Oxygen carrier as well as preparation method and application thereof

Abstract

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

Description

Technical Field

[0001] The invention belongs to the field of biomass thermal conversion, and in particular relates to an oxygen carrier, a preparation method and application thereof. Background Art

[0002] As a high-quality renewable energy, biomass has received extensive attention and research due to its "zero emission" raw material characteristics in its life cycle. my country has relatively rich biomass resources, including forestry waste, crop straw, large-scale livestock and poultry manure, domestic garbage and other types of biomass resources that can be used as resources, equivalent to about 500 million tons of standard coal per year. If all are used, it can reach about 10% of my country's total primary energy. In the context of my country's energy transformation, biomass utilization has great potential to be tapped.

[0003] Compared with biomass combustion, thermal conversion processes such as biomass pyrolysis and gasification can obtain synthesis gas products (H2+CO), which can be used as clean fuel or chemical raw materials to achieve more diversified applications of biomass. For biomass gasification, it can be divided into air gasification, water vapor gasification, pure oxygen / oxygen-enriched gasification, etc. according to different gasification agents. Among them, air gasification is relatively simple and economical, but due to the presence of a large amount of nitrogen in the air, the proportion of synthesis gas in the gasification product is low and the calorific value is low, which brings certain difficulties to downstream applications; although the synthesis gas obtained in the water vapor gasification process has a high calorific value and high hydrogen content, the process cannot maintain self-heating stable operation and requires a large amount of additional energy supply; pure oxygen or oxygen-enriched gasification requires an air separation unit, resulting in a relatively high utilization cost.

[0004] Chemical chain gasification technology is a new type of gasification technology that has attracted increasing attention. This technology uses metal oxides as oxygen carriers. In the fuel reactor, the lattice oxygen of the oxygen carrier reacts with biomass to convert it into products such as synthesis gas. The oxygen carrier after the reaction is sent to the air reactor to undergo oxidation reaction with air, thereby restoring to the initial oxidation state, and then sent back to the fuel reactor to react with biomass to complete a chemical chain cycle. Compared with traditional gasification technology, the advantages of chemical chain gasification are mainly as follows: using metal oxides as oxygen carriers avoids direct contact between biomass and air, thereby avoiding the introduction of nitrogen into the synthesis gas, simplifying the subsequent separation and purification process of the synthesis gas; the oxygen carrier is generally a metal oxide, and the reduced metal element has a catalytic effect, which can reduce the generation of carbon deposits and tar to a certain extent and improve the gasification efficiency; in addition, in addition to supplying oxygen, the oxygen carrier can also carry heat from the air reactor to the fuel reactor to achieve thermal self-sustaining of the system.

[0005] The development of oxygen carriers is the core of chemical chain gasification technology. Suitable oxygen carriers can effectively convert biomass into syngas and reduce the generation of complete oxidation products such as CO2 and H2O, that is, they have high CO selectivity (CO / (CO+CO2)). On the other hand, they should give full play to the role of inhibiting tar formation and catalytic cracking, reduce the yield of tar from biomass gasification, thereby improving biomass gasification efficiency and reducing the risks of stable and safe operation of equipment and environmental hazards caused by tar.

[0006] Fe2O3 is an oxygen carrier that has been widely studied and used, but its low activity leads to low biomass conversion rate. At the same time, due to its strong oxidation ability for CO, the CO2 content in the product is high, resulting in low product CO selectivity, which affects the quality of syngas. Increasing the amount of Fe2O3 can improve the biomass conversion rate to a certain extent, but at the same time it will cause a significant increase in the CO2 content, and there is a "seesaw" effect between carbon conversion rate and CO selectivity.

[0007] In recent years, researchers have developed a number of composite oxygen carriers to improve biomass conversion and CO selectivity. For example, Patent Document 1 discloses an oxygen carrier composed of NiO and Ca2Fe2O5, which is used for chemical chain gasification of cellulose solid waste. Without adding water vapor, its carbon conversion rate reaches 98.86%, but the CO selectivity is only about 70.7%. Although the hydrogen yield is increased after adding water vapor, the carbon conversion rate, especially the CO selectivity, gradually decreases, and the addition of water vapor will cause additional energy consumption.

