KR102081820B1 - Method for Disposing HFCs by Decomposition - Google Patents

Abstract

The present invention relates to a method of decomposing and treating hydrofluorocarbons (HFCs), which are non-CO_2 greenhouse gas, using aluminum oxide carrying divalent magnesium ions. Aluminum oxide (Al_2O_3) used in the HFCs decomposition treatment method according to the present invention not only has an average particle size of micrometers, but also carries divalent magnesium ions (Mg^(2+)) to have a large BET specific surface area and increase a catalyst life, and thus it is possible to provide a method for decomposing HFCs with excellent efficiency even at low temperatures (650°C) by using the same.

Description

Method for Disposing HFCs by Decomposition}

The present invention relates to a method for decomposing and treating HFCs, which are non-CO ₂ greenhouse gases, using aluminum oxide (hereinafter, 'Al ₂ O ₃ ') loaded with divalent magnesium ions (Mg ²⁺ ).

Greenhouse gases are known to affect global warming, climate change and environmental disasters (sea level rise, heat, droughts and floods).

Greenhouse gases such as CO ₂ , CH ₄ , N ₂ O and O ₃ are produced naturally, but their concentration increases due to human activity.

Among the various types of greenhouse gases, fluorinated greenhouse gases are not only synthesized and released by human activity but also have a much higher global warming potential (GWP) than other greenhouse gases.

Therefore, a lot of research is being conducted with an emphasis on minimizing such fluorinated greenhouse gases.

After the Montreal Protocol, the use of chlorofluorocarbons ('CFCs') as a refrigerant was banned, after which hydrofluorocarbons ('HFCs') were used as replacements for CFCs.

Of the various HFCs, 1,1,1,2-tetrafluoroethane (1,1,1,2-tetrauoroethane; hereinafter 'HFC-134a') is the most commonly used refrigerant in air conditioners, but the GWP value is higher than that of CO ₂ . It is 1,300 times higher, causing problems such as causing global warming.

The seriousness of HFC-134a was emphasized in the Kyoto Protocol and it was decided to reduce the use of HFC-134a in the Kigali Amendment.

Since the Kigali Revision Protocol, various techniques for decomposing the released HFC-134a have been used, such as the purification and reuse of HFC-134a using a polymeric membrane and the direct destruction of the waste HFC-134a. Has been.

However, although the discharged HFC-134a can be purified using the polymer membrane technology, the high cost of achieving the target HFC-134a purity required for reuse is difficult and technical limitations are difficult to overcome because of the HFC-134a. The direct destruction of is considered.

The direct destruction technology of HFC-134a can directly destroy HFC-134a by applying thermal conversion techniques such as incineration, plasma and pyrolysis.

Specifically, incineration in direct destruction techniques introduces combustion and auxiliary fuels in the air, but there are problems with additional fuel input costs and equipment corrosion due to excessive HF generation during incineration.

Another technology, steam plasma, is HFC-134a, which has high decomposition efficiency, but it is difficult to expand the plant due to the equipment's corrosion caused by high HF concentration in gas and unstable plasma discharge due to the use of steam, which makes high cost of plasma plant construction and operation. Due to this there is a problem that the actual commercialization is limited.

Another technique, pyrolysis, can be considered as an advantageous process for the decomposition of HFC-134a, but due to the high thermal stability of HFC-134a there is a problem that excessively high temperature (> 750 ℃) is required for pyrolysis.

Therefore, a catalytic pyrolysis method of HFC-134a has recently been proposed, and in the case of catalytic pyrolysis of HFC-134a, direct destruction of HFC-134a at low decomposition temperatures by using Ni / Al ₂ O ₃ , waste concrete and metal phosphate catalysts as catalysts Has been reported to be possible.

Specifically, the prior art discloses a comparison of HFC-134a decomposition efficiency of metal oxide catalysts such as CaO and Al ₂ O ₃ .

In this regard, Al ₂ O ₃ catalyst was reported to exhibit the highest destruction efficiency of HFC-134a, rapid deactivation of the Al ₂ O ₃ catalyst by conversion to AlF ₃ is to restrict the use of Al ₂ O ₃ catalyst.

However, there is no systematic research to increase the overall lifetime of catalysts used in the decomposition of HFCs, so it is urgent to study them.

Korean Patent Publication No. 10-2002-0000152

The present invention, as having been made in view of solving the disadvantages of the prior art, Al ₂ O was impregnated to a metal in the _third catalyst Al ₂ O ₃ treatment efficiency of the HFCs in Non-CO ₂ greenhouse gas emissions by increasing the life of the catalyst It is an object of the present invention to provide a decomposition treatment method of HFCs that can improve the efficiency.

