CN103212419A - Preparation method and application of catalyst for treating acrylonitrile contained waste gas - Google Patents

Abstract

A catalyst for acrylonitrile-containing waste gas, its preparation method and application, characterized in that the catalyst uses a metal oxide with a perovskite crystal form (ABO ₃ ) as the catalyst, through the screening and combination of A and B-site metal ions , using benzyl alcohol to legally synthesize a catalyst suitable for the removal of acrylonitrile-containing waste gas, and by controlling the catalytic combustion process conditions, acrylonitrile is converted into non-toxic and harmless products, namely N ₂ , H ₂ O and CO ₂ , especially It can prevent the generation of other nitrogen oxides, such as secondary pollution gases such as NO ₂ and NO, in the high temperature stage. It can be used to treat acrylonitrile-containing waste gas discharged from acrylonitrile factories and carbon fiber factories.

Description

A kind of catalyst preparation method and application for the treatment of waste gas containing acrylonitrile

technical field

The invention belongs to a preparation method and application of a catalyst for treating waste gas containing acrylonitrile, and specifically relates to a metal composite oxide with a perovskite crystal form for catalytic combustion of waste gas containing acrylonitrile and a preparation method of this type of catalyst. It can be used for the treatment of acrylonitrile-containing waste gas discharged from acrylonitrile factories and carbon fiber factories. the

Background technique

Because 95% of the current synthesis of acrylonitrile is the propylene ammoxidation process developed by BP. The waste gas of this production process is mainly the tail gas discharged from the absorption tower, which contains toxic components such as propylene, propane, carbon monoxide and trace amounts of acrylonitrile. If it is not treated, it will definitely cause damage to the human body and the environment. At present, the methods for dealing with low-concentration volatile organic compounds include adsorption method, biological treatment method, direct incineration method and catalytic combustion method. Catalytic combustion is recognized as the most efficient and energy-saving method. At present, there are many studies on the catalytic combustion of HCN in cyanide-containing waste gas (such as CN1511615A, CN101269297A, CN1462652A). Noble metal catalysts, although proven effective, have limited their applications due to their high cost. Using transition metals supported on mesoporous materials, Al ₂ O ₃ or SiO ₂ can effectively remove HCN off-gas, but there is no report on the treatment of acrylonitrile off-gas. Although patents CN101138699A and CN101362051A both report the acrylonitrile tail gas treatment process, the catalysts used are all noble metal catalysts. At present, there is no report on the catalytic combustion of acrylonitrile waste gas by using metal composite oxides with perovskite crystal form. The synthesis method of perovskite is divided into solid phase synthesis method and wet chemical method. The citric acid complexation method is a commonly used method for preparing perovskite. The low specific surface area of perovskite has been a major problem that has plagued its application. How to solve this difficult problem, the predecessors have also proposed many ways, as mechanical ball milling, flame spraying etc., but the effect is not obvious. Aiming at this problem, the present invention adopts a new non-aqueous solvent method to prepare perovskite with nano-scale particles, which has the characteristics of high specific surface area, anti-sintering, and good dispersion of spherical particles.

Contents of the invention

The purpose of the present invention is to solve the pollution problem of waste gas containing acrylonitrile, propose a novel catalyst preparation method, select the best catalyst, and adopt the method of catalytic combustion, and acrylonitrile can be directly selectively catalyzed at a lower temperature Combustion decomposes into carbon dioxide, nitrogen and water. The catalyst has high catalytic activity selectivity, simple raw materials, low cost, no by-products, and has industrial application value. the

A kind of catalyst preparation method and application for the treatment of waste gas containing acrylonitrile proposed by the present invention comprise the following steps:

