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    • 专利摘要:
    The invention relates to a device for regenerating activated carbon in the form of porous fibers by electro-Fenton reaction, a regeneration process for activated carbon loaded with organic pollutants using the device of the invention and the use of a filter. composed of porous activated carbon fibers, said filter having been previously loaded with organic pollutants by filtration of polluted water or polluted air, as cathode of an electro-Fenton reaction to regenerate the porous activated carbon fibers loaded with organic pollutants.
    公开号:FR3078899A1
    申请号:FR1852190
    申请日:2018-03-14
    公开日:2019-09-20
    发明作者:Mehmet Oturan；Yoan Pechaud；Clement Trellu；Nihal Oturan
    申请人:PARIS EST MARNE LA VALLEE, University of；Universite Paris Est Creteil Paris 12；
    IPC主号:
    专利说明:

    METHOD FOR REGENERATION OF ACTIVE CARBON BY ELECTRO-FENTON PROCESS INTRODUCTION
    The development of sustainable water treatment systems achieving high rates of micropollutant removal is an important challenge for environmental engineering. Activated carbon (AC) is currently widely used in water treatment plants because it has proven to be an effective adsorbent for removing organic compounds from water. 1 ' 3 This is due to its large specific surface, its internal microporosity as well as the presence of large quantities of various surface functional groups. 4
    However, this is a simple separation step; the organic pollutants are not degraded after this step and the CA is loaded / saturated with organic pollutants and is therefore a waste which must be treated. The treatment must lead both to the regeneration / reuse of the CA (in order to improve the durability and profitability of the CA process) and to the degradation of organic pollutants (in order to avoid any contamination of the environment).
    While the effectiveness and adsorption mechanisms of a wide range of organic compounds on various sales materials have been widely reported in the literature, March 5 it is still necessary to develop innovative and effective processes for regeneration CA used / saturated / loaded with organic pollutants.
    Thermal regeneration is the most widely used process. The effectiveness depends closely on the nature of the organic compounds adsorbed and on the nature of the interactions with the surface of the CA. Thermal regeneration with an inert atmosphere often leads to poor recovery of the adsorption capacity due to the insufficient elimination of the chemisorbed compounds. 6 In addition, additional treatment is necessary for the degradation of pollutants. Higher removal rates are achieved during heat treatment under oxidizing conditions but the microporous structure of CA is greatly affected. 6.7
    Chemical regeneration by oxidation using for example ozone or the Fenton reaction limits oxidation of CA but can also strongly affect its chemical and textural characteristics. In addition, low regeneration efficiency is often observed for microporous CAs and chemical regeneration is thus often applied only to mesoporous or non-porous materials. 8 '10
    Recently, the electro-Fenton (EF) process has emerged as a promising solution for the regeneration of CA. The continuous electro-generation of H2O2 from the reduction to 2 electrons of O2 on the surface of the CA combined with the supply of a catalytic quantity of iron (II) regenerated continuously at the cathode allows the formation of hydroxyl radicals (· ΟΗ) (éq 1). 11 '13
    Fe 2+ + H 2 0 2 -> Fe 3+ + ΌΗ + 0H “(k = 63 M ' 1 s' 1 ) (1)
    It has been observed that a wide range of organic pollutants is completely mineralized using the EF process. 11,13 '14 It has also been shown that · ΟΗ are capable of easily oxidizing organic compounds adsorbed on granular CA and that they thus participate in the regeneration of CA and in the degradation of pollutants. 15 In addition, Banuelos et al. (2015) observed that the cathodic polarization of granular CA during the EF process protects the surface from oxidation and can thus avoid the loss of adsorption capacity. 7 However, the development, improvement and scaling of the CA regeneration process by EF are still hampered by technical aspects when using the cathode 715 , mainly because of ohmic drops and a lack of interconnection at the microstructure leading to a very heterogeneous potential distribution in the CA grain beds used as cathode.
    Porous fibers have unique characteristics compared to granular or powdered CA 16 . The fine fiber shape reduces resistance to intra-particulate scattering and gives this material mechanical and geometric characteristics suited to the design of electrochemical reactors. In addition, CA fiber is an effective material for the adsorption of organic compounds and the generation of H2O2 during water treatment. 17.18 Compared to CA grain beds, porous CA fibers ensure a better level of interconnection at the level of the microstructure and thus reduce ohmic drops as well as dead zones (non-electro- active).
    The inventors looked at a technology based on electro-Fenton (EF), using activated carbon fiber (AC) as cathode and an anode covered with boron doped diamond (DDB) both for the regeneration of the CA and the mineralization of organic pollutants. The large specific surface area and the low resistance to intraparticle diffusion of porous CA fibers made it possible to achieve a high maximum adsorption capacity for phenol (PH) (3.7 mmol g ' 1 ) and rapid adsorption kinetics. . The porous fibers of spent / saturated CA were then used as the cathode during the EF process. After 6 h of treatment at 300 mA, 70% of PH were removed from the surface of the porous fibers of CAC. The inventors have surprisingly observed a high efficiency of the process attributed to (i) the direct oxidation of the PH adsorbed by the hydroxyl radicals generated, (ii) the continuous displacement of the adsorption equilibrium due to the oxidation of the compounds organic in the solution and (iii) local increase in pH at the cathode leading to repulsive electrostatic interactions. In addition, 91% of the PH eliminated from the CA was completely mineralized, thus avoiding the adsorption of degradation by-products and the accumulation of toxic compounds such as benzoquinone. The morphological and chemical characteristics of CA were not affected due to the effect of cathodic polarization protection. The porous fibers of CA have been successfully reused during 10 adsorption / regeneration cycles with a regeneration efficiency ranging from 65 to 78%, in accordance with the quantity of PH removed from the surface of CA at the end of each cycle of regeneration.
    Still surprisingly, the inventors have successfully combined the EF process with anodic oxidation using DDB as an anode. This promotes the oxidation of compounds adsorbed by mediated oxidation (production of ozone, persulfate, sulphate radical) 13,19 and increases the mineralization of desorbed pollutants and oxidation degradation by-products with · ΟΗ generated on the surface of the DDB anode coming from the discharge of the water (éq 2 in which M is the material of the anode). 19
    M + H 2 0 M (0H) + H + + e “(2)
    INVENTION
    The main drawbacks of conventional regeneration methods are avoided by using the EF process according to the invention. Compared to chemical oxidation, a much higher regeneration efficiency of a microporous adsorbent can be obtained. This process according to the invention can also completely mineralize organic molecules, while heating under inert conditions only leads to the desorption of pollutants. In addition, the adsorption capacity of porous CA fibers is not affected, unlike chemical oxidation and heat treatments under oxidizing conditions. The choice of porous fibers of CA as adsorbent plays an important role on the efficiency of the process because this material presents characteristics suitable for both the adsorption and regeneration stages.
