Method for synergistically removing multi-component VOCs (Volatile Organic Compounds)

Abstract

The invention provides a method for synergistically removing multi-component VOCs (Volatile Organic Compounds), which comprises the following steps that: to-be-treated gas passes through two catalysts which are sequentially arranged from front to back for removing VOCs, and the two catalysts are a catalyst I and a catalyst II which are respectively loaded with noble metal elements, the arrangement sequence of the catalyst I and the catalyst II is determined according to the following mode: calculating the heat of alkane contained in the gas to be treated by adopting a formula Q1 = q1 * V1, calculating the heat of olefin contained in the gas to be treated by adopting Q2 = q2 * V2, and when Q1 is smaller than or equal to Q2, arranging noble metal catalysts of the catalyst I and the catalyst II according to a first sequence; otherwise, when Q1 is larger than Q2, the catalysts I and II are arranged according to the second sequence. According to the present invention, the multi-component VOCs containing C6 or less alkane olefins sequentially pass through the noble metal catalysts with different arrangements, such that the advantages of the single-component noble metal catalysts on the VOCs degradation are combined so as to easily achieve the requirement of the mixed VOCs degradation efficiency; the catalyst is arranged according to the heat value of each VOCs in the waste gas, and precious metal in the catalyst is utilized to the maximum extent.

Description

Technical Field

[0001] The invention belongs to the field of VOCs treatment and chemical technology, and specifically relates to a method for collaborative removal of multi-component VOCs. Background Art

[0002] Volatile organic compounds (VOCs) are a general term for organic compounds with a melting point below room temperature and a boiling point below 200-260°C under standard atmospheric pressure, mainly including hydrocarbons, esters, alcohols, benzene series, etc. The anthropogenic sources of VOCs emissions mainly include fixed combustion sources, road mobile sources, industrial process sources, solvent use sources, etc. It is a major source of PM2.5 and O 3 It is an important precursor to pollution and seriously endangers human health.

[0003] The current VOCs treatment methods mainly include adsorption, absorption, condensation, membrane separation, plasma, photocatalysis and catalytic combustion, etc. Among them, the catalytic combustion method can treat medium and low concentrations of VOCs, achieve catalytic oxidation at a relatively low temperature, reduce energy consumption, and reduce the emission of secondary pollutants. It has become one of the most important technologies for eliminating VOCs.

[0004] The core of VOCs treatment is the selection, design and preparation of high-performance catalysts. Precious metal catalysts are a widely used type of catalysts due to their high catalytic activity and good thermal stability. At present, industrial VOCs oxidation catalysts are generally coated with a layer of γ-Al on the surface of the cordierite honeycomb ceramic substrate. 2 O 3 As a carrier, it is used to load the active components of precious metals and the coating of additives. However, precious metals are expensive and scarce, so it is of great significance to achieve efficient utilization of precious metals while ensuring the performance of the catalyst remains unchanged.

[0005] Actual industrial waste gas often contains a variety of VOCs components. When using precious metal catalysts to treat such waste in the existing technology, it is difficult to simultaneously achieve good removal effects of multiple VOCs components. Summary of the invention

[0006] The present invention provides a method for collaboratively removing multi-component VOCs by utilizing a catalyst combination arrangement. The method of the present invention is used to treat a gas to be treated containing multi-component VOCs of alkanes and alkenes below C6, which can achieve a high degradation efficiency of both low-carbon alkane and olefin VOCs components. Moreover, the present invention does not require the use of a complex composite noble metal catalyst, and the catalyst is easy to produce. The removal of multi-component VOCs by the method of the present invention is conducive to full utilization of the activity of the noble metal in the catalyst.

[0007] To achieve the above purpose, the present invention adopts the following technical solutions:

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

[0009] The gas to be treated is subjected to VOCs removal treatment by two catalysts arranged in sequence, wherein the two catalysts are catalyst I and catalyst II respectively loaded with precious metal elements, and the precious metal elements loaded by the two are different, and the precious metal elements are selected from Pt, Pd, Rh, Ru, Ag or Au;

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

[0011] Using the formula Q 1 =q 1 ×V 1 Calculate the heat of the alkanes contained in the gas to be treated, using Q 2 =q 2 ×V 2 Calculate the heat of the olefins contained in the gas to be treated, where q 1 represents the calorific value of the alkane, q 2 represents the calorific value of the olefin, V 1 represents the volume of the alkane, V 2 Respectively represent the volume of the olefin;

[0012] When Q 1 ≤Q 2 When Q 1 >Q 2 , 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 precious metal elements loaded in the catalysts I and II are arranged in an order according to the determined first order or the second order, with the catalyst with the loaded precious metal elements ranked higher being the front-end catalyst, and the catalyst with the loaded precious metal elements ranked lower being the back-end catalyst.

[0013] In some preferred embodiments, the noble metal elements of the catalyst I and the catalyst II are respectively loaded on a substrate; preferably, the catalyst I and the catalyst II also include one or more of a binder, an auxiliary agent and a carrier.

