Resource utilization method of heavy metal-enriched aquatic plants and application of resource utilization method

Abstract

The invention belongs to the technical field of renewable energy sources, and particularly relates to a resource utilization method and application of heavy metal-enriched aquatic plants. The method specifically comprises the following steps: 1) obtaining molten salt; 2) drying and crushing the heavy metal-enriched aquatic plants, then adding the crushed aquatic plants into molten salt, and performing pyrolysis in an inert atmosphere; (3) introducing water vapor into the fused salt, enabling a product obtained by pyrolyzing the aquatic plants to react with water to be converted into CO and H2, stopping introducing the water vapor until no CO and H2 are generated, and collecting to obtain synthesis gas; and 4) introducing hydrogen into the fused salt, reducing the heavy metals dissolved and suspended in the fused salt, and collecting the heavy metal elementary substance at the bottom of the fused salt. Based on the fused salt thermocatalysis technology, the aquatic plants rich in heavy metal can be efficiently converted into synthesis gas and metal simple substances, and high-value recycling of resources is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of renewable energy, and in particular relates to a resource utilization method of heavy metal-accumulating aquatic plants and an application thereof. Background Art

[0002] With the rapid development of industrialization and urbanization, the problem of heavy metal pollution in water bodies is becoming increasingly serious. Compared with physical and chemical methods to treat heavy metal pollution in water bodies, the use of aquatic plants has the advantages of being environmentally friendly, green, and economical. Aquatic plants can exchange and adsorb heavy metals in water bodies through root secretions and coexisting microbial systems, causing heavy metals to be enriched in the root cells of aquatic plants, thereby playing a role in purifying water bodies. With the promotion of the method of using aquatic plants to repair water bodies, a large number of aquatic plants that are enriched in heavy metals need to be post-treated. However, if these aquatic plants enriched in heavy metals are not handled properly, it will not only cause a waste of resources, but may also cause secondary pollution. Therefore, how to achieve the "three-in-one" treatment of repaired aquatic plants has become an important issue in the field of environmental remediation.

[0003] Aquatic plants after water body restoration are a kind of biomass resource, and are rich in high metal concentrations. By converting them into fuels, synthetic gas, vegetable oils, carbon materials, etc., and recovering the heavy metals therein, high-value resource utilization of aquatic plants rich in heavy metals can be achieved. Biomass thermal cracking technology can convert biomass into high-value-added chemicals of different types, such as solid, liquid and gas. Previous studies have found that because high-temperature molten salts (referring to molten inorganic salts) have the water-free and oxygen-free environment required by thermal cracking technology, and molten salts have excellent heat storage, heat transfer, dissolution and catalytic properties, molten salts are very suitable for biomass cracking. In addition, molten salts are widely available, low-priced, have excellent thermal properties, and can directly absorb solar energy to provide the heat energy required for high-temperature reactions. Therefore, the resource utilization of aquatic plants rich in heavy metals using molten salts as catalytic and heating media has great development prospects. Summary of the Invention

[0004] To address the deficiencies of the existing technology, the present invention provides a method for resource utilization of heavy metal-accumulating aquatic plants and its application. Based on molten salt thermal catalysis technology, the present invention can efficiently convert heavy metal-accumulating aquatic plants into synthesis gas and metal elements, achieving high-value resource recovery. Also based on molten salt thermal storage technology, solar energy can be used as part or all of the thermal energy source. This technology also features high catalytic efficiency, a simple process, a green process, low cost, and ease of scale-up.

[0005] The present invention adopts a technology that uses molten salts as a catalytic medium to convert heavy metal-enriched aquatic plants into syngas and metal elements. As a liquid catalyst, molten salts have the characteristics of high catalytic activity, large catalytic area, and self-renewability of the dynamic catalytic interface, which can fully contact the crushed aquatic plant particles and promote their pyrolysis process. Moreover, the carbon and heavy metal ions / oxides formed after pyrolysis have good dispersibility in the molten salts, which can fully react with water vapor, hydrogen, etc. to promote the formation of syngas and heavy metal elements.

[0006] The technical solution provided by the present invention is as follows:

[0007] A method for resource utilization of heavy metal-enriched aquatic plants, comprising the following steps: using molten salts as a catalytic medium to catalyze the conversion of heavy metal-enriched aquatic plants into syngas and / or metal elements.

[0008] Based on the above technical solution, based on the molten salt thermal catalytic technology, heavy metal-enriched aquatic plants can be efficiently converted into syngas and metal elements.

