Batch process bulk suspension

Today, HIPS is produced by two basic variants the batch process and the continuous process. Pre-polymerization, i.e. the polymerization phase up to completion of phase inversion, is identical in the two process variants. After completion of the pre-polymerization, the polymerization is continued in suspension in the batch process and in solution in the continuous process. The batch process is, therefore, also referred to as the bulk suspension process and the continuous variant as the solution process. The continuous process is a refinement of the original I.G. Farben process for standard polystyrene, which The Dow Chemical Company has adapted to the needs of rubber-containing styrene solutions. A number of modifications are now practiced. 

The bulk suspension process for HIPS was developed by Monsanto. Batch preparation and pre-polymerization are equivalent to the solution process. 

The earliest polymerization processes were either batch mode or semibatch. The semibatch method was used for products, where the two monomers differed greatly in reactivity, as in Union Carbide s early Dynel, acrylonitrile-vinyl chloride, process. Bulk, solution, and emulsion polymerization processes have also been developed for acrylonitrile and its copolymers. However, in recent years nearly every major acrylic fiber producer has used a continuous aqueous suspension process, employing a redox catalyst, followed by a series of steps, which includes slurry filtration and polymer drying. 

Currently, commercially pure batch processes play a major role for suspension and bulk polymerization but only a minor role for emulsion polymerizations. The most important procedure for effecting polymer dispersions by emulsion polymerization on a technical scale is semibatch or feed processes, which are very flexible regarding product properties. Depending on the required properties with respect to particle size distribution, molecular weight distribution, chemical composition in the case of copolymerization, and particle morphology, numerous feeding policies have been developed. Almost all kinds of consecutive... 

In batch operations, mixing takes place until a desired composition or concentration of chemical products or solids/crystals is achieved. For continuous operation, the feed, intermediate, and exit streams will not necessarily be of the same composition, but the objective is for the end/exit stream to be of constant composition as a result of the blending, mixing, chemical reaction, solids suspension, gas dispension, or other operations of the process. Perfect mixing is rarely totally achieved, but represents the instantaneous conversion of the feed to the final bulk and exit composition (see Figure 5-26). 

Classification of Processes and Reactors. Most styrene polymers are produced by batch suspension or continuous mass processes. Some are produced by batch mass processes. Mass in this sense includes bulk polymerization of the polymer... 

The second large-scale process was the batch mass suspension process. Monsanto did the pioneer work on this (41). In this process, prepolymerization is carried out in bulk and main polymerization in suspension the latter is taken to conversions of over 99%. In contrast to the continuous mass process, peroxide starters are used in order to achieve a high conversion at tolerable reaction times. Figure 3 shows a basic flow diagram of such a plant. A detailed discussion of advantages and disadvantages of the two processes can be found in R. Bishop s monograph published in 1971 (42), and it is continued in a paper by Simon and Chappelear in 1979 (43). It was a decisive factor for the economic success of impact polystyrene that these processes had been completely developed and mastered in theory and practice. 

The production of vinyl chloride monomer is only a part of PVC production. Polymerization of the monomer completes the process. Commercially, it is a batch operation by one of three methods suspension, emulsion, or bulk. In all three methods, the chemical reaction is a free radical-initiated chain reaction. Peroxides or redox systems generally are used to provide the initial free radicals. 

The commercial manufacture of polystyrene was batch mode through the 1930s and 1940s, with a gradual transition to continuous bulk polymerization beginning in the 1950s. Suspension polymerization was a common early polystyrene production process, where a single reactor produced a polymer slurry that had to be separated from the water and dried. This process was ideal for free radical... 

Even if the problems of poor crystal intergrowth due to local exhaustion of reactants in the autoclave and synthesis of zeolite material in the bulk of the solution were solved, an important problem remains, related to the fact that several batch synthesis cycles (with their associated heating and cooling processes) are often required to achieve a zeolite membrane of good quality. Thus, a synthesis procedure in which reactants are continuously supplied to the synthesis vessel while this is maintained at a constant temperature would clearly be desirable not only for performance but also for the feasibility of the scale-up. This type of approaches has already been tested for inner MFI and NaA zeolite membranes [33-35], and the results obtained indicate that the formation of concomitant phases and the amount of crystals forming in the liquid phase are greatly reduced. Similarly, the continuous seeding of tubular supports by cross-flow filtration of aqueous suspensions [36-37] has been carried out for zeolite NaA membrane preparation. 

The computer program simulates the batch polymerization of styrene and has been applied to the relatively low temperature peroxide-initiated polymerization typical of suspension processes and to higher temperature bulk, thermal conditions. It has been useful in the design of new suspension processes and for more general process analysis. 

Styrene, as a monomer, also has an uncommon versatility in that bulk, solution, suspension, and emulsion techniques may be used to produce high polymer. All four methods are used commercially, though solution polymerization is the most common because it reduces the viscous material transfer problems of bulk polymerization and eliminates the higher risk of contaminated product and the need for drying required by suspension and emulsion methods. Solution polymerization also lends itself to continuous processing, unlike the batch methods usually used for bulk polymerization. 

A second possible problem with batch reactors is composition drift of copolymer systems. As with bulk, solution, and suspension systems, the more reactive monomer polymerizes first, and the least reactive polymerizes last. Two additional factors must be considered in emulsion polymerization. First, the water solubilities of the monomers can influence the course of the polymerization because of reaction in the water phase to produce copolymer oligomers or even water-soluble polymer. These molecules can be rich in the water-soluble monomer even if its reactivity is relatively low. Second, the high degree of subdivision achieved by producing small polymer particles can lead to phase domains that are smaller than those in copolymer produced by other processes. 

Where physical attributes of the API are critical (e.g., APIs intended tor use in solid oral dosage forms or suspensions), blending operations should be validated to show homogeneity of the blended batch. Validation should include testing for critical attributes (e.g., particle size distribution, bulk, and tap density) that may be affected by the blending process. 

Esters of methacrylic acid are obtained directly from acetone cyanohydrin by reaction of the latter with concentrated sulfuric acid to give methacrylamide sulfate, followed by reaction with an alcohol. The process is continuous and the methacrylamide sulfate is not isolated. Acetone cyanohydrin is derived from acetone and hydrogen cyanide (Pig. 15-39), Polymerization Procedures. Of particular importmice to the acrylics is the cast or bulk method of polymerization. This method is employed to produce cast polymethyl methacrylate sheets which are widely used in industrial applications. Careful control of polymerization is required to obtain a bubble-free product with good optical clarity. A typical flow sheet for the production of cast eet is shown in fig. lfi-40. Solution, suspension, and particularly emulsion polymerizations are also, widely used with the acrylics. Such polymerization reactions involve relatively conventional batch-type processes. i... 

The batch suspension polymerization system considered in the present study, is schematically shown in Figure 1. It consists of a well mixed jacketed vessel. In the suspension polymerization process, liquid styrene is dispersed in the continuous aqueous phase by the combined action of stirring and the use of suspending agents. The reaction takes place in the monomer droplets. For modelling purposes, each droplet can be treated as a small batch bulk polymerization reactor. The heat of polymerization is transferred from the dispersed droplets to the aqueous phase and then to the coolant flowing through the reactor s jacket. 

Suspension processes are very widely used for the polymerization of styrene. These processes simplify the heat transfer problems associated with bulk methods and, unlike solution methods, they do not involve solvent removal and recovery. The disadvantages of the suspension technique are that it requires the added step of drying and it does not readily lend itself to continuous operation. Typically, polymerization is carried out batch-wise in a stirred reactor, jacketed... 

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