KR102235570B1 - Method for Decomposition HFCs Using Aluminum Oxide Supported with Divalent Magnesium Ion - Google Patents

Abstract

The present invention relates to a method of decomposing and treating HFCs, _{which is a non-CO 2} greenhouse gas, using aluminum oxide carrying divalent magnesium ions.
_{Aluminum oxide (Al 2} O ₃ ) used in the HFCs decomposition treatment method according to the present invention not only has an average particle size of micrometer level, but also supports divalent magnesium ions (Mg ²⁺ ), so that the BET specific surface area is wide and the catalyst life is increased. Since it can be increased, it is possible to provide a method for decomposing HFCs with excellent efficiency even at low temperatures (650° C.) by using this.

Description

Method for Decomposition HFCs Using Aluminum Oxide Supported with Divalent Magnesium Ion}

The present invention relates to a method of decomposing and treating HFCs, which are _{non-CO 2} greenhouse gases, using aluminum oxide (hereinafter referred to as'Al ₂ O ₃ ') on which divalent magnesium ions (Mg ^{2+) are supported.}

Greenhouse gases are known to be factors affecting global warming, climate change, and environmental disasters (sea level rise, heat, drought and flooding).

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 synthesized and released by human activities as well as have a much higher global warming potential (GWP) than other greenhouse gases.

Therefore, many studies are being conducted with an emphasis on minimizing these fluorinated greenhouse gases.

After the Montreal Protocol, the use of chlorofluorocarbons (hereinafter referred to as'CFCs') as refrigerants was banned, and then hydrofluorocarbons (hereinafter referred to as'HFCs') were used as replacements for CFCs.

Among various types of HFCs, 1,1,1,2-tetrafluoroethane (1,1,1,2-tetrauoroethane; hereinafter'HFC-134a') is the most frequently used refrigerant for air conditioners, but its GWP value is higher than that _{of CO 2.} It is 1,300 times higher, causing problems such as global warming.

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

After the Kigali revised protocol, various techniques for decomposing discharged HFC-134a have been used, such as a technique for reusing HFC-134a after purification using a polymeric membrane, and a technique for direct destruction of waste HFC-134a. Has been.

However, although the discharged HFC-134a can be purified using the polymer membrane technology, there is a problem that it is difficult to overcome technical and economic limitations due to high cost in achieving the purity of the target HFC-134a required for reuse. HFC-134a The direct destruction technique of was considered.

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

Specifically, in the case of incineration, among the direct destruction technologies, combustion in the air and auxiliary fuel are introduced, but there is a problem of additional fuel input cost and equipment corrosion due to excessive HF generation during incineration.

Another technology, steam plasma, is a technology with high decomposition efficiency of HFC-134a, but it is difficult to expand the plant due to the corrosion of equipment due to the high HF concentration in the gas and unstable plasma discharge due to the use of steam. Due to this, there is a problem that the actual commercialization is limited.

Another technique, pyrolysis, can be regarded 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 an excessively high temperature (> 750°C) is required during pyrolysis.

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

Specifically, a comparison of HFC-134a decomposition efficiency of metal oxide catalysts such _{as CaO and Al 2} O ₃ as a prior art has been disclosed.

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, since there is no systematic study to increase the overall life of the catalyst used in the decomposition of HFCs, research on this is urgent.

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 method for decomposing HFCs that can improve.

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

Magnesium divalent ion 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} It provides a method for decomposing HFCs by using a decomposition catalyst including (Mg ²⁺ )-supported aluminum oxide (Al ₂ O _{3 ).}

_{Al 2} O ₃ catalyst carrying magnesium divalent ions used in the decomposition treatment method of HFCs according to the present invention can increase the catalyst life by carrying magnesium divalent ions, and Al ₂ O carrying magnesium divalent ions ₃ By using a catalyst, it is possible to provide a method capable of decomposing HFCs with excellent efficiency even at a low temperature (650°C).

The method for decomposing HFCs according to the present invention can generate trifluoroethylene, a by-product, with excellent efficiency by decomposing HFCs with excellent efficiency.

