Zinc-based heterogeneous catalyst and a one pot synthesis of alkyl carbonates via trans-esterification

Abstract

The present invention relates to a heterogeneous catalyst for the synthesis of alkyl carbonates, comprising zinc-based mixed phases material having mixture of amorphous and crystalline porous particles of the catalyst, and with non-smooth, irregular / non-homogenous surface morphology. The invention also relates to a process of preparation of said zinc-based mixed phases heterogeneous catalyst. Further, the invention relates to a process of preparation of alkyl carbonates using said heterogeneous catalyst via a trans-esterification process.

Description

[0001] ZINC-BASED HETEROGENEOUS CATALYST AND A ONE POT SYNTHESIS OF ALKYL CARBONATES VIA TRANS-ESTERIFICATION

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to Zinc based catalyst of Formula I.

[0004] MxByCz

[0005] Formula I wherein:

[0006] M is group 2 A alkaline earth metals or group 3-12 transition metals,

[0007] B is Na or K;

[0008] C is metal hydroxyl, metal oxide, mixed metal oxides, metal-metal-hydroxyl, metal-metal oxides, metal acetate, metal carbonate or metal nitrate; x is 0.01-99.99%; y is 0.01-80%; and z is 0.01 to 99.99%.

[0009] Particularly, present invention relates to a process of one-pot synthesis of alkyl carbonates by trans-esterification using the zinc -based catalyst.

[0010] BACKGROUND OF THE INVENTION

[0011] Ethyl methyl carbonate (EMC) and Diethyl carbonate (DEC) are being used as fuel additives and are excellent electrolytes to enhance the low-temperature performance of rechargeable lithium-ion electrochemical cells. They also find applications for the production of polycarbonates, which are globally used in engineering plastics. Ethyl methyl carbonate (EMC) and Diethyl carbonate (DEC) were prepared by different methods such as transesterification, alcoholysis, etc.

[0012] Trans-esterification, or the exchange reaction of esters with alcohols (an alcoholysis reaction), is an important class of reactions which may be catalyzed by both acid and base catalysts. Examples of trans-esterification, in general, include chemical reactions involving organic carbonates and carboxylic acid esters as reactants, products, or both. Other trans-esterification reactions include the production of biodiesel by trans-esterification of triglycerides with ethanol or methanol. In the literature, there are several methods for the preparation of alkyl carbonates such as diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc., like carbonation of ethanol using CO2.

[0013] Reference may be made to the journal “Ind. Eng. Chem. Res. 2011, 50, 19, 11073-11086” which discloses sodium ethoxide as a homogeneous catalyst. This homogeneous nature of the catalyst gets deactivated in the reaction due to the formation of sodium hydrogen carbonate and, further, it leads to the form of sodium carbonate which makes it no longer available as a catalyst for the trans-esterification reactions due to the precipitation of the catalyst.

[0014] Reference may be made to the journal “Fuel Processing Technology, 92 (2011) 77-82” which discloses the trans-esterification process of DMC with ethanol, where they obtained 86.8% DMC conversion with 59% DEC selectivity at a temperature of 80°C in 4 hr. with 1:4 molar ratios (DMC: EtOH) and 2 wt. % loading of heterogeneous 40 wt. % of KF on AI2O3 catalyst. However, said literature -known methods have limitations / disadvantages such as a) CO2 stability and unfavorability; b) Requires higher temperatures above 180°C and higher pressure requirement; c) provide lesser yield and selectivity of products; d) produces higher amounts of impurities and side products; e) Less preferable considering its lower reusability; f) catalyst leaching in the final product; and g) high thermal stability issues of the catalyst due to its leaching during calcination.

[0015] Therefore, there is an unmet need in the art to develop a heterogeneous catalyst system for the easy synthesis of alkyl carbonates effectively in terms of higher selectivity, higher conversion rate, and better yields within lesser time and temperature.

[0016] The existing trans-esterification processes have drawbacks in the catalyst leaching of K+and F“ ions into the product mixture. The KF / AI2O3 is also having high thermal stability issues due to its leaching of K and F from the surface of the catalyst during high calcination temperatures ranging from 300 °C to 900 °C which results in a reduction in the basicity of the catalyst. Calcination at 600 °C resulted in leaching of both K and F (-10%) from the surface while that at 900 °C resulted in a higher loss of K (-60%) than F (-25%). This may be due to the formation of a highly stable K3AIF6 compound. The present invention discloses the synthesis of a zinc-based catalyst for selectively synthesizing alkyl carbonates at milder reaction conditions (20 to 70 °C) as compared to reported works.

