Selenium-doped copper-cobalt bimetallic sulfide demercuration adsorbent as well as preparation method and application thereof

Abstract

The invention provides a selenium-doped copper-cobalt bimetallic sulfide demercuration adsorbent and a preparation method and application thereof, CuCo2S4 of a spinel structure is used as a main body of the demercuration adsorbent, selenium is doped to form Se-Sn2-active sites, and the doping molar ratio of selenium is 2.5%-12.5%. The preparation process of the adsorbent comprises the following steps: dissolving cobalt salt, copper salt and trisodium citrate dehydrate into deionized water, performing ultrasonic treatment, performing microwave irradiation in a microwave synthesizer, and dropwise adding an aqueous solution containing Na2S and SeO2. After cooling to room temperature, centrifuging, washing and drying to obtain a sample. The problems that traditional metal sulfide is poor in stability and not easy to regenerate are solved, the preparation method is simple, the large-scale preparation cost is low, the method can be directly applied to removal of mercury in natural gas, and the cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the field of environmental pollution control, and particularly relates to a selenium-doped copper-cobalt bimetallic sulfide mercury removal adsorbent, its preparation method and application, which are applicable to the efficient purification of natural gas. Background Art

[0002] As a clean and efficient energy source, natural gas plays an important role in the global energy transition. However, natural gas often coexists with different forms of mercury, including gaseous elemental mercury (Hg 0 ), organic mercury and inorganic mercury compounds. The presence of mercury not only pollutes the environment but also seriously affects the safety and production efficiency of industrial equipment. Mercury can undergo amalgamation reactions with various metals, especially having strong corrosiveness to the aluminum heat exchangers in liquefied natural gas (LNG) plants, which may lead to equipment perforation and gas leakage. In addition, during the natural gas chemical process, mercury will poison the catalyst, occupy the active sites, reduce the reaction efficiency and affect the product quality.

[0003] Currently, the international control technologies for natural gas mercury pollution mainly include cryogenic separation, solution absorption, chemical adsorption, membrane separation, etc. Among them, cryogenic separation technology is more widely used in LNG plants, but the problem of secondary pollution is more serious. Although the solution absorption method has simple equipment, it is easy to produce mercury-containing waste liquid with high treatment costs. Membrane separation technology is still in the research stage and is limited in industrial applications. Chemical adsorption method has become the most mainstream mercury removal technology due to its high efficiency and wide applicability. Common mercury removal adsorbents include activated carbon, molecular sieve, metal oxide and metal sulfide, etc. Among them, metal sulfide has received extensive attention in recent years because of its rich sulfur active sites on the surface, which can efficiently capture Hg 0 and convert it into stable HgS.

[0004] In view of the deficiencies of the existing mercury removal technologies, the present invention develops a highly efficient mercury removal adsorbent of selenium-doped copper-cobalt sulfide, and optimizes the selenium doping ratio to improve the mercury removal performance and stability of the adsorbent. The present study uses microwave synthesis method to prepare this adsorbent, studies the effects of different preparation conditions on the material structure and mercury removal performance, and further explores the regenerability of the adsorbent, aiming to achieve the efficient recycling of the adsorbent and provide theoretical and technical support for the development of natural gas mercury removal technology. Summary of the Invention

[0005] The present invention provides a highly efficient selenium-doped copper-cobalt bimetallic sulfide adsorbent, and optimizes the selenium doping ratio to improve the mercury removal effect. This adsorbent is prepared by microwave synthesis method, has high mercury removal efficiency and regenerability, and is applicable to natural gas mercury removal.

[0006] The inventive concept of the present invention is as follows: The unique electronic effect and synergistic effect of bimetallic sulfides (such as CuCo2S4) can not only improve the thermal stability of the adsorbent, enhance the mercury capture ability, but also broaden the applicable temperature range. From the aspects of mercury affinity and chemical stability, selenium sulfide forms Se-Sn 2- active sites through the synergy of sulfur and selenium, significantly enhancing the affinity for mercury, and the generated mercury compounds have high stability. The solubility product of HgSe is much lower than that of HgS, and the Se-Sn 2- active sites are not easily decomposed at high temperatures and can maintain high-efficiency adsorption in a relatively wide temperature range.

[0007] The technical solution adopted by the present invention is as follows:

[0008] A selenium-doped copper-cobalt bimetallic sulfide adsorbent for natural gas mercury removal, which is prepared by a microwave synthesis method, with spinel-structured CuCo2S4 as the main body, and selenium element is doped to form Se-Sn 2- active sites, where the doping molar ratio of selenium is 2.5% to 12.5%.

