CONTINUOUS PROCESS FOR THE SYNTHESIS OF DIMETHYL CARBONATE OVER A CERIUM-BASED CATALYST FORMULATION

Abstract

The present invention discloses a continuous process for the synthesis of dimethyl carbonate from methanol and carbon dioxide over a ceria-based mixed metal oxide-silica catalyst formulation in the presence of a dehydrating or water trapping compound (2-Cyanopyridine).

Claims

1. A continuous process for synthesis of dimethyl carbonate (DMC), said process comprising contacting methanol with CO.sub.2 over a catalyst formulation; at a reaction temperature in a range of 120 to 160? C.; for a reaction time period in a range of 2 to 10 hours; reaction pressure in a range of 30 to 100 bar in the presence of an organic nitrile dehydrating or water trapping compound, wherein the catalyst formulation has at least 30 hours of catalytic stability; and wherein said catalyst formulation comprises: (a) mixed oxides of cerium (Ce) with other elements selected from the group consisting of zirconium (Zr), lanthanum (La), gallium (Ga) and combinations thereof and the metal oxides have an elongated hexagonal, spindle-shaped, rod-like or spherical morphology; and (b) a form of silica (SiO.sub.2) selected from the group consisting of colloidal silica, silicate, orthosilicate, Si/Al combinations and silica source material wherein the silica content in the catalyst formulation is in the range of 2 to 25 weight percent, and content of Ce-oxide in the mixed oxide portion is in the range of 50 to 95 mole percent; (c) wherein the hydrophobicity, represented by water adsorption capacity, is less than 10 weight percent of the catalyst, the crush strength of the catalyst is 2 to 7 Newton, and acidity/basicity molar ratio of the bi-functional catalyst is in the range of 0.5 to 2.5.

2. The process as claimed in claim 1, wherein molar ratio of methanol to dehydrating or water trapping compound is in the range of 1:1 to 3:1; and molar ratio of methanol to carbon dioxide is in the range of 1:3 to 2:1.

3. The process as claimed in claim 1, wherein the dehydrating or water trapping compound is 2-cyanopyridine (2-CP).

4. The process as claimed in claim 1, wherein flow rate of liquid feed containing methanol and dehydrating or water trapping compound that is expressed in terms of liquid hourly space velocity (LHSV) is in the range of 0.5 to 4 hour.sup.?1.

5. The process as claimed in claim 1, wherein flow rate of carbon dioxide that is expressed in terms of gas hourly space velocity (GHSV) is in the range of 400 to 1000 hour.sup.?1.

6. The process as claimed in claim 1, wherein said process is performed in a fixed-bed reactor, continuous stirred tank reactor or continuous-flow reactors.

7. The process as claimed in claim 1, wherein the yield of dimethyl carbonate is above 30 mole percent.

8. A catalyst formulation for a continuous process for synthesis of dimethyl carbonate, wherein said catalyst formulation comprises: (a) mixed oxides of cerium (Ce) with other elements selected from the group consisting of zirconium (Zr), lanthanum (La), gallium (Ga) and combinations thereof and the metal oxides have an elongated hexagonal, spindle-shaped, rod-like or spherical morphology respectively, and (b) a form of silica (SiO.sub.2) selected from the group consisting of colloidal silica, silicate, orthosilicate, Si/Al combinations and silica source material wherein the silica content in the catalyst formulation is in the range of 2 to 25 weight percent, and content of Ce-oxide in the mixed oxide portion is in the range of 50 to 95 mole percent; (c) wherein the hydrophobicity, represented by water adsorption capacity, is less than 10 weight percent of the catalyst, the crush strength of the catalyst is 2 to 7 Newton, and acidity/basicity molar ratio of the bi-functional catalyst is in the range of 0.5 to 2.5.

9. The catalyst formulation as claimed in claim 8, wherein said catalyst formulation is selected from ZrCeO.sub.2/SiO.sub.2, ZrGaCeO.sub.2/SiO.sub.2, ZrCeO.sub.2/Al.sub.2O.sub.3, ZrCeO.sub.2, CeO.sub.2/SiO.sub.2, CeO.sub.2/Al.sub.2O.sub.3, ZrLaCeO.sub.2/SiO.sub.2, GaCeO.sub.2/SiO.sub.2, LaCeO.sub.2/SiO.sub.2, ZrGaCeO.sub.2/SiO.sub.2, ZrGaCeO.sub.2/SiO.sub.2Al.sub.2O.sub.3, GaCeO.sub.2/SiO.sub.2Al.sub.2O.sub.3, LaCeO.sub.2/SiO.sub.2-Al.sub.2O.sub.3 and ZrLaCeO.sub.2/SiO.sub.2Al.sub.2O.sub.3.

10. The catalyst formulation as claimed in claim 8, wherein said catalyst formulation is shaped and formed into extrudates, trilobes, spheres or tablets.

11. The catalyst formulation as claimed in claim 8, wherein the part of cerium ions in said catalyst formulation is in partially reduced (+3) oxidation state.

12. The catalyst formulation as claimed in claim 8, wherein said catalyst formulation has specific surface area in the range of 100 to 300 m.sup.2/g and pore volume in the range of 0.1 to 0.35 cc/g.

