CN117185274A - A non-metallic phosphorus-doped lanthanum iron-based perovskite oxygen carrier, preparation method and application - Google Patents

Abstract

The invention discloses a non-metallic phosphorus-doped lanthanum iron-based perovskite oxygen carrier, preparation method and application. The general formula of the oxygen carrier is LaFe _1-x P _x O ₃ . In the biomass gasification stage, the non-metallic phosphorus-doped lanthanum iron-based perovskite oxygen carrier conducts heat and mass exchange with the biomass. Lattice oxygen partially oxidizes the biomass to generate synthesis gas, and at the same time, the non-metallic phosphorus-doped lanthanum iron-based perovskite oxygen carrier is reduced to generate a reduced oxygen carrier; in the oxidation stage, the reduced oxygen carrier and The oxygen reaction in the air realizes the replenishment of oxygen and restores the structure before reacting with biomass, thereby realizing the recycling and regeneration of the oxygen carrier. The oxygen carrier can effectively improve the surface acidity of the oxygen carrier and modulate its surface reactivity and lattice oxygen migration ability.

Description

A non-metallic phosphorus-doped lanthanum iron-based perovskite oxygen carrier, preparation method and application

Technical field

The invention belongs to the technical field of oxygen carriers. Specifically, it relates to a non-metallic phosphorus-doped lanthanum iron-based perovskite oxygen carrier, preparation method and application.

Background technique

The continued dependence of the world's economic development on fossil energy has caused greenhouse gas emissions, mainly _CO2 , to increase year by year. The resulting global climate change has become one of the biggest challenges facing mankind in this century. Therefore, the development and utilization of renewable energy and the development of efficient and economical carbon emission reduction technologies have become urgent tasks to alleviate resource, energy and environmental problems. As the only carbon-neutral renewable energy, biomass has the advantages of recyclable resources, sustainable sources, and energy storage. It is known as the world's "fourth largest energy source" after coal, oil and natural gas. The development and utilization of biomass energy can not only reduce the dependence of human society on fossil energy, promote the transformation of the modern energy system, and promote the "green recovery" of the world economy after the epidemic, it can also sequester carbon and reduce emissions, helping to achieve the "double carbon" goal.

Among the many biomass utilization technologies, the technical route of biomass gasification to produce syngas has great advantages in energy efficiency, It has significant advantages in efficiency and production cost, and is one of the ideal ways to effectively utilize biomass energy. Tar by-products are the biggest obstacle to the promotion and application of biomass gasification technology. The soot particles produced by tar combustion cause problems for dust removal. The liquid tar condensed at low temperatures can also cause pipeline blockage and pollution, affecting the gas utilization efficiency and the safe and stable operation of related equipment. The best way to solve the problem of tar is to crack it into small-molecule permanent gas, which can reduce the tar content and increase the production of syngas. Therefore, studying the method of tar cracking is an urgent problem that needs to be solved. Although using oxygen as the gasification medium can effectively reduce the production of tar, the use of oxygen means the need to install an air separation oxygen generation device, which has high operating costs and complicated system processes.

Biomass chemical looping gasification technology based on circulating oxygen carriers is a new biomass energy thermal conversion method with low system energy consumption, high calorific value of syngas, low pollutant emissions, and high efficiency and cleanliness. It uses the lattice oxygen in the metal oxide (oxygen carrier) to replace part or all of the traditional gasification medium, and completes the transfer of lattice oxygen and heat and production through the oxygen carrier alternately circulating in the gasification reactor and the oxidation reactor. Partial oxidation of substances while achieving self-heating operation. Compared with traditional biomass gasification technology, biomass chemical chain gasification has the following significant advantages: (1) The oxygen element required for biomass gasification is provided by the lattice oxygen in the metal oxide oxygen carrier, avoiding the use of The energy consumption generated by the air separation device to prepare pure oxygen and a large amount of water vapor reduces the system cost; (2) The heat generated when the oxygen carrier is oxidized and regenerated in the oxidation reactor is brought into the gasification reactor to generate electricity. Gasification of substances provides heat, and the oxygen carrier also acts as a heat carrier, eliminating the need for external heat sources and improving system efficiency; (3) Compared with gaseous oxygen, lattice oxygen is more conducive to partial oxidation of fuel, thereby improving synthesis gas The calorific value; (4) The oxygen body in the reducing atmosphere also acts as a catalyst, which can effectively catalyze the cracking of macromolecular tar, thereby reducing the blockage and corrosion problems of tar on subsequent industrial equipment. The decomposition of tar is also conducive to improving the synthesis Gas production; (5) Since there is no introduction of other gases such as nitrogen, on the one hand, the quality of the syngas is improved, and on the other hand, the production of pollutants such as nitrogen oxides is effectively reduced at high temperatures.

