Denitrogenation of biocrude oil from algal biomass in high temperature water and formic acid mixture over H+ZSM-5 nanocatalyst

Abstract

Due to the high protein content in algal species, these precursors require further catalytic removal of heteroatoms such as nitrogen, being upgraded to biofuels. In the current study, first, synthesis of Na+ZSM-5 nanocrystals with well-distribution in size was performed successfully with a novel technique in supercritical water. After converting to H+ZSM-5 type, it was applied for hydrodenitrogenation (HDN) of crude bio-oil, obtained from hydrothermal liquefaction (HTL) of chlorella sp. microalgae, in the presence of high temperature water and formic acid (HCOOH) mixture. The effects of reaction temperature (250–500°C), formic acid as a source of in-situ hydrogen, and nano-catalyst (compared with industrial type) on nitrogen elimination and H/C ratio were investigated comprehensively. Compared with non-catalytic upgrading conditions, a substantial amount of nitrogen removal was obtained in the presence of nano-catalyst and formic acid with the maximum amount of 75wt% at 400°C in comparison with the macron-size industrial catalyst (54wt%) at the same temperature. Due to more miscibility and consequently high degree of liquid fuel recovery (Yliq) with less coking as well as more HDN, T=400°C was chosen as the optimum temperature. Furthermore, H/C ratio of upgraded bio-oil, as an index of aromatization, had similar trend which indicates that in the presence of H+ZSM-5, higher temperature is more favorable to aromatization than cracking which makes HDN more difficult. In the absence of a catalyst, H/C ratio showed no substantial trend with temperature which demonstrates the significance of H+ZSM-5 catalyst for cracking.