FR2638098A1 - PROCESS FOR EXTRACTING IMPURITIES CONTAINED IN POWDER MATERIAL - Google Patents

Abstract

The invention relates to a method for removing impurities, to a high degree, contained in a powder or particulate material. The aim of the invention is on the one hand to extract, with an extracting agent, the impurities contained in a pulverulent or particulate solid material without causing the powder and the particles to stick together, nor the formation of a mass and on the other hand, to refine such a material. These objects are achieved by means of a method characterized in that it consists in charging an extractor with the solid material with a vacuum of 0.7 to 0.95. The invention applies more particularly to the extraction of impurities, to a high degree, contained in polymers, rubbers and the like, but also to the refining of such solid materials.

Description

"METHOD OF EXTRACTING IMPURITIES CONTAINED

  IN A MATERIAL IN THE FORM OF POWDER ".

  The present invention relates to a process for removing impurities or the like to a high degree contained in polymers, rubbers, etc. (hereinafter referred to as polymers) in the form of

powder or particles.

  Conventionally, as a method for removing impurities (eg, solvents, monomers, oligomers and by-products) remaining in the powder or particles, or the like of polymers, means such as

  evaporation by heating and evaporation under vacuum.

  However, small amounts of impurities remain and some of these impurities deteriorate the quality of the product or are dangerous for the human body. If the polymer is heated to reduce the level of impurities, the polymer, for example, changes in quality or softens, so that it is impossible to lower the remaining levels of impurities to certain values.

or below.

  Therefore, it has recently been suggested high pressure extraction methods using, for example, supercritical fluids. For example, Japanese Patent Specification No. 46972/1984 discloses a process in which cyclic oligomers are reduced in a polymer by the use of

supercritical fluids.

  However, when attempting to remove impurities to a high degree from a liquid polymer using the high pressure extraction method described in Japanese Patent Specification No. 46972/1984, as mentioned here in example 1 there is a limit to extraction to a high degree

  to reduce impurities to certain values or

  below. In addition, when a polymer in the form of a powder or particles or the like is subjected to the high pressure extraction process above to remove impurities to a high degree, the polymer particles bond to each other in some cases, due to a change such as softening or melting of the polymer that is caused under the extraction conditions. Further, if the temperature of the extraction conditions is equal to or less than the temperature at which a change, such as softening of the polymer occurs, the polymer volume increases due to the absorption of the agent. extraction when the polymer is subjected to extraction, depending on the particle size and particle size distribution of the polymer in the form of powder or particles, which sometimes causes the particles of the polymer to stick to each other. In other words, in the prior high pressure extraction processes, when a polymer is subjected to extraction, the polymer particles stick to each other as the extraction process progresses, thereby forming a polymer mass which raises a qualitative problem in the polymer product and which is unfavorable when the product is to be recovered from the extractor, and raises the need for a new process such as the

grinding the product.

  Therefore, it is contemplated to lower the temperature so that such bonding or mass formation can not occur. However, when the temperature is lowered, the extraction speed becomes low and the extraction requires a longer time which is economically disadvantageous because the installation must be larger and the quantity

  extraction agent must be increased.

  In particular, when the polymer is in the form of powder or particles having small particle sizes and a wide particle size distribution, bonding and mass formation are more likely to occur and

  the extraction to a high degree is impossible.

  Therefore, the first object of the present invention is to provide a method for removing by extraction impurities or the like contained in a polymer in the form of a powder or particles without causing the joining or

  forming a mass of powder or particles.

  A second object of the present invention is to provide a process for refining a powder or particles of a polymer in which the impurities contained in the polymer can be effectively extracted, and wherein the degree of extraction of the

impurities is very high.

  The objects, features and advantages of the above invention as well as others

  will emerge from the following detailed description and

  drawings in which: - Figure 1 is a block diagram showing an embodiment of the present invention; - Figure 2 shows the particle size distribution of a powder or particles for which the process of the present invention may be

applied properly.

  The inventors have conducted their research intensively to overcome the above-mentioned prior art problems involved in the removal of impurities in powdered or particulate products and have found that by charging a powdered polymer product or particles in an extractor, it is possible to prevent the particles from being joined together and the impurities can be effectively removed when the powdered or particulate product is brought into contact with an extraction agent in the supercritical state or under liquid form, the particle size distribution of a powdered or particulate product and the empty volume at the moment of loading thereof into the extractor being restricted respectively in the intervals

  prescribed, which leads to the present invention.

