Modeling and approval of vinyl acetate synthesis process from acetylene

The purpose of this work is to model and optimize the process of synthesis of vinyl acetate from acetylene and solve the listed problems for industrial production.
Key words: acetylene, acetic acid, vinylacetate, mathematical model, optimization.


INTRODUCTION
Vinyl acetate is one of the important monomers whose production is growing rapidly worldwide. Vinyl acetate is a raw material in the production of polyvinyl acetate, which is used as a binder in the preparation of polymer concrete, as a base for glues, as a film-forming agent in the production of emulsion varnishes and paints, and in the form of water dispersions for obtaining polyvinyl alcohol and polyvinyl acetals. Acidic or alkaline alcoholysis of polyvinyl acetate yields polyvinyl alcohol, which is widely used as an emulsifier in polymerization in the production of fibers, as well as pharmaceuticals, blood and plasma substitutes [1-2]. Vinyl chloride, ethylene, acrylic acid esters, styrene vinyl acetate copolymers are also widely used.
Industrial production of vinyl acetate is carried out in two ways:
1. Based on acetylene and acetic acid [3-4];
2. Based on ethylene, acetic acid and oxygen.
The method of obtaining vinyl acetate from acetylene and acetic acid is based on the vinylization reaction, which consists of adding acetic acid to acetylene:


The process of obtaining vinyl acetate from acetylene is carried out in the vapor phase as well as in the liquid phase. Vinylacetate was first obtained as a by-product in the liquid phase synthesis reaction of ethylidene diacetate. Later, this method was implemented as the first industrial method for obtaining vinylacetate: the reaction was carried out in acetic acid at 40-100oC in the presence of strong acids such as mercuric salts, oleum, etc. [5-6]. By changing the catalyst composition, temperature, stirring speed, it is possible to influence the selectivity of the process and obtain 80% yield of vinylacetate or ethylenediacetate in acetic acid.
At the end of the 30s, the production of vinyl acetate on heterogeneous catalysts began in Germany, this method has not lost its relevance even today: the reaction is carried out in a zinc acetate catalytic system on a carrier (activated carbon) at a temperature range of 160-240o C and at a pressure close to atmospheric pressure [7-8] . To reduce the release of ethylene diacetate, the reaction is carried out in an excess of acetylene (the ratio of acetylene to acetic acid = 4-10 : 1) [11-14]; the process is carried out either in tubular reactors or in pseudo-fluidized bed reactors of catalyst. Volume loading is 100-500 h-1, acetic acid conversion is about 50%, vinyl acetate productivity is 40-80 kg/m3 cat.h. Due to the accumulation of polymer and resin on the zinc acetate catalyst, it loses its activity over time, which forces the process temperature to gradually increase from 160-180oC to 220-240oC [9-10].
By-products in the synthesis of vinyl acetate from acetylene and acetic acid: croton aldehyde, ethylidene diacetate, acetone, acetaldehyde, polyvinyl acetate and methane. The selectivity of vinyl acetate to acetylene, which has entered into a chemical reaction, is around 95-99%, and to acetic acid is around 92-98% [7, 9, 10].
Currently, in addition to obtaining lower molecular alkenes by pyrolyzing lower alkanes, it is also important to obtain aromatic hydrocarbons (liquid fuel) by catalytic aromatization of methane, propane-butane fractions, and petroleum gasses. Today, world scientists are interested in obtaining ethylene from methane in one step (oxycondensation of methane), obtaining methanol and dimethyl ether from methane through carbon dioxide, and obtaining lower molecular unsaturated hydrocarbons from methanol and dimethyl ether. In this regard, large-scale work is being done and high results are being achieved[11-31].