Vinyl acetate azeotropes

However, consider some of the physical properties shown in Table 1. From Table 1, note that the boiling point is close to the temperature at which many vinyl polymerizations are often run (80°C). In fact, the water-vinyl acetate azeotrope boils even lower. Therefore, emulsion polymerizations have to be initiated at a moderate temperature. 

The physical properties of vinyl acetate are outlined in Table I [13a-18]. In particular note the water solubility of the monomer. This property appears to go through a minimum of 2.2 wt% at 29°C. The solubility data above 66 C are probably somewhat uncertain since these data are taken above the boiling point of the water-vinyl acetate azeotrope and are, therefore, pressure dependent. 

The fact that the water-vinyl acetate azeotrope boils at 66 C may affect the reproducibility of suspension and emulsion polymerizations which are frequently said to be carried out at about 70°C. 

Vinyl acetate is a colorless, flammable Hquid having an initially pleasant odor which quickly becomes sharp and irritating. Table 1 Hsts the physical properties of the monomer. Information on properties, safety, and handling of vinyl acetate has been pubUshed (5—9). The vapor pressure, heat of vaporization, vapor heat capacity, Hquid heat capacity, Hquid density, vapor viscosity, Hquid viscosity, surface tension, vapor thermal conductivity, and Hquid thermal conductivity profile over temperature ranges have also been pubHshed (10). Table 2 (11) Hsts the solubiHty information for vinyl acetate. Unlike monomers such as styrene, vinyl acetate has a significant level of solubiHty in water which contributes to unique polymerization behavior. Vinyl acetate forms azeotropic mixtures (Table 3) (12). 

Acetic acid-water-vinyl acetate Pinched, azeotropic system Self-entraining ... 

Table 10.4 presents basic physical properties of the key components. By boiling point the acetic acid is the heaviest. Vinyl acetate is a light species with a normal boiling point at 72.6 °C. Of major interest is the low-boiler heterogeneous azeotrope vinyl acetate/water with 25 mol% water and nbp at 65.5 °C. The very low solubility of vinyl acetate in water, less than 1 wt%, is to be noted. Low reciprocal solubility can be exploited for separating the mixtures vinyl acetate/water by azeotropic distillation. In addition the densities of water and vinyl acetate are sufficiently distinct to ensure good liquid-liquid decanting. 

The first separation step produces essentially the liquid ternary mixture vinyl acetate, water and acetic acid with some dissolved gases. Other light and heavy components are neglected. The RCM analysis indicated as feasible the separation of the heterogeneous azeotrope VAM/water in top followed by quantitative separation of components by decantation. The flowsheet configuration is shown in Figure 10.5. The feed of the column (C-3) collects the ternary mixture from the absorber combined with the water solution from the wash column. The column... 

Second component Azeotropic boiling point, °C Vinyl acetate, wt %... 

Step 1. For this process we must be able to set the production rate of vinyl acetate while minimizing yield losses to carbon dioxide. During the lifetime of the catalyst charge, catalyst activity decreases and the control system must operate under these different conditions. To maintain safe operating conditions, the oxygen concentration in the gas loop must remain outside the explosivity region for ethylene. The azeotropic distillation column must produce an overhead product with essentially no acetic acid and a bottoms product with no vinyl acetate. The absorber must recover essentially all of the vinyl acetate, water, and acetic acid from the gas recycle loop to prevent yield losses in the CCf removal system and purge,... 

Step 5. The azeotropic distillation column does not produce the final salable vinyl acetate product. Its primary role is to recover and recycle unreacted acetic acid and to remove from the process all of the vinyl acetate and water produced. So we want little acetic acid in the overhead because this represents a yield loss. Also, the bottoms stream should contain no vinyl acetate since it polymerizes and fouls the heat-exchange equipment at the elevated temperatures of the column base and the vaporizer. Hence we have two control objectives base vinyl acetate and top acetic acid compositions. And we have two manipula-... 

FIG. 13-95 Number of theoretical stages versus solvent-to-feed ratio for extractive distillation, (a) Close-boiling vinyl acetate-ethyl acetate system with phenol solvent, (b) Azeotropic acetone-methanol system with water solvent. 

Acetic acid-water-vinyl acetate Pinched, azeotropic system Self-entraining Element of recoveiy system for alternative to production of methyl acetate by reactive distillation alternative to extractive pressureswing distillation... 

