Heterogeneous catalyst containing platinum and ruthenium on a zeolite support and the use of such a catalyst in a process for producing ethers - Patent Application 20070122999

Abstract

1. A process for producing an ether, comprising treating (a) an ester with (b) hydrogen in the presence of (c) a heterogeneous catalyst to hydrogenatively reduce the ester to form an ether product, wherein the heterogeneous catalyst comprises platinum and ruthenium deposited on a zeolite support.

Description

[Technical Field]

[0001] The present invention relates to a process for producing ether compounds, more particularly, the present invention relates to a process for producing ether compounds directly from alkyl esters using molecular hydrogen over a heterogeneous catalyst. [Background technology]

[0002] Ethers are used in a variety of applications, including as solvents. Ethers are particularly desirable for use as solvents in various applications because of their excellent solvency, chemical stability, and compatibility with other organic solvents and formulation products. Known routes for synthesizing ethers include three routes: (1) alkyl halides treated with alkoxides (the so-called "Williamson ether synthesis"); (2) the addition of alcohols to olefins; and (3) the acid-catalyzed coupling of alcohols. However, the three routes described above have undesirable limitations, including: (1) the use of strongly acidic or basic conditions, which can lead to competing elimination reactions that produce undesired olefins; (2) limited options for biologically derived raw materials due to lack of reactivity with the above reactions, which limits the structural diversity of the products; and (3) the use of toxic raw materials and the generation of waste streams in the production process. Therefore, it is desirable to provide a viable route for producing ethers that can be successfully scaled up commercially without the limitations of the known routes.

[0003] For example, heretofore known methods for producing ethers include the following: (1) a process using a metal hydride / Lewis acid complex or a hydrosilane as a stoichiometric hydride donor in conjunction with a noble metal catalyst, as disclosed in J. Org. Chem., 2007, 72, 5920-5922; Tetrahedron Letters, 2017, 58, 3024-3027; (2) a process for producing thionates (salts or esters of thionic acid), such as thioethers (sulfides, which are compounds in which sulfur and two organic residues are combined), as disclosed in J. Org. Chem., 1981, 46, 831-832; (3) a process for catalytic reduction of α-monoglycerides using a 5 percent (%) Pd / C catalyst mixed with an acid promoter at approximately 700 psi (4.8 megapascals [MPa]) and 120 degrees Celsius (°C), as disclosed in U.S. Pat. No. 8,912,365; and (4) a process for catalytic reduction of α-monoglycerides using a 5 percent (%) Pd / C catalyst mixed with an acid promoter at approximately 700 psi (4.8 megapascals [MPa]) and 120 degrees Celsius (°C), as disclosed in Russian Chemical (5) a non-direct process for hydrogenating ethyl acetate to an ethanol intermediate followed by coupling to form a symmetrical ether by-product on Re / (gamma-AlO) or Re / (theta-AlO) with conversions up to 4.6% and selectivities up to 57%, as disclosed in Russian Chemical Bulletin 1988, 37(1), pp. 15-19 and Russian Chemical Bulletin 1986, 35, pp. 280-283; and (6) a process for hydrogenating lactones to cyclic ethers to produce tetrahydrofuran with high selectivities, e.g., greater than 90%, using various metal catalysts on various supports, as disclosed in U.S. Pat. Nos. 3,370,067, 3,894,054, and 4,973,717. (7) A process using a homogeneous metal complex catalyst (e.g., a ruthenium / triphos complex) that requires impractical separation of the catalyst from the product. Angewandte Chemie, International Edition, 2015, 54, 5196-5200; ChemSusChem, 2016, 9, 1442-1448. (7) Hydrogenation of ethyl butyrate using Co / γ-Al2O3 to products including ethanol, butanol, ethoxybutane, butyl butyrate, and C1-C4 linear alkanes.The asymmetric ether, ethyl butyl ether, has a selectivity of less than 9%. Journal of Catalysis, 2011, 277, 27-35. (8) Selective hydrogenation of esters to asymmetric ethers in high yields using ZrO2-supported Pt-Mo / ZrO catalysts, for example, a process for producing butyl ethyl ether from ethyl butyrate over Pt-Mo / ZrO2 in 72% yield. JACS Au, 2022, 2(3), 665-672. The catalysts reported in this publication include Pt-Mo / ZrO2, Ru-Mo / ZrO2, Rh-Mo / ZrO2, Pd-Mo / ZrO2, Pt-Re / ZrO2, Pt-W / ZrO2, Pt-V / ZrO2, Pt-Mo / TiO2, Pt-Mo / hydroxyapatite, Pt-Mo / CeO2, Pt-Mo / MgO, Pt / MoO3, Pt / ZrO2, and Mo / ZrO2. The ester substrates investigated include, but are not limited to, isobutyl acetate, 2-methyl butyrate, alkyl benzoates, isopropyl cyclohexanecarboxylate, and glyceryl ether. However, the results reported in this paper cannot be reproduced in this study. Under similar conditions, asymmetric ether selectivity of less than 12% was obtained over the Pt-Mo / ZrO2 catalyst. Comparative examples of such catalysts are included in this invention.

[0004] Recently filed U.S. patent application Ser. No. 63 / 107,739 describes a process for the direct conversion of esters to ethers using transition metals supported on metal oxide supports such as NbO and WO. While the invention reported high direct selectivities for ether formation by hydrogenation, the absolute selectivities for ether products from hydrogenation were generally low, typically in the range of 5-10%, with a maximum of 16%. Further improvements in catalyst selectivity are needed to make this process economically viable.