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

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

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

[0017] ii) preparing a noble metal catalyst: grinding a noble metal salt, a binder, an additive and a carrier into a slurry; immersing the substrate treated in step 1) into the slurry, preferably for 20-40 minutes, and then exhausting the air in the pores of the substrate to distribute the slurry on the wall surface of the substrate;

[0018] iii) Drying and calcining: drying, preferably at a drying temperature of 60-420° C., and then calcining, preferably at a calcination temperature of 500-600° C., and preferably for 4-6 hours, to obtain a noble metal catalyst.

[0019] In some preferred embodiments, the drying in step iii) is staged drying, and the staged drying temperatures are, for example, 60-65°C, 90-95°C, 120-130°C, 200-210°C and 420-430°C in sequence, and the drying times are, for example, 2 min, 2 min, 2 min and 0.5 min, 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 substrate is selected from cordierite honeycomb ceramics.

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

[0023] In some preferred embodiments, the carrier is selected from nano γ-Al 2 O 3 、Nano-TiO 2 、Nano-SiO 2 One or more of .

[0024] In some preferred embodiments, in the slurry, the mass content of the precious 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 matter is 20-35%.

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

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

[0027] The method for collaborative removal of multi-component VOCs provided by the present invention is to pass multi-component VOCs containing low-carbon alkanes and olefins through single precious metal-loaded catalysts of different combinations in sequence, and different precious metals show certain differences in the oxidation activity of different VOCs. In the method of the present invention, the catalysts used before and after are all single-component precious metal catalysts loaded with a precious metal element, and the two single-component precious metal catalysts are used in combination according to the method of the present invention, so that the advantages of each catalyst in the degradation of VOCs components are combined, and the single-component precious metal catalyst has better high dispersibility than the multi-component precious metal catalyst, and it is not easy to cause the phenomenon of precious metal migration and agglomeration. The combination method of the present invention is used to treat waste gas, which is conducive to realizing the demand for synchronous and efficient degradation of multiple VOCs components in mixed VOCs. The catalyst is arranged according to the calorific value of low-carbon alkanes and olefins VOCs in the waste gas, and the heat generated by the preferentially reacted VOCs provides energy for the subsequent reaction of VOCs, and the precious metals in the catalyst can be maximized, and a good VOCs treatment effect can be achieved under the condition of catalyst reduction. At the same time, the method of the present invention uses a single precious metal catalyst, which is easier to produce in series than a two-component precious metal catalyst, is not easy to form alloy agglomerates, has better stability, and can be well adapted to industries such as coal chemical industry and wind exhaust gas that have multi-component VOCs pollution emissions of alkanes and alkenes below C6. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of 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 TEM image of the mixed catalyst in Comparative Example 1-2 of the present invention;

[0032] Figure 4 Schematic diagram of catalyst arrangement in Example 2, Comparative Example 2-1 and Comparative Example 2-2 of the present invention. DETAILED DESCRIPTION

[0033] The present invention is further described below by means of specific embodiments. The embodiments of the present invention are only used as illustrations of the present invention and do not mean that the scope of the present invention is limited thereto.

[0034] Instruments: A spherical aberration-corrected projection electron microscope (JEMARM200F) was used to observe the morphology of precious 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 the noble metal catalyst comprises the following steps:

[0037] ① Preparation of Pt catalyst

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

[0039] ii) Preparation of noble metal catalyst: 0.2333 g of platinum nitrate solution (15 wt.%), 5.00 g of pseudo-boehmite, 1.50 g of concentrated nitric acid and 31.40 g of nano-γ-Al 2 O 3 Add to 61.87g of deionized water, put into a ball mill for 6h to form a uniform slurry. In the slurry, the mass content of pseudo-boehmite is 5.0%, the mass content of concentrated nitric acid is 1.5%, and the mass content of nano-γ-Al 2 O 3 The mass content of the raw materials is 31.4%, and the mass content of the solid matter is 35%; the slurry after ball milling is taken out and stirred continuously. After the slurry is cooled, the cordierite matrix is ​​immersed in the slurry for 20 minutes, taken out, and then the air in the pores is exhausted with a super air knife to make the slurry fully and evenly distributed on the wall surface of the matrix.

[0040] iii) Drying and calcination: After that, use a hot air gun to quickly dry it in stages at a temperature of 60-420°C (drying at 60°C for 2 min, drying at 90°C for 2 min, drying at 120°C for 2 min, drying at 200°C for 2 min, and drying at 420°C for 0.5 min), and then place it in a muffle furnace and calcine it at 550°C for 5h to obtain a monolithic catalyst with a precious metal Pt content of 0.1g / L.

[0041] ②Preparation of Pd catalyst

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

[0043] ii) Preparation of noble metal catalyst: 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-Al 2 O 3 Add to 51.50g deionized water, put into a ball mill for 12h to form a uniform 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 matter is 35%; take out the slurry after ball milling and stir it continuously. After the slurry cools down, immerse the cordierite matrix in the slurry for 20min, take it out, and then use a super air knife to exhaust the air in the pores to make the slurry fully and evenly distributed on the wall surface of the matrix.

