Patent GB-722322-A (GB)
Title: Improvements in or relating to the separation of mixtures of compounds by crystallization
Inventor: HACHMUTH KARL HENRY
IPC: B01D9/00
Filed: 1951-08-10
Abstract: A mixture of compounds is separated into higher-melting and lower-melting fractions by maintaining <PICT:0722322/III/1> <PICT:0722322/III/2> a temperature difference between the ends of an elongated confined body of the mixture, maintaining within the body a temperature such that on application a pressure a portion of the mixture can be caused to solidify, alternately increasing and decreasing the pressure on the body to cause alternate partial solidification and partial melting, moving solid to the warmer end of the body and liquid to the cooler end, and withdrawing a higher melting fraction from the warmer end and a lower melting fraction from the cooler end.  The alternating pressure changes tend to increase the rate at which equilibrium is established between liquid and solid at any point and increase the efficiency of the process. As the solid moves to the warmer end of the body it becomes enriched in the higher melting component, and vice versa for the liquid.  In the apparatus of Fig. 1 the mixture is fed under pressure to an insulated cylinder 13 from a reservoir 32.  The cylinder is cooled at 16 and warmed at 22.  A plunger 43 is reciprocated in the cylinder 13 by an air cylinder 42 to alternately increase and decrease the pressure on the mixture.  A conveyer screw within the cylinder is rotated by a shaft 34 driven by motor 37.  Products are withdrawn at 19 and 21 either continuously or in synchronism with the pressure pulsations, preferably at periods of low pressure.  The temperature at the heated end of the body is such that the product at that end is wholly liquefied.  In the apparatus of Fig. 4 two cylinders are provided, a heated cylinder 82 and a cooled cylinder 81, joined by a line 83 through which solid from 81 falls to cylinder 82.  Pressure fluctuations are obtained by a feed injector and pulsator 117 in feed line 118 operated by crank 123.  Product proportioning valves 111, 113 are opened and closed by cams 119, 121 on the crankshaft 122. The feed is preheated in heat exchangers 107, 108 by the products, and the cylinders 81 and 82 are cooled and heated respectively by fluid circulating through jackets 86, 91 and through heat exchangers 94, 103 through which flows a refrigerant circulated by pump 98.  The refrigerant, heated by compression in the pump, is cooled by expansion after passing valve 104 before passing through heat exchanger 94.  Instead of the cylinders 81, 82 being cooled and heated throughout their lengths, they may be cooled and heated adjacent the product outlets only.  In examples: (1) A mixture of 84.3 per cent. cyclohexane and 15.7 per cent. methylcyclopentane was separated into a higher-melting fraction of 95 per cent. cyclohexane and a lower-melting fraction of 78.2 per cent. cyclohexane, using a feed temperature of 76 DEG F., a temperature at the cold end of - 10 DEG F., a temperature at the warm end of 26 DEG F., alternate 30-second periods of no pressure and a pressure of 1,700 p.s.i.g., and a reflux ratio of 95 to 1; (2) similar to (1) but using, in different periods, various pressures, temperatures and reflux ratios.