A calcium-based carbon oxygen carrier and its preparation method and its application in adsorption enhanced chemical chain reforming PET hydrogen production

Abstract

The present invention provides a calcium-based carbon oxygen carrier and a preparation method thereof and an application in adsorption enhanced chemical chain reforming PET hydrogen production. The calcium-based carbon oxygen carrier of the present invention has good stability and can be regenerated after water vapor oxidation; at the same time, the calcium-based carbon oxygen carrier is modified by Ni doping to improve the activity of the oxygen carrier; the present invention uses a calcium-based carbon oxygen carrier to improve the reaction activity of the Ca2Fe2O5 oxygen carrier, reduce the reaction temperature, adsorb CO2 generated during the chemical chain gasification process and convert it in situ, improve the PET conversion efficiency, and thus realize the PET chemical chain to produce synthesis gas and hydrogen. The present invention adsorbs CO2 in situ in the fuel reactor, promotes the reaction equilibrium to move in the direction of PET conversion, and improves the synthesis gas yield; the calcium-based carbon oxygen carrier of the present invention has good stability and can be regenerated after water vapor oxidation; at the same time, the calcium-based carbon oxygen carrier is modified by Ni doping to improve the activity of the oxygen carrier.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical chaining hydrogen production, and in particular relates to a calcium-based carbon oxygen carrier and a preparation method thereof, and application thereof in adsorption-enhanced chemical chaining reforming PET hydrogen production. Background Art

[0002] Hydrogen is an ideal clean energy with high energy density. The development of hydrogen economy can reduce the emission of greenhouse gases and fine particulate matter. Countries and regions around the world have regarded hydrogen energy as the strategic development direction of future new energy and actively built a hydrogen low-carbon society. Coal-to-hydrogen is one of the main hydrogen production technologies. However, coal-to-hydrogen technology has the disadvantages of complex equipment structure, relatively low operation cycle, high desulfurization investment, many supporting devices, serious carbon emissions, and high hydrogen production cost. Therefore, the development of new hydrogen production technology is of great significance to the development of hydrogen economy.

[0003] The development of the packaging industry has led to a sharp increase in the production and demand for plastics around the world in the past decade. The plastics used in the packaging industry are mainly polyethylene (PE) and polyethylene terephthalate (PET). Among them, low-density polyethylene is mainly used to make handbags, while PET is used to make soft drink bottles and mineral water bottles. These wastes pollute marine and terrestrial ecosystems and even threaten human health. In addition, plastic materials are petroleum-based substances. The increase in daily demand for plastics may lead to the depletion of non-renewable fossil resources. Therefore, the recycling, disposal and reuse of plastic waste is one of the important tasks and one of the effective ways to achieve rational use of resources. Plastic solid waste is difficult to degrade naturally. Pyrolysis technology is widely used in the disposal of these solid wastes due to its environmental protection and sustainability. Therefore, the pyrolysis hydrogen production technology based on waste plastics has a good development prospect. This not only helps to develop new renewable energy hydrogen production processes, alleviate the fossil energy crisis, and reduce carbon emissions, but also provides ideas for the efficient utilization of waste plastics.

[0004] The original purpose of chemical looping combustion was to reduce the entropy change generated during the combustion of thermal power plant gases and improve energy efficiency. In the late 1990s, researchers began to study chemical looping combustion technology (CLC) as a new process for capturing and controlling CO2. The main idea of ​​CLC is to decompose the traditional combustion reaction into two independent oxidation reactions and reduction reactions, and use oxygen carriers to continuously circulate between the two reactions to provide the fuel with the oxygen needed for combustion. This avoids direct contact between air and fuel and achieves internal separation of carbon dioxide.

[0005] Chemical chaining gasification technology is derived from chemical chaining combustion technology. Chemical chaining gasification technology does not require a gasification medium, but uses lattice oxygen in the oxygen carrier to replace the gasifier of the conventional gasification reaction to provide the fuel with the oxygen element required for gasification. During the reaction process, it is necessary to control the ratio of lattice oxygen to fuel so that gasification occurs and a synthesis gas with CO and H2 as the main components is prepared. The main advantages of chemical chaining gasification technology are: the oxygen carrier can be recycled and provides oxygen elements for gasification, saving costs; in the air reactor, the oxygen carrier undergoes an oxidation reaction, and the heat released is brought to the fuel reactor by the oxygen carrier to provide heat for the gasification of the fuel, so that the reaction can proceed continuously without external heating; the solid lattice oxygen and the gaseous component undergo a heterogeneous gas-solid reaction on the solid surface. Compared with the homogeneous gas-gas reaction, the reaction can be carried out more completely in a limited space under normal pressure. In chemical chaining gasification technology, the conversion rate of solid fuel is highly dependent on the volatile content of the fuel. PET waste plastic is a solid fuel with high volatility, which is easier to apply to chemical chain gasification technology than coal.

[0006] However, there is currently no research on the application of PET waste plastics in chemical chaining to produce synthesis gas and hydrogen. Summary of the invention

[0007] In view of this, the present invention proposes a calcium-based carbon oxygen carrier and a preparation method thereof and application in adsorption enhanced chemical chain reforming of PET to produce hydrogen, so as to solve the technical problems existing in the prior art.

[0008] In a first aspect, the present invention provides a calcium-based carbon oxygen carrier, whose chemical formula is Ca2Ni x Fe 2-x O5, where 0≤x<2.

[0009] Preferably, for the calcium-based carbon oxygen carrier, 0.25≤x≤1.

