Oxygen carrier, and preparation method therefor and use thereof

Abstract

The present invention relates to an oxygen carrier, and a preparation method therefor and the use thereof. The oxygen carrier of the present invention comprises a composite oxide of iron and strontium, wherein the molar ratio of strontium to iron in the oxygen carrier is (1.1-5):1. The oxygen carrier of the present invention has the advantages of a high carbon conversion rate, a high synthesis gas yield, a high CO selectivity and a low tar yield in the process of biomass gasification, and can be prepared by means of a high-temperature solid phase method; and the preparation method is simple, and can easily realize large-scale production.

Description

An oxygen carrier, its preparation method and uses

[0001] This application claims priority to Chinese Patent Application No. 202411228416.9, filed on September 2, 2024, entitled "An Oxygen Carrier, Its Preparation Method and Use", which is incorporated herein by reference. Technical Field

[0002] This invention belongs to the field of biomass thermal conversion, specifically relating to an oxygen carrier, its preparation method, and its uses. Background Technology

[0003] Biomass, as a high-quality renewable energy source, has received widespread attention and research due to its "zero-emission" raw material characteristics throughout its life cycle. my country is relatively rich in biomass resources, including forestry waste, crop straw, large-scale livestock and poultry manure, and municipal solid waste. These potentially usable biomass resources are equivalent to approximately 500 million tons of standard coal annually, which, if fully utilized, could account for about 10% of my country's total primary energy consumption. Against the backdrop of my country's energy transition, biomass utilization has significant untapped potential.

[0004] Compared to biomass combustion, biomass pyrolysis and gasification processes can produce syngas (H2+CO), which can be used as clean fuels or chemical feedstocks, thus enabling more diversified applications of biomass. Biomass gasification can be categorized into air gasification, steam gasification, and pure oxygen / enriched oxygen gasification, depending on the gasifying agent. Air gasification is the simplest and most economical, but the presence of a large amount of nitrogen in the air results in a low proportion and low calorific value of the syngas produced, posing challenges for downstream applications. While steam gasification yields syngas with high calorific value and high hydrogen content, the process cannot maintain stable self-heating and requires a significant additional energy supply. Pure oxygen or enriched oxygen gasification requires air separation units, resulting in relatively high utilization costs.

[0005] Chemical looping gasification (CLP) technology is gaining increasing attention as a novel gasification technology. This technology uses metal oxides as oxygen carriers. In a fuel reactor, the lattice oxygen in the oxygen carrier reacts with biomass to convert it into syngas and other products. The reacted oxygen carrier is then sent to an air reactor where it undergoes an oxidation reaction with air, restoring it to its initial oxidized state. It is then returned to the fuel reactor to react with biomass, completing a chemical loop cycle. Compared to traditional gasification technologies, CLP offers several advantages: using metal oxides as oxygen carriers avoids direct contact between biomass and air, thus preventing the introduction of nitrogen into the syngas and simplifying subsequent syngas separation and purification processes; the oxygen carrier is typically a metal oxide, and its reduced metal components have catalytic properties, which can reduce coke and tar formation to some extent, improving gasification efficiency; furthermore, in addition to supplying oxygen, the oxygen carrier can carry heat from the air reactor to the fuel reactor, achieving system heat self-sufficiency.

[0006] The development of oxygen carriers is central to chemical looping gasification (CLP) technology. A suitable oxygen carrier can effectively convert biomass into syngas while reducing the generation of complete oxidation products such as CO2 and H2O, exhibiting high CO selectivity (CO / (CO+CO2)). On the other hand, it should fully utilize its role in inhibiting tar formation and catalytic cracking, reducing the yield of tar from biomass gasification, thereby improving biomass gasification efficiency and mitigating risks to equipment stability, safety, and environmental hazards caused by tar.

[0007] Fe2O3 is a widely studied and used oxygen carrier, but its low activity leads to low biomass conversion rates. Furthermore, its strong CO oxidation capacity results in high CO2 content in the products, leading to low CO selectivity and affecting syngas quality. Increasing the amount of Fe2O3 can improve biomass conversion rates to some extent, but it also significantly increases CO2 content, creating a "seesaw" effect between carbon conversion rate and CO selectivity.

[0008] In recent years, researchers have developed numerous composite oxygen carriers to improve biomass conversion efficiency and CO selectivity. For example, Patent Document 1 discloses an oxygen carrier composed of NiO and Ca2Fe2O5 for chemical looping gasification of cellulosic solid waste. Without the addition of water vapor, its carbon conversion efficiency reached 98.86%, but its CO selectivity was only about 70.7%. While the addition of water vapor increased hydrogen production, the carbon conversion efficiency, especially CO selectivity, gradually decreased, and the addition of water vapor resulted in additional energy consumption.

