Vanadium catalysts operation

Hu and coworker developed the silica, titania, ceria, and y-alumina supported vanadium catalyst, which shown unique reactivity for the direct amination of toluene with hydroxylamine hydrochloride, over 50 % total yield of toluidines was obtained on the y-alumina supported vanadium catalyst operated at optimal conditions [87]. They also investigated a sodium metavanadate catalyzed one-step amination of benzene to aniline with hydroxylamine [88], The reaction became more efficient in the presence of oxygen. A free-radical mechanism was proposed based on the results of EPR, NMR, and UV-Vis characterization. Moreover, the catalytic activity of a series of vanadium complexes with N,0- or 0,0-ligands for the liquid-phase direct amination of benzene with hydroxylamine to aniline has been investigated [89]. [VO(OAc>2] was proved to be the most active catalyst for the amination because of its relatively greater electrophilicity and smaller steric hindrance of ligand. 

Catalysts. In industrial practice the composition of catalysts are usuaUy very complex. Tellurium is used in catalysts as a promoter or stmctural component (84). The catalysts are used to promote such diverse reactions as oxidation, ammoxidation, hydrogenation, dehydrogenation, halogenation, dehalogenation, and phenol condensation (85—87). Tellurium is added as a passivation promoter to nickel, iron, and vanadium catalysts. A cerium teUurium molybdate catalyst has successfliUy been used in a commercial operation for the ammoxidation of propylene to acrylonitrile (88). 

As opposed to the problems associated with the formation of sequential block copolymers, the preparation of relatively random copolymers is much easier and the provision of polyethylenes having a controlled degree of branching by copolymerization with propylene and butene is now a well-established commercial operation. When ethylene and propylene are employed in approximately equal proportions the ethylene-propylene rubbers are obtained. For this purpose strictly random copolymers are desirable, for which soluble vanadium catalysts are often preferred (20). With TiCls-based catalyst the propylene monomer molecule prefers to add to a propylene end unit rather than to an ethylene end unit (and vice versa). This tends to produce nonrandom blocky copolymers. Thus a recent paper by Coover ef al. (21) selects as catalysts formulations which maximize this tendency and achieve the preparation of block copolymers in a TiCl3/AlEt2Cl catalyst system in the presence of butene and propylene together. 

Although air oxidation of the cyclohexanone-cyclohexanol mixtures on a Cu-Mn catalyst in acetic acid [140] is possible, the principal commercial operations entail oxidation with nitric acid. The reaction is usually carried out at 60 80°C and pressures of 0.1 to 0.4 MPa, employing 50-60% nitric acid and a copper-vanadium catalyst containing between 0.1 and 0.5% Cu and 0.1 and 0.2% V [141]. The yields of adipic acid are in the range of 90-96%. The main by-products are succinic acid and glutaric acid. Their concentration generally increases as the purity of the feed mixture decreases. The adipic acid is isolated by crystallization and purified by recrystallization from water. 

The process was commercialized in 1976. A vanadium catalyst with Geldard group A/C characteristics is used. The catalyst is circulated between a reactor operating at 400°C and a reoxidizer operating at 427°C. The reactor operating pressure is not reported but is expected to be 1 to 2 atmosphere. Catalyst losses are kept to a minimum by the use of sintered metal filters (Fig. 18). 

H20(g) and H2S04(g) do not condense at the active operational temperature of the vanadium catalyst or in the subsequent heat exchanger, >300 °C, ensuring condensa-tion/corrosion problems do not occur in or after the catalyst beds. 

BASF Platinized asbestos produced by impregnating asbestos with platinic chloride solution followed by reduction with formaldehyde. Operated up to 10-12 years in several 10 20 cm layers. Contained 8-10% platinum. Tubular reactors were still designed for vanadium catalysts until 1950s. Agreement with Grillo up to 1898. 

A common feature of the new vanadium catalysts, including those used in sulfuric acid production, was the need to reduce pentavalent vanadium by reaction with hydrochloric or oxalic acid solutions before the active compounds that improved catalyst performance were formed. It was well known, especially from sulfuric acid catalysts, that tetravalent vanadium also formed during operation. 

Simulation of catalytic cycles of three vanadium catalysts in the hydroxylation of benzene with HP in acetonitrile, at the B3LYP(IEF-PCM)//B3LYP/6-31 lG(2r/,2p) level, indicated that the main form of the operative catalyst is the binuclear vanadium species. 

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