[0010] In a second aspect, the present invention further provides a method for preparing the calcium-based carbon oxygen carrier, comprising the following steps:

[0011] The Ca precursor, the Ni precursor, the Fe precursor and the citric acid are mixed, and then water is added and stirred to obtain a gel;

[0012] The gel is dried and then calcined to obtain a calcium-based carbon oxygen carrier.

[0013] Preferably, in the preparation method of the calcium-based carbon oxygen carrier, the calcination temperature is 900-1100° C. and the calcination time is 8-12 hours.

[0014] Preferably, the preparation method of the calcium-based carbon oxygen carrier comprises mixing a Ca precursor, a Ni precursor, a Fe precursor and citric acid, then adding water, and stirring at 90-100° C. to obtain a gel;

[0015] The gel was dried at 100-110°C and then calcined.

[0016] Preferably, in the method for preparing the calcium-based carbon oxygen carrier, the Ca precursor includes at least one of calcium nitrate and calcium chloride;

[0017] The Ni precursor includes at least one of nickel nitrate, nickel sulfate and nickel chloride;

[0018] The Fe precursor includes at least one of ferric nitrate, ferric sulfate, ferric chloride, ferrous nitrate, ferrous sulfate, and ferrous chloride.

[0019] Preferably, in the method for preparing the calcium-based carbon oxygen carrier, the molar ratio of Ni to citric acid in the Ni precursor is (0.25-1):(0.5-2).

[0020] In a third aspect, the present invention also provides an application of the calcium-based carbon oxygen carrier or the calcium-based carbon oxygen carrier prepared by the preparation method in adsorption enhanced chemical chain reforming PET to produce hydrogen.

[0021] Preferably, the application comprises the following steps: placing a calcium-based carbon oxygen carrier in a fuel reactor, introducing PET pyrolysis gas and water vapor into the fuel reactor, reacting at 680-720° C. under a nitrogen atmosphere to obtain synthesis gas;

[0022] The calcium-based carbon oxygen carrier after the reaction in the fuel reactor is placed in a calcination reactor and heated to 850-950° C. under a nitrogen atmosphere to desorb carbon dioxide and eliminate carbon deposits on the calcium-based carbon oxygen carrier;

[0023] The calcium-based carbon oxygen carrier after desorption of carbon dioxide is placed in a steam reactor, and water vapor is introduced under a nitrogen atmosphere to react at 680-720° C. to obtain hydrogen and simultaneously realize regeneration of the calcium-based carbon oxygen carrier.

[0024] Preferably, in the application, in the step of introducing PET pyrolysis gas and water vapor into the fuel reactor, the feed rate of PET pyrolysis gas is 0.1-0.3 g / min.

[0025] The calcium-based carbon oxygen carrier and its preparation method and application of the present invention have the following beneficial effects compared with the prior art:

[0026] 1. The chemical formula of the calcium-based carbon oxygen carrier of the present invention is Ca2Ni x Fe 2-xO5, the oxygen carrier has good stability and can be regenerated after water vapor oxidation; at the same time, the calcium-based carbon oxygen carrier is modified by Ni doping to improve the activity of the oxygen carrier;

[0027] 2. The present invention adopts calcium-based carbon oxygen carrier CaO-Ca2Ni x Fe 2-x O5, improve the reaction activity of Ca2Fe2O5 oxygen carrier, reduce the reaction temperature, adsorb CO2 produced in the chemical chain gasification process and convert it in situ, improve the PET conversion efficiency, and thus realize the PET chemical chain to produce synthesis gas and hydrogen.

[0028] 3. The present invention adopts adsorption-enhancement technology to eliminate reaction carbon deposits before the water vapor reaction stage and improve the purity of hydrogen; the present invention adopts adsorption-enhancement technology to adsorb CO2 in situ in the fuel reactor, promote the reaction equilibrium to move in the direction of PET conversion, and improve the synthesis gas yield; the calcium-based carbon oxygen carrier of the present invention has good stability and can be regenerated after water vapor oxidation; at the same time, the calcium-based carbon oxygen carrier is modified by Ni doping to improve the activity of the oxygen carrier. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1 This is a schematic diagram of the application principle of the calcium-based carbon oxygen carrier of the present invention in the production of hydrogen and synthesis gas by the PET chemical chain;

[0031] Figure 2 is the XRD spectrum of the calcium-based carbon oxygen carrier prepared in Examples 1 to 5;

[0032] Figure 3 The calcium-based carbon oxygen carrier prepared in Examples 1 to 5,

[0033] Figure 4 is the Raman graph of the calcium-based carbon oxygen carrier prepared in Examples 1 to 5;

[0034] Figure 5 It is a fixed bed device diagram of the PET chemical loop reforming hydrogen production process in Examples 1 to 5;

[0035] Figure 6 The performance of the calcium-based carbon oxygen carriers prepared in Examples 1 to 5 in producing synthesis gas;

[0036] Figure 7The hydrogen production performance of the calcium-based carbon oxygen carrier prepared in Examples 1 to 5;

[0037] Figure 8 The CO2 desorption effect of the calcium-based carbon oxygen carrier prepared in Examples 1 to 5 in the calcination reactor;

[0038] Fig. 9 is the fuel conversion rate of the calcium-based carbon oxygen carrier prepared in Examples 1 to 5.

