Process for the preparation of a hydrophobic dioxin formation inhibitor and its use

Abstract

The present application relates to the technical field of flue gas treatment, in particular to a preparation method of a hydrophobic dioxin generation retarder and application thereof, the present application aims at the problem that the existing dioxin retarder has poor efficiency under the condition of water-containing flue gas, and proposes a preparation method of adding a layer of hydrophobic shell on the base oxidant, the traditional base oxidant retarder is modified by surface hydrophobization to obtain a new retarder with hydrophobic property. The retarder utilizes the hydrophobic effect of the high-silicon aluminum ratio molecular sieve on the shell, can effectively reduce the direct contact of water and the base oxidant, and the chlorine-containing gas such as hydrogen chloride and chlorine can pass through the hydrophobic shell and react with the base oxidant, thereby improving the problem that the performance of the original retarder is greatly affected by water, so as to improve the adsorption capacity of the retarder, and make it adapt to the condition of flue gas with high water content.

Description

Technical Field

[0001] This invention relates to the field of flue gas treatment technology, and in particular to a method for preparing a hydrophobic dioxin formation inhibitor and its application. Background Technology

[0002] Dioxins are an abbreviation for polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), two classes of compounds that pose a significant threat to human health. Dioxins are byproducts of combustion processes, and over 90% of dioxins in the environment are produced by human activities. Currently, my country's "Standard for Pollutant Control from Municipal Solid Waste Incineration" and "Emission Standard for Air Pollutants from Steelmaking Industry" both clearly limit the concentration of dioxins in flue gas emissions. Therefore, developing an efficient dioxin control method is extremely crucial.

[0003] Dioxin control methods, based on the principle of reducing dioxins, are mainly divided into pre-formation control, in-formation control, and post-formation control. Dioxin formation inhibition technology involves injecting inhibitors during flue gas cooling. These inhibitors react with chlorine or hydrogen chloride in the flue gas, reducing the chlorine source and thus lowering dioxin formation—a method of in-form control. Currently, commonly used dioxin inhibitors are basic inhibitors, primarily basic oxides, which can react with chlorine sources at a 1:2 molar ratio. However, in actual use, due to the high water content in the flue gas (5-20%), some water reacts with the basic oxides. The reaction products form a dense shell on the inhibitor surface, hindering the contact and reaction between the chlorine source and the inhibitor. This results in very low inhibitor utilization efficiency, with the molar ratio of reaction with the chlorine source being far lower than the theoretical value. Summary of the Invention

[0004] The technical problem this invention aims to solve is the poor efficiency of existing dioxin inhibitors under conditions of water-containing flue gas. It proposes a preparation method that adds a hydrophobic shell layer to a basic oxide, modifying the surface of a traditional basic oxide inhibitor to be hydrophobic, resulting in a novel inhibitor with hydrophobic properties. This inhibitor utilizes the hydrophobic effect of the high silica-to-alumina ratio molecular sieve on the shell to effectively reduce direct contact between water and the basic oxide. Meanwhile, chlorine-containing gases such as hydrogen chloride and chlorine can pass through the hydrophobic shell and react with the basic oxide, improving the performance of the original inhibitor, which is significantly affected by water. This enhances the inhibitor's adsorption capacity, enabling it to adapt to flue gas conditions with high water content. The specific steps of a method for preparing a hydrophobic dioxin formation inhibitor are as follows:

[0005] (1) Molecular sieves are prepared by uniformly mixing silicon source, aluminum source, template agent, and surface charge treatment agent in deionized water.

[0006] (2) Then add basic oxide powder to it, and then put it into a hydrothermal reactor. After reacting at 150-180℃ for 72-96h, filter, wash and dry it, and then calcine it at 400-550℃ for 2-6 hours to obtain a hydrophobic dioxin formation inhibitor. The core of the hydrophobic dioxin formation inhibitor is a basic oxide, and a hydrophobic molecular sieve shell is loaded on its surface.