  In other words, the present invention provides (1). a process for refining a pulverulent or particulate solid material by extracting impurities contained therein with an extraction agent, characterized in that it consists in charging an extractor with the solid material, the vacuum (fractional free volume: ratio free volume to apparent volume) being from 0.7 to 0.95 (hereinafter referred to as the first invention) and (2) a process for refining a powdery or particulate solid material by extracting the impurities contained therein with an extraction agent, characterized in that it consists in charging an extractor with the solid material whose particle diameter is made substantially uniform, or with the solid material in which the weight of all the particles whose particle diameter is less than the particle diameter indicating the maximum frequency of the particle size distribution is made to 40% or less of the total weight and extracting the solid material e charged, the vacuum being 0.36 to 0.95 (referenced hereinafter as the second

invention).

  An embodiment of the present

  The invention is described with reference to the drawings.

  Fig. 1 is a block diagram showing an embodiment of the present invention in which a fixed bed type extractor is used. In Fig. 1, an extractant is introduced from a storage tank (not shown) such as a reservoir or bomb of extractant, through a line 1 into a booster 2 for l extraction agent, the pressure of the extraction agent is increased to a pressure S suitable for extraction. The booster is a compressor when the extraction agent from line 1 is a gas, or a pump when the extraction agent is a liquid. The booster may comprise a plurality of elevators that can be arranged in series or in parallel. The extraction agent, whose pressure has been raised to a pressure for extraction, is introduced via a line 3 into a heat exchanger 4, where the temperature of the extraction agent is controlled at a temperature to the extraction using a fluid from a line, and the extraction agent is introduced via a line 6 into an extractor 7. A dispersion device 8 for the extraction agent located in a upper section of the extractor 7 is composed for example of a sintered metal plate. The extraction agent introduced via line 6 into the extractor 7 is dispersed uniformly through the device of

dispersion 8.-

  A support plate 14 consisting of a fine wire mesh filter or a porous metal is

  located at the bottom of the extractor 7.

  In FIG. 1, although the extraction agent is introduced through the upper part of the extractor 7, it can be introduced through the lower part of the extractor 7. In the latter case, the support plate 14 is placed at a lower part in the extractor 7 so that it can also serve as a dispersion device for the extraction agent. In addition, a suitable device can be placed at an upper part in the extractor 7 to prevent the diffusion of the powder

or particles.

  Under the dispersion device 8 of the extractor, an inlet 12 is charged with a prescribed quantity of powder or particles of a solid polymer containing impurities, which must be subjected to extraction. The extraction agent which has removed the impurities has passed from a line 9 into a pressure-controlling valve 10 and is discharged or recovered by a line 11. If the extraction agent is to be recovered and reused, the impurities contained therein are separated and removed by conventional means for applying a pressure reduction and / or temperature increase of the extractant or, for example, by means of a separation.

by adsorption.

  The powder or particles which have been subjected to the extraction are recovered by an outlet 13. In the present invention, the term "vacuum ()" means the ratio of the volume of the vacuum to the apparent volume (V) of the powder or of the particles. The void volume can be determined as the difference (V - Vp), where V is the apparent volume and Vp is the theoretical volume of the powder or particles. The theoretical volume Vp can be determined as a product of the ratio of the apparent density () to the theoretical density (p) and the apparent volume (V). Apparent density (y) can be determined by filling a container of a certain volume (V) with the powder or particles

  then measuring the weight (W) of it.

  In the present invention, when the vacuum is set higher than 0.7, the extraction can be carried out without being affected by the particle size distribution and without causing the joining or the formation of a mass. If the void equals 0.95 or

2638098-

  more, the efficiency of the volume of the extractor is

  lowered, which is not economical.

  Now the second invention will be described. When the vacuum is lowered below 0.7, the load in the extractor can be increased, thus favorably increasing the treatment capacity, but the joining or the formation of a mass sometimes occurs depending on the state of the process. the particle size distribution of the powder or particles. However, for powder or particles that are substantially uniform in particle diameter, if the void is at least 0.36, bonding or mass formation does not occur. Here, the term "substantially uniform in particle diameter" means that 95% or more of the total weight of the powder or particles is

  is in the range of + 10% of average diameter.

  In addition, for a powder or particles that are not uniform in particle diameter and therefore have a particle size distribution, if the powder or particles have a particle size distribution such as a portion of the small size of particle has been subtracted, and if the vacuum is equal to 0.36 or more, the joining or the formation of a mass will not occur. In this case, it is essential to exclude the most

  small particle sizes up to a certain degree.