The present invention, in order to achieve the above object,

Magnesium divalent ions having an average particle size of 1.0 to 2.0 mm, an average BET specific surface area of 200 to 250 m ² / g, an average pore size of 5 to 10 nm, and an average pore volume of 0.1 to 1 cm ³ / g. Provided is a method for treating HFCs, wherein the HFCs are decomposed using a decomposition catalyst containing (Mg ²⁺ ) ^-supported aluminum oxide (Al ₂ O ₃ ).

Al ₂ O ₃ catalyst containing magnesium divalent ions used in the decomposition treatment method of HFCs according to the present invention can increase the catalyst life by supporting magnesium divalent ions, Al ₂ O supported magnesium divalent ion By using _three catalysts, it is possible to provide a method for decomposing HFCs with excellent efficiency even at low temperatures (650 ° C.).

The decomposition treatment method of HFCs according to the present invention can generate by-product trifluoroethylene with excellent efficiency by decomposing HFCs with excellent efficiency.

1 is a schematic representation of a vertical plug flow reactor-gas chromatography / mass spectrometer (VPFR-GC / MS) system.
FIG. 2 shows the temperature desorption (NH ₃ -TPD) curves of ammonia of Al ₂ O ₃ catalysts and Mg / Al ₂ O ₃ catalysts fired at different temperatures (500 and 650 ° C.).
3 is a diagram showing the temperature desorption (CO ₂ -TPD) curve of carbon dioxide of an Al ₂ O ₃ catalyst and an Mg / Al ₂ O ₃ catalyst calcined at different temperatures (500 and 650 ° C.).
FIG. 4 shows X-ray diffraction (hereinafter 'XRD') patterns for Al ₂ O ₃ catalysts and Mg / Al ₂ O ₃ catalysts calcined at different temperatures (500 and 650 ° C.).
5 shows the conversion of 1,1,1,2-tetrafluoroethane (HFC-134a) with Al ₂ O ₃ catalyst and Mg / Al ₂ O ₃ catalyst calcined at different temperatures (500 and 650 ° C.) Drawing.
FIG. 6 shows trifluoroethylene (H 2 OF 3; HFO-1123, below) when catalytic decomposition of HFC-134a is carried out using Al ₂ O ₃ catalyst and Mg / Al ₂ O ₃ catalyst calcined at different temperatures (500 and 650 ° C.). 'TrFE') is a view showing the formation rate.
FIG. 7 shows a differential differential thermogravimetric (DTG) analysis curve of coke deposited on Al ₂ O ₃ catalysts and Mg / Al ₂ O ₃ catalysts calcined at different temperatures (500 and 650 ° C.). Drawing.
FIG. 8 is a diagram showing an XRD pattern of an Al ₂ O ₃ catalyst and an Mg / Al ₂ O ₃ catalyst after HFC-134a catalytic decomposition.
FIG. 9 is a graph showing the formation rate of CO ₂ during catalytic decomposition of HFC-134a using Al ₂ O ₃ catalyst and Mg / Al ₂ O ₃ catalyst calcined at different temperatures (500 and 650 ° C.).

Magnesium having an average particle size of 1.0 to 2.0 mm, an average BET specific surface area of 200 to 250 m ² / g, an average pore size of 5 to 10 nm and an average pore volume of 0.1 to 1 cm ³ / g The present invention provides a HFCs decomposition treatment method in which HFCs are decomposed using a decomposition catalyst including aluminum oxide (Al ₂ O ₃ ) carrying ^bivalent ions (Mg ²⁺ ).

In one embodiment of the present invention, Al ₂ O ₃ may be γ-Al ₂ O ₃ .

The decomposition catalyst provides an excellent decomposition effect as the specific surface area and the pore volume and the average pore size are small. Therefore, it provides an excellent decomposition effect of HFCs within the range described above.

In one embodiment of the present invention, the decomposition catalyst may comprise 2% to 10% based on the weight of magnesium divalent ions (Mg ²⁺ ). Specifically, the decomposition catalyst may include 2.5 to 7.5% or 3 to 6% based on the weight of magnesium divalent ions (Mg ²⁺ ). When the magnesium divalent ions (Mg ²⁺ ) is out of the content, the lifetime of the decomposition catalyst is reduced and the number of strong acid sites is increased, which leads to a problem in that decomposition efficiency is lowered when HFCs are decomposed.

