Method for extracting magnesium and seawater desalination from marine waste plastics in cooperation with seawater

Abstract

The present application relates to a method for extracting magnesium from marine waste plastics and seawater and desalination of seawater, which comprises the following steps: S00, filtering seawater containing waste plastics; S10, wet grinding the solid waste plastics to obtain waste plastic particles, and preparing lime milk simultaneously; S20, mixing the secondary concentrated seawater, the lime milk and the waste plastic particles and adding them into a magnesium hydroxide precipitation tank; S30, after the mixture of the magnesium hydroxide precipitation and the waste plastic particles is dewatered by pressure filtration, the mixture is sent into a calcination pyrolysis furnace to prepare magnesium oxide by calcination; S40, the pyrolysis gas is dewatered and used as a heating fuel gas to generate electricity for recycling, and the remaining part is stored for recycling; S50, the mixture of the magnesium oxide and the carbon particles is used to prepare solid crystalline magnesium and carbon monoxide gas, and the carbon monoxide gas is stored for recycling. The present application has the advantages of comprehensive utilization of marine waste plastics for energy utilization, preparation of desalinated seawater and extraction of magnesium from seawater, and comprehensive utilization of pollutants and low production cost.

Description

Technical Field

[0001] This invention relates to the field of energy technology, specifically to a method for extracting metallic magnesium from marine waste plastics in conjunction with seawater and for seawater desalination. Background Technology

[0002] Since industrialization, large amounts of domestic waste have been discharged into the sea, resulting in a significant amount of non-biodegradable waste plastics and microplastics in the ocean, severely impacting the marine ecosystem. Simultaneously, freshwater shortages are widespread, and many coastal cities need to desalinate seawater to provide high-quality freshwater in order to alleviate the water crisis.

[0003] Currently, most methods for treating marine plastic waste involve manual harvesting, which has limited commercial value and effectiveness. Seawater desalination requires a large amount of energy and heat, resulting in excessively high costs and impacting production and daily life.

[0004] Therefore, there is an urgent need for a method that can utilize marine waste plastics for seawater desalination and co-produce metallic magnesium, thereby reducing external energy consumption and costs, solving marine waste plastic pollution, and lowering the energy cost of seawater desalination. Summary of the Invention

[0005] The purpose of this invention is to address the aforementioned problems in the prior art by providing a method for the co-extraction of metallic magnesium from marine waste plastics and seawater desalination.

[0006] To achieve the above-mentioned objectives, the present invention employs the following technical solution: A method for extracting metallic magnesium from marine waste plastics in conjunction with seawater and for seawater desalination includes the following steps:

[0007] S00. Filter seawater containing waste plastics to separate solid waste plastics and filtered seawater;

[0008] S10. Solid waste plastics are wet-milled to obtain waste plastic microparticles. Filtered seawater is desalinated to obtain secondary concentrated seawater and distilled water. Lime milk is prepared simultaneously.

[0009] S20. Secondary concentrated seawater, lime slurry, and waste plastic microparticles are mixed and added to the magnesium hydroxide precipitation tank. By using the waste plastic microparticles as crystal seeds for magnesium hydroxide nucleation, a mixture of magnesium hydroxide precipitate and waste plastic microparticles is obtained.

[0010] S30. The mixture of magnesium hydroxide precipitate and waste plastic microparticles is dehydrated by pressure filtration and then fed into a calcination pyrolysis furnace for calcination to produce magnesium oxide, so as to obtain at least preheated gas, pyrolysis gas and a mixture of magnesium oxide and carbon particles.

[0011] S40. The pyrolysis gas is dehydrated and used as a heating gas energy source for power generation for recycling, and the remaining part is stored for recycling.

[0012] S50. A mixture of magnesium oxide and carbon particles is processed by carbothermic magnesium smelting and quenching condensation to obtain solid crystalline magnesium and carbon monoxide gas, and the carbon monoxide gas is stored for recycling.