    FIGURES
    Figure 1: General diagram of the device according to the invention by way of example
    Figure 2: Evolution of the concentration of phenol adsorbed on the activated carbon tissue (Phenol ads), phenol in the solution + adsorbed on the CA tissue (Total phenol) and total organic carbon in the solution + adsorbed on the CA tissue (Total TOC) during the electro-Fenton regeneration of the CA loaded with organic pollutant. The control experiment was carried out without current supply (I = 0). The concentrations are expressed as a percentage of the total initial concentration ([PH] o or TOCo) in the electrochemical cell, which corresponds to the initial amount of phenol adsorbed on the CA tissue.
    Figure 3: Evolution of the normalized concentration of phenol and the normalized concentration of TOC in the solution during the regeneration by the electro-Fenton process of the CA tissue loaded with organic pollutants. The error bars represent the standard deviations obtained from experiments carried out in triplicate.
    Figure 4: Evolution of the concentration in the solution of the main by-products of the degradation of phenol (Csol, t) during the electro-Fenton regeneration of CA tissue loaded with organic pollutants. The concentration of organic compounds is calculated in mg of carbon per liter and expressed as a percentage of the initial concentration of total organic carbon (TOCo) in the electrochemical cell. The error bars represent the standard deviations obtained from experiments carried out in triplicate.
    Figure 5: Evolution of the regeneration efficiency (RE) as a function of the number of adsorption / regeneration cycles performed. The dotted line corresponds to the rate of elimination of the phenol adsorbed after 6 h of regeneration by electro-Fenton. The error bar on the “cycle 1” point (contained in the data point) represents the standard deviation obtained from an experiment carried out in triplicate.
    Figure 6: Scanning electron microscope images of the initial activated carbon tissue (A, E) and after 10 regeneration cycles (B, F). Images C and D focus on the rupture zone of the porous fibers observed in the material after 10 regeneration cycles.
    Figure 7: (A) Ratio between equilibrium concentrations of benzoquinone (BQ) and hydroquinone (HQ) after adsorption of 0.9 mM HQ on activated carbon (CA) tissue, as a function of the concentration of added AC (B) Evolution of the concentrations of HQ and BQ during the dynamic adsorption experiment with 0.95 mM HQ and 2 g L ' 1 of CA.
    Figure 8: Evolution of the hydrogen peroxide concentration in an undivided electrochemical cell, depending on the cathode used (activated carbon felt, activated carbon fabric or conventional carbon felt). Operating conditions: V = 125 mL; [Na2SO4] = 0.1 M; pH = 3; I = 300 mA; Cathode area = 140 cm 2 ; Anode: platinum grid. H2O2 was analyzed by a spectrophotometric method based on the formation of a yellow complex in the presence of Ti 4+ in an acid medium.
    Figure 9: Evolution of the ratio between the phenol concentration in the solution ([PH] sol, t) and the initial concentration adsorbed on the activated carbon tissue ([PH] 0 = 6.4 mM) during electro-Fenton regeneration (EF) (I = 300 mA) and during the control experiment without power supply. The error bars represent the standard deviations obtained from experiments carried out in triplicate.
    Figure 10: Evolution of the concentration of phenol adsorbed on activated carbon felt (CA) (phenol ads), phenol in the solution + adsorbed on felt CA (total phenol) and total organic carbon in the solution + adsorbed on felt CA (Total TOC) during the electro-Fenton regeneration of the CA loaded with organic pollutants. The concentrations are expressed as a percentage of the total initial concentration ([PH] o or TOCo) in the electrochemical cell, which corresponds to the initial amount of phenol adsorbed on the felt CA.
    Figure 11: Adjustment of the curve of the Raman spectra (initial CA tissue) by combination of three lorentzian bands at approximately 1600 cm-1 (G), 1340 cm-1 (D1) and 1185 cm-1 (D2 ) and a band of Gaussian shape at 1545 cm-1 (D3). The crosses represent the experimental data.
    Figure 12: Evolution of the surface ratio of the Raman bands D1, D2, D3, D1 + D2 + D3 (Σ (D)) and G between the initial CA tissue and after one and 10 cycles of electro-Fenton regeneration. The error bars represent the standard deviations obtained from triplicate analyzes.
    Figure 13: Image of the solutions obtained after mixing for 24 h 250 ml of phenol (11 mM) with 2 g L ' 1 of regenerated charcoal tissue or felt (one cycle). The presence of a large amount of porous activated carbon fibers (CA) broken is observed when using activated carbon felt.
    SUMMARY OF THE INVENTION
    A first object of the invention relates to a device for regenerating activated carbon in the form of porous fibers (CA) by electro-Fenton reaction (EF), comprising at least one electrochemical cell comprising:
    at least one cathode and at least one anode immersed in an electrolytic solution:
    the cathode comprising activated carbon in the form of porous fibers having organic pollutants which are adsorbed on the porous fibers, the activated carbon in the form of porous fibers having served as a filter for organic pollutants; the anode comprising a non-active anode material, the non-active anode material being defined as a material having an oxygen release overvoltage greater than 0.4 V;
    an electrolytic solution with:
    an oxygen supply intended to be continuous during the regeneration of the activated carbon in the form of porous fibers;
    an initial supply of Fe 2+ ions intended to be continuously regenerated during the electro-Fenton reaction;
    the device making it possible to create, during the electro-Fenton reaction, oxidizing species at the level of the cathode and the anode, these oxidizing species mineralizing the organic pollutants at the level of the anode, the cathode and the electrolytic solution .
    A second object of the invention relates to a process for regenerating activated carbon loaded with organic pollutants using the device according to the invention.
    A third object of the invention relates to the use of a filter composed of porous fibers of activated carbon, said filter having been previously charged with organic pollutants by filtration of polluted water or polluted air, as a cathode of an electro-Fenton reaction to regenerate said porous activated carbon fibers loaded with organic pollutants.
