The Shape-selective Cracking Of Diisopropylbenzens

Diisopropylbenzenes(DIPBs)will be formed as byproduct during manufacturing cumene by alkylation of benzene with propylene to in phenol-acetone plants,and meta-DIPB is an important raw material,which mainly can be oxidized to resorcinol. Recently with the need of resorcinol increasing in many industries,the need of m-DIPB is also increasing.However,the boiling points of the three isomers of DIPB are very close: ortho-DIPB 205℃,meta-DIPB 203℃,para-DIPB 203.5℃,so it is difficult to separate meta-DIPB from the other isomers using normal distillation.In this paper,the certain zeolites which have the shape-selective function will be used as catalysts to crack DIPBs selectively. They have the appropriate pore diameter in order to let para-DIPB go into the pores of molecular sieves and will be cracking to benzene and cumene with the acid centers inside,but meta-DIPB(larger diameter than para-)can not go inside and does not react.So 99% meta-DIPB can be producted though distillation using the obvious differences of boiling points of products,(benzene 80.1℃,eumene 152.5℃).Shape-selective cracking of DIPB was investigated over zeolite catalysts,i.e.HZSM-5, HZSM-22,Hβand HY.The results showed that HZSM-5 zeolite appeared to be the most efficient catalysts for the reaction.Meanwhile,nano-HZSM-5 is the high-active catalyst for the reaction compared the different grain sizes of HZSM-5.The reaction conditions over nano-HZSM-5 were investigated,the cracking rate of para-DIPB can reach 93%,Content of m-DIPB in product DIPB 94%and the yield of meta-DIPB 75.7%at the optimum conditions: pressure 0.1MPa,reaction temperature 380℃,and weight hourly space velocity(WHSV)6h^-1 with N₂.Nano-HZSM-5 was modified with oxides of magnesium and lanthanum,the results show that the modified zeolites have the high activity during 40h,the stability is increasing,and the yielding of meta-DIPB is also increasing.The catalysts prepared with Mg(NO₃)₂ as the precursor of MgO have the higher cracking activity and stability than the catalysts prepared with Mg(CH₃COO)₂ as the precursor.Compared with the effects of different contents of lanthanum iron,the results indicate that 0.1%content the stability of catalysts increased obviously,and the cracking rate of para-DIPB can reach 92%,Content of m-DIPB in product DIPB 93%,the yield of meta-DIPB over 85%.Compared with modification by hydrothermal treatment in different time under the temperature of 160℃,the results indicate the catalysts modified by hydrothermal treatment in 2h hold high activity during 50h,and have the best stability.The stability of nano-HZSM-5 modified by hydrothermal treatment followed by lanthanum is better than modified by lanthanum followed by water,the cracking rate of para-DIPB can holding over 85%during 60h,Content of m-DIPB in product DIPB over 90%,the yield ofmeta-DIPB over 90%.