[0017] OBJECTIVES OF THE INVENTION Main objective of the present invention is to provide a heterogeneous Zinc based catalyst. Another objective of the present invention is to provide a process of preparation of the catalyst.

[0018] Yet another objective of the present invention is to provide a process of preparation of alkyl carbonates using the Zinc based catalyst.

[0019] BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 depicts XRD peak patterns with labels for the Zinc based catalyst of the present invention.

[0021] Figure 2 shows the FE-SEM morphological image of Zinc based catalyst of the present invention.

[0022] Figure 3 shows the elemental mapping study of the Zinc based catalyst of the present invention. Figure 3 confirms the formation of the homogeneous solid solution of Zn, Ca, and Na in oxide form as oxygen is abundantly available at the catalytic surface.

[0023] Figure 4 represents the reactor design for the trans-esterification process in order to produce alkyl carbonates. This is the general type of reactor which have at least a round bottom shape with a cooling condenser connected to it.

[0024] Figure 5 represents the effect on conversion and selectivity of a) Temperature, b) Time (min), c) catalyst loading (%), and d) Mole ratio (DMC: EtOH).

[0025] Figure 6 provides XRD graphs with different phases of the catalyst: A) Chemical formula- NaiCCE - Crystal system-Hexagonal / Space group-p63 / mmc; B) Chemical formula-Zn(0H)2- Crystal system-Hexagonal; C) Chemical formula- ZnCO3- Crystal system-Rhombohedral - Space group-R3c; D) Chemical formula-(Na2. ZmjCE - Crystal system-Hexagonal - Space group-p43212; E) Chemical formula- NaOH - Crystal system-Orthorhombic; F) Chemical formula- Hydrazine hydrate -N2H4H2O - Crystal system-Hexagonal - Space group-p3121; and G) Chemical formula- CH3COONa - Crystal system-Orthorhombic - Space group-pmnm.

[0026] SUMMARY OF THE INVENTION

[0027] Accordingly, the present invention provides a heterogeneous catalyst of Formula I MxByCz Formula I wherein:

[0028] M is selected from group 2A alkaline earth metals or group 3-12 transition metals, B is Na or K;

[0029] C is metal hydroxyl, metal oxide, mixed metal oxides, metal-metal-hydroxyl, metal-metal oxides, metal acetate, metal carbonate or metal nitrate; x is 0.01-99.99%; y is 0.01-80%; and z is 0.01 to 99.99%.

[0030] In an embodiment of the present invention, the group 2A alkaline earth metals is selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra) and the group 3-12 transition metal is selected from the group consisting of Zinc Cobalt, Nickel, Iron, Rhodium, Gold, Silver, Copper, Scandium, Titanium, Vanadium, and Manganese; preferably, the M is Zinc.

[0031] In another embodiment, the present invention relates to a Zinc based heterogeneous catalyst of Formula I,

[0032] MxByCz

[0033] Formula I wherein:

[0034] M is Zinc,

[0035] B is Na or K;

[0036] C is metal hydroxyl, metal oxide, mixed metal oxides, metal-metal-hydroxyl, metal-metal oxides, metal acetate, metal carbonate or metal nitrate; x is 0.01-99.99%; y is 0.01-80% and z is 0.01 to 99.99%.

[0037] In an embodiment, the present invention provides a process for the preparation of the heterogeneous catalyst of Formula I, comprising the steps of:

[0038] (a) dissolving metal source in deionized water to obtain a metal solution;

[0039] (b) dissolving promoter in deionized water to obtain a promoter solution;

[0040] (c) adding the metal solution as obtained in step (a) drop-wise to the promoter solution under room temperature to a obtain slurry; (d) aging the slurry as obtained in step (c) for a period in the range of 5-8 hours at a temperature in the range of 75-85°C, drying for a period in the range of 1.5 to 3 hrs. at a temperature in the range of 75 to 125 °C and calcining at a temperature in the range of 240-260°C for a period in the range of 3 to 5 hours to obtain the catalyst.

