JPH02117904A - Extraction - Google Patents

Abstract

PURPOSE:To suppress adhesion and solidification of powder or granules in an extractor, to effectively extract impurities and to obtain powder or granules purified in high purity by packing powder or granules into the interior of an extractor in a specific void, extracting and removing impurities contained in the powder or granules with an extractant. CONSTITUTION:Powder or granules (e.g., powdery polystyrene) are packed from an inlet 12 onto a support plate 14 of an extractor 7 of fixed layer type, etc., in 0.7-0.95 void, an extractant (e.g., carbon dioxide) is fed through a line 1 above an extractor 12 to a pressurizing device 2, pressurized, sent through a line 3 to a heat exchanger 4, adjusted to extraction temperature, then fed from a line 6 to the extractor 7, dispersed by a distributor 8 and impurities contained in the powder or granules packed in the interior of the extractor 7 are extracted and removed to give purified powder or granules having extremely high extraction degree of impurities.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to polymers, rubbers, etc. (hereinafter simply referred to as polymers).
The present invention relates to a method for highly removing impurities, etc. contained in powder and granular materials.

(Prior Art) As a method for removing impurities (solvents, monomers, oligomers, by-products, etc.) remaining in powder or granules, methods such as heating evaporation and vacuum evaporation have conventionally been used. However, a small amount of impurities still remained, which caused a decline in the quality of the product and some of which were harmful to the human body. If the copolymer is heated in order to further reduce the impurity content, deterioration and softening occur, so that the residual concentration of impurities cannot be reduced below a certain level.

Therefore, in recent years, high-pressure extraction methods using supercritical fluid or the like have been proposed. For example, Japanese Patent Publication No. 59-46972 discloses a method for reducing the oligomeric cyclic ether content in a polymer using a supercritical fluid.

(Problems to be Solved by the Invention) However, even when attempting to remove impurities from a liquid polymer using the high-pressure extraction method described in Japanese Patent Publication No. 59-46972, as described in Example 1 of the same publication, There is a limit to the high level of extraction that reduces impurities below a certain level.

In addition, when trying to extract and remove polymers such as granules at a high level using the above-mentioned high-pressure extraction method, polymers such as granules soften, melt, etc. May cause adhesion. In addition, even if the extraction conditions are below the temperature at which the polymer softens or otherwise changes, depending on the particle size and particle size distribution of the powder, the extractant may be absorbed during extraction and the volume of the polymer may increase. Body-to-body adhesion may occur.

In other words, when extracting polymers using conventional high-pressure extraction methods, polymers adhere to each other as the extraction progresses, leading to caking, which can lead to quality problems in the product polymer. This resulted in inconvenience in the operation of removing the product from the extraction vessel, and the need for new operations such as re-grinding the product.

Therefore, in order to prevent such adhesion and caking from occurring, it is considered to lower the temperature. However, lowering the temperature slows down the extraction rate and therefore increases the time required for extraction, resulting in economical disadvantages such as the need for thicker equipment and the need for a larger amount of extractant.

Particularly, when the polymer is a granular material with a small particle size and a wide particle size distribution, adhesion and caking are more likely to occur, making high-level extraction impossible.

(Means for Solving the Problems) As a result of extensive research by the present inventors in order to overcome the problems in removing impurities from the conventional powder and granular products described above,
When filling a polymer powder product into an extraction container, the particle size distribution of the powder product and the porosity at the time of filling the extractor are controlled within a predetermined range, and the product is brought into contact with a supercritical state or a liquid extractant. It has been discovered that by doing so, it is possible to prevent adhesion of powder and granular materials to each other and to efficiently remove impurities, and based on this knowledge, the present invention has been accomplished.

That is, the present invention (1) fills a powder into an extractor and extracts and removes impurities contained in the powder with an extractant, and extracts with a porosity of 0.7 to 0.95. An extraction method characterized by filling the inside of a container with the powder or granules (hereinafter referred to as the first invention); and (2) filling the inside of the extractor with the powder or granules to remove impurities contained in the powder or granules. When removing by extraction with an extractant, the particle size is made substantially uniform, or the total weight of particles with a particle size smaller than the particle size where the particle size distribution shows the maximum frequency is 40% or less of the total weight, Porosity 0.36~0.
The present invention provides an extraction method (hereinafter referred to as the second invention) characterized in that the inside of the extractor is filled with the granular material in step 95.

An example of an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a flow sheet illustrating one embodiment of the invention using a fixed bed extractor. In the figure, the extractant is supplied from a storage tank (not shown) such as an extractant tank or cylinder through a line 1 to an extractant pressurizing device 2, and is pressurized to a pressure suitable for extraction. The pressure booster is a compressor if the extractant from line 1 is gaseous, or a pump if it is liquid. Further, a plurality of boosters may be connected in series or in parallel. The extractant pressurized to the extraction pressure is supplied from line 3 to heat exchanger 4, adjusted to the extraction temperature by fluid from line 5, and supplied from line 6 to extractor 7. An extractant dispersion device 8 is installed in the upper part of the extractor 7.
For example, a sintered metal plate or the like is used. The extractant supplied from line 6 to extractor 7 is uniformly dispersed via dispersion device 8 .

