Nippon Shokubai Kagaku Kogyo Co., Ltd.

Youjirou Takahashi

Ikuo Kurimoto

Yoshiyuki Nakanishi

Shigemi Osaka

Shinichi Uchida

Yoji Akazawa

Toshimasa Kushihara

Junichi Toyoda

Hisashi Yoshikawa

An improved process for producing maleic anhydride which comprises catalytically oxidizing benzene with a molecular oxygen-containing gas in the vapor phase in a multitubular heat-exchanger-type reactor. The process is characterized in that

Process for producing maleic anhydride

In a method for the preparation of pyromellitic acid or its anhydride by catalytic vapor phase oxidation of a tetra-C.sub.1 -C.sub.4 -alkylbenzene using a catalyst comprising catalytically active material composed of 1 to 20 parts by weight of V.sub.2 O.sub.5, 99 to 80 parts by weight of TiO.sub.2 and/or SnO.sub.2 and/or ZrO.sub.2, and per one hundred parts by weight of V.sub.2 O.sub.5, TiO.sub.2 and/or SnO.sub.2 and/or ZrO.sub.2 0.02 to 10 parts by weight, calculated as P.sub.2 O.sub.5, of a phosphorus compound, 0.01 to 5 parts by weight, calculated as Nb.sub.2 O.sub.5, of a niobium compound, 0 to 1.2 parts by weight, calculated as oxide, of at least one metal selected from the group consisting of potassium, cesium, rubidium and thallium, and 0 to 10 parts by weight, calculated as Sb.sub.2 O.sub.3, of an antimony compound, and an inert carrier supporting said catalytically active material thereon, the improvement in which said catalyst is divided into at least two layers, a layer on the gas inlet side and a layer on the gas outlet side, and (i) the content of potassium, cesium, rubidium or thallium is higher in the catalyst layer on the gas inlet side than in the catalyst layer on the gas outlet side, or (ii) the content of the phosphorus compound is lower in the catalyst layer on the gas inlet side than in the catalyst layer on the gas outlet side, or (iii) the surface area of TiO.sub.2 and/or SnO.sub.2 and/or ZrO.sub.2 is lower in the catalyst layer on the gas inlet side than in the catalyst layer on the gas outlet side.

Method for preparing pyromellitic acid and/or pyromellitic anhydride

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Himeji, Japan

Youjirou Takahashi