JP2009279573A - Method for separating solute from solution containing supercritical carbon dioxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for selectively separating/recovering a selected solute on the surface of a specific material from a solution containing supercritical carbon dioxide, which method is friendly to the environment and is carried out while saving energy and reducing the treatment cost. <P>SOLUTION: The method for separating/recovering the solute in the solution comprises the steps of: putting the material having pores of predetermined pore size in the solution which contains supercritical carbon dioxide and in which the solute to be separated is dissolved by the amount equal to or smaller than the solubility; and precipitating the solute in the pores mainly by means of capillary condensation phenomena in pores. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates generally to a method for separating selected solutes in solution. The present invention particularly relates to a method for separating and recovering a solute by precipitating a selected solute from a solution containing supercritical carbon dioxide.

  A supercritical fluid is a fluid obtained by maintaining a substance at a pressure and temperature above a critical point, and is characterized by having solubility in a solute equivalent to a liquid and diffusibility equivalent to a gas. For example, supercritical carbon dioxide has a critical point of 73 atm (7.38 MPa) and 31 ° C. (304.1 K), and can be easily manufactured industrially. When the solute is dissolved to a pressure below the critical point Since carbon dioxide is vaporized, only the solute remains, and the vaporized carbon dioxide can be recovered and reused, so that it has already been put to practical use for the purpose of decaffeination of coffee beans. ing.

  In addition, by replacing various processes using conventional heavy metals and strong acids and processes using flammable and toxic solvents with processes using supercritical carbon dioxide, the negative impact on the environment can be reduced. From the viewpoint of environmentally friendly solvents, its replacement is expected. Supercritical carbon dioxide is expected to be used because it has a particularly high solubility in organic compounds, and even if carbon dioxide remains in the solute after decompression, it has almost no toxicity to the human body.

  On the other hand, it was thought that the solubility with respect to inorganic compounds, such as a metal salt, to supercritical carbon dioxide was small, and it could not be applied to an inorganic compound. However, in the 1990s, it was discovered that the charge of a metal can be extracted by neutralizing with an organic chelating agent as shown in Patent Document 1, and at present, as shown in Non-Patent Document 1, there are various types of extraction. Research and development aimed at industrial applications in the field are being conducted. In particular, as seen in Patent Document 2, the production of a functional material by attaching a metal compound to the surface of the material is becoming an important method for the creation of innovative new materials such as catalysts.

  When a solute dissolved in supercritical carbon dioxide is attached to the material surface by a method as disclosed in Patent Document 2, the solubility of the solute in supercritical carbon dioxide is lowered in order to ensure a sufficient amount of adhesion. In order to cause precipitation, supercritical carbon dioxide must be decompressed and vaporized. During the operation, carbon dioxide is one of the typical global warming gases, so it is required to be reused without being released into the environment. High pressure equipment for pressure and recycling is indispensable. However, high-pressure equipment is expensive, and a large amount of energy is required for repressurization, and there is a problem that the processing cost is generally increased. Furthermore, there is a problem that the solute deposits non-selectively not only on the object to be applied but also on the inner surface of the high-pressure device.

  US Patent 5,356,538   US Patent 7,294,528   A. S. Gopalan, C.I. M.M. Wai, H .; K. Edited by Jacobs, ACS Symposium Series 860 "" Separations and Processes Using Supercarbon Carbon Dioxide ""

  An object of the present invention is to provide a method for separating and recovering a solute selected from a solution containing supercritical carbon dioxide, which can reduce pressure reduction and vaporization operations or eliminate the use of an additional high-pressure apparatus. It is.

  Furthermore, an object of the present invention is to provide a method capable of selectively separating and recovering a solute selected from a solution containing supercritical carbon dioxide only on the surface of a specific substance.

  Another object of the present invention is to provide a method for separating and recovering a solute selected from a solution containing supercritical carbon dioxide, which is environmentally friendly, has a large energy saving effect, or can reduce processing costs. is there.

