Process for the synthesis of dialkyl carbonates

Abstract

The patent discloses a process for the synthesis of dialkyl carbonates catalyzed by a catalyst composition AB oxides, wherein A and B are rare earth metals or A and B are combination of rare earth and transition metals with ratios ranging from 0.5:10 to 10:0.5.

Claims

1. A process for the synthesis of dialkyl carbonates, using a catalyst of AB oxides supported on a support selected from carbon, neutral alumina or silica, the process comprising the steps of: a. charging alkyl carbamate and aliphatic alcohol (1:5) in a high pressure reactor, adding the catalyst and heating the reactor to 100-300 C. with stirring; and b. removing ammonia formed over the period of reaction and cooling the reaction to room temperature to obtain the desired alkyl carbonate; wherein the dialkyl carbonates are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC) or dibutyl carbonate (DBC); and wherein A and B are selected from rare earth, transition metals and alkaline earth metals and the AB oxide has an A:B ratio ranging from 0.5:10 to 10:0.5.

2. The process as claimed in claim 1, wherein the catalyst is a mixed metal oxide, said metal selected from rare earth/inner transition elements or transition metals.

3. The process as claimed in claim 2, wherein said catalyst is optionally a ternary mixed metal oxide having more than two elements used in combination in the molar ratio a:b:c, where element a is in a range of 0.1 to 1; element b is in a range of 0.1 to 1-x and element c is x, wherein x is in the range of 0.01 to 0.09, wherein said elements are selected from rare earth, transition metals and alkaline earth metals.

4. The process as claimed in claim 2, wherein the element is selected from Zr, Ce, Fe or La.

5. The process as claimed in claim 2, wherein metal oxide is CeZrO.

6. The process as claimed in claim 1, wherein the process is conducted with CO.sub.2 or N.sub.2 stripping.

7. The process as claimed in claim 1, wherein the process is conducted in batch or continuous mode in an autoclave, packed bed reactor or bubble column reactor.

8. The process as claimed in claim 1, wherein conversion of alkyl carbamate is >30% and selectivity is more than 30% to the corresponding alkyl carbonate.

9. A process for the synthesis of dialkyl carbonates using a catalyst, the process comprising the steps of: a. reacting an alkyl carbamate and an aliphatic alcohol in the presence of a catalyst in a pressurized reactor at 100-300 C. with stirring; b. removing ammonia formed over the period of reaction; c. cooling the reaction to room temperature; and d. isolating the synthesized dialkyl carbonate, the synthesized dialkyl carbonate selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC) and dibutyl carbonate (DBC); wherein the catalyst is an AB oxide having an A:B ratio ranging from 0.5:10 to 10:0.5, each of A and B being different elements selected from Mg, Sr, Zr, Ce, Fe and La.

10. The process of claim 9, wherein the catalyst is on a support, the support selected from carbon, neutral alumina or silica.

11. A process for the synthesis of dialkyl carbonates using a catalyst, the process comprising the steps of: a. reacting an alkyl carbamate and an aliphatic alcohol in the presence of the catalyst in a pressurized reactor at 100-300 C. with stirring; b. removing ammonia formed over the period of reaction; c. cooling the reaction to room temperature; and d. isolating the synthesized dialkyl carbonate, the synthesized dialkyl carbonate selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC) and dibutyl carbonate (DBC); wherein the catalyst is a mixed metal oxide having more than two elements used in combination in the molar ratio a:b:c, where element a is in a range of 0.1 to 1; element b is in a range of 0.1 to 1-x and element c is x, wherein x is in the range of 0.01 to 0.09, wherein elements a, b, and c of the mixed metal oxide are selected from rare earth, transition metals and alkaline earth metals.

12. The process of claim 11, wherein the catalyst is on a support, the support selected from carbon, neutral alumina or silica.

13. The process of claim 11, wherein each of a, b, and c of the mixed metal oxide are selected from Mg, Sr, Zr, Ce, Fe and La.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1: XRD of CeZrO catalyst.

(2) FIG. 2: SEM of CeZrO catalyst.

(3) FIG. 3: 3A Gas Chromatography Chart for Di methyl carbonate (DMC) and Methyl-; N-Methyl carbamate (MNMC) formation with CeZrO

(4) Catalyst: 3B Gas Chromatography Mass Spectroscopy (GCMS) Chart for DMC and MMC formation with CeZrO Catalyst.