In the chemical chain gasification process, the oxygen carrier is the hub connecting the two reactors. Therefore, screening oxygen carriers suitable for the chemical chain gasification process is crucial to improving the effect of chemical chain gasification reactions. Although Fe-based oxygen carriers have obvious advantages in terms of cost, they have poor reactivity and low oxygen carrying rate; Ni-based oxygen carriers have outstanding advantages in reactivity and catalytic tar cracking, but due to low mechanical strength, The development and application of Ni-based oxygen carriers are subject to certain restrictions because of their high cost and their harmful properties to the environment and people. Cu-based and Mn-based oxygen carriers are often used in chemical chain oxygen decomposition due to their ability to release molecular oxygen. Coupling (CLOU) process, but molecular oxygen is more likely to completely oxidize carbonaceous fuel than lattice oxygen. In addition, Cu-based oxygen carriers are easy to sinter under high temperature conditions, while Mn-based oxygen carriers have low mechanical strength and short particle life. Therefore, they have not been widely used in chemical chain gasification processes with syngas as the target product. It can be seen from the above that single metal oxygen carriers have their own advantages and are easy to obtain, but they also have their own shortcomings. In recent years, perovskite oxides have attracted much attention due to their unique _ABO structural characteristics and their potential as oxygen carriers, among which _LaFeO is the most widely used. Since the B-site element in this structure is an active phase, doping the B-site element can increase the fluidity of oxygen in the oxygen carrier lattice, strengthen the generation of oxygen vacancies, and improve the acidity and alkalinity of the oxygen carrier surface, thereby achieving Structural regulation and performance reconstruction of perovskite oxygen carriers provide an effective way for biomass chemical chain gasification and synthesis gas quality improvement. However, in current research, the element selection for doping LaFeO ₃ at the A and B sites focuses on metal elements. Although metal doping can effectively improve the performance of oxygen carriers, because metal doping generally uses corresponding metal nitrates as raw materials, the cost is high and there are safety risks such as explosion. In addition, the introduction of transition metal elements generally enhances the alkalinity of the active sites on the surface of the oxygen carrier. The decomposition of organic macromolecules in biomass tar requires not only basic active centers, but also certain acidic sites to deprive CH bonds of CH bonds. H ^- , converts the stable tar system into active carbocation, creating favorable conditions for CC bond breaking. Therefore, the common single metal oxides in the existing biomass chemical chain gasification reactions have low reactivity, low biomass gasification synthesis gas yield and high tar content. The surface acidity and alkalinity of the perovskite oxygen carrier is difficult to adjust. Technical problems such as poor reactivity.

Contents of the invention

The technical problem to be solved by the present invention is to provide a non-metallic phosphorus-doped lanthanum iron-based perovskite oxygen carrier, preparation method and application, which can effectively improve the surface acidity of the oxygen carrier and modulate its surface reactivity and lattice oxygen. Migration capabilities.

In order to solve the above technical problems, the present invention adopts the following technical solutions:

In a first aspect, embodiments of the present invention provide a non-metallic phosphorus-doped lanthanum iron-based perovskite oxygen carrier. The general formula of the oxygen carrier is LaFe _1-x P _x O ₃ , and the value range of x is 0 ≤x≤1.

As a preferred example, the crystal structure of the oxygen carrier is cubic crystal system.

As a preferred example, the value range of x is 0.01≤x≤0.05.

In a second aspect, embodiments of the present invention provide a method for preparing a non-metallic phosphorus-doped lanthanum iron-based perovskite oxygen carrier. The method includes the following steps:

Step 10, according to the stoichiometric ratio of LaFe _1-x P _x O ₃ , weigh 4.3300 parts by mass of La(NO ₃ ) ₃ ·6H ₂ O and 4.0402(1-x) parts by mass of Fe(NO ₃ ) ₃ · 9H ₂ O, 1.1503x mass parts of NH ₄ H ₂ PO ₄ and complexing agent are dissolved in deionized water at a preset temperature, and ammonia water is added dropwise to the solution to adjust the pH value of the solution to form a precursor solution;

Step 20: Evaporate the precursor solution in Step 10 to a gel state under stirring conditions, and then pre-combust to obtain a sponge-like porous precursor;

In step 30, the sponge-like porous precursor prepared in step 20 is calcined at a constant temperature to prepare the non-metallic phosphorus-doped lanthanum iron-based perovskite oxygen carrier.

As a preferred example, in step 10, the complexing agent includes citric acid and ethylenediaminetetraacetic acid. The molar ratio of citric acid and ethylenediaminetetraacetic acid is 2:1. The complexing agent and the precursor solution The molar ratio of the total amount of metal ions in is 3:1.

As a preferred example, in step 10, the preset temperature is 70-90°C, and the pH value of the precursor solution is 7-8.

As a preferred example, in the step 20, the stirring rate is 300~500 rpm, the evaporation temperature is 100~120°C, the pre-combustion is burned in a muffle furnace, and the pre-combustion temperature is 250°C; in the step 30, Transfer the sponge-like porous precursor prepared in step 20 to the crucible, and calcine at a constant temperature in a muffle furnace. The calcining temperature is 1000°C and the calcining time is 5 hours.

In a third aspect, embodiments of the present invention provide an application of a non-metallic phosphorus-doped lanthanum iron-based perovskite oxygen carrier in a biomass chemical chain gasification reaction. In the biomass gasification stage, the non-metallic phosphorus-doped lanthanum iron-based perovskite oxygen carrier is The hybrid lanthanum iron-based perovskite oxygen carrier performs heat and mass exchange with biomass. The non-metallic phosphorus-doped lattice oxygen in the lanthanum iron-based perovskite oxygen carrier partially oxidizes the biomass to generate synthesis gas. The non-metallic phosphorus-doped lanthanum iron-based perovskite oxygen carrier is reduced to generate a reduced oxygen carrier; in the oxidation stage, the reduced oxygen carrier reacts with oxygen in the air to supplement oxygen, returning to the state of the oxygen carrier. The structure of biomass before reaction, thereby realizing the recycling and regeneration of oxygen carriers.

As a preferred example, the raw material of the biomass is at least one of green algae, municipal sludge and cotton stalk, and the temperatures of the gasification stage and the oxidation stage are both 750-950°C.

As a preferred example, in the biomass gasification stage, the gas introduced is nitrogen and water vapor, and the water vapor volume percentage is 0 to 20%; in the oxidation stage, the gas introduced is air.

