Studies On Synthesis Of Pyridine Bases From Ethanol And Ammonia Over The ZSM-5Catalysts

Pyridine bases including pyridine and picolines (2-MP,3-MP and4-MP), which are important raw materials in fine chemicals, pharmaceutical intermediates and pesticides, are extensively used in many fileds. The production of pyridine bases is made by the tar extraction and catalytic synthesis. The former technology is the primary method for the synthesis of pyridine bases in China. However, because of serious pollution and difficult separation, the tar extraction was gradually gone out in foreign countries. In the world the proportion of the latter accounted for more than90%. In China, the production of pyridine and its derivatives is still in the initial stage and can’t meet the needs of our chemical production. In this thesis, on the basis of extensive literature research, my experimental program of the subject is ethanol-ammonia condensation to synthesize pyridine bases. As a result, with the rise of biomass ethanol, ethanol-ammonia reaction is a new way for pyridine and its derivatives.In this paper, through ethanol-ammonia reaction over a series of the microporous and mesoporous ZSM-5catalysts, we investigated the influence of reaction conditions, optimized the reaction technology and simultaneously calculated the carbon balance of the experimental results. The experimental results were listed as follows:1. ethanol-ammonia reaction over a series of microporous ZSM-5catalystsA series of microporous Zn/ZSM-5catalysts obtained by different preparation methods were characterized by XRD, FTIR, N2-physical adsorption and NH3-TPD. The effects of catalytic performance modified by different metal ions, metal load capability, preparation method and reaction temperature were investigated in ethanol-ammonia condensation reaction. The experimental results showed that:The highest selectivity and yield of pyridine bases reached48.8%and41%on Zn/ZSM-5, respectively. Moreover, the carbon balance was88.16%.2. ethanol-ammonia reaction over a series of micro-mesoporous ZSM-5catalysts by the alkali treatmentMicro-mesoporous ZSM-5was prepared by the different concentration alkali treatment (0.1-1.Omol/L) for parent ZSM-5zeolites, which were characterized by XRD, SEM, FTIR, N2-physical adsorption and NH3-TPD. The characterizations showed the intrinsic MFI structure of ZSM-5-AT zeolites was preserved under low concentration NaOH solutions and a number of mesopores by desilication were generated in the zeolites. The treatment concentration at0.5M could be regarded as optimal, combining an extensive mesopore formation, relatively uniform mespore sizes, a largely preserved microporosity and suitable acidity. The catalytic performance evaluation of ethanol and ammonia condensation over a series of micro-mesoporous Zn/ZSM-5-AT was studied. Through the reaction we investigated the effects of technological parameter:NaOH concentration, reaction temperature, ethanol-methanol ratio, alcohol ammonia ratio and other factors. The results showed that catalytic performances and stability over micro-mesoporous Zn/ZSM-5-AT could be greatly improved compared with microporous Zn/ZSM-5. The best selectivity and yield from ethanol-ammonia condensation were obtained on Zn/ZSM-5(0.5M)-AT under the conditions of410℃, which the best selectivity and yield of pyridine bases reached59.45%and50.27%, respectively. Furthermore, the carbon balance was93.6%.3. ethanol-ammonia reaction over the micro-mesoporous ZSM-5catalysts by the Nano-assemblyMicro-mesoporous ZSM-5-NA composite molecular sieves were successfully prepared with commercial ZSM-5zeolites as silica-alumina sources by the Nano-assembly method. The characterizations of XRD, SEM, FT-IR, N2-physical adsorption and NH3-TPD showed that ZSM-5-NA had good micro-mesoporous composite structure. The catalytic performance on the condensation reaction of ethanol-ammonia was illustrated over Zn/ZSM-5-NA. The experimental results showed that the catalyst had good selectivity and yield of pyridine bases. Therefore, The optimum reaction conditions:precursor alkali concentration of0.5mol/L, the crystallization temperature at110℃, crystallization time for48h,10%Zn/ZSM-5-NA micro-mesoporous composite zeolites as the catalyst, the highest yield and selectivity of pyridine bases were58.59%and67.12%. Meanwhile, the catalyst had much better catalytic stability and good resistance for carbon deposition.3. We also explored the reaction mechanism of pyridine bases by ethanol-ammonia condensation reaction. We concluded:firstly, ethanol was dehydrated to ethylene or oxidized to aldehydes. Then, ethylene and ammonia formed the imines. A series of deamination, cyclization and dehydrogenation formed pyridine bases by the imine transition state mechanism. Aldehyde-ammonia method was by acrolein transition state mechanism or imine transition state mechanism to synthesize pyridine bases. The mechanism was based mainly imine mechanism and the existence of acrolein mechanism.