Combined modified adsorbent for the removal of phenolic compounds and metal ions from CO2-based polyols

Abstract

The invention belongs to the technical field of carbon dioxide-based polyol purification, and provides a combined modified adsorbent for removing phenolic compounds and metal ions in carbon dioxide-based polyols. The adsorbent is prepared through the steps of pre-dispersion and combined modification, wherein the combined modification sequentially comprises nitrogen heterocycle-low-temperature plasma activation-carbon dioxide gas modification, has high-efficiency adsorption performance, is suitable for the purification of polymers with high molecular weight, high viscosity and complex components, and is applied to adsorbing phenolic compounds and metal ions in carbon dioxide-based polyols. The combined modified activated carbon adsorbent can exhibit excellent adsorption performance for phenolic compounds in carbon dioxide-based polyols within 6 hours, can quickly adsorb phenolic compound molecules, and achieve a phenolic compound removal rate of more than 90%, and metal ions in the polymer can be reduced from 260 ppm to less than 5 ppm, and can be desorbed by a high-pressure filter tank in a short time, and the operation is simple and convenient, and the cost is low.

Description

Technical Field

[0001] The invention belongs to the technical field of carbon dioxide-based polyol purification, and in particular relates to a combined modified adsorbent for removing phenolic compounds and metal ions in carbon dioxide-based polyol. Background Art

[0002] During the manufacturing process, polymers such as CO2-based polyols can exhibit diverse excellent properties by adding different types of initiators. However, when phenolic compounds, such as bisphenol A and hydroquinone, are used as additives to give polymer products high modulus, excellent acid resistance and hydrolysis resistance, a significant problem emerges: phenolic compound residues. This problem is particularly difficult because it directly affects the processing properties of the polymer and the performance of the final product. For example, residual bisphenol A and other phenolic compounds will react with other components in the polymer, resulting in changes in the molecular chain structure, which in turn affects the processing properties of the polymer, such as melt fluidity, moldability, and thermal stability. These changes will lead to reduced production efficiency, fluctuations in product quality, and increased costs. At the same time, phenolic compound residues also affect the final product properties of the polymer, such as mechanical properties, heat resistance, and weather resistance, thereby reducing the product's service life and market competitiveness.

[0003] In the production and application of CO2-based polyols, the residual problem of phenolic compounds does not exist in isolation. The presence of metal ions is also another major challenge that cannot be ignored. Metal ions come from raw materials and production processes, and they may also have an adverse effect on the performance of polymers, such as reducing the thermal stability and mechanical properties of the product and inducing unnecessary chemical reactions. In addition, the interaction between metal ions and phenolic compounds may further aggravate the residual problem, making the removal work more complicated and difficult.

[0004] For the removal of phenolic compounds or metal ions, adsorption is generally considered superior to other methods because of its ease of operation, low cost, ability to quickly and effectively remove pollutants, and low risk of secondary pollution. In the adsorption method, the performance of the adsorbent is crucial and is the factor that has the greatest impact on the adsorption efficiency. Commercial activated carbon, as an excellent adsorbent, is widely used to remove phenolic compound pollutants and metal ions.

[0005] However, existing studies on the removal of phenolic compounds by activated carbon adsorbents are all aimed at the problem in wastewater, and the adsorption environment of wastewater is relatively simple and easier to adjust, so that the adsorbent can better play a binding role with the adsorbate. For example, in the patent CN108408957A, a precipitation-activated carbon adsorption method is used for phenolic wastewater. In its embodiment, hydrochloric acid or sodium hydroxide is first used to adjust the acidity and alkalinity of phenolic wastewater. This step is the place where wastewater is more adjustable and controllable than carbon dioxide-based polyols. The acidity and alkalinity can be adjusted to a state that is favorable to the adsorbent in the wastewater. Under alkaline conditions, the adsorbent has a higher adsorption efficiency for phenolic compounds. Phenolic compounds usually have higher solubility and ionization within this range, which is conducive to combining with the active sites on the surface of the adsorbent. In Chinese patent CN112934175A, alkali-modified biochar is used to remove emerging pollutants such as bisphenol A in sewage. The chemical adsorption control interaction and physical adsorption control effect between the alkali-modified biochar and the pollutants mainly include electrostatic attraction, π-π electron interaction, pore filling and hydrophobic effect. The pore filling interaction depends not only on the specific surface area and pore size of the modified biochar, but also on the environment in which the pollutants are located. The force of water on pollutants in the wastewater environment can separate them through hydrophobic effect and easily adsorb them to biochar.

[0006] Carbon dioxide-based polyetherpolyols in industrial production are a type of high molecular weight, high viscosity polymer, which is significantly different from the aqueous solution treatment environment of wastewater. Compared with wastewater, there are more difficulties and challenges in removing phenolic compounds. The specific difficulties are mainly reflected in the following aspects:

[0007] (1) Low fluidity and uneven adsorption

[0008] Low fluidity: CO2-based polyols are a class of high molecular weight and high viscosity polymers. Usually, in the presence of phenolic initiators, the molecular weight can reach 1500-5000, and the viscosity is as high as 7000 mPa·s at 70°C. Its fluidity is much lower than that of aqueous solution, which makes it difficult for the simple pore filling and chemical adsorption of alkali-modified biochar in wastewater to be effectively carried out in CO2-based polyol polymers, because it is difficult for the adsorbent to fully contact the adsorbed phenolic compounds;

[0009] Uneven adsorption: Due to low fluidity, the diffusion and distribution of the adsorbent in the CO2-based polyols are restricted, resulting in uneven adsorption and low adsorption efficiency;

[0010] (2) Poor solubility and easy decomposition

[0011] Poor solubility: CO2-based polyols are insoluble in common solvents such as ethyl acetate, methanol, acetonitrile, and water, which makes it difficult to find a suitable solvent system to assist the adsorption process.

