CN115672299B - Titanium dioxide nanowire and preparation method thereof, denitration catalyst and preparation method thereof, and flue gas denitration method - Google Patents
Titanium dioxide nanowire and preparation method thereof, denitration catalyst and preparation method thereof, and flue gas denitration method Download PDFInfo
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Abstract
The invention relates to the field of catalysts, and discloses a titanium dioxide nanowire and a preparation method thereof, a denitration catalyst and a preparation method thereof and a flue gas denitration method. Based on the total weight of the titanium dioxide nanowire, the titanium dioxide nanowire comprises 99.9-100wt% of TiO 2, 0.001-0.004wt% of K 2 O,0.01-0.04wt% of Fe 2O3, 0.01-0.03wt% of Na 2 O and 0.01-0.03wt% of SO 3; the specific surface area of the titanium dioxide nanowire is 230-320m 2/g. The titanium dioxide nanowire has a large specific surface area, and when the titanium dioxide nanowire is used for preparing a denitration catalyst, doped active substances can be uniformly dispersed on a carrier, so that the service efficiency of active components is effectively improved, the aggregation of the active components is reduced, the number of active sites is increased, the gas diffusion and adsorption capacity are improved, and the denitration performance of the catalyst is further improved.
Description
Technical Field
The invention relates to the field of catalysts, in particular to a titanium dioxide nanowire and a preparation method thereof, a denitration catalyst containing the titanium dioxide nanowire and a preparation method thereof, and a flue gas denitration method.
Background
The combustion of coal produces a large amount of flue gas particles, nitrogen oxides, carbon oxides, sulfur dioxide and the like. Nitrogen oxides (NO x) are a collective name of NO and NO 2 species, NO x which is artificially discharged is mainly NO, and NO is rapidly oxidized in the air to form NO 2.NOx which is one of main pollutants in the atmosphere, and a large amount of nitrogen oxides in the atmosphere can not only directly harm ecological environment and human health, but also react with other pollutants to form secondary pollution with greater harm.
The Selective Catalytic Reduction (SCR) has become the mainstream denitration technology in coal-fired power plants because of its relatively mature technology and high efficiency in removing NO x. At present, the vanadium-tungsten-titanium catalyst has better denitration efficiency and sulfur dioxide poisoning resistance, is widely applied to removing nitrogen oxides discharged by fixed sources such as coal-fired thermal power plants, but the specific surface area of the carrier titanium dioxide or titanium-tungsten powder is smaller, the aperture is uneven, active components cannot be uniformly dispersed, and the active components are mostly covered on a TiO 2 carrier in the form of oxide clusters to influence gas mass transfer, so that the catalyst is easy to agglomerate and lose efficacy in the long-time operation process, thereby reducing the denitration efficiency, and the active temperature range is narrower (300-400 ℃). Therefore, the preparation of the TiO 2 carrier with larger specific surface area and uniform pore diameter is important to widening the temperature window of the denitration catalyst and reducing the activation temperature.
The existing commercial V-W-Ti catalysts are prepared by taking titanium dioxide as a carrier, and the titanium dioxide is prepared by taking ilmenite as a raw material. With the rising and rapid development of nanotechnology, nanomaterials have received a great deal of attention for their unique properties. The nano TiO 2 is widely applied to photocatalytic degradation, hydrogen production, solar cells, paint, catalyst carriers and the like due to the advantages of high chemical stability, no toxicity, acid and alkali resistance, simple preparation process, low cost and the like. How to effectively control the size and shape of nano particles, improve the performance of the nano particles through surface modification, reduce the agglomeration of nano TiO 2 and improve the dispersibility of the nano TiO 2 is a research hot spot in recent years. Compared with nano powder, the one-dimensional TiO 2 material has the advantages of large contact area with target degradation products, high dispersion of active components and the like, and is widely used as a carrier material of a catalyst. The existing preparation methods of the one-dimensional TiO 2 comprise a sol-gel method, a thermal decomposition method, a template method, a hydrothermal method and the like, wherein the hydrothermal method is most widely used due to the advantages of simplicity in operation, convenience in control of conditions, low cost and the like.
CN107445199a discloses a titanium dioxide nanowire array with a multilevel structure and a preparation method thereof, wherein the titanium dioxide nanowire array with a multilevel structure is an array formed by titanium dioxide nanowires, and the titanium dioxide nanowires have a multilevel structure and comprise titanium dioxide monocrystal nanowires and titanium dioxide nanoparticles coated on the surfaces of the titanium dioxide monocrystal nanowires. The titanium dioxide nano particles are coated on the surface of the titanium dioxide single-crystal nanowire, so that the formed array has high specific surface area and packing density, and electrochromic performance, capacitance performance, photoelectric performance and the like of the array can be improved.
CN107572582a discloses a preparation method of nano titanium dioxide nanowires, which comprises the following steps: preparing a reaction solution; the reaction solution consists of water, alkali with the molar concentration of 0.1M-0.5M, a titanium source, monohydric alcohol and/or polyhydric alcohol; heating the reaction solution by adopting a boiling reflux process or a hydrothermal method, so as to obtain titanate nanowires; pickling the titanate nanowire to obtain a titanate nanowire; and heating the titanic acid nanowire to obtain the titanium dioxide nanowire. By adopting the combined action of low-concentration alkali and monohydric alcohol and/or polyhydric alcohol, the titanium dioxide nanowire with uniform particle size and high purity can be prepared in a reaction solution with lower alkali concentration by adopting a hydrothermal method or a boiling reflux method, so that the process cost and the process danger are reduced.
CN109594067a discloses a method of rutile phase titanium dioxide nanowire array grown in the preferred orientation of the (001) crystal plane. The method comprises the following steps: 1) Preparing a Cr-doped titanium dioxide film as a seed crystal layer; 2) And (3) placing the Cr-doped titanium dioxide film seed layer prepared in the step (1) into a growth solution, and performing hydrothermal growth to obtain the rutile phase titanium dioxide nanowire array grown in preferred orientation. The method has the advantages of low cost, simple process requirement, good repeatability and large-scale manufacture, and the prepared titanium dioxide nanowire array has good preferential orientation growth and ultraviolet stimulated luminescence characteristics in the (001) direction.
