Method of adsorbing iodine or bromine

Abstract

The present invention relates to an iodine (I.sub.2) or bromine (Br.sub.2) adsorbent including a zeolite having a Si/Al ratio of 15 or greater; an I.sub.2 or Br.sub.2 carrier including the I.sub.2 or Br.sub.2 adsorbent; a column filled with the I.sub.2 or Br.sub.2 adsorbent; a article composed of the I.sub.2 or Br.sub.2 adsorbent or having the I.sub.2 or Br.sub.2 adsorbent attached thereto; a method for adsorbing or removing I.sub.2 or Br.sub.2 using the I.sub.2 or Br.sub.2 adsorbent; an iodine- or bromine-containing zeolite composite including a porous zeolite and iodine (I.sub.2) or bromine (Br.sub.2) confined in the pores of the zeolite; a semiconductor material including the iodine- or bromine-containing zeolite composite; and a method for preparing an iodine- or bromine-containing product using the iodine- or bromine-containing zeolite composite.

Claims

1. A method of adsorbing I.sub.2 or Br.sub.2 and converting neither the adsorbed I.sub.2 to I.sup. nor the adsorbed Br.sub.2 to Br.sup., comprising adsorbing I.sub.2 or Br.sub.2 on a I.sub.2 or Br.sub.2 adsorbent containing a zeolite having a Si/Al ratio of 15 or greater and a Sanderson partial negative charge on oxygen () of 0.2 or lower, wherein the zeolite is selected from the group consisting of SL-1F, Si-BEA and SL-1.

2. The method of claim 1, wherein the adsorbed iodine (I.sub.2) comprises radioactive iodine.

3. A method of removing I.sub.2 or Br.sub.2, comprising: adsorbing I.sub.2 or Br.sub.2 without converting the adsorbed I.sub.2 to I.sup. or the adsorbed Br.sub.2 to Br.sup., on a I.sub.2 or Br.sub.2 adsorbent containing a zeolite having a Si/Al ratio of 15 or greater and a Sanderson partial negative charge on oxygen () of 0.2 or lower, wherein the zeolite is selected from the group consisting of SL-1F, Si-BEA and SL-1; desorbing the adsorbed I.sub.2 or Br.sub.2 from the zeolite by contacting the I.sub.2 or Br.sub.2 adsorbent with an organic solvent dissolving I.sub.2 or Br.sub.2, by heating the I.sub.2 or Br.sub.2 adsorbent, or by blowing the I.sub.2 or Br.sub.2 adsorbent in heated air or heated nitrogen; and forming a precipitate by reacting the desorbed I.sub.2 or Br.sub.2 with AgNO.sub.3.

4. The method for removing I.sub.2 or Br.sub.2 according to claim 3, wherein the organic solvent is ethanol, diethyl ether, AcOH, benzene, CHCl.sub.3, carbon disulfide, or a mixture thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows absorption of I.sub.2 from its saturated aqueous solution onto activated carbon (AC) and various zeolites SL-1F, Si-BEA, SL-1, ZSM-5, AgMOR, SBA-15, NaY, MOR, NaX, NaA, and CaA as solid absorbents.

(2) FIG. 2 shows the absorbed amount (wt %) of iodine (I.sub.2) (the amount (g) of absorbed I.sub.2 per 100 g of zeolite) with time for activated carbon (AC) and various zeolites in aqueous solutions.

(3) FIG. 3 shows sublimation of I.sub.2 from solid I.sub.2, and its absorption into silicalite foam (SL-1 form) and silicalite powder (SL-1 powder).

(4) FIG. 4 compares the hydrophobicity of activated carbon (AC) and various zeolites through water vapor adsorption isotherms at 313 K (40 C.).

(5) FIG. 5 shows an apparatus for desorbing I.sub.2 by increasing temperature while injecting nitrogen gas.

(6) FIG. 6 shows the degree of desorption of I.sub.2 from solid absorbents according to temperature.

(7) FIG. 7 shows XRD patterns of MFI-type zeolite powder (freshly calcined), MFI-type zeolite with 0.1%, 1.0%, 6.9%, 22.3%, or 34.4% I.sub.2 adsorbed, and I.sub.2-adsorbed MFI-type zeolite which has been recalcined (recalcination).