A support plate 14 made of a fine wire mesh or porous metal is installed in the lower part of the extractor 7.

In FIG. 1, the extractant is supplied from the upper part of the extractor 7, but the extractant may be supplied from the lower part of the extractor 7. In this case, the support plate 14 also serves as an extractant dispersion device and the extractor 7
It is installed in the inner lower part. Furthermore, an appropriate device may be installed in the upper part of the extractor 7 to prevent scattering of powder and granules.

A predetermined amount of a powdery substance of a polymer containing impurities, which is a substance to be extracted, is filled into a lower part of the extractor 7 than the dispersion device 8 through the inlet 12 .

The extractant that has extracted impurities is sent from line 9 to the pressure regulating valve lO.
and is disposed of or recovered via line 11. When the extractant is recovered and reused, impurities contained in the extractant are separated and removed by a conventional method such as reducing the pressure and/or increasing the temperature, or by adsorption separation.

The treated granular material after the extraction process is taken out from the takeout port 13.

In the present invention, the porosity (ε) refers to the bulk volume (
It is the ratio of the volume of the void to V), and the volume of the void is:
The difference (V) between the bulk volume (V) and the true volume (Vp) of the powder
-Vp). Also, the true volume (
Vp) is determined by the product of the ratio of bulk density (ρ) to true density (ρ2) and bulk volume (V). Here, the bulk density (ρ
) is determined by filling a container (V) of a certain size with granular material and measuring its weight (W).

In the first aspect of the present invention, by setting the porosity to more than 0.7, the extraction process can be performed without being affected by the particle size distribution and without causing adhesion or caking. If the porosity is 0.95 or more, the volumetric efficiency of the extractor decreases and is not economical.

Next, regarding the second invention, it is preferable to lower the porosity to less than 0.7 in order to increase the filling amount in the extractor and increase the extraction throughput, but depending on the particle size distribution state of the particle size of the powder, May cause adhesion and caking. However, for powders with substantially uniform particle size, the porosity is at least 0.36.
If so, it will not cause adhesion or caking. Here, "the particle size is substantially uniform" means that 95% or more of the total weight of the powder or granules falls within the particle size ratio of ±0.1.

In addition, if the particle size is uneven and has a particle size distribution, if the particle size distribution is such that a certain proportion of the small particle size is removed, adhesion and caking will not occur with a porosity of 0.36 or more. . In this case, as shown in Figure 2, in the particle size distribution diagram of the target powder, it is assumed that the distribution of large and small particle size areas is approximately equal, with the particle size center showing the maximum frequency of the particle size distribution. For the particle size distribution of the granular material, the area of small particle size is at least 10
% of the total weight is excluded (so that the total weight of particles smaller than the particle size showing the maximum frequency is 4% of the total weight).
The portion of A that is less than 0%) 5, more preferably 50% is excluded. The porosity and particle size distribution can be adjusted by adjusting processing conditions such as pelletization, pulverization, and sieving in the polymer production process.

In the present invention, the powder or granular material is not particularly limited in its shape, and as is clear from the above, it is not limited to powder (, granular,
It is meant to include spherical and pellet shapes, and may be any one of these shapes or a mixture of two or more thereof.

In the present invention, there is no particular restriction on the particle size of the powder, but the average particle size is, for example, 0.1 mm or more, preferably 0.3 mm or more.

In the present invention, the smaller the particle size of the powder, the faster the extractant will diffuse into the interior (the extraction effect will be greater, and the extraction speed will be faster. ,
There are solid substances made into fine particles by pulverization or the like as described above. In the conventional method, caking of such powder easily occurs during extraction, but in the present invention, this can be prevented and the extraction effect and extraction rate can be increased.

The preferred powder or granular material is polymer (
Examples include polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyoxymethylene, polyacrylamide, copolymers or chlorinated products thereof, rubber, and chlorinated rubber.

Impurities to be extracted include residual monomers and oligomers in these polymers, such as residual formalin, styrene, trioxymethylene, moisture, and organic solvents.

The powder or granules suitable for the extraction process of the method of the present invention are polymers that have an appropriate swelling property with respect to the extractant, and the extraction process is performed using an extractant that appropriately dissolves and swells such granules. be able to.

The extractant used in the present invention is selected as appropriate for the powder to be extracted, and specific examples include (a) carbon dioxide, dinitrogen oxide, carbon disulfide, ethane, ethylene, propane, propylene, etc. hydrocarbons, halogenated hydrocarbons, (
b) A mixture of two or more of the above gases, and (c) a mixture of the above substances and a substance that serves as a second extraction solvent for impurities (normal organic solvent such as methanol, ethanol, toluene, etc.).