  According to the present invention, a substance having pores of a predetermined size is present in a solution containing supercritical carbon dioxide in which a solute to be separated is dissolved at or below its solubility, and the capillary condensation phenomenon in the pores is utilized. A method is provided for separating solutes in solution by precipitating solutes in the pores.

  ADVANTAGE OF THE INVENTION According to this invention, the pressure reduction and vaporization operation required when isolate | separating and collect | recovering a solute from the solution containing a supercritical carbon dioxide can be reduced.

  According to the present invention, energy required for separating and recovering a solute from a solution containing supercritical carbon dioxide can be reduced.

  According to the present invention, a solute can be selectively deposited only on the surface of a specific substance in a solution from a solution containing supercritical carbon dioxide.

  The best mode for carrying out the invention will be described with reference to examples. In the following examples, a case where a specific solute is used is described. However, the present invention is not limited to this, and can be applied to other solutes, and deviates from the gist of the present invention. It will be apparent to those skilled in the art that any modifications are possible without departing from the scope.

  First, an outline of an embodiment of the present invention will be described. Supercritical carbon dioxide has a high solubility in solutes composed of organic compounds or inorganic compounds chemically complexed with organic compounds, and a large diffusion permeability into the pores, while it is less polluting to the environment than organic solvents. It is a fluid medium that excels in not causing it. In the present invention, a solute dissolved in supercritical carbon dioxide can be easily and selectively recovered in a substance having pores of a predetermined size (for example, 1 micrometer or less) (in the pores). Then, the functional material can be obtained by supporting the decomposed material on the inner surface of the pores by a method such as heating the substance.

  According to the present invention, the object is a structure having pores with a representative diameter of, for example, 1 micrometer or less, and this is placed in advance in supercritical carbon dioxide in which a solute is dissolved or inserted later. As a result, the capillary condensation phenomenon is physically caused in the high-pressure fluid flowing into the pores, and the solute dissolved in the supercritical carbon dioxide can be precipitated by the pressure effectively reduced in the pores. . Thus, the solute can be recovered in the pores without reducing the pressure of the high-pressure fluid, and can be subjected to subsequent physicochemical operations. As a result, it is possible to rationalize the process composed of high-voltage equipment.

  As a solute having sufficient solubility in supercritical carbon dioxide, there is 1,5-cyclooctadiene dimethylplatinum (1,5-cyclooctadiene dimethylplatinum). This is first dissolved to near solubility in a solution of supercritical carbon dioxide. In this high-pressure fluid (supercritical carbon dioxide solution), stainless steel with a water-repellent film having irregularities as high as about 300 nanometers attached to the surface is inserted. Then, a capillary condensation phenomenon appears in the concave portion of the concavo-convex structure of about 300 nanometers, and 1,5 cyclooctadiene dimethyl platinum is precipitated in the concavo-convex structure. After discharging the high-pressure fluid in this state, the temperature of the stainless steel with the film is raised to 120 ° C. Then, 1,5 cyclooctadiene dimethyl platinum is thermally decomposed in the concavo-convex structure, and platinum fine particles are formed there. In this way, a water-repellent catalyst carrying platinum particles, that is, a functional material can be easily produced. A detailed example is shown in Example 1 below.

  If two kinds of solutes having different solubilities are dissolved in supercritical carbon dioxide during the above series of operations, precipitation corresponding to the difference in solubility occurs during capillary condensation. That is, the fact that a solute having a low solubility is precipitated first is utilized. As a result, two kinds of solutes can be separated and recovered from carbon dioxide without reducing the pressure. A detailed example is shown in Example 2 below. In addition, it is clear that the method shown in Example 2 can be extended to separation of two or more solutes, and an example thereof is shown in Example 3. Thus, the present invention is not limited to the separation of carbon dioxide and solute, but can be applied to the separation of two or more kinds of solutes.

