WO2015184911A1

WO2015184911A1 - Process for preparing vanadium-base scr catalyst coating for purifying tail gas of diesel vehicle

Info

Publication number: WO2015184911A1
Application number: PCT/CN2015/075250
Authority: WO
Inventors: 张鹏; 李云; 徐磊; 李奎; 吴春燕; 鲜建; 曾东
Original assignee: 四川中自尾气净化有限公司
Priority date: 2014-06-06
Filing date: 2015-03-27
Publication date: 2015-12-10
Also published as: CN103977790B; CN103977790A

Abstract

The present invention relates to a method for preparing a catalyst coating for removing nitrogen oxides from tail gas of a diesel vehicle. The catalyst is composed of V₂O₅, WO₃ and TiO₂. Fresh and aging sample bench tests show that the coating has a high nitrogen oxide removal rate (≥85%) at 250°C to 500°C, and the coating passes the ETC and ESC working condition cycle tests and conforms to the national IV emission limit. In the process, size mixing is conducted on the precursor to obtain catalyst slurry at one step, and the catalyst slurry is subjected to primary coating (the coated amount ≥210 g/L), drying, and roasting to obtain a honeycomb catalyst. The process is simple, has a low cost and high stability, and is suitable for mass production.

Description

Preparation process of vanadium-based SCR catalyst coating for diesel vehicle exhaust gas purification

Technical field

The invention relates to a preparation process of a catalyst coating, in particular to a preparation process of a nitrogen oxide removal catalyst coating, in particular to a mobile source represented by diesel exhaust gas and represented by a coal-fired power plant. A process for preparing a vanadium tungsten titanium catalyst coating with fixed source nitrogen oxides removed.

Background technique

Nitrogen oxides (NO _x ) are one of the most important pollutants in the atmosphere. Not only has strong biological toxicity (especially stimulating the respiratory system), but also one of the main causes of acid rain and photochemical smog. Now the serious air pollution control NO _x emissions without delay, the world has been widely introduced legally enforceable emission limits.

Various NO _x removal art, NH ₃ -SCR because efficient, durable, has become the mainstream technology is mature. Among them, vanadium-based SCR is widely used for its good activity, excellent sulfur resistance, mature technology and low price. In view of the high sulfur content of diesel in China, vanadium-based SCR has become an inevitable choice for heavy-duty diesel vehicles to pass the national IV emission standard due to its excellent sulfur tolerance. FAW, Yuchai, Zhongqi, Weichai, etc. have confirmed the plan. Almost all coal-fired power plants also use vanadium-based SCR as an aftertreatment system due to high sulfur content in the flue gas.

At present, the vanadium-based SCRs produced by the main domestic mobile source catalyst manufacturers Weifu Lida, Guiyan, and Zibo Catalyst can meet the national IV emission standards, so the focus of competition will be on cost and stability. At present, the mature products on the market are made of titanic acid or titanium dioxide impregnated with tungsten, dried and calcined to obtain titanium tungsten powder (patent CN 102698737A, CN102764662A, CN103586017A). The titanium tungsten powder is further impregnated with vanadium, dried and calcined to obtain a catalyst powder, and the powder is refined to obtain a catalyst slurry (CN103252232, CN103263912A, CN103263912A). This process uniformly disperses vanadium and tungsten into the pores of titanium dioxide by dipping, and forms insoluble matter by drying and baking to fix it. Mixing all the raw materials directly, that is, "one-pot cooking" is the most economical and effective method for preparing the catalyst. However, the slurry is directly mixed with titanium dioxide, vanadium and tungsten. The tungsten and vanadium in the solution will migrate and enrich as the water evaporates, resulting in uneven dispersion, easy sintering, and poor activity and durability. The process requires preparation of titanium tungsten powder, and further slurrying and coating is required, the process is long, the cost is high, and the stability is poor; the patent (CN102698736A) discloses a technique for preparing a slurry by adjusting the slurry using titanium tungsten powder as a carrier. Since it is not impregnated, dried, and calcined, vanadium oxalate in the solution will migrate during the drying process, resulting in uneven dispersion and inability to ensure durability. Patent (201010274007.4) A method for directly preparing a catalyst slurry by using titanium dioxide is disclosed. However, neither tungsten nor vanadium can be effectively dispersed and fixed, the durability of the catalyst can not be ensured, and the dispersion means is difficult, and the slurry is difficult to be coated at one time. Achieve sufficient uploads. The invention uses a titanium source, an active ingredient and an auxiliary agent to form a honeycomb catalyst by slurrying, primary coating, drying and calcination in four steps. When calcined, the carrier and the catalyst are simultaneously formed on the honeycomb substrate. The core technology is the use of anchoring dispersant, which can bond with tungsten and vanadium, and combine with titanium dioxide by adsorption and coordination, so that vanadium and tungsten in solution are uniformly dispersed and fixed into the pores of titanium dioxide, and dried. No migration occurred during the process, which ensured that tungsten and vanadium were uniformly dispersed on the titanium dioxide. For the first time, a one-pot boiling process was carried out to prepare a vanadium-based SCR catalyst with reliable performance. At the same time, the anchoring dispersant has a dispersing effect on the titanium dioxide, so that the slurry has good fluidity and no delamination, and the primary coating can exceed 210 g/L. Because the method has the advantages of low raw materials, simple process and short cycle, the cost is low and the product stability is good.

