Modified coconut shell activated carbon adsorbent as well as preparation method and application thereof

Abstract

The invention relates to the technical field of purification of cold hydrogenated slurry high-boiling residues, and provides a modified coconut shell activated carbon adsorbent as well as a preparation method and application thereof. The modified coconut shell activated carbon adsorbent is characterized by comprising a coconut shell activated carbon substrate; the alkaline nitrogen-containing functional group is covalently bonded on the coconut shell activated carbon substrate. The alkaline nitrogen-containing functional group is stably loaded on the surface of the activated carbon in a covalent bond mode instead of simple physical impregnation, and efficient and high-selectivity adsorption is achieved through the acid-base coordination effect of the alkaline nitrogen-containing functional group and aluminum and titanium impurities. The preparation method of the modified coconut shell activated carbon adsorbent comprises the following steps: carrying out first reaction on a coconut shell activated carbon substrate and oxidizing acid to obtain oxidized coconut shell activated carbon; and carrying out a second reaction on the oxidized coconut shell activated carbon and an amine-containing compound to obtain the modified coconut shell activated carbon adsorbent. The method is simple in steps, mild in reaction conditions and easy to industrialize.

Description

Technical Field

[0001] This invention relates to the field of purification technology for high-boiling-point substances in cold hydrogenated slurry, specifically to a modified coconut shell activated carbon adsorbent, its preparation method, and its application. Background Technology

[0002] The high-boiling-point slurry (commonly known as "high-boiling matter") produced as a byproduct of the polycrystalline silicon cold hydrogenation process contains 500-3000 ppm of impurities containing metals such as Al and Ti. These impurities undergo Lewis acid catalytic side reactions with Si–Cl bonds in the subsequent "high-boiling-point pyrolysis" step, generating AlCl3, TiCl4, and even higher-boiling-point Si–Al–Ti ternary complexes. This leads to problems such as the covering of the active sites of the pyrolysis catalyst, shortened catalyst lifespan, increased energy consumption, and higher solid content in the pyrolysis residue.

[0003] In related technologies, metal removal from high-boiling-point substances in cold hydrogenation slurry mainly relies on methods such as chemical complexation precipitation, cation exchange resin methods, and activated carbon. Chemical complexation precipitation often uses fluorides, phosphate esters, or 8-hydroxyquinoline with Al. 3+ Ti 4 + Precipitation is formed, followed by filtration and separation. However, this process easily generates large amounts of hazardous waste containing fluorine / phosphorus, the equipment is highly corrosive, the process is complex, and the wastewater treatment cost is high. The cation exchange resin method often uses sulfonic acid or carboxylic acid resins to capture Al. 3+ Ti 4+ However, in the chlorosilane system, Al and Ti mainly exist in the form of neutral AlCl3, TiCl4 or partially positively charged complexes, resulting in limited adsorption effect. At the same time, the resin skeleton is easily swollen by chlorosilanes, leading to high loss rate. For activated carbon, related technologies often use acid washing or introduce acidic functional groups (such as carboxyl groups and phosphonic acid groups) on the surface of activated carbon to adsorb metal cations. However, their adsorption capacity for neutral AlCl3, TiCl4 or their weak complexes with Si-Cl bonds is low, and the selectivity is poor. They are also prone to co-adsorption of SiCl4, leading to loss of effective silicon.

[0004] Therefore, the related technologies based on the ideas of "cation exchange" or "complex precipitation" cannot effectively capture neutral or weakly positively charged aluminum-titanium complexes in the chlorosilane system. They have poor selectivity, low adsorption capacity, easy dissolution of active components, poor long-term stability, and also have problems such as secondary pollution and equipment corrosion. Summary of the Invention

[0005] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, this invention provides a modified coconut shell activated carbon adsorbent, its preparation method, and its application. By stably loading basic nitrogen-containing functional groups onto an activated carbon matrix via covalent bonds, it can efficiently and selectively capture impurities such as neutral AlCl3, TiCl4, or partially positively charged Al and Ti metal complexes in a chlorosilane system through Lewis acid-base coordination. This extends the service life of high-boiling-point decomposition agents, prevents the dissolution of active components, and improves long-term stability.

[0006] A first aspect of the present invention provides a modified coconut shell activated carbon adsorbent, comprising: Coconut shell activated carbon matrix; Basic nitrogen-containing functional groups are covalently bonded to the coconut shell activated carbon matrix.

[0007] This invention is based on the Lewis acid-base theory. Neutral AlCl3, TiCl4, or partially positively charged Al and Ti metal complexes, representing aluminum and titanium impurities, are Lewis acids. By modifying the adsorbent surface with abundant Lewis base sites, efficient and selective adsorption of aluminum and titanium impurities can be achieved through acid-base coordination. Basic nitrogen-containing functional groups are typical Lewis base groups. Therefore, this invention, by loading basic nitrogen-containing functional groups onto the surface of a coconut shell activated carbon matrix, facilitates the selective and deep removal of aluminum and titanium impurities from chlorosilane systems.

[0008] According to an embodiment of the present invention, the basic nitrogen-containing functional group includes primary amine (-NH2), secondary amine (-NHR), tertiary amine (-NR2), and quaternary ammonium (-NR3). + One or more of the following, wherein R represents a modified or unmodified alkyl group of C1 to C20.

[0009] According to an embodiment of the present invention, the BET specific surface area of ​​the coconut shell activated carbon matrix is ​​1000~3000 m². 2 / g, preferably 1500~2500m 2 / g.

[0010] According to an embodiment of the present invention, the iodine value of the coconut shell activated carbon matrix is ​​800~1200 mg / g, preferably 800~1000 mg / g.