[0041] In another embodiment of the present invention, the percentage (%) of Zn and Na in the said catalyst is in the range of 15-24% and 74-83%, respectively.

[0042] In yet another embodiment of the present invention, the Zn in claimed catalyst is supporting metal, and Na and K have been used as promoter to enhance basic nature of the catalyst.

[0043] In yet another embodiment of the present invention, the metal source is selected from the group consisting of Zinc acetate dehydrate, Zinc nitrate, Zinc hydroxide, Zinc carbonate, Zinc chloride.

[0044] In yet another embodiment of the present invention, the promoter is selected from the group consisting of NaOH, KOH, sodium nitrate, sodium carbonate, sodium hydride, potassium carbonate, potassium nitrate, potassium chloride.

[0045] In yet another embodiment of the present invention, the heterogeneous catalyst comprises phases (also termed as multiphase) material having a mixture of amorphous and crystalline porous particles of the catalyst, and with a non-smooth, irregular / non-homogenous surface morphology.

[0046] In yet another embodiment of the present invention, the mixed phase or multiphase is tetragonal, hexagonal, orthorhombic and rhombohedral.

[0047] In still another embodiment of the present invention, the catalyst comprises the compounds / phases is selected from the group consisting of Zn(0H)2(in Hexagonal), NaOH (in Orthorhombic), Hydrazine hydrate -N2H4H2O (in Hexagonal), ZnO (in hexagonal), Na2CO3(in hexagonal), Na2(Zn2O3) (in hexagonal), CH3COONa (in Orthorhombic), and ZnCO3(in Rhombohedral).

[0048] In yet another embodiment of the present invention, the catalyst comprises the presence of non-homogenous and mixed phases of one or more of metal, metal hydroxyl, metal oxide, mixed metal oxides, metal-metal-hydroxyl, metal-metal oxides, metal acetate, and metal(s) carbonate / nitrate or mixture thereof.

[0049] In yet another embodiment, the present invention provides a process for the one-pot synthesis of alkyl carbonates using the heterogeneous catalyst of Formula I comprising the steps of: a) mixing primary linear alcohol and carbonate compound in the presence of zinc- based catalyst to obtain alkyl carbonates.

[0050] DETAILED DESCRIPTION OF THE INVENTION

[0051] The term "linear C1-C6alkyl ", as used herein, refers to linear straight chain alkyl groups having six or fewer carbon atoms. As used herein, (C1-C6) alkyl refers to an alkyl group having from 1 to 6 carbon atoms. Representative examples of alkyl include but are not limited to, methyl, ethyl, n-propyl, n-butyl, n-pentyl, and n-hexyl.

[0052] The present invention relates to Zinc based catalyst composition for a process of one-pot synthesis of alkyl carbonates by trans-esterification.

[0053] The present invention relates to a heterogeneous catalyst of Formula I

[0054] MxByCz

[0055] Formula I wherein:

[0056] M is selected from group 2A alkaline earth metals or group 3-12 transition metals, B is Na or K;

[0057] C is metal hydroxyl, metal oxide, mixed metal oxides, metal-metal-hydroxyl, metal-metal oxides, metal acetate, metal carbonate or metal nitrate; x is 0.01-99.99%; y is 0.01-80% and z is 0.01 to 99.99%.

[0058] The group 2A alkaline earth metals is selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra) and the group 3-12 transition metal is selected from the group consisting of Zinc Cobalt, Nickel, Iron, Rhodium, Gold, Silver, Cooper, Scandium, Titanium, Vanadium, and Manganese. Preferably, the M is Zinc.

[0059] The catalyst of the present invention comprises Na, Zn, O, and Ca elements.

[0060] The catalyst has non-smooth, irregular / non-homogenous surface morphology.

[0061] The catalyst comprises the compounds / phases selected from Zn(0H)2, NaOH, hydrazine hydrate -N2H4H2O, ZnO, Na2CO3, Na2(Zn2O3), CH3COONa, and ZnCO3. The catalyst comprises the presence of non-homogenous and mixed phases of one or more of metal, metal hydroxyl, metal oxide, mixed metal oxides, metal-metal-hydroxyl, metal-metal oxides, metal acetate, and metal(s) carbonate / nitrate or mixture thereof.

[0062] The catalyst comprises amorphous and crystalline nature of particles.

