Tubular reactor vinyl acetate

Solution Polymerization. Solution polymerization of vinyl acetate is carried out mainly as an intermediate step to the manufacture of poly(vinyl alcohol). A small amount of solution-polymerized vinyl acetate is prepared for the merchant market. When solution polymerization is carried out, the solvent acts as a chain-transfer agent, and depending on its transfer constant, has an effect on the molecular weight of the product. The rate of polymerization is also affected by the solvent but not in the same way as the degree of polymerization. The reactivity of the solvent-derived radical plays an important part. Chain-transfer constants for solvents in vinyl acetate polymerizations have been tabulated (13). Continuous solution polymers of poly(vinyl acetate) in tubular reactors have been prepared at high yield and throughput (73,74). 

Loop A continuous process for polymerizing aqueous emulsions of olefinic compounds such as vinyl acetate. Polymerization takes place in a tubular reactor (the loop) with recycle. Invented by Gulf Oil Canada in 1971 and further developed by several United Kingdom paint companies. It is now used for making copolymers of vinyl acetate with ethylene, used in solvent-free paints and adhesives. 

The residence time is typically in the range of 15 - 60 s. The temperature and pressure are a little lower then in a tubular reactor. Pressures are in the range of 130 - 220 MPa, and the temperatures mostly do not exceed 260°C. When ethylene-vinyl acetate resins are produced, single autoclaves are run at temperatures which are 30 - 50°C lower then in the production of homopolyethylene. 

When ethylene-vinyl acetate copolymers are manufactured, the decomposition products also contain carbon monoxide and carbon dioxide. When decomposition takes place in a tubular reactor or in a multi-chamber or cascade of autoclaves, up to 50% of the decomposition gases can consist of undecomposed ethylene. 

While vinyl acetate is normally polymerized in batch or continuous stirred tank reactors, continuous reactors offer the possibility of better heat transfer and more uniform quality. Tubular reactors have been used to produce polystyrene by a mass process (1, 2), and to produce emulsion polymers from styrene and styrene-butadiene (3 -6). The use of mixed emulsifiers to produce mono-disperse latexes has been applied to polyvinyl toluene (5). Dunn and Taylor have proposed that nucleation in seeded vinyl acetate emulsion is prevented by entrapment of oligomeric radicals by the seed particles (6j. Because of the solubility of vinyl acetate in water, Smith -Ewart kinetics (case 2) does not seem to apply, but the kinetic models developed by Ugelstad (7J and Friis (8 ) seem to be more appropriate. 

The objective of this study was to investigate the feasibility of using a tubular reactor for the seeded emulsion polymerization of vinyl acetate, and to study the effect of process variables on conversion rate and latex properties. 

Vinyl acetate is also made from ethylene in a vapor-phase process. The feed mixture is ethylene, acetic acid, and oxygen, and is circulated through a fixed-bed tubular reactor. The catalyst is a noble metal, probably palladium, and has a life of several years. 

Stamicarbon bv Polyethylene, LDPE-EVA Ethylene and vinyl acetate Advanced Clean Tubular reactor LDPE/low EVA reliable, flexible and low cost line size up to 400,000 tpy 9 2000... 

Application To produce low-density polyethylene (LDPE) homopolymers and ethylene vinyl acetate (EVA) copolymers using the high-pressure free radical process. Large-scale tubular reactors with a capacity in the range of 130,000 tpy-425,000 tpy, as well as stirred autoclave reactors with capacity around 125,000 tpy can be used. 

Tubular reactors are used in this process. The tubes are packed with a catalyst and the shell contains circulating boiler feed water which is flashed in an external drum to produce process steam. Reactor operating temperature is about 350°F and operating pressure is about 100 psig. The temperature is continuously increased from approximately 300°F to 350°F over the life of the catalyst to maintain the yield of vinyl acetate as the activity of the catalyst decreases. Catalyst life is from 2 to 3 years. 

The continuous loop reactor is likely to be the only tubular reactor used on commercial production of emulsion polymers [71], although its use is limited to production of vinyl acetate homopolymers and copolymers (with ethylene and VeovalO) [77-79]. A continuous-loop reactor consists of a tubular loop that connects the inlet and the outlet of a recycle pump. These reactors combine the heat transfer characteristics of a tubular reactor with the RTD of a CSTR. The main drawback of this reactor is that the requirements for the mechanical stability of the latex are stringent because the recycling pump may induce shear coagulation. 

Hamer, J. and Ray, W. H. (1986b) Continuous tubular polymerization reactors - II. Studies of vinyl acetate polymerization, Chem. Eng. Sci. 41, 3095-3100. 

The product mix of autoclave and tubular reactors are similar in terms of LDPE homopolymers (0.910-0.935 g/cc) and some specialty grades of polyethylene such as ethylene/vinyl acetate copolymers up to about 30 wt% vinyl acetate (VA). However, the autoclave process provides higher levels of vinyl acetate (40 wt%) in ethylene/VA copolymers and additional specialty grades of polyethylene such as ethylene/methyl acrylate, ethylene/acrylic acid and ethylene/n-butyl acrylate. Polyethylene molecular weight can be varied over a wide range with the high-pressure process, with Melt Index values (I ranging from 0.15 to 40. 

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