    DETAILED DESCRIPTION
    The invention relates to a device for regenerating activated carbon in the form of porous fibers by electro-Fenton reaction (EF), comprising at least one electrochemical cell comprising:
    at least one cathode and at least one anode immersed in an electrolytic solution:
    the cathode comprising activated carbon in the form of porous fibers having organic pollutants which are adsorbed on the porous fibers, the activated carbon in the form of porous fibers having served as a filter for organic pollutants; the anode comprising a non-active anode material, the non-active anode material being defined as a material having an oxygen release overvoltage greater than 0.4 V;
    an electrolytic solution with:
    an oxygen supply intended to be continuous during the regeneration of the activated carbon in the form of porous fibers;
    an initial supply of Fe 2+ ions intended to be continuously regenerated during the electro-Fenton reaction;
    the device making it possible to create, during the electro-Fenton reaction, oxidizing species at the level of the cathode and the anode, these oxidizing species mineralizing the organic pollutants at the level of the anode, the cathode and the electrolytic solution .
    The advantage of the EF reaction is to simultaneously promote the oxidation of organic compounds both in the solution and adsorbed on the CA tissue.
    The device according to the invention is particularly advantageous because it makes it possible to achieve faster degradation kinetics than the adsorption kinetics. Thus, the re-adsorption of the oxidation by-products on the CA tissue is avoided. The formation of more hydrophilic by-products as well as the electrostatic interactions due to the locally high pH at the surface of the CA tissue also contribute to preventing the adsorption on the CA of the degradation by-products.
    Total mineralization of pollutants prevents the accumulation of toxic by-products.
    The electrochemical cell has any shape allowing a suitable container to be delimited for the electrodes and the electrolytic solution, for example cylindrical or parallelepipedic.
    The electrochemical cell is made of any material allowing to delimit a container suitable for the electrodes and the electrolytic solution.
    It can be open or closed, divided or not. Preferably, it is open and not divided.
    Preferably, the activated carbon in the form of porous fibers having served as a filter for organic pollutants is saturated with organic pollutants.
    The porous fibers of activated carbon loaded with organic pollutants serve as a cathode. They are in the form of fabric (porous ordered woven fibers) or felt (porous non-woven porous fibers), preferably in the form of fabric. The fabric consists of thousands of thin porous fibers with a very high specific surface.
    Advantageously, the cathode consists of activated carbon in the form of porous fibers. They come from one or are a filter previously used to filter pollutants from water and / or air.
    Preferably, the diameter of the porous fibers is greater than 0.1 micrometer and less than 1000 micrometers, more preferably is greater than 1 micrometer and less than 100 micrometers.
    The specific surface (Sbet) of the porous fibers is preferably greater than 100 m 2 .g ' 1 , more preferably greater than 600 m 2 .g' 1 .
    Advantageously, the porous fibers have a porosity so that more than 30% of the porous volume of each of the porous fibers is constituted by pores of size less than 2 nm more preferably more than 80%.
    According to one embodiment, the anode is made of a non-active anode material.
    According to another embodiment, the anode consists of a substrate at least partially covered with a non-active anode material.
    According to the model proposed by Comninellis 4445 , the materials used as an anode for the electrooxidation of organic pollutants in an aqueous medium can be divided into two groups: active and non-active anodes.
    In the case of active anodes, the hydroxyl radical (· ΟΗ) formed is chemically adsorbed and weakly available to effect the oxidation of organic compounds in the solution. These materials rather favor the reaction of release of O2.
    In the case of non-active anodes (such as DDB), the overvoltage for the release of U2 is higher (compared to active anodes) and the · · radicals formed are physically adsorbed. In this case, they are no longer available and react directly with organic compounds. 44.45 ' 13 ' 19
    The non-active anode material is defined as a material having an oxygen release overvoltage greater than 0.4 V, preferably greater than 0.6 V.
    Preferably, the non-active anode material is chosen so that the oxidizing species created are at least: · ΟΗ, O3, preferably · ΟΗ, O3, SOZet S2O8 2 'if sulphate ions are present in the solution.
    · ΟΗ ions are used to attack the pollutants adsorbed at the cathode until they are mineralized. Advantageously, the cathodic polarization preserves, however, the surface of the porous fibers of activated carbon. Total mineralization of pollutants prevents the accumulation of toxic by-products.
    More preferably, the non-active anode material is boron-doped diamond (DDB) or a sub-stoichiometric titanium oxide (properties close to DDB in terms of overvoltage on release of oxygen). Particularly preferably, the non-active anode material is boron-doped diamond (DDB).
    The device of the invention can comprise several anodes, in particular several DDB anodes.
    By way of example, the device according to the invention may comprise an anode as defined above and two cathodes on either side of the anode as defined above. According to one embodiment, the anode consists of a substrate at least partially covered with a non-active anode material. Preferably, the anode then consists of a substrate entirely covered with a non-active anode material. Suitable substrates can be mentioned: Ti, Nb or Si. The thickness of the nonactive anode material on the substrate varies from 0.1 to 0.5 mm depending on the overall size of the electrode.
    The electrochemical solution provides a continuous supply of oxygen for the production of hydrogen peroxide. Oxygen is supplied by an inlet of bubbled oxygen or of bubbled air into the electrolytic solution, preferably by an inlet of bubbled air into the electrolytic solution. The bubbling contributes to the agitation of the electrochemical solution.
    Preferably, the initial supply of Fe 2+ ions has a catalytic concentration in the electrolytic solution greater than 10 ' 5 M and less than 10' 2 M, more preferably between 3 * 10 ' 5 M and 10' 3 M. The initial supply of Fe 2+ ions is advantageously low since these ions are regenerated at the cathode throughout the process (Figure 1).
    The electrodes are separated by a few centimeters, preferably less than 10 cm.
    The electrolyte will be chosen appropriately by a person skilled in the art. The presence of salt is necessary to ensure the conductivity of the solution, for example, Na 2 SO4., Na Cl, etc. The conductivity of the solution is greater than 0.01 S m ' 1 .
    The electrolyte concentration is between 10 ' 3 and 10' 1 M.
    Stirring of the electrochemical solution is ensured for example by magnetic or mechanical stirring.
    The pH is adjusted, preferably between 2 and 5, more preferably between 2.6 and 3.6.