[0063] The catalyst comprises multiphase particles selected from Zn(0H)2(in Hexagonal), NaOH (in Orthorhombic), Hydrazine hydrate -N2H4H2O (in Hexagonal), ZnO (in hexagonal), Na2CO3(in hexagonal), Na2(Zn2O (in3) hexagonal), CH3COONa (in Orthorhombic), and ZnCO3(in Rhombohedral).

[0064] The percentage (%) of Zn and Na in the said catalyst is in the range of 15-23% and 74-83%, respectively

[0065] The wt. % of Zn and Na in the said catalyst is 23.64 % and 76.35 % for Zn and Na, respectively.

[0066] The Zn in claimed catalyst is supporting metal, and Na and K have been used as promoter to enhance basic nature of the catalyst.

[0067] The present invention relates to a process for the preparation of a catalyst comprising the steps of

[0068] (a)dissolving metal source in deionized water to obtain a metal solution;

[0069] (b)dissolving promoter in deionized water to obtain a promoter solution;

[0070] (c) adding the metal solution as obtained in step (a) drop-wise to the promoter solution under room temperature to a obtain slurry;

[0071] (d)aging the slurry as obtained in step (c) for a period in the range of 5-8 hours at a temperature in the range of 75-85°C, drying for a period in the range of 1.5 to 3 hrs. at a temperature in the range of 75 to 125 °C and calcining at a temperature in the range of 240-260°C for a period in the range of 3 to 5 hours to obtain the catalyst.

[0072] The drying of step d) is done at a temperature in the range of 75 to 125 °C for time period in the range of 1.5 to 3 hrs.

[0073] Specifically, the drying of step d) is done at a temperature of about 100 °C for time period of about 2 hrs.

[0074] The calcining of step d) is done at a temperature in the range 240-260°C for time period in the range of 3 to 5 hours.

[0075] The metal source is Zinc acetate dehydrate, Zinc nitrate, Zinc hydroxide, Zinc carbonate, Zinc chloride. The promoter is NaOH, KOH, sodium nitrate, sodium carbonate, sodium hydride, potassium carbonate, potassium nitrate, potassium chloride.

[0076] The aging of the slurry is carried out for 5 to 8 hrs. or specifically for 5 hours, 6 hours, 7 hours or 8 hours. Preferably, for 6 hours.

[0077] The aging of the slurry is carried out at a temperature of 75-85°C, 75-80°C, or 80-85°C. Preferably, at a temperature of 75-80°C.

[0078] The catalyst of the present invention is a heterogeneous catalyst and hence, it is easy to separate from the reaction mixture after the experiment. The precursors or raw materials used to synthesize the catalyst of the present invention are cheap and easily available. The catalyst of the present invention is easy to re-produce (data file attached) and durable catalyst.

[0079] The present invention relates to a one-step process of preparing alkyl carbonate using the zinc-based catalyst comprising the step of mixing primary linear alcohol and carbonate compound in the presence of zinc -based catalyst to obtain alkyl carbonates at specific reaction conditions gives alkyl carbonates, as shown below. wherein:

[0080] R is linear C1-C6alkyl, and

[0081] R1is linear C1-C6alkyl.

[0082] The linear alcohol of formula II is methanol, ethanol, n-propanol, or hexanol.

[0083] The carbonate of formula III is dimethyl carbonate and the like. The compound of formula IV and V are diethyl carbonate, ethyl methyl carbonate, and the like.

[0084] The specific reaction conditions include one or more of: a) the Molar ratio of reactant III: reactant II is in the range of 1:6 to 1: 12, b) Said zinc -based catalyst loading is in the range of 1 to 8% wt / wt w.r.t. reagent III, c) Temperature is in range of 20 to 80 °C, d) Pressure is kept at 1 atmospheric (or 1.01 bar), e) Stirring speed is in range of 200 to 800 RPM, and f) time of the reaction kept is in range of 0.25 to 120 minutes.

[0085] The specific reaction conditions include one or more of a) Molar ratio of reactant III: reactant II is 1:6, 1:7, 1:8, 1:9, 1: 10, 1: 11 or 1: 12, b) Said zinc -based catalyst loading is 1, 2, 3, 4, 5, 6, 7 or 8% wt / wt w.r.t. reagent III, c) Temperature is 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75 or 80 °C, d) Pressure is kept at 1 atmospheric (or 1.01 bar), e) Stirring speed is in range of 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750 or 800 RPM, and f) Time of the reaction kept is in range of 0.5,1, 5, 10, 20, 30, 45, 60, 70, 75, 80, 90, 100, 110, 120, 130 or 150 minutes.

