Depolymerization of styrene-butadiene copolymer in near-critical and supercritical water

Many conventional solvents do not sufficiently dissolve cross-linked polyme rs such as styrene-butadiene rubber (SBR) to allow efficient depolymerizati on. Supercritical and near-critical water provides an alternative benign so lvent for this application. Supercritical water oxidation and thermal degra dation under supercritical water conditions provide a means to break down r ubbery materials into organic compounds that can then be recovered as a che mical feedstock. In this study, depolymerization reactions of styrene-butad iene copolymer are examined in a semicontinuous reactor. A statistical expe rimental analysis technique was used to investigate the effect of various o perating conditions: temperature (300-450 degreesC), pressure (135 and 170 bar), and the presence of hydrogen peroxide as an oxidant (0-5 wt %). The e xperimental results demonstrate the ability of supercritical and near-criti cal water to break down the SBR into a range of lower molecular weight orga nic compounds for potential recovery. Analysis of variance (ANOVA) shows th at the temperature and oxidant concentration are significant at the 1% leve l for destruction efficiency. Benzene, toluene, ethylbenzene, styrene, phen ol, acetophenone, benzaldehyde, and benzoic acid are identified as liquid p roducts using gas chromatography in both batch and semicontinuous reactors. The gas products were comprised of carbon monoxide, carbon dioxide, and wa ter as determined by Fourier transform infrared spectroscopy. The destructi on efficiency and a semiquantitative analysis of the liquid products show t hat both pyrolysis and oxidation products are observed, and low molecular w eight oxidation products are observed to be primary.