Synthesis Of Hierarchical Porous ZSM-5 Zeolites With Cellulose(Glucose)As Cotemplate And Its Application In Catalysing Of Polyolefin Plastics

Light olefins（ethylene,propylene,etc.）and light aromatics（benzene,toluene and xylene,etc.）are important basic raw materials for petrochemical industry,which have been mainly produced by petroleum-based route.As oil resources is beginning to tail off and the demand for light olefins and aromatics is increasing,developing new technologies for producing light olefins and aromatics via non-petroleum routes is imperative.Meanwhile,the use of polyolefin plastics is increasing gradually with the rapid development of society,how to treat waste plastics has always been an important problem.Catalytic cracking of waste plastics to produce high value-added chemicals such as light olefins and aromatics is not only helpful for solving white pollution problem,but also alleviating the energy crisis.The traditional synthesis of mesoporous molecular sieves usually depends on cationic surfactant as template,which is expensive and thus limits its application in large scale.In this paper,the tetrapropylammonium bromide（TPABr）as the main template and the microcrystalline cellulose（MCC）or glucose as cotemplate were used to produce hierarchical ZSM-5 zeolite by the method of hydrothermal synthesis.The catalytic activity of the catalysts were examined by cracking of high density polyethylene（HDPE）and polypropylene（PP）.The reaction conditions were optimized.The research of this paper mainly includes the following four aspects:（1）The hierarchical ZSM-5 zeolite with different Si/Al（MZ-X,X=27、80、150）was synthesized with MCC as co-template.BET analysis shows that compared with the ZSM-5 prepared without MCC addition（HZ-X）,the addition of MCC significantly increased the external specific surface area and mesoporous pore volume of MZ-X catalysts.MZ-27 obtained high liquid yield and BTEX aromatics selectivity in the catalytic cracking of HDPE and PP because of its proper strong acidity and larger pores structure.The results of optimization of process conditions shows that:the MZ-27 obtained the highest liquid yield and aromatics selectivity at 550°C and catalyst/feedstock ratio of0.75.The liquid yields from HDPE and PP were 21%and 32.6%,respectively;the selectivity of BTEX in liquid products were 88.1%and 82.6%,respectively.The selectivity to light olefins in gas products from cracking of HDPE and PP are relatively close,32.5%and 32.9%,respectively.（2）The hierarchical porous ZSM-5 zeolite with different Si/Al ratio（PZ-X,X=27、80、150）was synthesized with glucose as co-template.BET analysis showed that the addition of glucose increased the number of mesopores in PZ-X catalysts.The results of catalytic cracking showed that ZSM-5（HZ-150）with high Si/Al ratio and small pore size obtained more gas products and higher selectivity of low-carbon olefins,while PZ-27 with lower Si/Al ratio and large pore size obtained higher liquid yield and light aromatics selectivity.PZ-27obtained the highest liquid yield（22.6%）and S_BTEX（82.9%）from HDPE when the experiment was carried out at 550°C and catalyst/feedstock ratio at 1.Also,PZ-27 achieved the highest liquid yield（31.2%）and S_BTEX（78.5%）from cracking of PP under the same experimental condition.（3）The liquid yield,gas yield and S_BTEXobtained by catalytic cracking HDPE and PP with ZSM-5 synthezied by addition of different dosage of MCC were almost the same,indicating that the product distribution is mainly affected by the acidity of catalysts.The liquid yield from HDPE was 20.7-22%,S_BTEXwas about 79%,while the liquid yield from PP was 30-33%,S_BTEXwas about75%.After 600 min of continuous reaction,the catalytic activity of MZ-27 and PZ-27 decreased slightly,indicating that the stability of the catalyst should be further improved.