[0011] According to an embodiment of the present invention, the ash content of the coconut shell activated carbon matrix is ​​≤5%, preferably <1%.

[0012] According to an embodiment of the present invention, the strength of the coconut shell activated carbon matrix is ​​>96%, preferably >98%.

[0013] According to an embodiment of the present invention, the proportion of mesopores in the coconut shell activated carbon matrix to the total pore volume is >50%, preferably >75%.

[0014] According to an embodiment of the present invention, the nitrogen content of the modified coconut shell activated carbon adsorbent ranges from 1.0 to 3.5 mmol / g.

[0015] According to an embodiment of the present invention, the alkaline site density of the modified coconut shell activated carbon adsorbent ranges from 0.5 to 2.0 mmol / g.

[0016] According to an embodiment of the present invention, the modified coconut shell activated carbon adsorbent has an amine grafting rate of ≥60%.

[0017] A second aspect of the present invention provides a method for preparing the above-mentioned modified coconut shell activated carbon adsorbent, comprising the following steps: The coconut shell activated carbon matrix is ​​reacted with an oxidizing acid to obtain oxidized coconut shell activated carbon. The oxidized coconut shell activated carbon is reacted with an amine-containing compound in a second reaction to obtain a modified coconut shell activated carbon adsorbent.

[0018] The above technical solution can introduce active anchoring sites such as carboxyl and hydroxyl groups on the surface of coconut shell activated carbon through acid oxidation treatment. These active anchoring sites then react with amine-containing compounds, which firmly graft the amine groups onto the activated carbon surface through chemical bonds (such as amide bonds), thereby improving the adsorption selectivity and adsorption capacity for aluminum and titanium impurities. It also avoids the leaching of modifiers during use, improving the long-term stability of the adsorbent and the purity of chlorosilane products. The reaction conditions are mild and easy to industrialize.

[0019] According to an embodiment of the present invention, the first reaction temperature is 60~90℃, and the first reaction time is 2~4h.

[0020] According to an embodiment of the present invention, the oxidizing acid includes one or more of nitric acid, concentrated sulfuric acid, periodic acid, hypochlorous acid, and peracetic acid. Nitric acid with a mass concentration of 10%-30% is preferred.

[0021] According to embodiments of the present invention, the amine-containing compound includes one or more of polyethyleneimine, poly(allylamine), polyethyleneamine, ethylenediamine, and diethylenetriamine.

[0022] According to an embodiment of the present invention, the second reaction method is carried out by at least one of solution impregnation or in-situ grafting.

[0023] According to an embodiment of the present invention, the solution impregnation method includes: impregnating the oxidized coconut shell activated carbon in a solution of macromolecular amine compounds, stirring and reacting to obtain the modified coconut shell activated carbon adsorbent.

[0024] By adopting the above technical solution, the carboxyl groups on the oxidized coconut shell activated carbon can undergo amidation reactions with primary and secondary amine groups in macromolecular amine-containing compounds, causing the amine-containing compounds to covalently bond to the coconut shell activated carbon matrix, thereby introducing a large number of basic nitrogen-containing groups onto the surface of the oxidized coconut shell activated carbon. The abundant mesoporous structure of the coconut shell activated carbon matrix allows macromolecular amine-containing compounds to penetrate deep into the pores. Utilizing the multiple active primary and secondary amine groups on the macromolecular amine-containing compounds, they can achieve multi-point anchoring with the coconut shell activated carbon, thus forming a stable three-dimensional network coating layer, significantly increasing the amine group density and stability.

[0025] It should be noted that the macromolecular amine compound is a trimer or polymeric amine compound.

[0026] According to an embodiment of the present invention, the macromolecular amine-containing compound includes one or more of polyethyleneimine (PEI), poly(allylamine), and polyethyleneamine.

[0027] In one embodiment, the temperature of the stirring reaction in the solution impregnation method is 60~80°C, and the stirring reaction time is 6~10h.

[0028] According to an embodiment of the present invention, the in-situ grafting method includes: The oxidized coconut shell activated carbon was reacted with thionyl chloride to obtain an acyl chloride product; The acyl chloride product is reacted with a small molecule amine-containing compound to obtain the modified coconut shell activated carbon adsorbent.

[0029] Using the above technical solution, the carboxyl groups on the surface of the oxidized coconut shell activated carbon can be chlorinated with thionyl chloride. The acyl chloride reacts with the primary and secondary amine groups on the amine-containing compound through an amidation reaction, causing the amine-containing compound to be covalently bonded to the coconut shell activated carbon matrix. This introduces terminal basic nitrogen-containing groups on the surface of the oxidized coconut shell activated carbon, firmly grafting the amine groups onto the activated carbon surface, thereby improving the long-term stability, adsorption selectivity, and adsorption efficiency of the adsorbent.

[0030] It should be noted that the small molecule amine compound is an oligomeric or dimer amine compound.

[0031] According to an embodiment of the present invention, the preparation method of the modified coconut shell activated carbon adsorbent further includes post-treatment, which includes: separating solid products, washing, drying, and obtaining purified modified coconut shell activated carbon adsorbent.

[0032] The above technical solution can effectively remove physically adsorbed or residual free amines, ensuring that all measured amine groups are chemically loaded. This is beneficial for improving the stability of the adsorbent and the purity of chlorosilane products, and avoiding secondary pollution and equipment corrosion.

[0033] According to an embodiment of the present invention, the drying temperature is 80~100℃.

