Studies On Decarboxylation Reactions In High Temperature Liquid Water

Decarboxylation, as an important chemical reaction, was widely applied in chemical, biological, pharmaceutical and pabular fields. Currently, thermochemical and acid-, base-catalyzed decarboxylation, these raditional technologies, were usually employed by intrustry, which have the problems of low reaction efficiency and environment pollution, respectively. High temperature liquid water has the ability to decarboxylate some small molecular carboxylic acids without catalysis and decarboxylate the fatty acids with the co-catalysis of catalysts, which is very important for the production of fine chemicals, pharmaceutical intermediates and bio-fuels. However, there were few academic and applied researches on the non-catalytic and catalytic decarboxylation in high temperature liquid water, which claimed to be systematically studied and explored both in academy and application fields.In this thesis, to discover the rule of decarboxylation, explore the mechanism of decarboxylation, and provide the academic and experimental support for the production of pentafluorobenzoic acid, quinolinic acid and fatty acids in high temperature liquid water, studies on the non-catalytic decarboxylation of pentafluorobenzoic acid and quinolinic acid, and the catalytic decarboxylation of fatty acids in high temperature liquid water were carried out. The research work was summarized as below.Firstly, pentafluorobenzoic acid was selected as the model compound of aromatic carboxylic acid and quinolinic acid was selected as the model compound of heterocyclic carboxylic acid. The kinetics studies on non-catalytic decarboxylation of pentafluorobenzoic acid and quinolinic acid in high temperature liquid water of 110-150℃range were carried out. The results showed that non-catalytic decarboxylations of pentafluorobenzoic acid and quinolinic acid were achieved in high temperature liquid water of 110-150℃range. The effect of different initial reactant concentrations on the reaction rate revealed that both compounds exhibited first-order kinetics. The kinetics data at different temperatures were fitted by the first-order equation, and the activation energies of both reactions were obtained by Arrhenius plot, were 157 and 141 kJ·mol-1.Secondly, palmitic acid was selected as the model compound of fatty acid. The performances of several kinds of catalysts in high temperature liquid water were evaluated.5% Pt/C and 5% Pd/C were proved to be very effective for the decarboxylation of palmitic acid. Moreover, activated carbon and molybdenum carbide's interesting acitivities were also valuable for us to do further research work.Thirdly, the activity maintenance test, characterization, catalysis order and reaction order estimation of 5% Pt/C and 5% Pd/C, and the kinetics study of Pt/C-catalyzed decarboxylation of palmitic acid were carried out. The results showed that after reaction, the metal dispersion and micropore volume of both catalysts decreased remarkably without significant activity loss. The catalysis performance and activity maintenance of Pt/C were superior to Pd/C's. Pt/C-catalyzed decarboxylation of palmitic acid in high temperature liquid water exhibited first-order kinetics. The kinetics data at different temperatures were fitted by the first-order equation, and the activation energy of palmitic acid decarboxylation were obtained by Arrhenius plot, were 79kJ·mol-1.After that, the studies on Pt/C-catalyzed decarboxylation of palmitic acid, stearic acid, lauric acid, oleic acid, and linoleic acid in high temperature liquid water were carried out. The effect of different carbon numbers on the decarboxylation of saturated fatty acids and the effect of different unsaturation degree on the decarboxylation of fatty acids were investigated. The results showed that the decarboxylation rates of saturated fatty acids were independent on the carbon numbers. The unsaturation degrees of fatty acids had a strong effect on the yields of alkanes. Due to the double bond in their structures, oleic acid and linoleic acid were hydrogenated before decarboxylation. The main hydrocarbon product was heptadecane. In the same reaction condition, the heptadecane yields of oleic acid and linoleic acid reaction were much lower than the yield of stearic acid decarboxylation. Finally, the catalysis performances of two non-noble metal catalysts-activated carbon and molybdenum carbide were evaluated. The results showed that activated carbon-catalyzed decarboxylation of palmitic acid to pentadecane, and activated carbon-catalyzed reactions of oleic acid to heptadecane were achieved in high temperature liquid water. The heptadecane yields at different temperatures were fitted by the pseudo first-order method, and the activation energy of activated carbon-catalyzed decarboxylation of palmitic acid in high temperature liquid water were obtained by Arrhenius plot, were 222 kJ·mol-1, which is much higher than the activation energy of Pt/C-catalyzed decarboxylation of palmitic acid in high temperature liquid water. Moreover, increasing the pressure retards the activated carbon-catalyzed decarboxylation rate of palmitic acid in supercritical water. Molybdenum carbide mainly catalyzed palmitic acid to hexadecane in high temperature liquid water. However, molybdenum carbide is not stable and tended to be oxidated in high temperature liquid water, which led to the structural modification.