JP2006341185A - Decomposition treatment method of chlorofluorocarbon, and decomposition treating agent therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a decomposition method of chlorofluorocarbon which is capable of fixing fluorine and chlorine as a stable and non-toxic salt of an alkaline earth metal in the single reaction system without producing toxic materials such as an acidic gas, carbon tetrachloride and the like at all. <P>SOLUTION: The decomposition treatment method of chlorofluorocarbon comprises treating chlorofluorocarbon with a mixture of a magnesium chloride and calcium oxide which has undergone the acid treatment with sulfuric acid and phosphoric acid. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method and a treating agent for decomposing chlorofluorocarbon.

  Since chlorofluorocarbons are nonflammable and non-toxic, they are very widely used as refrigerants, sprays, digestives, foaming agents and the like as ideal gases. However, since used chlorofluorocarbons are difficult to decompose in the atmosphere due to their chemical stability, there is a concern about the serious impact on the global environment, such as destroying the ozone layer and causing global warming as a greenhouse gas. ing. For this reason, in parallel with the development of alternatives to chlorofluorocarbons, there is an urgent need to develop technologies for effectively decomposing used chlorofluorocarbons.

The chlorofluorocarbon decomposition process currently in practical use is mainly a hydrolysis reaction in which chlorofluorocarbon is treated at a high temperature in the presence of water vapor. Hydrolysis of chlorofluorocarbons, for example,
_{CCl 2 F 2 + 2H 2 O} ---> 2HF + 2HCl + CO 2
Thus, an acidic gas such as HF and HCl is generated. The generated acid gas is converted into NaCl and NaF by neutralizing with NaOH. NaCl is treated as waste water as it is. NaF, it is not possible to flow the effluent is treated with Ca _{(OH) 2} is converted to a solid CaF _2. In this way, the current chlorofluorocarbon decomposition process requires additional steps for neutralization after the decomposition reaction, and HF and HCl are generated during decomposition, so expensive corrosion-resistant materials are used in the processing equipment. This increases the processing cost. Furthermore, the production of HF and HCl has problems in terms of safety and environment.

As a chlorofluorocarbon decomposition method not based on hydrolysis, a very small amount of hydrofluoric acid is added and heated, and MgO having a part of the particle surface changed to MgF ₂ is reacted with chlorofluorocarbon.
CCl ₂ F ₂ + MgO ---> 1 / 2CO ₂ + 1 / 2CCl ₄ + MgF ₂
A method for immobilizing fluorine as an alkaline earth metal salt has also been reported (Tamai et al., Bull. Chem. Soc. Jpn., 77, 1239, 2004). Since alkaline earth metal halides are stable and harmless even at relatively high temperatures, the method of fixing halogens as alkaline earth metal salts is a desirable method. The method of Tamai et al. Reacts MgO with chlorofluorocarbons by reacting the surface of MgO, which is a basic substance, with hydrofluoric acid and changing part of the surface to MgF ₂ to give acid sites to MgO. Has succeeded in increasing However, in Tamai et al.'S method, fluorine can be immobilized as MgF ₂ , but chlorine remains as harmful carbon tetrachloride. In order to immobilize chlorine, for example, by reacting CaO with the generated CCl ₄ ,
CCl ₄ + 2CaO ---> CaCl ₂ + CO ₂
As described above, an additional treatment step for immobilizing chlorine as calcium chloride is required (BM Weckhuysen et al., J. Phys. Chem. B, 102, 3773, 1998).

As a method of immobilizing fluorine and chlorine of chlorofluorocarbon at once in a single reaction system, by reacting MgO supporting a transition metal oxide such as vanadium oxide with chlorofluorocarbon,
CCl ₂ F ₂ + 2MgO ---> CO ₂ + MgCl ₂ + MgF ₂
As described above, a method for efficiently immobilizing fluorine and chlorine has been reported (Tamai et al., Chem. Lett., 32, 436, 2003). However, in this method, when CCl ₂ F ₂ becomes excessive (conversion rate of MgO exceeds a certain value),
CCl ₂ F ₂ + MgCl ₂ ---> CCl ₄ + MgF ₂
As described above, once fixed chlorine is converted into carbon tetrachloride. In addition, there is another problem that vanadium oxide volatilizes during the decomposition reaction of chlorofluorocarbon.

