| Nicotinic acid, whose IUPAC name is 3-pyridine formic acid, also called as Vitamin B3, is important raw materials of chemical industries, intermediates of synthesizing medicine, additives of food, drink and feed. It is also applied to anti-oxidant in the active dyestuff, household chemicals,such as coloring-hair agent and hair tonic agent, plastic stabilizing agent and photo sensitive materials ect. The needs of Nicotinic acid was very tremendous. The methods of synthesizing nicotinic acid are various, including oxidation with chemical reagents, ammonia oxidation, air oxidation in gas or liquid phase, biooxidation and photooxidation, electrooxidation etc. The present oxidation methods have some disadvantage, the electrooxidation is promised to be a prospective way to synthesize nicotinic acid. 3-picoline is a kind of petroleum product which is cheap and frequent , it is considered to be the best feedstock of synthesizing nicotinic acid by electrolysis oxidation. However, there are few successful industry reports about using 3-picoline to produce nicotinic acid by electrolysis oxidation with high yield. The main reason is that it is a high-tech system, and there are still many problems concerning the electrolytic system and the separation method. According to literatures, the choice of electrodes material , exchange membrane and the comprose of electrolytic solution effected the electrolytic rerults when preparating nicotinic acid by electrooxidation method. (1)In an electrolytic cell with a proton exchange membrane, nicotinic acid was synthesized at a PbO2 anode. Effect of the concentration of sulfuric acid, the concentration of 3-picoline, anode potential and reaction temperature on the selectivity and the current efficiency were explored. The optimum conditions were determined by orthogonal experiments. The optimum conditions was H2SO4 1.5mol/L,3-picoline 1.2-1.4mol/L,anode potential 1.8V,temperature 30℃. Under optimum conditions the current efficiency and selectivity for synthesis of nicotinic acid might reach 65% and 89%, the exhaustion electrolysis of 3-picoline was carried out under the optimum conditions. The selectivity and current efficiency of nicotinic acid were decreased with 3-picoline electrolyzed. The constant concentration was proformed Under optimum conditions, the current efficiency to nicotinic acid was 55-65%, it's selectivity exceeded 90%. (2) In an electrolytic cell with proton exchange membrane, it was found that PbO2 is the most satisfied electrode material from electrooxidation of 3-picoline at PbO2/Ti, SnO2/Ti, graphite, Pt and MnO2/Ti electrodes. It was found that sulfuric acid is the best medium from electrooxidation of 3-picoline in sulfuric, perchloric, formic acid ,hydrochloric acid, phosphoric and acetic acid mediums. The electrooxidation conditions and electrocatalytic activity were studied with cyclic voltammetric and potentiostatic electrolytic experiments, the current efficiency and the selectivity in various conditions were compared and optimized. The study results demonstrated that the oxidation reactions at the PbO2 involves the oxidation of 3-picoline and oxygen evolution:(3) PbO2-SPE composite electrode was prepared by hot pressed method, the electrooxidation reactions of 3-picoline at the electrode was studied with cyclic voltammetry and steady state polarization curves. The relationship between current density and overpotential as well as overpotential and cell voltage were examined in different catholyte as well as with or without liquid supporting electrolyte in the anolyte. Possibility to produce nicotinic acid from 3-picoline at the electrode without supporting electrolyte in the liquid phase was explored. The selectivity and the current efficiency in specific conditions were given. But the better experiment results were required to carry out preferred experiment. (4) The factors that influence the oxidation of 3-methylpyridine in sulfuric acid-sodium sulfate-water were investigated systematically. Optimized electrolyte composition and electrooxidation condition were carefully selected. In this electrolysis system, the optimized electrolyte composition is: H2SO4 1.5mol/l, Na2SO4 1.0 mol/l, 3-picolie 0.4mol/l, the best electrolysis electrode potential is 1.70V(vs SCE). The current efficiency under optimized electrolysis condition is about 63%, and selectivity exceed 94%, much higher than those reported in literatures. Based on the electrolysis oxidation experiments, we studied the basic principle of the oxidation of 3-picoline in the systems via the measurement of static polarization curve. Upon the analysis of data of polarization curves, we calculated the exchange current and transfer coefficient of each electrode and...
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