Process Optimization Of MOCA Synthesis Over Heteropolyacids And Study On Catalyst Immobilization And Deactivation

In this work,the catalytic synthesis of 3,3'-dichloro-4,4'-diamino diphenylmethane(MOCA)from o-chloroaniline and formaldehyde over heteropolyacid catalysts was investigated in a Parr 5500-600mL autoclave,and the process of the synthetic optimized.Also,the immobilization,deactivation and regeneration of heteropolyacids were studied experimentally and theoretically.First of all,the catalytic performances of three heteropolyacid catalysts HPW,HSiW and HPMo for MOCA synthesis by condensation between o-chloroaniline and formaldehyde were comparetively investigated,screening out HPW catalyst as an effective and suitable catalyst for this synthetic reaction.Compared with high catalytic HY(7.5)zeolite,it was found that heteropolyacid catalyst gave better catalytic activity and required milder reaction conditions than the solid zeolite.Then,under various reaction conditions and with using HPW catalyst as catalyst,the yield and selectivity of main product MOCA were systematically evaluated and the process conditions optimized.The experimental results indicated that under the conditions of n(o-chloroaniline):n(formaldehyde)=8:1,w(catalyst):w(formaldehyde)=1:1,w(catalyst)=16.2g,70? temperature and 1h reaction time,the reaction of o-chloroaniline and formaldehyde condensation over HPW catalyst gave MOCA yield of 88.15%and selectivity of 89.06%,respectively.Then,the immobilization of HPW on activated carbon,SiO2,TiO2 and H?(100)were comparetively investigated,and activated carbon was confimed as the most suitable carrier to support HPW.Futhermore,the catalytic performance of the catalysts with different amount of HPW loading on activated C was tested.Based on experimental results,the most effective load ratio of HPW/C was 40%HPW,and under the same reaction conditions,the yield and selectivity of main product MOCA reached 30.84%and 32.53%,respectively.In the end,the experimental tests of catalyst reuse,deactivatition and regeneration of HPW/C catalysts were conducted,and in combination with the characterization of the fresh,deactivated and regenerated catalysts,the cause and mechanism of catalyst deactivation were explored.The results showed that after the catalyst repeatedly used for 4 times,the yield and selectivity of main product MOCA decreased from 30.84%and 32.53%to 0.07%and 1.12%,respectively.In order to regenerate the deactivated catalyst,the spent catalyst after reusing 4 times was treated by methods of calcination and benzene washing.The calcination could significantly recovered activity of the catalyst to give MOCA yield of 14.68%and selectivity of 16.06%,respectively.However,the effect of catalyst regeneration was still not ideal.