GB652624A - Isopropanol production - Google Patents

Abstract

<PICT:0652624/IV (b)/1> <PICT:0652624/IV (b)/2> Isopropyl alcohol is prepared by contacting a propylene-rich hydrocarbon fraction with sulphuric acid of 65-85 per cent concentration (by weight) at a temperature between 140 DEG and 190 DEG F. and pressure between 100 and 500 lbs./sq. inch in an absorption zone to form a propyl extract, passing the extract to a hydrolysis-stripping zone in which it is diluted with water to an acid concentration of 40-50 per cent, the diluted extract being maintained in the hydrolysis-stripping zone at an elevated temperature and for a sufficient time to cause substantial hydrolysis of the extract to isopropyl alcohol, stripping the isopropyl alcohol so formed from the stripping zone with steam, whereby dilute aqueous isopropyl alcohol is recovered as vapours overhead, washing this dilute aqueous alcohol to remove sulphuric acid, and fractionally distilling the product to recover concentrated isopropyl alcohol; the temperature in the absorption zone is controlled by continuously withdrawing a part of the extract, cooling it and recycling it to the absorption zone. In the Figures, propylene-rich gas or liquid, substantially free of unsaturated C4 compounds, particularly butadiene, is introduced through line 2 into absorber 1 by means of jets. Approximately 70 per cent sulphuric acid is continuously pumped from storage tank 4 through line 3 into the absorber at a point or points near the top thereof. The heat of reaction is removed by circulation of extract through line 5 and an external cooler 6 and thence back to the top of the absorber. The extract may be added to the acid line 3 as well as directly to the absorber. Residue gas leaves the absorber through line 7 and enters a packed scrubber 7a where it is counter-currently water-washed to extract the alcohol and acid content thereof. Water is fed to the scrubber through line 8 and the washed residue gas passes overhead from the scrubber through line 9, is caustic washed and then returned to the refinery for further use. The dilute aqueous mixture of alcohol and acid from the scrubber is removed through line 10 and led to the generator 12 for use in diluting the acid extract to 45 per cent for the completion of hydrolysis. This aqueous mixture also serves to remove entrained acid from the overhead passing through line 15. Alternatively, the dilute aqueous alcohol and acid mixture withdrawn from the scrubber may be withdrawn through line 13 and added to the extract leaving the absorber through line 11. In such a case the mixture passes to mixer 14 where the extract is diluted and mixed before passing to the top of the generator or hydrolysis zone 12. In the generator 12 the extract is diluted to approximately 45 per cent sulphuric acid and is maintained at a temperature of approximately 190 DEG C. for ten minutes. The generator also serves as a stripping zone, whereby the alcohol produced by the hydrolysis is steam-stripped and leaves the generator at a point near the top thereof by the line 15. Spent acid of approximately 45 per cent strength is withdrawn at the bottom of tower by the line 16 and led to the reboiler 17 for concentration to 70 per cent acid which is removed from the reboiler by line 20, cooled in cooler 21 and returned by line 22 to the acid storage tank 4. Vapour from the reboiler is returned to the generator by line 18 and serves as stripping steam. Additional stripping steam, if required, is supplied to the generator through line 19. Overheads from the generator, consisting of isopropyl alcohol of approximately 65 per cent strength (by volume), isopropyl ether and hydrocarbon gases, enter the alcohol scrubber 25 at a point near its mid-section. The overhead vapours are countercurrently scrubbed with water entering the top of the tower through line 26 and with dilute (5-10 per cent) aqueous caustic soda which enters the top of the tower through line 27. Spent caustic solution at the bottom of the scrubber is steam-stripped to remove the alcohol content by means of steam entering through line 28. Spent caustic is removed through line 29. Alcohol vapours from the scrubber are removed overhead through line 30, condensed in condenser 31 and cooled in cooler 32. Non-condensable gases from the condenser and cooler are removed through lines 36 and 35 and are water-washed in scrubber 38 supplied by water through line 39. Non-condensable gases are removed through line 40. The cool alcohol is removed from the cooler 32 through line 33 to storage drum 34. Vapours from the storage drum are passed through line 37 to scrubber 38. The dilute alcohol-water mixture leaving the bottom of the scrubber by means of pipe 41 is added to the crude aqueous alcohol in the storage drum together with additional water to dilute the crude alcohol to approximately 30-50 per cent strength (by volume). The alcohol may be allowed to settle to separate from any polymers and then passed through line 42 to a run-down tank. Crude isopropyl alcohol of 30-50 per cent strength (by volume) is led through line 42 to the preheating zone 43 and thence through line 44 to the heads column 45 where it is steam stripped to remove low-boiling water-insoluble impurities which pass through line 46. The weak aqueous alcohol is withdrawn as bottoms from the heads column. Ether and hydrocarbon vapours together with some alcohol and water are taken through line 46, condensed in condenser 47, cooled in cooler 48 and led to a reflux drum 49. Reflux is supplied to the top of the column from drum 49 through line 50. Part of the reflux is withdrawn through line 51 and carried to vessel 52 where the ether and polymers are water washed to recover the alcohol therefrom and allowed to settle into 2 layers. Part of the aqueous alcohol layer is withdrawn and refluxed to the heads column through line 53. The remainder is withdrawn through line 60 and sent to storage for later use in dilution of the crude alcohol before entering the finishing operation. Aqueous alcohol free of ether and light hydrocarbon polymers is withdrawn through line 55 and enters the alcohol column for concentration at a point near the bottom thereof. In the alcohol column the alcohol is concentrated to composition approaching its azeotrope with water, i.e. 91 per cent volume isopropyl alcohol and 90 per cent water. The mixture is taken overhead through line 57 and cooled in cooler 61. Part of the cooled material is returned to the column as reflux through the line 62. The balance of the alcohol is sent through line 63 to the acetone column 64 for removal of acetone. Any uncondensed material contained in the overhead from the alcohol column is returned via line 65 to the heads column for further treatment. In the acetone column, acetone is separated from the isopropyl alcohol, is taken through line 66 to cooler 67 and led to storage by line 68, a portion being passed as reflux to the column by line 69. Isopropyl alcohol free of acetone is removed from the acetone column through line 70, is cooled in cooler 71 and led to storage through line 72. The polymer material formed in the alcohol column 56 is withdrawn through line 59 and sent to vessel 52. Bottoms from the alcohol column consisting mainly of water are withdrawn through line 58.