In one embodiment of the present invention, the decomposition catalyst may be calcined at 500 to 650 ℃ for 1 to 3 hours. Specifically, the decomposition catalyst may be calcined at 650 ° C. for 2 hours. When the firing temperature is 650 ℃, the number of strong acid sites can be reduced, and by reducing the number of strong acid sites, the relative ratio of weak acid / strong acid acid (Weak Acid Amount / Strong Acid Amount) is increased, thereby improving the catalytic decomposition efficiency of HFCs. There is an expected benefit.

In one embodiment of the present invention, the decomposition catalyst may be a ratio of 0.7 to 1.5 with respect to the amount of weak acid / strong acid. Specifically, the decomposition catalyst may have a ratio of 1.2 to 1.5 or 1.3 to 1.4 with respect to the amount of weak acid / strong acid. Having a ratio with respect to the amount of weak acid / strong acid in the above range is that the number of strong acid sites is reduced, there is an advantage that can expect excellent catalytic decomposition efficiency of HFCs.

In one embodiment of the present invention, the HFCs may be a haloalkanes (Haloalkanes) compound in which a part of the hydrogen of the alkanes (C _n H _{2n + 2} ) is substituted with fluorine (F), specifically HFCs is HFC- 23, HFC-32, HFC-125, HFC-134a, HFC-152a, HFC-143a, HFC-227ea, HFC-236fa, HFC-245ca, or a mixed refrigerant including one or more of the above components.

HFCs have the following physical and chemical properties:

TABLE 1

In addition, examples of the HFCs mixed refrigerants include those listed in Table 2 below.

TABLE 2

In one embodiment of the present invention, the HFCs decomposition treatment method may be performed by catalytic pyrolysis at 300 to 650 ℃. It is more preferable to carry out at 550-650 degreeC specifically ,. When the decomposition is performed at 550 to 650 ° C., 100% decomposition duration of HFCs may be remarkably long.

In one embodiment of the present invention, the HFCs decomposition treatment method may be used by filling the column with a catalyst so that the space velocity per unit mass catalyst (WHSV) of 3000 ~ 7000 mL / gcat.h. By adjusting the space velocity per unit mass of the catalyst within the above range, HFCs decomposition treatment efficiency can be increased.

In one embodiment of the present invention, the step of obtaining by-products by the HFCs decomposition treatment may further include. Specifically, the byproduct may be trifluoroethylene (C ₂ HF ₃ ; HFO-1123). Since trifluoroethylene is an important feedstock for the synthesis of fluoroplastics and fluororubbers, trifluoroethylene can be efficiently obtained by the present HFCs decomposition treatment method.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

Hereinafter, examples will be described in detail to help understand the present invention. However, the following examples are merely to illustrate the content of the present invention is not limited to the scope of the present invention. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

<Production example>

1. Preparation of materials

Commercial HFC-134a was purchased and used by gas manufacturer RIGAS Co. Ltd., Daejeon, and commercial Al ₂ O ₃ catalyst and 5 wt% Mg / Al ₂ O ₃ catalyst were purchased from Sasol. The commercial Al ₂ O ₃ catalyst and 5 wt% Mg / Al ₂ O ₃ catalyst purchased were ground and sieved to produce small particles having an average particle size between 1.0 mm and 1.7 mm.

2. Al ₂ O ₃ -500 Preparation of the catalyst

The Al ₂ O ₃ catalyst was calcined at 500 ° C. for 2 hours, which was named 'Al ₂ O ₃ -500 catalyst'.

3. Al ₂ O ₃ -650 Preparation of the catalyst

The Al ₂ O ₃ catalyst was calcined at 650 ° C. for 2 hours, which was named 'Al ₂ O ₃ -650 catalyst'.

4. Mg / Al ₂ O ₃ Preparation of -500 Catalyst

The 5 wt% Mg / Al ₂ O ₃ catalyst was calcined at 500 ° C. for 2 hours, which was named 'Mg / Al ₂ O ₃ -500 catalyst'.

5. Mg / Al ₂ O ₃ Preparation of -650 Catalyst

The 5 wt% Mg / Al ₂ O ₃ catalyst was calcined at 650 ° C. for 2 hours, each named 'Mg / Al ₂ O ₃ -650 catalyst'.

<Example>

Example 1

Mg / Al ₂ O ₃ Decomposition Test of HFC-134a with -500 Catalyst

Catalyst efficiency for catalytic decomposition of HFC-134a using vertical plug ow reactor-gas chromatography / mass spectrometry (VPFR-GC / MS) as shown in FIG. Was tested.

The VPFR-GC / MS system consists of a gas supply, a reactor, an HF trap, and a valve-GC / MS (see FIG. 1).