However, in the prior art, titanium dioxide nanowires are hydrothermally synthesized by taking titanium dioxide or gas-phase titanium dioxide P25 as a raw material, and no report on preparation of titanium dioxide nanowires by taking inorganic nonmetallic ores or Ti (SO 4)2 as a raw material is yet available.
Disclosure of Invention
The invention aims to solve the problems of narrow denitration activity temperature window, limited active component dispersion degree and the like of an SCR denitration catalyst in the prior art, and provides a titanium dioxide nanowire, a preparation method thereof, a denitration catalyst, a preparation method thereof and a flue gas denitration method. Meanwhile, the titanium dioxide nanowire takes widely-distributed ilmenite as a raw material, ferrous sulfate waste residue obtained by deironing ilmenite in the preparation process is taken as an iron source, and can be used for preparing a denitration catalyst, so that all effective components Fe and Ti in the ilmenite are reasonably and efficiently utilized, and the comprehensive utilization rate of ilmenite resources is improved.
In order to achieve the above object, a first aspect of the present invention provides a titanium dioxide nanowire, characterized in that it comprises 99.9 to 100wt% of TiO 2, 0.001 to 0.004wt% of K 2 O,0.01 to 0.04wt% of Fe 2O3, 0.01 to 0.03wt% of Na 2 O, and 0.01 to 0.03wt% of SO 3, based on the total weight of the titanium dioxide nanowire;
The specific surface area of the titanium dioxide nanowire is 230-320m 2/g.
The second aspect of the present invention provides a method for preparing the titanium dioxide nanowire, which is characterized in that the method comprises the following steps:
(1) In the presence of a first dispersing agent, carrying out hydrolysis, aging and solid-liquid separation on the solution A to obtain a solid, and drying and calcining the solid to obtain nano TiO 2 particles;
(2) Mixing nano TiO 2 particles with an alkali solution in the presence of a second dispersing agent, performing hydrothermal crystallization reaction, and performing solid-liquid separation to obtain a solid;
(3) Sequentially carrying out acid washing and water washing on the solid obtained in the step (2), and roasting to obtain the titanium dioxide nanowire;
Wherein, in step (1), the solution a comprises TiOSO 4; in the step (3), the pickling conditions include: the acid concentration for acid washing is 0.01-0.2mol/L, and the acid washing time is 30-120min.
The third aspect of the invention provides a denitration catalyst, which comprises a carrier and active component elements loaded on the carrier, and is characterized in that the carrier is the titanium dioxide nanowire.
The fourth aspect of the present invention provides a method for producing the above-mentioned denitration catalyst, characterized in that the above-mentioned titanium dioxide nanowire is immersed in a solution containing an active component element.
A fifth aspect of the present invention provides a method for flue gas denitrification, comprising: in the presence of the denitration catalyst, the mixed gas containing ammonia, oxygen and nitrogen is subjected to catalytic denitration reaction.
Through the technical scheme, the titanium dioxide nanowire and the preparation method thereof, the denitration catalyst and the preparation method thereof and the flue gas denitration method obtain the following beneficial effects:
(1) The titanium dioxide nanowire provided by the invention has uniform morphology and large specific surface area, and when the titanium dioxide nanowire is used for preparing a denitration catalyst, doped active substances (transition metal elements or oxides) can be uniformly dispersed on a carrier, so that the use efficiency of active components is effectively improved, the aggregation of the active components is reduced, the number of active sites is increased, the gas diffusion and adsorption capacity is improved, and the denitration performance of the catalyst is further improved.
(2) According to the preparation method, ilmenite is used as a raw material to prepare the titanium dioxide nanowire material, the preparation method is simple to operate, low in cost, high in raw material utilization rate and high in titanium dioxide nanowire yield, and meanwhile, the method can realize the regulation and control of the morphology of the TiO 2 carrier to prepare the titanium dioxide nanowire with uniform morphology and larger specific surface area. The TiO 2 nano material produced by taking ilmenite as the raw material has both theoretical and practical significance and has more market application prospect. Realizing the high-efficiency recycling of ilmenite.
(3) In the invention, feSO 4 crystals generated in the process of preparing the titanium dioxide nanowire materials can be directly used for preparing the denitration catalyst and converted into active ingredients in the denitration catalyst, so that the aim of mineral resource utilization is fulfilled.
(4) According to the method for preparing the denitration catalyst, ilmenite widely distributed in China is fully utilized, so that the cost is saved, and Fe and Ti elements in the ilmenite are effectively utilized, so that the titanium dioxide nanowire denitration catalyst with excellent denitration performance is prepared.
Drawings
FIG. 1 is a process flow diagram of ilmenite for preparing a titanium dioxide nanowire denitration catalyst;
FIG. 2 is an X-ray powder diffraction pattern of nano TiO 2 particles and titanium dioxide nanowires produced in example 1;
FIG. 3 is a nitrogen adsorption-desorption isotherm plot of the titanium dioxide nanowire prepared in example 1;
FIG. 4 is an SEM image of the titanium dioxide nanowires prepared in example 1;
FIG. 5 is a graph showing the denitration activity of the titanium dioxide nanowire denitration catalyst obtained in example 1.
Detailed Description
The endpoints and any values of the ranges disclosed herein are not limited to the precise range or value, and are understood to encompass values approaching those ranges or values. For numerical ranges, one or more new numerical ranges may be found between the endpoints of each range, between the endpoint of each range and the individual point value, and between the individual point value, in combination with each other, and are to be considered as specifically disclosed herein.
The first aspect of the present invention provides a titanium dioxide nanowire, which is characterized by comprising 99.9-100wt% of TiO 2, 0.001-0.004wt% of K 2 O,0.01-0.04wt% of Fe 2O3, 0.01-0.03wt% of Na 2 O, and 0.01-0.03wt% of SO 3, based on the total weight of the titanium dioxide nanowire;
The specific surface area of the titanium dioxide nanowire is 230-320m 2/g.
