CN107199047B

CN107199047B - Nickel-based methanation catalyst dispersed in SBA-15 pore channel and preparation and application thereof

Info

Publication number: CN107199047B
Application number: CN201610151648.8A
Authority: CN
Inventors: 辛忠; 陶淼
Original assignee: East China University of Science and Technology
Current assignee: East China University of Science and Technology
Priority date: 2016-03-17
Filing date: 2016-03-17
Publication date: 2020-02-21
Anticipated expiration: 2036-03-17
Also published as: CN107199047A

Abstract

The invention relates to a nickel-based methanation catalyst dispersed in an SBA-15 pore channel and preparation and application thereof. In the catalyst, the content of metallic nickel element is 5-20 parts by weight, the content of additive is 10-40 parts by weight, and the rest is mesoporous molecular sieve SBA-15. The preparation method comprises the following steps: preparing a nickel salt solution and adding an additive; and B, soaking the SBA-15 in the mixed solution prepared in the step A at room temperature in a nickel salt solution, and then carrying out vacuum and roasting to prepare the nickel-based methanation catalyst. The invention prepares the nickel-based metal catalyst with active components highly dispersed in the carrier pore channel by adding the additive and taking the mesoporous molecular sieve SBA-15 with stable chemical properties, good heat conduction performance and large specific surface area as the carrier, and the obtained catalyst has the advantages of high catalytic activity, good methane selectivity, good thermal stability, longer catalyst life and the like. The catalyst can reach the CO conversion rate of 100 percent, the methane selectivity of 99.9 percent and the methane yield of 99.9 percent under the optimal condition, and has great industrial prospect.

Description

Nickel-based methanation catalyst dispersed in SBA-15 pore channel and preparation and application thereof

Technical Field

The invention belongs to the technical field of catalysts and preparation thereof, and particularly relates to a nickel-based methanation catalyst highly dispersed in SBA-15 pore canals, and preparation and application thereof.

Background

The energy structure of China is 'rich coal, lack of oil and little gas', the Synthetic Natural Gas (SNG) made of coal is actively developed to replace natural gas or urban gas, the increasing market demand is met, and the method has important significance on the aspects of energy safety, energy conservation, emission reduction and the like of China. Synthesis gas (CO and H)₂) Methanation is the most critical part of the synthesis of natural gas from coal, and methanation of high-concentration CO is a strong exothermic reaction, and when heat cannot be discharged in time, very high temperature rise can be caused instantaneously, so that the catalyst is sintered and carbon is deposited. Therefore, the research on the methanation catalyst with high temperature resistance and high activity is of great significance. The Ni-based catalyst is relatively suitable in price and high in catalytic activity, so that the Ni-based catalyst becomes a main catalyst for methanation reaction for preparing substitute natural gas by coal gasification. Preparation of current nickel-based catalystsThe preparation method is generally to perform coprecipitation on salts of the catalyst and other metal salts or impregnate a porous carrier with a salt solution of the catalyst, and then perform roasting and reduction to obtain a catalyst sample. By adopting the methods, the active component Ni is not easy to highly disperse, and the agglomeration of metal Ni microcrystals is easily caused in the subsequent high-temperature treatment and reduction processes, so that the dispersity is further reduced, and the catalytic activity is influenced.

In addition, a stable support is very critical for high temperature methanation reaction systems. Ordered mesoporous materials have been widely used in the field of catalytic chemistry due to their characteristics of high specific surface area, good thermal stability, easy modification, good dispersion effect on metal active components, and the like. Because the mesoporous molecular sieve is mostly pure SiO₂And are not catalytically active, the incorporation of metals/metal oxides into these molecular sieves or their surface modification is currently an effective method of using these molecular sieves in the catalytic field. The metal/metal oxide can be loaded on the mesoporous molecular sieve by an impregnation method, but the metal/metal oxide is mostly distributed on the surface of the mesoporous molecular sieve and is difficult to be uniformly dispersed. Research shows that the Ni/Al is prepared by adopting an immersion method₂O₃In the process, the addition of the surfactant effectively inhibits the eggshell type distribution of the metal, so that the metal is more uniformly distributed on the surface of the carrier. In addition, many researchers have studied the influence of the surfactant on the dispersion and catalytic performance of the metal in the metal catalyst, but most of the researchers use the deposition-precipitation method to prepare the catalyst, and compared with the impregnation method, the preparation method is more complicated in preparation process and higher in cost.

