A method for preparing a catalyst for coal-derived syngas using rare earth wastewater and its application

Abstract

The present invention belongs to the technical fields of rare earth wastewater treatment and coal chemical engineering, and discloses a method and application for preparing a coal-to-synthesis gas catalyst by using rare earth wastewater. The preparation method is as follows: wastewater containing rare earth elements is mixed with sodium oleate and an organic solvent, and then stirred and refluxed. Then, liquid separation is carried out to obtain the water phase as purified water and the oil phase as a mixture of the organic solvent and rare earth oleate; the oil phase is evaporated to obtain the regenerated organic solvent, and inorganic acid is added to the remaining product to adjust the pH. After sufficient mixing, liquid separation is carried out again. Oleic acid is obtained in the upper layer, and the aqueous phase in the lower layer is a rare earth element salt solution; a water-soluble complexing agent is added to the rare earth element salt solution and mixed thoroughly, and then filtered and dried to obtain a complex-type coal-to-synthesis gas catalyst. The catalyst obtained by the present invention has good catalytic activity, can significantly increase the methane concentration, reduce the residual carbon rate, and improve the utilization rate and gas production rate of coal. The present invention realizes the high-value utilization of rare earth wastewater and has environmental and economic benefits.

Description

Technical Field

[0001] The invention belongs to the technical field of rare earth wastewater treatment and coal chemical industry, and specifically relates to a method for preparing a coal-to-syngas catalyst by utilizing rare earth wastewater and its application. Background Art

[0002] Coal-to-syngas is a process that uses coal or coke as raw materials, oxygen (air, oxygen-enriched or pure oxygen), water vapor, etc. as gasifying agents, and converts the combustible part of coal or coke into gas through chemical reactions under high temperature conditions. Its effective components include carbon monoxide, hydrogen, and methane. Syngas can be further used for Fischer-Tropsch synthesis, synthetic ammonia, and methanol production. Methanation is the process of converting carbon monoxide and carbon dioxide into methane, and it is also a key step in converting coal into natural gas. In the process of coal-to-syngas, the higher the methane concentration, the higher the natural gas production efficiency. However, the current methane concentration in coal-to-syngas is generally low, so the development of coal gasification catalysts that increase the methane concentration in coal-to-syngas is very meaningful for the further development of coal chemical industry.

[0003] At present, the development of coal gasification catalysts is mainly centered around lowering the reaction temperature of coal gasification, increasing the reaction rate of coal gasification, and improving the composition of coal gas. The coal gas catalysts currently under research and development include: (1) monomer metal salt or oxide catalysts, (2) composite catalysts, and (3) disposable catalysts. The application of catalysts has promoted the development of coal-to-syngas. For example, CN105964242B discloses the preparation and application of a vanadium-containing material coal-to-syngas catalyst, which reduces the coal gasification reaction temperature while increasing the coal gas efficiency by more than double; CN106076313B discloses a method for preparing a vanadium-based coal gasification catalyst using vanadium-containing materials, which greatly reduces the production cost of coal-to-syngas catalysts; CN114700080A discloses an iron-based coal gasification catalyst and its loading method and application in microwave gasification of low-rank coal, which can well improve the gasification product. However, the above catalysts still have problems such as unsatisfactory catalytic performance, high cost, and high energy consumption. Therefore, the development of more efficient and low-cost catalysts is very meaningful for coal gasification.

[0004] Rare earth elements are often used as catalysts in the coal combustion process because of their high activity and good selectivity. For example, CN101838573B has developed a coal combustion catalyst containing 5-10 composite light rare earths, which can save 5-20% of coal and reduce pollutant emissions by 10-30%. CN107460018B has published an aqueous solution composed of rare earth compounds, transition metal salts, etc. as a coal combustion catalyst. These reports have proved the feasibility of rare earth metal elements as coal combustion catalysts, but there are few reports on the use of rare earth elements as coal-to-syngas catalysts. It is well known that nanomaterials as catalysts often have better catalytic performance than conventional size materials, but there are no corresponding reports on the use of rare earth wastewater to prepare nanowire catalysts. Summary of the invention

[0005] In view of the shortcomings and deficiencies of the above prior art, the primary purpose of the present invention is to provide a method for preparing a coal-to-syngas catalyst using rare earth wastewater. The present invention has developed a method for preparing a rare earth nanowire catalyst using rare earth wastewater, which exhibits excellent performance in coal-to-syngas, greatly reduces the residual carbon rate of the water-coal slurry residue in the coal-to-syngas process, and improves the gas conversion rate.