In the invention, the titanium dioxide nanowire has uniform morphology and large specific surface area, and when the titanium dioxide nanowire is used as a carrier for preparing a catalyst, particularly a denitration catalyst, active components can be uniformly dispersed on the carrier, so that the service efficiency of the active components is effectively improved, the aggregation of the active components is reduced, the number of active sites is increased, the gas diffusion and adsorption capacity is improved, and the denitration performance of the catalyst is further improved.
Further, in order to further facilitate the dispersibility of the active components, it is preferable to include 99.93 to 100wt% of TiO 2, 0.001 to 0.0031wt% of K 2 O,0.01 to 0.023wt% of Fe 2O3, 0.01 to 0.0204wt% of Na 2 O, and 0.01 to 0.0222wt% of SO 3, based on the total weight of the titanium dioxide nanowire;
The specific surface area of the titanium dioxide nanowire is 260-300m 2/g.
According to the invention, the titanium dioxide nanowire is in the form of anatase.
In the present invention, the morphology of the titanium dioxide nanowire is determined by SEM the present invention is exemplified in fig. 4, and it can be seen from fig. 4 that the titanium dioxide nanowire of the present invention is one-dimensional and linear.
According to the invention, the aspect ratio of the titanium dioxide nanowire is 4-40.
In the invention, the length of the titanium dioxide nanowire is 200-400nm, and the diameter is 10-50nm.
In the invention, the specific surface area of the titanium dioxide nanowire is measured by an N 2 adsorption method; the composition of the titanium dioxide nanowire is measured by Inductively Coupled Plasma (ICP); the crystal structure of the titanium dioxide nanowire is measured by XRD.
The second aspect of the present invention provides a method for preparing the titanium dioxide nanowire, which is characterized in that the method comprises the following steps:
(1) In the presence of a first dispersing agent, carrying out hydrolysis, aging and solid-liquid separation on the solution A to obtain a solid, and drying and calcining the solid to obtain nano TiO 2 particles;
(2) Mixing nano TiO 2 particles with an alkali solution in the presence of a second dispersing agent, performing hydrothermal crystallization reaction, and performing solid-liquid separation to obtain a solid;
(3) Pickling the solid obtained in the step (2), and roasting to obtain the titanium dioxide nanowire;
Wherein, in step (1), the solution a comprises TiOSO 4; in the step (3), the pickling conditions include: the acid concentration for acid washing is 0.01-0.2mol/L, and the acid washing time is 30-120min.
According to the invention, the titanium dioxide nanowire is prepared by adopting the method, particularly, the solid after hydrothermal crystallization is subjected to acid washing, and further, the morphology of the TiO 2 carrier can be regulated and controlled by strictly controlling the acid washing condition in the step (3), so that the titanium dioxide nanowire with uniform morphology and larger specific surface area is prepared.
In order to obtain a titanium dioxide nanowire with a more uniform morphology, preferably, in the step (3), the pickling conditions include: the acid concentration for acid washing is 0.05-0.15mol/L, and the acid washing time is 40-80min.
According to the present invention, the acid for acid washing is at least one selected from the group consisting of hydrochloric acid, sulfuric acid and acetic acid.
According to the invention, the conditions for pickling further comprise: the pickling is carried out until the pH value of the pickling solution is not more than 1, preferably 1.
According to the present invention, in the step (3), the solid obtained in the step (2) is washed with acid and water in this order, and then baked.
According to the invention, the solid subjected to hydrothermal crystallization is sequentially subjected to acid washing and water washing, so that the linear morphology of the prepared titanium dioxide nanowire is more stable.
According to the present invention, the conditions for the water washing include: the water washing temperature is 40-60 ℃.
According to the present invention, the conditions of the water washing further include: washing with water until the conductivity of the washing liquid is less than 600 mu s/cm.
In the present invention, preferably, in the step (3), the solid is baked after washing with acid and water for 1 to 7 times in order.
According to the invention, in step (1), the conditions of the calcination include: the calcination temperature is 600-900 ℃, the calcination time is 3-6h, and the heating rate is 4-10 ℃/min.
Further, the calcining conditions include: the calcination temperature is 800-900 ℃, the calcination time is 4-6h, and the heating rate is 4-6 ℃/min.
In the invention, the crystal form of the nano TiO 2 particles is anatase and rutile mixed crystal, the morphology is spherical, the pore volume is 0.20-0.40cm 3/g, the specific surface area is 53-75m 2/g, and the pore diameter is 14-16nm.
According to the invention, the conditions of the hydrolysis include: the hydrolysis temperature is 90-120 ℃; the hydrolysis time is 3-5h. Preferably, the conditions of the hydrolysis include: the hydrolysis temperature is 100-110 ℃; the hydrolysis time is 3.5-4.5h.
According to the invention, the aging conditions include: the aging temperature is 20-30 ℃ and the aging time is 12-24h. Preferably, the aging conditions include: the aging temperature is 22-28 ℃, and the aging time is 12-24 hours.
According to the present invention, the first dispersant is selected from at least one of PEG400, PEG 800 and PEG 2000.
According to the invention, the first dispersant is used in an amount of 1 to 10 g.L -1 based on the total volume of the solution A. Preferably, the first dispersant is used in an amount of 2 to 8 g.L -1 based on the total volume of the solution A.
In the invention, the content of TiOSO 4 in the solution A is 100-200g/L, preferably 150-180g/L, calculated by Ti 4+.
According to the present invention, the alkali solution is selected from at least one of NaOH solution, KOH solution and Na 2CO3 solution.
According to the invention, the molar concentration of the alkaline solution is 8-12mol/L. Preferably, the molar concentration of the alkali solution is 10-12mol/L.
According to the invention, the mass volume ratio of the nano TiO 2 particles to the alkali solution is 1:80-120g/mL, preferably 1:80-100g/mL.