DETAILED DESCRIPTION OF THE INVENTION

(5) Present invention provides a process for the synthesis of dialkyl carbonate catalyzed by mixed metal oxides of rare earth metals/transition metals calcined at higher temperature.

(6) The present invention provides a process for the synthesis of dialkyl carbonates comprising reacting methanol and methyl carbamate (MC) in presence of novel catalyst system is to obtain the desired carbonates.

(7) The present invention provides a process wherein dialkyl carbonates are selected from di methyl carbonate (DMC), di ethyl carbonate (DEC), di propyl carbonate (DPC) or di butyl carbonate (DBC).

(8) The present invention provides a process wherein the catalyst is a mixed metal oxide. The present invention provides a catalyst for the process wherein the Metal is selected from rare earth/inner transition elements or transition metals.

(9) In a more preferred embodiment, the present invention provides a catalyst for the process wherein the elements are selected from, but not limited to Zr, Ce, Fe or La.

(10) The present invention provides a catalyst for the process wherein the elements are used in combinations in the ratio 0.5:10 to 10:0.5.

(11) In a more preferred embodiment the present invention provides a catalyst for the process wherein the ratio is 1:1 to 5:1.

(12) The present invention provides a catalyst for the process wherein mixed metal oxide is CeZrO.

(13) in an aspect, the invention provides a process using mixed metal oxide catalysts for the preparation of di alkyl carbonates, wherein the catalysts are prepared by employing co-precipitation and urea hydrolysis method.

(14) In another aspect of the invention, mixed metal oxides contain combination of metal oxides synthesized from rare earth/inner transition elements or transition metals calcined at higher temperature, preferably in the range of 500 C. to 900 C. to obtain the catalyst.

(15) In yet another aspect of the invention, the catalyst is prepared by a process comprising: a. mixing solution A comprising of a first metal nitrate with solution B comprising of a second metal nitrate in distilled water; b. adding the solutions A and B of step (a) drop wise to water to cause precipitation by maintaining pH between 9-10 and aging the precipitate in mother liquor under stirring; c. filtering and washing the precipitate of step (b) with distilled water till pH 7 was obtained to get rid of alkali and NO.sub.3.sup. ions; d. drying the precipitate of step (c) and crashing to a fine powder; and e. calcining the powder of step (d) under air flow at 500 C. to 900 C. to obtain the desired catalyst.

(16) In step (b) of the co precipitation process for the preparation of the mixed metal oxide catalyst, pH adjustment may be carried out using agent selected from NaOH, citric acid or ammonia.

(17) In still another aspect, mixed metal oxides containing combination of metal oxides are synthesized using urea hydrolysis method from rare earth/inner transition elements or transition metals calcined at higher temperature preferably between 500 C. to 900 C. to obtain the catalyst.

(18) In another aspect of the invention, the catalyst is prepared by a process comprising: a. mixing solution A comprising of a first metal nitrate with solution B comprising of a second metal nitrate in distilled water and adding urea such that urea:nitrate ion ratio is 1.6:1; b. refluxing the solution of metal nitrates and urea of step (a) for 48 h; c. filtering and washing the solution of step (b) with distilled water and then with ethanol to remove any un-complexed nitrate ions to obtain a solid precursor as a precipitate; d. drying the precipitate of step (c) and crushing to a fine powder; and e. calcining the powder of step (d) under air flow to obtain the desired catalyst.

(19) The present invention provides a process wherein the catalyst is supported.

(20) The present invention provides a catalyst for the process wherein the support is selected from carbon, neutral alumina or silica.

(21) The present invention provides a process wherein the catalyst is without support.

(22) The catalyst is characterized with respect to surface area in the range of 50 to 150 m.sup.2/g. The catalyst is characterized by XRD and SEM (Refer FIGS. 1 and 2).

(23) The invention provides a process for the synthesis of dialkyl carbonates comprising the steps of: (a) Charging alkyl carbamate and aliphatic alcohol (1:5) in a high pressure reactor, adding the catalyst and heating the reactor to 100-300 C. with stirring; and (b) Removing ammonia formed over the period of reaction and cooling the reaction to room temperature in the range of 20 to 30 C. to obtain the desired alkyl carbonate.