  This is explained by FIG. 2 which represents the diagram of the particle size distribution of the particular powder or particles. In Figure 2, the center of the curve indicates the maximum frequency of the particle size distribution and it is assumed that the distribution of the largest particle sizes on the right-hand side of the center and the distribution of the smaller particle sizes on the left-hand side of the center are approximately equal. In this case, the part of the smaller particle sizes designated A which corresponds to at least 10% by weight of the entire distribution of the powder or particles is removed (i.e., the weight ratio of particles having particle sizes smaller on the left side of the center becomes less than 40% of the total weight of the particles). It is preferable that Part A to

  exclude 50% by weight of the distribution.

  The adjustment of such a vacuum and the particle size distribution can be obtained by controlling the processing conditions for, for example, pelletizing, grinding and sieving in the steps

of production of the polymer.

  In the present invention, the term "powder or particles" is not particularly limited in shape and, as it appears from the foregoing, does not only mean powders but also particles, spheres, pellets, etc. .. who

can be mixed.

  In the present invention, although there is no particular restriction on the particle diameter of the powder or particles, the average particle diameter is, for example, 0.1 mm or more, and preferably 0.3 mm or more. In addition, it is added that particles having a size of mm can be refined by the process of the present invention without being limited thereto as

upper limit.

  In the present invention, the smaller the particle diameter of the powder or particles, the faster the diffusion of the extracting agent therein, thereby increasing the effect

  extraction, to speed up the extraction speed.

  The powder or particles contain a body that is powdery by nature and a solid substance that has

  been finely ground, for example as mentioned above.

  above. In the prior art, such a powder or such particles readily formed a mass during extraction, whereas in the present invention such mass formation is prevented, which leads to an increase in the effect of extraction and extraction rate. Preferable powders or particles which are subject to the present invention are polymers (including rubbers) such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyoxymethylene, and polyacrylamide as well as copolymers thereof, as well as chlorinated products, rubbers, chlorinated rubbers. The impurities that must be extracted

  include monomers, oligomers, etc.

  remaining in such polymers, for example formaldehyde, styrene, trioxymethylene, water

  and remaining organic solvents.

  Preferable powders or particles suitable for the extraction treatment of the process of the present invention are those having a suitable swelling susceptibility for the particular extracting agent, and an extractant which can dissolve or swell in a manner suitable such powder or particles is used to achieve

the extraction treatment.

  The extracting agent used in the present invention is selected in a suitable manner for the particular powders or particles to be subjected to the extraction treatment and it may be mentioned as specific examples of the extractant, (a) carbon dioxide, nitrous oxide, carbon disulfide, hydrocarbons such as ethane, ethylene, propane and propylene and halogenated hydrocarbons, (b) a mixture of two or more of mentioned above and (c) a mixture prepared from the above material and a second extractant for the impurities (e.g. conventional organic solvents such as

  methanol, ethanol and toluene).

  The extraction agent used in the present invention is liquid or in a supercritical state, although it is preferred that the extraction agent be used in the supercritical state. In this case, although the pressure and the temperature of the extractor may vary depending on the powder or the particles, it is generally preferable for the pressure to be 40 to 500 kg / cm 2 (specific weight) and for the temperature to be 0. at 150 ° C. If the pressure is below kg / cm 2 (specific weight), the extraction capacity of the extraction agent is lowered and an adequate extraction effect can not be obtained, and other On the other hand, if the pressure is greater than 500 kg / cm 2 (specific weight), it is not economical in the sense of the increased cost of the device which must withstand the pressure and the direction of the power necessary to compress the agent. extraction. In addition, if the temperature is below OC, the extraction rate is lowered and, on the other hand, if the temperature is above 150 ° C, for example, a softening, aggregation, mass formation, or deterioration of the quality of the powder or

  particles subjected to extraction.

  In the present invention, several extractors can be arranged in parallel to carry out the continuous extraction, or can be

arranged in series.

  According to the present invention, the extraction treatment can be carried out without allowing the powder or particles to bunch up or form a mass. According to the present invention, not only can impurities be extracted effectively, but also the refinement of the powder or particles can be achieved, the extraction of impurities being

very high.

  The present invention will now be described in more detail with reference to the examples and

comparative examples.

