Developing a Novel CaO-Based Sorbent for Promoted CO2 Capture and Tar Reduction

Biomass gasification based on calcium looping sorption enhanced reforming (CLSER) has the advantages of generating syngas with high purity hydrogen and simultaneously capturing CO2 in process. This study first aims to develop a novel synthetic CaO-based sorbent, addressing its tar reduction potential and mechanical strength along with cyclic carbonation reactivity. The novel sorbent was synthesized by integrating CaO with iron catalyst and an inert support based on a two-step sol gel method. Comprehensive properties of the novel sorbent including chemical components, effects on biomass pyrolysis and tar reduction, cyclic CO2 capture reactivity, morphology, and mechanical strength were examined by using various methods and facilities. The characterized chemical and physical properties were also compared with pure CaO and two referenced synthetic sorbents. Results showed that a novel sorbent (Ca-Fe-Al) consisting of CaO, iron oxide (Fe2O3), and mayenite (Ca12Al14O33) was successfully synthesized. Evolutions of tar species and CO2 during wheat-straw pyrolysis were found to be lowered in the presence of Ca-Fe-Al as determined by thermogravimetric Fourier transform infrared (TG-FTIR). The enhanced evolutions of light gases such as CO, CH4, and CO2 at temperatures higher than 580 degrees C examined by thermogravimetry-mass spectrometry (TG-MS) indicated the catalysis effects of Ca-Fe-Al on biomass tar cracking and char decomposition. Different from CaO and other synthetic sorbents, Ca-Fe-Al sorbent showed increasing carbonation capacity and reactivity with growing cycle numbers. After being hydrated, the cyclic carbonation performance of Ca-Fe-Al sorbent became superior to other sorbents. Mechanical strength of Ca-Fe-Al sorbent was also greater than that of CaO and was more suitable for long term storage.