[0009] Patent 2 discloses a composite oxygen carrier of Fe2O3, NiO, and LaNiO3. The raw materials are prepared by sol-gel-impregnation method, which is a complex process. The entire biomass conversion process requires biomass pyrolysis, fuel reactor, steam oxidation reactor, and air reactor. The process is complicated and not easy to promote.

[0010] References:

[0011] Patent Document 1: CN115069256A;

[0012] Patent document 2: CN107537503A. Summary of the Invention

[0013] The problem the invention aims to solve

[0014] The oxygen carriers used in existing biomass gasification technologies still cannot simultaneously achieve both carbon conversion rate and CO selectivity. Furthermore, they suffer from problems such as excessive oxidation of biomass gasification products, complex and difficult-to-scale preparation processes of oxygen carriers, the need for gasifying agents, the requirement for additional energy input, and the high complexity of the gasification process.

[0015] Therefore, there is an urgent need to develop an oxygen carrier suitable for biomass gasification. Biomass gasification processes using this oxygen carrier have the characteristics of high carbon conversion rate, high syngas yield, high CO selectivity, low tar yield, no need to add gasifying agent, and simple process.

[0016] Solution for solving the problem

[0017] To address the aforementioned problems, the inventors conducted long-term and in-depth research and discovered that a composite oxide containing iron and strontium, with a specific Sr / Fe molar ratio, exhibits high carbon conversion rate, high syngas yield, high CO selectivity, and low tar yield during biomass gasification. Furthermore, the biomass gasification method using this oxygen carrier is simple and does not require the addition of gasifying agents, thus completing this invention.

[0018] Specifically, the present invention solves the problems of the present invention through the following solutions.

[0019] [1] An oxygen carrier comprising a composite oxide of iron and strontium, wherein the molar ratio of strontium to iron in the oxygen carrier is (1.1 to 5): 1, preferably (1.5 to 3.5): 1.

[0020] [2] According to the oxygen carrier described in [1], wherein the composite oxide comprises Sr3Fe2O x The crystal phases are SrO and SrO, where x is 5 to 7.

[0021] [3] The oxygen carrier according to [1] or [2] further comprises an inert carrier, which is an inert substance in the gasification reaction of biomass, and the inert carrier is preferably selected from one or more of Al2O3, SiO2, SiC, TiO2, CeO2 and ZrO2.

[0022] [4] The oxygen carrier according to [1] or [2] has a particle size of 50 to 800 μm, preferably 80 to 600 μm.

[0023] [5] The method for preparing the oxygen carrier according to any one of [1] to [4] includes the following steps:

[0024] (1) Calcination process: Calcination of the raw material mixture;

[0025] (2) Post-processing steps: optionally perform one or more operations selected from granulation, crushing, and screening on the calcined material in step (1);

[0026] The raw material mixture is a mixture containing iron, strontium and oxygen. Preferably, the raw material mixture contains iron raw material and strontium raw material. The iron raw material contains iron oxide and / or iron carbonate, and the strontium raw material contains strontium oxide and / or strontium carbonate.

[0027] Preferably, the calcination temperature is 700–1300℃ and the calcination time is 3–8 hours.

[0028] [6] According to the preparation method described in [5], it further includes:

[0029] Raw material preparation process: Mix iron raw materials and strontium raw materials to obtain a raw material mixture;

[0030] The mixing is preferably carried out by mechanical stirring and / or ball milling.

[0031] [7] Use of the oxygen carrier according to any one of [1] to [4] in the preparation of syngas from biomass.

[0032] [8] A method for preparing syngas, comprising the following steps:

[0033] (a) Contacting biomass with an oxygen carrier according to any one of [1] to [4] to cause biomass to undergo a gasification reaction;

[0034] (b) The oxygen carrier that has undergone step (a) is oxidized in air to regenerate the oxygen carrier.

[0035] [9] According to the method described in [8], the oxygen-to-carbon ratio of the oxygen carrier and the biomass as a whole is 1 to 3; preferably, no gasifying agent is used during the gasification reaction.

[0036]

[0010] According to the method of [8] or [9], wherein,

[0037] In step (a), the temperature of the gasification reaction is 700–1000°C; the pressure of the gasification reaction is -0.1–30 bar; the gasification reaction is carried out in a fuel reactor, which is preferably selected from one or more combinations of rotary kilns, fluidized beds, and moving beds.

[0038] The oxidation reaction in step (b) is carried out at a temperature of 700–1000 °C and a pressure of -0.1–30 bar. The oxidation reaction is carried out in an air reactor, which is preferably selected from one or more combinations of rotary kilns, fluidized beds, and moving beds.

[0039] The effects of the invention

[0040] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0041] (1) The oxygen carrier of the present invention has the advantages of high carbon conversion rate, high syngas yield, high CO selectivity and low tar yield in the biomass gasification process.

