(145d) Process Flow Simulation of Biogas Upgrading By Deep Eutectic Solvents.

Anaerobic digestion (AD) of food wastes is one of the most promising pathways to convert wastes to value added fuels (e.g., biogas) and products (e.g., fertilizer). As food wastes are heterogeneous and their composition changes from household-to-household, the resulting biogas composition varies significantly. Biogas from food wastes often contain 40-60 % methane (CH₄), 40-60 % carbon dioxide (CO₂), and 1-5 % impurities. Although the actual concentration may vary from the source of biomass and AD operating conditions, most common impurities found in the biogas are hydrogen sulfide (H₂S), ammonia (NH₃), octamethyltrisiloxane, and decamethylpentasiloxane. carbon capture and removal of the impurities are required prior to use or injection into a natural gas pipeline. CO₂ from the gaseous stream can be separated by physical (ionic liquid) or chemical solvents (amine-based solvents). Amine-based chemical solvents have higher adsorption capacity but are often expensive to regenerate and toxic for the environment. Physisorption solvents are generally expensive, and their adsorption capacity is lower, meaning that significantly higher amounts of physisorption solvents are required. In the context of carbon capture, the impurities are likely to play a significant role in adsorptive capacity of the solvents due to an influence on the molecular environment.

In a previous study, deep eutectic solvents (DES) were evaluated to upgrade biogas. In the previously published work several DES were evaluated for factors such as solubility of CO₂, selectivity for CH₄, and sensitivity to common contaminants. With these findings in mind the goal of this work is to create a sensitivity analysis through the creation of a process flow diagram modelled in ASPEN-Plus 13. Through this research it is observed that slight changes in selectivity, solubility, or sensitivity to contaminants have a large impact on the sizing and therefore cost of the processes described. With the inclusion of less common contaminants like siloxanes, multi-phase separations systems are required. Thus, when implementing the researched technology of new solvents like DES, highly detailed sensitivity analyses that can account for all variables are required to make the best economic choices.