Many studies have been performed in the hopes of developing an economically viable process for producing multi-carbon alcohols, such as butanol and hexanol. Because these multi-carbon alcohols may be used as fuel or fuel additives in an internal combustion engine, the multi-carbon alcohols present a possible solution to the problem of worldwide dependency on oil. In some cases, butanol and hexanol may present a better fuel option than ethanol because these compounds are more similar to gasoline than ethanol, e.g., similar longer hydrocarbon chains and non-polar characteristics. In addition to being used in fuel applications, butanol may also be used in the manufacture of pharmaceuticals, polymers, pyroxylin plastics, herbicide esters, and butyl xanthate. Butanol and/or hexanol may also be used as solvents for the extraction of essential oils; as an ingredient in perfumes; as an extractant in the manufacture of antibiotics, hormones, and vitamins; as a solvent for paints, coatings, natural resins, gums, synthetic resins, alkaloids, and camphor; as a softener; as a swelling agent in textiles; as a component of brake fluids, cleaning formulations, degreasers, and repellents; and as a component of ore floatation agents and of wood-treating systems.
Butanol is typically produced by reacting petrochemical feedstock propylene in the presence of a rhodium-based homogeneous catalyst. In this process, propylene is hydroformylated to butyraldehyde, which is then hydrogenated to produce butanol. The cost of producing butanol using this method, however, has become unpredictable due to the fluctuating natural gas and crude oil prices.
Butanol may also be produced via the condensation of ethanol over a basic catalyst at high temperature using the Guerbet reaction. The reaction mechanism of the Guerbet reaction may comprise the sequence shown in Reaction Scheme 1. Two ethanol molecules are oxidized to the respective intermediate aldehydes. Two of the aldehydes undergo an aldol condensation reaction to form crotonaldehyde, which is then reduced to butanol via hydrogenation.

Hexanol is typically produced via the oligomerization of ethylene using triethylaluminium followed by oxidation of alkylaluminium products. This process, however, presents significant safety hazards due to the high reactivity of triethylaluminum.
Although various reaction schemes may be known, there has been little, if any, disclosure relating to separation schemes that may be employed to effectively separate the multi-carbon alcohols, e.g., butanol and/or hexanol, from the crude reaction product formed via the various reaction schemes. Thus, the need exists for separation schemes capable of effectively yielding a purified multi-carbon alcohol product from the crude reaction product(s).
The references mentioned above are hereby incorporated by reference.