[0013] Furthermore, it also includes step S60, which specifically includes:

[0014] The stored carbon monoxide gas is converted into carbon dioxide and hydrogen through steam conversion. The mixture of carbon dioxide and hydrogen is then purified by removing carbon dioxide to obtain hydrogen. The hydrogen is then used to generate electricity for recycling.

[0015] Furthermore, the specific steps of step S50 are as follows:

[0016] S51. Magnesium is smelted by carbothermic reduction of a mixture of magnesium oxide and carbon particles through a magnesium smelting electric arc furnace to obtain a mixture of magnesium vapor and carbon monoxide.

[0017] S52. The mixture of magnesium vapor and carbon monoxide is cooled and separated by a quenching condenser, so that the magnesium vapor is condensed into solid crystalline magnesium, and the carbon monoxide is buffered and stored in a carbon monoxide gas storage tank.

[0018] Furthermore, it also includes step S70, which specifically includes:

[0019] Solid crystalline magnesium is distilled to produce commercial magnesium ingots, where the raw gas for the magnesium distillation process comes from stored pyrolysis gas.

[0020] Furthermore, in step S10, the raw materials used in the preparation of lime milk are marine shells and pyrolysis gas stored in step S50.

[0021] Furthermore, it also includes step S80, which specifically includes:

[0022] The preheated gas generated during the calcination and pyrolysis furnace to produce magnesium oxide is condensed to obtain crude hydrochloric acid, wherein the preheated gas includes moisture and hydrogen chloride gas.

[0023] Furthermore, in step S30, the calcination pyrolysis furnace includes a preheating section and a main body. The heating temperature of the preheating section is 300°C, so that the magnesium hydroxide precipitate undergoes a dehydration reaction and the waste plastic particles undergo partial pyrolysis to generate preheating gas. The heating temperature of the main body is 700-800°C, so that the waste plastic particles are completely and thoroughly pyrolyzed and pyrolysis gas is generated. The remaining carbon residue of the waste plastic particles remains in magnesium oxide.

[0024] Furthermore, in step S10, seawater desalination is carried out using the RO membrane method, and the electricity generated by the RO membrane method is supplied through the pyrolysis gas power generation in step S40 and / or the hydrogen power generation in step S60.

[0025] Furthermore, the pyrolysis gas obtained in step S30 is used as fuel for preparing lime milk in step S10 and for calcining magnesium oxide in step S30.

[0026] Furthermore, the steam supply step S10 generated during the steam conversion process is the seawater distillation and desalination stage in the secondary desalination of seawater.

[0027] Working principle and beneficial effects: 1. Compared with the existing technology, this application can directly use seawater containing waste plastics as raw material to extract metallic magnesium and desalinate seawater. The waste plastics can be used as a secondary energy source. This secondary energy source can be used multiple times in the entire process as heat and electricity in the seawater desalination and metallic magnesium extraction process. In this way, waste plastics can be used as a recyclable energy carrier to achieve energy synergy and material synergy with the two major seawater chemical industries of metallic magnesium extraction and seawater desalination (e.g., the waste plastics are ground up and used as nucleation seeds for magnesium hydroxide precipitation in seawater, promoting the precipitation of magnesium hydroxide in seawater; the waste plastics and magnesium hydroxide are pyrolyzed simultaneously in the calcination process, and while obtaining fuel gas, the residual carbon from the pyrolysis is used as a reducing agent to participate in the electrothermal reduction process of magnesium oxide). This realizes the commercial value of marine waste plastics.

[0028] 2. Compared with existing technologies, this application generates electricity through multiple energy recovery methods, which significantly reduces the dependence on other conventional commercial energy sources for seawater desalination and seawater extraction of metallic magnesium, thereby reducing costs;

[0029] 3. Compared with existing technologies, this method obtains metallic magnesium and fresh water from seawater while eliminating waste plastic pollution in seawater. It achieves the above three industrial and environmental objectives with almost no consumption of external bulk materials and energy. Attached Figure Description

[0030] Figure 1 This is a process structure diagram of a preferred embodiment of the present invention;

[0031] Figure 2 This is a process flow diagram of a preferred embodiment of the present invention.

