Utilising CO2 as a feedstock for chemicals and fuels could help mitigate climate change and reduce dependence on fossil fuels.

Pyrolysis is widely seen as a promising technology for converting plastic waste into a wax/oil product which can be used as a heavy fuel oil substitute or as raw material by the petrochemical industry. A pyrolysis plant with a capacity of 100 kg/h plastic waste is modelled in the process simulation software Aspen HYSYS. The production costs of the pyrolysis fuel product is estimated at £0.87/kg which is 58% higher than current market prices; therefore, a scaling-up analysis is also carried out to determine the plant capacity for which the pyrolysis process is economically feasible. The fuel production costs of the scaled-up cases considered are approximately 2.2-20.8 times lower than the existing market prices of residual fuel oil, indicating their economic feasibility. For the 1000 kg/h and 10,000 kg/h plant capacity cases the facility needs to operate approximately four years and one year respectively, to recover the capital investment, while the 100,000 kg/h case produces revenue and has a positive NPV within year one. A sensitivity analysis is also carried out revealing that the fuel production rate is the most sensitive parameter for the 100 kg/h plant, as well as the scaled-up plants.

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Biogas from anaerobic digestion of sewage sludge is a renewable resource with high energy content, which is composed mainly of CH 4 (40−75 vol %) and CO 2 (15−60 vol %). Other components, such as water (H 2 O, 5−10 vol %) and trace amounts of hydrogen sulfide and siloxanes, can also be present. A CH 4 -rich stream can be produced by removing the CO 2 and other impurities so that the upgraded biomethane can be injected into the natural gas grid or used as a vehicle fuel. The main objective of this paper is to assess the technical and economic performance of biogas upgrading processes using ionic liquids that physically absorb CO 2 . The simulation methodology is based on the COSMO-SAC model as implemented in Aspen Plus. Three different ionic liquids, namely, 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide, 1-hexyl-3methylimidazoliumbis[(trifluoromethyl)sulfonyl]imide, and trihexyl(tetradecyl)phosphonium bis[(trifluoromethyl)sulfonyl]imide, are considered for CO 2 capture in a pressure-swing regenerative absorption process. The simulation software Aspen Plus and Aspen Process Economic Analyzer is used to account for mass and energy balances as well as equipment cost. In all cases, the biogas upgrading plant consists of a multistage compressor for biogas compression, a packed absorption column for CO 2 absorption, a flash evaporator for solvent regeneration, a centrifugal pump for solvent recirculation, a preabsorber solvent cooler, and a gas turbine for electricity recovery. The evaluated processes are compared in terms of energy efficiency, capital investment, and biomethane production costs. The overall plant efficiency ranges from 71 to 86%, and the biomethane production cost ranges from $9.18−11.32 per GJ (LHV). A sensitivity analysis is also performed to determine how several technical and economic parameters affect the biomethane production costs. The results of this study show that the simulation methodology developed can predict plant efficiencies and production costs of large scale CO 2 capture processes using ionic liquids without having to rely on gas solubility experimental data.

Supercritical carbon dioxide (scCO 2 ) has been investigated for the generation of valuable waxy compounds and as an added-value technology in a holistic maize stover biorefinery. ScCO 2 extraction and fractionation was carried out prior to hydrolysis and fermentation of maize stover. Fractionation of the crude extracts by scCO 2 resulted in wax extracts having different compositions and melting temperatures, enabling their utilisation in different applications. One such fraction demonstrated significant potential as a renewable defoaming agent in washing machine detergent formulations. Furthermore, scCO 2 extraction has been shown to have a positive effect on the downstream processing of the maize stover. Fermentation of the scCO 2 extracted maize stover hydrolysates exhibited a higher glucose consumption and greater potential growth for surfactant (in comparison with non-scCO 2 treated stover) and ethanol production (a 40% increase in overall ethanol production after scCO 2 pre-treatment). This work represents an important development in the extraction of high value components from low value wastes and demonstrates the benefits of using scCO 2 extraction as a first-step in biomass processing, including enhancing downstream processing of the biomass for the production of 2 nd generation biofuels as part of an integrated holistic biorefinery.