13. A process of preparing a catalyst formulation as claimed in claim 8, wherein said process comprises: (a) co-precipitating precursor salt solutions of Ce and other element (Zr, La, Ga or combinations thereof) sequentially or once through at a temperature in the range of 20? C. to 30? C. using a precipitating agent; (b) mixing and ageing of the suspension of step (a) at a temperature in the range of 30? C. to 120? C.; (c) filtering and water washing of the formed precipitate; (d) drying the precipitate of step (c) at 25? C. to 100? C. followed by calcination at a temperature in the range of 400? C. to 600? C. to obtain mixed oxide catalyst; and (e) mixing the mixed oxide catalyst obtained of step (d) with a silica source selected from colloidal silica, ethyl silicate, ethyl orthosilicate, and Si/Al combination silica source and formulating and shaping the catalyst.

14. The process as claimed in claim 13, wherein the precipitating agent used in step (a) is selected from the group consisting of urea, sodium hydroxide, ammonium hydroxide, ammonium bicarbonate, tetraalkylammonium hydroxide, and the precursor salts are selected from the group consisting of Ga(NO.sub.3).sub.3.Math.xH.sub.2O, galium halide, Ce(NO.sub.3).sub.3.Math.6H.sub.2O, cerius sulphate, cerium oxalate, ZrO(NO.sub.3).sub.2.Math.xH.sub.2O, Zr(SO.sub.4).sub.2, zirconium alkoxide, zirconium halide, lanthanum nitrate, lanthanum halide and lanthanum carbonate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG. 1: Schematic process flow diagram for the reaction of methanol with CO.sub.2 in a fixed-bed continuous flow reactor. Abbreviations: CO.sub.2 cylinder=carbon dioxide gas cylinder, N.sub.2 cylinder=nitrogen gas cylinder, MFC=mass flow controller, NRV=non return valve, PI=pressure indicator, 2-CP=2-cyanopyridine, BPR=back pressure regulator, MeOH=methanol, MPI=methyl picolinimidate, MP=2-methylpicolinate.

[0034] FIG. 2: Catalytic activity data as a function of time in a fixed-bed reactor for the reaction of methanol with CO.sub.2 over CeO.sub.2/Al.sub.2O.sub.3(Catalyst #7). Reaction conditions: catalyst=6.3 g, catalyst bed height=5 cm, reaction temperature=120? C. or 150? C., reactor pressure=30 bar CO.sub.2, methanol:CO.sub.2 molar ratio=1:2.1, 2-CP:methanol molar ratio=1:2, LHSV=2.5 hour.sup.?1, GHSV (CO.sub.2)=1250 hour.sup.?1.

[0035] FIG. 3: Catalytic activity data as a function of time for the reaction of methanol with CO.sub.2 in a fixed-bed reactor over CeO.sub.2/SiO.sub.2 (Catalyst #6). Reaction conditions: catalyst=6.3 g, catalyst bed height=5 cm, reaction temperature=150? C., reactor pressure=30 bar CO.sub.2, methanol:CO.sub.2 molar ratio=1:2.1, 2-CP:methanol molar ratio=1:2, LHSV=2.5 hour.sup.?1, GHSV (CO.sub.2)=1250 hour.sup.?1.

[0036] FIG. 4: Catalytic activity data as a function of reaction time for the reaction of methanol with CO.sub.2 in a fixed-bed reactor over ZrCeO.sub.2/SiO.sub.2 (Catalyst #1). Reaction conditions: catalyst=6.3 g, catalyst bed height=5 cm, reaction temperature=150? C., reactor pressure=30 bar CO.sub.2, methanol:CO.sub.2 molar ratio=1:2.1, 2-CP:methanol molar ratio=1:2, LHSV=2.5 hour.sup.?1, GHSV (CO.sub.2)=1250 hour.sup.?1.

[0037] FIG. 5: Time-on-stream catalytic activity data for the reaction of methanol with CO.sub.2 in presence of 2-cyanopyridine (2-CP) over ZrCeO.sub.2/SiO.sub.2 (Catalyst #3) in a fixed-bed reactor. Reaction conditions: catalyst=7.6 g (4 cc), bed height of catalyst=3 to 4 cm, combined bed height of catalyst and diluents=10 cm, reaction temperature=150? C., reactor pressure=30 bar CO.sub.2, methanol:CO.sub.2 molar ratio=1:1, 2-CP:methanol molar ratio=1:2, LHSV=2.5 hour.sup.?1, GHSV (CO.sub.2)=630 hour.sup.?1.

[0038] FIG. 6: Time-on-stream catalytic activity data for the reaction of methanol with CO.sub.2 in presence of 2-cyanopyridine (2-CP) over ZrCeO.sub.2/Al.sub.2O.sub.3 (Catalyst #4) in a fixed-bed reactor. Reaction conditions: catalyst=7.09 g, silicon carbide diluents=7.21 g, bed height (catalyst+diluents)=8 cm, reaction temperature=150? C., reactor pressure=30 bar CO.sub.2, methanol:CO.sub.2 molar ratio=1:1, 2-CP:methanol molar ratio=1:2, LHSV=2.5 hour.sup.?1, GHSV (CO.sub.2)=625 hour.sup.?1.

[0039] FIG. 7: Catalytic activity data as a function of time for the reaction of methanol with CO.sub.2 over self-bound ZrCeO.sub.2 (Catalyst #5) in a fixed-bed reactor. Reaction conditions: catalyst=7.5969 g, bed height (catalyst+diluents)=10 cm, reaction temperature=150? C., reactor pressure=30 bar CO.sub.2, methanol:CO.sub.2 molar ratio=1:1, 2-CP:methanol molar ratio=1:2, LHSV=2.5 hour.sup.?1, GHSV (CO.sub.2)=625 hour.sup.?1.