[0008] Patent 2 discloses a composite oxygen carrier of Fe2O3, NiO, and LaNiO3, the raw materials of which are prepared by a sol-gel-impregnation method. The preparation process is complicated, and the entire biomass conversion process requires biomass pyrolysis, a fuel reactor, a steam oxidation reactor, and an air reactor. The process is complicated and difficult to promote.

[0009] References:

[0010] Patent document 1: CN115069256A;

[0011] Patent document 2: CN107537503A. Summary of the invention

[0012] Problem that the invention aims to solve

[0013] The oxygen carriers used in biomass gasification in the prior art still cannot take into account the dual indicators of carbon conversion rate and CO selectivity, and there are problems such as over-oxidation of biomass gasification products, complex oxygen carrier preparation process that is difficult to scale up, the need to use gasification agents, the need for additional energy input, and high complexity of the gasification process.

[0014] Therefore, there is an urgent need to develop oxygen carriers suitable for biomass gasification. The biomass gasification process using this oxygen carrier has the characteristics of high carbon conversion rate, high synthesis gas yield, high CO selectivity, low tar yield, no need to add gasification agent and simple process.

[0015] Solutions for solving problems

[0016] In response to the above problems, the inventors conducted long-term and in-depth research and found that an oxygen carrier comprising a composite oxide of iron and strontium and having a specific Sr / Fe molar ratio exhibits high carbon conversion rate, high synthesis gas yield, high CO selectivity, and low tar yield during biomass gasification. In addition, the biomass gasification method using the oxygen carrier has a simple process and does not require the addition of a gasifying agent, thereby completing the present invention.

[0017] Specifically, the present invention solves the problem of the present invention through the following solutions.

[0018] [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 (1.1-5):1, preferably (1.5-3.5):1.

[0019] [2] The oxygen carrier according to [1], wherein the composite oxide comprises Sr3Fe2O x Crystal phase and SrO crystal phase, where x is 5-7.

[0020] [3] The oxygen carrier according to [1] or [2] further comprises an inert carrier, wherein the inert carrier is a substance that is inert in the gasification reaction of biomass, and the inert carrier is preferably one or more selected from Al2O3, SiO2, SiC, TiO2, CeO2, and ZrO2.

[0021] [4] The oxygen carrier according to [1] or [2], wherein the particle size is 50 to 800 μm, preferably 80 to 600 μm.

[0022] [5] The method for preparing an oxygen carrier according to any one of [1] to [4], comprising the following steps:

[0023] (1) Calcination process: calcining the raw material mixture;

[0024] (2) post-treatment process: optionally performing one or more operations selected from granulation, crushing, and screening on the material calcined in step (1);

[0025] The raw material mixture is a mixture containing iron, strontium and oxygen, preferably the raw material mixture contains an iron raw material and a 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;

[0026] Preferably, the calcination temperature is 700-1300° C., and the calcination time is 3-8 hours.

[0027] [6] The preparation method according to [5], further comprising:

[0028] Raw material preparation process: mixing the iron raw material and the strontium raw material to obtain a raw material mixture;

[0029] The mixing is preferably performed by mechanical stirring and / or ball milling.

[0030] [7] Use of the oxygen carrier according to any one of [1] to [4] in producing synthesis gas using biomass as raw material.

[0031] [8] A method for preparing synthesis gas, comprising the following steps:

[0032] (a) contacting biomass with the oxygen carrier according to any one of [1] to [4] to cause the biomass to undergo a gasification reaction;

[0033] (b) subjecting the oxygen carrier obtained in step (a) to an oxidation reaction in air to regenerate the oxygen carrier.

[0034] [9] The method according to [8], wherein 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.

[0035]

[10] The method according to [8] or [9], wherein:

[0036] The temperature of the gasification reaction in step (a) 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, and the fuel reactor is preferably a combination of one or more selected from a rotary kiln, a fluidized bed, and a moving bed;

[0037] The temperature of the oxidation reaction in step (b) is 700-1000° C.; the pressure of the oxidation reaction is -0.1-30 bar; the oxidation reaction is carried out in an air reactor, and the air reactor is preferably a combination of one or more selected from a rotary kiln, a fluidized bed, and a moving bed.

