褐煤模型化合物中含氧官能团脱出反应的理论研究

Theoretical Studies on the Taking off of Oxygen-containing Functional Groups in Lignite Model Compounds

选取苯甲酸和苯酚作为褐煤含氧官能团模型化合物,采用密度泛函理论（DFT）中的B3LYP泛函和6-311＋G（d,p）基组,研究了羧基和羟基可能的脱出反应机理.结果表明,不同含氧官能团脱出方式不同,脱出所需的能量也有差异;含有羧基物质的自催化交联脱羧是相对容易发生的反应;考虑到水分子对含氧官能团脱出的影响,选取甲酸和丙三醇作为褐煤含氧官能团模型,研究了水分子参与反应的过渡态结构及其反应活化能的变化,结果表明,反应中水分子作为质子传递介质能降低反应活化能,加快反应速率,一般1-2个水分子的催化效果较佳;同时研究了Na^＋,K^＋及其羧酸盐对丙三醇中羟基脱出反应过渡态结构和反应活化能的影响,表明Na^＋和K^＋均能与模型化合物形成络合物,稳定过渡态结构,降低活化能,其中Na^＋的催化效果更佳;与单纯的离子相比,K^＋羧酸盐催化效果变化不大,Na^＋羧酸盐催化能力降低幅度较大.

The removal reaction mechanism of different kinds of oxygen-containing functional groups in lignite was investigated,benzoic and phenol were chosen as model compounds. Density function theory（ DFT） and DFT-based B3 LYP method along with mixed basis sets 6-311 ＋ G（ d,p） were applied in all calculations. The results suggest that removal approaches are different from different kinds of oxygen-containing functional groups and the taking off energy is also different. According to the reaction activation energy of different kinds of reactions,autocatalysis reaction of structure unit containing carboxyl is the easiest. Taking account of the influence of water molecular to the reaction,formic acid and glycerin were studied as model compounds. The results show that water molecular can reduce the reaction activation energy and accelerate the reaction process,the best catalytic effect is achieved with one or two water molecular. The effects of Na^＋,K^＋and their carboxylates to the reaction were studied on glycerin as well. The results suggest that Na^＋and K^＋can reduce the reaction activation energy by forming complexes with glycerin,which stabilizes the transition state structure. Na^＋has a better catalytic effect to the reaction. Comparing with sheer ions,the catalytic effects of carboxylate can＇t reach that good. However,potassium carboxylate＇s catalytic effect doesn＇t change a lot,while the catalytic effect of sodium carvoxylate has a significant decrease.