1 is a schematic diagram of a vertical plug flow reactor-gas chromatography/mass spectrometer (VPFR-GC/MS) system.
FIG. 2 is a diagram showing a temperature rise and desorption (NH ₃ -TPD) curve _{of ammonia of an Al 2} O ₃ catalyst and an Mg/Al ₂ O ₃ catalyst calcined at different temperatures (500 and 650° C.).
FIG. 3 is a diagram showing a temperature rise and 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 is a diagram showing X-ray diffraction (XRD) patterns for _{Al 2} O ₃ catalysts and Mg/Al ₂ O ₃ catalysts calcined at different temperatures (500 and 650° C.).
Figure 5 shows the conversion rate of 1,1,1,2-tetrafluoroethane (HFC-134a) when using _{Al 2} O ₃ catalyst and Mg/Al ₂ O ₃ catalyst calcined at different temperatures (500 and 650° C.) It is a drawing.
6 is a trifluoroethylene (C2HF3; HFO-1123, below) when catalytic decomposition of HFC-134a using _{an Al 2} O ₃ catalyst and Mg/Al ₂ O ₃ catalyst calcined at different temperatures (500 and 650° C.) It is a diagram showing the formation rate of'TrFE').
7 is a differential thermogravimetric (Differential Thermogravimetric; hereinafter'DTG') analysis curve of coke deposited on _{Al 2} O ₃ catalyst and Mg/Al ₂ O ₃ catalyst calcined at different temperatures (500 and 650° C.) It is a drawing.
8 is a diagram showing an XRD pattern for an _{Al 2} O ₃ catalyst and an Mg/Al ₂ O ₃ catalyst after decomposition of the HFC-134a catalyst.
9 is a view 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.).

The present invention has 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, magnesium To provide a method for decomposing HFCs by decomposing HFCs using a decomposition catalyst including aluminum oxide (Al ₂ O ₃ ) on which divalent ions (Mg ^{2+) are supported.}

In an embodiment of the present invention, the 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 pore volume are large and the average pore size is small. Therefore, it provides an excellent decomposition effect of HFCs within the range described above.

In an embodiment of the present invention, the decomposition catalyst may contain 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 content of the magnesium divalent ion (Mg ²⁺ ) is out of the content, the lifespan of the decomposition catalyst decreases and the number of strong acid sites increases, so that decomposition efficiency decreases when decomposing HFCs.

In an embodiment of the present invention, the decomposition catalyst may be calcined at 500 to 650° C. 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 (Weak Acid Amount/Strong Acid Amount) increases, thus improving the catalytic decomposition efficiency of HFCs. There are benefits to be expected.

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

In one embodiment of the present invention, the HFCs _{may be a haloalkanes compound in which a part of hydrogen of an alkane (C n} H _2n+2 ) is substituted with fluorine (F), and specifically, HFCs are HFC- 23, HFC-32, HFC-125, HFC-134a, HFC-152a, HFC-143a, HFC-227ea, HFC-236fa, HFC-245ca, or a mixed refrigerant containing one or more of the above components.

HFCs have the following physical and chemical properties.

[Table 1]

In addition, examples of the mixed refrigerant of HFCs 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°C. Specifically, it is more preferable to perform at 550 to 650°C. When the decomposition is performed at 550 to 650° C., the effect of remarkably lengthening the duration of 100% decomposition of HFCs can be obtained.

In one embodiment of the present invention, the HFCs decomposition treatment method may be used by filling the column with a catalyst such that the space velocity per catalyst unit mass (WHSV) is 3000 to 7000 mL/gcat·h. By controlling the space velocity per unit mass of catalyst within the above range, there is an effect that the efficiency of decomposing HFCs can be increased.

In one embodiment of the present invention, it may further include the step of obtaining a by-product by the HFCs decomposition treatment. Specifically, the by-product 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 HFCs decomposition treatment method of the present invention.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples.