  0.002 mol of powder of 1,5 cyclooctadiene dimethyl platinum was put in a high pressure autoclave having an internal volume of 100 ml. Next, 50 ml of Dixon packing having a diameter of 6 mm, which is a wire mesh-like filling made of stainless steel, was placed in the high-pressure autoclave. The Dickson packing has a concavo-convex film having a height (depth) of about 300 nanometers made of an organosilicon compound formed on the surface by CVD processing. Thereafter, liquid carbon dioxide was introduced into the high pressure autoclave and sealed, and then the temperature of the high pressure autoclave was maintained at 80 ° C. and the pressure at 180 atmospheres for 5 hours. During this operation, the liquid carbon dioxide became supercritical carbon dioxide, and 0.002 mol of 1,5 cyclooctadiene dimethyl platinum powder was uniformly dissolved in the supercritical carbon dioxide.

  After dissolution, due to the high diffusivity of supercritical carbon dioxide, the dissolved 1,5-cyclooctadiene dimethyl platinum entered the uneven film on the Dickson packing surface. Furthermore, in the concavo-convex film, capillary condensation, which is a physical phenomenon occurring in the pores, occurs, the effective pressure of the high-pressure fluid that has entered decreases, and 1,5-cyclooctadiene dimethyl platinum in supercritical carbon dioxide reaches solubility. And deposited in the uneven film.

  The results of observation of the stainless steel wire mesh on the surface of the Dickson packing before and after this operation with a scanning electron microscope are shown in FIGS. FIG. 1 is a photomicrograph before operation, and FIG. 2 is a photomicrograph after operation. From the comparison between FIG. 2 and FIG. 1, it can be seen that there is a clearly white deposit (precipitate) on the surface of the stainless steel wire mesh in FIG. At the same time, elemental analysis of the stainless steel wire mesh surface was performed by X-ray energy dispersive spectroscopy, and it was confirmed that the white deposit was a platinum compound (1,5 cyclooctadiene dimethyl platinum).

  Next, the high-pressure fluid in the autoclave was discharged, and liquid carbon dioxide was introduced again, and then the autoclave temperature was kept at 120 ° C. and the pressure was kept at 15 atmospheres for 6 hours. During this operation, the liquid carbon dioxide became supercritical carbon dioxide, which contributed to keeping the temperature inside the autoclave uniform. 1,5 cyclooctadiene dimethylplatinum precipitated in the uneven film on the surface of the stainless steel Dixon packing was thermally decomposed to become metal platinum and supported in the uneven film. FIG. 3 shows the result of observation of the stainless steel wire mesh on the surface of the Dickson packing after this operation with a scanning electron microscope. It can be seen that there is a clearly white deposit (precipitate) on the surface of the stainless steel wire mesh in FIG. At the same time, elemental analysis of the stainless steel wire mesh surface was performed by X-ray energy dispersive spectroscopy, and it was confirmed that the white deposit was platinum metal.

Further, when this stainless steel wire mesh supported by platinum metal was brought into contact with a mixture of hydrogen gas (H ₂ ) and deuterium gas (D ₂ ) for 30 minutes, an exchange reaction of hydrogen atoms occurred and HD molecules were generated. . From this, hydrogen atom exchange activity was observed, and platinum catalytic activity was observed. In the normal stainless steel Dixon packing performed for comparison, no exchange reaction occurred. As described above, it was confirmed that by using the present invention, a functional material such as a platinum catalyst can be produced by a simple operation.

  In the present invention, a functional material can also be produced using other substances that are soluble in supercritical carbon dioxide. Examples of the substance include phosphorus, copper (II) bishexafluoroacetylacetone hydrate (copper), trimethylindium (indium), tetratitanium (titanium dioxide), bispalladium (II) (palladium), and palladium (II). Examples include hexafluoroacetylacetone (palladium), nickel (II) hexafluoroacetylacetone (nickel), bisdiisobutyrylmethanite copper (copper), and copper (I) hexafluoroacetylacetone · 2 butyne (copper). A metal film (layer) in parentheses can finally be obtained. For example, from the third trimethylindium, an indium functional material can be obtained.

