Solvent-based fatty alcohol synthesis using supercritical butane: Flowsheet analysis and process design

The liquid-phase hydrogenolysis of fatty esters to fatty alcohols is an important step in the industrial manufacture of surfactants and detergents. High operating pressures are necessary, due to the low solubility of hydrogen in fatty esters feeds. In principle, these high operating pressures might be overcome by use of a suitable solvent, but only at the expense of large solvent recycle and cumbersome product-solvent separation. The employ of supercritical solvents may resolve these drawbacks, as an elegant solvent-product separation is possible by reverting to the subcritical regime. In the present work the hydrogenolysis of methyl palmitate in supercritical butane is investigated by simulation. Operating conditions are analyzed on the basis of vapor liquid equilibrium data and chemical equilibrium considerations. Separation and recycle problems are evaluated and discussed on the basis of a flowsheet analysis. It is demonstrated that an efficient hydrogenolysis process may be developed by using supercritical butane as solvent. A moderate operating pressure (9 MPa) and temperature (470 K) lead to high conversion levels and high product purity. A hydrogen to ester molar ratio of 4∶1 in the feed is achievable, which compares favorably to existing liquid-and gas-phase processes, and allows recycle streams to be reduced.