(8) FIG. 8a and FIG. 8b respectively show the amount (wt %) of iodide ion (I.sup.) formed inside a solid absorbent (8a) and in a solution (8b) by activated carbon (AC) and various zeolites with time. FIG. 8a shows the amount (wt %) of iodide ion (I.sup.) formed inside the solid absorbent, FIG. 8b shows the amount (wt %) of iodide ion (I.sup.) formed in an aqueous solution, and FIG. 8c shows the total amount of the formed iodide ion (I.sup.).

(9) FIG. 9 shows the relationship between the Sanderson partial charge on oxygen and the total amount (wt %) of iodide ion (I.sup.) formed inside a solid absorbent and in a solution for activated carbon (AC) and various zeolites.

(10) FIG. 10A shows the absorbed amount (wt %) of I.sub.2 by activated carbon (AC) and various zeolites from the I.sub.2-saturated aqueous iodide (I.sup.) solution with various concentrations of I.sup.. FIG. 10B shows the absorbed amount (wt %) of I.sub.2 by activated carbon (AC) and various zeolites from the I.sub.2-saturated seawater.

(11) FIG. 11 shows scattering and reflection UV-Vis spectra of Br.sub.2-adsorbed Si-BEA, ZSM-5, and SL-1 DML. It can be seen that the zeolites effectively adsorb Br.sub.2.

DETAILED DESCRIPTION

(12) The term zeolite collectively refers to crystalline aluminosilicates.

(13) The zeolite backbone is composed of tetrahedral units formed by [SiO.sub.4].sup.4 and [AlO.sub.4].sup.5, which are bridged by oxygen atoms. Since the Al of [AlO.sub.4].sup.5 has a formal charge of +3, whereas the Si of [SiO.sub.4].sup.4 has a formal charge of +4, each Al has one negative charge. Accordingly, cations are present for charge balancing. The cations are present not in the backbone but in the pores and the remaining space is usually occupied by water molecules.

(14) Because the site occupied by aluminum in the aluminosilicate backbone is negatively charged, there are cations for charge balancing in the pores and the inside of the pores is strongly polarized.

(15) Meanwhile, various analogues (zeotype molecular sieves), wherein the silicon (Si) and aluminum (Al) constituting the backbone structure of zeolite have been partially or entirely replaced by various other elements, are known. For example, a porous silicalite in which aluminum has been completely eliminated, an (AlPO.sub.4)-type zeolite analogue in which silicon has been replaced by phosphorus (P), and other zeolite analogues obtained by replacing the backbone metal atoms of a zeolite or a zeolite analogue with various metal elements such as Ti, Mn, Co, Fe, Zn, etc. are known. These analogues are also included in the scope of zeolite according to the present invention.

(16) Examples of an MFI-type zeolite or an analogue thereof may include ZSM-5, silicalite-1, TS-1, AZ-1, Bor-C, boralite C, encilite, FZ-1, LZ-105, monoclinic H-ZSM-5, mutinaite, NU-4, NU-5, TSZ, TSZ-III, TZ-01, USC-4, USI-108, ZBH, ZKQ-1B, etc. ZSM-5 is an MFI-type zeolite formed of silicon and aluminum of a specific ratio, silicalite-1 is a zeolite consisting only of silica (SiO.sub.2), and TS-1 is an MFI-type zeolite in which titanium (Ti) occupies some of the aluminum sites.

(17) Both SL-1 and SL-1F are MFI-type. SL-1 is synthesized without adding NH.sub.4F at all, whereas SL-1F is synthesized by adding NH.sub.4F to significantly increase hydrophobicity.

(18) The chemical composition and the Sanderson partial charge on oxygen of various zeolites are given in Table 1.