[0009] Furthermore, the particle size of the catalyst is 60-100 mesh.

[0010] As a preferred embodiment, the doping ratio of selenium is 10%, and the mercury removal efficiency of the corresponding adsorbent is not less than 90% in the temperature range of 40°C - 200°C.

[0011] Another object of the present invention is to claim the preparation method of the above mercury removal adsorbent, including the following steps:

[0012] a. Dissolve copper salt, cobalt salt and citrate in deionized water, and perform ultrasonic treatment to form a transparent mixed solution; b. Dissolve the sulfur source and selenium source in deionized water respectively;

[0013] c. Transfer the mixed solution in step a to a microwave reactor, microwave for 5-20 minutes at a power of 600-800W and a temperature of 90-95°C, and dropwise add the sulfur source solution and selenium source solution; the molar ratio of the selenium source to non-metals is 2.5% - 12.5%;

[0014] d. After the reaction is completed, cool to room temperature, centrifuge the product, wash it with deionized water and ethanol, and dry it at 60-80°C for 12 hours to obtain the selenium-doped copper-cobalt bimetallic sulfide adsorbent.

[0015] Preferably, the sulfur source is Na2S and the selenium source is SeO2.

[0016] The copper salt is preferably a hydrate of a copper-containing compound, more preferably CuSO4·5H2O; the cobalt salt is preferably a hydrate of a cobalt-containing compound, more preferably CoCl2·6H2O, and the citrate is preferably trisodium citrate dihydrate.

[0017] Preferably, the microwave irradiation time is preferably 20 minutes, the microwave power is 700 W, and the reaction temperature is 90 °C.

[0018] As a preferred embodiment of the present invention, a preparation method of a selenium-doped copper-cobalt bimetallic sulfide adsorbent for natural gas mercury removal includes the following steps:

[0019] 1) Dissolve CoCl2·6H2O, CuSO4·5H2O with a molar ratio of 1:1 and an excess of trisodium citrate dihydrate in deionized water, and ultrasonically treat for 30 min at room temperature to obtain a transparent solution.

[0020] 2) Dissolve Na2S and SeO2 in deionized water respectively, and stir with a magnetic stirrer for 30 min.

[0021] 3) Transfer the transparent mixed solution obtained in step 1) to a 250 ml round-bottom flask, and microwave at a power of 600 - 800 w at 90 - 95 °C for 5 - 20 min in a microwave synthesizer, and dropwise add an aqueous solution containing Na2S and an aqueous solution of SeO2.

[0022] 4) After the reaction mixture is maintained for 30 minutes, cool it to room temperature. Centrifuge the product, and wash it three times with deionized water and ethanol respectively; dry the obtained solid at 70 °C for 12 h to obtain an adsorbent mainly composed of spinel-structured CuCo2S4. Grind the above sample to 60 - 100 mesh to obtain the required selenium-doped copper-cobalt bimetallic sulfide adsorbent.

[0023] The present invention also claims the application of the above selenium-doped copper-cobalt bimetallic sulfide adsorbent, especially suitable for the efficient removal of gaseous mercury in natural gas.

[0024] The specific application conditions include: the simulated natural gas flow rate is 1 L / min. The gases used in the experiment include N2, CH4 and CO2 (concentrations are all ≥99.999%), O2 (N2 - 1% O2) and H2S (N2 - 1% H2S), containing CH4, 0 - 1600 ppm O2, 0 - 1000 ppm H2S, and 0 - 8% CO2, with N2 as the balance gas, and the space velocity ratio (GHSV) is set to 1.13×10 6 h -1 , the temperature range for the reaction test is 30 - 200 °C, more preferably 40 - 200 °C, and the initial mercury concentration is 25 - 150 μg / m 3 , preferably the initial mercury concentration is 50 μg / m 3 .

[0025] The beneficial effects that can be significantly achieved by the solution of the present invention compared with the prior art are as follows:

[0026] (1) The present invention improves the mercury adsorption performance through a simple modification method, solves the problem of poor thermal stability of metal sulfides, and has a larger adsorption capacity. The material prepared by the present invention is not only suitable for mercury removal in low-temperature environments, but also has good performance under high-temperature conditions, broadens the mercury removal temperature window, and the material has good mercury removal efficiency in a wide temperature window, which is more in line with the actual application conditions and reduces the actual use cost.