[0039] Figures 10-11 The tar degradation performance of the calcium-based carbon oxygen carrier prepared in Examples 1 to 5;

[0040] Fig.12 The calcium-based carbon oxygen carrier Ca2Ni prepared in Example 3 0.75 Fe 1.25 O5 redox curve;

[0041] Fig.13 The calcium-based carbon oxygen carrier Ca2Ni prepared in Example 3 0.75 Fe 1.25 SEM image of O5;

[0042] Fig.14 The calcium-based carbon oxygen carrier Ca2Ni prepared in Example 3 0.75 Fe 1.25 SEM image of O5 after 15 cycles;

[0043] Fig.15 is a SEM image of the calcium-based carbon oxygen carrier Ca2Fe2O5 prepared in Example 5;

[0044] Fig.16 This is the SEM image of the calcium-based carbon oxygen carrier Ca2Fe2O5 prepared in Example 5 after 15 cycles. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] In order to better understand the present invention but not to limit the scope of the present invention, all the numbers used in this application to express the amount, percentage, and other numerical values ​​should be understood as modified by the word "about" in all cases. Therefore, unless otherwise specified, the numerical parameters listed in the specification and the appended claims are approximate values, which may be changed according to the different ideal properties attempted to be obtained. Each numerical parameter should at least be regarded as obtained based on the reported significant figures and by conventional rounding methods.

[0047] It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments. In addition, in the description of the present application, the term "including" means "including but not limited to". Various embodiments of the present invention may be in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the numbered range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range. In addition, whenever a numerical range is indicated in this article, it is meant to include any cited numbers (fractions or integers) within the indicated range.

[0048] The present invention provides a calcium-based carbon oxygen carrier, whose chemical formula is Ca2Ni x Fe 2-x O5, where 0≤x<2.

[0049] The calcium-based carbon oxygen carrier of the present invention has a chemical formula of Ca2Ni x Fe 2-x O5, the oxygen carrier has good stability and can be regenerated after water vapor oxidation; at the same time, the calcium-based carbon oxygen carrier is modified by Ni doping to improve the activity of the oxygen carrier.

[0050] In some embodiments, for the calcium-based carbon oxide carrier, 0.25≤x≤1, specifically, x is 0.25, 0.50, 0.75, 1, etc.

[0051] Based on the same inventive concept, the present invention also provides a method for preparing the above-mentioned calcium-based carbon oxygen carrier, comprising the following steps:

[0052] S1, mixing a Ca precursor, a Ni precursor, a Fe precursor and citric acid, then adding water and stirring to obtain a gel;

[0053] S2. Grind the gel after drying it, and calcine it in a muffle furnace to obtain a calcium-based carbon oxygen carrier.

[0054] In some embodiments, the calcination temperature is 900-1100° C., and the calcination time is 8-12 h.

[0055] In some embodiments, a Ca precursor, a Ni precursor, a Fe precursor and citric acid are mixed, and then water is added and stirred at 90-100° C. to obtain a gel;

[0056] The gel was dried at 100-110°C and then calcined.

[0057] In some embodiments, the Ca precursor includes at least one of calcium nitrate and calcium chloride.

[0058] In some embodiments, the Ni precursor includes at least one of nickel nitrate, nickel sulfate, and nickel chloride.

[0059] In some embodiments, the Fe precursor includes at least one of ferric nitrate, ferric sulfate, ferric chloride, ferrous nitrate, ferrous sulfate, and ferrous chloride.

[0060] In some embodiments, the molar ratio of Ni to citric acid in the Ni precursor is (0.25-1):(0.5-2).

[0061] In some embodiments, the molar ratio of citric acid to water is (0.5-2):(50-60).

[0062] Based on the same inventive concept, the present invention also provides an application of the above-mentioned calcium-based carbon oxygen carrier or the calcium-based carbon oxygen carrier prepared by the above-mentioned preparation method in adsorption-enhanced chemical chain reforming of PET to produce hydrogen.

[0063] In some embodiments, the above application includes the following steps: placing a calcium-based carbon oxygen carrier in a fuel reactor, introducing PET pyrolysis gas and water vapor into the fuel reactor, reacting at 680-720° C. under a nitrogen atmosphere to obtain synthesis gas;

[0064] The calcium-based carbon oxygen carrier after the reaction in the fuel reactor is placed in a calcination reactor and heated to 850-950° C. under a nitrogen atmosphere to desorb carbon dioxide and eliminate carbon deposits on the calcium-based carbon oxygen carrier;

[0065] The calcium-based carbon oxygen carrier after desorption of carbon dioxide is placed in a steam reactor, and water vapor is introduced under a nitrogen atmosphere to react at 680-720° C. to obtain hydrogen and simultaneously realize regeneration of the calcium-based carbon oxygen carrier.

[0066] In some embodiments, in the above application, in the step of introducing PET pyrolysis gas and water vapor into the fuel reactor, the feed rate of PET pyrolysis gas is 0.1-0.3 g / min, and the mass of the calcium-based carbon oxygen carrier is 1-3 g.

[0067] Specific reference Figure 1 As shown, Figure 1 The schematic diagram of the reaction of chemical looping reforming to co-produce hydrogen and synthesis gas. Among them, Figure a is a schematic diagram of the reaction of ordinary chemical looping to co-produce hydrogen and synthesis gas, Figure b is a schematic diagram of the adsorption-enhanced chemical looping hydrogen production reaction, and Figure c is a schematic diagram of the adsorption-enhanced chemical looping co-production of hydrogen and synthesis gas applied for by the present invention. Unlike the ordinary chemical looping technology for co-preparing hydrogen and synthesis gas, a calcination reactor is added to eliminate carbon deposits present in the reaction and increase the hydrogen yield. In addition, CaO is used as an adsorbent to in-situ adsorb the CO2 generated in the fuel reactor, improve the purity of the synthesis gas and promote the forward movement of the fuel conversion reaction. Unlike the ordinary adsorption-enhanced chemical looping hydrogen production technology, synthesis gas is produced in the fuel reactor and hydrogen is produced in the steam reactor, which is beneficial to improve the fuel conversion rate and product purity.

