PEP Review 90-2-3
The SDS Polystyrene Process
Published: October 1991
Sulzer Brothers, Dainippon Ink & Chemicals, and Sumitomo Heavy Industries have jointly developed a new styrene polymerization process referred to as the SDS process. This process has been used for the production of both general purpose polystyrene (GPPS) and high impact grade polystyrene (HIPS). The uniqueness of the SDS process lies in the employment of Sulzer's SMX static mixers, SMXL static mixer-heat exchangers, and especially SMR static mixer-reactors; the latter have large heat transfer surface area per unit reactor volume and give a uniform temperature and velocity profile.
In the SDS process, a circulating loop consisting of elements of SMRs is used in the first half of the polymerization. High circulating rates give good axial mixing and the plug-flow behavior in the SMR results in good radial mixing. A series of SMR elements is used in the latter half of the polymerization. Two-step devolatilization in progressively lower pressures is employed to reduce the total content of volatile matter to less than 500 ppm. SMXL and SMXs are used as the preheater for devolatilization and for mixing water and additives with the polymer melt, respectively.
In this review, we evaluate the SDS process for GPPS and HIPS production. For 66 million Ib/yr (30,000t/yr) production capacity, the total capital investments are higher than a process using conventional agitated reactors. The higher capital investments result mainly from the employment of compact yet costly SMR reactors.
While the economics of the SDS process are comparable to those of a conventional process for HIPS production, comparison of economics for GPPS production slightly disfavors the SDS process, primarily because of the higher capital cost. However, less land requirement because of the smaller reactor volume, about half of that of a conventional process, could be an advantage of the SDS process, especially for locations where land cost becomes a larger part of the plant investment.