[0032] In the diagram, 101 is seawater containing waste plastic; 102 is a filtration device; 103 is filtered seawater; 104 is an RO membrane seawater desalination unit; 105 is a primary concentrated seawater tank; 106 is a multi-effect evaporation seawater desalination unit; and 107 is a secondary concentrated seawater tank.

[0033] 201. Solid waste plastics; 202. Wet grinding equipment; 203. Waste plastic microparticles;

[0034] 301. Marine shells; 302. Lime calcination kiln; 303. Lime slurry digestion tank; 401. Magnesium hydroxide precipitation tank; 402. Plate and frame filter press; 403. Returned seed crystals; 404. Calcination pyrolysis furnace; 405. Preheating gas condenser;

[0035] 501. Carbothermic magnesium smelting electric arc furnace; 502. Quenching condenser; 503. Carbon monoxide gas storage tank; 504. Steam conversion unit; 505. Carbon dioxide removal tower; 510. Magnesium distillation furnace; 511. Commercial magnesium ingot;

[0036] 601. Hydrogen fuel cell stack; 602. Power station; 603. Gas storage tank; 604. Steam storage tank; 605. Gas-fired power generation unit. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0038] Those skilled in the art should understand that, in the disclosure of this invention, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limiting this invention.

[0039] like Figure 1-2 As shown, the method for extracting metallic magnesium from marine waste plastics in conjunction with seawater and for seawater desalination includes the following steps:

[0040] S00. Filter seawater containing waste plastic to separate solid waste plastic 201 and filtered seawater 103;

[0041] In this embodiment, seawater containing waste plastic is filtered by a filter device 102 to separate solid waste plastic 201 and filtered seawater 103.

[0042] S10. Solid waste plastic 201 is wet-milled to obtain waste plastic microparticles 203. Filtered seawater 103 is subjected to secondary desalination treatment to obtain secondary concentrated seawater and distilled water. Lime milk is prepared simultaneously.

[0043] In this step, solid waste plastic 201, along with moisture, is wet-ground by a wet grinding device 202 to become waste plastic microparticles 203.

[0044] In this step, the raw materials for preparing lime milk are marine shells 301 and pyrolysis gas stored in step S50.

[0045] In this embodiment, marine shells 301 (mainly composed of calcium carbonate CaCO3) are collected and calcined in a lime calcination kiln 302 (the pyrolysis gas obtained in step S30 can be used as the combustion energy during the calcination process) to become lime CaO. Seawater is then added to the lime milk digestion tank 303 to become lime milk, i.e., Ca(OH)2.

[0046] In this step, seawater desalination is carried out using the RO membrane method, and the electricity generated by the RO membrane method is supplied through the pyrolysis gas power generation in step S40 and / or the hydrogen power generation in step S60.

[0047] In this embodiment, seawater 103 is filtered and then desalinated through a reverse osmosis membrane in an RO membrane desalination unit 104. Powered by a power supply station 602, the desalinated seawater is separated, and the remainder, which is primary concentrated seawater, enters a primary concentrated seawater tank 105. The seawater in the primary concentrated seawater tank 105 then passes through an MSF or MED multi-effect evaporation / distillation seawater desalination unit 106. Under the action of a steam storage tank 604, distilled water with a mass of 10-12 times the steam is produced, and the remainder, which is secondary concentrated seawater, enters a secondary concentrated seawater tank 107.