[0007] Furthermore, in the preparation method, depending on the actual situation, an alkaline substance, such as sodium hydroxide, is added during the preparation of molecular sieves in step (1) to provide the alkaline environment required for molecular sieve preparation.

[0008] Furthermore, the mass ratio of the molecular sieve precursor silicon source, molecular sieve precursor aluminum source, molecular sieve template agent, surface charge treatment agent and basic oxide powder is (13.5-60): (8-10): (15-25): (12-20): (12-15).

[0009] Furthermore, the basic oxide is one or more combinations of calcium oxide, calcium hydroxide, potassium oxide, magnesium oxide, zinc oxide, aluminum oxide, and iron oxide.

[0010] Furthermore, the hydrophobic molecular sieve shell is one of the following: high silica-to-alumina ratio molecular sieves: Beta, ZSM-5, MOR, SAPO-34, SSZ-13, and SSZ-39.

[0011] Furthermore, the silicon source of the molecular sieve precursor is one or more combinations of silica sol, tetraethyl orthosilicate, and silica.

[0012] Furthermore, the aluminum source of the molecular sieve precursor is one or more combinations of boehmite, sodium aluminate, and aluminosilicate.

[0013] Furthermore, the molecular sieve template agent is one or more combinations of hexadecyltrimethylammonium bromide, tetrapropylammonium hydroxide, tetrapropylammonium bromide, sodium dodecylbenzenesulfonate, N,N,N-trimethyl-1-adamantylammonium hydroxide, N,N-diisopropylethylamine, and tetraethylenepentamine.

[0014] Furthermore, the surface charge treatment agent is one or more combinations of polydiallyldimethylammonium chloride, aminopropyltriethoxysilane, and tetrabutyl titanate.

[0015] Furthermore, the drying temperature is 100°C and the drying time is 12 to 36 hours, preferably 12 hours.

[0016] Furthermore, the calcination temperature is 500~550℃ and the calcination time is 4~6 hours.

[0017] The present invention also provides the application of the hydrophobic dioxin formation inhibitor obtained by the above preparation method as a dioxin formation inhibitor.

[0018] The technical solution of the present invention has the following advantages and beneficial effects compared with the prior art:

[0019] Because high silica-alumina ratio molecular sieves have very few hydrogen bonds, they possess natural hydrophobic properties. By coating the surface of basic oxides with high silica-alumina ratio molecular sieves for hydrophobic modification, the molecular sieves, with few hydroxyl groups, have a weak attraction to water through hydrogen bonds, thus repelling water. This hydrophobicity of the molecular sieves can be used to prevent water from contacting the basic oxides, thereby improving the absorption capacity of the basic oxides for HCl. This addresses the problem of the original inhibitors being significantly affected by water, allowing them to maintain good performance even under flue gas conditions with high water vapor content, making them suitable as dioxin inhibitors.

[0020] On the other hand, the preparation method of the present invention is to directly synthesize it in situ in one step. In the reaction vessel, the basic oxide, the molecular sieve precursor silicon source, the molecular sieve precursor aluminum source, the molecular sieve template agent, and the surface charge treatment agent are added for hydrothermal synthesis. The surface charge modifier is mainly used to induce the growth of molecular sieve on the surface of basic oxide powder. In this way, the hydrophobic blocking agent can be synthesized through in situ reaction. Attached Figure Description

[0021] Figure 1 This is an HCl adsorption-through curve of the hydrophobic blocking agent prepared in Example 1 and the conventional blocking agent under simulated flue gas.

[0022] Figure 2 This is an HCl adsorption-through curve of the hydrophobic blocking agent prepared in Example 2 and the conventional blocking agent under simulated flue gas.

[0023] Figure 3 These are microscopic images taken with a scanning electron microscope after the hydrophobic blocking agent prepared in Example 2 and a conventional blocking agent reacted under simulated flue gas for 5 hours. Detailed Implementation

[0024] The technical solution of the present invention will be specifically described below through specific embodiments and in conjunction with the accompanying drawings.