(19) TABLE-US-00001 TABLE 1 Chemical composition (formula) .sub.0 SL-1 Si.sub.96O.sub.192 0.1501 Ag-MOR H.sub.4.0Ag.sub.1.2Al.sub.5.2Si.sub.42.8O.sub.96 0.1596 MOR H.sub.4.0Na.sub.1.2Al.sub.5.2Si.sub.42.8O.sub.96 0.1613 ZSM-5 H.sub.0.2Na.sub.0.75K.sub.2.75Al.sub.3.7Si.sub.94.3O.sub.192 0.1684 CaA H.sub.15Ca.sub.22.5Na.sub.34.5Al.sub.94.5Si.sub.97.5O.sub.384 0.2615 NaY Na.sub.52.3Al.sub.52.3Si.sub.139.7O.sub.384 0.2640 NaA H.sub.6Na.sub.88.5Al.sub.94.5Si.sub.97.5O.sub.384 0.3251 NaX H.sub.3Na.sub.92.7Al.sub.95.75Si.sub.96.25O.sub.384 0.3367

(20) When I.sup. is generated in an I.sub.2 adsorbent, the I.sub.2 adsorbent can no longer adsorb I.sub.2 and the I.sup. is difficult to remove therefrom. When the I.sup. exists in a solution, it can be removed using an anion exchange resin or a silver solution. However, when the I.sup. exists inside the adsorbent, it cannot be removed even with the anion exchange resin or silver solution. The inventors of the present invention have examined various zeolites for their I.sub.2-adsorbing ability and formation of I.sup. following I.sub.2 adsorption. As a result, the inventors have found that there are some zeolites which do not generate or hardly generate I.sup. after I.sub.2 adsorption, particularly in water.

(21) A more detailed description is given herein below.

(22) The I.sub.2 concentration of a saturated I.sub.2 aqueous solution is 1.5 mM. It was investigated whether activated carbon (AC) and various zeolites ZSM-5, SL-1 powder, SL-1 foam, Si-BEA, NaA, NaY, SBA-15, MOR, and AgMOR adsorb the I.sub.2 saturated in water well (FIG. 1). As seen from FIG. 1, activated carbon, zeolite ZSM-5, SL-1 powder, SL-1 foam, and Si-BEA can adsorb I.sub.2 in water.

(23) Meanwhile, the adsorption amount (wt %) of iodine (I.sub.2) with time for activated carbon (AC) and various zeolites SL-1F, Si-BEA (all-silica zeolite-), SL-1, ZSM-5, AgMOR, SBA-15, NaY, MOR, NaX, NaA, and CaA was measured in aqueous solutions. As seen from FIG. 2, activated carbon and zeolite SL-1F, BEA, SL-1, and ZSM-5 showed high iodine (I.sub.2) adsorption amount of 15 wt % or greater, whereas AgMOR, SBA-15, NaY, MOR, NaX, NaA, and CaA hardly adsorbed iodine (I.sub.2).

(24) In addition, the adsorption of I.sub.2 sublimating from solid I.sub.2 was confirmed for both silicalite-1 foam (SL form) and silicalite-1 powder (SL powder) which are MFI-type zeolites (FIG. 3). From FIG. 3, it can be seen that the color of the silicalite-1 foam and silicalite-1 powder turns violet due to the adsorption of I.sub.2.

(25) Meanwhile, the hydrophobicity of activated carbon (AC) and various zeolites SL-1F, Si-BEA, SL-1, ZSM-5, AgMOR, SBA-15, NaY, MOR, NaX, NaA, and CaA was investigated through water vapor adsorption isotherms at 313 K (40 C.). As seen from FIG. 4, the zeolites SL-1F, Si-BEA, SL-1, and ZSM-5 with a larger iodine (I.sub.2) adsorption amount exhibit higher hydrophobicity than other zeolites. That is to say, the iodine (I.sub.2) adsorption amount increases with hydrophobicity, suggesting that the adsorption of iodine (I.sub.2) in the zeolite is due to hydrophobic bonding. The hydrophobicity is in the order of ZSM-5<SL-1<Si-BEA<SL-1F. Since the hydrophobicity of the zeolite increases with the Si/Al ratio, the zeolite according to the present invention capable of adsorbing iodine (I.sub.2) has a Si/Al ratio (molar ratio) of 15 or greater, specifically 20 or greater, more specifically 30 or greater. For SL-1, SL-1F, and Si-BEA, which are free from Al, the Si/Al ratio is infinite ().

