CN103785374B - A kind of C nano pipe demercuration catalyst and preparation method thereof - Google Patents

Abstract

The invention discloses a C nanotube mercury removal catalyst and a preparation method thereof. The catalyst includes a carrier and an active material attached to the carrier, the carrier is a carbon nanotube, and the active material is an oxide of cerium and chromium; The oxide of cerium mentioned above is formed by roasting the soluble salt of cerium, and the oxide of chromium is produced by roasting the soluble salt of chromium. The preparation method of C nanotubes is as follows: using carbon nanotubes, soluble salts of cerium and soluble salts of chromium as raw materials, the molar ratio of Ce and Cr elements is 4~1:1, soaking carbon nanotubes with concentrated nitric acid 1. Adding the soluble salt of cerium and the soluble salt of chromium to impregnate, dry and roast to obtain the medium temperature demercuration catalyst. The catalyst has high activity and selectivity between 300 and 400°C, so it is very suitable for SCR denitrification devices with low ash layout. The catalyst has a wide range of raw materials and simple preparation process, and is a good medium temperature catalyst.

Description

A kind of C nanotube mercury removal catalyst and preparation method thereof

technical field

The invention relates to the technical field of mercury removal from flue gas, in particular to a C nanotube mercury removal catalyst and a preparation method thereof.

Background technique

Mercury is the only liquid metal element in nature, and its melting point is only -38.89°C. It has a long history as a poison and is among the most toxic trace elements. Although the pollution of mercury to the ecological environment is slow, it will accumulate in organisms after entering the atmosphere, water and soil, causing serious harm to the human ecological environment. The Ministry of Environmental Protection of China promulgated the latest "Emission Standards of Air Pollutants for Thermal Power Plants (GB13223-2011)", which requires that the emission of mercury and compounds in coal-fired flue gas of power plants be controlled at 0.03mg/nm ³ from 2015 onwards.

For the emission control of mercury in combustion flue gas, currently more mature mercury removal methods include SCR catalytic oxidation method and adsorption method represented by activated carbon. Because the activated carbon adsorption method has the characteristics of low capacity, poor mixing, and low thermodynamic stability, and the utilization rate of activated carbon is low, the consumption is large, and the cost of directly using the activated adsorption method is too high. SCR mercury removal technology can be divided into SCR with high ash arrangement, SCR with low ash arrangement and SCR with terminal arrangement according to different arrangement positions. However, due to the limitation of mercury removal temperature, most factories adopt high ash layout. In my country, due to the lack of clean coal technology, the content of fly ash after coal combustion is very high. It directly leads to serious catalytic blockage and passivation, the service life of the catalyst is shorter than that of foreign countries, and the cost of mercury removal in power plants is significantly increased.

Contents of the invention

In view of the above-mentioned problems existing in the prior art, an object of the present invention is to provide a mercury removal catalyst with high selectivity, strong anti-poisoning and excellent reactivity, which is suitable for various fixed source of mercury removal.

Another object is to provide a method for preparing the above-mentioned mercury removal catalyst.

In order to achieve the above object, the present invention adopts the following technical scheme: a C nanotube mercury removal catalyst, comprising a carrier and an active substance attached to the carrier, the carrier is a carbon nanotube, and the active substance is made of cerium and chromium Oxides; the cerium oxides are produced by roasting cerium soluble salts, and the chromium oxides are produced by roasting chromium soluble salts. Carbon nanotubes constitute the catalyst's support shell, and cerium and chromium oxides constitute the catalyst's active nanoparticle core.

As an optimization, the molar ratio of the carbon nanotubes, water, cerium soluble salt and chromium soluble salt is: 1:10~1000:0.0001~0.4:0.0001~0.1. The catalyst active components are configured within a reasonable range to achieve excellent mercury removal effects while saving catalyst raw materials.