According to the present invention, the conditions for hydrothermal crystallization include: the temperature of the hydrothermal crystallization is 120-150 ℃, and the time of the hydrothermal crystallization is 20-30h. Preferably, the hydrothermal crystallization conditions include: the temperature of the hydrothermal crystallization is 120-140 ℃, and the time of the hydrothermal crystallization is 22-28h.
In the invention, the hydrothermal crystallization reaction is carried out in a closed reaction kettle.
According to the invention, the conditions of the calcination include: roasting at 400-550 deg.c for 4-6 hr; preferably, the roasting conditions include: the roasting temperature is 500-550 ℃ and the roasting time is 4.5-5.5h.
According to the present invention, the second dispersant is at least one selected from PEG400, PEG 800 and PEG 2000.
In the present invention, the first dispersant and the second dispersant may be the same or different. Preferably, the first dispersant and the second dispersant are the same.
According to the invention, the weight ratio of the second dispersant to the nano TiO 2 particles is 1.5-1:1, preferably 1.2-1:1.
In the prior art, titanium dioxide nanowires are prepared by taking titanium dioxide or gas-phase titanium dioxide as a raw material through hydrothermal synthesis, however, ilmenite (which contains rich Ti elements and Fe elements) is taken as an ore with very rich reserves in China. In the invention, the inventor discovers a method for preparing the titanium dioxide nanowire by taking ilmenite as a raw material through a great deal of creative research, and the method can fully and comprehensively utilize the comprehensive utilization rate of ilmenite resources.
In a preferred embodiment of the invention, the solution a is obtained by means of an acid treatment of ilmenite.
According to the invention, the solution A is obtained in the following way:
s1, performing a first contact reaction on ilmenite and sulfuric acid to obtain a first mixed material;
S2, carrying out a second contact reaction on the first mixed material and iron, and carrying out solid-liquid separation on the obtained material to obtain a second solution;
S3, cooling and crystallizing the second solution, and carrying out solid-liquid separation on the material obtained after cooling and crystallizing to obtain the solution A and a third crystal containing FeSO 4·7H2 O crystals.
According to the preferred embodiment of the invention, the Ti component in ilmenite is used for preparing the titanium dioxide nanowire to be used as a carrier of a denitration catalyst, and the third crystal containing FeSO 4·7H2 O crystals is used as an active substance of a denitration catalyst, so that ilmenite is fully utilized, and the maximum resource utilization is realized. The method of using the third crystal containing FeSO 4·7H2 O crystals will be described in detail later in the catalyst preparation process.
According to the present invention, in step S1, the conditions of the first contact reaction include: the temperature is 120-160 ℃ and the time is 2-4h. Preferably, the conditions of the first contact reaction include: the temperature is 130-150 ℃ and the time is 2.5-4h.
According to the invention, the weight ratio of ilmenite to sulfuric acid is 1 (1.1-1.6), preferably 1 (1.2-1.5).
In the present invention, the molar concentration of sulfuric acid is 10 to 20mol/L, preferably 13 to 14mol/L.
In the invention, in order to fully separate titanium and iron in the first mixed material and avoid the influence of iron ions on the color purity of the titanium dioxide nanowire product, fe 3+ is required to be completely reduced into Fe 2+, namely, an iron reducing agent is added in the acidolysis process. The reaction equation is as follows:
Fe3++Fe→Fe2+。
according to the present invention, in step S2, the conditions of the second contact reaction include: the temperature is 20-30 ℃; the time is 15-30min. Preferably, the conditions of the second contact reaction include: the temperature is 22-28 ℃; the time is 20-30min.
According to the invention, the weight ratio of ilmenite to iron is 1 (0.03-0.06); preferably 1 (0.03-0.05).
In the present invention, for sufficient contact, the iron is preferably in the form of powder, i.e., iron powder.
According to the present invention, in step S3, the cooling crystallization conditions include: the temperature is 0-6deg.C, and the time is 36-60h.
By the above method, ti in ilmenite is made to enter the A solution mainly in the form of TiOSO 4, while Fe is made to enter the third crystal mainly in the form of FeSO 4·7H2 O crystals.
According to the invention, the method further comprises: the solid obtained by solid-liquid separation in step (1) is washed and dried before the calcination is performed. The washing is, for example, respectively washing 2-5 times with deionized water and absolute ethanol in sequence, wherein the aim of the washing is to make the pH value of the washing filtrate close to neutral. The drying conditions preferably include: the drying temperature is 90-120 ℃ and the drying time is 4-8h.
The third aspect of the invention provides a denitration catalyst, which comprises a carrier and active component elements loaded on the carrier, and is characterized in that the carrier is the titanium dioxide nanowire.
The titanium dioxide nanowire can be used as a carrier for preparing catalysts for various reactions, and is preferably used for preparing denitration catalysts. The specific pore structure and the high specific surface area of the titanium dioxide nanowire can enable active ingredient elements to be uniformly dispersed on the carrier, effectively improve the use efficiency of active ingredients, reduce the aggregation of the active ingredients, improve the number of active sites, improve the gas diffusion and adsorption capacity, and further improve the denitration performance of the catalyst.
According to the invention, the active component elements are Fe element and at least one transition metal element selected from V, mn, co, ni, ru, rh, W, nb, ta, mo, ce, sb, cu and La.
According to the invention, the content of Fe element is 5-8wt% based on the total weight of the denitration catalyst and calculated by Fe 2O3; the content of the transition metal element is 5-15wt% calculated by metal oxide; the content of the carrier is 80-85wt% calculated by TiO 2.
In the invention, the Fe element can be completely from the third crystal containing FeSO 4·7H2 O crystal in the step S3, and the Fe element is not required to be additionally added, so that all the effective components Fe and Ti in the ilmenite are reasonably and efficiently utilized, and the comprehensive utilization rate of ilmenite resources is improved.
In the present invention, in order to obtain a denitration catalyst having more excellent catalytic effect, preferably, the content of the Fe element is 5 to 8wt% based on Fe 2O3, based on the total weight of the denitration catalyst; the content of the transition metal element is 5-15wt% calculated by metal oxide; the content of the carrier is 77-90wt% calculated by TiO 2.
