Gas production by catalytic pyrolysis of herb residues using Ni/CaO catalysts

A series of Ni/CaO catalysts with different ratios of Ni content were prepared by using an isovolumetric impregnation method. The performance of Ni/CaO catalysts on cyclic CO2 absorption and catalytic pyrolysis of herb residues was investigated by using a thermogravimetry and differential thermal analyzer (TG-DTA) and a fixed micro-bed pyrolysis reactor system. The results of cyclic absorption experiments using Ni/CaO catalysts with different ratios of Ni content showed that the CO2 absorption capability of CaO decreased rapidly with increasing number of cycle, and the addition of Ni increased the anti-deactivation capability of CaO in cyclic CO2 absorption. Among the catalysts, the absorption rate of 10% (wt) Ni/CaO was up to 0.7 in the eighth cycle, which was 22.8% higher than that of pure CaO. The analysis of the catalytic pyrolysis products of herb residues indicated that the addition of CaO and 10% (wt) Ni/CaO resulted in effective removal of CO2 in the gaseous products, significant increase in the lower heating value (LHV), and reduction in the yield of condensable liquids such as tar. Compared with CaO, the addition of Ni increased effective gases production and the heating value of the gaseous product and further decreased the yield of condensable liquids. Under the conditions of 700 °C, 10% (wt) Ni/CaO catalyzed pyrolysis of herbal residues yielded an effective gas production of 325.3 mL/g and the lower heating value of 18.6 MJ/m3.