GB733580A - Method and apparatus for separating materials by continuous liquid thermal diffusion - Google Patents

Abstract

<PICT:0733580/III/1> <PICT:0733580/III/2> In the continuous separation of liquids by thermal diffusion, the liquid is passed through a narrow uniform slit formed between two walls spaced equidistantly apart at about 0.01-0.15 inch and maintained at different temperatures, a liquid-permeable membrane being arranged intermediate and parallel to the wall faces; liquid is fed into the space between the membrane and one of the walls, and one fraction is withdrawn from a point remote from the inlet on the same side of the membrane, and another fraction from the space on the other side of the membrane. In Fig. 1 the membrane 16 is arranged between two wall faces 17, 24 which are cooled and heated respectively by jackets 31, 36. Inlet and outlet ports 21, 22, 29, 30 are provided at the ends of the slit or at an intermediate point 40. In Fig. 28 (not shown) two slits have their hot walls arranged back to back and heated by an electric resistance element. Fig. 29 shows apparatus in which the slit-forming surfaces are in tubular form, membranes 52 being interposed between the surfaces of tubes 46, 47; the liquid treated and the fractions withdrawn flow through lines 61, 62, 64, 66, and heating or cooling media are circulated via lines 67, 69, 70, 71. The walls are made from material which is liquid impervious, heat conductive, and unreactive with the substances being separated; suitable materials are stainless steel, copper, aluminium, glass, brass and other alloys. Membranes may consist of paper (e.g. duplicator or tracing), a film of bentonite clay, a thin sheet of porous stainless steel, or a laminate of fibre glass impregnated with a clay filler. The slit may be in a vertical, horizontal, or inclined position; one of the fractions withdrawn may be passed to a second slit for further separation, and so on. A series of diagrams show various arrangements of input and withdrawal ports, and flow patterns for multiple slit operation. The directions of introduction and withdrawal are preferably such as not to interfere with thermal circulation within the slit; the rate of flow of liquid may, however, be greater than that of thermal circulation. Graphs show the relationship between the degree of separation and the feed rate, with different wall face areas, membranes and flow patterns; results obtained using slits without membrances are included for comparison. Examples relate to the separation of mixtures of cetane and methyl naphthalene, benzyl alcohol and ethylene glycol, and a petroleum lubricating oil into fractions of different viscosities. Reference is also made to the separation of isomeric hydrocarbons, vegetable oils, fats, and waxes, hormones, viruses, antibiotics and vitamins.