(24) The invention provides a process for the synthesis of alkyl carbonates wherein conversion of alkyl carbamate is >30%, with >30% selectivity to the corresponding alkyl carbonate.

(25) The process of synthesis of di alkyl carbonates is conducted with CO2 or N2 stripping.

(26) The process may be conducted in batch or continuous mode in an autoclave, packed bed reactor, bubble column reactor or such like.

EXAMPLES

(27) Following examples are given by way of illustration and therefore should not be construed to limit the scope of the invention.

Preparation of Mixed Metal Oxides

Example 1: ZrCe Oxide

(28) Hydrated ceria-zirconia oxide was obtained by co precipitation method. Cerium nitrate 0.3 mol and zirconyl nitrate 0.1 mol were dissolved in 100 ml water to prepare mixed nitrate solution. This solution was then added to 500 ml water at room temperature at 25 C. with constant stirring. This solution was maintained at pH 9 by adding 14.7 molar NH.sub.3 solution (17 ml). White precipitate thus obtained was aged overnight for 12 hr, isolated by filtration, dried and calcined at 900 C. for 4 hrs.

Example 2: ZrLa Oxide

(29) Hydrated lanthanum zirconia oxide was obtained by co precipitation method. Lanthanum nitrate 0.1 mol and zirconyl nitrate 0.3 mol were dissolved in 100 ml water to prepare mixed nitrate solution. This solution was then added to 500 ml water at room temperature at 25 C. with constant stirring. This solution was maintained at pH 9 by adding 14.7 molar NH.sub.3 solution (17 ml). White precipitate thus obtained was aged overnight for 12 hr. isolated by filtration, dried and calcined at 900 C. for 4 hrs.

Example 3: LaSrFeO3

(30) A 0.2M metal nitrate solution was prepared by dissolving Fe(NO3)3 (0.1 M), La(NO3)3 (0.07M) and Sr(NO3)3 (0.03 M) in distilled water, here Fe:La:Sr ratio was 1:(1-x):x.::1:0.7:0.3 solution was added to a 0.6M 100 ml citric acid solution slowly to get clear solution. Red gel was obtained by heating this solution in water bath at 80 c. for several hours. This gel was dried in oven at 120 c. for 5 hr in oven then temperature of oven was raised to 400 C. at rate of 1 c. and calcined 650 c. for 6 hrs.

Example 4: ZrMg Oxide

(31) Hydrated Magnesia-zirconia oxide was obtained by co precipitation method. Magnesium nitrate 0.3 mol and zirconyl nitrate 0.1 mol were dissolved in 1.00 ml water to prepare mixed nitrate solution. This solution was then added to 500 ml water at room temperature at 25 C. with constant stirring. This solution was maintained at pH 9 by adding 14.7 molar NH.sub.3 solution (16.4 ml). White precipitate thus obtained was aged overnight for 12 hr, isolated by filtration, dried and calcined at 900 C. for 4 hrs.

Example 5: CeMg Oxide

(32) Hydrated ceria-magnesia oxide was obtained by co precipitation method. Cerium nitrate 0.3 mol and Magnesium nitrate 0.1 mol were dissolved in 100 ml water to prepare mixed nitrate solution. This solution was then added to 500 ml water at room temperature at 25 C. with constant stirring. This solution was maintained at pH 9 by adding 14.7 molar NH.sub.3 solution (9.2 ml). White precipitate thus obtained was aged overnight for 12 hr. isolated by filtration, dried and calcined at 900 C. for 4 hrs.

Example 6

(33) Precursors for Ce.sub.(1-X)M.sub.xO.sub.2 solid solutions were obtained by refluxing aqueous solution containing appropriate amount of metal nitrates and urea for 48 hrs. Total metal nitrate concentration in this solution was 0.4 M where as initial urea:nitrate ion ratio was 1.6:1. Solid precursor thus obtained was isolated by pressure filtration and washed thoroughly 1.sup.st with water and then with ethanol to remove any uncomplexed ions. Solid was dried in an oven at 100 C. for 8 hrs. ceria containing solid solution were then obtained by calcining this precursor at 500 C. for 4 hrs. Employing above described method various Ce.sub.(1-X)M.sub.xO.sub.2 were prepared using Ce:Zr ratio ranging from 1:1, 2:1, 3:1 and 5:1.