[0086] The process of preparation of said alkyl carbonates can be done in any reactor or container known to a person skilled in the art, which is having a round bottom flask connected with a cooling condenser.

[0087] The alkyl carbonates prepared herein are useful as fuel-additives and are excellent electrolytes to enhance the low-temperature performance of rechargeable lithium-ion electro-chemical cells, reagent chemical in organic chemistry reactions, as a fertilizer component, as an alkylating agent, as a reagent in the synthesis of polycarbonates and essential polymers, etc. The alkyl carbonates prepared herein are useful in industries / domains like agrochemical, pesticides and fragrance industries, pharmaceutical industry as a solvent and in the synthesis of phenobarbital as well as in erythromycin intramuscular injections, etc.

[0088] The Zn catalyst of the present invention when calcined above 300 °C (or specifically at 500 °C), and then used for the above process of alkyl carbonate formation, it gives lesser yield, selectivity, and conversion with higher impurities and side products formation.

[0089] The alkyl carbonates are useful as a fuel additive alternative for MTBE, ETBE, FAME, etc., as an electrolyte in lithium-ion batteries to enhance low-temperature performance, as a chemical reagent in organic synthesis, as fertilizer, agrochemical, pesticides, and fragrance industries, useful in the pharmaceutical industry as solvent and in synthesis of phenobarbital as well as in erythromycin intramuscular injections, as alkylating agent and used in the synthesis of polycarbonate.

[0090] EXAMPLES

[0091] Following examples are given by way of illustration and therefore should not be construed to limit the scope of the invention. Example 1: Preparation of Catalyst

[0092] Catalyst prepared and used for trans-esterification of DMC with ethanol in present study is synthesized as per protocol described below.

[0093] Zinc acetate dihydrate as metal source and sodium hydroxide pellets are used as precipitating agent.

[0094] Step 1: 20.0022 gm of zinc acetate was dissolved in 75 ml of deionized water in separate flask stirred continuously at a temperature of 30 °C.

[0095] Step 2: 40.1023 gm NaOH was dissolved in 40 ml deionized water in another separate flask and kept under stirring at a temperature of 30 °C.

[0096] Step 3: Solution from step 1 was added drop-wise in the step 2 solution under atmospheric conditions as the addition was exothermic.

[0097] Step 4: Once, the addition was completed, the catalyst slurry obtained was aged for 6 hours at 80°C, followed by drying at temperature of 100°C for 2 hrs., and then calcined to 250°C for 4 hrs. with an initial temperature ramp rate of 10°C / min to obtain the catalyst of the present invention.

[0098] Catalyst characterization

[0099] Prepared Zn and Na metal-based multiphase catalyst was characterized by different technics including Powder X-ray diffraction, X-ray electron spectroscopy (XPS), Energy dispersive X-ray (EDS), Field emission scanning electron microscope (FE-SEM), High-resolution transmission electron microscope (HR-TEM) and Temperature programmed desorption.

[0100] Powder X-ray diffraction study of the prepared catalyst was performed using Rigaku Dmax 500 diffractometer using Cu Ka radiation (X=1.5405 A) over a 29 range of 0-80° and identified peaks were compared with JCPDS standards for phase identification. Figure 1 depicts the XRD peaks with different phases of the catalyst. The highest possible phase present in Zinc based catalysts is Zn(0H)2(Hexagonal) followed by NaOH (Orthorhombic), Hydrazine hydrate -N2H4H2O (Hexagonal), ZnO (hexagonal), NaiCO3(hexagonal), Na2(Zn2O3)(hexagonal), CH3COONa (Orthorhombic), and ZnCO3(Rhombohedral).

[0101] Field emission scanning electron microscope (FE-SEM) was used to study surface morphology. Figure 2 shows the FE-SEM images of the catalyst of present invention. FE- SEM image reveals the non-smooth, irregular / non-homogenous surface morphology of the catalyst of the present invention. Elemental analysis was carried out to confirm the presence of the elements in the catalyst of the present invention. The ED AX data confirms the presence of Na, Zn, O, and Ca elements in the catalyst. Table below provides the weight percent of the elements of the catalyst. The elemental mapping studies confirm the formation of homogeneous solid solution of Zn, Ca and Na in oxide form as oxygen is abundantly available at catalytic surface. Figure 3 shows the elemental mapping study of the Zinc based catalyst of the present invention and it confirms the formation of the homogeneous solid solution of Zn, Ca, and Na in oxide form as oxygen is abundantly available at the catalytic surface.