  It is known that metal salts such as ceric nitrate and neodymium nitrate can be dissolved in supercritical carbon dioxide when a complex is formed using a complexing agent such as tributyl phosphate (TBP). An organic solution was prepared by dissolving ceric ammonium nitrate and neodymium nitrate hexahydrate in pure TBP until saturated. The latter was referred to as a TBP neodymium nitrate solution, and a test was performed using the test apparatus 100 shown in FIG. In the test apparatus 100 of FIG. 4, the liquefied carbon dioxide was introduced from the liquefied carbon dioxide cylinder 10 into the high-pressure vessel 14 having an internal volume of 60 ml by a high-pressure pump 12 (Syringe pump D260 manufactured by Isco, USA). Furthermore, the TBP neodymium nitrate solution in another container 16 was introduced into the high pressure container 14 by another high pressure pump 18 (DP-8020 manufactured by Tosoh Corporation). Thereafter, the mixed solution in the high-pressure vessel 14 was stirred by a stirrer 20 provided on the lower side of the high-pressure vessel 14. It was confirmed by a video image taken from the observation window of the high-pressure vessel 14 that a single-phase uniform fluid was formed in the high-pressure vessel 14.

  In the test apparatus 100, the packed column 22 is a stainless steel column, and has pressure gauges 24 and 26 at the inlet and outlet, respectively. The piping on the outlet side of the packed column 22 is led to the collection container 30 via the back pressure control device 28. The inside of the packed column 22 was filled with the three types of packing shown in Table 1. The three types are (a) A type silica gel (Technosnakata Co., Ltd.) compliant with JIS standard, pulverized to a particle size of 180-212 micrometers, (b) B type compliant with JIS standard. Silica gel (manufactured by Technos Nakata) is pulverized to adjust the particle size to 180 to 212 micrometers, and (c) porous silica beads (GL Science, 80 to 100 mesh). The pore diameter, pore volume, and specific surface area in Table 1 are measured values.

In these three types of packing, (i) is a filler that has a large specific surface area and can be expected to be chemisorbed on the silica surface. (B) and (C) are fillers that can be expected to undergo capillary condensation rather than chemical adsorption because of the relatively large pore volume. FIG. 5 shows a part of the result of a test for actually supplying a high-pressure fluid to these fillers. FIG. 5 shows a so-called breakthrough curve, where the vertical axis represents the outflow concentration (cm ³ / min) of the TBP neodymium nitrate solution, and the horizontal axis represents the water passage time (min). From the left, the three curves are A for an empty column, B for (A) type A silica gel, and C for (B) type B silica gel. In this test, the adsorbed amounts of the TBP neodymium nitrate solution (a) and (b) were 0.543 g and 0.825 g per 1 g of silica gel, respectively.

From this test result, it was confirmed that the TBP neodymium nitrate solution dissolved in the supercritical carbon dioxide can be recovered on silica gel having pores of about 1 to 4 nanometers installed in the high-pressure fluid. In addition, it is confirmed that the adsorption due to the capillary condensation phenomenon is large, because (b) B type silica gel with larger pore volume than (B) type A silica gel with larger specific surface area is recovered. It was. As for neodymium nitrate recovered in the pores, 0.204 g of the obtained silica beads were immersed in 1 cm ³ of nitric acid solution having a concentration of 0.01 mol / liter for 10 minutes. It was possible to recover 100% as neodymium.

Next, the result of the separation test of the rare earth elements neodymium and cerium will be described. Using the test apparatus 100 of FIG. 4 already described in Example 2, a mixed solution in which a TBP neodymium nitrate complex solution and a TBP cerium nitrate solution were mixed was placed in the container 16. In the packed column 22, (c) porous silica beads (manufactured by GL Science, 80-100 mesh) were placed, and an experiment was conducted to separate neodymium and cerium. As a result, changes in the concentrations of neodymium and cerium in the recovered material obtained in the collection container 30 are shown in FIG. FIG. 6 shows a breakthrough curve, where the vertical axis represents the outflow concentration (cm ³ / min) of the TBP neodymium nitrate complex solution or the TBP cerium nitrate solution, and the horizontal axis represents the water passage time (min).