    The electrochemical cell is supplied with constant current. The current density is preferably set between 0.1 and 100 mA / cm 2 , preferably between 1 and 30 mA / cm 2 , of active carbon surface as soon as the spent / saturated CA cathode has been immersed in the electrolyte.
    The current density is determined to optimize the production of H2O2 and · ΟΗ and to minimize side reactions such as the evolution of oxygen and hydrogen.
    Another object of the invention relates to a process for the regeneration of activated carbon loaded with organic pollutants using the device according to the invention.
    Any type of activated carbon filter made from porous activated carbon fibers may be used as the cathode of the device according to the invention in order to be regenerated after its use as a filter for organic pollutants in the air and / or water and can thus be reused again as a filter for organic pollutants in air and / or water. This use / regeneration cycle can be repeated several times.
    Another object of the invention relates to the use of a filter composed of porous fibers of activated carbon, said filter having been previously loaded with organic pollutants by filtration of polluted water or polluted air, as a cathode of an electro-Fenton reaction to regenerate porous activated carbon fibers loaded with organic pollutants.
    EXAMPLES
    The following study aims to assess the regeneration efficiency of the CA fiber during the EF process using the DDB anode and the CA fiber loaded with organic pollutant as the cathode. By choosing phenol (PH) as a model organic pollutant, the objectives of this study were to assess (i) the adsorption capacity and the adsorption kinetics of PH and the main by-products of aromatic oxidation on porous fibers CA (ii) elimination of the PH from the surface of the CA fiber charged with organic pollutant by the EF process (iii) release into the solution of PH and degradation by-products and their subsequent mineralization (iv) the capacity d adsorption and characteristics of the regenerated material after 1 and 10 adsorption / regeneration cycles.
    MATERIAL AND METHODS
    1. Chemicals
    All chemicals are reagent grade purchased from Acros Organics (PH and iron (II) sulfate heptahydrate), Sigma Aldrich (hydroquinone (HQ), benzoquinone (BQ), catechol (CAT), methanol, sodium sulfate) or Fluka (sulfuric acid). All solutions are prepared using ultrapure water (resistivity> 18.2 MQ cm) from a Millipore Milli-Q system (Molsheim, France).
    2. Adsorption
    Microporous CA tissue (Dacarb, France), prepared from a phenolic resin, was used as the adsorption material. N2 adsorption isotherms were performed for the determination of the BET surface area, the total pore volume and the pore size distribution (using the two-dimensional non-local density functional theory method) . The main characteristics of the material are presented in Table 1. Some experiments were also carried out using CA felt prepared from phenolic resin (Dacarb, France) with different morphological characteristics but a specific surface and microporosity.
    Table 1 - Main characteristics of the activated carbon fabric used during the experiments
    CD (N o_ on (D
    O
    E
    CO (D
    O Q_ co (D O <u
    U CÜ M—
    D in to pore volume (cm 3 g ' 1 ) - distribution of pore size (DT
    Z3 on -----------------. Ξ - rxi ü = Microporous
    Q_ co (<1 nm)
    Microporous (1-2 nm)
    Mesoporous (2-20 nm)
    Porous macro (> 20 nm)
    Total
    0.5
    0.82
    1306%
    %
    1.7%
    0.2%
    0.54
    Before use, the CA was washed several times in deionized water and dried at 70 ° C. The pH was fixed at 3 for all the adsorption experiments, the pH value required for the regeneration step EF. Control tests without CA have shown that less than 3% of PH was lost by volatilization or adsorption on the glass after 24 h.
    Equilibrium adsorption experiments were carried out at room temperature (20 ° C) with single compounds in 500 ml glass bottles continuously shaken for 24 h on a rotary shaker set at 20 rpm. For isothermal experiments, 250 mL of PH (1 mM), BQ (0.5 mM), CAT (0.8 mM) or HQ (0.9 mM) were mixed with various CA concentrations from 0.08 to 1 g L-1. The most widely used models, Langmuir (éq 3) and Freundlich (éq 4), were used to model the experimental data.
    (3) where q e is the quantity of solute adsorbed per unit of weight of CA at equilibrium (mmol g-1), q m is the maximum adsorption capacity (mmol g-1), Kl is a bound constant at the free energy of adsorption (L mmol-1) and C e is the concentration of solute in the mother solution at equilibrium (mmol L-1).
    q e = κ Ρ ^ / η (4) where Kf and n are constants related to the capacity and the intensity of adsorption, respectively.
    The CAs loaded with organic pollutants used for the EF regeneration experiments were obtained by mixing 250 ml of pH at 11 mM with 500 mg of CA (2 g L-1).
    Dynamic adsorption experiments have been carried out with single compounds and using a configuration similar to that of electrochemical regeneration in order to ensure the same hydrodynamic conditions. The initial concentrations of CA (2 g L-1) and of organic compounds ([PH] = 1 mM; [HQ] = [CAT] = 0.1 mM; [BQ] = 0.05 mM) were chosen by depending on the experimental conditions observed during the EF regeneration step. The data were analyzed using both the pseudo-first order (eq 5) and the pseudo-second order (eq 6) ln (q e - q t ~) = lnq e -k ± t (5) where q t is the quantity of solute adsorbed per unit of weight of CA at time t and ki is the first order speed constant.
    Qt k 2 q e qe where k2 is the second order speed constant.
    3. EF regeneration of porous CA fibers loaded with organic pollutants
    The electrochemical regeneration of porous CA fibers charged with organic pollutant was carried out in batch mode using an open, cylindrical and undivided electrochemical cell, similar to the configuration previously described by Trellu et al. (2016). 20 500 mg of worn CA (55 cm x 0.5 mm 2) were used as cathode. The anode consisted of a thin film of DDB deposited on an Nb substrate (24 cm 2 x 0.2 cm, Condias Gmbh, Itzehoe, Germany). The electrodes were placed face to face with a space of 3 cm between the anode and the cathode. The CA cathode was fixed in the electrochemical cell using a Teflon grid. The oxygen supply for the production of hydrogen peroxide was ensured by a bubbling of continuous air through sintered glass.