[0034] A third aspect of the present invention provides an application of the modified coconut shell activated carbon adsorbent described above or the modified coconut shell activated carbon adsorbent prepared by the above preparation method in removing aluminum and titanium impurities in a chlorosilane system.

[0035] According to an embodiment of the present invention, the application includes: preheating the high-boiling-point substance and passing it through a fixed bed loaded with the adsorbent to remove impurities such as aluminum and titanium online, and then the purified liquid enters the pyrolysis unit for pyrolysis.

[0036] According to an embodiment of the present invention, the modified coconut shell activated carbon adsorbent can be recycled after adsorption saturation. The regeneration process includes acid desorption treatment, steam purging and neutralization, and thermal drying regeneration.

[0037] In one embodiment, the acid desorption treatment includes isolating the saturated adsorbent bed from the process pipeline and flushing the bed in a counter-current or forward direction with a dilute acid solution (such as dilute hydrochloric acid, dilute nitric acid, or dilute sulfuric acid) with a concentration of 0.1~2.0 mol / L. The flushing temperature is 20~80°C and the liquid hourly space velocity (LHSV) is 1~5 h⁻¹. - ¹, continue processing for 1 to 4 hours.

[0038] In one embodiment, the steam purging and neutralization includes thoroughly rinsing the bed with deionized water until the discharged water is neutral (pH≈6~7) to completely remove residual acid and metal ions. Then, low-temperature steam at 100~150°C is introduced to purge the bed for 0.5~2 hours to further remove residual moisture and volatile substances from the pores and to preliminarily activate the adsorbent framework.

[0039] In one embodiment, the thermal drying regeneration includes shutting off the steam, gradually raising the bed temperature to 150-250°C under the protection of an inert gas (such as nitrogen), maintaining this temperature for 1-3 hours to perform gentle thermal regeneration, and then re-entering the adsorption cycle after the bed cools down to the operating temperature.

[0040] Compared with related technologies, the present invention has at least the following beneficial effects: (1) This invention provides a modified coconut shell activated carbon adsorbent, its preparation method, and its application. It is the first to explicitly propose introducing basic nitrogen-containing groups onto the surface of coconut shell activated carbon via covalent bonds, acting as Lewis bases, to selectively capture Lewis acidic aluminum and titanium impurities in chlorosilane systems through coordination. This mechanism differs from traditional ion exchange, exhibiting stronger adsorption capacity for neutral or weakly charged metal complexes and significantly improved selectivity for aluminum and titanium impurities.

[0041] (2) Large adsorption capacity: The surface of modified coconut shell activated carbon contains a large number of amine groups, especially coconut shell activated carbon modified with high molecular weight such as polyethyleneimine, which can form high density adsorption sites on the surface and in the pores, thereby obtaining an adsorption capacity far exceeding that of acid washing or small molecule modification.

[0042] (3) Good functional group stability: The amine group is firmly grafted onto the activated carbon skeleton through chemical bonds, which avoids the dissolution of the modifier during use, improves the amine group retention rate after multiple hydrolysis and regeneration, ensures the long-term stability of the adsorbent and the purity of the chlorosilane product, and avoids secondary pollution and equipment corrosion.

[0043] (4) The preparation process is flexible and controllable: The method is simple and the strength and density of surface alkalinity can be adjusted by selecting amine compounds of different molecular weights and types to meet different purification needs. Detailed Implementation

[0044] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0045] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0046] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0047] In this document, the terms “comprising” or “including” are open-ended expressions, meaning that they include the contents specified in this invention, but do not exclude other aspects.

[0048] In this document, the terms “optionally,” “optionally,” or “optionally” generally refer to an event or condition that may, but may not, occur, and the description includes both cases in which the event or condition occurs and cases in which the event or condition does not occur.

[0049] To address the limitations of existing technologies based on "cation exchange" or "complex precipitation," which fail to effectively capture neutral or weakly positively charged aluminum-titanium complexes in chlorosilane systems due to poor selectivity, low adsorption capacity, easy dissolution of active components, poor long-term stability, and issues such as secondary pollution and equipment corrosion, this invention provides a modified coconut shell activated carbon adsorbent, its preparation method, and its applications. By covalently loading basic nitrogen-containing functional groups onto an activated carbon matrix, it can efficiently and selectively capture neutral AlCl3, TiCl4, or partially positively charged Al and Ti metal complexes in chlorosilane systems through "Lewis acid-base coordination," extending the lifespan of high-boiling-point decomposition agents, preventing the dissolution of active components, and improving long-term stability.

[0050] A first aspect of the present invention provides a modified coconut shell activated carbon adsorbent, comprising: Coconut shell activated carbon matrix; Basic nitrogen-containing functional groups are covalently bonded to the coconut shell activated carbon matrix.

[0051] This invention is based on the Lewis acid-base theory. Neutral AlCl3, TiCl4, or partially positively charged Al and Ti metal complexes, representing aluminum and titanium impurities, are Lewis acids. By modifying the adsorbent surface with abundant Lewis base sites, efficient and selective adsorption of aluminum and titanium impurities can be achieved through acid-base coordination. Basic nitrogen-containing functional groups are typical Lewis base groups. Therefore, this invention, by loading basic nitrogen-containing functional groups onto the surface of a coconut shell activated carbon matrix, facilitates the selective and deep removal of aluminum and titanium impurities from chlorosilane systems.

[0052] According to an embodiment of the present invention, the basic nitrogen-containing functional group includes primary amine (-NH2), secondary amine (-NHR), tertiary amine (-NR2), and quaternary ammonium (-NR3). + One or more of the following, wherein R represents a modified or unmodified alkyl group of C1 to C20.

