Study On 2,3,6-Trimethylphenol Oxidation Catalyzed By CuCl₂/FeCl₃

The catalytic oxidation of 2,3,6-trimethylphenol(TMP) is an important way to produce 2,3,5-trimethyl-1,4-p-benzoquinone(TMQ) which is a key intermediate for Vitamin E preparation. As a kind of cheap and environmental friendly oxidant, molecular oxygen is gradually replacing the traditional oxidants for TMP oxidation. The study of TMP multiphase oxidation was carried out when the aqueous solution of CuCl2/FeCl3 was used as catalyst, oxygen as oxidant and n-hexanol as solvent aimed at providing theoretical support for TMP multiphase oxidation reactor scale-up and optimization.GC-MS method was used to characterize the product structure and GC method was used to trace the reaction process. The results showed that two consecutive reactions of TMP-TMQ, TMP-2,2’,3,3’,5,5’-hextrimethylphenol(IP) and one consecutive reaction of TMP-4-chloride-2,3,6-trimethylphenol(C1TMP)-TMQ existed in the process. Cl- was able to inhibit the side reaction by promoting the formation of C1TMP which finally transformed to TMQ. The yield of desired product TMQ reached to 80.66% under the temperature of 358.15K after 8 hours’reaction with 7.57mol% CuCl2 and 3.78mol% FeCl3 as catalyst.The TMP gas-liquid oxidation was carried out through dissolving the catalyst aqueous solution into n-hexanol solution saturately. The TMP oxidation network was analyzed and the mechanism was proposed. Mixing gas as oxidant, the reaction would be under gas-film control in the initial period. Oxygen as oxidant, the reaction would be affected by liquid-film mass transfer and the liquid-film mass transfer resistance could be eliminated when the rotation speed surpassed 400rpm/min and the reaction would be under kinetics controll.The TMP gas-liquid-liquid oxidation was carried out when the catalyst aqueous solution and reagent n-hexanol solution were separated phases. The oxygen absorption rate was positively relative to the rotation speed and oxygen concentration, while the effect of ventalition on the oxygen absorption rate was limited under fixed rotation speed. Phase inversion took place when the water phase volume fraction reached 0.42, namely the system changed from W/O system to O/W system. The apparent viscosity of system maximized during the phase inversion and the trend of total oxygen absorption rate also changed significantly.A correlation equation of ko2,La in the n-hexanol phase was obtained by combing the rotation speed, impeller diameter, superficial velocity, ventalition and water phase volume fraction. The theoretical values of kO2,La were calculated by this equation compared with the experimental values. The maximum relative deviation was 10.15%, while the minimum relative deviation 1.18% and the average relative deviation was 4.53%, which showed that the equation fitting was reasonable.