    0.05 M Na2SO 4 (electrolyte) was dissolved in milli-Q water, the pH was adjusted to 3.0 with HzSO 4 and 0.1 mM Fe 2+ (catalyst) was added to the solution . 21 Continuous agitation was carried out by magnetic agitation and air bubbling. The constant current supply was provided by a supply (HAMEG, model 7042-5, Germany) set to 300 mA as soon as the cathode CA charged with organic pollutant was immersed in the electrolyte. This corresponds to 5.5 or 12.5 mA cm ' 2 as current density by considering either the area of the AC cathode or the area of the DDB anode, respectively. -The current density has been determined to optimize the production of OH OHzet and minimize side reactions such as the evolution of oxygen and hydrogen.
    4. Analytical methods
    Chemical analyzes were carried out in order to follow the evolution of the concentration of PH and of the degradation by-products in the solution and adsorbed on the porous fibers of CA. Aqueous samples (1 mL) were collected periodically from the solution during the treatment, while the analysis of the organic compounds adsorbed on CA required stopping the experiment in order to carry out a desorption step. The porous CA fibers used as the cathode were immersed in a solution of 90% ethanol - 10% 1M NaOH, and was placed for 30 minutes in an ultrasonic bath. After mixing with magnetic stirring for an additional 30 minutes, an aliquot was collected and analyzed. Different authors have observed that such conditions effectively remove adsorbed organic compounds from the surface of the CA. 22,23 Preliminary experiments have shown that more than 97% of the adsorbed PH was desorbed and recovered after repeating this procedure twice.
    The PH and the aromatic by-products were analyzed by reverse phase HPLC, while the carboxylic acids were identified and quantified by ion exclusion chromatography. The analysis conditions were similar to those of Pimentel et al. (2008). 24 The PH mineralization rate was followed by the measurement of total organic carbon (TOC) with a Shimadzu COT-V analyzer.
    5. Material characterization
    A scanning electron microscope (Phenom XL, PhenomWorld, The Netherlands) was used to analyze the surface morphology of the CA tissue. Since the CA is conductive, no surface treatment was necessary before the analysis.
    Raman measurements were carried out on a Renishaw INVIA spectrometer equipped with a microscope and a CCD detector (LGE, France). Details are given below (see Figures 11 and 12).
    Raman analysis
    A green laser at 532 nm in solid state (Nd: YAG) was used with a maximum power of 50 mW. The acquisitions were made using a Leica magnification objective (x50) after a calibration carried out on a silicon standard. With this configuration, the diameter of the beam did not exceed 2 microns. The Rayleigh scattering component was removed by an Edge filter, and the light scattered by Raman was scattered by a holographic network with 1,800 mm ' 1 lines. The integration time was fixed at 2 min. The acquisitions were repeated at 3 different points in the material. The spectral analysis was carried out with the WIRE software.
    RESULTS
    1. Sorption of phenol and the main aromatic oxidation by-products on AC tissues
    The first step in this study was to determine the adsorption behavior of PH and the main aromatic oxidation by-products on CA tissue. The adsorption isotherms of PH, BQ and CAT are presented in Table 2. As reported by the previous studies, a conventional L adsorption isotherm was obtained for all the compounds. 2.25 '26 The Langmuir and Freundlich equations are applicable but slightly higher correlation coefficients were obtained using the Langmuir equation for the three compounds, indicating that the assumptions on which the Langmuir model is based are appropriate for this material (adsorption of a monolayer of solutes on a homogeneous adsorbent surface with uniform adsorption energies). The maximum adsorption capacity of PH (3.73 mmol g ' 1 ) is higher than the previous results reported using granular CA (2.32 mmol g' 1 ). This is due to the larger BET surface (1,326 vs 929 m 2 g ' 1 ) as well as the microporous structure of the CA fiber since the adsorption energy is improved in the small pores. In addition, effective adsorption requires that the average pore size (0.82 nm) be greater than
    1.2 times 27 or 1.7 times 28 the second largest dimension of the adsorbed molecule (for the pH 0.42 nm). 29 A small steric hindrance effect is therefore expected in this study because this ratio reaches 2.0. 27 '29 Compared to PH, the by-products of aromatic oxidation (BQ and CAT) showed a much lower adsorption capacity on CA tissues (lower q m and Kf values). This is consistent with the lower hydrophobicity of the hydroxylated by-products, which are less likely to be adsorbed on the carbon surface. Physical adsorption probably plays the most important role for the adsorption of PH on porous CA fibers, in particular the tt-tt interactions. 29 However, other factors may be involved in the adsorption mechanisms, in particular the formation of an electron donor / acceptor complex between the solute and the surface of the CA), electrostatic interactions (depending on the pH of the solution), the molecular size and the effect of the solvent (competitive adsorption of water molecules). 2.29
    The kinetic study shows that a large amount of PH can be quickly adsorbed on the CA tissue. In a similar way to what has been demonstrated by several previous studies, the decisive step in the process of adsorption of PH on CA is intra-particle diffusion (linear relationship between q t and t 1/2 ). 29,30
    Resistance to intra-particle diffusion is greatly reduced compared to granular CA due to the structure of open pores. 29 The CA fabric is made up of thousands of thin porous fibers, which greatly increases the external surface. Much better correlation coefficients were obtained using the pseudosecond order model compared to the pseudo first order model. Such behavior is often observed for the adsorption of low molecular mass compounds on small adsorbent particles (adsorbent with a large external surface). 31 The adsorption processes also follow the pseudo-second order model when the initial concentration of solute is sufficiently low. 32 Experiments were carried out using concentrations of PH (1 mM), CAT (0.1 mM) and BQ (0.05 mM) corresponding to the maximum concentrations observed during the regeneration step. Consequently, the kinetic parameters could not be directly compared since the kinetic constants of pseudo-first order and pseudo-second order are complex functions of the initial concentration of solute. 32 However, Wu et al. (2009) 31 have shown that the parameter k2q e (éq 6) corresponds to the inverse of the half-life of the adsorption process and is a key parameter for the comparison of adsorption kinetics. Thus, from the observed values of k2q e , we can conclude that the adsorption becomes faster in the following order: PH>BQ> CAT. The kinetics of PH adsorption on CA tissue was slower than a previously reported study 29 , most likely due to the smaller average pore diameter affecting intra-particulate scattering. Steric hindrance may not affect the final amount of PH adsorbed but still reduce the kinetics of adsorption.
