Regeneration Of Activated Carbon Research Articles

Using microwave heating to improve the desorption efficiency of high molecular weight VOC from beaded activated carbon.

Incomplete regeneration of activated carbon loaded with organic compounds results in heel build-up that reduces the useful life of the adsorbent. In this study, microwave heating was tested as a regeneration method for beaded activated carbon (BAC) loaded with n-dodecane, a high molecular weight volatile organic compound. Energy consumption and desorption efficiency for microwave-heating regeneration were compared with conductive-heating regeneration. The minimum energy needed to completely regenerate the adsorbent (100% desorption efficiency) using microwave regeneration was 6% of that needed with conductive heating regeneration, owing to more rapid heating rates and lower heat loss. Analyses of adsorbent pore size distribution and surface chemistry confirmed that neither heating method altered the physical/chemical properties of the BAC. Additionally, gas chromatography (with flame ionization detector) confirmed that neither regeneration method detectably altered the adsorbate composition during desorption. By demonstrating improvements in energy consumption and desorption efficiency and showing stable adsorbate and adsorbent properties, this paper suggests that microwave heating is an attractive method for activated carbon regeneration particularly when high-affinity VOC adsorbates are present.

Adsorption of methanol from methanol–water mixture by activated carbon and its regeneration using photo-oxidation process

Activated carbon (AC) has been used as an adsorbent for centuries as a result of its ability to remove a large variety of compounds from contaminated waters. The objective of this study was to investigate the removal of methanol by adsorption and the use of advanced oxidation process for the regeneration of the exhausted AC as an alternative to thermal, biological, and chemical methods that are currently applied. Several experimental tests were carried out to examine the ability of AC for adsorbing methanol from methanol–water mixture. The results show fast saturation of the AC and short breaking time, especially for solutions consisting of methanol above 3% vol. However, adsorption capacity of exhausted AC with methanol, after washing, showed an improvement in its adsorption capacity over that of fresh AC. This improvement may be due to that methanol may harsh the surface of AC causing an increase in the sizes of pores and cavities. Large cavities were micrograph using scanning electron microscope (SEM). After saturation, AC was regenerated using the photo-catalytic process, the adsorption capacity of AC was fully restored. The results showed that the titanium dioxide with the aid of UV light can easily regenerate the AC by oxidizing the organic compounds adsorbed on the surface of AC. It was observed that the increase of UV light intensity had a positive effect on adsorption capacity. However, the increases of TiO2 concentrations had a limited effect on the adsorption capacity of the AC.

Physicochemical and porosity characteristics of thermally regenerated activated carbon polluted with biological activated carbon process

The characteristics of thermally regenerated activated carbon (AC) polluted with biological activated carbon (BAC) process were investigated. The results showed that the true micropore and sub-micropore volume, pH value, bulk density, and hardness of regenerated AC decreased compared to the virgin AC, but the total pore volume increased. XPS analysis displayed that the ash contents of Al, Si, and Ca in the regenerated AC respectively increased by 3.83%, 2.62% and 1.8%. FTIR spectrum showed that the surface functional groups of virgin and regenerated AC did not change significantly. Pore size distributions indicated that the AC regeneration process resulted in the decrease of micropore and macropore (D>10μm) volume and the increase of mesopore and macropore (0.1μm<D<10μm) volume in regenerated AC, which are benefit for water treatment. These results will provide a theoretical basis for the reuse of biological waste (spent AC) from BAC process.

Preparation and Characterization of Activated Carbons from Peanut Shell and Rice Bran and a Comparative Study for Cr(VI) Removal from Aqueous Solution

Low-cost activated carbons (AC) were prepared from peanut shell (PS) and rice bran (RB) by microwave heating with ZnCl2 as the activating agent and characterized by solid-state 13C-NMR, FT-IR, Boehm titration, and mass titration methods. The solid-state 13C-NMR spectra showed that aliphatic structures of the raw materials were almost completely transformed to condensed aromatic rings, a typical characteristic of AC. The potentials of ACs produced from peanut shell (PACs) and from rice bran (RACs) for Cr(VI) removal were examined by using iodine and methylene blue (MB) as adsorbates, respectively. The effects of solution pH, the dosage of AC, and the initial Cr(VI) concentration on Cr(VI) removal were investigated. The desorption experiments were also performed to examine the regeneration of AC. The results demonstrated that both PAC and RAC were excellent adsorbents for Cr(VI) removal. The maximum removal amounts of Cr(VI) by PAC and RAC reached to 96.27 and 76.04 mg/g, respectively. The adsorption capacity of PAC was higher than that of RAC because PAC held a larger surface area and a more microporous pore structure than RAC. The removal of Cr(VI) by PAC and RAC greatly depended on solution pH, with low pH (in a pH range of 2 to 6) being more conducive to the removal of Cr(VI). The adsorption-coupled reduction of Cr(VI) contributed to the removal of Cr(VI) by PAC and RAC.