Hereinafter, examples will be described in detail to aid understanding of the present invention. However, the following examples are merely illustrative of the contents of the present invention, and the scope of the present invention is not limited to the following examples. The embodiments of the present invention are provided to more completely describe the present invention to those of ordinary skill in the art.

<Production Example>

1. Preparation of ingredients

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

2. Al ₂ O ₃ -500 Preparation of catalyst

The Al ₂ O ₃ catalyst was calcined at 500° C. for 2 hours, and it _{was named “Al 2} O ₃ -500 catalyst”.

3. Al ₂ O ₃ -650 Preparation of catalyst

The Al ₂ O ₃ catalyst was calcined at 650° C. for 2 hours, and it _{was named “Al 2} O ₃ -650 catalyst”.

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

A 5% by weight Mg/Al ₂ O ₃ catalyst was calcined at 500° C. for 2 hours, and this _{was named “Mg/Al 2} O ₃ -500 catalyst”.

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

A 5% by weight Mg/Al ₂ O ₃ catalyst was calcined at 650° C. for 2 hours, and it _{was named “Mg/Al 2} O ₃ -650 catalyst”, respectively.

<Example>

Example 1

Mg/Al ₂ O ₃ Decomposition test of HFC-134a using -500 catalyst

Efficiency of the catalyst for catalytic decomposition of HFC-134a using vertical plug ow reactor-gas chromatography/mass spectrometry (hereinafter'VPFR-GC/MS') as shown in FIG. 1 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 the catalytic decomposition of HFC-134a, 1.2 g of Mg/Al ₂ O ₃ -500 catalyst was taken in the catalyst bed in the reactor, 98 mL/min of N ₂ gas and 2 mL/min of 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 as the pyrolysis temperature and catalytic cracking of HFC-134a was started.

The gas hourly space velocity (hereinafter referred to as'GHSV') and the weight hourly space velocity (hereinafter referred to as'WHSV') of the system are 1667 h ^-1 and 5000 mL g _cat ^-1 h ^{-1, respectively.} Was.

The product gas released from the reactor was transferred to a valve GC/MS system (7890A/5975C inert, Agilent, Santa Clara, USA) through 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 under the above conditions were confirmed by comparing the mass spectra of each peak on the chromatogram using an MS library (NIST 08th).

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

[Equation 1]

In Equation 1, A _in is the peak area of HFC-134a _{in the reaction gas, and A out} is the peak area of HFC-134a in the product gas.

Example 2

Mg/Al ₂ O ₃ Decomposition test of HFC-134a using -650 catalyst

A decomposition test of HFC-134a was performed 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 using -500 catalyst

A decomposition test of HFC-134a was performed under the same conditions as in Example 1, except that an Al ₂ O _{3 -500 catalyst was used.}

Comparative Example 2

Al ₂ O ₃ Decomposition test of HFC-134a using -650 catalyst

A decomposition test of HFC-134a was performed under the same conditions as in Example 1, except that an Al ₂ O _{3 -650 catalyst was used.}

Hereinafter, an experimental example will be described in detail to aid understanding of the present invention. However, the following experimental examples are merely illustrative of the contents of the present invention, and the scope of the present invention is not limited to the following experimental examples. Experimental examples of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art.

<Experimental Example>

1. Method

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 catalyst were measured using a BET analyzer (Micromeritics 3Flex). And the NH ₃ -TPD analysis and XRD of the catalyst were performed using the same procedure reported elsewhere.

2. Analysis of physicochemical properties of catalyst

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. 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) Al 2} O ₃ catalyst (Al ₂ O ₃ -500 catalyst and Al ₂ O ₃ -650 catalyst) was larger 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, which is a metal, to increase the BET specific surface area of the _{Al 2} O _{3 catalyst.}

2 and Table 4 respectively 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/ Al ₂ O ₃ -650 catalyst) of NH ₃ -TPD curve is shown.

