CN110711584A - Semicoke-loaded coke oil steam reforming catalyst and preparation method and application thereof - Google Patents

Abstract

The invention discloses a semi-coke-supported tar steam reforming catalyst and a preparation method and application thereof. The semi-coke-supported tar steam reforming catalyst uses low-rank coal pretreated with an oxidant as a catalyst carrier precursor, and Ni is Metal active components. The invention uses cheap low-rank coal as the catalyst carrier precursor, which enriches the surface acid sites of the catalyst, strengthens the carrier-metal interaction, improves the atom utilization efficiency, and further improves the catalyst activity. The production cost is greatly reduced, and it can be used to catalyze the steam reforming of biomass or low-order coal gasification tar, and has a high carbon conversion rate.

Description

Semi-coke supported tar steam reforming catalyst and its preparation method and application

technical field

The invention belongs to the technical field of energy and chemical industry, and particularly relates to a semi-coke supported tar steam reforming catalyst and a preparation and application method thereof.

Background technique

Gasification is one of the main technologies for clean and efficient coal conversion. It is widely used in chemical synthesis, industrial gas, metallurgical reduction gas production and coal-based polygeneration. It is its core and key.

Tar is an inevitable by-product of low-temperature gasification of low-rank coal. The gasification gas often contains pyrolysis tar ranging from 5 to 75 g/ ^Nm3 . This part of tar will block the pipeline, corrode downstream equipment, and make subsequent processes The deactivation of catalysts in low-rank coal causes many obstacles to the clean utilization of low-rank coal.

Among many tar removal technologies, catalytic reforming not only has high tar removal efficiency and relatively mild operating conditions, but also makes full use of a large amount of water vapor and CO ₂ in the crude syngas to reform tar into H ₂ , CO, etc. Therefore, catalytic reforming of tar is considered to be the most promising tar removal method for large-scale applications.

Different types of catalysts are used for the removal of tar from gasification gas, such as high-temperature roasted rocks, molecular sieves, iron ore, alkali and alkaline earth metals (AAEMs), nickel-based catalysts, and precious metal catalysts, among which nickel-based catalysts have optimum catalytic activity. Nickel-based catalysts are generally supported on metal oxide supports, molecular sieve supports, natural ore supports, and coke supports. Compared with other carriers, coal char or biomass coke, as a by-product of pyrolysis, is cheap and easy to obtain, and is rich in alkali metals and alkaline earth metals, with high specific surface area and oxygen-containing functional groups, and has a certain tar removal activity.

Wang et al. (Applied Energy, 2011, 88(5): 1656-1663) prepared NiO/biochar and NiO/coalchar catalysts by mechanically mixing NiO with coal char and biomass coke, respectively. The catalyst prepared by this method is difficult to achieve metal active components. The uniform dispersion on the carrier surface limits the catalytic performance.

CN 107715884A discloses a metal-supported biomass semi-coke catalyst and a preparation method thereof. Metal active components are loaded on the biomass precursor pretreated by pickling through equal volume impregnation, and the metal active components include active metal Ni and One of Fe, Co or Cu constitutes the second active metal, and then a tar reforming catalyst is prepared by temperature programming. The method adopts equal volume impregnation to load the active components, the active components are difficult to be uniformly dispersed in the pore structure of the carrier, and the carrier-metal interaction force is weak, and the utilization rate of the metal active components in the catalysis process is low.

CN 103846088A discloses a preparation and application method of a nickel-based biomass tar steam reforming catalyst. The catalyst uses lignite pretreated with sodium hydroxide as a carrier precursor, is subjected to ion operation and then is left to stand for filtration, and then removed by temperature-programmed removal. The volatile matter of the lignite is obtained as a nickel-based biomass tar steam reforming catalyst. In this method, after the lignite is treated with sodium hydroxide, the acidic sites (oxygen-containing functional groups) on the surface of the carrier are destroyed, and the interaction between the metal and the carrier is greatly weakened; secondly, after the ion exchange, there is no water washing step, and the excess nickel salt sticks to the surface. Attached to the surface of the carrier, the catalyst has a lower specific surface area and less pore structure.

SUMMARY OF THE INVENTION

The purpose of the present invention is to disclose a semi-coke-supported tar steam reforming catalyst and its preparation method and application, so as to overcome the above-mentioned defects in the prior art and meet the needs of application in related fields.