[0005] Another recently filed U.S. patent application, Serial No. 63 / 276,308, describes a process for producing ethers from esters with molecular hydrogen over a heterogeneous catalyst containing sulfonic acid-functionalized SiO2. Absolute ether product selectivities of 20-35% are reported to be achieved from this class of catalyst.

[0006] Another recently filed US patent application Ser. No. 63 / 276,311 describes a class of transition metal on zeolite supported catalysts which achieved absolute ether product selectivities of about 20-50%.

[0007] Therefore, it would be desirable to have an improved catalyst for the direct production of ethers from esters that can be produced commercially and that offers advantages over existing processes, including increased hydrogenation rates and improved absolute and / or direct selectivities. Summary of the Invention

[0008] The present invention relates to a novel process for producing ether products from ester starting materials using a bimetallic transition metal catalyst on a zeolite support.

[0009] In a broad embodiment, the process of the present invention involves producing ethers by hydrogenating esters in the presence of a heterogeneous catalyst.

[0010] In one embodiment, the process of the present invention involves the selective reduction of carboxylic acid derivatives directly to ethers using molecular hydrogen and an appropriate catalyst formulation to achieve high (e.g., >10%) absolute ether selectivity along with high (e.g., >80%) direct ether selectivity. Absolute ether selectivity is the proportion of total products formed in the reaction, and direct ether product selectivity is the proportion of direct ether product relative to total ether products.

[0011] In another embodiment, the process of the present invention for producing an ether comprises combining (a) at least one ester in the presence of (b) hydrogen and (c) a heterogeneous bimetallic catalyst to hydrogenatively reduce the ester to form the ether.

[0012] In yet another embodiment, the present invention comprises a solvent comprising the above ether product produced by the above process.

[0013] Some of the advantageous features that may be provided by one or more embodiments of the process of the present invention include, for example: (1) An active catalyst is used in a one-step process: the catalyst is active for reducing esters to form ethers by direct hydrogenation of the ester, rather than via the known two-step ether-forming process, such as (i) ester hydrogenolysis to form alcohols, followed by (ii) alcohol dehydration. (2) Use of a relatively inexpensive route. This process uses inexpensive molecular hydrogen as the reducing agent, rather than expensive hydrosilanes, metal hydrides, or metal hydride / Lewis acid complexes as hydride donors. The highly reactive hydrosilanes or metal hydrides used in the prior art processes also require complex and expensive process designs to ensure the safety of operators running the prior art processes. (3) Use of a bimetallic heterogeneous catalyst. The heterogeneity of the catalyst, rather than the homogeneity, can contribute to reducing production costs due to the reusability and separability of the catalyst. (4) Use efficient processes. (5) Use of a flexible process: The process is applicable to general ester compounds (cyclic or acyclic) as raw materials, and is not limited to a specific ester compound. DETAILED DESCRIPTION OF THE INVENTION

[0014] In one embodiment, the present invention comprises a unique and novel method for synthesizing ethers from esters using a platinum-ruthenium bimetallic heterogeneous catalyst. Reactions of esters over heterogeneous catalysts include a variety of chemical reaction routes or pathways, such as hydrogenolysis, hydrolysis, dehydration, hydrogenation, and transesterification. In a general embodiment, the process of the present invention involves producing ethers by hydrogenation of esters, such as propyl acetate, in the presence of a heterogeneous catalyst. The novel hydrogenation reaction pathway or scheme of the present invention, for example, the hydrogenation of propyl acetate reduction reaction scheme where R1 is -CH3 and R2 is -CH2CH3, is generally shown below as Reaction Scheme (I).

[0015] [ka]

[0016] In the above Reaction Scheme (I), water is produced by the reduction process, and the produced water can be separated by conventional processes such as distillation or other procedures known in the art. The functional groups R1 and R2 can be alkyl functional groups, including linear or branched alkyl groups, cyclic or acyclic alkyl groups, and mixtures thereof. Examples of esters herein include, but are not limited to, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, butyl propionate, and mixtures thereof. The desired ether product obtained from the above Reaction Scheme (I) can be a symmetrical ether when R1 is equivalent to R2, or an asymmetrical ether when R1 is not equivalent to R2; for example, the asymmetrical ether can be ethyl propyl ether.

[0017] By "symmetric ether" herein is meant an ether containing two identical functional groups, where R1 is equal to R2. By "unsymmetric ether" herein is meant an ether containing two different functional groups, where R1 is not equal to R2.

[0018] In the present invention, the desired reaction scheme, Reaction Scheme (I), is a direct hydrogenation route to obtain the desired ether product. "Direct hydrogenation" or "direct selective reduction" refers to the removal of the carbonyl oxygen from an ester (R1COOCH2R2) by hydrogenation to form an ether (R1CH2OCH2R2) while maintaining the alkoxy group intact. The process of the present invention differs from known processes because it does not follow the typical route of ester (R1COOCH2R2) hydrogenation, in which the ester is first decomposed into two alcohols (R1CH2OH + R2CH2OH molecules) via hydrogenolysis, and then a mixture of ethers (R1CH2OCH2R1 + R1CH2OCH2R2 + R2CH2OCH2R2) is formed via dehydration. Direct hydrogenation can maintain the ether structure from the ester by simply removing the carbonyl oxygen. Therefore, the asymmetric ester provided in this process advantageously results in the direct production of the asymmetric ether, since this process does not decompose the ester into two alcohol molecules via hydrogenolysis. The selectivities of ethyl propyl ether in the reaction examples are listed in Tables III and V described in the Examples below.