Chinese patent CN104549411A discloses the preparation of a nickel-based catalyst based on SBA-15 and the application thereof in the preparation of SNG, but active components can migrate in the drying and roasting processes, finally, metals are difficult to be uniformly dispersed on the surface of a carrier, and most of Ni as the active component is gathered on the outer surface of a mesoporous molecular sieve.

Therefore, a method which is simple and easy to operate is needed to be found for preparing the high-dispersion nickel-based methanation catalyst, and the high-dispersion nickel-based methanation catalyst is required to have excellent high-temperature resistance and stability while high activity is ensured.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a nickel-based methanation catalyst highly dispersed in an SBA-15 pore channel as well as preparation and application thereof.

The purpose of the invention is realized by the following technical scheme:

the first purpose of the invention is to provide a nickel-based methanation catalyst dispersed in SBA-15 pore channels, wherein the catalyst takes a mesoporous molecular sieve SBA-15 as a carrier and takes metal Ni as a main active component; wherein, the content of metallic nickel element is 5-20 parts by weight, the content of additive is 10-40 parts by weight, and the rest is mesoporous molecular sieve SBA-15; the additive is organic micromolecules such as citric acid and the like, and surfactants such as cetyl trimethyl ammonium bromide or lauryl sodium sulfate and the like.

The pore size of the mesoporous molecular sieve SBA-15 can be adjusted within 4.6-30 nm, the pore wall thickness is 3-9 nm, and the pore volume is 0.85cm 3/g. The mesoporous molecular sieve SBA-15 is a molecular sieve material with larger pore diameter at present, and the SBA-15 has larger pore diameter size, thicker pore wall structure and better hydrothermal stability than the traditional MCM-41 while keeping a highly ordered two-dimensional hexagonal structure, so the mesoporous molecular sieve shows wide potential application prospects in the fields of adsorption, catalysis, biomedicine, new material processing and the like.

The active component metallic nickel element is NiO or Ni₂O₃Exist in the form of (1).

The second purpose of the invention is to provide a preparation method of the nickel-based methanation catalyst dispersed in an SBA-15 pore channel, which comprises the following steps:

(1) preparing a nickel salt solution and adding an additive; the additive is organic micromolecules such as citric acid and the like, and surfactants such as cetyl trimethyl ammonium bromide or lauryl sodium sulfate and the like; wherein the weight ratio of the metallic nickel element in the nickel salt solution to the additive is 5-20: 10-40;

(2) soaking the mesoporous molecular sieve SBA-15 in the mixed solution prepared in the step A at room temperature for 2-12 hours in the nickel salt solution, drying in vacuum at the temperature of 30-80 ℃ for 5-12 hours after soaking, roasting at the temperature of 400-800 ℃ for 1-10 hours, and thus obtaining the nickel-based methanation catalyst; the nickel loading amount in the catalyst is 10-20 mol%.

Further, the nickel salt in the step (1) is nickel chloride, nickel sulfate, nickel acetate, nickel oxalate or nickel nitrate; the solvent of the nickel salt solution is deionized water, ethanol, acetic acid, chloroform or acetone.

Further, the impregnation in the step (2) adopts an excess impregnation method.

Further, the dipping time in the step (2) is 8-10 hours.

Further, the temperature of vacuum drying in the step (2) is 40-60 ℃, and the time is 6-8 hours.

Further, the roasting temperature in the step (2) is 500-600 ℃, and the roasting time is 5-6 hours.

Further, the catalyst obtained after calcination was ground into fine powder and filtered with a 100-mesh sample sieve.

The invention further aims to provide the application of the nickel-based methanation catalyst dispersed in the SBA-15 pore channel in the preparation of coal-based natural gas.

Specifically, the volume space velocity of the synthesis gas treated by the catalyst is 3000-30000 h^-1The pressure is normal pressure to 3.0Mpa, the temperature is 200 to 600 ℃, and H in the synthesis gas₂The ratio of/CO is 2-4.

Compared with the prior art, the invention has the following positive effects:

(1) the catalyst shows excellent activity and methane selectivity in the reaction of preparing methane from synthesis gas, and has activity in the temperature range of 200-600 ℃, wherein the activity of the catalyst is the best in the temperature range of 300-450 ℃, the CO conversion rate can reach more than 100%, and the methane selectivity reaches more than 92%;

(2) the catalyst takes mesoporous molecular sieve SBA-15 with stable chemical properties and good thermal conductivity as a carrier, and the prepared catalyst has the advantages of high metal dispersion degree, high catalytic activity, good thermal stability (the catalytic activity is not reduced after 2h of high-temperature calcination at 700 ℃), longer service life (the catalytic activity is not reduced in a 100h service life experiment) and the like;

(3) the catalyst does not contain precious metal components, the preparation method is simple and easy to implement, the catalytic performance is high, and the catalyst has great advantages in cost performance.

