CN111001406A - Catalyst for catalytic combustion of chlorine-containing volatile organic compounds and preparation method thereof - Google Patents

Catalyst for catalytic combustion of chlorine-containing volatile organic compounds and preparation method thereof Download PDF

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CN111001406A
CN111001406A CN201910996629.9A CN201910996629A CN111001406A CN 111001406 A CN111001406 A CN 111001406A CN 201910996629 A CN201910996629 A CN 201910996629A CN 111001406 A CN111001406 A CN 111001406A
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noble metal
chlorine
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屠黎丽
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Luohe Xinwang Chemical Co ltd
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Ningbo Honglang Environmental Protection Technology Co Ltd
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Abstract

The invention belongs to the technical field of catalytic combustion of chlorine-containing volatile organic compounds, and particularly relates to a catalyst for catalytic combustion of chlorine-containing volatile organic compounds and a preparation method thereof. The catalyst comprises a ceramic substrate, a gamma-alumina oxide layer and a metal active component layer; the precursor solution of the gamma-alumina carrier layer can be coated on the ceramic substrate by an electrostatic spinning method, and the gamma-alumina carrier layer formed by spraying has a microstructure of nano long fibers, and the specific surface area of the gamma-alumina carrier layer is far larger than that of a catalytic material coated by a common method; the noble metal active component is loaded on the outer surface of the long fiber structure of the gamma-alumina carrier layer through an electrophoresis effect. The catalyst is prepared by four steps of preparation of spinning glue solution, spinning forming of a gamma-alumina carrier layer, preparation of electrophoresis glue solution and loading of metal active components, and the formed catalyst structure has the characteristics of high thermal stability, high activity and high selectivity.

Description

Catalyst for catalytic combustion of chlorine-containing volatile organic compounds and preparation method thereof
Technical Field
The invention belongs to the technical field of catalytic combustion of chlorine-containing volatile organic compounds, and particularly relates to a catalyst for catalytic combustion of chlorine-containing volatile organic compounds and a preparation method thereof.
Background
chlorine-Containing Volatile Organic Compounds (CVOCs) have been shown to be highly toxic and bioaccumulative, and have caused numerous environmental and human health problems. Among CVOCs, methyl chloride (DCM) and Vinyl Chloride (VC) are widely used in modern industrial production, and their usage is large and application is wide, and demand is increasing year by year, inevitably bringing about more environmental pollution, so its management is particularly urgent.
The catalytic combustion is considered to be one of the most promising technologies for processing CVOCs due to the advantages of low processing temperature, low energy consumption, high efficiency, simple process and the like, and the catalyst with high efficiency and good stability becomes the key of the catalytic combustion of the dichloromethane.
Currently, ceramic matrix monolithic catalysts are generally used for catalytic combustion, and the monolithic catalysts generally consist of a ceramic carrier, a coating carrier with a large specific surface area and a catalytic active component. For example, the catalyst is formed by coating a gamma-alumina carrier layer on a ceramic substrate and then loading active components such as noble metals on the gamma-alumina carrier layer, and the preparation method thereof has two key points, wherein the gamma-alumina carrier layer is used as a base carrier, and the noble metals (Pt, Pd, Rh and the like) are used as the active components. Wherein, the gamma-alumina carrier layer mainly plays a role of highly dispersing active components so as to ensure the activity of the catalyst.
However, when the monolithic catalyst is used for actually purifying chlorine-containing volatile organic compounds, the γ -alumina support layer is likely to crack and fall off during combustion, and the catalytic effect of the catalyst is affected by the absence of active ingredients. Moreover, the combustion reaction of the chlorine-containing volatile organic compound mainly occurs on the gamma-alumina support layer, part of chlorine can be deposited on the surface of the catalyst in the reaction process to form Al-Cl bonding with Al, and the catalyst is prevented from being inactivated due to the adsorption and activation of the chlorine-containing volatile organic compound. Therefore, the development of a catalyst with high structural stability and high activity is a technical problem which needs to be solved urgently at present.
Disclosure of Invention
In view of the defects in the prior art, the first object of the present invention is to provide a catalyst for catalytic combustion of chlorine-containing volatile organic compounds, which has the advantages of high thermal stability and high activity, and can effectively improve the catalytic combustion efficiency of chlorine-containing volatile organic compounds.
