A method for synergistically removing multi-component vocs

Abstract

The application provides a method for removing multi-component VOCs, comprising: removing VOCs from the to-be-processed gas by two catalysts arranged in sequence, the two catalysts being catalyst I and catalyst II respectively loaded with noble metal elements, and the arrangement order of the catalyst I and the catalyst II being determined in the following manner: calculating the heat of alkanes contained in the to-be-processed gas by a formula Q1=q1*V1, calculating the heat of alkenes contained in the to-be-processed gas by a formula Q2=q2*V2, when Q1<=Q2, arranging the catalyst I and the catalyst II noble metal catalysts in a first order; otherwise, when Q1>Q2, arranging the catalyst I and the catalyst II in a second order. By sequentially passing multi-component VOCs containing C6 or below alkenes through noble metal catalysts arranged in different orders, the advantages of each single-component noble metal catalyst in degrading VOCs are combined, and the degradation efficiency requirement of mixed VOCs is easily achieved. According to the heat values of each VOC in the waste gas, the noble metals in the catalysts are maximally utilized.

Description

Technical Field

[0001] This invention belongs to the field of VOCs treatment and chemical technology, specifically relating to a method for the synergistic removal of multi-component VOCs. Background Technology

[0002] Volatile organic compounds (VOCs) are a class of organic compounds with melting points below room temperature and boiling points below 200-260℃ under standard atmospheric pressure. They mainly include hydrocarbons, esters, alcohols, and benzene compounds. Anthropogenic sources of VOC emissions mainly include stationary combustion sources, roadside mobile sources, industrial process sources, and solvent use sources. They are important precursors to PM2.5 and O3 pollution, seriously endangering human health.

[0003] Current methods for VOCs treatment mainly include adsorption, absorption, condensation, membrane separation, plasma, photocatalysis, and catalytic combustion. Among these, catalytic combustion can treat medium- and low-concentration VOCs, achieving catalytic oxidation at relatively low temperatures, reducing energy consumption and emissions of secondary pollutants, and has become one of the most important technologies for eliminating VOCs.

[0004] The core of VOCs treatment lies in the selection, design, and preparation of high-performance catalysts. Noble metal catalysts are widely used due to their high catalytic activity and good thermal stability. Currently, industrial VOCs oxidation catalysts typically consist of a coating on a cordierite honeycomb ceramic substrate, using γ-Al₂O₃ as a support to load noble metal active components and additives. However, noble metals are expensive and scarce; therefore, achieving efficient utilization of noble metals while maintaining catalyst performance is of great significance.

[0005] Industrial waste gas often contains multiple VOCs. When using precious metal catalysts to treat such waste, existing technologies face challenges such as difficulty in simultaneously achieving good removal of multiple VOCs. Summary of the Invention

[0006] This invention provides a method for synergistic removal of multi-component VOCs using a combination of catalysts. When used to treat multi-component VOCs containing alkanes and alkenes with C6 or fewer carbon atoms, this method achieves high degradation efficiency for both low-carbon alkanes and olefins. Furthermore, this invention eliminates the need for complex composite noble metal catalysts, making the catalysts easier to produce. The removal of multi-component VOCs using this method also facilitates the full utilization of the noble metal activity in the catalyst.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] The first aspect of this invention provides a method for the synergistic removal of multi-component VOCs, the method comprising:

[0009] The gas to be treated is subjected to VOCs removal treatment by passing through two catalysts arranged sequentially. The two catalysts are catalyst I and catalyst II, which are respectively loaded with noble metal elements, and the noble metal elements loaded on the two are different. The noble metal elements are selected from Pt, Pd, Rh, Ru, Ag or Au.

[0010] The order of arrangement of catalyst I and catalyst II is determined as follows:

[0011] The calorific value of the alkane contained in the gas to be treated is calculated using the formula Q1 = q1 × V1, and the calorific value of the olefin contained in the gas to be treated is calculated using the formula Q2 = q2 × V2, where q1 represents the calorific value of the alkane, q2 represents the calorific value of the olefin, V1 represents the volume of the alkane, and V2 represents the volume of the olefin.

[0012] When Q1≤Q2, catalysts I and II are arranged in a first order; when Q1>Q2, catalysts I and II are arranged in a second order; wherein, the first order is Pt>Pd>Rh>Ru>Ag>Au, and the second order is Pd>Pt>Rh>Ru>Ag>Au; the noble metal elements loaded in catalyst I and catalyst II are arranged according to the determined first or second order, with the catalyst with the noble metal element ranked first being the front catalyst and the catalyst with the noble metal element ranked last being the back catalyst.

[0013] In some preferred embodiments, the noble metal elements of catalyst I and catalyst II are respectively supported on a matrix; preferably, catalyst I and catalyst II also include one or more of binders, additives and supports.

[0014] In some preferred embodiments, the loading of the noble metal element is 0.1-1.4 g / L, based on the volume of the matrix.

[0015] In some preferred embodiments, the preparation of catalyst I or catalyst II includes the following steps:

[0016] i) Pretreatment of the matrix: The matrix is ​​preheated and boiled in a 20-50 wt.% oxalic acid aqueous solution, preferably for 1-1.5 h, then cooled and soaked, preferably for 8-30 h, then taken out, rinsed with deionized water and placed in a drying oven for drying, preferably at a temperature of 80-200 °C.