The extractant used in the present invention is in a liquid state or in a supercritical state, but it is more preferable to use it in a supercritical state. The pressure and temperature of the extractor in this case vary depending on the target powder, but the forward pressure is 40 to 500 kg/crr?
G is preferred, and the temperature is preferably 0 to 150°C. If the pressure is less than 40 kg/cni"G, the extraction ability of the extractant is low and sufficient extraction effect cannot be obtained, and the pressure is less than 500 kg/cni"G.
If the pressure exceeds dG, it is not economical considering the increased production cost for pressure-resistant design of the device and the power required to compress the extractant. Also, if the temperature is lower than 0℃, the extraction rate will decrease,
If the temperature exceeds 150°C, softening, adhesion, caking, and deterioration of the powder and granular material to be extracted will occur.

In the present invention, a plurality of extractors may be provided in parallel so that extraction can be performed continuously, or a plurality of extractors may be provided in series.

(Effects of the Invention) According to the present invention, extraction processing can be performed without adhesion or caking of powder or granules in the extractor. Furthermore, according to the method of the present invention, not only can impurities be extracted effectively (but also powder and granules with an extremely high degree of impurity extraction can be purified).

(Examples) Next, the present invention will be described in more detail based on Examples and Comparative Examples.

Example 1 Chlorinated rubber (residual solvent concentration: 6.9%, residual solvent was carbon tetrachloride) was extracted based on the flow sheet shown in FIG. The extractor was filled with 68 g of powdered chlorinated rubber, and the porosity was measured to be 0.7. Carbon dioxide was supplied as an extractant from the top of the extractor at a rate of 2.5 J2/min. Inside the extractor, the pressure is 100 kg/crrrG and the temperature is 30'C.
After holding for a period of time, the supply of carbon dioxide was stopped. After the pressure in the extractor reached atmospheric pressure, the chlorinated rubber was taken out and subjected to analysis. No caking was observed in the powder, and the concentration of the solvent was 6.
．． It decreased from 9% to 0.5%.

Comparative Example 1 Extraction was carried out under the same conditions as in Example 1 based on FIG. The extractor was filled with 109 g of chlorinated polypropylene, and the porosity was measured to be 0.6. In the chlorinated polypropylene powder used for extraction, the weight of particles smaller than the particle size showing the maximum frequency in the particle size distribution was 50% of the total weight. After extraction, the powder in the extractor was in the form of large clumps.

Example 2 Powdered polystyrene (HIPS, residual monomer concentration 20
00 p pm) was divided using a 48-mesh sieve, and the large particle size part (the weight of particles smaller than the particle size that indicates the maximum frequency in the particle size distribution is 10% of the total weight) is shown in the flow sheet shown in Figure 1. Extraction was performed using carbon dioxide as an extractant based on the following. The extractor was filled with 20 g of powdered raw material, and the porosity was measured to be 0.4. The inside of the extractor was maintained at a pressure of 245 kg/crtrG and a temperature of 80°C. No particular caking was observed in the powder after extraction, and the residual monomer concentration was 500 ppm or less.

Comparative Example 2 Powdered polystyrene (HIPS, residual monomer concentration 20
00 pp pm) was extracted using carbon dioxide as an extractant based on the flow sheet shown in FIG. 20g of powdered polystyrene was filled into the extractor without being divided through a 48-mesh sieve, and the porosity was measured and found to be 0.
It was 35.

Pressure inside the extractor is 245 kg/crrfG, iFA
The temperature was maintained at 80''C. After extraction, the powder in the extractor was in the form of large clumps.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing one embodiment of the present invention. FIG. 2 shows the particle size distribution of a powder suitable for applying the method of the present invention. Explanation of symbols 2... Boosting device 4... Heat exchanger 7...
Fixed bed extractor 8... Dispersion device IO... Pressure adjustment valve 12... Inlet port 13... Outlet port
14... Support plate patent applicant Toyo Engineering Co., Ltd. Asahi Denka Kogyo Co., Ltd. Figure 1 Figure 2 Particle size - large particle size distribution

Claims (2)

[Claims] (1) When filling powder into an extractor and extracting and removing impurities contained in the powder with an extractant, the porosity is 0.
．． An extraction method characterized by filling the inside of an extractor with the powder at a concentration of 7 to 0.95. (2) When filling a powder into an extractor and extracting and removing impurities contained in the powder with an extractant, the particle size is made substantially uniform or the particle size distribution is maximized. The total weight of particles with a particle size smaller than the particle size indicating the frequency is 4 to the total weight.
An extraction method characterized by filling the inside of an extractor with the granular material at a porosity of 0.36 to 0.95, with the porosity being 0% or less.