Manufacture of alcohols from alkyl sulphates

摘要

Alcohols are prepared by the acid hydrolysis of acid mixtures of mono- and di-alkyl sulphates, viz. mixtures containing one or more mono- and one or more di-alkyl sulphates having at least 5 carbon atoms in each alkyl radical and containing aqueous acid, such as sulphuric acid, sufficient in amount at least to initiate the hydrolysis of the said mono-alkyl sulphates, by a continuous process carried out in at least two reactors arranged in series for cascade flow wherein the said acid mixture is heated in the first reactor, if necessary after the addition of water, the resulting mixture of an oil phase comprising dialkyl sulphate and alcohol and an aqueous acid phase is subjected in the second reactor to steam distillation for hydrolysis of dialkyl sulphate and removal of alcohol, the rate of flow of the mixture through the first reactor is such that substantially all the monoalkyl sulphate but substantially none of the dialkyl sulphate is hydrolysed in the first reactor, the residual mixture discharged from the second reactor is withdrawn from the lower end thereof, and the rates of inflow of the liquid in this reactor and removal of alcohol therefrom are such as to allow at least a partial separation of the phases therein, with the result that the residence time of the oil phase therein exceeds that of the denser aqueous phase. The steam distillation removes the alcohol formed in the first reactor and also, as it is formed, that produced in the second reactor; accordingly owing to the shorter residence time of the aqueous acid phase in the second reactor, the residence time of the dialkyl sulphate contained in the oil phase can be increased to the extent required for substantially complete hydrolysis without appreciable loss of alcohol by its dehydration by the acid, the concentration of which otherwise increases as the hydrolysis proceeds. The invention also includes apparatus suitable for use in the process, comprising as shown, two reactors 1, 2 arranged in series for cascade flow, the first being adapted to be heated and having at its upper part a discharge pipe 13 discharging, at a level substantially below its inlet, into the second reactor 2 provided with a steam injection pipe 15, an outlet 17 for vapour and a U-pipe 14 whose inlet is at the lower end of the reactor 2 and its outlet is substantially above its inlet, whereby the desired level of liquid in the reactor is maintained. To ensure completeness of hydrolysis it is preferred to provide, as shown, at least one more reactor in series with the second reactor, the additional reactor or reactors being the same as the second reactor in function and mode of operation. The alkyl sulphate starting materials may conveniently be obtained by sulphation of olefin mixtures derived from cracked wax distillates and containing, for example, 5 to 12 carbon atoms. In an example, a cracked wax distillate (A) containing mainly C7 olefins is sulphated with sulphuric acid B in a reactor 10, for example, in the manner described in Specification 655,459, and the resulting mixture of mono- and di-alkyl sulphates, sulphuric acid, polymers and unreacted hydrocarbons is fed together with water into first reactor 1 via inlet 11 and heated therein by steam injector 12, whereby the bulk of the mono-alkyl sulphate is hydrolysed. The mixture then passes via line 13 into the second reactor 2 where it forms an upper mainly oily layer and a lower mainly aqueous layer. The aqueous phase of water and sulphuric acid runs through the reactor in a comparatively short time and flows out from the bottom through U-pipe 14. The oily layer remains longer in the reactor and is subjected to the action of steam introduced via pipe 15 whereby dialkyl sulphate and residual monoalkyl sulphate are hydrolysed and alcohol distilled off. The alcohol vapour and steam pass through a cyclone 17 to a condenser and separator 19 from which alcohol is removed via line 21 and water via line 20. The aqueous acid phase with entrained oil phase leaving reactor 2 through line 14 is led into a third reactor 3 where an oily layer again forms and is treated as in the previous reactor while the aqueous layer passes via U-shaped outlet pipe 14a to a separator 22 wherein a lower layer of dilute sulphuric acid is separated from an upper layer of any residual polymer or other by-products. Syphon breakers 24, 24a vented to the atmosphere via reflux condensers are provided on U-pipes 14, 14a. The above process may be modified by effecting steam distillation of a portion of alcohol from reactor 1.