Removal of Neutral Red from aqueous solution by using modified hectorite

The object of this work was to study the modified hectorite as effective adsorbent for Neutral Red (NR) from aqueous solution. The adsorbent capacity of modified hectorite was discussed. The effects of surfactant content, adsorbent content, pH and adsorption temperature on the sorption of NR on modified hectorite were studied. Experimental results showed that the equilibrium adsorption data fitted well with Langmuir isotherm and the adsorption capacity was 393.70 mg/g for the modified cetylpyridinium bromide hectorite (CPB-Hect). Kinetic studies showed that the dynamical data fitted well with the pseudo-second-order kinetic model. For thermodynamic studies, parameters such as the Gibbs free energy (ΔG⁰), the enthalpy (ΔH⁰) and the entropy (ΔS⁰) indicated that the adsorption process was spontaneous and endothermic in nature.     

Wall to liquid mass transport and diffusion controlled corrosion in fixed bed reactors

The diffusion controlled corrosion at the inner wall of a fixed bed reactor was studied in terms of the wall to liquid mass transfer coefficient. Variables studied are solution flow rate, physical properties, and packing size and geometry. The effect of drag reducing polymers on the rate of mass transfer and on the rate of corrosion was studied. The presence of the drag reducing polymer decreased the rate of both mass transfer and corrosion by a factor ranging from 8.92% to 39.47%. All variables were correlated by dimensionless equations. Possible applications of these data in heat transfer were highlighted.     

Numerical analysis of fixed bed adsorption kinetics using orthogonal collocation

Fixed bed adsorption kinetics is analyzed to test the validity of the simplified model based on the linear driving force approximation by comparison with the exact model by using the orthogonal collocation method. The axial dispersion, the external film diffusion, and the intraparticle diffusion are considered to be the major mass transfer phenomena involved with the fixed bed adsorption kinetics in this study. It is assumed that a local equilibrium is attained at the fluid-solid interface and the equilibrium can be described by the Langmuir isotherm. A homogeneous particle diffusion model is employed to describe the intraparticle diffusion.     

Air oxidation of aqueous cyanides in a countercurrent fixed bed reactor

This study was conducted to discuss the removal of cyanides from water by air oxidation. Experiments were carried out in a countercurrent fixed bed reactor for three different values of temperature, concentration, gas and liquid flow rates. It was operated at pH 12 by using delrin (formaldehyde polymer) as packing material. Effects of some operating parameters on the conversion were studied, and it was observed that the conversion percent increased by increasing temperature and decreasing gas and liquid flow rates. Effect of concentration was not steady. A conversion of 89% was achieved under optimum conditions while it ranges from 44 to 79% at room temperature.     

Adsorption behavior of Congo red from aqueous solution on La2O3-doped TiO2 nanotubes

Composite adsorbent, TiO₂ nanotubes doped by La₂O₃, were prepared and characterized by IR, XRD, SEM, and XPS, their adsorption properties were investigated in the aqueous solution employing Congo red as the target pollutant. The adsorption experiments exhibited that adsorption equilibrium of Congo red over the adsorbent was rapidly achieved within 10 min, and the adsorption kinetics was in accord with the pseudo-second-order kinetics model. Moreover, intraparticle diffusion was not the determining step in the entire adsorption process, and the adsorption belonged to a chemical adsorption. Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isothermal equations were utilized to fit the equilibrium adsorption data, in which the Temkin equation was verified to fit the adsorption behaviors most satisfactorily with the correlation coefficient of 0.998. The adsorption mechanism was also studied.     

Hydrogenation of CO2 over Fe-K based catalysts in a fixed bed reactors at elevated pressure

Catalytic hydrogenation of CO₂to produce hydrocarbons was conducted in a fixed bed reactor (1.6 cm-IDx60 cm-High). Fe-K based catalysts (KRICAT-A, B) were used for more than 850 hours to maintain CO₂ conversion level up to 30 C-mol% in the fixed bed micro-reactor. Effects of operating variables on the CO₂ conversion, hydrocarbon yield and its selectivity were investigated. The CO₂ conversion and total hydrocarbon yield increased with increasing reaction temperature (250-325 °C), pressure (0.5-2.5 MPa) and H₂/CO₂ mol ratio (2-5); however, they decreased with increasing space velocity (1,000-4,000 ml/g_cathr) in the reactor. The selectivities of liquid products increased with increasing reaction pressure; however, they decreased with increasing temperature, space velocity and H₂/CO₂ ratio. From the results of an experimental study, optimum operating conditions for the maximum yield of olefinic liquid products were found as T=315 °C, P=1.5 MPa, SV=2,000 ml/g_cathr and H₂/CO₂ ratio=3 in the fixed bed reactor within these experimental conditions. Presented at the Int’l Symp. on Chem. Eng. (Cheju, Feb. 8-10, 2001), dedicated to Prof. H. S. Chun on the occasion of his retirement from Korea University.     

