Oxidation reactions Alkylation Application of copper chromite catalysts 1 Commercial application

method retained a spinel structure evidenced by the large amount of Cu 2+ species. In hydrogenolysis reactions, the precipitated catalyst showed a higher catalytic activity than the impregnated catalyst. Thus, the reduced copper chromite spinel structure, which constitutes a single phase, appears to be responsible for the high catalytic activity in the hydrogenolysis of glycerol to propylene glycol. Copper chromite catalysts are useful for a variety of chemical reactions in the processing of oleo chemical feedstocks. Major oleo chemical applications include hydrogenolysis of fatty esters to fatty alcohols including both methyl ester and wax ester processes, alkylation of alcohols with amines and amination of fatty alcohols. The catalysts have unique performance for selective hydrogenation of vegetable oils and can be used in the conversion of bio renewable feedstocks into industrial chemicals. Dovell and Greenfield [113] used copper chromite as a catalyst for the preparation of alkylaryl secondary amines by the reductive alkylation of a primary aromatic amine with an aliphatic ketone in the presence of hydrogen eqn. 14. ArNH 2 + ORCR′ + H 2 → ArNHRCHR′ + H 2 O 14 The noble metals cause both nuclear hydrogenation and formation of alkylamines [114] by hydrogenolysis of the carbon nitrogen bond between the alkyl group and the nitrogen atom in the secondary amine i.e.: ArNHR + H 2 → ArH + RNH 2 . Copper chromite catalysts avoid these undesirable side reactions, but a large amount of ketone is reduced to the corresponding alcohol. Fatty alcohols are an important raw material for surfactants as well as constitute one of the largest groups within the oleochemicals. The fraction of natural fatty alcohols, i.e. fatty alcohols based on natural fats and oils, is steadily growing [115]. The fatty alcohols can be produced by hydrogenation of fatty acid methyl esters, a product from natural abundant coconut and palm kernel oils, to form high alcohol in the presence of a CuCr 2 O 4 catalyst [116]. The hydrogenation of methyl esters and of fatty acids to form fatty alcohols is given by the following general eqns. 15 and 16 respectively: CuCr RCOOCH + 2H 2 ↔ RCH 2 OH + CH 3 OH 15 Methyl ester Fatty alcohol CuCr RCOOH + 2H 2 ↔ RCH 2 OH + H 2 O 16 Fatty acid Fatty alcohol Copper chromite catalyst also converts any unsaturated carbon double bonds so that only saturated fatty alcohols are formed [87]. The hydrogenation process is carried out at 25 30 MPa and a temperature of 250 300 C in a tubular column.

2.1.4 Oxidation reactions

Oxidation of ethylbenzene liquid phase with t butyl hydroperoxide TBHP as an oxidant is feasible over nickel substituted copper chromite catalysts [4]. Effective utilization of ethylbenzene, available in the xylene stream of the petrochemical industry, for more value added products is an interesting option. Oxidation of ethylbenzene is of much importance for the production of the aromatic ketone, acetophenone, one of the key products in the industries. It is used as a component of perfumes and as an intermediate for the manufacture of pharmaceuticals, resins, alcohols and tear gas. The oxidation pathways of ethylbenzene are presented in fig. 6. Benzaldehyde is used in perfumery and pharmaceutical industries. Choudhary et al [117] prepared benzaldehyde in liquid phase oxidation of benzyl alcohol by tert butyl hydroperoxide using Cu Cr containing layered double hydroxides andor mixed hydroxides selectively. The reaction is given by eqn. 17: C 6 H 5 CH 2 OH + CH 3 3 COOH → C 6 H 5 CHO + CH 3 C OH + H 2 O 17 George and Sugunan [118] prepared spinel system with the composition of [Cu 1 x Zn x Cr 2 O 4 ] by Copyright © 2011, BCREC, ISSN 1978 2993 Fig. 6. Reaction scheme of ethylbenzene oxidation [117]. co precipitation method and reported cyclohexane oxidation at 273 K using TBHP as oxidant. 69.2 selectivity to cyclohexanol and cyclohexanone at 23 conversion of cyclohexane. Oxidation of cyclohexane is one of the important bulk processes for the production of polyamide fibres and plastics, such as nylon 6 and nylon 6,6.

2.1.5 Alkylation

Alkylation reactions are of great interest in the petrochemical industry as they lead to several commercially important alkyl aromatics. Cumene is one such alkyl aromatic produced by isopropylation of benzene. The commercial importance of cumene is felt by the world’s growing phenol demand, 90 of which is met through cumene. In the cumene route for the production of phenol, acetone is produced as a low value by product. Barman et al. [119] synthesised cumene with 100 selectivity, by reductive alkylation of benzene with acetone in the presence of a bifunctional catalyst system comprising a solid acid material, H mordenite HM, as alkylation functional and nano copper chromite as hydrogenation functional, eqn. 18. C 6 H 6 + CH 3 COCH 3 + H 2 → C 6 H 5 CHCH 3 2 + H 2 O 18 Copper chromite has been reported as a catalyst for the reductive N alkylation of aniline with acetone [120,100]. Pillai [121] prepared different aliphatic secondary amines by reductive alkylation of methylamine and ethanolamine with carbonyl compounds over copper chromite catalyst. Almost 100 selectivity was observed in all cases. Under optimum conditions of reaction the yield of N isopropylaniline was 91 and that of N benzyl ethanolamine was 94.

2.1.6 Cyclization