[0006] Another object of the present invention is to provide a coal-to-syngas catalyst prepared by the above method.

[0007] Another object of the present invention is to provide application of the above catalyst in catalysis of coal-to-syngas.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] A method for preparing a coal-to-syngas catalyst using rare earth wastewater comprises the following preparation steps:

[0010] (1) mixing wastewater containing rare earth elements with sodium oleate and an organic solvent, stirring and refluxing, and then separating the liquids to obtain an aqueous phase of purified water and an oil phase of a mixture of the organic solvent and rare earth oleate;

[0011] (2) evaporating the oil phase in step (1) to obtain a regenerated organic solvent, adding an inorganic acid to the residual product after evaporation to adjust the pH, and then fully mixing and separating the liquids to obtain oleic acid in the upper layer and a rare earth element salt solution in the lower aqueous phase;

[0012] (3) Adding an aqueous complexing agent to the rare earth element salt solution obtained in step (2), mixing the mixture thoroughly, filtering and drying the mixture, and obtaining a complexed coal-to-syngas catalyst.

[0013] Preferably, the rare earth element in step (1) includes but is not limited to one or more rare earth elements selected from the group consisting of lanthanum, neodymium, samarium, gadolinium, cerium, and the like.

[0014] Preferably, the amount of sodium oleate added in step (1) is 2 to 20 times the molar amount of the rare earth element ions.

[0015] Preferably, the organic solvent in step (1) includes but is not limited to one or more of petroleum ether, n-hexane, cyclohexane, toluene, gasoline, benzene, etc.

[0016] Preferably, the amount of the organic solvent added in step (1) is 20% to 100% of the volume of the wastewater containing rare earth elements.

[0017] Preferably, the reflux temperature in step (1) is 50°C to 100°C.

[0018] Preferably, the inorganic acid in step (2) includes but is not limited to one or more of hydrochloric acid, nitric acid and sulfuric acid.

[0019] Preferably, the concentration of the inorganic acid in step (2) is 0.02 to 1 mol / L.

[0020] Preferably, in step (2), the pH is adjusted to between 5 and 11.

[0021] Preferably, the regenerated organic solvent and oleic acid obtained in step (2) are reused in step (1).

[0022] Preferably, the aqueous complexing agent in step (3) includes but is not limited to one or more of citric acid, sodium citrate, and sodium ethylenediaminetetraacetate.

[0023] Preferably, the amount of the aqueous complexing agent added in step (3) is 1% to 10% of the mass of the wastewater containing rare earth elements.

[0024] The process flow chart and mechanism diagram of the above-mentioned method for preparing coal-to-syngas catalyst using rare earth wastewater are as follows: Figure 1 and Figure 2 shown.

[0025] A coal-to-syngas catalyst is prepared by the above method.

[0026] Application of the above catalyst in coal-to-syngas catalysis.

[0027] Furthermore, the above catalyst is used in the catalysis of coal-to-syngas production by water-coal slurry gasification, wherein the water-coal slurry gasification includes but is not limited to coal gasification using air + water vapor, carbon dioxide + oxygen, air + carbon dioxide + water vapor, etc. as gasifying agents.

[0028] Further preferably, in the above application process, the amount of catalyst added is 0.5‰ to 15‰ of the amount of coal used.

[0029] The technical principle of the present invention is: first, the rare earth elements are removed from the wastewater by a two-phase method and fixed in oleic acid to form rare earth oleate, then the rare earth elements are transferred from the oil phase to a soluble salt solution by using a strong acid to produce a weak acid, and an appropriate amount of a complexing agent is added to convert the rare earth elements into a complex type coal-to-syngas catalyst. The rare earth metal elements in the catalyst can promote the occurrence of coal gasification reaction, which enables the rare earth elements to be fully utilized, improves efficiency, and reduces pollution emissions.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The present invention uses waste wastewater containing rare earth elements as raw materials for preparing catalysts, which greatly reduces economic costs.

[0032] (2) The catalyst prepared by the present invention is used to produce synthesis gas from coal, thereby increasing the added value of rare earth wastewater.

[0033] (3) The present invention converts rare earth wastewater into a coal-to-syngas catalyst, thereby solving the environmental problems caused by rare earth wastewater.

