Difunctional copper-based composite oxygen carrier as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of combustion chemical industry and materials, and particularly relates to a difunctional copper-based composite oxygen carrier and a preparation method and application thereof. The oxygen carrier is composed of a CuO active component, a CaO additive and a ZrO2 inert carrier; based on the total mass percentage of the composite oxygen carrier, the content of CuO is 62.5-65 wt%, the content of CaO is 5-7.5 wt%, and the content of ZrO2 is 30 wt%. According to the preparation method of the bifunctional copper-based composite oxygen carrier, the prepared composite oxygen carrier is large in specific surface area and high in reaction activity, has the dual functions of medium and low temperature catalytic cracking and in-situ dechlorination, and is suitable for the garbage chemical chain oxygen decoupling combustion synergistic dechlorination process.

Description

Technical Field

[0001] The present invention belongs to the technical field of combustion chemical engineering and materials, and particularly relates to a bifunctional copper-based composite oxygen carrier and its preparation method and application. Background Art

[0002] Chemical looping oxygen uncoupling combustion is a new combustion technology based on the cyclic oxygen supply of metal oxygen carriers. The cyclic use of the oxygen carrier provides cheap active oxygen for combustion. By controlling the ratio of the oxygen carrier to the fuel, the complete conversion of energy elements is achieved, and the combustion efficiency is high. In addition, this technology avoids the direct contact between the fuel and air, significantly reduces the generation probability of NOx, Cl2 and dioxins, and has the advantage of internal separation of CO2, greatly reducing the difficulty and cost of CO2 separation and capture.

[0003] Copper-based oxygen carriers have high oxygen transport capacity, high oxygen generation rate, and high reactivity, and can use cheap and easily available copper smelting waste slag, copper ore, etc. as the precursor for preparing the oxygen carrier. Therefore, they are widely used in chemical looping oxygen uncoupling combustion. However, compared with other solid fuels, garbage usually contains a relatively high chlorine component. With the wide use of chlorine-containing disinfectants as household disinfection products, future domestic waste is very likely to be in a chlorine-rich state. As is well known, chlorine elements in fuels can significantly promote the formation of heavy metal chloride volatiles with low boiling points and high vapor pressures, such as Pb, Cd, and Cu, during the thermal conversion process. In the process of chemical looping oxygen uncoupling combustion based on copper-based oxygen carriers, the interaction reaction between copper oxide and its reduction products and chlorine not only induces the loss of volatile chlorides of active components of the oxygen carrier (such as gaseous volatile CuCl and complex Cu3Cl3) and irreversible solid-state chlorination, but also the competition between energy elements and chlorine for active sites will promote the unbalanced diffusion of copper ions and oxygen ions, exacerbating the aggregation and sintering of cations on the surface of the oxygen carrier particles. The above behaviors greatly reduce the combustion efficiency of high-chlorine domestic waste chemical looping oxygen uncoupling combustion, as well as the reactivity and service life of the oxygen carrier. In addition, the unfixed chlorine elements will also enter the combustion tail gas in the form of gaseous HCl, posing a potential threat to the subsequent carbon dioxide capture equipment. Therefore, it is necessary to scientifically and reasonably regulate and modify the copper-based oxygen carrier to prepare a new type of copper-based composite oxygen carrier. This composite oxygen carrier can not only inhibit the loss of active components of the copper-based oxygen carrier due to chlorination and poisoning inactivation, but also improve the oxygen uncoupling combustion efficiency and efficiently purify HCl. Summary of the Invention

[0004] In order to solve the problems such as the loss of active components due to chlorination and the decline of combustion efficiency in the process of chemical looping oxygen uncoupling combustion of high-chlorine domestic waste based on copper-based oxygen carriers, the primary object of the present invention is to provide a bifunctional copper-based composite oxygen carrier. This composite oxygen carrier can inhibit the loss of active components due to chlorination, improve the low-temperature catalytic cracking ability of the oxygen carrier, and achieve the goal of improving the oxygen uncoupling combustion efficiency and synergistic dechlorination.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned dual-functional copper-based composite oxygen carrier.

[0006] Another object of the present invention is to provide the application of the above-mentioned dual-functional copper-based composite oxygen carrier.