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

[0045] 2) Arranging a noble metal catalyst, comprising the following steps:

[0046] The above-mentioned noble metal catalyst is used for catalytic oxidation of methane (CH 4 ) / ethylene(C 2 H 4 ) mixed gas, the mixed gas contains 20vol.% O 2 , C 2 H 4 The content is 350ppm, CH 4 The content is 500ppm, H 2 O content is 5 vol.%, and the rest is air. Methane calorific value q 1 is 39.82J / L, and the calorific value of ethylene is q 2 It is 63.4J / L.

[0047] a) Using Q 1 =q 1 ×V 1 Calculate the heat of an alkane, Q 1 =q1 ×V 1 =39.82×500×10 -6 ×V=1.99×10 -2 V(J), using Q 2 =q 2 ×V 2 Calculate the heat of olefins, Q 2 =q 2 ×V 2 =63.4×350×10 -6 ×V=2.22×10 -2 V(J), where q 1 represents the calorific value of the alkane, q 2 represents the calorific value of olefins, V represents the total volume of the mixed gas, V 1 represents the volume of the alkane, V 2 represents the volume of the olefin;

[0048] b) Due to Q 1 2 , the precious metal catalysts are arranged in the first order; the first order is Pt>Pd, the Pt catalyst is used as the front catalyst, the Pd catalyst is used as the rear catalyst, and the front and rear catalysts each account for half of the total volume of the catalyst. The mixed gas is processed by the front catalyst and the rear catalyst in turn.

[0049] Comparative Example 1-1

[0050] The Pd catalyst is used as the front-end catalyst, and the Pt catalyst is used as the back-end catalyst. The front-end catalyst and the back-end catalyst each occupy half of the total volume of the catalyst. Other settings are the same as in Example 1.

[0051] Comparative Example 1-2

[0052] ③Preparation of mixed precious metal catalysts

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

[0054] Weigh 0.1167 g of platinum nitrate solution (15 wt.%), 1.05 g of palladium nitrate solution (15 wt.%), 5.00 g of pseudo-boehmite, 15.00 g of urea and 31.4 g of nano-γ-Al 2 O 3 Add to 47.43g of deionized water, put into a ball mill for 12h to form a uniform slurry. In the slurry, the mass content of pseudo-boehmite is 5.0%, the mass content of urea is 15.0%, and the mass content of nano-γ-Al 2 O 3 ​The content is 31.4%, and the mass content of solid matter is 35%; the slurry after ball milling is taken out and stirred continuously. After the slurry is cooled, the cordierite matrix is ​​immersed in the slurry for 20 minutes, then taken out, and then the air in the pores is exhausted with a super air knife to make the slurry fully and evenly distributed on the wall surface of the matrix.

[0055] After that, use a hot air gun to quickly dry it in stages at a temperature of 60-420°C (60°C drying for 2 minutes, 90°C drying for 2 minutes, 120°C drying for 2 minutes, 200°C drying for 2 minutes, and 420°C drying for 0.5 minutes), and then place it in a muffle furnace and calcine it at 550°C for 5 hours to obtain a monolithic catalyst with a precious metal content of 0.5g / L, wherein the Pt content is 0.05g / L and the Pd content is 0.45g / L, which is a Pt-Pd catalyst. The Pt-Pd catalyst is placed in the reaction bed, and its volume is equal to the sum of the volumes of the Pt catalyst and the Pd catalyst in Example 1. The arrangement of the precious metal catalyst is as follows Figure 1 Schematic diagram of catalyst arrangement in Example 1.

[0056] The catalysts arranged in the three ways of Example 1, Comparative Example 1-1 and Comparative Example 1-2 were used to catalyze the oxidation of methane (CH 4 ) / ethylene(C 2 H 4 ) mixed gas, the reaction space velocity is 20000h -1 , a continuous online monitoring method was adopted to examine the catalytic performance of the catalyst under the treatment conditions of 200-500℃.

[0057] Table 1 Catalyst activity in Example 1

[0058]

[0059] The olefins in the mixed gas have high heat, and the precious metal catalyst is arranged in the first order; the front-end Pt-based catalyst in Example 1 has a high heat release rate. 2 H 4 High activity, fast combustion, the catalyst activity is higher than the other two arrangements. 2 H 4 The heat released by combustion increases CH 4 The catalytic activity of the catalyst is higher than that of the other two catalysts. In addition, the amount of precious metal contained in the catalyst of Example 1 is the same as that of the catalyst of Comparative Examples 1-2, but the utilization rate of the precious metal is significantly improved.

[0060] The catalysts in Example 1 and Comparative Example 1-1 were characterized by TEM, and it was found that the active components of the Pt and Pd single-component noble metal catalysts were highly dispersed, and some were monolayer dispersed. However, the noble metal particles of the Pt-Pd two-component catalyst in Comparative Example 1-2 were unevenly dispersed, and some particles were larger in size, resulting in poor activity. 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 This is the TEM image of the mixed catalyst in Comparative Example 1-2.