[0040] FIG. 8: Scanning electron microscopy (SEM) image showing elongated hexagonal morphology of ceria-based mixed oxide component in Catalyst #3.

DETAILED DESCRIPTION OF THE INVENTION

[0041] The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated.

[0042] The present invention provides a process for the synthesis of DMC, in a continuous process, by contacting methanol with CO.sub.2 over an improved catalyst formulation in the presence of a dehydrating or water trapping compound, wherein said improved catalyst formulation comprises of: (a) mixed oxides of cerium (Ce) with other elements selected from the group consisting of zirconium (Zr), lanthanum (La), gallium (Ga) and combinations thereof, and (b) a form of silica (SiO.sub.2) derived from group of silica precursors selected from group consisting of colloidal silica, ethyl silicate, ethyl orthosilicate, Si/Al combinations or like silica material, characterized in that, silica content in the catalyst formulation is between 2 and 25 weight percent, content of Ce-oxide in the mixed oxide portion is between 50 and 95 mole percent, mixed oxide possesses an elongated hexagonal, spindle-shaped, rod-like or spherical morphology and formulation is hydrophobic with water adsorption capacity not more than 10 weight percent, possesses a crush strength between 2 and 7 Newton, and stable in the continuous DMC synthesis reaction.

[0043] The molar ratio of methanol to dehydrating agent is in the range of 1:1 to 3:1.

[0044] The molar ratio of methanol to carbon dioxide is in the range of 1:3 to 2:1.

[0045] The liquid hourly space velocity of liquid feed (LHSV=volume of liquid feed per unit volume of catalyst per hour) is 0.5 to 4 hour.sup.?1 and gas hourly space velocity of carbon dioxide (GHSV=volume of CO.sub.2 per volume of catalyst per hour) is 400 to 1000 hour.sup.?1.

[0046] The reaction temperature is in the range of 120? C. to 160? C.

[0047] The reaction time period for stirred tank, batch reactor process is in a range of 2 to 10 hours.

[0048] The reaction pressure is in the range of 30 to 100 bar and the catalyst formulation has at least 30 hours of catalytic stability.

[0049] The dehydrating (or water trapping or water scavenging) compound is selected from organic nitrile compounds, more preferably 2-cyanopyridine (2-CP).

[0050] The carbon dioxide used in DMC synthesis reaction is 100% pure or is admixed with carbon monoxide, hydrogen and/or hydrocarbons.

[0051] Methanol used in the reaction has purity of 90 to 100%.

[0052] The continuous reaction of making DMC from methanol and CO.sub.2 is performed in a fixed-bed reactor, continuous stirred tank reactor or like continuous-flow reactors.

[0053] The process for making DMC is conducted preferably in a fixed-bed continuous-flow reactor.

[0054] Dehydrating compound2-cyanopyridine (2-CP) is converted mainly into 2-picolinamide (2-PA) and a small quantity of 2-methyl picolinate (MP) and methyl picolinimidate (MPI). Methanol conversion to dimethyl ether (DME) over the catalyst formulation is negligible (<0.2%).

[0055] The dimethyl carbonate yield in the process is above 30 mole percent.

[0056] In another embodiment, the present invention provides a stabilized, formulated ceria-based mixed metal oxide supported on silica compound as a catalyst for use in continuous production of DMC from methanol and CO.sub.2.

[0057] In an embodiment, the present invention provides an improved, stabilized, solid catalyst formulation essentially comprising: (a) mixed oxides of cerium (Ce) with other elements selected from the group consisting of zirconium (Zr), lanthanum (La), gallium (Ga) and combinations thereof, and (b) a form of silica (SiO.sub.2) derived from group consisting of silica precursors selected from colloidal silica, ethyl silicate, ethyl orthosilicate, Si/Al combinations or like silica material, characterized in that, silica content in the catalyst formulation is between 2 and 25 weight percent, content of Ce-oxide in the mixed oxide portion is between 50 and 95 mole percent, mixed oxide possesses an elongated hexagonal, spindle-shaped, rod-like or spherical morphology and formulation is hydrophobic with water adsorption capacity not more than 10 weight percent, possesses a crush strength between 2 and 7 Newton, and stable in the continuous DMC synthesis reaction.

[0058] The catalyst is selected from ZrCeO.sub.2/SiO.sub.2, ZrGaCeO.sub.2/SiO.sub.2, ZrCeO.sub.2/Al.sub.2O.sub.3, ZrCeO.sub.2, CeO.sub.2/SiO.sub.2, CeO.sub.2/Al.sub.2O.sub.3, ZrLaCeO.sub.2/SiO.sub.2, GaCeO.sub.2/SiO.sub.2, LaCeO.sub.2/SiO.sub.2, ZrGaCeO.sub.2/SiO.sub.2, ZrGaCeO.sub.2/SiO.sub.2Al.sub.2O.sub.3, GaCeO.sub.2/SiO.sub.2Al.sub.2O.sub.3, LaCeO.sub.2/SiO.sub.2-Al.sub.2O.sub.3 and ZrLaCeO.sub.2/SiO.sub.2Al.sub.2O.sub.3.

[0059] The catalyst formulation is shaped and formed into extrudates, trilobes, spheres or tablets.