[0017] ii) Preparation of noble metal catalyst: take noble metal salt, binder, additive and support and grind into slurry; immerse the matrix treated in step 1) into the slurry, preferably for 20-40 min, and then purge the air in the pores of the matrix so that the slurry is distributed on the matrix wall.

[0018] iii) Drying and calcination: After drying, preferably at a temperature of 60-420℃, the catalyst is then calcined, preferably at a temperature of 500-600℃ and for a time of 4-6 hours, to obtain the precious metal catalyst.

[0019] In some preferred embodiments, the drying in step iii) is segmented drying, and the segmented drying temperatures are, for example, 60-65℃, 90-95℃, 120-130℃, 200-210℃ and 420-430℃ respectively, and the drying times are, for example, 2min, 2min, 2min and 0.5min respectively.

[0020] In some preferred embodiments, the noble metal element is selected from Pt, Pd, Rh or Ru; preferably, the noble metal element is selected from Pt or Pd.

[0021] In some preferred embodiments, the matrix is ​​selected from cordierite honeycomb ceramics.

[0022] In some preferred embodiments, the binder is selected from boehmite, aluminum sol, or silica sol; the additive is selected from urea or concentrated nitric acid (68 wt.%).

[0023] In some preferred embodiments, the support is selected from one or more of nano-γ-Al2O3, nano-TiO2, and nano-SiO2.

[0024] In some preferred embodiments, the slurry contains 0.2-3.3% by mass of the noble metal salt, 5-25% by mass of the binder, 1.5-15% by mass of the additives, 9.2-31.4% by mass of the carrier, and 20-35% by mass of the solids.

[0025] In some preferred embodiments, the gas to be treated is derived from coal chemical gas or exhaust gas containing multi-component VOCs of alkanes and olefins with C6 or less.

[0026] The technical solution provided by this invention has the following beneficial effects:

[0027] The present invention provides a method for the synergistic removal of multi-component VOCs. This method involves sequentially passing multi-component VOCs, including low-carbon alkanes and olefins, through different combinations of single-noble-metal supported catalysts. Different noble metals exhibit varying oxidation activities for different VOCs. In this method, both catalysts used are single-component noble-metal catalysts supported on a single noble metal element. The two single-component noble-metal catalysts are combined according to the method described in this invention, combining the advantages of each catalyst in VOCs degradation. Furthermore, single-component noble-metal catalysts have better dispersibility than multi-component noble-metal catalysts, reducing the likelihood of noble metal migration and aggregation. This combination method, combined with the present invention, facilitates the simultaneous and efficient degradation of multiple VOC components in mixed VOCs. The catalyst arrangement is based on the calorific value of the low-carbon alkanes and olefins in the waste gas. Simultaneously, the heat generated by the preferentially reacting VOCs provides energy for the subsequent VOCs reactions, maximizing the utilization of the noble metals in the catalyst and achieving good VOCs treatment results while reducing catalyst volume. Meanwhile, the methods of this invention all use single precious metal catalysts, which are easier to produce in series than two-component precious metal catalysts, are less prone to alloy agglomeration, have better stability, and can be well adapted to industries such as coal chemical industry and exhaust gas industry that have multi-component VOCs pollution emissions of alkanes and olefins with C6 or less. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the catalyst arrangement in Example 1, Comparative Example 1-1, and Comparative Example 1-2 of the present invention;

[0029] Figure 2 (a) is a TEM image of the Pt catalyst in Example 1 of the present invention;

[0030] Figure 2 (b) is a TEM image of the Pd catalyst in Example 1 of the present invention;

[0031] Figure 3 These are TEM images of the mixed catalysts in Comparative Examples 1-2 of this invention;

[0032] Figure 4 This is a schematic diagram of the catalyst arrangement in Example 2, Comparative Example 2-1, and Comparative Example 2-2 of the present invention. Detailed Implementation

[0033] The present invention will be further illustrated below with specific embodiments. These embodiments are merely illustrative and do not imply that the scope of the invention is limited thereto.

[0034] Instrumentation: Aberration-corrected transmission electron microscope (JEMARM200F) was used to observe the morphology of noble metals in the catalyst, and a laboratory-built integrated catalyst evaluation device was used to evaluate the catalytic performance.

[0035] Example 1

[0036] 1) The preparation of noble metal catalysts includes the following steps:

[0037] ①Preparation of Pt catalysts

[0038] i) Pretreatment of the substrate: The 2cm×2cm×2.5cm cordierite honeycomb ceramic was preheated and boiled in a 20wt.% oxalic acid aqueous solution for 1h, then cooled and soaked for 30h. After that, it was taken out, rinsed with deionized water and placed in a drying oven for drying at 120℃.

[0039] ii) Preparation of noble metal catalyst: 0.2333 g of platinum nitrate solution (15 wt.%), 5.00 g of boehmite, 1.50 g of concentrated nitric acid, and 31.40 g of nano-γ-Al₂O₃ were weighed and added to 61.87 g of deionized water. The mixture was then ball-milled in a ball mill jar for 6 hours to form a homogeneous slurry. The slurry contained 5.0% boehmite, 1.5% concentrated nitric acid, 31.4% nano-γ-Al₂O₃, and 35% solids. The ball-milled slurry was continuously stirred. After cooling, the cordierite matrix was immersed in the slurry for 20 minutes, then removed. Air was then removed from the pores using a super air knife to ensure the slurry was evenly distributed on the matrix wall.