[0061] Example 2

[0062] 1) The preparation of the noble metal catalyst comprises the following steps:

[0063] ① Preparation of Pt catalyst

[0064] i) Pretreatment of substrate: The same method as in Example 1 was used to pretreat a 2 cm×2 cm×2.5 cm substrate cordierite honeycomb ceramic.

[0065] ii) Preparation of noble metal catalyst: 0.2666 g of platinum nitrate solution (15 wt.%), 15.00 g of pseudo-boehmite, 10.00 g of urea and 9.20 g of nano-γ-Al 2 O 3 Add to 65.53g of deionized water, put into a ball mill for 3h to form a uniform slurry. In the slurry, the mass content of pseudo-boehmite is 15.0%, the mass content of urea is 10.0%, and the mass content of nano-γ-Al 2 O 3 The mass content of the ball mill is 9.2%, and the mass content of the solid matter is 20%; the slurry after ball milling is taken out and stirred continuously. After the slurry is cooled, the cordierite matrix is ​​immersed in the slurry for 20 minutes, taken out, and then the air in the pores is exhausted with a super air knife to make the slurry fully and evenly distributed on the wall surface of the matrix.

[0066] iii) Drying and calcination: After that, use a hot air gun to quickly dry it in stages at a temperature of 60-420°C (drying at 60°C for 2 min, drying at 90°C for 2 min, drying at 120°C for 2 min, drying at 200°C for 2 min, and drying at 420°C for 0.5 min), and then place it in a muffle furnace and calcine it at 500°C for 6 hours to obtain a monolithic catalyst with a precious metal Pt content of 0.2 g / L.

[0067] ②Preparation of Pd catalyst

[0068] i) Pretreatment of substrate: The same method as in Example 1 was used to pretreat a 2 cm×2 cm×2.5 cm substrate cordierite honeycomb ceramic.

[0069] ii) Preparation of noble metal catalyst: 1.0667 g of palladium nitrate solution (15 wt.%), 15.00 g of pseudo-boehmite, 10.00 g of urea and 9.2 g of nano-γ-Al 2 O 3 Add to 64.73g of deionized water, put into a ball mill and mill for 3h to form a uniform slurry. In the slurry, the mass content of pseudo-boehmite is 15.0%, the mass content of urea is 10.0%, and the mass content of nano-γ-Al 2 O 3 The mass content of the ball mill is 9.2%, and the mass content of the solid matter is 20%; the slurry after ball milling is taken out and stirred continuously. After the slurry is cooled, the cordierite matrix is ​​immersed in the slurry for 20 minutes, taken out, and then the air in the pores is exhausted with a super air knife to make the slurry fully and evenly distributed on the wall surface of the matrix.

[0070] iii) Drying and calcination: After that, use a hot air gun to quickly dry it in stages at a temperature of 60-420°C (drying at 60°C for 2 min, drying at 90°C for 2 min, drying at 120°C for 2 min, drying at 200°C for 2 min, and drying at 420°C for 0.5 min), and then place it in a muffle furnace and calcine it at 500°C for 6 hours to obtain a monolithic catalyst with a precious metal Pd content of 0.8 g / L.

[0071] 2) Arranging a noble metal catalyst, comprising the following steps:

[0072] The above-mentioned noble metal catalyst is used for catalytic oxidation of methane (CH 4 ) / ethylene(C 2 H 4 ) mixed gas, the mixed gas contains 20vol.% O 2 , CH 4 The content is 750ppm, C 2 H 4 The content is 250ppm, H 2 O content is 5 vol.%, and the rest is air. Methane calorific value q 1 is 39.82J / L, and the calorific value of ethylene is q 2 It is 63.4J / L.

[0073] a) Using Q 1 =q 1 ×V 1 Calculate the heat of an alkane, Q 1 =q 1 ×V 1 =39.82×750×10 -6 ×V=2.99×10 -2 V(J), using Q 2 =q 2 ×V 2Calculate the heat of olefins, Q 2 =q 2 ×V 2 =63.4×250×10 -6 ×V=1.59×10 -2 V(J), where q 1 represents the calorific value of the alkane, q 2 represents the calorific value of olefins, V represents the total volume of the mixed gas, V 1 represents the volume of the alkane, V 2 represents the volume of the olefin;

[0074] b) Due to Q 1 >Q 2 , the precious metal catalysts are arranged in the second order; the second order is Pd>Pt, the Pd catalyst is used as the front catalyst, the Pt catalyst is used as the rear catalyst, and the front and rear catalysts each account for half of the total volume of the catalyst. The mixed gas is processed by the front catalyst and the rear catalyst in turn.

[0075] Comparative Example 2-1

[0076] The Pt catalyst is used as the front-end catalyst, and the Pd catalyst is used as the back-end catalyst. The front-end catalyst and the back-end catalyst each occupy half of the total volume of the catalyst. Other settings are the same as those in Example 2.