(26) Meanwhile, using an apparatus for desorbing I.sub.2 by increasing temperature while injecting nitrogen gas as shown in FIG. 5, the degree of iodine desorption depending on temperature was investigated for activated carbon (AC) and the various zeolites Si-BEA, SL-1F, and SL-1 (FIG. 6). Although I.sub.2 is highly volatile, it is not desorbed easily even at high temperatures once it is adsorbed to the zeolite. As seen from FIG. 6, I.sub.2 was desorbed at 175 C. for the zeolites Si-BEA, SL-1F, and SL-1, unlike activated carbon (AC). That is to say, I.sub.2 is desorbed from all of these adsorbents when hot air or hot nitrogen above a certain temperature is injected. For activated carbon (AC), some of the adsorbed I.sub.2 that turned to I.sup. remained and iodine was not completely desorbed.

(27) The XRD patterns of SL-1 powder (freshly calcined), SL-1 with 0.1%, 1.0%, 6.9%, 22.3% or 34.4% I.sub.2 adsorbed, and I.sub.2-adsorbed SL-1 which has been recalcined (recalcination) were investigated. As seen from FIG. 7, it was observed that the peaks related to porosity disappeared when the nanowire channel in SL-1 was completely filled with I.sub.2 (34.4%). In addition, it can be seen from the XRD patterns shown in FIG. 7 that the porosity-related peaks appeared again for the I.sub.2-adsorbed SL-1 which had been recalcined (recalcination), as in the fresh SL-1. This confirms that the backbone structure is maintained regardless of the adsorption and desorption of I.sub.2.

(28) Meanwhile, the amount (wt %) of iodide ion (I.sup.) formed inside the solid adsorbent and in a solution with time was measured for activated carbon (AC) and the various zeolites SL-1F, Si-BEA, SL-1, ZSM-5, AgMOR, SBA-15, NaY, MOR, NaX, NaA, and CaA. The results are shown in FIG. 8a and FIG. 8b, respectively. FIG. 8a shows the amount (wt %) of iodide ion (I.sup.) formed inside the solid adsorbent, FIG. 8b shows the amount (wt %) of iodide ion (I.sup.) formed in a solution, and FIG. 8c shows the total amount of the formed iodide ion (I.sup.).

(29) As seen from FIGS. 8a-8c, the amount of iodide ion (I.sup.) formed inside the solid adsorbent was the highest for activated carbon (AC). The amount of iodide ion (I.sup.) formed in solutions was in the order of NaX>NaA>CaA>NaY. For MOR, AgM, ZSM-5, SL-1F, SL-1, Si-BEA, and SBA-15, iodide ion (I.sup.) was hardly formed either inside the solid adsorbent or in the solution.

(30) FIG. 9 shows the relationship between the Sanderson partial charge on oxygen and the total amount (wt %) of iodide ion (I.sup.) formed inside the solid adsorbent and in the solution for activated carbon (AC) and the various zeolites SL-1F, Si-BEA, SL-1, ZSM-5, AgMOR, SBA-15, NaY, MOR, NaX, NaA and CaA.

(31) From FIG. 9, it can be seen that the formation amount (wt %) of iodide ion (I.sup.) is proportional to the Sanderson partial charge on oxygen for activated carbon (AC) and the various zeolites. Accordingly, the zeolite used as an iodine (I.sub.2) adsorbent for preventing iodide ion (I.sup.) formation may have a Sanderson partial charge on oxygen (.sup.0) of specifically 0.2 or lower, more specifically 0.1-0.2.

(32) As seen from FIGS. 1-9, the zeolites SL-1F, Si-BEA, SL-1, and ZSM-5 are advantageous in that they exhibit a high iodine (I.sub.2) adsorption amount and hardly show iodide ion (I.sup.) formation inside the solid adsorbent and in the solution. The zeolites SL-1F, Si-BEA, SL-1, and ZSM-5 have stronger hydrophobicity and a lower Sanderson partial charge on oxygen as compared to other zeolites.

