Supported calcium-iron-based catalyst as well as preparation method and application thereof

Abstract

The preparation method comprises the following steps: mixing and stirring calcium chloride dihydrate, aluminum chloride hexahydrate, ethylene glycol, polyoxyethylene and formamide to obtain a clear and stable solution, cooling the solution to 0 DEG C, dropwise adding epoxypropane and gel, aging, drying wet gel, and drying to obtain the supported calcium-iron-based catalyst. A porous mayenite block is obtained after heat treatment, the porous mayenite block is ground and smashed to obtain CaO-Cal2Al14O33 powder, the molar ratio of the adding amount of calcium to the adding amount of aluminum is 24-36: 14, Fe is impregnated and loaded, the loading amount of Fe is 12-18 wt%, and the supported calcium-iron-based catalyst is prepared and used in biomass pyrolysis gasification. The porous mayenite block is used as the carrier, the dispersity of the active component iron is effectively improved, the calcium oxide content in the catalyst is controlled by controlling the calcium-aluminum ratio in the preparation process of the catalyst carrier, the carbon deposition resistance of the iron-based catalyst is effectively improved, and the H2 ratio in produced gas is increased.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of biomass pyrolysis hydrogen production catalysts, and particularly relates to a supported calcium-iron-based catalyst and a preparation method and application thereof. BACKGROUND

[0003] Biomass pyrolysis hydrogen production technology has become an important path for producing "green hydrogen". This technology uses renewable biomass as raw material to produce hydrogen through thermochemical conversion, which can realize carbon cycle (biomass growth absorbs CO2) and handle organic waste such as straw and sawdust, and has both environmental and resource benefits.

[0004] Biomass pyrolysis gasification is the core conversion process, which needs to be completed in anoxic or limited oxygen, 700-1000℃ high temperature environment through four stages of drying, pyrolysis, oxidation and reduction. In the drying stage, the moisture of biomass is removed first; in the pyrolysis stage, the biomass is decomposed into volatile matter containing tar, methane and solid coke; in the oxidation stage, a small amount of oxygen is introduced to react with part of the coke and volatile matter to release heat and provide energy for the subsequent reaction; in the reduction stage, CO2 and water vapor that are not completely oxidized react with coke to generate synthesis gas mainly composed of CO and hydrogen. However, the product system is complex, the gas phase contains CO2 and a small amount of tar, and CO2 will reduce the hydrogen yield and needs to be removed in situ. Experiments have shown that CaO can achieve this goal; tar will cause energy loss and corrosion of equipment, and water washing to remove tar will easily pollute water bodies, so tar cracking is more effective, and Fe-based catalysts are superior to Ni-based catalysts which are easy to lose activity due to their low cost and good activity.

[0005] Iron oxide is a high-quality catalyst for this process with significant advantages. Its raw material iron has a much higher crustal reserve than noble metals, and its preparation process is mature and low-cost, making it easy to be applied on a large scale; Fe 2+ / Fe 3+ The variable valence state makes it have high catalytic activity and wide applicability, and it can replace toxic catalysts; it is non-toxic and has good biocompatibility without secondary pollution; its performance can be adjusted by doping and supporting, and it is easy to recover due to its partial magnetism; it has strong chemical stability and is not easy to lose activity under complex working conditions.

[0006] Calcium oxide (CaO) is a core material for removing CO2. Its raw material is abundant and inexpensive, has a large absorption capacity and high efficiency, and can efficiently react to reduce CO2 concentration at 300-800℃; the generated calcium carbonate is stable and easy to store or resource utilization, reducing secondary carbon emissions; and it has good regeneration and recycling performance and can be reused.

[0007] In addition, mayenite is an ideal composite catalyst carrier. It has a compact crystal structure, high temperature resistance (partially resistant to 1000 DEG C or above), and is not easy to sinter and collapse in high temperature reaction; it has high chemical inertness, and is not easy to cause side reactions with active components and reaction medium, and can maintain the stability of the catalytic system; the raw materials are calcium carbonate (or CaO) and aluminum oxide with abundant reserves, and the preparation process is mature, so that large-scale production is difficult and the cost is controllable, which can meet the industrial catalytic demand. SUMMARY

[0008] In view of the above problems, the purpose of the present application is to provide a supported calcium-iron-based catalyst and a preparation method and application thereof.