  In FIG. 6, curve D is for TBP cerium nitrate and curve E is for TBP neodymium nitrate. Since two liquid mixtures having the same molarity were supplied to the container 16, the same amount may be recovered in the solution obtained in the collection container 30, but as is apparent from FIG. The cerium concentration D is higher. This is presumably because neodymium is more easily condensed in the pores of the porous silica bead filler (c). In order to confirm this, the solubility in supercritical carbon dioxide was examined.

  FIG. 7 shows the measurement results of the solubility of the TBP neodymium nitrate solution and the TBP cerium nitrate solution. The vertical axis represents pressure (MPa), and the horizontal axis represents the molar fraction of each complex. Curve F is for TBP neodymium nitrate and curve G is for TBP cerium nitrate. In FIG. 7, each complex is dissolved in supercritical carbon dioxide at a pressure higher than each curve. On the other hand, when the pressure decreases and becomes below each curve, each complex precipitates (condenses). That is, from FIG. 7, the method of dissolving neodymium (curve F) requires high pressure to dissolve in supercritical carbon dioxide, so that capillary condensation occurs in the pores of the porous silica bead filler. First, it can be seen that the neodymium complex is condensed and then the cerium complex is condensed. This result is consistent with the test result of FIG. 6, and it was confirmed that neodymium is more easily condensed in the pores of the porous silica bead filler (c).

  It is a drawing substitute micrograph of the stainless steel wire mesh of the Dickson packing surface before the process of one Example of this invention.   It is a drawing-substituting micrograph of the stainless steel wire mesh on the surface of the Dickson packing after the processing of one example of the present invention.   It is a drawing substitute micrograph of the stainless steel wire mesh of the Dickson packing surface after the heating of one Example of this invention.   It is a figure which shows the structure of the test apparatus of one Example of this invention.   It is a figure which shows the breakthrough curve in Example 2 of this invention.   It is a figure which shows the breakthrough curve in Example 3 of this invention.   It is a figure which shows the solubility in Example 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Liquefied carbon dioxide cylinder 12, 18 High pressure pump 14 High pressure container 16 Container 20 Stirrer 22 Packing column 24, 26 Pressure gauge 28 Back pressure control device 30 Collection container 100 Test apparatus

Claims (6)

  A substance having pores of a predetermined size is present in a solution containing supercritical carbon dioxide in which a solute to be separated is dissolved at or below the solubility, and the capillary condensation phenomenon in the pores is used to make the inside of the pores. A method of separating the solute in the solution by precipitating the solute on the surface.   The method according to claim 1, further comprising thermally decomposing a solute precipitated in the pores at a predetermined temperature to support a specific element contained in the solute in the pores.     The method according to claim 1, wherein the solution includes two or more kinds of solutes having different solubilities, and selectively precipitates a solute having a low solubility from the solutes in the pores.   The substance having pores of a predetermined size is one substance selected from the group including silica gel, B-type silica gel, a material having fine irregularities on its surface, a mesh material, and Dixon packing. The method of any one of these.   The solutes are 1,5 cyclooctadiene methylplatinum, ceric nitrate complex, neodymium nitrate complex, triphenylphosphine, copper (II) bishexafluoroacetylacetone hydrate, trimethylindium, tetratitanium, bispalladium (II) At least one compound selected from the group consisting of: palladium (II) hexafluoroacetylacetone, nickel (II) hexafluoroacetylacetone, bisdiisobutyrylmethanite copper, and copper (I) hexafluoroacetylacetone · 2 butyne Item 5. The method according to any one of Items 1 to 4. Contacting a material having fine irregularities on the surface with a solution containing supercritical carbon dioxide in which 1,5-cyclooctadienemethylplatinum is dissolved below its solubility;
Utilizing the capillary condensation phenomenon in the fine irregularities on the surface of the material, depositing the 1,5 cyclooctadiene methyl platinum in the irregularities;
A step of thermally decomposing 1,5 cyclooctadiene methyl platinum deposited in the irregularities at a predetermined temperature and supporting platinum contained in the 1,5 cyclooctadiene methyl platinum in the irregularities. A method for producing a catalyst.

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