[0040] iii) Drying and calcination: Then, the catalyst is rapidly dried in stages at a temperature of 60-420℃ using a hot air gun (60℃ for 2 min, 90℃ for 2 min, 120℃ for 2 min, 200℃ for 2 min, and 420℃ for 0.5 min). Then, it is placed in a muffle furnace and calcined at 550℃ for 5 h to obtain an integral catalyst with a precious metal Pt content of 0.1 g / L.

[0041] ②Preparation of Pd catalysts

[0042] i) Pretreatment of the substrate: The 2cm×2cm×2.5cm cordierite honeycomb ceramic was preheated and boiled in a 20wt.% oxalic acid aqueous solution for 1h, then cooled and soaked for 30h. After that, it was taken out, rinsed with deionized water and placed in a drying oven for drying at 120℃.

[0043] ii) Preparation of noble metal catalyst: Weigh 2.10 g of palladium nitrate solution (15 wt.%), 5.00 g of pseudo-boehmite, 10.00 g of urea and 31.40 g of nano-γ-Al2O3 respectively, add them to 51.50 g of deionized water, and put them into a ball milling tank to ball mill for 12 h to form a homogeneous slurry. In the slurry, the mass content of pseudo-boehmite is 5.0%, the mass content of urea is 10.0%, the mass content of nano-γ-Al2O3 is 31.4%, and the mass content of solid substances is 35%; Take out the ball-milled slurry and stir continuously. After the slurry cools, immerse the cordierite substrate in the slurry for 20 min, then take it out, and then use a super air knife to drain the air in the pores, so that the slurry is evenly distributed on the wall of the substrate.

[0044] iii) Drying and calcination: Then use a hot air gun to quickly dry in segments at a temperature of 60 - 420 °C (dry at 60 °C for 2 min, 90 °C for 2 min, 120 °C for 2 min, 200 °C for 2 min, 420 °C for 0.5 min), and then place it in a muffle furnace and calcine at 550 °C for 5 h to obtain a monolithic catalyst with a noble metal Pd content of 0.9 g / L.

[0045] 2) Arrangement of noble metal catalyst, including the following steps:

[0046] Use the above combined noble metal catalyst to catalytically oxidize a methane (CH4) / ethylene (C2H4) mixture. The mixture contains 20 vol.% O2, the C2H4 content is 350 ppm, the CH4 content is 500 ppm, the H2O content is 5 vol.%, and the rest is air. The calorific value q1 of methane is 39.82 J / L, and the calorific value q2 of ethylene is 63.4 J / L.

[0047] a) Calculate the heat of alkanes using Q1 = q1×V1, Q1 = q1×V1 = 39.82×500×10 -6 ×V = 1.99×10 -2 V (J), calculate the heat of olefins using Q2 = q2×V2, Q2 = q2×V2 = 63.4×350×10 -6 ×V = 2.22×10 -2 V (J), where q1 represents the calorific value of the alkanes, q2 represents the calorific value of the olefins, V represents the total volume of the mixture, V1 represents the volume of the alkanes, and V2 represents the volume of the olefins;

[0048] b) Since Q1 < Q2, arrange the noble metal catalyst in the first order; The first order is Pt > Pd. Use the Pt catalyst as the front-stage catalyst and the Pd catalyst as the back-stage catalyst. The front-stage and back-stage catalysts each account for half of the total volume of the catalyst. The mixture passes through the front-stage catalyst and the back-stage catalyst in sequence for treatment.

[0049] Comparative Example 1-1

[0050] The Pd catalyst was used as the front catalyst and the Pt catalyst was used as the back catalyst. The front and back catalysts each accounted for half of the total catalyst volume. Other settings were the same as in Example 1.

[0051] Comparative Examples 1-2

[0052] ③ Preparation of mixed noble metal catalysts

[0053] The pretreatment steps for the 2cm×2cm×5cm cordierite honeycomb ceramic matrix are the same as in Example 1.

[0054] 0.1167 g of platinum nitrate solution (15 wt.%), 1.05 g of palladium nitrate solution (15 wt.%), 5.00 g of boehmite, 15.00 g of urea, and 31.4 g of nano-γ-Al₂O₃ were weighed and added to 47.43 g of deionized water. The mixture was then placed in a ball mill and milled for 12 hours to form a homogeneous slurry. The slurry contained 5.0% boehmite, 15.0% urea, 31.4% nano-γ-Al₂O₃, and 35% solids. The milled slurry was continuously stirred and cooled. The cordierite matrix was then immersed in the slurry for 20 minutes, removed, and the air in the pores was purged using a super air knife to ensure that the slurry was evenly distributed on the matrix wall.

[0055] The catalyst was then rapidly dried in stages at temperatures ranging from 60 to 420°C using a hot air gun (60°C for 2 min, 90°C for 2 min, 120°C for 2 min, 200°C for 2 min, and 420°C for 0.5 min). It was then calcined in a muffle furnace at 550°C for 5 h to obtain a monolithic catalyst with a noble metal content of 0.5 g / L, containing 0.05 g / L of Pt and 0.45 g / L of Pd, thus a Pt-Pd catalyst. The Pt-Pd catalyst was placed in a reaction bed with a volume equal to the sum of the volumes of the Pt and Pd catalysts in Example 1. The arrangement of the noble metal catalyst is as follows... Figure 1 Schematic diagram of catalyst arrangement in Example 1.

