Gorzin Fatemeh, Towfighi Darian Jafar, Yaripour Fereydoon, Mousavi Seyyed Mohammad
Department of Chemical Engineering, Tarbiat Modares University P. O. Box 14115-143 Tehran Iran
Catalysis Research Group, Petrochemical Research & Technology Company, National Iranian Petrochemical Company P. O. Box: 1493 Tehran Iran.
RSC Adv. 2018 Dec 7;8(72):41131-41142. doi: 10.1039/c8ra08624a.
In the present work, mesoporosity is introduced into highly siliceous HZSM-5 zeolites (SiO/AlO = 400) by a two-step path including desilication using NaAlO and TPAOH (tetrapropylammonium hydroxide) mixtures, followed by acid washing treatment. The physicochemical properties of conventional microporous HZSM-5 and all treated samples were characterized by ICP-OES, XRD, FE-SEM, BET and NH-TPD methods. The catalytic performance of the HZSM-5 samples was determined in methanol to propylene conversion reaction at 460 °C and methanol WHSV of 0.9 h using feed containing 50 wt% methanol in water. The results showed that the porosity of the desilicated samples has been mainly blocked by sodium aluminate derived deposits and silicon-containing debris. After a subsequent acid washing step with hydrochloric acid, the blocking species were removed which resulted in improving the mesoporosity generated in the desilication step. It was found that alkaline-acid treatment in a NaAlO/TPAOH solution with TPAOH/(NaAlO + TPAOH) = 0.4 followed by acid washing, leads to the formation of narrow and uniform mesoporosity without severely destroying the crystal structure. Also, it exhibits higher selectivities to propylene (37.7 30.7%) and total butylenes (21.2 16.1%), propylene to ethylene ratio (4.0 2.7), as well as total light olefins (68.4 57.9%) compared to the parent catalyst, while its selectivities to C-C alkanes (9.6 13.7%) and heavy hydrocarbons (13.8 28.4%) are relatively lower. The lifetime of the optimum alkaline-acid treated sample (640 h) showed a significant increase compared to that of the parent catalyst (425 h). The results exhibited that desilication process leads to a considerable mesoporosity development, while acid washing treatment mostly influences on the catalyst acidity. Therefore, the combination of the alkaline-acid treatment leads to hierarchical HZSM-5 catalyst formation with tailored pore architecture and surface acidic properties.
在本工作中，通过两步法将介孔引入高硅HZSM-5沸石（SiO/AlO = 400）中，该两步法包括使用偏铝酸钠和氢氧化四丙基铵（TPAOH）混合物进行脱硅，随后进行酸洗处理。通过ICP-OES、XRD、FE-SEM、BET和NH-TPD方法对传统微孔HZSM-5和所有处理过的样品的物理化学性质进行了表征。在460℃、甲醇质量空速为0.9 h、进料中甲醇质量分数为50 wt%的甲醇制丙烯转化反应中测定了HZSM-5样品的催化性能。结果表明，脱硅样品的孔隙率主要被偏铝酸钠衍生的沉积物和含硅碎片堵塞。在用盐酸进行后续酸洗步骤后，堵塞物质被去除，这导致脱硅步骤中产生的介孔率得到改善。研究发现，在TPAOH/(偏铝酸钠 + TPAOH) = 0.4的偏铝酸钠/TPAOH溶液中进行碱酸处理，随后进行酸洗，会形成狭窄且均匀的介孔，而不会严重破坏晶体结构。此外，与母体催化剂相比，它对丙烯（37.7 30.7%）和总丁烯（21.2 16.1%）的选择性更高，丙烯与乙烯的比例（4.0 2.7）以及总轻质烯烃（68.4 57.9%）也更高，而其对C-C烷烃（9.6 13.7%）和重烃（13.8 28.4%）的选择性相对较低。最佳碱酸处理样品的寿命（640 h）与母体催化剂（425 h）相比有显著增加。结果表明，脱硅过程导致了相当程度的介孔率发展，而酸洗处理主要影响催化剂的酸度。因此，碱酸处理的组合导致形成具有定制孔结构和表面酸性性质的分级HZSM-5催化剂。