The second object of the present invention is to provide a method for preparing a catalyst for catalytic combustion of chlorine-containing volatile organic compounds, which is easy and convenient to handle and can stably and firmly embed a noble metal active component in a porous alumina layer.
In order to achieve the first object, the invention provides the following technical scheme:
a catalyst for catalytic combustion of chlorine-containing volatile organic compounds comprises a ceramic matrix, a gamma-alumina oxide layer and a noble metal active component; the precursor solution of the gamma-alumina support layer is coated on the ceramic substrate by an electrostatic spinning method, and the gamma-alumina support layer formed by spraying has a long nano-fiber structure; the noble metal active component is loaded on the outer surface of the long fiber structure of the gamma-alumina carrier layer through an electrophoresis effect.
By adopting the technical scheme, in the application, the precursor solution of the gamma-alumina carrier layer can be rapidly and firmly combined on the ceramic substrate by an electrostatic spinning method to form stable ionic bonding, and on the other hand, the bonding of Cl and Al can be effectively reduced, and the specific surface area of the precursor solution is far larger than that of a catalytic material coated by a common method; then the noble metal active component is matched and stably fixed on the surface of the nano fiber through the electrophoresis effect, so that the high-temperature sintering growth of the nano fiber can be prevented; therefore, the prepared catalyst has the characteristics of high structural stability and high activity, and is beneficial to improving the adsorption and activation of the catalyst on the chlorine-containing volatile organic compounds, so that the CVOCs can be subjected to catalytic treatment with high selectivity.
Furthermore, the high-voltage power supply is a direct-current positive power supply superposed with fundamental waves in the nanofiber spinning process;
further, in the spinning process, the voltage range is 5-25kV, and the jet flow is 0.01-2 mL/min;
further, the thickness of the gamma-alumina support layer is 0.1-0.5 mm.
Further, the porosity of the gamma-alumina support layer is 70-90%.
Further, the length-diameter ratio of the nano-fibers in the gamma-alumina carrier layer is 50-200: 1.
by adopting the technical scheme, when the thickness of the gamma-alumina carrier layer is 0.1-0.5mm, the porosity is 70-90%, and the length-diameter ratio of the nano-fiber is 50-200: 1, the noble metal active component can be stably loaded on the surface of the gamma-alumina nano-fiber carrier, so that the two can fully exert respective effects, and the catalytic effect can be obviously improved.
Further, the loading amount of the noble metal active component is 0.5-4 wt% of the gamma-alumina carrier layer.
By adopting the technical scheme, when the loading amount of the noble metal active component is lower than 0.5%, the catalytic efficiency is low, and a certain amount of Cl is still deposited on the surface of the catalyst to form Al-Cl bonding with Al, so that the halogen poisoning of the catalyst is caused and the service life of the catalyst is shortened. When the loading of the noble metal active component is higher than 4%, the cost of the catalyst is greatly increased, the economic practicability is reduced, and the catalytic effect of the catalyst tends to increase first and then decrease along with the increase of the using amount of the noble metal active component. Therefore, a loading of 0.5 to 4% is preferred.
Further, the noble metal active component consists of noble metal and hetero metal, and the mole ratio of noble metal/hetero metal is (12-15): (5-6).
By adopting the technical scheme, the mixed metal is added into the noble metal according to the molar ratio, so that the excellent catalytic effect of the catalyst can be ensured, and the using amount of the noble metal can be reduced as much as possible, thereby reducing the production cost of the catalyst.
Further, the noble metal is Pt or a mixture of Pt and one or more of Pd, Rh and Au.
Further, the mixed metal is one or a mixture of more of Fe, Ni, Cr, Bi and Mn.
Further, in the noble metal active component, the noble metal is a mixture of Pt and Pd, the hetero metal is Mn, and the molar ratio of Pt/Pd/Mn is 8:5: 6.