[0007] The object of the present invention is achieved by the following technical solutions:

[0008] The present invention first discloses a dual-functional copper-based composite oxygen carrier, which is composed of a CuO active component, a CaO additive and a ZrO2 inert carrier; calculated by the total mass percentage of the composite oxygen carrier, the content of CuO is 62.5-65 wt%, the content of CaO is 5-7.5 wt%, and the content of ZrO2 is 30 wt%.

[0009] Preferably, the content of CuO is 62.5 wt%, the content of CaO is 7.5 wt%, and the content of ZrO2 is 30 wt%.

[0010] The present invention also discloses a method for preparing a dual-functional copper-based composite oxygen carrier, which includes the following steps:

[0011] 1) Disperse nano-ZrO2 in water, then add a copper source and a calcium source, and stir until evenly mixed;

[0012] 2) After adjusting the pH value of the mixed solution, heat and stir the mixed solution until a viscous substance is formed, and then subject the viscous substance to air drying and segmented high-temperature calcination to obtain a CuO@CaO / ZrO2 copper-based composite oxygen carrier, that is, the above-mentioned dual-functional copper-based composite oxygen carrier.

[0013] Furthermore, in step 1), nano-ZrO2 is dispersed in water by stirring and ultrasonic oscillation, the stirring temperature is room temperature, and the time is 1-2 h; the ultrasonic oscillation frequency is 40 kHz, and the time is 0.5-1 h. The preferred stirring time is 1 h, and the preferred oscillation time is 0.5 h.

[0014] Furthermore, in step 1), the copper source and the calcium source are Cu(NO3)2·3H2O and Ca(CH3COO)2·H2O respectively, and the mass ratio of ZrO2, Cu(NO3)2·3H2O and Ca(CH3COO)2·H2O is 30:(189.94-197.53):(15.73-23.60). The preferred mass ratio is 30:189.94:23.60.

[0015] Furthermore, the stirring temperature in step 1) is room temperature, and the time is 1-2 h. The preferred stirring time is 2 h.

[0016] Further, an appropriate amount of NH3·H2O solution is added in step 2) to adjust the pH value. The NH3·H2O solution is an ammonia water solution with a concentration of 25 wt%, and the addition amount is 1 / 10 of the water consumption in step 1); the ultrasonic oscillation frequency is 40 kHz, and the time is 0.5 - 1 h. The preferred oscillation time is 0.5 h.

[0017] Further, the temperature of the heating and stirring in step 2) is 60 - 90 °C, and the time is 2 - 12 h; the air drying temperature is 105 - 120 °C, and the time is 6 h - 12 h. The preferred heating temperature is 70 °C, the preferred heating time is 8 h, the preferred air drying temperature is 105 °C, and the preferred drying time is 6 h.

[0018] Further, the staged high-temperature calcination in step 2) is the first stage at 500 °C for 2 h; the second stage at 950 °C for 2 h.

[0019] Further, the product obtained after calcination in step 2) is also ground and sieved. The sieving is through a 40 - 80 mesh sieve, preferably through a 60 mesh sieve.

[0020] The present invention also discloses the application of the above-mentioned bifunctional CuO@CaO / ZrO2 copper-based composite oxygen carrier in the chemical looping oxy-fuel combustion and co-dechlorination of municipal solid waste.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] Compared with the traditional ordinary mechanical method or the copper-based composite oxygen carrier without adding CaO, a bifunctional CuO@CaO / ZrO2 copper-based composite oxygen carrier prepared by the present invention has a larger specific surface area and higher reaction activity. By introducing CaO active sites, this composite oxygen carrier can inhibit the chloride loss of the active components of the copper-based oxygen carrier while enabling it to have the dual capabilities of mid-low temperature catalytic cracking and efficient cyclic dechlorination. This characteristic makes the composite oxygen carrier of the present invention more suitable for the chemical looping oxy-fuel combustion process of high-chlorine municipal solid waste. Description of the Drawings

[0023] Figure 1 XRD spectra of three copper-based composite oxygen carriers prepared in Example 1, Comparative Example 1, and Comparative Example 2 in the fresh state (a) and after 10 cycles of redox reactions (b).

[0024] Figure 2 XRD spectra of three copper-based composite oxygen carriers prepared in Example 1, Comparative Example 1, and Comparative Example 2 and municipal solid waste (1:30) after 1 reduction reaction (a) and after 10 cycles of redox reactions (b).

[0025] Figure 3H2-TPR spectra of three copper-based composite oxygen carriers prepared in Example 1, Comparative Example 1, and Comparative Example 2.