[0038] Effects of the Invention

[0039] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0040] (1) The oxygen carrier of the present invention has the advantages of high carbon conversion rate, high synthesis gas yield, high CO selectivity and low tar yield in the biomass gasification process;

[0041] (2) The oxygen carrier of the present invention can be prepared by a high-temperature solid phase method, which is simple and easy to scale up;

[0042] (3) When the oxygen carrier of the present invention is used for biomass gasification, it is allowed not to add a gasifying agent during the gasification process, and the gasification process is more convenient. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 is the cyclic stability test result of the oxygen carrier of Example 2;

[0044] Figure 2 1 is an X-ray diffraction (XRD) spectrum of the oxygen carriers of Example 2 and Comparative Example 1 before and after being used for biomass gasification. DETAILED DESCRIPTION

[0045] In order to facilitate those skilled in the art to understand and implement the present invention, the present invention is further described in detail below in conjunction with embodiments. It should be understood that the implementation examples described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0046] <Terms and Definitions>

[0047] In this specification, "biomass gasification" refers to the process of converting biomass into synthesis gas through thermal conversion, and "gasification reaction" of biomass refers to the reaction of thermal conversion of biomass into synthesis gas.

[0048] In this specification, "biomass" has a common meaning, including but not limited to forestry waste, crop straw, large-scale livestock and poultry manure, domestic garbage, etc.

[0049] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints A and B.

[0050] In the present specification, a numerical range expressed using "above" or "below" means a numerical range including the number.

[0051] In this specification, the word "may" means both performing a certain process and not performing a certain process.

[0052] In this specification, the use of "optionally" or "optional" indicates that certain substances, components, execution steps, application conditions and other factors are used or not used.

[0053] In this specification, the references to "preferred embodiments", "embodiments", etc., mean that the specific elements (e.g., features, structures, properties and / or characteristics) described in connection with the embodiments are included in at least one embodiment described herein, and may or may not exist in other embodiments. In addition, it should be understood that the elements may be combined in various embodiments in any suitable manner.

[0054] <Oxygen carrier>

[0055] An object of the present invention is to provide an oxygen carrier comprising a composite oxide of iron and strontium, wherein the molar ratio of strontium to iron in the oxygen carrier (Sr / Fe) is (1.1-5):1.

[0056] In a preferred embodiment, in the oxygen carrier of the present invention, the Sr / Fe molar ratio is (1.2-4.9):1, preferably (1.3-4.8):1, more preferably (1.4-4.7):1, and 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.

[0057] In one embodiment, the composite oxide comprises Sr3Fe2O x Crystal phase and SrO crystal phase, wherein x is 5 to 7, such as 5.5, 6, 6.5, etc. The above crystal phase can be determined, for example, by XRD diffraction.

[0058] 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, further preferably (1.3-4.8):1, more preferably (1.4-4.7):1, and 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.

[0059] In one embodiment, the content of the composite oxide in the oxygen carrier is 50 mass % or more, preferably 60 mass % or more, more preferably 70 mass % or more, further preferably 80 mass % or more, and even preferably 90 mass % or more, for example 95 mass %, 96 mass %, 97 mass %, 98 mass %, 99 mass %, 100 mass %.

[0060] In one embodiment, the oxygen carrier of the present invention further comprises an inert carrier, wherein the composite oxide can be loaded on the inert carrier. The inert carrier is a substance that is inert (i.e., not acting as a reactant or a catalyst) in the gasification reaction of biomass. Specifically, the inert carrier can be one or more selected from Al2O3, SiO2, SiC, TiO2, CeO2, and ZrO2.

[0061] In one embodiment, the total content of the composite oxide and the inert carrier in the oxygen carrier is 80 mass % or more, preferably 85 mass % or more, more preferably 90 mass % or more, further preferably 95 mass % or more, even preferably 98 mass % or more, for example 99 mass %, 100 mass %.

[0062] In one embodiment, the oxygen carrier of the present invention is in granular form, and the particle size is preferably 50-800 μm, more preferably 80-600 μm, further preferably 100-500 μm, even preferably 120-400 μm, such as 200 μm, 300 μm, etc.

[0063] <Method for preparing oxygen carrier>

[0064] An object of the present invention is to provide a method for preparing the oxygen carrier of the present invention, which comprises the following steps:

[0065] Calcination step: calcining the raw material mixture;

[0066] Post-processing step: optionally performing one or more operations selected from granulation, crushing, and screening on the calcined material;

[0067] The raw material mixture is a mixture containing iron, strontium and oxygen. Preferably, the raw material mixture contains an iron raw material and a 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.