[0012] Easy to decompose: CO2-based polyols are prone to decomposition in acidic or alkaline conditions. This instability increases the complexity of handling because conditions that may cause their decomposition need to be avoided.

[0013] (3) Catalyst residues affect the adsorption of phenolic compounds

[0014] Residual heavy metal ions: The process of carbon dioxide-based polyols uses double metal cyanide complex catalysts, which contain heavy metal ions such as Zn, Co, etc. These heavy metal ions only play a catalytic role in the copolymerization reaction and will not be consumed, so they will all remain in the carbon dioxide-based polyol products. This residue not only affects the color and transparency of the product, but also has an adverse effect on its use and storage; in addition, carbon dioxide-based polyols are important raw materials for polyurethane, and their quality directly affects the performance of polyurethane products. Residual heavy metal ions will produce thermally unstable allophanates when applied to polyurethane products downstream, thereby affecting the mechanical properties, heat resistance and service life of polyurethane.

[0015] Interaction between metal ions and adsorbents: Residual heavy metal ions may interact with the adsorbent, affecting the performance and effectiveness of the adsorbent in removing phenolic compounds.

[0016] (4) Adsorption conditions are more stringent

[0017] Harsh treatment environment: Compared with the removal of phenolic compounds in wastewater, the treatment of phenolic compounds in CO2-based polyols requires more stringent adsorbent performance and treatment environment. The adsorbent not only needs to have high adsorption capacity and selectivity, but also needs to be stable under specific temperature, pressure and pH conditions, and not affect the performance of CO2-based polyol polymers.

[0018] Process complexity: For the reasons mentioned above, handling phenolic compounds in CO2-based polyols may require more complex processes and equipment.

[0019] In summary, the prior art does not have an activated carbon adsorbent specifically used for carbon dioxide-based polyols that can simultaneously and efficiently remove phenolic compounds and heavy metal ions and a preparation method thereof. Summary of the invention

[0020] In view of the problems existing in the prior art, the present invention provides a combined modified adsorbent for removing phenolic compounds and metal ions in carbon dioxide-based polyols. The adsorbent is prepared through the steps of pre-dispersion and combined modification, and the combined modification sequentially includes specific nitrogen heterocycle modification, low-temperature plasma activation and carbon dioxide gas modification. The combined modified activated carbon adsorbent prepared by the method of the present invention has high adsorption performance and is suitable for purification of polymers with high molecular weight, high viscosity and complex components. The combined modified activated carbon adsorbent is applied to adsorb phenolic compounds and heavy metal ions in carbon dioxide-based polyols, and can show excellent adsorption performance for phenolic compounds in carbon dioxide-based polyols within 6 hours, can quickly adsorb phenolic compound molecules, and the removal rate of phenolic compounds reaches more than 90%. At the same time, heavy metal ions in the polymer are reduced from 260 ppm to less than 5 ppm, and the adsorption method is simple, convenient and low in cost.

[0021] The technical solution of the present invention is as follows:

[0022] The present invention provides a combined modified adsorbent for removing phenolic compounds and metal ions in carbon dioxide-based polyols. The combined modified adsorbent is prepared through the steps of pre-dispersion and combined modification, and specifically comprises:

[0023] (1) Pre-dispersion: Dispersing activated carbon in deionized water to prepare an activated carbon dispersion to form an active and stable activated carbon precursor;

[0024] (2) Combined modification: The combined modification includes nitrogen heterocycle-low temperature plasma activation-carbon dioxide gas modification in sequence;

[0025] The nitrogen heterocycle modification method comprises adding the nitrogen heterocycle modifier to the activated carbon dispersion at a mass ratio of the nitrogen heterocycle modifier to the activated carbon of 1:0.5-20, and heating and refluxing to prepare the nitrogen heterocycle modified activated carbon;

[0026] The low-temperature plasma activation method comprises subjecting the nitrogen heterocyclic modified activated carbon to low-temperature plasma surface treatment to obtain an activated adsorbent; the low-temperature plasma activation time is 10-60 min; when the activation time is less than 10 min, the specific surface area will be less than 3000 m 2 / g, the average volume particle size will be higher than 40 μm, and when the activation time is higher than 60 min, the specific surface area will decrease with time; the gas required for low-temperature plasma activation is nitrogen, and this gas environment can promote the increase of nitrogen-containing functional groups on the surface of activated carbon, while if other environmental gases are used, it will lead to the increase of its oxygen-containing acidic functional groups, which is not conducive to the adsorption of phenolic compounds; the low temperature of the low-temperature plasma refers to the temperature range of 10°C-150°C;

[0027] The method for modifying the carbon dioxide gas is to prepare a solution of the activated adsorbent using water as a solvent, disperse and immerse it, and purge it with low-pressure carbon dioxide gas at a pressure of 0.2-1.5 MPa until the solution pH is 6-8, filter it, and vacuum dry it to obtain the combined modified adsorbent.

[0028] The combined modified adsorbent used for removing phenolic compounds and metal ions in carbon dioxide-based polyols of the present invention has the steps of specific nitrogen heterocycle-low-temperature plasma activation-carbon dioxide gas modification in sequence, and the above steps are interconnected and progressive, and play an overall synergistic role. The low-temperature plasma activation described in the present invention etches and roughens the surface of the activated carbon. The high-energy particles in the low-temperature plasma can bombard the surface of the activated carbon, causing a slight etching effect, thereby increasing the surface roughness. This roughening helps to increase the specific surface area of ​​the activated carbon and improve its adsorption capacity for pollutants. The low-temperature plasma surface treatment can use the high-energy particles in the plasma to deeply etch and functionalize the surface of the activated carbon at a relatively low temperature, thereby achieving efficient modification of nitrogen heterocycles. This modification not only increases the roughness and specific surface area of ​​the activated carbon surface, but also introduces new functional groups, significantly improving its adsorption performance and selectivity. The low-temperature plasma treatment can keep the activated carbon between 10 and 40 μm. The activated carbon within this range can not only ensure the good dispersibility of the activated carbon particles in the carbon dioxide-based polyol, but also form an effective filter cake, while avoiding the problems of product mixing and filtration difficulties. The activated carbon is not prone to clogging problems. With the appropriate filtering means, the purified product can be obtained quickly and efficiently.