[0077] Comparative Example 2-2

[0078] ③Preparation of mixed precious metal catalysts

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

[0080] Weigh 0.1333 g of platinum nitrate solution (15 wt.%), 0.5333 g of palladium nitrate solution (15 wt.%), 15.00 g of pseudo-boehmite, 10.00 g of urea and 9.20 g of nano-γ-Al 2 O 3 Add to 65.13g of deionized water, put into a ball mill for 3h to form a uniform slurry. In the slurry, the mass content of pseudo-boehmite is 15.0%, the mass content of urea is 10.0%, and the mass content of nano-γ-Al 2 O 3 The mass content of the ball mill is 9.2%, and the mass content of the solid matter is 20%; the slurry after ball milling is taken out and stirred continuously. After the slurry is cooled, the cordierite matrix is ​​immersed in the slurry for 20 minutes, taken out, and then the air in the pores is exhausted with a super air knife to make the slurry fully and evenly distributed on the wall surface of the matrix.

[0081] After that, use a hot air gun to quickly dry it in stages at a temperature of 60-420°C (60°C drying for 2 minutes, 90°C drying for 2 minutes, 120°C drying for 2 minutes, 200°C drying for 2 minutes, and 420°C drying for 0.5 minutes), and then place it in a muffle furnace and calcine it at 500°C for 6 hours to obtain a monolithic catalyst with a precious metal content of 0.5g / L, wherein the Pt content is 0.1g / L and the Pd content is 0.4g / L, which is a Pt-Pd catalyst. The Pt-Pd catalyst is placed in the reaction bed, and its volume is equal to the sum of the volumes of the Pt catalyst and the Pd catalyst in Example 2. The arrangement of the precious metal catalyst is as follows Figure 4 Schematic diagram of catalyst arrangement in Example 2.

[0082] The catalysts arranged in the three ways of Example 2, Comparative Example 2-1 and Comparative Example 2-2 were used to catalyze the oxidation of methane (CH 4 ) / ethylene(C 2 H 4 ) mixed gas, the reaction space velocity is 20000h -1 , a continuous online monitoring method was adopted to examine the catalytic performance of the catalyst under the treatment conditions of 200-500℃.

[0083] Table 2 Catalyst activity in Example 2

[0084]

[0085] The alkane in the mixed gas has high heat, and the precious metal catalyst is arranged in the second order; the front-end Pd-based catalyst in Example 2 has a great effect on CH 4 High activity, fast combustion, the catalyst activity is higher than the other two arrangements. 4 The heat released by combustion increases C 2 H 4 The catalytic activity of the catalyst is higher than that of the other two catalysts. In addition, the amount of precious metal contained in the catalyst of Example 2 is the same as that of the catalyst of Comparative Example 2-2, but the utilization rate of the precious metal is significantly improved.

[0086] Example 3

[0087] 1) The preparation of the noble metal catalyst comprises the following steps:

[0088] ① Preparation of Pt catalyst

[0089] i) Pretreatment of substrate: The same method as in Example 1 was used to pretreat a 2 cm×2 cm×2.5 cm substrate cordierite honeycomb ceramic.

[0090] ii) Preparation of precious 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-Al 2 O 3 Add to 46.30g of deionized water, put into a ball mill for 6h to form a uniform slurry. In the slurry, the mass content of aluminum sol is 20.0%, the mass content of concentrated nitric acid is 2.0%, and the mass content of nano-γ-Al 2 O 3 The mass content of the raw materials is 31.0%, and the mass content of the solid matter is 35%; the slurry after ball milling is taken out and stirred continuously. After the slurry is cooled, the cordierite matrix is ​​immersed in the slurry for 20 minutes, taken out, and then the air in the pores is exhausted with a super air knife to make the slurry fully and evenly distributed on the wall surface of the matrix.

[0091] iii) Drying and calcination: After that, use a hot air gun to quickly dry it in stages at a temperature of 60-420°C (drying at 60°C for 2 min, drying at 90°C for 2 min, drying at 120°C for 2 min, drying at 200°C for 2 min, and drying at 420°C for 0.5 min), and then place it in a muffle furnace and calcine it at 500°C for 6 hours to obtain a monolithic catalyst with a precious metal Pt content of 0.3 g / L.

[0092] ②Preparation of Rh catalyst

[0093] i) Pretreatment of the carrier: The same method as in Example 1 was used to pretreat a 2 cm×2 cm×2.5 cm base cordierite honeycomb ceramic.

[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-Al 2 O 3 Add to 34.38g of deionized water, put into a ball mill for 6h to form a uniform slurry. In the slurry, the mass content of aluminum sol is 25.0%, the mass content of urea is 10.0%, and the mass content of nano-γ-Al 2 O 3 The mass content of the raw materials is 30.0%, and the mass content of the solid matter is 35%; the slurry after ball milling is taken out and stirred continuously. After the slurry is cooled, the cordierite matrix is ​​immersed in the slurry for 20 minutes, taken out, and then the air in the pores is exhausted with a super air knife to make the slurry fully and evenly distributed on the wall surface of the matrix.