[0053] According to an embodiment of the present invention, the BET specific surface area of ​​the coconut shell activated carbon matrix is ​​1000~3000 m². 2 / g, preferably 1500~2500m 2 / g. For example, 1000m 2 / g、1200m 2 / g, 1500m 2 / g、2000m 2 / g、2200m 2 / g、2500m 2 / g、2800m 2 / g、3000m 2 / g etc.

[0054] By adopting the above technical solution, sufficient "substrate area" can be provided to load the subsequently grafted amine functional groups, ensuring the density of basic nitrogen-containing functional groups without clogging the pores. If the BET specific surface area is too low, the surface amine density may be too high under the same amine loading, causing the pores to be blocked by polymer chains. Compared with the preferred value range, the diffusion coefficient of aluminum and titanium impurities decreases and the dynamic adsorption capacity decreases.

[0055] According to an embodiment of the present invention, the iodine value of the coconut shell activated carbon matrix is ​​800~1200 mg / g, preferably 800~1000 mg / g. Specifically, values ​​include 800 mg / g, 850 mg / g, 900 mg / g, 950 mg / g, 1000 mg / g, 1050 mg / g, 1100 mg / g, 1150 mg / g, and 1200 mg / g.

[0056] It should be noted that the iodine value of activated carbon reflects its adsorption capacity for small molecules. Within the aforementioned range, an iodine value ensures the rapid entry and exit of small SiCl4 molecules while blocking larger aluminum and titanium impurities in the mesopore region, achieving "size sieving" to aid selectivity. If the iodine value is too low, the carboxyl groups generated during amination preferentially enter the micropores, potentially leading to a decrease in the grafting amount in the mesopore region and a reduction in the Al and Ti capacities relative to the optimal range. Conversely, if the iodine value is too high, it may increase the co-adsorption of SiCl4, resulting in a higher effective silicon loss relative to the optimal range.

[0057] According to an embodiment of the present invention, the ash content of the coconut shell activated carbon matrix is ​​≤5%, preferably <1%. Specifically, it is 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, etc.

[0058] It should be noted that oxides such as Al, Fe, and Ca in ash are Lewis acids, which may combine with grafted basic nitrogen-containing groups, reducing the effective alkali sites. Simultaneously, ash is easily dissolved during nitric acid oxidation, potentially causing scaling on equipment. Therefore, excessive ash content may lead to a decrease in the effective amine site density, an increased scaling rate during the oxidation stage, and increased secondary pollution.

[0059] According to an embodiment of the present invention, the strength of the coconut shell activated carbon matrix is ​​>96%, preferably >98%. Specifically, it includes values ​​such as 96.5%, 97%, 97.5%, 98%, 98.5%, 99%, 99.5%, and 100%.

[0060] It should be noted that the strength mentioned, as determined by GB / T 12496.6, refers to the percentage of activated carbon particles that remain within their original particle size range after undergoing specified mechanical abrasion.

[0061] By adopting the above technical solution, the fixed bed height and pressure during adsorption can be guaranteed. If the strength is too low, the pressure drop may increase after long-term operation, the adsorbent may break, the broken powder may enter the cracking furnace and be deposited on the catalyst surface, and the catalyst life may be reduced relative to the preferred value range.

[0062] According to an embodiment of the present invention, the proportion of mesopores in the coconut shell activated carbon matrix to the total pore volume is >50%, preferably >75%; specifically, such as 52%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, etc.

[0063] The mesopores have a pore size of 2-50 nm. The mesopores can provide channels to match larger impurities such as neutral AlCl3 and TiCl4 aggregates or partially positively charged Al and Ti metal complexes. The high proportion of mesopores facilitates the rapid diffusion of the aforementioned aluminum and titanium impurities to the inner surface, avoiding pore blockage and shortening the equilibrium time.

[0064] According to an embodiment of the present invention, the nitrogen content of the modified coconut shell activated carbon adsorbent ranges from 1.0 to 3.5 mmol / g, specifically such as 1.0 mmol / g, 1.5 mmol / g, 2.0 mmol / g, 2.5 mmol / g, 3.0 mmol / g, 3.5 mmol / g, etc.

[0065] It should be noted that a higher nitrogen content usually means more theoretical coordination sites and a larger theoretical saturation capacity of Al / Ti; however, when the nitrogen content is too high, polymer chains can easily block the pores, which may lead to a surge in SiCl4 co-adsorption and increase the risk of nitrogen dissolution.

[0066] According to an embodiment of the present invention, the alkaline site density of the modified coconut shell activated carbon adsorbent ranges from 0.5 to 2.0 mmol / g, specifically such as 0.5 mmol / g, 0.8 mmol / g, 1.0 mmol / g, 1.2 mmol / g, 1.5 mmol / g, 1.8 mmol / g, 2.0 mmol / g, etc.

[0067] It should be noted that the density of alkaline sites directly determines the effective adsorption capacity and selectivity. Generally speaking, the higher the density, the higher the adsorption rate and selectivity of aluminum and titanium impurities. However, when the density of alkaline sites is too high, it is easy to increase the pore resistance, which may increase the pressure drop of the bed and increase the pump consumption.

[0068] According to an embodiment of the present invention, the modified coconut shell activated carbon adsorbent has an amine grafting rate of ≥60%, specifically such as 60%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, etc.

[0069] By adopting the above implementation scheme, amino groups can be covalently bonded to the carbon skeleton through covalent bonds, which is beneficial to improve the desorption rate and cycle capacity retention rate. If the amino group grafting rate is too low, it may lead to a decrease in the desorption rate and cycle capacity retention rate, and a shortened service life.

