Development of nitrogen-containing materials for capture and catalytic conversion of carbon dioxide to value-added chemicals

Sammanfattning: Anthropogenic carbon dioxide (CO2) emissions have become a critical environmental issue because a large amount of CO2 releasing into the atmosphere, particularly from the massive use of fossil fuels, is the major factor promoting the global warming and climate change. To mitigate the CO2 emissions, Carbon Capture, Utilization and Storage (CCUS) can be one of important solutions. Inspired by the CCUS approach, the aims of this thesis are to develop materials for CO2 capture (Papers I, II) and conversion of CO2 to value-added chemicals (Papers III, IV) such as dimethyl carbonate (DMC) and cyclic carbonates (CCs). The main idea is to focus on nitrogen-containing materials because basic nitrogen sites can increase the chemical affinity towards CO2, which is a weak Lewis acid gas.In practice, aqueous monoethanolamine (aq MEA) is widely used to capture CO2 from flue gases in CCUS projects. However, this solvent suffers from several major drawbacks such as high energy consumption for regeneration of MEA, degradation and evaporation. In Paper I, aq pentaethylenehexamine (PEHA) was proposed as an alternative solvent for chemical absorption of CO2. A comprehensive study was performed, including the influence of water content on CO2 capacity, chemical composition of absorption products, viscosities before and after absorption, regeneration of PEHA, correlation between CO2 capacity with Kamlet-Taft parameters, comparison with aq MEA. In Paper II, aq PEHA was further studied for CO2 capture from bio-syngas resulting from pilot-scale gasification of biomass to investigate the influence of other compositions on the capture performance. Additionally, this solvent was simultaneously used as a reagent for chemical pretreatment of biomass to investigate the influence of pretreatment on biomass gasification and CO2 capture.The conversion of captured CO2 to value-added chemicals gains increasing attentions in both academia and industry because CO2 represents a renewable, virtually inexhaustible, and nontoxic building block. In addition, this approach can provide economic incentives for CO2 capture facilities by selling their captured CO2 to other interested users or by benefiting from their own additional facilities using the CO2. In Paper III, 1,8-diazabicyclo[2.2.2]undec-7-ene (DBU) was used to capture and subsequent conversion of CO2 to DMC at ambient conditions. In Paper IV, mesoporous melamine-formaldehyde resins were prepared, characterized and studied as heterogeneous catalysts for synthesis of CCs from epoxides and CO2. These low-cost polymeric catalysts were reusable and demonstrated excellent performance in a flow reactor under industrially relevant conditions (120 °C, 13 bar, solvent-free/co-catalyst-free).Applications of ionic liquids (ILs) in capture and conversion of CO2 to organic carbonates were briefly reviewed in Paper V (mini review). The viscosity of ILs for CO2 capture and the mechanism involved in the CO2 binding were also discussed.In conclusion, this thesis will hopefully contribute to the sustainable development of society in the fields of reducing anthropogenic CO2 emissions and production of chemicals.