Techno-economic assessment for processes of bioconversion of CO2-to-chemicals

Despite the progress the EU countries have achieved in cutting down their CO2 emissions, companies are still looking for novel technologies to comply with the EU’s regulations more easily. An alternative pathway for reducing emissions is to integrate CO2 into industrial processes as a carbon source for production of commodity chemicals. Thus, turning waste streams into valuable feedstock. However, CO2-conversion processes must be catalysed. For this purpose, biological catalysts could have advantages over other technologies due to their ability to operate at atmospheric conditions and with low-carbon concentration feedstock. Several biotechnology institutes, among them the Flemish Institute for Technology Research, (VITO), have worked developing processes for bioconversion of CO2-to-chemicals. Most of VITO’s achievements with said bioprocesses have been limited to the experimental stage. For that reason, they were interested in assessing their biotechnologies’ potential to be implemented in industrial scale remaining economically feasible. In that context, this Thesis was carried out with the objective of testing two CO2-to-chemicals bioprocesses developed by VITO, in terms of the technical feasibility for being implemented as economically feasible, industrial-scale plants using existing CO2 sources as feedstock. Two productions schemes were defined: CO2 to acetic acid and bioplastic, polyhydroxybutyrate (PHB) production. For the former, VITO bioprocess, microbial electrosynthesis (MES) was to be compared against autotrophic fermentation of H2. Meanwhile, for the PHB production scheme, VITO bioprocess, 2-stage fermentation of CO2 was to be tested against pure heterotrophic fermentation. The methodology followed for this Thesis consisted on several steps. First, experimental data from the 4 bioprocesses was compiled and the main technical limitations that could hinder large-scale implementation were listed. Afterwards, actual industrial sources of CO2 active in Belgium were selected to scale up the bioprocesses into production plants. The pretreatment of feedstock, reactor and product recovery areas of these plants were designed and the block flow diagrams and mass balances for each were elaborated. The CAPEX of the proposed plants’ main units and their operational costs and revenues were calculated; their economic feasibility indicators were also estimated during a set lifetime. The two plants in each production scheme were compared in terms of their net present value (NPV). For each plant, the key factors affecting the economic feasibility were identified and their impact measured via sensitivity analysis. Finally, realistic best-case scenarios for assured economic feasibility for the plants based on VITO’s bioprocesses were elaborated and discussed. The Thesis was completed successfully. The analysis showed that MES bioprocesses had more technical limitations for large-scale implementation than autotrophic fermentation units and that 2-stage fermentation was more limited than pure heterotrophic fermentation. Two viable CO2 sources were identified, namely, a Belgian combined heat and power generation engine and a Belgian biogas production industry. Conceptual production plants based on each of the 4 bioprocesses were designed to a size that matched the selected CO2 sources. Block flow diagrams, mass and energy balances and equipment lists were constructed. The CAPEX of the MES plant was determined to be lower than the H2 fermentation plant and the CAPEX of the heterotrophic fermentation was lower than the 2-stage fermentation plant. Similarly, The operational costs of the MES plant and the heterotrophic fermentation plant were lowest of the two production schemes. None of the 4 plants were economically feasible but the MES plant was closer to feasibility in the CO2 to acetic acid production scheme and heterotrophic fermentation was closer in the PHB production one. The critical factors affecting the economic feasibility of each of the plants were determined. Realistic, best case scenarios for the MES plant required a shift to ethanol production and improvement of cathode efficiency. For the 2-stage fermentation plant, it required a reduction of the costs of H2 and glycerol and an increase in PHB concentration