酸改性高岭土在合成气一步法制备二甲醚中的应用

分别以1.0mol/L的硫酸、盐酸、硝酸为改性剂,采用浸渍法制备了一系列酸改性高岭土;以酸改性高岭土为甲醇脱水催化剂,与甲醇合成催化剂XNC-98混合制备了适用于合成气一步法制备二甲醚(DME)的双功能催化剂;考察了双功能催化剂对DME合成反应的活性,并采用X射线衍射、N2吸附-脱附实验表征了酸改性后高岭土的结构和性能。表征结果显示,高岭土经酸改性后,其比表面积及高岭土中高岭石的结晶度显著提高。活性评价实验结果表明,以硫酸改性的高岭土作为甲醇脱水催化剂,可显著提高高岭土催化甲醇脱水的性能。还考察了硫酸浓度对DME合成反应的影响,实验结果表明,在处理时间7h、处理温度50℃的条件下,硫酸浓度为0.5mol/L时,CO转化率和DME收率最高。在V(H2)∶V(CO)=1、250℃、3M Pa、空速3 000mL/(g.h)的反应条件下,CO转化率为56.1%,DME收率为37.2%,DME选择性为99.9%。

Application of Acid-Modified Kaolin in One-Step Synthesis of Dimethyl Ether from Syngas

A series of kaolin samples were separately modified with 1.0 mol/L sulfuric acid,hydrochloric acid and nitric acid by impregnation.One-step synthesis of dimethyl ether from syngas was carried out in a fixed-bed continuous flow reactor over a bifunctional catalyst.The catalyst was composed of a part for methanol synthesis-XNC-98 catalyst(including 52%CuO,20%ZnO,8%Al2O3 in mass fraction) and another part for methanol dehydration-acid modified kaolin.The ratio of two part was 6 ∶1.The structure and properties of acid-modified kaolin were characterized by XRD and BET.Specific surface area of acid-modified kaolin and crystallinity of kaolinite in kaolin increased remarkably,and the crystallite size became smaller.Modification of kaolin with sulfuric acid remarkably improved conversion of carbon monoxide and activity of methanol dehydration.Effect of sulfuric acid concentration on the reaction was investigated.The optimal acid treatment conditions were: treatment temperature 50 ℃,treatment time 7 h and concentration of sulfuric acid 0.5 mol/L.Optimal conditions for one-step synthesis of DME were: V(H2) ∶V(CO) 1,250 ℃,3 MPa,and space velocity 3 000 mL/(g·h),under which conversion of carbon monoxide was 56.1%,yield to DME was 37.2% and selectivity to DME is 99.9%.