| Cyclohexanone and cyclohexanol (also known as KA oil) are important raw materials in chemical industry, over about one million tons per year of cyclohexanone and cyclohexanol are made by cyclohexane oxidation. Since they are not only used as important reagents in the preparation of caprolactam and adipic acid for the production of nylon-6and nylon-66, but also used as solvents directly.In traditional process of the production of cyclohexanol and cyclohexanone, the potential risk of oxidation explosion is of critical concern in addition to the disadvantages of low conversion, low selectivity and energy-wasting. Micro reactors including microchannels have superior heat and mass transfer characteristic because of the scale effect, so it will have the very attractive prospects in the improvement of the safety, intensification of the gas-liquid mass transfer and obtaining good reactive performance. So my work focuses on cyclohexane oxidation in microcapillary reactor, and the main contents are as follows:Fluent software is used to model the gas-liquid mixer and the appropriate type of gas liquid mixer is selected. It is indicated that T type impinging mixer performs better than the Y type impinging mixer and T type shear flow mixer. The length of gas bubble and liquid slug is1.74cm and1.81cm respectively, when the gas and liquid velocity is0.02m/s. Visualilation research indicates that the coiling diameter of micro-reactor influences the mixing of gas and liquid, and the optimal coiling diameter is observed to be10cm.Oxygen is used as the oxidants to study on the cyclohexane oxidation in microcapilliary reactor. The effect of temperature, pressure, gas-liquid molar ratio, residence time, and the diameter of the microcapilliary on cyclohexane oxidation is also studied. At180℃,1.5MPa, gas-liquid molar ratio being0.3and the residence time1.9min, the conversion of uncatlyzed cyclohexane oxidation reaches6.07%and the selectivity to cyclohexanone and cyclohexanol is56.35%in the microcapillary reactor with the innner diameter of0.508mm. And it is observed that high temperature, short residence time is good for the reaction. At200℃,8.0MPa, gas-liquid molar ratio being0.15and the residence time1.4min, the conversion of cyclohexane can reach10.10%, the selectivity to cyclohexanone and cyclohexanol is75.71%in the microcapillary reactor with the innner diameter of0.508mm. Experiments are also carried out in the microcapillary reactor with different inner diameters, and it is found that the wall of the microcapilliary has positive effect on unselective side reactions.The wall of the microcapillary is coated with1%Au/Al2O3catalyst to form monolith microcapillary reactor, the gold load efficiency and degree of dispersion is very high, and the mean particle size of gold is3-5nm. At180℃,1.5MPa, gas-liquid molar ratio being0.3and the residence time1.5min, the conversion of cyclohexane reaches3.10%and the selectivity to cyclohexanone and cyclohexanol is72.16%in the microcapillary reactor of1.0mm coated with Au/Al2O3, compared with the conversion of uncatlyzed cyclohexane oxidation reaches3.54%and the selectivity to cyclohexanone and cyclohexanol is38.91%in the microcapillary reactor under the same reaction conditions. It is showed that the catalyst coated on the wall of the microcapillary has positive effect on the selectivity of cyclohexanol and cyclohexanone.At last, Spielman model plus mass balance equations are used to build the reaction model of cyclohexane oxidation in the microcaplliary reactor. It fits well with the experiment and the effect of the specific surface area and oxygen concerntration is also studied by using this model. It concludes that high surface area and oxygen concerntration is is favorable to cyclohexane oxidation but the reaction time must be strictly controlled. |
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