Continuous process for the synthesis of dimethyl carbonate over a cerium-based catalyst formulation

1 . A continuous process for synthesis of dimethyl carbonate (DMC), said process comprising contacting methanol with CO 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 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 −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 −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 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 Zr—CeO 2 /SiO 2 , Zr—Ga—CeO 2 /SiO 2 , Zr—CeO 2 /Al 2 O 3 , Zr—CeO 2 , CeO 2 /SiO 2 , CeO 2 /Al 2 O 3 , Zr—La—CeO 2 /SiO 2 , Ga—CeO 2 /SiO 2 , La—CeO 2 /SiO 2 , Zr—Ga—CeO 2 /SiO 2 , Zr—Ga—CeO 2 /SiO 2 —Al 2 O 3 , Ga—CeO 2 /SiO 2 —Al 2 O 3 , La—CeO 2 /SiO 2 —Al 2 O 3 and Zr—La—CeO 2 /SiO 2 —Al 2 O 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 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 3 ) 3 ·xH 2 O, galium halide, Ce(NO 3 ) 3 ·6H 2 O, cerius sulphate, cerium oxalate, ZrO(NO 3 ) 2 ·xH 2 O, Zr(SO 4 ) 2 , zirconium alkoxide, zirconium halide, lanthanum nitrate, lanthanum halide and lanthanum carbonate.