The semi-coke-based supported tar steam reforming catalyst of the present invention uses low-rank coal pretreated with an oxidant as a catalyst carrier precursor, and Ni is a metal active component. Wherein, the mass percentage of Ni is 7-13%, preferably 7.2-12.1%;

The preparation method of the semi-coke-based supported tar steam reforming catalyst comprises the following steps:

(1) Mix the oxidant aqueous solution with the target coal, stir at 30～50℃, preferably 40℃ for 2～6h, preferably 4h, then collect the low-rank coal oxidized by the oxidant from the system;

The ratio of the target coal to the oxidant is 5-10 mL/g, preferably 5 mL/g;

The oxidant is selected from nitric acid or hydrogen peroxide, and the mass concentration of the oxidant aqueous solution is 10% to 30%;

The target coal is a low-rank coal particle with a particle size of 80-160 mesh, and the industrial analysis and elemental analysis of the target coal sample are shown in Table 1;

Table 1 Industrial analysis and elemental analysis of target coal samples

The method for collecting oxidized low-rank coal includes filtering, washing with water until neutral, and drying at 60-80° C. until the moisture content is less than 5%, mass;

(2) mixing the product of step (1) with an aqueous nickel salt solution with a pH of 10 to 12, stirring at 25 to 35° C. for 16 to 32 hours, preferably 24 hours, and then collecting the catalyst precursor from the system;

The collection method includes the following steps:

The obtained mixture is filtered, the filter residue is collected, washed with water until neutral, and dried at 60-80° C., preferably 70° C., to a moisture content of less than 5%, mass;

The concentration of the nickel salt aqueous solution is 0.1-0.3 mol/L, preferably 0.2 mol/L;

Described nickel salt is selected from more than one in tetrahydrate nickel acetate, hexahydrate nickel nitrate, hexahydrate nickel sulfate or anhydrous nickel chloride, preferably tetrahydrate nickel acetate;

The preparation method of the described nickel salt aqueous solution is conventional, and wherein, pH can be adjusted with alkaline substances, such as ammonia water, sodium hydroxide solution or potassium hydroxide solution, preferably ammonia water;

The mixing ratio of the nickel salt solution and the oxidized low-rank coal is 5-15 mL/g, preferably 10 mL/g.

(3) pyrolyzing the catalyst precursor described in step (2) in an inert atmosphere to stabilize the crystal form of elemental nickel on the surface of the catalyst, remove the volatile matter in the carrier, increase the specific surface area of the catalyst, and after pyrolysis, The semi-coke supported tar steam reforming catalyst can be obtained;

Described pyrolysis comprises the following steps:

Heating from room temperature to 550～700℃, preferably 600℃;

The heating rate is 5～10℃/min, preferably 10℃/min;

The residence time is 1 to 3 hours, preferably 2 hours;

The semi-coke supported tar steam reforming catalyst can be used for catalyzing biomass or low-order coal gasification tar steam reforming.

In the present invention, cheap low-rank coal is used as catalyst carrier precursor, and in the process of loading active components, the low-rank coal is fully considered to be rich in oxygen-containing functional groups, and the low-rank coal is oxidized to different degrees to adjust the coal. The number of oxygen-containing functional groups in the MgO improves the nickel loading while maintaining good dispersion and crystallite size. In addition, the number of oxygen-containing functional groups on the surface of the support is increased by oxidation treatment, which enriches the surface acid sites of the catalyst, strengthens the interaction between the support and the metal, improves the atom utilization efficiency, and further improves the catalyst activity.

The beneficial effects of the present invention are:

The raw material of the carrier of the catalyst of the invention is low-rank coal, and the oxidation pretreatment increases the number of oxygen-containing functional groups on the surface of the coal, which provides more exchange sites for the effective loading of Ni ²⁺ on the coal sample. The catalyst maintains good Ni dispersion and small crystallite size during the process;

While increasing the catalyst loading, the invention strengthens the carrier-metal interaction of the catalyst, the catalyst is easy to form more defect structures with negative electrons during the catalytic tar steam reforming process, and the combination with activated tar fragments is increased. chance to further improve the atom utilization efficiency of the catalyst;