(1) Preparation of perovskite-type metal oxide catalysts, perovskite-type metal oxides can be expressed as: ABO ₃ , where A is generally an alkaline earth metal, and B is generally a transition metal, which can be one type of metal or multiple kind of metal. The nitrate of the metal element at the A position and the acetylacetonate salt of the metal element at the B position are in a ratio of 1:100 to 120 according to the molar ratio of the metal salt to benzyl alcohol (the molar concentration ratio of the metal ions at the A and B positions is A:B =1:1 or A:B ₁ :B ₂ =1:0.2:0.8) dissolved in benzyl alcohol solution to form a mixed solution, fully dissolved at 70°C to 80°C, kept for 20 minutes, then transferred to static reaction Place the reaction kettle in an oven at 200°C for 24 hours, take it out after cooling at room temperature, and centrifuge to obtain a solid substance, which is washed 3 to 5 times with absolute ethanol until the benzyl alcohol is completely removed. The obtained solid material was transferred to a 100°C oven for drying for 24 hours, calcined in a muffle furnace at a heating rate of 2°C/min, and calcined at 450°C to 550°C for 6 hours, and then naturally lowered to room temperature to obtain the desired perovskite metal oxides.

(2) Put the catalyst prepared in step (1) in a fixed-bed quartz tube reactor. The mixed gas with nitrogen is passed into the reaction furnace at a volumetric space velocity of 80000h ^-1 to 120000h ^-1 , and the waste gas is removed by catalytic combustion. Among them, the volume composition of the mixed gas is acrylonitrile: oxygen = 0.3:1 ~ 10, and nitrogen is used as the balance gas;

In the method of the present invention, the selected solvent is benzyl alcohol, lanthanum nitrate is selected as the metal ion at the A position, and iron acetylacetonate, copper acetylacetonate, cobalt acetylacetonate, chromium acetylacetonate, manganese acetylacetonate and other organic salts are selected for B as the metal ion one or more. The dissolution mixing temperature was 80°C and maintained for 20 minutes. The molar ratio of metal ions to benzyl alcohol is 1:120, and the molar concentration of metal ions is A:B=1:1 and A:B ₁ :B ₂ =1:0.2:0.8.

In the method of the present invention, the selected synthesis method is static reactor synthesis, and the temperature condition is selected to be 200° C. for 24 hours. The calcination temperature is 450-550° C. and maintained for 6 hours. the

In the method of the present invention, the selected catalysts include LaFeO ₃ , LaCoO ₃ , LaMnO ₃ , La ₂ CuO ₃ , LaCrO ₃ , LaCu _0.2 Co _0.8 O ₃ , LaCu _0.2 Fe _0.8 O ₃ , LaCu _0.2 Mn _0.8 O ₃ and LaCu _0.2 Cr _0.8 O ₃ .

In the method of the present invention, step (2) is applied to the treatment of acrylonitrile (C ₃ H ₃ N ) waste gas. The condition for catalytic combustion of acrylonitrile waste gas is that the space velocity is 120000h ^-1 , and the processing capacity is increased while ensuring the catalytic effect , reduce the amount of catalyst. The volume ratio of acrylonitrile to oxygen is preferably 0.3:1.2. The optimum reaction temperature range is 350°C to 550°C.

The present invention is characterized in that:

(1) For the first time, benzyl alcohol was used as a solvent to prepare a metal composite oxide with a perovskite crystal form under low temperature and high pressure, which increased its specific surface area (56m ² /g), while the citric acid complexation method (traditional method ) The average specific surface area of perovskite prepared is lower than 15m ² /g. The catalyst prepared by this method improves the selectivity of the catalyst.

(2) Through the screening and combination of B-site metal ions, a catalyst that can be applied to the removal of acrylonitrile tail gas was successfully obtained. Controlling the operating conditions of the reaction for selective catalytic combustion can convert acrylonitrile into harmless N ₂ , H ₂ O and CO ₂ with high selectivity.

(3) In the present invention, the light-off temperature of the catalyst is low, and excessive oxidation of nitrogen can be avoided in the high-temperature section to form another pollutant NO _X . This reaction is an exothermic reaction with low energy consumption.

Description of drawings:

Fig. 1 is the X-ray diffraction figure (XRD) of the _LaFeO3 that the inventive method and traditional method prepare, wherein (a) is the XRD figure of the product obtained by benzyl alcohol method (method in the present invention), (b) is lemon The XRD pattern of the product prepared by the acid complexation method (traditional method), compared with the standard spectrum (no.74-2203), the products prepared by the two methods both have a perovskite crystal structure, indicating that the new method can also prepare a crystal structure Preferred perovskite metal oxides.