[0070] A second aspect of the present invention provides a method for preparing the above-mentioned modified coconut shell activated carbon adsorbent, comprising the following steps: The coconut shell activated carbon matrix is ​​reacted with an oxidizing acid to obtain oxidized coconut shell activated carbon. The oxidized coconut shell activated carbon is reacted with an amine-containing compound in a second reaction to obtain a modified coconut shell activated carbon adsorbent.

[0071] The above technical solution can introduce active anchoring sites such as carboxyl and hydroxyl groups on the surface of coconut shell activated carbon through acid oxidation treatment. These active anchoring sites then react with amine-containing compounds, which firmly graft the amine groups onto the activated carbon surface through chemical bonds (such as amide bonds), thereby improving the adsorption selectivity and adsorption capacity for aluminum and titanium impurities. It also avoids the leaching of modifiers during use, improving the long-term stability of the adsorbent and the purity of chlorosilane products. The reaction conditions are mild and easy to industrialize.

[0072] According to an embodiment of the present invention, the first reaction temperature is 60~90℃, and the first reaction time is 2~4h.

[0073] It should be noted that the milder reaction conditions allow for improved controllability of acidic oxidation, enabling the generation of sufficient anchoring sites while avoiding excessive oxidation that could damage the skeletal structure and pores of the activated carbon.

[0074] According to an embodiment of the present invention, the oxidizing acid includes one or more of nitric acid, concentrated sulfuric acid, periodic acid, hypochlorous acid, and peracetic acid. Nitric acid with a mass concentration of 10%-30% is preferred.

[0075] The above technical solution enables the introduction of oxygen-containing functional groups such as carboxyl (-COOH), hydroxyl (-OH), or lactone groups into the carbon skeleton of activated carbon (especially at edge defect sites) through surface oxidation, while simultaneously cleaning the activated carbon surface. These oxygen-containing functional groups can serve as active anchoring sites for subsequent amination reactions with amine compounds, forming the basis for covalent grafting. This invention achieves controllable oxidation, generating a sufficient number of anchoring sites while avoiding excessive oxidation that could damage the skeleton structure and pores of the activated carbon.

[0076] According to embodiments of the present invention, the amine-containing compound includes one or more of polyethyleneimine, poly(allylamine), polyethyleneamine, ethylenediamine, and diethylenetriamine.

[0077] According to an embodiment of the present invention, the second reaction method is carried out by at least one of solution impregnation or in-situ grafting.

[0078] According to an embodiment of the present invention, the solution impregnation method includes: impregnating the oxidized coconut shell activated carbon in a solution of macromolecular amine compounds, stirring and reacting to obtain the modified coconut shell activated carbon adsorbent.

[0079] By adopting the above technical solution, the carboxyl groups on the oxidized coconut shell activated carbon can undergo amidation reactions with primary and secondary amine groups in macromolecular amine-containing compounds, causing the amine-containing compounds to covalently bond to the coconut shell activated carbon matrix, thereby introducing a large number of basic nitrogen-containing groups onto the surface of the oxidized coconut shell activated carbon. The abundant mesoporous structure of the coconut shell activated carbon matrix allows macromolecular amine-containing compounds to penetrate deep into the pores. Utilizing the multiple active primary and secondary amine groups on the macromolecular amine-containing compounds, they can achieve multi-point anchoring with the coconut shell activated carbon, thus forming a stable three-dimensional network coating layer, significantly increasing the amine group density and stability.

[0080] It should be noted that the macromolecular amine compound is a trimer or polymeric amine compound.

[0081] According to an embodiment of the present invention, the macromolecular amine-containing compound includes one or more of polyethyleneimine (PEI), poly(allylamine), and polyethyleneamine.

[0082] In one embodiment, the temperature of the stirring reaction in the solution impregnation method is 60~80°C, and the stirring reaction time is 6~10h.

[0083] According to an embodiment of the present invention, the in-situ grafting method includes: The oxidized coconut shell activated carbon was reacted with thionyl chloride to obtain an acyl chloride product; The acyl chloride product is reacted with a small molecule amine-containing compound to obtain the modified coconut shell activated carbon adsorbent.

[0084] Using the above technical solution, the carboxyl groups on the surface of the oxidized coconut shell activated carbon can be chlorinated with thionyl chloride. The acyl chloride reacts with the primary and secondary amine groups on the amine-containing compound through an amidation reaction, causing the amine-containing compound to be covalently bonded to the coconut shell activated carbon matrix. This introduces terminal basic nitrogen-containing groups on the surface of the oxidized coconut shell activated carbon, firmly grafting the amine groups onto the activated carbon surface, thereby improving the long-term stability, adsorption selectivity, and adsorption efficiency of the adsorbent.

[0085] It should be noted that the small molecule amine compound is an oligomeric or dimer amine compound.

[0086] According to an embodiment of the present invention, the preparation method of the modified coconut shell activated carbon adsorbent further includes post-treatment, which includes: separating solid products, washing, drying, and obtaining purified modified coconut shell activated carbon adsorbent.

[0087] The above technical solution can effectively remove physically adsorbed or residual free amines, ensuring that all measured amine groups are chemically loaded. This is beneficial for improving the stability of the adsorbent and the purity of chlorosilane products, and avoiding secondary pollution and equipment corrosion.

[0088] According to an embodiment of the present invention, the drying temperature is 80~100℃. A mild drying temperature is beneficial for maintaining the activity of functional groups and pore structure, thereby improving the adsorption effect of the adsorbent.