    During the adsorption of HQ on the tissue of CA, the release of BQ in the solution was observed simultaneously; then, the adsorption of BQ was also observed (FIG. 7B). This can be explained by the oxidation of HQ by molecular IO2 bound to graphite. 2 During the increase in tissue concentrations of CA during equilibrium experiments, a linear correlation was observed between the ratio [BQ] eq / [HQ] eq and the concentration of CA (Figure 7A), indicating that l oxidation of HQ at the surface of the CA is governed by a stoichiometric ratio. In addition, no oxidation of HQ was observed in the absence of CA. This confirms that the CA tissue acted as a mediator for the oxidation of HQ to BQ.
    Table 2 - Langmuir and Freundlich parameters of adsorption isotherms and kinetic constants of pseudo-first order and pseudo-second order for adsorption of phenol (PH), benzoquinone (BQ) and catechol (CAT) on CA tissue at 25 ° C. Kinetic studies were carried out with 2 g L ' 1 of activated carbon tissue and the following initial concentrations: [PH] = 1.0 mM; [BQ] = 0.05 mM; [CAT] = 0.1 mM.
    PH BQ CATR 2 0,994 0.995 0.997 Langmuir q m (mmol g ' 1 ) 3.73 1.41 1.88Kl (L mmol ' 1 ) 19.1 44.3 29.6 isothermal R 2 0.991 0,994 0,992 Freundlich not 3.30 3.47 4.37Kf ((mmol g ' 1 ) (L mmol' 1 / n )) 4.24 1.97 2.14 Pseudo- R 2 0.911 0.943 0.982 first q e (mmol g ' 1 ) 0.31 0.016 0,042 order ki (min ' 1 ) 0.089 0.092 0.066 kinetics R 2 1.00 0,999 0,999 Pseudo-second q e (mmol g ' 1 ) 0.62 0,026 0,054 order kî (g mmol ' 1 min' 1 ) 0.78 14.0 2.65k2q e (min ' 1 ) 0.48 0.37 0.14
    2. Elimination of phenol from porous CA fibers and mineralization of organic compounds during EF regeneration
    The porous fibers of CA are in the form of fabric. The CA tissue charged with PH was regenerated using the EF method with a DDB anode and the CA tissue charged with PH as a cathode. Preliminary experiments have shown that the CA tissue is capable of producing a greater amount of H2O2 than a conventional carbon felt usually used for the EF process (Figure 8). This is probably a beneficial effect of the microporous structure of CA, which leads to a larger electroactive surface.
    After the adsorption step, the amount of phenol adsorbed on the CA was 3.2 mmol g '1; this corresponds to a concentration in the electrochemical cell of 6.4 mM PH ([PH] 0) and a TOC concentration of 461 mg L ' 1 (TOCo). After 6 h of treatment at 300 mA, 70% of the initial adsorbed PH was removed from the surface of the CA tissue (FIG. 2). In comparison, only 12.5% PH was desorbed from the CA tissue during the currentless control experiment. This 12.5% is only due to a desorption process in accordance with the sorption balance between the solution and the CA.
    Various phenomena can contribute to the elimination of PH from the surface of the CA. First of all, a greater increase in the concentration of PH in the solution was observed during the first minutes of electro-oxidation at 300 mA, compared with the control experiment without current supply (FIG. 9). This is attributed to a local increase in pH in the vicinity of the cathode due to the reduction of water and the generation of OH '. Indeed, this leads to repulsive interactions between the anionic form of the PH and the surface of the CA. The conventional cathodic regeneration process is based on this mechanism 33 . Unfortunately, the desorption induced by the pH is often not sufficient to achieve a high regeneration efficiency of saturated CAs, in particular in the event of chemical (irreversible) sorption of pollutants. 34.35 The advantage of the EF process is to simultaneously promote the oxidation of organic compounds both in the solution and adsorbed on the tissue of CA.
    The adsorbed organic compounds can react directly with oxidizing species such as · ΟΗ from the EF process and electrochemically generated redox reagents (H2O2, O3, persulfate, sulfate radical). By carrying out the conventional Fenton oxidation, a very low efficiency of regeneration of microporous CA has been reported due to the limited availability of the molecules adsorbed in the micropores towards oxidizing species. 8 During the EF process, H2O2 is generated on the surface of the CA pores, therefore · ΟΗ can be produced near the target pollutants adsorbed on the surface of the CA according to the electrochemically supported Fenton reaction (éq 1). This increases the availability of pollutants adsorbed for oxidation. Thus, a better regeneration efficiency of the microporous CA can be obtained by EF compared to the conventional Fenton oxidation. In addition, the low resistance to intra-particulate diffusion of porous CA fibers promotes the diffusion of oxidizing species in the microporosity of CA, thereby improving the availability of the adsorbed compounds towards oxidizing species. In addition, a high rate of degradation of PH in the solution involves a shift in the sorption equilibrium and the continuous release of PH from the CA tissue to the solution.
    Similar experiments were also performed using porous CA fibers in the form of CA felt instead of the CA fabric (Figure 10). A higher elimination rate of adsorbed PH (88% after 9 h) was observed using CA felt during EF regeneration. This could be attributed to a lower resistance to intraparticle diffusion, which promotes the desorption kinetics and the diffusion of oxidizing species in the microporosity of CA. However, this material has mechanical properties that are less suitable for treating water.
    Whether using felt or CA tissue, the PH was mainly removed from the cathode for the first 3 hours, then the efficiency of the process was greatly reduced. This could be linked to the presence of physisorbed and chemisorbed pollutants and to the slower elimination of chemisorbed PH. In addition, a lower availability (with respect to oxidizing species) of the PH molecules adsorbed in the smallest pores of the porous fibers of CA could also reduce the effectiveness after the first 3 hours of treatment.
