Activated carbon supported palladium catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of solid waste recovery, and particularly discloses an activated carbon supported palladium catalyst as well as a preparation method and application thereof. According to the method, a mixture of a waste circuit board nonmetal component and a waste three-way catalyst is sequentially subjected to low-temperature pyrolysis detoxification, medium-high-temperature carbonization, high-temperature activation and ultrahigh-temperature gasification to prepare the activated carbon supported palladium catalyst (Pd / AC). According to the method disclosed by the invention, the prepared Pd / AC catalyst has good catalytic oxidation and catalytic dehydrogenation activity; and moreover, non-metal components of the waste circuit board can be subjected to debromination safety treatment, and the recycling efficiency of platinum group metals in the waste three-way catalyst is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of solid waste recycling, and in particular relates to an activated carbon-supported palladium catalyst and a preparation method and application thereof. Background Art

[0002] With the massive generation of electronic waste, the amount of waste circuit boards has also increased dramatically. Waste circuit boards generally include metals such as copper and non-metallic components such as glass fiber, resin, and bromine-containing flame retardants. The metal components are highly valuable and can be efficiently recycled through physical separation. However, the non-metallic components in crushed waste circuit boards are stored in large quantities due to their low value and complex composition. The brominated flame retardants contained in them can migrate to the environmental medium during the storage process, posing a huge threat to human health and the environment. Therefore, the recycling and disposal of non-metallic components of waste circuit boards urgently requires safe detoxification and high-value reuse technologies. At present, research on the recovery of non-metallic components of waste circuit boards includes physical recovery methods, chemical decomposition methods, and thermal treatment methods that use them as fillers. The safety of using them directly as fillers in the physical recovery method is difficult to guarantee, and the chemical decomposition method has high costs and difficulty in subsequent treatment of waste liquid. The thermal treatment method mainly uses high-temperature (700-800℃) pyrolysis, which has a high yield of pyrolysis oil and gas, complex components, and contains a variety of brominated organic pollutants, making it difficult to use them later. The main component of the pyrolysis residue is charcoal, with low economic benefits.

[0003] Three-way catalysts are generally used for automobile exhaust treatment, which can purify carbon monoxide, hydrocarbons and nitrogen oxides in automobile exhaust. Such catalysts generally include a carrier (such as ceramics) and a catalyst coating attached to the carrier containing one or more platinum group metals (commonly used Pt, Pd, Rh) as catalytic active materials. The three-way catalyst has a certain safe life. After the service life is exceeded, the catalyst will be no longer used after failure or catalytic efficiency is reduced. This part of the catalyst is called a waste three-way catalyst. The global reserves of platinum group metals are scarce. According to statistics from the United States Geological Survey, the proven reserves are only 69,000 tons. More than 65% of platinum group metals are used in the production of three-way catalysts. At the same time, the annual output of scrapped three-way catalysts in my country is as high as 200,000 tons. Therefore, waste three-way catalysts are important secondary resources of platinum group metals. The main methods for recovering platinum group metals from waste three-way catalysts are pyrometallurgy, hydrometallurgy and bioleaching. Pyrometallurgy can capture platinum group metals at a high temperature of over 1000°C by adding capture agents such as copper and iron, and the resulting alloy products need to be further purified. Hydrometallurgy dissolves the spent three-way catalyst by adding hydrochloric acid (containing oxidants), cyanide or halide, and then collects platinum group metals from the leaching solution. However, the waste liquid generated during the hydrometallurgical process poses a huge threat to the environment. Bioleaching is a relatively green method that dissolves the platinum group metals in the spent three-way catalyst through cyanide produced by cyanogenic microorganisms, but the low efficiency of bioleaching limits the development of its industrial application. Therefore, the road to recovering and reusing platinum group metals from spent three-way catalysts is long and difficult.

[0004] At present, in view of the defects in the recycling technology of non-metallic components of waste circuit boards and waste three-way catalysts, it is urgently necessary to develop a green recycling and high-value resource technology for non-metallic components of waste circuit boards and waste three-way catalysts. Summary of the invention

[0005] In view of the problems involved in the above-mentioned prior art, such as the difficulty in safely disposing of non-metallic components of waste circuit boards by debromination, the low value of recovered products and the low efficiency of recycling platinum group metals in waste three-way catalysts, the present invention will provide an activated carbon-supported palladium catalyst and its preparation method and application.

