Techno-economic analysis of sustainable bio-based lubricant production from lignin and waste cooking oil

The aim of this thesis is to evaluate the techno-economic feasibility of a high-value biolubricant production process, starting from lignin and waste cooking oil, as a side process in a generic biorefinery in the U.S. that uses corn stover as lignocellulosic feedstock for ethanol production. In the proposed process, lignin is sourced from the unhydrolyzed solids (UHS), which represent the portion of the biomass feedstock that is not utilized for ethanol production. Typically, this lignin-rich residue is burned to generate steam and electrical energy for internal plant operations. In the proposed process, however, the lignin is converted into its aromatic monomers through hydrothermal liquefaction (HTL) using pressurized water at 320 °C, resulting in a mixture of phenolic compounds, mainly phenol. These phenolic compounds undergo hydrodeoxygenation (HDO) to produce benzene, while fatty acid methyl esters (FAMEs) are obtained through transesterification of waste cooking oil (WCO). The final biolubricant product is produced through aromatic alkylation of FAMEs with benzene, forming phenyl-branched FAMEs (PBFAMEs). PBFAMEs exhibit improved lubricity and oxidative stability compared to standard FAMEs, making them a suitable lubricant improver for ultra-low sulfur diesel (ULSD) engines. This biolubricant can be sold as a by-product of the biorefinery. Process simulations are performed using the Aspen Plus software, while the economic analysis uses as a benchmark the design and economics of a generic biorefinery in the U.S., as proposed by the National Renewable Energy Laboratory (NREL) of the U.S. Department of Energy (DOE). The final goal of this study is to compare the minimum ethanol selling price (MESP) with and without the integration of the biolubricant production process, to determine its techno-economic feasibility. The results indicate an improvement in the economic performance of the biorefinery, with the MESP decreasing from $3.02 per gallon in the base case (ethanol production only) to $2.64 per gallon when the bio-lubricant process is included. This represents approximately a 13% reduction in the selling price of ethanol.