Extraction and Purification of Renewable Chemicals from Hydrothermal Liquefaction Bio-oil Using Supercritical Carbon Dioxide: A Techno-economic Evaluation

Abstract

Supercritical fluid extraction (SFE) and fractionation of products from a complex mixture such as bio-oil, where many compounds are present in low concentrations, is a difficult process to model. This difficulty arises from the uncertainty associated with those interactions between mixture components for which fundamental vapor–liquid equilibrium (VLE) data are not available. In this work a novel extraction and purification concept is investigated using a predictive model developed from VLE data of binary solute–solvent systems; solute–solute interactions in the supercritical carbon dioxide (scCO2) phase are neglected. The predictive component of the work employs an equation of state (EOS) model to achieve the above task. The results of pilot plant trials utilizing a biocrude feedstock were shown to be in good agreement with the model predictions. Aspen Plus process simulations were developed for the extraction process which comprised supercritical extraction and subsequent purification steps utilizing distillation and multistage evaporation. A techno-economic analysis of different process designs were evaluated for comparison. In particular, distillation as the primary separation process with and without multistage evaporation were simulated to compare the economics of supercritical extraction to distillation. It was found from simulation results that distillation is a very energy intensive process, and total operating costs for it are always greater than supercritical extraction counterparts. Combining multistage evaporation with distillation will bring the total operating cost slightly lower than supercritical extraction processes. However, the internal rate of return (IRR) value was similar for both SFE and distillation combined with multistage evaporation processes. Solvent/bio-oil (S/B) ratio will have considerable impact on total profits of SFE process in relation to distillation combined with multistage evaporation.