Effect of process variables on the chemical characteristics of crumb rubber desulfurized by waste cooking oil and its desulfurization mechanism

Abstract Resource recovery from waste has emerged as one of the grand challenges for civil engineers in the 21st century. Waste cooking oil (WCO) and crumb rubber (CR) are both promising renewable resources and more and more attention has been paid to them. This study explores the effect of the process variables - mass ratio of WCO to binary mixture, reaction temperature and reaction time - on the chemical characteristics of CR desulfurized by WCO. Chemical component, molecular weight distribution and morphology were characterized through thermogravimetric analysis, gel permeation chromatography, scanning electron microscopy. Based on the results, the desulfurization mechanism of crumb rubber was investigated by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Results showed that with the increasing temperature and the dosage of WCO, more rubber hydrocarbon with smaller molecules was generated, while cross-linked structure was destroyed and complex structural changes occurred. An increased dosage of WCO has significant influence on the morphologies of vulcanized rubber, manifesting a decreased roughness and a clearer “groove” structures. Reaction temperature has little effect of that due to enough high desulfurization degree. Before 2 h of the desulfurization, the effect of reaction time is similar to that of dosage of WCO, but the desulfurization degree decreases due to chain growth after 2 h. In order to ensure effective desulfurization and avoid energy consumption, the time of less than 2 h, at least the temperature of 260 °C and 0.4 to 0.5 mass ratio of WCO are recommended.