As an optimization, the carbon nanotubes are single-wall nanotubes or multi-wall nanotubes, which increase their surface area and improve their catalytic activity. The diameter of the carbon nanotubes is between 8 and 10 nm.

A method for preparing the above-mentioned C nanotube mercury removal catalyst, comprising the following steps:

1) Using carbon nanotubes, water, soluble salts of cerium and soluble salts of chromium as raw materials, the carbon nanotubes are first purified with concentrated nitric acid with a mass fraction of 60% to 90%, and the carbon nanotubes are purified at a constant temperature of 70 to 90°C. Stir in a water bath for 2-10 hours, then rinse with deionized water until the pH is 6-7, and finally dry at 60-150°C;

2) Use the impregnation method to load active substances on the carbon nanotubes, specifically: first configure the soluble salt of cerium and the soluble salt of chromium into cerium solution and chromium solution respectively, and then add the carbon nanotubes obtained in step 1) to the cerium solution and chromium solution in a mixed solution of stirring and impregnating for 2 to 20 hours, then drying at 60 to 150°C, and finally burning under nitrogen protection for 2 to 10 hours at a burning temperature of 300 to 700°C to obtain catalyst samples, wherein , The molar ratio of cerium and chromium is 4~1:1, and the molar ratio of the sum of cerium and chromium to carbon is 0.01~0.5:1.

As an optimization, the soluble salt of cerium in the step 1) is one or more of cerous nitrate, ammonium cerium nitrate, cerous sulfate, ammonium ceric sulfate and cerium acetate; the soluble salt of chromium is chromium nitrate, carbonic acid One or more of chromium, manganese chromium sulfate. Catalyst active components come from a wide range of sources and are easy to purchase and prepare. If the soluble salts of cerium and chromium are prepared by mixing various soluble salts, the calculated value of the molar ratio of Ce and Cr in the various soluble salts can be within the range of the above requirements. .

Compared with the prior art, the present invention has the following advantages:

1. The mercury removal catalyst provided by the present invention is a carbon-based material loaded with cerium and chromium. The catalyst has high activity and selectivity between 300 and 400 °C, so it is very suitable for SCR denitrification devices with low ash layout. The catalyst has wide sources of raw materials and simple preparation process, and is a good medium temperature catalyst.

2. The mercury removal catalyst provided by the present invention is a breakthrough in the field of mercury removal technology. For the first time, it is proposed to use carbon-based materials as the carrier to support active substances to remove mercury, and it no longer completely depends on the traditional activated carbon adsorption method and titanium-tungsten-based SCR catalyst. Very good application prospects.

3. Due to the special confinement effect and quantum effect, the growth of active nanoparticles is restricted, and their size becomes smaller, which helps to generate more nanoparticle defects and oxygen vacancies, enhances its catalytic activity, and effectively enhances the selectivity of the reaction. . Once the oxides of cerium and chromium enter the confinement space of carbon nanotubes, their catalytic activity and selectivity will be effectively enhanced.

4. Excellent anti-poisoning ability. Compared with various traditional granular mercury removal catalysts, the tube wall of the mercury removal catalyst for C nanotubes provided by the present invention isolates solid toxic substances from the tube wall so that it cannot contact the active nanoparticles located inside the tube, avoiding The poisonous effect of the poison on the active nanoparticles.

Detailed ways

The present invention will be described in further detail below in conjunction with specific embodiments.

Example 1:

The catalyst raw materials are carbon nanotubes, water, cerium acetate, cerous nitrate and chromium nitrate. Carbon nanotubes are prepared by chemical vapor deposition. This method has the advantages of controllable preparation conditions and easy mass production. The diameter of carbon nanotubes is between 8 and 10 nm. The carbon nanotubes were first soaked in 68% concentrated nitric acid, stirred in a constant temperature water bath at 70°C for 2 hours, then rinsed with deionized water until the pH was 6, and finally dried at 60°C. Take 2 grams of concentrated nitric acid-treated carbon nanotubes, add 0.2 grams of cerium acetate, 0.2 grams of cerous nitrate (dissolved in an appropriate amount of water) and 0.2 grams of chromium nitrate (dissolved in 5ml saturated oxalic acid solution), stir well and impregnate After 2 hours, it was dried at 80°C, and then burned at 300°C for 3 hours under the protection of nitrogen to obtain the finished catalyst.