[0068] In one embodiment, the preparation method of the present invention further comprises:

[0069] Raw material preparation step: Mix the iron raw material and the strontium raw material to obtain a raw material mixture.

[0070] The preparation method of the present invention is a high-temperature solid phase method, which has abundant raw material sources, simple process and easy scale-up.

[0071] The various steps of the preparation method of the present invention are described below.

[0072] Raw material preparation steps

[0073] In the raw material preparation step, a raw material mixture is prepared, which is a mixture of iron, strontium and oxygen, wherein the molar ratio of strontium to iron conforms to the provisions of the present invention for oxygen carriers and / or composite oxides, and there is no particular limitation on the amounts of oxygen and other elements.

[0074] For example, an iron raw material and a strontium raw material may be mixed to obtain a raw material mixture. In the case where the oxygen carrier further comprises an inert carrier, the inert carrier is mixed with the iron raw material and the strontium raw material to obtain a raw material mixture.

[0075] Iron raw material comprises iron oxide and / or iron carbonate, wherein iron oxide refers to the oxide containing iron element, such as FeO, Fe2O3 and Fe3O4, and can also be the composite oxide of iron element and other metals, and iron carbonate can be ferrous carbonate (FeCO3) etc. as iron raw material. As iron raw material, iron oxide, iron carbonate and their arbitrary mixture can be directly used, and other raw materials including iron oxide and / or iron carbonate, such as iron ore etc. can also be used. As iron ore, magnetite, hematite, siderite and limonite etc. can be listed. The iron raw material used in the present invention is abundant in source, environmentally friendly and cheap.

[0076] The strontium raw material includes strontium oxide and / or strontium carbonate, wherein strontium oxide refers to an oxide containing strontium element, such as SrO, SrO2, etc., and may also be a composite oxide of strontium element and other metals, and strontium carbonate may be, for example, strontium carbonate (SrCO3), etc. As the strontium raw material, strontium oxide, strontium carbonate and any mixture thereof may be directly used, and an ore containing strontium oxide and / or strontium carbonate, such as strontianite, etc. may also be used.

[0077] A composite oxide containing iron and strontium may also be used as the iron raw material and / or the strontium raw material, and other iron raw materials and / or strontium raw materials may be additionally used so that the strontium / iron molar ratio is within a specified range.

[0078] The mixing in this step can be performed by any suitable means as long as the various raw materials can be fully physically mixed, preferably by mechanical stirring and / or ball milling, more preferably by ball milling the raw materials in a planetary ball mill.

[0079] 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 preferably the mass ratio of the three types of grinding balls is (4.5 to 5.5):(2.5 to 3.5):(1.5 to 2.5), more preferably 5:3:2.

[0080] Preferably, the ratio of the total mass of the ball mill material (i.e., the total mass of each raw material) to the total mass of the grinding balls is 1:(5-10);

[0081] Preferably, ethanol, for example 15 to 25 ml of ethanol, is added to the ball mill during ball milling.

[0082] Preferably, the ball milling is performed at a rotation speed of 550 rpm, in an alternating rotation mode, in a forward direction for 60 minutes, in a reverse direction for 60 minutes, for a total of 130 minutes.

[0083] Preferably, after ball milling, the ball mill jar is opened and placed in an oven, and dried at 90-120° C. (eg, 105° C.) for 1-3 h (eg, 2 h). After drying, the material can be taken out and scraped off to obtain a raw material mixture.

[0084] Calcination step

[0085] In the calcining step, the raw material mixture is calcined.

[0086] Preferably, the calcination temperature is 700 to 1300°C, preferably 800 to 1200°C.

[0087] Preferably, the calcination time is 3 to 15 hours, preferably 4 to 12 hours.

[0088] Preferably, calcination is carried out in two stages, the calcination temperature of the first stage is 700-1000°C (preferably 800-950°C, for example 900°C), and the calcination time is 1-5h (preferably 2-4h, for example 3h), and the calcination temperature of the second stage is 1000 (not included)-1300°C (preferably 1050-1200°C, for example 1100°C), and the calcination time is 2-10h (preferably 3-8h, for example 5h).

[0089] More preferably, the temperature is increased from room temperature to the calcination temperature of the first stage at a rate of 2 to 10°C / min (e.g. 5°C / min) for calcination, and then the temperature is increased again to the calcination temperature of the second stage at a rate of 2 to 10°C / min (e.g. 5°C / min) for calcination.

