JPH02126902A - Method for purifying crystal by filtration - Google Patents

Abstract

PURPOSE:To stably obtain a high purity crystal component over a long period of time by keeping a filter medium at above a temp. at which mother liquor is crystallized during at least filtering operation. CONSTITUTION:When a soln. contg. a crystal component is separated into the crystal component and mother liquor by passing through a filter medium 3, the filter medium 3 is kept at above a temp. at which the mother liquor is crystallized with a heater 4 during at least the filtering operation. The crystal component having high purity can stably be obtd. over a long period of time.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for purifying crystals by filtration.

More specifically, when refining organic crystals, it is necessary to recover the desired crystal component from a solvent, to separate a desired crystal from a eutectic crystal, or to attach it from a solid solution crystal. The present invention is applied to separation of mother liquor, etc.

[Prior Art and Problems to be Solved by the Invention] A purification operation is often performed in which a mother liquor is separated from a liquid containing crystals by a filtration operation to extract the crystals or to purify the crystals.

For example, (1) when a crystalline component of an organic substance dissolved in a solvent is separated from a mother liquor and taken out as crystals, this is conventionally carried out using a centrifuge, a continuous filter, a horizontal tray filter, or the like. At this time, the liquid containing the crystal component is a saturated solution, and at the beginning of the operation, the filter medium and the members that come into contact with it are at room temperature, which is lower than the operating temperature for boat fishing, and the substance to be manipulated is The liquid is cooled during the process of contacting and passing through the filter medium, for example, because it is made of a material with a large heat capacity that influences the thermal conditions,
Crystal precipitation occurs, and especially on the day when the filter medium blooms, the crystals adhere to it and cause clogging.

This phenomenon occurs in both batch and continuous systems, and when the filter medium becomes clogged, the filtration capacity is significantly reduced, resulting in a product with low purity and a low yield. descend. Therefore, it becomes necessary to periodically wash the filter medium, which leads to a decrease in the operating rate.

(2) For mechanical separation or purification of eutectic crystal slurry, the so-called sweating method is widely known, and the MBW method is a typical example thereof. This method involves attaching crystals to the inner surface of the cooler and increasing the temperature of the attached crystals to cause impurities contained within or between the crystals that have a lower melting point than the crystals to flow down in a liquid state. This method is then heated to a temperature higher than the melting point of the crystal to obtain the pure component in a molten state.

However, since the driving force for the gravity flow of sweated impurity liquid is exclusively gravity, its separation performance is not high.

Another method for refining eutectic crystal slurry is to supply the slurry from the upper part of the purification tower, and then remove the product from the upper part.
This is a method in which the molten material containing many impurities is taken out from the bottom.

Although this method is suitable for purifying pure substances in that the crystals are purified in the column, it requires the crystals to flow down into the melt and the pure melt to rise. It is not very suitable for crystals of organic matter with a small difference in specific gravity, and if it were to be used, a column with a large cross-sectional area would be required, which would increase equipment costs.

Even in the case of eutectic slurry, the crystal components can be purified using a centrifugal separator, continuous filter, horizontal tray filter, etc., but the same problem as described in (1) remains.

(3) When refining solid solution crystals, obtain crystals with a composition of A component and B component, and when obtaining crystals from the mother liquor of the solid solution, the mother liquor inside the crystal may be trapped or the mother liquor may adhere to the crystal. This results in poor purity and purification efficiency.
As a result, the number of stages required for separation increases, which is impractical.

The same problem arises when mechanical operations similar to those described in (1) are performed during the purification of solid solution crystals.

Therefore, the main object of the present invention is to obtain a crystal component of high purity stably for a long period of time.

[Means for Solving the Problems] The present invention for solving the above-mentioned problems involves separating a crystal component from a mother liquor by passing a liquid containing a crystal component through a filter medium; It is characterized by maintaining the temperature above the temperature at which crystallization of the mother liquor occurs.

Such a filter medium temperature can be achieved by heating the support of the filter medium or by ensuring that the temperature of the medium such as the cleaning liquid or the gas passing through the filter medium is sufficiently high.

Further, the present invention is an apparatus for separating a crystal component and a mother liquor by passing a liquid containing a crystal component through a filter medium, and is characterized in that: A heating element for heating the filter medium is provided on the back side of the filter medium. .

In this case, the heating body includes a heat transfer tube through which a heat medium is passed, and a heating body itself that generates heat, for example, when it is energized.

[Function] As shown in Figure 1, in the conventional purification method by filtration operation, a certain crystal component receives the cooling effect from the filter medium during the filtration process, and becomes below the crystallization temperature of the mother liquor. As a result, they precipitate on the filter media or during the flowering period of the filter media, causing clogging of the filter media.

However, in the present invention, as shown in the figure, the temperature of the filter medium is
Since the temperature is higher than the crystallization temperature of the base material, there is no precipitation of crystals on the filter medium or between the meshes of the filter medium, thereby preventing clogging of the filter medium.