[0060] The bi-functional catalyst has both acidic and basic sites on its surface with acidity/basicity molar ratio in the range of 0.5 to 2.5.

[0061] The part of cerium ions in the catalyst is in partially reduced (+3) oxidation state.

[0062] The catalyst formulation has specific surface area in the range of 100 to 300 m.sup.2/g and pore volume in the range of 0.1 to 0.35 cc/g.

[0063] In an embodiment, the present invention further provides a process for the preparation of a stabilized, formulated ceria-based mixed metal oxide supported on silica compound as a catalyst for use in continuous production of DMC from methanol and CO.sub.2.

[0064] The present invention provides a process for the preparation of the above said catalyst formulation comprising the steps of: [0065] a) co-precipitating precursor salt solutions of Ce and other element (Zr, La, Ga or combinations thereof) sequentially or once through at a temperature in the range of 20? C. to 30? C. using a precipitating agent; [0066] b) mixing and ageing of the suspension in step (a) at a temperature in the range of 30? C. to 120? C.; [0067] c) filtering and water washing of the formed precipitate; [0068] d) drying the precipitate of step (c) at 25? C. to 100? C. followed by calcination at a temperature in the range of 400? C. to 600? C. to obtained mixing metal oxide, and [0069] e) mixing the mixed oxide catalyst obtained in step (d) with a silica source selected from colloidal silica, ethyl silicate, ethyl orthosilicate, Si/Al combinations and like silica source and formulating and shaping of the catalyst.

[0070] The precipitating agent is selected from the group consisting of urea, sodium hydroxide, ammonium hydroxide, ammonium bicarbonate, tetra-alkylammonium hydroxide and such like, and more preferably ammonium bicarbonate.

[0071] The salt precursors are selected from the group consisting of Ga(NO.sub.3).sub.3.Math.xH.sub.2O, galium halide, Ce(NO.sub.3).sub.3.Math.6H.sub.2O, cerius sulphate, cerium oxalate, ZrO(NO.sub.3).sub.2.Math.xH.sub.2O, Zr(SO.sub.4).sub.2, zirconium alkoxide, zirconium halide, lanthanum nitrate, lanthanum halide and lanthanum carbonate.

[0072] The catalyst formulation catalyzes the reaction of any alcohol with CO.sub.2 forming the corresponding alkyl carbonate.

[0073] Two moles of methanol and one mole of CO.sub.2 react over the catalyst to form one mole of DMC and one mole of water. The catalyst should contain acidic as well as basic sites in right strength and proportion to activate CO.sub.2 and methanol to form DMC. Dehydrating compound removes water formed in the reaction. Water can compete with methanol for adsorption on the acidic sites and lead to lower DMC yields. Thus, some of the improvements and modifications contemplated include: (1) a catalyst with hydrophobic surface that can limit water adsorption on the catalyst surface and enhance DMC yield. (2) a catalyst with acid sites of moderate strength only to avoid adsorption of dehydrating compound-derived products and thereby, poisoning/deactivating the catalyst. And (3) a catalyst formulation with the support enabling optimum binding strength and doesn't alter the acid-base and adsorption properties of the oxide component.

[0074] In an embodiment of the invention it is found that a catalyst formulation comprising of: (a) mixed oxides of cerium (Ce) with other elements selected from the group consisting of zirconium (Zr), lanthanum (La), gallium (Ga) and combinations thereof, and (b) a form of silica (SiO.sub.2) derived from group of silica precursors of colloidal silica, silicate, orthosilicate, Si/Al compositions and like silica material has the desired physicochemical properties and is highly active and selective for making DMC from methanol and CO.sub.2 in presence of a dehydrating or water trapping compound selected from organic nitriles, more preferably 2-cyanopyridine (2-CP).

[0075] In another embodiment, the catalyst of the invention is stable for several hours in a continuous flow operation. Catalyst formulations can be accomplished with active component and several reducible or non-reducible oxides. It is surprising to find that a formulation made out of mixed oxides of Ce and silica compound shows remarkably stable catalytic performance in the continuous production of DMC from methanol and CO.sub.2 in presence of a dehydrating or water trapping compound.

[0076] In a comparative embodiment, the stability of the self-bound extrudate catalyst of example 5 (Catalyst #5) is depicted in example 13 and FIG. 7, while the enhanced stability of the catalysts of the current invention i.e. Catalyst #1 and Catalyst #3 is depicted in FIGS. 4 and 5.

EXAMPLES

[0077] Following examples are given by way of illustration and therefore should not be construed to limit the scope of the invention.

Example 1

[0078] This example reports the synthesis procedure of cylindrical extrudates of ZrCeO.sub.2/SiO.sub.2 (herein after referred as Catalyst #1) employing ethyl silicate as silica source. Firstly, ZrCeO.sub.2 mixed oxide was prepared as follows: Solution-A was prepared by dissolving 62.6 g of Ce(NO.sub.3).sub.3.Math.6H.sub.2O and 3.7 g of ZrO(NO.sub.3).sub.2.Math.xH.sub.2O in 1920 ml of water while stirring. Solution-B was prepared by dissolving 78.4 g of ammonium bicarbonate, (NH.sub.4)HCO.sub.3 in 640 ml of water while stirring till a clear solution formed. Solution-B was added to Solution-A over 30 min while stirring. The suspension was allowed to age at room temperature (25? C.) for 2 hours under stirring condition. The solid formed was separated by centrifugation/filtration and washed with 2.5% ethanol in water solution (4000 ml). It was dried at 80? C. for 24 hours and calcinied at 600? C. for 5 hours. Yield of ZrCeO.sub.2 mixed oxide recovered was 24 g. Then, the mixed oxide powder was added to ethyl silicate (in 82.5:17.5 weight ratio of mixed oxide to ethyl silicate). It was aged at 25? C. till dough-like paste formed which was then shaped into cylindrical extrudates (2 mm diameter) using an extruder, dried at 25? C. for 16 hours and calcinied at 550? C. for 5 hours. The catalyst thus formed was referred as Catalyst #1.

