| Benzaldehyde is an important intermediate in the field of organic chemical engineering. It is wildly used in pharmaceutical, perfumery and dyestuff industries. At presently, the mainly synthesis process of benzaldehyde is hydrolysis of chlorobenzene, but the benzaldehyde under the process contains chlorine in the nucleus, so its range of use is limited especially for the grade conforming to pharmaceutical and perfumery. We try to search for another reasonable and economical method for production of benzaldehyde free of chlorine. The selective oxidation of toluene to benzaldehyde in liquid phase by air highly deserves to be discussed. Firstly, we use toluene and air as raw material, compared with the price of product benzaldehyde, they are much lower, if the process is industrialized, its has great profit. Secondly, under the batch operation in our laboratory, the yield of benzaldehyde is up to 13.1%, if the recycling of toluene is also practical, it will be a great achievement of our country.This paper discusses various factors which have effect on the reaction result, in addition to dynamic analysis and reactor selection experiment, we arrange uniform test and give the optimal condition. According to the experiment of catalyst types and use level, we know Co salt have high catalyst activity for the reaction, the activity of V salt is less than Co salt, if we use Mn salt only, the initiation time is long and yield is low. For Co salt, organic anion is better than inorganic anion. We choose WULCo as catalyst, since it dissolves easily in toluene and the operation is convenient. It is economical if we use Co and Mn as catalyst according to an appropriate proportion. When the use level of weight percentage concentration of Co is less than 0.3%, the result is satisfied to us, while the use level is beyond 0.3%, there will be a lot of tar and the reactor is liable to be blocked. Form the cocatalysts experiment, we conclude that cocatalysts is indispensable, reaction doesn't proceed without Br reagent. The effect of KBr and NaBr is resemble for the reaction, and NH4Br is better than them,TMAB and TBAB is the worst. BRNBS, as a new reagent, have good effect ,such as little tar, short initiation time, high yield. We choose two ventilation means, one is opening the blow-down valve after initiation of the reaction, the other is opening the valve from beginning to end, we found the first method is better. We should keep temperatureabove 150℃, otherwise, the reaction can't proceed smoothly, as temperature rise, toluene conversion rise also, when benzaldehyde yield and selectivity rise to a maximum point and then decrease, we control temperature between 160℃ and 180 ℃. When we discuss air flow, the result is oxygen absorption and mass transfer rate increase as air flow increase, within 1 L/min, the reaction time for same yield decrease as air flow increase. Kinetics studies showed that the rate of reaction is first order with respect to toluene and zero order to oxygen concentration, the rate constant is 5.8689× 10-3 min-1. Reactor experiment shows the Hatter parameter of the reaction in packed column,orifice column and stirred tank reactor is within 0.02-3, belong to mid-rate reaction and it is controlled by interphase mass transfer and reaction in liquid phase. After conditional experiment, we choose three factors and five levels to arrange uniform test, they are weight percentage concentration of Co and Br as well as reaction time. Through regression analysis, we get the equation y = 16.65+13.9x1+1.10x2-0.029x3, the optimal process conditions of the oxidation reaction of toluene to benzaldehyde is as following: when weight percentage concentration of Co(WULCo) and Br(BRNBS) is 0.25% and 0.5% respectively, the reaction time is 4hr20min, the yield of benzaldehyde is up to 13.1%.
|
PDF Full Text Request