[0048] S20. Secondary concentrated seawater, lime slurry, and waste plastic microparticles 203 are mixed and added to magnesium hydroxide sedimentation tank 401. By using waste plastic microparticles 203 as crystal seed for magnesium hydroxide nucleation (which plays a core role in strengthening crystal precipitation), a mixture of magnesium hydroxide precipitate and waste plastic microparticles 203 is obtained. Part of the mixed precipitate is mixed with waste plastic microparticles 203 and used as a return seed crystal 403. Most of the remaining precipitate enters plate and frame filter press 402 for filter dewatering.

[0049] The chemical formula for magnesium hydroxide precipitated from seawater is:

[0050] Ca(OH)2+MgCl2=Mg(OH)2↓+CaCl2;

[0051] S30. The mixture of magnesium hydroxide precipitate and waste plastic microparticles 203 is dehydrated by pressure filtration and then fed into calcination pyrolysis furnace 404 for calcination to produce magnesium oxide, so as to obtain at least preheated gas, pyrolysis gas and a mixture of magnesium oxide and carbon particles.

[0052] In this step, the calcination pyrolysis furnace 404 (recovering pyrolysis gas from the gas storage tank 603) includes a preheating section and a main body. The heating temperature of the preheating section is 300℃, so that the magnesium hydroxide precipitate undergoes a dehydration reaction and remains. The waste plastic microparticles 203 undergo partial pyrolysis, producing preheating gas (moisture and HCl gas, the HCl gas comes from the heating of chlorine in the waste plastic). The heating temperature of the main body is 700-800℃, so that the waste plastic microparticles 203 are completely and thoroughly pyrolyzed and pyrolysis gas (CO, H2, CH4, CO2 and moisture, etc.) is produced. The remaining carbon residue of the waste plastic microparticles 203 remains in the magnesium oxide (a mixture of magnesium oxide and carbon particles).

[0053] In this step, the pyrolysis gas obtained in step S30 is used as fuel for preparing lime milk in step S10 and for calcining magnesium oxide in step S30.

[0054] In this step, the chemical formula for heating a simple magnesium hydroxide precipitate is:

[0055]

[0056] In this step, if it is calcined and pyrolyzed together with waste plastic microparticles 203, the equation is:

[0057]

[0058] Therefore, the pyrolysis gas is a combustible gas. After cooling, H2O and HCl are liquefied, and the remaining non-condensable gas mainly consists of CO, H2, CH4, CO2, etc., which can be used as fuel gas.

[0059] S40. The pyrolysis gas is dehydrated and used as heating gas energy to generate electricity to power station 602 for recycling. The remaining part is stored for recycling.

[0060] In this embodiment, when the pyrolysis gas is first generated, it is dehydrated and stored in the gas storage tank 603 for use as heating gas energy. A portion of the gas is used to generate electricity through the gas power generation unit 605, which is then supplied to the entire plant via the power station 602. The remaining portion is stored as gas in the gas storage tank 603 for later use.

[0061] S50. A mixture of magnesium oxide and carbon particles is processed by carbothermic magnesium smelting and quenching and condensation to obtain solid crystalline magnesium and carbon monoxide gas, and the carbon monoxide gas is stored for recycling.

[0062] The specific steps of S50 are as follows:

[0063] S51. Magnesium oxide and carbon particles are processed by carbothermic reduction magnesia in a carbothermic electric arc furnace 501 to obtain a mixture of magnesium vapor and carbon monoxide.

[0064] In this embodiment, a mixture of magnesium oxide and carbon particles is hot-charged into a carbide-magnesium smelting electric arc furnace 501. After electrical energy is input into the power supply station 602, the furnace charge is heated to 1900-2100°C under the action of the electric arc. In an oxygen-isolated environment, a mixture of metallic magnesium vapor and carbon monoxide is obtained.

[0065] The chemical formula for carbothermic reduction of magnesium is:

[0066]

[0067] S52, the mixture of magnesium vapor and carbon monoxide is cooled and separated by quenching condenser 502 so that the magnesium vapor is condensed into solid crystalline magnesium, and the carbon monoxide enters the carbon monoxide gas storage tank 503 for buffer storage.