[0089] A third aspect of the present invention provides an application of the modified coconut shell activated carbon adsorbent described above or the modified coconut shell activated carbon adsorbent prepared by the above preparation method in removing aluminum and titanium impurities in a chlorosilane system.

[0090] According to an embodiment of the present invention, the application includes: preheating the high-boiling-point substance and passing it through a fixed bed loaded with the adsorbent to remove impurities such as aluminum and titanium online, and then the purified liquid enters the pyrolysis unit for pyrolysis.

[0091] According to an embodiment of the present invention, the modified coconut shell activated carbon adsorbent can be recycled after adsorption saturation. The regeneration process includes acid desorption treatment, steam purging and neutralization, and thermal drying regeneration.

[0092] In one embodiment, the acid desorption treatment includes isolating the saturated adsorbent bed from the process pipeline and flushing the bed in a counter-current or forward direction with a dilute acid solution (such as dilute hydrochloric acid, dilute nitric acid, or dilute sulfuric acid) with a concentration of 0.1~2.0 mol / L. The flushing temperature is 20~80°C and the liquid hourly space velocity (LHSV) is 1~5 h⁻¹. - ¹, continue processing for 1 to 4 hours.

[0093] In one embodiment, the steam purging and neutralization includes thoroughly rinsing the bed with deionized water until the discharged water is neutral (pH≈6~7) to completely remove residual acid and metal ions. Then, low-temperature steam at 100~150°C is introduced to purge the bed for 0.5~2 hours to further remove residual moisture and volatile substances from the pores and to preliminarily activate the adsorbent framework.

[0094] In one embodiment, the thermal drying regeneration includes shutting off the steam, gradually raising the bed temperature to 150-250°C under the protection of an inert gas (such as nitrogen), maintaining this temperature for 1-3 hours to perform gentle thermal regeneration, and then re-entering the adsorption cycle after the bed cools down to the operating temperature.

[0095] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0096] Example 1 This embodiment uses polyethyleneimine to modify coconut shell activated carbon adsorbent via solution impregnation, and includes the following steps: Take 20g of coconut shell activated carbon matrix, add 250mL of 25wt% nitric acid solution, reflux and stir in an oil bath at 85℃ for 3h, cool and filter, wash with deionized water until neutral, and dry at 110℃ for 12h to obtain oxidized coconut shell activated carbon. 10g of oxidized coconut shell activated carbon was impregnated in a 150mL mixed solution of water and ethanol containing 6g of PEI, and the mixture was stirred continuously at 75℃ for 8h. The volume ratio of water to ethanol in the mixed solution was 1:1. The solid was filtered and washed repeatedly with hot water and ethanol until the washing liquid showed no obvious color development when tested with ninhydrin reagent. It was then vacuum dried at 80℃ for 10 hours to obtain the modified coconut shell activated carbon adsorbent.

[0097] The BET specific surface area of ​​the coconut shell activated carbon matrix is ​​1500 m². 2 / g, iodine value 1000 mg / g, ash content 2%, strength 98.5%, and mesopores account for 65% of the total pore volume.

[0098] Example 2 This embodiment uses ethylenediamine to modify coconut shell activated carbon adsorbent via in-situ grafting, and includes the following steps: Take 20g of coconut shell activated carbon matrix, add 250mL of 25wt% nitric acid solution, reflux and stir in an oil bath at 85℃ for 3h, cool and filter, wash with deionized water until neutral, and dry at 110℃ for 12h to obtain oxidized coconut shell activated carbon. Take 5g of oxidized coconut shell activated carbon, add 50mL of SOCl2 and 20mL of THF mixture, reflux at 70℃ for 24 hours, remove excess SOCl2 by vacuum distillation to obtain acyl-chlorinated coconut shell activated carbon; quickly transfer the acyl-chlorinated coconut shell activated carbon to 100mL of ethylenediamine, and react at 60℃ for 12 hours under nitrogen protection. The mixture was filtered, thoroughly washed with ethanol, and vacuum dried at 70°C for 12 hours to obtain the modified coconut shell activated carbon adsorbent.

[0099] The BET specific surface area of ​​the coconut shell activated carbon matrix is ​​1500 m². 2 / g, iodine value 1150 mg / g, ash content 2%, strength 98.5%, and mesopores account for 65% of the total pore volume.

[0100] Example 3 This embodiment uses triethylenetetramine (TETA) to modify coconut shell activated carbon adsorbent via solution impregnation, including the following steps: Take 20g of coconut shell activated carbon matrix, add 250mL of 25wt% nitric acid solution, reflux and stir in an oil bath at 85℃ for 3h, cool and filter, wash with deionized water until neutral, and dry at 110℃ for 12h to obtain oxidized coconut shell activated carbon. Mix 10g of oxidized coconut shell activated carbon with 50g of TETA, add 100mL of deionized water, and stir continuously at 80℃ for 10h. The mixture was filtered, washed with a large amount of hot water until the washing liquid was neutral, and then vacuum dried at 90°C for 8 hours to obtain the modified coconut shell activated carbon adsorbent.

[0101] The BET specific surface area of ​​the coconut shell activated carbon matrix is ​​1500 m². 2 / g, iodine value 1150 mg / g, ash content 1%, strength 99%, and mesopores account for 75% of the total pore volume.

[0102] Comparative Example 1 This comparative example uses the same coconut shell activated carbon matrix as in Example 1 without any chemical modification.

[0103] Comparative Example 2 This comparative example is based on Example 1, and the only difference from Example 1 is that this comparative example only oxidizes activated carbon and does not modify it with amine compounds.