For catalytic cracking of HFC-134a, 1.2 g of Mg / Al ₂ O ₃ -500 catalyst was taken to the catalyst bed in the reactor, 98 mL / min N ₂ gas and 2 mL / min HFC-134a Gas was supplied to the VPFR-GC / MS system through a gas supply.

After stabilization of the VPFR-GC / MS system, a temperature of 600 ° C. was set to the pyrolysis temperature and catalytic decomposition of HFC-134a began.

The gas hourly space velocity (GHSV) and the weight hourly space velocity (WHSV) per unit mass of the catalyst are 1667 h ^-1 and 5000 mL g _cat ^-1 h ^{-1, respectively.} It was.

The product gas released from the reactor was transferred to a valve GC / MS system (7890A / 5975C inert, Agilent, Santa Clara, USA) via an HF trap containing CaO.

Table 3 below shows the GC / MS conditions performed in the decomposition test of HFC-134a.

TABLE 3

Peaks on the GC / MS chromatogram obtained through GC / MS performed at the above conditions were confirmed by comparing the mass spectra of each peak on the chromatogram using MS library (NIST 08th).

The conversion rate (unit:%) of HFC-134a was calculated using Equation 1 below.

[Equation 1]

In Equation 1, A _in represents the peak area of HFC-134a _in the reaction gas, and A _out represents the peak area of HFC-134a in the product gas.

Example 2

Mg / Al ₂ O ₃ Decomposition Test of HFC-134a with -650 Catalyst

The decomposition test of HFC-134a was carried out under the same conditions as in Example 1 except that the Mg / Al ₂ O ₃ -650 catalyst was used.

Comparative Example 1

Al ₂ O ₃ Decomposition Test of HFC-134a with -500 Catalyst

The decomposition test of HFC-134a was performed under the same conditions as in Example 1 except that the Al ₂ O ₃ -500 catalyst was used.

Comparative Example 2

Al ₂ O ₃ Decomposition Test of HFC-134a with -650 Catalyst

The decomposition test of HFC-134a was performed under the same conditions as in Example 1 except that the Al ₂ O ₃ -650 catalyst was used.

Hereinafter, an experimental example will be described in detail to help the understanding of the present invention. However, the following experimental examples are merely to illustrate the content of the present invention is not limited to the scope of the present invention. Experimental examples of the present invention is provided to more completely explain the present invention to those skilled in the art.

Experimental Example

1. How to

BET specific surface area and pore volume of Al ₂ O ₃ -500, Al ₂ O ₃ -650, Mg / Al ₂ O ₃ -500 and Mg / Al ₂ O ₃ -650 catalysts were measured using a BET analyzer (Micromeritics 3Flex) NH ₃ -TPD analysis and XRD of the catalyst were carried out using the same procedure reported elsewhere.

2. Analysis of Physical and Chemical Properties of Catalysts

The BET specific surface area of the Mg / Al ₂ O ₃ catalyst is 246 m ² / g In the case of Mg / Al ₂ O ₃ -500 catalyst, in the case of Mg / Al ₂ O ₃ -650 catalyst was 227 m ² / g. However, BET specific surface area of the Al ₂ O ₃ catalyst is 139 m ² / g In the case of Al ₂ O ₃ -500 catalyst, in the case of Al ₂ O ₃ -650 catalyst was 140 m ² / g. The BET specific surface area of Mg / Al ₂ O ₃ catalyst (Mg / Al ₂ O ₃ -500 catalyst and Mg / Al ₂ O ₃ -650 catalyst) is Al ₂ O ₃ catalyst (Al ₂ O ₃ -500 catalyst and Al ₂ O ₃ -650 catalyst) was greater than the BET specific surface area value.

This suggests that the Al ₂ O ₃ catalyst (Al ₂ O ₃ -500 catalyst and Al ₂ O ₃ -650 catalyst) was impregnated with Mg as a metal to increase the BET specific surface area of the Al ₂ O ₃ catalyst.

2 and Table 4 show Al ₂ O ₃ catalyst (Al ₂ O ₃ -500 catalyst and Al ₂ O ₃ -650 catalyst) and Mg / Al ₂ O ₃ catalyst (Mg / Al ₂ O ₃ -500 catalyst and Mg / NH ₃ -TPD curve of Al ₂ O ₃ -650 catalyst) is shown.

TABLE 4

Referring to Table 4, the Mg / Al ₂ O ₃ -500 catalyst (0.77) and Mg / Al ₂ O ₃ -650 (0.65) catalyst is Al ₂ O ₃ -500 catalyst (0.26) and Al ₂ O _3- The amount of weak acid was much higher than that of the 650 catalyst (0.23).

