| Propylene is a basic organic raw material of great importance,which mainly comes from the process of petroleum steam cracking.The traditional steam cracking method has high requirements for the operation of an apparatus,high economic cost,and will cause problems such as the consumption of raw materials.Moreover,the simple improvement of process equipments can not meet our growing demand for propylene.In this case,propylene production increasing technology is in urgent need of transformation.Compared with methanol to olefin,propylene disproportionation and other propylene production technologies,FCC process has grown very mature in China’s oil refining industry,and has a good equipment foundation,which does not need large-scale improvement of equipments,addition of plants and other production advantages.Therefore,the use of FCC technology combined with a series of mature catalysts as auxiliary is a hot spot in propylene production.In FCC process,adding FCC propylene promoter is the most effective method,and the most recognized catalyst promoter is ZSM-5 molecular sieve.Compared with the extensive application of ZSM-5molecular sieve,there are less researches on ZSM-11 molecular sieve in FCC process.These two kinds of molecular sieves belong to a pentasil family and have similar structure and function,so this paper focuses on the catalytic cracking performance of ZSM-11 zeolites.This thesis starts with the traditional hydrothermal synthesis of ZSM-11 molecular sieve.In the first part,the synthesis chemistry of ZSM-11 molecular sieve is studied,and the influences of the amount of raw materials and crystallization conditions on the crystallization effect of ZSM-11 molecular sieve are investigated in detail.ZSM-11 molecular sieve can only be synthesized in the presence of a template.The mold silicon ratio M = 0.12～0.16 is suitable for the feeding range of the template.The growth of ZSM-11 zeolite needs a strong alkaline environment.When the alkali silica ratio N =0.12～0.2,the synthesized zeolite sample has a good pore structure.The synthesis of ZSM-11 requires a relatively long crystallization time,and its crystallization degree will increase with the extension of crystallization time,but it is difficult to produce ZSM-11 crystal phase when the crystallization time is less than 1.5d.Finally,when the ratio of water to silicon is in the range of G-8～G～G+8,increasing or decreasing the amount of water has little effect on the relative crystallinity data of a sample.In the second part of this thesis,the feasibility of the synthesis of ZSM-11 molecular sieve by pre-crystallization liquid method is verified.Experiment shows that the synthesis of molecular sieves can be realized by using the pre-set crystal seed solution instead of the template,and the use of the template can be reduced.In addition,the effects of the amount of pre-crystallization liquid,pre-crystallization time and the length of the whole mixed liquid crystallization time on the properties of ZSM-11 molecular sieve are investigated.With the increase of the pre-set seed crystal liquid,the crystallization effect increases first and then decreases.When the addition amount is27.93% ～ 38.33%,the effect is the best.When the pretreatment time of the pre-crystallization liquid is about 2 ～ 4h,the effect is the best.The crystallization degree of molecular sieve samples is optimized with the extension of the whole mixed liquid crystallization time.In the third part of this thesis,the catalytic performance of ZSM-11 molecular sieve,synthesized by pre-crystallization liquid method,as FCC catalyst is studied.At first,a series of ZSM-11 molecular sieves samples with different Si/Al ratios are synthesized by pre-crystallization liquid method.The samples are prepared as catalysts and evaluated by FCC micro reaction,and n-octane is used as the simulated compound.The results show that the Si/Al ratio is negatively related to the acidity of molecular sieve.The lower the ratio of Si/Al,the better the catalytic effect.As ZSM-11 synthesized by pre-crystallization liquid method is microporous molecular sieve,the products of microporous ZSM-11 molecular sieve and microporous industrial ZSM-5with similar Si/Al ratio are analyzed.It is found that ZSM-11 molecular sieve improves the yield of propylene to a certain extent compared with ZSM-5 and the increase is about 8.7%,which proves that ZSM-11’s unique straight channel has certain advantages over ZSM-5 in increasing propylene production.The products of mesoporous ZSM-5,microporous ZSM-5 and microporous ZSM-11 samples with similar Si/Al ratio are analyzed.It is found that the ethylene yield is increased by 34.3% and the propylene yield is increased by 33.7% compared with the latter two samples.It is proved that the existence of mesoporous is conducive to the diffusion of small molecules to achieve the effect of increasing propylene production.Therefore,the preparation of ZSM-11 molecular sieve with mesoporous channels,as catalyst promoter is of sustainable research significance. |
