Study On Synthesis Of High Quality O-cresol By Selective Alkylation Of Phenol With Methanol Catalyzed By ?-Fe₂O₃

O-Cresol made in China has long been produced by cresol coking and cresol sulfonation,which fail to meet the requirements of high-end fine chemical products,such as synthetic resins used in electronic packaging materials,and pharmaceutical intermediates.Thus,the supply of high-quality o-cresol(purity ? 99.5%)relies on imports and its production technology is tightly blocked by multinational companies.For this reason,the achievements from existing national key technicalprojects have not been successfully applied into the industry.Thus,it is significant to develop a set of production processes with independent intellectual property rights that integrate catalyst,synthesis process,andphenol wastewater clean-treatment.In this work,with industrial phenoland industrial methanol as raw materials,and self-developed a-Fe2O3 as catalyst,we investigated the selective o-cresol synthesis from gas-phase phenol-methanol alkylation on a fixed-bed and a tube array reactor.The main innovations are listed below.Firstly,the effects of preparation process on the catalytic performance were investigated in detail.By analyzing the effects of preparation factors on catalytic performances,we invented a coprecipitation-microwave drying combined technique for the preparation of an efficient and eco-friendly nanoscale catalyst ?-Fe2O3 with high ortho-selectivity.The surface properties,morphology,active centers of?-Fe2O3,and cause of inactivation were characterized via X-ray diffractometry(XRD),transmission electron microscopy(TEM),NH3-temperature programmed desorption(NH3-TPD),Brunauer-Emmett-Teller method(BET),differential thermal analysis(DTA),and X-ray photoelectron spectroscopy(XPS).These characterizations would largely reveal the inherent structural advantages that contribute to the high activity,selectivity and long lifecycle of?-Fe2O3.Under the optimized process conditions,the per-pass phenol conversion rate is up to 67.0%,o-cresol selectivity is above 90%,and the total selectivity of o-cresol and 2,6-xylenol reaches 99.7%.This catalyst is superior with high repeatability and reproducibility,and after 2000 h of continuous run,it still maintains high catalytic activity.Secondly,the dynamic behaviors of ?-Fe2O3-catalyzed phenol-methanol alkylation and the thermal hazard of this process were systematically investigated.Results show the phenol conversion at 300-350 ? is a 1-order reaction and its apparent activation energy Ea is calculated by the Arrhenius equation to be 233.1 kJ/mol,and the pre-exponential factor lnA0 is 46.3.Then the kinetic equation of overall reaction for o-cresol synthesis from gas-phase phenol-methanol alkylation was proposed for the first time and fully validated via experiments.Moreover,the dynamic rules of methanol decomposition were determined,thus providing sufficient data for the safety design of this process.The guiding effect of scientific theory study on process innovations was further strengthened from the perspectives of reaction kinetics and thermodynamics.Thirdly,the scale-up test of o-cresol production on fixed-bed wit 5L scale,and single tube array reactor whole-flow pilot test were conducted comprehensively.The scaling-up effect and thermal effect of pilot scale reaction,and the activity,selectivity,stability and reproducibility of the catalyst were investigated to further validate the feasibility and technical reliability of this o-cresol synthesis process.These findings provide with reliable basic data for industrial design and offer theoretical guidance and operation basis for industrial production.Last but not least,the causes for phenol coking during industrial-scale separation and the situation of industrial applications were adequately investigated.The main causes for the coupling reaction of phenols to form heavy phenols or coking were attributed to iron powder catalysis and air oxygen.Results show a 15000 ton/year o-cresol industrial installation worked successfully on its first start-up,and the catalyst exhibited high performance and stability.Under the optimal process conditions,the per-pass phenol conversion rate is up to 50%,the o-cresol selectivity is maintained at 90%,the total selectivity of o-cresol and 2,6-xylenol exceeds 99.5%,the per-pass service life of the catalyst is above 3000 h,and the product purity is stably maintained above 99.8%.This set of process techniques fills up the technical gaps in the o-cresol synthesis for fine chemical industry in China.The product examination and industrial application of this process were tested by Sinopec Baling Petrochemical Company,South Asia Plastics Corporation of Formosa Plastics Group,and Japan Asahi Kasei Corporation.The product shows superior quality to imported products,and fully satisfies the application requirements for high-end fine chemicals in China.