[0019] As used herein, the term "direct ether product" refers to an ether formed by a one-step reduction process of an ether from an ester.

[0020] As used herein, the term "indirect ether product" refers to an ether formed by a two-step reduction process of an ether from an ester, the two-step reduction process comprising the steps of (i) hydrogenolysis and (ii) dehydration.

[0021] The term "direct ether product selectivity" as used herein means the ratio of direct ether products to total ether products. For example, for the reduction of propyl acetate, ethyl propyl ether is the direct ether product, and the direct ether product selectivity is the ratio of ethyl propyl ether to total ether products (ethyl propyl ether + dipropyl ether + diethyl ether).

[0022] As used herein, the term "absolute ether product selectivity" refers to the proportion of ether products among all products (e.g., ethers, alcohols, and alkanes) formed in a reaction.

[0023] Advantageously, one unique factor of the present invention involves increased direct ether selectivity using the one-step process of the present invention over known two-step processes.

[0024] In one embodiment, the process of the present invention for producing an ether comprises treating (a) an ester with (b) hydrogen and (c) in the presence of a heterogeneous catalyst to hydrogenolytically reduce the ester to form the ether.

[0025] In one desirable embodiment, as shown in Reaction Scheme (I) above, the process of the present invention for producing an ether includes the steps of: (A) feeding an ester compound, such as propyl acetate, component (a), to a reactor; (B) feeding hydrogen, component (b), to the reactor to form a hydrogen atmosphere within the reactor; (C) charging the reactor with a heterogeneous catalyst system, component (c), comprising a platinum-ruthenium bimetallic transition metal on a zeolite support sufficient to cause a hydrogenation reaction within the reactor; and (D) heating the reactor contents, components (a) through (c), at a temperature sufficient to reduce the ester compound to form an ether compound. For example, heating step (D) can be carried out at a temperature between 350 Kelvin (K) and 650 K. It will also be readily apparent to those skilled in the art that the order of the listed steps may be varied in particular circumstances, or that the steps may be carried out simultaneously.

[0026] As is commonly known in the art, a "heterogeneous catalyst" refers to a catalyst whose phase (e.g., solid, liquid, or gas) is different from that of the reactants. For example, the reactants (ester and hydrogen) and product (e.g., ether) may be in a liquid or gas phase, but the catalyst is a solid.

[0027] In the present invention, the heterogeneous bimetallic catalyst system of the present invention is a combination of platinum-ruthenium metals and a zeolite support. For example, the catalyst used in some embodiments of the present invention can include 0.1 weight percent (wt%) to 20 wt% of a transition metal supported on a zeolite support element. Preferably, the molar ratio of platinum to ruthenium is 0.1 to 10, more preferably 0.5 to 5, with a ratio of about 1:1 (e.g., 0.9 to 1.1) being most preferred.

[0028] As is generally known in the art, zeolites are crystalline aluminosilicate materials composed of corner-sharing AlO4 and SiO4 tetrahedra bound in a three-dimensional framework with molecular-sized pores. The presence of aluminum in the zeolite framework results in a negative charge that is balanced by cations. The zeolite of the present invention advantageously has a framework type that can be selected from the group consisting of the following framework types: FAU, MOR, BEA, CHA, FER, MFI, and combinations thereof, which framework types correspond to the naming conventions of the International Zeolite Association. The preferred zeolite framework type for the present invention is MOR.

[0029] The atomic Si / Al ratio is often used in catalytic practice to characterize zeolites and refers to the number of silicon-containing sites (typically SiO) present per alumina-containing site (typically HAlO). Zeolites for use in the present invention may have a Si:Al ratio ranging from 1 to 300. In some embodiments, the ratio may be from 5 to 250. For some applications of the present invention, a Si:Al ratio in the range of 75:125 may be preferred.

[0030] As depicted in Reaction Pathway Reaction Scheme (I), the direct ether reduction route is promoted by synergistic effects from both the bimetallic transition metal component and the zeolite support component. Without the combination of the transition metal and zeolite support elements as disclosed herein, the undesirable two-step ether formation route would occur. Steady-state rates and product selectivities for the competing reaction pathways of model ester compounds are obtained, for example, in packed-bed and / or trickle-bed reactors as a function of reactant pressure, temperature, and ester conversion, controlled by superficial residence time.

[0031] Component (a), the ester compound to be reduced to an ether, can include, for example, one or more ester compounds containing carboxylic acid derivatives, esters containing linear or branched alkyl groups, and cyclic or acyclic alkyl groups, and mixtures thereof. In some embodiments, the asymmetric ether comprises reaction scheme (I) in which the R group is not equal to the R group. In some embodiments, the ester useful in the present invention can be, for example, propyl acetate (available from Sigma-Aldrich), butyl acetate (available from Sigma-Aldrich), butyl propionate, glycerin esters, and mixtures thereof.

[0032] The concentration of component (a), the ester, is not particularly critical. However, in some embodiments, it may be advantageous for the ester to be present in an amount of at least 1 wt. % to provide a desired production rate and / or avoid increased separation costs. In some embodiments, the concentration of the ester is from 1 wt. % to 100 wt. The concentration of the ester is based on the total weight of the ester compounds in the liquid feedstock.

