Separation of alkanes and alcohols with supercritical fluids. Part I: Phase equilibria and viability study

The chemical conversion of detergent range alkanes (12–14 carbon atoms) to alcohols is often incomplete and results in a large amount of residual alkane. This paper shows that these alkanes and alcohols can be separated by supercritical fluids. Ethane, propane and carbon dioxide were selected as possible supercritical solvents while n-tetradecane and 1-dodecanol were selected to represent the alkane–alcohol mixture, as these would be the two most difficult compounds to separate in a C12 to C14 alkane–alcohol mixture. A phase behaviour study and relative solubility analysis revealed that both ethane and carbon dioxide show promise in separating n-tetradecane and 1-dodecanol. Propane was eliminated as possible solvent because the phase behaviour of n-tetradecane and 1-dodecanol in supercritical propane is too similar. A pilot plant study showed that both supercritical ethane and carbon dioxide can be used to separate n-tetradecane and 1-dodecanol, with indications that supercritical ethane may affect a superior separation. An economic analysis, considering the energy requirements, revealed that the most important parameter with regard to energy consumption is the solvent-to-feed ratio. The process utilising ethane is more energy intensive, yet the energy requirements for both processes compare well with other petrochemical separation processes using supercritical fluids. Further investigations with both ethane and carbon dioxide should be conducted to determine which of these two solvents are superior and to optimise the operating parameters.

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► Comparison of phase behaviour of 1-dodecanol and n-tetradecane in supercritical fluids.
► Ethane and carbon dioxide show differences in phase behaviour.
► Pilot plant experiments separated 1-dodecanol and n-tetradecane.
► Viable to separate heavy alkanes and alcohol with supercritical ethane and carbon dioxide.