New Approaches to Desulfurization of Recycled Base Oils.

Abstract

My research developed two new, innovative methods for processing spent lubricant to the pre-commercial stage. The methods have demonstrated processing benefits and represent economic and environmental gains. Developing the processing methods required undertaking a detailed sulfur speciation study of spent lubricants to determine the most effective approaches to desulfurisation. This combined prescribed (quantitative) and common (qualitative) instrumental methods along with newly developed analytical methods. Recycling spent lubricant has significant environmental and economic benefits but usually results in low-grade products. Higher grade products are becoming the norm and require removal of sulfur species coming from lubricant additives. Sulfide mostly comes from the anti-wear additive Zinc dialkyldithiophosphate (ZdDP) and this is predominantly oxidised during lubricant use. The remaining sulfur mostly comes from high molecular weight alkylbenzene sulfonates salts (LAS). Petrochemical sulfur removal is either molecular through solid or liquid phase extraction, or elemental by hydrodesulfurisation or oxidation/phase separation for low molecular mass fuels. While hydrodesulfurisation is common in the re-refining industry it requires catalysts passivated by lubricant additives and requires extensive post treatment. Liquid phase extraction is also popular for re-refining, but my research shows sulfonates react during re-refining hampering phase extraction. A membrane-assisted supercritical CO2 extraction process was developed to remove sulfurous compounds. This process ultimately didn't achieve sufficient sulfur reduction. However, calculated operating and capital expenses showed a factor improvement over traditional 'front end' processing. Volatile hydrocarbon plasma desulfurisation removed sulfur more efficiently and economically than traditional hydrodesulfurisation within a retrofittable process. The major operating and cost advantages are no requirement for catalyst, high purity hydrogen, or post treatment. During my plasma research a novel means of plasma hydrocarbon synthesis was discovered with some initial investigation and development.