[0068] Specifically, PET particles are heated to 880-920° C. to generate PET pyrolysis gas; a calcium-based carbon oxygen carrier is placed in a fuel reactor, and PET pyrolysis gas and water vapor are introduced into the fuel reactor, and react at 680-720° C. under a nitrogen atmosphere to obtain synthesis gas; the calcium-based carbon oxygen carrier can be used as an adsorbent in the fuel reactor to adsorb carbon dioxide, and the calcium-based carbon oxygen carrier is reduced at the same time. Since carbon (i.e., carbon deposition) is inevitably formed in the PET pyrolysis gas during the reaction, it will be attached to the calcium-based carbon oxygen carrier; at this time, The calcium-based carbon oxygen carrier after the reaction in the fuel reactor is placed in a calcination reactor and heated to 850-950°C under a nitrogen atmosphere to desorb carbon dioxide from the calcium-based carbon oxygen carrier. At the same time, the desorbed carbon dioxide reacts with carbon deposits to generate CO, thereby achieving regeneration of the adsorption capacity of the calcium-based carbon oxygen carrier. Finally, the calcium-based carbon oxygen carrier after desorbing carbon dioxide is placed in a steam reactor, and water vapor is introduced under a nitrogen atmosphere to react at 680-720°C to obtain hydrogen, thereby achieving regeneration of the calcium-based carbon oxygen carrier and carrying out the next cycle.

[0069] Specifically, the defects of chemical chain hydrogen production in the prior art are: low purity of hydrogen production, low synthesis gas yield, poor activity of oxygen carriers, and easy sintering of oxygen carriers (poor cycle stability); the present invention adopts adsorption-enhancement technology to eliminate reaction carbon deposits before the water vapor reaction stage and improve the purity of hydrogen; the present invention adopts adsorption-enhancement technology to in-situ adsorb CO2 in the fuel reactor, promote the reaction equilibrium to move in the direction of PET conversion, and improve the synthesis gas yield; the calcium-based carbon oxygen carrier of the present invention has good stability and can be regenerated after water vapor oxidation; at the same time, the calcium-based carbon oxygen carrier is modified by Ni doping to improve the activity of the oxygen carrier.

[0070] In the process of chemical chain gasification, CO2 is inevitably generated, which affects the quality of the synthesis gas. By adding a calcium-based carbon oxygen carrier, which can be used as a CO2 adsorbent (the calcium-based carbon oxygen carrier of the present invention contains CaO, so it can be used as a CO2 adsorbent), the adsorption of CO2 can be achieved, and the purity of the synthesis gas can be improved. Among the many CO2 adsorbents, CaO has the advantages of abundant natural reserves, high adsorption capacity, and fast adsorption rate, and has become a currently recognized suitable adsorbent for high-temperature CaO adsorption. CaO adsorbs CO2 at medium and low temperatures to generate CaCO3, and the generated CaCO3 is decomposed and regenerated at high temperature to obtain CaO, thereby recycling CaO. During the reaction process, CaO adsorbs CO2 generated from hydrocarbon reforming and water gas reaction (CO+H2O→CO2+H2), thereby causing the chemical equilibrium to move toward the direction of cracking tar to generate H2, thereby increasing the concentration and yield of H2 while also increasing the tar removal rate. In general, the introduction of CaO brings about many improvements: 1) CaO captures CO2 in situ in FR, improving the purity of syngas; 2) CaO promotes the shift of reaction equilibrium toward PET reforming and oxidation, improving fuel conversion. As the degree of OCs reduction deepens, 3) CaO particles adhere to the sample surface to form a porous surface, which ensures the diffusion of oxygen, hinders the aggregation and sintering of active metals, and increases hydrogen production.

[0071] In order to achieve efficient production of hydrogen and adsorption of CO2 generated during the chemical chain gasification of PET waste plastics, the present invention adopts a calcium-based carbon / oxygen carrier CaO-Ca2Ni x Fe 2-x O5, improve the reaction activity of Ca2Fe2O5 oxygen carrier, reduce the reaction temperature, adsorb CO2 produced in the chemical chain gasification process and convert it in situ, improve the PET conversion efficiency, and thus realize the PET chemical chain to produce synthesis gas and hydrogen.

[0072] The calcium-based carbon oxygen carrier of the present application and its preparation method and application are further described below with specific examples. This section further illustrates the content of the present invention in conjunction with specific examples, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0073] Example 1

[0074] The present invention provides a method for preparing a calcium-based carbon oxygen carrier, comprising the following steps:

[0075] S1. Mix Ca(NO3)2·4H2O, Ni(NO3)2·6H2O, Fe(NO3)3·9H2O and citric acid, then add water and stir at 95°C to obtain a gel;

[0076] S2. Place the gel in a drying oven at 105°C until the sample is completely dry;

[0077] S3, grinding the dried sample, placing it in a muffle furnace and calcining it at 1000° C. for 10 h, and grinding and sieving it to a size range of less than 212 μm (70 mesh) after cooling, to obtain a calcium-based carbon oxygen carrier;

[0078] Among them, the molar ratio of Ca(NO3)2·4H2O, Ni(NO3)2·6H2O, Fe(NO3)3·9H2O and citric acid is 2:0.25:1.75:2;

[0079] The molar ratio of citric acid to water is 1:55;

[0080] The chemical formula of the prepared calcium-based carbon oxygen carrier is Ca2Ni 0.25 Fe 1.75 O5.