Comparison of Activity for Catalyst Prepared by Both Urea and Co-Precipitation Method Out in 2 Liter CSTR

Example 7

(34) Methyl carbamate (MC) 125 g (1665 mmol) and methanol 265 g (8281.2 mmol) with 3.3 g of CeZrO (Ce:Zr::3:1) were charged to a 2000 ml reactor connected to a CO2 reservoir from gas inlet valve. The reservoir was fitted to reactor through constant pressure regulator which was set at 340 psi. A back pressure regulator was fitted to reactor at gas outlet valve. Back pressure regulator was set at 300 psi. The pressure difference of 40 psi was maintained between constant pressure regulator and back pressure regulator to ensure positive flow of CO2. This will help in stripping of CH.sub.3OH along with NH.sub.3 that is formed during reaction. The reactor was then pressurized with CO2 to 300 psi prior to heating from inlet valve. The inlet valve was closed at this point keeping outlet valve open. The contents were heated to 180 C. under very slow stirring condition. After attaining the temperature the inlet valve was opened. The methanol feeding was done at the rate of 7 ml/min. The reaction was continued for 6 h. During this period methanol along with NH.sub.3 was expelled due to the set positive pressure of CO2. This methanol along with dissolved NH.sub.3 was collected in a trap (cooled with ice and salt mixture) connected to BPR outlet. After completion of reaction the reactor was cooled to room temperature at 27 C. Reaction mixture from bomb as well as from trap was analyzed by Gas Chromatography. From GC analysis 68.1% conversion of methyl carbamate and 67.3% selectivity to DMC and 1.85% selectivity to MMC was observed in the reaction

Example 8

(35) Methyl carbamate (MC) 125 g (1665 mmol) and methanol 265 g (8281.2 mmol) with 3.3 g of CeZrO (Ce:Zr::3:1) were charged to a 2000 nil reactor connected to a N.sub.2 reservoir from gas inlet valve. The reservoir was fitted to reactor through constant pressure regulator which was set at 340 psi. A hack pressure regulator was fitted to reactor at gas outlet valve. Back pressure regulator was set at 300 psi. The pressure difference of 40 psi was maintained between constant pressure regulator and back pressure regulator to ensure positive flow of CO2. This will help in stripping of CH.sub.3OH along with NH.sub.3 that is formed during reaction. The reactor was then pressurized with N2 to 300 psi prior to heating from inlet valve. The inlet valve was closed at this point keeping outlet valve open. The contents were heated to 180 C. under very slow stirring condition. After attaining the temperature the inlet valve was opened. The methanol feeding was done at the rate of 7 ml/min. The reaction was continued for 6 h. During this period methanol along with NH.sub.3 was expelled due to the set positive pressure of N2. This methanol along with dissolved NH.sub.3 was collected in a trap (cooled with ice and salt mixture) connected to BPR outlet. After completion of reaction the reactor was cooled to room temperature at 30 C. Reaction mixture from bomb as well as from trap was analyzed by Gas Chromatography. From GC analysis 25.4% conversion of methyl carbamate and 44.8% selectivity to DMC and 0.33% selectivity to MMC was observed in the reaction

Example 9

(36) Methyl carbamate (MC) 12.5 g (1665 mmol) and methanol 265 g (8281.2 mmol) with 3.3 g of CeZrO (Ce:Zr::1:1) were charged to a 2000 ml reactor connected to a CO2 reservoir from gas inlet valve. The reservoir was fitted to reactor through constant pressure regulator which was set at 340 psi. A back pressure regulator was fitted to reactor at gas outlet valve. Back pressure regulator was set at 300 psi. The pressure difference of 40 psi was maintained between constant pressure regulator and back pressure regulator to ensure positive flow of CO2. This will help in stripping of CH.sub.3OH along with NH.sub.3 that is formed during reaction. The reactor was then pressurized with CO2 to 300 psi prior to heating from inlet valve. The inlet valve was closed at this point keeping outlet valve open. The contents were heated to 180 C. under very slow stirring condition. After attaining the temperature the inlet valve was opened. The methanol feeding was done at the rate of 7 ml/min. The reaction was continued for 6 h. During this period methanol along with NH.sub.3 was expelled due to the set positive pressure of CO2. This methanol along with dissolved NH.sub.3 was collected in a trap (cooled with ice and salt mixture) connected to BPR outlet. After completion of reaction the reactor was cooled to room temperature at 25 C. Reaction mixture from bomb as well as from trap was analyzed by Gas Chromatography. From GC analysis 35.6% conversion of methyl carbamate and 47.4% selectivity to DMC and 1.22% selectivity to MMC was observed in the reaction

