WO2012174729A1

WO2012174729A1 - Process for preparing vinyl esters of tertiary carboxylic acids

Info

Publication number: WO2012174729A1
Application number: PCT/CN2011/076241
Authority: WO
Inventors: Hang Wang; Chongwei LAI; Jian ZENG; Huiru JIA; Jiong LIAO; Xuan Liu; Zhenbo MAO; Chengzhu JI; Guizhong JIANG; Xiaohua Chen
Original assignee: The Southwest Research & Design Institute Of Chemical Industry; Celanese International Corporation
Priority date: 2011-06-24
Filing date: 2011-06-24
Publication date: 2012-12-27

Abstract

A process for preparing vinyl esters of tertiary carboxylic acids by liquid phase addition of acetylene and tertiary carboxylic acids in the presence of metal salts of the tertiary carboxylic acids is disclosed. By subjecting the catalyst into a pre-activation and controlling the per pass conversation rate of free tertiary carboxylic acid during the reaction, the activity of catalyst, the selectivity of tertiary carboxylic acid for vinyl ester thereof, the per pass conversion rate of acetylene, and/or the selectivity of acetylene for vinyl ester of the tertiary carboxylic acid are improved.

Description

PROCESS FOR PREPARING VINYL ESTERS OF

TERTIARY CARBOXYLIC ACIDS

BACKGROUND OF THE INVENTION

1 . Field of the Invention

[0001 ] The present invention relates to a process for preparing vinyl esters of carboxylic acids. Specifically, the invention relates to a process for preparing vinyl esters of tertiary carboxylic acids by liquid phase addition of acetylene and tertiary carboxylic acids in the presence of metal salts of the tertiary carboxylic acids.

2. Description of the Related Art

[0002] Vinyl esters of tertiary carboxylic acids, also known as Neo Acid Vinyl Esters or NAVEs in short, are widely used polymeric monomers. NAVEs are typically classified according to the number of carbon atoms contained in the molecules, and generally contain from 9 to 11 such carbon atoms. All of them are homologous monomers having different glass transition temperature, but similar properties.

[0003] NAVEs can be used as a co-monomer with vinyl acetate to prepare random copolymer emulsion, whereby produce high performance latex coating. The highly branched structure of NAVEs imparts excellent water, ultraviolet, thermal and/or base resistances to the copolymer coatings obtained therefrom, which have far better performance than their vinyl acetate (VA) analogues, and even better than acrylic copolymer latex coatings known for their performance. NAVE-VA copolymer and coating thereof have the structure below:

[0004] The processes for preparing NAVEs with acetylene and tertiary carboxylic acids as starting materials can be classified in two categories: gas-solid catalytic process and liquid phase process, the majority of which employ Zn catalyst. Liquid phase process is generally used for higher carboxylic acids due to their high gasification temperature. The liquid phase process can be further divided into high pressure liquid phase process and low pressure liquid phase process. The high pressure liquid phase process is restricted by a number of limitations, including safety concerns associated with high pressure operation, general requirement for addition of diluent gas such as nitrogen in starting material gas, high requirements imposed on the apparatus, and poor reaction effect. The current researches mainly focus on low pressure liquid phase process, and most of them are directed to catalyst.

[0005] US patent Nos. 3,455,998 and 6,891 ,052 disclose that addition of various additives such as Lewis acid, and water has auxiliary effect on catalyst or side reactions in the system. However, the addition of additives such as Lewis acid will increase the complex of the system, and even raise the requirements imposed on the apparatus; if water is added (US 6,891 ,052), acetylene will be hydrated to produce acetaldehyde in the presence of catalyst, so that the selectivity of acetylene will decrease, and the catalytic activity will be greatly affected in case of addition of too much water.

[0006] GB 1 ,036,674 and US 3,646,077 employ the operation process in which a highly excessive acetylene gas is continuously introduced to bring out NAVE produced in the liquid reaction system; as a result, the usage of the gas is generally 2-3 times, or even above 5 times, of the actual consumption, resulting in a low conversion rate of acetylene of below 50%.

[0007] US 3,285,941 also employs the process in which the gasified tertiary carboxylic acid is mixed with acetylene, and reacted in a high-temperature liquid phase catalytic system, and then the product is discharged by gasification; however, because gasification of tertiary carboxylic acid and NAVE at normal pressure requires high temperature, generally of above 250°C, the process energy consumption is high and the operation is difficult.