[0081] Example 2

[0082] The preparation method of the calcium-based carbon oxygen carrier provided in this embodiment is the same as that in Example 1, except that the molar ratio of Ca(NO3)2·4H2O, Ni(NO3)2·6H2O, Fe(NO3)3·9H2O and citric acid is 2:0.5:1.5:2, and the chemical formula of the prepared calcium-based carbon oxygen carrier is Ca2Ni 0.5 Fe 1.5 O5.

[0083] Example 3

[0084] The preparation method of the calcium-based carbon oxygen carrier provided in this embodiment is the same as that in Example 1, except that the molar ratio of Ca(NO3)2·4H2O, Ni(NO3)2·6H2O, Fe(NO3)3·9H2O and citric acid is 2:0.75:1.25:2, and the chemical formula of the prepared calcium-based carbon oxygen carrier is Ca2Ni 0.75 Fe 1.25 O5.

[0085] Example 4

[0086] The preparation method of the calcium-based carbon oxygen carrier provided in this embodiment is the same as that in Example 1, except that the molar ratio of Ca(NO3)2·4H2O, Ni(NO3)2·6H2O, Fe(NO3)3·9H2O and citric acid is 2:1:1:2, and the chemical formula of the prepared calcium-based carbon oxygen carrier is Ca2Ni1Fe1O5.

[0087] Example 5

[0088] The preparation method of the calcium-based carbon oxygen carrier provided in this embodiment is the same as that in Example 1, except that Ni(NO3)2·6H2O is not added during the preparation process. The specific preparation method includes the following steps:

[0089] S1. Mix Ca(NO3)2·4H2O, Fe(NO3)3·9H2O and citric acid, then add water and stir at 95°C to obtain a gel;

[0090] S2. Place the gel in a drying oven at 105°C until the sample is completely dry;

[0091] S3, grinding the dried sample, placing it in a muffle furnace and calcining it at 1000° C. for 10 h, and grinding and sieving it to a size range of less than 212 μm (70 mesh) after cooling, to obtain a calcium-based carbon oxygen carrier;

[0092] Among them, the molar ratio of Ca(NO3)2·4H2O, Fe(NO3)3·9H2O and citric acid is 2:2:2;

[0093] The molar ratio of citric acid to water is 1:55;

[0094] The chemical formula of the prepared calcium-based carbon oxygen carrier is Ca2Fe2O5.

[0095] Example 6

[0096] This embodiment provides the application of calcium-based carbon oxygen carrier in PET chemical chain hydrogen production and synthesis gas. The specific experimental device is as follows: Figure 5 shown. Figure 5The fixed bed device diagram for simulating the PET chemical chain reforming hydrogen production process. The whole device consists of a feeding unit, a carrier gas unit, a reaction unit and a product collection unit. The feeding unit consists of two fully automatic injection pumps and matching syringes and PET feeding devices, which are responsible for the feeding operations of water and PET particles respectively. The carrier gas unit is mainly composed of a gas cylinder and a mass flow meter. The reaction unit consists of two vertical tube furnaces and a quartz tube. The entire reaction unit is divided into two parts. The No. 1 vertical tube furnace (A in the figure) is used for pyrolysis and gasification of PET particles, and the temperature is maintained at 900°C. The No. 2 vertical tube furnace (B in the figure) is used for the reaction of PET pyrolysis gas with oxygen carriers to produce synthesis gas. The oxygen carrier is placed in the middle of the No. 2 vertical tube furnace. A porous quartz sand interlayer is provided at the bottom of the quartz tube to place the oxygen carrier. The quartz tube consists of a PET pyrolysis section and a pyrolysis gas adsorption catalytic section. The entire quartz tube is 1000mm long, 50mm in outer diameter, and 6mm thick. The tube furnace uses electric heating and insulation, and is equipped with a thermocouple to detect the temperature inside the furnace. The generated pyrolysis gas passes through the ethanol solvent, condensing agent and desiccant in sequence, and then enters the online gas analyzer to continuously analyze and record the gas concentration (including CO, CO2, CH4, H2 and O2) online, while collecting fine particles and removing the condensable components of the pyrolysis gas.