Example 10

(37) Methyl carbamate (MC) 125 g (1665 mmol) and methanol 265 g (8281.2 mmol) with 3.3 g of CeZrO (Ce:Zr::2:1) were charged to a 2000 ml reactor connected to a CO2 reservoir from gas inlet valve. The reservoir was fitted to reactor through constant pressure regulator which was set at 340 psi. A back pressure regulator was fitted to reactor at gas outlet valve. Back pressure regulator was set at 300 psi. The pressure difference of 40 psi was maintained between constant pressure regulator and back pressure regulator to ensure positive flow of CO2. This will help in stripping of CH.sub.3OH along with NH.sub.3 that is formed during reaction. The reactor was then pressurized with CO2 to 300 psi prior to heating from inlet valve. The inlet valve was closed at this point keeping outlet valve open. The contents were heated to 180 C. under very slow stirring condition. After attaining the temperature the inlet valve was opened. The methanol feeding was done at the rate of 7 ml/min. The reaction was continued for 6 h. During this period methanol along with NH.sub.3 was expelled due to the set positive pressure of CO2. This methanol along with dissolved NH.sub.3 was collected in a trap (cooled with ice and salt mixture) connected to BPR outlet. After completion of reaction the reactor was cooled to room temperature at 26 C. Reaction mixture from bomb as well as from trap was analyzed by Gas Chromatography. From GC analysis 35.7% conversion of methyl carbamate and 28.9% selectivity to DMC and 1.89% selectivity to MMC was observed in the reaction.

Example 11

(38) Methyl carbamate (MC) 125 g (1665 mmol) and methanol 265 g (8281.2 mmol) with 3.3 g of CeZrO (prepared by urea hydrolysis procedure, Ce:Zr::5:1) were charged to a 2000 ml reactor connected to a CO2 reservoir from gas inlet valve. The reservoir was fitted to reactor through constant pressure regulator which was set at 340 psi. A back pressure regulator was fitted to reactor at gas outlet valve. Back pressure regulator was set at 300 psi. The pressure difference of 40 psi was maintained between constant pressure regulator and back pressure regulator to ensure positive flow of CO2. This will help in stripping of CH.sub.3OH along with NH.sub.3 that is formed during reaction. The reactor was then pressurized with CO2 to 300 psi prior to heating from inlet valve. The inlet valve was closed at this point keeping outlet valve open. The contents were heated to 180 C. under very slow stirring condition. After attaining the temperature the inlet valve was opened. The methanol feeding was done at the rate of 7 ml/min. The reaction was continued for 6 h. During this period methanol along with NH.sub.3 was expelled due to the set positive pressure of CO2. This methanol along with dissolved NH.sub.3 was collected in a trap (cooled with ice and salt mixture) connected to BPR outlet. After completion of reaction the reactor was cooled to room temperature at 25 C. Reaction mixture from booth as well as from trap was analyzed by Gas Chromatography. From GC analysis 52.2% conversion of methyl carbamate and 62.6% selectivity to DMC and 1.93% selectivity to MMC was observed in the reaction.

Example 12

(39) Methyl carbamate (MC) 125 g (1665 mmol) and methanol 265 g (8281.2 mmol) with 4 g of CeZrO (prepared by urea hydrolysis procedure, Ce:Zr::3:1) were charged to a 2000 ml reactor connected to a CO2 reservoir from gas inlet valve. The reservoir was fitted to reactor through constant pressure regulator which was set at 340 psi. A back pressure regulator was fitted to reactor at gas outlet valve. Back pressure regulator was set at 300 psi. The pressure difference of 40 psi was maintained between constant pressure regulator and back pressure regulator to ensure positive flow of CO2. This will help in stripping of CH.sub.3OH along with NH.sub.3 that is formed during reaction. The reactor was then pressurized with CO2 to 300 psi prior to heating from inlet valve. The inlet valve was closed at this point keeping outlet valve open. The contents were heated to 180 C. under very slow stirring condition. After attaining the temperature the inlet valve was opened. The methanol feeding was done at the rate of 7 ml/min. The reaction was continued for 6 h. During this period methanol along with NH.sub.3 was expelled due to the set positive pressure of CO2. This methanol along with dissolved NH.sub.3 was collected in a trap (cooled with ice and salt mixture) connected to BPR outlet. After completion of reaction the reactor was cooled to room temperature at 25 C. Reaction mixture from bomb as well as from trap was analyzed by Gas Chromatography. From GC analysis 70.7% conversion of methyl carbamate and 64.2% selectivity to DMC and 1.57% selectivity to MMC was observed in the reaction

