Synthesis And MTO Catalytic Performance Of SSZ-13 Zeolite

In recent years,the chemical industry has developed rapidly all over the country,and people's demand for low-carbon olefins?ethylene,propylene?is increasing day by day.Therefore,it is not enough to prepare the required low-carbon olefins only through the production route of petroleum cracking.So,non-petroleum production of low-carbon olefins has been emphasized and developed,which methanol?through methanol or natural gas synthesis?as a raw material for the production of low-carbon olefins?methanol to olefins,MTO?developed most rapidly.The key of MTO technology lies in the design and development of low-cost,environmentally friendly and efficient catalysts.SSZ-13 zeolite is a high-silicon CHA topology zeolite with unique structure,excellent hydrothermal stability and adjustable acidity.It exhibits excellent performance in terms of methanol to olefins,removal and cleaning of nitrogen oxides in exhaust gas and automobile exhaust,and gas adsorption separation,etc.However,in the MTO reaction,SSZ-13 zeolite is particularly prone to carbon deposition and then inactivated.Moreover,the conventional hydrothermal synthesis method for preparing SSZ-13 zeolite has the disadvantages of long synthesis cycle,low yield,and waste water,which limits its application in MTO reaction.Therefore,the orientation modification of SSZ-13 zeolite,the optimization of synthesis conditions,and the development of a better synthetic route are great significance for its wide application and promotion.Based on the above background,this paper studied SSZ-13 zeolite from the following aspects:?1?Microporous SSZ-13 zeolite were synthesized by traditional hydrothermal method using TMAdaOH as template.The effects of synthesis factors?aluminum source,templating agent dosage and crystallization time?on SSZ-13 zeolite were explored.The SSZ-13 zeolite synthesized under different conditions were analyzed by XRD,SEM,nitrogen adsorption desorption,NH₃-TPD,etc.The results showed that when the aluminum source was aluminum nitrate,the crystallization time was144 hours,and the molar ratio of each component was 2.6Al₂O₃:100SiO₂:10Na₂O:10TMAdaOH:4400H₂O,the crystallinity of the synthesized SSZ-13 zeolite reached the highest.Under such conditions,it had good catalytic performance in the MTO reaction.?2?On the basis of the traditional hydrothermal synthesis method,the high-crystallization hierarchical SSZ-13 zeolite was synthesized via in situ growth-etching with the assistance of excess HF,and it was compared with the conventional microporous SSZ-13 zeolite without HF.The results showed that the addition of HF can shorten the time required for crystallization.When the crystallization time was shortened to 12 hours,the crystallinity of the synthesized zeolite was still higher than that of the SSZ-13 zeolite synthesized at 144 hours after the fluorine-free system.Moreover,the specific surface area of??the obtained hierarchical SSZ-13 zeolite is larger than the specific surface area of??the microporous SSZ-13 zeolite.In addition,in the MTO reaction,the catalytic activity of hierarchical SSZ-13 was enhanced,and the selectivity of C₂H₄ and C₃H₆ was increased.?3?On the basis of the traditional hydrothermal synthesis method,the waste crystallization mother liquor was fully utilized.A series of SSZ-13 zeolites were synthesized by economical and green synthesis methods using crystallization mother liquor recycling.The physicochemical properties of the SSZ-13 zeolite sample synthesized by waste crystallization mother liquor were characterized by XRD,SEM,nitrogen adsorption desorption and NH₃-TPD,and its catalytic performance in MTO was investigated.The results showed that the SSZ-13 zeolite synthesized by the crystallization mother liquor had similar cubic morphology,surface area,micropore volume and particle size to the initially synthesized SSZ-13 zeoite.And in the MTO reaction,the catalyst SSZ-13 zeolite synthesized by three times of crystallization mother liquor still maintains a high CH₃OH conversion rate and C₂H₄ plus C₃H₆selectivity.