Temperature vinyl acetate monomer process

After the polymerization reactors, the unreacted monomer must be removed from the polymer stream. In your company s existing polymerization units, the monomer is removed in a distillation/stripping column. Methanol vapor is fed to the bottom of the column and a mixture of methanol and vinyl acetate monomer is taken as an overhead product. The PVAC exits from the bottom of the column in a methanol solution. To minimize product color formation, column temperatures should not exceed 240°F. The bottoms from the PVAC/methanol column must have a solids content of 36 to 40% to be suitable for existing processing equipment downstream. 

The two-carbon short-chain acetic acid is start material for the production of vinyl acetate monomer (VAM). This application consumes one third of the world s production of acetic acid (Cheung et al. 2005). The product of the condensation of two molecules of acetic acid is acetic anhydride. The worldwide production of acetic anhydride is a further major application and uses approximately 25-30 % of the global production of acetic acid. The main process involves dehydration of acetic acid to give ketene at the temperature of 700-750 °C. Ketene is thereafter reacted with acetic acid to obtain the anhydride (Held et al. 2005). Acetic anhydride is an acetylation agent. As such, its major application is for cellulose acetate, a... 

In poly(vinyl acetate) copolymer emulsions, the properties are significantly affected by the composition of the aqueous phase and by the stabilizers and buffers used iu the preparation of these materials, along with the process conditions (eg, monomer concentrations, pH, agitation, and temperature). The emulsions are milk-white Hquids containing ca 55 wt % PVAc, the balance being water and small quantities of wetting agents or protective coUoids. 

Because the polymer degrades before melting, polyacrylonitrile is commonly formed into fibers via a wet spinning process. The precursor is actually a copolymer of acrylonitrile and other monomer(s) which are added to control the oxidation rate and lower the glass transition temperature of the material. Common copolymers include vinyl acetate, methyl acrylate, methyl methacrylate, acrylic acid, itaconic acid, and methacrylic acid [1,2]. 

The final product of emulsion polymerization is an emulsion —a stable, heterogeneous mixture of fine polymer beads in an aqueous solution, sometime called a latex emulsion. Water-based paints, for example, can be formed from the emulsion polymerization of vinyl acetate. In this process, I m of water containing 3% poly(vinyl alcohol) and 1% surfactant are heated to 60°C in a reaction vessel (see Figure 3.27) The temperature rises to around 80°C over a 4 to 5 hour period as monomer and an aqueous persulfate solution are added. The rate at which heat can be removed limits the rate at which monomer can be added. 

Monomers such as vinyl acetate or vinylidene chloride may be copolymerized with vinyl chloride, Up to 15% of the comonomer may be employed. Vinyl acetate increases die solubility, film formation and adhesion. Processing or forming temperatures are generally lowered. Chemical resistance and tensile strength decrease with increasing amount of vinyl acetate. 

Copolymerization. Vinyl chloride can be copolymerized with a variety of monomers. Vinyl acetate, the most important commercial comonomer, is used to reduce crystallinity, winch aids fusion and allows lower processing temperatures. Copolymers are used in flooring and coatings. This copolymer sometimes contains maleic add or vinyl alcohol (hydrolyzed from the poly(vinyl acetate ) to improve the coating s adhesion to other materials, including metals, Copolymers with vinylidene chloride are used as barrier films and coatings. Copolymers of vinyl chlonde with acrylic esters in latex from are used as film formers in paint, nonwoven fabric binders, adhesives, and coatings. Copolymers with olefins improve thermal stability and melt flow, but at some loss of heat-deflection temperature,... 

High-Temperature Application. Vinyl Acetate Distribution in Copoly (ethylene-vinyl acetate). In the characterization of polymers, molecular distribution and composition are two critical parameters. Every physical property and processing change of the material can be related to these two parameters. With copolymers, IR spectroscopy can be used for determination of the distribution of one or both monomers within the molecular weight distribution. 

In addition to homopolymers of varying molecular and particle structure, copolymers are also available commercially in which vinyl chloride is the principal monomer. Comonomers used commercially include vinyl acetate, vinylidene chloride, propylene, acrylonitrile, vinyl isobutyl ether, and maleic, fumaric and acrylic esters. Of these the first three only are of importance to the plastics industry. The main function of introducing comonomer is to reduce the regularity of the polymer structure and thus lower the interchain forces. The polymers may therefore be processed at much lower temperatures and are useful in the manufacture of gramophone records and flooring compositions. 

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