This is because the Al ₂ O ₃ catalyst (Al ₂ O ₃ -500 catalyst and Al ₂ O ₃ -650 catalyst) is impregnated with Mg, which is a metal, to the Al ₂ O ₃ catalyst (Al ₂ O ₃ -500 catalyst and Al ₂ O ₃ -650). It is suggested that the weak acidity of the catalyst) is increased, and that weak Lewis acidity can be increased by adding Mg. Therefore, it can be concluded that the addition of Mg, a metal, to the Al ₂ O ₃ catalyst (Al ₂ O ₃ -500 catalyst and Al ₂ O ₃ -650 catalyst) increased the weak Lewis acidity.

In addition, the Al ₂ O ₃ -650 catalyst (0.86) and the Mg / Al ₂ O ₃ -650 catalyst (1.70) were respectively higher than those of the Al ₂ O ₃ -500 catalyst (0.98) and the Mg / Al ₂ O ₃ -500 (2.49) catalyst. Small acid sites (Total Acid Amount) were shown.

In particular, the Al ₂ O ₃ -650 catalyst (0.29) and the Mg / Al ₂ O ₃ -650 catalyst (0.47) were respectively higher than those of the Al ₂ O ₃ -500 catalyst (0.47) and Mg / Al ₂ O ₃ -500 (1.06). There were few strong acid sites.

This suggests that at higher temperatures (650 ° C.), the number of strong acid sites can be reduced due to the firing of the Al ₂ O ₃ catalyst and the Mg / Al ₂ O ₃ catalyst.

Weak Acid Amount / Strong Acid Amount was increased with increasing Mg impregnation and firing temperature (see Table 4).

3 shows the CO ₂ -TPD curves of the Al ₂ O ₃ catalyst and the Mg / Al ₂ O ₃ catalyst.

Mg / Al ₂ O ₃ -500 catalyst and Mg / Al ₂ O ₃ -650 catalyst showed higher basicity than Al ₂ O ₃ -500 catalyst and Al ₂ O ₃ -650 catalyst, which increased the basicity by Mg impregnation. Suggests.

In addition, Al ₂ O ₃ -650 catalyst and the Mg / Al ₂ O ₃ -650 catalysts large number of weak base region than the respective Al ₂ O ₃ -500 catalyst and the Mg / Al ₂ O ₃ -500 catalysts of the strong base sites were less .

Firing Al ₂ O ₃ catalyst and Mg / Al ₂ O ₃ catalyst at high temperature (650 ° C) through NH ₃ -TPD and CO ₂ -TPD results increases the number of weak and weak bases, Suggests that the number can be reduced.

Balanced weak Lewis acidity and basicity can affect the catalytic degradation of HFC-134a.

4 shows the XRD patterns of Al ₂ O ₃ catalysts and Mg / Al ₂ O ₃ catalysts calcined at different temperatures (500 and 650 ° C.).

Specifically, the XRD patterns of the Al ₂ O ₃ catalyst and the Mg / Al ₂ O ₃ catalyst showed characteristic broad peaks of Al ₂ O ₃ showing γ phase at 46.6 °, 67.1 ° and 60.9 ° 2θ (JCPDS 29-63). It was.

On the other hand, XRD peaks can be distinguished by intensity. Since the intensity of the XRD peaks varies depending on the elemental composition, the impregnation of Mg on the alumina reduced the intensity of the peak compared to the Al ₂ O ₃ catalyst (see FIG. 4).

Also, typical XRD peaks of Mg particles were hardly seen in the XRD patterns of Mg / Al ₂ O ₃ catalysts. This suggests that Mg has penetrated into the substitutional sites of the Al lattice.

Compared to the XRD peak of the Al ₂ O ₃ catalyst, the XRD peak of the Mg / Al ₂ O ₃ catalyst has a wider peak than the XRD peak of the Al ₂ O ₃ catalyst, and the 2θ value is shifted to a slightly lower value. (See Figure 4).

As a result, it was confirmed that 2θ of the Al peak was shifted in the XRD pattern of Mg / Al ₂ O ₃ by the penetration of Mg atoms into the Al matrix.

Mg ²⁺ ions can be considered to have penetrated the Al lattice because Mg ²⁺ ions (86 pm), which have a larger ion radius than Al ³⁺ (67.5 pm), have less movement and no secondary phase is observed.