(4) In the preparation process of the catalyst, the additives are added, so that the size of active component particles can be reduced, the active component particles are uniformly dispersed in pore channels of the carrier, and meanwhile, the active component particles can be prevented from sintering due to the limited action in the reduction process of the catalyst, so that the dispersion degree of the active component nickel in the catalyst is improved, and the activity and the stability of the catalyst are finally influenced.

Drawings

FIG. 1 is an XRD pattern of catalysts prepared in examples 1-4; wherein, (A) diffraction at small angle, (B) diffraction at wide angle;

FIG. 2 is a TEM picture of the carrier SBA-15 used in the present invention;

FIG. 3 is a TEM picture of 10% Ni/S15(S1) of the catalyst prepared in example 1;

FIG. 4 is a graph showing the catalytic performance of the methanation catalysts of examples 1 to 4 of the present invention in the methanation reaction of synthesis gas, i.e., the result of example 5; wherein (A) CO conversion rate and (B) CH₄The yield was found.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.

The sources of the raw materials used in the following examples are illustrated below:

mesoporous molecular sieve SBA-15: the method is self-made in a laboratory and comprises the following specific processes: 4.0g of triblock surfactant P123 (EO) are introduced at a constant temperature of 40 DEG₂₀PO₇₀EO₂₀M5800) (from Sigma-Aldrich) was dissolved in 125g of deionized water and 36-38% by weight HCl solution 23 was added6 g. After complete dissolution, 8.5g of ethyl orthosilicate were slowly added, keeping vigorous stirring for 24 h. Then dissolving 46mg of NH4F in 5mL of deionized water, adding the solution, transferring the mixed solution into a polytetrafluoroethylene bottle, crystallizing at 110 ℃ for 24h, filtering, washing, drying, and finally roasting the dried product at 550 ℃ for 6h (the heating rate is 1 ℃/min) to remove the template agent, thus obtaining white powder of the carrier SBA-15 mesoporous molecular sieve.

Sodium lauryl sulfate, citric acid, nickel nitrate hexahydrate, nickel acetate tetrahydrate: supplied by Shanghai Linfeng Chemicals Ltd

Example 1

(1) 0.55g of nickel nitrate hexahydrate and 0.55g of Sodium Dodecyl Sulfate (SDS) were dissolved in 10g of deionized water;

(2) weighing 1.0g of SBA-15 white powder, adding the SBA-15 white powder into the solution, soaking for 10 hours, taking out after soaking, drying in vacuum at 50 ℃ for 8 hours, roasting in air at 500 ℃ for 5 hours, and naturally cooling to room temperature to obtain the Ni/SBA-15 catalyst, wherein the Ni/S15 is recorded as 10% Ni/S15(S1), and the nickel loading is 10 mol%.

The small-angle and wide-angle XRD patterns of the 10% Ni/S15(S1) prepared in the example are shown in FIG. 1, and the TEM picture is shown in FIG. 3. As can be seen from FIG. 1(A), the sample has relatively clear (100), (110) and (200) peaks, which are characteristic peaks of the regular mesoporous molecular sieve SBA-15, indicating that the introduction of metallic nickel does not destroy the original ordered mesoporous structure of the carrier. As can be seen from fig. 1(B), the wide-angle XRD spectrum of the sample shows distinct broad peaks (15-35 °) characteristic to silica, and also has peaks characteristic to the NiO particles (2 θ ═ 37.5 °,43.7 °,63.7 °), and the average particle size of NiO on the catalyst surface is about 10nm according to the Scherrer equation. As can be seen from FIG. 2, the pore structure of SBA-15 is that, in the (110) direction, one-dimensional straight pores are arranged closely; as can be seen from fig. 3, the addition of the additive to the impregnation solution can effectively improve the dispersion degree of the active component nickel, so that the nickel particles are more uniformly distributed and smaller. In combination with the BET results (significant reduction in specific surface area), it was concluded that the nickel was uniformly distributed in the channels of support SBA-15 in catalyst 10% Ni/S15 (S1).

Example 2

The Ni/SBA-15 catalyst, reported as 10% Ni/S15(CA), with a nickel loading of 10 mol%, was prepared in the same manner as example 1, except that citric acid was used in place of the sodium lauryl sulfate in example 1.