Removal of methylene blue and acid orange 7 from aqueous solutions by activated carbon coated with zinc oxide (ZnO) nanoparticles: equilibrium, kinetic, and thermodynamic study

Various industries like textile, plastic, pulp, and paper produce dye containing wastewaters that have harmful effects on the environment as well as human health. The aim of this study was to investigate the effect of granular activated carbon (AC) coated by zinc oxide nanoparticles (ZnO-np) in the removal of dyes, methylene blue (MB) and acid orange 7 (AO7), from aqueous solutions. The morphology of the AC and AC–ZnO was determined by SEM and the FTIR spectra confirmed the strong interaction between AC and ZnO. The effect of various parameters, such as nanoparticles loading onto the AC, pH, contact time, dye concentration, ion strength, temperature, and adsorbent regeneration, was studied on the adsorption. The results showed that the surface structure of the raw AC was porous and had irregular shapes, but the surface of the modified AC (AC–ZnO) due to the homogenous coating of the ZnO-np onto the AC was approximately uniform and regular. The sorption capacity and optimum contact time for the removal of MB (32.22 mg/g) and AO7 (32.13 mg/g) by AC–ZnO were obtained as 32.22 mg/g during 120 min and 32.13 mg/g over 150 min, respectively. The optimum pH for the sorption of MB occurred at pH 11 and for AO7 was obtained at pH 3. The results also showed that Langmuir isotherm and pseudo-second-order kinetic models fitted the experimental data better than other isotherm and kinetic models. It is obviously clear that AC–ZnO, in comparison with raw AC, was more efficient sorbent for the removal of MB and AO7 and it can be proposed for the removal of these dyes from aqueous solutions.

Research on Environment Materials with Progress on Regeneration of Active Carbon

Now activated carbon has been used greatly in all walks of life, thus the regeneration of spent activated carbon is of great significance. The advantages and disadvantages of the regeneration methods of the spent activated carbon are introduced and discussed in this paper, mainly including thermal regeneration, chemical regeneration, electrochemical regeneration, microwave radiation regeneration, wet air oxidation and supercritical fluid regeneration etc. Then a new recycling method of the spent activated carbon is proposed.

Effect of microwave heating on the regeneration of modified activated carbons saturated with phenol

The purpose of this work was to investigate the effect of microwave irradiation on the regeneration of modified activated carbons (GAC/MW, GAC/Ni, and GAC/Cu). The untreated activated carbon (GAC pure) was used for blank experiment. Microwave heating was used for preparation and regeneration of the modified activated carbons. The effect of loading Ni2+ and Cu2+ ions on the activated carbon adsorption capacity was investigated. The results showed that the activated carbon loaded with Ni2+ has no significant effect on phenol adsorption, while the adsorption capacity of activated carbon loaded with Cu2+ significantly decreased. Microwave irradiation showed a positive effect on activated carbon adsorption capacity. Under optimal conditions, the results showed that there was no effect when changing temperature and pH. The effect of ions Ni2+ and Cu2+ loaded into activated carbon were also investigated. During the regeneration process, the activated carbon loaded with Ni2+ showed a strong microwave energy adsorption than the activated carbon loaded with Cu2+. The effect increasing Ni2+ quantity decreases the activated carbon regeneration efficiency. During the regeneration of activated carbons, the highest temperature was observed in the cases of GAC/Ni. During regeneration, the temperature increases when the quantity Ni2+ loaded increases. The regeneration efficiency of activated carbons reaches 98 % even after 10 times of regeneration cycles. After several regenerations, MW/GAC and GAC/Ni regeneration efficiency was high, while regeneration efficiency of GAC/Cu decreased considerably. GAC regeneration efficiency also decreased several cycles. During regeneration process, phenol was simply desorbed from activated carbons under microwave irradiation.