Example 13

(40) Methyl carbamate (MC) 125 g (1665 mmol) and methanol 265 g (8281.2 mmol) with 3.3 g of CeZrO (prepared by urea hydrolysis procedure, Ce:Zr::3:1) were charged to a 2000 ml reactor connected to a CO2 reservoir from gas inlet valve. The reservoir was fitted to reactor through constant pressure regulator which was set at 340 psi. A back pressure regulator was fitted to reactor at gas outlet valve. Back pressure regulator was set at 300 psi. The pressure difference of 40 psi was maintained between constant pressure regulator and back pressure regulator to ensure positive flow of CO2. This will help in stripping of CH.sub.3OH along with NH.sub.3 that is formed during reaction. The reactor was then pressurized with CO2 to 300 psi prior to heating from inlet valve. The inlet valve was closed at this point keeping outlet valve open. The contents were heated to 180 C. under very slow stirring condition. After attaining the temperature the inlet valve was opened. The methanol feeding was done at the rate of 7 ml/min. The reaction was continued for 6 h. During this period methanol along with NH.sub.3 was expelled due to the set positive pressure of CO2. This methanol along with dissolved NH.sub.3 was collected in a trap (cooled with ice and salt mixture) connected to BPR outlet. After completion of reaction the reactor was cooled to room temperature at 25 C. Reaction mixture from bomb as well as from trap was analyzed by Gas Chromatography. From GC analysis 68.1% conversion of methyl carbamate and 67.3% selectivity to DMC and 1.85% selectivity to MMC was observed in the reaction.

Example 14

(41) Methyl carbamate (MC) 125 g (1665 mmol) and methanol 265 g (8281.2 mmol) with 3.3 g of CeZrO (prepared by urea hydrolysis procedure, Ce:Zr::3:1) were charged to a 2000 ml reactor connected to a CO2 reservoir from gas inlet valve. The reservoir was fitted to reactor through constant pressure regulator which was set at 340 psi. A back pressure regulator was fitted to reactor at gas outlet valve. Back pressure regulator was set at 300 psi. The pressure difference of 40 psi was maintained between constant pressure regulator and back pressure regulator to ensure positive flow of CO2. This will help in stripping of CH.sub.3OH along with NH.sub.3 that is formed during reaction. The reactor was then pressurized with CO.sub.2 to 300 psi prior to heating from inlet valve. The inlet valve was closed at this point keeping outlet valve open. The contents were heated to 190 C. under very slow stirring condition. After attaining the temperature the inlet valve was opened. The methanol feeding was done at the rate of 7 ml/min. The reaction was continued for 6 h. During this period methanol along with NFL was expelled due to the set positive pressure of CO2. This methanol along with dissolved NH.sub.3 was collected in a trap (cooled with ice and salt mixture) connected to BPR outlet. After completion of reaction the reactor was cooled to room temperature at 25 C. Reaction mixture from bomb as well as from trap was analyzed by Gas Chromatography. From GC analysis 69% conversion of methyl carbamate and 63.7% selectivity to DMC and 2.25% selectivity to MMC was observed in the reaction.

