Sun Baizhong, Liu Chuanqun, Che Deyong, Liu Hongpeng, Guo Shuai
School of Energy and Power Engineering, Northeast Electric Power University Jilin 132000 China
RSC Adv. 2020 Jul 31;10(47):28431-28436. doi: 10.1039/d0ra05482h. eCollection 2020 Jul 27.
As sludge pyrolysis produces large amounts of toxic NH and HCN, many works have studied nitrogen transfer during this process, commonly employing amino acids as models of sludge protein. Herein, density functional theory is used to probe the production of HCN and NH during the pyrolysis of phenylalanine as a model, revealing the existence of two formation paths for each gas. In the first (lower-energy-barrier) NH formation path, the hydrogen bonding-assisted transfer of carboxyl group hydrogen to the amino group is followed by direct NH generation decarboxylation, and the second (higher-energy-barrier) path features decarboxylation followed by the transfer of carboxyl group hydrogen to the adjacent carbon atom to form phenethylamine, the deamination of which affords NH and styrene. For HCN, the first (lower-energy-barrier) path features C2-C3 bond cleavage to afford dehydroglycine, which further decomposes to produce HCN, while in the second path, the decomposition of phenylalanine into phenethylamine, CO, and HO is followed by internal hydrogen transfer in phenethylamine to generate HCN. The overall energy barrier of the two HCN formation paths exceeds that of NH formation paths, , phenylalanine is more prone to afford NH than HCN upon pyrolysis.
由于污泥热解会产生大量有毒的NH和HCN，许多研究工作都对该过程中的氮转移进行了研究，通常采用氨基酸作为污泥蛋白质的模型。在此，利用密度泛函理论以苯丙氨酸热解为模型来探究HCN和NH的生成情况，揭示了每种气体存在两条生成路径。在第一条（能量势垒较低）NH生成路径中，羧基氢通过氢键辅助转移至氨基，随后直接生成NH并脱羧；第二条（能量势垒较高）路径的特征是先脱羧，然后羧基氢转移至相邻碳原子形成苯乙胺，苯乙胺再脱氨基生成NH和苯乙烯。对于HCN，第一条（能量势垒较低）路径的特征是C2-C3键断裂生成脱氢甘氨酸，脱氢甘氨酸进一步分解产生HCN；而在第二条路径中，苯丙氨酸先分解为苯乙胺、CO和HO，然后苯乙胺内部发生氢转移生成HCN。两条HCN生成路径的总能量势垒超过了NH生成路径的总能量势垒，即苯丙氨酸热解时生成NH比生成HCN更容易。
