Vapor Phase Synthesis Of Alkyl Pyrazine Over Metal Oxide Catalysts

Alkyl pyrazine is a special kind of edible flavor and is a important chemical raw material and pharmaceutical intermediate.Due to the wide range of uses,alkyl pyrazine’s synthetic study gets more and more attention of researchers at home and abroad.Firstly,a series of ZnFe2O4/ZnO catalysts were prepared by an improved amorphous citric precursor method and were used to the reaction of 2,3-butadiene alcohol and ethylene diamine.The target product of reaction was 2,3-dimethylpyrazine.The results demonstrated that the performance of the ZnFe2O4/ZnO catalyst with n(Zn):n(Fe)=2:1 was the best.Under the condition of the reaction temperature was 380oC,the conversion rate of 2,3-butanediol was 93%,and the yield of 2,3-dimethylpyrazine was 22%,the yield of 2-methylpyrazine was 63%.After the reaction time was 10 h,the catalytic activity of fresh catalyst began to degrade.The stability of regenerated catalyst was very close to the stability of fresh catalyst.Secondly,the research of synthesis of 2,5-dimethyIpyrazine by the reaction with isopropylalcohol.This part was mainly divided into the following three parts:(1)The CuO/ZnO/Al2O3 catalysts were prepared by an coprecipitation method.Under the condition of reaction temperature was 290oC,the catalytic activity of 10%CuO-7%Al2O3-ZnO was higher than other catalysts.The conversion of isopropanolamine was 94%,the selectivity of 2,5-dimethy1pyrazine was 61%,and the yield of 2,5-dimethylpyrazine was 57%.Highly fragmented CuO was the activity center of dehydrogenation.A12O3 and ZnO could adjust the acid-basic sites of catalyst playing the role of acid-based sites.The acid-basic sites reached appropriate matching to play the role of acid-basic sites synergy effect for the synthesis of 2,5-dimethylpyrazine.(2)NiO-modified 7%Al2O3-10%CuO-ZnO catalysts were prepared by coprecipitation method.Under the condition of reaction temperature was 290℃,the catalytic activity of 5%NiO-10%CuO-7%Al2O3-ZnO was higher than other catalysts.The conversion of isopropanolamine was 94%,the selectivity of 2,5-dimethylpyrazine was 94%,and the yield of 2,5-dimethylpyrazine was 86%.NiO could not only improve the dispersion of the sample,but also adjuste the acid-basic sites of catalysts,conduciving to the synthesis of 2,5-dimethylpyrazine.The cyclization dehydrogenation mechanism over metal oxides catalyst was discussed.(3)A series of 5%NiO-10%CuO-7%Al2O3-ZnO-Molecular sieve catalysts were prepared by impregnation method.Firstly,ZSM-5(50),ZSM-5(25),β(20～40),β(80～120),13X(1.25)were chosen for the carrers.The results showed that β(20～40)molecular sieve was most conducive to the catalytic reaction.Carrier had not on Only physical functions,such as scattered,stability,support,heat transfer and dilution,but also chemistry function.Carrier and active component interacted with each other in chemistry.That could lead to the change of the catalyst activity,selectivity and stability.Acid-basic properties of the carrier could affect the catalytic activity of metal oxides.The effect of the loading of NCAZ on catalytic activity was studied.When the loading was greater than 25%,with the loading further increased,the catalytic activity of the catalysts had a little change.Under the condition of the reaction temperature was 310℃,the catalytic activity of 25%NCAZ-β(20～40)was better than others,the conversion of isopropanolamine was 94%,the selectivity of 2,5-dimethylpyrazine was 91%,and the yield of 2,5-dimethy1pyrazine was 85%.