[0026] Figure 4 TG (a) and DTG diagrams of the thermal weight loss of three copper-based composite oxygen carriers prepared in Example 1, Comparative Example 1, and Comparative Example 2 and garbage (1:30). Detailed implementation manners

[0027] The present invention will be further described in detail below in conjunction with examples and drawings, but the implementation manners of the present invention are not limited thereto. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the technical field. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0028] Example 1

[0029] Weigh 3.0 g of nano-ZrO2 (particle size ≤ 100 nm) and 100 mL of deionized water and add them to a beaker. Then, stir magnetically at a speed of 300 rpm for 1 h at room temperature and ultrasonically oscillate at a frequency of 40 kHz for 30 min to uniformly disperse the nano-ZrO2 in the deionized water, obtaining a mixed solution for standby. Add 18.994 g of Cu(NO3)2·3H2O and 2.360 g of Ca(CH3COO)2·H2O to the mixed solution and stir magnetically at a speed of 300 rpm for 2 h at room temperature. While stirring, slowly add 10 mL of an NH3·H2O solution with a mass concentration of 25 wt% to the mixed solution, and then ultrasonically oscillate again at a frequency of 40 kHz for 30 min. Heat to 70 °C in a magnetic stirring heater and stir magnetically at a speed of 300 rpm for 8 h until a viscous substance is formed. Place the viscous substance in an air drying oven at 105 °C and dry it for 6 h, then transfer it to a muffle furnace, heat it at a heating rate of 4 °C / min to 500 °C, calcine for 2 h, and then heat it to 950 °C and calcine for 2 h. Grind evenly and pass through a 60-mesh sieve to obtain a CuO@CaO / ZrO2 copper-based composite oxygen carrier (the contents of CuO and CaO in this oxygen carrier are 62.5% and 7.5% respectively).

[0030] Comparative Example 1

[0031] Compared with Example 1, in this example, a conventional mechanical mixing method was used to prepare the CuO-CaO / ZrO2 composite oxygen carrier. The specific steps are as follows: Weigh 6.25 g of CuO (analytical pure, ≥99%), 0.75 g of CaO (analytical pure, ≥98%), and 3.0 g of ZrO2 (analytical pure, ≥99%) and add them to a beaker containing 100 mL of deionized water. Heat to 70 °C in a magnetic stirring heater and magnetically stir at a speed of 300 rpm for 8 h until a viscous substance is formed. Place it in an air drying oven at 105 °C and dry for 6 h, then transfer it to a muffle furnace, heat it at a heating rate of 4 °C / min to 500 °C, calcine for 2 h, and then heat it to 950 °C and calcine for 2 h. Grind it evenly and pass through a 60-mesh sieve to obtain the CuO-CaO / ZrO2 copper-based composite oxygen carrier.

[0032] Comparative Example 2

[0033] Compared with Example 1 and Comparative Example 1, in this example, SiO2 (analytical pure, ≥99.99%) was used as an additive to replace CaO in Comparative Example 1. As a commonly used inert material, SiO2 has been proven not to interact with the active component CuO. The specific process is the same as that in Comparative Example 1, and finally, the CuO-SiO2 / ZrO2 composite oxygen carrier was prepared.

[0034] The copper-based composite oxygen carriers prepared in the above examples and comparative examples were placed in a fixed bed at a temperature of 950 °C for 1 cycle of oxidation-reduction reaction. The gas in the reduction stage was N2, with a flow rate of 200 mL / min and a time of 20 min; the gas in the oxidation stage was air, with a flow rate of 200 mL / min and a time of 20 min. Repeat the above process 10 times to obtain the copper-based composite oxygen carrier after 10 cycles of oxidation-reduction reaction.

[0035] Using municipal solid waste (the main component content is shown in Table 1) as fuel and the copper-based composite oxygen carrier prepared in the above example, a chemical looping oxygen uncoupling combustion cycle reaction was carried out in a fixed bed at a temperature of 950 °C. The mass ratio of the waste to the composite oxygen carrier was 1:30. The gas in the reduction stage was N2, with a flow rate of 200 mL / min and a time of 20 min; the gas in the oxidation stage was air, with a flow rate of 200 mL / min and a time of 20 min. Repeat the above process 10 times to obtain the copper-based composite oxygen carrier after 1 reduction reaction with the waste and 10 cycles of oxidation-reduction reaction.