[0102] Elemental analysis of Zinc based catalyst

[0103] Example 2: Synthesis of DEC (Diethyl carbonate) and EMC (Ethyl methyl carbonate)

[0104] Figure 4 represents the reactor design for the trans -esterification process in order to produce alkyl carbonates. This is the general type of reactor which have at least a round bottom shape with a cooling condenser connected to it.

[0105] Reaction conditions:

[0106] 1. Temperature: 70°C

[0107] 2. Mole ratio (DMC; EtOH): 1: 12

[0108] 3. DMC weight: 3 gm

[0109] 4. EtOH weight: 18.5 gm

[0110] 5. Catalyst loading (wt%): 5wt %

[0111] 6. Catalyst quantity (gm): 0.15 gm

[0112] 7. Time (min): 0.25 to 120min

[0113] 8. RPM: 200

[0114] Step 1: Initially we take DMC (3gm or 0.0333 moles) and ethanol (18.49gm or 0.4016 moles) in 50 ml glass round bottom flask and put magnetic needle in flask to ensure uniform mixing of reaction mass. Step 2: Heat the reaction flask using oil bath (heated by electric heating mantle) to the desired reaction temperature.

[0115] Step 3: Allow the reaction for a required reaction time and.

[0116] Step 4: Once the reaction is over, reaction mass is immediately cooled to room temperature to stop the reaction using an ice-bath.

[0117] Step 5: After the reaction is cooled to room temperature, samples are analyzed using gas chromatography.

[0118] Results: In the initial 5 minutes, DMC conversion is 93.3% and EMC selectivity is 54.5% and yield is 51.22% in mole% at 50°C. After that, in 2 hrs. DMC conversion is 97.3% and DEC selectivity is 71% and DEC yield is 69.01%. Figure 5 (a) shows the effect of temperature on DMC conversion and selectivity of DEC at 2% catalyst loading, 1:6 mole ratio in 2 hours, (b) depicts the effect of reaction time on DMC conversion and selectivity of DEC at 2% catalyst loading, 1:6 mole ratio and at 70°C, (c) shows the effect of catalyst loadings on DMC conversion and selectivity of DEC at 70°C, 1:6 mole ratio and in 2 hours and (d) depicts the effect molar ratio (DMC: EtOH) on DMC conversion and selectivity of DEC at 70°C, 5% (w / w) catalyst loading w.r.t. DMC and in 2 hours.

[0119] ZK: Z (Zinc) based catalyst with K (potassium) as promoter.

[0120] PB: Psedobohemite (used as promotor to enhance selectivity)

[0121] Reaction conditions: 1. Temperature: 70°C

[0122] 2. Catalyst loading (wt.%): 5wt %

[0123] 3. Catalyst quantity (gm): 0.81 gm

[0124] 4. Mole ratio (DMC: EtOH): l:6 5. DMC weight: 10.2 gm or 0.113 moles

[0125] 6. EtOH weight: 32.5 gm or 0.705 moles

[0126] 7. Time: 240 min

[0127] FTIR plot for reaction mixture (70°C, 2hr, 5% (w / w) catalyst loading w.r.t. DMC, 200 rpm, and 1: 12 molar ratio) has been studied for the confirmation of formation of alkyl carbonates as products. The table below provides infrared bands assignments of the species for stds. of

[0128] DEC, EMC, MeOH, EtOH and reaction mixture (by using ZN-250 catalyst).

[0129] The C-0 stretching adsorption peaks of adsorbed carbonyl (C-0 species of alcohol) for std. ethanol, methanol, EMC, DEC and reaction mixture (RM-ZN-250) depicts the presence of all these compounds in ranging of 1093-1029 with red shift in ethanol, EMC, DEC and RM- ZN-250 and blue shift in MeOH respectively. Similarly, the species C=O confirms the presence carbonyl group / carbonate esters of DEC (1747 cm-1), EMC (1753 cm-1), and DMC (1753 cm-1), in the reaction sample (1752-1731 cm-1).