Example 2

[0079] This example reports the synthesis procedure of ZrGaCeO.sub.2/SiO.sub.2 extrudates (hereafter referred as Catalyst #2). Firstly, ZrGaCeO.sub.2 mixed oxide was prepared, in which, Solution-A was prepared by dissolving 62.6 g of Ce(NO.sub.3).sub.3.Math.6H.sub.2O, 1.48 g of ZrO(NO.sub.3).sub.2.Math.xH.sub.2O and 2.457 g of Ga(NO.sub.3).sub.3.Math.xH.sub.2O in 1920 ml of water by stirring for 10 min. Solution-B was prepared by dissolving 78.5 g of ammonium bicarbonate in 640 ml of water by stirring for 10 min till a clear solution formed. Solution-B was added to solution-A over a period of 30 min. The resulting suspension was stirred for another 2 hours at room temperature (25? C.). The solid formed was separated by filtration and washed several times with 2.5% ethanol in water solution (4,000 ml). It was dried at 80? C. in an oven for 24 hours and calcinied in a muffle furnace (in air) at 500? C. for 3 hours. Yield of ZrGaCeO.sub.2 obtained was 24.5 g. The ZrGaCe mixed oxide powder and ethyl silicate in 82.5:17.5 weight ratio was mixed. It was aged at 25? C. till dough-like paste formed which was then, shaped into extrudates of 2 mm diameter using an extruder. The material was dried at 25? C. for 16 hours and calcinied at 550? C. for 5 hours. The material thus formed was labeled as Catalyst #2.

Example 3

[0080] This example provides the preparation method of trilobes of ZrCeO.sub.2/SiO.sub.2 (hereafter referred as Catalyst #3) employing colloidal silica as silica source. In typical synthesis, Solution-A was prepared dissolving 183.463 g of Ce(NO.sub.3).sub.3.Math.6H.sub.2O and 10.873 g of ZrO(NO.sub.3).sub.2.Math.xH.sub.2O in 5625 ml of H.sub.2O while stirring for 30 min. Solution-B was prepared by dissolving 229.75 g of ammonium bicarbonate (NH.sub.4)HCO.sub.3 in 1875 ml of water by stirring until a clear solution was observed. Then, Solution-B was added drop-wise to Solution-A with constant stirring. The stirring was continued for another 30 min at room temperature (25? C.). The resulting suspension was taken into a partially closed flask and aged for 2.5 hours at 95? C. (placing in a temperature-controlled oil bath) while stirring at a speed of 230 rpm. After the heat treatment, the precipitate was filtered and washed with 2.5% ethanol in water solution. The solid obtained was dried at 110? C. for 16 hours and calcinied in the presence of air at 550? C. for 4 hours. The yield of ZrCeO.sub.2 mixed oxide powder recovered was 75 g. It was converted into dough by adding about 30 ml of 40% colloidal silica. Trilobes of this material were formed using an extruder. They were dried at 110? C. for 12 hours and calcinied in air at 550? C. The material thus prepared was designated as Catalyst #3. X-ray photoelectron spectroscopy revealed that the content of reduced Ce ions (Ce.sup.3+) in this sample is 14.5% and the ratios of Ce.sup.4+/Ce.sup.3+=5.89.

Example 4

[0081] This example provides the preparation method of trilobes of ZrCeO.sub.2/Al.sub.2O.sub.3 (hereafter referred as Catalyst #4). In typical synthesis, Solution-A was prepared dissolving 183.463 g of Ce(NO.sub.3).sub.3.Math.6 H.sub.2O and 10.873 g of ZrO(NO.sub.3).sub.2.Math.xH.sub.2O in 5625 ml of H.sub.2O while stirring for 30 min. Solution-B was prepared by dissolving 229.75 g of (NH.sub.4)HCO.sub.3 in 1875 ml of water by stirring until a clear solution was observed. Then, Solution-B was added drop-wise to Solution-A with constant stirring. The stirring was continued for another 30 min at room temperature (25? C.). The resulting suspension was taken into a partially closed flask and aged for 2.5 hours at 95? C. (placing in a temperature-controlled oil bath) while stirring at a speed of 230 rpm. After the heat treatment, the precipitate was filtered and washed with 2.5% ethanol in water solution. The solid obtained was dried at 110? C. for 16 hours and calcinied in the presence of air at 550? C. for 4 hours. The yield of ZrCeO.sub.2 mixed oxide powder recovered was 75 g. It was converted into dough by adding pseudo-boehmite calcimined at 900? C. (ZrCeO.sub.2 powder:Al.sub.2O.sub.3 mass ratio=80:20) and 5% acetic acid solution. Trilobes of this material were formed using an extruder. They were dried at 110? C. for 12 hours and calcined in air at 550? C. The material thus prepared was designated as Catalyst #4.

