Investigation On The Pyrolysis Process Of Isobutyric Anhydride And Isobutyric Acid

The pyrolysis of isobutyric anhydride(ANIB)and isobutyric acid(AIB)is not only the main process for preparation of dimethylketene(DMK)in large-scale,but also the key step for the production of polyester diol monomer 2,2,4,4-tetramethyl-1,3-cyclobutanediol(CBDO).In this work,the pyrolysis of ANIB and AIB were investigated,and the mechanism was proposed.The theoretical study,pyrolysis experiments and catalytic reactions for preparing DMK reaction system were carried out,and the preparation process of DMK was optimized.The main contents of this work are list as below:Fixed bed differential reactor was used to investigate the cracking efficiency of ANIB,AIB and the mixture of them.The results show that the selectivity of DMK decreases with the increase of temperature.partial pressure and contact time.The conversion of DMK increases with the increase of temperature.partial pressure and contact time.The optimum molar yield of DMK obtained by ANIB pyrolysis is 68.1%,when the contact time was 1.00 s and the partial pressure of ANIB was 5.22 kPa at 450℃.However,for AIB pyrolysis,the optimum molar yield of DMK is only 18.5%.The cracking efficiency of ANIB is better than that of AIB.The suitable cracking temperature of ANIB and AIB varies greatly.Thermodynamic and quantum mechanical calculations of ANIB and AIB reaction systems show that the equilibrium composition of the main reaction is limited by thermodynamic equilibrium.The change of temperature and partial pressure will affect the equilibrium composition.In order to obtain high molar yield of DMK,the product DMK needs to be separated quickly to prevent further reaction.The reaction barriers of AIB direct pyrolysis to prepare DMK are 76.11 kcal*mol-1 and the rate constant is 6.50E-09 s-1.The reaction barriers of AIB dehydration to prepare ANIB and ANIB pyrolysis to prepare DMK are 44.14 kcal*mol-1 and 36.24 kcal*mol-1,respectively,and the rate constant is large.ANIB may be the intermediate product of AIB pyrolysis to prepare DMK.In order to prepare DMK efficiently from AIB at lower temperature,the reaction of AIB on MgO,γ-Al2O3,TiO2 and functionalized silica were studied.AIB can be efficiently converted to ANIB with a mole selectivity of 84.2%in the presence of MgO catalyst which exhibited high stability.The addition of metal oxides such as γ-Al2O3 and TiO2 will promote ketonation reaction.Functionalized silica catalyst is the promising catalyst,the calcination temperature will affect the concentration and morphology of hydroxyl groups on the surface of the catalyst.The optimum molar yield of DMK is 31.0%under experimental conditions.Under these conditions,the conversion of AIB is 67.8%.Compared with pyrolysis,catalytic cracking greatly improves the reaction efficiency,and the catalytic conditions have further optimization opportunity.