According to the invention, the total content of the active component elements, calculated as metal oxide, does not exceed 20wt.%, based on the total weight of the denitration catalyst.
The fourth aspect of the present invention provides a method for producing the above-mentioned denitration catalyst, characterized in that the above-mentioned titanium dioxide nanowire is immersed in a solution containing an active component element.
The impregnation is carried out in a manner conventional in the art, and in order to make the impregnation more uniform, it is preferable to use a multi-impregnation method, that is, a method of drying after impregnation and then impregnating, and repeating the impregnation a plurality of times.
According to various embodiments, the solution containing the active ingredient element is obtained by dissolving the iron source and the transition metal source in water, preferably deionized water.
In order to fully utilize all the effective components Fe and Ti in the ilmenite, the comprehensive utilization rate of ilmenite resources is improved, and preferably, the iron source is the third crystal in the step S3.
In the present invention, the transition metal source is selected from at least one soluble salt of transition metal element selected from V, mn, co, ni, ru, rh, W, nb, ta, mo, ce, sb, cu and La. Preferably, the soluble salt is selected from at least one of oxalate, nitrate and sulfate.
In the invention, the method further comprises the following steps: drying and calcining the impregnated solid. Preferably, the drying conditions include: the drying temperature is 90-120 ℃ and the drying time is 4-8h. Preferably, the conditions of the calcination include: the calcination temperature is 500-600 ℃, the calcination time is 5-8h, and the temperature rising rate is 4-10 ℃/min.
In the present invention, the above-mentioned drying may be performed in a rotary evaporator.
A fifth aspect of the present invention provides a method for flue gas denitrification, comprising: and in the presence of the denitration catalyst, carrying out catalytic denitration reaction on the gas to be denitration containing the nitrogen oxides.
Preferably, the conditions for catalyzing the denitration reaction include: the temperature is 100-450 ℃, and the volume space velocity of the gas to be denitrified is 3000-150000h -1.
Preferably, the gas to be denitrated containing nitrogen oxides is formed by combining industrial waste gas containing nitrogen oxides with mixed gas containing ammonia, oxygen and nitrogen.
Preferably, in the industrial waste gas, the volume concentration of the nitrogen oxides in terms of NO is 100-1000ppm.
Preferably, in the mixture gas, the molar ratio of the amount of ammonia gas to the industrial waste gas in terms of NO is (1-3): 1, a step of; the oxygen content is 3-5% by volume; the remaining gas was N 2 (as balance gas).
The present invention will be described in detail by examples.
In the following examples, the crystal structure of the produced titanium dioxide nanowires was measured by XRD analysis, using D8 ADVANCE from Bruker, germany, at a test scan rate of 0.5 °/min-5 °/min;
the pore structure and the mesoporous pore diameter of the prepared titanium dioxide nanowire are measured by an N 2 adsorption method, and an ASAP 2020 physical adsorption instrument of Micromerics company in the United states is used, wherein the adsorption medium is N 2;
the morphology of the prepared titanium dioxide nanowires was determined by SEM using a Nova NanoSEM450 scanning electron microscope from zeck FEI company.
The ingredients in terms of oxides (in weight%) in the ilmenite used in the following examples are shown in table 1;
the other raw materials used in the examples and comparative examples are all commercially available.
TABLE 1 analysis results of chemical composition of ilmenite (wt.%)
| Al2O3 | SiO2 | TiO2 | Fe2O3 | FeO | K2O | CaO | MnO | MgO | Others | |
| Ilmenite of ilmenite | 1.23 | 4.68 | 44.6 | 3.05 | 35.75 | 0.134 | 1.06 | 0.64 | 4.52 | 4.336 |
Example 1
(I) Preparation of titanium dioxide nanowires
(I-1) mixing 10g of ilmenite with 11.76g of concentrated sulfuric acid (13.5 mol/L) and reacting at 120 ℃ for 1h to obtain a first mixture; and adding 0.3g of iron powder into a liquid phase obtained by solid-liquid separation of the first mixture, and carrying out contact reaction for 20min. Stopping heating, cooling to normal temperature, and suction filtering to obtain filtrate.
And (I-2) placing the filtrate at 2 ℃ for 48 hours, performing suction filtration to obtain solid crystals and filtrate, marking the filtrate as A solution, marking the crystals as A crystals, and sealing and preserving the crystals for later use.
(I-3) the A solution was slowly added to a beaker containing deionized water and stirred for 20 minutes. Then, the temperature is raised to 90 ℃ under stirring to carry out hydrolysis, the dispersing agent PEG2000 is added according to the amount of 10 g.L -1, and the constant temperature hydrolysis is kept for 4 hours. After the reaction, aging for 12 hours at room temperature (25 ℃) to obtain a mixed solution B.
And (I-4) carrying out suction filtration on the mixed solution B to obtain a filter cake C, washing the filter cake C with deionized water and absolute ethyl alcohol for 3 times respectively, drying at 80 ℃ for 1h, and finally heating to 400 ℃ in a muffle furnace at a heating rate of 5 ℃/min for calcination for 4h, thereby obtaining the nano TiO 2 particles.
(I-5) 1g of the nano TiO 2 particles are added into 100mL of 10mol/L NaOH solution, 1.3g of dispersing agent PEG2000 is added, stirring is carried out at normal temperature, the uniformly mixed solution is transferred into a stainless steel reaction kettle with a polytetrafluoroethylene lining, and hydrothermal crystallization is carried out for 24h at 140 ℃.
And (I-6) filtering and separating the product after the hydrothermal crystallization to obtain a filter cake. And (3) adding the filter cake into 0.1mol/L dilute hydrochloric acid for pickling for 60min, washing until the pH value of the pickling solution is 1, stirring for 1h at 140 ℃, and centrifugally filtering to obtain the filter cake. And (3) placing the filter cake in hot water at 50 ℃ for water washing, stirring and water washing for five times in a beaker, centrifuging, continuing water washing and ultrasonic until the conductivity of the water washing liquid is less than 600 mu s/cm, filtering and separating, placing the obtained filter cake G in a drying oven for drying at 130 ℃, and roasting for 2 hours at 400 ℃ in a muffle furnace to obtain the titanium dioxide nanowire A1.