[0009] Specifically, the method for resource utilization of heavy metal-enriched aquatic plants comprises the following steps:

[0010] 1) Obtain molten salts;

[0011] 2) Dry and crush the heavy metal-enriched aquatic plants, and then add the crushed aquatic plants to the molten salts and carry out pyrolysis under an inert atmosphere;

[0012] 3) Pass water vapor into the molten salts to react the products after pyrolysis of the aquatic plants with water to be converted into CO and H2, and stop passing water vapor until no more CO and H2 are generated, and collect the obtained syngas;

[0013] 4) Pass hydrogen into the molten salts to reduce the heavy metals dissolved and suspended in the molten salts, and collect the heavy metal elements at the bottom of the molten salts.

[0014] Specifically, in step 1): the molten salts at least include hydroxides.

[0015] Based on the above technical solution:

[0016] Using molten salt as a catalytic and heating medium, aquatic plants enriched in heavy metals are added to the molten salt for thermal cracking. After pyrolysis, the aquatic plants will form carbon and heavy metal ions / oxides. At this time, water vapor is introduced into the molten salt. On the one hand, the carbon can directly react with the water vapor to produce CO and H2. On the other hand, the carbon can also reduce the hydroxide molten salt to produce CO, H2 and oxide salts. At the same time, the oxide salt can absorb water vapor to produce hydroxide, replenishing the consumed hydroxide. This process is equivalent to the hydroxide acting as a catalyst, promoting the reaction of water vapor and pyrolytic carbon to produce synthesis gas. When the carbon formed after pyrolysis is completely converted into synthesis gas, the heavy metals enriched in the aquatic plants will dissolve or suspend in the molten salt in the form of ions or oxides. At this time, H2 is introduced into the molten salt to reduce these substances, and metal elements can be obtained and deposited at the bottom of the molten salt for easy collection.

[0017] Further:

[0018] The molten salt also includes carbonate and / or chloride salt;

[0019] The molar ratio of the carbonate to the hydroxide is (0.2:1) to (5:1);

[0020] The molar ratio of the chloride salt to the hydroxide is (0.2:1) to (5:1).

[0021] Based on the above technical solution, by adding carbonate and / or chloride salt, the melting point of molten salt can be lowered and the cost of molten salt can be reduced.

[0022] Specifically, the hydroxide is any one or more of lithium hydroxide, calcium hydroxide or sodium hydroxide.

[0023] Specifically, the carbonate is any one or more of lithium carbonate, calcium carbonate or sodium carbonate.

[0024] Specifically, the cations of the hydroxide and the carbonate are the same or different.

[0025] Specifically, the chloride salt is any one or more of calcium chloride, lithium chloride, sodium chloride or potassium chloride.

[0026] Specifically, the cations of the hydroxide and the chloride salt are the same or different.

[0027] Furthermore: the molten salt also includes 0.5%-5% borax in a molar ratio.

[0028] Based on the above technical solution, adding borax can adjust the pH of the molten salt and control the CO / H2 ratio in the product.

[0029] Specifically: the operating temperature of the molten salt is 300-900°C.

[0030] Further: solar energy is used as part or all of the heat energy source to heat the raw materials for forming the molten salt to a molten state.

[0031] Based on the above technical solution, it is possible to combine molten salt solar thermal power generation technology to realize the utilization of solar energy. For example, using a molten salt thermal storage device similar to existing solar molten salt solar thermal power generation systems, hydroxides, carbonates, chlorides, etc. as the thermal storage medium to absorb solar energy, the temperature can reach as high as 400-800°C, thus meeting the required pyrolysis temperature for catalytic biomass without the use of an external heat source.

[0032] Specifically, the mass ratio of heavy metal-accumulating aquatic plants to molten salt is (0.01-1):1.

[0033] For example, the pyrolysis time is 10-60 minutes.

[0034] For example, the flow rate of the water vapor is 10 ml / min-50 L / min, and the time of the water vapor introduction is 10-60 minutes.

[0035] For example, the flow rate of hydrogen gas is 10 ml / min-50 L / min, and the time of hydrogen gas introduction is 10-60 min.

[0036] For example, the inert atmosphere is argon or nitrogen.

[0037] The present invention also provides an application of a method for resource utilization of heavy metal-accumulating aquatic plants, which uses solar energy as an energy source to carry out resource utilization of heavy metal-accumulating aquatic plants.

[0038] Based on the above technical solution, the resource utilization technology of heavy metal-accumulating aquatic plants can be combined with solar energy technology, such as solar thermal power generation technology.

[0039] Compared with the prior art, the present invention has the following characteristics and beneficial effects:

[0040] The present invention uses molten salt as a catalytic medium to efficiently convert heavy metal-rich aquatic plants into synthesis gas and metal elements, achieving high-value resource recovery.