Example 5

[0082] This example provides the preparation method of ZrCeO.sub.2 and its shaped form (hereafter referred as Catalyst #5) via., self-binding using acetic acid as peptizing agent. In a typical preparation, cerium nitrate (244.6 g) and zirconyl nitrate (14.5 g) were dissolved in 7500 ml of de-mineralized water (Solution-A). (NH.sub.4)HCO.sub.3 (306.3 g) was dissolved in 2500 ml of de-mineralized water (Solution-B). Solution-B was added drop-wise to Solution-A with constant stirring over a period of 30 min. The suspension was kept for aging at room temperature (25? C.) for 2 hours while stirring. The solid was separated by centrifugation and washed with 2.5% ethanol solution (16,000 ml). It was dried at 80? C. for 1 day and calcinied at 600? C. for 5 hours. The obtained mixed oxide powder was converted in dough by adding 5% acetic acid solution and shaped into trilobes using an extruder, followed by drying at 110? C. for 12 hours and calcining at 550? C. for 5 hours. The material thus prepared was labeled as Catalyst #5.

Example 6

[0083] This comparative example provides the preparation method of cylindrical extrudates of CeO.sub.2/SiO.sub.2 (hereafter referred as Catalyst #6). Commercial CeO.sub.2 powder (with no pre-activation) and tetraethyl orthosilicate (TEOS) in 82.5:17.5 weight ratio were mixed. It was aged at room temperature (25? C.) till suitable dough-like paste formed. Then, it was shaped into cylindrical extrudates (of 2 mm diameter) using an extruder, dried at 25? C. for 16 hours and calcinied at 550? C. for 5 hours. The material thus prepared was labeled as Catalyst #6.

Example 7

[0084] This comparative example provides the preparation method of cylindrical extrudates of CeO.sub.2/Al.sub.2O.sub.3 (hereafter referred as Catalyst #7). Commercial CeO.sub.2 powder (without any pre-treatment) and pseudo-boehmite in 80:20 weight ratio were mixed in presence of a small quantity of water or 5% acetic acid solution till a suitable dough formed. Then, it was extruded (2 mm diameter), dried at room temperature (25? C.) for 24 hours and calcinied at 550? C. for 5 hours. The material thus prepared was labeled as Catalyst #7.

Example 8

[0085] This example reports the synthesis procedure of ZrGaCeO.sub.2 powder (hereafter referred as Catalyst #8). Solution-A was prepared by dissolving 1.9540 g of Ce(NO.sub.3).sub.3.Math.6H.sub.2O, 0.0462 g of ZrO(NO.sub.3).sub.2.Math.xH.sub.2O and 0.0767 g of Ga(NO.sub.3).sub.3.Math.xH.sub.2O in 60 ml of water by stirring for 10 min. Solution-B was prepared by dissolving 2.4507 g of ammonium bicarbonate in 20 ml of water by stirring for 5 min. Solution-B was added drop-wise to solution-A over a period of 30 min. The resulting was stirred for another 2 hours at 25? C. The solid formed was separated by filtration and washed several times with 2.5% ethanol in water solution (375 ml). It was dried at 80? C. in an oven for 24 hours and calcinied in a muffle furnace (in air) at 500? C. for 3 hours. The mixed oxide material thus formed was labeled as Catalyst #8.

Example 9

[0086] This example reports the synthesis procedure of ZrCeO.sub.2 powder (hereafter referred as Catalyst #9). Solution-A was prepared by dissolving 1.9540 g of Ce(NO.sub.3).sub.3.Math.6H.sub.2O and 0.1159 g of ZrO(NO.sub.3).sub.2.Math.xH.sub.2O in 60 ml of water by stirring. Solution-B was prepared by dissolving 2.4507 g of ammonium bicarbonate in 20 ml of water by stirring. Solution-B was added drop-wise to solution-A over a period of 30 min. The resulting was stirred for another 2 hours at 25? C. The solid formed was separated by centrifugation and washed with 2.5% ethanol in water solution (125 ml). It was dried at 80? C. in an oven for 24 hours and calcinied in a muffle furnace (in air) at 600? C. for 5 hours. The mixed oxide material thus formed was labeled as Catalyst #9.

Example 10

[0087] This example provides the experimental procedure for evaluation of shaped catalysts (#1, #6 and #7) in the reaction of methanol (MeOH) with CO.sub.2 in presence of 2-cyanopyridine (2-CP) as dehydrating or water-trapping compound. The experiments were performed in a fixed-bed, down-flow stainless steel reactor (FIG. 1). The reactor tube had the following dimensions: internal diameter=1.5 cm, outer diameter=1.9 cm and length=30 cm. Sized catalyst extrudate beads (diameter=2 mm and length=3 mm) were placed in an isothermal zone of the reactor with a sufficient layer of inert material near inlet to ensure proper pre-heating and distribution of feed before it reaches the catalyst zone. Typically, about 6.3 g of catalyst extrudes (with catalyst volume=4.8 ml and bed height of about 5 cm) were loaded in the reactor. The loaded catalyst was activated in nitrogen at 200? C. for 5 hours.

