造核-包衣法制备Al_(2)O_(3)小球及其在丙烷直接脱氢反应中的应用研究

Study on preparation of spherical Al_(2)O_(3) by nucleation-coating method and its application in propane dehydrogenation

氧化铝(Al_(2)O_(3))载体是应用最广泛的催化剂的核心材料之一,而球形Al_(2)O_(3)载体取代条形Al_(2)O_(3)载体已成为大趋势,因此亟需发展绿色可行的制备球形Al_(2)O_(3)载体新方法。首先对滚球法进行了优化,以拟薄水铝石粉体为原料,硝酸为胶溶剂,羟丙基甲基纤维素为粘结剂,采用造核-包衣法制备了球形度好、强度高且比表面积大的Al_(2)O_(3)小球。结合X射线衍射(XRD)、扫描电子显微镜(SEM)等表征手段考察了水粉比(质量比)、酸粉比(质量比)、粘结剂含量(质量分数)和抛丸时间对Al_(2)O_(3)小球的强度和孔结构的影响。结果表明,控制酸粉比为0.050、水粉比为0.88、粘结剂含量为3%(质量分数)和每次抛丸时间为5 min,能够制备出粒径均匀、成品率高且强度高达43.0 N的Al_(2)O_(3)小球。在此基础上,制备了球形和粉末PtSn/Al_(2)O_(3)催化剂,并在温度为618℃、H_(2)和C_(3)H_(8)流量分别为3.6 mL/min和6.0 mL/min的条件下应用于丙烷直接脱氢反应,发现球形PtSn/Al_(2)O_(3)催化剂表现出与粉末PtSn/Al_(2)O_(3)催化剂接近的反应活性和选择性。造核-包衣法是一种绿色高效的制备球形Al_(2)O_(3)载体的方法,可为球形Al_(2)O_(3)载体国产化提供新的思路。

Aluminum oxide(Al_(2)O_(3))support is one of the most widely used catalytic materials,and replacing linear Al_(2)O_(3) support with spherical Al_(2)O_(3) support has become a major trend,so it is urgent to develop novel green and feasible methods for producing spherical Al_(2)O_(3) support.Firstly,spherical Al_(2)O_(3) with excellent sphericity,high strength and large specific surface area was prepared by nucleation-coating method:using pseudo boehmite as the raw material,nitric acid as the peptiser and hydroxypropyl methyl cellulose as the binder to optimize the rolling ball method.The effects of water-powder ratio(mass ratio),acid-powder ratio(mass ratio),binder content(mass fraction)and blasting time on the strength and pore structure of spherical Al_(2)O_(3) were investigated by characterization methods such as X-ray diffraction(XRD)and scanning electron microscopy(SEM).The results show that spherical Al_(2)O_(3) with uniform particle size,high yield and high average compressive strength of 43.0 N can be prepared by controlling the acid-powder ratio of 0.050,water-powder ratio of 0.88,binder content of 3%(mass fraction)and blasting time of 5 min.Furthermore,spherical and powder PtSn/Al_(2)O_(3) catalysts were prepared and applied to propane dehydrogenation at 618℃,H_(2) and C_(3)H_(8) flow rate of 3.6 mL/min and 6.0 mL/min,respectively.The spherical PtSn/Al_(2)O_(3)catalyst shows similar activity and selectivity as the powder PtSn/Al_(2)O_(3)catalyst.Nucleation-coating method is green and efficient to prepare spherical Al_(2)O_(3) support,which provides inspirations for localization of spherical Al_(2)O_(3) support.