Effects of channel structure and acidity of molecular sieves in hydroisomerization of n -octane over bi-functional catal
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Catalysis Letters Vol. 100, Nos. 1–2, March 2005 ( 2005) DOI: 10.1007/s10562-004-3086-9
Effects of channel structure and acidity of molecular sieves in hydroisomerization of n-octane over bi-functional catalysts Hu Yunfeng,a,b Wang Xiangsheng,a Guo Xinwen,a,* Li Silue,b Hu Sheng,c Sun Haibo,b and Bai Liangb a
Department of Catalysis Chemistry and Engineering, State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, 116012 P R China b PetroChina Daqing Refining & Chemical Company, Daqing, 163411 P R China c Research Institute of PetroChina Daqing Petrochemical Company, Daqing, 163714 P R China
Received 12 August 2004; accepted 17 November 2004
SAPO-5, -11, -31, -41, -34, ZSM-5, -22 and -23 were synthesized by using the hydrothermal method and characterized by various methods such as XRD, SEM, XRF and TPD of NH3. They are representative of large-pore, medium-pore, small-pore, weak acid, strong acid, monodimensional channel and zigzag channel type of molecular sieves. Effects of pore size, the number of acid sites over medium-pore SAPOs, acid strength and shape of medium-pore channel on hydroisomerization of n-octane were examined over Pt-loaded corresponding molecular sieves. These results indicate that the selectivity to isomerization in hydroisomerization of n-octane is highly influenced by channel structure in molecular sieves and the conversion activity of n-octane is dependent on acidity of molecular sieves. Monodimensional medium-pore molecular sieves are ideal catalytic materials for higher isomerization selectivity in hydroisomerization of n-octane regardless of acid strength, such as SAPO-11, -31, -41, ZSM-22 and -23. KEY WORDS: Hydroisomerization; bi-functional catalyst; n-octane; channel; acidity; SAPO-41; SAPO-31; SAPO-11; ZSM-22; ZSM-23.
1. Introduction Catalytic dewaxing process was first commercialized by Mobil using ZSM-5 catalyst [1] and the process is carried out by selective cracking long chain n-paraffins, resulting in significant yield loss during increasing the low temperature performance of the lubes. Lubes and middle-distillate fuels with advanced performance, environmental and safety benefits are in increasing demand [2]. The hydroisomerization of n-paraffins has made possible the production of higher quality lubes and fuels with low pour points at higher yield. Bi-functional catalysts containing the noble metal for hydrogenation/dehydrogenation and molecular sieve for carbon–carbon bond rearrangement are known to be very effective in hydroisomerization of n-paraffins. Recently catalysts with high selectivity for the hydroisomerization of long-chain n-paraffin have been reported. These catalysts were composed of medium-pore silicoaluminophosphate (SAPO) molecular sieves [3–11], e.g., SAPO-11 (AEL), SAPO-31 (ATO) and SAPO-41 (AFO). Some reports [10, 12] revealed that the high activity and selectivity of these catalysts in isomerization were due to their unique combination of mild acidity and shape selectivity. Generally speaking, acid strength of SAPOs is weaker than that of zeo
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