[0088] The system was pressurized up to 30 bar with CO.sub.2 and the temperature was allowed to reach desired value (120-150? C.). The mixture of MeOH and 2-CP (in molar ratio of 2:1) was pumped into the reactor using a high-performance liquid chromatography pump (HPLC pump) (at a flow rate of methanol=4.24 g/hour and 2-CP=6.92 g/hour; density of feed solution=0.93 g/ml; LHSV=2.5 hour.sup.?1). CO.sub.2 gas flow rate was 100 ml/min (GHSV=1250 hour.sup.?1). Liquid mass balance was more than 98%. To 8 ml of the product, 30 ml of ethanol and 0.202 g of nonane-1-ol were added as a solvent and internal standard, respectively. It was stirred for 10 min till the solid dissolved and a liquid was a clear solution. It was analyzed with the help of a Varian 3400 GC equipped with a flame ionization detector and CP-SIL5CB column (60 m-long?0.32 mm-i.d.?0.25 ?m-film thickness). Injector port temperature=column temperature=detector port temperature=270? C. Injection volume=1 microliter. GC program: 40? C. to 80? C. @ 10? C./min, hold for 6 min and then 80? C. to 270? C. @ 20? C./min and hold for 8 min. The results of the catalytic activity and observations are listed in Table 1. Catalytic activity data as a function of time are presented in FIGS. 2 to 4.

TABLE-US-00001 TABLE 1 Comparative catalytic activity data for the reaction of methanol with CO.sub.2 Reaction Yield of DMC (mol %) temperature At 3 Catalyst (? C.) hours At the end Observation Catalyst #7 120 8 4.5 (after 30 hours) Unstable Catalyst #7 150 22 13.2 (after 20 hours) Unstable Catalyst #6 150 38 24 (after 32 hours) Unstable Catalyst #1 150 40 40 (after 30 hours) Stable

Example 11

[0089] This example provides the experimental procedure for the evaluation of shaped Catalysts #3 in the reaction of methanol (MeOH) with CO.sub.2 in presence of 2-cyanopyridine (2-CP) as dehydrating or water-trapping compound. The experiments were performed in a fixed-bed, down-flow stainless steel reactor. The reactor tube had the following dimensions: internal diameter=1.57 cm and length=62 cm. The catalyst was placed in an isothermal zone of the reactor with a sufficient layer of inert material near inlet to ensure proper pre-heating and distribution of feed before it reaches the catalyst zone. During the loading process, the catalyst was typically divided into multiple beds. Following each bed of the catalyst, silicon carbide (80-120 mesh) was packed into the void spaces of the catalyst bed to ensure uniformity in gas-liquid flow distribution. Typically, about 4 cc of sized catalyst trilobes (1.5 mm diameter and 0.5 to 2 cm length) were loaded into the reactor. Catalyst bed height was about 3 to 4 cm. The loaded catalyst was activated in helium flow at 170 ml/min (200? C. for 7 hours). The system was pressurized up to 30 bar with CO.sub.2 (GHSV=630 hour.sup.1) and the temperature was allowed to reach 150? C. The mixture of MeOH+2-CP (in molar ratio of 2:1) was pumped into the reactor using a high-performance liquid chromatography pump (HPLC pump) at a flow rate of 0.15 ml/min. CO.sub.2 gas flow was 42 ml/min and overall liquid hourly space velocity (LHSV) of the feed (MeOH+2-CP) was 2.25 hour-. To 8 ml of the product, 30 ml of ethanol and 0.202 g of nonane-1-ol were added as a solvent and internal standard, respectively. It was stirred for 10 min till the solid dissolved and the liquid obtained was a clear solution. It was analyzed with the help of a Varian 3400 GC equipped with a flame ionization detector and CP-SIL5CB column (60 m-long?0.32 mm-i.d.?0.25 ?m-film thickness). Injector port temperature=column temperature=detector port temperature=270? C. Injection volume=1 microliter. GC program: 40? C. to 80? C. @ 10? C./min, hold for 6 min and then, 80? C. to 270? C. @ 20? C./min and hold for 8 min. Methanol conversion of 63 mol % and DMC yield of 40 mol % were obtained. 2-CP conversion of 52 mol % and 2-picolinamide (2-PA) yield 46% was observed. The catalytic activity (methanol conversion and DMC yield) was stable over a period of 60 hours in a continuous run (FIG. 5).

Example 12

[0090] This example provides the experimental procedure for the evaluation of shaped catalyst #4 in the reaction of methanol (MeOH) with CO.sub.2 in presence of 2-cyanopyridine (2-CP) as dehydrating or water-trapping compound. The experiments were performed in a fixed-bed, down-flow stainless steel reactor. The reactor tube had the following dimensions: internal diameter=1.5 cm, outer diameter=1.9 cm and length=32 cm. The catalyst was placed in an isothermal zone of the reactor with a sufficient layer of inert material near inlet to ensure proper pre-heating and distribution of feed before it reaches the catalyst zone.

[0091] During the loading process, the catalyst was typically broken into uniform beds of diameter=2 mm and length=3 mm. Silicon carbide (80-120 mesh) was used as a diluent to ensure uniformity in gas-liquid flow distribution. Typically, about 7.09 g (4.8 cc) of catalyst trilobes and 7.21 g (4.8 ml) of silicon carbide diluent were loaded into the reactor. The bed height (catalyst+diluents) was 8 cm. The loaded catalyst was activated in nitrogen at 200? C. for 5 hours. The system was pressurized up to 30 bar with CO.sub.2 and the temperature was allowed to reach 150? C. The mixture of MeOH+2-CP (in molar ratio of 2:1) was pumped (0.2 ml/min) into the reactor using a high-performance liquid chromatography pump (HPLC pump) (LHSV=2.5 hour.sup.?1). CO.sub.2 gas flow was 50 ml/min (GHSV=625 hour.sup.?1).