Tamai et al., Bull. Chem. Soc. Jpn., 77, 1239, 2004 B.M.Weckhuysen et al., J. Phys. Chem. B, 102, 3773, 1998 Tamai et al., Chem. Lett., 32, 436, 2003

  An object of the present invention is to provide a stable and harmless alkaline earth metal that generates fluorine and chlorine in a single reaction system without producing any of the above-mentioned harmful substances such as acid gas and carbon tetrachloride as a method for decomposing chlorofluorocarbon. An object of the present invention is to provide a method that can be immobilized as a salt and a decomposition treatment agent therefor.

According to the present invention, there is provided a method for decomposing chlorofluorocarbon, characterized in that chlorofluorocarbon is treated with a mixture of magnesium oxide and calcium oxide treated with sulfuric acid or phosphoric acid.
Further, according to the present invention, there is provided a chlorofluorocarbon decomposition treatment agent comprising a mixture of magnesium oxide and calcium oxide acid-treated with sulfuric acid or phosphoric acid.

  According to the present invention, fluorine and chlorine in chlorofluorocarbons are produced as stable and harmless alkaline earth metal salts in a single reaction system without producing any harmful gases such as acidic gases such as HF and HCl and carbon tetrachloride. Can be immobilized. The method of the present invention can be carried out with a simple apparatus that does not require corrosion resistance, the decomposition treatment agent can be prepared at a low cost, and the transition metal is not included, so the environmental load is small.

The method for decomposing chlorofluorocarbon according to the present invention is characterized in that chlorofluorocarbon is treated with a mixture of magnesium oxide and calcium oxide that has been acid-treated with sulfuric acid or phosphoric acid. Chlorofluorocarbon is a generic name for chlorinated and fluorinated methane and ethane, and is generally represented by the formula CCl _n F _4-n or C ₂ Cl _n F _6-n , but some of them contain hydrogen or bromine. Such chlorofluorocarbons are also subject to decomposition treatment according to the present invention. Examples of _{chlorofluorocarbons, CClF 3, CCl 2 F 2} , CCl 3 F, CClF 2 -CF 3, CClF 2 -CClF 2, CCl 2 F-CClF 2 and the like. The chlorofluorocarbon may be treated alone or as a mixture of two or more. The chlorofluorocarbon is preferably treated as a mixed gas with a carrier gas in the decomposition treatment. As the carrier gas, dry air, helium, nitrogen, argon or the like can be used. In the mixed gas with the carrier gas, the concentration of chlorofluorocarbon is preferably 0.1% by volume or more, and more preferably 0.5% by volume or more. The chlorofluorocarbon can also be treated as 100% chlorofluorocarbon without dilution with a carrier gas.

According to the present invention, such a chlorofluorocarbon is treated with a mixture of magnesium oxide (MgO) and calcium oxide (CaO) acid-treated with sulfuric acid or phosphoric acid. By acid-treating MgO with sulfuric acid (H ₂ SO ₄ ) or phosphoric acid (H ₃ PO ₄ ), acid sites are given to the surface of MgO, which is a basic substance, and thus the acid-treated MgO has a resistance to chlorofluorocarbon Catalytic activity is improved. The amount of acid sites or acid strength can be measured by a method of adsorbing ammonia (NH ₃ ) in a temperature rising detriment method (TPD) (hereinafter referred to as “NH ₃ -TPD method”). In the present specification, for the sake of convenience, MgO treated with sulfuric acid or phosphoric acid is represented as MgSO ₄ —MgO and Mg ₃ (PO ₄ ) ₂ —MgO, respectively. As the acid treatment amount of MgO, the NH ₃ adsorption amount measured by the NH ₃ -TPD method is preferably 0.1 μmol / m ² or more, more preferably 0.3 μmol / m ² per unit BET surface area. The amount of treatment is set to m ² or more, more preferably 0.5 micromol / m ² or more. When the NH ₃ adsorption amount is less than 0.1 μmol / m ² per unit BET surface area, the intended chlorofluorocarbon decomposition reaction does not proceed. There is no special limitation on the upper limit of the adsorbed NH ₃ amount.