[Table 4]

Referring to Table 4, the Mg/Al ₂ O ₃ -500 catalyst (0.77) and the Mg/Al ₂ O ₃ -650 (0.65) catalyst are respectively 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 Al ₂ O ₃ catalyst (Al ₂ O ₃ -500 catalyst and Al ₂ O ₃ -650 catalyst) is impregnated with Mg, a metal, and Al ₂ O ₃ catalyst (Al ₂ O ₃ -500 catalyst and Al ₂ O _3- 650 catalyst), suggesting that the weak acidity of the catalyst) is increased, and that the weak Lewis acidity can be increased by the addition of Mg. Therefore, it can be concluded that weak Lewis acidity increased when Mg, which is a metal, was added to the _{Al 2} O ₃ catalyst (Al ₂ O ₃ -500 catalyst and Al ₂ O _{3 -650 catalyst).}

In addition, the Al ₂ O ₃ -650 catalyst (0.86) and the Mg/Al ₂ O ₃ -650 catalyst (1.70) were _{compared to the Al 2} O ₃ -500 catalyst (0.98) and the Mg/Al ₂ O ₃ -500 (2.49) catalyst, respectively. It showed a small number of Total Acid Amount.

In particular, the Al ₂ O ₃ -650 catalyst (0.29) and the Mg/Al ₂ O ₃ -650 catalyst (0.47) were _{compared to the Al 2} O ₃ -500 catalyst (0.47) and the Mg/Al ₂ O ₃ -500 (1.06) catalyst, respectively. There were fewer areas of strong acid.

This suggests that the number of strong acid sites can be reduced due to the sintering of the _{Al 2} O ₃ catalyst and the Mg/Al ₂ O ₃ catalyst at a higher temperature (650° C.).

The relative ratio of weak acid/strong acidity (Weak Acid Amount/Strong Acid Amount) increased with increasing Mg impregnation and firing temperature (see Table 4).

3 shows the CO ₂ -TPD curve of the Al ₂ O ₃ catalyst and the Mg/Al ₂ O _{3 catalyst.}

The Mg/Al ₂ O ₃ -500 catalyst and the Mg/Al ₂ O ₃ -650 catalyst _{showed higher basicity than the Al 2} O ₃ -500 catalyst and the Al ₂ O ₃ -650 catalyst, which was increased by Mg impregnation. Suggests that it is.

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 .

NH ₃ -TPD and CO _{2 -TPD results show that when the Al 2} O ₃ catalyst and Mg/Al ₂ O ₃ catalyst are calcined at high temperature (650 ℃), the number of weak acid and weak base sites is increased, and the number of strong acid and strong base sites is increased. It suggests that the number can be reduced.

It can be seen that a balanced weak Lewis acidity and basicity can affect the catalytic decomposition of HFC-134a.

4 shows the XRD pattern of _{the Al 2} O ₃ catalyst and the Mg/Al ₂ O ₃ catalyst fired 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 representing the γ phase at 46.6˚, 67.1˚ and 60.9˚ 2θ (JCPDS 29-63). I got it.

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

In addition, the typical XRD peak of the Mg particles was hardly seen in the XRD pattern _{of the Mg/Al 2} O _{3 catalyst.} This suggests that Mg penetrated into the substitutional sites of the Al lattice.

As compared to the XRD peak of Al ₂ O ₃ catalyst, XRD peak of the Mg / Al ₂ O ₃ catalyst, it was confirmed that has a wider peak compared to XRD peak of Al ₂ O ₃ catalyst, 2θ values are moved to a slightly lower value (See Fig. 4).

Through this, it was confirmed that the 2θ of the Al peak shifted in the XRD pattern of _{Mg/Al 2} O _{3 due to} the penetration of Mg atoms into the Al matrix.

^{Mg 2+} ions (86 pm), which have a larger ionic radius than Al ³⁺ (67.5 pm), have less migration and no secondary phase is observed, so the Mg ²⁺ ions can be considered to have penetrated the Al lattice.

The Mg/Al ₂ O ₃ -650 catalyst showed _{a strong peak compared to the Mg/Al 2} O ₃ -500 catalyst, and it was confirmed that the height of the XRD peak was increased by increasing the firing temperature from 500 ℃ to 650 ℃. .

