Nippon Shokubai Co., Ltd.

Nippon Shokubai Kagaku Kogyo Co., Ltd.

Yoji Akazawa

Kazuhiko Sakamoto

Masatoshi Ueoka

Masao Baba

Yoshiyuki Nakanishi

Takahiro Takeda

Ikuo Kurimoto

Takehiko Suzuki

Shinichi Uchida

Noriaki Ikeda

Youjirou Takahashi

Hiroaki Tanaka

Hisashi Yoshikawa

Disclosed herein is a method for inhibiting polymerizable (meth)acrylic acid and esters thereof from polymerizing during their production, transportation and storage by using as the inhibitor N-oxyl compound and more than one compound selected from the group consisting of manganese salt compound, copper salt compound, 2,2,6,6,-tetramethylpiperidine compound and nitroso compound. The N-oxyl compound is one or more kinds selected from 2,2,6,6,-tetramethylpiperidinooxyl, 4-hydroxy-2,2,6,6,-tetramethylpiperidinooxyl and 4,4',4'-tris-(2,2,6,6,-tetramethylpiperidinooxyl)phosphite. The combined use of the inhibitors provides superior inhibiting effect to use alone.

Method for inhibiting polymerization of (meth) acrylic acid and esters

Disclosed herein is a method for inhibiting polymerizable (meth)acrylic acid and esters thereof from polymerizing during their production and storage by using as the inhibitor N-oxyl compound, phenol compound, and phenothiazine compound in combination with one another. The combined use of the three inhibitors provides superior inhibiting effect to use alone alone or in pairs.

A process for producing acrylic acid is described, which process comprising providing a mixed gas of acrylic acid and by-products produced by catalytic gas phase oxidation of propylene and/or acrolein, contacting the mixed gas with water to obtain an aqueous solution, and adding an azeotrope solvent to the aqueous solution for distillation to obtain a mixture of the by-products, water and the azeotrope solvent from a tower top and acrylic acid from a tower bottom. Highly pure acrylic acid is obtained by using, as the azeotrope solvent, a mixed solvent of solvent A selected from diethyl ketone, methyl propyl ketone, methyl isobutyl ketone, methyl-tert-butyl ketone, n-propyl acetate and mixtures thereof and solvent B selected from toluene, heptane, methyl cyclohexane and mixtures thereof.

Process for purification of acrylic acid

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

A catalyst for the production of phthalic anhydride by the catalytic vapor-phase oxidation of o-xylene or naphthalene with molecular oxygen, said catalyst comprising a catalytically active material composed of 1 to 20 parts by weight of V.sub.2 O.sub.5 of vanadium oxide and 99 to 80 parts by weight as TiO.sub.2 of anatase-type titanium oxide being porous and having a particle diameter substantially of 0.4 to 0.7 micron and a specific surface area of 10 to 60 m.sup.2 /g, and per 100 parts by weight of the sum of these two components, 0.01 to 1 part by weight as Nb.sub.2 O.sub.5 of niobium, 0.05 to 1.2 parts by weight as oxide of potassium, cesium, rubidium or thallium, 0.2 to 1.2 parts by weight as P.sub.2 O.sub.5 of phosphorus and 0.5 to 10 parts by weight as Sb.sub.2 O.sub.3 of antimony, said catalytically active material being supported on a porous carrier in an amount of 3 to 200 g/100 cc of carrier.

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Himeji, Japan

Yoji Akazawa