Activation of biomass (cola nut shell) with KOH and K2C2O4: The distinct influence on evolution of volatiles and pore structures of activated carbon

KOH and K2C2O4 are frequently used for activation of biomass to produce activated carbon (AC) but they could impact the evolution of pore characteristics of AC and bio-oil/gas during activation in different ways. This was investigated herein by activation of cola nut shell with KOH or K2C2O4 at 600 to 800 °C. The results indicated that cracking and gasification reactions dominated with presence of either KOH or K2C2O4, diminishing the production of solid products and shifting main products from bio-oil to gases. Nevertheless, KOH was more active than K2C2O4 for cracking of carboxylic acids, furans, nitrogen-containing organics, diminishing their formation in bio-oil while promoting the formation of phenolics from lignin. Additionally, K2C2O4 was more effective than KOH in developing pores at a lower temperature of 600 °C but not at 800 °C (1232.20 cm2g-1 with K2C2O4 versus 1376.0 cm2g-1 with KOH). Nevertheless, K2C2O4 favored formation of macropores, which, however, did not help to enhance the adsorption of phenol. The in-situ IR characterization suggested that KOH or K2C2O4 were highly active to crack -OH and C=O, suppressing their transformation to unsaturated functionalities. Substantial amount of oxygen species could be retained in resulting AC, but mainly in the thermally more stable form of C-O-C bonds for bridging benzene rings.