The prepared catalysts were put into a fixed-bed quartz tube reactor for activity and selectivity tests. The flue gas conditions are reaction conditions: the total gas flow rate is 1L/min, the mercury concentration is 50ug/m ³ , C _O2= 4%, C _CO2 =12%, C _HCl =5ppm, C _SO2 =400ppm, C _NO =150ppm, NH ₃ /NO=1:1, N ₂ is used as the balance gas, and the space velocity is 60000h ^-1 . In the reaction temperature range of 300-400°C, the mercury removal rate is stable above 85%.

Example 2:

The catalyst raw materials are carbon nanotubes, water, cerous nitrate, cerous sulfate and chromium carbonate. Carbon nanotubes were prepared by chemical vapor deposition. First soak carbon nanotubes with 80% concentrated nitric acid, stir in a constant temperature water bath at 80°C for 4 hours, then wash with deionized water until the pH is 6.5, and finally in 80°C drying. Take 2 grams of concentrated nitric acid-treated carbon nanotubes, add 1 gram of cerous nitrate, 0.5 g of cerous sulfate (dissolved in an appropriate amount of water) and 0.1 gram of chromium carbonate (dissolved in 5 ml of saturated oxalic acid solution), and stir evenly. After impregnation for 5 hours, dry at 60°C, and then burn at 400°C for 3 hours under the protection of nitrogen to obtain the finished catalyst.

The prepared catalysts were put into a fixed-bed quartz tube reactor for activity and selectivity tests. The flue gas conditions are reaction conditions: the total gas flow rate is 1L/min, the mercury concentration is 50ug/m ³ , C _O2= 4%, C _CO2 =12%, C _HCl =5ppm, C _SO2 =400ppm, C _NO =150ppm, NH ₃ /NO=1:1, N ₂ is used as the balance gas, and the space velocity is 60000h ^-1 . In the reaction temperature range of 300-400°C, the mercury removal rate is stable above 85%.

Example 3:

The catalyst raw materials are carbon nanotubes, water, cerous nitrate and manganese chromium sulfate. Carbon nanotubes were prepared by chemical vapor deposition. First soak the carbon nanotubes with 85% concentrated nitric acid, stir them in a constant temperature water bath at 80°C for 8 hours, then wash them with deionized water until the pH is 7, and finally place them at 100°C. drying. Take 2 grams of concentrated nitric acid-treated carbon nanotubes, add 0.2 grams of cerous nitrate (dissolved with an appropriate amount of water) and 0.1 grams of manganese chromium sulfate (dissolved with 5ml saturated oxalic acid solution), stir well and soak for 10 hours. °C, and then burned at 550 °C for 3 hours under the protection of nitrogen to obtain the finished catalyst.

The prepared catalysts were put into a fixed-bed quartz tube reactor for activity and selectivity tests. The flue gas conditions are reaction conditions: the total gas flow rate is 1L/min, the mercury concentration is 50ug/m ³ , C _O2= 4%, C _CO2 =12%, C _HCl =5ppm, C _SO2 =400ppm, C _NO =150ppm, NH ₃ /NO=1:1, N2 is used as the balance gas, and the space velocity is 60000h ^-1 . In the reaction temperature range of 300-400°C, the mercury removal rate is stable above 80%.

