 2  transformation energies. 
         FIG. 2  is the Cs 2 CO 3  to Cs 2 C 2 O 4  transformation energies. 
         FIG. 3  is the Cs 2 C 2 O 4  to DMO transformation energies. 
         FIG. 4  is the Cs 2 CO 3  regeneration from CsOH transformation energies. 
         FIG. 5  is a schematic of a one reactor system to produce disubstituted oxalates of the present invention. 
         FIG. 6  is a schematic of a two reactor system to produce disubstituted oxalates of the present invention. 
     
    
    
     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. 
     DETAILED DESCRIPTION OF THE INVENTION 
     A discovery has been made that provides an elegant solution to the problem of diminishing feedstocks for the production of disubstituted oxalates such as dimethyl oxalate. The discovery is premised on selectively converting a cesium salt (e.g., Cs 2 CO 3 ) to Cs 2 C 2 O 4  via feed stock mixtures that can include a combination of CO 2  and H 2 , or CO and O 2 . The produced Cs 2 C 2 O 4  can then be selectively converted to a disubstituted oxalate (e.g., dimethyl oxalate) when contacted with one or more alcohols and CO 2  under appropriate reaction conditions. The following reaction equation (1) includes the overall general reaction: 
     
       
         
         
             
             
         
       
     
     where ROH can be the same or different alcohols and R 1  and R 2  are defined below. In a preferred embodiment, ROH is methanol and the disubstituted oxalate is dimethyl 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. Cesium Oxalate Production 
     Cesium oxalate production can be produced in the context of the present invention by contacting cesium carbonate with (i) CO 2  and H 2  or (ii) CO and O 2 . The cesiuim carbonate can be supported (e.g., alumina or silica support) or be used in an unsupported form (i.e., bulk catalyst). 
     In one embodiment of the present invention, cesium oxalate can be generated by reacting cesium carbonate with carbon dioxide and H 2  as shown in reaction equation (2) and as described in more detail below and in the Examples section. 
       Cs 2 CO 3 +H 2 +CO 2 →Cs 2 (C 2 O 4 )  (2).
 
     In some embodiments, the carbon dioxide and H 2  are added in a sequential manner as shown in reaction equation (3). The sequential addition of carbon dioxide and then hydrogen can inhibit or substantially inhibit the formation of cesium formate (HCO 2 Cs). Limiting the formation of cesium formate can limit the formation of alkyl formate in subsequent reactions with alcohols. In some instances, cesium formate is not formed in the production of cesium oxalate. 
     
       
         
         
             
             
         
       
     
     In yet another alternative process, the cesium oxalate can be generated by the reaction of cesium carbonate with carbon monoxide and O 2  as shown in reaction equation (4) as described in more detail below. 
       Cs 2 CO 3 +O 2 +CO→Cs 2 (C 2 O 4 )  (4).
 
     With respect to reaction equation (4), and without wishing to be bound by theory, it is believed that the use of molecular oxygen lowers the heat requirement as compared to the other processes as the reaction between CO and O 2  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 CO 2  can bind with cesium carbonate to form a CO 2 —Cs 2 CO 3  adduct, which has an enthalphy of fusion as at molecular level. This enthalpy of fusion can be compensated by the CO+0.5 O 2  to CO 2  energy of 122.8 kcal/mol. The remaining carbon monoxide can then transform CO 2 —Cs 2 CO 3  adduct into cesium oxalate.  FIG. 2  shows the overall Cs 2 CO 3  to Cs 2 C 2 O 4  transformation energies. Thus, overall reaction equation (4) is exothermic with a calculated free energy (DFT) change of −23.4 kcal/mol making the reaction favorable for low heating requirements. 
     B. Disubstituted Oxalate 
     The produced cesium oxalate product from Section A can then be reacted with a desired alcohol in the presence of carbon dioxide to produce a desired disubstituted oxalate. In some instances, the produced cesium oxalate product is first purified before being converted to a disubstituted oxalate. Such purification may help with reducing or avoiding the formation of undesired by-products during disubstituted oxalate production. Reaction equations (5) through (7) show the overall reaction starting with a cesium salt (CsX), preferably cesium carbonate. Reaction conditions are described in more detail below and in the Examples Section. 
     