Fig. 2 is a scanning electron microscope (SEM) image of LaFeO ₃ synthesized by the benzyl alcohol method in the method of the present invention. The morphology is all similar to small spheroids, and the particle dispersion is relatively obvious.

Fig. 3 is the activity evaluation diagram of _LaFeO3 prepared by two different methods in Example 1 and Comparative Example 1 in the present invention, the conversion rate of acrylonitrile and the curves of the change of product carbon dioxide and nitrogen with temperature. Wherein (a) represents the result obtained with the catalyst in Example 1, and (b) represents the result obtained with the catalyst in Comparative Example 1. It can be seen from the figure that the catalyst synthesized by the new method can significantly increase the yield of N ₂ .

Fig. 4 is in the method of the present invention, adopts LaFeO ₃ as catalyst at different volume ratios of acrylonitrile and oxygen, the production rate of nitrogen varies with temperature. In the figure, 1%, 1.2%, and 8% respectively represent different oxygen concentrations, and the concentration of acrylonitrile is 0.3%. It can be seen from this figure that the selectivity of the catalyst to nitrogen is optimal at an oxygen concentration of 1.2%.

Figure 5 is an evaluation diagram of the catalytic combustion of acrylonitrile for different types of perovskite-type metal composite oxides when the B sites are Co, Cu, Cr, Mn and Fe elements under the condition of an oxygen concentration of 1.2%, where (a ) is the change curve of acrylonitrile conversion rate with temperature, (b) is the change curve of N ₂ yield with temperature.

Figure 6 shows the catalytic combustion of propylene by different types of perovskite metal composite oxides under the condition of oxygen concentration of 1.2%, when the B site is bimetallic and Cu: M (Co, Cr, Mn, Fe) = 0.2:0.8 Nitrile activity evaluation graph, where (a) is the curve of acrylonitrile conversion rate versus temperature, and (b) is the graph of _N2 yield versus temperature.

Detailed ways

Embodiment 1: Measure 60ml of benzyl alcohol and pour it into a 100ml small beaker, add a magnetic stirring bar and stir and heat in a constant temperature magnetic stirrer, and set the temperature to 80°C. Weigh 2.209 grams of lanthanum nitrate and pour it into a small beaker. After it is completely dissolved, add 1.802 grams of iron acetylacetonate. After 20 minutes, the mixed solution is transferred to a high-pressure static reactor. Reactor is put into the oven that temperature is 200 ℃, maintains 24 hours, takes out afterwards. Centrifuge with a centrifuge (8000 rpm, 10 minutes), pour off the upper layer solution, wash with absolute ethanol, and centrifuge twice. The resulting precipitate was mixed with absolute ethanol, transferred to a drying dish, and dried in an oven. Grind the loose powder to make the particles fine enough. Put it into a muffle furnace and bake at 450°C for 6 hours. Finally, a metal oxide LaFeO ₃ with a perovskite crystal form is obtained.

The prepared metal powder was pressed into tablets, and 40-60 mesh particles were screened out, and 0.2 g of catalyst particles were weighed, placed in a micro-fixed-bed quartz reactor, and then the activity evaluation experiment was carried out by simulating the tail gas condition of acrylonitrile under normal pressure. A mixed gas containing acrylonitrile (0.3vol%), O ₂ (1.2%) and N ₂ (as balance gas) was introduced into the reaction furnace at a space velocity of 120000 ^h ℃ test once, the reaction temperature is: 100 ~ 600 ℃. An American Nicolet Nexus 470 infrared spectrometer with a 2.4m optical path gas analysis cell was used for on-line gas quantitative analysis to obtain the conversion rate of acrylonitrile and the yield of each reaction product. The experimental results obtained are shown in Figure 3.

Example 2: LaFeO ₃ obtained by the preparation method of the catalyst in Example 1 was evaluated under the condition that the volume ratio of acrylonitrile to oxygen was 0.3:1.0, and other conditions were the same as in Example 1. The experimental results obtained are shown in Figure 4 .

Example 3: LaFeO ₃ obtained by the preparation method of the catalyst in Example 1 is evaluated under the condition that the volume ratio of acrylonitrile to oxygen is 0.3:8.0, and the other conditions are the same as in Example 1. The experimental results obtained are shown in Figure 4 .

