Nickel loaded on carbon materials prepared from co-pyrolysis of biochar and caking coal for catalytic conversion of volatiles

Abstract

The carbon material prepared by co-pyrolysis of biochar and caking coal has been proved that it acts in catalytic conversion of volatiles and could be used in a granular bed duster as filter medium due to its high abrasive resistance in the coal pyrolysis technology. In this work, inactive carbon material loaded by nickel (Ni/ICM) was prepared by pyrolysis of the blend of biochar ion exchanged with nickel and caking coal, and then was steam activated obtaining activated carbon material loaded by nickel (Ni/ACM). The study investigated the in-situ catalytic conversion process of coal pyrolysis volatiles over Ni/ICM and Ni/ACM in a continuous pyrolysis downer-bed reactor. The physical and chemical properties of Ni/ICM and Ni/ACM, pyrolysis product distribution and the component of tar were analyzed, especially, the coke suspended in tar (Coke-S) was separated from tar and characterized in detail. Results show that the crystallite size of Ni and NiO in Ni/ICM is about 5–7 nm, and that is slightly larger in Ni/ACM. Compared to Ni/ICM, more nickel species, pores, acid sites, oxygen-containing functional groups and carbon defects are contained in Ni/ACM. The yields of tar and light tar (boiling point below 360 °C) are higher over Ni/ICM than over Ni/ACM. Ni/ICM further improves the tar quality compared to ICM, and the content of light oil in tar increases from 22.0 wt% over ICM to 30.6 wt% over Ni3.2/ICM. The highest light oil yield is obtained over Ni1.9/ICM as 3.6 wt% and the lowest pitch yield is obtained over Ni3.2/ICM as 3.5 wt%. The characterization of Coke-S shows that it is composed of large aromatic clusters crosslinked by oxygen and fine ash particles. The large aromatic clusters, as heavy component in tar, are found that its H/C molar ratio increases and condensation degree decreases over Ni/ICM and Ni/ACM in comparison with ICM and ACM, respectively, which also means that the quality of tar is improved. Besides, the oxygen in the tar may have been transferred to the coke.