[0033] The concentration of hydrogen, component (b), useful in the process of the present invention, is, for example, 3 wt. % to 100 wt. % in one embodiment, 10 wt. % to 100 wt. % in another embodiment, and 50 wt. % to 100 wt. % in yet another embodiment. Low concentrations of hydrogen, for example, less than 3 wt. % (<3 wt. %), may reduce reactivity or ether selectivity, thereby necessitating an undesirable increase in reaction pressure. The concentration of hydrogen is based on the total weight of hydrogen in the gaseous feed.

[0034] In a broad embodiment, the catalyst, component (c), used in the process of the present invention can comprise one or more heterogeneous catalyst compounds. The catalyst used in the process of the present invention, for example, comprises a combination of platinum and ruthenium (ci) supported on a zeolite support (carrier) element (cii). For example, the transition metal (component (ci)) may also comprise other transition metals, such as palladium (Pd), cobalt (Co), copper (Cu), rhodium (Rh), rhenium (Re), nickel (Ni), and mixtures thereof. Preferably, the transition metal component consists solely of platinum and ruthenium. The acidic zeolite support component (component (cii)) can be derived from any zeolite or mixture of zeolites, including, for example, faujasite zeolite ("FAU"), sodium Y zeolite (NaY) (sodium ion-exchanged Y zeolite), mordenite zeolite ("MOR"), beta zeolite ("BEA"), chabazite zeolite ("CHA"), ferrierite zeolite ("FER"), Mobil-five zeolite ("MFI"), and mixtures thereof. These zeolites can preferably have a Si to Al ratio ranging from 2 to 250. In some preferred embodiments, the heterogeneous catalyst useful in the present invention can be Pt—Ru supported on MOR. In addition to the Pt-Ru catalyst, one or more additional catalysts may be used, such as Pd on an FAU support; Pt on an FAU, MOR, FER, or CHA support; Rh on an FAU support, and mixtures thereof.

[0035] The heterogeneous catalysts of the present invention exhibit several advantageous properties. For example, the heterogeneous catalysts useful in the present invention provide a synergistic effect between the bimetallic compound of the catalyst and the zeolite support of the catalyst to catalyze direct ester hydrogenation, which may otherwise result in reduced ether selectivity.

[0036] The heterogeneous catalyst of component (c) may, for example, in one embodiment, contain 0.01 wt % to 20 wt % of metal compounds based on the total weight of the heterogeneous catalyst, in another embodiment, 0.1 wt % to 10 wt % of total metal compounds based on the total weight of the heterogeneous catalyst, and in yet another embodiment, 1 wt % to 5 wt % of total metal compounds based on the total weight of the heterogeneous catalyst. Preferably, the molar ratio of platinum to ruthenium is 0.1 to 10, more preferably 0.5 to 5, with a ratio of about 1:1 (e.g., 0.9 to 1.1) being most preferred.

[0037] The process equipment used to carry out the reduction process can be any conventional reactor, such as a packed bed reactor or a trickle bed reactor. As is generally understood in the art, ester conversion and ether selectivity can be controlled by reactor pressure, temperature, and superficial residence time.

[0038] For example, the pressure of the process of the present invention is, in one embodiment, from 0.1 MPa to 10 MPa, in another embodiment from 2 MPa to 6 MPa, and in yet another embodiment from 6 MPa to 10 MPa. Pressures below the aforementioned ranges may result in lower reactivity or lower ether selectivity than disclosed herein. Pressures higher than the aforementioned ranges may be sufficient for use in the present invention, but may require higher costs in reactor construction and operation.

[0039] For example, the temperature of the process of the present invention is 350 K to 650 K in one embodiment, 400 K to 500 K in another embodiment, and 500 K to 650 K in yet another embodiment. Temperatures below the aforementioned ranges may result in lower reactivity than disclosed herein. Temperatures above the aforementioned ranges may result in undesirable alkane and alcohol by-products, and therefore, in such cases, ether selectivity may be reduced.

[0040] For example, the ester conversion rate of the process of the present invention is 1% to 100% in one embodiment, 1% to 50% in another embodiment, and 50% to 100% in yet another embodiment. In some embodiments, ester conversion rates higher than the aforementioned conversion ranges may result in the formation of side reaction products.

[0041] The process of the present invention can be carried out as a batch process or a continuous process. In some embodiments, when a batch process is used, the residence time of the process of the present invention is, for example, from 0.1 hour (hr) to 24 hours in one embodiment, from 0.1 hour to 8 hours in another embodiment, and from 1 hour to 24 hours in yet another embodiment. In some embodiments, residence times below the aforementioned residence time ranges may result in lower ester conversion rates, while in some embodiments, residence times above the aforementioned residence time ranges may result in undesirable side reaction products.

[0042] In some embodiments, when a continuous process is used, the residence time for the process of the present invention is, for example, from 0.1 seconds to 100 seconds in one embodiment, from 1 second to 10 seconds in another embodiment, and from 10 seconds to 100 seconds in yet another embodiment. Residence times below the aforementioned residence time ranges may result in lower ester conversion rates, while in some embodiments, residence times above the aforementioned residence time ranges may result in undesirable side reaction products.

[0043] Some advantageous properties and / or benefits of using the reduction process of the present invention include, for example, that the process of the present invention can achieve a steady-state rate and that the process can provide better selectivity of products relative to competing reaction pathways of ester compounds, even better than other heterogeneous catalysts that do not feature a zeolite support. Also, conventional processes for producing ethers also produce salts, whereas the process of the present invention does not produce salts.