(II) preparation of the catalyst
(II-1) dissolving the A crystal and the transition metal manganese salt obtained in the step (I-2) in deionized water to obtain an active component solution.
(II-2) immersing the obtained titanium dioxide nanowires in the active component solution obtained in the step (II-1). After impregnation the solid was rotary evaporated to dryness at 70 ℃ and then calcined at 550 ℃ for 5h to give the denitration catalyst, designated C1.
Fig. 2 is an XRD pattern of the nano TiO 2 particles and the titanium dioxide nanowires prepared in example 1, and it can be seen from fig. 2 that the prepared nano TiO 2 particles mainly consist of two crystal forms of rutile and anatase, and belong to mixed crystal form TiO 2. And all diffraction peaks of the titanium dioxide nanowire A1 are identical to those of anatase type TiO 2, the crystallinity is higher, and no impurity appears, namely the crystal form of the obtained titanium dioxide nanowire is anatase.
Fig. 3 is an N 2 adsorption/desorption isothermal curve of the titanium dioxide nanowire A1, respectively. Fig. 3 shows that the adsorption curve of the titanium dioxide nanowire prepared in example 1 is langmuir IV, and belongs to a typical mesoporous material adsorption curve, i.e. a large hysteresis loop appears with the increase of adsorption partial pressure. The value of the relative pressure P/P 0 corresponding to the adsorption amount steep increase point in the adsorption isotherm represents the pore size of the sample. The specific surface area, composition and aspect ratio of the titanium dioxide nanowire A1 are shown in table 2.
FIG. 4 is an SEM image of a titanium dioxide nanowire A1, and it can be seen from FIG. 4 that the morphology of the nano TiO 2 is linear, 250-300nm long, 20-30nm in diameter and 12-15 in aspect ratio.
Example 2
Titanium dioxide nanowires were prepared as in example 1, except that: in the step (I-6), the concentration of the dilute hydrochloric acid for acid washing is 0.05mol/L, and the time is 40min. Titanium dioxide nanowires and a denitration catalyst C2 were produced, wherein the specific surface area, composition, and aspect ratio of the titanium dioxide nanowires are shown in Table 2.
Example 3
Titanium dioxide nanowires were prepared as in example 1, except that: in the step (I-6), the concentration of the dilute hydrochloric acid for pickling was 0.15mol/L for 80 minutes. Titanium dioxide nanowires and a denitration catalyst C3 were produced, wherein the specific surface area, composition, and aspect ratio of the titanium dioxide nanowires are shown in Table 2.
Example 4
Titanium dioxide nanowires were prepared as in example 1, except that: in the step (I-6), the concentration of the dilute hydrochloric acid for pickling was 0.02mol/L for 35 minutes. Titanium dioxide nanowires and a denitration catalyst C4 were produced, wherein the specific surface area, composition, and aspect ratio of the titanium dioxide nanowires are shown in Table 2.
Example 5
Titanium dioxide nanowires were prepared as in example 1, except that: in the step (I-6), the temperature of the water washing was 25 ℃. Titanium dioxide nanowires and a denitration catalyst C5 were produced, wherein the specific surface area, composition, and aspect ratio of the titanium dioxide nanowires are shown in Table 2.
Example 6
Titanium dioxide nanowires were prepared as in example 1, except that: in the step (I-6), no washing with water was performed. Titanium dioxide nanowires and a denitration catalyst C6 were produced, wherein the specific surface area, composition, and aspect ratio of the titanium dioxide nanowires are shown in Table 2.
Example 7
Titanium dioxide nanowires were prepared as in example 1, except that: in the step (I-6), the order of acid washing and water washing is different. Titanium dioxide nanowires and a denitration catalyst C7 were produced, wherein the specific surface area, composition, and aspect ratio of the titanium dioxide nanowires are shown in Table 2.
Comparative example 1
TiO 2 material and denitration catalyst D1 were prepared according to CN 110697768A. The specific surface area, composition and aspect ratio of the prepared TiO 2 material are shown in Table 2.
Comparative example 2
Titanium dioxide nanowires were prepared as in example 1, except that: in the step (I-6), no acid washing was performed. Titanium dioxide nanowires cannot be obtained, and the prepared TiO 2 is an irregular nanosphere. The TiO 2 nanospheres were prepared into a denitration catalyst D2 according to the method of example 1. The specific surface area, composition and length-diameter ratio of the prepared TiO 2 nanospheres are shown in Table 2.
Comparative example 3
Titanium dioxide nanowires were prepared as in example 1, except that: in the step (I-6), the concentration of the dilute hydrochloric acid for acid washing is 2mol/L, and the time is 150min. The titanium dioxide nanowire can not be obtained, and the prepared TiO 2 powder can not be obtained. The TiO 2 powder was prepared as a denitration catalyst D3 in the same manner as in example 1. The specific surface area, composition and aspect ratio of the obtained TiO 2 powder are shown in Table 2.
Comparative example 4
Denitration catalyst D4 was produced as in example 1, using commercially available titanium dioxide (BET 74.28m 2/g,TiO2 content > 97.9%). The specific surface area, composition and aspect ratio of the titanium dioxide are shown in table 2.