In the process of ion exchange, ammonia water was used to adjust the pH of the metal salt solution. On the one hand, the nickel salt mainly existed in the form of Ni(NH ₄ ) ₆ ²⁺ ; (NH ₄ ) ₆ ²⁺ forms bonds with oxygen-containing functional groups on the surface of coal;

The carrier of the catalyst of the present invention is selected from low-rank coal, and the specific surface area of the catalyst is increased by oxidation pretreatment, and after the ion exchange step is completed, the excess nickel salt is washed away by the water washing step, which helps to improve the Ni dispersion;

The semi-coke-supported tar steam reforming catalyst carrier of the present invention selects low-rank coal itself, and the supported nickel salt is reduced in-situ during the pyrolysis and devolatilization process of the coal sample to obtain a reduced Ni component, and the hydrogen reduction step is omitted. , easy to use;

As a kind of ore resources, coal is rich in alkali metals and alkaline earth metals, which can play a catalytic role as a catalyst promoter in the process of tar steam reforming, and improve the catalytic performance of the catalyst to a certain extent. Compared with other types of tars The reforming catalyst omits the additive addition step, which greatly reduces the production cost;

Description of drawings

Fig. 1 is the TEM image of the semi-coke supported tar steam reforming catalyst prepared in Example 3 of the present invention;

Fig. 2 is the TEM image of the semi-coke supported tar steam reforming catalyst prepared in Example 5 of the present invention;

Fig. 3 is the XRD pattern of the semi-coke supported tar steam reforming catalyst prepared by each embodiment of the present invention;

Detailed ways

The semi-coke supported tar steam reforming catalyst can be evaluated by the following methods:

The above-mentioned catalyst was placed in a fixed-bed reactor, and nitrogen was used as a carrier gas. After being vaporized in a preheating furnace, toluene and water vapor were sent into the reactor. The space velocity of the reactant in the reactor was 7200 h ^-1 , and the reaction temperature was At 600 °C, small molecular gas products such as CO and H ₂ are obtained.

通过控制进入反应器的甲苯流速以及反应时间，得到

然后计算碳转化率，甲苯碳转化率的定义如式(1)：The product gas was collected, and the gas composition was detected by a Raman gas analyzer (RLGA) to obtain n _CO ,

By controlling the flow rate of toluene entering the reactor and the reaction time, the

Then calculate the carbon conversion rate, the definition of toluene carbon conversion rate is as formula (1):

in:

n _CO represents the amount of CO species in the product;

代表产物中CO₂物质的量；

represents the amount of _CO species in the product;

代表产物中CH₄物质的量；

represents the amount of _CH4 species in the product;

代表反应物甲苯中碳的物质的量；

represents the amount of carbon species in the reactant toluene;

In the examples, unless otherwise specified, the amounts of substances are all by mass.

Example 1

Prepare 100 mL of hydrogen peroxide aqueous solution with a mass fraction of 10%.

Preparation of oxidized low-rank coal:

Immerse 20 g of low-rank coal in the above hydrogen peroxide solution with a mass fraction of 10%, mix evenly, stir at 40°C for 4 hours, filter and wash the filter residue to neutrality, and dry at 70°C to a water content of 5%; rank coal;

Preparation of metal salt solution: Weigh 5g of nickel acetate tetrahydrate and dissolve it in 100mL of deionized water; add ammonia water with a mass concentration of 25% to adjust the pH of the salt solution to 11;

Ion exchange: add 10 g of the oxidized low-rank coal to the above prepared nickel salt solution, stir at 30°C for 24 hours, filter, wash the filter residue with water until neutral, and dry at 70°C to a water content of 3%;

Catalyst molding: the above-mentioned dried filter residue is pyrolyzed in an inert atmosphere to stabilize the crystal form of elemental nickel on the surface of the catalyst, remove the volatile matter in the carrier, and increase the specific surface area of the catalyst. semi-coke supported tar steam reforming catalyst;

Described pyrolysis comprises the following steps:

Heating from room temperature to 600 ℃;

The heating rate is 10℃/min;

Residence time 2h;

The Ni loading of the catalyst was analyzed by inductively coupled plasma optical emission spectrometer (ICP-OES), and it was found that the mass fraction of Ni in the catalyst was 7.9%.

_nCO = 0.29mol;

The carbon conversion was calculated according to formula (1): the carbon conversion was 72.2%.