Therefore, since the long-term filtration ability is high and almost constant, stable operation is possible, and as a result, highly pure crystals can be obtained.

[Specific Structure of the Invention] In order to further understand the present invention, the present invention will be further explained in detail by giving some specific examples.

2 and 3 show examples using a horizontal tray filter, in which a filtrate outlet 2 is formed on the bottom surface of a dish-shaped vessel 1,
Further, a filter medium 3 made of a filter cloth or the like is arranged above the vessel 1. A heating element 4 is provided preferably in contact with the lower surface of the filter medium 3, and in turn supports the filter cloth 3.

For example, as shown in the same figure, the heating body 4 is made up of a supply pipe 4A, a discharge pipe 4B, and a communication pipe 4C that connects these.The heating medium ho, such as hot water or steam, is fed under pressure from the supply pipe 4A, and is discharged from the discharge pipe 4B. It is something that makes you 5 is a stay.

In such an apparatus, the heat from the heating element 4 is transferred to the filter medium 3, and the temperature of the filter medium is maintained higher than the crystallization temperature of the mother liquor of the feed slurry F, so that clogging of the filter medium 3 due to long-term operation is avoided. is prevented. The filtrate is discharged from the discharge port 2.

Figure 4 shows the above horizontal tray filter at least 180 mm.
This is an example of a device that can be rotated by degrees.

In other words, it is a container fixed to the ground with a substantially cone-shaped lower part.
A rotary shaft 11 is rotatable around a horizontal axis within O. This rotation is performed by transmitting the rotational output of a driving means such as the motor 12 to the driven gear 13. A tray 14 is integrated with this rotating shaft 11, and within this tray 14 is provided a heating element 40 similar to that of the above example, and a filter medium 15 is stretched over the heating element 40. 16 is a stay.

The filtrate outlet 14a of the tray 4 is led out to the outside through the rotating shaft 11, and communicates with the filtrate tank 18 via the swivel joint 17. A gas circulation path 19 that returns to the tray 14 is configured in the upper part of the filtrate tank 18, and a cooler 20, a compressor (or vacuum pump) 21, and a gas heater 22 are arranged in the middle of the path, and the filtrate extracted from the discharge port 14a is After separating the filtrate from the gas in the filtrate tank 18, the gas is once cooled in the cooler 20 to reduce the load on the compressor 21. The purpose is to remove the mother liquor mainly trapped between crystals on the filter medium 15 by passing the heated gas through the filter medium 15 due to the pressure difference between the upper and lower surfaces of the filter medium 15.

In this case, as the temperature of the filter medium 15 is raised by the heating body 40,
By raising the temperature of the filter medium 15 by the heated gas passing through the filter medium 15, crystallization of the mother liquor during the filtration operation is prevented.

Further, since the gas must be circulated in an airtight state, a seal is provided using an O-ring 23 or the like.

On the other hand, a melting heater 24 is provided at the bottom of the container 10,
When the required filtration operation is completed, the motor 12 is started, the tray 14 is rotated 180 degrees, the crystals in the crystal-containing liquid on the filter medium 15 are melted by the crystal heater 24, and the crystals are melted at the discharge port 10a.
It should be discharged from the tank.

FIG. 5 shows an example in which the present invention is applied to a horizontal belt filter, in which an endless belt filter medium 30 is wound around a group of rolls 31, and the tension of the filter medium 30 is performed by rolls 31A and 31B. Further, on the lower surface of the filter medium 30, a plurality of trays 32 are arranged in a row in a longitudinal direction, for example. These trays 32 groups can be physically reciprocated on the rails 34 in the left and right directions in the figure by the moving cylinders 33, so that when the filter medium 30 rotates clockwise, they move rightward at the same speed. It has become. Each tray 32 has a filtrate tank 36 connected to a filtrate pump 35.
The e! was connected and I took it out! , t; L are all discharged, or if necessary, as shown in the figure, the filtrate on the downstream side is returned onto the cake and used for washing. 37 is washing water.

Further, the filter medium 30 and the group of trays 32 are housed in a sealed chamber 38. 4, the gas from which the filtrate has been removed is circulated through the filter medium 30 as a heated gas by the cooler 20, the compressor 21, and the gas heater 22.

As shown in FIG. 6, a heating element 41 through which a heat medium flows is provided at the top of each tray 32 to heat the filter medium 30. 39 is a stay, and 32a is a filtrate outlet.

5 and 6, the heating element 41 and the heated circulating gas cause the heating element 41 and the heated circulating gas to
Precipitation of crystals between the two meshes is prevented, and the filter medium 32 is prevented from being clogged.

When the -th filtration operation is completed, the tension on the filter medium 30 is released, and each tray 32 is returned to the left in FIG. 7 by the cylinder 33, and waits for the slurry to be fed F again.

