Calcium-based adsorbent for preparing hydrogen-rich synthesis gas through sludge gasification as well as preparation method and application of calcium-based adsorbent

Abstract

The invention discloses a calcium-based adsorbent for preparing hydrogen-rich synthesis gas through sludge gasification and a preparation method and application thereof.The calcium-based adsorbent comprises an active adsorbent, a supporting material and an auxiliary, the active adsorbent is CaO, the supporting material is one of Al2O3, La2O3 or ZrO2, and the auxiliary is CoO; the modified calcium-based adsorbent prepared by adopting a sol-gel method has relatively high cycle stability, and can still keep relatively high carbonation degree after ten cycles; meanwhile, for preparing hydrogen-rich synthesis gas through sludge gasification, the modified calcium-based adsorbent can effectively improve the concentration and yield of hydrogen.

Description

Technical Field

[0001] The present invention relates to a calcium-based adsorbent for producing hydrogen-rich syngas by sludge gasification, and also relates to a preparation method and application of the above calcium-based adsorbent. Background Art

[0002] Sludge is a solid waste generated in the sewage treatment process. With the rapid progress of urbanization, the requirements for sewage treatment are becoming more and more strict, and the sludge production has increased sharply. Because sludge contains high concentrations of heavy metals and organic toxins, traditional sludge treatment methods, such as landfill, ocean dumping, agricultural composting, direct incineration, etc., will have an adverse impact on the environment and bring a burden to human survival. Developing safe sludge treatment technologies is extremely urgent. As a biomass with a relatively high energy density, gasification is a promising treatment method for sludge, which can greatly reduce the sludge accumulation while generating combustible gas for power generation or as a chemical raw material.

[0003] Traditional sludge treatment methods will have an adverse impact on the environment, while sludge gasification to produce hydrogen-rich syngas has attracted extensive attention due to its environmental friendliness and relatively high energy utilization efficiency, especially calcium-based adsorbent enhanced biomass gasification. As a by-product of syngas production, the removal of carbon dioxide can promote the reaction to proceed in the direction of syngas production, thereby increasing the yield of syngas and the concentration of hydrogen in the syngas. Calcium oxide reacts with carbon dioxide to form calcium carbonate, and calcium carbonate can be decomposed back into calcium oxide and carbon dioxide at high temperatures. While improving the gasification efficiency, carbon dioxide capture can also be achieved. However, the research on calcium looping in sludge gasification is not in-depth. At present, commercial calcium-based adsorbents have problems of easy sintering and agglomeration, which lead to the reduction of their pore channels and a significant decrease in the activity of the adsorbent with the progress of the cycle, and the cycle performance is weak, hindering their large-scale use. Therefore, it is of great significance to provide a calcium-based adsorbent that can improve the sludge gasification efficiency and has cycle stability. Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to provide a calcium-based adsorbent for producing hydrogen-rich syngas by sludge gasification, and also provide a preparation method of the above calcium-based adsorbent and its application in sludge gasification treatment.

[0005] Technical Solution: The present invention discloses a calcium-based adsorbent for producing hydrogen-rich syngas by sludge gasification, which includes an active adsorbent, a support material, and an auxiliary agent. Among them, the active adsorbent is CaO, the support material is one of Al2O3, La2O3, or ZrO2, and the auxiliary agent is CoO.

[0006] Among them, for the calcium-based adsorbent, calculated by the total weight percentage of the composite material, the content of CaO is 65-75%, the content of the support material is 20%, and the content of CoO is 5-15%.

[0007] Among them, the size of the calcium-based adsorbent is 0.10 to 0.15 mm.

[0008] The preparation method of the above-mentioned calcium-based adsorbent includes the following steps:

[0009] (1) Take the precursors of Ca, the precursor of the support material, and the precursor of Co, mix them, add citric acid and water, mix evenly, heat and stir in a water bath until a sol-gel is formed, and stop stirring;

[0010] (2) Place it at room temperature, after sufficient drying and calcination, grind and sieve to obtain the calcium-based adsorbent for producing hydrogen-rich syngas from sludge gasification.

[0011] Among them, in step (1), the mass ratio of the precursor of Ca, the precursor of the support material, and the precursor of Co is 13 to 25:4:1 to 3.

[0012] Among them, the precursor of Ca is Ca(NO3)2·4H2O, the precursor of Al is Al(NO3)3·9H2O, the precursor of La is La(NO3)3·6H2O, the precursor of Zr is Zr(NO3)2·5H2O, and the precursor of Co is Co(NO3)2·6H2O.