[0097] The specific steps of the experiment are as follows: before the experiment begins, weigh 2 grams of PET particles into the feeding device, then weigh 2 grams of oxygen carrier and place it on the porous quartz sand interlayer at the bottom of the quartz tube, and place a small crucible with a porous quartz sand bottom on the top of the quartz tube to catch the PET particles dropped from the upper feeding device. The entire reaction process is carried out in a nitrogen atmosphere, and the nitrogen flow rate is controlled to be 500mL / min. The No. 1 vertical tube furnace is heated from room temperature to 900℃ at a heating rate of 20℃ / min under a nitrogen atmosphere and remains unchanged, and the No. 2 vertical tube furnace is heated from room temperature to 700℃ at a heating rate of 20℃ / min under a nitrogen atmosphere. After the temperature stabilizes, the fuel reactor (FR) stage is carried out, the PET feeding device and the upper water vapor injection pump are turned on, the PET feeding rate is 0.2g / min, and the water flow rate of the No. 1 injection pump (C in the figure) is set to 0.05mL / min. PET is pyrolyzed in tube furnace No. 1, and the pyrolysis gas enters tube furnace No. 2 after nitrogen purge, where it reacts to produce synthesis gas. After PET feeding is completed, the PET feeding device and the water vapor injection pump are turned off. After the concentration of each gas is reduced to below 0.5%, the No. 2 vertical electric heating furnace is heated to 900°C, and the reaction enters the calcination reactor (CR) stage, in which the adsorbed CO2 is desorbed and converted into CO in situ, while carbon deposits are eliminated and the adsorbent CaO is regenerated. After the gas concentration is reduced to below 0.5%, the lower water vapor injection pump (D in the figure) is turned on to enter the water vapor reactor (SR) stage. Water vapor enters the fixed bed reactor at a set flow rate to produce high-purity hydrogen. When the concentration of each gas is reduced to below 0.5%, the entire reaction is completed.

[0098] Performance Testing

[0099] Hereinafter, C2F2 represents the calcium-based carbon oxygen carrier Ca2Fe2O5 prepared in Example 5, N 0.25 F 1.75 The Ca2Ni prepared in Example 1 0.25 Fe 1.75 O5, N 0.5 F 1.5 The calcium-based carbon oxygen carrier Ca2Ni prepared in Example 2 0.5 Fe 1.5 O5; N 0.75 F 1.25 The calcium-based carbon oxygen carrier Ca2Ni prepared in Example 3 0.75 Fe 1.25 O5; N1F1 represents the calcium-based carbon oxygen carrier Ca2Ni1Fe1O5 prepared in Example 4.

[0100] Figure 2 : XRD spectra of the calcium-based carbon oxygen carriers prepared in Examples 1 to 5.

[0101] from Figure 2 As can be seen, all samples show Ca2Ni x Fe 2-x O5 phase, the main peaks include 2θ = 31.95°, 33.41° and 46.59°. In the Ni-doped calcium iron ore sample, CaO (characteristic peak is 37.01°) and NiO (characteristic peak is 43.29°) were detected. As the Ni doping gradually increases, the intensity of the characteristic peaks of these two substances increases, which means the increase in the content of these two phases. The precipitation of NiO is due to the fact that a part of Ni cannot be completely doped into the calcium iron ore phase. At the same time, due to the limited content of Ni in calcium iron ore, excess Ca also precipitates and forms CaO.

[0102] Figure 3 Detailed content diagram of each phase in the calcium-based carbon oxygen carrier prepared in Examples 1 to 5.

[0103] Figure 3 The horizontal axis is the Ni doping amount, where the Ni doping amount of 0 represents the calcium-based carbon oxygen carrier Ca2Fe2O5 prepared in Example 5, and the Ni doping amounts of 0.25, 0.5, 0.75, and 1 represent the calcium-based carbon oxygen carriers prepared in Examples 1 to 4, respectively. The vertical axis reflects the content of each phase under different Ni doping ratios, where gray represents CaO, green represents NiO, and purple represents Ca2Ni x Fe 2-x The precise content of the phase is derived from the Rietveld refinement analysis of the XRD pattern.

[0104] from Figure 3 It can be seen that the contents of CaO and NiO increase with the doping of Ni, which is consistent with Figure 2 In the N1F1 sample, the contents of CaO and NiO are both over 20wt.%. CaO can in-situ adsorb the CO2 produced in the reaction, which is beneficial to the generation of synthesis gas.

[0105] Figure 4 The Raman images of the calcium-based carbon oxygen carriers prepared in Examples 1 to 5 are used to study the structural changes of the carbon oxygen carriers.

[0106] from Figure 4 It can be seen that compared with the C2F2 sample, the Ni-doped brown millite sample is located at 552 cm -1 T 2g The vibration peak is enhanced, which represents the internal vibration change of the octahedral structure. -1 The vibration at is also strongly affected by the introduction of Ni, which is attributed to the E of Fe-O in the octahedron. g After Ni doping, E g The rotation peak blue-shifted to 253 cm-1 , indicating the bond elongation and lattice distortion.

[0107] Figure 6 The performance of the calcium-based carbon oxygen carrier prepared in Examples 1 to 5 in producing synthesis gas in a fuel reactor. Figure 6 Syngas means the synthesis gas yield (Y syngas ,ml / g PET), Syngas purity indicates the purity of synthetic gas (P syngas ,%).

[0108] Specifically, the synthesis gas yield (Y syngas ,ml / g PET) and purity (P syngas ,%) is calculated as follows:

[0109]

[0110]

[0111] Among them, V CO is the volume of CO produced, is the volume of H2 produced, V total is the total volume of gas produced, m PET It is the mass of PET added.

[0112] from Figure 6 It can be seen that with the increase of Ni doping content, the syngas yield increases and the purity also increases at the same time. Through a comprehensive analysis of the purity and yield of the gas phase product, when the Ni doping amount is x = 0.75, the performance of calcium iron ore in producing syngas is the best (the yield is 888.53ml / g PET and the purity is 72.18%). The increase in syngas yield is mainly due to the fact that Ni doping increases the lattice oxygen activity and the active sites for fuel decomposition. On the one hand, Ni doping promotes the formation of oxygen vacancies, thereby increasing the activity of lattice oxygen. On the other hand, NiO attached to the surface provides efficient active sites for cracking PET volatiles. In addition, the catalytic cracking activity of Ni produced by NiO reduction cannot be ignored in fuel decomposition. The improvement in syngas purity is mainly attributed to CaO, which captures the carbon dioxide produced during the reaction in situ and promotes the reaction equilibrium to the direction of fuel oxidation.