Therefore, Mg / Al ₂ O ₃ catalyst is Al ₂ O ₃ catalyst larger and a BET specific surface area of Mg / Al ₂ O is a number of ₃ weak acid sites of the Al ₂ O caused by Mg penetration of atoms of the substituted portion of the Al lattice It can be seen that it is due to the structural change of _3.

3. Results of catalytic decomposition of HFC-134a

5 shows the conversion rate of HFC-134a obtained by catalytic decomposition of HFC-134a using _{Al 2} O ₃ and Mg/Al ₂ O ₃ catalysts at 600°C.

Since the temperature required for non-catalytic decomposition of HFC-134a is 750 ℃ or higher, HFC-134a at 600 ℃ was not decomposed by non-catalytic decomposition, but Al ₂ O ₃ catalysts (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) caused catalytic decomposition, and the initial decomposition rate of HFC-134a was more than 99.0% It appeared high.

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

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

Mg/Al ₂ O ₃ catalyst (Mg/Al ₂ O ₃ -500 and Mg/Al ₂ O ₃ -650) for a longer time than _{Al 2} O ₃ catalyst (Al ₂ O ₃ -500 and Al ₂ O _{3 -650)} HFC-134a was digested.

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

The Mg/Al ₂ O ₃ catalyst (Mg/Al ₂ O ₃ -500 and Mg/Al ₂ O ₃ -650) has a BET ratio compared to the _{Al 2} O ₃ catalyst (Al ₂ O ₃ -500 and Al ₂ O _{3 -650).} Since the surface area is large, there are many weak Lewis acid sites, and _{there are many weak base sites of the Mg/Al 2} O ₃ catalyst, the catalyst life for decomposition of HFC-134a could be increased.

Through this, it was confirmed that the greater the surface area of the catalyst, the better the mass transfer is possible, and thus the catalyst can provide a better opportunity to contact HFC-134a.

_{In addition, Al 2} O ₃ -650 and Mg/Al ₂ O ₃ -650 fired at 650° C. had a longer life 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, as the calcination temperature of the catalyst increased, the total acidity _{of the Al 2} O ₃ catalyst and the Mg/Al ₂ O _{3 catalyst decreased.}

It was confirmed that the decrease in the number of strong acid sites in the catalyst calcined at 650° C. is a major factor in increasing the life 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, reducing 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 site/strong acid site.

In the catalyst calcined at 650° C., the increase of the weak base site and the decrease of the strong base site may 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 is an Al 2} O ₃ catalyst (Al ₂ O ₃ -500 and Al ₂ O ₃ -650) calcined at different temperatures (500 and 650 °C) and a Mg/Al ₂ O ₃ catalyst (Mg/Al ₂ O _3- 500 and Mg/Al ₂ O ₃ -650), which is a by-product formed by catalytic decomposition of HFC-134a, trifluoroethylene (C ₂ HF ₃ , triuoroethylene; hereinafter'TrFE').

Compared to Al ₂ O ₃ catalyst (Al ₂ O ₃ -500 and Al ₂ O ₃ -650), Mg/Al ₂ O ₃ catalyst (Mg/Al ₂ O ₃ -500 and Mg/Al ₂ O ₃ -650) Produced a greater amount of TrFE over a longer period of 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 the catalyst impregnated with Mg and calcined at 650° C. (Mg/Al ₂ O ₃ -650 catalyst) can increase the catalyst life for not only decomposition of HFC-134a, but also formation of TrFE, a by-product.

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 issue.

TrFE can be produced through hydrolysis of trichlorotriuoroethane, but since this hydrolysis process is difficult and expensive, efficient TrFE formation through catalytic decomposition of HFC-134a to _{Mg/Al 2} O _{3 catalyst is not possible.} It can be considered meaningful when considering cost efficiency.

