Effect of boron-based additives on char agglomeration and boron doped carbon microspheres structure from lignin pyrolysis

To prevent the thermal softening of lignin during the pyrolysis process, the influence of boron-based additives (boric acid, sodium borate and potassium borate) on lignin softening, pyrolysis process were investigated with metal bases (Ca(OH)2 and Mg(OH)2) as comparison, and the influence mechanism of boron based additives was explored in depth. It is found that the boron additives can effectively inhibit the agglomeration of lignin particles. For pyrolysis products, boron additive promoted the carbon-forming reaction of lignin with carbon sequestration more than 70 wt%, and inhibited the release of volatiles, especially for phenolic compounds. It also inhibited the generation of CO2 and CH4, while promoted the release of CO. The boron element in lignin char mainly exists in the form of BCO2 and B2O3 with more hydroxyl groups on the surface. Furthermore, boron-modified lignin chars are spherical with more uniform and smaller particle size compared with metal bases modified lignin chars.