Example 2

Prepare 100 mL of 20% hydrogen peroxide aqueous solution by mass fraction.

Preparation of oxidized low-rank coal:

Immerse 20 g of low-rank coal in the above hydrogen peroxide solution with a mass fraction of 20%, mix evenly, stir at 30°C for 6 hours, filter and wash the filter residue to neutrality, and dry at 80°C to a water content of 3%; rank coal;

Preparation of metal salt solution:

Weigh 3.9g of anhydrous nickel chloride and dissolve it in 100mL of deionized water; add ammonia water with a mass concentration of 25% to adjust the pH of the salt solution to 10;

Ion exchange: add 20 g of the oxidized low-rank coal to the above-prepared nickel salt solution, stir at 25°C for 32 hours, filter, wash the filter residue with water until neutral, and dry at 80°C to a water content of 3%;

Catalyst molding: the above-mentioned dried filter residue is pyrolyzed in an inert atmosphere to stabilize the crystal form of elemental nickel on the surface of the catalyst, remove the volatile matter in the carrier, and increase the specific surface area of the catalyst. semi-coke supported tar steam reforming catalyst;

Described pyrolysis comprises the following steps:

Heating from room temperature to 550°C;

The heating rate is 5°C/min;

Residence time 3h;

The Ni loading of the catalyst was analyzed by inductively coupled plasma optical emission spectrometer (ICP-OES), and it was found that the mass fraction of Ni in the catalyst was 8.5%.

_nCO = 0.33mol;

The carbon conversion rate was calculated according to formula (1): the carbon conversion rate was 74.7%.

Example 3

100 mL of hydrogen peroxide aqueous solution with a mass fraction of 30% was prepared.

Preparation of oxidized low-rank coal:

Immerse 10g of low-rank coal in the above hydrogen peroxide solution with a mass fraction of 30%, mix evenly, stir at 50°C for 2 hours, filter and wash the filter residue to neutrality, and dry at 60°C to a water content of 4%. rank coal;

Preparation of metal salt solution: Weigh 2.7g of nickel nitrate hexahydrate and dissolve it in 100mL of deionized water; add sodium hydroxide solution with a mass concentration of 40% to adjust the pH of the salt solution to 12;

Ion exchange: add 7 g of the oxidized low-rank coal to the above-prepared nickel salt solution, stir at 35°C for 16 hours, filter, wash the filter residue with water until neutral, and dry at 60°C to a water content of 4%;

Catalyst molding: the above-mentioned dried filter residue is pyrolyzed in an inert atmosphere to stabilize the crystal form of elemental nickel on the surface of the catalyst, remove the volatile matter in the carrier, and increase the specific surface area of the catalyst. semi-coke supported tar steam reforming catalyst;

Described pyrolysis comprises the following steps:

Heating from room temperature to 700 ℃;

The heating rate is 8°C/min;

Residence time 1h;

The Ni loading of the catalyst was analyzed by inductively coupled plasma optical emission spectrometer (ICP-OES), and it was found that the mass fraction of Ni in the catalyst was 9.9%.

_nCO = 0.35mol;

Calculate the carbon conversion rate according to formula (1): the carbon conversion rate is 76.7%;

It can be seen from the TEM spectrum in Figure 1 that the metal nanoparticles are uniformly embedded in the coke matrix, showing good nickel dispersion, and the average nickel particle size is only 4.3 nm.

Example 4

Prepare 100 mL of 20% nitric acid aqueous solution.

Preparation of oxidized low-rank coal:

Immerse 15 g of low-rank coal in the above-mentioned 20% nitric acid aqueous solution, mix well, stir at 40°C for 4 hours, filter and wash the filter residue to neutrality, and dry at 70°C to a water content of 5%; obtain oxidized low-rank coal ;

Preparation of metal salt solution: Weigh 5.3g of nickel sulfate hexahydrate and dissolve it in 100mL of deionized water; add potassium hydroxide solution with a mass concentration of 30% to adjust the pH of the salt solution to 11;

Ion exchange: add 10 g of the oxidized low-rank coal to the above prepared nickel salt solution, stir at 30°C for 26 hours, filter, wash the filter residue with water until neutral, and dry at 80°C to a water content of 5%;

Catalyst molding: the above-mentioned dried filter residue is pyrolyzed in an inert atmosphere to stabilize the crystal form of elemental nickel on the surface of the catalyst, remove the volatile matter in the carrier, and increase the specific surface area of the catalyst. semi-coke supported tar steam reforming catalyst;

Described pyrolysis comprises the following steps:

Heating from room temperature to 650°C;

The heating rate is 10℃/min;

Residence time 2h;

The Ni loading of the catalyst was analyzed by inductively coupled plasma optical emission spectrometer (ICP-OES), and it was found that the mass fraction of Ni in the catalyst was 10.8%.