Embodiment 4: Measure 60ml of benzyl alcohol and pour it into a 100ml small beaker, add a magnetic stirring bar and stir and heat in a constant temperature magnetic stirrer, and set the temperature to 80°C. Weigh 2.209 grams of lanthanum nitrate and pour it into a small beaker. After it is completely dissolved, add 1.336 grams of copper acetylacetonate. After 20 minutes, transfer the mixed solution into a high-pressure static reaction kettle. Reactor is put into the oven that temperature is 200 ℃, maintains 24 hours, takes out afterwards. Centrifuge with a centrifuge (8000 rpm, 10 minutes), pour off the upper layer solution, wash with absolute ethanol, and centrifuge twice. The resulting precipitate was mixed with absolute ethanol, transferred to a drying dish, and dried in an oven. Grind the loose powder to make the particles fine enough. Put it into a muffle furnace and bake at 550°C for 6 hours. Finally, a metal oxide La ₂ CuO ₄ with a perovskite crystal form is obtained. All the other steps are the same as in Example 1. The experimental results obtained are shown in Figure 5(a) and Figure 5(b).

Embodiment 5: Measure 65ml of benzyl alcohol and pour it into a 100ml small beaker, add a magnetic stirring bar and stir and heat in a constant temperature magnetic stirrer, and set the temperature to 80°C. Weigh 2.209 grams of lanthanum nitrate and pour it into a small beaker. After it is completely dissolved, add 1.782 grams of chromium(III) acetylacetonate. After 20 minutes, transfer the mixed solution into a high-pressure static reaction kettle. Reactor is put into the oven that temperature is 200 ℃, maintains 24 hours, takes out afterwards. Centrifuge with a centrifuge (8000 rpm, 10 minutes), pour off the upper layer solution, wash with absolute ethanol, and centrifuge twice. The resulting precipitate was mixed with absolute ethanol, transferred to a drying dish, and dried in an oven. Grind the loose powder to make the particles fine enough. Put it into a muffle furnace and bake at 500°C for 6 hours. Finally, the metal oxide LaCrO° with perovskite crystal form was obtained. All the other steps are the same as in Example 1. The experimental results obtained are shown in Figure 5(a) and Figure 5(b). the

Embodiment 6: Measure 60ml of benzyl alcohol and pour it into a 100ml small beaker, add a magnetic stirring bar and stir and heat in a constant temperature magnetic stirrer, and set the temperature to 80°C. Weigh 2.209 grams of lanthanum nitrate and pour it into a small beaker. After it is completely dissolved, add 1.818 grams of cobalt acetylacetonate. After 20 minutes, transfer the mixed solution into a high-pressure static reaction kettle. The reaction kettle was put into an oven with a temperature of 200oC, maintained for 24 hours, and then taken out. Centrifuge with a centrifuge (8000 rpm, 10 minutes), pour off the upper layer solution, wash with absolute ethanol, and centrifuge twice. The resulting precipitate was mixed with absolute ethanol, transferred to a drying dish, and dried in an oven. Grind the loose powder to make the particles fine enough. Put it into a muffle furnace and bake at 550°C for 6 hours. Finally, the metal oxide LaCoO° with perovskite crystal form was obtained. All the other steps are the same as in Example 1. The experimental results obtained are shown in Figure 5(a) and Figure 5(b). the

Embodiment 7: Measure 60ml of benzyl alcohol and pour it into a 100ml small beaker, add a magnetic stirring bar and stir and heat in a constant temperature magnetic stirrer, and set the temperature to 80°C. Weigh 2.209 grams of lanthanum nitrate and pour it into a small beaker. After it is completely dissolved, add 1.292 grams of manganese (II) acetylacetonate. After 20 minutes, transfer the mixed solution into a high-pressure static reaction kettle. Reactor is put into the oven that temperature is 200 ℃, maintains 24 hours, takes out afterwards. Centrifuge with a centrifuge (8000 rpm, 10 minutes), pour off the upper layer solution, wash with absolute ethanol, and centrifuge twice. The resulting precipitate was mixed with absolute ethanol, transferred to a drying dish, and dried in an oven. Grind the loose powder to make the particles fine enough. Put it into a muffle furnace and bake at 550°C for 6 hours. Finally, a metal oxide LaMnO ₃ with a perovskite crystal form is obtained. All the other steps are the same as in Example 1. The experimental results obtained are shown in Figure 5(a) and Figure 5(b).