The Mg / Al ₂ O ₃ -650 catalyst was found to have a higher XRD peak height by increasing the firing temperature from 500 ° C. to 650 ° C. through a strong peak compared to the Mg / Al ₂ O ₃ -500 catalyst. .

Therefore, the Mg / Al ₂ O ₃ catalyst has a higher BET specific surface area than the Al ₂ O ₃ catalyst and more weak acid sites of Mg / Al ₂ O ₃ , indicating that Al ₂ O is caused by atomic infiltration of Mg into the substitution site of the Al lattice. It can be seen that due to the structural change of ₃ .

3. Catalytic Decomposition of HFC-134a

FIG. 5 shows the conversion of HFC-134a obtained by catalytic decomposition of HFC-134a with Al ₂ O ₃ and Mg / Al ₂ O ₃ catalysts at 600 ° C. FIG.

Since the temperature required for noncatalytic decomposition of HFC-134a is higher than 750 ℃, HFC-134a was not decomposed by noncatalytic decomposition at 600 ℃, but Al ₂ O ₃ catalyst (Al ₂ O ₃ -500 and Al ₂ O ₃ -650) and Mg / Al ₂ O ₃ catalyst (Mg / Al ₂ O ₃ -500 and Mg / Al ₂ O ₃ -650), catalytic decomposition occurred, and the initial decomposition rate of HFC-134a was higher than 99.0%. It was high.

The high rate of decomposition of HFC-134a (> 99%) for all catalysts was maintained for more than 6 hours, but the rate of degradation decreased with some catalysts.

5 shows the conversion of 1,1,1,2-tetra fluoroethane (HFC-134a) for various catalysts calcined at different temperatures (500 and 650 ° C.).

Mg / Al ₂ O ₃ catalysts (Mg / Al ₂ O ₃ -500 and Mg / Al ₂ O ₃ -650) have a longer duration than Al ₂ O ₃ catalysts (Al ₂ O ₃ -500 and Al ₂ O ₃ -650) HFC-134a was decomposed.

This suggests that Mg impregnated on the surface of Al ₂ O ₃ may play a decisive role in the decomposition reaction of HFC-134a.

Mg / Al ₂ O ₃ catalysts (Mg / Al ₂ O ₃ -500 and Mg / Al ₂ O ₃ -650) have a higher BET ratio than Al ₂ O ₃ catalysts (Al ₂ O ₃ -500 and Al ₂ O ₃ -650) Due to the large surface area, the weak Lewis acid sites and the weak base sites of the Mg / Al ₂ O ₃ catalyst, the catalyst life for the decomposition of HFC-134a could be increased.

This confirms that the greater the surface area of the catalyst, the better the mass transfer, and thus the better the catalyst can be in contact with HFC-134a.

In addition, Al ₂ O ₃ -650 and Mg / Al ₂ O ₃ -650 calcined at 650 ° C. had a longer lifetime than Al ₂ O ₃ -500 and Mg / Al ₂ O ₃ -500 in terms of catalytic decomposition of HFC-134a.

The BET specific surface areas of Al ₂ O ₃ -650 and Mg / Al ₂ O ₃ -650 were similar to those of Al ₂ O ₃ -500 and Mg / Al ₂ O ₃ -500, respectively.

In addition, the total acidity of the Al ₂ O ₃ catalyst and the Mg / Al ₂ O ₃ catalyst decreased with increasing catalyst firing temperature.

The reduction of the number of strong acid sites of the catalyst calcined at 650 ° C. was found to be a major factor in increasing the lifetime of the Al ₂ O ₃ catalyst and the Mg / Al ₂ O ₃ catalyst.

The strong acid sites of the Al ₂ O ₃ catalyst can lead to higher coke formation and reduce catalyst life.

In particular, as described above (see Table 3), it was confirmed that the catalytic activity has a close correlation with the ratio of the weak acid sites / strong acid sites.

In the catalyst calcined at 650 ° C., the increase in the weak base site and the decrease in the strong base site can also be an important factor in increasing the lifetime of the Al ₂ O ₃ catalyst and the Mg / Al ₂ O ₃ catalyst.

6 shows Al ₂ O ₃ catalysts (Al ₂ O ₃ -500 and Al ₂ O ₃ -650) and Mg / Al ₂ O ₃ catalysts (Mg / Al ₂ O ₃ −) calcined at different temperatures (500 and 650 ° C.). The formation rate of trifluoroethylene (C ₂ HF ₃ , triuoroethylene; hereinafter 'TrFE') which is a by-product formed by catalytic decomposition of HFC-134a to 500 and Mg / Al ₂ O ₃ -650) is shown.