[0042] (2) The oxygen carrier of the present invention can be prepared by high-temperature solid-phase method, which is simple and easy to scale up.

[0043] (3) When using the oxygen carrier of the present invention for biomass gasification, it is permissible not to add a gasifying agent during the gasification process, making the gasification process simpler. Attached Figure Description

[0044] Figure 1 shows the cyclic stability test results of the oxygen carrier in Example 2;

[0045] Figure 2 shows the X-ray diffraction (XRD) spectra of the oxygen carriers of Example 2 and Comparative Example 1 before and after use in biomass gasification. Detailed Implementation

[0046] To facilitate understanding and implementation of the present invention by those skilled in the art, the present invention will be further described in detail below with reference to embodiments. It should be understood that the embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0047] <Terminology and Definitions>

[0048] In this specification, "biomass gasification" refers to the process by which biomass is converted into syngas through thermal conversion, and "gasification reaction" refers to the reaction in which biomass is thermally converted into syngas.

[0049] In this manual, "biomass" has the general meaning, including but not limited to forestry waste, crop straw, large-scale livestock and poultry manure, and domestic waste.

[0050] In this specification, the range of values ​​referred to as "value A to value B" refers to the range including the endpoint values ​​A and B.

[0051] In this specification, the numerical range indicated by "above" or "below" refers to the numerical range that includes the stated number.

[0052] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0053] In this specification, the terms "optionally" or "optionally" are used to indicate the use or non-use of certain substances, components, procedures, application conditions, etc.

[0054] In this specification, references to "preferred embodiments," "implementation methods," etc., mean that a specific element (e.g., feature, structure, property, and / or characteristic) related to that embodiment is included in at least one of the embodiments described herein, and may or may not be present in other embodiments. Furthermore, it should be understood that the elements may be combined in any suitable manner in various embodiments.

[0055] <Oxygen carrier>

[0056] One object of the present invention is to provide an oxygen carrier comprising a composite oxide of iron and strontium, wherein the molar ratio (Sr / Fe) of strontium to iron in the oxygen carrier is (1.1 to 5):1.

[0057] In a preferred embodiment, the Sr / Fe molar ratio in the oxygen carrier of the present invention is (1.2–4.9):1, preferably (1.3–4.8):1, more preferably (1.4–4.7):1, and also, for example, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, 3:1, 3.1:1, 3.2:1, 3.3:1, 3.4:1, 3.5:1, 3.6:1, 3.7:1, 3.8:1, 3.9:1, 4:1, 4.1:1, 4.2:1, 4.3:1, 4.4:1, 4.5:1, 4.6:1, etc.

[0058] In one embodiment, the composite oxide comprises Sr3Fe2O xThe crystal phases are SrO crystal phases, where x is 5 to 7, for example 5.5, 6, 6.5, etc. These crystal phases can be determined, for example, by XRD diffraction.

[0059] In one embodiment, the molar ratio of strontium to iron in the composite oxide is (1.1–5):1, preferably (1.2–4.9):1, even more preferably (1.3–4.8):1, more preferably (1.4–4.7):1, and also, for example, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 2.1:1, 2.2:1, 2.3:1. 1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, 3:1, 3.1:1, 3.2:1, 3.3:1, 3.4:1, 3.5:1, 3.6:1, 3.7:1, 3.8:1, 3.9:1, 4:1, 4.1:1, 4.2:1, 4.3:1, 4.4:1, 4.5:1, 4.6:1, etc.

[0060] In one embodiment, the content of the composite oxide in the oxygen carrier is 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more, for example 95% by mass, 96% by mass, 97% by mass, 98% by mass, 99% by mass, or 100% by mass.

[0061] In one embodiment, the oxygen carrier of the present invention further comprises an inert support, wherein the composite oxide can be loaded onto the inert support. The inert support is a substance that is inert in the biomass gasification reaction (i.e., it does not act as a reactant or a catalyst). Specifically, the inert support can be one or more selected from Al₂O₃, SiO₂, SiC, TiO₂, CeO₂, and ZrO₂.

[0062] In one embodiment, the total content of the composite oxide and the inert carrier in the oxygen carrier is 80% by mass or more, preferably 85% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 98% by mass or more, for example 99% by mass or 100% by mass.

[0063] In one embodiment, the oxygen carrier of the present invention is in the form of particles, preferably 50-800 μm, more preferably 80-600 μm, even more preferably 100-500 μm, and even more preferably 120-400 μm, such as 200 μm, 300 μm, etc.

[0064] <Preparation method of oxygen carrier>

[0065] One object of the present invention is to provide a method for preparing the oxygen carrier of the present invention, which includes the following steps:

[0066] Calcination step: Calcination of the raw material mixture;

[0067] Post-processing steps: optionally perform one or more operations on the calcined material, selected from granulation, crushing, and screening;

[0068] The raw material mixture is a mixture containing iron, strontium and oxygen. Preferably, the raw material mixture contains iron raw material and strontium raw material. The iron raw material contains iron oxide and / or iron carbonate, and the strontium raw material contains strontium oxide and / or strontium carbonate.