[0090] Preferably, the raw material mixture is tableted before calcination and then calcined. More preferably, a tablet press is used at 10 to 20 MPa (preferably 15 MPa) for 5 to 10 minutes.

[0091] Post-processing steps

[0092] After calcination, the calcined material is optionally subjected to one or more operations selected from granulation, crushing, and screening.

[0093] Preferably, the calcined material is crushed and sieved to obtain an oxygen carrier with a desired particle size, wherein the crushing is preferably performed by grinding.

[0094] Preferably, a sieve of 20 to 200 mesh, preferably 60 to 100 mesh, is used for sieving.

[0095] The present invention also relates to the oxygen carrier obtained by the preparation method of the present invention.

[0096] <Biomass Gasification>

[0097] The present invention also relates to the use of the oxygen carrier of the present invention in preparing synthesis gas (biomass gasification) using biomass as raw material.

[0098] An object of the present invention is to provide a method for preparing synthesis gas, comprising the following steps:

[0099] (a) contacting biomass with the oxygen carrier of the present invention to cause a gasification reaction of the biomass;

[0100] (b) subjecting the oxygen carrier obtained in step (a) to an oxidation reaction in air to regenerate the oxygen carrier.

[0101] The method for preparing synthesis gas of the present invention adopts chemical chain gasification technology, has a simple process flow, and the oxygen carrier can be recycled.

[0102] The various steps of the method for preparing synthesis gas according to the present invention are described below respectively.

[0103] Step (a)

[0104] In one embodiment, the oxygen-carbon ratio of the oxygen carrier and the biomass as a whole is 1 to 3, preferably 1.1 to 2.5, more preferably 1.2 to 2, and for example 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, etc. When the oxygen-carbon ratio is within the above range, it is more conducive to achieving high syngas yield, high carbon conversion rate, high CO selectivity, and low tar yield.

[0105] In this specification, the "oxygen-carbon ratio of the oxygen carrier and the biomass as a whole" refers to the molar ratio of the sum of the theoretical oxygen supply in the oxygen carrier (the oxygen that can be released when the Sr-Fe composite oxide is converted into SrO and Fe elemental substances) plus the oxygen in the biomass to the carbon in the biomass.

[0106] 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, which includes but is not limited to water vapor, air, carbon dioxide, oxygen or other oxygen-containing gases (preferably oxygen-rich gases, such as gases with an oxygen content of 22 mol % or more), etc.

[0107] Preferably, the temperature of the gasification reaction in step (a) is 700-1000°C, preferably 800-1000°C, more preferably 900-1000°C.

[0108] Preferably, the pressure (gauge pressure) of the gasification reaction is -0.1 to 30 bar, which may be slightly negative pressure, normal pressure or pressurized pressure.

[0109] Preferably, the gasification reaction is carried out in a fuel reactor, and the fuel reactor is preferably a combination of one or more selected from a rotary kiln, a fluidized bed, and a moving bed.

[0110] In this specification, a combination of multiple or more reactors means connecting these reactors in series or in parallel.

[0111] Step (b)

[0112] Preferably, the temperature of the oxidation reaction in step (b) is 700-1000°C.

[0113] Preferably, the pressure (gauge pressure) of the oxidation reaction is -0.1 to 30 bar, which may be slightly negative pressure, normal pressure or pressurized pressure.

[0114] Preferably, the oxidation reactor is carried out in an air reactor, and the air reactor is preferably a combination of one or more selected from a rotary kiln, a fluidized bed, and a moving bed.

[0115] In the method for preparing synthesis gas of the present invention, the synthesis gas yield is 750 mL / g or more, preferably 800 mL / g or more, more preferably 850 mL / g or more, further preferably 900 mL / g or more, even 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.

[0116] In the method for preparing synthesis gas of the present invention, the carbon conversion rate is 70% or more, preferably 75% or more, more preferably 80% or more, still more preferably 85% or more, even more preferably 90% or more, further preferably 95% or more.

[0117] In the method for preparing synthesis gas of the present invention, the CO selectivity is above 80%, preferably above 84%, more preferably above 90%, further preferably above 92%, even preferably above 93%, for example above 94%, above 95%, above 96%, above 97%, or above 98%.

[0118] The above-mentioned synthesis gas yield, carbon conversion rate and CO selectivity can be obtained by the test methods described in the examples.

