تاثیر افزایش مزوحفره‌ها بر فعالیت زئولیت HZSM-5 با نسبت سیلیس به آلومینیوم بالا در فرآیند تبدیل متانول به الفین‌ها

نوع مقاله: مقاله پژوهشی

نویسندگان

1 دانشکده مهندسی شیمی و نفت، دانشگاه صنعتی شریف، تهران، ایران

2 گروه پژوهش‌های کاتالیستی، شرکت پژوهش و فناوری پتروشیمی، شرکت ملی صنایع پتروشیمی، تهران، ایران

چکیده

در این تحقیق تاثیر افزایش مزوحفره‌ها بر عملکرد زئولیت HZSM-5 با نسبت سیلیس به آلومینیوم بالا در فرآیند تبدیل متانول به الفین‌ها مورد بررسی قرار گرفت. بدین‌منظور از روش سیلیس‌زدایی با مواد سدیم هیدروکسید، تتراپروپیل‌آمونیوم هیدروکسید و ستیل‌تری‌متیل‌آمونیوم‌‌برمید جهت ایجاد مزوحفره‌ها استفاده شد. آنالیزهای XRD ،FESEM ،N2 Adsorption/Desorption و NH3-TPD نیز جهت تعیین خصوصیات کاتالیست‌ها بر‌روی نمونه‌ها انجام شد. نتایج آنالیز XRD نشان داد که استفاده از تتراپروپیل‌آمونیوم هیدروکسید در عملیات سیلیس‌زدایی توسط سدیم هیدروکسید در نمونه مزوحفره شده Na-TPA، سبب حفظ ساختار کریستالی زئولیت مرجع Ref-ZSM-5 در این نمونه شده است. تصاویر FESEM این نمونه ایجاد شکاف‌ها و حفرات کوچک بر‌روی سطح کریستال‌ها را نشان داده است. نتایج آنالیز N2 Adsorption/Desorption، افزایش سطح و حجم حفرات مزو را در نمونه زئولیت Na-TPA نسبت به زئولیت مرجع                                  Ref-ZSM-5 تائید کرده است. حفرات مزو تشکیل شده با افزایش دسترسی به سایت‌های فعال داخل ساختار، سبب بهبود فعالیت کاتالیستی این زئولیت شده است. به‌طوری‌که انجام تست راکتوری طولانی مدت بر‌روی این کاتالیست (Na-TPA) پایداری آن را به‌مدت 41 روز با تبدیل متانول بالای 90% نشان داد. متوسط انتخاب‌پذیری پروپیلن، کل الفین‌ها و نسبت پروپیلن به اتیلن نیز در این مدت به‌ترتیب 43، 76 و 6% است. درحالی‌که نتایج زئولیت سلیکون‌زدایی شده با استفاده از ستیل‌تری‌متیل‌آمونیوم‌ برمید و سدیم‌هیدروکسید نشان داد که ساختار زئولیت مرجع Ref-ZSM-5 به‌طور کامل تغییر کرده و غربال مولکولی کاملاً مزوحفره Al-MCM-41 تشکیل شده است. این غربال مولکولی به‌علت ساختار کاملاً مزوحفره و توزیع سایت‌های اسیدی با قدرت کم در فرآیند تبدیل متانول به الفین‌ها هیچ‌گونه فعالیتی نداشت.
 

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

The Effect of Mesoporous Increasing On Activity High Silica HZSM-5 Zeolite in the Methanol Conversion to Olefins

نویسندگان [English]

  • somayeh ahmadpour 1
  • Fereydoon Yaripour 2
  • Farhad Khorasheh 1
1 Department of Chemical and Petroleum Engineering, Sharif University of Technology, Tehran, Iran
2 Catalysis Research Group, Petrochemical Research and Technology Company, National Iranian Petrochemical Company, Tehran, Iran
چکیده [English]

In this paper, the effect of mesoporous increasing on activity high silica ZSM-5zeolite in methanol conversion to olefins investigated. Therefore, for forming the mesoporous, desiliction method with Sodium Hydroxide, tetrapropylammonium hydroxide and cetyltrimethylammonium bromide materials are used. The samples were characterized by XRD, FESEM, N2 Adsorption/Desorption and NH3-TPD techniques. The XRD results indicated that using Tetrapropylammonium hydroxide in desilication process by Sodium Hydroxide (in meso pore Na-TPA sample) caused high crystallinity preservation for Ref-ZSM-5 zeolite. FESEM images for this sample showed cracks and small holes on the surface of crystals. The N2 Adsorption/Desorption results confirmed an increase in the meso pore volume and meso surface area in Na-TPA sample compare to Ref-ZSM-5 zeolite. These new mesoporous, with increasing access to active sites in framework, caused improvement on the catalytic performance. Performing the reactor test on catalyst in same reaction condition showed that this catalyst with methanol conversion higher than 90% in 41 days had acceptable stability. During this time, average of propylene selectivity, total olefins selectivity and propylene to ethylene ratio were 43%, 76% and 6% respectively. While the desilicated sample with Sodium Hydroxide and cetyltrimethylammonium bromide showed complete change from Ref-ZSM-5zeolite to mesoporous Al-MCM-41molecular sieves. This molecular sieves with completely mesoporous structure and, acid sites with low strength did not show activity in the methanol to olefin reaction.
 

کلیدواژه‌ها [English]

  • HZSM-5 zeolite
  • Methanol Conversion to Olefins
  • Desilication
  • Sodium Hydroxide
  • Cetyltrimethylammonium Bromide

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