[0025] In the following examples, the calcium oxide powder is the undersize product after grinding and passing through a 300-mesh sieve.

[0026] Example 1: A method for preparing a dioxin formation inhibitor, the specific steps of which are as follows:

[0027] Add 45 g of silica sol with a mass concentration of 30% (silica), 8 g of sodium aluminate, 25 g of N,N,N-trimethyl-1-adamantyl ammonium hydroxide, and 20 g of aminopropyltriethoxysilane to 180 g of deionized water. After stirring evenly, add 12 g of calcium oxide powder and transfer the solution to a hydrothermal reactor. Then, react at 180°C for 96 hours, filter, and wash the obtained solid with deionized water until the washing liquid is neutral. Dry the washed solid at 100°C for 12 hours until completely dry, then calcine it in a muffle furnace at 550°C for 5 hours. Finally, take it out, grind it, and pass it through a 300-mesh sieve to obtain a hydrophobic inhibitor (SH-1) with SSZ-13 as the hydrophobic outer layer.

[0028] Example 2: A method for preparing a dioxin formation inhibitor, the specific steps of which are as follows:

[0029] Add 60 g tetraethyl orthosilicate, 10 g boehmite, 8 g sodium hydroxide (to provide the alkaline environment and Na ions required for molecular sieve preparation), 15 g tetrapropylammonium hydroxide, and 12 g polydiallyldimethylammonium chloride to 220 g deionized water. After stirring evenly, add 15 g calcium oxide powder and transfer the solution to a hydrothermal reactor. Then, react at 150°C for 72 hours, filter, and wash the resulting solid with deionized water until the washing liquid is neutral. Dry the washed solid at 100°C for 12 hours until completely dry, then calcine it in a muffle furnace at 500°C for 4 hours. Finally, take it out, grind it through a 300-mesh sieve to obtain a hydrophobic blocking agent (SH-2) with ZSM-5 as the hydrophobic outer layer.

[0030] Test case

[0031] The hydrophobic dioxin formation inhibitor described in this invention was evaluated using a fixed-bed method, with calcium oxide, a traditional inhibitor, used as a comparative example.

[0032] Using HCl as the chlorine source, the adsorption capacity of the HCl inhibitor was evaluated by monitoring the outlet HCl concentration online, further assessing the inhibitor's performance. In the test, the inhibitor and quartz sand were placed in a quartz fixed bed with an inner diameter of 6 mm at a 1:1 mass ratio. A simulated gas was used, with the following composition: HCl (200 ppm), H₂O (10%), and N₂ as the equilibrium gas. The total gas flow rate was 100 ml / min, and the reaction temperature was 450℃. The HCl concentration of the inlet and outlet gases was measured online using a Fourier transform infrared spectroscopy (FTIR) instrument. The tail gas after the reaction was absorbed using a sodium hydroxide aqueous solution.

[0033] Figure 1 This is the HCl adsorption-through curve of SH-1 and the traditional inhibitor calcium oxide in simulated flue gas, i.e., the real-time concentration of HCl in the fixed-bed outlet gas during the test. Figure 1 As can be seen, the calcium oxide inhibitor caused a rapid increase in the outlet HCl concentration at the start of the reaction, and it reached near saturation after about 130 minutes, indicating that the calcium oxide inhibitor has a very limited adsorption capacity for HCl under conditions of water-containing flue gas. The SH-1 inhibitor, with SSZ-13 as its hydrophobic outer layer, showed a significant improvement in performance. The rate of increase in outlet HCl concentration was significantly slower than that of the traditional calcium oxide inhibitor, and its upward trend only gradually slowed down after 300 minutes of reaction, indicating that SH-1 had a greater adsorption capacity for HCl and a better reaction effect under conditions of water-containing flue gas.