(33) Accordingly, the present invention is characterized in that a zeolite having a Si/Al ratio of 15 or greater is used as a zeolite for adsorbing iodine (I.sub.2) and, among such zeolites, a zeolite having a Sanderson partial charge on oxygen (.sup.0) of 0.2 or lower is used to prevent formation of iodide ion (I.sup.) from the adsorbed I.sub.2.

(34) FIG. 10A shows the I.sub.2-saturated adsorption amount (wt %) of activated carbon (AC) and the various zeolites Si-BEA, SL-1F, and SL-1 under different I.sup. concentrations. It can be seen that the zeolite according to the present invention can adsorb I.sub.2 even when it is dissolved in water as I.sup..

(35) Additionally, FIG. 10B shows the I.sub.2-saturated adsorption amount (wt %) of activated carbon (AC) and the various zeolites Si-BEA, SL-1F, and SL-1 in artificial seawater (ASW). It can be seen that the zeolite according to the present invention can adsorb I.sub.2 even when it is dissolved in seawater.

(36) I.sub.2 is more soluble in seawater because it forms a complex. The zeolite according to the present invention can readily remove I.sub.2, particularly radioactive I.sub.2, when it is dissolved in seawater, underground water, etc.

(37) Meanwhile, the zeolites of the present invention can also adsorb Br.sub.2 in water (FIG. 11).

(38) The zeolite according to the present invention can adsorb I.sub.2 having not only stable I-127 but also all the isotopes of I described in Table 2.

(39) TABLE-US-00002 TABLE 2 Decay Main -X-ray energy (keV) Isotope Half-life mode E.sub.max (keV) (abundance) .sup.123I 13.27 h EC + .sup.+ 1074.9 (97%, EC) .sup.159 (83%) .sup.124I 4.18 d EC + .sup.+ 2557 (25%, EC), 3160 602.7 (63%), 723 (10%), (24%, EC), 1535 (12%, .sup.+), 1691 (11%) 2138 (11%, .sup.+) .sup.125I 59.41 d EC 150.6 (100%) 35.5 (6.68%), 27.2 (40%), 27.5 (76%) .sup.126I 13.11 d EC + .sup.+, .sup. 869.4 (32%, .sup.), 1489 (29%, 338.6 (34%), 666.3 (33%) EC), 2155 (23%, EC) .sup.127I Stable .sup.128I 24.99 m .sup., EC + .sup.+ 2119 (80%, .sup.) 442.9 (17%) .sup.129I 1.57 10.sup.7 y .sup. 154.4 (100%) 39.6 (7.5%), 29.5 (20%), 29.8 (38%) .sup.130I 12.36 h .sup. 587 (47%), 1005 (48%) 536 (99%), 668.5 (96%), 739.5 (82%) .sup.131I 8.02 d .sup. 606 (90%) 364.5 (82%) .sup.132I 2.30 h .sup. 738 (13%), 1182 (19%), 667.7 (99%), 772.6 (76%) 2136 (19%) .sup.132mI 1.39 h IT, .sup. 1483 (8.6%, .sup.) 600 (14%), 173.7 (8.8%) .sup.133I 20.8 h .sup. 1240 (83%) 529.9 (87%) .sup.134I 52.5 m .sup. 1307 (30%) 847 (95%), 884 (65%) .sup.135I 6.57 h .sup. 970 (22%), 1388 (24%) 1260 (29%) Half-lives of the isotopes are given as m: minutes; h: hours; d: days; and y: years. The decay mode: EC for electron capture; .sup.+ for positron emission; .sup. for beta emission; IT for internal transfer. An isotope may decay by more than one mode.

(40) Meanwhile, the solubility (wt %) of iodine (I.sub.2) of SL-1F and BEA was compared in various organic solvents. The results are shown in Table 3. Electron donor solvents can dissolve a large amount of I.sub.2 because they form electron donor-acceptor complexes. Even though silicalite-1 (SL-1F) is a weak electron donor, the solvent can dissolve a very large amount of I.sub.2.