Al ₂ O ₃ catalyst (Al ₂ O ₃ Al ₂ O ₃ -500 and -650) and, Mg / Al ₂ O ₃ catalyst (Mg / Al ₂ O ₃ -500, and Mg / Al ₂ O ₃ -650) as compared Produced a greater amount of TrFE for a longer time.

In addition, the catalyst calcined at 650 ° C. (Mg / Al ₂ O ₃ -650) produced a greater amount of TrFE than the catalyst calcined at 500 ° C.

This suggests that Mg impregnation and calcined catalyst at 650 ° C. (Mg / Al ₂ O ₃ -650 catalyst) can increase the catalyst lifetime for the formation of by-product TrFE as well as the decomposition of HFC-134a.

Since TrFE is an important feedstock for the synthesis of fluoroplastics and fluororubbers, the method of efficiently forming TrFE by HFC-134a decomposition is an important problem.

TrFE can be produced through hydrolysis of trichlorotriuoroethane, but this hydrolysis process is difficult and expensive, so efficient TrFE formation through catalytic decomposition of HFC-134a over Mg / Al ₂ O ₃ catalyst Considering cost efficiency, it makes sense.

7 shows the oxidation TG and DTG curves of the deactivated catalyst collected after sequential decomposition of HFC-134a.

Catalytic cracking of HFC-134a on Mg / Al ₂ O ₃ -650 catalyst formed a small amount of coke (3.7% ± 1%), followed by Mg / Al ₂ O ₃ -500 catalyst (3.9% ± 1%), HFC-134a decomposition efficiency was shown in the order of Al ₂ O ₃ -650 catalyst (11.9% ± 1%) and Al ₂ O ₃ -500 catalyst (16.0% ± 1%) (see FIG. 7).

This suggests that the catalytic cracking efficiency and catalyst life of HFC-134a are also closely related to the amount of coke formed during catalytic cracking of HFC-134a.

Mg / Al ₂ O ₃ catalysts (Mg / Al ₂ O ₃ -500 and Mg / Al ₂ O ₃ -650) are less than Al ₂ O ₃ catalysts (Al ₂ O ₃ -500 and Al ₂ O ₃ -650) Positive coke was produced and the oxidation temperature of the coke deposited on Mg / Al ₂ O ₃ catalyst (Mg / Al ₂ O ₃ -500 and Mg / Al ₂ O ₃ -650) was also observed on the Al ₂ O ₃ catalyst. It was found to be lower than deposited.

This is more prolonged than with Al ₂ O ₃ catalysts using Mg / Al ₂ O ₃ catalysts (Mg / Al ₂ O ₃ -500 and Mg / Al ₂ O ₃ -650) due to the small amount of coke deposition with lower oxidation temperatures. Means that it can provide high decomposition efficiency.

FIG. 8 shows Al ₂ O ₃ catalyst (Al ₂ O ₃ -500 and Al ₂ O ₃ -650) and Mg / Al ₂ O ₃ catalyst (Mg / Al) collected in a furnace after sequential catalytic decomposition of HFC-134a XRD patterns of ₂ O ₃ -500 and Mg / Al ₂ O ₃ -650) are shown.

Typical XRD peak patterns of Al ₂ O ₃ catalysts (Al ₂ O ₃ -500 and Al ₂ O ₃ -650) before use in catalytic cracking were not observed in the XRD patterns of Al ₂ O ₃ catalysts after use, but after use _{The 2} 0 ₃ catalysts (Al ₂ 0 ₃ -500 and Al ₂ 0 ₃ -650) showed typical XRD peak patterns of AlF ₃ (25 °, 42 °, 52 ° and 58 ° 2θ).

This suggests that Al ₂ O ₃ catalyst (Al ₂ O ₃ -500 -650, and Al ₂ O _{3) 2} Al catalyst for decomposition of HFC-134a for O ₃ catalyst is converted to AlF _3.

Based on the product distribution and the presence of MgF ₃ , the decomposition mechanism of HFC-134a using Al ₂ O ₃ catalysts (Al ₂ O ₃ -500 and Al ₂ O ₃ -650) can be expressed using Equation 2 as follows. Can be.

[Equation 2]

9 shows Al ₂ O ₃ catalyst (Al ₂ O ₃ -500 and Al ₂ O ₃ -650) and Mg / Al ₂ O ₃ catalyst (Mg / Al ₂ O ₃ -500 and Mg / Al ₂ O ₃ -650) Rate of CO ₂ formation during catalytic cracking of HFC-134a for

Referring to FIG. 9, Mg / Al ₂ O ₃ catalysts (Mg / Al ₂ O ₃ -500 and Mg / Al ₂ O ₃ -650) are Al ₂ O ₃ catalysts (Al ₂ O ₃₎ during the decomposition reaction of HFC-134a. -500 and Al ₂ O ₃ -650) produced higher TrFE rates and less CO ₂ .

