GB703708A - Continuous process for solvent extraction of castor oil from castor seed - Google Patents

Abstract

<PICT:0703708/III/1> <PICT:0703708/III/2> Castor oil is continuously extracted by a solvent from castor seed in the following steps:-(a) comminuting the seed in the presence of a volatile aliphatic hydrocarbon solvent, (b) converting the seed proteins to a non-gelatinous form, (c) separating the miscella from the solids, (d) cooling the miscella to a temperature at which it separates into two liquid layers, (e) separating the lower layer from the upper layer of the cooled miscella and (f) recovering the castor oil from the solvent of the lower layer by distillation. The commination may be effected in a rotating blade machine or in a ball mill. The solvents specified comprise naphtha of distillation range 65.5 DEG C. to 137.8 DEG C., hexane, <PICT:0703708/III/3> <PICT:0703708/III/4> heptane and octane and gasoline. The seed proteins may be converted to a non-gelatinous form by heating the seed-solvent slurry to 65.5 DEG to 82.2 DEG C., which produces a granular form, or by the use of chemicals such as formaldehyde, tannic acid, acetic acid, mineral acids and heavy metal salts, e.g. lead salts. The miscella is separated from the solids by a rotary vacuum filter, with or without string discharge, or by a mechanical classifier or by gravity decantation. The miscella is cooled to a temperature below 10 DEG C. but above the temperature at which the oil crystallizes therefrom. The layers are separated by gravity, the solvent-rich upper layer is re-cycled through the extraction units, and the lower layer is passed through heat-exchangers to a steam stripping column to recover the oil. Whilst the oil is in solution in the solvent it may be refined with caustic soda solution to remove acids, and with bleaching solids, such as acid-activated earths from montmorillonite, clays such as fuller's earth, and activated carbons, to remove colour. A suitable plant is shown in the flow sheet of Fig. 1, where the seeds and solvent are fed into a ball mill, then to a heater and agitator and afterwards to a rotary filter. The filtrate flows through a cooler to a separation column, from which the upper, mainly solvent, layer is re-cycled to the solvent storage tank and the lower oil-rich layer is fed to a solvent stripper, from which part of the solvent is re-cycled to the storage tank and part is fed to a mixing tank wherein it is mixed with the filter cake from the rotary filter. The mixture from the latter is fed to a second rotary filter, whence the solvent is fed back to the storage tank and the residual cake is fed to a heater and dryer. After steaming, the cake passes to a storage container. The oil from the stripper is collected in an oil storage tank. A suitable ball mill for the comminuting step comprises a drum 10, Fig. 3, with input pipe 12 and delivery pipe 29 carried in trunnions 13, 14, respectively, and a perforated outlet plate 17. Pairs of rotary brushes 22, 23 and 27, 27 are mounted on a fixed shaft 19, the bristles contacting each side of the rotating plate 17. Rotation of the drum drives the cleaning brushes frictionally, thereby preventing clogging of the perforations in the plate 17. A suitable rotary vacuum filter 30, Fig. 6, comprises a drum 41 supporting a rigid perforated cylinder 43, Fig. 8, carrying a backing screen 44 on which is superposed a filter cloth 45. End plates 47 are provided projecting beyond the periphery of the drum 41 to provide walls for compartments 52 extending radially from the drum, the compartments 52 being separated from each other by partition plates 48. The mixture to be filtered is fed on to the top part of the rotary filter and is held in the compartments. Suction is applied through pipes 60 to withdraw the filtrate into compartments 61 corresponding to the compartments 52 outside the filter drum. As the filter rotates the pipe 60 communicating with an individual compartment approaches the lower-most position in its path of travel, and a valve arrangement disconnects the pipe 60 from the suction line and connects it to a gas-pressure pipe line for blowing the filter cake out of the compartments as they travel over the lower part of their cycle. The filter cloth 45 may be a single layer of heavy nylon cloth of 34,000 openings per sq. in. with a backing layer comprising a 100-mesh screen, the backing screen 44 comprising a 20-mesh screen. Specifications 487,366, 630,615 and 632,304 are referred to.