[0006] To achieve the above purpose, the following technical solutions are specifically included:

[0007] In a first aspect, the present invention provides a method for preparing an activated carbon-supported palladium catalyst, comprising the following steps:

[0008] A mixture of waste three-way catalyst and non-metallic components of waste circuit boards is subjected to pyrolysis treatment at a first temperature, carbonization treatment at a second temperature, activation treatment at a third temperature, and gasification treatment at a fourth temperature in sequence, and then separated to obtain an activated carbon-supported palladium catalyst; the waste three-way catalyst contains palladium elements, and the non-metallic components of waste circuit boards contain carbon elements; the first temperature is greater than 200°C, the fourth temperature is greater than 1100°C, and the fourth temperature is greater than the third temperature, the second temperature is greater than the first temperature.

[0009] The method of the present invention is to prepare an activated carbon supported palladium catalyst (Pd / AC) catalyst by sequentially subjecting a mixture of non-metallic components of waste circuit boards and waste three-way catalysts to low-temperature thermal detoxification, medium-high temperature carbonization, high-temperature activation, and ultra-high temperature gasification in four stages. The method not only enables the prepared Pd / AC catalyst to have good catalytic oxidation and catalytic dehydrogenation activity; but also enables the non-metallic components of waste circuit boards to achieve safe debromination disposal, and improves the recycling efficiency of platinum group metals in non-metallic components of waste circuit boards and waste three-way catalysts. At the same time, the method of the present invention is simple and convenient, does not require the addition of chemical reagents such as acids and alkalis, avoids secondary pollution, realizes the green recycling and high-value resource utilization of non-metallic components of waste circuit boards and waste three-way catalysts, and helps my country's comprehensive green transformation of economic and social development. In addition, the Pd / AC catalyst prepared by the method of the present invention is a material with good catalytic oxidation and catalytic dehydrogenation activity, which can be applied to pollution prevention and control such as volatile organic compounds (VOCs) treatment, hydrogen storage hydrogen release, and new energy fields, has a high application value, and can help my country's comprehensive green transformation of economic and social development.

[0010] Specifically, firstly, the platinum group metal Pd in ​​the waste three-way catalyst has a strong affinity for halogens, and can participate in the co-pyrolysis catalytic debromination reaction of the non-metallic components of waste circuit boards, thereby realizing the safe and efficient detoxification disposal of the non-metallic components of waste circuit boards; secondly, after the pyrolysis residue of the non-metallic components of the waste circuit boards is carbonized, the main component is carbon, which can be converted into activated carbon after activation treatment; finally, during the high-temperature gasification treatment process, the platinum group metal Pd in ​​the waste three-way catalyst can be gasified and migrated to the pores of the activated carbon, thereby obtaining an activated carbon-loaded palladium (Pd / AC) catalyst.

[0011] Preferably, the waste three-way catalyst is further subjected to crushing treatment and ball milling treatment, which can expose the wrapped Pd again, thereby reactivating the waste three-way catalyst and improving its catalytic effect.

[0012] Preferably, the average particle size of the spent three-way catalyst is less than 600 nm.

[0013] Preferably, the mass ratio of the waste three-way catalyst to the non-metallic components of the waste circuit boards is 1:(1-2).

[0014] Preferably, the first temperature is 250-300° C., the pyrolysis treatment time is 15-45 min, and the pyrolysis treatment is performed under vacuum, and the vacuum degree of the vacuum is less than 150 Pa.

[0015] Preferably, the second temperature is 450-700° C., the carbonization treatment time is 15-45 min, and the carbonization treatment is performed under vacuum, and the vacuum degree of the vacuum is less than 150 Pa.

[0016] Preferably, the third temperature is 800-1000° C., the activation treatment time is 30-60 min, and the activation treatment is performed in an atmosphere containing oxygen.

[0017] Preferably, the fourth temperature is 1190-1300° C., the time of the gasification treatment is 30-60 min, and the gasification treatment is performed under vacuum, and the vacuum degree of the vacuum is <5 Pa.

[0018] Preferably, the heating rate of heating to the first temperature and / or the second temperature and / or the third temperature and / or the fourth temperature is 5-10° C. / min.

[0019] Preferably, the separation comprises separation by photoelectric sorting.

[0020] The waste three-way catalyst includes a carrier, which can be effectively separated from the produced activated carbon-supported palladium (Pd / AC) catalyst by photoelectric separation.