_nCO = 0.27mol;

Calculate the carbon conversion rate according to formula (1): the carbon conversion rate is 66.9%;

Example 5

Prepare 100 mL of 30% nitric acid aqueous solution.

Preparation of oxidized low-rank coal:

Immerse 20 g of low-rank coal in the above-mentioned 30% nitric acid aqueous solution, mix evenly, stir at 50°C for 5 hours, filter and wash the filter residue to neutrality, and dry at 80°C to a water content of 1%; obtain oxidized low-rank coal ;

Preparation of metal salt solution: Weigh 2.5g of nickel acetate tetrahydrate and dissolve it in 100mL of deionized water; add ammonia water with a mass concentration of 25% to adjust the pH of the salt solution to 10;

Ion exchange: add 5g of the oxidized low-rank coal to the above-prepared nickel salt solution, stir at 30°C for 24h, filter, wash the filter residue with water until neutral, and dry at 70°C to a water content of 4%;

Catalyst molding: the above-mentioned dried filter residue is pyrolyzed in an inert atmosphere to stabilize the crystal form of elemental nickel on the surface of the catalyst, remove the volatile matter in the carrier, and increase the specific surface area of the catalyst. semi-coke supported tar steam reforming catalyst;

The described pyrolysis comprises the following steps: heating from room temperature to 600°C;

The heating rate is 10℃/min;

Residence time 2h;

The Ni loading of the catalyst was analyzed by inductively coupled plasma optical emission spectrometer (ICP-OES), and it was found that the mass fraction of Ni in the catalyst was 12.1%.

_nCO = 0.26mol;

Calculate the carbon conversion rate according to formula (1): the carbon conversion rate is 67%;

It can be seen from the TEM spectrum in Fig. 2 that the metal nanoparticles are embedded in the coke matrix, showing good nickel dispersion, and the average nickel particle size is 6.4 nm.

As shown in FIG. 3 , the metal crystal forms of the catalysts prepared in each example were characterized by XRD, and each catalyst maintained a stable nickel elemental crystal form.

The average crystallite size of Ni of the catalysts of each example was obtained by calculating the Ni(111) crystal plane by the Debye-Scherrer formula, and the specific surface area of some catalysts was measured by nitrogen adsorption method. The measurement results are shown in Table 2.

Table 2 The results of the characterization of the physical properties of the catalyst

Comparative Example 1

Preparation of metal salt solution: Weigh 5g of nickel acetate tetrahydrate and dissolve it in 100mL of deionized water; add ammonia water with a mass concentration of 25% to adjust the pH of the salt solution to 11;

Ion exchange: add 10g of raw coal carrier to the prepared nickel salt solution, stir at 30°C for 24h, filter, wash the filter residue until neutral, and dry at 70°C to a water content of 5%;

Catalyst molding: the above-mentioned dried filter residue is pyrolyzed in an inert atmosphere to stabilize the crystal form of elemental nickel on the surface of the catalyst, remove the volatile matter in the carrier, and increase the specific surface area of the catalyst. semi-coke supported tar steam reforming catalyst;

Described pyrolysis comprises the following steps:

Heating from room temperature to 600 ℃;

The heating rate is 10℃/min;

Residence time 2h;

The Ni loading of the catalyst was analyzed by inductively coupled plasma optical emission spectrometer (ICP-OES), and it was found that the mass fraction of Ni in the catalyst was 5.7%.

_nCO = 0.05mol;

The carbon conversion was calculated according to formula (1): the carbon conversion was 22%.

Comparative Example 2

Preparation of metal salt solution: 4.3 g of nickel acetate tetrahydrate was taken and prepared into 10 mL of aqueous solution.