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

Catalytic decomposition 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%), Al ₂ O ₃ -650 catalyst (11.9% ± 1%) and Al ₂ O ₃ -500 catalyst (16.0% ± 1%) showed the decomposition efficiency of HFC-134a in the order (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 the 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 coke deposited on the _{Mg/Al 2} O ₃ catalyst (Mg/Al ₂ O ₃ -500 and Mg/Al ₂ O _{3 -650) was also on the Al 2} O ₃ catalyst. It was confirmed that it was lower than that deposited.

This is better for longer periods of time than _{Al 2} O ₃ catalysts due to the deposition of small amounts of coke at lower oxidation temperatures when using Mg/Al ₂ O ₃ catalysts (Mg/Al ₂ O ₃ -500 and Mg/Al ₂ O _{3 -650).} It means that it can provide high decomposition efficiency.

_{8 is an 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 ₂ O ₃ -500 and Mg/Al ₂ O ₃ -650).

The typical XRD peak pattern of _{Al 2} O ₃ catalysts (Al ₂ O ₃ -500 and Al ₂ O ₃ -650) before use in catalytic decomposition was _{not observed in the XRD pattern of Al 2} O ₃ catalysts after use, but Al after use _{The 2} O ₃ catalysts (Al ₂ O ₃ -500 and Al ₂ O 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 mechanism of decomposition 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. I can.

[Equation 2]

9 is an Al ₂ O ₃ catalyst (Al ₂ O ₃ -500 and Al ₂ O ₃ -650) and a Mg/Al ₂ O ₃ catalyst (Mg/Al ₂ O ₃ -500 and Mg/Al ₂ O ₃ -650) _{The rate of CO 2} formation during catalytic decomposition of HFC-134a is shown.

9, the Mg/Al ₂ O ₃ catalyst (Mg/Al ₂ O ₃ -500 and Mg/Al ₂ O _{3 -650) is an Al 2} O ₃ catalyst (Al ₂ O ₃₎ during the decomposition reaction of HFC-134a. -500 and Al ₂ O ₃ -650) higher TrFE formation rates and lower levels of CO ₂ .

Based on the product distribution and the presence of _{MgF 3,} the mechanism of decomposition 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:} It 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 was produced.

This _{may explain the number of weakly acidic sites increased by Mg impregnation for the Al 2} O ₃ catalyst, which may increase the relative ratio of weak acidic sites compared to strong acidic sites that intensify 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 described above, it was observed in the XRD patterns (24˚, 42˚ and 52˚ 2θ) of the Mg/Al ₂ O ₃ catalyst (Mg/Al ₂ O ₃ -500 and Mg/Al ₂ O _{3 -650) after use.}

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

Compared with the Al ₂ O ₃ catalyst (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 a higher weak Lewis acidity and basicity.

Relatively in Al ₂ O ₃ catalyst (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 strongly acidic sites decreased as the firing temperature increased from 500°C to 650°C, reducing the amount of coke formation and increasing the life of the catalyst.

TrFE, a by-product obtained by catalytic decomposition of HFC-134a, is 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 used to obtain a high yield.

*

As described above, although the present invention has been described by limited embodiments and drawings, the present invention is not limited thereto, and the technical spirit of the present invention and the following by those of ordinary skill in the technical field to which the present invention pertains. It goes without saying that various modifications and variations are possible within the range of equality of the claims to be described in.

Claims (1)

Magnesium divalent ion (Mg) having 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+} ) is to decompose HFC-134a using a decomposition catalyst containing aluminum oxide (γ-Al ₂ O _{3) supported,}
The decomposition catalyst contains 5% based on the weight of magnesium divalent ions (Mg ^{2+ ),}
The decomposition catalyst has a ratio of weak acidity/strong acidity to the amount of 1.3 to 1.4,
The decomposition catalyst is calcined at 650° C. for 2 hours,
The HFCs decomposition treatment method is carried out by catalytic pyrolysis at 570 ~ 610 °C,
The HFCs decomposition treatment method is to use a catalyst packed in a column so that the space-time velocity (WHSV) per unit mass of the catalyst is 5000 mL/g _cat·h,
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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