The Research On Catalyst For The Systhesis Of 2,5-Dimethyl-2,4-Hexadiene

2,5-dimethyl-2,4-hexadiene is an important chemical raw material, which can be condensed in obutylene/isobutyraldehyde system。 The system is a simple process that with no corrosion of equipment and environmental pollution, which not only can fully use of downstream petrochemical products, but has mild reaction conditions, so there is high selectivity and good development prospect. However, the catalyst used in this process requires high reaction pressure, so the strit equipment demandment restricts the promotion of the process.Since niobate has been used to catalyze the reaction, so niobate is the carrier in this paper. With the impregnation method, the heteropoly acid is impregnated into the surface of niobic acid, so under pressure 0.5Mpa and at low temperatures there has been a better catalytic active catalyst. In this paper, phosphotungstic acid and phosphomolybdic acid were impregnated separately and the effects of different concentrations of the impregnating liquid impregnated catalysts were studied.The results show that phosphotungstic acid can improve the catalytic activity of the catalyst by making the heteropoly acid load to the niobate surface with the impregnation method. Catalytic activity increases with the increasing load continues and the temperature continuously decreases at the high activity, but the catalyst coke is also increasingly easy.To obtain good activity and the uneasy coke catalyst under a low pressure, this paper changes the material of the reaction of isobutene, alternative with tert-butyl alcohol, condensed with isobutyraldehyde to make 2,5-dimethyl-2,4-hexadiene. In this reaction SAPO-11 is the catalyst, with citric acid to improve the catalyst activity, so the catalyst has difficult coke characteristics.The results showes 0.1 mol · L-1 of citric acid catalysts has the highest activity. After the processing of a low concentration of citric acid zeolite formed reasonable structure and acidic, which helps to transfer reactive substances, and the small pore zeolite suppresses the formation of macromolecular substances to improve the selectivity of the catalyst. When the concentration of citric acid is too high, it will destroy the structure of SAPO-11 molecular sieve, so the amount of acid zeolites is reduced and activity is reduced. The SAPO-11 with the process of citric acid has a suitable acid strength and acid site, playing a catalytic dehydration of tert-butanol and 2,5-dimethyl-2.4- hexadiene synthesis.