分子筛晶粒大小及磷改性对ZSM-5催化甲醇转化制丙烯的影响

 采用水热法合成了晶粒大小分别为5、1和0.25 ?m的3种ZSM-5分子筛样品，并对0.25 ?m 粒径的ZSM-5分子筛进行磷改性。采用SEM、NH3-TPD和TGA等技术对它们进行了表征，并将它们作为催化剂用于甲醇转化制丙烯反应，考察了ZSM-5分子筛晶粒大小和磷改性对催化剂活性和稳定性的影响。结果表明，尽管3种晶粒尺寸的分子筛具有相近的表面酸性，但小晶粒的ZSM-5分子筛(粒径0.25 μm)具有微孔短、外比表面积大和孔口多的特点，表现出较高的丙烯收率和较好的稳定性。适量的磷改性可显著提高小晶粒ZSM-5分子筛催化剂的活性和稳定性。在常压、甲醇空速(WHSV)为3 h-1和温度为500 ℃的反应条件下，丙烯的初始收率达48％以上，维持在45％以上的时间长达100 h以上。

EFFECTS OF CRYSTAL SIZE AND PHOSPHORUS MODIFICATION OF ZSM-5 ZEOLITE ON ITS CATALYTIC PERFORMANCE IN THE CONVERSION OF METHANOL TO PROPYLENE

Three ZSM-5 zeolite samples with different crystal sizes of 5, 1 and 0.25 μm, respectively, were synthesized hydrothermally, and the effect of crystal size on the catalytic performance of ZSM-5 zeolite for conversion of methanol to propylene was studied by SEM, NH3-TPD and TGA techniques. The results showed that although the three ZSM-5 zeolite samples had similar amount of acid sites, the sample with small crystal size (0.25 μm) showed higher selectivity of propylene and better durability in the catalytic conversion of methanol, which might be due to its shorter pore length, higher surface area and more pore mouth. Modification with suitable amount of phosphorous greatly increased the activity and stability of the HZSM-5 zeolite with small crystal size (0.25 μm). Under the reaction conditions of atmospheric pressure, WHSV=3 h-1 and reaction temperature=550℃, a high initial propylene yield of higher than 48 % could be obtained, and the reaction time in which propylene yield remaining higher than 45 % could be prolonged to over 100 h.