[0104] The specific preparation steps include: Take 20g of coconut shell activated carbon matrix, add 250mL of 25wt% nitric acid solution, reflux and stir in an oil bath at 85℃ for 3h, cool and filter, wash with deionized water until neutral, and dry at 110℃ for 12h to obtain oxidized coconut shell activated carbon. The parameters of the coconut shell activated carbon matrix, such as BET specific surface area, iodine value, ash content, strength, and the proportion of mesopores to total pore volume, are the same as in Example 1.

[0105] Comparative Example 3 This comparative example is based on Example 1, and the only difference from Example 1 is that the PEI in this comparative example is obtained by physical impregnation of activated carbon without heating reaction.

[0106] The specific preparation steps include: Take 20g of coconut shell activated carbon matrix, add 250mL of 25wt% nitric acid solution, reflux and stir in an oil bath at 85℃ for 3h, cool and filter, wash with deionized water until neutral, and dry at 110℃ for 12h to obtain oxidized coconut shell activated carbon. 10g of oxidized coconut shell activated carbon was impregnated in a 150mL mixed solution of water and ethanol containing 6g of PEI, and the mixture was stirred continuously at 25°C for 8h. The volume ratio of water to ethanol in the mixed solution was 1:1. Filter the solid and wash it repeatedly with hot water and ethanol until the washing solution shows no obvious color when tested with ninhydrin reagent. Dry it under vacuum at 80°C for 10 hours. In this sample, PEI mainly adheres through physical adsorption and pore filling, with extremely weak interactions.

[0107] Effect test Adsorption conditions: The adsorbents of Examples 1-3 and Comparative Examples 1-3 of this invention were packed into a small fixed-bed adsorption column (inner diameter 10 mm, length 200 mm), with a packing amount of 1.00 g. The column was fixed at the top and bottom with quartz wool, and a simulated feed solution (in which Al) was introduced. 3+ The concentration is 100 mg / L, Ti 4+ The concentration was 50 mg / L, the simulated hydrocarbon concentration was 50 g / L, and the pH was 5. The temperature was 80℃ and the space velocity was 2 h⁻¹. -1 Adsorption experiments were conducted.

[0108] Regeneration conditions: The adsorbent was washed with 1.0 mol / L HCl solution at 60℃ for 2 h (LHSV=3 h). - ¹), wash with deionized water until neutral, purge with steam at 120°C for 1 h, and dry at 180°C for 2 h under N2 protection.

[0109] Specific testing and calculation methods for each performance indicator: 1. Adsorption capacity Test method (dynamic penetration curve method): Collect the effluent at the column outlet at regular intervals and determine the concentrations (Ct) of aluminum and titanium. Continue flushing until the outlet concentration (Ct) is reached. t The adsorption concentration reached 95% of the imported concentration (CO) (i.e., complete penetration). The concentrations of aluminum and titanium impurities before and after adsorption were determined by inductively coupled plasma optical emission spectrometry (ICP-OES), and the adsorption capacity of each sample was calculated according to the following formula. The results are recorded in Table 1.

[0110]

[0111] Among them, Q e Adsorption capacity (mg / g) refers to the total amount of impurities adsorbed per unit mass of adsorbent. F represents the volumetric flow rate of the feed liquid (L / min); C0 represents the initial concentration of impurities in the feed solution (mg / L); C t Let t be the concentration of impurities in the outlet liquid (mg / L). t total The total time (in minutes) from start to complete penetration; m represents the adsorbent loading mass (g).

[0112] 2. Desorption rate Test method: The adsorbent was adsorbed until it was completely saturated under the above adsorption conditions, and the total amount of adsorption was determined by ICP-OES. The saturated adsorbent was removed and rinsed with 1.0 mol / L HCl solution at 60°C for 2 h (LHSV=3 h). - ¹), the total amount of desorption is obtained by multiplying the concentrations of Al and Ti in the eluent by the volume of the eluent using ICP-OES. The desorption rate of each sample is calculated using the following formula, and the results are recorded in Table 1.

[0113] Desorption rate (%) = (Total desorbed / Total adsorbed) × 100% Wherein, the total adsorption amount is the total amount of impurities loaded on the adsorbent in the saturated adsorption state; the total desorption amount is the total amount of impurities actually desorbed during the desorption process.

[0114] 3. Separation coefficient Test method (two-component competitive adsorption experiment): Formulating a solution containing only the target impurity ion Al³ + (Component A) and background ion Na + (Component B) An adsorption experiment was conducted on solutions of the two key components. The separation coefficient (α) for each sample was calculated using the following formula. A / B ), when α A / B A value greater than 1 indicates that the adsorbent has a higher selectivity for component A than for component B, α A / B The larger the value, the better the selectivity. The results are recorded in Table 1.

[0115]

[0116] Among them, C 0,A and C 0,B These are the initial concentrations of components A and B, respectively. C e,A and C e,B These represent the residual concentrations of components A and B after adsorption.

[0117] 4. Retention rate Test method: For the same adsorbent sample, under the adsorption and regeneration conditions described above, the adsorbent was adsorbed until completely saturated and then regenerated. This was recorded as one cycle, and the cycle was repeated 10 times. The adsorption capacity measured after each cycle was recorded, and the retention rate after n cycles was calculated using the following formula and recorded in Table 1.

[0118] Retention rate = Q e,n / Q e,0 ×100% Where n is the number of cycles, Qe,n is the adsorption capacity after n cycles, and Q e,0 This represents the initial adsorption capacity.

[0119] Table 1 shows the adsorption performance test results of the adsorbents described in Examples 1-3 and Comparative Examples 1-3.