Experiments Using Catalyst Prepared by Co-Precipitation Method Under Batch Mode

Example 15

(42) Methyl carbamate (MC) 7.5 g (100 mmol) and methanol 65 g (2030 mmol) were charged to a 300 ml reactor with 1 g of CeZrO (Ce:Zr::3:1). The contents were heated to 190 C. with slow stirring. After attaining the temperature; stirring speed was increased to 1000 rpm and the time was noted as zero time. The reaction was continued for 8 hours. Ammonia formed during the reaction was removed using cooled high pressure condenser (condenser was cooled to 15 C.) fitted above the gas outlet valve of the reactor. Ammonia was removed at the interval of 1 hour during the course of the reaction. After 8 h reaction; the reactor was cooled to room temperature at 25 C. Reaction mixture was analyzed by Gas Chromatography. 44.7% conversion of MC was observed with 18.9% selectivity towards dimethyl carbonate (DMC).

Example 16

(43) Methyl carbamate (MC) 7.5 g (100 mmol) and methanol 65 g (2030 mmol) were charged to a 300 ml reactor with 1 g of LaZrO (La:Zr::1:3). The contents were heated to 190 C. with slow stirring. After attaining the temperature; stirring speed was increased to 1000 rpm and the time was noted as zero time. The reaction was continued for 8 hours. Ammonia formed during the reaction was removed using cooled high pressure condenser (condenser was cooled to 15 C.) fitted above the gas outlet valve of the reactor. Ammonia was removed at the interval of 1 hour during the course of the reaction. After 8 h reaction; the reactor was cooled to morn temperature. Reaction mixture was analyzed by Gas Chromatography. 11.3% conversion of MC was observed with 10.9% selectivity towards dimethyl carbonate (DMC).

Example 17

(44) Methyl carbamate (MC) 7.5 g (100 mmol) and methanol 65 g (2030 mmol) were charged to a 300 ml reactor with 1 g of LaFeSrO (Fe:La:Sr::1:0.7:0.3). The contents were heated to 190 C. with slow stirring. After attaining the temperature stirring speed was increased to 1.000 rpm and the time was noted as zero time. The reaction was continued for 8 hours. Ammonia formed during the reaction was removed using cooled high pressure condenser (condenser was cooled to 15 C.) fitted above the gas outlet valve of the reactor. Ammonia was removed at the interval of 1 hour during the course of the reaction. After 8 h reaction; the reactor was cooled to room temperature at 25 C. Reaction mixture was analyzed by Gas Chromatography. 53.7% conversion of MC was observed with 13.2% selectivity towards dimethyl carbonate (DMC).

Example 18

(45) Methyl carbamate (MC) 125 g (1665 mmol) and methanol 265 g (8281.2 mmol) with 3.3 g of CeZrO (3:1::Ce:Zr prepared by urea hydrolysis) were charged to a 2000 ml reactor connected to a CO2 reservoir from gas inlet valve. The reservoir was fitted to reactor through constant pressure regulator which was set at 340 psi. A hack pressure regulator was fitted to reactor at gas outlet valve. Back pressure regulator was set at 300 psi. The pressure difference of 40 psi was maintained between constant pressure regulator and back pressure regulator to ensure positive flow of CO2. This will help in stripping of CH.sub.3OH along with NH.sub.3 that is formed during reaction. The reactor was then pressurized with CO2 to 300 psi prior to heating from inlet valve. The inlet valve was closed at this point keeping outlet valve open. The contents were heated to 180 C. under very slow stirring condition. After attaining the temperature the inlet valve was opened. The methanol feeding was done at the rate of 7 ml/min. The reaction was continued for 6 h. During this period methanol along with NH.sub.3 was expelled due to the set positive pressure of CO2 This methanol along with dissolved NH.sub.3 was collected in a trap (cooled with ice and salt mixture) connected to BPR outlet. After completion of reaction the reactor was cooled to room temperature at 25 C. Reaction mixture from bomb as well as from trap was analyzed by Gas Chromatography. From GC analysis 68.1% conversion of methyl carbamate and 67.3% selectivity to DMC and 1.85% selectivity to MMC was observed in the reaction