[0044] After the ester compound undergoes a reduction process, the resulting ether product is formed. The turnover rate from ester to ether product is typically in the range of 10-150%. -8 moles of ether / grams of catalyst / second (moles / g cat s)~10 -5 moles / g cat ·s, 5×10 -8 moles / g cat s~5×10 -6 moles / g cat Ester turnover rates below the aforementioned rate ranges may result in lower ether production rates, and in some embodiments, ester turnover rates above the aforementioned residence time ranges may result in undesirable side reaction products.

[0045] The selectivity to the ether product may depend on whether a vapor or liquid process is used to form the ether, and whether a batch or continuous process is used. Generally, the selectivity to the direct ether product is greater than 10% in one embodiment, between 10% and 25% in another embodiment, and between 25% and 60% in yet another embodiment.

[0046] The ether products produced by the process of the present invention can be symmetrical or asymmetrical ethers, but for purposes of illustration and not limitation, the process of the present invention will be described with reference to asymmetrical ethers. Surprisingly, it has been discovered that the process of the present invention is selective for asymmetrical ethers, since the esters are converted directly to ethers without undergoing ester hydrogenolysis and alcohol dehydration. Ester hydrogenolysis and alcohol dehydration are two processes known to be unselective for certain ethers.

[0047] When an asymmetric ether is desired for a particular process or end use, use of the process of the present invention has advantages over conventional processes for the following reasons. (1) The ether products are more stable than the corresponding ester products under basic and acidic conditions, and the ether products of the present invention are typically not susceptible to hydrolysis, which can occur at high humidity and / or high temperature. (2) The hydrogen reaction chemistry of the present process is believed to keep the backbone of the ester product intact. During hydrogenation, only the oxygen molecules are cleaved from the backbone, leaving the carbon molecules and backbone oxygens unchanged. In conventional reaction processes, the reaction breaks the backbone and recombines parts together under different reaction conditions. Therefore, direct hydrogenation / reduction of esters to ethers does not occur. (3) The process of the present invention minimizes undesirable side reactions that can adversely affect the selectivity of the desired ether product.

[0048] Because the ether products of the present invention are derived from organic and renewable sources, the ether products of the present invention have minimal impact on the environment. For example, the ether products can be advantageously used as green and bio-based solvents on a global scale to address strict regulations imposed on chemical industry solvents regarding toxicity, non-biodegradability, volatile organic compound (VOC) emissions, etc. Green and bio-based solvents are typically used in paint and coating applications. Other applications include adhesives, pharmaceuticals, and printing inks. In some embodiments, the ether products can be used as foam control agents and flavor additives. In other embodiments, the ether products can be used in cosmetics and personal care applications.

[0049] The present invention provides bio-based solvents that have cost and performance advantages over solvents known in industry. In addition, the chemical transformations provided by the process of the present invention may be useful, for example, for producing bio-based surfactants, antifoams, and lubricants in an economical and environmentally friendly process.

[0050] The ether production process of the present invention can also be used to develop (1) a more robust capping process to overcome the problem of limited reactant alkyl chloride type and final product impurities, (2) novel capped low viscosity-low volatility lubricants, and (3) novel surfactants and novel bio-based antifoams for food and pharmaceutical applications, metalworking fluid applications, and other applications utilizing ether solvents. [Example]

[0051] The following Inventive Example (Inv. Ex.) and Comparative Example (Comp. Ex.) (collectively "Examples") are presented herein to further illustrate the present invention, but should not be construed as limiting the scope of the claims. Unless otherwise indicated, all parts and percentages are by weight.

[0052] catalyst The catalyst ("Cat.") formulations used in the examples are listed in Table 1 (for the inventive examples) and Table 2 (for the comparative examples).

[0053] [Table 1]

[0054] [Table 2]

[0055] The specified transition metal particles (Pt, Ru, Pd, Co, and / or Ni) are deposited onto the specified support (MOR zeolite or ZrO2) using incipient wetness impregnation (IWI) or rotary evaporation techniques, as specified.

[0056] The "IWI" and "IWI, Co-impregnation" methods involve impregnating a designated support with an aqueous solution of precursor(s) for the designated transition metal, as follows: The precursors used for Pt, Ru, Pd, Co, Ni, and Mo are Pt(NH3)4(NO3)2, Ru(NO)(NO3)3, Pd(NH3)4(NO3)2, Co(NO3)2·6H2O, Ni(NO3)2·6H2O, and (NH4)6Mo7O, respectively. 24 MOR zeolites are commercially available from ACS Materials (Si / Al=10) and Tosoh (Si / Al=120). The IWI method involves preparing an aqueous solution with precursor concentrations adjusted to the indicated weight loading. A volume equal to the support pore volume is added dropwise to the support to achieve incipient wetness. The impregnated support is then dried in a static oven at 353 K for more than 12 hours and then calcined in air at 773 K for 2 hours (100 cm). 3 min -1 Finally, the sample was heated at 423 K for 2 h (5 K min ) under a 20% H / He flow. -1 ) was reduced.