[0009] The specific technical solutions are as follows:

[0010] A preparation method of a supported calcium-iron-based catalyst, comprising the following steps:

[0011] 1) Dissolve calcium chloride dihydrate and aluminum chloride hexahydrate in a mixed solvent of deionized water and ethanol, then add ethylene glycol, polyethylene oxide and formamide, stir to obtain a clear and stable solution, cool the clear and stable solution to 0 DEG C, drop propylene oxide, continue to stir after drop completion to make it uniformly mixed, seal, remove bubbles in the solution by ultrasonic, and transfer to an oven for gelation and aging;

[0012] 2) After aging, dry the wet gel in an oven to obtain mayenite dry gel blocks, heat treat to obtain porous mayenite blocks, and grind and crush to obtain CaO-Ca l2 Al 14 O 33 powder;

[0013] 3) Dissolve FeNO3 solution by deionized water, and then add CaO-Ca l2 Al 14 O 33 powder into the FeNO3 solution for impregnation, stir to achieve sufficient solid-liquid mixing, and obtain a slurry;

[0014] 4) Dry the slurry in a constant temperature drying oven, and grind and crush to obtain solid powder, which is calcined, cooled to room temperature, ground and sieved to obtain a supported calcium-iron-based catalyst Fex / CaO-C 12 A7, wherein x represents the mass fraction of Fe loaded on the mayenite carrier; x is 12-18wt%;

[0015] The molar ratio of the added mayenite in step 1) is 24-36:14.

[0016] Further, the mass ratio of aluminum chloride hexahydrate, calcium chloride dihydrate, ethylene glycol, formamide and polyethylene oxide in step 1) is 80-150:60-150:2.5-3:3-4:1, ethylene glycol (EG) is used as a chelating agent, formamide (FA) is used as a drying control agent, propylene oxide (PO) is used as a gelation promoter, polyethylene glycol (PEO) is used as a phase separation inducer, water and ethanol are used as solvents, and a porous mayenite bulk material is prepared by a sol-gel method accompanied by phase separation.

[0017] Further, the dropping speed of propylene oxide in step 1) is 1-2 mL / min. When propylene oxide is added to the system, it will undergo ring-opening reaction with chloride ions in the system, thereby consuming a large amount of H ions in the system, causing the pH of the system to uniformly and mildly rise, and promoting the occurrence of gelation. Too fast dropping speed will lead to: premature gelation, incomplete pore structure, local violent reaction, introduction of bubbles, uneven precursor distribution, etc. Too slow dropping speed will lead to: excessive phase separation, skeleton collapse, solvent evaporation and component imbalance, too long gelation time, and decreased stability, etc.

[0018] Further, the aging temperature in step 1) is 40-45℃. If the oven temperature is too high, it will accelerate the ring-opening reaction rate of propylene oxide (PO), causing the pH of the system to rise rapidly, and the sol to complete gelation in advance. At this time, the phase separation process has not been fully carried out (for example, the PEO-induced solid-liquid two-phase has not formed a uniform co-continuous distribution), and the gel cannot “freeze” the ideal macroporous structure. Finally, the material is prone to present a dense region with small and unevenly distributed pore sizes, and even a local non-porous structure, and the porosity is significantly reduced. If the oven temperature is too low, it will significantly slow down the ring-opening reaction of PO and the hydrolysis polymerization rate of Al 3+ , and the gelation start time is greatly extended. During this period, the phase separation process will continue: PEO as a phase separation inducer will continue to promote the solid-liquid two-phase separation, causing the solid skeleton to break down due to long-term gravity or surface tension, and finally forming a granular morphology with no co-continuous structure, a wide pore size distribution, and a loss of macropore connectivity.

[0019] Further, the heat treatment process in step 2) is to heat treat at 400-1100℃ for 2-3h at a heating rate of 4-5℃ / min to obtain a porous mayenite bulk.

[0020] Further, the drying process of the slurry in step 4) is to place the slurry in a constant temperature drying oven at 100-105℃ for 10-12h, and the calcination process is to calcine at 700-800℃ for 4-6h.

[0021] A supported calcium-iron-based catalyst prepared by the above preparation method.

[0022] The application of a supported calcium-iron-based catalyst in biomass pyrolysis gasification comprises the following steps:

[0023] 1) uniformly spread the supported calcium-iron-based catalyst powder on the quartz wool carrier and completely wrap the catalyst powder;

[0024] 2) load the biomass material in the first-stage reactor of the fixed-bed reaction device using a special funnel, load the molten salt at the bottom of the reaction kettle for assisting the pyrolysis of the material, load the supported calcium-iron-based catalyst powder in the second-stage reactor, introduce N2 to discharge the air in all the reaction devices and pipelines, stop the aeration until the end of the experiment, pyrolyze the material in the first-stage reactor to 500-600 DEG C, heat the second-stage reactor to 600-900 DEG C, and catalytically crack the pyrolysis steam generated in the first-stage reactor on the surface of the catalyst in the second-stage reactor under the carrying of N2 to produce hydrogen.

