Original Article:
Effect of Ba impregnation on Al2O3 catalyst for 1-octene production by 1-octanol dehydration
Young-eun Kim, et al.
Fuel 281 (2020): 118791.
10.1016/j.fuel.2020.118791
Linear α-olefins (LAOs) have double bonds at the end of the linear carbon chain and are useful feedstocks for various petrochemicals. Among them, 1-butene, 1-hexene, and 1-octene are in particularly high demand, and they are used as comonomers in linear low-density polyethylene (LLDPE) and engineering polymers such as plastomers and elastomers. In the production process of 1-octene, the boiling point difference between 1-octene and its isomers (cis- and trans-octene) is only 1-2°C, and their other physical properties are also similar, which means complicates the separation process. In this work, the researchers report an efficient catalytic system for the dehydration of 1-octanol to produce 1-octene with high 1-octene selectivity and fewer isomers.
How to choose the catalyst for the dehydration of 1-octanol to 1-octene?
The catalytic activity of alcohol dehydration depends on the nature of acidic sites as active sites. It has been reported that the acidic sites on the surface of Al2O3 catalysts are closely related to the conversion of 1-octanol during the dehydration reaction. However, highly acidic catalysts such as SiO2-Al2O3 and zeolites will generate a high proportion of isomers during alcohol dehydration because the acidic sites will re-adsorb the generated 1-alkenes for further isomerization reactions. Therefore, the key to the high selectivity of LAO in alcohol dehydration is to control the acidity of the catalyst.
According to the results of Davis et al., Al2O3 modified with alkali metals exhibited different ratios of cis/trans and 2-octene/1-octene in 2-octanol dehydration compared with unmodified Al2O3. The reason is that the basicity of the metal oxide affects the tendency of OH to dehydrate. In addition, the addition of alkali metals to Al2O3 and ThO2 can change the acidity of the catalysts, resulting in higher 1-alkene selectivity.
Therefore, in this study, alkaline earth metal barium and Al2O3 catalysts were used to study the conversion process of 1-octanol dehydration to 1-octene.
Optimum Catalytic Conditions for Dehydration of 1-Octanol to 1-Octene
- In the catalytic system of this study, the intensity distribution of the Lewis acid sites (LAS) of the catalyst changed with the increase of Ba content.
- Compared with pure Al2O3, at 400 °C and LHSV = 7 h-1, the Ba/ Al2O3 catalyst showed similar 1-octanol conversion, as well as higher 1-octene selectivity and 1-octene purity.
- When LHSV > 21 h-1, the catalyst showed a decrease in 1-octanol conversion but maintained high 1-octene selectivity and 1-octene purity.
- When the Ba content reached 2.0 wt%, the 1-octene selectivity decreased because the formation of dioctyl ether became more active than olefin production.
- In conclusion, considering 1-octanol conversion, 1-octene selectivity and 1-octene yield, 1.5wt% Ba/Al2O3 is the best catalytic condition for 1-octanol production of 1-octene.
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