ACETYLENE CATALYTIC ACETYLATION OF VINYL ACETATE IN THE LABORATORY

ABSTRACT

Among the oxygen compounds produced in the chemical and basic organic synthesis industry, vinyl ethers occupy one of the first places. Vinyl acetate is of particular importance. Aqueous solutions of Zn(CH₃COO)₂, Cd(CH₃COO)₂, ZrO(NO₃)₂ salts were used for sol-gel synthesis of nano-sized particles. Qualitative analysis was carried out by the method of "witnesses", quantitative analysis was carried out by the method of internal normalization. Zinc acetate, zinc acetate and cadmium acetate and zinc acetate, cadmium acetate and zirconium oxynitrate mixture catalysts were obtained from acetylene and acetic acid. Synthesis products were analyzed by gas-liquid chromatography with a flame ionization detector under the following normal conditions. Reactors of processes for obtaining vinyl acetate by catalytic acetylation of acetylene were mathematically modeled.

АННОТАЦИЯ

Среди кислородных соединений, получаемых в промышленности химического и основного органического синтеза, виниловые эфиры занимают одно из первых мест. Винилацетат имеет особое значение. Водные растворы солей Zn(CH₃COO)₂, Cd(CH₃COO)₂, ZrO(NO₃)₂ использовали для золь-гель синтеза наноразмерных частиц. Качественный анализ проводился методом «свидетелей», количественный анализ – методом внутренней нормализации. Катализаторы из смеси ацетата цинка, ацетата цинка и ацетата кадмия и смеси ацетата цинка, ацетата кадмия и оксинитрата циркония получали из ацетилена и уксусной кислоты. Продукты синтеза анализировали методом газожидкостной хроматографии с пламенно-ионизационным детектором при следующих нормальных условиях. Математически смоделированы реакторы процессов получения винилацетата каталитическим ацетилированием ацетилена.

Keywords: acetylene, catalyst, acetic acid, vinyl acetate, sol-gel technology

Ключевые слова: ацетилен, катализатор, уксусная кислота, винилацетат, золь-гель технология

Introduction

Among the oxygen compounds produced in the chemical and basic organic synthesis industry, vinyl ethers take one of the first places. Vinyl acetate is of particular importance. Vinyl acetate was studied since 1909 and was first obtained and isolated in 1912 by the German chemist F. Klatte.

C₂H₂+2CH₃COOH→ CH₃CH(OCOCH₃)₂

C₂H₂+CH₃COOH → CH₂=CHOCOCH₃

Vinyl acetate is one of the most important monomers, the production of which is growing rapidly all over the world. The value of vinyl acetate has increased dramatically with the development of the plastics industry, as they polymerize to form resins with good optical and mechanical properties. Among the polymers synthesized from vinyl acetate, polyvinyl alcohol, polyvinyl acetate and polyvinyl acetals, it is the most widely used. Polyvinyl acetate has high viscosity properties and is used for adhesives, water-soluble latex paints, fabric sizing, and other.

Experimental part

The most effective method for obtaining mesoporous catalysts is the ‘sol-gel’ technology, which allows controlling the particle size, surface area, and pore structure of the catalyst at any stage.

Aqueous solutions of Zn(CH₃COO)₂, Cd(CH₃COO)₂, ZrO(NO₃)₂ salts were used for sol-gel synthesis of nano-sized particles. A nanocatalyst with the following structure was selected for catalytic acetylation of acetylene.

After that, we studied the effect of the mass ratio of the catalyst active components on the catalyst activity in the catalytic acetylation reaction of acetylene. The obtained results are presented in Table 1.

Table 1.

The influence of the mass ratio of catalyst active components on catalyst activity in the catalytic acetylation reaction of acetylene

As it can be seen from Table 2, the influence ratio of catalyst active components mass ratios on catalyst activity in the catalytic acetylation reaction of acetylene Zn(CH₃COO)₂:Cd(CH₃COO)₂:ZrO(NO₃)₂=11.5:11.5:1.0 (in mass percent) the productivity of the catalyst will have the highest value.

Figure 1. Scheme of production of vinyl acetate in the laboratory:
1 - needle valve; 2 - rheometer; 3 – absorbent with hydroxylamine; 4 – drying column; 5 - evaporator; 6 - bathroom; 7 - reactor; 8 - thermowell; 9 – transformer; 10 - voltmeter; 11 – reactor temperature control unit; 12 - air cooler; 13 - water-cooled refrigerator; 14 - xylene traps; 15 - exhaust gas line

A metal reactor (7) with a diameter of 40 mm and a height of 380 mm is equipped with a mesh-substrate on the bottom. The upper flange cover is equipped with two fittings: a steam-gas mixture (acetylene saturated with acetic acid vapors) and a thermowell (8). The lower flange-bottom part is equipped with fittings for removing reaction products.