[0056] Catalysts arranged according to the three configurations described in Example 1, Comparative Example 1-1, and Comparative Example 1-2 were used to catalytically oxidize a methane (CH4) / ethylene (C2H4) mixture with the same composition as described in Example 1, with a reaction space velocity of 20,000 h⁻¹. -1 The catalytic performance of the catalyst under treatment conditions of 200-500℃ was investigated by continuous online monitoring.

[0057] Table 1 Catalyst activity in Example 1

[0058]

[0059] The olefins in the mixed gas have high calorific value, so the noble metal catalysts are arranged in the first order. In Example 1, the front-end Pt-based catalyst exhibits high activity for C2H4, resulting in rapid combustion and higher catalyst activity compared to the other two arrangements. Simultaneously, the heat released from C2H4 combustion increases the catalytic activity of CH4, making it higher than the other two catalyst arrangements. Furthermore, although the catalysts in Example 1 and Comparative Examples 1-2 contain the same amount of noble metals, the utilization rate of the noble metals is significantly improved.

[0060] TEM characterization of the catalysts in Example 1 and Comparative Example 1-1 revealed that the active components of the Pt-Pd single-component noble metal catalysts were highly dispersed, with some exhibiting monolayer dispersion. In contrast, the Pt-Pd dual-component catalyst in Comparative Example 1-2 showed uneven dispersion of the noble metal particles, with some particles being larger, resulting in poorer activity. (See also...) Figure 2 (a) is a TEM image of the Pt catalyst in Example 1; Figure 2 (b) is a TEM image of the Pd catalyst in Example 1; Figure 3 The images show TEM images of the mixed catalysts in Comparative Examples 1-2.

[0061] Example 2

[0062] 1) The preparation of noble metal catalysts includes the following steps:

[0063] ①Preparation of Pt catalysts

[0064] i) Pretreatment of the substrate: The 2cm×2cm×2.5cm cordierite honeycomb ceramic substrate was pretreated using the same method as in Example 1.

[0065] ii) Preparation of noble metal catalyst: 0.2666 g of platinum nitrate solution (15 wt.%), 15.00 g of boehmite, 10.00 g of urea, and 9.20 g of nano-γ-Al₂O₃ were weighed and added to 65.53 g of deionized water. The mixture was then ball-milled in a ball mill jar for 3 hours to form a homogeneous slurry. The slurry contained 15.0% boehmite, 10.0% urea, 9.2% nano-γ-Al₂O₃, and 20% solids. The ball-milled slurry was continuously stirred. After cooling, the cordierite matrix was immersed in the slurry for 20 minutes, then removed. Air in the pores was then removed using a super air knife to ensure the slurry was evenly distributed on the matrix wall.

[0066] iii) Drying and calcination: Then, the catalyst is rapidly dried in stages at a temperature of 60-420℃ using a hot air gun (60℃ for 2 min, 90℃ for 2 min, 120℃ for 2 min, 200℃ for 2 min, and 420℃ for 0.5 min). Then, it is placed in a muffle furnace and calcined at 500℃ for 6 h to obtain a monolithic catalyst with a Pt content of 0.2 g / L.

[0067] ②Preparation of Pd catalysts

[0068] i) Pretreatment of the substrate: The 2cm×2cm×2.5cm cordierite honeycomb ceramic substrate was pretreated using the same method as in Example 1.

[0069] ii) Preparation of noble metal catalyst: Weigh 1.0667 g of palladium nitrate solution (15 wt.%), 15.00 g of boehmite, 10.00 g of urea, and 9.2 g of nano-γ-Al2O3 and add them to 64.73 g of deionized water. Place the mixture in a ball mill jar and ball mill for 3 hours to form a uniform slurry. The mass content of boehmite in the slurry is 15.0%, the mass content of urea is 10.0%, the mass content of nano-γ-Al2O3 is 9.2%, and the mass content of solid matter is 20%. Take out the ball-milled slurry and stir continuously. After the slurry cools, immerse the cordierite matrix in the slurry for 20 minutes, then remove it. Afterward, use a super air knife to remove the air from the channels, so that the slurry is fully and uniformly distributed on the wall surface of the matrix.

[0070] iii) Drying and calcination: Then, the catalyst is rapidly dried in stages at a temperature of 60-420℃ using a hot air gun (60℃ for 2 min, 90℃ for 2 min, 120℃ for 2 min, 200℃ for 2 min, and 420℃ for 0.5 min). Then, it is placed in a muffle furnace and calcined at 500℃ for 6 h to obtain a monolithic catalyst with a precious metal Pd content of 0.8 g / L.

[0071] 2) Arrange the noble metal catalyst, including the following steps:

[0072] The above-mentioned combination of noble metal catalysts was used for the catalytic oxidation of a methane (CH4) / ethylene (C2H4) mixture. The mixture contained 20 vol.% O2, 750 ppm CH4, 250 ppm C2H4, 5 vol.% H2O, and the remainder air. The calorific value of methane, q1, was 39.82 J / L, and the calorific value of ethylene, q2, was 63.4 J / L.

[0073] a) The heat of the alkane is calculated using Q1 = q1 × V1, where Q1 = q1 × V1 = 39.82 × 750 × 10 -6 ×V=2.99×10 -2V(J), the heat of the olefin is calculated using Q2 = q2 × V2, Q2 = q2 × V2 = 63.4 × 250 × 10 -6 ×V=1.59×10 -2 V(J), where q1 represents the calorific value of the alkane, q2 represents the calorific value of the olefin, V represents the total volume of the mixture, V1 represents the volume of the alkane, and V2 represents the volume of the olefin.