[0057] The "rotary evaporation" method is as published in JACS Au, 2022, 2(3), 665-672. (NH4)6Mo7O 24 An aqueous solution of HPtCl (37.5 mM) and ZrO (15 g) are added to distilled water (500 mL) at room temperature. The water is removed by rotary evaporation under reduced pressure to obtain a solid product, and the resulting sample is dried overnight at 343 K. An aqueous solution of the dried powder and HPtCl (100 mM) is added to distilled water (500 mL). Rotary evaporation is then reintroduced to remove the water. The powder is dried overnight at 343 K. The sample is then dried in a stream of air (200 cm 3 min -1 ) 773K for 3 hours (5K min -1 ) and then calcined in a 20% H2 / He stream at 423 K for 2 h (5 K min -1 )Reducing.

[0058] liquid phase reaction Catalysts 1–13 are tested in a liquid-phase reactor. The liquid-phase reactor is a trickle-bed reactor consisting of a stainless steel tube (3 / 8” OD) containing 1–6 g of catalyst (30–60 mesh), which is held in the center of the reactor using a pyrex glass rod and packed glass wool. The reactor is heated with an aluminum clamshell containing two heating cartridges controlled by an electronic temperature controller. The reaction temperature is measured by a K-type thermocouple contained within a 1 / 8” stainless steel sheath coaxially aligned within the reactor and submerged within the aluminum clamshell. The system is pressurized to 6.6 MPa using a dome-loaded backpressure regulator controlled by an electronic pressure regulator. The reactor pressure is monitored using a digital pressure gauge. The H2 (ultrapure) and He (ultrapure) gas flows are controlled using mass flow controllers. Pure propyl acetate (PA) is dried using molecular sieve 3A beads (1–2 mm) before injecting the reactants into the reactor. Dry PA(CH) in liquid phase 10 The flow rate of O2, 99.5%, is controlled using an HPLC pump, fed through a stainless steel tube (1 / 16'' outer OD, 0.006'' ID) in cross-flow with H2 and He. 5 K min -1 The catalyst was pretreated in situ by heating to 503 K in 1000 K and then pretreated with a mixture of H (20 kPa, ultra-high purity) and He (81 kPa, ultra-high purity) (50 cm 3 min -1The reactor was then held for 1 hour with flowing water. The reactor effluent was passed through a stainless steel cooling chamber containing cold water (approximately 283 K), and then a stainless steel gas-liquid separator was used to separate the gas and liquid products into gas and liquid streams. The liquid products collected in the gas-liquid separator were delivered to a high-pressure liquid sampling valve (LSV, 1 μL injection volume) attached to an online gas chromatograph using an automated product delivery system consisting of an HPLC pump and a wet / wet differential pressure transducer (0-10 in HO). A manual BPR was installed at the outlet of the LSV to maintain the liquid pressure at 1.4 MPa to prevent the product from evaporating within the LSV sampling system. The gas and liquid products were characterized using online gas chromatography. The gas sampling valve and LSV were used to inject the gas and liquid products into the split / splitless inlet, respectively. The gas chromatograph (GC) is equipped with two capillary columns (GS-GASPRO, 60 m long, 0.32 mm internal diameter for the gas product; DB-Wax UI, 60 m long, 0.25 mm internal diameter, 0.25 μm for the liquid product) connected to two flame ionization detectors (FIDs) to quantify species concentrations. Sensitivity factors for the gas and liquid products are determined using gas standards and methanizers, respectively. Control of reaction pressure and temperature, reactant and product flow rates, and GC sampling are automated to allow continuous measurements. Conversion is calculated on a carbon basis based on the amount of carbon appearing in the product. Carbon balances are within ±10%. Catalyst deactivation is corrected by linear interpolation of time-on-stream data.

[0059] The reactions for Examples 1-4 of the present invention and Comparative Examples A-G are carried out at 383 K under 6431 kPa H pressure and 119 kPa ester pressure. The reactions for Comparative Examples H-I are carried out at 373 K under 6462 kPa H pressure and 88 kPa ester pressure, similar to the conditions published in JACS Au, 2022, 2(3), 665-672. In the liquid-phase reactor, the ester is maintained in a liquid state due to its high concentration in the feed mixture under the reaction pressure and temperature. The results of the liquid-phase experiments are shown in Table 3.

[0060] [Table 3]

[0061] In Examples 1-4 of the present invention, the selectivities for the formation of dipropyl ether and diethyl ether from propyl acetate are less than 3% in most cases, while the relative selectivity for ethyl propyl ether among all three ether products is greater than 90% in most cases. Because alcohol dehydration does not have a selectivity preference for symmetric or asymmetric ethers, such performance indicates that substantially all of the ethyl propyl ether is formed via the direct hydrogenation reaction pathway of propyl acetate. Furthermore, the absolute ethyl propyl ether selectivities for Examples 1-4 of the present invention are all greater than 20%. These results significantly exceed the performance of prior art transition metal / metal oxide catalysts, such as U.S. Patent Application No. 63 / 107,739, which claims absolute ethyl propyl ether selectivities of greater than 5% and direct ether selectivities of greater than 85%.

[0062] Comparing the results of Inventive Example 1 and Inventive Example 2, Pt-Ru on MOR with a Si / Al ratio of 120 (Catalyst 2) shows better performance than Pt-Ru on MOR with a Si / Al ratio of 10 (Catalyst 1). The hydrogenation rate of Catalyst 2 was 8.83×10 -7 (mol C5H 10 O2)·(g cat ·s) -1 and 2.77 × 10 under the same reaction conditions.-7 (mol C5H 10 O2)·(g cat ·s) -1 Furthermore, catalyst 2 has a direct ether selectivity of 98.4%, which is higher than that of catalyst 1, which is 91.2%.

