The Recycle Of Metallic Cobalt Catalyst For The Liquid Phase Oxidation Process Of Methyl Aromatics Hydrocarbon To Aldehydes Dissertation

Aromatic aldehydes,with a yearly increasing demand,are widely used as essential intermediates in the fields of medicine,pesticides and dyes manufacture,etc.And its marketing demand increases with years.Methyl aromatic hydrocarbon can be easily obtained for the rapid development of petrochemical and coal chemical industry.Hence how to manufacture value-added aromatic aldehydes from toluene derivatives is extraordinarily interesting and attractive.Most of the domestic aromatic aldehydes are mainly produced by the hydrolysis of benzal chloride.This process suffers greatly from serious disadvantages,such as heavy pollutions and the residual chlorine in the product,owing to the usage of chlorine gas.To make matter worse,the residual chlorine restricts the products to be applied as food additives resulting in the reducing the value-added of the products.There is no doubt that the liquid-phase oxidation of methyl aromatic hydrocarbon with pure oxygen and certain conditions of temperature and pressure is one of the most important applications.There are two methods for the liquid-phase oxidation of methyl aromatic hydrocarbon,homogeneous and heterogeneous catalysts.Heterogeneous catalysts were first tried for the easy recovery.However,these catalysts are usually synthesized through complex process or applied under harsh reaction conditions.What's worse,the yeild of aldehyde with the heterogeneous catalysts stayed so low for either low conversion or low selectivity that limited their industrial application.Homogeneous catalysts has been widespread used in the liquid-phase oxidation of toluene due to good activity and mild operation conditions.The core catalyst of liquid-phase oxygen oxidation is cobalt acetate.However,recovery and recycling of homogeneous catalyst are huge obstacles for the liquid oxidation of aromatic hydrocarbons.Therefore,the study of cobalt catalyst recycling is an important part of industrial-scale production of aromatic aldehydes.This paper concentrates on the liquid-phase oxidation of methyl aromatics hydrocarbon to aldehyde with Co/Br catalyst.Firstly,the characteristics of oxidation were carefully investigated with Co/Br catalytic system being optimized to determine the amount of the catalyst for recovery.Various methods of MC catalyst recovery for the manufacture of PTA has been reported and partly applied.We choose to separate the metal catalysts soon after the oxidation to prevent further oxidation of aldehydes with cyclohexane for the reason that aromatic aldehyde can be easily over-oxidized to aromatic acid.The simulated experiment of catalyst recovery provides evidence and guidance for the testing activity experiment of Co/Br catalyst.The main research contents are as follows:(1)For reducing the cost of cobalt ion detection,UV spectrophotometer analysis was defined as a method for detecting the concentration of cobalt ion after literature research and laboratory tests.In the simulating experiment,toluene,acetic acid,benzaldehyde,benzoic acid,cobalt(?)acetate tetrahydrate(Co(OAc)2),sodium bromide were mixed(toluene 50wt%,benzaldehyde 12-16wt%,benzoic acid 30wt%)to simulate the components in the reaction liquor when the toluene conversion reaching 50%.The influences of the parameters including phase separation time,temperature,agent amount and water content on the phase splitting and catalyst recovery from the mother liquors,were carefully discussed.It is found that the amount of water and phase splitting agent play an important and complex role for the phase separation which provides a reference for catalyst recycling.When the water content was 4%and the volume of cyclohexane is about 1.5 times the mother liquors,the recovery coefficient of cobalt salts is above 97%at room temperature.(2)The reaction process of methyl aromatics hydrocarbon(Toluene,P-tert-butyltoluene,Methoxy-toluene)oxidized to aldehydes catalyzed by Co/Br in acetic acid solvent was studied with V acetic acid/V methyl aromatice hydrocarbon=1:1,oxygen flow rate 60 mL/min at 98?.The effects of the amount of Co,the amount of Br and the amount of water were studied to draw the follovwing conclusions:the effect of cobalt acetate is orderly so it' s easy to determine the concentration of cobalt acetate in the recovery.But the effect of the Sodium bromide in the oxidation is complex.Experimental results show that the bromine will be consumed out when the content of bromine was lower or equal than 0.2%Which makes the experiment of testing catalysts activity can be conducted in a single variable.(3)For the oxidation of toluene,nCo/ntoluene=2.5%,nBr/ntoluene=0.2%is chosed as the amount of the recycled catalyst.In the oxidation of p-tert-butyltoluene,nCo/n p-tert-butyltoluene=2.0%,nBr/n p-tert-btryltoluene=0.2%is chosed as the amount of the recycled catalyst.Methoxy-toluene can be oxidized to the corresponding aldehyde without bromide source so nCo/n Methoxy-toluene=1.5%,nBr/n Methoxy-toluene=0 1s chosen as the amount of the recycled catalyst.the activity of the catalyst remain almost unchanged for 10 cycles,showing an excellent cycle of cobalt salt.