| The production of phenol from cumene through the hydroperoxide is one of the main industrial processes of phenol which involves the following steps:oxidation of cumene to cumene hydroperoxide(CHP) in presence of alkali solutions such as NaOH;acid cleavage of CHP to phenol and acetone. Compared with the traditional processes,peroxidation process is featured by low pollution and 100%utilization of reactant atoms.The oxidation process includes two main problems which are low reaction rate and low selectivity of hydroperoxides.Thus,it is difficult to apply the oxidation process to produce diphenols.The key point is to develop new catalysts which can increase the yield of isopropyl-benezene hydroperoxides.In this dissertation,cumene and m-diisopropylbenzene were chosen as the main subject and the catalysts for oxidation as well as the mechanism were investigated.The analysis of oxidation products of cumene and m-diisopropylbenzene (DIPB) was performed on the high performance liquid chromatography (HPLC).Under the condition that using Intersil SIL-100 A chromatography column,5μm×4.6 mm×250 mm,the hexane-isopropyl alcohol mixture as mobile phase(volume ratio 95:5),flow rate 1.0 mL/min at room temperature and with UV detection at 257 nm,the products were separated well with relative short operation period and the precise analysis results were obtained.Qualitative analysis of the oxidation products was established on the base of LC-MS.The sequence of the oxidation products in HPLC chromatography was as followed:DIPB, 1-acetyl-3-isopropyl-benzene(MKT),1,3-diisopropylbenzene monohydroperoxide (MHP),1-isopropyl-3-(2-hydroxy-2-propyl)-benzene(MCL), 1,3-diisopropylbenzene dihydroperoxides(DHP),1-acetyl-3-(2-hydroperoxy -2-propyl)-benzene(KHP),1-(2-Hydroperoxy-2-propyl)-3-(2-hydroxy -2-propyl)-benzene(HHP),1-acetyl-3-(2-hydroxy-2-propyl)-benzene (KCL) and 1,3-Bis(2-propanol)benzene(DCL).The catalysts MxOy-MgO(M=Ni,Fe,Co,Cu) were prepared by co-precipitation method,and then characterized by X-ray diffraction (XRD),H2-temperature programmed reduction(H2-TPR) and X-ray photoelectron spectroscopy(XPS).The activities of the catalysts were followed in the order 10%Fe2O3-MgO＜10%NiO-MgO＜10%CoO-MgO＜10%CuO-MgO.The reaction under the catalysis of 10%Fe2O3-MgO stoped quickly.It may be concluded that the Fe2O3/MgO sites,localized on Mg atoms,are acidic(presumably Lewis-type) in nature and that these results provide evidence for the heterolytic decay of the hydroperoxide to phenol and acetone.It was found that the activity of the catalysts had relationship with their redox behaviour.The temperature of the reduced peak in H2-TPR of different catalysts increased in the followed order 10%CuO-MgO＜10%CoO-MgO＜10%NiO-MgO.Among the catalysts, the activity of CuO-MgO was the best.In order to study the performance of CuO-MgO,CuO-MgO catalysts with different compositions were prepared by co-precipitation method.The conversion of cumene increased with increase of the content of Cu.But the selectivity of CHP decreased with increase of the content of Cu.The reults of DIPB oxidation using 10%CuO-MgO as catalyst were better than that of NaOH.In order to improve the performance of CuO-MgO,the performance of rare metal oxide CeO2 was studyed.The activity of CeO2-MgO was affected by the content of Ce.With the increase of the content of Ce,the conversion of IPB firstly increased and then decreased.The optimal contnet of ce existed for the cativity.The active sites on the MgO are benificial for the oxidation.The active sites may be covered by CeO2 when the content of CeO2 was large.When the content of CeO2 did not reach the optimal value, the interaction of CeO2 and MgO would be benificial for the oxidation.The selectivity of CHP was improved by adding Ce to CuO-MgO catalyst.The mechanisms of the metal oxides were investigated.It was found by IR that the hydrogen atom at the position of the tertiary C of cumene may be adsorbed on the site of O2- in MgO.Due to the interaction of the hydrogen atom and O2-,the tertiary C-H bond of cumene was weakened. Thus,the reaction progressed at a faster rate.In order to understand of role of the Cu ion,CuO-MgO was prepared by different methods.It was found that the acticities of CuO-MgO by co-precipitation and incipient wetness impregnation method were different.By studying the H2-TPR property,the activity had relationship with the redox behaviour.The hydroperoxide may be decomposed by Cu2+ to form alkoxyl free radicals,which increased the rate of the whole reaction.In the meanwhile,1-butyl-3-methylimidazolium hydroxide([bmim]OH) was studyed for the oxidation of cumene and DIPB.The oxidation reaction was speeded up by[bmim]OH.After reaction for 45 h in the presence of NaOH,the conversion of DIPB was 85%,the yield of DHP and the total yield of DHP,HHP,DCL were 27%and 34%,respectively.Under the same condition using[bmim]OH as catalyst,the conversion of DIPB was 99%,the yield of DHP and the total yield of DHP,HHP,DCL were 29% and 83%.Finally,the influence of the cation and anion of different ionic liquids on the oxidation was studyed.As for the 1,3-alkyl substituted imidazolium ionic liquids,CHP selectivity increased in the order[bmim]Cl＜[bmim]Br＜[bmim]BF4＜[bmim]OH.The CHP could be induced to decompose by the ionic liquids with high polarity.Three types of ionic liquids(Ils), namely imidazolium-based ILs,pyridinium-based ILs and pyrrolidinium-based ILs,were chosen to study the effect of the acidic hydrogen atoms of the ionic liquids.The CHP selectivity increased in the order[bmim]Br＜[bdmim]Br≈[bPy]Br＜[MP4]Br.The more acidic hydrogen atoms the ionic liquid possessed,the lower the CHP selectivity was.
|
PDF Full Text Request