According to statistics, more than 90% of phenol in the world is produced by cumene method. The process steps are as follows: benzene reacts with propylene to obtain cumene; Cumene is oxidized by oxygen or air to produce cumene hydroperoxide (CHP); CHP is decomposed into phenol and acetone. The phenol method of KBR company is the most typical method. Besides producing high-purity phenol and acetone from cumene, α -methylstyrene (AMS) and acetophenone (AP) were also recovered. In this process, the efficiency of air oxidation of cumene to CHP can reach more than 95%, and CHP can be concentrated and decomposed into phenol and acetone under the action of acid catalyst, and the yield can reach more than 99%. AMS is hydrogenated to cumene for cyclic oxidation or recovery. Using AMS hydrogenation process, 1.3 1 ton cumene can produce 1 ton phenol and 0.6 1.05 ton acetone. KBR phenol process has the characteristics of low energy consumption, low raw material consumption, low production cost and low emission pollution. At present, 30 sets of production devices have been built in this process, and the total phenol production capacity exceeds 2.8 million tons/year. At the end of 1990s, Aristech Company of the United States and Shell Chemical Company built 6,543.8+10,000 tons/year and 225,000 tons/year devices respectively, and China Petrochemical Shanghai Gao Qiao Branch also introduced this process. The phenol produced by this method accounts for more than 50% of the world production capacity. ExxonMobil also developed a catalytic distillation technology to produce phenol from cumene hydroperoxide (CHP). The solid catalyst of zirconium, iron and tungsten oxide is used in the catalyst bed of this tower, and the conversion rate can reach 100%. The selectivity of phenol and acetone is high, while the amount of high-boiling impurities such as 4- cumylphenol, α -methylstyrene (AMS) dimer and tar is very small. The selectivity of this process to phenol is 89.5%, which is slightly lower than the traditional process with sulfuric acid as catalyst. The operating conditions of catalyst bed in the reactor are: 50~90, 34Kpa, liquid hourly space velocity 4h- 1. The selectivity of by-products α -methylstyrene and acetophenone was 9.7% and 0.8%, respectively. The catalytic distillation process effectively utilizes the reaction heat in the acetone distillation process, combines the reaction process with the distillation process, and reduces energy consumption and investment. Because the solid acid catalyst is used to replace the general sulfuric acid catalyst, the neutralization process of the product can be avoided.
Toluene-benzoic acid method firstly oxidizes toluene into benzoic acid in liquid phase, and then benzoic acid is converted into phenol. It has the advantages of wide sources of toluene raw materials and simple process.
At present, cumene method has the problem of co-production of a large amount of acetone (the yield ratio of acetone to phenol is 0.6: 1), and phenol needs to be refined and consumes energy. A one-step reaction method for direct oxidation of benzene to phenol was developed. Japanese researchers have developed a one-step method using precious metal catalysts. Solutia Company has developed a one-step method for direct catalytic oxidation of benzene to phenol using nitrous oxide as oxidant.
Recently, the National Institute of Advanced Industrial Science and Technology (AIST) of Japan has developed a one-step process to synthesize phenol from benzene, but the conventional process needs three steps to synthesize phenol from benzene and produces waste acid that needs to be buried. AIST process uses a reactor consisting of stainless steel outer tube and porous α -alumina inner tube. The key element is palladium membrane catalyst with the thickness of 1μm, which is coated on the outside of alumina tube by chemical vapor deposition. This membrane was jointly developed by AIST, Maruyama Petrochemical Company and NOK Company. The reactor was placed in a heating furnace and heated to 65438 050 ~ 250℃. Benzene and oxygen flow through the alumina inner tube, and hydrogen with a pressure of 0.2MPa passes along the outer side of the tube. Hydrogen is adsorbed on the membrane, dissociated and activated here, and then passes through the inner surface of alumina tube. The activated hydrogen traps oxygen molecules on the inner surface of the tube to generate active oxygen, which reacts with the double bond of benzene ring and generates phenol from benzene through benzene ring oxide. In the laboratory, when the conversion rate is lower than 3%, the selectivity of phenol is greater than 90%. When the conversion is 10%~ 15%, the selectivity is greater than 80%. The output of phenol is 1.5kg/HR/kg catalyst. With the improvement of the process, the conversion rate is expected to increase.