Embodiment 8: Measure 120ml of benzyl alcohol and pour it into a 200ml small beaker, add a magnetic stirring bar, stir and heat in a constant temperature magnetic stirrer, and set the temperature to 80°C. Weigh 4.418 grams of lanthanum nitrate and pour it into a small beaker. After it is completely dissolved, add 2.067 grams of manganese (II) acetylacetonate and 0.534 grams of copper acetylacetonate, wherein La:Mn:Cu=1:0.8:0.2, uniform After stirring for 20 minutes, the mixed solution was transferred to a high-pressure static reactor. Reactor is put into the oven that temperature is 200 ℃, maintains 24 hours, takes out afterwards. Centrifuge with a centrifuge (8000 rpm, 10 minutes), pour off the upper layer solution, wash with absolute ethanol, and centrifuge twice. The resulting precipitate was mixed with absolute ethanol, transferred to a drying dish, and dried in an oven. Grind the loose powder to make the particles fine enough. Put it into a muffle furnace and bake at 550°C for 6 hours. Finally, the metal oxide LaCu _0.2 Mn _0.8 O ₃ with perovskite crystal form was obtained. All the other steps are the same as in Example 1. The experimental results obtained are shown in Figure 6(a) and Figure 6(b).

Embodiment 9: Measure 120ml of benzyl alcohol and pour it into a 200ml small beaker, add a magnetic stirring bar, stir and heat in a constant temperature magnetic stirrer, and set the temperature to 80°C. Weigh 4.418 grams of lanthanum nitrate and pour it into a small beaker. After it is completely dissolved, add 2.852 grams of chromium (II) acetylacetonate and 0.534 grams of copper acetylacetonate, wherein La:Cr:Cu=1:0.8:0.2, uniform After stirring for 20 minutes, the mixed solution was transferred to a high-pressure static reactor. Reactor is put into the oven that temperature is 200 ℃, maintains 24 hours, takes out afterwards. Centrifuge with a centrifuge (8000 rpm, 10 minutes), pour off the upper layer solution, wash with absolute ethanol, and centrifuge twice. The resulting precipitate was mixed with absolute ethanol, transferred to a drying dish, and dried in an oven. Grind the loose powder to make the particles fine enough. Put it into a muffle furnace and bake at 550°C for 6 hours. Finally, the metal oxide LaCu _0.2 Cr _0.8 O ₃ with perovskite crystal form was obtained. All the other steps are the same as in Example 1. The experimental results obtained are shown in Figure 6(a) and Figure 6(b).

Example 10: Measure 120ml of benzyl alcohol and pour it into a 200ml small beaker, add a magnetic stirring bar, stir and heat in a constant temperature magnetic stirrer, and set the temperature to 80°C. Weigh 4.418 grams of lanthanum nitrate and pour it into a small beaker. After it is completely dissolved, add 2.908 grams of cobalt (II) acetylacetonate and 0.534 grams of copper acetylacetonate, wherein La:Co:Cu=1:0.8:0.2, uniform After stirring for 20 minutes, the mixed solution was transferred to a high-pressure static reactor. Reactor is put into the oven that temperature is 200 ℃, maintains 24 hours, takes out afterwards. Centrifuge with a centrifuge (8000 rpm, 10 minutes), pour off the upper layer solution, wash with absolute ethanol, and centrifuge twice. The resulting precipitate was mixed with absolute ethanol, transferred to a drying dish, and dried in an oven. Grind the loose powder to make the particles fine enough. Put it into a muffle furnace and bake at 500°C for 6 hours. Finally, the metal oxide LaCu _0.2 Co _0.8 O ₃ with perovskite crystal form was obtained. All the other steps are the same as in Example 1. The experimental results obtained are shown in Figure 6(a) and Figure 6(b).

