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Experimental study and computer simulation of a two‐stage continuous polymerization process for the production of methyl methacrylate
Author(s) -
Carratt G. M.,
Shervin C. R.,
Soong D. S.
Publication year - 1984
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760240609
Subject(s) - materials science , exothermic reaction , continuous stirred tank reactor , viscosity , mixing (physics) , polymerization , chemical engineering , heat transfer , shutdown , thermal runaway , work (physics) , methyl methacrylate , thermodynamics , nuclear engineering , composite material , chemistry , organic chemistry , polymer , power (physics) , physics , battery (electricity) , quantum mechanics , engineering
The two major problems encountered in industrial liquid‐phase addition polymerization are: the heat released by highly exothermic reactions and the great increase in viscosity with conversion. The high rate or heat generation, coupled with the low thermal diffusivity of the reacting system, often lead to thermal runaway. Even with the process kept under marginal control, large temperature variations broaden the product molecular‐weight distribution. Temperature control is particularly difficult in the Trommsdorff region, where reaction rate rapidly increases as temperature rises and viscosity builds up. A two‐stage process is developed in this work to attack these problems and to achieve continuous operation of poly(methyl methacrylate) bulk polymerization. This process utilizes a continuous stirred‐tank reactor (CSTR) as a first‐stage prepolymerizer and a spray tower as the second‐stage finishing reactor. Use of a CSTR offers good temperature control and product uniformity during the early stages of reaction and eases delivery of the reacting system to the second stage at the desired conversion and molecular‐weight level. Spraying the partially polymerized mixture into the tower as fine droplets prior to the onset of gel effect eliminates the problems of transporting, agitating, and mixing a reacting system with a rapidly increasing viscosity. Heat of reaction is efficiently removed by a countercurrent stream of nitrogen in the tower, in direct contact with the falling droplets. The high surface‐to‐volume ratio of these small droplets facilitates heat transfer, and the problem of heat buildup can be efficiently controlled. Products from the bottom of the tower can then be melt‐processed by conventional methods, such as extrusion. Experiments performed in the laboratory have demonstrated the feasibility of this proposed concept. Process optimization was in no way achieved due to serious space and equipment limitations. The process was thus further examined by computer simulation and model parameter sensitivity study. A practical design was recommended based on the model predictions.