[0074] b) Since Q1 > Q2, the noble metal catalysts are arranged in the second order; the second order is Pd > Pt, with Pd catalyst as the front catalyst and Pt catalyst as the back catalyst, each occupying half of the total catalyst volume. The mixed gas is treated sequentially through the front catalyst and then the back catalyst.

[0075] Comparative Example 2-1

[0076] The Pt catalyst was used as the front catalyst and the Pd catalyst was used as the back catalyst. The front and back catalysts each accounted for half of the total catalyst volume. Other settings were the same as in Example 2.

[0077] Comparative Example 2-2

[0078] ③ Preparation of mixed noble metal catalysts

[0079] The pretreatment steps for the 2cm×2cm×5cm cordierite honeycomb ceramic matrix are the same as in Example 2.

[0080] 0.1333g of platinum nitrate solution (15wt.%), 0.5333g of palladium nitrate solution (15wt.%), 15.00g of boehmite, 10.00g of urea, and 9.20g of nano-γ-Al₂O₃ were weighed and added to 65.13g of deionized water. The mixture was then placed in a ball mill and milled for 3 hours to form a homogeneous slurry. The slurry contained 15.0% boehmite, 10.0% urea, 9.2% nano-γ-Al₂O₃, and 20% solids. The milled slurry was continuously stirred and cooled. The cordierite matrix was then immersed in the slurry for 20 minutes, removed, and the air in the pores was purged using a super air knife to ensure the slurry was evenly distributed on the matrix wall.

[0081] The catalyst was then rapidly dried in stages at temperatures ranging from 60 to 420°C using a hot air gun (60°C for 2 min, 90°C for 2 min, 120°C for 2 min, 200°C for 2 min, and 420°C for 0.5 min). It was then calcined in a muffle furnace at 500°C for 6 h to obtain a monolithic catalyst with a noble metal content of 0.5 g / L, containing 0.1 g / L of Pt and 0.4 g / L of Pd, thus a Pt-Pd catalyst. The Pt-Pd catalyst was placed in a reaction bed with a volume equal to the sum of the volumes of the Pt and Pd catalysts in Example 2. The arrangement of the noble metal catalyst is as follows... Figure 4 Schematic diagram of catalyst arrangement in Example 2.

[0082] Catalysts arranged according to the three configurations described in Example 2, Comparative Example 2-1, and Comparative Example 2-2 were used to catalytically oxidize a methane (CH4) / ethylene (C2H4) mixture with the same composition as described in Example 2, with a reaction space velocity of 20,000 h⁻¹. -1 The catalytic performance of the catalyst under treatment conditions of 200-500℃ was investigated by continuous online monitoring.

[0083] Table 2 Catalyst activity in Example 2

[0084]

[0085] The mixed gas contains high-calorific-value alkanes, so the noble metal catalysts are arranged in the second order. In Example 2, the front-end Pd-based catalyst exhibits high activity for CH4, resulting in rapid combustion and higher catalyst activity compared to the other two arrangements. Simultaneously, the heat released from CH4 combustion increases the catalytic activity of C2H4, making it higher than the other two catalyst arrangements. Furthermore, although the catalysts in Example 2 and Comparative Example 2-2 contain the same amount of noble metals, the utilization rate of the noble metals is significantly improved.

[0086] Example 3

[0087] 1) The preparation of noble metal catalysts includes the following steps:

[0088] ①Preparation of Pt catalysts

[0089] i) Pretreatment of the substrate: The 2cm×2cm×2.5cm cordierite honeycomb ceramic substrate was pretreated using the same method as in Example 1.

[0090] ii) Preparation of noble metal catalyst: 0.70 g of platinum nitrate solution (15 wt.%), 20.00 g of aluminum sol (20 wt.%), 2.00 g of concentrated nitric acid, and 31.00 g of nano-γ-Al2O3 were weighed and added to 46.30 g of deionized water. The mixture was then ball-milled in a ball mill jar for 6 hours to form a homogeneous slurry. The slurry contained 20.0% aluminum sol, 2.0% concentrated nitric acid, 31.0% nano-γ-Al2O3, and 35% solids. The ball-milled slurry was continuously stirred. After cooling, the cordierite matrix was immersed in the slurry for 20 minutes, then removed. Air in the pores was then removed using a super air knife to ensure the slurry was evenly distributed on the matrix wall.

[0091] iii) Drying and calcination: Then, the catalyst is rapidly dried in stages at a temperature of 60-420℃ using a hot air gun (60℃ for 2 min, 90℃ for 2 min, 120℃ for 2 min, 200℃ for 2 min, and 420℃ for 0.5 min). Then, it is placed in a muffle furnace and calcined at 500℃ for 6 h to obtain a monolithic catalyst with a Pt content of 0.3 g / L.

[0092] ②Preparation of Rh catalysts

[0093] i) Pretreatment of the carrier: The 2cm×2cm×2.5cm cordierite honeycomb ceramic substrate was pretreated using the same method as in Example 1.

[0094] ii) Preparation of noble metal catalyst: 0.6125 g of rhodium chloride trihydrate (38.5-42.5 wt.%), 25.00 g of aluminum sol (20 wt.%), 10.00 g of urea, and 30.00 g of nano-γ-Al2O3 were weighed and added to 34.38 g of deionized water. The mixture was then placed in a ball mill and milled for 6 hours to form a uniform slurry. The slurry contained 25.0% aluminum sol, 10.0% urea, 30.0% nano-γ-Al2O3, and 35% solids. The milled slurry was continuously stirred and cooled. The cordierite matrix was then immersed in the slurry for 20 minutes, removed, and the air in the pores was purged using a super air knife to ensure the slurry was evenly distributed on the matrix wall.