[0095] iii) Drying and calcination: After that, use a hot air gun to quickly dry it in stages at a temperature of 60-420°C (drying at 60°C for 2 min, drying at 90°C for 2 min, drying at 120°C for 2 min, drying at 200°C for 2 min, and drying at 420°C for 0.5 min), and then place it in a muffle furnace and calcine it at 500°C for 6 hours to obtain a monolithic catalyst with a precious metal Rh content of 0.7 g / L.

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

[0097] The above-mentioned noble metal catalyst is used for catalytic oxidation of methane (CH 4 ) / ethylene(C 2 H 4 ) mixed gas, the mixed gas contains 20vol.% O 2 , CH 4 The content is 150ppm, C 2 H 4 The content is 840ppm, H 2 The O content is 5 vol.%, and the rest is air.

[0098] a) Using Q 1 =q 1 ×V 1 Calculate the heat of an alkane, Q 1 =q 1 ×V 1 =39.82×150×10 -6 ×V=0.60×10 -2 V(J), using Q 2 =q 2 ×V 2 Calculate the heat of olefins, Q 2 =q 2 ×V 2 =63.4×840×10 -6 ×V=5.32×10 -2 V(J), where q 1 represents the calorific value of the alkane, q 2 represents the calorific value of olefins, V represents the total volume of the mixed gas, V 1 represents the volume of the alkane, V 2 represents the volume of the olefin;

[0099] b) Due to Q 1 2 , the precious metal catalysts are arranged in the first order; the first order is Pt>Rh, the Pt catalyst is used as the front catalyst, the Rh catalyst is used as the rear catalyst, and the front and rear catalysts each occupy half of the total volume of the catalyst. The mixed gas is processed by the front catalyst and the rear catalyst in turn.​

[0100] Comparative Example 3-1

[0101] The Rh catalyst is used as the front-end catalyst, and the Pt catalyst is used as the back-end catalyst. The front-end catalyst and the back-end catalyst each occupy half of the total volume of the catalyst. Other settings are the same as those in Example 3.

[0102] Comparative Example 3-2

[0103] ③Preparation of mixed precious metal catalysts

[0104] The pretreatment steps of the 2cm×2cm×5cm base cordierite honeycomb ceramic are the same as those in Example 3.

[0105] Weigh 0.3500 g of platinum nitrate solution (15 wt.%), 0.3062 g of rhodium chloride trihydrate (38.5-42.5 wt.%), 25.00 g of aluminum sol (20 wt.%), 15.00 g of urea and 30.00 g of nano-γ-Al 2 O 3 Add to 29.34g deionized water, put into a ball mill for 9h to form a uniform slurry. In the slurry, the mass content of aluminum sol is 25.0%, the mass content of urea is 15.0%, and the mass content of nano-γ-Al 2 O 3 The mass content of the raw materials is 30.0%, and the mass content of the solid matter is 35%; the slurry after ball milling is taken out and stirred continuously. After the slurry is cooled, the cordierite matrix is ​​immersed in the slurry for 20 minutes, taken out, and then the air in the pores is exhausted with a super air knife to make the slurry fully and evenly distributed on the wall surface of the matrix.

[0106] After that, the catalyst was dried in sections at 60-420°C (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) with a hot air gun, and then placed in a muffle furnace and calcined at 500°C for 6 h to obtain a monolithic catalyst with a noble metal content of 0.5 g / L, wherein the Pt content was 0.15 g / L and the Rh content was 0.35 g / L, which was a Pt-Rh catalyst. The Pt-Rh catalyst was placed in a reaction bed, and its volume was equal to the sum of the volumes of the Pt catalyst and the Rh catalyst in Example 3.

[0107] The catalysts arranged in the three ways of Example 3, Comparative Example 3-1 and Comparative Example 3-2 were used to catalyze the oxidation of methane (CH 4 ) / ethylene(C 2 H 4 ) mixed gas, the reaction space velocity is 20000h -1, a continuous online monitoring method was adopted to examine the catalytic performance of the catalyst under the treatment conditions of 200-500℃.

[0108] Table 3 Catalyst activity in Example 3

[0109]

[0110] The olefins in the mixed gas have high heat, and the precious metal catalyst is arranged in the first order; the front-end Pt-based catalyst in Example 3 has a great influence on the C 2 H 4 High activity, fast combustion, the catalyst activity is higher than the other two arrangements. 2 H 4 The heat released by combustion increases CH 4 The catalytic activity of the catalyst is higher than that of the other two catalysts. In addition, the amount of precious metal contained in the catalyst of Example 3 is the same as that of Comparative Example 3-2, but the utilization rate of the precious metal is significantly improved.

[0111] Example 4

[0112] 1) The preparation of the noble metal catalyst comprises the following steps:

[0113] ①Preparation of Pd catalyst

[0114] i) Pretreatment of substrate: The same method as in Example 1 was used to pretreat a 2 cm×2 cm×2.5 cm substrate cordierite honeycomb ceramic.