TABLE 2
| BET(m2/g) | TiO2(wt％) | K2O(wt％) | Fe2O3(wt％) | Na2O(wt％) | SO3(wt％) | Aspect ratio (L/D) | |
| Example 1 | 282.17 | 99.95 | 0.0015 | 0.014 | 0.015 | 0.0195 | 12-15 |
| Example 2 | 273.46 | 99.94 | 0.0029 | 0.02 | 0.020 | 0.0171 | 10-26 |
| Example 3 | 286.93 | 99.96 | 0.0030 | 0.012 | 0.013 | 0.012 | 26-40 |
| Example 4 | 254.78 | 99.92 | 0.0032 | 0.026 | 0.025 | 0.0258 | 18-38 |
| Example 5 | 260.64 | 99.89 | 0.001 | 0.01 | 0.06 | 0.04 | 15-27 |
| Example 6 | 274.66 | 99.85 | 0.0012 | 0.02 | 0.08 | 0.05 | 23-36 |
| Example 7 | 235.78 | 99.9 | 0.032 | 0.024 | 0.021 | 0.023 | 12-18 |
| Comparative example 1 | 180.35 | 99.93 | 0.017 | 0.016 | 0.032 | 0.005 | 1 |
| Comparative example 2 | 103.45 | 99.91 | 0.0018 | 0.020 | 0.012 | 0.0562 | 1 |
| Comparative example 3 | 74.89 | 99.90 | 0.0016 | 0.015 | 0.020 | 0.0634 | 1 |
As can be seen from table 2, compared with examples 1 to 7, comparative example 2, which was not acid-washed, and comparative example 3, which was not acid-washed with acid concentration and acid-washing time within the scope of the present invention, failed to produce titanium dioxide nanowires, while comparative example 1 of the prior art failed to produce titanium dioxide nanowires, and the BET of the TiO 2 material produced was too low, and the content of Na 2 O, etc. in TiO 2 was too high, resulting in that the catalytic activity of the denitration catalyst produced from TiO 2 failed to meet the demand.
In example 5, example 6, in which the washing temperature was too low, and example 7, in which the washing treatment was not performed, and the washing and washing sequence was changed, the content of Na 2 O or the like in the titanium dioxide nanowires prepared in comparison with examples 1 to 4 was too high, which was disadvantageous in improving the catalytic activity of the denitration catalyst prepared from the titanium dioxide nanowires.
Test case
The denitration catalyst prepared in the examples and comparative examples was used for denitration of a gas.
The specific test steps are as follows: catalyst samples were pelletized (40-60 mesh) and the denitration activity was measured in a fixed bed with a catalyst loading of 0.3g.
The denitration efficiency at 100 ℃, 150 ℃, 200 ℃, 250 ℃, 300 ℃, 350 ℃, 400 ℃ and 450 ℃ was tested respectively.
Denitration efficiency (%) = [ ([ NO x]in-[NOx]out)/[NOx]in ] ×100%)
NO x is the sum of NO and NO 2 concentrations, [ NO x]out is the concentration of outlet NO x, [ NO x]in is the concentration of inlet NO x.
Fig. 5 is a graph of denitration activity of the denitration catalyst C1, and as can be seen from fig. 5, the denitration activity can reach more than 90% at 150-400 ℃.
TABLE 3 Table 3
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As can be seen from the results of Table 3, the denitration efficiency under low-temperature conditions was remarkably improved by using the denitration catalysts prepared in examples 1 to 7 of the present invention, as compared with the denitration catalysts provided in comparative examples 1 to 4. And along with the rise of denitration temperature, denitration efficiency can promote rapidly to in the broad temperature range, all keep higher denitration efficiency.
The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, a number of simple variants of the technical solution of the invention are possible, including combinations of the individual technical features in any other suitable way, which simple variants and combinations should likewise be regarded as being disclosed by the invention, all falling within the scope of protection of the invention.
Claims (38)
1. A titanium dioxide nanowire, characterized by comprising 99.9-100wt% of TiO 2, 0.001-0.004wt% of K 2 O,0.01-0.04wt% of Fe 2O3, 0.01-0.03wt% of Na 2 O,0.01-0.03wt% of SO 3, based on the total weight of the titanium dioxide nanowire;
The specific surface area of the titanium dioxide nanowire is 230-320m 2/g;
the preparation method of the titanium dioxide nanowire comprises the following steps:
(1) In the presence of a first dispersing agent, hydrolyzing, aging and calcining a solid obtained by solid-liquid separation of the solution A to obtain nano TiO 2 particles;
(2) Mixing nano TiO 2 particles with an alkali solution in the presence of a second dispersing agent, performing hydrothermal crystallization reaction, and performing solid-liquid separation to obtain a solid;
(3) Pickling the solid obtained in the step (2), and roasting to obtain the titanium dioxide nanowire;
Wherein, in step (1), the solution a comprises TiOSO 4; in the step (3), the pickling conditions include: the concentration of acid for acid washing is 0.01-0.2mol/L, and the time for acid washing is 30-120min;
wherein the solution A is obtained by acid treatment of ilmenite.
2. The titanium dioxide nanowire according to claim 1, wherein the titanium dioxide nanowire comprises 99.93-100wt% of TiO 2, 0.001-0.0031wt% of K 2 O,0.01-0.023wt% of Fe 2O3, 0.01-0.0204wt% of Na 2 O,0.01-0.0222wt% of SO 3, based on the total weight of the titanium dioxide nanowire;
The specific surface area of the titanium dioxide nanowire is 260-300m 2/g.
3. The titanium dioxide nanowire according to claim 1 or 2, wherein the crystalline form of the titanium dioxide nanowire is anatase.
4. The titanium dioxide nanowire according to claim 1 or 2, wherein the aspect ratio of the titanium dioxide nanowire is 4-40.
5. A method of producing a titanium dioxide nanowire as claimed in any one of claims 1 to 4, characterized in that the method of producing comprises the steps of:
(1) In the presence of a first dispersing agent, hydrolyzing, aging and calcining a solid obtained by solid-liquid separation of the solution A to obtain nano TiO 2 particles;
(2) Mixing nano TiO 2 particles with an alkali solution in the presence of a second dispersing agent, performing hydrothermal crystallization reaction, and performing solid-liquid separation to obtain a solid;
(3) Pickling the solid obtained in the step (2), and roasting to obtain the titanium dioxide nanowire;
Wherein, in step (1), the solution a comprises TiOSO 4; in the step (3), the pickling conditions include: the concentration of acid for acid washing is 0.01-0.2mol/L, and the time for acid washing is 30-120min;
wherein the solution A is obtained by acid treatment of ilmenite.
6. The production method according to claim 5, wherein in the step (3), the conditions for pickling include: the acid concentration for acid washing is 0.05-0.15mol/L, and the acid washing time is 40-80min.