[0027] (2) The selenium-doped copper-cobalt bimetallic sulfide adsorbent obtained by the preparation method of the present invention has low production cost, good reproducibility, and can be regenerated, and there is no problem of secondary pollution when using the mercury removal agent. It has long cycle stability, high active sites, and a large active surface area. The mercury removal efficiency of the adsorbent is not less than 95% during 72 hours of continuous operation, and it has potential application value in natural gas mercury removal. Description of the Drawings

[0028] Figure 1 It is the influence of Se doping on the mercury removal performance;

[0029] Figure 2 It is the influence of the initial mercury concentration on the mercury removal performance of the adsorbent with different microwave durations;

[0030] Figure 3 It is the influence of different reaction temperatures on the mercury removal performance of 20-0.1Se-M-11;

[0031] Figure 4 It is the influence of gas components on the mercury removal performance of 20-0.1Se-M-11. Detailed Embodiments

[0032] The following are specific embodiments of the present invention, which further describe the technical solutions of the present invention, but do not limit the present invention accordingly. The following non-limiting embodiments can enable those of ordinary skill in the art to more comprehensively understand the present invention, but do not limit the present invention in any way.

[0033] The test methods described in the following embodiments are all conventional methods unless otherwise specified; the reagents and materials are all commercially available unless otherwise specified.

[0034] Unless otherwise defined, technical or scientific terms used in the present invention shall have the ordinary meanings as understood by those of ordinary skill in the art to which the present invention pertains. The use of the term "a" or "an" in the present invention does not exclude a plurality. Words such as "comprising" or "including" mean that the elements or items appearing before this word cover the elements or items listed after this word and their equivalents, without excluding other elements or items.

[0035] For easier understanding of the present invention, certain technical and scientific terms are specifically defined below. Unless otherwise clearly defined elsewhere in this document, all other technical and scientific terms used herein have the meanings commonly understood by those of ordinary skill in the art to which the present invention pertains.

[0036] In the present invention, an adsorbent with a spinel-structured CuCo2S4 as the main body. This sample is named M-11.

[0037] After adding Na2S, different proportions of SeO2 are added dropwise, and the obtained samples are named xSe-M-11 respectively, where x = 0.025 - 0.125.

[0038] 0.025Se-M-11 represents an adsorbent with a Se doping amount of 2.5%;

[0039] 0.05Se-M-11 represents an adsorbent with a Se doping amount of 5%;

[0040] ...And so on.

[0041] 10-0.1Se-M-11 represents an adsorbent with a Se doping amount of 10% and a microwave duration of 10 min;

[0042] 15-0.1Se-M-11 represents an adsorbent with a Se doping amount of 10% and a microwave duration of 15 min;

[0043] 20-0.1Se-M-11 represents an adsorbent with a Se doping amount of 10% and a microwave duration of 20 min;

[0044] The present invention selects a selenium-doped copper-cobalt bimetallic sulfide adsorbent as a mercury removal adsorbent. The simulated natural gas flow rate is 1 L / min. The gases used in the experiment include N2, CH4, and CO2 (concentrations are all ≥ 99.999%), O2 (N2 - 1% O2), and H2S (N2 - 1% H2S), containing CH4, 0 - 1600 ppm O2, 0 - 1000 ppm H2S, and 0 - 8% CO2, with N2 as the balance gas, and the space velocity ratio (GHSV) is set to 1.13×10 6 h -1 , and the temperature range for the reaction test is 40 - 200 °C.

[0045] The mercury removal performance of the adsorbent is evaluated by two indicators: mercury removal efficiency and average mercury removal efficiency. The specific calculation methods are as follows:

[0046] Mercury removal efficiency:

[0047] (1 - C t / C0) × 100%

[0048] Average mercury removal efficiency in 3 h:

[0049]

[0050] Wherein, C0 and C t , are the Hg 0 concentration at the inlet of the quartz reaction tube and the Hg 0 concentration at the outlet of the quartz reaction tube at time t, respectively, μg / m 3 . t is the adsorption time, in minutes.

[0051] Example 1

[0052] The preparation method of selenium-doped copper cobalt sulfide provided in this example includes the following steps:

[0053] (1) Dissolve 1 mmol of CuSO4·5H2O, 1 mmol of CoCl2·6H2O, and 3 mmol of trisodium citrate in 90 mL of deionized water, and ultrasonically stir for 30 min.