Example 4:

The catalyst raw materials are carbon nanotubes, water, cerous sulfate, ceric ammonium nitrate and chromium nitrate. Carbon nanotubes were prepared by chemical vapor deposition. First soak carbon nanotubes with 90% concentrated nitric acid, stir in a constant temperature water bath at 90°C for 10 hours, then wash with deionized water until the pH is 7, and finally immerse them in 150°C. drying. Take 2 grams of carbon nanotubes treated with concentrated nitric acid, add 2 grams of ammonium cerium nitrate, 1 gram of cerous sulfate (dissolved with an appropriate amount of water) and 0.2 grams of chromium nitrate (dissolved in 5 ml of saturated oxalic acid solution), stir well and After impregnating for 20 hours, dry at 120°C, and then burn at 700°C for 3 hours under the protection of nitrogen to obtain the finished catalyst.

The prepared catalysts were put into a fixed-bed quartz tube reactor for activity and selectivity tests. The flue gas conditions are reaction conditions: the total gas flow rate is 1L/min, the mercury concentration is 50ug/m ³ , C _O2= 4%, C _CO2 =12%, C _HCl =5ppm, C _SO2 =400ppm, C _NO =150ppm, NH ₃ /NO=1:1, N ₂ is used as the balance gas, and the space velocity is 60000h ^-1 . In the reaction temperature range of 300-400°C, the mercury removal rate is stable above 85%.

From the above examples and activity and selectivity tests, it can be seen that mercury removal by carbon nanotubes is feasible. Its mercury removal rate can reach about 80%. At the same time, the catalyst has wide sources of raw materials and a simple preparation process, and is a good medium-temperature catalyst. It has potential commercial research value and practical significance.

Finally, it is noted that the above embodiments are only used to illustrate the technical solutions of the present invention without limitation. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be carried out Modifications or equivalent replacements without departing from the spirit and scope of the technical solution of the present invention shall be covered by the claims of the present invention.

Claims (4)

1. a C nano pipe demercuration catalyst, is characterized in that: comprise carrier and be attached to the active material in carrier, described carrier is CNT, and described active material is the oxide of cerium and chromium; The oxide of described cerium generates after the soluble-salt roasting by cerium, and the oxide of chromium generates after the soluble-salt roasting by chromium;

The mol ratio of Ce elements and chromium element is 4 ~ 1:1, and the mol ratio of Ce elements and chromium element sum and carbon is 0.01 ~ 0.5:1.

2. C nano pipe demercuration catalyst as claimed in claim 1, is characterized in that: described CNT is single-walled nanotube or many walls nanotube.

3. prepare a method for C nano pipe demercuration catalyst according to claim 1, it is characterized in that, comprise the following steps:

1) with the soluble-salt of the soluble-salt of CNT, water, cerium and chromium for raw material, with mass fraction be first 60% ~ 90% red fuming nitric acid (RFNA) purification process is carried out to CNT, and stir 2 ~ 10 hours in the water bath with thermostatic control of 70 ~ 90 DEG C, then be 6 ~ 7 with deionized water rinsing to pH, finally dry at 60 ~ 150 DEG C;

2) infusion process carrying active substance is on the carbon nanotubes adopted, be specially: first the soluble-salt of the soluble-salt of cerium and chromium is configured to cerium solution and chromium solution respectively, then the CNT that step 1) obtains is joined in the mixed solution of cerium solution and chromium solution and stir dipping 2 ~ 20 hours, then dry at 60 ~ 150 DEG C, last calcination under nitrogen protection 2 ~ 10 hours, calcination temperature is 300 ~ 700 DEG C, obtain catalyst sample, wherein, the mol ratio of Ce elements and chromium element is 4 ~ 1:1, the mol ratio of Ce elements and chromium element sum and carbon is 0.01 ~ 0.5:1.

4. prepare as claimed in claim 3 the method for C nano pipe demercuration catalyst, it is characterized in that: in described step 1) the soluble-salt of cerium be in cerous nitrate, ammonium ceric nitrate, cerous sulfate, Cericammoniumsulfate and cerous acetate one or more; The soluble-salt of described chromium be in chromic nitrate, chromium carbonate, manganese sulfate chromium one or more.