[0029] The nitrogen functional groups in the nitrogen heterocycle described in the present invention are rich in variety, mainly including pyridinic nitrogen (N-6), pyrrolic nitrogen (N-5), quaternary nitrogen and protonated pyridinic nitrogen (NQ), etc. The presence of these nitrogen functional groups significantly changes the surface properties of activated carbon. Due to the high electronegativity of nitrogen atoms, their introduction makes the charge distribution on the surface of activated carbon more complex, thereby enhancing the ability of activated carbon to adsorb phenolic compounds. Nitrogen functional groups can also provide more active sites and enhance the adsorption capacity for specific pollutants. Nitrogen-containing heterocycles can interact with phenolic compounds through various mechanisms such as hydrogen bonds and electrostatic effects, thereby improving the adsorption effect of activated carbon on phenolic compounds, among which the hydrogen bonding effect of the present invention has a major influence on adsorption.

[0030] The nitrogen atoms in the nitrogen heterocycle usually carry lone pairs of electrons, which makes the surface of the activated carbon show stronger alkalinity. The presence of the alkaline surface is conducive to the adsorption of pollutants in CO2-based polyols. The enhancement of the alkaline surface enables the activated carbon to show higher selectivity during the adsorption process, and is more inclined to adsorb phenolic compounds in CO2-based polyols, thereby reducing the adsorption of non-target pollutants and improving the efficiency of CO2-based polyol treatment. The nitrogen functional groups and alkaline surfaces of the nitrogen heterocycle have many effects on activated carbon. They not only change the surface properties and adsorption performance of the activated carbon, but also have a positive effect on the adsorption of pollutants in CO2-based polyols.

[0031] However, the enhancement of the alkaline surface brought by the nitrogen heterocycle forms a competitive relationship with the metal ions, which will reduce the adsorption of the adsorbent to the metal ions to a certain extent. The adsorption in the aqueous solution is relatively simple, and this side effect may not be obvious, but the adsorption in the carbon dioxide-based polyols is difficult to remove phenolic compounds and metal ions due to the problems of high viscosity, poor fluidity, insolubility in water, and difficulty in dispersing the adsorbent. The alkaline surface is particularly weakened for the adsorption of metal ions. Therefore, the present invention uses a combined modification method for the characteristics of carbon dioxide-based polyols, and further adopts carbon dioxide gas purge modification after nitrogen heterocycle modification and low-temperature plasma activation. Different from the prior art that uses carbon dioxide for gas physical activation in the low-temperature plasma step or high-temperature calcination activation, the present invention uses carbon dioxide gas purging modification after low-temperature plasma activation. The carbon dioxide gas purging modification has two functions at the same time: (1) neutralizing the alkalinity brought by the nitrogen heterocycle to prevent the alkaline adsorbent from causing decomposition of the carbon dioxide-based polyol; the prior art uses hydrochloric acid for neutralization, but hydrochloric acid itself is a strong acid and has strong corrosiveness to activated carbon. During the treatment process, if the operation is improper, it will destroy the internal structure of the activated carbon, especially the pore structure, thereby reducing its adsorption performance. In contrast, carbon dioxide purging will not cause this situation; (2) at the same time, the carbon dioxide gas purging modification of the present invention can form a weak acidic substance with the lone pair of electrons in the nitrogen-containing heterocycle modification, thereby improving the adsorption capacity of metal ions; at the same time, the activated carbon with nitrogen functional groups can also form hydrogen bond interactions with phenolic compounds in the carbon dioxide-based polyol, making the structure of the carbon dioxide-based polyol more stable during the adsorption of phenolic compounds. Specifically, the present invention adopts carbon dioxide gas modification to first reduce the alkaline substances that are not absorbed on the surface of modified activated carbon, and form weakly acidic substances, which will enhance the acidic functional groups on the surface of activated carbon, improve the adsorption capacity of metal ions, and will not cause the reduction of nitrogen heterocyclic functional groups, and make the entire modified activated carbon in a state close to neutral, so that the adsorbent of the present invention maintains a high adsorption capacity for phenolic compounds. At the same time, carbon dioxide gas modification in the present invention makes the modified activated carbon in a state close to neutral, which is particularly critical in the treatment of carbon dioxide-based polyols. Carbon dioxide-based polyol products will decompose in an alkaline environment, and polymer chain segment rupture will form more small molecules. Therefore, phenolic compounds and metal ions in carbon dioxide-based polyols can be efficiently adsorbed, and the structural properties of carbon dioxide-based polyols themselves can be maintained in this state. Therefore, the preparation method of the present invention needs to accurately control the overall synergistic effect.

[0032] In one embodiment of the present invention, the activated carbon is commercial activated carbon, selected from any one or more of fruit shell activated carbon, coconut shell activated carbon, coal columnar activated carbon, wood activated carbon, medical activated carbon, apricot shell activated carbon, and medicinal activated carbon, more preferably coconut shell activated carbon.

[0033] In one embodiment of the present invention, the nitrogen heterocyclic modifier is selected from a nitrogen heterocyclic compound containing at least one nitrogen atom and the lone pair of electrons on the nitrogen atom is not bound; the lone pair of electrons is not bound means that in the nitrogen heterocyclic compound, the lone pair of electrons is freer than other electrons, but is still attracted by the nitrogen nucleus and affected by other atoms in the molecule. They are not completely free electrons, and are different from free electrons and cannot be called free electrons.

[0034] In one embodiment of the present invention, the nitrogen heterocyclic modifier is selected from any one or more of pyrridine, pyrrole, imidazole, pyrimidine, quinoline, benzimidazole compounds and their derivatives, and is more preferably pyridine.