7. The production method according to claim 5 or 6, wherein the acid for acid washing is at least one selected from hydrochloric acid, sulfuric acid and acetic acid.
8. The production method according to claim 5 or 6, wherein the conditions for acid washing further include: and (3) pickling until the pH value of the pickling solution is not more than 1.
9. The process according to claim 5 or 6, wherein in step (3), the solid obtained in step (2) is washed with acid and then with water, followed by calcination.
10. The preparation method according to claim 9, wherein the conditions of the water washing include: the temperature of the water washing is 40-60 ℃.
11. The preparation method according to claim 9, wherein the conditions of the water washing further comprise: washing with water until the conductivity of the washing liquid is less than 600 mu s/cm.
12. The production method according to any one of claims 5, 6, 10, 11, wherein in step (1), the conditions of calcination include: the calcination temperature is 600-900 ℃, the calcination time is 3-6h, and the heating rate is 4-10 ℃/min.
13. The production method according to any one of claims 5, 6, 10, 11, wherein the conditions of the hydrolysis include: the hydrolysis temperature is 90-120 ℃; the hydrolysis time is 3-5h.
14. The production method according to any one of claims 5, 6, 10, 11, wherein the aging conditions include: the aging temperature is 20-30 ℃ and the aging time is 12-24h.
15. The production method according to any one of claims 5, 6, 10, 11, wherein the first dispersant is at least one selected from PEG400, PEG 800, and PEG 2000.
16. The production method according to any one of claims 5, 6, 10, 11, wherein the first dispersant is used in an amount of 1 to 10 g.l -1 based on the total volume of the a solution.
17. The production method according to any one of claims 5, 6, 10, 11, wherein in the step (2), the alkali solution is at least one selected from a NaOH solution, a KOH solution, and a Na 2CO3 solution.
18. The production method according to any one of claims 5, 6, 10, 11, wherein the molar concentration of the alkali solution is 8 to 12mol/L.
19. The preparation method of any one of claims 5, 6, 10 and 11, wherein the mass-to-volume ratio of the nano TiO 2 particles to the alkaline solution is 1:80-120g/mL.
20. The production method according to any one of claims 5, 6, 10, 11, wherein the conditions for hydrothermal crystallization include: the temperature of the hydrothermal crystallization is 120-150 ℃, and the time of the hydrothermal crystallization is 20-30h.
21. The production method according to any one of claims 5, 6, 10, 11, wherein the conditions of calcination include: the roasting temperature is 400-550 ℃ and the roasting time is 4-6h.
22. The method of any one of claims 5,6, 10, 11, wherein the second dispersant is selected from at least one of PEG400, PEG 800, and PEG 2000.
23. The preparation method according to any one of claims 5, 6, 10, 11, wherein a weight ratio of the second dispersant to the nano TiO 2 particles is 1.5-1:1.
24. The method of any one of claims 5, 6, 10, 11, wherein the a solution is obtained by:
s1, performing a first contact reaction on ilmenite and sulfuric acid to obtain a first mixture material;
S2, carrying out a second contact reaction on the first mixed material and iron, and carrying out solid-liquid separation on the obtained material to obtain a second solution;
S3, cooling and crystallizing the second solution, and carrying out solid-liquid separation on the material obtained after cooling and crystallizing to obtain the solution A and a third crystal containing FeSO 4·7H2 O crystals.
25. The production method according to claim 24, wherein in step S1, the conditions of the first contact reaction include: the temperature is 120-160 ℃ and the time is 2-4h.
26. The process according to claim 24, wherein the weight ratio of ilmenite to sulfuric acid is 1 (1.1-1.6).
27. The production method according to claim 24, wherein in step S2, the conditions of the second contact reaction include: the temperature is 20-30 ℃; the time is 15-30 min.
28. The process according to claim 24, wherein the weight ratio of ilmenite to iron is 1 (0.03-0.06).
29. The production method according to claim 24, wherein in step S3, the conditions for cooling crystallization include: the temperature is 0-6deg.C, and the time is 36-60h.
30. The method of any one of claims 5, 6, 10, 11, 25, 27-29, wherein the method comprises: the solid obtained by solid-liquid separation in step (1) is washed and dried before the calcination is performed.
31. A denitration catalyst comprising a carrier and an active component element supported on the carrier, characterized in that the carrier is the titanium dioxide nanowire as claimed in any one of claims 1 to 4.
32. The denitration catalyst according to claim 31, wherein the active component elements are Fe element and at least one transition metal element selected from V, mn, co, ni, ru, rh, W, nb, ta, mo, ce, sb, cu and La.
33. The denitration catalyst according to claim 32, wherein the content of the Fe element is 5 to 8wt% in terms of Fe 2O3 based on the total weight of the denitration catalyst; the content of the transition metal element is 5-15wt% calculated by metal oxide; the carrier is present in an amount of 77 to 90wt% based on titanium dioxide.
34. A denitration catalyst as claimed in claim 31 or 32 wherein the total content of the active component elements is not more than 20wt% on a metal oxide basis based on the total weight of the denitration catalyst.
35. A method for preparing the denitration catalyst as claimed in claim 31 or 32, characterized in that the titanium oxide nanowire is immersed in a solution containing an active component element.
36. The method according to claim 35, wherein the solution containing an active ingredient element is obtained by dissolving an iron source and a transition metal source in water;
the solution A is obtained in the following way:
s1, performing a first contact reaction on ilmenite and sulfuric acid to obtain a first mixture material;
S2, carrying out a second contact reaction on the first mixed material and iron, and carrying out solid-liquid separation on the obtained material to obtain a second solution;
S3, cooling and crystallizing the second solution, and carrying out solid-liquid separation on the material obtained after cooling and crystallizing to obtain the solution A and a third crystal containing FeSO 4·7H2 O crystals.
37. The method of claim 36, the iron source being the third crystal.
38. A method for flue gas denitrification, the method comprising: catalytic denitrification of a gas to be denitrified containing nitrogen oxides in the presence of a denitrification catalyst according to any one of claims 31-34.
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