The acid treatment can be carried out by suspending granular MgO in water, adding a predetermined amount of sulfuric acid or phosphoric acid thereto, stirring and mixing, and then evaporating the water. At that time, the acid treatment amount of MgO can be adjusted by changing the addition amount of sulfuric acid or phosphoric acid. The stirring and mixing may be performed at room temperature for 1 to 24 hours, preferably about 3 to 18 hours. Moisture evaporation can be performed by heating to about 70 to 90 ° C. Since the acid-treated MgO after moisture evaporation contains magnesium hydroxide Mg (OH) _2, it is preferable to perform drying and baking after moisture evaporation for the dehydration treatment. Drying can be performed by heating to about 100 to 120 ° C. in an air atmosphere. Moreover, baking can be performed by processing at 500-700 degreeC for 2 to 5 hours in air | atmosphere.

  The shape of the acid-treated MgO is preferably granular from the viewpoint of air permeability and contact efficiency in the chlorofluorocarbon decomposition treatment step. In this case, those skilled in the art can determine an appropriate range in consideration of the balance between air permeability and contact efficiency. In general, if the particle size is less than 0.01 mm, there is a disadvantage of pressure loss. On the contrary, if it exceeds 10 mm, the contact efficiency is lowered and the decomposition treatment capacity is impaired, which is not preferable. The particle diameter of the acid-treated MgO is preferably 0.01 to 10 mm, more preferably 0.1 to 6 mm.

  Thus, by mixing calcium oxide (CaO) with MgO acid-treated with sulfuric acid or phosphoric acid, a chlorofluorocarbon decomposition treatment agent is obtained. Although there is no restriction | limiting in particular in CaO to mix, From the point of the breathability and contact efficiency of the decomposition | disassembly process of a chlorofluorocarbon, like the acid treatment MgO, a shape is granular and the particle size becomes like this. It is preferable that it is in the range of 01 to 10 mm, more preferably 0.1 to 6 mm. In order to facilitate mixing with the acid-treated MgO, it is preferable to reduce the difference between the particle sizes of the two, and it is more preferable that the particle sizes of the two are substantially the same.

  The mixing ratio of the acid-treated MgO and CaO is generally within a range of 1:20 to 5: 1, preferably 1: 5 to 2: 1 as a molar ratio. When the amount of acid sites added to the acid-treated MgO is large, the mixed molar ratio of the acid-treated MgO can be reduced, and thus the mixed molar ratio of CaO can be increased. When the mixing molar ratio of the acid-treated MgO is outside the lower limit of the above range, the decomposition reactivity with respect to the chlorofluorocarbon decreases. On the other hand, if the mixing molar ratio of the acid-treated MgO is outside the upper limit of the above range, CaO becomes insufficient and the halogen absorption and fixation efficiency decreases. The mixing method of acid-treated MgO and CaO is not particularly limited as long as the physical mixture of both is formed uniformly.

In the decomposition treatment method according to the present invention, all halogens (fluorine and chlorine) contained in the chlorofluorocarbon are fixed in a form that is absorbed by calcium oxide. This is because Ca halides (CaF ₂ , CaClF, etc.) are thermodynamically more stable than Mg halides (MgF ₂ , MgClF, etc.). In effect, the acid-treated MgO is involved only as a catalyst for the chlorofluorocarbon decomposition reaction. The product of the decomposition treatment method according to the present invention varies depending on the ratio of fluorine and chlorine contained in the chlorofluorocarbon. Therefore, for example, when the chlorofluorocarbon is CCl ₂ F ₂ , the decomposition reaction formula is mainly CCl ₂ F ₂ + 2CaO −−> 2CaClF + CO ₂ (however, a part of CaClF may be divided into CaF ₂ and CaCl ₂ ).
For example, when the chlorofluorocarbon is CCl ₃ F, the decomposition reaction formula is mainly CCl ₃ F + 2CaO ---> CaClF + CaCl ₂ + CO ₂ (however, a part of CaClF may be divided into CaF ₂ and CaCl ₂ ).
Next, for example, when chlorofluorocarbon is CClF _3, the decomposition reaction formulas mainly _{CClF 3 + 2CaO ---> CaClF +} CaF 2 + CO 2 ( although some CaClF there if divided into CaF ₂ and CaCl _2.)
It becomes. Thus, according to the method of the present invention, fluorine and chlorine can be converted into a single reaction system without using transition metal oxides and without generating any harmful gases such as acidic gases such as HCl and HF and carbon tetrachloride. Can be immobilized as a stable and harmless alkaline earth metal (Ca) salt.