[0054] (2) In a microwave synthesizer, irradiate at a power of 700 W at 90 °C for 5 min, and dropwise add Na2S solution.

[0055] (3) After reacting for 5 min, cool to room temperature, centrifuge and separate, and wash three times with deionized water and ethanol.

[0056] (4) Dry at 70 °C for 12 h to obtain copper cobalt sulfide adsorbent M-11.

[0057] Perform a 3-h mercury removal test on M-11 at 40 °C with an initial mercury concentration of 50 μg / m 3 , under a N2 atmosphere. The average mercury removal rate in 3 h is 87%.

[0058] Example 2

[0059] The difference from Example 1 is that after dropping Na2S, different proportions of SeO2 are dropped, and the obtained samples are respectively named xSe-M-11. Grind the samples to 60 - 100 mesh to obtain the required selenium-doped copper cobalt bimetallic sulfide adsorbent.

[0060] The performance evaluations of M-11, 0.025Se-M-11, 0.05Se-M-11, 0.075Se-M-11, 0.1Se-M-11, and 0.125Se-M-11 materials were carried out respectively. As Figure 1 shown, the mercury adsorption and removal rate of the single M-11 adsorbent was 87%, and the mercury adsorption performance of the adsorbent was significantly enhanced after doping with Se. Especially when the Se doping amount was 10%, the 0.1Se-M-11 adsorbent had the best mercury removal performance, and the mercury removal rate was 98.4%.

[0061] Example 3

[0062] The difference from Example 1 was that the initial mercury concentration gradient was set to change as 25 μg / m 3 , 50 μg / m 3 , 100 μg / m 3 , 150 μg / m 3 , and the microwave duration was set to 10 min, 15 min, and 20 min.

[0063] The performance evaluations of the 10-0.1Se-M-11, 15-0.1Se-M-11, and 20-0.1Se-M-11 adsorbents were carried out respectively at the initial mercury concentrations of 25 μg / m 3 , 50 μg / m 3 , 100 μg / m 3 , 150 μg / m 3 to judge the applicable range of the materials. As Figure 2 shown, as the initial mercury concentration increased from 25 μg / m 3 to 150 μg / m 3 , the mercury removal performance of the adsorbent showed a trend of first increasing and then decreasing. When the initial mercury concentration was 50 μg / m 3 , the mercury removal efficiencies of the three adsorbents were all good, about 98%. When the microwave duration was 20 minutes, the mercury removal efficiency of the adsorbent remained above 90% within the initial mercury concentration range of 25 μg / m 3 -100 μg / m 3 , showing the best mercury removal performance.

[0064] Example 4

[0065] The difference from Example 1 was that the adsorbent was 20-0.1Se-M-11, and the mercury removal temperature was set to 30-200 °C.

[0066] The mercury removal performance of the best adsorbent 20-0.1Se-M-11 was tested within the wide temperature window range of 30-200 °C. As Figure 3As shown, with the gradual increase in temperature, the mercury removal efficiency of the 0.1Se-M-11 adsorbent first slowly rises and then falls. In the temperature range of 30°C to 80°C, the mercury removal efficiency gradually increases from 88.7% and finally approaches 98%. When the temperature is in the range of 80°C to 200°C, the mercury removal efficiency drops from 98% to 90%. However, in the broad temperature range of 40°C - 200°C, the mercury removal efficiency of the 0.1Se-M-11 adsorbent can still be maintained above 90%. Especially when the temperature is in the range of 40°C - 80°C, the mercury removal efficiency always remains at a high level. This indicates that the adsorbent has good stability in mercury removal performance within a certain temperature fluctuation range.

[0067] Example 5

[0068] The difference from Example 1 is that the adsorbent is 20 - 0.1Se-M-11, the reaction temperature is set at 30°C, and different reaction atmospheres are set.

[0069] In addition to low-carbon alkanes and trace oxygen in natural gas, there are also large amounts of CO2 and H2S, and the concentrations of these components vary depending on the origin and source of natural gas. As Figure 4 shown, in a pure N2 or CH4 atmosphere, the mercury removal efficiency of the 20 - 0.1Se-M-11 adsorbent is about 98%. When CO2 is introduced into the gas stream, the mercury removal efficiency of the 20 - 0.1Se-M-11 adsorbent decreases, but as the CO2 concentration continues to decrease, the mercury removal rate does not continue to decline. When H2S or O2 is added to the gas stream, the mercury removal rate does not decrease. In a simulated natural gas atmosphere, the mercury removal rate is about 99%, showing application prospects.