[0035] In one embodiment of the present invention, during the pre-dispersion, the activated carbon is immersed and stirred for 2-12 hours to form an activated carbon precursor;

[0036] In one embodiment of the present invention, the soaking temperature is 10-50°C;

[0037] In one embodiment of the present invention, the mass of the deionized water is 10-20 times the mass of the activated carbon.

[0038] In one embodiment of the present invention, in the combined modification, the mass ratio of the nitrogen heterocyclic modifier to the activated carbon is 1:5-1:15;

[0039] In one embodiment of the present invention, the heating reflux temperature is 100-160°C;

[0040] In one embodiment of the present invention, the heating reflux time is 3-16 h.

[0041] In one embodiment of the present invention, in the combined modification, during the low-temperature plasma activation, the gas flow rate of the nitrogen gas is 10-50 mL / min, and the processing power is 30-150 W.

[0042] In one embodiment of the present invention, in the combined modification, during the carbon dioxide gas modification, the carbon dioxide purge temperature is 30-90° C. and the time is 2-6 h.

[0043] In one embodiment of the present invention, in the combined modification, the carbon dioxide gas modification method is: using a carbon dioxide purge device, such as Figure 1 As shown, carbon dioxide gas is continuously introduced from the bottom pipeline, the activated adsorbent enters from the upper part of the reaction tank, and excess carbon dioxide gas circulates into the reaction tank from the upper part of the reaction tank through the compressor. A sampling port is set at the bottom of the reaction tank. When the pH is detected to be 6-8, the adsorbent is discharged from the bottom pipeline to obtain the adsorbent.

[0044] In one embodiment of the present invention, the specific surface area of ​​the combined modified adsorbent is 3000-5000 m 2 / g, and the average volume particle size is 10-40 μm.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] The combined modified adsorbent for removing phenolic compounds and metal ions in carbon dioxide-based polyols of the present invention adopts activated carbon as a raw material and is prepared through the steps of pre-dispersion and combined modification. The combined modification sequentially comprises specific nitrogen heterocycles-low-temperature plasma activation-carbon dioxide gas modification. On the one hand, the nitrogen heterocycle functional groups in the nitrogen heterocycle modifier can form hydrogen bonds with hydroxyl groups in phenolic compounds, thus playing a key chemical adsorption effect on phenolic compounds. On the other hand, the alkaline surface generated by the lone pair of electrons of the nitrogen heterocycle forms a competitive relationship with metal ions, which reduces the adsorption effect of the adsorbent on metal ions to a certain extent. At the same time, alkalinity will also affect the stability of the carbon dioxide-based polyol structure. Therefore, in order to avoid the negative impact of nitrogen heterocyclic modification, the present invention further adopts carbon dioxide gas purging modification after nitrogen heterocyclic modification and low-temperature plasma activation. On the one hand, the alkalinity is neutralized to make the environment of the entire modified activated carbon close to neutral, thereby avoiding the decomposition of the carbon dioxide-based polyol by the alkaline adsorbent; on the other hand, the carbon dioxide gas purging modification can generate weak acidic substances with the lone pair electrons of the nitrogen heterocyclic modification, thereby improving the adsorption capacity of metal ions; at the same time, the generated weak acidic substances can also help adjust the pH value of the carbon dioxide-based polyol to make it more stable. The preparation method of the present invention requires precise control of parameters such as the type of heterocyclic modifier in the combined modification, the amount of nitrogen heterocyclic modifier, the time of low-temperature plasma activation and the type of activation gas, the pressure of carbon dioxide gas, etc. The above steps are linked to each other, progressive, and play an overall synergistic role. The three steps in the combined modification are indispensable. The prepared adsorbent has high-efficiency adsorption performance and is suitable for the purification of polymers with high molecular weight, high viscosity and complex components. The modified activated carbon adsorbent is used to adsorb phenolic compounds and metal ions in carbon dioxide-based polyols. The phenolic compounds in the carbon dioxide-based polyols can show excellent adsorption performance within 6 hours, and the phenolic compound molecules can be quickly adsorbed. The removal rate of the phenolic compounds reaches more than 90%, and the metal ions in the polymer are reduced from 260 ppm to less than 5 ppm. The adsorption method is simple, convenient and low in cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 Schematic diagram of the carbon dioxide purge device of the present invention. DETAILED DESCRIPTION

[0048] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only intended to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0049] The instrument used for the low-temperature plasma treatment used in the embodiment of the present invention is: Nan Technology NE-PE10; vacuum range: -0.1-1.0 MPa; gas pressure: 0.4-0.6 MPa; gas type: oxygen, argon, nitrogen, hydrogen, etc.; the operation process of the low-temperature plasma treatment instrument of the present invention: loading activated carbon - vacuuming - flushing reaction gas - plasma discharge treatment - taking out activated carbon; process control: treatment time control: 1 second - 120 minutes continuously adjustable; plasma discharge pressure: vacuum pump maximum capacity (-0.1-1.0 MPa); power setting range: 0-300W continuously adjustable; flow setting range: 0-500SCCM (500 mL / min);

[0050] The test method of the specific surface area of ​​the present invention is: using the Quantachrome automatic gas adsorption system (AUTOSORB-1-C) of the full adsorption instrument for detection, and using the BET technology N2 adsorption curve to calculate the specific surface area. Before the test, the adsorbent is treated at 200°C under vacuum for 1 hour to prevent dust or water adsorbed in the pores from affecting the test results.

[0051] Average volume particle size test method: The average volume particle size is measured by Nicomp 380 ZLS equipment produced by PSS Company of the United States. Before the measurement, the solid powder is dispersed with deionized water and the suspension is broken up with ultrasound.

[0052] Example 1

[0053] (1) Pre-dispersion: Disperse 5 g of coconut shell activated carbon in 50 g of deionized water and soak for 2 h at a temperature of 10 °C.