[0034] (4) The process flow of the present invention is simple and easy to implement, does not require high-energy-consuming measures such as high temperature, is simple and economical, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a process flow chart of the present invention for preparing a coal-to-syngas catalyst using rare earth wastewater.

[0036] Figure 2 This is a schematic diagram of the mechanism of using rare earth wastewater to prepare a coal-to-syngas catalyst according to the present invention.

[0037] Figure 3 This is a diagram showing the experimental phenomena during the catalyst preparation process in Example 1.

[0038] Figure 4 This is an electron microscope image of the catalyst obtained in Example 1.

[0039] Figure 5 This is a diagram showing the experimental phenomena of the catalyst preparation process in Example 2.

[0040] Figure 6 This is an electron microscope image of the catalyst obtained in Example 2.

[0041] Figure 7 This is a diagram showing the experimental phenomena of the catalyst preparation process in Example 3.

[0042] Figure 8 This is an electron microscope image of the catalyst obtained in Example 3.

[0043] Fig. 9 The XRD patterns of the catalysts obtained in Examples 1 to 3 are shown in FIG. DETAILED DESCRIPTION

[0044] The present invention is further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0045] Example 1

[0046] A method for preparing a coal-to-syngas catalyst using rare earth wastewater in this embodiment has the following specific steps:

[0047] (1) Add 0.5 g of sodium oleate to 50 ml of 0.27 mg / L wastewater containing rare earth elements (from an environmental protection company in Guangdong Province, where the molar concentrations of lutetium and cerium are 0.08 mg / L and 0.05 mg / L, respectively), then add 5 ml of petroleum ether and 5 ml of n-hexane, mix thoroughly, stir and reflux at 80°C, and then separate the liquids to obtain an aqueous phase, which is purified water that can be recycled, and an oil phase, which is a mixture of an organic solvent and rare earth oleate.

[0048] (2) The oil phase in step (1) is evaporated to obtain regenerated petroleum ether and n-hexane, which can be used back in step (1); 0.05 mol / L hydrochloric acid is added to the residual product after evaporation to adjust the pH to 6, and the mixture is separated after being fully mixed, and the upper layer is oleic acid recovery, and the lower aqueous phase is a rare earth element salt solution.

[0049] (3) Add 1 g of citric acid to the rare earth element salt solution obtained in step (2), mix thoroughly, filter and dry to obtain a complex coal-to-syngas catalyst.

[0050] The experimental phenomenon of the catalyst preparation process in this embodiment is shown in the figure Figure 3 As shown (the left picture is the wastewater initially containing rare earth elements, the middle picture is the experimental phenomenon after liquid separation in step (1), and the right picture is the experimental phenomenon after adding aqueous complexing agent citric acid in step (3)).

[0051] The electron microscope image of the catalyst obtained in this example is as follows Figure 4 As shown. Figure 4 It can be seen that the rare earth catalyst obtained in the present invention has a nanowire structure.

[0052] The XRD pattern of the catalyst obtained in this example is as follows Fig. 9 As shown, it shows that the main crystal phase of the catalyst is 0.75 Lu 0.25 )C 2 The results matched, indicating that the catalyst was successfully synthesized.

[0053] The catalyst obtained in this example is used in the catalytic production of synthesis gas from coal by gasification of water-coal slurry. The catalyst is added at 0.5‰ of the amount of coal used. Air + water vapor is used as the gasifying agent. The CO and H 2 , CO2 , CH 4 The results showed that the coal consumption of the experimental group with the catalyst of this embodiment was 72 kg / h and the gas flow rate was 255 m 3 / h, gas composition: CO: 9.48%, CO 2 :4.93%,H 2 :6.85%,CH 4 : 36.68%, residual carbon rate 13.4%. The coal consumption of the blank control group was 34kg / h, and the gas flow rate was 110m 3 / h, gas composition: CO: 21.34%, CO 2 : 9.48%, H 2 :15.46%,CH 4 : 3.28%, residual carbon rate 32%.

[0054] It can be seen from the above results that the catalyst prepared by the present invention can greatly reduce the residual carbon rate of water-coal slurry residue in the process of coal-to-syngas, can significantly increase the methane concentration, and improve the utilization rate of coal and the gas production rate.

