| 摘要 |
1,197,859. Crystallizing. MERCK & CO. Inc. 25 March, 1968 [29 March, 1967], No. 14235/ 68. Heading B1G. In a fluidized bed crystallizer column, large crystals which fall to the base of the column are fractured by ultrasonic vibrations, e.g. at 19,500 cycles/sec. Supersaturated solution may be introduced into the column at 5-50 psi. 5-75% of the fluidized crystal 'bed is preferably below the crystal withdrawal point. As shown, an externally heated column 11 comprises an upper cylindrical portion 12, an intermediate frustoconical portion 13, a lower cylindrical portion 14, and a base 16. The frusto-conical portion may be 15-60% of the overall height, its maximum diameter may be 2-4 times its minimum diameter, and its walls may be at an angle of 63-89‹ with the horizontal. The base 16 has apertures which communicate with a base chamber 49 and into which are inserted the upper ends of a pair of ultra-sonic vibrators 38, the tips 41 of which are flush with the base 16. Below chamber 49 is a nitrogen-cooled transducer chamber 54 which has a pressure-controlled switch (to shut off the genarator when the nitrogen pressure falls below a safe value) and a sight glass (to show the presence of any leaking solution). Supersaturated solution is pumped into the lower portion of the column through a pipe 17, a slurry of crystals is withdrawn near the top of the conical portion through a pipe 72, and spent solution is withdrawn from the top. The crystals are preferably withdrawn intermittently. The spent solution and solution separated from the product pass through pipes 87 and 79 respectively to a heated dissolver tank 80 to which are added crude crystals. The resulting strong solution passes though a filter 95, a holding tank 99, further filter 106, an indirect heat-exchange cooler 102, and the base chamber 49 before passing into the column. A small proportion of the filtrate may be bled off to a drain 109. The fluidized bed may be maintained without simultaneous crystallization by by-passing the dissolver tank by means of a pipe 111. Overflow from the holding tank may be returned to the dissolver tank through a pipe 113. In modifications, (a) the supersaturated solution passes directly from chamber 49 to the column (via the annular gap around the vibrator tips), (b) the strong solution is cooled by evaporation or by introducing a cold gas into the solution, (c) crystals are withdrawn at or near the bottom of the crystallizer, (d) an indirect heat-exchange heater precedes the second filter, (e) provision is made for adding seed crystals during operation (Fig. 9), and (f) a vibrator is inserted into the lower portion of the column from the side (Fig. 8). Two columns in parallel or series may effect simultaneous recovery of d- and 1- isomers from a mixture (Fig. 5), the relative amounts of products withdrawn being adjusted to correspond to relative strengths in the mixture. A single generator may operate the vibrators of each column alternately. |