    The great advantage of this process is to avoid the accumulation of organic compounds in the solution. Only 6% of the initial adsorbed TOC is found in the solution after 6 h of treatment (Figure 3). This means that 91% of the 70% of PH removed from the tissue of CA was completely mineralized in CO2 and H2O. The concentration of PH and TOC in the solution increases rapidly during the first 20 minutes due to the rapid desorption of part of the adsorbed PH. Then, the evolution of the concentration of PH and TOC depends on: (i) the kinetics of desorption and degradation of the PH adsorbed on the CA, (ii) the kinetics of degradation of PH in the solution and the displacement of l balance of adsorption leading to the desorption of the PH and iii) the kinetics of mineralization of the oxidation by-products in the solution. A higher accumulation of TOC was observed in the solution, compared to the PH concentration. Indeed, the TOC in the solution comes from both the desorption of the PH and the release of the oxidation by-products of the adsorbed and dissolved PH. However, a rapid decrease in TOC in the solution was observed due to the high production rate of · ΟΗ both in the solution (éq 1) and at the surface of the DDB anode (éq 2). In addition, no degradation byproduct was detected as adsorbed on the CA tissue during treatment. The process achieves faster degradation kinetics than adsorption kinetics. Thus, the re-adsorption of the oxidation by-products on the CA tissue is avoided. The formation of more hydrophilic byproducts, the occupation of adsorption sites by residual PH and water molecules as well as electrostatic interactions due to the locally high pH on the surface of the CA tissue also help to prevent adsorption of degradation by-products.
    Total mineralization of pollutants prevents the accumulation of toxic by-products such as BQ (Figure 4). The other aromatic intermediates identified were mainly CAT and HQ. Resorcinol was only detected in very small quantities since the hydroxylation of phenol is mainly favored in the para (HQ) and ortho (CAT) positions. 37 The CAT quickly reached its maximum concentration at t = 30 min (2.2% TOCo) because its rate of production from the oxidation of PH is highest at the start of the experiment and then decreases continuously due to the lower concentration of PH. The BQ concentration also quickly reached its maximum at t = 20 min (1.8% TOCo) and then rapidly decreases below the detection limit at t = 120 min. By comparison, the HQ concentration reached its maximum later (t = 90 min, 2.8% TOCo) and decreased much more slowly. Pimentel et al. (2008) observed similar behavior when removing PH by EF with a conventional carbon cathode. 24 As suggested in the literature, this could be explained by taking into account the balance of the HQ / BQ redox couple (E ° = 0.70 V) and the possible reduction of BQ in HQ. 37.38 In addition, Mousset et al. (2016) reported that the kinetic constants of degradation of oxidation of BQ to muconic and maleic acids is around one order of magnitude greater than that of oxidation of HQ to the same degradation by-products . 37 The aromatic byproducts undergo aromatic ring opening reactions to form short chain carboxylic acids. 11 Succinic, oxalic and formic acids were the main short chain carboxylic acids detected and reached their maximum concentration at 90, 120 and 90 min of electrolysis, respectively. The evolution of the concentrations of oxidation by-products in the solution depends on (i) the quantity generated by the degradation of the PH in the solution or adsorbed on the CA tissue and (ii) the kinetics of degradation in the solution. and on the surface of the anode. Thus, the concentration of short chain carboxylic acids decreased more slowly than that of aromatic by-products due to their slower reaction kinetics with · 0Η. 37.39
    3. Reuse of regenerated CA fiber
    Additional experiments were carried out to assess the potential of this technology for the reuse of regenerated CA. Porous CA fibers in the form of CA fabric were chosen as the most promising material because the CA felt had insufficient mechanical properties for water treatment. Several adsorption cycles followed by regeneration EF were implemented in order to follow the evolution of the efficiency of the regeneration process (Figure 5). In addition, the morphological texture and the chemical structure of the surface of the CA were characterized after one and ten adsorption / regeneration cycles. The optimal regeneration time by EF was set at 6 h because the efficiency of the process decreases between 6 and 9 h of treatment.
    The regeneration efficiency (RE) was calculated by comparing the amount of PH which can be adsorbed on the regenerated CA (q re§ ) and the amount of PH adsorbed on the initial CA (q, j (éq 7)
    RE (%) = x 100 (7)
    RE was 78% after one cycle, while only 70% of the adsorbed PH was removed from the surface of the CA after 6 h of treatment. Thus, taking into account both the residual PH (30% of the initial adsorption capacity of the CA) and the new PH adsorbed on the CA (78%) after the first regeneration cycle, the adsorption capacity of the CA regenerated is greater than that of the original material.
    Raman analyzes were carried out to assess the evolution of the chemical composition of the tissue of CA. The spectra were analyzed using the following deconvolution procedure: a combination of three lorentzian bands at approximately 1600 cm ' 1 (G), 1340 cm' 1 (D1) and 1185 cm ' 1 (D2) and a 1 545 cm-1 Gaussian strip (D3) was used (an example is given in Figure 11). These bands correspond to different modes of vibration. Overall, the results show that the chemical composition of the CA tissue is not strongly modified after 10 cycles of EF adsorption / regeneration (Figure 12). However, a slight decrease of 8% in the ratio between the integrated intensity of the sum of the D bands and the G band (IZD / IG) was observed after a regeneration cycle. A larger decrease in the ID2 / IG (21%) and ID3 / IG (15%) ratio was observed compared to IDl / IG (6%). The bands D1, D2 and D3 are described as characteristic of the edges of the layers of graphene, ionic impurities and amorphous carbon, respectively 40,41 . These results therefore indicate that the greater adsorption capacity of the regenerated CA (after 1 cycle) could be attributed to a cleaning effect on the surface of the CA by the EF process. Certain impurities from the virgin CA tissue are removed during the first EF regeneration.
    A slight decrease in ER was observed in cycles 2 (74%) and 3 (70%). RE then reached a plateau, with a slight variation between 65% and 72%. The high ER obtained throughout the 10 regeneration cycles demonstrates the relevance of this treatment strategy. Cathodic polarization prevents damage to the surface of the AC. While the Raman analyzes showed a cleaning effect of the CA tissue, the comparison of the SEM images shows the absence of any change in the morphological texture of the CA tissue between the initial and regenerated samples (10 cycles) (Figure 6). The CA fabric consists of thousands of porous fibers with a diameter of about 10 µm which are closely intertwined. The initial and regenerated CA tissues in both cases contain broken porous fibers. The morphological texture of the porous fibers is very similar in the two samples, even near the breaking point of a fiber. Since the regeneration EF does not affect the morphological and chemical structure of the tissue of CA, the rupture of porous fibers seems to come only from mechanical stresses. Using CA tissue, the release of fibers into water was not visible and was not detectable by TOC analysis. In contrast, using the CA felt, the stirring conditions during the adsorption step led to the release into the water of large quantities of small porous fibers (Figure 13). This is why CA fabric seems to be more suitable than CA felt for this type of application.
