Copolymerization, continuous stirred

The three papers just referred to share a further assumption, namely that a steady state is set up in the continuous reactor, so that all time derivatives in the kinetic equations may be equated to zero. Graessley (91) considered the unsteady state during the start-up of a continuous stirred reactor and found that Mw may in certain cases increase without bound instead of reaching a steady state this will occur if a branching parameter exceeds a critical value. His reaction scheme is restricted to mono-radicals, and the effect of loss of radicals from the reactor is not taken into account. If a steady state is set up, the MWD obtained is Beasley s, when termination by combination and branching by copolymerization of terminal double bonds are absent. Since there is reason (92) to doubt the validity of Beasley s conclusions, as discussed above, the same doubt must apply to this work of Graessley s. 

More recent efforts (primarily at the simulation level) on the optimization of styrene-related systems include Cavalcanti and Pinto [4], suspension reactor for styrene-acrylonitrile, and Hwang et al. [5], thermal copolymerization in a continuously stirred tank reactor (CSTR). 

In addition to the above investigations, free-radical high-pressure polymerizations should also be studied in continuously operated devices for three reasons. (1) Because of the wealth of kinetic information contained in the polymer properties, product characterization is mandatory. Sufficient quantities of polymer, produced under well defined conditions of temperature, pressure, and monomer conversion, are best provided by continuous polymerization, preferably in a continuously stirred tank reactor (CSTR). (2) Copolymerization of monomers that have rather dissimilar reactivity ratios, such as in ethene-acry-late systems, will yield chemically inhomogeneous material if the reaction is carried out in a batch-type reactor up to moderate conversion. To obtain larger quantities of copolymer of analytical value, the copolymerization has to be performed in a CSTR. (3) Technical polymerizations are exclusively run as continuous processes. Thus, in order to stay sufficiently close to the application and to investigate aspects of technical polymerizations, such as testing initiators and initiation strategies, fundamental research into these processes should, at least in part, be carried out in continuously operated devices. 

Using the device in Figure 4.6-4 with only one continuously stirred tank reactor, CSTRl, is sufficient to investigate homo- and copolymerization... 

Hamielec, A. E. and MacGregor, J. F. (1983) Thermal and chemical-initiated copolymerization of styrene/acrylic acid at high temperatures and conversions in a continuous stirred tank reactor, Proc. Internat. Berlin Workshop on Polymer Reaction Engineering, Berlin. 

Liquid monomer is polymerized in continuous stirred tank reactors in a number of processes. The Hypol process, developed by Mitsui Petrochemical, uses a cascaded series of stirred reactors for homopolymerization, followed by fluidized bed gas-phase reactors for copolymerization (274). El Paso (now Himtsman) converted the Rexall liquid monomer process to use high yield catalysts eliminating the sections required for deashing and removal of atactic material (275). Shell (now Basell) developed the LIPP process to produce homopolymers and random copolymers, using their high yield catalysts. 

The styrene and acrylonitrile can be copolymerized by free radical methods using a continuous stirred tank reactor (CSTR). The reactivity ratios r,2 and rj, can be taken as 0.04 and 0.41, respectively. Construct a first-order Markov model using the dyad probabilities derived in Section 11.1. 

In addition to the semi-batch slurry experiments, 9/MAO was used in solution in a continuous stirred tank reactor (CSTR) to further investigate the influence of [ethylene]/[macromonomer] ratio on LCB. Figure 7 shows a quantitative analysis of the C-NMR-based LCB content in polyethylene as a function of the [ethylene]/ [macromonomer] ratio [85]. The LCB content was the highest at low ratios and rapidly decreased with an increase in the [ethylene]/[macromonomer] ratio. This is in line with LCB formation via the copolymerization reaction. 

Tosun, G. (1997). A study of diffusion and reaction in unpremixed step growth copolymerization in a micro-segregated continuous stirred reactor, Ind. Eng. Chem., 36, 4075-4086. 

Most commercial processes involve copolymerization of ethylene with the acid comonomer followed by partial neutralization, using appropriate metal compounds. The copolymerization step is best carried out in a weU-stirred autoclave with continuous feeds of all ingredients and the free-radical initiator, under substantially constant environment conditions (22—24). Owing to the relatively high reactivity of the acid comonomer, it is desirable to provide rapid end-over-end mixing, and the comonomer content of the feed is much lower than that of the copolymer product. Temperatures of 150—280°C and pressures well in excess of 100 MPa (1000 atm) are maintained. Modifications on the basic process described above have been described (25,26). When specific properties such as increased stiffness are required, nonrandom copolymers may be preferred. An additional comonomer, however, may be introduced to decrease crystallinity (10,27). 

A continuous polymerization train consisting of two stirred tanks in series is used to copolymerize styrene, rx = 0.41, and acrylonitrile, vy = 0.04. The flow rate to the first reactor is 3000 kg/h and a conversion of 40% is expected. Makeup styrene is fed to the second reactor and a conversion of 30% (based on the 3000 kg/h initial feed) is expected there. What should be the feed composition and how much styrene should be fed to the second reactor if a copolymer containing 58 wt% styrene is desired ... 

When such a stirring is absolutely absent in a continuous flow system, as it takes place in the piston reactor (PR), regularities of the batch processes with the same residence time 0 are realized. This implies that in order to describe copolymerization in continuous PR one can apply all theoretical equations known for a common batch process having replaced the current time t for 0. As for the equations presented in Sect. 5.1, which do not involve t al all, they remain unchanged, and one can employ them directly to calculate statistical characteristics of the products of continuous copolymerization in PR. It is worth mentioning that instead of the initial monomer feed composition x° for the batch reactor one should now use the vector of monomer feed composition xin at the input of PR. In those cases where copolymer is being synthesized in CSTR a number of specific peculiarities inherent to the theoretical description of copolymerization processes arises. 

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