Valorisation of used automotive lubrication oil
Authors:   , Van Zyl Taegan 
Published: September 2021

This study has explored the production of Light Oil 10 (LO10) fuel from used automotive lubrication oil, thus providing a method for producing a cheaper alternative to diesel and paraffin for the South African industrial heating fuel market. Used automotive lubrication oil has different physical properties to that of the specified properties for Light Oil 10 fuel and therefore has to undergo processing that aligns the properties of the two. The low availability of Light Oil 10 fuel in the South African industrial heating market is driving companies such as a Durban based oil refinery to develop a continuous process that will produce Light Oil 10 fuels without the supplementation of paraffin. The supplementation has been done to retain customers but this resulted in the company selling Light Oil 10 fuel at a loss. Used automotive lubrication oil was of particular interest for use as the raw material for the new process as it is of low cost and is readily available. The viscosity (a measure of how easily a fluid flows at a particular temperature) of used lubrication oil was too high and needed to be reduced before it could qualify as Light Oil 10. The reduction of the viscosity of a fluid means that the ability of the fluid to flow at a particular temperature has improved. Additionally the additive package and the impurity content of the used automotive oil were too high. The additive package is added to mineral oil to give it the properties that new automotive lubrication oil requires; this package is still present in used automotive lubrication oil and is responsible for the high level of impurity content because it prevents impurities from agglomerating and dropping out of the oil. The new process was therefore required to be able to reduce the viscosity of used automotive lubrication oil and break the additive package. The required process and operating variables were developed / identified through literature review (qualitative) and the optimum operating variables were identified through experimentation (quantitative). A design of experiment was carried out using Design Expert software. This identified the matrix of runs that were required in identifying the optimum temperature, pressure and residence time for the ranges specified. The product from each of the runs was analysed in the Durban based oil refinery Research and Development lab. The results from the lab along with the corresponding run conditions were used to develop a model, and the model used to identify the optimum operating conditions. The research and experimentation took a total of two years to complete. The literature review found an existing refinery process, the drum type visbreaker to be the most suitable process for reducing the viscosity and breaking the additive package of used automotive lubrication oil. The drum type visbreaker holds oil in the drum for a period of time known as the residence time, at temperatures and pressures of 443oC and 15 bar respectively. These three variables are the critical operating variables in the visbreaking process. The high temperature breaks the large molecules into smaller molecules thereby reducing the viscosity via a process known as thermal cracking. This process also breaks down the additive package. The results from the experimental runs revealed that it is possible to produce Light Oil 10 from used automotive lubrication oil using the drum type visbreaker. The model produced through experimentation was found to be reliable and accurate within the range of variables investigated at predicting results for future runs. The model was also successfully used to identify the optimum operating conditions at which Light Oil 10 is produced from used automotive lubrication oil. The conditions were found to be 475oC, 15 bar and 60 minutes, confirmed by three confirmation runs. In conclusion this study has identified through literature and experimentation that thermal cracking via the free radical mechanism is the preferred process for producing Light Oil 10 from used automotive lubrication oil at liquid yields greater than 90%. An appropriate model was generated using the critical operating variables to predict future viscosity results. It was recommended that the Durban based oil refinery design and build a production scale pilot plant that includes all equipment and the feed heating coil (furnace used to heat feed to 475oC) that a full scale plant would have. This is because the run lengths due to coking (build up of hard carbon on the surfaces of heat exchange equipment) and functionality of the process need to be confirmed before the process can be deemed to be economically viable. Once this has been achieved a full scale production facility can be built.