[0070] Example 6

[0071] The difference from Example 1 is that the adsorbent is 20 - 0.1Se-M-11, the reaction temperature is set at 30°C, the reaction duration is set at 72 h, and the atmosphere is a simulated natural gas atmosphere.

[0072] After 72 hours of continuous adsorption, the mercury removal performance of the adsorbent still remains above 95%, with strong stability.

[0073] Example 7

[0074] The difference from Example 1 is that the adsorbent is the regenerated 20 - 0.1Se-M-11 adsorbent after reaction, the reaction temperature is set at 30°C, and the atmosphere is a simulated natural gas atmosphere.

[0075] The steps of the adsorbent regeneration method are as follows: In an atmosphere of N2 and 400 ppm H2S, the mercury-adsorbed adsorbent is calcined at 350°C for 1 h for mercury removal testing. The mercury removal rate of the regenerated adsorbent is about 99%, and the mercury removal rate is still above 95% after 5 regenerations, indicating that the adsorbent has good regeneration performance.

[0076] Comparative Example 1

[0077] After continuous adsorption of M-11 for 72 hours, the mercury removal performance of the adsorbent decreased to less than 90%. Comparing with Example 6, it can be seen that the doping of an appropriate amount of Se improved the stability of the adsorbent.

[0078] Comparative Example 2

[0079] The adsorbent after mercury adsorption was calcined at 350 °C for 1 h, and the mercury removal rate of the regenerated adsorbent was 81%. Comparing with Example 7, it shows that thermal regeneration reduces the active sites of the adsorbent, while H2S replenishes the active sites of the adsorbent, and the adsorbent can be better regenerated in an atmosphere containing H2S.

Claims

1. A selenium-doped copper-cobalt bimetallic sulfide mercury removal adsorbent, characterized in that, The adsorbent uses CuCo2S4 with a spinel structure as the main material and dopes selenium element to form Se-Sn 2- active sites, where the doping molar ratio of selenium is 2.5% to 12.5%.

2. The mercury removal adsorbent according to claim 1, wherein the particle size of the adsorbent is 60 - 100 mesh.

3. The mercury removal adsorbent according to claim 1, characterized in that, The doping ratio of selenium is 10%.

4. A preparation method of the selenium-doped copper-cobalt bimetallic sulfide mercury removal adsorbent according to claim 1, characterized in that, It includes the following steps: a. Dissolve copper salt, cobalt salt and citrate in deionized water, and perform ultrasonic treatment to form a transparent mixed solution; b. Dissolve the sulfur source and selenium source in deionized water respectively; c. Transfer the mixed solution in step a to a microwave reactor, microwave for 5 - 20 minutes under the conditions of a power of 600 - 800 W and a temperature of 90 - 95 °C, and dropwise add the sulfur source solution and selenium source solution, and the molar ratio of selenium source to non-metal is 2.5% - 12.5%; d. After the reaction is completed, cool to room temperature, centrifuge, separate, wash and dry to obtain a selenium-doped copper-cobalt bimetallic sulfide adsorbent.

5. The preparation method according to claim 4, characterized in that, The sulfur source is Na2S, and the selenium source is SeO2.

6. The preparation method according to claim 4, characterized in that, The copper salt is preferably a copper compound hydrate; the cobalt salt is preferably a cobalt compound hydrate, and the citrate is preferably trisodium citrate dihydrate.

7. The preparation method according to claim 4, characterized in that, The microwave irradiation time is preferably 20 minutes, the microwave power is 700 W, and the reaction temperature is 90 °C.

8. Use of the mercury removal adsorbent of selenium-doped copper-cobalt bimetallic sulfide according to claim 1, characterized in that, It is applicable to the efficient removal of gaseous mercury in natural gas.

9. The application according to claim 8, wherein The application conditions include: the natural gas contains 0 - 1600 ppm O2, 0 - 1000 ppm H2S, 0 - 8% CO2, and the rest is N2 or CH4; the operating temperature is 30 - 200 °C, and the space velocity ratio is 1.13×10 6 h -1 ; the initial mercury concentration is 25 - 150 μg / m 3 .

10. The application according to claim 8, characterized in that The adsorbent has the best regeneration performance in an atmosphere containing H2S.

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