Study On The Molding Process Of HZSM-5 Catalyst

Molding is very important for the practical application of molecular sieve catalysts,which is a must to enable them showing required shape and compressive strength.Meanwhile,the use of rnolding additives show significant impact on the physicochemical properties of molecular sieves,which can even be adjusted.In this paper,the molding product was obtained by adding the molding additive and using the extrusion method.Compared with the original powder,the compressive strength of the product increased significantly after the molding,the catalytic activity of the MTO was improved,the hydrothermal treatment was 216 h,and the physicochemical properties of the product were stable,but the product was catalyzed.The life span is short,and the cause of its inactivation needs further study.The extrusion molding of HZSM-5 powder was studied employing phosphoric acid,pseudoboehmite,carboxymethyl cellulose(CMC),hydroxypropyl methylcellulose(HPMC)and kaolin as binders.Toward methanol to olefin(MTO)reaction in a fixed bed reactor,the effect of process conditions on the physicochemical properties and catalytic properties of the molding products was investigated.The formula of binder was optimized and the properties of the molded products characterized.HZSM-5 powder was composed of regular twin crystals with a size of 6 jim.The specific surface area,micropore volume and mesopore volume was 358.8 m2�g-1,0.1446 cm3�g-1,0.0634 cm3�g-1,respectively.Total acid amount was 0.243 mmol�g-1.Used for MTO at 480 ?,the selectivity of C2-C4 olefins,C3H6 and CH4 was 60.85%,26.14%,4.86%,respectively,with 100%conversion of methanol,the selectivity of CH4 reached 14.29%after 10 h reaction.After steam treatment at 480 ? for 216 h,the crystallinity of the pristine powder was decreased.The specific surface area and the micropore volume was reduced by 11.9%and 12.5%,respectively.The weak acid and strong acid was decreased by 0.089 mmol�g-1 and 0.02 mmol�g-1,respectively.In MTO reaction,the conversion of methanol was 100%.The selectivity of C2-C4 olefins,C3H6 and CH4 was 64.41%,34.67%,and 1.82%,respectively.This can mainly ascribed to reduced number of acid centers.The selectivity of CH4 was 3.16%after 10 h reaction.Hydride transer and carbon deposition were reduced.The selectivity of CH4 was 3.16%after 10 h reaction.Hydride transer and carbon deposition were reduced.Effect of phosphorus/aluminum ratio of the binderThe mass ratio is HZSM-5 original powder:Tianjing powder:nitric acid:polyethylene glycol:phosphoric acid:pseudo-boehmite:water=1:0.028:0.12:0.1:(0-0.0743):(0-0.176):0.7,as the P/Al ratio of phosphoric acid and pseudo-boehmite binder was increased,the specific surface area and strong acid site of the extruded product was decreased.The compressive strength was increased gradually,which showed a maximum of 36.67 N/cm at the P/Al ratio of 1.4.The product by the P/Al ratio of 1.2 showed the best catalytic performance for MTO.The selectivity of CH4,C2H4,C3H6 and C2-C4 olefins was 1.05%,11.54%,49.7%and 68.53%,respectively,with the complete conversion of methanol.The product with P/Al ratio of 1.2 showed the best activity for MTO,lifetime is 54 h,the selectivity of CH4 was 2.7%.Effect of auxiliaryBased on the extrusion product with the P/Al ratio of 1,the effect order of additives on molding was CMC>kaolin>HPMC,in terms of the compressive strength and activity activity.The compressive strength of the 8%CMC product was up to 63.47 N/cm.With the increase of CMC,HPMC and kaolin,the product particles appeared agglomeration.The specific surface area,pore volume,and strong acid site of the extruded product were lowered compared with the pristine powder.The product with addition of 2%CMC showed the best catalytic activity for MTO.In complete conversion of methanol,the selectivity of CH4,O2H4,C3H6 and C2-C4 olefins was 2.31%,21.88%,45.16%and 79.33%,respectively.Stability of catalytic activityAfter the extrusion product with the P/Al ratio of 1.2 was exposed to steam treatment at 480 0 C for 72 h,144 h and 216 h,the ciystallinity was decreased.The specific surface area and the micropore volume was decreased by 3%and 4.2%,respectively.The weak acid amount and strong acid amount was decreased by 0.06 mmol�g-1,0.008 mmol�g-1.For MTO reaction,the selectivity of CH4,C3H6 and C2-C4 olefins was 2.78%,39.21%,and 81.32%,respectively.The hydrothermal treatment removed part of the framework aluminum,which reduced the strong acid sites and side reactions whereas increased the stability.As the reaction time extended,the catalyst was covered by earbon deposition,resulting in a significant decrease in the activity.