(61b) Adsorption: A New Look at an Old Unit Operation

While benzene is a widely used feedstock in the production of polymers, lubricants, dyes, pharmaceuticals, and pesticides; it is increasingly a cause for concern due to its carcinogenicity. Thus, removing trace amounts of benzene from contaminated chemical inventories becomes an important step in chemical processing. Such contamination may occur in plant storage tanks, transfer lines, and poorly flushed batch and semi-batch process equipment.

Removal of parts-per-million benzene through distillation is costly and often produces product and by-product streams that still contain measurable amounts of benzene. Similarly, liquid extraction could achieve the desired product purity but still involves an expensive distillation step to recover the solvent.

Using an adsorbent to remove benzene from a liquid solution can be both more effective and economical than distillation. However, benzene does not readily adsorb onto activated alumina, and activated carbon will non-selectively adsorb all hydrocarbons. Alternatively, molecular sieves can be used to adsorb benzene by taking advantage of their size exclusion properties.

In this presentation we show thermodynamic data and discuss the implications for the liquid-phase adsorption of benzene from 1-hexene and n-hexane on molecular sieves. Additionally, we discuss future work on the development of a continuous process in the form of a packed bed adsorber as well as modeling and scale-up possibilities.