Based on the product distribution and the presence of MgF ₃ , the decomposition mechanism of HFC-134a using Mg / Al ₂ O ₃ catalysts (Mg / Al ₂ O ₃ -500 and Mg / Al ₂ O ₃ -650) is as follows: Can be expressed using 3.

[Equation 3]

In addition, Mg / Al ₂ O ₃ catalysts (Mg / Al ₂ O ₃ -500 and Mg / Al ₂ O ₃ -650) are smaller than Al ₂ O ₃ catalysts (Al ₂ O ₃ -500 and Al ₂ O ₃ -650). Coke of was produced.

This may explain the number of weak Lewis acidic sites increased by Mg impregnation for Al ₂ O ₃ catalysts, which may increase the relative ratio of weak acid sites relative to the strong acid sites that aggravate coke formation (see Table 3). ).

When Mg / Al ₂ O ₃ catalysts (Mg / Al ₂ O ₃ -500 and Mg / Al ₂ O ₃ -650) are used, typical peaks of MgF ₂ are also shown in FIGS. 9 (c) and 9 (d). As used, it was observed in XRD patterns (24 °, 42 ° and 52 ° 2θ) of Mg / Al ₂ O ₃ catalysts (Mg / Al ₂ O ₃ -500 and Mg / Al ₂ O ₃ -650).

This suggests that Mg is also directly involved in the defluorination reaction of HFC-134a according to the following reaction.

Compared to the Mg / Al ₂ O ₃ -500 catalyst, reduced coke formation in the Mg / Al ₂ O ₃ -650 catalyst indicates that a relatively large number of strong acid sites are associated with catalyst deactivation during catalytic decomposition of HFC-134a. Confirmed.

Compared to Al ₂ O ₃ catalysts (Al ₂ O ₃ -500 and Al ₂ O ₃ -650), Mg / Al ₂ O ₃ (Mg / Al ₂ O ₃ -500 and Mg / Al ₂ O ₃ -650) It had a larger BET specific surface area and higher weak Lewis acidity and basicity.

Relatively on Al ₂ O ₃ catalysts (Al ₂ O ₃ -500 and Al ₂ O ₃ -650) and Mg / Al ₂ O ₃ (Mg / Al ₂ O ₃ -500 and Mg / Al ₂ O ₃ -650) The number of strong acidic sites decreased as the firing temperature increased from 500 ° C. to 650 ° C., resulting in reduced coke formation and increased catalyst life.

TrFE, a by-product obtained by catalytic cracking of HFC-134a, was found to be Mg / Al ₂ O ₃ (Mg / Al ₂ O ₃ -500 and more) than Al ₂ O ₃ catalysts (Al ₂ O ₃ -500 and Al ₂ O ₃ -650). Mg / Al ₂ O ₃ -650) was obtained in a high yield.

As described above, although the present invention has been described by way of limited embodiments and drawings, the present invention is not limited thereto, and the technical idea of the present invention and the following by those skilled in the art to which the present invention pertains. Of course, various modifications and variations are possible within the scope of equivalents of the claims to be described.

Claims (11)

Magnesium divalent ions (Mg) with an average particle size of 1.0 to 2.0 mm, an average BET of 200 to 250 m ² / g, an average pore size of 5 to 10 nm and an average pore volume of 0.1 to 1 cm ³ / g. ²⁺ ) to decompose HFC-134a using a decomposition catalyst containing supported aluminum oxide (γ-Al ₂ O ₃ ),
The decomposition catalyst comprises 5% based on the weight of magnesium divalent ions (Mg ²⁺ ),
The decomposition catalyst is a ratio of the amount of weak acid / strong acid is 1.3 to 1.4,
The decomposition catalyst is to be calcined at 650 ℃ for 2 hours,
The HFCs decomposition treatment method is to be carried out by catalytic pyrolysis at 550 ~ 650 ℃,
The HFCs decomposition treatment method is to use the catalyst packed in the column so that the space-time velocity (WHSV) per unit mass of the catalyst is 3000 ~ 7000 mL / g _cat · h,
The HFC-134a decomposition treatment method further comprising the step of obtaining trifluoroethylene (Trifluoroethylene, C ₂ HF ₃ ; HFO-1123) by the HFC-134a decomposition treatment.
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