[0068] S60. The stored carbon monoxide gas is converted into carbon dioxide and hydrogen by the steam conversion unit 504 (WGSR). The mixture of carbon dioxide and hydrogen is decarbonized to obtain hydrogen. The hydrogen is used to generate electricity to power station 602 for recycling.

[0069] The chemical formula for water vapor shift is:

[0070]

[0071] In this step, the steam generated in the steam conversion process is supplied to the seawater distillation and desalination stage of the secondary seawater desalination process in step S10. That is, the high-temperature sensible heat and chemical reaction heat of the quench condenser (quench condenser 502) and the steam conversion unit 504 are recovered to the steam storage tank 604 using steam.

[0072] In this step, the mixture of carbon dioxide and hydrogen gas passes through carbon dioxide removal tower 505 to remove CO2, and the remaining hydrogen gas is purified and used to generate electricity using a high-temperature fuel cell stack (MCFC) or a room-temperature proton membrane fuel cell stack (PEMFC). The generated DC power is then inverted and boosted to power station 602 to supply power to other equipment.

[0073] S70. Solid crystalline magnesium is subjected to magnesium distillation process in magnesium distillation furnace 510 to obtain commercial magnesium ingot 511, wherein the raw material gas for magnesium distillation process comes from stored pyrolysis gas.

[0074] S80. The preheated gas generated during the calcination and pyrolysis furnace 404 to produce magnesium oxide is condensed to obtain crude hydrochloric acid, wherein the preheated gas includes water and hydrogen chloride gas. In this step, the preheated gas is condensed through the preheated gas condenser 405 to cool the HCl and water, i.e., the crude hydrochloric acid solution, for comprehensive utilization.

[0075] The parts of this invention not described in detail are prior art, therefore they are not described in detail here.

[0076] It is understood that the term "a" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element can be one, while in another embodiment, the number of the element can be multiple, and the term "a" should not be understood as a limitation on the number.

[0077] Although this paper extensively uses waste plastic-containing seawater 101, filtration device 102, filtered seawater 103, RO membrane seawater desalination unit 104, primary concentrated seawater tank 105, multi-effect evaporation seawater desalination unit 106, secondary concentrated seawater tank 107, solid waste plastic 201, wet grinding device 202, waste plastic microparticles 203, marine shells 301, lime calcination kiln 302, lime slurry digestion tank 303, magnesium hydroxide sedimentation tank 401, and plate and frame filter press 402. The terms used include seed crystal 403, calcination pyrolysis furnace 404, preheating gas condenser 405, carbothermic magnesium smelting electric arc furnace 501, quenching condenser 502, carbon monoxide gas storage tank 503, steam conversion unit 504, carbon dioxide removal tower 505, magnesium distillation furnace 510, commercial magnesium ingot 511, hydrogen fuel cell stack 601, power station 602, gas storage tank 603, steam storage tank 604, and gas-fired power generation unit 605, but the possibility of using other terms is not excluded. These terms are used merely for the convenience of describing and explaining the essence of the invention; interpreting them as any additional limitation would contradict the spirit of the invention.

[0078] This invention is not limited to the preferred embodiments described above. Anyone can derive other products in various forms under the guidance of this invention. However, regardless of any changes made to their shape or structure, any technical solution that is the same as or similar to that of this application falls within the protection scope of this invention.