       
         
         
             
             
         
       
     
     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 Cs 2 C 2 O 4  to DMO transformation energies. Thus, the exothermic formation of cesium oxalate from cesium carbon monoxide and oxygen illustrated in reaction equation (7) can provide energy for this step, thereby requiring less overall energy (e.g., heat input). 
     C. Sustainability 
     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 Cs 2 CO 3  regeneration from CsOH transformation energies. The overall process is shown in the schematic below. In the reactions, ROH can be any alcohol or a mixture of alcohols, preferably methanol. As discussed above and throughout this specification, the combination of “reactant 1” and “reactant 2” in the schematic can be a combination of CO 2 +H 2 , or CO+O 2 . 
     
       
         
         
             
             
         
       
     
     D. System and Processes to Prepare Cesium Oxalate and Disubstituted Oxalate 
     1. Single Reactor Preparation of Cesium Oxalate and Disubstituted Oxalate 
     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 oxalates is described. In system  100 , cesium salt precursor (e.g., cesium carbonate (Cs 2 CO 3 )) can be provided to a reactor unit  102  via solids inlet  104 . CO, CO 2 , O 2 , or H 2  or any combination thereof can be provided to reactor  102  via gas inlets  106  and  108 . By way of example, CO 2  can be provided to reactor  102  via gas inlet  106  and H 2  via gas inlet  108 . Even further, CO can be provided via gas inlet  106  and O 2  via gas inlet  108 . Alternatively, CO 2  and H 2 , or CO and O 2 , can be provided to the reactor  102  via gas inlet  106  as mixtures (e.g., a mixture of CO 2  and H 2  or a mixture of CO and O 2 ,). 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 H 2  is used, the H 2  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 H 2  pressure is about 0.1 MPa. In other embodiments when O 2  is used, the O 2  can be provided to reactor  102  at a pressure ranging from 0.05 MPa to 5 MPa, 0.1 to 1.5, or about 0.1 MPa. CO 2  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 CO 2  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, CO 2  CO, O 2 , or H 2 , and can be provided to reactor unit  102  via the same inlet. In certain embodiments, mixtures of CO 2 , CO, O 2 , and H 2  are used. 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  can range 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 CO 2 . Reactor  102  can be heated to a temperature sufficient to promote the reaction of cesium carbonate with CO 2  and H 2  or with CO and O 2  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., 201° C., 202° C., 203° C., 204° C., 205° C., 206° C., 207° C., 208° C., 209° C., 210° C., 211° C., 212° C., 213° C., 214° C., 215° C., 216° C., 217° C., 218° C., 219° C., 220° C., 221° C., 222° C., 223° C., 224° C., 225° C., 226° C., 227° C., 228° C., 229° C., 230° C., 231° C., 232° C., 233° C., 234° C., 235° C., 236° C., 237° C., 238° C., 239° C., 240° C., 241° C., 242° C., 243° C., 244° C., 245° C., 246° C., 247° C., 248° C., 249° C., 250° C., 251° C., 252° C., 253° C., 254° C., 255° C., 256° C., 257° C., 258° C., 259° C., 260° C., 261° C., 262° C., 263° C., 264° C., 265° C., 266° C., 267° C., 268° C., 269° C., 270° C., 271° C., 272° C., 273° C., 274° C., 275° C., 276° C., 277° C., 278° C., 279° C., 280° C., 281° C., 282° C., 283° C., 284° C., 285° C., 286° C., 287° C., 288° C., 290° C., 291° C., 292° C., 293° C., 294° C., 295° C., 296° C., 297° C., 298° C., 299° C., 300° C., 301° C., 302° C., 303° C., 304° C., 305° C., 306° C., 307° C., 308° C., 309° C., 310° C., 311° C., 312° C., 313° C., 314° C., 315° C., 316° C., 317° C., 318° C., 319° C., 320° C., 321° C., 322° C., 323° C., 324° C., 325° C., 326° C., 327° C., 328° C., 329° C., 330° C., 331° C., 332° C., 333° C., 334° C., 335° C., 336° C., 337° C., 338° C., 339° C., 340° C., 341° C., 342° C., 343° C., 344° C., 345° C., 346° C., 347° C., 348° C., 349° C., 350° C., 351° C., 352° C., 353° C., 354° C., 355° C., 356° C., 357° C., 358° C., 359° C., 360° C., 361° C., 362° C., 363° C., 364° C., 365° C., 366° C., 367° C., 368° C., 369° C., 370° C., 371° C., 372° C., 373° C., 374° C., 375° C., 376° C., 377° C., 378° C., 379° C., 380° C., 381° C., 382° C., 383° C., 384° C., 385° C., 386° C., 337° C., 388° C., 390° C., 391° C., 392° C., 393° C., 394° C., 395° C., 396° C., 397° C., 398° C., or 399° 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 and O 2  are used, the reaction time can be about 1 to 3 hours or preferably about 2 hours. When H 2  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 H 2  for an additional 1 to 3 hours, (e.g., 1, 1.5, 2, 2.5, 3 hours). 
     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 100° C. to 160° C., or 130° C. to 150° C., or about 150° C. at a pressure of 0.101 MPa to 1 MPa. 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 CO 2  is not necessary. 