[0119] In one embodiment, step (a) and step (b) are repeated alternately, and the oxygen carrier regenerated in step (b) is reused in step (a).

[0120] Preferably, step (a) and step (b) are repeated alternately more than 2 times, preferably more than 3 times, for example more than 5 times, more than 10 times, more than 15 times, more than 20 times, more than 30 times, etc. There is no particular limitation on the upper limit of the number of times in the present invention, for example, it can be 1000 times.

[0121] Preferably, in the method for preparing synthesis gas of the present invention, step (a) and step (b) are repeated alternately for more than 3 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%.

[0122] In one embodiment, the method for preparing synthesis gas of the present invention is a continuous process, both step (a) and step (b) are carried out in a continuous manner, and the oxygen carrier regenerated in step (b) is continuously reused in step (a).

[0123] Specifically, when the process is running stably, biomass and the oxygen carrier regenerated in step (b) are continuously fed into the reactor of step (a), gas 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).

[0124] Example

[0125] The present invention is further described by enumerating specific implementation cases below. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content recorded in the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the present invention equally.

[0126] <Oxygen carrier and its preparation>

[0127] Example 1

[0128] Weigh a certain mass of Fe2O3 and SrCO3 so that the molar ratio of Sr to Fe is 1.5:1, put Fe2O3 and SrCO3 into a ball mill together, grind and mix at a speed of 550r / min for 2h, take out the evenly mixed oxide, put it into a muffle furnace and calcine it at 900℃ for 3h, then calcine it at 1100℃ for 5h, grind and sieve the calcined oxide to obtain an oxygen carrier of 60-100 mesh.

[0129] Example 2

[0130] An 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.

[0131] Example 3

[0132] An oxygen carrier was obtained in the same manner as in Example 1 except that the molar ratio of Sr to Fe was 5:1.

[0133] Comparative Example 1

[0134] An oxygen carrier was obtained in the same manner as in Example 1, except that only Fe2O3 was used and SrCO3 was not used.

[0135] Comparative Example 2

[0136] An oxygen carrier was obtained in the same manner as in Example 1 except that the molar ratio of Sr to Fe was 1:1.

[0137] Comparative Example 3

[0138] An oxygen carrier was obtained in the same manner as in Example 1 except that the molar ratio of Sr to Fe was 1:12.

[0139] Comparative Example 4

[0140] The oxygen carrier was obtained in the same manner as in Example 1, except that CaCO3 was used instead of SrCO3 so that the molar ratio of Ca to Fe was 2.5:1.

[0141] Comparative Example 5

[0142] An oxygen carrier was obtained in the same manner as in Example 1, except that BaCO3 was used instead of SrCO3 so that the molar ratio of Ba to Fe was 2.5:1.

[0143] The types and proportions of the raw materials in the above embodiments are shown in Table 1.

[0144] Table 1

[0145] Fe Sr Ca Ba Example 1 1 1.5 Example 2 1 2.5 Example 3 1 5 Comparative Example 1 1 0 Comparative Example 2 1 1 Comparative Example 3 12 1 Comparative Example 4 1 2.5 Comparative Example 5 1 2.5

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

[0147] Poplar sawdust was used as the biomass raw material, and synthesis gas was prepared using the oxygen carriers obtained in Examples 1 to 3 and Comparative Examples 1 to 5. At the same time, the chemical chaining gasification performance of the oxygen carriers obtained in Examples 1 to 3 and Comparative Examples 1 to 5 was evaluated, and the biomass carbon conversion rate, carbon monoxide selectivity, tar yield, and synthesis gas yield were used as parameters for evaluating the effectiveness of the oxygen carrier.

