Abstract:

In order to prepare lignin-based high-performance electrocatalytic carbon materials for fuel cells, enzymatic hydrolysis lignin was used as raw material to prepare urea or melamine modified enzymatic hydrolysis lignin. TG and DSC were used to study the pyrolysis process of these three kinds of lignin. Meantime, lignin pyrolysis experiments were conducted by a vertical tube furnace at different pyrolysis temperatures. The yield of solid products was calculated, and the carbon, nitrogen, and hydrogen content of these solid products were tested by elemental analyzer. The results show that urea or melamine modified enzymatic hydrolysis lignin exhibit a significantly different pyrolysis process from unmodified enzymatic hydrolysis lignin. The pyrolysis of urea modified enzymatic hydrolysis lignin mainly take place in the temperature range of 180-360 ℃, and melamine modified enzymatic hydrolysis lignin in a narrower temperature range of 280-350 ℃. Although melamine is basically thermally decomposed at 400 ℃, melamine modified enzymatic hydrolysis lignin produce a carbon product with a nitrogen content of more than 10% at 900 ℃. Moreover, the yield of char derived from melamine-modified lignin is equivalent to that of unmodified lignin. Conclusively, the melamine modification produces a significant effect on the pyrolysis of lignin. Further comparative analysis revealed that melamine modification result into the formation of a large amount of nitrogen-containing organic compounds with high chemical activity during the lignin pyrolysis, which greatly increased the probability of secondary pyrolysis reactions of melamine modified lignin at a lower temperature, thus significantly affecting the yield and nitrogen content of the final solid products.

Key words: lignin, carbon material, electrocatalysis, urea, melamine, pyrolysis