Acetonitrile is a widely used in the pharmceutical and fine chemicals industries. Many of these application also involve in water and as part of the process an acetonitrile/water mixture is produced. However, acetonitrile forms an azeotrope with water at 85% acetonitrile. The traditional method of separating the mixture is pressure swing distillation. A first vaccum column is used to produce 95% acetonitrile. The second high pressure column produces dry acetonitrile (99.7% acetonitrile) as a bottoms products and 85% acetonitrile in the overhead vapor. The overhead is recycled to the vaccum column feed. Operation of this unit is straightforward but steam consumption is high at about 4 tons per ton of acetonitrile.
The SolSep zeolite membrane process replaces the large vaccum distillation column with a compact membrane unit producing 99.5% acetonitrile vapor. Almost complete recovery of the acetonitrile feed is achieved and steam consumption is cut in half.
A 10,000 ton/year acetonitrile plant separating water from 78 wt% acetonitrile producing 99 wt% acetonitrile.