Study On The Technology Of Reducing Template Synthesized By ZSM-5 Molecular Sieve

The conventional preparation method of ZSM-5 molecular sieve is hydrothermal synthesis,and the template is often used as an organic template,which has the disadvantages of toxicity,high cost and strong pollution.The development of ZSM-5 molecular sieve synthesis technology for reducing the dosage of template agent is of great significance to the production of ZSM-5 catalyst.In this thesis,a method to synthesize ZSM-5 molecular sieve by reducing 50% template was developed by adding crystal seeds.The synthetic raw materials of molecular sieves were selected as water glass and aluminum sulfate by means of XRD and SEM,and the optimum synthesis effect of four ethyl ammonium bromide as template under different dosage was explored.The evaluation result of the xylene isomerization catalyst shows that the evaluation results after reducing the dosage of the template can still reach the expected index,which shows the feasibility of this method.On the other hand,the effect of crystallization time on the dosage of different templates and the dosage of different crystal seeds was explored.In this paper,the optimum conditions for the synthesis of molecular sieves with 50% templates are obtained by orthogonal test.The ratio of alkali to silicon is 0.21,the time of synthesis is 30 h,and the amount of crystal seed is 3 m%.Under these conditions,the relative crystallinity of zeolite is over 92%,the conversion of ethylbenzene is 63%,and the selectivity of p-xylene is 23.63%.Then the experiment was carried out in the 2 L crystallization kettle,and the process control conditions were optimized by orthogonal test.The heating rate was 30 °C/h,the stirring mode was 30 r/min,the aging time was 90 min,and the feeding rate was 40 g/min.Under the conditions,the relative crystallinity of the molecular sieve can reach 92%,the conversion rate of ethylbenzene is 62.69%,the selectivity of p-xylene is 23.64%,and the index is satisfied.It is proved that the amplification experiment is also feasible.The first filtrate of the product is synthesized by molecular sieve.The relative crystallinity of the synthetic molecular sieve is up to 85%.It shows that the residue of the tail liquid can be recycled and reused,which can play the role of crystal seed,and the relative crystallinity of the tail liquid enlargement experiment can reach 90%.On the basis of this,the 10 L crystallization kettle was tested.According to the optimum ratio of raw materials and the optimum technological conditions,the relative crystallinity of the ZSM-5 zeolite was above 95%,the ratio of silicon and aluminum was above 85,the conversion rate of ethylbenzene was 61.23%,and the selectivity of p-xylene was 23.60%,which laid a practical and effective technical foundation for industrial production.