Research On Novel Catalyst And Industrial Technology For Hydroxylation Of Phenol

Dihydroxybenzene, including catechol and hydroquinone, are important chemical intermediates widely used in petroleum chemical industry, medicine, pesticide, dyestuff, perfume, rubber, etc. With their large market potential, their derivative products have great and important applications in the above fields.Catechol was prepared by hydrolysis of o-chlorophenol and hydroquinone was prepared by oxidation of phenylamine in traditional process. And those were gradually eliminated because of serious environment pollution and poor production capacity. Among the current synthetic routes, hydroxylation of phenol by hydrogen peroxide featured with atom economy reaction was considered as the most efficient and prospective process. In 1980's, the 10,000 ton-class industrial apparatus had been established abroad catalyzed by inorganic acid/salts. But many problems were not solved such as the catalyst's separation from reaction mixture, low phenol conversion. Until now, study on novel catalyst and technology were the hot spots all over the world. In China, breaking through the foreign country's technology restrict and grasping our own knowledge property right of manufacture technology of dihydroxybenzene became the attractive topic in fine chemical engineering fields in order to catch up with foreign country's level. Although a 2000 ton-class industrial apparatus was established inland, great disparity still existed compared with foreign apparatus because of the technological reason. There are abundant resources of low concentration (30%) of hydrogen peroxide inland. Hydroxylation of phenol by aqueous hydrogen peroxide was undoubtedly the most efficient and prospective route. This paper emphasized on novel catalyst with industrial economic benefit, operational conditions, kinetics and reaction apparatus. It paved the way for the domestic production of industrial dihydroxybenzene manufacture technology and apparatus.As everyone knows, the development of catalyst is the key point of phenol/H2O2 hydroxylation . There were hundreds of catalysts from the first single inorganic acid (salts) to current heterogeneous catalysts such as metallic oxide, heteroatom molecular sieve and heteropoly acid catalyst. The shortcoming of inorganic acid (salts)catalyst lies in low conversion of phenol, insecurity of operation resulted from application of high concentration hydrogen peroxide solution, difficulty of recover of catalyst and hard environmental pollution. And industrial application of molecular sieve catalyst represented by TS-1 was greatly limited because of complexity of preparation,, stiff price, high consumption and long reaction time. In this paper, a series of ferrite acid salts were prepared by co-precipitation. And spinel Fe-Cu catalyst was selected out because of its high catalytic activity for phenol/H2O2 hydroxylation. Analysis and characterization on structure of these catalysts were taken. Influence of different metal element selection and composition of core element on phenol hydroxylation was studied. It was concluded that the optimal ferrous source was Fe(NO3)3 · 9H2O, the optimal copper source was Cu(CH3COO)2 · H2O and the optimal Fe/Cu molar ratio was 7.The foundation of confirming industrial operational conditions is optimization of process conditions for hydroxylation of phenol. The influence of operational condition on phenol/FbC^ hydroxylation with self-made Fe-Cu catalyst was discussed in detail. The optimal process conditions were obtained that m(catalyst)/m(phenol)= l/100(wt.) with water as solvent, initial concentration of phenol was 25%, reaction temperature was 65 ℃, n(phenol)/n(H2O2)=2~3 and reaction time was 1 hour. Under the above operational conditions, the conversion of phenol was about 20~25%, the total selectivity of dihydroxybenzene reached 90% and catechol/hydroquinone was about 1.5/1.The control of H2O2 concentration distribution was very important for improving conversion and selectivity of phenol hydroxylation during reaction course. The influence of H2O2 concentration distribution on conversion of reactant, selectivity and yield of product was quantitatively studied through changing adding rate and adding mode of H2O2. And the result showed that more H2O2 continuously adding sections were superior to single adding section. More sections, higher effective use ration of hydrogen peroxide and conversion of phenol and yield of dihydroxybenzene. Especially with 6 adding sections of H2O2, phenol conversion was 47% which was approximate to phenol theoretical conversion, H2O2 effective use ratio reached 80%and dihydroxybenzene yield was about 40%. The result was superior to that of TS-1 and/or magnesium ferrite catalyst. On this basis, the experiments about 8 times recycling of Fe-Cu catalyst proved that Fe-Cu had excellent catalytic activity and recycling effect. It was proved that optimal result with optimization experiment of process conditions could be repeated by phenol hydroxylation with Fe-Cu catalyst through three 50 times-scale parallel experiments. All these optimized data about operational condition parameters were very important for the further industry application.The research on reaction kinetics of phenol hydroxylation with ferrite acid salts catalyst was a blank till now. However, the reaction kinetics could serve an important basis for amplification of industrial apparatus and optimization of operational conditions. A parallel-consecutive reaction network was proposed. The reactionmechanism was raised that dihydroxybenzene and tar were produced from phenol andOHH2O2 which adsorbed on the activation site of Fe-Cu catalyst, FeCu2+. And the reaction kinetics model was derived including consumption rate of phenol andproduction rate of dihydroxybenzene. The parameters of reaction kinetics with Fe-Cu, Fe-Cu/Al2O3 catalysts were obtained fitted by kinetics data from CSTR experiments. The calculated value was in good agreement with experimental data.The simulation experiments were carried out in four series reactors. And the influences of different operational conditions on phenol hydroxylation were observed. The optimal operational c onditions w ere obtained that W/FAo=0.235g c at./ (mol/h), the temperature of 1, 2 reactor was 60℃ and 3,4 reactor was 70℃, H2O2 adding rate was 3.6ml/h in reactor 1 and 1.2ml/h in reactor 2. The conversion of phenol was 21.7% and total selectivity of dihydroxybenzene was 87.1% under the above conditions.