[0130] ADVANTAGES OF THE INVENTION • The present invention provides a heterogeneous catalyst for one-pot synthesis of alkyl carbonates having excellent catalytic activity at the mild reaction temperature of 50°C.

[0131] • The present invention provides the heterogeneous Zinc based catalyst showing high yield and high selectivity in the process of preparation of alkyl carbonates.

[0132] • The present invention provides the heterogeneous zinc-based catalyst that is proactive for the production of mono as well as di-alkyl carbonates which fulfills two needs with one deed.

Claims

AMENDED CLAIMS received by the International Bureau on 28 April 2025 (28.04.2025)We Claim A heterogeneous catalyst of Formula IMxByCzFormula I wherein:M is a metal selected from group 2 A alkaline earth metals or group 3-12 transition metals, B is a metal of Na or K;C comprises phases of M and / or B, in the form of a combination of one or more of metal hydroxyl, metal oxide, mixed metal oxides, metal-metal-hydroxyl, metal-metal oxides, metal acetate, metal carbonate and metal nitrate; x is in the range of 0.01-99.99%; y is in the range of 0.01-80%; and z is in the range of 0.01 to 99.99%. The heterogeneous catalyst as claimed in claim 1, wherein the group 2A alkaline earth metals is selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra) and the group 3-12 transition metal is selected from the group consisting of Zinc Cobalt, Nickel, Iron, Rhodium, Gold, Silver, Copper, Scandium, Titanium, Vanadium, and Manganese; preferably, the M is Zinc. A process for the preparation of the heterogeneous catalyst of Formula I as claimed in claim1, comprising the steps of(a) dissolving metal source in deionized water to obtain a metal solution;(b) dissolving promoter in deionized water to obtain a promoter solution;(c) adding the metal solution as obtained in step (a) drop-wise to the promoter solution under room temperature to a obtain slurry;(d) aging the slurry as obtained in step (c) for a period in the range of 5-8 hours at a temperature in the range of 75- 85 °C, drying for a period in the range of 1.5 to 3 hrs. at a temperature in the range of 75 to 125 °C and calcining at a temperature in the range of 240- 260°C for a period in the range of 3 to 5 hours to obtain the catalyst. The process as claimed in claim 3, wherein the percentage (%) of Zn and Na in the said catalyst is in the range of 15-24% and 74-83%, respectively.The process as claimed in claim 3, wherein the Zn in claimed catalyst is supporting metal, and Na and K have been used as promoter to enhance basic nature of the catalyst. The process as claimed in claim 3, wherein the metal source is selected from the group consisting of Zinc acetate dehydrate, Zinc nitrate, Zinc hydroxide, Zinc carbonate, Zinc chloride and the promoter is selected from the group consisting of NaOH, KOH, sodium nitrate, sodium carbonate, sodium hydride, potassium carbonate, potassium nitrate, potassium chloride. The process as claimed in claim 3, wherein the heterogeneous catalyst comprises phases also termed as multiphase) material having a mixture of amorphous and crystalline porous particles of the catalyst, and with a non-smooth, irregular / non-homogenous surface morphology and the mixed phase or multiphase is tetragonal, hexagonal, orthorhombic and rhombohedral.The process as claimed in claim 3, wherein the catalyst comprises the compounds / phases is selected from the group consisting of Zn(0H)2(in Hexagonal), NaOH (in Orthorhombic), Hydrazine hydrate -N2H4H2O (in Hexagonal), ZnO (in hexagonal), Na2CO3(in hexagonal), Na2(Zn2O3) (in hexagonal), CH3COONa (in Orthorhombic), and ZnCO3(in Rhombohedral). The process as claimed in claim 3, wherein the catalyst comprises the presence of non- homogenous and mixed phases of one or more of metal, metal hydroxyl, metal oxide, mixed metal oxides, metal-metal-hydroxyl, metal-metal oxides, metal acetate, and metal(s) carbonate / nitrate or mixture thereof. A process for the one-pot synthesis of alkyl carbonates using the heterogeneous catalyst of Formula I as claimed in claim 1, comprising the step of: a) mixing primary linear alcohol and carbonate compound in the presence of the heterogeneous catalyst of Formula I to obtain alkyl carbonates.

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