Experimental Study On Liquid Phase Catalytic Oxidation Of Toluene In A Tubular Reactor

Benzoic acid,benzoic alcohol,and benzaldehyde are important chemicals and intermediates.They have high additional value,and are widely used in pharmaceutical,pesticide,spices,dye,cosmetics and other fields.Now,the common methods for the production of these chemicals are hydrolysis of benzyl chloride method and direct air oxidation of toluene in liquid phase?DAOTLP?.Among them,higher standards of equipment are required in the hydrolysis of benzyl chloride method which tends to cause corrosion,and the off-gas discharged brings about environment pollution.What's more,there are halogen in the product,which seriously affected the application in the area of medicine and spices.And the process of DAOTLP is a kind of green and environmentally-friendly process and it enjoys mild reaction conditions and good security.Therefore,DAOTLP becomes the main method of their production.In this process,the yield of benzoic acid is up to 95%,but the yield of benzoic alcohol,and benzaldehyde is pretty low due to the nature of chain reaction,operation conditions,and the structure of reactor,which results in the out-of-balance in product structure.It is very important to further study DAOTLP process in order to raise the economic benefits of the production enterprises.The typical production technique for DAOTLP is Italian SNIA process.The catalyst system of this process becomes mature,mainly being cobalt naphthenate or cobalt acetate.The type of reactor remains tank reactor with the contact between air and toluene solution,although there are some changes in the ratio of length to diameter,stirring method and heat exchanging.This type of reactor is near to CSTR,which has large back-mixing and disadvantageous to raise the selectivity of benzaldehyde.Tubular reactor is proposed in this thesis as a candidate commercial reactor to replace present tank type reactor.The experiments were made on the experimental tubular reactor with self-design and making in order to explore the reaction pattern and the possibility of the replacement.The experimental tubular reactor is consist of four vertical annular tube with 1m length,and in head-tail connection.There are some static mixer loadings in the tubular reactor to enhance the effect of gas liquid mass transfer.There is a sampling mouth in each reaction tube exit.With the Co salt as catalyst and benzoic acid as promoter,it is found in the study that under the optimal operating conditions of four tubular reactors:Co²⁺is 0.015 wt%,benzoic acid is 0.1 wt%,reaction pressure is 0.9 MPa,temperature is 165?,and oxygen content of reaction gas is 30%.When the reaction devices are increased to eight vertical tubular reactors,it is found that the rate of toluene conversion gets bigger with the residence time of toluene in tubular reactor increasing,benzoic acid selectivity gets gradually higher,the selectivity of benzaldehyde lowers after they rise.The maximum of benzaldehyde selectivity is up to 43%when the residence time was 10min and the conversion rate was 4.2%.In this article,synthesis of diethylene glycol benzoate,downstream product of benzoic acid,was experimental studied.A reaction-reaction coupling process was proposed with combining the oxidation of toluene and the esterification of benzoic acid and diethylene glycol.The esterification of benzoic acid and diethylene glycol was firstly studied and high conversion ratio was reached.However,in the experiments with tubular reactor for the coupling process,the results were not good due to no removal of by product water.The further experiments need to be made.