JPS6010762B2 - Method and apparatus for crystallizing substances from solutions - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for crystallizing a substance from a liquid by cooling.

In the production of fats and oils, it is necessary to separate triglyceride mixtures and fatty acids.

The method employed is to identify individual groups of components.
is separated from the solution by crystallization. The solvents used are, for example, hexane, isopropanol, acetone, petroleum ether or similar organic solvents. The supersaturation required for a phase change from a liquid phase to a crystalline phase can in principle be achieved by changing the concentration, temperature or pressure of the solution, but in practice generally changes the temperature, ie cools the solution. The heat is removed by convection in a crystallizer equipped with a coagulator, which can additionally be equipped with a special device for classifying the crystals according to particle size.

Because relatively little heat exchange occurs on the surface of such a crystallizer with a rope scratcher, the heat exchange noise surface (scratched
It is very common to use crystallizers, so-called "scratched coolers", with heatexchan bags;
Heat transfer is thereby considerably improved compared to convection coolers.

In particular, crystallizers and scraper coolers used for fat fractionation are designed to operate in batch mode and can achieve relatively long crystallization or residence times on the order of about 3 G minutes. Only.

The maximum cooling rate that can be obtained is on the order of 80 degrees per hour. Another disadvantage of the known methods is that they cannot be operated continuously, ie all the crystallization takes place in a vessel from which the crystallized material has to be removed.

Such discontinuous operation is disadvantageous for process-related technical reasons. Finally, the irregular shape of the crystals produced by the known method often causes problems during subsequent furnace heating.

The object of the invention is to provide a method for crystallizing substances from a solution by cooling and an apparatus for carrying out such a method, in which the disadvantages mentioned above do not occur.

In particular, it is intended to propose a method and a device which substantially reduces the required operating time and which allows continuous operation. According to the present invention, there is provided a method for crystallizing a substance from a solution by cooling, the solution being evaporatively cooled under reduced pressure to at least 500 qo
A method is provided for rapidly cooling to a temperature below the crystallization temperature at an hourly cooling rate and transferring the supercooled, and therefore supersaturated, but not yet crystallized solution to a holding tank where crystallization occurs. .

In another aspect of the invention, there is provided an apparatus for crystallizing a substance from a solution by cooling, the cooling tank being connected to a vacuum pump and rapidly cooling the solution to a temperature below the crystallization temperature; , and a pump for transferring the supersaturated but not yet crystallized solution from the cooling tank to a holding tank where crystallization takes place. The advantages achieved with the present invention are based on the following considerations: An investigation of the various steps determining the rate of crystallization of fats and oils from the solvent-containing mother liquor revealed that the rate of the entire process was determined by cooling the surface. It can be seen that it depends essentially on the heat removed from the solution,
Served.

Since it is not possible to increase the size of the cooling surface infinitely, there is a lower limit to the rate at which the heat can be removed from the solution, and therefore to the speed of the entire process, resulting in a process time on the order of 30 minutes to 1 hour. Crystallization or residence time is required. For the purpose of improving the cooling rate, experiments were carried out on evaporative cooling under reduced pressure, and it was possible to achieve a cooling rate of 500 q/hour to 1000° C./hour.

At this fast cooling rate, it was observed that when the mother liquor is cooled to a temperature below the equilibrium precipitation temperature, the undercooled and therefore supersaturated mother liquor remains in this state without forming any crystals. It stayed there for 90 minutes.

After the end of this time interval, crystallization to break supersaturation occurs rapidly, and the heat of released crystallization heats the suspension. Since no crystals are formed during the molten phase of the mother liquor, the solution can be removed from the condenser with a suitable pump.

Therefore, it is possible to operate such evaporation crystallization continuously, rather than simply batchwise. In this method, it is essential to rapidly bring the mother liquor to a supercooled state in which a crystal-free phase occurs.

This can be easily achieved by evaporative cooling.
This method results in a relatively short residence time in the cooling device itself, on the order of about 1 minute, after which the subcooled, and therefore supersaturated, but not yet crystallized mother liquor is removed and transferred to a conventional container, where it is exclusively used for crystallization. cause analysis. The residence time in this crystallization container is approximately 5 minutes, so the total cropping time is 6 to 6 minutes.
It is 8 minutes.

This should be compared with the residence time of at least 30 minutes required in the case of a surface cooler.

Furthermore, the short residence time of the mother liquor in the cooling device itself and the resulting short transfer to the crystallizer allows the use of devices with small residence time volumes, so that the overall cooling device and crystallizer Dimensions can be substantially reduced. The short residence time also results in short paths along the control system, which makes it possible to carry out all changes in the operating parameters very quickly, which is advantageous for the control of the process.

Crystallization of the supercooled solution is carried out adiabatically, and the resulting crystallization (
It is advantageous not to allow the heat of crystallization to escape, but to use it to heat the mother liquor and thereby influence the rate of diffusion and thus the rate of crystallization. This has an overall effect of linearized crystal growth (lisp and stalgrow ratios), which in turn favors the shape of the crystal.

It makes it possible to obtain ideal spheroid crystals of size 0.1 leg, which can be separated from the mother liquor by simple filtration. Aspects of the invention will now be described, by way of example, with reference to the accompanying drawings.

FIG. 1 is a temperature/time diagram for cooling a mother liquor containing acetone as solvent and a common fat mixture. In region 1, the mother liquor is heated to a temperature of about 0°C (
Cool to about 5° C. below the crystallographic equilibrium temperature).