[0008] In recent years, some published patents, such as US 5,430,179, are also directed to non-zinc based catalytic route, for example, active carbon supported Ru, Pt phosphine complex, as well as carbonyl compound, oxide, and chloride of Re, Mn, W, Mo, and Cr, or Re salt; however, these rare or noble metals are expensive, which seriously affects their industrial feasibility.

[0009] Thus, despite the foregoing efforts, a need still exists for a process for preparing high purity NAVEs with low cost and high efficiency.

BRIEF SUMMARY OF THE INVENTION

[0010] As a result of an extensive study of the present inventors, it has been found the activity of catalyst, the selectivity of tertiary carboxylic acid for vinyl ester thereof, the per pass conversion rate of acetylene, and/or the selectivity of acetylene for vinyl ester of the tertiary carboxylic acid can be dramatically improved by subjecting the catalyst into a suitable pre-activation and controlling the per pass conversation rate of free tertiary carboxylic acid, during the reaction. The present invention is accomplished based on those findings.

[001 1 ] Thus, the object of the present invention is to provide a novel process for preparing vinyl ester of tertiary carboxylic acid. Upon the present process, NAVEs with a purity of as high as 99% can be obtained by using low cost catalysts, such as zinc salts of the tertiary carboxylic acids, under mild reaction conditions, without using any other additives.

DETAILED DESCRIPTION OF THE INVENTION

[0012] For the purposes of this description, unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the description and claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following description and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0013] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific Examples are reported as precisely as possible. Any numerical value, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0014] It is noted that, as used in this description and the appended claims, the singular forms "a", "an" and "the" include plural referents unless expressly and unequivocally limited to one referent.

[0015] In the context of the present specification, the term "C-10" is meant tertiary carboxylic acid having 10 carbon atoms in its structure, also known as neodecanoic acid. Vinyl ester of C-10 is also called "NAVE-10".

[0016] In a typical reaction, A kg of C-10 and B kg acetylene forms C kg of NAVE-10; while D kg of C-10 and E kg of acetylene did not react: R₂ R₂

RrC -C O O H + C 2H 2— ¾^L-*- ( R C -C O O -CH =CH ₂)

R , R,

Molecular weight (g/mol) 172 26 198

Reacted (Kg) A B C

[0017] In the context of the present specification, the term "activity of catalyst" is meant amount of produced NAVE-10 (grams) per mole of catalyst per hour.

"selectivity of tertiary carboxylic acid for vinyl ester thereof is meant

[0019] The term "per pass conversion rate of acetylene" is meant xl00% .

B + E

[0020] The term "per pass conversion rate of C10" is meant xl00% .

A + D

[0021 ] The term "selectivity of acetylene for vinyl ester of the tertiary carboxylic acid" is

Cx(%₈)

meant ^^-xl00% .

B

[0022] In the present invention, a process for preparing vinyl ester of tertiary carboxylic acid is provided, comprising the steps of:

(a) providing a liquid mixture comprising tertiary carboxylic acid having 9 to 11 carbon atoms and a catalyst comprising metal salt of the tertiary carboxylic acid;

(b) optionally heating the liquid mixture at an activation temperature to activate the catalyst;

(c) introducing acetylene into the liquid mixture under reaction conditions for converting the tertiary carboxylic acid to vinyl ester thereof, wherein the conditions are controlled to ensure the presence of un-reacted free tertiary carboxylic acid in the reaction mixture throughout the reaction; and

(d) recycling the catalyst and optionally the un-reacted free tertiary carboxylic acid to step (a).

[0023] In some embodiments of the present invention, suitable metals salts of the tertiary carboxylic acid can be metals salts of Group 2, 8, 1 1 , 12,13 and 14 metals in periodic table such as magnesium, iron, copper, zinc, cadmium, boron, aluminum and tin salts of the tertiary carboxylic acids, preferably Group 12 metals salts like zinc salts. For example, suitable catalysts can be any compounds having a molar a ratio of Zn to tertiary carboxylic acid group of 1 :1 .0-1 :3 as formed by reacting Zn or Zn compounds such as ZnO, Zn(OH)₂, ZnCO3 and Zn salts of lower carboxylic acids with the tertiary carboxylic acid, which is being used the starting compound in preparing the NAVE. The content of the catalyst in step (a) can be 0.5-10% by weight, preferably 2-7% by weight, calculated as Zn metal, based on the weight of the liquid mixture.

[0024] Water can be removed by vacuum during the preparation of the catalyst. Preferably, the amount of water can be decreased to a level of up to 1 .5% by weight, more preferably 0.8% by weight, most preferably 0.3% by weight of the catalyst. In some embodiments according to the present invention, the preparation of the catalyst is conducted in absence of water.

