Liquid-Phase Oxidation Of Several Oganics In A Microchannel Reactor And The Determination Of Relative Data

Liquid phase oxidation of organics is one of main production routes for many chemicals, such as converting toluene to benzaldehyde, cyclohexane to KA oil, cyclohexanone to adipic acid, and so forth. Many liquid phase oxidations of organics are gas-liquid phase reaction processes. Herein, for a fast complex oxidation reaction, the mass transfer rate of gas-liquid phase is important for reaction rate and yield (or selcetivity) of oxidation products. Therefor, developing and designing a suitable gas-liquid phase oxidation reactor and relative reaction process has been a research hotspot in this field. Reacently, microreactor technology has received a great deal of attention and has been rapidly developed in many application areas for its advantages of high mixing efficiency, good mass and heat transferring and the residence time controlling etc., all of which has been shown a great application prospect in liquid-phase oxidation of organics. In this paper, the liquid-phase oxidation of toluene to benzaldehyde, oxidation of cyclohexane to KA oil and oxidation of cyclohexanone to adipic acid in microchannel reactor were studied, respectively. Additionally, the solubilities of adipic acid in the relavent solvents were determined for new routes to adipic acid by an in-situ FTIR method at higher temperatures.Liquid-phase air oxidation of toluene in a microchannel reactor with a stainless steel microchannel tube of 0.762 mm inside diameter and 20 m length was studied. The effects of apparent liquid velocity, apparent gas velocity, reaction temperature, pressure, and catalyst concentration etc. were investigated. It was found that the apparent liquid velocity has an important influence on oxidant reaction. An over 30% selectivity of benzaldehyde was obtained even when an above 10% conversion of toluene was choosed, resulting to a maximum 4.13% yield of benzaldehyde with the apparent liquid velocity from 0.002 to 0.005 m/s. In contrast, apparent gas velocity has a weaker effect. An appropriate increase of temperature, pressure, or catalyst concentration is helpful for conversion of toluene, respectively, comparing with a deep degree of adverse reaction and reduing yield of benzaldehyde if out of range. The conversion of toluene can be increased when oxygen was used as an oxidant, which will decrease the selectivity of benzaldehyde. The kinetics of the oxidant reaction was simulated and compared with the experimental values. A good consistency between the effects of reaction conditions on concertration of oxidation products description with the simulated results from Jin’s model and with the experimental values.Liquid-phase O2 oxidation of cyclohexane in the abovementioned microchannel reactor was researched. The effects of apparent liquid velocity, apparent gas velocity, reaction temperature, pressure, and catalyst concentration etc. were studied. Under the conditons of apparent liquid velocity of 0.004 m/s, apparent gas velocity of 1.800 m/s, 165℃,1.4 MPa, cyclohexanone 0.2 wt.% and catalyst concentration of 10 ppm, the conversion of cyclohexane can reach 4.57% and the selectivity of cyclohexanol, cyclohexanone, KA oil and adipic acid are 61.72%,34.87%,96.59% and less than 3.00% respectively.A new route to adipic acid from liquid-phase O2 oxidation of cyclohexanone in cyclohexane in the aforementioned microchannel reactor was studied. The effects of mass fraction of cyclohexanone in the mixture, apparent liquid velocity, apparent gas velocity, reaction temperature, pressure, and catalyst concentration etc. were researched. Under the conditons of mass fraction of cyclohexanone of 0.8, apparent liquid velocity of 0.004 m/s, apparent gas velocity of 1.800 m/s,110℃,0.7 MPa, Co(acac)2 of 200 ppm and NHPI of 100 ppm, the conversion of cyclohexanone can reach 18.32%, meanwhile selectivity and maximum yield of adipic acid are 93.07% and 17.05%, respectively,.To provide thermodynamic data of solubility for other new routes to adipic acid from air or O2 oxidation, the solubilities of adipic acid in cyclohexanone+cyclohexane mixtures from 303.0 to 378.5 K and in cyclohexanol+cyclohexanone mixtures from 303.0 to 353.0 K were determined, respectively. The solubility of adipic acid in cyclohexanone+cyclohexane mixtures increases with increasing mass fraction of cyclohexanone in the mixtures at given temperatures. However, the solubility of adipic acid in cyclohexanol+cyclohexanone mixtures reaches the maximum at cyclohexanone mass fraction of 0.4, which is is considered as maximum-solubility effect. An in-situ FTIR method for solubility determination at higher temperatures was established and verified to be reliable, and applied to determine the solubility of adipic acid in pure cyclohexanol and pure cyclohexanone from 303.0 to 388.8 K. The results show that the in-situ FTIR method can directly obtain solubility data without any sampling operations, which is helpful to reduce the data deviation possibly caused by solvent evaporation and sampling errors during the sampling process under higher temperatures. Wilson equation, Apelblat equation and λh equation were employed to correlate the experimental data. It was shown that Wilson equation and Apelblat equation have the better correlation results, with an averaged relative deviation less than 5.0%. The thermodynamics functions of the dissolution process, including the enthalpy, entropy and Gibbs free energy were calculated by Van’t Hoff equation.