Extraction of alcohols with phosphine oxides

#The extraction of lower alcohols, especially ethanol, from aqueous solutions thereof, especially very dilute solutions, in order to recover the alcohol has become increasingly important in recent years.

#J. W. Roddy, Ind. Eng. Chem. Process Des. Dev., 1981, 20, 104-108 discloses the increased interest in the use of alcohol as an additive to gasoline to improve the octane rating and extend its supply. The use of ethanol, in particular, for this purpose has become increasingly important. Present methods for recovering ethanol, however, have proven expensive in connection with cost and energy consumed because of the need to recover ethanol from water by distillation. Since most ethanol containing waste streams are very dilute in ethanol concentration, distillation has proven to be too costly. It has been determined that a balance between distillation cost and the amount of ethanol recovered centers at aqueous concentrations of ethanol of about 15-25%. Roddy discusses the use of various phosphorus solvents such as triisobutyl phosphate, tris(2-methylbutyl)phosphate, tri-n-butyl phosphate, tris-2-ethylhexyl phosphate and diamyl amyl phosphonate for the extraction of ethanol from aqueous solutions thereof and, although functional, these solvents and the others related therein have not proven to be as effective as at first believed because of their undesirable water-solubility and hydrolytic instability.

#U.S. Pat. No. 4,346,241 is directed to the extraction of alcohols from aqueous solutions utilizing liquid secondary amines and aromatic cyclic amines such as quinoline, 4-n-propylpyridine. These extractants, although relatively insoluble in water are not as effective extractants for ethanol as is required because of their instability at temperatures of distillation. The amines decompose into colored species during distillation and are therefore unacceptable as well as being non-recoverable under these conditions.

#The following examples are set forth for purposes of illustration only and are not to be construed as limitations on the present invention except as set forth in the appended claims. All parts and percentages are by weight unless otherwise specified.

#To a suitable reaction vessel is charged a 10 wt. % aqueous solution of ethanol and a diluent solution of a phosphine oxide. The vessel is sealed and the contents stirred for 15 minutes at 25.degree. C. The results are set forth in Table I, below.

#TABLE I ______________________________________ wt. % Phosphine Ethanol Run Oxide wt. % Diluent A/O Extracted ______________________________________ a TOPO 39 Heptane .23 59 b THPO/TOPO 80 Heptane .43 70 50/50 c TOPO 39 Exxon 100 .19 65 d NONE 0 Heptane .23 4 ______________________________________ TOPO = trin-octylphosphine oxide THPO = trin-hexylphosphine oxide