[0054] (2) Combination modification:

[0055] (2-1) Nitrogen heterocyclic modification: 0.34 g of pyridine modifier was added to the coconut shell activated carbon solution prepared in the above (1), heated under reflux at 100 °C for 3 h, and then filtered and dried to obtain activated carbon containing pyridine modifier;

[0056] (2-2) Low-temperature plasma activation: The pyridine-modified activated carbon obtained in (2-1) was subjected to low-temperature plasma surface treatment and activated with a nitrogen gas flow of 10 mL / min for 60 min to obtain activated activated carbon;

[0057] (2-3) Carbon dioxide gas modification: The activated carbon was purged with 0.2 MPa carbon dioxide for 2 h at a temperature of 30 °C, and then filtered and dried to obtain carbon dioxide-purged nitrogen heterocyclic modified activated carbon.

[0058] Example 2

[0059] (1) Pre-dispersion: Disperse 5 g of medical activated carbon in 100 g of deionized water and soak for 12 h at 50 °C.

[0060] (2) Combination modification:

[0061] (2-1) Nitrogen heterocyclic modification: 1 g of pyrrole modifier was added to the coconut shell activated carbon solution prepared in the above (1), heated under reflux at 160 °C for 16 h, and then filtered and dried to obtain activated carbon containing pyrrole modifier;

[0062] (2-2) Low-temperature plasma activation: The pyrrole-modified activated carbon obtained in (2-1) was subjected to low-temperature plasma surface treatment and activated with a nitrogen gas flow of 50 mL / min for 10 min to obtain activated activated carbon;

[0063] (2-3) Carbon dioxide gas modification: The activated carbon was purged with 1.5 MPa carbon dioxide for 6 h at a purging temperature of 90 °C, and then filtered and dried to obtain carbon dioxide-purged nitrogen heterocyclic modified activated carbon.

[0064] Example 3

[0065] (1) Pre-dispersion: 5 g of wood activated carbon was dispersed in 60 g of deionized water and soaked for 6 h at 40 °C.

[0066] (2) Combination modification:

[0067] (2-1) Nitrogen heterocyclic modification: 0.5 g of pyrimidine modifier was added to the wood activated carbon solution prepared in the above (1), heated under reflux at 140 °C for 9 h, and then filtered and dried to obtain activated carbon containing pyrimidine modifier;

[0068] (2-2) Low-temperature plasma activation: The pyrimidine-modified activated carbon obtained in (2-1) was subjected to low-temperature plasma surface treatment and activated with a nitrogen gas flow of 30 mL / min for 30 min to obtain activated activated carbon;

[0069] (2-3) Carbon dioxide gas modification: The activated carbon was purged with 1.0 MPa carbon dioxide for 4 h at a temperature of 50 °C, and then filtered and dried to obtain carbon dioxide-purged nitrogen heterocyclic modified activated carbon.

[0070] Example 4

[0071] (1) Pre-dispersion: Disperse 5 g of medicinal activated carbon in 75 g of deionized water and soak for 8 h at 30 °C.

[0072] (2) Combination modification:

[0073] (2-1) Nitrogen heterocyclic modification: 0.42 g of quinoline modifier was added to the coconut shell activated carbon solution prepared in the above (1), heated under reflux at 120 °C for 6 h, and then filtered and dried to obtain activated carbon containing quinoline modifier;

[0074] (2-2) Low-temperature plasma activation: The quinoline-modified activated carbon obtained in (2-1) was subjected to low-temperature plasma surface treatment and activated with a nitrogen gas flow of 20 mL / min for 20 min to obtain activated activated carbon;

[0075] (2-3) Carbon dioxide gas modification: The activated carbon was purged with 0.6 MPa carbon dioxide for 3 h at a temperature of 80 °C, and then filtered and dried to obtain carbon dioxide-purged nitrogen heterocyclic modified activated carbon.

[0076] Example 5

[0077] (1) Pre-dispersion: 5 g of apricot shell activated carbon was dispersed in 90 g of deionized water and soaked for 4 h at 20 °C.

[0078] (2) Combination modification:

[0079] (2-1) Nitrogen heterocyclic modification: 0.5 g of benzimidazole modifier was added to the apricot shell activated carbon solution prepared in the above (1), heated under reflux at 150 °C for 10 h, and then filtered and dried to obtain activated carbon containing benzimidazole modifier;

[0080] (2-2) Low-temperature plasma activation: The benzimidazole-modified activated carbon obtained in (2-1) was subjected to low-temperature plasma surface treatment and activated with a nitrogen gas flow of 40 mL / min for 50 min to obtain activated activated carbon;

[0081] (2-3) Carbon dioxide gas modification: The activated carbon was purged with 0.8 MPa carbon dioxide for 3 h at a temperature of 60 °C, and then filtered and dried to obtain carbon dioxide-purged nitrogen heterocyclic modified activated carbon.

[0082] Comparative Example 1

[0083] Referring to the preparation method of Example 1, the only difference is that the carbon dioxide gas modification step is changed to hydrochloric acid neutralization, and the preparation steps are as follows:

[0084] (1) Disperse 5 g of coconut shell activated carbon in 50 g of deionized water and soak for 2 h at a temperature of 10 °C;

[0085] (2) adding 0.34 g of pyridine modifier to the coconut shell activated carbon solution prepared in the above (1), heating under reflux at 100 °C for 3 h, and then filtering and drying to obtain activated carbon containing pyridine modifier;

[0086] (3) The pyridine-modified activated carbon obtained in (2) was subjected to low-temperature plasma surface treatment and activated by 10 mL / min nitrogen gas flow for 60 min to obtain activated activated carbon;

[0087] (4) The activated carbon obtained is neutralized in 0.1 M hydrochloric acid, and then filtered and dried to obtain hydrochloric acid-neutralized nitrogen heterocyclic modified activated carbon.