Impregnation: add 10g of raw coal carrier to the prepared nickel salt solution, stir at 30°C for 8h, and dry at 70°C until the water content is 3%;

Catalyst molding: the above-mentioned dried filter residue is pyrolyzed in an inert atmosphere to stabilize the crystal form of elemental nickel on the surface of the catalyst, remove the volatile matter in the carrier, and increase the specific surface area of the catalyst. semi-coke supported tar steam reforming catalyst;

Described pyrolysis comprises the following steps:

Heating from room temperature to 600 ℃;

The heating rate is 10℃/min;

Residence time 2h;

The mass fraction of Ni in the catalyst is 10%.

_nCO = 0.005mol;

Calculate the carbon conversion rate according to formula (1): the carbon conversion rate is 4.6%;

Comparative Example 3

Preparation of metal salt solution: take 5.0 g of nickel acetate tetrahydrate and prepare 40 mL of aqueous solution.

Pressurized impregnation: add 10g of raw coal carrier to the above-prepared nickel salt solution, mix evenly, place it in an autoclave and seal it, keep it at 140°C for 5h, keep the obtained mixture at rest for 1h, filter and dry at 70°C to a water content of 4 %;

Catalyst molding: the above-mentioned dried filter residue is pyrolyzed in an inert atmosphere to stabilize the crystal form of elemental nickel on the surface of the catalyst, remove the volatile matter in the carrier, and increase the specific surface area of the catalyst. semi-coke supported tar steam reforming catalyst;

Described pyrolysis comprises the following steps:

Heating from room temperature to 600 ℃;

The heating rate is 10℃/min; the residence time is 2h;

_nCO = 0.003mol;

The carbon conversion was calculated according to formula (1): the carbon conversion was 4.9%.

Claims (10)

1. The semicoke-loaded coke oil-steam reforming catalyst is characterized in that low-rank coal pretreated by an oxidant is used as a catalyst carrier precursor, and Ni is used as a metal active component.

2. The semicoke-supported coke steam reforming catalyst according to claim 1, wherein the mass percentage of Ni is 7 to 13%.

3. The semicoke-supported coke steam reforming catalyst according to claim 2, wherein the mass percentage of Ni is 7.2 to 12.1%.

4. The preparation method of the semicoke-based supported tar steam reforming catalyst is characterized by comprising the following steps of:

(1) mixing and stirring an oxidant aqueous solution and target coal, and then collecting low-rank coal oxidized by an oxidant from a system;

(2) mixing and stirring the product obtained in the step (1) and a nickel salt aqueous solution with the pH value of 10-12, and then collecting a catalyst precursor from a system;

(3) and (3) pyrolyzing the catalyst precursor in the step (2) in an inert atmosphere to obtain the semicoke-loaded coke-oven water vapor reforming catalyst.

5. The method according to claim 4, characterized in that in the step (1), the mixture is stirred for 2-6 hours at 30-50 ℃, and then the low-rank coal oxidized by the oxidant is collected from the system, wherein the ratio of the target coal to the oxidant is 5-10 mL/g; the oxidant is selected from nitric acid or hydrogen peroxide.

6. The method according to claim 4, wherein in the step (2), the product obtained in the step (1) is mixed with a nickel salt aqueous solution with the pH value of 10-12, the mixture is stirred for 16-32 hours at the temperature of 25-35 ℃, and then a catalyst precursor is collected from the system;

the pH value of the nickel salt aqueous solution is adjusted by ammonia water;

the mixing ratio of the nickel salt solution to the low-rank coal oxide is 5-15 mL/g.

7. The method of claim 6, wherein the nickel salt is selected from one or more of nickel acetate tetrahydrate, nickel nitrate hexahydrate, nickel sulfate hexahydrate, and anhydrous nickel chloride.

8. The method according to claim 6, wherein the concentration of the nickel salt aqueous solution is 0.1 to 0.3 mol/L.

9. The method of claim 4, wherein in step (3), said pyrolyzing comprises the steps of: heating from room temperature to 550-700 ℃, wherein the heating rate is 5-10 ℃/min, and the retention time is 1-3 hours.

10. The application of the semicoke-supported tar steam reforming catalyst according to any one of claims 1 to 3, wherein the catalyst is used for catalyzing biomass or low-rank coal gasification tar steam reforming.

Images