Heterogeneous Cracking Reaction of Tar over Biomass Char, Using Naphthalene as Model Biomass Tar

Abstract

The tar problems are the major limit for development of biomass gasification. Biomass char has been proven to be an economical and effective catalyst of tar destruction for both utilizations inside the gasifier and in downstream processes after the gasifier. In order to investigate the mechanism of catalytic cracking of tar over a biomass char bed, experimental research was performed in a bench-scale tube flow reactor, choosing rice straw char as the catalyst bed, naphthalene as the model tar compound, and argon as the inert atmosphere. The effects of temperature (700−1000 °C), tar concentration, time on stream (0−330 min), presence of syngas, and pretreatment of char (treated with deionized water or Ni(NO 3 ) 2 solution) on tar conversion were evaluated. The variation of the inner pore structure of biomass char during the process of tar removal was also investigated. Results showed that the original biomass char exhibited good catalytic activity in tar cracking and better stability compared with Ni(NO 3 ) 2 pretreated char. However, because of the naphthalene cracking reaction, soot was formed on the active sites of the inner pore surface of the char, leading to the deactivation of the char. A rapid decline in specific surface area of the char was observed from 262 to 4.6 m 2 /g when the test had begun to run for 5 min with high tar concentration (25 g/Nm 3 ) and a temperature of 800 °C. The presence of syngas in the atmosphere could slow the process of deactivation of char.

Activity of chars and activated carbons for removal and decomposition of tar model compounds – A review

“…CH 4 reacting in a N 2 atmosphere rapidly deactivated the carbon catalyst, probably because of the pores closure due to carbon deposition. In agreement with results from other studies ( [37][38][39]), the presence of CO 2 or H 2 O was found to prevent the pores blocking and to maintain the char catalytic activity.…”

“…Zhang et al [39]. compared the heterogeneous cracking of naphthalene over char with homogeneous decomposition in inert atmosphere.…”

Autocatalytic Pyrolysis of Wastewater Biosolids for Product Upgrading

“…42 The destruction of tar using certain chars as catalysts has proven to be effective. [43][44][45][46][47][48][49] In particular, biochar derived from wood and corn stover were used as catalysts to increase py-gas yield. 44,50,51 Research on the catalytic effect of wastewater biosolids-derived biochar (WB-biochar) during wastewater biosolids pyrolysis is lacking.…”

On-line liquid quench sampling and UV–Vis spectroscopy for tar measurements in wood gasification process gases

“…Results, obtained by the UV-Vis method, overestimate the fractional yield due to an overestimated outlet concentration of benzene. Assuming that the decomposition of naphthalene can form benzene as well [52], an overall fractional yield Φ Benz/T ol+Naph of benzene from toluene and naphthalene can be defined as in eq. (7).…”