Patent GB-716423-A (GB)
Title: Improvements in or relating to the purification of alcohols
IPC: C07C29/74
Filed: 1950-11-16
Abstract: <PICT:0716423/IV (b)/1> A crude C4-C20Oxo alcohol contaminated by sulphur-containing impurities as well as by high-boiling impurities which decompose upon the application of heat is purified by introducing the crude alcohol into a primary distillation zone wherein the bottoms temperature is maintained substantially above the normal boiling point of the alcohol whereby heat-sensitive impurities are decomposed, removing overhead from said primary distillation zone an Oxo alcohol-rich product which is essentially free of high-boiling impurities but which contains a light heads fraction boiling below the Oxo alcohol and also at least some low-boiling sulphur-containing impurities, contacting the thus removed Oxo alcohol-rich product with hydrogen at an elevated temperature, preferably at 255 DEG  to 400 DEG  F., and in the presence of a solid contact material effective to remove sulphur whereby said product is desulphurized without effecting any substantial decomposition of Oxo alcohol, passing the thus purified alcohol to a second distillation zone in which the bottoms temperature is maintained lower than that in the primary distillation zone and from which a fraction boiling appreciably below the Oxo alcohol is removed as an overhead stream, and removing purified Oxo alcohol from a lower portion of said second distillation zone.  The process has particular utility in the case of Oxo alcohols prepared by the use of sulphur-insensitive hydrogenation catalysts such as nickel sulphide, tungsten sulphide, or molybdenum sulphide. The hydrodesulphurization stage is preferably carried out in the presence of a sulphur-sensitive hydrogenation catalyst such as nickel, copper, or cobalt metals which are used in finely divided form.  It is preferred to use methanized hydrogen in the desulphurization stage.  The quality of the purified alcohol may be measured by the ester colour as determined from the absorbency of light of the phthalate ester which may be prepared by esterifying the alcohol with phthalic anhydride in the presence of steel filings and by the sulphur content of the alcohol product. The initial and final distillation stages are preferably carried out continuously although they may also be carried out batchwise and pressures other than atmospheric can be employed in either distillation stage, thus reduced pressure may be used in the second distillation stage and super-atmospheric pressure in the initial distillation stage.  In examples (1) the hydro desulphurization of crude iso-octyl alcohol, obtained by oxonation of a C7 olefin and subsequent hydrogenation at 350 DEG  F. and 2700 pounds per square inch gauge hydrogen pressure in the presence of nickel on kieselguhr catalyst, is carried out at 400 DEG  F. under the same hydrogen pressure and with the same catalyst; (2) the hydrodesulphurization of crude iso-octyl alcohol resulting from the use of molybdenum sulphide in the primary hydrogenator in the Oxo synthesis is carried out with methanized hydrogen at 350 DEG  F. in the presence of nickel on kieselguhr as catalyst and at pressures of 100 and 400 pounds per square inch gauge, the molar ratio of hydrogen to alcohol varying from 9.4 to 0.41; (3) an iso-octyl alcohol-rich product prepared by catalytically hydrogenating the oxonation product with a sulphide hydrogenation catalyst is hydrodesulphurized at 290 DEG  F. and 300 DEG  F. in the presence of the catalyst used in (2); (4) as in (2) except that the hydrodesulphurization is carried out at 300 DEG  F.; (5) a mixture of octyl aldehydes prepared by oxonation of a C7 olefin stream in reactor 2 is passed into primary hydrogenator 4 where hydrogenation is effected in the presence of a sulphur-insensitive hydrogenation catalyst, e.g. molybdenum sulphide.  The crude alcohol mixture formed is then passed to an intermediate point of an alcohol stripper fractionating tower 22 which is preferably operated at atmospheric pressure, the vapour temperature at the upper portion of the column being maintained at about 185 DEG  C. whilst a somewhat higher temperature is maintained in the lower portion of the column.  The alcohol product which contains lower boiling impurities is removed overhead and passed via a condenser to the secondary hydrogenator 5 where it is contacted at elevated temperature in the presence of hydrogen with a sulphur-sensitive hydrogenation catalyst such as nickel and the de-sulphurized alcohol is then passed to an intermediate portion of heads column 27 where material boiling below about 180 DEG  C. is removed as an overhead stream, condensed, and at least a part of the condensed liquid returned to the column as reflux whilst the desired alcohol product is removed by line 30.  Bottoms from column 27 may be recycled to the stripper column 22.  The bottoms product from column 22 containing small amounts of alcohol, undecomposed acetals, esters and ethers is removed through line 24.