Carbon isotopic characterisation of dissolved organic matter during water treatment

Water treatment is a series of physio-chemical processes to aid organic matter (OM) removal, which helps to minimise the formation of potentially carcinogenic disinfection by-products and microbial regrowth. Changes in OM character through the treatment processes can provide insight into the treatment efficiency, but radiogenic isotopic characterisation techniques have yet to be applied. Here, we show for the first time that analysis of 13C and 14C of dissolved organic carbon (DOC) effectively characterises dissolved OM through a water treatment works. At the sites investigated: post-clarification, DOC becomes isotopically lighter, due to an increased proportion of relatively hydrophilic DOC. Filtration adds ‘old’ 14C-DOC from abrasion of the filter media, whilst the use of activated carbon adds ‘young’ 14C-DOC, most likely from the presence of biofilms. Overall, carbon isotopes provide clear evidence for the first time that new sources of organic carbon are added within the treatment processes, and that treated water is isotopically lighter and typically younger in 14C-DOC age than untreated water. We anticipate our findings will precipitate real-time monitoring of treatment performance using stable carbon isotopes, with associated improvements in energy and carbon footprint (e.g. isotopic analysis used as triggers for filter washing and activated carbon regeneration) and public health benefits resulting from improved carbon removal.

Study on Thermal Regeneration for Caffeine-Saturated Activated Carbon

Waste activated carbon (AC) containing caffeine was produced during the process of the production for caffeine. The process of treatment caffeine-saturated AC using thermal regeneration was explored and factors on the regeneration of activated carbon were investigated. The optimum conditions obtained were: temperature is 650 °C, the regeneration time is 180 min, the carrier gas velocity is 0.002 m/s, carbon layer thickness is 0.1 m. Under these conditions, activated carbon regeneration efficiency reached 90.3%. In addition, the pore structure of activated carbon before and after regeneration was characterized and the activated carbon surface area and pore size distribution under optimum conditions were determined by the adsorption isotherms.

Optimization of Ultrasonic-Assisted Regeneration Process for Coconut Shell Activated Carbon Based on Response Surface Method

The single-factorial design of experiments and response surface methodology was applied to optimize ultrasonic-assisted regeneration of coconut shell activated carbon. With the pH values of the solution, solid-liquid ratio, irradiation time chosen as the independent variable and the activated carbon release of antimony as response values, the central composite design method was used to study each of the variables and their interactions on coconut shell activated carbon regeneration. The results of this study showed that: the optimum pH value was 13; solid-liquid ratio was 372 mL·g-1; irradiation time was 6.7 h. The average content of the release of Sb from the activated carbon was 6233.95 μg·g-1 under the optimum condition. Regeneration rate of the activated carbon was 84.45%. This demonstrated that the adsorption efficiency of Sb was close in regenerative carbon and the original carbon. The results proved that the ultrasonic-associated coconut shell activated carbon regeneration process was accurate and reliable, and can provide a reference for the regeneration of coconut shell activated carbon which had adsorbed Sb.

Regeneration of activated carbon saturated with odors by non-thermal plasma

The dielectric barrier discharge (DBD) regeneration process of an activated carbon (AC) saturated with dimethyl sulfide was studied on a laboratory scale. The results showed sustainable high regeneration efficiency (RE) (>90%) in successive regeneration cycles (10 cycles). Energy density, humidity and oxygen content were key factors for DBD system, with optimum conditions of 761JL−1, 0–1vol% and 5%, respectively. The high efficiency was likely attributed to the improvement of structure and surface properties of AC by DBD. After the first regeneration, surface area, micropore volume and total pore volume of AC increased by 8%, 23% and 15% respectively, while average pore size decreased by 9.5%. The number of carboxylic groups doubled (from 0.22 to 0.48mmolg−1) while that of phenolic groups remarkably decreased (from 0.48 to 0.26mmolg−1) after successive regeneration cycles, which helped to maintain high RE. The results suggested DBD as a novel, efficient alternative process for odor-saturated AC regeneration.

Detection of hydroxyl radicals during regeneration of granular activated carbon in dielectric barrier discharge plasma system

To understand the reactions taking place in the dielectric barrier discharge (DBD) plasma system of activated carbon regeneration, the determination of active species is necessary. A method based on High Performance Liquid Chromatography with radical trapping by salicylic acid, has been developed to measure hydroxyl radical (•OH) in the DBD plasma reactor. The effects of applied voltage, treatment time, and gas flow rate and atmosphere were investigated. Experimental results indicated that increasing voltage, treatment time and air flow rate could enhance the formation of •OH. Oxygen atmosphere and a suitable GAC water content were contributed to •OH generation. The results give an insight into plasma chemical processes, and can be helpful to optimize the design and application for the plasma system.