[0069] In one embodiment, the preparation method of the present invention further includes:

[0070] Raw material preparation steps: Mix iron raw materials and strontium raw materials to obtain raw material mixture.

[0071] The preparation method of the present invention is a high-temperature solid-state method, which has abundant raw material sources, a simple process, and is easy to scale up.

[0072] The following describes each step of the preparation method of the present invention.

[0073] Raw material preparation steps

[0074] In the raw material preparation step, a raw material mixture is prepared. The raw material mixture is a mixture containing iron, strontium and oxygen. The molar ratio of strontium to iron should conform to the provisions of this invention for oxygen carriers and / or composite oxides. There are no particular restrictions on the amount of oxygen and other elements.

[0075] For example, iron and strontium raw materials can be mixed to obtain a raw material mixture. In cases where the oxygen carrier also contains an inert support, the inert support is mixed with the iron and strontium raw materials to obtain a raw material mixture.

[0076] The iron raw materials comprise iron oxides and / or iron carbonates. Iron oxides refer to oxides containing iron, such as FeO, Fe₂O₃, and Fe₃O₄, or composite oxides of iron and other metals. Iron carbonates can be, for example, ferrous carbonate (FeCO₃). Iron oxides, iron carbonates, and any mixtures thereof can be used directly as iron raw materials, or other raw materials containing iron oxides and / or iron carbonates, such as iron ore. Examples of iron ore include magnetite, hematite, siderite, and limonite. The iron raw materials used in this invention are abundant, environmentally friendly, and inexpensive.

[0077] Strontium raw materials include strontium oxides and / or strontium carbonates. Strontium oxides refer to oxides containing strontium, such as SrO and SrO2, or composite oxides of strontium and other metals. Strontium carbonates can be, for example, strontium carbonate (SrCO3). As strontium raw materials, strontium oxides, strontium carbonates, and any mixtures thereof can be used directly, or ores containing strontium oxides and / or strontium carbonates, such as strontium ore.

[0078] Composite oxides containing iron and strontium can also be used as iron and / or strontium raw materials, and other iron and / or strontium raw materials can be used in addition to ensure that the strontium / iron molar ratio is within the specified range.

[0079] The mixing in this step can be carried out in any suitable manner, as long as the various raw materials can be fully physically mixed. It is preferred to carry out the mixing by mechanical stirring and / or ball milling, and more preferably by ball milling the raw materials in a planetary ball mill.

[0080] Preferably, a ball mill is used for mixing, wherein the diameter of the grinding balls is 5 to 15 mm, preferably three types of grinding balls with diameters of 5, 10 and 15 mm are used, and the mass ratio of the three types of grinding balls is preferably (4.5 to 5.5): (2.5 to 3.5): (1.5 to 2.5), more preferably 5:3:2.

[0081] Preferably, the ratio of the total mass of the ball-milled material (i.e., the total mass of all raw materials) to the total mass of the grinding balls is 1:(5-10);

[0082] Preferably, ethanol, for example 15-25 ml, is added to the ball milling jar during ball milling.

[0083] Preferably, the ball milling is performed at a speed of 550 rpm, alternating rotation mode, 60 minutes of forward rotation, 60 minutes of reverse rotation, for a total of 130 minutes.

[0084] Preferably, after ball milling, the ball mill jar is placed open in an oven and dried at 90–120°C (e.g., 105°C) for 1–3 hours (e.g., 2 hours). After drying, the material can be removed and scraped off to obtain a raw material mixture.

[0085] Calcination steps

[0086] In the calcination step, the raw material mixture is calcined.

[0087] Preferably, the calcination temperature is 700–1300℃, more preferably 800–1200℃.

[0088] Preferably, the calcination time is 3 to 15 hours, more preferably 4 to 12 hours.

[0089] Preferably, the calcination is carried out in two stages. The calcination temperature of the first stage is 700-1000℃ (preferably 800-950℃, for example 900℃), and the calcination time is 1-5h (preferably 2-4h, for example 3h). The calcination temperature of the second stage is 1000℃ (excluding)-1300℃ (preferably 1050-1200℃, for example 1100℃), and the calcination time is 2-10h (preferably 3-8h, for example 5h).

[0090] More preferably, the calcination is carried out by heating from room temperature to the first stage calcination temperature at a rate of 2 to 10 °C / min (e.g., 5 °C / min), and then heating again to the second stage calcination temperature at a rate of 2 to 10 °C / min (e.g., 5 °C / min).