[0021] In a second aspect, the present invention provides an activated carbon-supported palladium catalyst prepared by the preparation method of the activated carbon-supported palladium catalyst.

[0022] In a third aspect, the present invention provides an application of the activated carbon-supported palladium catalyst in the dehydrogenation reaction of dodecahydro-N-ethylcarbazole.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The method of the present invention prepares a Pd / AC catalyst by subjecting a mixture of non-metallic components of waste circuit boards and waste three-way catalysts to four stages of low-temperature thermal detoxification, medium-high temperature carbonization, high-temperature activation, and ultra-high temperature gasification. This method not only enables the prepared Pd / AC catalyst to have good catalytic oxidation and catalytic dehydrogenation activities, but also enables the non-metallic components of waste circuit boards to be safely disposed of by debromination, and improves the recovery efficiency of platinum group metals in waste three-way catalysts.

[0025] (2) The method of the present invention is simple and convenient, does not require the addition of chemical reagents such as acid and alkali, avoids secondary pollution, and realizes the green recycling and high-value resource utilization of non-metallic components of waste circuit boards and waste three-way catalysts, thus contributing to the comprehensive green transformation of my country's economic and social development.

[0026] (3) The Pd / AC catalyst prepared by the method of the present invention is a material with good catalytic oxidation and catalytic dehydrogenation activity, which can be applied to pollution prevention and control such as volatile organic compounds (VOCs) control, hydrogen release from hydrogen storage bodies, and new energy fields. It has high application value and can help my country's comprehensive green transformation of economic and social development. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The present invention is a flow chart of the preparation of the activated carbon supported palladium catalyst. DETAILED DESCRIPTION

[0028] In order to better illustrate the purpose, technical scheme and advantages of the present invention, the present invention will be further described below through specific examples. The test methods used in the examples and / or comparative examples are conventional methods unless otherwise specified; the materials, reagents, etc. used can be obtained from commercial channels unless otherwise specified.

[0029] The "non-metallic components of waste circuit boards" referred to herein include bromine-containing flame retardants, and may also include non-metallic components such as glass fiber, resin, and some impurities that cannot be excluded, such as impure copper (content less than 5wt.%), solder (content less than 0.5wt.%), etc. The non-metallic components of waste circuit boards used in the following examples and comparative examples are all the same, which are obtained by physically separating the metals from the substrates of the components removed from the waste circuit boards after crushing, and are mainly composed of phenolic resin, epoxy resin, brominated flame retardant, curing agent, and other components. The non-metallic component samples of waste circuit boards used in the following examples and comparative examples are particles with an average particle size of 1-2mm and a bromine content of 3.22wt.%.

[0030] The three-way catalyst carrier is usually processed into a honeycomb shape, and then the carrier is filled with a coating containing platinum group metals. The common carrier of the three-way catalyst is cordierite (2MgO·2Al 2 O 3 5SiO 2 ), in addition to the main components of cordierite, Mg, Al, Si, and O, the three-way catalyst also contains CeO 2 、ZrO 2The "waste three-way catalyst" referred to herein is a discarded, old or scrapped three-way catalyst. The waste three-way catalysts used in the following examples and comparative examples are all the same, which are three-way catalysts scrapped from automobile exhaust outlets, and include a honeycomb cordierite carrier, CeO2 loaded on the carrier, 2 、ZrO 2 And the Pd element component. The Pd element content in the waste three-way catalyst was measured by ICP-MS and was found to be 154.19 mg / kg.

[0031] Example 1

[0032] A method for preparing an activated carbon-supported palladium catalyst comprises the following steps:

[0033] S1. Pre-treating the waste three-way catalyst by crushing and ball milling to obtain waste three-way catalyst powder, wherein the average particle size of the powder is less than 600 nm;

[0034] S2. The waste three-way catalyst powder and the non-metallic components of the waste circuit board are fully mixed in a mass ratio of 1:2 and placed in a corundum crucible. The crucible is placed in a tubular pyrolysis furnace connected to a vacuum pump to perform a four-step gradient temperature increase to prepare a Pd / AC catalyst:

[0035] (1) Low-temperature detoxification process: the air inlet valve was closed, the vacuum pump was turned on, the vacuum degree was controlled to be 100 Pa, the temperature was raised from room temperature to a first temperature of 260°C at a heating rate of 8°C / min, and the temperature was kept at this temperature for 30 min. The debromination effect of the non-metallic components was tested, and the debromination rate reached 99.95%;