[0063] Comparing Inventive Example 2, Inventive Example 3, and Inventive Example 4, which are Pt-Ru catalysts (Catalyst 2, Catalyst 3, and Catalyst 4) all having different Pt to Ru ratios, demonstrate good hydrogenation rates, absolute ether selectivities, and relative ether selectivities while maintaining the same total metal moles. The best hydrogenation rate is obtained from Catalyst 2, which has a Pt to Ru ratio of 1.

[0064] Comparative Examples A-C are derived from monometallic Pt or Ru MOR zeolite catalysts (Catalyst 5, Catalyst 6, and Catalyst 7). The purpose of providing these comparative examples is to demonstrate the superior performance of bimetallic Pt-Ru MOR catalysts over the corresponding monometallic MOR catalysts. Comparing Inventive Example 1 and Comparative Example A, the Pt-Ru-MOR10 catalyst (Catalyst 1) exhibited a 10-fold higher hydrogenation rate than the Pt-MOR10 (Catalyst 5), at 2.77 × 10 -7 (mol C5H 10 O2)·(g cat ·s) -1 vs. 2.53 x 10 -8 (mol C5H 10 O2)·(g cat ·s) -1 On the other hand, the absolute ether selectivity from Pt-Ru-MOR10 is comparable to that of Pt-MOR10, ranging from 25.8% to 27.4%. In contrast, Ru-MOR10 (catalyst 6) exhibits a poor hydrogenation rate (5.53 × 10 -9 (mol C5H 10 O2)·(g cat ·s) -1) and absolute ether selectivity (1.5%). These results indicate that the bimetallic Pt-Ru-MOR has better performance for ester reduction to ethers compared to either the Pt-MOR or Ru-MOR monometallic catalysts. Similar conclusions can be drawn from a comparison of Inventive Example 2 and Comparative Example C, because the bimetallic Pt-Ru-MOR 120 (Catalyst 2) exhibited a 8.83 x 10 -7 (mol C5H 10 O2)·(g cat ·s) -1 which is 1.12 x 10 -7 (mol C5H 10 O2)·(g cat ·s) -1 This is seven times higher than that of monometallic Pt-MOR120 (Catalyst 7), which has a hydrogenation rate of 1.5%. However, Pt-MOR120 exhibits better absolute ether selectivity (48.9%) than Pt-Ru-MOR120 (25.4%). In general, the results show that the bimetallic Pt-Ru zeolite catalyst significantly improves hydrogenation rates, exceeding the performance of prior art monometallic zeolite catalysts by 5 to 10 times (see U.S. Patent Application No. 63 / 276,311).

[0065] The results of Comparative Examples D through G (Catalysts 8 through 11) show that not all Pt-M bimetallic MOR zeolites exhibit improved performance for ester reduction to ethers, either in terms of hydrogenation rate or ether selectivity. Pt-Pd-MOR120 (Catalyst 8) exhibits high absolute ether selectivity, up to 39.7%, but also forms symmetric ether products, resulting in a low relative ether selectivity of 68.8%. Pt-Co-MOR120 (Catalyst 9), Pt-Ni-MOR120 (Catalyst 10), and Pt-Mo-MOR120 (Catalyst 11) all exhibit low absolute ether selectivities of less than 15%, indicating that these catalysts are not very effective for reducing esters to ethers.

[0066] The results for Comparative Examples F and G are obtained from prior art bimetallic catalysts (JACS Au, 2022, 2(3), 665-672) relevant to the present invention. Catalyst 12, a Pt-Mo / ZrO2 catalyst, is a catalyst regenerated using a method described by the prior art. An IWI version of the Pt-Mo / ZrO2 catalyst (Catalyst 13) is also prepared and tested under prior art reaction conditions. First, the Pt-Mo / ZrO2 catalysts show low absolute selectivity for the desired ether, 1.6% from Catalyst 12 and 11.1% from Catalyst 13. The products produced from the Pt-Mo / ZrO2 catalyst contain significant amounts of by-products such as alcohols and light alkanes. Second, the hydrogenation rates for Catalysts 12 and 13 are 2.76 x 10 -10 (mol C5H 10 O2)·(g cat ·s) -1 and 3.30 x 10 -9 (mol C5H 10 O2)·(g cat ·s) -1 The Pt-Ru-MOR bimetallic catalysts disclosed in this invention generally have hydrogenation rates that are more than two orders of magnitude higher than these prior art catalysts.

[0067] Gas-phase reactions Catalysts 2 and 7 are also tested in a gas-phase reactor. The gas-phase reactor is a trickle-bed reactor. Rate and selectivity measurements are performed in a packed-bed reactor held in a stainless steel tube (3 / 8" OD) containing approximately 10 mg to 200 mg of catalyst, which is held in the center of the reactor using a glass rod and packed glass wool. The tubular reactor is placed in a three-zone furnace controlled by an electronic temperature controller. The catalyst temperature is measured by a K-type thermocouple housed in a 1 / 16" stainless steel sheath aligned coaxially within the reactor and submerged in the catalyst bed. The volume of the catalyst bed is increased to 1.4 cm by mixing excess SiC (Carborex green 36) with the desired amount of catalyst. 3The reactor pressure is kept constant at 1000 W / L. The system is pressurized using a back pressure regulator controlled by an electronic pressure regulator (EPR). A digital pressure gauge and an EPR are used to monitor the reactor pressure upstream and downstream of the catalyst bed, respectively.