[0041] This technology uses molten salt as a liquid catalyst, which has the characteristics of high catalytic activity, large catalytic area, and self-renewability of the dynamic catalytic interface. It can fully contact with the crushed aquatic plant particles to promote their pyrolysis process. Moreover, the carbon formed after pyrolysis and heavy metal ions / oxides, etc. have good dispersibility in the liquid molten salt, and can fully react with water vapor and hydrogen, etc. to promote the formation of syngas and heavy metal elements. This technology has high catalytic efficiency, simple process, low cost, and easy control of operating conditions, is suitable for large-scale industrial applications, has a wide range of CO / H2 ratios in the preparation of syngas and is easy to regulate, and has a high recovery rate of heavy metals. Detailed implementation mode

[0042] The principles and features of the present invention are described below. The examples given are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0043] Unless otherwise specified, the test methods used in the examples are all conventional methods; the materials, reagents, etc. used, unless otherwise specified, are reagents and materials that can be obtained from commercial channels.

[0044] The heavy metal-enriched aquatic plants can be obtained by planting according to conventional methods or purchased from a cultivation base.

[0045] Example 1

[0046] Take the LiOH-Li2CO3 mixed salt with a molar ratio of 80:20 as the catalytic medium and heat it to 600 °C. Then, dry and crush the Siberian iris adsorbed with heavy metal Cu (the source is obtained by planting according to conventional methods), add it to the molten salt and pyrolyze it for 90 min under an argon atmosphere. Then, introduce 100 mL / min of water vapor into the molten salt to obtain CO and H2, and stop introducing water vapor after no more CO and H2 are produced. Then, introduce 200 mL / min of H2 into the molten salt for 30 min to reduce the heavy metal ions or heavy metal oxides dissolved and suspended in the molten salt, and collect the heavy metal Cr element at the bottom of the molten salt. The weight of the Siberian iris is 10 g. The weight of the molten salt is 100 g.

[0047] Detect the selectivity of CO at the gas outlet and the molar ratio of CO and H2 generated by gas chromatography. Calculate the recovery rate of heavy metals by comparing the heavy metal content in the aquatic plants and the mass of the recovered heavy metal elements.

[0048] After testing, the selectivity of CO at the gas outlet in Example 1 is 100%, the molar ratio of CO and H2 is 3:2; the recovery rate of heavy metal Cu is 99%.

[0049] Example 2

[0050] Take a Ca(OH)2-CaCO3 mixed salt with a molar ratio of 85:15 containing 1 mol% borax as the catalytic medium and heat it to 800 °C. Then, dry and crush water hyacinths (obtained from conventional cultivation) adsorbed with heavy metal Zn, add them to the molten salt, and pyrolyze for 60 min under an argon atmosphere; then, introduce steam at 50 mL / min into the molten salt to obtain CO and H2, and stop introducing steam after no more CO and H2 are produced; then, introduce H2 at 300 mL / min into the molten salt for 60 min to reduce the heavy metal ions or heavy metal oxides dissolved and suspended in the molten salt, and collect the elemental heavy metal Zn at the bottom of the molten salt. The weight of the water hyacinths is 50 g. The weight of the molten salt is 200 g.

[0051] Detect the selectivity of CO at the gas outlet and the molar ratio of CO and H2 generated by gas chromatography. Calculate the recovery rate of heavy metals by comparing the heavy metal content in aquatic plants and the mass of the recovered elemental heavy metals.

[0052] After testing, the selectivity of CO at the gas outlet in Example 2 is 100%, the molar ratio of CO and H2 is 1:1; the recovery rate of heavy metal Zn is 98%.

[0053] Example 3

[0054] Take a NaOH-Li2CO3-NaCl mixed salt with a molar ratio of 58:32:10 as the catalytic medium and heat it to 700 °C. Then, dry and crush hydrilla verticillata (obtained from conventional cultivation) adsorbed with heavy metal Ni, add them to the molten salt, and pyrolyze for 70 min under an argon atmosphere; introduce steam at 200 mL / min into the molten salt to obtain CO and H2, and stop introducing steam after no more CO and H2 are produced; then, introduce H2 at 600 mL / min into the molten salt for 40 min to reduce the heavy metal ions or heavy metal oxides dissolved and suspended in the molten salt, and collect the elemental heavy metal Ni at the bottom of the molten salt. The weight of the hydrilla verticillata is 150 g. The weight of the molten salt is 500 g.

[0055] Detect the selectivity of CO at the gas outlet and the molar ratio of CO and H2 generated by gas chromatography. Calculate the recovery rate of heavy metals by comparing the heavy metal content in aquatic plants and the mass of the recovered elemental heavy metals.

[0056] After testing, the selectivity of CO at the gas outlet in Example 3 is 100%, the molar ratio of CO and H2 is 2:1; the recovery rate of heavy metal Ni is 99%.