Example 11: Measure 120ml of benzyl alcohol and pour it into a 200ml small beaker, add a magnetic stirring bar, stir and heat in a constant temperature magnetic stirrer, set the temperature to 80°C. Weigh 4.418 grams of lanthanum nitrate and pour it into a small beaker. After it is completely dissolved, add 2.883 grams of iron acetylacetonate and 0.534 grams of copper acetylacetonate, wherein La:Fe:Cu=1:0.8:0.2, and stir evenly for 20 minutes Afterwards, the mixed solution was transferred to a high-pressure static reactor. Reactor is put into the oven that temperature is 200 ℃, maintains 24 hours, takes out afterwards. Centrifuge with a centrifuge (8000 rpm, 10 minutes), pour off the upper layer solution, wash with absolute ethanol, and centrifuge twice. The resulting precipitate was mixed with absolute ethanol, transferred to a drying dish, and dried in an oven. Grind the loose powder to make the particles fine enough. Put it into a muffle furnace and bake at 450°C for 6 hours. Finally, the metal oxide LaCu _0.2 Fe _0.8 O ₃ with perovskite crystal form was obtained. All the other steps are the same as in Example 1. The experimental results obtained are shown in Figure 6(a) and Figure 6(b).

Comparative Example 1: Weigh 8.660g of La(NO ₃ ) ₃ 6H ₂ O (chemically pure reagent) and 8.080g of Fe(NO ₃ ) ₂ 9H ₂ O (chemically pure reagent), dissolve them in 300ml of In deionized water, in which the molar ratio of La and Fe is 1:1, 8.403g of citric acid (chemically pure reagent) is added at the same time, and the molar ratio of citric acid to the sum of metal ions is 1:1 and dissolved to form a solution. Place the prepared mixed liquid in a magnetic stirring heating mantle at about 80°C. After heating for 3 to 4 hours, a sol will form. When the remaining liquid is 15 ml, transfer it to an oven at 80°C to dry for 24 hours. Add 5ml of absolute ethanol under low temperature, ignite for combustion, transfer the burnt material to the muffle furnace, and raise it from room temperature to 650°C at 2°C/min in the air atmosphere, and keep it for 6 hours. After cooling to room temperature, a metal oxide catalyst powder LaFeO ₃ with a perovskite crystal form was finally obtained. All the other are with embodiment 1. The experimental results obtained are shown in Figure 3.

Claims (3)

1. A preparation method for a catalyst containing acrylonitrile waste gas treatment, characterized in that: by using benzyl alcohol as solvent and metal organic salt as metal ion source, adopting static reactor, at 70 ℃～80 ℃ and the reaction time is 20-minutes, then place the static reaction kettle in an oven at 200°C for 24 hours, take it out after cooling at room temperature, and centrifuge to obtain a solid substance, which is washed with absolute ethanol until the benzyl alcohol is completely removed; the obtained solid substance Transfer to 100°C oven and dry for 24 hours, calcined in a muffle furnace, calcined at 450°C-550°C for 6 hours, and naturally lowered to room temperature to obtain the desired perovskite metal oxide ABO ₃ ; where A Alkaline earth metal, B is a transition metal, metal nitrate is selected as the metal organic salt at the A position, and acetylacetonate is selected as the metal organic salt at the B position; the molar ratio of the metal organic salt to benzyl alcohol is 1:100-120. 2. The preparation method according to claim 1, characterized in that: the synthesized metal composite oxides include: LaFeO ₃ , LaCoO ₃ , LaMnO ₃ , La ₂ CuO ₃ , LaCrO ₃ , LaCu _0.2 Co _0.8 O ₃ , LaCu _0.2 Fe _0.8 O ₃ , LaCu _0.2 Mn _0.8 O ₃ and LaCu _0.2 Cr _0.8 O ₃ ; the screening and combination of B-site metal ions are Cu:Fe=0.2:0.8, Cu:Cr=0.2:0.8 and Cu:Mn=0.2 : 0.8, the above ratios are molar ratios. 3. The application of a catalyst for the treatment of acrylonitrile-containing waste gas prepared by the preparation method of claim 1, characterized in that it is applied to the treatment of acrylonitrile waste gas, and the experimental conditions are a space velocity of 80000-120000h ^-1 , acrylonitrile and oxygen The concentration to volume ratio is 0.3:1 to 10, and the reaction temperature is 350°C to 550°C.

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