Chemical Looping Processes of Renewable Fuel and Chemical Synthesis

Authors: 
Tong, A., The Ohio State University

The Biomass-to-Syngas (BTS) chemical looping process is an efficient thermochemical gasification process for the conversion of biomass to syngas via partial oxidation. The BTS process combines an iron-titanium composite metal oxide (ITCMO) oxygen carrier and a co-current gas-solid packed moving bed reducer design. The thermodynamics of the ITCMO oxygen carrier favors the controlled partial oxidation of the biomass feedstock and, hence, the generation of high purity syngas with minimal full oxidation products. The gas-solid co-current moving bed reducer operation ensures a sufficient gas and solid residence time for the full conversion of biomass volatiles and char, resulting in a syngas composition that is close to the thermodynamic equilibrium. The addition of steam to the system can adjust the composition of the syngas product to a desired H2:CO ratio for the downstream chemical and fuel synthesis. In addition to the BTS process, the chemical looping hydrogen generation (CLHG) process is effective method to converted renewable fuels, such as biogas, to high purity, high pressure renewable hydrogen. The CLHG process uses a counter current gas-solid contacting pattern in a packed moving bed reactor to convert biogas to CO2 in on reactor (i.e. the reducer) and another counter current moving bed reactor to convert steam to H2 (i.e. the oxidizer). The BTS and CLHG processes have been experimentally tested in a bench scale moving bed reducer and oxidizer. In the BTS process, the composition of syngas, including tar content, is quantified. In the CLHG, the composition of CO2 from the reducer and H2 from the oxidizer have been studied. The results confirm that the BTS process is capable of producing high purity syngas with adjustable H2:CO ratio, and that the ITCMO oxygen carrier can effectively crack and convert tars from biomass and the CLHG process is capable of producing high purity H2 from low purity reducing gas feedstocks. A techno-economic analysis (TEA) focused on a biomass to methanol plant using the BTS process shows an increased process efficiency and decreased methanol required selling price.