Amination And Hydroxylation Of Benzene Using Non-thermal Plasma And Catalyst

Aniline and phenol are the important chemical raw materials. But there are many shortcomings in the traditional production process such as complex steps, harsh operating conditions, additional reagents and byproducts, environmental pollution and corrosion of equipments. The research workers have tried to make amino or hydroxyl group directly introduced into the benzene ring to get aniline or phenol, so that the multi-step reaction becomes one step, the atomic utilization is effectively improved, and the reaction byproducts are environmental friendly, which meet the concept of green chemistry and sustainable development. Therefore, how to achieve direct ammoniation and hydroxylation of benzene under mild conditions remains one of the major challenges faced by synthetic chemistry.Non-thermal equilibrium plasma processing technology is one kind of effective means of molecular activation, plasma can produce a large number of active particles and realize some reactions at atmospheric pressure which cannot or be difficult to react by the conventional method.It has many advantages, such as mild conditions, simple process, energy saving, low pollution, economic efficiency and so on. In this paper, dielectric barrier discharge plasma and catalyst were used to research amination and hydroxylation of benzene, the effects of input power, ration of raw materials, the temperature of reactor and other factors on the reaction were investigated under DBD plasma, the copper-based, nickel-based, cobalt-based and iron-based supported catalyst were made, the influence of catalyst type, active ingredient content and the amount of catalyst on the reaction were discussed, the optimized experimental parameters and process were acquired, the reaction mechanism of amination and hydroxylation were initially speculated.The flatbed dielectric barrier discharge plasma reactor was used, amination and hydroxylation reagents was ammonia water and hydrogen peroxide respectively. The raw materials were carried with argon and into the plasma reactor, the products were collected and analyzed at the outlet of reactor, the technological process is simple and easy to achieve. The qualitative analysis of product was obtained by the method of mass spectrometry combined with standard chromatogram, the main products of amination reaction are aniline, phenol, 1,5-pentanediol, biphenyl aminophenol and other organic matter; the main product hydroxylation reaction was phenol and fewer byproducts.The cobalt-based, nickel-based, iron-based and copper-based catalysts in the experiment were prepared by ultrasound-assisted impregnation.The catalyst was screened from them in favor of the amination or hydroxylation reaction under plasma. The surface structure, specific surface area and pore volume of the catalyst were analyzed by the scanning electron microscope and specific surface area analyzer, respectively. The specific surface area, pore volume,and average pore diameter, in order, are 264.474 m2/g, 0.435 cm3/g, and 24.714 nm.Amination of benzene was investigated in the combination of plasma and catalyst, the preferred conditions of the process are:discharge gap is 13.40 mm, volume percentage composition of ammonia is 50%, the temperature of benzene is 40℃, the temperature of plasma reactor is 40℃, the input power is 52.5W. The preferred metal active component is cobalt, the catalyst carrier is Si O2, the concentration of cobalt acetate solution is 0.25mol/L,and catalyst loading amount is 0.25 g. Under the appropriate technological conditions, the selectivity of aniline is 73.74%.The repeat performance of catalyst was detected in this condition, the result showed that the catalyst still retain some catalytic activity after repeated use. It was found the addition of oxidizing agent is not conducive to amination reaction in the reaction system.The hydroxylation behavior of benzene were studied in the presence of plasma, the orthogonal test of 5 factors and 4 levels was done to optimize the process parameters, the primary and secondary order of all factors was determined, that is:hydrogen peroxide temperature> benzene temperature> hydrogen peroxide content of> plasma reactor temperature> input power; the best combination is: input power 42.5W, benzene temeperature 25℃, hydrogen peroxide temperature 40℃, reactor temperature 50℃, hydrogen peroxide content is 50%. Under the condition of optimal combination, the selectivity of phenol reaches up to 93.26%.It is found that home-made catalysts have counter catalysis for hydroxylation reaction of benzene.The amination and hydroxylation reaction mechanism of benzene were discussed under the condition of plasma. It is found that both reaction courses were similar, including free radical generation stage and the reaction stage. The reaction schemes of radicals include three main types: combining with each other to form intermediate product, aniline, phenol or other byproducts; forming more free radicals through the split of covalent bonds, the separation of bonding electrons and the exchange of electron pair; producing a large amount of mall molecules by completely oxidized of fragments.