The catalyst 10% Ni/S15(CA) prepared in this example had a small and wide angle XRD pattern as shown in FIG. 1. As can be seen from fig. 1(a), the order of the mesoporous molecular sieve still exists after the nickel metal is introduced; as can be seen from FIG. 1(B), the intensity of the characteristic diffraction peak of NiO was increased compared to that of catalyst 10% Ni/S15(S1), indicating that the particle size of NiO in the catalyst was increased.

Example 3

The same procedure used in example 1 was repeated except for using 0.6g of nickel acetate tetrahydrate in place of 0.55g of nickel nitrate hexahydrate in example 1 to produce a Ni/SBA-15 catalyst, designated 10% Ni/S15(AC), with a nickel loading of 10 mol%.

As can be seen from FIG. 1(A), the sample has relatively clear (100), (110) and (200) peaks, which are characteristic peaks of the regular mesoporous molecular sieve SBA-15, indicating that the introduction of metallic nickel does not destroy the original ordered mesoporous structure of the carrier. As can be seen from fig. 1(B), in addition to the characteristic broad peak (15 to 35 °) of silicon oxide, the wide-angle XRD spectrum of the sample exhibited distinct peaks of NiO particles (2 θ ═ 37.5 °,43.7 °, and 63.7 °).

Example 4

(1) 1.24g of nickel nitrate hexahydrate and 0.18g of Sodium Dodecyl Sulfate (SDS) were dissolved in 10g of deionized water;

(2) weighing 1.0g of SBA-15 white powder, adding the SBA-15 white powder into the solution for dipping for 2h, taking out after dipping, drying in vacuum at 30 ℃ for 5h, then roasting in air at 400 ℃ for 1h, and naturally cooling to room temperature to obtain the Ni/SBA-15 catalyst, wherein the Ni/S15 is recorded as 20% Ni/S15(S2), and the nickel loading is 20 mol%.

The catalysts prepared in examples 1 to 4 were respectively loaded in a fixed bed microreactor with an inner diameter of 8mm, and N was used before the reaction₂Blowing air, and introducing pure H at 500 deg.C₂The catalyst was reduced for 2 hours. And then catalyzing the methanation reaction of the raw material gas by using the catalyst obtained after reduction. The composition of the feed gas and the catalytic reaction conditions were as follows:

the raw material gas composition is as follows: CO: 20% of H₂：60％，N₂：20％；

Catalyst loading: 500 mg;

reaction temperature: 300-500 ℃;

reaction pressure: 0.3 Mpa;

the reaction space velocity: 15000h^-1。

The composition of raw material gas and catalytic reaction conditions applicable to the catalyst of the invention can also be as follows: the volume space velocity of the synthesis gas is 3000-30000 h^-1The pressure is normal pressure to 3.0Mpa, the temperature is 200 to 600 ℃, and H in the synthesis gas₂The ratio of/CO is 2-4.

CO conversion and CH were determined and calculated as follows₄The yields, results are shown in FIG. 4:

conversion rate of CO: x_CO(1-amount of CO contained in product/amount of CO contained in raw material gas). times.100%

CH₄Yield: s_CH4Is converted to CH₄CO amount of (1)/CO amount contained in raw material gas) x 100%

As can be seen from fig. 4, the activity of all catalysts shows a trend of increasing first and then decreasing as the temperature increases. When the reaction temperature is 350 ℃, the activity of the catalyst 10 percent Ni/S15(S1) is optimal, the CO conversion rate reaches 100 percent, and the CH content is high₄The yield reaches 99.9 percent.

Application examples

This example illustrates the high temperature resistance of various catalysts in the reaction of synthesizing coal to produce methane

The catalysts prepared in examples 1 to 4 and comparative catalysts D1-D4 were loaded in a fixed bed microreactor having an inner diameter of 8mm, and N was used before the reaction₂Purging air, reusing pure H₂Reducing catalyst with CO and H as raw material gas₂Mixing, filtering, putting into a reactor, measuring the activity of the catalyst at the optimal temperature of 400 ℃, calcining the catalyst at 700 ℃ for 2h in the atmosphere of raw material gas, and then reducing the reaction temperature to the optimal temperature of 400 ℃ to investigate the activity of the catalyst. The gas obtained by the reaction was analyzed on-line by gas chromatography, and the CO conversion and CH were calculated in the same manner as in example 5₄The selectivity results are shown in Table 1. The test conditions were: the temperature T is 350 deg.C, pressure P is 0.3MPa, raw material gas CO is H₂1:3, airspeed 15000h^-1。

The above comparative catalysts D1-D4 are specifically illustrated below:

comparative catalyst D1: 1.0g of SBA-15 is taken as a carrier, and 0.55g of nickel nitrate hexahydrate is dissolved in 10g of deionized water; soaking SBA-15 in the solution for 12h, taking out after soaking, vacuum drying at 50 ℃ for 12h, then roasting at 500 ℃ in air for 5h, and naturally cooling to room temperature to obtain the Ni/SBA-15 catalyst, which is recorded as 10% Ni/S15 (D1).

