High-pressure crystallization process

High pressure crystallization process has already been applied In Industry to separate a pure substance from a mixture. In this process, pressure Is used for crystallization. Instead of cooling In the conventional method. Although the pressure Is usually applied In Industry so quickly that It reaches 200 MPa In 10 sec, a sufficient amount of crystals can be grown, which results In attaining the separation and refining of a short cycle within a few minutes (U. 

Features Of the High-Pressure Crystallization Process in Industrial Use... 

Advantages of high pressure crystallization are simple control of process parameters, and a solvent-free system. 

Processes without catalysts are only of minor industrial importance, since they provide only gray graphite-contaminated diamond powder with a maximum crystal size of ca, 50 Xm and require significantly higher pressures of 120 to 300 kbar. In the dynamic process operated by DuPont the pressure and temperature are produced for a few microseconds in a shock wave apparatus. The starting material is also graphite, which should be as crystalline as possible. Static high pressure synthesis processes without catalysts are industrially unimportant. 

In Japan, Kobe Steel has sometime ago developed a high pressure crystallization technique known as Fine Cry Process in which m-, p-cresol mixture is introduced into a high pressure vessel of the piston-cylinder type and is crystallized adiabatically at 200 MPa. After draining off the mother liquor the system is decompressed and p-cresol emerges as the pure crystalline product [1]. 

Summarizing, the DELOS process is a promising new high-pressure crystallization technique, which can be a useful processing tool in the particle engineering of different compounds and materials of industrial interest. 

In this research, a possibility of separating the chiral from D-, L-mandelic acid solutions was studied on the basis of the idea shown in Figure 2. At first, the solubility of mandelic acid in water was measured under high pressure, and then the experiments separating L-mandelic acid from its D- and L-mixtures in Zone I and in Zone II were performed by use of high pressure crystallization. Finally, a novel separation process is proposed for mandelic acid. 

A proposed separation process of Inform crystal from L-rich D-,L-mandelic acid mixture is presented. This is based on the exp imental results described above and the idea shown in Figure 2. This process consists of three steps. In Step 1, the feed mixture is separated by high pressure crystallization (1) from the eutectic mixture at atmospheric pressure. In Step 2, L-form crystals with high purity are obtained from this feed using high pressure crystallization (2). In Stq> 3, the eutectic mixtures removed by high pressure crystaUization (1 and 2) is concentrated to a nearly eutectic composition at atmospheric pressure, by means of evsporation and cooling crystallization. 

The possibility of a process which can separate Lrform crystals from L-rich D-,L-mandelic aqueous mixture, by combining high pressure crystallization and cooling crystallization has been clarified. 

An analysis of obtained cakes and an observation of pinholes in them revealed that the sweating progressed uniformly even in a vessel with a large diameter. In addition,in high pressure crystallization, there is no need for stirring in the crystallizer. When stirring is needed, the slurry content has to be limited for about twenty percent or so. There is no such limitation in this process. Sometimes, the solid fraction could exceed 50% of the feed even in the adiabatic process. This is also due to the uniformity of the pressure. 

Simple Flow System. In this process, the crystallization, the separation and purification are all carried out in a high pressure vessel.There is no need for respective apparatus and conveyer apparatus between them, as there is with cooling crystallization. Because high purity is obtainable in the high pressure crystallizer, washing with solvent and recrystallization are not required. 

Special crystallization processes such as zone melting, monocrystal growth, high-pressure crystallization and crystallization by transfer reaction are not discussed here. Introductory literature, for example, is given in [0.4 and 7.1]). 

Except for helium, all of the elements in Group 18 free2e into a face-centered cubic (fee) crystal stmeture at normal pressure. Both helium isotopes assume this stmeture only at high pressures. The formation of a high pressure phase of soHd xenon having electrical conductivity comparable to a metal has been reported at 33 GPa (330 kbar) and 32 K, and similar transformations by a band-overlap process have been predicted at 15 GPa (150 kbar) for radon and at 60 GPa (600 kbar) for krypton (51). 

Other Industrial Applications. High pressures are used industrially for many other specialized appHcations. Apart from mechanical uses in which hydrauhc pressure is used to supply power or to generate Hquid jets for mining minerals or cutting metal sheets and fabrics, most of these other operations are batch processes. Eor example, metallurgical appHcations include isostatic compaction, hot isostatic compaction (HIP), and the hydrostatic extmsion of metals. Other appHcations such as the hydrothermal synthesis of quartz (see Silica, synthetic quartz crystals), or the synthesis of industrial diamonds involve changing the phase of a substance under pressure. In the case of the synthesis of diamonds, conditions of 6 GPa (870,000 psi) and 1500°C are used (see Carbon, diamond, synthetic). 

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