[0068] The hydrogen (H, ultra-high purity 5.0) and helium (He, ultra-high purity 5.0) gas flows are controlled using mass flow controllers. 10 The flow rate of O2 (≥99.5%) is controlled using a stainless steel syringe pump with a Hastelloy cylinder fed through PEEK tubing (1 / 16" outer OD, 0.01" ID), the outlet of which is placed in a small bed of non-porous sand (SiO2 particle size 50-70 mesh) in a cross-flow of H2. To avoid condensation, heating tape is used to maintain the transfer lines surrounding the liquid inlet at 373 K. All transfer lines downstream of the liquid inlet are heated above 373 K using heating tape, and line temperatures are monitored with type K thermocouples displayed on a digital reader.

[0069] Before all catalytic measurements, -1 Heat to the desired temperature at 100cm 3 minutes -1The catalyst is pretreated in situ by flowing hydrogen (H2, ultra-high purity 5.0) at 101 kPa for the desired time. The reactor effluent is characterized using online gas chromatography. The gas chromatograph (GC) is equipped with a capillary column (DB-624 UI, 30 m long, 0.25 mm internal diameter, 1.40 μm) connected to a flame ionization detector to quantify the concentration of combustible species. Sensitivity factors and retention times for all components are determined using gas and liquid standards. Control of reactor pressure and temperature, reactant flow rates, and GC sampling are automated to allow continuous measurements. Conversion is calculated on a carbon basis based on the amount of carbon appearing in the product. Carbon and oxygen balances are within ±20%. Reactor conditions during rate and selectivity measurements are varied by sequentially decreasing and then increasing reactant pressure over the entire range, such that one or more of the conditions are measured at least twice throughout the experiment to ensure that any trends measured are not the result of systematic deactivation.

[0070] In Inventive Example 5 and Comparative Example J, hydrogenation is carried out in a gas-phase reactor using the catalyst indicated. The reactions for Inventive Example 5 and Comparative Example J are carried out at 356-383 K under 6431 kPa H pressure and 10 kPa ester pressure. In a gas-phase reactor, the ester is maintained in a gaseous state due to its lower concentration in the feed mixture under the reaction pressure and temperature compared to a liquid-phase reactor. Ether product selectivities are listed in Table 4.

[0071] [Table 4]

[0072] The results of Example 5 of the present invention are obtained from Catalyst 2 in a gas-phase reactor. The results show that Pt-Ru-MOR120 is also effective in the reduction of esters to ethers, with high selectivity and rate. The absolute selectivity of the desired ether ranges from 34.7% to 39.9% at temperatures varying from 356 to 383 K, while maintaining a high relative ether selectivity of over 85%. The hydrogenation rate is approximately 5.20 x 10 -7 (mol C5H 10 O2)·(g cat ·s) -1 ~1.17×10 -6 (mol C5H 10 O2)·(g cat ·s) -1 It is measured as:

[0073] The results for Comparative Example J are obtained from the corresponding monometallic Pt-MOR120 catalyst (Catalyst 7) ​​for comparison purposes with Pt-Ru-MOR120 (Catalyst 2) under the same reaction conditions. Pt-MOR120 exhibits good absolute ether selectivity of 46.1-47.7% under the reaction temperatures tested, and also exhibits good relative ether selectivity of over 85%. However, when comparing hydrogenation rates, the results from the bimetallic Pt-Ru-MOR120 are over 5 times higher than the monometallic Pt-MOR120, which is approximately 8.74 x 10 -8 (mol C5H 10 O2)·(g cat ·s) -1 ~2.03×10 -6 (mol C5H 10 O2)·(g cat ·s) -1 It is measured as:

Claims

1. 1. A process for producing an ether product by the direct selective reduction of an ester, comprising: treating (a) at least one ester with (b) hydrogen; and (c) in the presence of a heterogeneous catalyst to directly and selectively reduce the at least one ester by hydrogenation to form at least one ether, wherein the heterogeneous catalyst comprises platinum and ruthenium deposited on a zeolite support.

2. 10. The process of claim 1, wherein the ester is an ester containing a straight or branched chain alkyl group, a cyclic or acyclic alkyl group, and mixtures thereof.

3. 2. The process of claim 1, wherein the molar ratio of platinum to ruthenium is in the range of 0.1 to 10.

4. 10. The process of claim 1, wherein the total amount of transition metals deposited on the zeolite support is from 0.01 to 20 weight percent of the amount of metal compounds, based on the total weight of the heterogeneous catalyst.

5. 10. The process of claim 1, wherein the zeolite comprises at least one of FAU, sodium Y zeolite, MOR, BEA, CHA, FER, MFI, and mixtures thereof.

6. 2. The process of claim 1, wherein the zeolite has a Si to Al ratio in the range of 1 to 300.

7. 2. The process of claim 1, wherein the process temperature is between 350K and 650K and the process pressure is between 0.1 MPa and 10 MPa.

8. 2. The process of claim 1, wherein the ether is an asymmetric ether.

9. 10. The process of claim 1, wherein the process is a vapor phase reduction process conducted under vapor phase process conditions.

10. 10. The process of claim 1, wherein the process is a liquid phase reduction process carried out under liquid phase process conditions.

11. 2. The process of claim 1, wherein the zeolite support is MOR.

12. 10. A solvent comprising an ether produced from the process of claim 1.

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