HZSM-5型分子筛硅铝比对一步法合成二甲醚的影响  

Study of the effects of Si/Al ratio of HZSM-5 on the direct synthesis of DME

作　　者：鲁皓[1] 常杰[1] 付严[1] 王铁军[1] 

机构地区：[1]中国科学院广州能源研究所

出　　处：《燃料化学学报》2005年第3期324-328,共5页Journal of Fuel Chemistry and Technology

基　　金：国家高技术研究发展计划(2002AA514020);广东省科技计划项目(2003B30803)。~~

摘　　要：以Cu/Zn/Al(摩尔比为6∶3∶1)甲醇合成催化剂与HZSM-5型分子筛混合,制备了一步法二甲醚合成催化剂。通过改用三种不同Si/Al摩尔比(摩尔比为25、38和50)的HZSM-5型分子筛,考察了催化剂中脱水组分(HZSM5分子筛)的酸性对二甲醚合成的影响。结果表明,随着催化剂Si/Al摩尔比的降低,分子筛的酸性增强,使得CO单程转化率提高。当催化剂Si/Al=38时,CO对二甲醚的选择性最高,可达到68.13%,其次是催化剂Si/Al=50,选择性最差的是Si/Al=25的催化剂。在553K、3MPa和4000h-1的条件下,Si/Al=25和Si/Al=38的催化剂CO单程转化率和DME的选择性接近一致。在此条件下,两者的时空产率达到试验的最大值,分别为0.38gDME/(gcat·h)和0.36gDME/(gcat·h),在试验范围内,一步法合成二甲醚催化剂最佳的Si/Al摩尔比为25。Direct DME synthesis catalyst contains methanol synthesis catalyst and solid acid catalyst for methanol dehydration. The general solid acid catalyst is γAl2O3, zeolite, or SiO2-Al2O3. And the optimal reaction temperature of HZSM-5 zeolite matches the methanol synthesis catalyst best. The key effect on the direct DME synthesis is due to the acidity of the HZSM-5. However the acidity of the HZSM-5 is up to the Si/Al ratio on the bone of the zeolite. In this paper, several kinds of HZSM-5 with different Si Al ratios are used to investigate their effects on the direct DME synthesis. The acidity of the zeolite is tested by NH3-TPD. The HZSM-5 zeolites with different Si Al ratios are mechanically mixed with the methanol synthesis catalyst respectively. The bi-functional catalyst is tested on the micro-reactor with an online tail gas analysis system. The feed gas composition is H2:CO:N2:CO2:CH4 = 60:30:3:4:3. The reaction conditions are 493 K-553 K, 2 MPa-4 MPa, and 1000 h-1-4000 h-1. With the decrease of the Si/Al ratio, the acidity of the HZSM-5 increases and the CO single pass conversion increases. The selectivity order of CO to DME with different Si Al ratio is sDME (cat38) > SDME (cat50) > sDME (cat25). The highest space time yield (STY) is 0.38 gDMEgcat·h-1 at the reaction condition of 553 K, 3 MPa and 4000 h-1 on the catalyst with Si Al ratio 25, which is the best Si Al ratio among the reaction condition range. From the NH3-TPD spectrum, the smaller the Si Al value is, the stronger the acidity on the strong acid site (Bronsted acid) is. The dehydration process happens on the B acid site of the zeolite. With small Si Al ratio, the results of methanol dehydration on the zeolite will be better. It can enhance the CO hydrogenation. So the CO single pass conversion increase with the decrease of the Si Al ratio. If the Si/Al ratio is too small, the acidity on the B acid site will become too strong and the DME formed on the zeolite will be dehydrated further to form hydrocarbons such as C2H2 and C2H4. According to our

关 键 词：二甲醚 HZSM-5 硅铝比 

分 类 号：O643.32[理学—物理化学]