[0088] Comparative Example 2

[0089] Referring to the preparation method of Example 1, the only difference is that no nitrogen heterocyclic modification is used, and the preparation steps are as follows:

[0090] (1) 5 g coconut shell activated carbon was surface treated with low-temperature plasma and activated with 10 mL / min nitrogen flow for 60 min to obtain activated carbon;

[0091] (2) The activated carbon was purged with 0.2 MPa carbon dioxide for 2 h at a purging temperature of 30°C, and then filtered and dried to obtain carbon dioxide-purged modified activated carbon.

[0092] Comparative Example 3

[0093] The preparation method of Example 1 is referred to, except that the nitrogen heterocycle is replaced by an oxygen heterocycle benzofuran.

[0094] Modification, the preparation steps are as follows:

[0095] (1) Disperse 5 g of coconut shell activated carbon in 50 g of deionized water and soak for 2 h at a temperature of 10 °C;

[0096] (2) adding 0.34 g of benzofuran modifier to the coconut shell activated carbon solution prepared in the above (1), heating under reflux at 100 °C for 3 h, and then filtering and drying to obtain activated carbon containing benzofuran modifier;

[0097] (3) The benzofuran-modified activated carbon obtained in (2) was subjected to low-temperature plasma surface treatment and activated by 10 mL / min nitrogen gas flow for 60 min to obtain activated activated carbon;

[0098] (4) The activated carbon was purged with 0.2 MPa carbon dioxide for 2 h at a temperature of 30°C, and then filtered and dried to obtain carbon dioxide-purged oxygen-heterocyclic modified activated carbon.

[0099] Comparative Example 4

[0100] Referring to the preparation method of Example 1, the only difference is that the purge pressure during carbon dioxide modification is 5.0 MPa high pressure state, and the preparation steps are as follows:

[0101] (1) Disperse 5 g of coconut shell activated carbon in 50 g of deionized water and soak for 2 h at a temperature of 10 °C;

[0102] (2) adding 0.34 g of pyridine modifier to the coconut shell activated carbon solution prepared in the above (1), heating under reflux at 100 °C for 3 h, and then filtering and drying to obtain activated carbon containing pyridine modifier;

[0103] (3) The pyridine-modified activated carbon obtained in (2) was subjected to low-temperature plasma surface treatment and activated by 10 mL / min nitrogen gas flow for 60 min to obtain activated activated carbon;

[0104] (4) The activated carbon was purged with 5 MPa carbon dioxide for 2 h at a temperature of 30°C, and then filtered and dried to obtain carbon dioxide-purged nitrogen heterocyclic modified activated carbon.

[0105] Comparative Example 5

[0106] Referring to the preparation method of Example 1, the only difference is that the activated carbon does not undergo an intermediate low-temperature plasma activation process, and the preparation steps are as follows:

[0107] (1) Disperse 5 g of coconut shell activated carbon in 50 g of deionized water and soak for 2 h at a temperature of 10 °C;

[0108] (2) adding 0.34 g of pyridine modifier to the coconut shell activated carbon solution prepared in the above (1), heating under reflux at 100 °C for 3 h, and then filtering and drying to obtain activated carbon containing pyridine modifier;

[0109] (3) The obtained activated carbon was purged with 0.2 MPa carbon dioxide for 2 h at a purging temperature of 30°C, and then filtered and dried to obtain carbon dioxide-purged nitrogen heterocyclic modified activated carbon.

[0110] Comparative Example 6

[0111] Referring to the preparation method of Example 1, the only difference is that the low-temperature plasma activation process is replaced by a high-temperature calcination activation process. The preparation steps are as follows:

[0112] (1) Disperse 5 g of coconut shell activated carbon in 50 g of deionized water and soak for 2 h at a temperature of 10 °C;

[0113] (2) adding 0.34 g of pyridine modifier to the coconut shell activated carbon solution prepared in the above (1), heating under reflux at 100 °C for 3 h, and then filtering and drying to obtain activated carbon containing pyridine modifier;

[0114] (3) Activating the pyridine-modified activated carbon obtained in (2) above at 600° C. in a muffle furnace for 60 min to obtain activated activated carbon;

[0115] (4) The activated carbon was purged with 0.2 MPa carbon dioxide for 2 h at a purging temperature of 30 °C, and then filtered and dried to obtain carbon dioxide-purged nitrogen heterocyclic modified activated carbon.

[0116] Comparative Example 7

[0117] Referring to the preparation method of Example 1, the only difference is the low-temperature plasma activation time, and the preparation steps are as follows:

[0118] (1) Disperse 5 g of coconut shell activated carbon in 50 g of deionized water and soak for 2 h at a temperature of 10 °C;

[0119] (2) adding 0.34 g of pyridine modifier to the coconut shell activated carbon solution prepared in the above (1), heating under reflux at 100 °C for 3 h, and then filtering and drying to obtain activated carbon containing pyridine modifier;

[0120] (3) The pyridine-modified activated carbon obtained in (2) was subjected to low-temperature plasma surface treatment and activated by 10 mL / min nitrogen gas flow for 120 min to obtain activated activated carbon;

[0121] (4) The activated carbon was purged with 0.2 MPa carbon dioxide for 2 h at a purging temperature of 30 °C, and then filtered and dried to obtain carbon dioxide-purged nitrogen heterocyclic modified activated carbon.

[0122] Application examples and comparative application examples

[0123] The modified activated carbons prepared in the above Examples 1-5 and Comparative Examples 1-7 were used to purify carbon dioxide-based polyols according to the following adsorption-desorption method, which are respectively recorded as Application Examples 1-5 and Comparative Application Examples 1-7, and the unmodified commercial coconut shell activated carbon is recorded as Comparative Application Example 8. The specific parameters are described in Table 1.

[0124] This application takes a carbon dioxide-based polyol containing heavy metal ions of zinc and cobalt as an example: the carbon dioxide-based polyol is prepared by copolymerization of carbon dioxide and propylene oxide under the condition of a phenol initiator using a zinc-cobalt double metal cyanide complex as a catalyst, and the process parameters of the copolymerization reaction can be conventional processes in the art. The carbon dioxide-based polyol has a number average molecular weight of 1000-15000, a molecular weight distribution of less than 2, and a viscosity of more than 7000 mPa·s at 70°C.

