Synthesis And Modification Of ZSM-48 Zeolitess And Their Performance For Hydroisomerization Of Hexadecane

ZSM-48 consists of one-dimensional 10 niembered ring channels with a pore diameter of 0.53nm × 0.56nm.Zeolites with 10 membered ring channels can improve the selectivity of monobranched hydrocarbons through the shape selecting catalysis and suppress the generation of multibranched hydrocarbons which can easily lead to cracking reaction.Meanwhile,10-membered-ring zeolites can reduce coke formation and increase the catalyst life.Therefore,it is considered to be the suitable acidity supports for the hydroisomerization reaction.Based on the unique pore structure and acidity features of ZSM-48,ZSM-48 as acidity support has been applied in the hydroisomerization reaction of long-chain paraffin.In this work,the selectivity and yield of i-C₁₆ over the bifunction catalysts supported on ZSM-48 were improved through modifying ZSM-48.The main research contents aind results are listed as follows:?1?ZSM-48 with SiO₂/Al₂O₃?400 was synthesized in the hydrothermal system of Na₂O-SiO₂-Al₂O₃-HDA.The different crystallization conditions were investigated and t:he optimal conditions were confirmed.The micropore volume of ZSM-48 with alkali treatment remained unchanged and in addition the mesopore volume was formed.The selectivity of i-C₁₆ was increased for the formation of mesopores improving the diffusivity.However,uncontrolled silicon extraction has been identified in the solution of sodium hydroxide.A novel way was used to suppress uncontrolled silicon extraction in which hexanediamine?HDA?was added into the solution of sodium hydroxide.The enrichment of Si at the ZSM-48 surface and the formation of mesopores improved the selectivity of i-C₁₆ from 35 wt%to 50 wt%by decreasing the cracking reactions,because HDA could prevent the uncontrolled silicon extraction acting as a Si protecting agent during the NaOH treatment.?2?ZSM-48 with SiO₂/Al₂O₃=200 and EU-l/ZSM-48 were synthesized in the hydrothermal system of Na₂O-SiO₂-A1hO3-HMBr₂.EU-1/ZSM-48 with different content of EU-1 was synthesized through controlling the synthesis condition of ZSM-48.The acidity of ZSM-48 was changed by varying the content of EU-1.EU-1/ZSM-48 showed outstangding catalytic performance for the conversion of C₁₆ and selectivity of i-C₁₆ because of unique structure and acidity property.The catalytic performance of EU-1-ZSM-48-200 was quite different from those of the pure ZSM-48-200 and the conversion of Cig and selectivity of i-C₁₆ Over EU-l-ZSM-48-200 were higher than ZSM-48-200.The conversion of C₁₆ could improve from 25wt%to70wt%and selectivity of i-C₁₆ could improve from 20xwt%to 70wt%.The conversion of C₁₆ and selectivity of i-C₁₆ at various temperatures over the intergrowth zeolite catalyst were obviously higher than the physical mixture zeolite catalyst.The yield of i-C₁₆ could improve from 18wt%to 40wt%.Because of the synergistic effect of EU-1 and ZSM-48,superior catalytic performance of EU-1-ZSM-48 could be obtained.?3?ZSM-22,ZSM-23,ZSM-35 and ZSM-48 zeolites were synthesized in the hydrothermal system.Four different 10-ring zeolites showed remarkably different catalytic performances in the conversion of C₁₆.The higher conversion was obtained over Pt/ZSM-35 and the higher selectivity was obtained over Pt/ZSM-23 at low temperature and short contact time while at high temperature and long contact time over Pt/ZSM-48.The mixture of zeolites catalysts displayed interesting conversion and selectivity and improved the catalytic performance and yield of i-C₁₆.Small differences in the channel systems had a notable influence on the product distribution of hexadecane hydroisomerization over 10-ring zeolites.The combination of no multi-branched products and the length of hexadecane molecule indicates that the hexadecane hydroisomerization conforms to as pore mouth reaction mechanism.?4?The acidity of ZSM-48 was changed through varying the content of Nb₂O₅.The yield of i-C₁₆ and selectivity of i-C₁₆ over Pt/Nb₂O₅/ZSM-48 were higher than Pt/ZSM-48.The selectivity of i-C₁₆ could improve from 30wt%to 90wt%.The metal actidity of Pt-Ni/ZSM-48 was changed through varying the content of Pt.Pt-Ni/ZSM-48 enhanced the hydrogenation acidity of metal.The conversion of C₁₆ and selectivity of i-C₁₆ over Pt-Ni/ZSM-48 were higher than Pt/ZSM-48 and Ni/ZSM-48.10Ni0.3Pt/ZSM-48 shown the highest catalytic activity.The selectivity of i-C₁₆ could improve from 60wt%to 95wt%and yield of i-C₁₆ could improve from 25wt%to 75wt%.