负载Pd的分子筛催化剂上烷烃的异构化反应

Isomerization of Alkane on Molecular Sieves Catalyst Loaded with Palladium

采用吡啶吸附红外光谱和氨程序升温脱附法对负载Pd的几种分子筛催化剂(Pd/,βPd/ZSM-22,Pd/SAPO-11)的表面酸性进行了测定,并以正十二烷为模型化合物,在连续流动固定床微型反应器上考察了这几种分子筛催化剂的异构化反应性能。实验结果表明,Pd/β催化剂的酸量大且具有强酸中心;Pd/SAPO-11和Pd/ZSM-22催化剂的酸强度分布类似,但前者的酸量较小,后者的酸量适中。在正十二烷的转化率为65%左右时,对于单、双甲基C12异构体的选择性,Pd/ZSM-22催化剂与Pd/SAPO-11催化剂相近,高于Pd/β催化剂,而催化活性的高低顺序为:Pd/β>Pd/ZSM-22>Pd/SAPO-11,说明Pd/ZSM-22催化剂比较适合于大分子烷烃的异构化反应。在100mL中试装置上,以大庆减四线糠醛精制油为原料,对实验结果进行了验证。

Isomerization of n-dodecane on molecular sieves catalyst loaded with palladium, namely Pd/β, Pd/ZSM-22 and Pd/SAPO-11, in fixed-bed microreactor was investigated. The catalysts were characterized by means of IR and NH3-TPD to determine their surface acidity. Pd/β catalyst possessed high acidity and strong acid sites. Pd/SAPO-11 and Pd/ZSM-22 catalyst possessed similar medium strength acid sites, but Pd/SAPO-11 catalyst had less acid amount than Pd/ZSM-22 catalyst. Isomerization of n-dodecane on these catalysts showed that when n-dodecane conversion reached 65 %, order of selectivity to monomethyl and dimethyl isomers of dodecane was Pd/ZSM-22 ≈ Pd/ SAPO-11 〉 Pd/fl, while activity order was Pd/β 〉 Pd/ZSM-22 〉 Pd/SAPO-11. Pd/ZSM-22 catalyst was the most suitable for isomerization of long-chain alkanes. Reaction results from both microreactor and pilot plant revealed that activity of the molecular sieve-based Pd catalysts mainly depended upon acid strength and number of the acid sites, while their selectivity depended upon acid strength distribution.