[0125] (1) 1 g of the modified adsorbent was placed in a container containing 100 g of CO2-based polyol and stirred at 300 r / min for 5 h.

[0126] (2) heating and stirring the mixture in step (1) for 5 h;

[0127] (3) transferring the adsorbed mixture into a pressurized filter tank;

[0128] (4) The pressurized filter tank uses 0.1 MPa nitrogen pressure to filter;

[0129] (5) Collecting the filtered carbon dioxide-based polyol to obtain purified carbon dioxide-based polyol.

[0130] Determination of heavy metal ion Zn and Co content in CO2-based polyols before and after adsorption: Accurately weigh about 1 g of the test substance (accurate to 0.0001 g) and accurately record the weight M 二氧化碳基多元醇 , place the object to be tested in a 100 mL crucible, seal it and preheat it in an electric heating jacket to convert the liquid into a solid. The purpose of sealing is to prevent Zn and Co from being brought into the air with the gas or smoke produced by combustion, causing errors. Usually, a lid is used. Then, place the crucible containing the object to be tested in a muffle furnace, set the temperature to 500°C, heat it for 2 h, and keep it at a constant temperature for 2 h, so that the sample is completely ashed, while Zn and Co remain on the lid and wall of the crucible. Then, use 7% hydrochloric acid solution to dissolve the Zn and Co remaining in the crucible, and prepare a solution in a 100 mL volumetric flask for testing.

[0131] Determination of Zn and Co content in the solution in the volumetric flask by ICP i ,ICP , in ppm, calculate the Zn and Co contents in the sample to be tested according to formula (1);

[0132] C i =(C i ,ICP ×100) / M 二氧化碳基多元醇 (1)

[0133] In the formula, C i Refers to the Zn or Co content in the purified CO2-based polyol sample, ppm;

[0134] C i ,ICP Refers to the Zn or Co content in the test solution measured by ICP, ppm;

[0135] C i ,ICP The Co content before adsorption was 257 ppm, and the Zn content before adsorption was 264 ppm;

[0136] M 二氧化碳基多元醇 Refers to the mass in the sample, g.

[0137] Removal rate of phenolic compounds: The absorbance corresponding to the maximum absorption wavelength (Amax) of phenolic compounds was detected by ultraviolet spectrophotometer, and then the standard curve was calculated according to the Lambert-Beer law, and finally the concentration of phenolic compounds in carbon dioxide-based polyols was obtained.

[0138]

[0139] ŋ represents the adsorption rate of modified activated carbon for phenolic compounds (%), C0 represents the initial concentration of phenolic compounds in carbon dioxide-based polyols (mg / L), C t It represents the concentration of phenolic compounds in CO2-based polyols after adsorption by modified activated carbon (mg / L).

[0140] Table 1 Purification conditions and product performance test table of application examples and comparative application examples

[0141]

[0142] As can be seen from Table 1, the combined modified adsorbent prepared by the method of the present invention has excellent purification effect in the application example, the Zn content and Co content in the purified product are both less than 5 ppm, and the removal rate of phenolic compounds reaches more than 90%. In the comparative application, due to the change of the preparation parameters of the present invention when preparing the combined modified adsorbent, the adsorbent obtained has significant differences in adsorption effect. For example, in comparative application example 8, unmodified commercial activated carbon is directly used for adsorption, and the Zn content in the adsorbed product is 230 ppm, the Co content is 256 ppm, and the removal rate of phenolic compounds is less than 25%. It can be seen from the comparison that the present invention has efficient adsorption performance for the purification of carbon dioxide-based polyol polymers through the combined modification of nitrogen heterocycles and carbon dioxide.

[0143] Compared with Example 1, the neutralization method used in the modified activated carbon is different. Comparative Example 1 uses hydrochloric acid for neutralization. The nitrogen atom in the nitrogen heterocycle usually has a lone pair of electrons, which makes the activated carbon surface show stronger alkalinity. The presence of the alkaline surface is conducive to the adsorption of phenolic compounds in the carbon dioxide-based polyols, but the presence of alkalinity has a negative effect on the carbon dioxide-based polyols, which will lead to the decomposition of the carbon dioxide-based polyols. The hydrochloric acid neutralization is too acidic for the nitrogen heterocycle and is easy to affect the internal pores of the nitrogen heterocycle modified activated carbon, which correspondingly affects the adsorption capacity of the activated carbon for metal ions and reduces the specific adsorption capacity of the modified activated carbon for phenolic compounds, thereby reducing its adsorption removal rate. Therefore, the carbon dioxide purge neutralization alkalinity has the ability to improve the adsorption capacity for metal ions while maintaining the adsorption capacity for phenolic compounds.

[0144] In Comparative Example 2, nitrogen heterocycle modification was not used, while oxygen heterocycle was used in Comparative Example 3. Compared with nitrogen heterocycle, oxygen heterocycle has relatively poor stability and is more susceptible to steric hindrance during the process of doping and modifying activated carbon, resulting in unstable or uneven doping effect. In addition, nitrogen heterocycle is more conducive to forming a pore structure that is conducive to the adsorption of phenolic compounds, and is also easier to introduce more active nitrogen species, which are more advantageous in the targeted adsorption of compounds.

[0145] In Comparative Example 4, a relatively high pressure is used for carbon dioxide purging. Under high pressure conditions, carbon dioxide molecules will produce a compression effect on the pore structure of activated carbon, and the adsorption performance of activated carbon depends largely on its porous structure. These pores provide adsorption sites for phenolic compounds and metal ions. When subjected to high pressure, the pores will be compressed, resulting in a smaller pore size or even closure, which reduces the adsorption performance of activated carbon.