[0025] The application has the following beneficial effects:

[0026] The application uses the impregnation method combined with the sol-gel method to prepare the calcium-iron-based catalyst, uses the porous huntite block as the carrier, effectively improves the dispersion degree of the active component iron, increases the number of the active component, inhibits the aggregation and sintering of the active component iron at high temperature, on the other hand, controls the calcium aluminate ratio in the preparation process of the catalyst carrier to control the calcium oxide content in the catalyst, which not only can improve the alkalinity of the catalyst, but also can effectively absorb the carbon dioxide produced in the pyrolysis process, promote the reaction between the carbon dioxide and the carbon on the surface of the catalyst, at the same time, the iron oxide has good oxygen storage / release capacity, the released oxygen can also react with the carbon on the surface of the catalyst, thereby effectively improving the carbon deposition resistance of the iron-based catalyst and increasing the H2 proportion in the produced gas. DETAILED DESCRIPTION

[0027] The application will be further described in combination with the examples, but the protection scope of the application is not limited to this.

[0028] Example 1

[0029] Preparation of Ca 12 Al 14 O 33 Catalyst carrier

[0030] 1) weigh calcium chloride dihydrate 27.8g and aluminum chloride hexahydrate 53.2g (the molar ratio of Ca / Al is 12:14), dissolve them in 500ml of mixed solvent of deionized water and ethanol (mixed in a volume ratio of 1:1), then sequentially add 1.0g of ethylene glycol, 0.4g of polyethylene oxide (PEO, Mv=3x10 5) and 1.2 g of formamide, after stirring for 1 h at room temperature, a clear and stable solution was obtained. The resulting solution was cooled to 0 °C in an ice-water mixture and then 2 ml of propylene oxide was slowly added to it using a syringe (drop rate of about 1 mL / min), after the addition was completed, it was stirred for 2 min to mix well, and the high-speed stirring was maintained during this period. Subsequently, the container was sealed, placed in an ultrasonic instrument for about 30 s to remove the gas bubbles in the solution, and then transferred to an oven for gelation and aging process.

[0031] 2) Calcination reduction: after aging for 24 h, the wet gel was placed in an oven at 60 °C and slowly dried for 72 h to obtain a dry gel body sample of mayenite, which was heat treated at 1100 °C for 1.5 h at a heating rate of 4 °C / min, and finally about 28 g of porous mayenite block was obtained, which was ground and crushed to obtain Ca 12 Al 14 O 33 Catalyst support.

[0032] Example 2

[0033] Preparation of CaO-Ca 12 Al 14 O 33 Catalyst support (molar ratio of Ca / Al is 24:14)

[0034] The operation process is the same as that of Example 1, the difference is that calcium chloride dihydrate 55.6 g, aluminum chloride hexahydrate 53.2 g, 1.3 g of ethylene glycol, 0.5 g of polyethylene oxide (PEO, Mv = 3 x 10 5 ) and 1.6 g of formamide.

[0035] Example 3

[0036] Preparation of CaO-Ca 12 Al 14 O 33 Catalyst support (molar ratio of Ca / Al is 36:14)

[0037] The operation process is the same as that of Example 1, the difference is that calcium chloride dihydrate 83.4 g, aluminum chloride hexahydrate 53.2 g, 1.6 g of ethylene glycol, 0.6 g of polyethylene oxide (PEO, Mv = 3 x 10 5 ) and 1.9 g of formamide.

[0038] Example 4

[0039] Study on the effect of calcium-iron-based catalyst Fe loading on hydrogen production from biomass and waste plastic pyrolysis assisted by molten salt

[0040] This experiment only verifies the influence of Fe loading on the experimental results, so the content of CaO is 0, that is, the catalyst prepared in Example 1, and the Fex / Ca 12 Al 14 O 33 Catalyst, the specific operation process is as follows:

[0041] 1) Take FeNO3·9H2O, dissolve in 500 ml deionized water and prepare FeNO3 solution;

[0042] 2) Add Ca 12 Al 14 O 33 Powder into the above solution for impregnation, mechanical stirring for 6h to achieve solid-liquid fully mixed;

[0043] 3) The obtained slurry is placed in a constant temperature drying oven, dried at 100℃ for 12h, and ground;

[0044] 4) The dried solid powder is placed in a muffle furnace, calcined at 700℃ for 6h, naturally cooled to room temperature, and ground and sieved to obtain Fex / Ca 12 Al 14 O 33 Catalyst.