[0013] Among them, in step (1), it includes Ca 2+ , Co 2+ , Al 3+ , La 3+ , Zr 2+ The molar ratio of all metal cations including water is 1:10, and the molar ratio of all the above metal cations to citric acid is 1:2 for mixing.

[0014] Among them, in step (1), the temperature of the water bath heating is 80 to 85 °C, preferably 80 °C, and heating and stirring are carried out in a water bath pot.

[0015] Among them, in step (2), for the drying, the temperature is 100 to 110 °C, preferably 100 °C, and drying is carried out in an air atmosphere.

[0016] Among them, in step (2), for the calcination, pre-calcination is carried out at 300 to 350 °C for 1 to 1.5 h, and then the temperature is raised to 700 to 750 °C for calcination for 2 to 3 h; preferably, pre-calcination is carried out at 300 °C for 1 h, and then the temperature is raised to 700 °C for calcination for 2 h.

[0017] The present invention also discloses the application of the above-mentioned calcium-based adsorbent in producing hydrogen-rich syngas from sludge gasification, and the mass ratio of the calcium-based adsorbent to the sludge is 0.4 to 0.6.

[0018] Among them, the application is gasification in a gasification reactor. The reaction conditions are 700 °C and 35 min, the reaction atmosphere is 15% CO2 + 85% N2, and the gas flow rate is 0.1 L / min. Then, it enters the regeneration reactor, where the reaction conditions are 850 °C and 20 min, the reaction atmosphere is 100% N2, and the gas flow rate is 0.1 L / min. The cyclic reaction is carried out to obtain the product.

[0019] Among them, the reaction conditions are preferably 700 - 750 °C, 35 - 40 min, the reaction atmosphere is 15% CO2 + 85% N2, and the gas flow rate is 0.1 - 0.3 L / min. Then, it enters the regeneration reactor, where the reaction conditions are 850 - 900 °C, 20 - 25 min, the reaction atmosphere is 100% N2, and the gas flow rate is 0.1 - 0.3 L / min. The cyclic reaction is carried out to obtain the product.

[0020] Principle of the invention: The calcium-based adsorbent of the present invention is a modified calcium-based adsorbent doped with Al and Co. Al2O3 serves as an inert support material and forms Ca 12 Al 14 O 33 at high temperatures, which is beneficial for forming a strong pore structure to improve the cyclic stability of the calcium-based adsorbent. As a transition metal element, Co has a catalytic effect on coke gasification, methane reforming, tar cracking, and water-gas shift reactions during the gasification process, which is beneficial for the production of hydrogen-rich syngas.

[0021] Advantages: Compared with the prior art, the present invention has the following remarkable advantages: (1) The calcium-based adsorbent of the present invention has more stable cyclic performance. After ten cycles, it can still maintain a relatively high degree of carbonation and has high activity. When applied to the gasification of sludge to produce hydrogen-rich syngas, it can effectively increase the hydrogen concentration and cold gas efficiency of the syngas, achieving the effect of efficient sludge gasification. The hydrogen production of the calcium-based adsorbent doped with Al and Co is increased by 2 - 8 times, and the cyclic performance is improved by 26%; (2) The preparation method of the calcium-based adsorbent of the present invention uses the sol-gel method, which is simple to operate and easy to obtain materials with uniform doped elements. Description of the drawings

[0022] Figure 1 is the XRD pattern of calcium-based adsorbents with different support materials;

[0023] Figure 2 is the degree of carbonation of calcium-based adsorbents with different support materials during the repeated cycling process;

[0024] Figure 3 is the composition of the syngas produced by gasifying calcium-based adsorbents with different support materials;

[0025] Figure 4is the hydrogen production generated by the gasification of calcium-based adsorbents with different support materials;

[0026] Figure 5 is the cold gas efficiency of the syngas produced by the gasification of calcium-based adsorbents with different support materials;

[0027] Figure 6 is the XRD pattern of calcium-based adsorbents doped with different proportions of Co;

[0028] Figure 7 is the degree of carbonation of calcium-based adsorbents doped with different proportions of Co during the repeated cycle;

[0029] Figure 8 is the syngas composition produced by the gasification of calcium-based adsorbents doped with different proportions of Co;

[0030] Figure 9 is the hydrogen production generated by the gasification of calcium-based adsorbents doped with different proportions of Co;

[0031] Figure 10 is the cold gas efficiency of the syngas produced by the gasification of calcium-based adsorbents doped with different proportions of Co. Detailed implementation mode

[0032] The technical solution of the present invention will be further described below in conjunction with the embodiments. The test materials used in the embodiments can be obtained through conventional channels.

