物理化学学报 >> 2010, Vol. 26 >> Issue (12): 3291-3298.doi: 10.3866/PKU.WHXB20101133

催化和表面结构 上一篇    下一篇

正庚烷在HZSM-5催化剂上的催化裂解行为

胡晓燕, 李春义, 杨朝合   

  1. 中国石油大学(华东)重质油国家重点实验室, 山东青岛266555
  • 收稿日期:2010-07-12 修回日期:2010-09-01 发布日期:2010-12-01
  • 通讯作者: 李春义 E-mail:chyli@upc.edu.cn
  • 基金资助:

    国家重点基础研究发展规划项目(973) (2006CB202505)资助

Catalytic Cracking Behavior of n-Heptane over HZSM-5 Catalyst

HU Xiao-Yan, LI Chun-Yi, YANG Chao-He   

  1. State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao 266555, Shandong Province, P. R. China
  • Received:2010-07-12 Revised:2010-09-01 Published:2010-12-01
  • Contact: LI Chun-Yi E-mail:chyli@upc.edu.cn
  • Supported by:

    The project was supported by the National Key Basic Research Program of China (973) (2006CB202505).

摘要:

以正庚烷为轻质直馏石脑油中烷烃的模型化合物, 研究了它在HZSM-5 催化剂上的裂解反应, 并与1-庚烯裂解反应进行了对比, 考察了水热处理和载体性质对裂解反应的影响. 结果表明: 正庚烷裂解产物中的氢气、甲烷和乙烷等小分子烷烃的含量远高于1-庚烯裂解的情况, 推测主要由烷烃独特的单分子裂解路径造成, 并且液化气(LPG)中丙烯、丁烯等低碳烯烃含量低; 催化剂经水热处理后, 酸量急剧减少, 并且强B 酸(Brönsted acid)的相对含量减少, 导致催化剂的活性显著降低, 氢转移反应减少, 裂化气中烯烃度显著提高. 同时, 产物中C3/C4的摩尔比降低, 推测裂解反应中单分子路径的几率减少. 载体对于正庚烷的裂解反应行为也有较大的影响, 载体中L酸(Lewis acid)的存在, 对于正庚烷的转化有促进作用, 提高了双分子裂解路径在初始反应中所占的比例. 总体来说, 与烯烃分子相比, 烷烃具有较低的反应活性和烯烃选择性, 因此对于在分子筛类催化剂上的催化裂解反应以生产低碳烯烃来说, 并不是一种理想的原料.

关键词: 催化裂解, HZSM-5, 单分子裂解, 低碳烯烃选择性, 酸性, 载体, C3/C4摩尔比

Abstract:

The catalytic cracking of n-heptane, which was selected as a model compound for the paraffin of light straight-run naphtha, was studied over HZSM-5 catalyst in a fixed-bed microreactor. Its catalytic behavior was compared with that of 1-heptene and the effects of hydrothermal treatment and catalyst carrier were evaluated. The results showed that compared with the cracking of 1-heptene, the concentration of hydrogen, methane, and ethane was much higher in the cracked gas obtained from the cracking of n-heptane. We concluded that this mainly originated from the monomolecular cracking pathway while the content of propylene and butylene in liquefied petroleum gas (LPG) was much lower. Upon hydrothermal treatment, the total amount of acid decreased sharply, especially the strong Brönsted acid (B acid) sites, leading to a steep decline in catalytic activity. This was accompanied by the improved propylene/ propane and butylene/butane molar ratios in the products. Meanwhile, the ratio between the C3 and C4 products decreased, suggesting a decrease in the occurrence of monomolecular cracking. The carrier also significantly influenced the cracking behavior of n-heptane. We found that the presence of Lewis acid (L acid) sites in the carrier improved the n-heptane conversion and promoted the bimolecular cracking pathway. Generally, compared with the olefin reactant, paraffin usually shows much lower reactivity and light olefin selectivity and, therefore, it is not a desirable feed for the catalytic cracking reaction over the zeolite catalyst for the purpose of light olefin production.

Key words: Catalytic cracking, HZSM-5, Monomolecular cracking, Light olefin selectivity, Acidity, Carrier, C3/C4 molar ratio

MSC2000: 

  • O643