Process intensification :thin film spinning disc reactor for controlled continuous photo-polymerisation of acrylates

Abstract

In the last three decades the utilisation of UV radiation to initiate the polymerisation of acrylates and methacrylates has centred on UV curing of thin films to produce highly crosslinked networks. Very little attention has been paid to the initiation of bulk polymerisations using this method. In part this is due to the difficulties of ensuring UV penetration of more than several centimetres into reaction vessels and also to the strongly exothermic nature of the bulk polymerisation of liquid acrylates and methacrylates. This investigation explores the potential for the use of a thin film spinning disc reactor for the continuous photo-polymerisation of acrylates and methacrylates, considering nbutyl acrylate as a test case. The benefits offered by spinning disc reactors are the controlled formation of thin films, good mixing and enhancement of heat and mass transfer rates. The spinning disc reactor used in this investigation has a novel internal cooling/heating system designed to allow close control of the reaction surface temperature and provide a means of removing the heat of reaction from fast exothermic reactions, such as photo-initiated free-radical polymerisations. The investigation comprises three individual studies; static film polymerisation (as a benchmark), spinning disc polymerisation and preliminary heat transfer measurement. Conversions of up to 23 % and molecular weights (Mw) of up to 296115 kg/kmol were achieved in the static film polymerisation with corresponding polydispersity indices of 1.98 to 4.43. By comparison, conversions of up to 66 % and M of up to 604518 kg/kmol were achieved in the spinning disc polymerisation, with corresponding polydispersity indices of 1.36 to 2.74, indicating a tighter control of molecular weight distribution on the spinning disc. Overall heat transfer coefficients of up to 9 kW/m2 were achieved for the internally cooled disc system.