[0036] Table 1

[0037] C％ H％ O％ N％ S％ Cl％ Ash content Municipal solid waste 43.13 6.04 28.54 5.47 1.60 5.66 9.56

[0038] Note: The contents in the table are mass fractions.

[0039] The fresh and reacted copper-based oxygen carriers prepared in the above embodiments were characterized by X-ray diffractometer (XRD), hydrogen temperature-programmed reduction (H2-TPR), and a fully automatic specific surface area and porosity analyzer.

[0040] The XRD analysis results of the three copper-based oxygen carriers prepared in Example 1, Comparative Example 1, and Comparative Example 2 in the fresh state, after 10 cycles of redox reactions, after 1 reduction reaction with refuse, and after 10 cycles of redox reactions are shown in Figure 1 - Figure 2 : Compared with Comparative Example 2, the CuO crystal phase positions of the fresh and re-oxidized copper-based oxygen carriers in Example 1 and Comparative Example 1 are exactly the same, and no new phases of Cu-Ca interaction reaction are detected. In addition, the active component CuO can be completely transformed into Cu2O after the reduction reaction with refuse. These results indicate that the addition of CaO does not interact with the active component CuO and does not affect the transformation between CuO and Cu2O. The bifunctional copper-based oxygen carrier prepared in the present invention effectively ensures the oxygen decoupling ability of CuO.

[0041] The H2-TPR test results of the three copper-based oxygen carriers prepared in Example 1, Comparative Example 1, and Comparative Example 2 are shown in Figure 3 . It can be seen from the figure that compared with Comparative Example 2, the number of CuO reduction peaks in Example 1 and Comparative Example 1 changed from two to one, and the peak temperature of the reduction peak decreased significantly from 376 °C to 254 °C and 255 °C. This shows that the addition of CaO not only highly disperses the active component CuO in the oxygen carrier but also improves the reaction activity of the oxygen carrier.

[0042] The BET specific surface area test results of the three copper-based oxygen carriers prepared in Example 1, Comparative Example 1, and Comparative Example 2 are shown in Table 2. It can be seen that the BET specific surface area of Example 1 is 3.87 times and 2.75 times that of Comparative Example 1 and Comparative Example 2, respectively. After 10 cycles, the BET specific surface area of Example 1 only decreased by 21.77%, while those of Comparative Example 1 and Comparative Example 2 decreased by 50.16% and 44.33%, respectively. The bifunctional copper-based oxygen carrier prepared in the present invention not only has a large specific surface area but also can maintain a good specific surface area during the cyclic reaction, which is beneficial for the oxygen carrier to maintain good reaction activity.

[0043] Table 2

[0044]

[0045] The comprehensive thermogravimetric analyzer (TGA) was used to conduct the chemical looping oxy-combustion test of the garbage. Weigh 15 ± 0.1 mg of the fully pre-mixed garbage-copper-based oxygen carrier sample (1:30) and place it in an alumina crucible. TGA was heated from 30 °C to 950 °C in a nitrogen environment (80 mL / min) at a heating rate of 20 °C / min and kept at a constant temperature of 950 °C for 40 min. Subsequently, the reaction atmosphere was switched to air (80 mL / min) and maintained at 950 °C for another 40 min. The TGA test results of the reaction between the copper-based composite oxygen carrier prepared in the above examples and comparative examples and the garbage are shown in Figure 4 . The TGA test results showed that there were two weight loss peaks in Comparative Example 2 in the medium and low temperature reaction range of 300 - 650, while only one weight loss peak was observed in Example 1 and Comparative Example 1 with the addition of CaO. The maximum weight loss peak rates of Example 1 and Comparative Example 1 were -0.25% / min and -0.26% / min respectively, which were higher than the maximum weight loss peak rate of -0.21% / min in Comparative Example 2. This result indicated that the introduction of CaO improved the medium and low temperature catalytic cracking ability of the composite oxygen carrier.

[0046] The tail gas of the chemical looping oxy-combustion of the garbage was introduced into an absorption bottle containing an absorption solution composed of 0.01 mol·L -1 Na2CO3 and 0.01 mol·L -1 NaHCO3 to absorb the chlorides in the flue gas. The absorption solution was added with deionized water to a constant volume of 50 mL, and then the chloride ion concentration in the absorption solution was detected by the ShengHan ion chromatograph. The dechlorination efficiency of the copper-based composite oxygen carrier prepared in the above examples and comparative examples was calculated by the following formula, and the cyclic dechlorination efficiency is shown in Table 3.