  In the decomposition treatment method according to the present invention, since the catalytic activity of acid-treated MgO imparted with acid sites to chlorofluorocarbons is high, the atmospheric temperature during decomposition treatment of chlorofluorocarbons can be kept relatively low, and also in terms of treatment costs. It is advantageous. Specifically, according to the present invention, the chlorofluorocarbon can be decomposed at an atmospheric temperature in the range of preferably 400 to 700 ° C, more preferably 450 to 600 ° C.

  The decomposition treatment method according to the present invention can be implemented using, for example, a distribution system apparatus as shown in FIG. A reaction tube equipped with a heater (eg, electric furnace) that provides a desired ambient temperature is filled with the decomposition treatment agent (acid-treated MgO + CaO) according to the present invention, and a carrier gas (eg, helium) as necessary. The chlorofluorocarbon diluted with 1 may be circulated at a predetermined flow rate. The flow rate is appropriately determined by those skilled in the art so that the chlorofluorocarbon is 100% decomposed at the outlet of the apparatus depending on the amount of the decomposition treatment agent, the type of chlorofluorocarbon to be processed, the concentration in the carrier gas, and other reaction variables. Can be determined. Further, since the decomposition treatment agent according to the present invention is a reactant and consumed, the chlorofluorocarbon can be continuously decomposed by appropriately supplying the decomposition treatment agent. For example, it is conceivable to provide a plurality of reaction tubes whose flow paths can be switched in the flow system as shown in FIG.

MgO used in the examples was prepared as follows. 10 g of MgO (“100A” manufactured by Ube Materials Co., Ltd.) was suspended in 150 mL of distilled water, stirred overnight at room temperature, then heated to 80 ° C. to evaporate the water until it became a paste. The obtained paste was dried at room temperature for several days to obtain Mg (OH) ₂ . The obtained Mg (OH) ₂ was dehydrated by a baking treatment in which the temperature was raised to 600 ° C. for 2 hours under a He stream and held at that temperature for 3 hours to obtain MgO.

Reference Example The expression of acid sites by various acid treatments of MgO was examined. HF, HCl, H ₂ SO ₄ and H ₃ PO ₄ were used as acids for the acid treatment. 2 g of MgO obtained by the above method was suspended in 50 mL of distilled water, and each acid aqueous solution was dropped into the suspension. The dropping amounts are MgF ₂ , MgCl ₂ , MgSO ₄ and Mg ₃ (PO ₄ ) ₂ , respectively, MgF ₂ -MgO, MgCl ₂ -MgO, MgSO ₄ -MgO and Mg ₃ (PO ₄ ) ₂ -MgO. It prepared so that it might become 10 mol% of the whole. After each acid aqueous solution was dropped, the mixture was stirred at room temperature for 8 hours, and then heated to 80 ° C. to remove water by evaporation. Each MgO after the acid treatment was further dried at a temperature of 110 ° C. in a dryer. After drying, each MgO was baked in a helium stream at 600 ° C. for 3 hours in a baking furnace. The prepared samples are denoted as MgF ₂ -MgO, MgCl ₂ -MgO, MgSO ₄ -MgO, and Mg ₃ (PO ₄ ) ₂ -MgO, respectively. For each acid treatment samples were prepared and the BET specific surface area and _NH 3 -TPD. The results are shown in Table 1 below together with the untreated MgO data.

