Biomass derived wood ash with amine modification for post-combustion CO2 capture

Large quantities of wood ashes derived from biomass materials combustion potentially threaten the ecological environment. Recycling of the wood ashes as solid sorbents for pollutants control is an economical and environmentally friendly route. In this work, waste wood ashes (WAs) were modified with tetraethylenepentamine (TEPA), monoethanolamine (MEA), diethanolamine (DEA), polyethyleneimine (PEI), and diethylenetriamine (DETA) to synthesize solid sorbents with enhanced CO2 capture performances. CO2 capture behaviors of the synthesized sorbents were tested under 60°C, 5.0%CO2+5%H2O using a fixed-bed reactor, and sorbent regeneration behaviors were evaluated under 120°C, 10°C/min and 100%N2. The sorbent synthesized of ashes collected from straw-fired power plants modified with TEPA (TEPA-WA-1) is identified as the optimum candidate with superior capability for CO2 capture and sorbent regeneration. CO2 capture capacity of TEPA-WA-1 increases first and then decreases with the increase of amine loading. Sufficient amine loading can provide substantive active sites for enhanced CO2 chemisorption, whereas excessive loading will cause particle aggregation and pore structure blockage and affect its CO2 capture capacity adversely. The maximum CO2 capture capacity of 2.02mmol CO2/g is obtained with an amine loading of 45wt.%. The desired sorbent is demonstrated to be stable during 10 cyclic operations. Moreover, the presence of acid impurities (SO2 and NO2) exerts negative effect on the cyclic CO2 capture and sorbent regeneration performances of the synthesized sorbent. It is mainly attributed to sorbent deactivation induced by the formation of byproducts and weakened physical properties for the sorbent exposed in acid impurities.