Experimental study and computer simulation of a two‐stage continuous polymerization process for the production of methyl methacrylate

Abstract

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.

Parametric sensitivity of chain polymerization reactors exhibiting the trommsdorff effect

“…It is well recognized and documented (1 1) that all these models are about equally and fairly successful in explaining experimental rate data on polymethyl methacrylate (PMMA) and polystyrene (PS) under a variety of conditions. For this reason, the mathematically simple model of Chiu, past to study several important engineering aspects of PMMA reactors, for example, the performance (13, Termination by Combination [19][20][21][22] and optimization (23) of non-isothermal PMMA reactors, including continuous flow stirred tank reactors (CSTRs) and spray tower reactors (22). In addition, the multiplicity of steady states in continuous flow stirred tank reactors (24) has also been studied using this model.…”

“…Similarly, in their work Carratt, et al (22), use different constants than those in Eq 7 or 8. Hence, there exists a certain amount of flexibility in the choice of these constants.…”

Parameter Estimation for Solution Polymerization of Methylmethacrylate

“…< (T) = 8.366x10-15 exp [^IMmol)] (9) We can, thus, use either of the following two forms for θ ι for this system: Λ , Ν 2.8883xl0' 18 Γ 148.924 (kJ/mol)l ^ " . .…”