[0033] The proximate analysis and ultimate analysis of the sludge on a dry basis are shown in the following table.

[0034]

[0035] Example 1

[0036] The calcium-based adsorbent of the present invention includes an active adsorbent, a support material, and an auxiliary agent. Among them, the active adsorbent is CaO, the support material is Al2O3, and the auxiliary agent is CoO. Calculated by the total weight percentage of the composite material, the content of CaO is 75%, the content of the support material is 20%, and the content of CoO is 5%.

[0037] Its preparation method includes the following steps:

[0038] (1) Take three nitrates, Ca(NO3)2·4H2O, Al(NO3)3·9H2O, and Co(NO3)2·6H2O, mix them evenly in a mass ratio of 15:4:1, and then mix the mixture with citric acid and deionized water in a molar ratio of 1:2:10 (the molar number of the mixture is replaced by the molar number of metal cations), put it in a water bath at 80°C and heat and stir until a sol-gel is formed, and stop stirring;

[0039] (2) Leave it at room temperature for 24 h; dry it at 100 °C in an air atmosphere for 12 h, then put it into a muffle furnace, pre-calcine it at 300 °C for 1 h, and then raise the temperature to 700 °C and calcine it for 2 h; finally, grind and sieve it to obtain a calcium-based adsorbent with a particle size of 0.10 - 0.15 mm, labeled as #2-2.

[0040] Example 2

[0041] The calcium-based adsorbent of the present invention comprises an active adsorbent, a support material and an auxiliary agent. Among them, the active adsorbent is CaO, the support material is Al2O3, and the auxiliary agent is CoO. Calculated by the total weight percentage of the composite material, the content of CaO is 70%, the content of the support material is 20%, and the content of CoO is 10%.

[0042] Its preparation method comprises the following steps:

[0043] (1) Take three nitrates of Ca(NO3)2·4H2O, Al(NO3)3·9H2O, and Co(NO3)2·6H2O, mix them evenly according to a mass ratio of 7:2:1, and then mix the mixture with citric acid and deionized water according to a molar ratio of 1:2:10 (the molar number of the mixture is replaced by the molar number of metal cations), put it into a water bath at 80 °C, heat and stir until a sol-gel is formed, and then stop stirring;

[0044] (2) Leave it at room temperature for 24 h; dry it at 100 °C in an air atmosphere for 12 h, then put it into a muffle furnace, pre-calcine it at 300 °C for 1 h, and then raise the temperature to 700 °C and calcine it for 2 h; finally, grind and sieve it to obtain a calcium-based adsorbent with a particle size of 0.10 - 0.15 mm, labeled as #2-3.

[0045] Example 3

[0046] The calcium-based adsorbent of the present invention comprises an active adsorbent, a support material and an auxiliary agent. Among them, the active adsorbent is CaO, the support material is Al2O3, and the auxiliary agent is CoO. Calculated by the total weight percentage of the composite material, the content of CaO is 65%, the content of the support material is 20%, and the content of CoO is 15%.

[0047] Its preparation method comprises the following steps:

[0048] (1) Take three nitrates, Ca(NO3)2·4H2O, Al(NO3)3·9H2O, and Co(NO3)2·6H2O, mix them evenly in a mass ratio of 13:4:3. Then mix the mixture with citric acid and deionized water in a molar ratio of 1:2:10 (the molar amount of the mixture is replaced by the molar amount of metal cations), and place it in a water bath at 80 °C for heating and stirring until a sol-gel is formed, then stop stirring;

[0049] (2) Place it at room temperature for 24 h; dry it at 100 °C for 12 h in an air atmosphere, then put it into a muffle furnace, pre-calcine it at 300 °C for 1 h, and then raise the temperature to 700 °C for calcination for 2 h; finally, grind and sieve to obtain a calcium-based adsorbent with a particle size of 0.10 - 0.15 mm, labeled as #2-4.

[0050] Comparative Example 1

[0051] A calcium-based adsorbent, and its preparation method includes the following steps:

[0052] Take Ca(NO3)2·4H2O, citric acid, and deionized water and mix them evenly in a molar ratio of 1:2:10, place it in a water bath at 80 °C for heating and stirring until a sol-gel is formed, then stop stirring; place it at room temperature for 24 h; dry it at 100 °C for 12 h in an air atmosphere, then put it into a muffle furnace, pre-calcine it at 300 °C for 1 h, and then raise the temperature to 700 °C for calcination for 2 h; finally, grind and sieve to obtain a calcium-based adsorbent with a particle size of 0.10 - 0.15 mm, labeled as #1-1.

