| Industrial dipentene is a by-product of camphor and terpineol manufactures from turpentine, which is a mixture of monocylic terpenes containing mainly limonene, terpinolene,α-terpinene,γ-terpinene, and p-cymene. About 6 000-7 000 tons of industrial dipentene are put out annually in China at present and it is mainly used to prepare p-menthane, p-menthane hydroperoxide and p-cymene. In this study, the process was optimized to prepare p-cymene by continuous catalytic dehydrogenation of industrial dipentene. The relationship between the structure of catalyst Pd/C and its activity was studied. The possible catalytic dehydrogenation mechanism of dipentene was discussed, and thermochemical analysis of dehydrogenation was carried out. Ultrasonic atomization technology was introduced to the process of preparing p-cymene from industrial dipentene over Pd/C. The selective oxidation of p-cymene was preliminarily studied, too. The results could be used as a base for engineering and industrialization development of p-cymene, and exploratory research of p-cymene derivatives.The results of continuous catalytic dehydrogenation of industrial dipentene by Pd/C catalyst in 20 t/a equipment indicated that mass fraction of p-cymene in product and yield of p-cymene were increased synchronously with the increasing of temperature at the conditions of industrial dipentene feed rate 4 L/h, nitrogen flow rate 2 L/min, and reaction temperature range 260-310℃. The mass fraction of p-cymene in product was from 86.26 % up to 90.40 %, and the yield of p-cymene was from 92.65 % up to 97.09 % at 260-280℃. The growth rate of mass fraction of p-cymene in product and yield of p-cymene was respectively 4.14 % and 4.44 % in the temperature difference of 20℃. The mass fraction of p-cymene in product was between 90.40 % and 91.95 %, and the yield of p-cymene was between 97.09 % and 98.76 % at 280-310℃. The growth rate of mass fraction of p-cymene in product and yield of p-cymene was only 1.55 % and 1.67 % respectively in the temperature difference of 30℃. The selected temperature for long-time running was 280℃, and the yield of p-cymene was 97.09 % at this time.The ultrasonic spraying in pilot equipment for preparation of p-cymene was studied. By comparing with common spraying, it was found that ultrasonic spraying could improve dehydrogenation of industrial dipentene. The allowed running temperatures of preheater and spray room were all relatively lower. The growth rates of p-cymene yields in ultrasonic spraying mode were respectively 2.45 %-6.23 % and 0.31 %-1.10 % at the reaction temperature of 210-270℃and 280-310℃. The yield of p-cymene was up to 99.25 % in the condition of reactor temperature 310℃, flow rate of industrial dipentene 4 L/h, nitrogen flow rate 2 L/min based on Pd/C catalyst and ultrasonic spraying.The standard enthalpy of formation, Gibbs free energy and heat capacity of different reactants to p-cymene or by-products were calculated by Benson's methods of bond contribution and group contribution. The relationships of ?rHm°, ?rGm°, and lnK of dehydrogenation of different reactants with temperature were obtained through thermochemical calculation. The comprehensive enthalpy change and comprehensive Gibbs free energy change of industrial dipentene to p-cymene at 553 -583 K was respectively -21.26 kJ/mol (553 K) to -21.33 kJ/mol (583 K), and -118.11 kJ/mol (553 K) to -123.39 kJ/mol (583 K). The study could provide a theory base of thermodynamics for engineering and industrialization development of preparation of p-cymene from industrial dipentene by dehydrogenation.In the selective oxidation process of p-cymene with potassium permanganate as oxidant, the reaction rate and selectivity were affected by the amount of potassium permanganate and sulfuric acid, reaction time, reaction temperature, solvent type and other factors. The suitable conditions are molar ratio of p-cymene to potassium permanganate 1:3, molar ratio of sulfuric acid to potassium permanganate 0.13:1, water and acetic acid as solvent, reaction temperature 80℃, and reaction time 9 h. Under the conditions, the conversion rate of p-cymene was 92.21 %, the selectivity of main product p-cymen-8-ol was 69.65 %, and by-products were p-isopropylbenzoic acid, p-isopropylbenzaldehyde and p-methylacetophenone. The oxidation reaction is still needed more intensive researches.
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