复合催化剂中H-ZSM-5酸性对合成气制二甲醚的影响

Effects of Acidities of H\|ZSM\|5 Zeolites on Dimethyl Ether Synthesis from Syngas over Composite Catalysts

对合成气制二甲醚（ Ｄ Ｍ Ｅ）复合催化剂中脱水组分 Ｈ Ｚ Ｓ Ｍ ５ 分子筛进行水热处理及 Ｎ Ｈ３ Ｔ Ｐ Ｄ、 Ｃ Ｏ２ Ｔ Ｐ Ｄ 表征． 研究结果表明， 在 Ｈ Ｚ Ｓ Ｍ ５ 分子筛脱水组分上具有两种酸性中心，高温 Ｎ Ｈ３ 的脱附峰代表强酸中心， 低温 Ｎ Ｈ３ 的脱附峰代表弱酸中心． 同时， 亦有两种不同强度的碱中心． 随 Ｈ Ｚ Ｓ Ｍ ５ 水热处理温度的提高， 总酸量及强酸中心数量逐渐降低， 碱性中心数目随 Ｈ Ｚ Ｓ Ｍ ５ 水热处理温度的提高略有增加， Ｄ Ｍ Ｅ的选择性随之提高． Ｄ Ｍ Ｅ 主要是在 Ｈ Ｚ Ｓ Ｍ５ 分子筛的弱酸中心上生成． 对 Ｈ Ｚ Ｓ Ｍ５ 于 ６００ ℃处理后与铜基催化剂混合制得的复合催化剂， 对其反应性能考察后发现， 当 Ｈ２／ Ｃ Ｏ≈２ 时， ４～６ Ｍ Ｐａ、２ ０００～３ ０００ ｈ－ １、２６０ ℃为最适宜反应条件． 此时， Ｃ Ｏ 的转化率≥ ９０％ ， 对 Ｄ Ｍ Ｅ 和甲醇的选择性为９６％ ， Ｄ Ｍ Ｅ 在所有有机产物中的选择性≥ ８０％ ， Ｄ Ｍ Ｅ的含量≥ ２０％ ． 提高反应压力， Ｃ Ｏ 的转化率及 Ｄ Ｍ Ｅ 在产物中的含量有较大提高， 但对 Ｄ Ｍ Ｅ的选择性影响不大．

The H\|ZSM\|5 zeolites as dehydration component of composite catalyst for dimethyl ether (DME) synthesis were treated by steam at different temperatures, and the effects of different acid sites of H\|ZSM\|5 zeolites on DME formation have been investigated. The profiles of NH 3\|TPD show that there were two desorption peaks of a mmonia over H\|ZSM\|5 zeolites. The low\|temperature desorption peak is usually acribed to the weak acidic OH group, and the high\|temperature one to the strong Brnsted\|type OH group. CO 2\|TPD also gives two different basic sites. The amount of acid sites of H\|ZSM\|5 zeolites , especially that of strong acid sites decreased more drastically with the increasing hydrothermal treatment temperature. The experimental results indicate that DME was formed mainly on the weak acidic site of H\|ZSM\|5 zeolite. The H\|ZSM\|5 zeolites treated by steam at 600 ℃ exhibited high activity for DME formation. When it was used as dehydration component, CO conversion is more than 90%, selectivities to DME and MeOH are higher than 96%, DME selectivity to all organic products is more than 80%, and the content of DME in products is more than 20%(%) under the reaction conditions: H 2/CO≈2, 4~6 MPa, 2 000~3 000 h -1 , 260 ℃. Enhancement of reaction pressure increases the CO conversion and DME content in products, but has no significant effect on thd selectivity to DME.