Depolymerization of Styrene−Butadiene Copolymer in Near-Critical and Supercritical Water

Abstract

Many conventional solvents do not sufficiently dissolve cross-linked polymers such as styrenebutadiene rubber (SBR) to allow efficient depolymerization. Supercritical and near-critical water provides an alternative benign solvent for this application. Supercritical water oxidation and thermal degradation under supercritical water conditions provide a means to break down rubbery materials into organic compounds that can then be recovered as a chemical feedstock. In this study, depolymerization reactions of styrene-butadiene copolymer are examined in a semicontinuous reactor. A statistical experimental analysis technique was used to investigate the effect of various operating conditions: temperature (300-450 °C), pressure (135 and 170 bar), and the presence of hydrogen peroxide as an oxidant (0-5 wt %). The experimental results demonstrate the ability of supercritical and near-critical water to break down the SBR into a range of lower molecular weight organic compounds for potential recovery. Analysis of variance (ANOVA) shows that the temperature and oxidant concentration are significant at the 1% level for destruction efficiency. Benzene, toluene, ethylbenzene, styrene, phenol, acetophenone, benzaldehyde, and benzoic acid are identified as liquid products using gas chromatography in both batch and semicontinuous reactors. The gas products were comprised of carbon monoxide, carbon dioxide, and water as determined by Fourier transform infrared spectroscopy. The destruction efficiency and a semiquantitative analysis of the liquid products show that both pyrolysis and oxidation products are observed, and low molecular weight oxidation products are observed to be primary.

Screening of common synthetic polymers for depolymerization by subcritical hydrothermal liquefaction

“…Single synthetic polymers subcritical HTL has been reported for specific materials in several publications, including reports on HTL of: high-impact polystyrene, poly-acrylonitrile-butadiene-styrene (ABS), polycarbonate and polyamide 6 (Iwaya et al, 2006;Zhao et al, 2018a); epoxy printed circuit boards (Yildirir et al, 2015); polyethylene naphthalate and terephthalate (Arai et al, 2010;Zenda and Funazukuri, 2008); polystyrene-butadiene (Park et al, 2001); polyurethane (Dai et al, 2002). These studies show that monomers, other valuable chemical compounds or an oil product may be recovered using HTL.…”

“…A similar polymer to PS, a co-polymer of styrene with butadiene, has been reported to decompose in the presence of water at 350 ºC with depolymerization as high as 61% for a reaction time of 60 min. (Park et al, 2001) Near supercritical HTL (370 ºC) was also reported to decompose PS into valuable chemicals in short residence times (Kwak et al, 2005), however, supercritical PS HTL (Kwak et al, 2005;Park et al, 2001) was recently found to have the most efficient condition at 490 ºC with carbon liquefaction efficiency as high as 80%. (Bai et al, 2019) In the present study, the aromatic-containing polymer PS has shown to be stable under subcritical conditions.…”

Production of Chemicals in Supercritical Water

“…Park et al employed partial oxidation in the semi-batch reactor and obtained various product of destruction including benzene, toluene, ethylbenzene, styrene, phenol, acetophenone, benzaldehyde, and benzoic acid [58]. Partial oxidation is addition of small amount of oxygen, which is not sufficient for complete oxidation of the feedstock.…”

Nonstationary model of the semicontinuous depolymerization of polycarbonate

“…Results are in good agreement with experimental data only at low conversions. Park et al15 studied the depolymerization of styrene–butadiene copolymer in near‐critical and supercritical water in a batch reactor using a detailed statistical analysis. Kao et al16 determined the kinetics of hydrolytic depolymerization of melting PET in a batch reactor considering an autocatalytic mechanism.…”