M.S.

Any operation that will effect a saving in heat is vitally important to industry. A principle which has reseived increasing attention during the past few years from those who are concerned with the separation of close boiling mixtures is extractive distillation. The selective action of a solvent, which is relatively non-volatile compared to the components of a mixture to be separated, is utilized. The solvent and extract are then separated by distillation, and part of the extract is recycled as reflux. A spiral-packed column for use in extractive distillation was designed and constructed. The extraction assembly consists of a single helicoid flight with a pitch of two, wound around and welded to a standard two-inch pipe, and machined to a “light driving fit” within a five-foot length of standard five-inch heavy duty pipe which had been bored to a diameter of five inches. The five-foot length of annular space between the two pipes is thus converted into a 27.9 foot spiral column of 1.175 by 1.75 inches cross-section. The principle of design involved is an attempt to obtain the effect of a 28-foot tower in one compact five-foot column. The feed from overhead tanks enters at a point midway in the column through a dispersion device. The solvent enters at the top of the column, and is saturated with a recycle of the raffinate product. A calculated amount of extract product is recycled as reflux near the base of the column. The raffinate product leaves the column at the top, and the solvent saturated with extract flows from the bottom. The equipment was tested with the system methylcyclohexane-petroleum naphtha-aniline at 25°C. ± 1°C. Saturation of equilibrium data with the corresponding refractive indices were determined. Rates of flow and reflux ratios were calculated by the material balance of Varteressian and Fenake which is based on the properties of the triangular diagram. From a 50-50 per cent mixture by weight on a solvent-free basis of methylcyclohexane and petroleum naphtha, a product containing 63 per cent by weight on a solvent-free basis of petroleum naphtha at a reflux ratio of 2.69, and a product containing 74 per cent by weight on a solvent-free basis of petroleum naphtha using a reflux of 6.5 can be obtained. / M.S.