[0120]

[0121] As can be seen from Table 1, the adsorption capacity, desorption rate, separation coefficient and retention rate of the adsorbents in Examples 1-3 are significantly higher than those in Comparative Examples 1-3. This indicates that the adsorbents described in this invention successfully introduce covalently bonded basic nitrogen-containing functional groups, which can enhance chemical adsorption and coordination of impurities such as aluminum and titanium through Lewis acid-base coordination, significantly improving adsorption capacity, selectivity, regeneration efficiency and long-term stability, and reducing the dissolution of active components. In Example 2, the in-situ grafting method of ethylenediamine was used, which resulted in a higher functional group grafting density and less steric hindrance, exhibiting the highest adsorption capacity, separation coefficient and retention rate. This indicates that the in-situ grafting method described in this invention is more conducive to improving the adsorption capacity, selectivity and long-term stability of the adsorbent. Comparative Example 1 used the original coconut shell activated carbon matrix, which had the weakest adsorption capacity and almost no selectivity for aluminum ions. Its adsorption capacity mainly relied on physical adsorption or weak chemical action, and the retention rate was acceptable, but the absolute performance was poor. Compared with Comparative Example 1, Example 1 proved that the adsorbent described in this invention, through covalent bonding of basic nitrogen-containing functional groups, can enhance chemical adsorption and coordination through Lewis acid-base coordination, significantly improving adsorption capacity, selectivity, regeneration efficiency, and long-term stability, while reducing the dissolution of active components. Comparative Example 2 introduces some oxygen-containing acidic functional groups, which have a certain complexing ability for metal cations. However, the acidic functional groups are weak for neutral or weakly positively charged aluminum-titanium complexes in the chlorosilane system. Therefore, the adsorption capacity and separation coefficient of Comparative Example 2 are much lower than those of Example 1, and the desorption rate and retention rate are also significantly lower. This proves that the present invention, by covalently bonding basic nitrogen-containing functional groups, is more conducive to improving the adsorption capacity, selectivity, regeneration efficiency and long-term stability of the adsorbent compared with traditional acid washing and oxidation. Comparative Example 3, which uses PEI physical impregnation, also shows an improved adsorption capacity. However, since the PEI and the carrier are mainly physically adsorbed, the binding force is weak and it is easily lost during washing and use. Therefore, the adsorption capacity and retention rate of Comparative Example 3 are much lower than those of Example 1, and the desorption rate and separation coefficient are also reduced. This proves that the present invention, by covalently bonding basic nitrogen-containing functional groups, is more conducive to improving the adsorption capacity, selectivity, regeneration efficiency and long-term stability of the adsorbent than physical impregnation, and reduces the dissolution of active components.

[0122] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0123] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A modified coconut shell activated carbon adsorbent, characterized in that, include: Coconut shell activated carbon matrix; Basic nitrogen-containing functional groups are covalently bonded to the coconut shell activated carbon matrix.

2. The modified coconut shell activated carbon adsorbent according to claim 1, characterized in that, The basic nitrogen-containing functional groups include -NH2, -NHR, -NR2, and -NR3. + One or more of the following, wherein R represents a substituted or unsubstituted alkyl group of C1 to C20.

3. The modified coconut shell activated carbon adsorbent according to claim 1 or 2, characterized in that, At least one of the following conditions must be met: The nitrogen content of the modified coconut shell activated carbon adsorbent ranges from 1.0 to 3.5 mmol / g; The density of basic sites ranges from 0.5 to 2.0 mmol / g; Amino grafting rate ≥60%.

4. The modified coconut shell activated carbon adsorbent according to claim 1 or 2, characterized in that, The coconut shell activated carbon matrix satisfies at least one of the following conditions: BET has a specific surface area of ​​1000~3000 m² 2 / g; Iodine value is 800~1200mg / g; Ash content ≤5%; Strength > 96%; The proportion of the central hole to the total hole volume is greater than 50%.

5. A method for preparing a modified coconut shell activated carbon adsorbent as described in any one of claims 1 to 4, characterized in that, Includes the following steps: The coconut shell activated carbon matrix is ​​reacted with an oxidizing acid to obtain oxidized coconut shell activated carbon. The oxidized coconut shell activated carbon is reacted with an amine-containing compound in a second reaction to obtain a modified coconut shell activated carbon adsorbent.

6. The preparation method according to claim 5, characterized in that, At least one of the following conditions must be met: The first reaction temperature is 60~90℃; The first reaction time is 2-4 hours; The oxidizing acid includes one or more of nitric acid, concentrated sulfuric acid, periodic acid, hypochlorous acid, and peracetic acid.

7. The preparation method according to claim 5, characterized in that, The second reaction is carried out by at least one of solution impregnation or in-situ grafting.

8. The preparation method according to claim 7, characterized in that, The solution impregnation method includes: The oxidized coconut shell activated carbon is impregnated in a solution of macromolecular amine compounds and stirred to obtain the modified coconut shell activated carbon adsorbent.

9. The preparation method according to claim 7, characterized in that, The in-situ grafting method includes: The oxidized coconut shell activated carbon was reacted with thionyl chloride to obtain an acyl chloride product; The acyl chloride product is reacted with a small molecule amine-containing compound to obtain the modified coconut shell activated carbon adsorbent.

10. The application of a modified coconut shell activated carbon adsorbent as described in any one of claims 1 to 4, or a modified coconut shell activated carbon adsorbent prepared by the preparation method described in any one of claims 5 to 9, in removing aluminum and titanium impurities in a chlorosilane system.

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