(583bj) Preparation of Y Zeolite Catalysts for Purifying the Para-Xylene | AIChE

(583bj) Preparation of Y Zeolite Catalysts for Purifying the Para-Xylene

Authors 

Shi, L. - Presenter, East China University of Science and Technology
Pu, X., East China University of Science and Technology



Effective method of removing olefins from para-xylene has attracted much attention. Because the undesirable olefins in the paraxylene (PX) are able to lead to the ADS-7 (a highly selective adsorbent for separate and produce PX) toxicosis. In order to protect the adsorbent, the product stream will have a bromine index which is an indicator of the presence of olefinic bonds less than 20. Two processes have been discovered for removing trace olefins from PX1,2 (i.e., particulate clay treating and catalytic hydrogenation treating). However, both have some drawbacks, for example, the clay have very limited lifetime and cannot be reused. Pressure from legislative and environmental bodies together with a growing awareness within the chemical industry has led to a search for new eco-friendly products and processes to replace polluting reactions.

Herein, we report the purifying process over Y zeolite catalysts. This catalyst has a high catalytic activity and can be regenerated. Modification of the zeolites was performed by citric acid treatment. Acid properties were investigated by NH3-TPD and in-situ IR spectroscopy 3. The values of olefins conversion (X) = (no – ni)/no, where no was initial content of olefins; ni was final content of olefins. The modified Y zeolite gave much better result, the running time reached 5 hours with the conversion above 80 %. The weight hourly space velocity (WHSV) was 30 h-1, 30 times as high as that of the industrial unit. For comparison, the life of the clay, widely used in refineries, was only 2 hours at the same condition. To clarify the difference in the catalytic performance between modified zeolite and clay, the acid properties of theses samples were investigated in detail by in-situ IR spectroscopy. The IR spectra of these samples after pyridine adsorption revealed that both samples had Brønsted and Lewis acid sites. Note that the proportion of weak Lewis acid sites, which can be ascribed to the IR band appeared at 1450 cm-1, to total acid sites in modified zeolite sample was higher than that in clay sample. It can be assumed that the weak Lewis acid sites were generated by the acid-treatment and thus formed acid sites can activate olefin molecule. More attention should be paid to the experiment of regeneration which did reuse of the zeolite. It had been proven that the Y zeolite can be regenerated at least third time with the better performance than the clay sample. This result can help the refineries to solve the problem of solid waste, if they use this modified zeolite.

In conclusion, Y zeolite catalysts were found to be promising catalysts for purifying the Para-xylene. The type of weak Lewis acid sites is responsible for the reaction with a high catalytic activity.

 

Acknowledgment: we thank the Sinopec Zhenhai Refining and Chemical Company for their help in the experiments.

Reference

(1)   Brown, S. H.; Helton, T. E.; Werner, A. P. Decreasing Br-reactive Contaminants in Aromatic Streaks U. S. Patent 6,781,023, 2004.

(2)   Li, G. L.; Luan, J. N.; Zeng, X. S.; Shi, L. Removal of Trace Olefins from Aromatics over Metal-Halides-Modified Clay and Its Industrial Test. Ind. Eng. Chem. Res. 2011, 50 (11), 6646–6649

(3)   Xin Pu; Nai-wang Liu; Zheng-hong Jiang;Li Shi. Acidic and catalytic properties of modified clay for removing trace olefin from aromatics and its industrial test. Ind. Eng. Chem. Res. 2012,51(43), 13891–13896