Comparative catalyst D2: using 1.0g MCM-41 as a support, and the remainder as comparative catalyst D1, a Ni/M41 catalyst was prepared, designated 10% Ni/M41 (D2).

Comparative catalyst D3: with 1.0g of Al₂O₃As a carrier, the rest was subjected to Ni/Al reaction with comparative catalyst D1₂O₃Catalyst, 10% Ni/Al₂O₃(D3)。

Comparative catalyst D4: at 1.0g SiO₂As a carrier, the rest is compared with a comparative catalyst D1 to prepare Ni/SiO₂Catalyst, recorded as 10% Ni/SiO₂(D4)。

TABLE 1

As can be seen from Table 1, prepared by the excess impregnation method with addition of additivesAfter the catalyst is calcined for 2 hours at 700 ℃ in the atmosphere of raw material gas, the CO conversion rate is still maintained at 100 percent, and the CH content is maintained₄The yield decrease was within 0.1%, while the comparative examples contained 10% Ni/S15(D1), 10% Ni/M41(D2), and 10% Ni/Al₂O₃(D3) And 10% Ni/SiO₂(D4) The activity of the catalyst is respectively reduced by 23.2 percent, 26.8 percent, 29.5 percent and 30.5 percent, which shows that the catalyst Ni/SBA-15(S1) prepared by adopting an excess impregnation method of adding the additive has good catalytic activity and good high-temperature resistance.

On the basis of the traditional preparation method (impregnation method) of the methanation catalyst, the nickel-based metal catalyst with active components highly dispersed in carrier channels is prepared by adding the additive and taking the mesoporous molecular sieve SBA-15 with stable chemical properties, good heat conduction performance and large specific surface area as a carrier, and the obtained catalyst has the advantages of high catalytic activity, good methane selectivity, good thermal stability, long catalyst service life and the like. The catalyst can reach the CO conversion rate of 100 percent, the methane selectivity of 99.9 percent and the methane yield of 99.9 percent under the optimal condition, and has great industrial prospect.

The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are given by way of illustration of the principles of the present invention, and that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims

1. The nickel-based methanation catalyst dispersed in SBA-15 pore channels is characterized by being prepared by a preparation method comprising the following steps:

(1) preparing a nickel salt solution and adding an additive, wherein the additive is sodium dodecyl sulfate;

wherein the weight ratio of the metallic nickel element in the nickel salt solution to the additive is 5-20: 10-40;

(2) soaking the mesoporous molecular sieve SBA-15 in the mixed solution prepared in the step (1) by adopting an excess soaking method at room temperature for 8-10 hours, stopping soaking, filtering, and drying the obtained solid in vacuum at the temperature of 30-80 ℃ for 5-12 hours; then roasting at 400-800 deg.c for 1-10 hr to obtain the target product.

2. The nickel-based methanation catalyst of claim 1, wherein the mesoporous molecular sieve SBA-15 has a pore diameter of 4.6nm to 30nm, a pore wall thickness of 3nm to 9nm, and a pore volume of 0.85cm³/g。

3. The nickel-based methanation catalyst according to claim 1, wherein the nickel salt used in step (1) is nickel chloride, nickel sulfate, nickel acetate, nickel oxalate or nickel nitrate; the solvent for preparing the nickel salt solution is deionized water, ethanol, acetic acid, chloroform or acetone.

4. The nickel-based methanation catalyst according to claim 1, wherein in the step (2), the temperature of vacuum drying is 40 ℃ to 60 ℃ and the time is 6 hours to 8 hours.

5. The nickel-based methanation catalyst according to claim 1, wherein in the step (2), the calcination temperature is 500 ℃ to 600 ℃ and the calcination time is 5 hours to 6 hours.

6. Use of a nickel-based methanation catalyst according to any of claims 1 to 5 as a catalyst for the preparation of methane from synthesis gas;

wherein the reaction temperature for preparing methane by the synthesis gas is 200-600 ℃, the reaction pressure is normal pressure-3.0 MP a, and the volume space velocity of the synthesis gas is 3,000h^-1～30,000h^-1H in synthesis gas₂The ratio of/CO is 2-4.