From the measurement results of NH ₃ -TPD, it can be seen that MgO treated with HF, H ₂ SO _4, and H ₃ PO ₄ has a significantly increased acid point as compared with MgO before treatment. FIG. 2 shows the XRD pattern of each acid-treated MgO. From Figure _2, for the H 2 SO ₄ treated MgO (d), it can be seen that the portion of the surface is converted to MgSO _4. HF-treated and H ₃ PO _4- treated MgO, whose acid sites are increased from Table 1, are not shown in the XRD diagram, probably because of the low crystallinity of the salt due to the reaction between the acid and MgO.

Example 1
The decomposition treatment reaction of chlorofluorocarbon was investigated by physically mixing CaO with MgSO ₄ -MgO. 10 g of CaO (Aldrich, purity 99.9%) was suspended in 150 mL of distilled water and stirred for 10 hours. Thereafter, the mixture was heated to 80 ° C. to evaporate water. Subsequently, it dried at 110 degreeC with the dryer, and obtained Ca (OH) ₂ was heated at 5 K / min, and it baked at 450 degreeC for 2 hours, and then at 600 degreeC for 4 hours, and obtained CaO. Using a chlorofluorocarbon decomposition apparatus as shown in FIG. 1, put MgSO ₄ -MgO (0.20 g) and CaO (0.28 g) together in an agate mortar in the center of a quartz reaction tube. A mixed powder (mixing molar ratio of 1: 1) having a particle size of about 0.2 mm ground with an agate pestle was mixed. Next, the filled MgSO ₄ —MgO + CaO was heat-treated at 600 ° C. for 3 hours in an electric furnace. Thereafter, the temperature was lowered to a predetermined reaction temperature (450 ° C.) to carry out the reaction. CCl ₂ F ₂ was used as the chlorofluorocarbon, which was diluted to 1% by volume with helium (He) and circulated through the reaction tube at a flow rate of 30 mL / min. When the reaction outlet gas was analyzed by a gas chromatograph (GC-TCD) equipped with a thermal conductivity detector, the gas produced by the reaction was only CO _{2 and} no harmful gases such as CCl ₄ and CCl ₃ F were detected. It was. The results of the chlorofluorocarbon decomposition reaction with MgSO ₄ —MgO + CaO are shown in FIG. In the figure, _CCl 2 _{F 2} conversion on the vertical axis, wherein: {1- (the concentration of _CCl 2 _{F 2} which is introduced into the concentration / reaction tube unreacted _CCl 2 _{F 2} was passed through the reaction tube)} × 100 ( %). As can be seen from FIG. 3, about 70% of the introduced CCl ₂ F ₂ reacted and converted to harmless CO ₂ at the beginning. Thereafter, the activity gradually decreased, but the conversion rate of about 30% was maintained even after 5 hours. Moreover, the XRD pattern 5 hours after reaction is shown in FIG. FIG. 4 shows that chlorofluorocarbon halogen was immobilized as CaClF and a small amount of CaF ₂ in a system in which CaO was physically mixed with MgSO ₄ —MgO. Incidentally, CaCl ₂ corresponding to the CaF ₂ in the XRD pattern is not observed. This is because CaCl ₂ has poor crystallinity and cannot be detected by XRD. It can also be seen that part of the carbon of the chlorofluorocarbon was fixed as CaCO ₃ .