In this supercooled and therefore supersaturated state, no approx. (area 0).
After this time interval of approximately 60 to 9 hours, rapid crystallization occurs naturally and supersaturation is broken.

If this crystallization is carried out in an insulated container, that is, without heat exchange with the surroundings, the heat of crystallization (crystallization) released will contaminate the mother liquor, and eventually at the end of region m, the final temperature of crystallization will be reached. The equilibrium temperature, in the example of FIG. 1, reaches approximately 5°C. FIG. 1 also shows that approximately 2 minutes are required to cool the mother liquor in region 1 from the processing temperature to the subcooling temperature. After about 5 more minutes, a final equilibrium temperature is reached at which substantially all the oil crystals have completely crystallized. This figure is based on a cooling rate of 75 pi/hour, which means that even shorter times can be achieved with higher cooling rates.

FIG. 2 shows an apparatus for carrying out such a method semi-continuously. A mother liquor, which is a solution of fat or oil in a solvent (eg acetone), is fed from a supply line 1 to a conventional cooling tank 2. A vacuum pump 3 is connected to the tank 2 to suck the vapors, condense them and optionally return them to the process. Cooling rates of about 500 to 1000 DEG C./hour can thereby be achieved as previously defined, so that the mother liquor is cooled to a temperature of about 2 to 5 DEG C. below the crystallization temperature in about 1 to 2 minutes. As soon as the entire mother liquor reaches a state of supersaturation due to this supercooling, it is pumped by pump 4 to three holding tanks 5, 6, 7, where crystallization takes place exclusively.

The plurality of holding tanks 5, 6, 7 are sequentially filled.

The crystallizing mother liquor remains in these tanks 5, 6, 7 for about 5 minutes, and then the crystallizing material is removed from the tanks and conveyed to further processing. FIG. 3 shows a different embodiment from FIG. 2, which uses one holding tube 15 instead of individual tanks that are filled in sequence, which operates on the principle of the Archimedean spiral and which Rotated around an axis by a drive motor.

A spiral is conceptually illustrated inside the holding tube 15. This tube 1
5 is continuously filled with the pump 4, the fats and oils in the mother liquor crystallize in the tube 15 and are simultaneously discharged as crystallized substances in the direction of the arrow shown at the right end of FIG.

In the holding vessels 5, 6, 7, 15 the crystallization takes place adiabatically, ie without heat exchange with the surroundings, so that the released heat of crystallization is returned to the mother liquor.

When using a conventional crystallization method, for example, using a scratched surface cooler to process 1 liter of acetone/fat mixture per hour, the cooler is required to have a capacity of 1 liter.

On the other hand, in the embodiment shown in FIG. 2, the cooler has a capacity of 166k9, i.e. this technically and structurally complex device has only about 16% the volume of the corresponding known device. Only.

The holding tanks 5, 6, and 7 each have a capacity of 1. Occupies mottled areas.

However, these tanks are not technically demanding and do not pose any difficulties. Vacuum pump 3 is approximately 6 at 0℃
Should have a suction capacity of 0.000 per hour.

Such pumps can be purchased on the market. From the above comparison it is clear that a counterfeit operating in the manner according to the invention offers substantial advantages in terms of investment and operating costs compared to conventional crystallizers.

[Brief explanation of the drawing]

FIG. 1 is a temperature/time diagram representing the cooling, subcooling and subsequent crystallization of a fat mother liquor using acetone as the solvent; FIG. 2 is a schematic diagram of a first embodiment of an apparatus for carrying out such a process; FIG. 3 is a schematic diagram of a second embodiment of a counterfeit machine implementing such a method. 1... Supply V supply pipe, 2... Cooling tank, 3...
...Vacuum pump, 4...Pump, 5, 6, 7
...Holding tank, 15...Holding pipe. FIG. IFIG. 2 FIG. 3

Claims (1)

[Scope of Claims] 1 (a) The solution is evaporated under reduced pressure to cool at least 5
rapidly cooling to a temperature below the crystallization temperature at a cooling rate of 00 °C per hour; (b) transferring the supercooled, and therefore supersaturated, but not yet crystallized solution to a holding tank;
A method for crystallizing a substance from a solution by cooling, the method comprising the step of crystallizing the solution from the solution in a holding tank. 2. The method of claim 1, wherein said cooling is performed at a rate of about 750°C per hour. 3. The method of claim 1 or 2, wherein the solution is cooled to a temperature of about 2 to 10C below the crystallization temperature. 4. The method of claim 3, wherein the solution is cooled to a temperature about 5° C. below the crystallization temperature. 5. The method according to any one of claims 1 to 4, wherein the crystallization is carried out adiabatically in a holding tank. 6. The method according to any one of claims 1 to 5 for crystallizing fats and oils from a mother liquor containing a solvent. 7 A device for crystallizing substances from liquids by cooling, comprising a cooling tank connected to a vacuum pump and rapidly cooling the solution to a temperature below the crystallization temperature, and a cooling tank which is subcooled and therefore supersaturated but still crystallized. and a pump for transferring the solution that does not crystallize from the cooling tank to a holding tank where crystallization occurs. 8. Claim 7, further comprising a plurality of holding tanks connected to the pump and filled in sequence.
Apparatus described in section. 9. The device of claim 7, wherein the holding tank is a holding tank that is rotatable about its longitudinal axis and functions in principle as an Archimedean spiral.