[0053] Comparative Example 2

[0054] A calcium-based adsorbent, and its preparation method includes the following steps:

[0055] Take two nitrates, Ca(NO3)2·4H2O and Al(NO3)3·9H2O, mix them evenly in a mass ratio of 4:1. Then mix the mixture with citric acid and deionized water in a molar ratio of 1:2:10 (the molar amount of the mixture is replaced by the molar amount of metal cations), place it in a water bath at 80 °C for heating and stirring until a sol-gel is formed, then stop stirring; place it at room temperature for 24 h; dry it at 100 °C for 12 h in an air atmosphere, then put it into a muffle furnace, pre-calcine it at 300 °C for 1 h, and then raise the temperature to 700 °C for calcination for 2 h; finally, grind and sieve to obtain a calcium-based adsorbent with a particle size of 0.10 - 0.15 mm, labeled as #1-2 and #2-1.

[0056] Comparative Example 3

[0057] A calcium-based adsorbent, and its preparation method includes the following steps:

[0058] Take two nitrates, Ca(NO3)2·4H2O and La(NO3)3·6H2O, mix them evenly at a mass ratio of 4:1. Then mix the mixture with citric acid and deionized water in a molar ratio of 1:2:10 (the molar number of the mixture is replaced by the molar number of metal cations), and place it in a water bath at 80 °C for heating and stirring until a sol-gel is formed, then stop stirring. Let it stand at room temperature for 24 h, dry it in an air atmosphere at 100 °C for 12 h, then put it into a muffle furnace, pre-calcine it at 300 °C for 1 h, and then raise the temperature to 700 °C for calcination for 2 h. Finally, grind and sieve to obtain a calcium-based adsorbent with a particle size of 0.10 - 0.15 mm, labeled as #1-3.

[0059] Comparative Example 4

[0060] A calcium-based adsorbent, and its preparation method includes the following steps:

[0061] Take two nitrates, Ca(NO3)2·4H2O and Zr(NO3)2·5H2O, mix them evenly at a mass ratio of 4:1. Then mix the mixture with citric acid and deionized water in a molar ratio of 1:2:10 (the molar number of the mixture is replaced by the molar number of metal cations), and place it in a water bath at 80 °C for heating and stirring until a sol-gel is formed, then stop stirring. Let it stand at room temperature for 24 h, dry it in an air atmosphere at 100 °C for 12 h, then put it into a muffle furnace, pre-calcine it at 300 °C for 1 h, and then raise the temperature to 700 °C for calcination for 2 h. Finally, grind and sieve to obtain a calcium-based adsorbent with a particle size of 0.10 - 0.15 mm, labeled as #1-4.

[0062] Take the calcium-based adsorbents prepared in the above examples and comparative examples, and conduct a performance study on the production of hydrogen-rich syngas from sludge gasification:

[0063] The operation includes the following steps:

[0064] (1) Dry the sludge at 110 °C for 12 h, grind and sieve the particles with a particle size of 0.15 - 0.35 mm as experimental materials.

[0065] (2) Take 2 g of a mixture of sludge and a calcium-based adsorbent with different support materials, where Ca:C is 1:1, and place the mixture on a fixed bed.

[0066] (3) In the gasification stage, the reaction conditions are 700 °C, 35 min, the reaction atmosphere is 15% CO2 + 85% N2, the gas flow rate is 0.1 L / min, and the steam flow rate is 0.2 g / min;

[0067] (4) Regeneration stage, with reaction conditions of 850 °C, 20 min, reaction atmosphere of 100% N2, and gas flow rate of 0.1 L / min. During the experiment, both the gas and steam were preheated to 500 °C before entering the reaction device.

[0068] Among them, #0 is without calcium-based adsorbent.

[0069] From Figure 2 It can be seen that although #1-1 showed a carbonation degree of approximately 81% during the first cycle, after ten cycles, its carbonation degree decreased rapidly to approximately 62%, indicating its low cycle stability. #1-2, #1-3, and #1-4 have better cycle stability. Under comprehensive comparison, although the initial carbonation degree of #1-2 is relatively low, at 53%, during the first five cycles, its carbonation degree increased, and it showed a carbonation degree of 68% during the tenth cycle, proving its good cycle stability. This is because the support material Al2O3 and calcium oxide formed Ca 12 Al 14 O 33 , which is beneficial to reducing the agglomeration and sintering of the adsorbent. At the same time, Figure 4 , Figure 5 pointed out that compared with the other four groups of experiments, the hydrogen production and cold gas efficiency of #1-2 are the highest.

