Because butanol has a higher boiling point than water, therefore, distillation is not suitable for butanol recovery. Other processes such as adsorption, pervaporation, membrane pertrac — tion, reverse osmosis and gas stripping have been developed to improve recovery perform­ance and reduce costs (Oudshoorn et al., 2009; Ezeji et al., 2004b).

4.1. Adsorption process

Adsorption is the technology operating easily for the butanol separation. Butanol can be ad — sorpted by the adsorbents in the fermenter and then the butanol was obtained by desorp­tion. A variety of materials can be used as adsorbents for butanol recovery and silicalite is the common one used (Qureshi et al., 2005b; Ezeji et al., 2007). Silicalite is a form of silica with a zeolite-like structure and hydrophobic properties, it can selectively adsorb small or­ganic molecule like C1-C5 alcohols from dilute aqueous solutions (Zheng et al., 2009). How­ever, adsorption separation process is not suitable on an industrial or semi-technical scale because the capacity of adsorbent is very low.