[0146] In Comparative Example 5, low-temperature vacuum plasma activation was not used. Low-temperature plasma activation is an efficient surface modification technology that can introduce new functional groups and change the chemical properties of the activated carbon surface. Without this technology, the surface chemical properties of the activated carbon may be relatively simple, and the adsorption of phenolic compounds is not ideal; and in the high-temperature calcination process of Comparative Example 6, although high-temperature calcination can optimize the pore structure of activated carbon, excessive temperature causes the pore structure of activated carbon to collapse or be destroyed, thereby reducing its adsorption performance. High-temperature calcination mainly improves the thermal stability and chemical stability of activated carbon, but the change in its surface chemical properties is limited, and the adsorption effect on phenolic compounds and metal ions is not competitive. In Comparative Example 7, the low-temperature plasma activation time is too long, resulting in a decrease in the adsorption efficiency of activated carbon. On the one hand, long-term low-temperature plasma treatment may cause changes in the pore structure of the activated carbon surface, thereby affecting its adsorption performance; on the other hand, excessive oxidation occurs, resulting in a decrease in its specific surface area, and a decrease in the adsorption effect on metal ions and phenolic compounds.

[0147] In summary, it can be seen from the above embodiments and comparative data that the combined modified adsorbent for removing phenolic compounds and metal ions in carbon dioxide-based polyols according to the present invention adopts activated carbon as raw material, and is prepared by pre-dispersion and combined modification steps, wherein the combined modification includes specific nitrogen heterocycle-low temperature plasma activation-carbon dioxide gas modification in sequence, and the preparation method of the present invention needs to accurately control the type of heterocyclic modifier in the combined modification, the amount of nitrogen heterocyclic modifier, the time of low temperature plasma activation and the type of activated gas, the pressure of carbon dioxide gas and other parameters, and the above steps are related before and after, progressive layer by layer, and play an overall synergistic effect. The three steps in the combined modification are indispensable, and the prepared adsorbent has efficient adsorption performance. It can show excellent adsorption performance to phenolic compounds in carbon dioxide-based polyols within 6 h, can quickly adsorb phenolic compound molecules, and achieve a phenolic compound removal rate of more than 90%, and metal ions in polymers are reduced from 260 ppm to less than 5 ppm, and can be desorbed by high pressure filter tanks in a short time, and the operation is simple and convenient, and the cost is low.

[0148] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments can still be modified, or some of the technical features can be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. Use of a combined modified adsorbent for removing phenolic compounds and metal ions from carbon dioxide-based polyols, characterized in that: The combined modified adsorbent is prepared through the steps of pre-dispersion and combined modification, specifically comprising: (1) Pre-dispersion: Dispersing activated carbon in deionized water to prepare an activated carbon dispersion to form an active and stable activated carbon precursor; (2) Combined modification: The combined modification includes nitrogen heterocycle-low temperature plasma activation-carbon dioxide gas modification in sequence; The nitrogen heterocycle modification method comprises adding the nitrogen heterocycle modifier to the activated carbon dispersion at a mass ratio of the nitrogen heterocycle modifier to the activated carbon of 1:0.5-20, and heating and refluxing to prepare the nitrogen heterocycle modified activated carbon; The method of low-temperature plasma activation is to subject nitrogen heterocyclic modified activated carbon to low-temperature plasma surface treatment to obtain an activated adsorbent; the low-temperature plasma activation time is 10-60 min; the low-temperature plasma activation gas is nitrogen; the low temperature of the low-temperature plasma refers to 10°C-150°C; The carbon dioxide gas modification method is to prepare a solution of the activated adsorbent using water as a solvent, disperse and soak it, and purge it with a low-pressure carbon dioxide gas at a pressure of 0.2-1.5 MPa until the solution pH is 6-8, filter it, and vacuum dry it to obtain the combined modified adsorbent; The nitrogen heterocyclic modifier is selected from nitrogen heterocyclic compounds containing at least one nitrogen atom with unbound lone pair of electrons on the nitrogen atom.

2. The use according to claim 1, characterized in that The activated carbon is commercial activated carbon, selected from any one or more of fruit shell activated carbon, coconut shell activated carbon, coal columnar activated carbon, wood activated carbon, medical activated carbon, apricot shell activated carbon, and medicinal activated carbon.

3. The use according to claim 1, characterized in that The nitrogen heterocyclic modifier is selected from any one or more of pyridine, pyrrole, imidazole, pyrimidine, quinoline, benzimidazole compounds and their derivatives.

4. The use according to claim 1, characterized in that During the pre-dispersion, the activated carbon is immersed and stirred at 10-50° C. for 2-12 hours to form an activated carbon precursor; the mass of the deionized water is 10-20 times the mass of the activated carbon.

5. The use according to claim 1, characterized in that: In the combined modification, the mass ratio of the nitrogen heterocyclic modifier to the activated carbon is 1:5-1:15; the heating reflux temperature is 100-160° C., and the heating reflux time is 3-16 h.

6. The use according to claim 1, characterized in that: In the combined modification, during the low-temperature plasma activation, the gas flow rate of the nitrogen gas is 10-50 mL / min, and the processing power is 30-150 W.

7. The use according to claim 1, characterized in that In the combined modification, during the carbon dioxide gas modification, the carbon dioxide purge temperature is 30-90° C. and the time is 2-6 h.

8. The use according to claim 1, characterized in that In the combined modification, the method of carbon dioxide gas modification is: using a carbon dioxide purge device, continuously introducing carbon dioxide gas from the bottom pipeline, the activated adsorbent enters from the top of the reaction tank, and the excess carbon dioxide gas circulates from the top of the reaction tank into the reaction tank through a compressor. A sampling port is set at the bottom of the reaction tank, and when the pH is detected to be 6-8, the combined modified adsorbent is discharged from the bottom pipeline to obtain.

9. The use according to claim 1, characterized in that The specific surface area of ​​the combined modified adsorbent is 3000-5000 m 2 / g, and the average volume particle size is 10-40 μm.

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