Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Patent
1991-10-31
1993-08-24
Dees, Jose G.
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
562545, C07C 5116
Patent
active
052391159
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a method for producing methacrylic acid, and more specifically to a method for producing methacrylic acid by conducting a catalytic gas phase oxidative reaction of methacrolein by the use of a catalyst containing divanadyl pyrophosphate as an active ingredient.
BACKGROUND ART
Heteropoly-acids such as molybdophosphoric acid and molybdovanadophosphoric acid are known as catalysts used for catalytic gas phase oxidative reactions of methacrolein. However, said heteropoly-acids are thermally unstable and liable to deteriorate. Although an alkali metal or the like can be added to a heteropoly-acid to form an alkali metal salt which has improved thermal resistance, the alkali metal salt exhibits only insufficient catalytic activity and its use results in inferior redox efficiency since catalytic activity for methacrolein oxidation rigidly derives only from free heteropoly-acid.
DISCLOSURE OF THE INVENTION
This invention was achieved by perceiving the above circumstances and its object is to provide a method for producing methacrylic acid by the use of a catalyst free from the above inconveniences and exhibiting catalytic activity for the catalytic gas phase oxidative reaction of methacrolein.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
After intensive researches to develop a catalyst other than catalysts consisting of heteropoly-acids or their salts and having inferior thermal resistance which has activity for the catalytic gas phase reaction of methacrolein, selectivity for methacrylic acid and superior thermal resistance, the inventor found that vanadium-phosphoric acid complex compounds exhibit a superior catalytic activity in the gas phase oxidation of methacrolein and have favorable thermal resistance. Thus this invention was considered.
The above vanadium-phosphoric acid complex compounds consist of vanadyl phosphate which contains pentavalent vanadium and divanadyl pyrophosphate which contains tetravalent vanadium and each of these compounds can be further classified by their crystal structure into several groups. Since divanadyl pyrophosphate has a specially high activity although all these compounds exhibit catalytic activity for methacrolein oxidation, divanadyl pyrophosphate was determined to be the essential active ingredient in the catalyst used in this invention. Therefore, the catalyst used in this invention may consists of the above active ingredient alone as a matter of course or may contain both the above active ingredient and vanadyl phosphate.
A catalyst containing excess phosphorus in addition to divanadyl pyrophosphate or vanadyl phosphate which contains a chemical equivalent amount of phosphorus is more desirable for this invention because the catalytic activity is further increased and the catalyst is not easily oxidized. However, an excessive amount of phosphorus results in excessive oxidation of methacrolein and an increased amount of acetic acid produced as a by-product. Therefore the excess amount of phosphorus is preferably in the range of between 0.001 to 40 mole %, more preferably between 1 and 10 mole %, calculated in phosphoric acid equivalent.
A specially great effect can be achieved by using the aforementioned VO(H.sub.2 PO.sub.4).sub.2 for an excess of phosphorus in the catalyst. The above VO(H.sub.2 PO.sub.4).sub.2 can easily be produced, for example, by adding to isobutyl alcohol vanadium pentoxide in such an amount that the atomic ratio of phosphorus to vanadium becomes 2.00 and then reducing vanadium pentoxide by passing hydrogen chloride gas through the mixture, followed by adding orthophosphoric acid prior to heating and agitating the mixture under reflux.
Although divanadyl pyrophosphate which contains tetravalent vanadium was mentioned to ve preferable, joint use of this compound with vanadyl phosphate which contains pentavalent vanadium tends to result in increased catalytic activity. In particular, divanadyl pyrophosphate wherein some of the vanadium atoms have been oxidized into pentavalent ones can further incr
REFERENCES:
patent: 3238253 (1966-03-01), Kerr
patent: 3579573 (1971-05-01), Gilde et al.
patent: 3875220 (1975-04-01), White et al.
Conrad, III Joseph M.
Dees Jos,e G.
Nippon Shokubai Co. , Ltd.
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