[0095] iii) Drying and calcination: Then, the catalyst is rapidly dried in stages at a temperature of 60-420℃ using a hot air gun (60℃ for 2 min, 90℃ for 2 min, 120℃ for 2 min, 200℃ for 2 min, and 420℃ for 0.5 min). Then, it is placed in a muffle furnace and calcined at 500℃ for 6 h to obtain a monolithic catalyst with a noble metal Rh content of 0.7 g / L.

[0096] 2) Arranging the noble metal catalyst, including the following steps:

[0097] Using the above combined noble metal catalyst to catalytically oxidize a methane (CH4) / ethylene (C2H4) mixture gas, the mixture gas contains 20 vol.% of O2, the CH4 content is 150 ppm, the C2H4 content is 840 ppm, the H2O content is 5 vol.%, and the rest is air.

[0098] a) Calculating the heat of the alkane using Q1 = q1×V1, Q1 = q1×V1 = 39.82×150×10 -6 ×V = 0.60×10 -2 V (J), calculating the heat of the olefin using Q2 = q2×V2, Q2 = q2×V2 = 63.4×840×10 -6 ×V = 5.32×10 -2 V (J), where q1 represents the calorific value of the alkane, q2 represents the calorific value of the olefin, V represents the total volume of the mixture gas, V1 represents the volume of the alkane, and V2 represents the volume of the olefin;

[0099] b) Since Q1 < Q2, arranging the noble metal catalyst in the first order; the first order is Pt > Rh, using the Pt catalyst as the front-stage catalyst and the Rh catalyst as the rear-stage catalyst, and the front-stage and rear-stage catalysts each account for half of the total volume of the catalyst. The mixture gas passes through the front-stage catalyst and the rear-stage catalyst in sequence for treatment.

[0100] Comparative Example 3-1

[0101] Using the Rh catalyst as the front-stage catalyst and the Pt catalyst as the rear-stage catalyst, and the front-stage and rear-stage catalysts each account for half of the total volume of the catalyst. Other settings are the same as in Example 3. <00​​​​​​​​​0.3500g of platinum nitrate solution (15wt.%), 0.3062g of rhodium chloride trihydrate (38.5-42.5wt.%), 25.00g of aluminum sol (20wt.%), 15.00g of urea, and 30.00g of nano-γ-Al2O3 were weighed and added to 29.34g of deionized water. The mixture was then ball-milled in a ball mill jar for 9 hours to form a homogeneous slurry. The slurry contained 25.0% aluminum sol, 15.0% urea, 30.0% nano-γ-Al2O3, and 35% solids. The ball-milled slurry was continuously stirred and cooled. The cordierite matrix was then immersed in the slurry for 20 minutes, removed, and the air in the pores was purged using a super air knife to ensure the slurry was evenly distributed on the matrix wall.

[0106] The catalyst was then rapidly dried in stages at temperatures ranging from 60 to 420°C using a hot air gun (60°C for 2 min, 90°C for 2 min, 120°C for 2 min, 200°C for 2 min, and 420°C for 0.5 min). It was then calcined in a muffle furnace at 500°C for 6 h to obtain a monolithic catalyst with a precious metal content of 0.5 g / L, including 0.15 g / L Pt and 0.35 g / L Rh, designated as a Pt-Rh catalyst. The Pt-Rh catalyst was placed in a reaction bed with a volume equal to the sum of the volumes of the Pt and Rh catalysts in Example 3.

[0107] Catalysts arranged according to the three configurations described in Example 3, Comparative Example 3-1, and Comparative Example 3-2 were used to catalytically oxidize a methane (CH4) / ethylene (C2H4) mixture with the same composition as described in Example 3, with a reaction space velocity of 20,000 h⁻¹. -1 The catalytic performance of the catalyst under treatment conditions of 200-500℃ was investigated by continuous online monitoring.

[0108] Table 3 Catalyst activity in Example 3

[0109]

[0110] The mixed gas contains high amounts of olefins, so noble metal catalysts are arranged in the first order. In Example 3, the front-end Pt-based catalyst exhibits high activity towards C2H4, resulting in rapid combustion and higher catalyst activity compared to the other two arrangements. Simultaneously, the heat released from C2H4 combustion increases the catalytic activity of CH4, making it higher than the other two catalyst arrangements. Furthermore, although the catalysts in Example 3 and Comparative Examples 3-2 contain the same amount of noble metals, the utilization rate of noble metals is significantly improved.

[0111] Example 4

[0112] 1) The preparation of noble metal catalysts includes the following steps:

[0113] ①Preparation of Pd catalysts

[0114] i) Pretreatment of the substrate: The 2cm×2cm×2.5cm cordierite honeycomb ceramic substrate was pretreated using the same method as in Example 1.