[0113] Figure 7 The performance of the calcium-based carbon oxygen carrier prepared in Examples 1 to 5 in producing hydrogen in a steam-containing reactor; Figure 7 H2 represents the hydrogen yield (Y H2 ,mmol / g OC), H2purity indicates the purity of hydrogen (P syngas ,%).

[0114] Specifically, the hydrogen yield (YH2 ,mmol / g OC) and purity (P syngas ,%) is calculated as follows:

[0115]

[0116]

[0117] in, is the amount of H2 produced (molar amount), V total is the total volume of gas produced, m OC is the mass of oxygen carrier used.

[0118] from Figure 7 It can be seen that with the increase of Ni doping content, the hydrogen yield is greatly improved. In the water vapor reactor stage, H2 mainly comes from the reaction between steam and reduced oxygen carriers. At the same time, steam will also react with carbon deposits, which will produce additional CO, thus affecting the purity of H2. The H2 yield of C2F2 is only 3.52mmol / g OC. Due to the limited ability of C2F2 to convert PET, carbon deposition is avoided, so that the H2 purity reaches a high level (91.45%). After Ni doping, the hydrogen production performance is improved. Since most of the carbon deposits in the calcination reactor are consumed, the addition of Ni has no negative impact on the hydrogen purity, except for the N1F1 sample. After being deeply reduced by the fuel in the fuel reactor, the nickel-doped oxygen carrier exhibits better water decomposition performance. In general, N 0.75 F 1.25 It has good hydrogen production performance, with H2 purity of 90.14% and yield of 6.73mmol / g OC. However, further increase in Ni doping content leads to a decrease in H2 purity, because a large amount of carbon deposits produced by PET reforming cannot be completely eliminated in the calcination reactor. In general, the addition of Ni greatly improves the conversion rate of PET and the yield of H2.

[0119] Figure 8 The CO2 desorption effect of the calcium-based carbon oxygen carrier prepared in Examples 1 to 5 in the calcination reactor. CO2 yield (Y CO2 ,ml / g PET) and CO yield (Y CO ,ml / g PET) is calculated as follows:

[0120]

[0121]

[0122] Among them, V CO is the volume of CO produced, is the volume of CO2 produced, V total is the total volume of gas produced, mPET It is the mass of PET added.

[0123] The main gaseous products in the calcination reactor (CR) stage are CO and CO2, which are produced by the decomposition of CaCO3 formed by the adsorption of CO2 in the previous stage. CO is mainly generated by the reaction of CO2 with carbon deposits. Figure 8 It can be seen that the gas production of the Ni-doped oxygen carrier is more than three times that of C2F2. On the one hand, Ni doping promotes the formation of CaO and improves the adsorption capacity of carbon oxygen carriers for CO2; on the other hand, the enhancement of lattice oxygen activity promotes the conversion of PET in FR and the generation of CO2, making the increased adsorption capacity available.

[0124] Fig. 9 is the fuel conversion rate of the calcium-based carbon oxygen carrier prepared in Examples 1 to 5 in the fuel reactor. Specifically, the PET conversion rate ( %) is calculated as follows:

[0125]

[0126] Among them, n CO represents the amount of substance producing CO, represents the amount of substance CO2, Represents the amount of CH4 substance, n C-PET Represents the amount of substance in the PET used.

[0127] from Fig. 9 It can be seen that the fuel conversion rate gradually increases with the Ni doping content, which means that Ni doping has a promoting effect on the conversion of PET. In FR, oxygen carriers are deeply reduced by PET, which is beneficial to the production of hydrogen in SR.

[0128] Figures 10-11 The tar degradation performance of the calcium-based carbon oxygen carrier prepared in Examples 1 to 5.

[0129] The tar produced in the PET chemical chain reforming hydrogen production process was collected and dissolved in ethanol solution for further study. Fig.10 It can be seen that with the increase of Ni addition, the color of tar gradually becomes lighter, indicating that the tar content decreases. The collected tar was analyzed by gas chromatography-mass spectrometry to determine the detailed components and explore the promotion effect of Ni on tar cracking, such as Fig.11As shown. When C2F2 was used as the oxygen carrier, the collected tar consisted of 13 components, among which the relative concentration of light mononuclear aromatic hydrocarbons with toluene, styrene, 2,4,6-trimethylphenol and styrene as the main components reached 49.98%. In contrast, fewer than 10 tar components were detected in the Ni-doped samples, and they decreased with the increase of Ni content. There were no heavy alkanes in these samples, and the contents of esters and ketones decreased, indicating that Ni had a catalytic effect on the cracking of relatively easily decomposable substances in the tar. With the addition of Ni, the main components of the tar were aromatic compounds such as biphenyl, toluene and naphthalene, with a relative concentration of more than 95%. These aromatic compounds with benzene rings have stable structures and are not easy to decompose. Overall, the incorporation of Ni enhanced the reactivity and catalytic activity of PET pyrolysis gas, which was manifested in the increase of fuel conversion rate and synthesis gas yield and the decrease of tar component content. The tar produced during the reaction was collected, and it was found that with the doping of Ni, the content and types of tar decreased, proving that Ni doping was helpful for the conversion of tar.