[0045] When the Fe loading is 12wt%, the amount of FeNO3·9H2O added is 17.36g, the amount of Ca 12 Al 14 O 33 Powder is 16.5g, and the prepared catalyst is marked as Fe12 / Ca 12 Al 14 O 33 ;

[0046] When the Fe loading is 15wt%, the amount of FeNO3·9H2O added is 21.7g, the amount of Ca 12 Al 14 O 33 Powder is 15.7g, and the prepared catalyst is marked as Fe15 / Ca 12 Al 14 O 33 ;

[0047] When the Fe loading is 18wt%, the amount of FeNO3·9H2O added is 26.0g, the amount of Ca 12 Al 14 O 33 Powder is 14.8g, and the prepared catalyst is marked as Fe18 / Ca 12 Al14 O 33 .

[0048] Application: The selected biomass feedstock is corn stalk (CS) from Lianyungang (Jiangsu, China) with particle size in the range of 0.18-0.21 mm. Polyethylene (PE) plastic particles were purchased from FHT Polymeric Material Co. (Guangdong, China) with the same particle size as corn stalk. The corn stalk and PE plastic were dried in an oven at 105°C for 24 h, and then mixed with a mass ratio of 1:1, respectively. The contents of C, H, N, S in the feedstock were determined using an organic elemental analyzer (Elementar Unicube, Germany), and the content of O was calculated by difference method. The results of proximate analysis and elemental analysis of the feedstock are listed in Table 1.

[0049] Table 1. Lower heating value, proximate analysis and elemental analysis of corn stalk and PE

[0050]

[0051] Note: ad: air-dried basis, *: O element content calculated by difference method

[0052] The molten salt used was lithium carbonate, sodium carbonate and potassium carbonate (analytical purity > 99%, Arlab Biochemical Technology Co., Ltd., Shanghai, China). The three carbonates were mechanically mixed in a mass ratio of 1:1:1, then ground thoroughly in a mortar to ensure uniform mixing, and the mixed carbonates were dried in a constant temperature drying oven for 24 h and stored for use.

[0053] Experimental procedure: This study used a molten salt pyrolysis system and a biomass pyrolysis catalytic system for experiments, which included a stainless steel reactor, a horizontal tube furnace, a temperature-controlled electric heating furnace, a gas flow controller, a volatile condensation device and a gas collection device. During the experiment, 180 g of ternary carbonate was placed at the bottom of the reactor, and the reactor was heated to the target temperature (stainless steel reactor 500°C, horizontal tube furnace 700°C) at a heating rate of 8°C / min under N2 atmosphere (150 mL / min). After stabilization, the stainless steel basket at the top of the reactor containing 6 g of experimental sample (a mixture of corn stalk and PE plastic with a mass ratio of 1:1) was pushed into the molten salt, and after 30 min the basket was lifted. The biomass and waste plastic were preferentially subjected to molten salt-assisted pyrolysis to produce pyrolysis gas, which was introduced into the horizontal tube furnace containing 6 g of calcium-iron-based catalyst (wrapped in quartz wool carrier, steam and carbon ratio S / C = 2) for the next step of catalytic reforming experiment. The pyrolysis oil and pyrolysis gas were collected by water bath condensation device and collection bag, respectively, during the experiment process.

[0054] When studying the effect of different Fe loadings on the hydrogen production from biomass and waste plastic pyrolysis assisted by molten salt, the types of calcium-iron machine catalysts (Fe12 / Ca 12 Al 14 O 33 , Fe15 / Ca 12 Al 14 O 33 , Fe12 / Ca 12 Al 14 O 33 ) were changed for the study. The H2 content of the collected gas was detected by GC instrument. The detection results showed that the hydrogen production rates of different iron loadings were 53% (Fe12 / Ca 12 Al 14 O 33 ), 58% (Fe15 / Ca 12 Al 14 O 33 ), and 61% (Fe18 / Ca 12 Al 14 O 33 ), respectively. With the increase of iron loading, the increase of hydrogen production rate gradually decreased. Further increasing the iron loading would increase the cost of catalyst preparation. Therefore, the Fe loading of 15-18wt% was more appropriate, and 18wt% was the most preferred, which was used to screen the Ca / Al molar ratio.

[0055] Example 5

[0056] Effect of Ca / Al molar ratio of calcium-iron-based catalyst on the reforming of each gas component of the catalyst

[0057] The catalyst supports of Examples 1-3 were used to load iron according to the operation steps of Example 4, and the Fe loading was 18wt%. According to the different Ca / Al molar ratios, the catalysts were marked as Fe18 / CA0.85, Fe18 / CA1.71, and Fe18 / CA2.57.