Regeneration of activated carbon adsorbed EDTA by electrochemical method

Activated carbon after saturated adsorption of EDTA was used as particle electrode in a three-dimensional electrode reactor to treat EDTA-containing wastewater. Electrochemical method was used to regenerate activated carbon after many times of electrolysis. Based on the analysis of infrared spectra of activated carbon after adsorption and repeated electrolysis, EDTA was degraded into glycine, and then non-catalytic activated associated complex was formed with N—H bond on the activated carbon. The catalytic ability of the activated carbon vanished and the EDTA degradation efficiency was dropped. Activated carbon could be effectively regenerated by electrochemical method in the three-dimensional reactor. Effects of electric current, conductivity and pH on activated carbon regeneration were investigated, and the optimum conditions were concluded as follows: 100–300 mA of current intensity, 1.39 mS/cm of electric conductivity, 60 min of electrolysis time and pH 6.0-8.0. Under the optimized conditions, the activity of the activated carbon can be recovered and the residual total organic carbon (TOC) was below 10 mg/L (the initial TOC was 200 mg/L) in the three-dimensional electrode reactor.

Regeneration of Activated Carbon Loaded with Cyclohexane Using Supercritical Carbon Dioxide: Experimental Results and Modeling

AbstractRegeneration of granular activated carbon loaded with cyclohexane by supercritical carbon dioxide was investigated at varying temperatures and pressures. Cyclohexane concentration‐time profiles were measured by means of a supercritical extraction apparatus coupled with an online GC analyzer. The maximum yield of regeneration was 68 % at 55 °C and 140 bar. A mathematical model was proposed which agreed well with the experimental data. Both the Toth and the Langmuir‐Freundlich isotherms were used as adsorption isotherms under equilibrium condition. The mathematical model for activated carbon regeneration was able to adjust the experimental data with relative absolute average deviations of about 4 % and 3.25 %, respectively, for the Toth and the Langmuir‐Freundlich isotherms.

Regeneration of activated carbons contaminated by phenol using supercritical water

The purpose of this study was to efficiently regenerate activated carbons (ACs) saturated with phenol using supercritical water at 260bar and 400–500°C. Regeneration temperature and time were the variables that most affected the process. Times close to 10min provided efficiencies of 100%, such that the procedure can be considered to be very fast and efficient.A study of temperature-programmed desorption using liquid and supercritical water as the carrier fluid indicated that a fraction of the phenol retained on the ACs was physisorbed while another fraction was chemisorbed. ACs subjected to successive cycles of adsorption–regeneration were not completely regenerated when the regeneration times were short (3min). The study also addressed the regeneration of ACs saturated with phenol aged over long periods of time (0.5–60 days). The difficulty in regenerating the ACs increased with the saturation of phenol and the ageing time.

Regeneration of Caramel Saturated Activated Carbon jointly by Microwave and Extractive Method

Abstract In this study, the spent activated carbon (AC) saturated with caramel was regenerated using solvent assisted with microwave radiation. The efficiency of regeneration was evaluated under parameters such as power and time of microwave radiation, and concentrations and pH of an activator. The quality of regenerated AC (RAC) was assessed by methylene blue (MB) and iodine adsorption. The optimum condition for AC regeneration was under a microwave power of 680 W and 10 min radiation, with 20% ethyl alcohol in the activator and pH of 9–10. Under this condition, the adsorption of iodine and MB on RAC was 878 and 218 mg/g, respectively. The micro structure of RAC was characterized by SEM observation. The surface area of RAC was determined under N2 sorption. The pore size distributions of virgin and RAC determined by Horvath–Kawazoe (HK) and DFT methods resulted in a mean pore diameter of 1.2 nm and a pore volume of 1 cm3/g. A regeneration efficiency of more than 85% could be achieved by microwave assisted solvent regeneration.