[0070] From Figure 7 It can be seen that the calcium-based adsorbents doped with Al and Co are both very stable. Compared with #2-1 (i.e., #1-2), the carbonation degrees of #2-2, #2-3, and #2-4 have all increased, reaching 74%, 70%, and 64% respectively. The increase in the Co doping ratio results in a decrease in the carbonation degree. Figure 9 shows the hydrogen production under different Co doping ratios. Co has a catalytic effect on reactions such as coke gasification, methane reforming, tar cracking, and water-gas shift, so the hydrogen production gradually increases. However, with the increase in Co loading, the adsorption of carbon dioxide is inhibited, so the proportion of hydrogen decreases and the proportion of carbon dioxide increases. At 650 °C, the influence of the Co doping ratio on the cold gas efficiency is relatively small, basically within the range of 33.2% - 33.6%. But at 700 °C and 750 °C, with the increase in the Co ratio, the cold gas efficiency also increases, reaching 44.4%, 50.8%, and 55.4% respectively. Compared with the adsorbent without Co addition, both the hydrogen production and cold gas efficiency have been significantly improved.

[0071] Therefore, the calcium-based adsorbent for sludge gasification to produce hydrogen-rich syngas of the present invention has more stable cycle performance, maintains a relatively high carbonation degree and activity. When applied to sludge gasification to produce hydrogen-rich syngas, it can effectively increase the hydrogen concentration and cold gas efficiency of the syngas, achieving the effect of efficient sludge gasification.

Claims

1. A calcium-based adsorbent for sludge gasification to produce hydrogen-rich syngas, characterized in that: The calcium-based adsorbent includes an active adsorbent, a supporting material and an auxiliary agent, wherein the active adsorbent is CaO, the supporting material is one of Al2O3, La2O3 or ZrO2, and the auxiliary agent is CoO.

2. The calcium-based adsorbent according to claim 1, characterized in that The calcium-based adsorbent, calculated based on the total weight percentage of the composite material, has a CaO content of 65-75%, a supporting material content of 20%, and a CoO content of 5-15%.

3. A method for preparing the calcium-based adsorbent according to claim 1, characterized in that: The following steps are involved: (1) Mix the precursor of Ca, the precursor of the support material and the precursor of Co, add citric acid and water to mix evenly, heat and stir in a water bath until a sol-gel is formed, and stop stirring; (2) The mixture is placed at room temperature, fully dried, calcined, ground and sieved to obtain a calcium-based adsorbent for sludge gasification to produce hydrogen-rich synthesis gas.

4. The preparation method according to claim 3, characterized in that: In step (1), the mass ratio of the precursor of Ca, the precursor of the supporting material and the precursor of Co is 13-25:4:1-3.

5. The preparation method according to claim 4, characterized in that: The precursor of Ca is Ca(NO3)2·4H2O, the precursor of Al is Al(NO3)3·9H2O, the precursor of La is La(NO3)3·6H2O, the precursor of Zr is Zr(NO3)2·5H2O, and the precursor of Co is Co(NO3)2·6H2O.

6. The preparation method according to claim 3, characterized in that: In step (1), Ca 2+ 、Co 2+ 、Al 3+ ,La 3+ 、Zr 2+ The molar ratio of all metal cations to water is 1:10, and the molar ratio of all metal cations to citric acid is 1:2; the water bath heating temperature is 80-85°C.

7. The preparation method according to claim 3, characterized in that: In step (2), the drying temperature is 100-110°C.

8. The preparation method according to claim 3, characterized in that: In step (2), the calcination is performed by pre-calcining at 300-350° C. for 1-1.5 h, and then the temperature is raised to 700-750° C. for calcination for 2-3 h.

9. An application of the calcium-based adsorbent according to claim 1 in sludge gasification to produce hydrogen-rich synthesis gas, characterized in that: The mass ratio of calcium-based adsorbent to sludge is 0.4 to 0.

6.

10. The application according to claim 9, wherein the application is to carry out gasification in a gasification reactor, the reaction conditions are 700-750°C, 35-40 min, the reaction atmosphere is 15% CO2+85% N2, and the gas flow rate is 0.1-0.3 L / min; thereafter, entering a regeneration reactor, the reaction conditions are 850-900°C, 20-25 min, the reaction atmosphere is 100% N2, and the gas flow rate is 0.1-0.3 L / min, and the cyclic reaction is obtained.

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