Example 2
CaO was physically mixed with Mg ₃ (PO ₄ ) ₂ —MgO, and the decomposition treatment reaction of chlorofluorocarbon was examined. CaO was prepared in the same manner as in Example 1. Using a chlorofluorocarbon decomposition apparatus as shown in FIG. 1, together with Mg ₃ (PO ₄ ) ₂ -MgO (0.20 g) and CaO (0.28 g) in the center of a quartz reaction tube, agate It was put in a mortar and filled with a mixed powder (mixing molar ratio of 1: 1) having a particle size of about 0.2 mm, which was ground with an agate pestle so as to be sufficiently mixed. Next, the filled Mg ₃ (PO ₄ ) ₂ —MgO + CaO was heat-treated at 600 ° C. for 3 hours in an electric furnace. Thereafter, the temperature was lowered to a predetermined reaction temperature (450 ° C.) to carry out the reaction. CCl ₂ F ₂ was used as the chlorofluorocarbon, which was diluted to 1% by volume with helium (He) and circulated through the reaction tube at a flow rate of 30 mL / min. When the reaction outlet gas was analyzed by a gas chromatograph (GC-TCD) equipped with a thermal conductivity detector, the gas produced by the reaction was only CO _{2 and} no harmful gases such as CCl ₄ and CCl ₃ F were detected. It was. The results of the chlorofluorocarbon decomposition reaction with Mg ₃ (PO ₄ ) ₂ —MgO + CaO are shown in FIG. In the figure, the conversion rate of CCl ₂ F _{2 on} the vertical axis is as defined in Example 1. As can be seen from FIG. 3, about 60% of the introduced CCl ₂ F ₂ reacted and converted to harmless CO ₂ in the initial stage. Thereafter, the activity gradually decreased, but a conversion rate of about 20% was maintained even after 5 hours. Moreover, the XRD pattern 5 hours after reaction is shown in FIG. FIG. 4 shows that the halogen of chlorofluorocarbon was immobilized as CaClF and a small amount of CaF ₂ in a system in which CaO was physically mixed with Mg ₃ (PO ₄ ) ₂ —MgO. Incidentally, CaCl ₂ corresponding to the CaF ₂ in the XRD pattern is not observed. This is because CaCl ₂ has poor crystallinity and cannot be detected by XRD. It can also be seen that part of the carbon of the chlorofluorocarbon was fixed as CaCO ₃ .

Comparative Example 1
The decomposition treatment reaction of chlorofluorocarbon was examined by physically mixing CaO with MgF ₂ -MgO. CaO was prepared in the same manner as in Example 1. Using a chlorofluorocarbon decomposition apparatus as shown in FIG. 1, put MgF ₂ -MgO (0.20 g) and CaO (0.28 g) together in an agate mortar in the center of a quartz reaction tube. A mixed powder (mixing molar ratio of 1: 1) having a particle size of about 0.2 mm ground with an agate pestle was mixed. Next, the filled MgF ₂ —MgO + CaO was heat-treated at 600 ° C. for 3 hours in an electric furnace. Thereafter, the temperature was lowered to a predetermined reaction temperature (450 ° C.) to carry out the reaction. CCl ₂ F ₂ was used as the chlorofluorocarbon, which was diluted to 1% by volume with helium (He) and circulated through the reaction tube at a flow rate of 30 mL / min. When the reaction outlet gas was analyzed by a gas chromatograph (GC-TCD) equipped with a thermal conductivity detector, no product other than unreacted CCl ₂ F ₂ gas was detected. As with Examples 1 and 2, the change with time in the CCl ₂ F ₂ conversion (%) is shown in FIG. It can be seen that the system in which CaO is physically mixed with MgF ₂ -MgO has no reactivity to chlorofluorocarbons. In this system,
MgF ₂ + CaO ---> MgO + CaF ₂ (ΔH ⁰ = −63 kJ / mol)
This is because the halogen exchange reaction as shown in FIG. This can be seen from the absence of CaClF and CaCO ₃ found in Examples 1 and 2 although CaF ₂ is observed in the XRD pattern after 5 hours shown in FIG.

It is the schematic which shows an example of the distribution system apparatus which can implement the method by this invention. It is a XRD pattern figure of each acid processing MgO. It is a graph which shows the result of the chlorofluorocarbon decomposition | disassembly reaction by each acid treatment MgO + CaO. It is a XRD pattern figure 5 hours after reaction.

Claims (2)

  A method for decomposing chlorofluorocarbons, comprising treating chlorofluorocarbons with a mixture of magnesium oxide and calcium oxide acid-treated with sulfuric acid or phosphoric acid.   A decomposition treatment agent for chlorofluorocarbon, comprising a mixture of magnesium oxide and calcium oxide treated with sulfuric acid or phosphoric acid.

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