Summary of the invention

In view of the shortcomings of existing vanadium-based SCR catalysts, in order to solve the disadvantages of high raw material cost, complicated process and poor stability of vanadium-based SCR catalysts, the present invention provides for the first time to realize a fusion of carrier preparation technology, catalyst powder preparation technology and slurry preparation technology. The catalyst slurry is prepared in one step by using a titanium source, an active ingredient and an auxiliary agent, and the technique of preparing a honeycomb catalyst coating by one coating, drying and calcination is carried out. May be used in diesel vehicles as the representative of the movement source to the flue gas and coal-fired power source represented by a fixed NO _x removal, the present invention is preferably used for catalytic NO _x purifying diesel exhaust.

Accordingly, an object of the present invention to provide a process for the preparation of titanium-tungsten, vanadium oxide catalyst coating for the removal of NO _x.

In order to achieve the above object, the present invention adopts the following technical solutions:

(1) Mixing the vanadium source and the tungsten source, adding an anchoring dispersant to form a mixed solution.

(2) Adding a titanium source and heating and aging.

(3) Adding a binder

(4) applying the slurry prepared in the step (3) to a cordierite ceramic honeycomb carrier

(5) Drying and roasting

In the step (1), the vanadium source is selected from the group consisting of vanadate, vanadium or vanadium oxide, preferably from vanadate, vanadyl sulfate, vanadium pentoxide, vanadium oxychloride, vanadium pentoxide. Kind or a mixture of at least two.

In the step (1), the tungsten source is selected from the group consisting of ammonium metatungstate, ammonium tungstate, ammonium paratungstate, or a mixture of at least two.

In the step (1), the solvent is selected from the group consisting of OP-10, citric acid, tartaric acid, polyacrylic acid, hydrogen peroxide, or a mixture of at least two.

In the step (2), the titanium source is selected from any one or a mixture of metatitanic acid and titanium dioxide.

In the step (3), the binder is any one or a mixture of at least two of pseudoboehmite, aluminum sol, silica sol, zirconium sol, and zirconium acetate.

In the step (3), the aging temperature is 50 to 90 ° C, preferably from 50 to 60 ° C.

In the step (3), the aging time is 0.5 - 5 h, preferably from 0.5 - 1 h.

In the step (4), the coating was carried out using an automatic coating machine once.

In the step (5), the drying temperature is from 10 to 170 ° C, preferably from 70 to 80 ° C.

In the step (5), the drying time is from 0.5 to 5 h, preferably from 0.5 to 1 h.

In the step (5), the calcination temperature is from 250 to 650 ° C, preferably from from 250 to 300 ° C.

In the step (5), the calcination time is from 0.5 to 5 h, preferably from 1 to 2 h.

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

(1) The preparation process of the vanadium-titanium-tungsten catalyst is short, the production cycle is short, the raw materials are cheap, and the manufacturing cost is greatly reduced compared with the conventional process.

(2) The preparation process of the vanadium-titanium-tungsten catalyst is good, and the product consistency is higher than the conventional process.

(3) The vanadium-titanium-tungsten catalyst preparation process adopts a single coating process, which effectively reduces the damage of the cordierite carrier caused by repeated coating, drying and roasting.

(4) The preparation process of the vanadium-titanium-tungsten catalyst does not produce solid or liquid waste, and the post-treatment cost is low.

detailed description

In order to better explain the present invention, it is convenient to understand the technical solution of the present invention, and a typical but non-limiting embodiment of the present invention is as follows:

Example 1

1 kg of citric acid and 0.5 kg of polyacrylic acid were dissolved in 25 kg of deionized water. 0.97kg was added ammonium vanadate (NH ₄ VO _3), 1.06kg of ammonium metatungstate dissolved with stirring. 20.20 kg of titanium dioxide was added with stirring until a uniform suspension was formed, which was then aged at 50 ° C for 2 h. Add silica sol (SiO ₂ content 25%)

4.2 kg and stirred uniformly to obtain a catalyst slurry.

The obtained slurry was applied to a cordierite ceramic carrier by a coater, dried at 80 ° C for 1 hour, and then calcined at 300 ° C for 1 hour to obtain a honeycomb catalyst called catalyst A.

The other conditions were the same as in Example 1, and no anchoring dispersant was added. The obtained honeycomb catalyst was referred to as Catalyst D.