     After the addition of the alcohol, and, optionally, CO 2 , 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 125° C. to 225° C., 130° C. to 180° 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., 195° C., 200° C., 205° C., 210° C., 215° C., or 220° C.). Preferably, the reaction temperature is about 150° 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., 1.25 hours, 2 hours, 5 hours, 10 hours, 15 hours, 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 oxalate reaction conditions can be further varied based on the type of the reactor used. 
     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 (CsHCO 3 ). 
     2. Two Reactors 
     In some embodiments, reactor  102  can be depressurized and cooled to a temperature sufficient to allow the cesium oxalate containing product composition to 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 CO 2  in combination with H 2  or CO in combination with O 2  as described above (See,  FIG. 1 ) to generate the cesium oxalate. 
     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 225° C., 130° C. to 180° 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., 195° C., 200° C., 205° C., 210° C., 215° C., or 220° 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 oxalate reaction conditions may be further varied based on the type of the reactor used. 
     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 (e.g., DMO) via product outlet  210 . The product composition can be collected for further use or commercial sale. 
     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 (O 2 ) gas in the reaction is low or virtually absent in the reaction such that O 2  has a negligible effect on reaction performance (i.e., conversion, yield, efficiency, etc.). 
     E. Reactants and Products 
     CO 2  gas, CO gas, O 2  gas, and H 2  gas can be obtained from various sources. In one non-limiting instance, the CO 2  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) 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 various forms of combustion. O 2  can come from various sources, including streams from water-splitting reactions, 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, or conversion of methane to aromatics. In some embodiments, the gases are obtained from commercial gas suppliers. When a mixture of gases is used to prepare cesium oxalate, for example, mixtures of CO 2  and H 2  or CO and O 2 , the gas can be premixed or mixed when added separately to the reactor. When the reactor contains a mixture of CO 2  and H 2 , the pressure ratio of CO 2 :H 2  in the reactor can be greater than 0.1. In some embodiments, the CO 2 :H 2  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 CO 2 :H 2  pressure ratio is about 35:1. The partial pressure at room temperature (about 25° C.) of CO 2 :H 2  in the reactor can range from 4.5 to 1 MPa or from 1:0.1 MPa. When the reactor contains a mixture of CO and O 2 , the pressure ratio of CO:O 2  in the reactor can be greater than 0.1. In some embodiments, the CO:O 2  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. Preferably, the CO:O 2  pressure ratio is about 35:1. In one example, cesium carbonate is contacted with CO 2  and H 2  to form cesium oxalate. The mole ratio of CO 2  and H 2  to cesium carbonate can be 100:1 to 300:1, preferably 150:1 to 250:1, or more preferably about 200:1 and all ranges and values there between. In another example, cesium carbonate is contacted with CO and H 2  to form cesium oxalate. The mole ratio of CO and O 2  to cesium carbonate can be 1:0.1 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 (N 2 ), 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.). 
     Alcohols may be purchased in various grades from commercial sources. 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, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, 1-pentanol, 2-pentanol, 3-pentanol, 3-methyl-1-butanol, 2-methyl-1-butanol, 2,2-dimethyl-1-propanol, 3-methyl-2-butanol, 2-methyl-2-butanol, 1-hexanol, 2-hexanol, 3-hexanol, 1heptanol, 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, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, 1 -pentanol, 2,2-dimethyl-1-propanol (neopentanol), hexanol, or combinations thereof. When DMO is produced, the preferred alcohol is methanol. 
     Cesium carbonate (Cs 2 CO 3 ) may be purchased in various grades from commercial sources. Preferably, the alcohol and Cs 2 CO 3  are highly pure and substantially devoid of water. A non-limited commercial source of the alcohols and Cs 2 CO 3  for use in the present invention includes Sigma-Aldrich®, (USA). In some embodiments, Cs 2 CO 3  is mixed with an inert material. Non-limiting examples of inert materials include alumina (acidic, basic or neutral), silica, zirconia, ceria, lanthanum oxides or mixtures thereof. In preferred embodiments, the Cs 2 CO 3  is mixed with alumina or silica using solid-solid mixing. Providing the Cs 2 CO 3  as a Cs 2 CO 3 /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. 
     The process of the present invention can produce a product stream that includes a composition containing a disubstituted oxalate and optionally cesium bicarbonate (CsHCO 3 ) 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 can be directly reacted under conditions sufficient to form oxalic acid or ethylene glycol. The product composition can include 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.). 
     The disubstituted oxalate produced by the process of the present invention can have the general structure of: 
     