[0025] According to an embodiment of the present invention, catalyst can be obtained by the following steps:

120-200 g of ZnO and 500-700 g of tertiary carboxylic acid is added into a reactor, and heated to 60-200°C for 30-60 min while removing water produced, and in a later stage, water is removed as possible in vacuum to obtain the prepared catalyst stock solution, in which the content of Zn is about 10-20% by weight. Due to the high viscosity, zinc salt of tertiary carboxylic acid will even become a solid after high temperature treatment, so a portion of solvent used in reaction, such as liquid paraffin, can be added in preparation of the catalyst stock solution.

Tertiary carboxylic acid can be added at an appropriately excessive amount, and the undesired tertiary carboxylic acid can be removed by distillation under reduced pressure and at elevated temperature after ZnO is completely dissolved, and the addition of the solvent used in reaction makes the operation easier, and can reduce the viscosity of the catalyst stock solution for easy use.

[0026] In some embodiments of the present invention, suitable tertiary carboxylic acid can be any tertiary carboxylic acid having 9 to 11 carbon atoms. Particularly suitable tertiary carboxylic acids include, but not limited to, neodecanoic acid and neononanoic acid and neoundecylic acid. Preferably, the content of the tertiary carboxylic acid in step (a) can be 5 to 40% by weight, preferably 10 to 20% by weight, based on the weight of the liquid mixture.

[0027] In some embodiments of the present invention, the liquid mixture may comprise inert organic solvents. Suitable organic solvents inert to the reaction mixture at the reaction temperature can be selected by one skilled in the art. As examples of inert organic solvents suitable for the present invention, saturated esters, ethers, alkanes and aromatic hydrocarbons with high boiling point and good thermal stability, can be mentioned. Most preferably, liquid paraffin having a boiling range of greater than 300°C can be used. Preferably, the content of the inert organic solvent can be 30 to 80% by weight, preferably 40 to 60% by weight, based on weight of the liquid mixture.

[0028] In some embodiments of the present invention, the liquid mixture may further comprise polymerization inhibitor. Polymerization inhibitors known in the art can be used, such as phenols and amines. As examples of inhibitors, sodium aminobenzenesulfonate, polyphenol, pyrogallic acid, hydroquinone, p-methoxyphenol, or a mixture thereof, can be mentioned. Preferably, the content of the polymerization inhibitors can be 0.001 to 1 % by weight, based on the weight of the liquid mixture.

[0029] In some embodiments of the present invention, the activation in step (b) can be conducted by heating the liquid mixture to a temperature of 200 to 280°C under an inert gas atmosphere, for preferably 5 to 120 mins.

[0030] In some embodiments of the present invention, the reaction in step (c) can be conducted at a temperature of 160 to 260°C, preferably 190 to 230°C. Pressure suitable for the present invention can be from 0.06 to 0.25 MPa(a). Preferably, the reaction mixture is substantially free of water.

[0031 ] During the reaction, the feed rate of acetylene can be controlled. For example, the feed rate of acetylene can be 1 .0-1 .5 times of the gas consumption rate in the reaction.

[0032] In the present invention, the reaction conditions are preferably controlled so that the molar ratio between the sum of the un-reacted free tertiary carboxylic acid and tertiary carboxylic acid group associated with Zn ion and Zn ion, in the reaction mixture throughout the reaction, is kept no less than 1 .5:1 , preferably greater than 2:1 .

[0033] The present process can be a batch process. In the present invention, the per pass conversation rate of the free tertiary carboxylic acid should be below 100%, preferably 70 to 95%. After completion of the previous batch, the bottom liquid after removal of the product by rectification is recycled, which contains free tertiary carboxylic acid, and when it is supplemented with additional fresh tertiary carboxylic acid and continues to react, the conversion rate of the supplemented tertiary carboxylic acid can be up to 100%, while the conversion rate of total free tertiary carboxylic acid in the liquid system should be still maintained below 100%, preferably 70-95%.

[0034] According to one embodiment of the present invention, NAVE can be obtained by the following steps:

(i) The initial feedstock containing 40-60% by weight of liquid paraffin, 10-20% by weight of neodecanoic acid, 0.001 -0.5% by weight of a polymerization inhibitor, and catalyst formulation equivalent to 2-7% by weight based on Zn is added into a reactor equipped with a stirrer, a thermometer and a reflux condenser, and heated to 200-280°C with stirring under the protection of nitrogen to activate for 5-120 mins, then acetylene is introduced for reaction while controlling the temperature at 190-230°C, a tail gas venting rate of 1 -10 L/h is kept at the same time, after reacting for a period of time, the temperature is lowered, and the introduction of acetylene is stopped to finish the reaction. The material is simply distilled to obtain a crude product, which is then rectified to produce a fine product and the mother liquor is recycled back to the reactor.

