49 P P P e e e t t t r r r o o o l l l e e e u u u m m m & & & C C C o o o a a a l l l ISSN 1337-7027 Available online at www.vurup.sk/pc Petroleum & Coal 46 (3), 49-55, 2004 DIRECT HYDROXYLATION OF BENZENE TO PPHENOL Michal Bahidsky and Milan Hronec Slovak University of Technology Department of Organic Technology, 812 37 Bratislava, Slovak Republic, email: milan.hronec@stuba.sk Abstract Direct synthesis of phenol from benzene, which could replace the multistage cumene process, is an object of intensive research. We have studied the gas phase conversion of benzene to phenol over bimetallic hydroxyphosphates comprising calcium and copper. We have found that nitrous oxide, pro- duced in-situ from the catalytic oxidation of ammonia with air, enables selective hydroxylation of ben- zene. A reaction mechanism was proposed comprising nitrous oxide formation and phenyl radical reac- tion. Beside benzene also toluene, ethylbenzene and cumene were employed in this catalytic system and the products were identified. Keywords: hydroxylation, benzene, phenol, copper-calcium phosphate Introduction Several catalytic systems for the direct ben- zene hydroxylation to phenol in the gas phase have been designed. Benzene is se- lectively converted to phenol with hydrogen peroxide over Cu-Pd/SiO 2 [1,2] or Pt-VO x /SiO 2 [3] . Hydrogen peroxide is formed in-situ from a mixture of O 2 and H 2 in the presence of a catalyst and subsequently decomposed to hydroxyl radicals. More likely applicable is the process utilizing waste nitrous oxide as a selective oxidant. Nitrous oxide decomposes leaving so called active oxygen inside the pore system of ZSM 5 zeolites [4,5] . Benzene reacts directly with active oxygen forming phenol. The direct hydroxylation of benzene over calcium-copper phosphate was first reported by Matsuda and Kato [6] . We have examined this potential way for the direct hydroxylation of benzene with a mixture of ammonia and air. An optimal catalyst com- position and reaction conditions were deter- mined [7] . In this work, we have examined the influence of reaction mixture composition on the selectivity and product distribution em- ploying benzene and substituted aromatics. Experimental The hydroxylation reaction was carried out in a 75 cm long stainless steel reactor with an internal diameter of 10 mm. The catalyst bed consisted of 2g of catalyst with a particle size of 0,3-0,6 mm placed on a stainless steel net. Benzene, water or an aqueous solution of ammonia were fed by linear dozers to the reactor. The flow of gases was regulated by mass flow controllers. The reaction products were led to a cold trap. The condensed products were taken in desired time inter- vals, homogenised with methanol and ana- lysed by a gas chromatograph equipped with