[0115] ii) Preparation of precious 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-SiO 2 Add to 35.0663g of deionized water, put into a ball mill for 6h to form a uniform slurry. In the slurry, the mass content of silica sol is 16.7%, the mass content of urea is 15.0%, and the mass content of nano-SiO 2 The mass content of the raw materials is 30.0%, and the mass content of the solid matter is 35%; the slurry after ball milling is taken out and stirred continuously. After the slurry is cooled, the cordierite matrix is ​​immersed in the slurry for 20 minutes, taken out, and then the air in the pores is exhausted with a super air knife to make the slurry fully and evenly distributed on the wall surface of the matrix.

[0116] iii) Drying and calcination: After that, use a hot air gun to quickly dry it in stages at a temperature of 60-420°C (drying at 60°C for 2 min, drying at 90°C for 2 min, drying at 120°C for 2 min, drying at 200°C for 2 min, and drying at 420°C for 0.5 min), and then place it in a muffle furnace and calcine it at 500°C for 6 hours 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 same method as in Example 1 was used to pretreat a 2 cm×2 cm×2.5 cm base cordierite honeycomb ceramic.

[0119] ii) Preparation of noble metal catalyst: 0.5250 g rhodium trichloride (35.0-42 wt.%), 16.667 g silica sol (30 wt.%), 10.00 g urea and 30.00 g nano-SiO 2 Add to 42.81g deionized water, put into a ball mill for 3h to form a uniform slurry. In the slurry, the mass content of silica sol is 16.7%, the mass content of urea is 10.0%, and the mass content of nano-SiO 2 The mass content of the raw materials is 30.0%, and the mass content of the solid matter is 35%; the slurry after ball milling is taken out and stirred continuously. After the slurry is cooled, the cordierite matrix is ​​immersed in the slurry for 20 minutes, taken out, and then the air in the pores is exhausted with a super air knife to make the slurry fully and evenly distributed on the wall surface of the matrix.

[0120] iii) Drying and calcination: After that, use a hot air gun to quickly dry it in stages at a temperature of 60-420°C (drying at 60°C for 2 min, drying at 90°C for 2 min, drying at 120°C for 2 min, drying at 200°C for 2 min, and drying at 420°C for 0.5 min), and then place it in a muffle furnace and calcine it at 500°C for 6 hours to obtain a monolithic catalyst with a precious metal Ru content of 0.6 g / L.

[0121] 2) Arranging a noble metal catalyst, comprising the following steps:

[0122] The above-mentioned noble metal catalyst is used for catalytic oxidation of methane (CH 4 ) / ethylene(C 2 H 4 ) mixed gas, the mixed gas contains 20vol.% O 2 , CH 4 The content is 750ppm, C 2 H 4 The content is 250ppm, H 2 The O content is 5 vol.%, and the rest is air.

[0123] a) Using Q 1 =q 1 ×V 1 Calculate the heat of an alkane, Q 1 =q 1 ×V 1 =39.82×750×10 -6 ×V=2.99×10 -2 V(J), using Q2 =q 2 ×V 2 Calculate the heat of olefins, Q 2 =q 2 ×V 2 =63.4×250×10 -6 ×V=1.59×10 -2 V(J), where q 1 represents the calorific value of the alkane, q 2 represents the calorific value of olefins, V represents the total volume of the mixed gas, V 1 represents the volume of the alkane, V 2 represents the volume of the olefin;

[0124] b) Due to Q 1 >Q 2 , the precious metal catalysts are arranged in the second order; the second order is Pd>Ru, the Pd catalyst is used as the front catalyst, the Ru catalyst is used as the rear catalyst, and the front and rear catalysts each account for half of the total volume of the catalyst. The mixed gas is processed by the front catalyst and the rear catalyst in turn.

[0125] Comparative Example 4-1

[0126] The Pd catalyst is used as the front-end catalyst and the Ru catalyst is used as the back-end catalyst. The front-end catalyst and the back-end catalyst each occupy half of the total volume of the catalyst. Other settings are the same as those in Example 4.

[0127] Comparative Example 4-2

[0128] ③Preparation of mixed precious metal catalysts

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

[0130] Weigh 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-SiO 2 Add to 36.4375g deionized water, put into a ball mill for 9h to form a uniform slurry. In the slurry, the mass content of aluminum sol is 16.7%, the mass content of urea is 15.0%, and the mass content of nano-SiO 2 The mass content of the raw materials is 30.0%, and the mass content of the solid matter is 35%; the slurry after ball milling is taken out and stirred continuously. After the slurry is cooled, the cordierite matrix is ​​immersed in the slurry for 20 minutes, taken out, and then the air in the pores is exhausted with a super air knife to make the slurry fully and evenly distributed on the wall surface of the matrix.

[0131] After that, the catalyst was dried in stages at 60-420°C (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) using a hot air gun, and then placed in a muffle furnace and calcined at 500°C for 6 h to obtain a monolithic catalyst with a noble metal content of 1.0 g / L, wherein the Pd content was 0.7 g / L and the Ru content was 0.3 g / L, which was a Pd-Ru catalyst. The Pd-Ru catalyst was placed in a reaction bed, and its volume was equal to the sum of the volumes of the Pd catalyst and the Ru catalyst in Example 4.