(ii) The mother liquor recycled back from step (i) after distillation is supplemented with a suitable amount of tertiary carboxylic acid, and reacted, distilled and rectified under the same conditions as those in step (i). The resulting mother liquor is also recycled.

[0035] Part or all of the following technical effects can be achieved by the present invention:

- the space time yield of the reaction can be greater than 400 g/(h-L);

- the catalytic activity can be greater than 370 g/(mol-h);

- the selectivity of tertiary carboxylic acid for vinyl ester thereof can be greater than 98%;

- the per pass conversion rate of acetylene can be greater than 80%;

- the selectivity of acetylene for vinyl ester of the tertiary carboxylic acid can be greater than 95%; and/or

- the purity of the obtained NAVE can be as high as 99%.

[0036] While not intending to be bound by any theory, it's believed that the rate for reaction of acetylene and tertiary carboxylic acid to produce NAVE and the selectivity of acetylene are closely correlated with the coordination status of Zn²⁺ in the catalyst. The possible ligands for Zn²⁺ in the reaction may include, for example, OH^", H₂O, tertiary carboxylic acid group, acetylene, free tertiary carboxylic acid and NAVE, and coordination competition exists among each ligand. In the preparation of the catalyst, OH^" included in ligands for Zn²⁺ will further interact with tertiary carboxylic acid to produce a zinc-water complex. The zinc-water complex, due to the occupation of coordination position by water, has reduced catalytic effect for the reaction of tertiary carboxylic acid and acetylene to produce NAVE, so that the reaction rate is low, and with the consumption of H₂O, the ligands acetylene, and tertiary carboxylic acid included in ligands for Zn²⁺ increase, so the production rate of NAVE is improved. When the content of tertiary carboxylic acid in the reaction system decreases to a certain extent, ligand tertiary carboxylic acid included in ligands for Zn²⁺ decreases, and ligand acetylene increase, so the production rate of NAVE is decreased, and the rate for side reactions involving acetylene will increase. Therefore, the compositional proportions of the ligands and the operation conditions must be controlled in order to achieve the most desirable catalytic effect.

[0037] It is found in the studies that the conversion rate of free tertiary carboxylic acid can exceed 100% in batch tank reaction, this is because after the fed free tertiary carboxylic acid is completely converted (the conversion rate is 100%), acetylene will continue to consume tertiary carboxylic acid group bound to zinc, thus destroying the catalyst structure and decreasing the catalytic activity. Therefore, the per pass conversion rate of free tertiary carboxylic acid in the liquid phase should be below 100%, and considering the activation effect, the catalytic activity can be up to above 370 g ester/(rnol_Zinc-h). Furthermore, well mixing of gas and liquid, and circulation of the gas in the reactor can be achieved by stirring; therefore the venting amount of the gas can be greatly reduced to below 10%, such that the per pass conversion rate of the gas can be above 90%. By reducing the water content as possible to prevent hydration of acetylene to acetaldehyde, the selectivity of the gas can be improved to above 95%.

[0038] The following Examples are included to demonstrate preferred embodiments of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the Examples which follow represent techniques discovered by the inventor to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.

EXAMPLES

[0039] Unless indicated to the contrary, all parts and percentages are by weight. Example 1 (preparation of catalyst)

[0040] 200 g of zinc oxide, and 700 g of C-10 tertiary carboxylic acid (neodecanoic acid) were weighed out, mixed and heated to 120°C for 30 min in a 2L three-necked flask equipped with a stirrer, while removing water produced, and in a later stage, water was removed as possible in vacuum to produce a catalyst stock solution, in which the content of Zn was analyzed to be 18.61 % by weight.

Example 2 (comparative)

[0041 ] The prepared catalyst, solvent, and neodecanoic acid (C-10 acid) were mixed into the reactor, stirred and heated to a desired temperature (230°C). Acetylene was charged from the bottom of the reactor via a sparger. After acetylene consumption rate decreased significantly, the reaction was allowed to continue for another 10 to 20 minutes to let all free C-10 acid react completely. Acetylene feed was stopped and the reactor was allowed to cool to room temperature and the reaction mixture was released. Then, the reaction mixture was distilled at 250-260°C under 10kPa vacuum to remove NAVE-10 product and the rest is the recycled mother liquor (without any free C-10 acid). The recycled mother liquor was used along with additional C10 in reactions with acetylene.