[0091] Preferably, the raw material mixture is compressed into tablets before calcination, and then calcined. More preferably, a tablet press is used to compress the tablets at 10–20 MPa (preferably 15 MPa) for 5–10 minutes.

[0092] Post-processing steps

[0093] After calcination, the calcined material may optionally undergo one or more operations selected from granulation, crushing, and screening.

[0094] Preferably, the calcined material is crushed and sieved to obtain an oxygen carrier with a desired particle size. Crushing is preferably carried out by grinding.

[0095] Preferably, a sieve with a mesh size of 20 to 200, or more preferably 60 to 100 mesh, is used for sieving.

[0096] The present invention also relates to an oxygen carrier obtained by the preparation method of the present invention.

[0097] <Biomass Gasification>

[0098] This invention also relates to the use of the oxygen carrier of this invention in the preparation of syngas (biomass gasification) from biomass.

[0099] One object of the present invention is to provide a method for preparing syngas, comprising the following steps:

[0100] (a) Bring biomass into contact with the oxygen carrier of the present invention to cause the biomass to undergo a gasification reaction;

[0101] (b) The oxygen carrier that has undergone step (a) is oxidized in air to regenerate the oxygen carrier.

[0102] The method for preparing syngas according to the present invention adopts chemical looping gasification technology, which has a simple process flow and allows for the recycling of oxygen carriers.

[0103] The following describes each step of the method for preparing syngas according to the present invention.

[0104] Step (a)

[0105] In one embodiment, the oxygen-to-carbon ratio of the oxygen carrier and the overall biomass is 1 to 3, preferably 1.1 to 2.5, more preferably 1.2 to 2, and also, for example, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, etc. An oxygen-to-carbon ratio within the above range is more conducive to achieving high syngas yield, high carbon conversion rate, high CO selectivity, and low tar yield.

[0106] In this specification, "the oxygen-to-carbon ratio of the oxygen carrier to the whole biomass" refers to the sum of the theoretical oxygen supply in the oxygen carrier (the oxygen released when Sr-Fe composite oxide is converted into SrO and Fe elemental) and the oxygen in the biomass, and the molar ratio of carbon in the biomass.

[0107] In one embodiment, no gasifying agent is used in the gasification reaction process, wherein the gasifying agent refers to the gaseous medium required in the biomass gasification process, including but not limited to water vapor, air, carbon dioxide, oxygen or other oxygen-containing gases (preferably oxygen-enriched gases, such as gases with an oxygen content of 22 mol% or more).

[0108] Preferably, the temperature of the gasification reaction in step (a) is 700–1000°C, more preferably 800–1000°C, and even more preferably 900–1000°C.

[0109] Preferably, the pressure (gauge pressure) of the gasification reaction is -0.1 to 30 bar, which can be slightly negative pressure, normal pressure, or pressurized pressure.

[0110] Preferably, the gasification reaction is carried out in a fuel reactor, which is preferably selected from one or more combinations of rotary kilns, fluidized beds, and moving beds.

[0111] In this specification, a combination of multiple reactors refers to connecting these reactors in series or in parallel.

[0112] Step (b)

[0113] Preferably, the oxidation reaction in step (b) is carried out at a temperature of 700–1000 °C.

[0114] Preferably, the pressure (gauge pressure) of the oxidation reaction is -0.1 to 30 bar, which can be slightly negative pressure, normal pressure, or pressurized pressure.

[0115] Preferably, the oxidation reactor is carried out in an air reactor, which is preferably selected from one or more combinations of rotary kilns, fluidized beds, and moving beds.

[0116] In the method for preparing syngas of the present invention, the syngas yield is 750 mL / g or more, preferably 800 mL / g or more, more preferably 850 mL / g or more, even more preferably 900 mL / g or more, and even more preferably 950 mL / g or more, for example 1000 mL / g or more, 1100 mL / g or more, 1200 mL / g or more, or 1300 mL / g or more.

[0117] In the method for preparing syngas of the present invention, the carbon conversion rate is 70% or more, preferably 75% or more, more preferably 80% or more, even more preferably 85% or more, and even more preferably 90% or more, and even more preferably 95% or more.

[0118] In the method for preparing syngas of the present invention, the CO selectivity is 80% or more, preferably 84% or more, more preferably 90% or more, even more preferably 92% or more, and even more preferably 93% or more, for example 94% or more, 95% or more, 96% or more, 97% or more, and 98% or more.

[0119] The syngas yield, carbon conversion rate, and CO selectivity described above can be obtained through the test methods described in the examples.

[0120] In one implementation, steps (a) and (b) are repeated alternately, with the oxygen carrier regenerated in step (b) being reused in step (a).

[0121] Preferably, steps (a) and (b) are repeated alternately more than twice, preferably more than three times, such as more than five times, more than ten times, more than fifteen times, more than twenty times, more than thirty times, etc. The present invention does not have a particular limit on the upper limit of the number of times, for example, it can be 1000 times.