By adopting the technical scheme, Pt, Pd, Rh and Au are common noble metals, and when one or a mixture of more of Fe, Ni, Cr, Bi and Mn is doped into the noble metals, the oxidizing capability of the noble metals is ensured to be proper, so that more Cl is converted into HCl, and the noble metals have excellent halogen poisoning resistance and durability. Among them, when the noble metal active component is Pt/Pd/Mn in a molar ratio of 8:5:6, the performance thereof is remarkably superior to that of other compositions, and thus it is preferable.
In order to achieve the second object, the invention provides the following technical scheme:
a preparation method of a catalyst for catalytic combustion of chlorine-containing volatile organic compounds comprises the following steps:
① preparation of spin dope
Dissolving a proper amount of guar gum in deionized water to prepare spinning dispersion liquid with the guar gum concentration of 20 wt%, putting organic aluminum or pseudo-boehmite into the dispersion liquid, and uniformly stirring to obtain spinning glue liquid with the solid content of 40-50%;
② spinning and shaping of gamma-alumina carrier layer
Injecting spinning glue solution into electrostatic spinning equipment, respectively communicating an aluminum foil and a nozzle of the electrostatic spinning equipment with a positive electrode and a negative electrode of a power supply, placing a ceramic matrix between the aluminum foil and the nozzle, controlling outlet flow by using a pressure pump of the electrostatic spinning equipment, ejecting the spinning glue solution from the nozzle at an ejection flow of 0.01-2mL/min in a high-voltage direct-current electric field of 5-25kV, receiving the ejected glue solution to the ceramic matrix, and drying to form a gamma-alumina oxide layer with a nano long fiber structure;
③ preparation of electrophoresis glue solution
Dissolving a proper amount of guar gum in deionized water to prepare electrophoresis dispersion liquid with the concentration of 10 wt%, putting noble metal salts into the electrophoresis dispersion liquid, and uniformly stirring to obtain electrophoresis glue liquid with the solid content of 20-30%;
④, loading of noble metal active component
Immersing the ceramic substrate coated with the gamma-alumina carrier layer and the copper rod into an electrophoresis glue solution, taking the ceramic substrate as a negative electrode and the copper rod as a positive electrode, simultaneously carrying out ultrasonic oscillation, gathering the noble metal active component in the gamma-alumina carrier layer of the ceramic substrate by utilizing the electrophoresis effect, taking out the ceramic substrate, and calcining at the temperature of 300-500 ℃ for 15-20min to obtain the final catalyst.
By adopting the technical scheme, the guar gum is a safe and harmless thickening agent, is used as a matrix for electrostatic spinning and electrophoresis in the application, and is beneficial to ensuring the stability of the active components of the organic aluminum or the pseudo-boehmite and the precious metal, and promoting the dispersion of the active components to be uniform and have certain fluidity. In the spinning forming process of the gamma-alumina carrier layer, the content of guar gum is high, so that the prepared spinning glue solution can be smoothly subjected to electrostatic spinning; during the electrophoresis of the noble metal active component, the content of guar gum is obviously reduced, which is beneficial to the rapid loading of the noble metal active component in the gamma-alumina carrier layer; in the period, the ultrasonic oscillation can effectively reduce the sedimentation of the noble metal active component on one hand, and can promote the noble metal active component with low load firmness to drop in the gamma-alumina carrier layer on the other hand, thereby ensuring that the noble metal active component loaded in the gamma-alumina carrier layer has good structural stability and the stability of the catalytic effect of the catalyst.
In conclusion, the invention has the following beneficial effects:
1. according to the method, the gamma-alumina carrier layer is firmly combined on the ceramic substrate by using an electrostatic spinning method, and the precious metal active component is stably loaded on the outer surface of the long fiber structure of the gamma-alumina carrier layer by using an electrophoresis effect, so that the prepared catalyst has the characteristics of high structural stability, high activity and high selectivity;
2. the noble metal active component consists of noble metal and mixed metal, so that the excellent catalytic effect of the catalyst is ensured, and the using amount of the noble metal is reduced as much as possible, thereby reducing the production cost of the catalyst;
3. according to the preparation method, the thickening performance of guar gum is used as a matrix for electrostatic spinning and electrophoresis, so that the stability of gamma-alumina and precious metal active components is guaranteed, and the gamma-alumina and precious metal active components are dispersed uniformly and have certain fluidity.