Compared with the existing technology, the present invention has the following beneficial effects: the non-metallic phosphorus-doped lanthanum iron-based perovskite oxygen carrier, preparation method and application of the present invention can effectively improve the surface acidity of the oxygen carrier, modulate Its surface reactivity and lattice oxygen migration capabilities. The oxygen carrier has a perovskite structure, and its general formula is LaFe _1-x P _x O ₃ , 0≤x≤1. Using this oxygen carrier to carry out biomass chemical chain gasification reaction can improve the carbon conversion rate of biomass and the synthesis gas yield.

Description of the drawings

Figure 1(a) is the XRD pattern of the non-metallic phosphorus-doped lanthanum iron-based perovskite oxygen carrier prepared in Examples 1 to 4 of the present invention;

Figure 1(b) is an enlarged view of the dotted box in Figure 1(a), that is, an enlarged view of the diffraction peak at a diffraction angle between 31 and 33°;

Figure 2(a) is an SEM image of the oxygen carrier LaFeO ₃ prepared in Example 1 of the present invention;

Figure 2(b) is an SEM image of the oxygen carrier LaFe _0.97 P _0.03 O ₃ prepared in Example 3 of the present invention;

Figure 2(c) is the EDX energy spectrum of the oxygen carrier LaFeO ₃ prepared in Example 1 of the present invention;

Figure 2(d) is the EDX spectrum of the oxygen carrier LaFe _0.97 P _0.03 O ₃ prepared in Example 3 of the present invention;

Figure 3 shows the results of gasification thermogravimetric analysis of biomass chemical chains for various oxygen carriers at a heating rate of 40°C/min;

Figure 4(a) shows the mass spectrometry test results of hydrogen in the synthesis gas component in the biomass chemical chain gasification thermogravimetric analysis of various oxygen carriers;

Figure 4(b) is a graph showing the mass spectrometry test results of carbon monoxide in the syngas components in the biomass chemical chain gasification thermogravimetric analysis of various oxygen carriers;

Figure 5 is a graph showing the gas component distribution results of direct gasification of municipal sludge and cotton stalk mixed biomass and quartz sand of Comparative Example 1 at 850°C and a water vapor volume fraction of 20%;

Figure 6 is a diagram showing the distribution results of the gasification gas components of the chemical chain gasification of municipal sludge and cotton stalk mixed biomass based on the LaFeO ₃ oxygen carrier prepared in Example 1 at 850°C and a water vapor volume fraction of 20%;

Figure 7 shows the distribution results of gasification gas components of municipal sludge and cotton straw mixed biomass chemical chain based on the LaFe _0.99 P _0.01 O ₃ oxygen carrier prepared in Example 2 at 850°C and a water vapor volume fraction of 20%. picture;

Figure 8 shows the distribution results of gasification gas components of municipal sludge and cotton stalk mixed biomass chemical chain based on the LaFe _0.97 P _0.03 O ₃ oxygen carrier prepared in Example 3 at 850°C and a water vapor volume fraction of 20%. picture;

Figure 9 shows the distribution results of gasification gas components of municipal sludge and cotton stalk mixed biomass chemical chain based on the LaFe _0.95 P _0.05 O ₃ oxygen carrier prepared in Example 4 at 850°C and a water vapor volume fraction of 20%. picture;

Figure 10 shows the direct gasification of municipal sludge and cotton stalk mixed biomass and the quartz sand of Comparative Example 1 at 850°C and a water vapor volume fraction of 20%, as well as the phosphorus-doped mixture prepared based on Examples 1 to 4 The gas yield and H ₂ /CO ratio results of biomass chemical chain gasification of hybrid lanthanum iron perovskite oxygen carrier;

Figure 11 is an XRD pattern of the oxygen carrier prepared in Examples 1 to 4 after one biomass chemical chain gasification oxidation-reduction cycle at 850°C and a water vapor volume fraction of 20%;

Figure 12 is a diagram showing the XPS characterization results of the oxygen carriers prepared in Examples 1 to 4.

Detailed ways

The present invention will be further described below in conjunction with the examples. These examples are only used to illustrate the invention and are not intended to limit the scope of the invention. In the following examples, if the experimental method with specific conditions is not specified, then the conventional conditions in the field or the conditions recommended by the manufacturer are usually followed; the raw materials, reagents, etc. used, unless otherwise specified, are all available from the conventional market. Raw materials and reagents obtained from commercial sources. Any non-substantive changes and substitutions made by those skilled in the art on the basis of the present invention shall fall within the scope of protection claimed by the present invention.

A non-metallic phosphorus-doped lanthanum iron-based perovskite oxygen carrier according to the embodiment of the present invention has a general formula of LaFe _1-x P _x O ₃ , 0≤x≤1.

The crystal structures of the above-mentioned oxygen carriers are all cubic crystal system, which shows that doping with a small amount of phosphorus element does not significantly change the crystal structure of LaFeO ₃ perovskite. The prepared phosphorus-doped lanthanum iron-based perovskite oxygen carrier Has good structural stability.

Preferably, the value range of x is 0.01≤x≤0.05. According to the structural tolerance coefficient formula proposed by GoldSchmidt, the structural deviation t of the perovskite structure should be between 0.75 and 1. Therefore, as the amount of phosphorus doping increases, the perovskite will undergo significant lattice shrinkage, and if x exceeds 0.05, it will be difficult for the P element to be doped into the B site of the perovskite, and the pure phase of the perovskite cannot be obtained.

The above-mentioned oxygen carrier is a composite oxide oxygen carrier ABB'O ₃ with a perovskite structure. The value range of x is 0≤x≤1, where A is the rare earth metal lanthanum, B is the transition metal iron, and B' is non The metallic element phosphorus uses non-metallic phosphorus to partially replace Fe in LaFeO ₃ perovskite without changing the crystal structure of the perovskite, and prepares phosphorus-doped lanthanum iron bases with cubic crystal structures and different Fe:P molar ratios. Perovskite oxygen carrier LaFe _1-x P _x O ₃ .