[0122] Preferably, in the method for preparing syngas of the present invention, steps (a) and (b) are repeated alternately more than three times, wherein when step (a) is performed for the third time, the carbon conversion rate is more than 90% and the CO selectivity is more than 98%.

[0123] In one embodiment, the method for preparing syngas according to the present invention is a continuous process, wherein steps (a) and (b) are carried out continuously, and the oxygen carrier obtained by regeneration in step (b) is continuously reused in step (a).

[0124] Specifically, during stable operation of the process, biomass and the oxygen carrier regenerated in step (b) are continuously fed into the reactor of step (a), and gaseous products and used oxygen carrier are continuously discharged from the reactor of step (a). The used oxygen carrier is continuously fed into the reactor of step (b) for regeneration, and the regenerated oxygen carrier is continuously discharged from the reactor of step (b).

[0125] Example

[0126] The following specific embodiments further illustrate the present invention. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the contents of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by this invention.

[0127] <Oxygen Carriers and Their Preparation>

[0128] Example 1

[0129] Weigh a certain mass of Fe2O3 and SrCO3 to make the molar ratio of Sr to Fe 1.5:1. Put Fe2O3 and SrCO3 into a ball mill and grind and mix them at 550 r / min for 2 hours. After the oxide is uniformly mixed, put it into a muffle furnace and calcine it at 900℃ for 3 hours, and then at 1100℃ for 5 hours. After grinding and sieving, the calcined oxide is used to obtain an oxygen carrier of 60-100 mesh.

[0130] Example 2

[0131] The oxygen carrier was obtained in the same manner as in Example 1, except that the molar ratio of Sr to Fe was 2.5:1.

[0132] Example 3

[0133] Except that the molar ratio of Sr to Fe is 5:1, the oxygen carrier is obtained in the same manner as in Example 1.

[0134] Comparative Example 1

[0135] The oxygen carrier was obtained in the same manner as in Example 1, except that only Fe2O3 was used and SrCO3 was not used.

[0136] Comparative Example 2

[0137] Except that the molar ratio of Sr to Fe is 1:1, the oxygen carrier is obtained in the same manner as in Example 1.

[0138] Comparative Example 3

[0139] Except that the molar ratio of Sr to Fe is 1:12, the oxygen carrier is obtained in the same manner as in Example 1.

[0140] Comparative Example 4

[0141] Except that CaCO3 was used instead of SrCO3 to make the molar ratio of Ca to Fe 2.5:1, the oxygen carrier was obtained in the same manner as in Example 1.

[0142] Comparative Example 5

[0143] Except that BaCO3 was used instead of SrCO3 to make the molar ratio of Ba to Fe 2.5:1, the oxygen carrier was obtained in the same manner as in Example 1.

[0144] The types and proportions of raw materials in the above embodiments are shown in Table 1.

[0145] Table 1

[0146] <Synthesis Gas Preparation and Biomass Chemical Loop Gasification Performance Evaluation>

[0147] Using poplar sawdust as biomass feedstock, syngas was prepared using oxygen carriers obtained in Examples 1-3 and Comparative Examples 1-5. At the same time, the chemical looping gasification performance of the oxygen carriers obtained in Examples 1-3 and Comparative Examples 1-5 was evaluated, with biomass carbon conversion rate, carbon monoxide selectivity, tar yield, and syngas yield used as parameters to evaluate the effectiveness of the oxygen carriers.

[0148] Chemical looping gasification experiments of poplar sawdust were conducted in a fixed-bed quartz tube reactor with an inner diameter of 12 mm and a length of 520 mm. First, 0.3 g of poplar sawdust was mixed with the oxygen carrier obtained in Examples 1-3 or Comparative Examples 1-5 and compressed into tablets to prepare samples, ensuring a molar ratio (O / C) of 1.3 between oxygen (the theoretical oxygen supply of the oxygen carrier plus oxygen in the poplar sawdust) and carbon (carbon in the poplar sawdust). The samples were then loaded into a stainless steel mesh drum. Nitrogen gas was introduced at a rate of 30 ml / min through the upper and lower inlets of the mesh drum to purge air from the reactor. The fixed bed was then heated to a specified temperature (850, 900, 950 °C, etc.) at a rate of 14 °C / min. After the fixed bed temperature stabilized, the mesh drum and the sample were dropped into the fixed bed to initiate the reaction. To ensure a complete reaction, the reaction was continued for 40 min. The products obtained from the gasification reaction were collected using a gas bag after removing tar and moisture through a tar collection system. The main gases, including H2, CO, CH4, and CO2, in the gas bag after the reaction were determined using a gas chromatograph (Agilent micro GC 990). In addition, to determine the tar yield, the bottom of the quartz reaction tube, the tar collection bottle, and the connecting tubing were cleaned with dichloromethane solution. The collected dichloromethane-tar mixture was dehydrated by adding anhydrous sodium sulfate, filtered, and then diluted to 500 ml. 200 ml of this solution was then placed in an Erlenmeyer flask and distilled for 45 min in a rotary evaporator at 25°C and -75 kPa negative pressure to remove the dichloromethane solvent. The mass of the Erlenmeyer flask before and after the dichloromethane reaction was measured to obtain the tar mass, from which the tar yield was calculated.