[0055] Example 2

[0056] A method for preparing a coal-to-syngas catalyst using rare earth wastewater in this embodiment has the following specific steps:

[0057] (1) Add 2 g of sodium oleate to 50 ml of 0.13 mg / L rare earth element wastewater (from an environmental protection company in Guangdong Province, where the mass concentration of samarium is 0.05 mg / L), then add 10 ml of cyclohexane and 10 ml of benzene, mix thoroughly, stir and reflux at 80°C, and then separate the liquids to obtain an aqueous phase, which is purified water that can be recycled, and an oil phase, which is a mixture of an organic solvent and rare earth oleate.

[0058] (2) The oil phase in step (1) is evaporated to obtain regenerated cyclohexane and benzene, which can be used in step (1); 0.5 mol / L sulfuric acid is added to the residual product after evaporation to adjust the pH to 7, and the mixture is separated after being fully mixed, and the upper layer is oleic acid recovered, and the lower aqueous phase is a rare earth element salt solution.

[0059] (3) Add 0.5 g of sodium citrate to the rare earth element salt solution obtained in step (2), mix thoroughly, filter and dry to obtain a complex coal-to-syngas catalyst.

[0060] The experimental phenomenon of the catalyst preparation process in this embodiment is shown in the figure Figure 5 As shown (the left picture is the wastewater initially containing rare earth elements, the middle picture is the experimental phenomenon after adding dilute acid to adjust the pH in step (2), and the right picture is the experimental phenomenon after adding aqueous complexing agent sodium citrate in step (3)).

[0061] The electron microscope image of the catalyst obtained in this example is as follows Figure 6 As shown. Figure 6 It can be seen that the rare earth catalyst obtained in the present invention has a nanowire structure.

[0062] The XRD pattern of the catalyst obtained in this example is as follows Fig. 9 As shown, it shows that the catalyst was successfully prepared.

[0063] The catalyst obtained in this example is used in the catalytic production of synthesis gas from coal by gasification of water-coal slurry. The amount of catalyst added is 1‰ of the amount of coal used. Air + carbon dioxide + water vapor is used as the gasifying agent. The CO and H 2 , CO 2 , CH 4 The results showed that the coal consumption of the experimental group with the catalyst of this embodiment was 70 kg / h and the gas flow rate was 336 m 3 / h, gas composition: CO: 16.58%, CO 2 : 26.2%, H 2 :8.63%,CH 4 : 30.23%, residual carbon rate 13.6%. The coal consumption of the blank control group was 36kg / h, and the gas flow rate was 157m 3 / h, gas composition: CO: 35.43%, CO 2 : 34.32%, H 2 :19.58%,CH 4 : 5.26%, residual carbon rate 36%.

[0064] It can be seen from the above results that the catalyst prepared by the present invention can greatly reduce the residual carbon rate of water-coal slurry residue in the process of coal-to-syngas, can significantly increase the methane concentration, and improve the utilization rate of coal and the gas production rate.

[0065] Example 3

[0066] A method for preparing a coal-to-syngas catalyst using rare earth wastewater in this embodiment has the following specific steps:

[0067] (1) Add 5 g of sodium oleate to 60 ml of 0.35 mg / L rare earth element wastewater (from an environmental protection company in Guangdong Province, where the concentration of neodymium is 0.012 mg / L), then add 8 ml of gasoline and 12 ml of toluene, mix thoroughly, stir and reflux at 80°C, and then separate the liquids to obtain an aqueous phase, which is purified water that can be recycled, and an oil phase, which is a mixture of an organic solvent and rare earth oleate.

[0068] (2) The oil phase in step (1) is evaporated to obtain regenerated gasoline and toluene, which can be used in step (1); 1 mol / L nitric acid is added to the residual product after evaporation to adjust the pH to 9, and the liquid is separated after sufficient mixing, and the upper layer is oleic acid recovery, and the lower aqueous phase is a rare earth element salt solution.

[0069] (3) Add 2 g of sodium ethylenediaminetetraacetate to the rare earth element salt solution obtained in step (2), mix thoroughly, filter and dry to obtain a complex coal-to-syngas catalyst.

[0070] The experimental phenomenon of the catalyst preparation process in this embodiment is shown in the figure Figure 7 As shown (the left picture is the wastewater initially containing rare earth elements, the middle picture is the experimental phenomenon after adding dilute acid to adjust the pH in step (2), and the right picture is the experimental phenomenon after adding aqueous chelating agent sodium ethylenediaminetetraacetate in step (3)).

