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Abstract
Free-radical polymerization of styrene conducted in a spinning disc reactor (SDR) results in significant increases in conversion in one disc pass, equivalent to a few seconds of residence time, with little change in the number average and weight average molecular weights and polydispersity compared to a SDR feed pre-polymerized in a batch reactor. Results of our experimental studies are presented in this paper and a rationale, based on simulation studies, is offered to explain these observations. It is shown that phenomena such as large increases in conversion that do not impact on molecular weights and molecular weight distribution is a result of a simultaneous increase in both the initiator decomposition rate and the propagation rate. The increases in these rate constants, predicted by our modeling studies, provide the driving forces that characterize a polymerization process in a SDR reactor, with the centrifugal force having different degrees of influence on individual reaction steps. This is attributed to different molecular sizes being involved in each of the polymerization reaction steps. The highest impact is observed on the initiator decomposition rate constant, as this reaction step involves a small molecule. Lesser impact is observed on the propagation rate constant, as this reaction step involves interaction of one small molecule and one large reactive species, whilst no or very small effect is seen in the case of the termination rate constant as large reactive species are involved. Developed constant variance model was used to estimate reaction parameters at different temperatures (i.e., initiator efficiency f, rate constants kd, kp, and kt) from the acquired experimental data in order to estimate activation energy (Ea) and pre-exponential factor (A) in a SDR. Data analysis at various SDR operating temperatures suggested activation energy for the styrene polymerization in the SDR as 40.59 ± 1.11 kJ mol−1.
Highlights
Polymerization of styrene and many other commercial monomers such as acrylics and vinyls is usually carried out on a commercial scale by free-radical polymerization technique (Odian, 1991; Su, 2013)
We aim to provide more definitive understanding of the polymerization kinetics through simulation studies validated by experiments in the spinning disc reactor (SDR)
Spinning Disc Reactor (SDR): Background It has been reported that polymerization of styrene with benzoyl peroxide (BPO) as an initiator and in the presence of small quantities of toluene as a solvent in a spinning disc reactor results in significant increase in conversion, while number average (Mn) and weight average molecular weight (Mw) stay approximately unchanged (Boodhoo, 1999; Boodhoo and Jachuck, 2000a)
Summary
Polymerization of styrene and many other commercial monomers such as acrylics and vinyls is usually carried out on a commercial scale by free-radical polymerization technique (Odian, 1991; Su, 2013). Styrene Polymerisation in SDR processes capable of achieving higher heat and mass transfer rates by orders of magnitude than the conventional batch reactors (Reay et al, 2008; Boodhoo and Harvey, 2013a) These reactors are able to provide appropriate mixing environment for improving product quality, reducing reaction times and enhancing selectivity (Boodhoo and Harvey, 2013b). Numerous surface waves in the thin film provide an ideal environment for a high degree of mixing, altogether making this type of reactor suitable for performing fast, exothermic and mass transfer limited reactions This reactor has been shown to improve reaction rates as well as selectivity when used as a catalytic reactor (Vicevic et al, 2004, 2007) and significantly improve control and rates of polymerization reactions (Boodhoo and Jachuck, 2000a; Vicevic et al, 2006a,b).
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