Process for preparing tetrahydrofuran

Claim 1

A process for preparing tetrahydrofuran by the dehydrocyclization reaction of 1,4-butanediol in the presence of an acid catalyst, consisting essentially of; (a) supplying 1,4-butanediol and a non-volatile acid catalyst to a reaction zone, (b) reacting said butanediol and said catalyst at a temperature between above the boiling point of an azeotropic mixture of water and tetrahydrofuran and below the boiling point of 1,4-butanediol, (c) continuously removing a vapor mixture of water and tetrahydrofuran from said reaction zone, (d) supplying said vapor mixtures to a first distillation column maintained under a pressure lower than that in said reaction zone and in the range of from atmospheric pressure to 3 kg/cm 2 gauge, (e) distilling a first azeotropic mixture of water and tetrahydrofuran to form a first distillate, (f) supplying said first distillate to a second distillation column maintained under a pressure higher than that in said first distillation column by 3 to 20 kg/cm 2 gauge, (g) distilling a second azeotropic mixture of water and tetrahydrofuran from the top of said second distillation column to form a second distillate, (h) recycling said second distillate to said first distillation column, (i) supplying a substantially water-free-bottom of said second distillation column to a third distillation column maintained under atmospheric pressure or a pressure slightly higher than atmospheric pressure, (j) recycling the bottom of said third distillation column into said reaction zone, and (k) obtaining tetrahydrofuran from the top of said third distillation column.