(89g) Optimizing the Liquid Phase Partial Oxidation of Sec-Butylbenzene to Hydroperoxide

Optimizing the liquid phase partial oxidation of sec-butylbenzene to hydroperoxide

Weizhen Sun, Junfeng Qiu, Ling Zhao

State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China

    Phenol is an important industrial commodity as a precursor to plastic materials and chemical compounds. Currently the dominant route accounting for 95% of productions is the partial oxidation of cumene (also known as isopropylbenzene) via the Hock rearrangement reaction. However, for economic operation of this process, there must be demand for both phenol and the by-product acetone. One promising alternative process for phenol production is the liquid phase partial oxidation of sec-butylbenzene (sBB) to sBB hydroperoxide (sBBHP), which further decomposes to phenol and methyl ethyl ketone (MEK). MEK is an effective and common solvent with a wide application in the manufacture of plastics and textiles. As for the sBB, it can be manufactured through the catalytic alkylation of benzene with 1-butene, which is widely available and inexpensive.

    The liquid phase partial oxidation of sBB to sBBHP is the key procedure for the whole route to produce phenol starting from sBB. However, there is less literature to be referred regarding the reaction kinetics and preliminary optimization for this oxidation process. In this work, we focus on 1) the measurement of reaction kinetics of sBB oxidation to sBBHP, 2) the establishment of kinetic model based on detailed reaction mechanism, and 3) the process optimization of liquid phase partial oxidation of sBB to sBBHP.

    The liquid phase partial oxidation of sBB to sBBHP by air in absence of catalyst was investigated via semi-continuous experiments. To eliminate the influence of mass transfer, the experiments under various conditions were carried out involving the effect of speed of agitator inside reactor, amount of air supply, and air pressure. Under conditions excluding the influence of mass transfer, the reaction kinetics of sBB partial oxidation to sBBHP was measured at temperatures ranging from 388 to 413 K. Two main by-products, i.e. acetophenone (ACP) and 2-phenyl-2-butanol (PBO) were considered aside from sBB and sBBHP.

    Based on the detailed free radical chain reaction mechanism, the kinetic model with 10 parameters was developed involving elementary reaction pathways. Fitting the model to experimental kinetic data, the rate constants were estimated. It was found that the rate constants could be treated constant except the initiation rate constant k₁ within investigated conditions. In addition, the confidence intervals of each parameter estimated with 95% confidence level were reasonably small compared to the corresponding rate constants.

    The model fitting results demonstrated that the agreement between the model prediction and experiments was satisfactory. It should be notable that in our model, the addition reaction of hydrocarbon free radical to oxygen was considered. According to the model formulation, the apparent rate constant concerning the addition reaction of free radical to oxygen, i.e. k₆ should have a linear relationship with oxygen partial pressure. The correlation results showed that there was a good linearity between k₆ and oxygen partial pressure, which verified the validation of the kinetic model developed in this work.   

    The well-mixed reactor (WMR) model was established for the process optimization calculation. Various process optimization strategies were put forward, such as single WMR, multi WMRs in series with different volumes, and multi WMRs in series with different operating temperatures. It was concluded that the highest sBBHP yield could be reached when the multi WMRs in series, and a temperature rise sequence in one reactor by another were used.