[0148] A chemical chain gasification experiment of poplar sawdust was carried out 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 to 3 or Comparative Examples 1 to 5 and pressed into tablets to prepare a sample so that the molar ratio (O / C) of oxygen element (theoretical oxygen supply of the oxygen carrier plus oxygen in the poplar sawdust) to carbon element (carbon in the poplar sawdust) in the obtained sample was 1.3. The sample was then loaded into a stainless steel mesh barrel. Then, 30 ml / min of nitrogen was introduced into the upper and lower air inlets of the mesh barrel to remove the air in the reactor. Subsequently, the fixed bed was heated to a specified temperature (850, 900, 950°C, etc.) at a rate of 14°C / min. After the temperature of the fixed bed stabilized, the mesh barrel and the sample therein were dropped into the fixed bed for reaction. To ensure that the reaction is fully carried out, the reaction will last for 40 minutes. The product obtained by the gasification reaction is collected by an air bag after the tar and moisture are removed by a tar collection system. After the reaction, the main gases such as H2, CO, CH4, and CO2 in the air bag were measured using a gas chromatograph (Agilent micro GC 990). In addition, in order to determine the tar yield, a dichloromethane solution was used to clean the bottom of the quartz reaction tube, the tar collection bottle, and the connecting pipes. The collected dichloromethane-tar mixture was dehydrated by adding anhydrous sodium sulfate, filtered, and then fixed to 500 ml. Then 200 ml was taken and put into a conical flask. The dichloromethane solvent was removed by distillation in a rotary evaporator at 25°C and -75kPa negative pressure for 45 minutes. The mass before and after the conical flask was weighed to obtain the mass of tar, and then the tar yield was calculated.

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

[0150] Oxygen-carbon ratio O / C:

[0151]

[0152] Among them is the number of moles of oxygen in biomass (mol), is the maximum number of moles of oxygen element that the oxygen carrier can theoretically provide (mol), is the mole number of carbon in biomass (mol).

[0153] Yield of various gases in syngas V i(Unit ml / g, i = H2, CH4, CO, CO2, C 2+ gas):

[0154]

[0155] Among them and are the concentrations of nitrogen and oxygen detected by the GC instrument, is the nitrogen flow rate entering the reactor, t is the reaction time, m b is the mass of biomass put into the reactor.

[0156] Synthesis gas yield V Syn (Unit: ml / g):

[0157]

[0158] Carbon conversion rate η C (Unit %) is defined as follows:

[0159]

[0160] Among them, j i Indicates the number of C atoms in the molecular formula of each gas, i, V i is the yield of each gas, V m is the gas molar volume (unit: ml / mol), is the mass of C element contained in unit mass of biomass (unit: g / g)

[0161] CO Selectivity S CO (unit%):

[0162]

[0163] Tar yield R tar (Unit %) is defined as follows:

[0164]

[0165] Among them, m tar is the mass of tar measured, m b is the mass of biomass put into the reactor.

[0166] In the chemical looping gasification activity evaluation experiment using the oxygen carriers of Examples 1 to 3 and Comparative Examples 1 to 5, the test results of carbon conversion, CO selectivity, tar yield and synthesis gas yield at different reaction temperatures are shown in Table 2.

[0167] Table 2

[0168]

[0169] As can be seen from Table 1, at a temperature of 850°C, the CO selectivity of the oxygen carrier materials of the present invention in Examples 1 to 2 is significantly higher than that of the Fe2O3 oxygen carrier in Comparative Example 1, the carbon conversion rate is equivalent to that of Comparative Example 1, 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 than that of Comparative Example 1, and its syngas yield is more than twice that of Comparative Example 1. This shows that the oxygen carrier of the present invention has significantly better biomass chemical chain gasification activity.

[0170] In the chemical chain gasification evaluation experiment at different temperatures using the oxygen carriers of Example 2 and Comparative Example 1, as the reaction temperature increases, the carbon conversion rate of the oxygen carrier of Example 2 of the present invention increases significantly, the CO selectivity is basically maintained at about 95%, and the carbon conversion rate increases from 71.3% to 97.1%. Above 900°C, the carbon conversion rate and CO selectivity of Example 2 are significantly higher than those of the Fe2O3 oxygen carrier of Comparative Example 1, the tar yield is less than 0.5%, and the syngas yield exceeds 1000mL / g-biomass, while the syngas yield of Comparative Example 1 does not exceed 650mL / g-biomass at most.

[0171] By comparing Examples 1 to 2 and Comparative Examples 2 to 3, it can be seen that the CO selectivity of Examples 1 to 2 is significantly higher than that of Comparative Examples 2 to 3, resulting in a higher final syngas yield than that of Comparative Examples 2 to 3. This indicates that a better gasification effect cannot be achieved when the Sr / Fe molar ratio is less than or equal to 1:1.

[0172] It can also be seen from Table 1 that under the same operating conditions, Example 2 is significantly better than Comparative Examples 4 to 5 in terms of carbon conversion rate and CO selectivity, and the syngas yield of Example 2 is 913 mL / g-biomass, which is significantly better than 620.3 mL / g-biomass of Comparative Example 4 and 816.1 mL / g-biomass of Comparative Example 5. This shows that under the same molar ratio of alkaline earth metal to Fe (the ratio of Example 2 and Comparative Examples 4 to 5 is 2.5:1), the use of alkaline earth metal Sr has a better effect than Ca and Ba.