Drawings
FIG. 1 is a diagram of a process for preparing a catalyst of the present application.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
1. Examples of the embodiments
1.1, example 1
A catalyst for catalytic combustion of volatile organic compounds containing chlorine is composed of ceramic matrix, gamma-alumina carrier layer and noble metal as active component. Wherein the ceramic substrate is a silicon carbide wafer with the thickness of 1 mm. The gamma-alumina carrier layer is coated on the outer side of the ceramic substrate and has a long nanofiber structure, the thickness of the gamma-alumina carrier layer is 0.2mm, the porosity is 80%, and the length-diameter ratio of nanofibers is 100: 1. the gamma-alumina support layer comprises trialkylaluminum, and the trialkylaluminum is coated on the ceramic substrate by an electrospinning method. The noble metal active component consists of noble metal and mixed metal, and is loaded in the crystal structure of the gamma-alumina carrier layer through an electrophoresis effect, wherein the loading amount is 2%. The noble metal in this example was a mixture of Pt and Pd, the hetero-metal was Mn, and the Pt/Pd/Mn molar ratio was 8:5: 6.
The preparation method of the catalyst for catalytic combustion of the chlorine-containing volatile organic compounds is shown in figure 1 and comprises the following steps:
① preparation of spin dope
Dissolving a proper amount of guar gum in deionized water to prepare spinning dispersion liquid with the concentration of 20 wt%, putting trialkyl aluminum (300 meshes) into the dispersion liquid, and uniformly stirring to obtain spinning glue liquid with the solid content of 40%;
② spinning and shaping of gamma-alumina carrier layer
Injecting spinning glue solution into electrostatic spinning equipment, respectively communicating an aluminum foil and a nozzle of the electrostatic spinning equipment with a positive electrode and a negative electrode of a high-voltage power supply, placing a ceramic substrate between the aluminum foil and the nozzle, controlling outlet flow by using a pressure pump of the electrostatic spinning equipment, setting a high-voltage electrostatic field to be 20kV, and setting the distance between a gamma-alumina oxide layer on the ceramic substrate and the nozzle to be 15cm, under the action of the pressure pump and the electric field of the electrostatic spinning equipment, spraying the spinning glue solution from the nozzle at the spraying flow of 0.5mL/min to be received on the ceramic substrate, and drying at 85 ℃ for 2h to form the gamma-alumina oxide layer with a nano long fiber structure;
③ preparation of electrophoresis glue solution
Dissolving a proper amount of guar gum in water to prepare electrophoresis dispersion liquid with the concentration of 10 wt%, putting noble metal active components into the electrophoresis dispersion liquid, and uniformly stirring to obtain electrophoresis glue liquid with the solid content of 25%;
④, loading of noble metal active component
Immersing the ceramic substrate coated with the gamma-alumina carrier layer and a copper rod into an electrophoresis glue solution, wherein the ceramic substrate is used as a negative electrode, the copper rod is used as a positive electrode, the voltage is set to be 10V, the current is set to be 2.5A, the electrolytic oxidation time is set to be 4h, simultaneously along with ultrasonic oscillation, the precious metal active component is gathered in the gamma-alumina carrier layer of the ceramic substrate by utilizing the electrophoresis effect, taking out the ceramic substrate, and calcining for 18min at the temperature of 350 ℃ to obtain the final catalyst.
The reagents are all commercial products, and the prepared catalyst is less influenced by specifications of different manufacturers, so that the sources of the reagents are not further developed.
1.2, examples 2 to 6
Examples 2-6 the catalyst parameters were adjusted based on the procedure of example 1, see table one below.
TABLE A parameter Table for the catalysts of examples 1-6
Figure BDA0002239932570000061
Figure BDA0002239932570000071
1.3, example 7
Example 7 in addition to the method of example 1, trialkylaluminum was replaced with a common alumina powder (300 mesh).
2. Comparative example
2.1, comparative example 1
In the method technology of the embodiment 1, the gamma-alumina carrier layer is obtained by directly coating spinning glue solution on a ceramic substrate and calcining.
