Continuous high-temperature polymerisation of methyl methacrylate

As the need for lower mol. wt. acrylates for specialty and molding applications increases, industry is looking for substitute prodn. processes. An alternative to the increasing of initiator and chain transfer agent concn. is working at higher temps. However, the high temp. polymn. of acrylates is a rather complex process with various new aspects to investigate, among others depropagation and thermal initiation. Addnl., all equipment has to be designed for this temp. range. In the scope of this work, the radical polymn. of Me methacrylate (MMA) is investigated for temps. between 140 DegC and 180 DegC in a continuous pilot scale tubular reactor. The reaction kinetics were detd. in batch expts. and implemented in a PREDICI model for the simulation of the continuous process. This model includes the initiation by MMA peroxides, which can form in the monomer from dissolved mol. oxygen, as well as a high temp. gel effect model and the depolymn. of the living chains. The pilot plant consist of Sulzer SMXL equipped DN20 tubes and has a max. throughput of 10kg/h. The first part is a loop reactor with a recycle ratio of approx. 45:1, which is followed by a tubular part. Both reaction zones contain high temp. ultrasound probes for inline conversion measurement. A micro-dosing pump allows further addn. of initiator or stabilizers into the process between the two reaction zones. For devolatilization of the polymer, a one-step flash chamber with a two-phase preheater is employed. The process is evaluated with respect to final monomer conversion, mol. wt. distribution and residual volatiles' concn. (VOC) of the produced polymer. First runs with the pilot plant have led to satisfying results, which show the feasibility of the high temp. polymn. and the agreement with the modeling. Final monomer conversion was limited to 60% by the choice of an appropriate initiator and mol. wts. between 150.000 and 200.000 g/mol were obtained.