[0149] The parameters used in performance evaluation are defined as follows:

[0150] Oxygen-to-carbon ratio (O / C):

[0151] Among them The number of moles (mol) of oxygen in biomass. This represents the theoretically maximum number of moles (mol) of oxygen that the oxygen carrier can provide. This represents the number of moles of carbon in biomass (mol).

[0152] Yields V of various gases in syngas i (Unit: ml / g, i = H2, CH4, CO, CO2, C) 2+ gas):

[0153] Among them and These represent the concentrations of nitrogen and oxygen detected by the GC instrument, respectively. The nitrogen flow rate entering the reactor is given by t, and the reaction time is given by m. b The mass of biomass fed into the reactor.

[0154] Syngas yield V Syn (Unit: ml / g):

[0155] Carbon conversion rate η C (unit %) is defined as follows:

[0156] j i Indicate the number of C atoms i and V in the molecular formula of various gases. i V represents the yield of various gases. m The molar volume of the gas (unit: ml / mol) The mass of carbon (C) per unit mass of biomass (in g / g).

[0157] CO Selective S CO (unit%):

[0158] Tar yield R tar (unit %) is defined as follows:

[0159] where m tar To determine the mass of tar, m b The mass of biomass fed into the reactor.

[0160] Table 2 shows the test results of carbon conversion, CO selectivity, tar yield and syngas yield at different reaction temperatures in the chemical looping gasification activity evaluation experiments conducted using the oxygen carriers of Examples 1-3 and Comparative Examples 1-5.

[0161] Table 2

[0162] As shown in Table 1, at a temperature of 850℃, the CO selectivity of the oxygen carrier materials of the present invention in Examples 1 and 2 is significantly higher than that of the Fe2O3 oxygen carrier in Comparative Example 1. The carbon conversion rate is comparable to that of Comparative Example 1, while the tar yield is significantly reduced and the syngas yield is significantly increased. Under the same conditions, the carbon conversion rate and CO selectivity of Example 3 are slightly lower than those of Comparative Example 1, but the tar yield is much lower, and its syngas yield is more than twice that of Comparative Example 1. This indicates that the oxygen carrier of the present invention has significantly better biomass chemical looping gasification activity.

[0163] In the chemical looping gasification evaluation experiments conducted at different temperatures using the oxygen carriers of Example 2 and Comparative Example 1, as the reaction temperature increased, the carbon conversion rate of the oxygen carrier of the present invention in Example 2 significantly increased, while the CO selectivity remained at approximately 95%, and the carbon conversion rate increased from 71.3% to 97.1%. Above 900°C, the carbon conversion rate and CO selectivity of Example 2 were significantly higher than those of the Fe2O3 oxygen carrier in Comparative Example 1, with a tar yield of less than 0.5% and a syngas yield exceeding 1000 mL / g-biomass, while the syngas yield of Comparative Example 1 did not exceed 650 mL / g-biomass at its highest.

[0164] A comparison of Examples 1-2 and Comparative Examples 2-3 shows that the CO selectivity of Examples 1-2 is significantly higher than that of Comparative Examples 2-3, resulting in a higher final syngas yield. This indicates that a Sr / Fe molar ratio of less than or equal to 1:1 does not achieve better gasification performance.

[0165] Table 1 also shows that, under the same operating conditions, Example 2 significantly outperformed Comparative Examples 4-5 in terms of carbon conversion and CO selectivity. The syngas yield of Example 2 was 913 mL / g biomass, significantly better than the 620.3 mL / g biomass of Comparative Example 4 and 816.1 mL / g biomass of Comparative Example 5. This indicates that, under the same molar ratio of alkaline earth metal to Fe (2.5:1 in both Example 2 and Comparative Examples 4-5), using the alkaline earth metal Sr is more effective than using Ca and Ba.