2.2 comparative example 2
This comparative example is based on the procedure of example 1, the noble metal active component of the present application being supported on a gamma-alumina support layer by calcination. The method specifically comprises the following steps: PdCl2、H2PtCl6·6H2O and MnCl2Dissolving Pt, Pd, Mn, 8:5:6 in deionized water to form an active component impregnating solution with the weight concentration of 10%, immersing the ceramic substrate coated with the gamma-alumina oxide layer in the active component impregnating solution for 20min, taking out, drying at 120 ℃ for 3H and roasting at 500 ℃ for 3H in an air atmosphere, and finally, roasting in H2/N2Atmosphere (H)2/N25:95, V/V), reduction at 200 ℃ for 4h gave the final catalyst.
3. Performance testing
The catalysts of examples 1-7 and comparative examples 1-2 were used for chlorine-containing voc catalytic combustion and tested for their performance on methyl chloride (DCM) or Vinyl Chloride (VC) catalytic combustion by the following test methods:
3.1 structural stability
And observing whether the gamma-alumina carrier layer on the ceramic substrate and the noble metal active component on the gamma-alumina carrier layer crack and fall off or not by using an electron microscope.
3.2 catalytic efficiency
The flat catalyst sample was cut to 4mm2The chips were uniformly mixed with silica sand (50 mesh) and then packed in a silica reaction tube having an inner diameter of 10 mm. Introducing nitrogen into a methyl chloride (DCM) or Vinyl Chloride (VC) saturated evaporator at a constant temperature, and regulating the generation concentration of the methyl chloride (DCM) or the Vinyl Chloride (VC) by controlling the temperature of the saturated evaporator. Nitrogen with methyl chloride (DCM) or Vinyl Chloride (VC)Mixing with oxygen, introducing into a quartz reaction tube filled with a catalyst, and controlling the reaction temperature by a thermocouple arranged in the center of a catalyst bed layer;
the composition of 120mL/min inlet mixture was controlled to 900ppm, DCM/20%, O2(V%)/N2The F/w of the reaction was set at 25000 mL/(h.g) (the mass of the ceramic matrix was not included in the calculation of the mass of the catalyst). The gas concentrations before and after the reaction were analyzed by an on-line gas chromatography equipped with an ECD detector (G-3900B column: CP-Sil 8CB 0.53 mm. times.30 m, Toshiba, Japan). And introducing HCl in the outlet gas into NaOH aqueous solution for bubbling absorption, and carrying out quantitative analysis by a titration method. Molecular chlorine (Cl) produced2) Absorbing with 0.1N KI solution, and adding 0.1N Na2SO3Quantitative analysis was performed by iodometry.
The test results are shown in table two below:
TABLE II test results of examples 1-7 and comparative examples 1-2
Figure BDA0002239932570000081
Figure BDA0002239932570000091
By comparing the results of the tests of examples 1-3 and examples 4-6 with each other, it can be seen that the test results of examples 1-3 are closer, and that the CH of examples 1-3 increases to 350 ℃ when the temperature rises2Cl2Conversion was over 95%, better than over 93% CH for examples 4-62Cl2Conversion, in addition, when the temperature is raised to 450 ℃, CH of the present application2Cl2Can achieve complete conversion, and thus the catalyst of the present application has excellent catalytic effect. Except for CH2Cl2Conversion, other parameters indicating catalytic efficiency, e.g. CH3Cl selectivity, HCl selectivity, Cl2The selectivity and the mass balance ratio of Cl element are lower than those of examples 1-3.
Therefore, when the thickness of the gamma-alumina carrier layer is 0.1-0.5mm, the porosity is 70-90%, and the length-diameter ratio of the nano-fiber is 50-200: 1; the loading amount of the noble metal active component is 0.5-4 wt% of the gamma-alumina carrier layer; the noble metal active component consists of noble metal and hetero metal, and the mole ratio of the noble metal to the hetero metal is (12-15): (5-6) ", the catalyst obtained therefrom has more excellent structural stability and catalytic effect. Of examples 1 to 6, examples 1 to 3 are preferred examples.
Comparing the test results of example 1 and example 7, it can be seen that the use of organoaluminum or pseudo-boehmite according to the present application can effectively improve the structural stability and catalytic efficiency of the catalyst.