Claims

1. A method for extracting metallic magnesium from marine waste plastics in conjunction with seawater and for seawater desalination, characterized in that, Includes the following steps: S00. Filter seawater containing waste plastics to separate solid waste plastics and filtered seawater; S10. The solid waste plastic is wet-milled to obtain waste plastic microparticles, and the filtered seawater is subjected to secondary desalination treatment to obtain secondary concentrated seawater and distilled water, while lime milk is prepared simultaneously. S20. Secondary concentrated seawater, lime slurry, and waste plastic microparticles are mixed and added to the magnesium hydroxide precipitation tank. By using the waste plastic microparticles as crystal seeds for magnesium hydroxide nucleation, a mixture of magnesium hydroxide precipitate and waste plastic microparticles is obtained. S30. The mixture of magnesium hydroxide precipitate and waste plastic microparticles is dehydrated by pressure filtration and then fed into a calcination pyrolysis furnace for calcination to produce magnesium oxide, so as to obtain at least preheating gas, pyrolysis gas, and a mixture of magnesium oxide and carbon particles; the calcination pyrolysis furnace includes a preheating section and a main body. The heating temperature of the preheating section is 300°C, so that the magnesium hydroxide precipitate undergoes a dehydration reaction and the waste plastic microparticles undergo partial pyrolysis to generate preheating gas. The heating temperature of the main body is 700~800°C, so that the waste plastic microparticles are completely and thoroughly pyrolyzed and pyrolysis gas is generated. The residual carbon of the waste plastic microparticles remains in the magnesium oxide. S40. The pyrolysis gas is dehydrated and used as a heating gas energy source for power generation for recycling, and the remaining part is stored for recycling. S50. A mixture of magnesium oxide and carbon particles is processed by carbothermic magnesium smelting and quenching and condensation to obtain solid crystalline magnesium and carbon monoxide gas, and the carbon monoxide gas is stored for recycling. The pyrolysis gas obtained in step S30 is used as fuel for preparing lime milk in step S10 and for calcining magnesium oxide in step S30.

2. The method for extracting metallic magnesium from marine waste plastics and desalination of seawater according to claim 1, characterized in that, It also includes step S60, which specifically includes: The stored carbon monoxide gas is converted to carbon dioxide and hydrogen through steam conversion. The mixture of carbon dioxide and hydrogen is then purified by removing carbon dioxide to obtain hydrogen. The hydrogen is then used to generate electricity for recycling.

3. The method for extracting metallic magnesium from marine waste plastics and desalination of seawater according to claim 1, characterized in that, The specific steps of step S50 are as follows: S51. Magnesium is smelted by carbothermic reduction of a mixture of magnesium oxide and carbon particles through a magnesium smelting electric arc furnace to obtain a mixture of magnesium vapor and carbon monoxide. S52. The mixture of magnesium vapor and carbon monoxide is cooled and separated by a quenching condenser, so that the magnesium vapor is condensed into solid crystalline magnesium, and the carbon monoxide is buffered and stored in a carbon monoxide gas storage tank.

4. The method for extracting metallic magnesium from marine waste plastics and desalination of seawater according to claim 1, characterized in that, It also includes step S70, which specifically includes: The solid crystalline magnesium is subjected to a magnesium distillation process to obtain commercial magnesium ingots, wherein the raw gas for the magnesium distillation process is derived from the stored pyrolysis gas.

5. The method for extracting metallic magnesium from marine waste plastics and desalination of seawater according to claim 1, characterized in that, In step S10, the raw materials used in the preparation of lime milk are marine shells and the pyrolysis gas stored in step S50.

6. The method for extracting metallic magnesium from marine waste plastics and desalination of seawater according to claim 1, characterized in that, It also includes step S80, which specifically includes: The preheated gas generated during the calcination pyrolysis furnace to produce magnesium oxide is condensed to obtain crude hydrochloric acid, wherein the preheated gas includes moisture and hydrogen chloride gas.

7. The method for extracting metallic magnesium from marine waste plastics and desalination of seawater according to claim 2, characterized in that, In step S10, seawater desalination is carried out using the RO membrane method, and the electricity generated by the RO membrane method is supplied through the pyrolysis gas power generation in step S40 and / or the hydrogen power generation in step S60.

8. The method for extracting metallic magnesium from marine waste plastics and desalination of seawater according to claim 2, characterized in that, In step S60, the steam generated in the steam conversion process is supplied to the seawater distillation and desalination stage in the secondary seawater desalination process in step S10.

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