[0132] The catalysts arranged in the three ways of Example 4, Comparative Example 4-1 and Comparative Example 4-2 were used to catalyze the oxidation of methane (CH 4 ) / ethylene(C 2 H 4 ) mixed gas, the reaction space velocity is 20000h -1 , continuous online monitoring was used to examine the catalytic performance under the treatment conditions of 200-500℃.

[0133] Table 4 Catalyst activity in Example 4

[0134]

[0135] The alkane in the mixed gas has high heat, and the precious metal catalyst is arranged in the second order; the front-end Pd-based catalyst in Example 4 has a great effect on CH 4 High activity, fast combustion, the catalyst activity is higher than the other two arrangements. 4 The heat released by combustion increases C 2 H 4 The catalytic activity of the catalyst is higher than that of the other two catalysts. In addition, the amount of precious metal contained in the catalyst of Example 4 is the same as that of Comparative Example 4-2, but the utilization rate of the precious metal is significantly improved.

[0136] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for synergistic removal of multi-component VOCs, It is characterized in that The method comprises: The gas to be treated is subjected to VOCs removal treatment by two catalysts arranged in sequence, wherein the two catalysts are catalyst I and catalyst II respectively loaded with precious metal elements, and the precious metal elements loaded by the two are different, and the precious metal elements are selected from Pt, Pd, Rh, Ru, Ag or Au; The front and rear arrangement order of the catalyst I and the catalyst II is determined as follows: Using the formula Q 1 =q 1 ×V 1 Calculate the heat of the alkanes contained in the gas to be treated, using Q 2 =q 2 ×V 2 Calculate the heat of the olefins contained in the gas to be treated, where q 1 represents the calorific value of the alkane, q 2 represents the calorific value of the olefin, V 1 represents the volume of the alkane, V 2 represents the volume of said olefin; When Q 1 ≤Q 2 When Q 1 >Q 2 , 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 precious metal elements loaded in the catalysts I and II are arranged in an order according to the determined first order or the second order, with the catalyst with the loaded precious metal elements ranked higher being the front-end catalyst, and the catalyst with the loaded precious metal elements ranked lower being the back-end catalyst.

2. The method for synergistic removal of multi-component VOCs according to claim 1, It is characterized in that The noble metal elements of the catalyst I and the catalyst II are respectively loaded on a substrate; Preferably, the catalyst I and catalyst II further include one or more of a binder, an auxiliary agent and a carrier.

3. The method for synergistic removal of multi-component VOCs according to claim 2, It is characterized in that Based on the volume of the substrate, the loading amount of the noble metal element is 0.1-1.4 g / L.

4. The method for synergistic removal of multi-component VOCs according to claim 2, It is characterized in that The preparation of the catalyst I or catalyst II comprises the following steps: i) Pretreatment of the substrate: the substrate is heated and boiled in a 20-50wt.% oxalic acid aqueous solution in advance, preferably for 1-1.5 hours, then cooled and soaked, preferably for 8-30 hours, then taken out, rinsed with deionized water and placed in a drying oven for drying, preferably at 80-200°C; ii) preparing a noble metal catalyst: grinding a noble metal salt, a binder, an additive and a carrier into a slurry; immersing the substrate treated in step 1) into the slurry, preferably for 20 to 40 minutes, and then exhausting the air in the pores of the substrate to distribute the slurry on the wall surface of the substrate; iii) Drying and calcining: drying is then performed, preferably at a drying temperature of 60-420° C., and then calcining is performed, preferably at a calcination temperature of 500-600° C. and preferably for 4-6 hours, to obtain a noble metal catalyst.

5. The method for synergistic removal of multi-component VOCs according to any one of claims 1 to 4, It is characterized in that The noble metal element is selected from Pt, Pd, Rh or Ru; preferably, the noble metal element is selected from Pt or Pd.

6. The method for synergistic removal of multi-component VOCs according to any one of claims 2 to 4, It is characterized in that The substrate is selected from cordierite honeycomb ceramics.

7. The method for synergistic removal of multi-component VOCs according to any one of claims 2 to 4, It is characterized in that The binder is selected from pseudo-boehmite, aluminum sol or silica sol; the auxiliary agent is selected from urea or concentrated nitric acid.

8. The method for synergistic removal of multi-component VOCs according to any one of claims 2 to 4, It is characterized in that The carrier is selected from nano γ-Al 2 O 3 、Nano-TiO 2 、Nano-SiO 2 One or more of .

9. The method for synergistic removal of multi-component VOCs according to claim 4, It is characterized in that 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 matter is 20-35%.

10. The method for synergistic removal of multi-component VOCs according to any one of claims 1 to 9, It is characterized in that The gas to be treated is derived from coal chemical gas or exhaust air containing multi-component VOCs of alkanes and alkenes below C6.

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