GB713759A - Improvements relating to short-path fractionating stills - Google Patents

Abstract

<PICT:0713759/III/1> <PICT:0713759/III/2> <PICT:0713759/III/3> A short-path fractionating still comprises a rectangular container within which a plurality of elongated evaporating compartments are arranged in step-like formation at progressively increasing heights and are disposed transversely of the longitudinal axis, and substantially across the width, of the container, a sloping cooled surface being provided over each compartment in such a manner that the liquid evaporated from one compartment and condensing on the corresponding cooled surface will run down that surface and drip therefrom into the next higher evaporating compartment. The still may be constructed so that the series of evaporating compartment forms the main body of the still, to which a cover member is attached by means of a fluid-tight joint, the cooling surfaces being mounted on the underside of the cover member. The main body of the still and the cover member form together a vacuum-tight container so that it is not necessary to enclose the still in a vacuum chamber. In Fig. 1, the main body 1 is formed of a plurality of compartments 11, and a plurality of electric heaters 2 are secured on the underside. Solid bodies 4 having sloping surfaces 4a terminating in edges 13 are attached to the underside of cover member 6. The bodies 4 are provided with internal ducts 5 for the cooling medium, the supply pipes 5a for the ducts being passed through the cover members 6 (Fig. 2). The side walls 12 of the still are provided with a cooling jacket 3 and are spaced from the sides of the row of condenser bodies 4 so as to leave longitudinal ducts 7 through which the non-condensable vapours and gases evolved during distillation may be pumped away. Baffles 8, attached to the condenser bodies 4 and cooled by conduction, prevent an excessive flow of evaporated molecules into the ducts 7. The baffles 8 have openings 9 which lead from the space between the condenser bodies 4 into the ducts 7, which are provided at one or more places with pipes 10 connected to vacuum pumps. Distilland is introduced by means of feed-pipe 16 into one of the compartments 11. Distillate is withdrawn from the uppermost compartment 11 through outlet 17 having a valve 18. Distillation-residue is withdrawn from the lowest compartment through outlet 19. If desired means may be provided for the controlled withdrawal of fractions from any of the intermediate compartments. The compartments are provided with outlets 14 (Fig. 3) to control the direction of flow of the distilland through the still; in each alternate compartment there is an outlet at the centre, while the adjacent compartments have outlets at both sides. The condenser bodies are shaped so as to deliver liquid into each side of the former compartments and into the centre of the latter. The rate at which distillate is withdrawn from the uppermost compartment may be controlled by valve 18 so as to obtain a reflux effect, excess distillate being allowed to overflow from the uppermost into the next lower compartment. Specification 655,323 is referred to.