Vinyl acetate-ethyl acetate Propane-propylene Ethanol-isopropanol Hydrochloric acid-water Nitric acid-water Close-boiling Close-boihng Close-boihng Maximum-boiling azeotrope Maximum-boiling azeotrope Phenol, aromatics Acrylonitrile Methyl benzoate Sulfuric acid, calcium chloride for salt process Sulfuric acid, magnesium nitrate for salt process Alternative to simple distillation Alternative to simple distillation, adsorption Alternative to simple distillation Sulfuric acid process rehes heavily on boundary curvature Sulfuric acid process rehes heavily on boundary curvature... 

Emulsion polymerization reactors are made of stainless steel and are normally equipped with top-entry stirrers and ports for addition of reactants. Control of the reaction exotherm and particle size distribution of the polymer latex is achieved most readily by semibatch (also called semicontinuous) processes, in which some or all of the reactants are fed into the reactor during the course of the polymerization. Examples are given in Chapter 8. In vinyl acetate copolymerizations, a convenient monomer addition rate is such that keeps the vinyl acetate/water azeotrope retluxing. at about 70°C. 

Table II presents the results of further work in grafting vinyl acetate to pre-iiradiated starch. Again, excess monomer was used, and azeotropically dried, swollen, and gelatinized starches were irradiated, as well as starch as is. In this case, the monomer was allowed to penetrate the starch for 48 hours before the temperature was raised. The starch received a total dose of 8 Mrep prior to treatment with monomer.

The separation section takes advantage from the heterogeneous azeotrope formed by vinyl acetate and water. Significant energy saving, up to 70 %, can be obtained by making use of a dehydration gas pre-treatment. In this way the exothermic reaction can cover up to 90 % from the energy requirements of the distillations. 

Crude vinyl acetate is separated from acetic acid and water in an azeotropic distillation system. Acetic acid is recycled to the acetic acid vaporizer and the vinyl acetate product is separated from other by-products in a two-column recovery section. Light ends are removed in the first column followed by a heavy ends in the final column. The light ends, primarily methyl acetate, and the heavy ends, mostly ethyl acetate and acetaldehyde, are incinerated. The vinyl acetate product from the overhead of the heavy ends column is cooled and sent to storage. 

The purification procedures of vinyl acetate for precise kinetic studies are not entirely satisfactory. Many of the impurities mentioned in Table II, for example, may form azeotropic compositions with the monomer. Dissolved oxygen seems... 

An azeotropic mixture of methyl acetate and methanol is a common coproduct from the manufacture of poly(vinyl alcohol) from poly(vinyl acetate) in the presence of methanol and sodium methoxide. The polymerization of vinyl acetate in this azeotropic solution, with the total removal of oxygen from the system, and using conventional free radical initiators is said to afford high-molecular weight poly(vinyl acetate) [106]. 

It should be noted again that in the procedure attributed to Wilson [123], as in many other suspension polymerization procedures mentioned above and in many procedures for emulsion polymerizations to be described later, reaction temperatures are given which are above the boiling point of the monomer (72.7°C at 760 mm Hg), not to mention, above the boiling point of the vinyl acetate-water azeotrope (66°C) (composition, 92.7% vinyl acetate, 7.3% water, cf. Table I). For reactions carried out in sealed ampoules or closed bottles, this reaction temperature is readily explained. How such reaction temperatures are reached in a reflux apparatus open to the atmosphere is in question. It is hardly likely that the rate of polymerization is so rapid that no free monomer exists when it is added with conventional initiators to hot water. We presume that most of the polymerizations reported to proceed at about 66 C in an aqueous medium are simply run at reflux. At such a temperature, initiation by dibenzoyl peroxide is rather slow. If the suspension polymerization is to be forced at higher temperatures, provisions will have to be made to force the monomer into the... 

Solution polymerization under employment of methanol seems to be the best process from the practical point of view. Methanol is a good solvent of polyvinyl acetate the solvent transfer constant of methanol is small compared to that of a common solvent such as acetone, so that PVA of a sufficiently high DP is obtained even when a comparatively large amount of methanol is used in polymerization. Methanol and vinyl acetate form an azeotrope at 60°C, the latent heat of which is so large that it is easier to remove the heat of polymerization. 

Based on this information BCI is requesting that your company design a cost effective process to make 300 MM PPY of crude vinyl acetate. Since vinyl acetate and water form a heterogeneous azeotrope we refer to crude vinyl acetate as the acetic acid free , liquid product which could be... 

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