7 and 8 show an example in which the present invention is applied to a drum filter, in which a drum 50 is rotated about a horizontal axis by a rotary drive motor 52 via its support shaft 51. There is.

53 is a liquid tank. On the other hand, a heating element 42 is provided in the divided surface chamber 55 of the drum 50 in almost contact with the lower surface of the filter medium 54, and the supply and return of these heating mediums are as follows.
This is done via a double pipe and an access chamber with sufficient sealing structure according to the prior art. That is, the supplied heat medium passes through the outer pipe 57 from the supply chamber 56 and is led to each heating body 42 via the branch outgoing pipe 58 to each divided surface chamber 55, and the discharged heat medium passes through the divided return pipe 59. After being collected in the header 60, it is discharged through an inner pipe 61 and a discharge chamber 62.

In addition, the filtrate in each surface chamber 55 is discharged from the outlet 63.63.
It is designed to be discharged from the machine through a discharge pipe 64.

On each of the above-mentioned sides, the heating body passes a heat medium, but the heating body itself may be made of, for example, an electrically conductive material so that it generates heat by being energized. Also, when heating the filter medium,
It is free to use one or more combinations of heating by the heating body, heating by the gas flowing through the filter medium, and heating by the cleaning liquid. In this case, heating by the cleaning liquid is not described in detail, but its mode can be easily inferred from the example of gas heating. However, for example, as shown in FIG. 5, this can be done by providing a cleaning fluid heater 70 in the return cleaning fluid path.

[Example] Next, an example will be explained.

(Example 1) Crude caprolactam (purity 62%) was dissolved in Penzol, cooled to 45°C, and filtered at a filtration pressure of 1.5° using a filter tray with a pitch of 3° and 20 heating coils arranged in parallel.
A comparative experiment was conducted under the conditions listed in Table 1 below at a pressure of 5 bar and a crystal thickness of 40 B.

The results are also listed in the same table.

Table 1 * Purity of lactam obtained after benzene removal (Example 2
) Synthesized paradichlorobenzene 73.0wt%, orthodichlorobenzene 24%, metadichlorobenzene 12%
%, the remainder being trichlorobenzene, a slurry was obtained by cooling crystallization, a cake was obtained by vacuum filtration, and the slurry was purified by the method of the present invention.

The conditions and results are shown in Table 2.

Table 2 (Example 3) A solid solution mixture of 91.5% naphthalene, 7.9% thionaphthene, and 0.6% other components was cooled to 35°C, and
Pressure filtration was performed at bar. The conditions and results are shown in Table 3.

As shown in Table 3 and above, it was found that by using the method of the present invention, the purification ability was clearly improved compared to the conventional method.

[Effects of the Invention] As described above, according to the present invention, there is no clogging of the filter medium, so high filtration ability can be maintained for a long time without periodic cleaning, and stable operation is possible. Furthermore, there are advantages such as the purity of the crystals obtained is much higher than in the case of conventional filters.

[Brief Description of the Drawings] Part 1 is an explanatory diagram of the method of the present invention, Fig. 2 is a cross-sectional view of the horizontal tray filter (view from the n-mg arrow in Fig. 3), and Fig. 3 is its plan view. Figure 4 is a cross-sectional view of an overturning tray filter, Figure 5 is a schematic front view of a horizontal belt filter, Figure 6 is a plan view of the arrangement of heating elements used there, Figure 7 is a cross-sectional view of a drum filter, and Figure 7 is a cross-sectional view of a drum filter. FIG. 8 is a plan view of the arrangement of the heating body. 1... Bencel, 3... Filter medium, 4... Heating body, 1
0... Container, 12... Motor, 14... Tray
15... Filter medium, 18... Filtrate tank, 21... Compressor (vacuum pump), 22... Gas heater,
24... Heater for melting, 30... Filter medium, 32...
Tray, 33...Moving shilling, 4...Rail, 6...Filtrate tank, 40°41°2...Heating element, 0...Drum.

Claims (4)

[Claims] (1) When separating a crystal component from a mother liquor by passing a liquid containing a crystal component through a filter medium; at least during the filtration process, the temperature of the filter medium must be maintained at a temperature higher than the temperature at which the mother liquor crystallizes. Characteristic crystal purification method by filtration. (2) In an apparatus for separating a crystal component from a mother liquor by passing a liquid containing a crystal component through a filter medium; an apparatus for purifying crystals by filtration, characterized in that a heating element for heating the filter medium is provided on the back side of the filter medium. . (3) The method according to claim 1, wherein the temperature of the washing liquid for the crystals on the filter medium is controlled to maintain the temperature of the filter medium at a temperature higher than the temperature at which crystallization of the mother liquor occurs. (4) Control the temperature of the medium passing through the filter medium to
Claim 1: The temperature is maintained at a temperature higher than that at which crystallization of the mother liquor occurs.
Method described.