[0130] Fig.12 The redox cycle curves of the calcium-based carbon oxygen carriers prepared in Examples 1 to 5; specifically, the test method of the redox cycle curves of the calcium-based carbon oxygen carriers is as follows:

[0131] The redox cycle test of the calcium-based carbon oxygen carrier sample was carried out on a thermogravimetric analyzer (TGA). During the reaction, three atmospheres of H2-O2-N2 were introduced in sequence to simulate the reduction and oxidation reaction conditions in a fixed bed reactor. The specific experimental steps are: 50 mg of the oxygen carrier was placed in an aluminum crucible and heated to 700 degrees under an inert atmosphere. First, hydrogen (10 vol% H2 / N2, 100 ml / min) was introduced for 25 minutes to reduce the oxygen carrier, and then air (20.8 vol% O2 / N2, 100 ml / min) was introduced for 25 minutes to regenerate the oxygen carrier. Finally, nitrogen (99.99 vol% N2, 100 ml / min) was introduced for 10 minutes to purge the oxygen in the reactor. After the nitrogen purge was completed, hydrogen was introduced again and the next cycle was carried out.

[0132] The oxygen carrying capacity (oxygen carrying capacity) is calculated as follows:

[0133]

[0134] Among them, m O and m R Represent the mass of oxygen carriers that are completely oxidized and reduced, respectively.

[0135] Considering that the oxygen carrier needs to undergo multiple redox reactions in the switched reactor, the TGA cycle experiment was performed to evaluate the cyclic stability of the sample in multiple cycles. Fig.12It can be seen that Ni doping shows good cycling performance in the first 5 cycles, which is due to the excellent regeneration ability of the brown millite structure. 0.25 F 1.75 The samples were inactivated after several cycles, and the OTC dropped to 6.92% and 13.06% at the 15th cycle. 0.5 F 1.5 It also shows slight attenuation after 10 cycles. 0.75 F 1.25 and Ni1F1 samples exhibited better redox cycling performance, which was related to the increase of their CaO content.

[0136] Fig.13 The calcium-based carbon oxygen carrier Ca2Ni prepared in Example 3 0.75 Fe 1.25 SEM image of O5, Fig.14 The calcium-based carbon oxygen carrier Ca2Ni prepared in Example 3 0.75 Fe 1.25 SEM image of O5 after 15 cycles; Fig.15 This is a SEM image of the calcium-based carbon oxygen carrier Ca2Fe2O5 prepared in Example 5. Fig.16 This is the SEM image of the calcium-based carbon oxygen carrier Ca2Fe2O5 prepared in Example 5 after 15 cycles.

[0137] from Figures 13-16 It can be seen that the samples C2F2 and Ni with poor cycle performance 0.25 F 1.75 It has undergone sintering and deactivation. The lack of pores and the dense surface hinder the diffusion and reaction of gas molecules, which is the reason why the oxygen carrying capacity of the oxygen carrier decreases. 0.75 F 1.25 After the reaction with Ni1F1, pores developed and small particles attached to the surface. During the oxygen carrier reduction process, CaO particles adhered to the sample surface, hindering the aggregation and sintering of active metals such as Fe and Ni. Overall, Ni-doped brownmillerite exhibited excellent reactivity and cycling performance.

[0138] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. Application of a calcium-based carbon oxygen carrier in adsorption-enhanced chemical chain reforming of PET for hydrogen production; The application comprises the following steps: The calcium-based carbon oxygen carrier is placed in a fuel reactor, PET pyrolysis gas and water vapor are introduced into the fuel reactor, and the reaction is carried out at 680-720° C. under a nitrogen atmosphere to obtain synthesis gas; The calcium-based carbon oxygen carrier after the reaction in the fuel reactor is placed in a calcination reactor, and heated to 850-950° C. under a nitrogen atmosphere to desorb carbon dioxide and eliminate carbon deposits on the calcium-based carbon oxygen carrier; The calcium-based carbon oxygen carrier after desorption of carbon dioxide is placed in a steam reactor, and water vapor is introduced under a nitrogen atmosphere to react at 680-720° C. to obtain hydrogen, and at the same time, the calcium-based carbon oxygen carrier is regenerated; In the step of introducing PET pyrolysis gas and water vapor into the fuel reactor, the feeding rate of PET pyrolysis gas is 0.1-0.3 g / min; The chemical formula of the calcium-based carbon oxygen carrier is Ca2Ni 0.75 Fe 1.25 O5; The preparation method of the calcium-based carbon oxygen carrier comprises the following steps: The Ca precursor, the Ni precursor, the Fe precursor and the citric acid are mixed, and then water is added and stirred to obtain a gel; The gel is dried and then calcined to obtain a calcium-based carbon oxygen carrier; The calcination temperature is 900-1100°C and the calcination time is 8-12h; The Ca precursor includes at least one of calcium nitrate and calcium chloride; The Ni precursor includes at least one of nickel nitrate, nickel sulfate and nickel chloride; The Fe precursor includes at least one of ferric nitrate, ferric sulfate, ferric chloride, ferrous nitrate, ferrous sulfate, and ferrous chloride.

2. The use according to claim 1, characterized in that The Ca precursor, the Ni precursor, the Fe precursor and the citric acid are mixed, and then water is added and stirred at 90-100° C. to obtain a gel; The gel was dried at 100-110°C and then calcined.

3. The use according to claim 1, characterized in that The molar ratio of Ni to citric acid in the Ni precursor is (0.25-1):(0.5-2).

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