[0166] Cyclic stability experiments were conducted using the oxygen carrier obtained in Example 2. The experimental procedure for cyclic stability was as follows: following the description in the evaluation of chemical looping gasification performance, a gasification experiment was conducted at 900°C with an oxygen-to-carbon ratio (O / C) of 1.3. After the experiment, nitrogen gas was continuously introduced for 10 minutes, and after the gas was purged, air was introduced at 900°C for 30 minutes to oxidize the oxygen carrier. Subsequently, the temperature was lowered to room temperature under nitrogen conditions, the oxygen carrier was removed and mixed with 0.3 g of fresh biomass sample, and the above procedure was repeated. The syngas yield, carbon conversion rate, and CO selectivity data of the cyclic experiment are shown in Figure 1. As can be seen from Figure 1, in the 10 chemical looping tests, the syngas (H2+CO) yield of biomass remained above 1100 mL / g, the carbon conversion rate remained above 90%, and the CO selectivity increased to above 98% after 2 cycles. This indicates that the oxygen carrier of the present invention has excellent chemical looping cycle stability.

[0167] X-ray diffraction (XRD)

[0168] The crystalline phase of the oxygen carrier was analyzed using an X-ray diffractometer (Smart Lab). The specific test conditions were: Cu Kα radiation (λ = 0.15046 nm), target current 40 mA, target voltage 40 kV, diffraction angle (2θ) scan range 10–80°, and step size 0.0167° / s. The crystalline phase of the oxygen carrier was determined by comparison with JCPDS (Joint Committee on Powder Diffraction Standards) documents.

[0169] X-ray diffraction (XRD) tests were performed on the oxygen carriers obtained in Example 2 and Comparative Example 1. The spectra and analysis results are shown in Figure 2. As can be seen from Figure 2, the oxygen carrier of Comparative Example 1 (Fe2O3) mainly consists of elemental Fe crystal phase after the reaction, and also contains small amounts of FeO and F3O4 crystal phase. Due to the addition of strontium, the fresh sample of Example 2 contains Sr3Fe2O3. 6.74 The SrO crystal phase transforms into Sr3Fe2O6 and SrO after reacting with biomass, along with a small amount of Fe. This indicates that the addition of strontium forms a composite ferrite. Because the presence of strontium controls the release of lattice oxygen in the iron oxide, deep oxidation of the gasification products does not occur, resulting in high CO selectivity for the gasification products.

[0170] Industrial availability

[0171] The oxygen carrier and its preparation method of the present invention can be widely used in thermal conversion processes such as biomass pyrolysis and gasification.

Claims

1. An oxygen carrier, characterized in that, A composite oxide containing iron and strontium, wherein the molar ratio of strontium to iron in the oxygen carrier is (1.1-5):1, preferably (1.5-3.5):

1.

2. The oxygen carrier according to claim 1, characterized in that, The composite oxide contains Sr3Fe2O x The crystal phases are SrO and SrO, where x is 5 to 7.

3. The oxygen carrier according to claim 1 or 2, characterized in that, It also includes an inert carrier, which is a substance that is inert in the gasification reaction of biomass, and the inert carrier is preferably selected from one or more of Al2O3, SiO2, SiC, TiO2, CeO2, and ZrO2.

4. The oxygen carrier according to claim 1 or 2, characterized in that, The particle size is 50–800 μm, preferably 80–600 μm.

5. The method for preparing the oxygen carrier according to any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Calcination process: Calcination of the raw material mixture; (2) Post-processing steps: optionally perform one or more operations selected from granulation, crushing, and screening on the calcined material in step (1); The raw material mixture is a mixture containing iron, strontium and oxygen. Preferably, the raw material mixture contains iron raw material and strontium raw material. The iron raw material contains iron oxide and / or iron carbonate, and the strontium raw material contains strontium oxide and / or strontium carbonate. Preferably, the calcination temperature is 700–1300℃ and the calcination time is 3–8 hours.

6. The preparation method according to claim 5, characterized in that, Also includes: Raw material preparation process: Mix iron raw materials and strontium raw materials to obtain a raw material mixture; The mixing is preferably carried out by mechanical stirring and / or ball milling.

7. Use of the oxygen carrier according to any one of claims 1 to 4 in the preparation of syngas from biomass.

8. A method for preparing syngas, characterized in that, Includes the following steps: (a) Contacting biomass with an oxygen carrier according to any one of claims 1 to 4 to cause the biomass to undergo a gasification reaction; (b) The oxygen carrier that has undergone step (a) is oxidized in air to regenerate the oxygen carrier.

9. The method according to claim 8, characterized in that, The oxygen-to-carbon ratio of the oxygen carrier and the biomass as a whole is 1 to 3; preferably, no gasifying agent is used during the gasification reaction.

10. The method according to claim 8 or 9, characterized in that, In step (a), the temperature of the gasification reaction is 700–1000°C; the pressure of the gasification reaction is -0.1–30 bar; the gasification reaction is carried out in a fuel reactor, which is preferably selected from one or more combinations of rotary kilns, fluidized beds, and moving beds. The oxidation reaction in step (b) is carried out at a temperature of 700–1000 °C and a pressure of -0.1–30 bar. The oxidation reaction is carried out in an air reactor, which is preferably selected from one or more combinations of rotary kilns, fluidized beds, and moving beds.

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