[0058] The experiment was carried out according to the application operation of Example 4, the operation process and parameters were the same as those in the application process of Example 4, and the difference was that different catalysts with different molar ratios of Ca / Al were replaced. When the molar ratio of Ca / Al was 12:14, the content of H2 in the final mixed gas was 63.01%, and as the molar ratio of Ca / Al increased to 24:14, the content of H2 increased to 66.95%, and as the molar ratio of Ca / Al increased to 36:14, the content of H2 was 67.15%. The CaO in the bifunctional catalyst carried out the adsorption reaction to reduce the CO2 content in the component, so as to promote the water gas reaction of CO to move to the direction of generating CO2 and H2. Due to the increase of the content of CaO, the content of CO2 showed a downward trend. In summary, after Ca / Al is 24:14, the increase of H2 content is not significant, and the increase of CaO content has little significance and will increase the cost, so when Ca / Al is 24:14, the cost performance is the highest.

Claims

1. A method for preparing a supported calcium-iron-based catalyst, characterized in that, Comprising the following steps: 1) dissolving calcium chloride dihydrate and aluminum chloride hexahydrate in a mixed solvent of deionized water and ethanol, then adding ethylene glycol, polyethylene oxide and formamide, stirring to obtain a clear and stable solution, cooling the clear and stable solution to 0℃, adding propylene oxide dropwise, continuing to stir after the dropwise addition is completed to make it uniformly mixed, sealing, ultrasonic removal of bubbles in the solution, transferring to an oven for gelation and aging; 2) After aging, the wet gel is dried in an oven to obtain a calcium aluminate dry gel block, and a porous calcium aluminate block after heat treatment, and a CaO-Ca l2 Al 14 O 33 powder; 3) Deionized water dissolves to prepare FeNO3 solution, CaO-Ca l2 Al 14 O 33 powder is added to the FeNO3 solution for impregnation, stirring to achieve solid-liquid full mixing, and a slurry is obtained; 4) The slurry is dried in a constant temperature drying oven and ground, the obtained solid powder is calcined, cooled to room temperature, and ground and sieved to obtain the supported calcium-iron-based catalyst Fex / CaO-C 12 A7, wherein x represents the mass fraction of Fe supported on the mayenite carrier; x is 12-18 wt%; The molar ratio of the amount of calcium aluminum added in step 1) is 24-36:

14.

2. The process for the preparation of a supported calcium iron-based catalyst according to claim 1, characterized in that, The mass ratio of aluminum chloride hexahydrate, calcium chloride dihydrate, ethylene glycol, formamide and polyethylene oxide in step 1) is 80-150:60-150:2.5-3:3-4:

1.

3. The process for the preparation of a supported calcium iron-based catalyst according to claim 1, characterized in that, The dropwise addition rate of propylene oxide in step 1) is 1-2 mL / min.

4. The process for the preparation of a supported calcium iron-based catalyst according to claim 1, characterized in that, The aging temperature in step 1) is 40-45℃.

5. The process for the preparation of a supported calcium iron-based catalyst according to claim 1, characterized in that, The heat treatment process in step 2) is heat treatment at 400-1100℃ for 2-3h at a heating rate of 4-5℃ / min to obtain porous humite bulk.

6. The process for the preparation of a supported calcium iron-based catalyst according to claim 1, characterized in that, The drying process of the slurry in step 4) is placing the slurry in a constant temperature drying oven at 100-105℃ for 10-12h, and the calcination process is calcination at 700-800℃ for 4-6h.

7. A supported calcium-iron-based catalyst prepared by the preparation method of any one of claims 1-6.

8. Use of the supported calcium-iron based catalyst according to claim 7 in the pyrolysis gasification of biomass, characterized in that, Comprising the following steps: 1) uniformly spreading the supported calcium-iron-based catalyst powder on the quartz wool carrier and completely wrapping the catalyst powder; 2) loading biomass material in the first stage reactor of the fixed bed reaction device using a special funnel, loading molten salt at the bottom of the reaction kettle for assisting material pyrolysis, loading supported calcium-iron-based catalyst powder in the second stage reactor, purging all reaction devices and pipelines with N2 to remove air until the experiment is stopped, pyrolyzing the first stage reactor to 500-600℃, the second stage reactor to 600-900℃, and the pyrolysis steam generated in the first stage reactor is catalytically cracked on the surface of the catalyst in the second stage reactor under the carrying of N2 to produce hydrogen.

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