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    权利要求:
    Claims (16)
    [1" id="c-fr-0001]
    1. Device for regenerating activated carbon in the form of porous fibers by electro-Fenton reaction, comprising at least one electrochemical cell comprising:
    at least one cathode and at least one anode immersed in an electrolytic solution:
    - The cathode comprising activated carbon in the form of porous fibers having organic pollutants which are adsorbed on the porous fibers, the activated carbon in the form of porous fibers having served as a filter for organic pollutants;
    - The anode comprising a non-active anode material, the non-active anode material being defined as a material having an oxygen overvoltage greater than 0.4 V;
    an electrolytic solution with:
    - an oxygen supply intended to be continuous during the regeneration of the activated carbon in the form of porous fibers;
    - an initial supply of Fe 2+ ions intended to be continuously regenerated during the electro-Fenton reaction;
    the device making it possible to create, during the electro-Fenton reaction, oxidizing species at the level of the cathode and the anode, these oxidizing species mineralizing the organic pollutants at the level of the anode, the cathode and the electrolytic solution .
    [2" id="c-fr-0002]
    2. Device according to claim 1, in which the initial supply of Fe 2+ ions has a catalytic concentration in the electrolytic solution greater than 10 ' 5 M and less than 10' 2 M.
    [3" id="c-fr-0003]
    3. Device according to one of claims 1 to 2, in which the non-active anode material is chosen so that the oxidizing species created at the anode are at least: · ΟΗ, O 3 , preferably : · ΟΗ, O 3 , SO 4 2 and SïOs 2 '.
    [4" id="c-fr-0004]
    4. Device according to any one of claims 1 to 3, wherein the non-active anode material is boron doped diamond (DDB).
    [5" id="c-fr-0005]
    5. Device according to any one of claims 1 to 3, wherein the non-active anode material is a sub-stoichiometric titanium oxide.
    [6" id="c-fr-0006]
    6. Device according to any one of claims 1 to 5, wherein the porous fibers of activated carbon are in the form of fabric.
    [7" id="c-fr-0007]
    7. Device according to any one of claims 1 to 5, wherein the porous fibers of activated carbon are in the form of felt.
    [8" id="c-fr-0008]
    8. Device according to any one of claims 1 to 7, in which the activated carbon in the form of porous fibers having served as a filter for organic pollutants is saturated with organic pollutants.
    [9" id="c-fr-0009]
    9. Device according to any one of claims 1 to 8, wherein the cathode comprises only activated carbon in the form of porous fibers.
    [10" id="c-fr-0010]
    10. Device according to any one of claims 1 to 9, in which the diameter of the porous fibers is greater than 0.1 micrometer and less than 1000 micrometers.
    [11" id="c-fr-0011]
    11. Device according to any one of claims 1 to 10, in which the specific surface (Sbet) of the porous fibers is greater than 600 m 2 .g ' 1 and the porous fibers have a porosity so that more than 30% of the pore volume of each of the porous fibers is constituted by pores of size less than 2 nm.
    [12" id="c-fr-0012]
    12. Device according to one of claims 1 to 11, in which the oxygen supply is produced by an inlet of bubble air into the electrolytic solution.
    [13" id="c-fr-0013]
    13. Method for regenerating activated carbon in the form of porous fibers and loaded with organic pollutants, using the device according to one of claims 1 to 12.
    [14" id="c-fr-0014]
    14. The regeneration method according to claim 13, comprising the application to the electrochemical cell of a constant current with a current density of between 0.1 and 100 mA / cm 2 of surface of activated carbon.
    [15" id="c-fr-0015]
    15. Use of a filter composed of porous activated carbon fibers, said filter having been previously loaded with organic pollutants by filtration of polluted water or polluted air, as the cathode of an electro-Fenton reaction to regenerate the porous activated carbon fibers loaded with organic pollutants.
    [16" id="c-fr-0016]
    16. Use according to claim 15, said porous fibers of activated carbon being in the form of felt or fabric.
    1/13
    Regeneration of activated carbon fibers (CA) by electro-Fenton reaction with a DDB anode> Elimination of pollutants from the CA surface> Mineralization of organic compounds> AC protection by cathodic polarizationPower supply+/ -% z-xU U I
    Balanced
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    同族专利:
    公开号 | 公开日
    US20210053027A1|2021-02-25|
    WO2019175038A1|2019-09-19|
    FR3078899B1|2021-03-05|
    EP3765186A1|2021-01-20|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    US5904832A|1996-12-20|1999-05-18|Huron Tech Canada, Inc.|Regeneration of active carbon and polymeric adsorbents|
    CN108503097B|2018-03-16|2021-04-09|昆明理工大学|Treatment method of organic matter polluted water|
    CN110918060A|2019-12-16|2020-03-27|扬州大学|Pyrolytic carbon-loaded zero-valent iron composite material and preparation method and application thereof|
    CN111185089B|2020-01-09|2021-09-28|青岛理工大学|Novel technology for performing electro-Fenton catalytic degradation on VOCs|
    WO2021167536A1|2020-02-20|2021-08-26|National University Of Singapore|A sequential reactor for adsorption of pollutants onto activated carbon and electrochemical regeneration of the activated carbon|
    法律状态:
    2019-03-12| PLFP| Fee payment|Year of fee payment: 2 |
    2019-09-20| PLSC| Publication of the preliminary search report|Effective date: 20190920 |
    2020-02-14| PLFP| Fee payment|Year of fee payment: 3 |
    2021-02-10| PLFP| Fee payment|Year of fee payment: 4 |
    2022-01-18| PLFP| Fee payment|Year of fee payment: 5 |
    优先权:
    申请号 | 申请日 | 专利标题
    FR1852190A|FR3078899B1|2018-03-14|2018-03-14|ACTIVATED CARBON REGENERATION PROCESS BY ELECTRO-FENTON PROCESS|
    FR1852190|2018-03-14|FR1852190A| FR3078899B1|2018-03-14|2018-03-14|ACTIVATED CARBON REGENERATION PROCESS BY ELECTRO-FENTON PROCESS|
    EP19709917.9A| EP3765186A1|2018-03-14|2019-03-08|Device for regenerating activated carbon|
    PCT/EP2019/055803| WO2019175038A1|2018-03-14|2019-03-08|Device for regenerating activated carbon|
    US16/980,584| US20210053027A1|2018-03-14|2019-03-08|Device For Regenerating Activated Carbon|
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