(41) TABLE-US-00003 TABLE 3 Solubility of I.sub.2 at Solvent density Solvent weight Concentration Solvent 25 C. (g/100 mL) (g/mL) (g) (%) wt % Ethanol 21.43 0.79 79.0 21.34 27.12 Diethyl ether 25.20 0.71 71.0 26.19 35.49 AcOH 14.09 1.05 105.0 11.83 13.42 Benzene 14.09 0.88 88.0 13.80 16.01 CHCl.sub.3 14.09 1.48 148.3 8.68 9.50 CCl.sub.4 2.603.sup.a 1.59 159.0 1.61 1.64 Carbon disulfide (CS.sub.2) 16.47 1.26 126.0 11.56 13.07 Water 0.029.sup.b, 1.00 100.0 0.029, 0.029, 0.078.sup.c 0.078 0.078 Hexane (exp. 0.94 0.66 65.9 1.41 1.43 data) Silicalite-1 63.72 1.80 180.0(100 mL) 26.14 35.40 (SL-1F) BEA 56.96 1.61 161.0(100 mL) 26.25 35.60 AC 11.55 0.32 32.0(100 mL) 26.52 36.10 .sup.aat 35 C., .sup.bat 20 C., .sup.cat 50 C., density of I.sub.2 = 4.93 g/mL.

(42) As can be seen from Table 3, although the I.sub.2 adsorbed to the zeolite according to the present invention cannot be removed in water, it can be removed using organic solvents exhibiting high solubility for I.sub.2. However, the I.sub.2 adsorbed to activated carbon (AC) cannot be removed even when organic solvents exhibiting high solubility for I.sub.2 are used. Since the zeolite according to the present invention is hydrophobic, it has a strong tendency to absorb the organic solvent and the absorbed organic solvent dissolves I.sub.2, thereby releasing I.sub.2 from the zeolite.

(43) The zeolite according to the present invention can be recycled indefinitely since the I.sub.2 adsorbed thereto can be completely removed using organic solvents such as ethanol. In contrast, activated carbon (AC) must be discarded after 3-4 uses because the I.sub.2 adsorbed thereto cannot be removed by water or organic solvents. Accordingly, whereas the zeolite according to the present invention can be used indefinitely when filled into a fixed-bed column since I.sub.2 adsorbed thereto can be completely removed using organic solvents, the activated carbon (AC) being filled into a fixed-bed column as an I.sub.2 adsorbent requires routine replacement.

(44) Non-limiting examples of the organic solvent for dissolving I.sub.2 from the zeolite may include ethanol, diethyl ether, AcOH, benzene, CHCl.sub.3, carbon disulfide or a mixture thereof.

(45) Meanwhile, the I.sub.2 recovered from the zeolite and remaining dissolved in the organic solvent may be converted to small-sized AgI or AgIO precipitates by reacting with a AgNO.sub.3 aqueous solution for permanent burial.

(46) The inventors of the present invention found that an iodine- or bromine-containing zeolite composite including a porous zeolite and iodine (I.sub.2) or bromine (Br.sub.2) confined in the pores of the zeolite exhibits semiconductor properties with a narrow band gap energy (E.sub.g). For example, it may have a band gap energy E.sub.g<3.0 eV and an electrical conductivity of 0.1 siemens/m or greater.

(47) Specifically, a result of measuring the electrical conductivity of iodine-containing silicalite-1 (I.sub.2@SL-1) by electron force microscopy was as follows:
.sub.a along a-axis=1.6710.sup.4Sm.sup.1
.sub.b along b-axis=1.9910.sup.4Sm.sup.1

(48) In addition, since the iodine (I.sub.2) captured in the iodine-containing zeolite composite according to the present invention is not evaporated at temperatures of 50 C. or lower, it allows accurate quantification of iodine. It can be applied for a variety of chemical reactions requiring iodine because an accurate known amount of iodine is released by an organic solvent if the iodine-containing zeolite composite which has been quantitated is added to a reactor.

(49) Additionally, the iodine-containing zeolite composite according to the present invention may be used as a controlled-release system by slowly adding a solvent that enables release of iodine.

(50) This application also holds true for the bromine-containing zeolite composite.