[0036] (2) Medium-high temperature carbonization process: close the air inlet valve, start the vacuum pump, control the vacuum degree to 100 Pa, continue to heat up to the second temperature of 700 °C at a heating rate of 8 °C / min, and stay at this temperature for 30 min;

[0037] (3) High temperature activation process: the air inlet valve is opened, the vacuum pump is turned on, air is pumped into the system, and the temperature is continued to rise to the third temperature of 800°C at a heating rate of 8°C / min, and stay at this temperature for 30 min;

[0038] (4) Ultra-high temperature gasification process: the air inlet valve is closed, the vacuum pump is turned on, the vacuum degree is adjusted to be lower than 1 Pa, the temperature is continued to rise to the fourth temperature of 1190°C at a heating rate of 8°C / min, the vacuum pump is turned off, and the temperature is kept at this temperature for 30 min;

[0039] S3. The Pd / AC catalyst (black) is separated from the Pd-removed spent three-way catalyst carrier powder (milky white) by using the airflow of photoelectric separation to obtain the Pd / AC catalyst.

[0040] Example 2

[0041] The present embodiment is different from the embodiment 1 in that, in the present embodiment, the high temperature carbonization process is heated to a second temperature of 500° C. and stays at this temperature for 15 minutes, and the rest is the same.

[0042] Example 3

[0043] The present embodiment is different from the embodiment 1 in that the high temperature activation process of the present embodiment is heated to the third temperature of 900° C. and stays at this temperature for 60 minutes, and the rest is the same.

[0044] Example 4

[0045] The present embodiment is different from the embodiment 1 in that the ultra-high temperature gasification process of the present embodiment is heated to a fourth temperature of 1300° C. and stays at this temperature for 60 minutes, and the rest is the same.

[0046] Example 5

[0047] The present embodiment is different from the embodiment 1 in that the high temperature carbonization process in the present embodiment is heated to a second temperature of 450° C., and the rest is the same.

[0048] Example 6

[0049] The present embodiment is different from the embodiment 1 in that the high temperature activation process of the present embodiment is heated to the third temperature of 1000° C., and the rest is the same.

[0050] Comparative Example 1

[0051] The difference between this comparative example and Example 1 is that the temperature of the ultra-high temperature gasification process in this example is raised to a fourth temperature of 1100° C., and the rest is the same.

[0052] Application Examples

[0053] The catalysts prepared in the above examples and comparative examples are used for the catalytic dehydrogenation reaction of dodecahydro-N-ethylcarbazole (12H-NEC), which specifically comprises the following steps:

[0054] (1) The catalysts prepared in the above examples and comparative examples were placed in a 25 mL three-necked flask at a ratio of 0.3% of the amount of Pd element substance to the amount of 12H-NEC substance in the catalyst, and reacted at a reaction temperature of 180° C. for 6 h;

[0055] (2) Use gas chromatography to obtain the H produced by the reaction 2 Amount of substance n 1 , divided by the amount of hydrogen in 12H-NEC 0 , the hydrogen release rate (%) is obtained, that is, hydrogen release rate (%) = n 1 / n 0 ×100.

[0056] The specific surface area and Pd content of the catalysts prepared in the above examples and comparative examples were tested.

[0057] The specific surface area, Pd content and hydrogen release rate of the catalysts of the examples and comparative examples are shown in Table 1.

[0058] Table 1

[0059]

[0060]

[0061] As can be seen from the examples, the activated carbon supported palladium catalyst (Pd / AC) is prepared by subjecting the mixture of the non-metallic components of the waste circuit board and the waste three-way catalyst to four stages of low-temperature thermal detoxification, medium-high temperature carbonization, high-temperature activation and ultra-high temperature gasification. In Examples 1-6, the specific surface area of ​​Pd / AC is 300-1400m 2 / g, the Pd content is 15-55mg / kg, and the hydrogen release rate for the catalytic dehydrogenation reaction of dodecahydro-N-ethylcarbazole (12H-NEC) is 35-95%. It can be seen that the preparation method of the present invention not only makes the prepared Pd / AC catalyst have good catalytic oxidation and catalytic dehydrogenation activities; but also can achieve debromination and safe disposal of non-metallic components of waste circuit boards, and improve the recovery efficiency of platinum group metals in waste three-way catalysts.

[0062] It can be seen from Examples 1, 2 and 5 that increasing the temperature of medium-high temperature carbonization can increase the specific surface area, Pd content and hydrogen release rate of the Pd / AC catalyst.

