Toluene steam reforming properties of CaO based synthetic sorbents for biomass gasification process

Biomass gasification process generates undesired Topping Atmosphere Residue (TAR), removable by catalytic steam reforming. The use of a CO2-sorbent powder inside the reactor bed can minimize the content of carbon dioxide and carbon monoxide by enhancing the water gas shift (WGS) reaction, offering a fuel gas rich of H2. The present study addresses the practical feasibility of such concepts, using toluene as a representative TAR and a hybrid compound Ni/CaO–Ca12Al14O33 as reactor bed material, simultaneously acting as reforming catalyst and CO2 sorbent. In fact, the CaO is the effective sorbent, whereas the Ca12Al14O33 is a support for both the CaO and the active metallic Ni particles. A different synthesis route with respect to the literature has been developed for the production of the Ni/CaO–Ca12Al14O33 and a total of three different bed reactor powders have been tested and compared: (i) a mixture of olivine and commercial nickel catalyst, (ii) a mixture of CaO–Ca12Al14O33 and commercial nickel catalyst, and (iii) the Ni/CaO–Ca12Al14O33 combined catalyst and sorbent. The best performances have been observed in the latter, with toluene conversion close to 99%, and the volume fraction of hydrogen in the gas over 95%. During multi-cycle tests, the synthetic Ni/CaO–Ca12Al14O33 combined catalyst and sorbent exhibited superior resistance to carbon deposition and stability in toluene conversion compared to the other bed materials that suffer from decreased conversion efficiency after few cycles.