Study On The Pyrolysis Of Isobutyric Anhydride And Isobutyric Acid

Pyrolysis of isobutyric anhydride(IBAN)and isobutyric acid(IBA)is not only the major preparation method for dimethylketene(DMK),but also the key stage in the industrial production of 2,2,4,4-tetramethyl-1,3-cyclobutanediol(CBDO).In this article,the pyrolysis reaction kinetics,reaction mechanism and catalytic reaction mechanism of IBAN and IBA were studied.The main content includes the following three components:1.The IBAN pyrolysis experiment was performed in a differential reactor.In conditions of 748 K,residence time of 0.4 s and IBAN partial pressure of 10 kPa,IBAN conversion was 81%and DMK selectivity was 86%.The reaction network and the corresponding kinetic model of IB AN pyrolysis under experimental conditions were summarized,and the kinetic parameters of each reaction step were obtained by fitting the experimental data.In addition,the reaction path of anhydride crack was studied at the theoretical level of CBS-QB3.The IBAN crack potential barrier was 38.8 kcal/mol.The reactants and transition states were treated by one-dimensional hindered rotor method,and the rate constant was calculated by tunneling correction.2.The IBA pyrolysis experiment was performed in a differential reactor.Under the experimental conditions discussed,the mole fraction of by-products increased with the increase of temperature and contact time.CBS-QB3 method was used to study the reaction path of unimolecular dissociation,isomerization,H-atom abstraction,β-scission and pyrolysis of DMK.The calculated potential barriers of dehydration and indirect dehydration of IBA to prepare DMK were 74.9 kcal/mol and 77.2 kcal/mol,respectively.Based on the experimental data and theoretical calculation,a detailed kinetic model including 271 species and 3122 reactions was developed,the results show that the model can well predict the variation of the pyrolysis products.Through rate of production analysis and sensitivity analysis,at high temperature,the free radical mechanism plays an important role in the pyrolysis of IBA,reducing the reaction temperature and increasing the reaction rate of IBA dehydration can improve the yield of DMK.3.The adsorption of carboxylic acid on CeO2(111)and corresponding carboxylic acid radical at CeO2-x(111)were studied by density functional theory,and the reaction mechanism of isobutyrate to produce DMK on CeO2-x(111)was further explored.The results show that the α-H pyrolysis of isobutyrate would occur on CeO2-x(111)with a potential barrier of 30.30 kcal/mol.The carbon-oxygen bond would cleavage in the CH3C(CH3)=COO intermediate to form DMK with a potential barrier of 29.58 kcal/mol.Therefore,the reaction cycle mechanism of CeO2(111)could promote the preparation of DMK by IB A dehydration.