TEN-06 heating elements with a total power of 3.6 kV are evenly distributed around the reactor vessel (7), which are connected to the 220 V network through a control transformer (9). It is not allowed to supply more than 220 V to prevent overheating.

The surface of the reactor is insulated and wrapped to conserve heat and maintain a stable temperature. The temperature in the reactor was measured by a THC thermocouple with signals output to the temperature control unit (11), the readings were recorded on the KSP potentiometer or indicating device.

The acetylene used from the cylinder is purified from acetone in an absorber with 10% hydroxylamine (3), and the acetylene is dried in a drying column with calcium chloride (4).

To carry out the synthesis, a certain amount of catalyst is loaded into the reactor. The catalyst is heated in a stream of nitrogen. When the temperature reached 180 °C, the valve in the mixed gas line (1') of workshop No. 007 was opened (or acetylene concentrate from the cylinder), and the valve in the nitrogen line (1) was closed. For saturation with acetic acid, the gas was passed through an acetic acid evaporator placed in a water bath with a temperature of ≈95-100 °C. Then the gas saturated with acetic acid entered the reactor, where the acetylation reaction took place on the catalyst at a temperature of 180-210°C. During the reaction, the parameters of the technological mode, temperature conditions, and the flow rate of the delivered components were measured.

The gaseous reaction products were cooled first in an air cooler (12) and then in a water-cooled refrigerator (Liebig) (13). Condensate and vinyl acetate vapors are absorbed in absorbers with xylene (14) placed in an ice bath (3-8°C). The reaction products obtained with the collected xylene were chromatographically analyzed for their constituents. Inlet and outlet gases were periodically analyzed by gas chromatography.

Discussion part

Synthesis products were analyzed by gas-liquid chromatography with a flame ionization detector under the following normal conditions: 15% Lestosil in Svetochrom-545 with a stationary liquid phase particle size of 0.250-0.315 nm, a glass with a size of 2x0.004 m column, column temperature 100°C, carrier gas-nitrogen flow consumption 30 ml/min.

As a result of the conducted research, the following optimal condition of the analysis was chosen.

Table 2.

Chromatographic optimal conditions of the products of the catalytic acetylation reaction of acetylene

Qualitative analysis was carried out by the method of ‘witnesses,’ quantitative analysis was carried out by the method of internal normalization. Chromatograms obtained from acetylene and acetic acid on zinc acetate, zinc acetate and cadmium acetate and zinc acetate, cadmium acetate and zirconium oxynitrate mixture catalysts are presented in Figures 2, 3 and 4 below.

1-acetylene; 2-acetaldehyde; 3-acetone; 4-vinylacetate; 5-croton aldehyde; 6-acetic acid; 7-ethylenediacetate

Figure 2. Chromatogram of crude vinyl acetate obtained on ZnO/ ceramsite catalyst

1-acetylene; 2-acetaldehyde; 3-acetone; 4-vinylacetate; 5-croton aldehyde; 6-acetic acid; 7-ethylenediacetate

Figure 3. Chromatogram of crude vinyl acetate obtained on ZnO∙CdO /ceramsite catalyst

1-acetylene; 2-acetaldehyde; 3-acetone; 4-vinylacetate; 5-croton aldehyde; 6-acetic acid; 7-ethylenediacetate

Figure 4. Chromatogram of crude vinyl acetate obtained on ZnO∙CdO∙ZrO₂/ceramzite catalyst

As can be seen from the chromatograms, the amounts of acetylene, acetaldehyde, acetone, croton aldehyde, acetic acid, and ethylidene acetate adducts in ZnO∙CdO∙ZrO₂/keramzite catalysts are less than those formed in ZnO/ceramzite and ZnO∙CdO/keramzite catalysts. .

Product yield in the synthesis of vinyl acetate from acetylene depends on 3 factors: process temperature, acetylene volumetric rate (x₂), height of the catalyst layer. A series of preliminary experiments was conducted according to the plan of 23 fully factorial experiments. The complete factorial experiment design matrix and its results are presented in Table 3 below.

Table 3.

Plan-matrix of full factorial experiment and its results

As a result of processing the results of the experiment, the following polynomial was obtained: .

To carry out analytical optimization of the model, if we consider the model as an incomplete quadratic equation and optimize it, we will have two linear equations:

Then the optimized equation takes the following form:

Conclusion

Thermally stable, high activity, selectivity and productivity nanocatalysts for ZnO·CdO·ZrO₂/ceramzite reactions for catalytic acetylation of acetylene from local raw materials were created based on ‘sol-gel’ technology. Catalytic acetylation reactions of acetylene were thermodynamically justified. Reactors of processes for obtaining vinyl acetate by catalytic acetylation of acetylene were mathematically modeled.

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