The preparation method of the above-mentioned non-metallic phosphorus-doped lanthanum iron-based perovskite oxygen carrier includes the following steps:

Step 10, according to the stoichiometric ratio of LaFe _1-x P _x O ₃ , weigh 4.3300 parts by mass of La(NO ₃ ) ₃ ·6H ₂ O and 4.0402(1-x) parts by mass of Fe(NO ₃ ) ₃ · 9H ₂ O, 1.1503x mass parts of NH ₄ H ₂ PO ₄ and complexing agent are dissolved in deionized water at a preset temperature, and ammonia water is added dropwise to the solution to adjust the pH value of the solution to form a precursor solution.

Preferably, the complexing agent includes citric acid (CA) and ethylenediaminetetraacetic acid (EDTA). The molar ratio of citric acid and ethylenediaminetetraacetic acid is 2:1. The complexing agent and the metal ions in the precursor solution The total molar ratio is 3:1. The preset temperature is 70~90℃, and the pH value of the precursor solution is 7~8.

During the evaporation of the precursor solution to prepare the gel, if the temperature is too low, metal nitrates will easily precipitate, reducing the uniformity of the sample, and the sol will be relatively viscous, affecting the stirring and dispersion effect; if the temperature is too high, uneven evaporation will occur, and similarly Affects the uniformity of xerogel, so the selected temperature is 70~90℃. Citric acid is a polybasic weak acid, which will undergo multi-step dissociation in the solution. The dissociated ions have different equilibrium states at different pH values, causing different complexing methods between metal cations and citric acid, thereby affecting the polymerization effect. Therefore, the pH value of the precursor solution will affect the crystallization state and particle size of the product. When the pH value of the precursor solution is small, the ionization degree of citric acid under strong acidic conditions is low, the number of hydroxyl groups that can be coordinated is very small, the metal cation complexing effect is poor, the gel contains a large number of free metal cations, and the precursor composition is uneven, and ultimately More impurity phases are formed; the pH value of the precursor solution is too high, which will cause the metal cations in the solution to form precipitation and affect the purity of the product. Therefore, keeping the pH value of the precursor solution at a weakly alkaline condition of 7 to 8 is more suitable for preparing an oxygen carrier with a pure perovskite phase.

Step 20: The precursor solution in Step 10 is evaporated to a gel state under stirring conditions, and then pre-combusted to obtain a sponge-like porous precursor. Preferably, the stirring rate is 300-500 rpm, and the evaporation temperature is 100-120°C. Preferably, the pre-combustion is performed in a muffle furnace, and the pre-combustion temperature is 250°C.

In step 30, the sponge-like porous precursor prepared in step 20 is calcined at a constant temperature to prepare the non-metallic phosphorus-doped lanthanum iron-based perovskite oxygen carrier. Preferably, in step 30, the sponge-like porous precursor obtained in step 20 is transferred to a crucible and calcined at a constant temperature in a muffle furnace; the calcining temperature is 1000°C and the calcining time is 5 hours.

The preparation method of the above-mentioned oxygen carrier is simple and low-cost, which is conducive to industrial promotion and use. This method uses ammonium dihydrogen phosphate as the phosphorus source, has low cost, and avoids the introduction of other metal elements during the preparation process. Compared with traditional metal doping that uses metal nitrate as the doping raw material, this method uses ammonium dihydrogen phosphate as the phosphorus dopant. The surface of the oxygen carrier made has more active oxygen and oxygen vacancies, which is beneficial to biomass. Chemical chain gasification to produce synthesis gas.

Application of the above-mentioned non-metallic phosphorus-doped lanthanum iron-based perovskite oxygen carrier in biomass chemical chain gasification reaction. In the biomass gasification stage, the non-metallic phosphorus-doped lanthanum iron-based perovskite oxygen carrier Performing heat and mass exchange with biomass, the non-metallic phosphorus is doped with lattice oxygen in the lanthanum iron-based perovskite oxygen carrier to partially oxidize the biomass to generate synthesis gas, and at the same time, the non-metallic phosphorus is doped with lanthanum iron-based calcium The titanium oxygen carrier is reduced to generate a reduced oxygen carrier. The general formula is LaFe _1-x P _x O _3-δ . The value range of δ is 0≤δ≤3; in the oxidation stage, the reduced oxygen carrier The oxygen body reacts with oxygen in the air to replenish oxygen and restore the structure before reacting with biomass. The general formula is LaFe _1-x P _x O ₃ , thereby realizing the recycling and regeneration of the oxygen carrier.

Preferably, the raw material of the biomass is at least one of green algae, municipal sludge and cotton stalk, and the temperatures of the gasification stage and the oxidation stage are both 750-950°C.

Preferably, in the biomass gasification stage, the incoming gases are nitrogen and water vapor, and the water vapor volume percentage is 0 to 20%; wherein nitrogen is the carrier gas and balance gas, and water is the carrier gas. Steam is used to adjust the synthesis gas H ₂ /CO ratio; in the oxidation stage, the incoming gas is air.

In the above application, in the biomass gasification stage, as shown in formula (1), biomass (biomass) is first pyrolyzed to generate tar (tar), coke (biochar), small molecular gas (gas) and a small amount of ash (ash) . As shown in equations (2) and (3), thanks to the abundant surface active oxygen species and oxygen vacancies of the phosphorus-doped lanthanum iron-based perovskite oxygen carrier, the biomass tar has a significant role in active oxygen and metal and non-metal activities. Under the joint action of the sites (Fe, P), it is catalytically oxidized into small molecule gas. As shown in formula (4), the lattice interaction between coke and oxygen carrier generates CO, thus promoting the generation of synthesis gas. In this process, as shown in formula (5), the oxygen carrier loses part of the lattice oxygen to generate the reduced oxygen carrier LaFe _1-x P _x O _3-δ .

biomass → gas (H ₂ , CO, CO ₂ , CH ₄ ) + biochar + tar +ash Formula (1)

C _n H _m + chemically adsorbed oxygen species→C _i H _j +CO+H ₂ +CO ₂ +H ₂ O Formula (2)

C+lattice oxygen→CO formula (4)

LaFe _1-x P _x O ₃ →LaFe _1-x P _x O _3-δ +δO Formula (5)

In formula (2) and formula (3), C _n H _m refers to tar molecules.