[0034] Figure 2 This is a graph showing the HCl adsorption-throughput curves of SH-2 and a traditional calcium oxide inhibitor in simulated flue gas. From... Figure 2 As can be seen, the performance of SH-2 inhibitor with ZSM-5 as hydrophobic shell is significantly improved. Compared with calcium oxide inhibitor, the HCl concentration at the SH-2 outlet is still only about 10 ppm after more than 10 hours of reaction, indicating that the adsorption of HCl by SH-2 has not reached saturation at this time, and the adsorption capacity of HCl by SH-2 is much higher than that of calcium oxide inhibitor.

[0035] Compare Figure 1 and Figure 2 SH-1 may have a lower silica-to-alumina ratio or poor coverage of CaO, resulting in a lack of proper CaO coating and thus weak hydrophobicity. In contrast, SH-2 has a better coating effect and therefore stronger resistance to water.

[0036] Figure 3 These are microscopic images taken with a scanning electron microscope after (a) SH-2 and (b) calcium oxide inhibitor reacted under simulated flue gas for 5 hours. The images show that after 5 hours of reaction, the calcium oxide inhibitor produced a noticeable paste-like substance covering the particle surface. This substance, generated from the reaction between water and calcium oxide, adhered to the particle surface, hindering the contact reaction between HCl and calcium oxide. In contrast, after the same reaction time, SH-2 particles remained clearly visible, and their surfaces were not covered by any other substances. This indicates that the hydrophobic outer shell effectively reduces the reaction between water and the calcium oxide inner shell, avoiding the influence of reaction byproducts and effectively improving the inhibitor's absorption capacity with chlorine sources under aqueous conditions.

Claims

1. A method for preparing a hydrophobic dioxin formation inhibitor, comprising the following specific steps: (1) Molecular sieves are prepared by uniformly mixing silicon source, aluminum source, template agent, and surface charge treatment agent in deionized water. (2) Then add basic oxide powder to it, and then put it into a hydrothermal reactor. After reacting at 150-180℃ for 72-96h, filter, wash and dry it, and then calcine it at 400-550℃ for 2-6h to obtain a hydrophobic dioxin formation inhibitor. The core of the hydrophobic dioxin formation inhibitor is a basic oxide, and a hydrophobic molecular sieve shell is loaded on its surface. The hydrophobic molecular sieve shell is one of the following: high silica-to-alumina ratio molecular sieves: Beta, ZSM-5, MOR, SAPO-34, SSZ-13, and SSZ-39. The basic oxide is one or more of the following: calcium oxide, calcium hydroxide, potassium oxide, magnesium oxide, zinc oxide, aluminum oxide, and iron oxide. The molecular sieve template agent is one or more combinations of hexadecyltrimethylammonium bromide, tetrapropylammonium hydroxide, tetrapropylammonium bromide, sodium dodecylbenzenesulfonate, N,N,N-trimethyl-1-adamantylammonium hydroxide, N,N-diisopropylethylamine, and tetraethylenepentamine; the surface charge treatment agent is one or more combinations of polydiallyldimethylammonium chloride, aminopropyltriethoxysilane, and tetrabutyl titanate. The silicon source of the molecular sieve precursor is one or more of silica sol, tetraethyl orthosilicate, and silica; the aluminum source of the molecular sieve precursor is one or more of boehmite, sodium aluminate, and aluminosilicate.

2. The preparation method according to claim 1, characterized in that, In the preparation method, an alkaline substance is added during the preparation of molecular sieve in step (1) to provide the alkaline environment required for molecular sieve preparation.

3. The preparation method according to claim 1, characterized in that, The mass ratio of the molecular sieve precursor silicon source, molecular sieve precursor aluminum source, molecular sieve template agent, surface charge treatment agent and basic oxide powder is (13.5-60): (8-10): (15-25): (12-20): (12-15).

4. The preparation method according to claim 1, characterized in that, The drying temperature is 100℃ and the drying time is 12~36 hours.

5. The application of the hydrophobic dioxin formation inhibitor obtained by the preparation method according to any one of claims 1-4 as a dioxin formation inhibitor.

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