       
         
         
             
             
         
       
     
     where R 1  and R 2  can be each independently alkyl group, a substituted alkyl group, an aromatic group, a substituted aromatic group, or a combination thereof R 1  and R 2  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 R 1  and R 2  include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, 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, R 1  and R 2  are a methyl group, an ethyl group, a propyl group, an isopropyl group, a n-butyl group, a sec-butyl group, a tent-butyl group, a pentyl group, a neopentyl, a hexyl group, or combinations thereof. In certain embodiments, R 1  and R 2  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 R 1  and R 2  are each methyl groups. 
     EXAMPLES 
     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. 
     Cesium carbonate (Cs 2 CO 3 ) was obtained from Sigma-Aldrich® (U.S.A) in powder form and 99.9% purity. Methanol was obtained from Fisher Scientific (HPLC grade, U.S.A.) in 99.99% purity.  13 C NMR was performed on a 400 MHz Bruker instrument (Bruker, U.S.A). The Parr reactor used was obtained from Parr Instrument Company, USA. 
     Example 1 
     One-Step Process for the Preparation of Dimethyl Oxalate with Cs 2 CO 3 , CO 2 , and H 2    
     Cs 2 CO 3  (500 mg, 0.15 mmol) was added to a 100 mL Parr reactor in a glove box. CO 2  (35 bar, 3.5 MPa) and H 2  (1 bar, 0.1 MPa) gases were then charged and the mixture was stirred for 1-2 hour at 325° C. and cooled to room temperature by applying cool air to the reactor. The reactor was cooled to 25° C. and depressurized. The reaction mixture contained cesium oxalate, cesium formate, and cesium bicarbonate. Methanol (5 mL) was added to the reactor, and the reactor was pressurized with CO 2  (35 bar, 3.5 MPa). The mixture was heated to 150° C., stirred overnight, and then depressurized. The remaining solvent (methanol) was removed by evaporation under vacuum. The product composition was analyzed and identified as being a mixture of dimethyl oxalate, cesium formate, and cesium bicarbonate. The overall yield of DMO was 54% and yield of cesium formate as byproduct was about 4-5%.  13 C NMR (CD 3 OD, in ppm): 53 (—OMe), 158 (—CO—), 161 (CsHCO 3 ), and 171 (CsHCOO). 
     Example 2 
     Two-Step Process for the Preparation of Dimethyl Oxalate with Cs 2 CO 3 , CO 2 , and H 2    
     In the first step, Cs 2 CO 3  (500 mg, 0.15 mmol) was added to a 100 mL Parr reactor in a glove box. CO 2  (35 bar, 3.5 MPa) and H 2  (1 bar, 0.1 MPa) gases were then charged and the mixture was stirred for 1-2 hour at 325° C. and cooled to room temperature by applying cool air to the reactor. The reactor cooled to 25° C. and depressurized. The reaction mixture was removed from the reactor. Analysis of the reaction mixture contained cesium oxalate, cesium formate, and cesium bicarbonate. In the second step, the reaction mixture and methanol (5 mL) were added to the reactor, and the reactor was pressurized with CO 2  (35 bar, 3.5 MPa). The mixture was heated to 150° C., stirred overnight, and then depressurized. The remaining solvent (methanol) was removed by evaporation under vacuum. The product composition was analyzed and identified as being a mixture of dimethyl oxalate, cesium formate, and cesium bicarbonate. The overall yield of DMO was 58% and yield of cesium formate as byproduct was about 8-10%.  13 C NMR (CD 3 OD, in ppm): 53 (—OMe), 158 (—CO—), 161 (CsHCO 3 ), and 171 (CsHCOO).