In the oxidation stage, as shown in formula (6), the reduced oxygen carrier LaFe _1-x P _x O _3-δ reacts with oxygen in the air to supplement oxygen and return to the structure LaFe before reacting with biomass _1-x P _x O ₃ , thereby realizing the cyclic regeneration of the oxygen carrier and releasing heat for the biogasification process.

LaFe _1-x P _x O _3-δ +δ/2O ₂ →LaFe _1-x P _x O ₃ formula (6)

The non-metallic phosphorus-doped lanthanum iron-based perovskite oxygen carrier of the above embodiment is used in biomass chemical chain gasification, and has the characteristics of good lattice oxygen mobility and reactivity, high synthesis gas yield, and low tar content. advantage. Since the high-valence P ⁵⁺ replaces the low-valence Fe ³⁺ in LaFeO ₃ , in order to maintain the electrical neutrality of the crystal structure, low-valence Fe ²⁺ and additional oxygen vacancies are generated to compensate for the doping band. Comes with positive electricity. The formation of oxygen vacancies increases the mobility of lattice oxygen in the oxygen carrier, strengthens the transformation of lattice oxygen into surface-adsorbed oxygen species, and promotes the transformation of biomass tar into small molecule synthesis gas, thus reducing the tar content. Improve synthesis gas yield.

The present invention uses low-cost NH ₄ H ₂ PO ₄ as the doping raw material to do B-site non-metal phosphorus doping of LaFeO ₃ . Using NH ₄ H ₂ PO ₄ as the doping raw material can significantly reduce the preparation cost. At the same time, the doping of phosphorus can promote the generation of surface active oxygen species and oxygen vacancies, increase surface active sites, and facilitate the decomposition of macromolecule tar. The present invention uses NH ₄ H ₂ PO ₄ as the phosphorus source, which can effectively avoid the introduction of other metal ions, thereby avoiding the influence of alkali metals on the gasification of the biomass chemical chain.

Specific examples and comparative examples are provided below.

Comparative example 1

Quartz sand is used as bed material. Quartz sand molecular formula SiO ₂ , CAS number: 14808-60-7.

Measure 40 mg of quartz sand and mix it evenly with 100 mg of green algae (the mass ratio of quartz sand to biomass is 0.4:1) to form a mixture. Take 10 mg of the mixture and place it in a synchronous thermal analyzer model STA 409PC manufactured by NETZSCH, Germany, in an Ar atmosphere of 240 mL/min and a heating rate of 10°C/min from room temperature to 900°C for thermogravimetric analysis. Room temperature usually refers to 25℃.

Example 1 Preparation method of oxygen carrier LaFeO ₃

Step 10, weigh 4.3300g of lanthanum nitrate hexahydrate La(NO ₃ ) ₃ ·6H ₂ O, 4.0402g of iron nitrate nonahydrate Fe (NO ₃ ) ₃ ·9H ₂ O, and 5.842g of ethylenediaminetetraacetic acid ( EDTA) and 7.685g of anhydrous citric acid CA were dissolved in deionized water at 85°C, and ammonia water was added dropwise to the solution to adjust the pH value of the solution to 8 to form a precursor solution; where, EDTA:CA: The molar ratio of metal ions is 1:2:1.

Step 20: Evaporate the precursor solution of Step 10 to a gel state at 120°C at a stirring rate of 300 rpm, and then place it in a muffle furnace to heat up to 250°C at a heating rate of 5°C/min, and keep the temperature constant for 5 hours. Pre-combustion obtains sponge-like porous precursor.

Step 30: Transfer the sponge-like porous precursor prepared in Step 20 into a crucible, heat it in a muffle furnace to 1000°C at a heating rate of 5°C/min, and keep the temperature constant for 5 hours, and then calcine to obtain undoped lanthanum iron. Based on the perovskite oxygen carrier LaFeO ₃ , 60-mesh oxygen carrier particles were obtained through sieving.

Example 2 Preparation method of oxygen carrier LaFe _0.99 P _0.01 O ₃

Step 10, weigh 4.3300g of lanthanum nitrate hexahydrate La(NO ₃ ) ₃ ·6H ₂ O, 3.9998g of iron nitrate nonahydrate Fe(NO ₃ ) ₃ ·9H ₂ O, and 0.0115g of ammonium dihydrogen phosphate NH ₄ H ₂ PO ₄ , 5.842g of ethylenediaminetetraacetic acid (EDTA) and 7.685g of anhydrous citric acid CA were dissolved in deionized water at 70°C, and ammonia water was added dropwise to the solution to adjust the pH value of the solution. is 7, where the molar ratio of EDTA:CA:metal ions is 1:2:1.

Step 20: Evaporate the precursor solution in Step 10 to a gel state at 110°C with a stirring rate of 400 rpm, and then place it in a muffle furnace to heat up to 250°C at a heating rate of 5°C/min, and keep the temperature constant for 4 hours. Pre-combustion obtains sponge-like porous precursor.

Step 30: Transfer the sponge-like porous precursor prepared in Step 20 to a crucible, heat it in a muffle furnace to 1000°C at a heating rate of 5°C/min, and calcine at a constant temperature for 5 hours to obtain non-metallic phosphorus-doped lanthanum. The iron-based perovskite oxygen carrier LaFe _0.99 P _0.01 O ₃ was screened to obtain 60-mesh oxygen carrier particles.