Example 2

The other conditions were the same as in Example 1. The anchoring dispersant was changed to 0.6 kg of tartaric acid and 0.4 kg of OP-10, and the obtained honeycomb catalyst was referred to as Catalyst B.

Example 3

Other conditions were the same as in Example 1. The anchoring dispersant was changed to 0.5 kg of hydrogen peroxide and 1 kg of OP-10, and the obtained honeycomb catalyst was referred to as Catalyst C.

The evaluation of the activity of the catalyst provided by the present invention comprises the following steps:

1, tungsten vanadium titanium catalyst A prepared in Example 1-3 embodiment, B, C, D for NO _x removal efficiency investigated in a fixed bed reactor.

The catalyst used was 1*1 in., 400 cpsi. The composition of the mixed gas is: [NO]=[NH ₃ ]=500ppm, [O ₂ ]=10%, [H ₂ O]=8%, N ₂ as the equilibrium gas, the space velocity is 40,000h ^-1 , the reaction temperature 200–500 ° C. The gas components are all detected by infrared. Conversion of NO _x which are shown in Table 1. The letters in parentheses represent the state, f represents freshness, and a represents ageing, such as B(a) indicating the aging of Catalyst B. Aging conditions: temperature 600 ° C, water vapor content 5%, airspeed 40,000 h ^- .

The results are shown in Table 1. It can be seen that the catalyst prepared by the process has good activity in fresh and aged samples. Among them, the performance of A full temperature section is balanced, the performance of fresh aging is balanced; B is biased towards high temperature performance; C is biased towards low temperature performance. It can be seen that citric acid and polyacrylic acid are the best anchoring dispersants. D fresh sample has good low temperature activity and high temperature difference. After aging, the whole temperature range is obviously degraded, which fully demonstrates the effect of anchoring agent in improving the activity and durability in "one pot cooking".

2, a titanium-tungsten vanadium catalyst A prepared in Example 1 stage embodiment NO _x removal efficiency test, and the conditions for the ETC cycle ESC cycle. The catalyst used was 267*152 cm, 400 cpsi; the latter was 267*101 cm, 400 cpsi. The engine is Weichai WP7 with a displacement of 7.14L. The exhaust gas is quantitatively detected using an infrared gas pool. The catalyst was subjected to cycle aging for a period of 500 h. After the aging is completed, the ETC cycle and the ESC cycle condition test are performed. Which NO _x removal ratio shown in Table 2.

The results are shown in Table 2. It can be seen that the fresh, aged ETC and ESC cycle emissions of the catalyst prepared in Example 1 are lower than the national IV emission limits.

3. A large sample of 10 samples was prepared by the method described in Example 1, and 10 large samples were prepared by a conventional method, and a small sample was subjected to a simulation test to calculate the variance of the conversion rate at 250 and 500 °C. As can be seen from Table 3, the variance of the conversion rate of the present invention is significantly smaller than that of the conventional process, that is, the stability is significantly better than the conventional process.

The Applicant clarifies that the detailed composition and method of the present invention are described by the above embodiments, but the present invention is not limited to the above detailed composition methods, and does not mean that the present invention must be implemented by relying on the above detailed compositions and methods. It should be apparent to those skilled in the art that any modification of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific means, etc., fall within the scope of protection and disclosure of the present invention. .

NO _x conversion catalyst Table 1 Example 1-3

Table 2 Comparison of fresh and aged nitrogen oxide emissions from the catalyst rack of Example 1

Table 3: Comparison of the conversion rate between the process of the present invention and the traditional process

Claims

A catalyst coating for removing nitrogen oxides, the catalytic component consisting of vanadium, tungsten and titanium, the mass ratio of which is 0.5% to 6% for V 2 O 5 and 0.3% to 15% for WO 3 , TiO 2 It is 80%–96%.
The method for preparing a catalyst coating according to claim 1, wherein the following steps are carried out:

(1) Mixing the vanadium source and the tungsten source, adding an anchoring dispersant to form a mixed solution.

(2) Adding a titanium source and heating and aging.

(3) Add a binder.

(4) The slurry prepared in the step (3) is applied onto a cordierite ceramic honeycomb support.

(5) Drying and roasting.
The method according to claim (1), wherein the vanadium source is any one or at least two of ammonium vanadate, vanadyl sulfate, vanadium pentoxide, vanadium oxychloride, vanadium pentoxide. Kind of mixture.
The method according to claim (1), wherein the tungsten source is any one or a mixture of two kinds of ammonium metatungstate, ammonium tungstate, ammonium paratungstate.
The method according to claim (1), wherein the anchor dispersant is any one or a mixture of at least two of OP-10, citric acid, tartaric acid, polyacrylic acid, hydrogen peroxide.
The method according to claim (2), wherein the titanium source is any one or a mixture of metatitanic acid and titanium dioxide.
The method according to claim (3), wherein the binder is any one or a mixture of at least two of pseudoboehmite, aluminum sol, silica sol, zirconium sol, and zirconium acetate. .