[0057] Example 4

[0058] Take the mixed salt of LiOH-Li2CO3-K2CO3 with a molar ratio of 25:65:10 as the catalytic medium and heat it to 750 °C. Then, dry and crush the reed adsorbed with heavy metal Co (the source is obtained by planting according to the conventional method), add it to the molten salt, and pyrolyze it in an argon atmosphere for 40 min; introduce steam at 150 mL / min into the molten salt to obtain CO and H2, and stop introducing steam after no more CO and H2 are produced; then introduce H2 at 800 mL / min into the molten salt for 55 min to reduce and dissolve the heavy metal ions or heavy metal oxides suspended in the molten salt, and collect the elemental heavy metal Co at the bottom of the molten salt. The weight of the reed is 150 g. The weight of the molten salt is 400 g.

[0059] Detect the selectivity of CO at the gas outlet and the molar ratio of CO and H2 generated by gas chromatography. Calculate the recovery rate of heavy metals by comparing the heavy metal content in aquatic plants and the mass of the recovered elemental heavy metals.

[0060] After testing, the selectivity of CO at the gas outlet in Example 4 is 100%, the molar ratio of CO and H2 is 1:1; the recovery rate of heavy metal Co is 97%.

[0061] Example 5

[0062] Take LiOH as the catalytic medium and heat it to 500 °C. Then, dry and crush the Siberian iris adsorbed with heavy metal Cu (the source is obtained by planting according to the conventional method), add it to the molten salt, and pyrolyze it in an argon atmosphere for 90 min; then, introduce steam at 1 L / min into the molten salt to obtain CO and H2, and stop introducing steam after no more CO and H2 are produced; then introduce H2 at 2 L / min into the molten salt for 30 min to reduce and dissolve the heavy metal ions or heavy metal oxides suspended in the molten salt, and collect the elemental heavy metal Cr at the bottom of the molten salt. The weight of the Siberian iris is 500 g. The weight of the molten salt is 800 g.

[0063] Detect the selectivity of CO at the gas outlet and the molar ratio of CO and H2 generated by gas chromatography. Calculate the recovery rate of heavy metals by comparing the heavy metal content in aquatic plants and the mass of the recovered elemental heavy metals.

[0064] After testing, the selectivity of CO at the gas outlet in Example 5 is 100%, the molar ratio of CO and H2 is 3:2; the recovery rate of heavy metal Cu is 99%.

[0065] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A resource utilization method for heavy metal-enriched aquatic plants, characterized in that It includes the following steps: Using molten salt as a catalytic medium, catalytically enrich heavy metal aquatic plants into syngas and / or metallic elements.

2. The resource utilization method of heavy metal-enriched aquatic plants according to claim 1, characterized in that It includes the following steps: 1) Obtain molten salt; 2) Dry and crush the heavy metal-enriched aquatic plants, and then add the crushed aquatic plants to the molten salt and pyrolyze them under an inert atmosphere; 3) Pass steam into the molten salt to react the products after pyrolysis of the aquatic plants with water to be converted into CO and H2, and stop passing steam until no more CO and H2 are generated, and collect the syngas; 4) Pass hydrogen into the molten salt to reduce the heavy metals dissolved and suspended in the molten salt, and collect the metallic elements at the bottom of the molten salt.

3. The resource utilization method of heavy metal-enriched aquatic plants according to claim 2, characterized in that In step 1): The molten salt includes at least hydroxides.

4. The method for resource utilization of heavy metal-enriched aquatic plants according to claim 3, characterized in that: The molten salt further includes carbonates and / or chlorides; The molar ratio of the carbonate to the hydroxide is (0.2:1) to (5:1); The molar ratio of the chloride to the hydroxide is (0.2:1) to (5:1).

5. The method for resource utilization of heavy metal-enriched aquatic plants according to claim 4, characterized in that: The hydroxide is any one or more of lithium hydroxide, calcium hydroxide or sodium hydroxide; The carbonate is any one or more of lithium carbonate, calcium carbonate or sodium carbonate; The chloride is any one or more of calcium chloride, lithium chloride, sodium chloride or potassium chloride; The cations of the hydroxide and the carbonate are the same or different; The cations of the hydroxide and the chloride are the same or different.

6. The resource utilization method of heavy metal-enriched aquatic plants according to claim 2, characterized in that: The molten salt further includes borax with a molar ratio of 0.5%-5%.

7. The resource utilization method of heavy metal-enriched aquatic plants according to claim 1, characterized in that: The working temperature of the molten salt is 300-900 °C.

8. The resource utilization method of heavy metal-enriched aquatic plants according to any one of claims 1 to 7, characterized in that: Using solar energy as part or all of the energy source to heat the raw materials for forming the molten salt to the molten state.

9. Application of a resource utilization method for heavy metal-enriched aquatic plants according to any one of claims 1 to 8, characterized in that: Using solar energy as the heat source for the resource utilization of heavy metal-enriched aquatic plants.