Example 19

(46) Propyl carbamate (PC) 94.5 g (916.9 mmol) and propanol 275.5 g (4587 mmol) with 3 g of CeZrO (3:1::Ce:Zr prepared by urea hydrolysis) were charged to a 2000 ml reactor connected to a CO2 reservoir from gas inlet valve. The reservoir was fitted to reactor through constant pressure regulator which was set at 340 psi. A back pressure regulator was fitted to reactor at gas outlet valve. Back pressure regulator was set at 300 psi. The pressure difference of 40 psi was maintained between constant pressure regulator and back pressure regulator to ensure positive flow of CO2. This will help in stripping of CH.sub.3OH along with NH.sub.3 that is formed during reaction. The reactor was then pressurized with CO2 to 300 psi prior to heating from inlet valve. The inlet valve was closed at this point keeping outlet valve open. The contents were heated to 180 C. under very slow stirring condition. After attaining the temperature the inlet valve was opened. The methanol feeding was done at the rate of 7 ml/min. The reaction was continued for 6 h. During this period methanol along with NH.sub.3 was expelled due to the set positive pressure of CO2. This methanol along with dissolved NH.sub.3 was collected in a trap (cooled with ice and salt mixture) connected to BPR outlet. After completion of reaction the reactor was cooled to room temperature at 25 C. Reaction mixture from bomb as well as from trap was analyzed by Gas Chromatography. From GC analysis 21.8% conversion of propyl carbamate and 52.7% selectivity to DPC was observed in the reaction.

Example 20

(47) Ethyl carbamate (EC) 94.5 g (1060 mmol) and ethanol 245 g (5321 mmol) with 3 g of CeZrO (3:1::Ce:Zr prepared by urea hydrolysis) were charged to a 2000 ml reactor connected to a CO2 reservoir from gas inlet valve. The reservoir was fitted to reactor through constant pressure regulator which was set at 340 psi. A back pressure regulator was fitted to reactor at gas outlet valve. Back pressure regulator was set at 300 psi. The pressure difference of 40 psi was maintained between constant pressure regulator and back pressure regulator to ensure positive flow of CO2. This will help in stripping of CH.sub.3OH along with NH.sub.3 that is formed during reaction. The reactor was then pressurized with CO2 to 300 psi prior to heating from inlet valve. The inlet valve was closed at this point keeping outlet valve open. The contents were heated to 180 C. under very slow stirring condition. After attaining the temperature the inlet valve was opened. The methanol feeding was done at the rate of 7 ml/min. The reaction was continued for 6 h. During this period methanol along with NH.sub.3 was expelled due to the set positive pressure of CO2. This methanol along with dissolved NH.sub.3 was collected in a trap (cooled with ice and salt mixture) connected to BPR outlet. After completion of reaction the reactor was cooled to room temperature at 27 C. Reaction mixture from bomb as well as from trap was analyzed by Gas Chromatography. From GC analysis 49.1% conversion of ethyl carbamate and 17% selectivity to DEC was observed in the reaction

Example 21

(48) Butyl carbamate (BC) 89.5 g (764.9 mmol) and butanol 283 g (3820 mmol) with 3 g of CeZrO (3:1::Ce:Zr, prepared by urea hydrolysis) were charged to a 2000 ml reactor connected to a CO2 reservoir from gas inlet valve. The reservoir was fitted to reactor through constant pressure regulator which was set at 340 psi. A back pressure regulator was fitted to reactor at gas outlet valve. Back pressure regulator was set at 300 psi. The pressure difference of 40 psi was maintained between constant pressure regulator and back pressure regulator to ensure positive flow of CO2. This will help in stripping of CH.sub.3OH along with NH.sub.3 that is formed during reaction. The reactor was then pressurized with CO2 to 300 psi prior to heating from inlet valve. The inlet valve was closed at this point keeping outlet valve open. The contents were heated to 185 C. under very slow stirring condition. After attaining the temperature the inlet valve was opened. The methanol feeding was done at the rate of 7 ml/min. The reaction was continued for 6 h. During this period methanol along with NH.sub.3 was expelled due to the set positive pressure of CO2. This methanol along with dissolved NH.sub.3 was collected in a trap (cooled with ice and salt mixture) connected to BPR outlet. After completion of reaction the reactor was cooled to room temperature at 28 C. Reaction mixture from bomb as well as from trap was analyzed by Gas Chromatography. From GC analysis 20.7% conversion of butyl carbamate and 24.3% selectivity to DBC was observed in the reaction

ADVANTAGES OF THE INVENTION

(49) 1. With use of suitable preparation method and combination of rare earth/inner transition metals with transition metals or lanthanides it will be possible to tune acid base properties of mixed metal oxide catalysts to improve DMC selectivity, 2. Provides environmentally benign process for the synthesis of DMC 3. Catalyst provided is easy to separate.