Abstract: This invention relates to the vapor-phase oxidation of hydrocarbons by passing a gaseous mixture comprising of a molecular oxygen-containing gas and hydrocarbons which may contain substituents to a fixed bed of catalyst and provides a process for vapor-phase oxidation to be effected by passing a gaseous mixture of raw materials to a fixed bed of catalyst in which the void ratio of the catalyst layers increases by stages in one step or more from upstream downward in the flow of the gaseous mixture of raw materials. For example, the process can oxidize in vapor phase such hydrocarbons as naphthalene, xylene, benzene, toluene, durene, butene, acenaphthene, anthracene, indene and their derivatives in high yields with high productivity. Moreover, the process can prepare phthalic anhydride in high yields with high productivity by the vapor-phase oxidation of naphthalene or ortho-xylene.

Abstract: Pyromellitic dianhydride, useful as raw material for the manufacture of polyimides, is prepared in high yield and purity by the reaction of benzene derivatives such as ethylbenzene, diethylbenzenes, and triethylbenzenes with an ethylating agent in the presence of a Friedel-Crafts catalyst, the separation of tetraethylbenzenes from the reaction products by distillation, the separation of 1,2,4,5-tetraethylbenzene from other tetraethyl benzenes by differential centrifugal precipitation at -10 to -30 degrees Celsius, and the catalytic vapor-phase oxidation of tetraethyl benzenes, using a catalyst containing vanadium pentoxide and titanium dioxide.

Abstract: A method for the manufacture of phthalic anhydride by the catalytic oxidation of naphthlene and/or ortho-xylene which comprises contacting a mixed gas containing naphthalene and/or ortho-xylene and a molecular oxygen-containing gas with a catalyst bed comprising a first catalyst packed on the upstream side of the flow of mixed gas and a second catalyst packed on the downstream side of the flow, wherein the first catalyst has carried on a nonporous inactive carrier a catalytically active component composed of 90 to 67% by weight of titanium dioxide, 8 to 30% by weight of vanadium pentoxide, 2 to 5% by weight of a cesium compound and 0.11 to 0.2 of cesium compound/vanadium pentoxide (molar ratio) (calculated as Cs.sub.2 SO.sub.4), and the second catalyst has carried on the nonporous inactive carrier a catalytically active component composed of 94 to 67% by weight of titanium dioxide, 5 to 30% by weight of vanadium pentoxide and not more than 0.

Abstract: A method for the manufacture of phthalic anhydride by the catalytic oxidation of naphthelene or ortho-xylene which comprises contacting a mixed gas consisting of naphthalene or ortho-xylene and a molecular oxygen-containing gas with a catalyst bed comprising a first catalyst packed on the upstream side of the flow of mixed gas and a second catalyst packed on the down-stream side of the flow, wherein the first catalyst has carried on a nonporous inactive carrier a catalytically active component composed of 67 to 90% by weight of titanium dioxide, 9 to 30% by weight of vanadium pentoxide and 0.7 to 3% by weight of a rubidium compound (calculated as Rb.sub.2 SO.sub.4), and the second catalyst has carried on the nonporous inactive carrier a catalytically active component composed of 67 to 94% by weight of titanium dioxide, 5 to 30% by weight of vanadium pentoxide and at least one member selected from the group consisting of 0.1 to 1% by weight of a tin compound (calculated as SnO.sub.2) and 0.