  Example: A chlorinated rubber (concentration of residual solvents: 6.9%, residual solvent: carbon tetrachloride) is extracted according to the principle diagram shown in FIG. 1. The extractor is loaded with 68 g of chlorinated rubber. and the void is 0.7. Carbon dioxide is supplied as extractant from the top of the extractor at a rate of 2.5 l / min (normal conditions of temperature and pressure). The pressure and the temperature in the extractor are maintained at 100 kg / cm 2 (specific weight) and 30 ° C. respectively for 6 hours, and then the supply of carbon dioxide is stopped. The pressure in the extractor reaches atmospheric pressure, then the chlorinated rubber is removed and analyzed. The formation of mass in the powder is not observed and the concentration of the solvent in the powder is reduced by

6.9% to 0.5%.

  Comparative Example 1: An extraction is carried out under the same conditions as those of Example 1 based on FIG. 1. The extractor is loaded with 109 g of chlorinated polypropylene and the vacuum is measured which is 0.6. The chlorinated polypropylene powder used for the extraction is such that the weight of the particles having particle sizes smaller than the particle size indicating the maximum frequency in the particle size distribution of the powder of

  chlorinated polypropylene is equal to 50% of the total weight.

  After extraction, the residual concentration of the solvent is 0.7%, but the powder forms a

wide mass in the extractor.

Example 2

  Powdered polystyrene ("HIPS" polystyrene, residual monomer concentration: about 2,000 ppm) was sieved through a sieve of 48 mesh and the portion having larger particle sizes (the weight of the particles having smaller particle sizes) was separated by sieving. the particle size indicating the maximum frequency which in the particle size distribution is equal to 10% of the total weight) is subjected to extraction with

  carbon based on the block diagram of Figure 1.

  The extractor is charged with 20 g of pulverulent raw material, and the vacuum is measured at 0.4. The pressure and the temperature in the extractor are maintained at 245 kg / cm 2 (specific weight) and 80 ° C. respectively. After extraction, no particular mass formation is observed in the powder and the residual monomer concentration is equal to

500 ppm or below.

  Comparative Example 2: Powder polystyrene ("HIPS" polystyrene, residual monomer concentration: about 2,000 ppm) was subjected to extraction with carbon dioxide based on the principle route of FIG. g of powdered polystyrene which has not been sieved with a

  48 mesh screen and measure the vacuum which is 0.35.

  The pressure and the temperature in the extractor are maintained at 245 kg / cm 2 (specific weight) and 80 ° C., respectively. After extraction, the residual monomer concentration is about 500 ppm but the

  powder forms a large mass in the extractor.

  Since the invention has been described in accordance with the embodiment, it is obvious that the invention

  is not limited by any details of the description

  except otherwise specified but is largely conceived in the spirit and scope

appended claims.

Claims (8)

  1 - Process for refining a powdery or particulate solid material by extracting the impurities contained therein with an extraction agent, characterized in that it consists in charging an extractor with the solid material with a empty from 0.7 to 0.95.   2 - Process for refining a powdery or particulate solid material by extracting the impurities contained therein with an extraction agent, characterized in that it consists in charging an extractor with the solid material, the particle diameter of which is practically rendered uniformly, or with the solid material in which the weight of all particles having a particle diameter smaller than that indicating the maximum frequency of the particle size distribution is made to 40% or less of the total weight, and extracting the solid material   charged with a vacuum of 0.36 to 0.95.   3 - Process according to claim 1 or 2, characterized in that the solid material is a polymer or a rubber selected from the group consisting of polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyoxymethylene, polyacrylamide, and their copolymers, and products   chlorinated, rubbers, and chlorinated rubbers.   4 - Process according to claim 1 or 2, characterized in that the solid material has a   average particle diameter of 0.1 mm or more.   5 - Process according to claim 1 or 2, characterized in that the extractor product is selected from the group consisting of carbon dioxide, nitrous oxide, carbon disulfide, a hydrocarbon and a halogenated hydrocarbon, a mixture of two or more thereof, and a mixture prepared therefrom and a second extractant for the impurities. 6 - Process according to claim 1 or 2, characterized in that an agent is used extraction in the liquid state.   7 - Process according to claim 1 or 2, characterized in that an agent is used   extraction in the supercritical state.   8 - Process according to claim 1 or 2, characterized in that the pressure in the extractor is in the range of 40 to 500 kg / cm 2 (specific weight).   20.9 - Process according to claim 1 or 2, characterized in that the temperature in the extractor   is in the range of 0 to 150 C.   - Process according to claim 2, characterized in that 95% or more of the total weight of the solid material is in the range of + 10% of average diameter.