[0173] The oxygen carrier obtained in Example 2 was used to conduct a cyclic stability experiment. The experimental process of cyclic stability is as follows: according to the description in the chemical chain gasification performance evaluation, the gasification experiment was carried out at 900°C and an oxygen-carbon ratio (O / C) of 1.3; after the experiment, nitrogen was continuously introduced for 10 minutes, and after the gas was exhausted, air was introduced at 900°C for 30 minutes to oxidize the oxygen carrier; then the temperature was cooled to room temperature under nitrogen conditions, the oxygen carrier was taken out and mixed with 0.3g of fresh biomass sample, and the above process was repeated. The syngas yield, carbon conversion rate and CO selectivity data of the cyclic experiment are shown in Figure 2. Figure 1 As shown. Figure 1It can be seen that in the 10 chemical chain cycle tests conducted, the syngas (H2+CO) yield of biomass was maintained above 1100 mL / g, the carbon conversion rate was maintained above 90%, and the CO selectivity increased to above 98% after 2 cycles. This shows that the oxygen carrier of the present invention has excellent chemical chain cycle stability.

[0174] X-ray diffraction (XRD)

[0175] The crystal phase of the oxygen carrier was analyzed by X-ray diffractometer (Smart lab), and the specific test conditions were: Cu Kα radiation (λ=0.15046nm), target current of 40mA, target voltage of 40kV, diffraction angle (2θ) scanning range of 10-80°, step of 0.0167° / s. The crystal phase of the oxygen carrier was determined by comparing with JCPDS (Joint Committee on Powder Diffraction Standards) files.

[0176] The oxygen carriers obtained in Example 2 and Comparative Example 1 were subjected to X-ray diffraction (XRD) tests, and the spectra and analysis results are shown in FIG. Figure 2 As shown. Figure 2 It can be seen that after the reaction, the comparative example 1 (Fe2O3 oxygen carrier) is mainly a single Fe crystal phase, and also contains a small amount of FeO and F3O4 crystal phase. However, due to the addition of strontium, the fresh sample of Example 2 contains Sr3Fe2O 6.74 and SrO crystal phase, and after reacting with biomass, the crystal phase transforms into Sr3Fe2O6 and SrO, and a small amount of Fe. This shows that after the addition of strontium, a composite ferrite is formed. Due to the presence of strontium, the release process of lattice oxygen in iron oxide is controlled, and there is no deep oxidation of the gasification product, which makes the gasification product have a high CO selectivity.

[0177] Industrial Applicability

[0178] The oxygen carrier and the preparation method thereof can be widely used in thermal conversion processes such as biomass pyrolysis and gasification.

Claims

1. An oxygen carrier, It is characterized in that A composite oxide comprising 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, It is characterized in that The composite oxide contains Sr 3 Fe 2 O x Crystal phase and SrO crystal phase, where x is 5-7.

3. The oxygen carrier according to claim 1 or 2, It is characterized in that It also comprises an inert carrier, which is a substance inert in the gasification reaction of biomass, and the inert carrier is preferably selected from Al 2 O 3 、SiO 2 、SiC、TiO 2 、CeO 2 、ZrO 2 One or more of .

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

5. The method for preparing an oxygen carrier according to any one of claims 1 to 4, It is characterized in that The following steps are involved: (1) Calcination process: calcining the raw material mixture; (2) post-treatment process: optionally performing one or more operations selected from granulation, crushing, and screening on the material calcined in step (1); The raw material mixture is a mixture containing iron, strontium and oxygen, preferably the raw material mixture contains an iron raw material and a 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° C., and the calcination time is 3-8 hours.

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

7. Use of the oxygen carrier according to any one of claims 1 to 4 in preparing synthesis gas using biomass as raw material.

8. A method for preparing synthesis gas, It is characterized in that The following steps are involved: (a) contacting biomass with the oxygen carrier according to any one of claims 1 to 4 to cause the biomass to undergo a gasification reaction; (b) subjecting the oxygen carrier obtained in step (a) to an oxidation reaction in air to regenerate the oxygen carrier.

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

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