Example 3 Preparation method of oxygen carrier LaFe _0.97 P _0.03 O ₃

Step 10, weigh 4.3300g of lanthanum nitrate hexahydrate La(NO ₃ ) ₃ ·6H ₂ O, 3.919g of iron nitrate nonahydrate Fe(NO ₃ ) ₃ ·9H ₂ O, and 0.0345g of ammonium dihydrogen phosphate NH ₄ H ₂ PO ₄ , 5.842g of ethylenediaminetetraacetic acid (EDTA) and 7.685g of anhydrous citric acid CA were dissolved in deionized water at 90°C, and ammonia was added dropwise to the solution to adjust the pH of the solution to 7.5, where the molar ratio of EDTA:CA:metal ions is 1:2:1.

Step 20: Evaporate the precursor solution of Step 10 to a gel state at 115°C with a stirring rate of 450 rpm, then place it in a muffle furnace and heat it to 250°C at a heating rate of 5°C/min, and keep the temperature constant for 4 hours. Pre-combustion obtains sponge-like porous precursor.

Step 30: Transfer the sponge-like porous precursor prepared in Step 20 to a crucible, heat it in a muffle furnace to 1000°C at a heating rate of 5°C/min, and calcine at a constant temperature for 5 hours to obtain non-metallic phosphorus-doped lanthanum. The iron-based perovskite oxygen carrier LaFe _0.97 P _0.03 O ₃ was screened to obtain 80-mesh oxygen carrier particles.

Example 4 Preparation method of oxygen carrier LaFe _0.95 P _0.05 O ₃

Step 10, weigh 4.3300g of lanthanum nitrate hexahydrate La(NO ₃ ) ₃ ·6H ₂ O, 3.8382g of iron nitrate nonahydrate Fe(NO ₃ ) ₃ ·9H ₂ O, and 0.0575g of ammonium dihydrogen phosphate NH ₄ H ₂ PO ₄ , 5.842g of ethylenediaminetetraacetic acid (EDTA) and 7.685g of anhydrous citric acid CA were dissolved in deionized water at 80°C, and ammonia water was added dropwise to the solution to adjust the pH value of the solution. is 7.8, where the molar ratio of EDTA:CA:metal ions is 1:2:1.

Step 20: Evaporate the precursor solution of Step 10 to a gel state at 100°C with a stirring rate of 500 rpm, and then place it in a muffle furnace to heat up to 250°C at a heating rate of 5°C/min, and keep the temperature constant for 4 hours. Pre-combustion obtains sponge-like porous precursor.

Step 30: Transfer the sponge-like porous precursor prepared in Step 20 to a crucible, heat it in a muffle furnace to 1000°C at a heating rate of 5°C/min, and calcine at a constant temperature for 5 hours to obtain non-metallic phosphorus-doped lanthanum. The iron-based perovskite oxygen carrier LaFe _0.95 P _0.05 O ₃ was screened to obtain 80-mesh oxygen carrier particles.

Experiments were conducted on the oxygen carriers prepared in Comparative Example 1 and Examples 1 to 4 above.

1. Conduct X-ray diffraction (XRD) testing on the oxygen carriers prepared in Examples 1 to 4. Test conditions: The radiation source is the Kα ray generated by the Cu target, the wavelength λ=0.15418nm, the scanning rate is set to 10°/min, the scanning interval is set to 2θ=10-90°, and the interval is 0.02°. The testing instrument is a powder diffractometer model of Rigaku Smartlab, a Japanese physical and chemical company. X-ray diffraction tests were performed according to conventional methods. The test results are shown in Figure 1. It can be seen from Figure 1(a) that the prepared phosphorus-doped lanthanum iron-based perovskite oxygen carriers all have a perovskite phase with a single cubic crystal structure. Figure 1(b) is an enlarged view of the dotted frame in Figure 1(a). It can be seen from the enlarged diffraction peak pattern in Figure 1(b) that as the phosphorus doping amount increases, the diffraction peak shifts toward a larger diffraction angle. This is due to the replacement of Fe ³⁺ with a larger ionic radius by P ⁵⁺ with a smaller ionic radius, resulting in distortion of the crystal lattice. This also shows that phosphorus element is successfully doped into the bulk structure of _LaFeO3 perovskite.

2. Conduct scanning electron microscope (SEM) and energy spectrum (EDX-mapping) tests on the oxygen carrier LaFeO ₃ prepared in Example 1 and the oxygen carrier LaFe _0.97 P _0.03 O ₃ prepared in Example 3. The test instruments are ZEISS sigma500 environmental scanning electron microscope (FE-SEM) and JEM-2100F X-fluorescence spectrum analyzer. Scanning electron microscopy and energy spectroscopy tests were performed according to conventional methods. The test results are shown in Figure 2. It can be seen from Figure 2(a) and Figure 2(b) that the LaFeO ₃ and phosphorus-doped LaFe _0.97 P _0.03 O ₃ perovskite oxygen carrier is in the shape of fine particles, with uniform grain size and good dispersion. It can be seen from Figure 2(c) and Figure 2(d) that the LaFeO ₃ oxygen carrier prepared by the method of the present invention contains La, Fe and O elements, while the LaFe _0.97 P _0.03 O ₃ oxygen carrier contains in addition to La, Fe and O elements, and also contains phosphorus. This shows that the preparation method of the present invention successfully dops phosphorus element into the bulk structure of LaFeO ₃ perovskite.

3. Simultaneous thermal analysis experiments. The synchronous thermal analyzer is a synchronous thermal analyzer model STA409PC manufactured by the German manufacturer NETZSCH.