[0115] ii) Preparation of noble metal catalyst: 3.2667 g of palladium nitrate solution (15 wt.%), 16.6667 g of silica sol (30 wt.%), 15.00 g of urea, and 30.00 g of nano-SiO2 were weighed and added to 35.0663 g of deionized water. The mixture was then ball-milled in a ball mill jar for 6 hours to form a homogeneous slurry. The slurry contained 16.7% silica sol, 15.0% urea, 30.0% nano-SiO2, and 35% solids. The ball-milled slurry was continuously stirred. After cooling, the cordierite matrix was immersed in the slurry for 20 minutes, then removed. Air was then removed from the pores using a super air knife to ensure the slurry was evenly distributed on the matrix wall.

[0116] iii) Drying and calcination: Then, the catalyst is rapidly dried in stages at a temperature of 60-420℃ using a hot air gun (60℃ for 2 min, 90℃ for 2 min, 120℃ for 2 min, 200℃ for 2 min, and 420℃ for 0.5 min). Then, it is placed in a muffle furnace and calcined at 500℃ for 6 h to obtain a monolithic catalyst with a precious metal Pd content of 1.4 g / L.

[0117] ②Preparation of Ru catalyst

[0118] i) Pretreatment of the carrier: The 2cm×2cm×2.5cm cordierite honeycomb ceramic substrate was pretreated using the same method as in Example 1.

[0119] ii) Preparation of noble metal catalyst: 0.5250 g of rhodium trichloride (35.0-42 wt.%), 16.667 g of silica sol (30 wt.%), 10.00 g of urea, and 30.00 g of nano-SiO2 were weighed and added to 42.81 g of deionized water. The mixture was then placed in a ball mill and milled for 3 hours to form a uniform slurry. The slurry contained 16.7% silica sol, 10.0% urea, 30.0% nano-SiO2, and 35% solids. The milled slurry was continuously stirred and cooled. The cordierite matrix was then immersed in the slurry for 20 minutes, removed, and the air in the pores was purged using a super air knife to ensure the slurry was evenly distributed on the matrix wall.

[0120] iii) Drying and calcination: Then, the catalyst is rapidly dried in stages at a temperature of 60-420℃ using a hot air gun (60℃ for 2 min, 90℃ for 2 min, 120℃ for 2 min, 200℃ for 2 min, and 420℃ for 0.5 min). Then, it is placed in a muffle furnace and calcined at 500℃ for 6 h to obtain a monolithic catalyst with a Ru content of 0.6 g / L.

[0121] 2) Arrange the noble metal catalyst, including the following steps:

[0122] The above-mentioned combination of noble metal catalysts was used to catalytically oxidize a methane (CH4) / ethylene (C2H4) mixture containing 20 vol.% O2, 750 ppm CH4, 250 ppm C2H4, 5 vol.% H2O, and the remainder being air.

[0123] a) The heat of the alkane is calculated using Q1 = q1 × V1, where Q1 = q1 × V1 = 39.82 × 750 × 10 -6 ×V=2.99×10 -2 V(J), the heat of the olefin is calculated using Q2 = q2 × V2, Q2 = q2 × V2 = 63.4 × 250 × 10 -6 ×V=1.59×10 -2 V(J), where q1 represents the calorific value of the alkane, q2 represents the calorific value of the olefin, V represents the total volume of the mixture, V1 represents the volume of the alkane, and V2 represents the volume of the olefin.

[0124] b) Since Q1>Q2, the noble metal catalysts are arranged in the second order; the second order is Pd>Ru, with Pd catalyst as the front catalyst and Ru catalyst as the back catalyst, each occupying half of the total catalyst volume. The mixed gas is treated sequentially through the front catalyst and then the back catalyst.

[0125] Comparative Example 4-1

[0126] The Pd catalyst was used as the front catalyst and the Ru catalyst was used as the back catalyst. The front and back catalysts each accounted for half of the total catalyst volume. Other settings were the same as in Example 4.

[0127] Comparative Example 4-2

[0128] ③ Preparation of mixed noble metal catalysts

[0129] The pretreatment steps for the 2cm×2cm×5cm cordierite honeycomb ceramic matrix are the same as in Example 4.

[0130] 1.6333 g of palladium nitrate solution (15 wt.%), 0.2625 g of ruthenium trichloride solution (35.0-42 wt.%), 16.6667 g of silica sol (30 wt.%), 15.00 g of urea, and 30.00 g of nano-SiO2 were weighed and added to 36.4375 g of deionized water. The mixture was then placed in a ball mill and milled for 9 hours to form a homogeneous slurry. The slurry contained 16.7% aluminum sol, 15.0% urea, 30.0% nano-SiO2, and 35% solids. The milled slurry was continuously stirred and cooled. The cordierite matrix was then immersed in the slurry for 20 minutes, removed, and the air in the pores was purged using a super air knife to ensure the slurry was evenly distributed on the matrix wall.

[0131] The catalyst was then rapidly dried in stages at temperatures ranging from 60 to 420°C using a hot air gun (60°C for 2 min, 90°C for 2 min, 120°C for 2 min, 200°C for 2 min, and 420°C for 0.5 min). It was then calcined in a muffle furnace at 500°C for 6 h to obtain a monolithic catalyst with a noble metal content of 1.0 g / L, containing 0.7 g / L Pd and 0.3 g / L Ru, thus forming a Pd-Ru catalyst. The Pd-Ru catalyst was placed in a reaction bed with a volume equal to the sum of the volumes of the Pd and Ru catalysts in Example 4.

[0132] Catalysts arranged according to the three configurations described in Example 4, Comparative Example 4-1, and Comparative Example 4-2 were used to catalytically oxidize a methane (CH4) / ethylene (C2H4) mixture with the same composition as described in Example 4, with a reaction space velocity of 20,000 h⁻¹. -1 The catalytic performance of the catalyst under treatment conditions of 200-500℃ was investigated by continuous online monitoring.