[0071] The electron microscope image of the catalyst obtained in this example is as follows Figure 8 As shown. Figure 8 It can be seen that the rare earth catalyst obtained in the present invention has a nanowire structure.

[0072] The XRD pattern of the catalyst obtained in this example is as follows Fig. 9 As shown, it shows that the catalyst was successfully prepared.

[0073] The catalyst obtained in this example is used in the catalytic production of synthesis gas from coal by gasification of water-coal slurry. The amount of catalyst added is 1‰ of the amount of coal used. Carbon dioxide + oxygen is used as the gasifying agent. The CO and H 2 , CO 2 , CH 4 The results showed that the coal consumption of the experimental group with the catalyst of this embodiment was 75 kg / h and the gas flow rate was 326 m 3 / h, gas composition: CO: 12.3%, CO 2 : 18.46%, H 2 :6.24%,CH 4 : 43.2%, residual carbon rate 14.5%. The coal consumption of the blank control group was 33kg / h, and the gas flow rate was 142m 3 / h, gas composition: CO: 34.8%, CO 2 : 38.32%, H 2 :18.39%,CH 4 : 3.47%, residual carbon rate 35.8%.

[0074] It can be seen from the above results that the catalyst prepared by the present invention can greatly reduce the residual carbon rate of water-coal slurry residue in the process of coal-to-syngas, can significantly increase the methane concentration, and improve the utilization rate of coal and the gas production rate.

[0075] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing a coal-to-synthesis gas catalyst using rare earth wastewater, characterized in that, it includes the following preparation steps: (1) Mix the wastewater containing rare earth elements with sodium oleate and an organic solvent, stir and reflux, and then separate the liquid to obtain the water phase as purified water and the oil phase as a mixture of the organic solvent and rare earth oleate; (2) Evaporate the oil phase in step (1) to obtain the regenerated organic solvent, add inorganic acid to the remaining product after evaporation to adjust the pH, mix well and then separate the liquid. Oleic acid is obtained in the upper layer, and the water phase in the lower layer is a rare earth element salt solution; (3) Add an aqueous complexing agent to the rare earth element salt solution obtained in step (2), mix well, filter and dry to obtain a complex-type coal-to-synthesis gas catalyst, wherein the aqueous complexing agent contains one or several of citric acid, sodium citrate, and sodium ethylenediaminetetraacetate; the addition amount of the aqueous complexing agent is 1% - 10% of the mass of the wastewater containing rare earth elements.

2. A method for preparing a coal-to-synthesis gas catalyst using rare earth wastewater according to claim 1, characterized in that, the rare earth elements in step (1) include one or more rare earth elements among lanthanum, neodymium, samarium, gadolinium, and cerium.

3. A method for preparing a coal-to-synthesis gas catalyst using rare earth wastewater according to claim 1, characterized in that, the addition amount of sodium oleate in step (1) is 2 - 20 times the molar amount of rare earth element ions.

4. A method for preparing a coal-to-synthesis gas catalyst using rare earth wastewater according to claim 1, characterized in that, the organic solvent in step (1) includes one or several of petroleum ether, n-hexane, cyclohexane, toluene, gasoline, and benzene; the addition amount of the organic solvent is 20% - 100% of the volume of the wastewater containing rare earth elements; the reflux temperature is 50°C - 100°C.

5. A method for preparing a coal-to-synthesis gas catalyst using rare earth wastewater according to claim 1, characterized in that, the inorganic acid in step (2) includes one or several of hydrochloric acid, nitric acid, and sulfuric acid, and the concentration of the inorganic acid is 0.02 - 1 mol / L; adjust the pH to between 5 and 11.

6. A method for preparing a coal-to-synthesis gas catalyst using rare earth wastewater according to claim 1, characterized in that, the regenerated organic solvent and oleic acid obtained in step (2) are reused in step (1).

7. A coal-to-synthesis gas catalyst, characterized in that, it is prepared by the method described in any one of claims 1 - 6.

8. The application of the catalyst according to claim 7 in the catalysis of coal-to-synthesis gas.

9. The application of the catalyst according to claim 7 in the catalysis of coal-to-synthesis gas by water coal slurry gasification, characterized in that, the water coal slurry gasification includes gasifying coal with air + steam, carbon dioxide + oxygen, or air + carbon dioxide + steam as the gasifying agent; the catalyst addition amount is 0.5‰ - 15‰ of the coal usage.

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