Catalytic Cracking of Primary Tar Vapor from Biomass over High Ash-Containing Paper Sludge Ash

High ash-containing paper sludge ash (PSA) has been investigated in terms of its use as a low-cost catalyst for primary pyrolysis tar cracking in the two-stage pyrolysis of biomass. Experimental results showed that tar yields decreased significantly using PSA as catalyst in comparison with the thermal cracking experiments. A consequent increase in total gas yield was obtained. The yields of H-2, CH4, and CO2 increased significantly under the catalytic effect of PSA, particularly the H-2 yield almost doubled, while CO yields showed a slight decrease due to the consumption reactions. Thermogravimetric analysis of the fresh and spent PSA showed that carbon particles formed along with the tar decomposition, while the catalytic reactivity of the PSA was not reduced because of the participation of carbon particles in tar reforming. XRD spectrograms revealed that calcium-ferrite oxide (Ca2Fe2O5) was formed in PSA, which has excellent stability and catalytic effect on tar cracking and H-2 production. The PSA still showed high tar catalytic conversion efficiency and stable yields of the gas components after use for three cycles. GC-MS results of the tar samples showed that using PSA as catalyst has less effect on the composition of the tar. The tar conversion using PSA, CaO, Fe2O3, and CaO/Fe2O3 reached 62.8%, 73.8%, 63.7%, and 68.9% at 700 degrees C, implying that the performance of PSA as a catalyst for biomass tar cracking could be comparable to that of the pure metal oxides.