Condenser vinyl chloride monomer process

In the manufacture of polyvinyl chloride (PVC), an offgas stream is produced that contains unreacted vinyl chloride monomer. This stream is usually compressed and condensed to recover as much monomer as possible. However, the vent stream from the condenser still contains a significant amount of monomer. Baker et al. (1991) described an installation that recovers 100 to 200 Ib/hr of monomer from a condenser vent stream. The process vent stream is compressed to 63 psig and sent to a condenser operating at 14°F. The condenser vent stream, containing 30% vinyl chloride monomer, is sent to the membrane unit. The... 

The polymerization process can be an addition reaction or a condensation reaction. Addition involves monomers containing a carbon-carbon double bone like this CH2=CH-R. If R is hydrogen, then the monomer is ethylene. If R is chlorine, then the monomer is vinyl chloride if it s a methyl group, then the monomer is propylene a benzene ring, then it s styrene and so on to more complicated structures. 

Hyperbranched polymers may be prepared by the self-condensing vinyl polymerization (SCVP) [257] of AB star monomers by a controlled free radical process, such as ATRP [258]. The result, under certain conditions, is a highly branched, soluble polymer that contains one double bond and, in the absence of irreversible termination, a large quantity of halogen end groups equal to the degree of polymerization which can be further functionalized [87] (Fig.35). Two examples explored in detail by ATRP are vinyl benzyl chloride (VBC, p-chlo-romethylstyrene) [258] and 2-(2-bromopropionyloxy)ethyl acrylate (BPEA) [259-261] both depicted in Fig. 35. Several other (meth)acrylates with either 2-... 

There are two fundamental polymerization mechanisms. Classically, they have been differentiated as addition polymerization and condensation polymerization. In the addition process, no by-product is evolved, as in the polymerization of vinyl chloride (see below) whereas in the condensation process, just as in various condensation reactions (e.g., esterification, etherification, amidation, etc.) of organic chemistry, a low-molecular-weight by-product (e.g., H2O, HCl, etc.) is evolved. Polymers formed by addition polymerization do so by the successive addition of unsaturated monomer units in a chain reaction promoted by the active center. Therefore, addition polymerization is called chain polymerization. Similarly, condensation polymerization is referred to as step polymerization since the polymers in this case are formed by stepwise, intermolecular condensation of reactive groups. (The terms condensation and step are commonly used synonymously, as we shall do in this book, and so are the terms addition and chain. However, as it will be shown later in this section, these terms cannot always be used synonymously. In fact, the condensation-addition classification is primarily applicable to the composition or structure of polymers, whereas the step-chain classification applies to the mechanism of polymerization reactions.)... 

General Considerations. The terms addition and condensation polymers were first used by Carothers and are based on whether the repeating unit, mer, of a polymer chain contains the same atoms as the monomer Addition polymers have the same atoms as the monomer in the repeat unit, with the atoms in the backbone typically being only carbon. Condensation polymers typically contain fewer atoms within the repeat unit than the reactants because of the formation of byproducts during the polymerization process, and the polymer backbone typically contains atoms of more than one element. Polystyrene, poly(vinyl chloride), polyethylene, and poly(vinyl alcohol) are illustrative of addition polymers, and polyesters and polyamides (nylons) are illustrative of condensation polymers. The corresponding polymerizations are then called addition and condensation polymerizations. 

Most addition polymers are formed from polymerizations exhibiting chain-growth kinetics. Such processes include the typical polymerizations of the vast majority of vinyl monomers such as ethylene, styrene, vinyl chloride, propylene, methyl acrylate, and vinyl acetate. Furthermore, most condensation polymers are formed from systems exhibiting stepwise kinetics. Industrially, such systems include those used for the formation. pa of polyesters and polyamides. Thus, a large overlap exists between the terms... 

These factors alone may contribute significantly to variations in experimental results obtained in the polymerization of vinyl chloride. For example, at superatmospheric pressures, variation in the liquid volume of the monomer to the total free space of a closed reactor means a variation in the amount of gaseous monomer that can condense and/or diffuse into the polymer at some stage of the polymerization process. This vapor-phase monomer level may represent a monomer reservoir somewhat analogous to the monomer droplets postulated for the emulsion polymerization mechanism by Smith and Ewart. 

Ecolyte plastics are made by copolymerizing ketone-containing comonomers in small amounts with ethylene, styrene, or other monomers used in the manufacture of commercial plastics. The process is covered by a number of patents [17]. Condensation polymers such as nylon and polyesters can also be made photodegradable by this method [18]. It is even possible with polymers such as poly(vinyl chloride) [19] and poly(acrylonitrile) [20] which normally do not degrade by chain scission. Poly(ethylene... 

A more recent application of ultrasonics has been the characterization of the extent of polymerization in a condensation or radical process. The first observations were made by Sokolov, and subsequent reports of measurements on polystyrene, poly(vinyl chloride) and poly(vinyl acetate) " have confirmed the utility of the method. It is clear that this type of study is still in its infancy however, certain facts emerge which demonstrate the importance of this method. The compressibility of a solution containing monomer and polymer is directly related to the proportion of each component present. It is therefore possible to quantitatively estimate the extent of conversion from the observed velocity of sound. In a suspension polymerization, the glass transition of the polymer forming the bead is itself a function of the extent to which unreacted monomer is retained in the system. In this case, observation of the attenuation can indicate the extent to which polymerization has occurred in the system. Unfortunately the data are not sufficiently extensive to estimate the general validity of the method for the monitoring of polymerization in reactors, although the potential has been clearly demonstrated. 

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