Patent GB-715483-A (GB)
Title: Improvements in or relating to modified weak-acid isopropanol process
Inventor: JR ERWIN HAMER AMICK
IPC: C07C29/06
Filed: 1951-09-06
Abstract: <PICT:0715483/IV (b)/1> A continuous process for the production of isopropanol comprises absorbing propylene countercurrently in sulphuric acid of 60 to 70, preferably 65 to 68 weight per cent concentration in an absorbtion zone, removing from the absorption zone an acid extract containing 0.6 to 1.5 moles of propylene and propylene derivatives per mole of sulphuric acid, passing said acid extract into a generator-stripper zone, removing a hydration product distillate from the generator-stripper zone comprising 3 to 20 weight per cent of the propylene derivatives in the acid extract, recovering isopropanol from the distillate and in the absorption zone absorbing fresh propylene in residual acid extract of acid strength 60 to 70 weight per cent, which has been, if necessary diluted with water to restore its acid strength to 60 to 70 weight per cent.  In Fig. 1, propylene rich gas or liquid substantially free from C4 unsaturated compounds, particularly butadiene is introduced through line 2 into absorber 1.  Recycled sulphuric acid-propylene extract previously prepared by absorbing 0.6 to 1.5 moles of propylene in each mole of sulphuric acid and stripping and diluting in generator-stripper 6, is withdrawn and pumped through lines 13 and 3 into absorber 1 at a point or points near the top thereof.  The absorber may be operated at elevated temperature and pressure.  The extract is removed via line 5 to the alcohol generation without dilution with water and unabsorbed gases leave the tower via line 4.  The generator stripper is operated under a subatmospheric pressure maintained, e.g. by a steam ejector 32 or vacuum pump.  Alternatively stripping is carried out with the aid of an inert gas such as nitrogen or carbon dioxide or with a propylene containing gas such as the propylene feed gas or propylene-containing gases recovered from the water scrubber via lines 31 and 34, when pressures up to and including atmospheric pressure may be employed.  When steam is employed only sufficient is introduced into the generator-stripper via line 7 to replace water consumed in the formation of the products removed.  The partially stripped hot acid extract is removed via line 9, cooled in cooler 10, led by line 11 to pump 12 and returned via lines 13 and 3 to the upper section of the absorber 1.  If necessary, further acid is added to the extract via line 14.  Overhead vapours from the generator-stripper consisting of isopropyl alcohol, isopropyl ether and propylene are scrubbed with dilute aqueous caustic solution in scrubber 15, condensed in condenser 19 and pass via drum 21 and pump 23 to storage.  Uncondensed gases are vented from the condensate drum and scrubbed in scrubber 26 in countercurrent to water introduced through line 27.  The aqueous solution of alcohol and ether produced passes through lines 28 and 30 and pump 29 to storage.  Overhead vapours consisting substantially of propylene are removed through the steam ejector 32 and line 34 and may be burnt or recycled to the absorption zone.  Isopropyl ether stripped from the crude alcohol may be returned to the absorption zone to repress ether formation.  In a working example propylene is employed as starting material, the generator stripper zone is operated under reduced pressure and a distillate containing isopropanol and isopropyl ether is obtained and concentrated.  Acid extract from the bottom of the vaporization zone is returned to the top of the absorber where additional propylene is absorbed.  Water is added to restore the acid concentration to the initial value.  Variations of distillate composition and yield with absolute pressure on distillation of an acid extract are illustrated in Figs. 2 and 3 (not shown).