[0133] Table 4 Catalyst activity in Example 4

[0134]

[0135] The mixed gas contains high-calorific-value alkanes, so the noble metal catalysts are arranged in the second order. In Example 4, the front-end Pd-based catalyst exhibits high activity for CH4, resulting in rapid combustion and higher catalyst activity compared to the other two arrangements. Simultaneously, the heat released from CH4 combustion increases the catalytic activity of C2H4, making it higher than the other two catalyst arrangements. Furthermore, although the catalysts in Example 4 and Comparative Example 4-2 contain the same amount of noble metals, the utilization rate of the noble metals is significantly improved.

[0136] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for multi-component VOCs co-removal, characterized in that, The method comprises: The removal of VOCs in the gas to be treated is carried out by passing the gas through two catalysts arranged in sequence, the two catalysts being catalyst I and catalyst II, each of which is loaded with a noble metal element, and the noble metal elements loaded in the two catalysts being different, the noble metal element being selected from Pt, Pd, Rh, Ru, Ag or Au; The arrangement order of the catalyst I and the catalyst II is determined in the following manner: The heat of the alkanes contained in the gas to be treated is calculated by the formula Q1=q1×V1, and the heat of the alkenes contained in the gas to be treated is calculated by the formula Q2=q2×V2, wherein q1 represents the calorific value of the alkanes, q2 represents the calorific value of the alkenes, V1 represents the volume of the alkanes, and V2 represents the volume of the alkenes; When Q1≤Q2, the catalyst I and the catalyst II are arranged in a first order; when Q1>Q2, the catalyst I and the catalyst II are arranged in a second order; wherein the first order is Pt>Pd>Rh>Ru>Ag>Au, and the second order is Pd>Pt>Rh>Ru>Ag>Au; the noble metal elements loaded in the catalyst I and the catalyst II are arranged in the order of the first order or the second order, the catalyst with the noble metal element arranged in the front is the front catalyst, and the catalyst with the noble metal element arranged in the rear is the rear catalyst.

2. The method of multi-component VOCs co-removal according to claim 1, wherein, The noble metal elements of the catalyst I and the catalyst II are loaded on a substrate.

3. The method of multi-component VOCs co-removal according to claim 1, wherein, The catalyst I and the catalyst II each further comprise one or more of a binder, an auxiliary agent and a carrier.

4. The method of multi-component VOCs co-removal according to claim 2, wherein, The loading amount of the noble metal element is 0.1-1.4 g / L based on the volume of the substrate.

5. The method of multi-component VOCs co-removal according to claim 2, wherein, The preparation of the catalyst I or the catalyst II comprises the following steps: i) Pretreatment of the substrate: the substrate is heated and boiled in advance in a 20-50 wt.% oxalic acid aqueous solution, then cooled, soaked, taken out, washed with deionized water, and then placed in a drying oven for drying treatment; ii) Preparation of the noble metal catalyst: the noble metal salt, the binder, the auxiliary agent and the carrier are ground into a slurry; the substrate treated in step 1) is immersed in the slurry, and then the air in the pores of the substrate is discharged to make the slurry distributed on the wall surface of the substrate; iii) Drying and calcination: then drying and calcination are carried out to obtain the noble metal catalyst.

6. The method of multi-component VOCs co-removal according to claim 5, wherein, In step i), the heating and boiling treatment time is 1-1.5 h; the soaking time is 8-30 h; and the drying is carried out at a temperature of 80-200 ℃.

7. The method of multi-component VOCs co-removal according to claim 5, wherein, In step ii), the immersion time of the substrate treated in step 1) in the slurry is 20-40 min.

8. The method of multi-component VOCs co-removal according to claim 5, wherein, In step iii), the drying temperature is 60-420 ℃, and the calcination temperature is 500-600 ℃.

9. The method of multi-component VOCs co-removal of claim 8, wherein, In step iii), the calcination time is 4-6 h.

10. The method of multi-component VOCs co-removal according to any one of claims 1-9, wherein, The noble metal element is selected from Pt, Pd, Rh or Ru.

11. The method of multi-component VOCs co-removal of claim 10, wherein, The noble metal element is selected from Pt or Pd.

12. The method of multi-component VOCs co-removal according to any one of claims 2 or 4-9, wherein, The substrate is selected from cordierite honeycomb ceramics.

13. The method of multi-component VOCs co-removal according to any one of claims 3 or 5-9, wherein, The binder is selected from pseudoboehmite, aluminum sol or silicon sol; and the auxiliary agent is selected from urea or concentrated nitric acid.

14. The method of multi-component VOCs co-removal according to any one of claims 3 or 5-9, wherein, The carrier is selected from one or more of nano gamma-Al2O3, nano TiO2, nano SiO2.

15. The method of multi-component VOCs co-removal of claim 5, wherein, In the slurry, the mass content of the noble metal salt is 0.2-3.3%, the mass content of the binder is 5-25%, the mass content of the auxiliary agent is 1.5-15%, the mass content of the carrier is 9.2-31.4%, and the mass content of the solid substance is 20-35%.

16. The method of multi-component VOCs co-removal according to any one of claims 1-9, wherein, The gas to be treated is derived from a coal chemical gas or a vent air with multi-component VOCs having alkylene alkanes below C6.

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