[0047]

[0048] Table 3

[0049]

[0050] Note: "-" represents that the experiment was not carried out.

[0051] It can be found from Table 3 that the first reaction dechlorination efficiency of Comparative Example 2 is only 4.4%, indicating that the -CuO-SiO2 / ZrO2 composite oxygen carrier with added SiO2 does not have the ability of synergistic dechlorination during combustion. The first dechlorination efficiencies of Example 1 and Comparative Example 1 are 87.3% and 70.3% respectively, indicating that CuO@CaO / ZrO2 and CuO-CaO / ZrO2 with added CaO have the ability of synergistic dechlorination during combustion. However, further, with the progress of the chemical looping oxygen decoupling combustion cycle reaction, the dechlorination efficiency of Comparative Example 1 drops sharply from 70.3% to 5.1% (the fifth time); while that of Example 1 only decreases from 87.3% to 70.2%, still maintaining a relatively high dechlorination efficiency. This shows that the CuO@CaO / ZrO2 copper-based composite oxygen carrier prepared by the present invention has stable cyclic high-efficiency dechlorination ability.

[0052] In summary, a bifunctional CuO@CaO / ZrO2 copper-based composite oxygen carrier prepared by the present invention not only has a large specific surface area and high reaction activity, but also has the dual abilities of medium and low temperature catalytic cracking and cyclic high-efficiency dechlorination, making it better suitable for the chemical looping oxygen decoupling combustion process of high-chlorine domestic waste.

[0053] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A bifunctional copper-based composite oxygen carrier, characterized in that, The oxygen carrier is composed of a CuO active component, a CaO additive, and a ZrO2 inert carrier; based on the total mass percentage of the composite oxygen carrier, the content of CuO is 62.5 - 65 wt%, the content of CaO is 5 - 7.5 wt%, and the content of ZrO2 is 30 wt%.

2. The bifunctional copper-based oxygen carrier according to claim 1, characterized in that, The content of CuO is 62.5 wt%, the content of CaO is 7.5 wt%, and the content of ZrO2 is 30 wt%.

3. The preparation method of a bifunctional copper-based oxygen carrier according to claim 1 or 2, characterized in that, It includes the following steps: 1) Disperse nano-ZrO2 in water, then add a copper source and a calcium source, and stir until evenly mixed; 2) After adjusting the pH value of the mixed solution, heat and stir the mixed solution until a viscous substance is formed, and then subject the viscous substance to air drying and staged high-temperature calcination to obtain a CuO@CaO / ZrO2 copper-based composite oxygen carrier, that is, the bifunctional copper-based composite oxygen carrier.

4. The preparation method according to claim 3, characterized in that, In step 1), the copper source and the calcium source are respectively Cu(NO3)2·3H2O and Ca(CH3COO)2·H2O, and the mass ratio of ZrO2, Cu(NO3)2·3H2O, and Ca(CH3COO)2·H2O is 30:(189.94 - 197.53):(15.73 - 23.60).

5. The preparation method according to claim 3, characterized in that, In step 1), the mass ratio of ZrO2, Cu(NO3)2·3H2O, and Ca(CH3COO)2·H2O is 30:189.94:23.

60.

6. The preparation method according to claim 3, characterized in that, In step 2), an appropriate amount of NH3·H2O solution is added to adjust the pH value. The NH3·H2O solution is a 25 wt% ammonia water solution, and the addition amount is 1 / 10 of the water consumption in step 1; the ultrasonic oscillation frequency is 40 kHz, and the time is 0.5 - 1 h.

7. The preparation method according to claim 3, characterized in that, In step 2), the temperature of the heating and stirring is 60 - 90 °C, and the time is 2 - 12 h; the air drying temperature is 105 - 120 °C, and the time is 6 h - 12 h.

8. The preparation method according to claim 7, characterized in that, The temperature of the heating and stirring is 70 °C, and the time is 8 h.

9. The preparation method according to claim 3, characterized in that, The staged high-temperature calcination in step 2) is the first stage at 500 °C for 2 h; the second stage at 950 °C for 2 h.

10. Application of the bifunctional copper-based composite oxygen carrier according to claim 1 or 2 in the chemical looping oxygen uncoupling combustion and co-dechlorination of garbage.

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