Conversion of Tire Waste Using Subcritical and Supercritical Water Oxidation

Abstract

The properties designed into tires that make them strong and chemically resistant also inhibit their ability to be recycled easily Conventional liquid solvents do not sufficiently dissolve waste tires and tire production material for convenient separation. Supercritical water oxidation (SCWO) may provide an alternative solution to this environmental problem. Partial SCWO can be used as a means to partially break down rubber (polymeric) waste materials into lower molecular weight components that could be recovered as a chemical feedstock. In this study, the feasibility of converting waste material from tire production into useful products is explored. Batch SCWO studies illustrate the ability to efficiently break down the waste tire production material into a range of lower molecular weight organics for possible reuse depending on reaction conditions. Furthermore, a semi-continuous process has been developed and preliminary results are presented. Destruction efficiencies of greater than 0.9 were obtained in all runs regardless of reactor type. The results show SCWO to be a promising remediation alternative to the waste tire problem.

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

“…Gas chromatography−mass spectrometry (GC−MS) analysis revealed that many organic compounds were formed during the reactions of SBR in supercritical water. In a previous study, Park et al showed that SCWO of waste tire production material (of which SBR is the primary component) produced volatile liquid products as well as gaseous products. The amount of liquid products obtained was calculated by quantitative analysis of GC−MS results.…”

“…Separation and reaction processes that utilize supercritical and near-critical water as a solvent, such as supercritical water oxidation (SCWO), are effective and environmentally attractive techniques for the remediation of certain waste materials. − The SCWO process is conducted at temperatures and pressures above the critical temperature and pressure of water, 374 °C and 22.1 MPa, respectively. Organic compounds are readily oxidized by an oxidizing agent, such as oxygen or hydrogen peroxide, in the presence of water during the SCWO process.…”

“…SCWO has been applied to many different wastes, from pure components − to complex industrial waste. − As an example, Funazukuri and co-workers showed that supercritical water extraction of tire waste was very effective in producing lower molecular weight organics. Additionally, Dhawan et al , have shown that under supercritical conditions aromatic solvents react with either styrene−butadiene or used tires to produce hundreds of volatile products.…”

“…Additionally, Dhawan et al , have shown that under supercritical conditions aromatic solvents react with either styrene−butadiene or used tires to produce hundreds of volatile products. Recently, Park et al examined the conversion of tire waste material to lower molecular weight organics using SCWO. Other recent work in this area has focused on the feasibility of using supercritical fluids to treat other polymer materials, such as polyolefins and natural rubber …”

“…In these previous studies, the conversion of polymer waste material, such as SBR and tires, to valuable chemical compounds through thermal depolymerization and oxidative degradation in supercritical water has been demonstrated. In particular, our previous examination of the conversion of waste tire material using SCWO showed conversion of waste tire to lower molecular weight products . The objective of the work presented in this paper was to investigate the thermal and oxidative degradation of SBR, the major polymeric component of waste tire, under near-critical and supercritical water conditions.…”