Comparing the test results of example 1 with those of comparative examples 1 to 2, it can be seen that the catalyst prepared by the electrospinning method and the electrophoresis effect according to the present application has high structural stability and high activity.
The present embodiment is only for explaining the present invention, and it is not limited to the present invention, and those skilled in the art can make modifications of the present embodiment without inventive contribution as needed after reading the present specification, but all of them are protected by patent law within the scope of the claims of the present invention.

Claims (9)

1. A catalyst for catalytic combustion of chlorine-containing volatile organic compounds comprises a ceramic matrix, a gamma-alumina oxide layer and a noble metal active component; the preparation method is characterized in that the precursor solution of the gamma-alumina carrier layer is coated on the ceramic substrate by an electrostatic spinning method, and the gamma-alumina carrier layer formed by spraying has a microstructure of nano long fibers; the noble metal active component is loaded on the outer surface of the long fiber structure of the gamma-alumina carrier layer through an electrophoresis effect.
2. The catalyst for catalytic combustion of chlorine-containing volatile organic compounds according to claim 1, wherein the thickness of the γ -alumina support layer is 0.1-0.5 mm.
3. The catalyst for catalytic combustion of chlorinated volatile organic compounds according to claim 1, wherein the γ -alumina support layer has a porosity of 70-90%.
4. The catalyst for catalytic combustion of chlorine-containing volatile organic compounds according to claim 1, wherein the loading of the metal active component is 0.5-4 wt% of the γ -alumina support layer.
5. The catalyst for the catalytic combustion of chlorine-containing volatile organic compounds according to claim 1, wherein the noble metal active component consists of noble metals and transition metals, and the molar ratio of noble metal/transition metal is (12-15): (5-6).
6. The catalyst for catalytic combustion of chlorine-containing volatile organic compounds according to claim 5, wherein the noble metal is Pt or a mixture of Pt and one or more of Pd, Rh and Au.
7. The catalyst for catalytic combustion of chlorine-containing volatile organic compounds according to claim 5, wherein the hetero-metal is one or a mixture of Fe, Ni, Cr, Bi and Mn.
8. The catalyst for catalytic combustion of chlorine-containing volatile organic compounds according to claim 5, wherein in the noble metal active component, the noble metal is a mixture of Pt and Pd, the hetero metal is Mn, and the molar ratio of Pt/Pd/Mn is 8:5: 6.
9. The method for preparing the catalyst for the catalytic combustion of chlorine-containing volatile organic compounds according to any of claims 1 to 8, comprising the following steps:
① preparation of spin dope
Dissolving a proper amount of guar gum in deionized water to prepare spinning dispersion liquid with the guar gum concentration of 20 wt%, putting organic aluminum or pseudo-boehmite into the dispersion liquid, and uniformly stirring to obtain spinning glue liquid with the solid content of 40-50%;
② spinning and shaping of gamma-alumina carrier layer
Injecting spinning glue solution into electrostatic spinning equipment, respectively communicating an aluminum foil and a nozzle of the electrostatic spinning equipment with a positive electrode and a negative electrode of a power supply, placing a ceramic matrix between the aluminum foil and the nozzle, controlling outlet flow by using a pressure pump of the electrostatic spinning equipment, spraying the spinning glue solution from the nozzle to the ceramic matrix in a high-voltage direct-current electric field of 20kV, and drying to form a gamma-alumina support layer with a nano long fiber structure;
③ preparation of electrophoresis glue solution
Dissolving a proper amount of guar gum in deionized water to prepare electrophoresis dispersion liquid with the concentration of 10 wt%, putting noble metal salts into the electrophoresis dispersion liquid, and uniformly stirring to obtain electrophoresis glue liquid with the solid content of 20-30%;
④, loading of noble metal active component
Immersing the ceramic substrate coated with the gamma-alumina carrier layer and the copper rod into an electrophoresis glue solution, taking the ceramic substrate as a negative electrode and the copper rod as a positive electrode, simultaneously carrying out ultrasonic oscillation, gathering the noble metal active component in the gamma-alumina carrier layer of the ceramic substrate by utilizing the electrophoresis effect, taking out the ceramic substrate, and calcining at the temperature of 300-500 ℃ for 15-20min to obtain the final catalyst.
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