The experimental method is as follows: measure 40 mg of oxygen carrier and mix it evenly with 100 mg of green algae to form a mixture. The mass ratio of oxygen carrier to biomass is 0.4:1. Take 10 mg of the mixture and put it in a synchronous thermal analyzer, in an Ar atmosphere of 240 mL/min, and heat it from room temperature to 900°C at a set heating rate, and perform thermogravimetric analysis.

Experiments were conducted on the oxygen carriers prepared in Comparative Example 1 and Examples 1-4 respectively. The set heating rate is 40°C/min.

The experimental results are shown in Figure 3. In Figure 3, the abscissa represents the reaction temperature in °C; the ordinate represents the weight loss of the sample in wt.%. It can be seen from Figure 3 that: compared with the addition of Comparative Example 1, the weight loss of green algae after adding the oxygen carriers of Examples 1 to 4 increased significantly, and the phosphorus-doped oxygen carriers were compared with those without phosphorus. LaFeO ₃ , the sample loses more weight. Judging from the heating rate of 40°C/min, the weight loss after phosphorus doping is greater. It shows that the conversion rate of green algae is higher under the same oxygen carrier addition amount, proving that phosphorus-doped oxygen carriers are more beneficial to the conversion of green algae biomass.

4. Mass spectrometry experiment. The mass spectrometer was a Thermo Fisher Scientific iS 50 mass spectrometer.

The experimental method is as follows: measure 40 mg of oxygen carrier and mix it evenly with 100 mg of green algae to form a mixture. The mass ratio of oxygen carrier to biomass is 0.4:1. Take 10 mg of the mixture and put it in a synchronous thermal analyzer, in an Ar atmosphere of 240 mL/min, and heat it from room temperature to 900°C at a heating rate of 40°C/min. The generated product enters the mass spectrometer, and the gas components are detected online using the mass spectrometer. . The generated gas components include CO, CO ₂ , H ₂ and CH ₄ for Comparative Example 1; and include CO and H ₂ for Examples 1-4.

In the experiment, the above mass spectrometry analysis experiments were performed on the oxygen carriers prepared in Comparative Example 1 and Examples 1-4 respectively. The experimental results are shown in Figure 4. In Figure 4, the abscissa represents the reaction temperature, unit: °C; the ordinate represents the ion current intensity of each sample gas component; MA represents the sample of Comparative Example 1, MA-LF represents the sample of Example 1, and MA-LFP1 represents the implementation For the sample of Example 2, MA-LFP3 represents the sample of Example 3, and MA-LFP5 represents the sample of Example 4. As can be seen from Figure 4: Compared with the direct mixed pyrolysis of green algae biomass and quartz sand and the _mixed samples of green algae biomass with undoped _LaFeO3 oxygen carrier, phosphorus doped _{LaFe1- xPxO3} (0.01≤x≤0.05) Oxygen carrier can significantly promote the generation of syngas. After 750°C, the CO production increased significantly. This indicates that the lattice oxygen in the phosphorus-doped perovskite oxygen carrier enhances the gasification of biomass coke to generate CO.

5. Biomass chemical chain gasification reaction experiment. The gas analyzer adopts the gas analyzer model MRU VARIO PLUS.

Measure 0.2g of municipal sludge with a particle size of 0.1-0.125 μm and 0.3g of cotton stalk biomass particles with a particle size of 0.1-0.125 μm, and mix them evenly to make a biomass mixture. The mass ratio of municipal sludge to cotton straw is 2:3. Weigh 0.2g of the oxygen carrier and biomass mixture and mix them evenly, then place them in a crucible for later use. The mass ratio of oxygen carrier to biomass mixture is 0.4:1. Under a _N2 atmosphere of 200mL/min, the fixed bed reactor was heated from room temperature to 850℃ at a heating rate of 10℃/min. When the temperature stabilized, water vapor with a volume fraction of 20% was introduced, and then the reactor was filled with water. The crucible of the oxygen carrier and biomass mixture is placed in the reaction area of the reactor, and a gas analyzer is used to analyze the gas components. After the reaction is completed, air is introduced to oxidize the oxygen carrier. The oxygen carrier used is in an oxidized state because it is calcined in an air atmosphere during the preparation process. It is reduced after reacting with the biomass. After the biomass gasification reaction, oxygen is introduced to realize the re-oxidation of the oxygen carrier. This process is A cycle.

The above experiments were conducted on the oxygen carriers of Comparative Example 1 and Examples 1 to 4 respectively. The experimental results are shown in Figures 5 to 10. Figures 5 to 9 show the changes in gas components with reaction time under different oxygen carrier conditions. The abscissa represents the reaction time, and the ordinate represents the gas volume fraction. Figure 10 shows the cumulative yield of each gas component in the above process, in which the abscissa indicates the type of oxygen carrier and the ordinate indicates the gas yield, unit: m ³ /kg. As can be seen from Figure 10: Compared with quartz sand and undoped _LaFeO oxygen carrier, the synthesis gas yield during the biomass chemical chain gasification process using phosphorus-doped perovskite oxygen carrier is significantly improved. . This shows that the phosphorus-doped perovskite oxygen carrier has good reactivity and can promote the directional conversion of tar macromolecules into small-molecule syngas.

As shown in Figure 11, the XRD pattern of the above-mentioned phosphorus-doped perovskite oxygen carrier after a biomass chemical chain gasification cycle reaction. It can be seen from Figure 11: Compared with the perovskite oxygen carrier that has been prepared but has not yet participated in the biomass chemical chain gasification cycle reaction, the oxygen carrier that has undergone one cycle reaction still has obvious cubic perovskite properties. structure. This shows that the reduced phosphorus-doped perovskite oxygen carrier LaFe _1-x P _x O _3-δ can return to the original structure LaFe _1-x P _x O ₃ after oxidation reaction.

