摘要
BrФnsted-acidic zeolite and zeotype materials are potential catalysts for the conversion of ethene to higher alkenes. In this study, two materials with AFI structure but different acid strength, H-SAPO-5 and H-SSZ-24, were subject to studies of ethene, cis-2-butene and ethene-butene mixture conversion under conditions where C3-C5 alkene formation is thermodynamically favoured over higher hydrocarbons(673-823 K, 1 atm). Ethene and cis-2-butene partial pressures were varied in the range 9-60 and 0.9-8.1 kPa, respectively, and contact times were varied in the range 3.78-756 and 0.573-76.4 s.μmol H+/cm^3 over H-SAPO-5 and H-SSZ-24, respectively. Less than 1% conversion of ethene and less than 10% conversion of butene was obtained in the range of conditions used for elucidation of rate parameters. The ethene conversion rates were more than an order of magnitude higher over the more acidic H-SSZ-24 than over H-SAPO-5(6.5 vs. 0.3 mmol/mol H+.s at 748 K, Pethene = 33 kP a), with corresponding lower reaction order in ethene(1.5 vs. 2.0 at 673 K) and lower apparent activation energy(52 vs. 80 kJ/mol at 698-823 K). Propene selectivity was substantially higher over H-SSZ-24 than over H-SAPO-5(68% vs. 36% at 0.5% ethene conversion). A similar difference in apparent reaction rates was observed for cis-2-butene conversion over the two catalysts, and for co-feeds of ethene and cis-2-butene. However, the cis-2-butene conversion to C3-C5 alkenes was found to be severely influenced by thermodynamic limitations, impeding a detailed kinetic analysis, and leading predominantly to isobutene formation at the highest temperatures.
B酸型分子筛和分子筛型材料是乙烯转化为高级烯烃的潜在催化剂.本文在C3-C5烯烃形成热力学优于高碳氢化合物的条件下(673-823 K, 1 atm),研究了两种具有AFI结构但酸强度不同的H-SAPO-5和H-SSZ-24催化剂上乙烯、顺式-2-丁烯和乙烯-丁烯混合物的转化反应.乙烯和顺式-2-丁烯分压分别在9-60和0.9-8.1 kpa范围内变化,接触时间分别在3.78-756和0.573-76.4 s.μmol H^+/cm^3范围内变化.在用于计算速率常数的条件范围内,乙烯转化率小于1%,丁烯转化率小于10%.在酸性较强的H-SSZ-24上乙烯转化率比H-SAPO-5高一个数量级(748 K时为6.5对0.3 mmol/mol H+.S,戊烯=33KPa),乙烯中相应的反应级数较低(673 K时为1.5对2.0),表观活化能较低(698-823 K时52对80 k J/mol).两种催化剂上顺式-2-丁烯转化率以及乙烯和顺式-2-丁烯共进料的表观反应速率存在相似的差异.然而,顺式-2-丁烯转化为C3-C5烯烃受热力学限制的影响很大,妨碍了详细的动力学分析,并导致在最高温度下主要生成异丁烯.