[0092] The continuous run was conducted for 30 hours. Methanol conversion decreased over 30 hours from 55 to 24 mol % and DMC yield decreased from 39 to 17 mol % with the selectivity being about 70 mol % (FIG. 6).

Example 13

[0093] This example provides the experimental procedure for the evaluation of shaped catalyst #5 in the reaction of methanol (MeOH) with CO.sub.2 in presence of 2-cyanopyridine (2-CP) as dehydrating or water-trapping compound. The experiments were performed in a fixed-bed, down-flow stainless steel reactor. The reactor tube had the following dimensions: internal diameter=1.5 cm, outer diameter=1.9 cm and length=32 cm. The catalyst was placed in an isothermal zone of the reactor with a sufficient layer of inert material near inlet to ensure proper pre-heating and distribution of feed before it reaches the catalyst zone. During the loading process, the catalyst was typically broken into uniform beds of diameter=3 mm and length=4 mm. Silicon carbide (80-120 mesh) was used as a diluent to ensure uniformity in gas-liquid flow distribution. Typically, about 7.5969 g (4.8 ml) of catalyst and 6.5578 g (4.8 ml) of ceramic ball diluent were loaded into the reactor. The bed height (catalyst+diluents) was 10 cm. The loaded catalyst was activated in nitrogen at 200? C. for 5 hours. The system was pressurized up to 30 bar with CO.sub.2 and the temperature was allowed to reach desired reaction temperature. The mixture of MeOH+2-CP (in molar ratio of 2:1) was pumped (0.2 ml/min) into the reactor using a high-performance liquid chromatography pump (HPLC pump; LHSV=2.5 hour.sup.?1). CO.sub.2 gas flow was 50 ml/min (GHSV=625 hour.sup.1). Reaction temperature was 130? C. for the initial 25 hours and then 140? C. for another 25 hours. Methanol conversion decreased from 65 to 53 mol % and DMC yield decreased from 39 to 32 mol % in 48 hours (FIG. 7).

Example 14

[0094] This example reports the catalytic performance of mixed oxides (Catalysts #8 and #9) in a batch reactor. The reaction was conducted in a 100 cc stainless-steel Parr high pressure autoclave equipped with a magnetic drive stirrer, thermocouple and programmable controller unit. 3.2 g of methanol, 5.2 g of 2-cyanopyridine (2-CP) and 0.1 g of catalyst powder were taken in the reactor which was later pressurized with CO.sub.2 to 5 MPa at 25? C. The temperature of the reactor was raised to 120? C. and the reaction was conducted while stirring at a speed of 600 rpm for 12 hours. At the end of the reaction, the reactor was cooled to 25? C. and unreacted CO.sub.2 was vented out. Then, 30 ml of ethanol and 0.202 g of nonane-1-ol were added as a solvent and internal standard, respectively. The contents of the reactor were stirred for 10 min to dissolve the solid organic product completely in the liquid portion. The contents were transferred to the centrifuge tube. The catalyst was separated from the liquid products by centrifugation/decantation. The liquid products were analyzed and quantified with the help of a Varian 3400 GC equipped with a flame ionization detector and CP-SIL5CB column (60 m-long?0.32 mm-i.d.?0.25 ?m-film thickness). Injector port temperature=column temperature=detector port temperature=270? C. Injection volume=1 microliter. GC program: 40? C. to 80? C. @ 10? C./min, then hold for 6 min. Later, 80? C. to 270? C. @ 20? C./min and hold for 8 min. The results are presented in Table 2.

TABLE-US-00002 TABLE 2 Catalytic activity data of ZrCeO.sub.2 and ZrGaCeO.sub.2 in batch reactor Catalyst Methanol conversion(mol %) DMC yield (mol %) Catalyst #8 71.9 60.7 Catalyst #9 77.1 71.7

[0095] Physicochemical characteristics of the shaped catalysts prepared in Examples 1 to 9 are listed in Table 3. SEM image showing typical morphology of cerium-based mixed oxide component in Catalyst #3 is depicted in FIG. 8.

TABLE-US-00003 TABLE 3 Physiochemical properties of the catalysts Specific Average Water surface Pore pore Crushing adsorption area (S.sub.BET; volume size Acidity Basicity strength capacity Catalyst m.sup.2/g) (cc/g) (nm) (mmol/g) (mmol/g) (Newton) (wt %) Catalyst #1 149 0.18 2.5 2.5 Catalyst #3 113 0.17 6.0 0.28 0.26 5.4 1.5 Catalyst #5 49 0.08 0.14 0.068 2.2 Catalyst #6 147 0.24 5.7 0.29 0.10 3.7 Catalyst #7 84 0.14 3.4 0.16 0.10 3.9

Advantages of the Invention

[0096] Highly stable catalyst under the reaction conditions of DMC synthesis. [0097] Continuous flow process for making DMC. [0098] Heterogeneous, bifunctional, hydrophobic catalyst-based industrially feasible process. [0099] Economically beneficial, sustainable process for DMC.

[0100] Used catalyst can be reactivated or regenerated by known procedures of solvent wash and activation in air or oxygen atmosphere at high temperature.