[0063] It can be seen from Examples 1, 3 and 6 that as the temperature of high-temperature activation increases, the specific surface area, Pd content and hydrogen release rate of the Pd / AC catalyst by catalytic dehydrogenation decrease. The present invention utilizes air activation, and no additional reagents are required; during the high-temperature activation process, because oxygen is introduced, it can react with the carbonized non-metallic components to form an oxidation reaction, thereby forming a pore structure at the reaction site. When the activation temperature is high, the degree of oxidation reaction will intensify, the pores will be large in diameter and small in number (small pores will be strung together into one large pore, reducing the number of pores), compared to the multiple, tiny pores formed at a moderate degree of reaction, the specific surface area becomes smaller, and the amount of Pd that can be adsorbed after gasification is also reduced, so the hydrogen release rate also decreases. Therefore, the method of the present invention can select a high-temperature activation temperature of 800-1000°C, and further preferably 800-900°C, Pd / AC has a better catalytic effect.

[0064] It can be seen from Comparative Example 1, Example 1 and Example 4 that at a relatively low ultra-high temperature gasification temperature (1100°C), no Pd element was detected in the obtained catalyst, indicating that no Pd was loaded. As the ultra-high temperature gasification temperature increases, the specific surface area, Pd content and hydrogen release rate of the catalyst during catalytic dehydrogenation increase. When the temperature continues to increase to 1300°C, the specific surface area, Pd content and hydrogen release rate of the catalyst during catalytic dehydrogenation remain basically unchanged. Therefore, an ultra-high temperature gasification temperature of 1190-1300°C can be selected.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing an activated carbon-supported palladium catalyst, characterized in that: The steps include: The mixture of the waste three-way catalyst and the non-metallic components of the waste circuit board is subjected to a pyrolysis treatment at a first temperature, a carbonization treatment at a second temperature, an activation treatment at a third temperature, and a gasification treatment at a fourth temperature in sequence, and then separated to obtain an activated carbon-supported palladium catalyst; The waste three-way catalyst contains palladium, and the non-metallic components of the waste circuit board contain carbon; The first temperature>200° C., the fourth temperature>1100° C., the fourth temperature>the third temperature>the second temperature>the first temperature.

2. The method for preparing an activated carbon-supported palladium catalyst as claimed in claim 1, wherein The mass ratio of the waste three-way catalyst to the non-metallic components of the waste circuit board is 1:(1-2).

3. The method for preparing an activated carbon-supported palladium catalyst as claimed in claim 1, wherein The first temperature is 250-300° C., the pyrolysis treatment time is 15-45 min, and the pyrolysis treatment is performed under vacuum, and the vacuum degree of the vacuum is less than 150 Pa.

4. The method for preparing an activated carbon-supported palladium catalyst as claimed in claim 1, wherein The second temperature is 450-700° C., the carbonization treatment time is 15-45 min, and the carbonization treatment is performed under vacuum, and the vacuum degree of the vacuum is less than 150 Pa.

5. The method for preparing an activated carbon-supported palladium catalyst as claimed in claim 1, wherein The third temperature is 800-1000° C., the activation treatment time is 30-60 min, and the activation treatment is performed in an atmosphere containing oxygen.

6. The method for preparing an activated carbon-supported palladium catalyst as claimed in claim 1, wherein The fourth temperature is 1190-1300° C., the time of the gasification treatment is 30-60 min, and the gasification treatment is carried out under vacuum, and the vacuum degree of the vacuum is less than 5 Pa.

7. The method for preparing an activated carbon-supported palladium catalyst as claimed in claim 1, wherein The average particle size of the waste three-way catalyst is less than 600 nm.

8. The method for preparing an activated carbon-supported palladium catalyst as claimed in claim 1, wherein Include at least one of the following: The heating rate of heating to the first temperature and / or the second temperature and / or the third temperature and / or the fourth temperature is 5-10°C / min; The waste three-way catalyst is also subjected to crushing treatment and ball milling treatment; The separation includes separation by photoelectric sorting.

9. An activated carbon-supported palladium catalyst obtained by the method for preparing an activated carbon-supported palladium catalyst according to any one of claims 1 to 8.

10. Use of the activated carbon-supported palladium catalyst according to claim 9 in the dehydrogenation reaction of dodecahydro-N-ethylcarbazole.

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