Removal of chlorinated organic volatile compounds by gas phase adsorption with activated carbon

This paper discusses the removal of chlorinated volatile organic compounds (Cl-VOCs) from gas streams by means of fixed-bed adsorption with a commercial activated carbon (AC). Column experiments were performed at different conditions (inlet concentration, temperature, pressure, gas flow rate and bed length). A two-parameter model introduced by Yoon and Nelson was applied to predict the entire breakthrough curves for chloromethane adsorption. Complete regeneration of the exhausted AC was performed at mild conditions (atmospheric pressure and room temperature). In order to gain a better knowledge on the effect of the surface chemistry of AC on the adsorption of Cl-VOCs, the quantum-chemical COSMO-RS method was used to simulate the interactions between AC surface groups and different Cl-VOCs as monochloromethane, dichloromethane and trichloromethane. This information can be useful for tailoring the ACs with the objective of improving their adsorption capacities by further functionalization. To confirm this, the commercial AC tested was modified by means of different thermal and oxidative treatments (nitric acid and ammonium persulfate), being the surface chemistry and textural properties of the resulting materials characterized by different techniques. The modified ACs were then tested in column adsorption experiment with different Cl-VOCs. The uptake of these compounds increased with the basic character of the AC surface.

Regeneration of Spent Activated Carbon by Yeast and Chemical Method

In this study, spent activated carbon (AC) saturated with caramel was regenerated by using yeast and NaOH. The efficiency of regeneration was evaluated under parameters such as amount, treatment time, temperature, pH value, stirring temperature of yeast and NaOH concentration. The optimum condition for AC regeneration was 8 h for yeast treatment time, 35°C for 0.075% yeast culture temperature, a pH value of 6 for the yeast dealing with the spent AC, 90°C for NaOH stirring temperature of AC and 6% NaOH for washing after the spent AC was treated by yeast. Under these conditions, methylene blue (MB) adsorption was 213 mg·g−1 in comparison with 60 mg·g−1 of spent AC. The micro structure and surface area of the regenerated AC were characterized by scanning electron microscope (SEM) and N2 sorption, respectively. The pore size distributions of virgin and regenerated AC were analyzed by means of H-K equation, resulting in a mean pore diameter of 1.28 nm and a pore volume of 1.13 cm3·g−1. This study provides data for theoretical support of the AC regeneration technology.

Assessment and Modeling of a Sequential Process for Water Treatment—Adsorption and Batch CWAO Regeneration of Activated Carbon

A new sequential process, AD–OX, for (post)treatment of water polluted by poorly biodegradable organic compounds has been investigated. It is based on hybridizing classical adsorption on a fixed bed of activated carbon (AC) followed by batch wet catalytic oxidation at higher temperature and pressure on the same bed of AC, which is then regenerated in situ. The basic idea is to take advantage of both operations: 1-efficient water purification at room temperature by adsorption, 2-effective concentrated pollutant degradation by batch air oxidation achieving simultaneously AC regeneration. A small fixed bed reactor, 10 mm diameter, 0.18 m long, filled with granular activated carbon and equipped with convenient 3-way valves, may achieve successively the two main steps. Several AD–OX cycles have been performed with a phenol solution to quantify the regeneration of the activated carbon adsorption capacity. Results show that activated carbon is quickly damaged during the first cycles, due to oxidative coupling, but then a quasi-steady state is obtained proving that significant oxidative regeneration has been achieved. A dynamic model of the adsorption step has been first developed, including intraparticle diffusion, liquid–solid external mass transfer, and axial dispersion of the liquid phase. It has been applied to simulate the performance of the regenerated activated carbon. Using oxidation kinetics over this aged carbon and its adsorption isotherm, separately determined in an autoclave at reaction temperature, the oxidation step after several cycles has been simulated including the heating period, where desorption and oxidation simultaneously occur. The proposed model conveniently predicts the complex phenol concentration–time profile and gives insight to the hydrodynamic behavior of the recycle reactor and the role of mass transfer resistances.

Regeneration of activated carbons saturated with pyridine or phenol using supercritical water oxidation method enhanced with hydrogen peroxide

While activated carbon (AC) is widely employed for treating water resources contaminated with hazardous organic compounds, regeneration of AC after saturation has been a concerning issue. Supercritical water oxidation (SCWO) in a batch reactor was used to regenerate two commercial activated carbons (CAL and COCO) saturated with pyridine or phenol. BET surface area, pore volume and pore size distribution of CAL and COCO were characterized before and after their regeneration. Decomposition of pyridine and phenol was examined at 400, 450, 525 °C with the presence or absence of hydrogen peroxide. The SCWO regeneration efficiency was determined from the amount of pyridine or phenol adsorbed and desorbed in successive adsorption-regeneration cycles. Effects of SCWO on adsorption capacity of CAL and COCO were experimentally investigated. With SCWO enhanced by H 2O 2, adsorbed organic compounds could be converted to carbon dioxide, hydrogen and nitrogen.