[0042] To 782 g of the recycled mother liquor (containing catalyst zinc salt, solvent liquid paraffin and polymerization inhibitor hydroquinone, but no free neodecanoic acid) by distillation after 100% conversion of the previous batch of free C-10 tertiary carboxylic acid in liquid phase. 174.7 g of C-10 tertiary carboxylic acid (Neodecanoic acid) was added, and the total feedstock contained zinc of 6.52% by weight, and polymerization inhibitor of 0.1 % by weight, and the resting being solvent. The temperature was raised to 230°C under the protection of nitrogen, and the pressure was maintained at 0.04 MPa. Then 31 .78 L of acetylene was introduced in 90 min, and 5.45 L of tail gas acetylene was vented at the same time. The reaction was stopped, 189.41 g of NAVE and 0.88 g of unreacted C-10 tertiary carboxylic acid were obtained after reducing temperature and distilling at reduced pressure; the calculated catalytic activity was 133.1 1 g/(mol-h), the conversion rate of acetylene was 82.85%, and the selectivity of acetylene was 81 .38%.

Example 3 (the invention)

[0043] The prepared catalyst, solvent, and neodecanoic acid (C-10 acid) were mixed into the reactor, stirred and heated to a desired temperature (230°C). Acetylene was charged from the bottom of the reactor via a sparger. After 40-50 minutes (before acetylene consumption rate decreased significantly), the acetylene feed was stopped and the reactor was allowed to cool to room temperature and the reaction mixture was released. Then, the reaction mixture was distilled at 180-200°C under 10kPa vacuum to remove NAVE-10 product and the rest is the recycled mother liquor (with free C-10 acid). The recycled mother liquor was used along with additional C-10 in reactions with acetylene.

[0044] To 692 g of the recycled mother liquor (containing catalyst zinc salt, solvent liquid paraffin, polymerization inhibitor hydroquinone, and 43.49 g of free C-10 tertiary carboxylic acid) by distillation after 72.02% conversion of the previous batch of free C-10 tertiary carboxylic acid (Neodecanoic acid) in liquid phase. 1 10.1 1 g of C-10 tertiary carboxylic acid (Neodecanoic acid) was added, and the total feedstock contained zinc of 6.4% by weight, and polymerization inhibitor of about 0.1 % by weight, and the rest being solvent. The reaction temperature was 230°C, and the other operations were similar to those in Example 2. 13.06 L of acetylene was introduced in 37 min, and 2.23 L of tail gas acetylene was vented at the same time. The reaction was stopped, 92.09 g of NAVE and 61 .53 g of unreacted C-10 tertiary carboxylic acid were obtained after reducing temperature and distilling at reduced pressure; the calculated catalytic activity was 181 .34 g/(mol.h), the conversion rate of acetylene was 82.92%, and the selectivity of acetylene was 96.20%.

Example 4 (the invention)

[0045] To 674 g of the recycled mother liquor (containing catalyst zinc salt, solvent liquid paraffin and polymerization inhibitor hydroquinone, but no free neodecanoic acid) by distillation after 100% conversion of the previous batch of free C-10 tertiary carboxylic acid (Neodecanoic acid) in liquid phase. 155.0 g of C-10 tertiary carboxylic acid (Neodecanoic acid) was added, and the total feedstock contained zinc of 6.39% by weight, and polymerization inhibitor of about 0.1 % by weight, and the rest being solvent. The temperature was raised to 250°C under the protection of nitrogen to activate for 30 min, and then reduced to 230°C for reaction. The other operations were similar to those described in Example 2. 20.55 L of acetylene was introduced in 34 min, and 2.1 1 L of tail gas acetylene was vented at the same time. The reaction was stopped, 135.75 g of NAVE and 33.81 g of unreacted C-10 tertiary carboxylic acid were obtained after reducing temperature and distilling at reduced pressure; the calculated catalytic activity was 293.93g/(mol.h), the conversion rate of acetylene was 89.72%, and the selectivity of acetylene was 96.65%.

[0046] The conversion rate in the comparative examples above also can be any value below 100%.