6. X-ray photoelectron spectroscopy (XPS) analysis experiment. A Thermo EscaLab 250Xi XPS energy spectrometer was used, using an Al Kα X-ray source (hν = 1486.6eV) with a resolution of 0.25eV. The electron binding energy values were calibrated using the sample contaminating carbon (C1s=284.8eV) as the internal standard. It is carried out through XPSPEAK 41 software, using Shirley or Liner background, and applying the Voigt function with indefinite Lorentz component for component deconvolution, and performing peak fitting processing on the XPS spectrum. XPS analysis was performed on the oxygen carriers prepared in Examples 1 to 4. The analysis results are shown in Figure 12. In Figure 12, O _I represents physically adsorbed oxygen species, which generally exist in the form of adsorbed water molecules; O _II represents surface chemically adsorbed oxygen species; O _III represents electron-rich superoxide oxygen, whose concentration is closely related to the surface oxygen vacancy content; O _IV is the lattice oxygen species. The contents of O _II and O _III are closely related to the activity of oxygen carriers. It can be seen from Figure 12 that the ratio of O _II + O _III on the oxygen carrier surface increases significantly after phosphorus doping. This shows that phosphorus doping can significantly improve the oxygen activity of the oxygen carrier. At the same time, the Fe ²⁺ ratio increases with the increase in phosphorus doping amount, indicating that phosphorus is successfully embedded into the perovskite bulk phase.

The above are only preferred embodiments of the present invention. It should be noted that those of ordinary skill in the art will realize that the above specific embodiments are only illustrative and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made by those of ordinary skill in the art under the inspiration of the present invention shall be included in the protection scope of the present invention.

Claims (10)

1. The nonmetallic phosphorus doped lanthanum iron-based perovskite oxygen carrier is characterized in that: the general formula of the oxygen carrier is LaFe _{1- x} P _x O ₃ The value range of x is more than or equal to 0 and less than or equal to 1.

2. The non-metallic phosphorus doped lanthanum-iron-based perovskite oxygen carrier according to claim 1, wherein the oxygen carrier has a cubic crystal structure.

3. The nonmetallic phosphorus-doped lanthanum-iron-based perovskite oxygen carrier according to claim 1, wherein the value range of x is more than or equal to 0.01 and less than or equal to 0.05.

4. A method for preparing the nonmetallic phosphorus-doped lanthanum-iron-based perovskite oxygen carrier according to claim 1, wherein the method comprises the following steps:

step 10, according to LaFe _1-x P _x O ₃ Is prepared by weighing 4.3300 parts by mass of La (NO ₃ ) ₃ ·6H ₂ O,4.0402 (1-x) mass part of Fe (NO) ₃ ) ₃ ·9H ₂ O, 1.1503x mass portion of NH ₄ H ₂ PO ₄ Dissolving a complexing agent in deionized water at a preset temperature, dropwise adding ammonia water into the solution, and adjusting the pH value of the solution to form a precursor solution;

step 20, evaporating the precursor solution in the step 10 to a gel state under the stirring condition, and then pre-burning to obtain a spongy porous precursor;

and step 30, calcining the spongy porous precursor prepared in the step 20 at a constant temperature to prepare the nonmetallic phosphorus-doped lanthanum-iron-based perovskite oxygen carrier.

5. The method of claim 4, wherein in step 10, the complexing agent comprises citric acid and ethylenediamine tetraacetic acid, the molar ratio of citric acid to ethylenediamine tetraacetic acid is 2:1, and the molar ratio of the complexing agent to the total amount of metal ions in the precursor solution is 3:1.

6. The method according to claim 4, wherein in the step 10, the preset temperature is 70-90 ℃, and the pH of the precursor solution is 7-8.

7. The method according to claim 4, wherein in the step 20, the stirring speed is 300-500 rpm, the evaporating temperature is 100-120 ℃, the pre-burning is carried out in a muffle furnace, and the pre-burning temperature is 250 ℃;

in the step 30, the spongy porous precursor prepared in the step 20 is transferred into a crucible, and is calcined at a constant temperature in a muffle furnace, wherein the calcining temperature is 1000 ℃ and the calcining time is 5 hours.

8. Use of a non-metallic phosphorus doped lanthanum-iron-based perovskite oxygen carrier according to any one of claims 1-3 in a biomass chemical chain gasification reaction, wherein in a biomass gasification stage, the non-metallic phosphorus doped lanthanum-iron-based perovskite oxygen carrier performs a heat and mass exchange with biomass, lattice oxygen in the non-metallic phosphorus doped lanthanum-iron-based perovskite oxygen carrier oxidizes biomass partially to generate synthesis gas, and simultaneously the non-metallic phosphorus doped lanthanum-iron-based perovskite oxygen carrier is reduced to generate a reduced oxygen carrier; in the oxidation stage, the reduced oxygen carrier reacts with oxygen in the air to supplement oxygen, and the structure before the reaction with biomass is restored, so that the cyclic regeneration of the oxygen carrier is realized.

9. The application of the nonmetallic phosphorus doped lanthanum-iron-based perovskite oxygen carrier in the chemical chain gasification reaction of biomass according to claim 8, wherein the raw material of the biomass is at least one of green algae, municipal sludge and cotton stalk, and the temperature of the gasification stage and the oxidation stage is 750-950 ℃.

10. The application of the nonmetallic phosphorus-doped lanthanum-iron-based perovskite oxygen carrier in the chemical chain gasification reaction of biomass according to claim 8, wherein the introduced gas is nitrogen and water vapor in the biomass gasification stage, and the volume percentage of the water vapor is 0-20%; in the oxidation stage, the gas is air.