Example 5 (the invention)

[0047] To 707.3 g of the recycled mother liquor (containing catalyst zinc salt, solvent liquid paraffin, polymerization inhibitor hydroquinone, and 37.3 g of free C-10 tertiary carboxylic acid) by distillation after 76.45% conversion of the previous batch of free C-10 tertiary carboxylic acid in liquid phase. 121 .4 g of C-10 tertiary carboxylic acid (Neodecanoic acid) was added, and the total feedstock contained zinc of 6.39% by weight, and polymerization inhibitor of 0.1 % by weight, and the resting being solvent. The temperature was raised to 250°C under the protection of nitrogen to activate for 30 min, and then reduced to 230°C for reaction. The other operations were similar to those described in Example 2. 17.61 L of acetylene was introduced in 28 min, and 1 .83 L of tail gas acetylene was vented at the same time. The reaction was stopped, 143.17 g of NAVE and 32.92 g of unreacted neodecanoic acid were obtained after reducing temperature and distilling at reduced pressure; the calculated catalytic activity was 376.42 g/(mol.h), the conversion rate of acetylene was 90.32%, and the selectivity of acetylene was 97.71 %.

[0048] Table 1 shows the effects of different per pass conversion rates of the free acid and activation operation on the catalytic activity, gas conversion rate, and gas selectivity etc, and specific Examples will not be detailed further here.

Table 1 : Effects of different conversion rates of free acid and activation operation on catalytic activity, gas conversion rate, and gas selectivity etc.

Note: in the table, the experimental conditions are the same except for the free acid content in the mother liquor and activation, in which the reaction temperature is 230°C, the pressure is 0.04 MPa, the zinc content is about 6.4% by weight, and the free C-10 tertiary carboxylic acid (Neodecanoic acid) content is about 18% by weight.

[0049] All of the methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the products and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention.

Claims

WHAT IS CLAIMED IS:

1 . A process for preparing vinyl ester of tertiary carboxylic acid, comprising:

2. The process according to claim 1 , wherein the metal salt is zinc salt of the tertiary carboxylic acid.

3. The process according to claim 1 or 2, wherein the conditions are controlled to keep the molar ratio between the sum of the un-reacted free tertiary carboxylic acid and tertiary carboxylic acid group associated with Zn ion, on the one hand, and Zn ion, on the other hand, in the reaction mixture throughout the reaction, is no less than 1 .5:1 preferably greater than 2:1 .

4. The process according to any one of claims 1 to 3, wherein the content of the catalyst in step (a) is 0.5-10% by weight, preferably 2-7% by weight, calculated as Zn metal, based on the weight of the liquid mixture.

5. The process according to any one of claims 1 to 4, wherein the content of the tertiary carboxylic acid in step (a) is 5 to 40% by weight, preferably 10 to 20% by weight, based on the weight of the liquid mixture.

6. The process according to any one of claims 1 to 5, wherein the liquid mixture in step (a) further comprises inert organic solvent, such as liquid paraffin having a boiling range of above 300°C.

7. The process according to claim 6, wherein the content of the inert organic solvent is 30 to 80% by weight, preferably 40 to 60% by weight, based on weight of the liquid mixture.

8. The process according to any one of claims 1 to 7, wherein the tertiary carboxylic acid is selected from the group consisting of neodecanoic acid neononanoic acid and neoundecylic acid.

9. The process according to any one of claims 1 to 8, wherein the activation in step (b) is conducted by heating the liquid mixture to a temperature of 200 to 280°C under an inert gas atmosphere, for preferably 5 to 120 mins.

10. The process according to any one of claims 1 to 9, wherein the reaction in step (c) is conducted at a temperature of 160 to 260°C, preferably 190 to 230°C.

1 1 . The process according to any one of claims 1 to 10, wherein the reaction in step (c) is conducted under a pressure of 0.06 to 0.25 MPa(a).

12. The process according to any one of claims 1 to 11 , wherein the reaction mixture is substantially free of water.

13. The process according to any one of claims 1 to 12, wherein the space time yield of the reaction is greater than 400 g/(h-L).

14. The process according to any one of claims 1 to 13, wherein the catalytic activity is greater than 370 g/(mol-h).

15. The process according to any one of claims 1 to 14, wherein the selectivity of tertiary carboxylic acid for vinyl ester thereof is greater than 98%.

16. The process according to any one of claims 1 to 15, wherein the per pass conversion rate of acetylene is greater than 80%.

17. The process according to any one of claims 1 to 16, wherein the selectivity of acetylene for vinyl ester of the tertiary carboxylic acid is greater than 95%.

18. The process according to any one of claims 1 to 17, wherein the process is a batch process.