Removal of Congo red from aqueous solution using a chitosan/organo‐ montmorillonite nanocomposite

To further improve the adsorption capacity of chitosan (CTS), a series of novel chitosan/organo‐montmorillonite nanocomposites (CTS/OMMT) were synthesized and the adsorption abilities for Congo red (CR) investigated in this study. The nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction analysis (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the results indicated that an exfoliated nanostructure was formed in CTS/OMMT nanocomposites. Compared with the adsorption capacity of OMMT (192.4 mg g^?1), CTS/OMMT with an amount of cetyltrimethylammonium bromide equal to 0.75 CEC of MMT and molar ratio of CTS to OMMT of 1:10 exhibited the higher adsorption capacity (290.8 mg g^?1). The adsorption behaviours of OMMT and CTS/OMMT showed that the adsorption kinetics and isotherms were in good agreement with a pseudo‐second‐order equation and the Langmuir equation, respectively. The IR spectra revealed that a chemical interaction occurred between CTS/OMMT and CR. The adsorption capacity of CTS/OMMT nanocomposite was higher than that of other absorbents; this study suggested that the CTS/OMMT nanocomposite could be used as an adsorbent to remove CR dye from aqueous solution. Copyright © 2007 Society of Chemical Industry     

Adsorption of chlorinated volatile organic compounds in a fixed bed of activated carbon

Adsorption isotherms of dichloromethane and 1,1,2-trichloro-1,2,2-trifluoroethane on an activated carbon pellet, Norit B4, were studied. For these chemicals, the Sips equation gave the best fit for the single component adsorption isotherm. The adsorption affinity on activated carbon was greater for dichloromethane than that of 1,1,2-trichloro-1,2,2-trifluoroethane. An experimental and theoretical study was made for the adsorption of dichloromethane and 1,1,2-trichloro-1,2,2-trifluoroethane in a fixed bed. Experimental results were used to examine the effect of operation variables, such as feed concentration, flow rate and bed height. Intraparticle diffusion was able to be explained by a surface diffusion mechanism. An adsorption model based on the linear driving force approximation (LDFA) was found to be applicable to fit the experimental data.     

Adsorption characteristics of 2,4-dichlorophenoxyacetic acid and 2,4-dinitrophenol in a fixed bed adsorber

The influence of temperature and initial pH of aqueous solution on adsorption has been discussed in detail using the Sips equation. Single-component adsorption equilibria of 2,4-D and 2,4-DNP dissolved in water have been measured for three kinds of GACs (F400, SLS103, and WWL). For 2,4-D, the magnitude of adsorption capacity was in the order of F400>SLS103>WWL, and that for 2,4-DNP was SLS103>F400>WWL. These results may come from the effects of the pore size distribution, surface area, surface properties, and difference in adsorption affinity. Kinetic parameters were measured in a batch adsorber to analyze the adsorption rates of 2,4-D and 2,4-DNP. The internal diffusion coefficients were determined by comparing the experimental concentration curves with those predicted from surface diffusion model (SDM) and pore diffusion model (PDM). The linear driving force approximation (LDFA) model was used to simulate isothermal adsorption behavior in a fixed bed adsorber and successfully simulated experimental adsorption breakthrough behavior under various operation conditions. Efficiency of desorption for 2,4-D and 2,4-DNP was about 80% using distilled water at pH of 6.     

Removal of Brill Red 5B from an aqueous solution using Cicca acida biomass

The biosorption of Brill Red 5B from an aqueous solution, using Cicca acida plant's leaves was investigated in a batch system with the influence of pH (1–6), temperature (25–35°C) and initial dye concentration (10–100 mg/L). Maximum biosorption was observed at initial pH of 2.0, temperature of 30°C and at the initial dye concentration of 100 mg/L. Batch biosorption kinetic was studied using the pseudo first and pseudo‐second‐order rate equations. From the result, it was observed that pseudo‐second‐order rate expression fitted the experimental data well when compared to pseudo first order kinetic model. The intra‐particle diffusion coefficient (K_i) and effective diffusion coefficient (D_i) values obtained for the sorption of Brill Red 5B using C. acida plant's leaves were found to be increased with increase in initial dye concentration.     

MXene@CS复合絮凝剂的制备及其对刚果红去除的研究

壳聚糖（CS）因具有大量的羟基和氨基,可为吸附色素污染物提供较多活性位点,但其在酸性条件易于溶解。MXene可为CS提供支撑位点,从而构建新型MXene@CS复合材料。研究构建了新型Ti₃C₂T_X@CS有机无机复合材料,并应用于刚果红的去除研究。通过对Ti₃C₂T_X@CS的微观形貌、晶体结构、表面官能团等进行表征分析,发现Ti₃C₂T_X@CS的复合过程为物理复合。絮凝实验结果表明：在Ti₃C₂T_X@CS投加量为30 mg、溶液pH为9、反应时间为30 min、温度为25~60 ℃条件下,Ti₃C₂T_X@CS对50 mL质量浓度为500 mg/L刚果红（CR）溶液的脱色率达到99%以上。通过实验结果和反应前后Ti₃C₂T_X@CS电位变化推断,Ti₃C₂T_X@CS对刚果红的去除机理主要是电中和作用和吸附架桥作用。     

Investigation of Reactive Red Dye 198 removal using multiwall carbon nanotubes in aqueous solution

The present study evaluates the performance of multiwalled carbon nanotubes (MWCNTs) for removing Reactive Red Dye 198 (RR198) from the color wastewater. In this study, the influence of pH, adsorbent dose, initial dye concentration, and contact time on the RR198 adsorption by MWCNTs was investigated. The results showed increasing the dye concentration from 20 to 200 mg/L, removal efficiency decreased from 99.62% to 66.99%. Moreover, by increasing the pH from 3 to 10, the efficiency of dye removal decreased from 76.34% to 54.98%. Freundlich isotherm and pseudo-second-order kinetic model were the best models for describing the adsorption reactions.     

Potential of Green Nanoemulsions in Removal of Congo Red from Aqueous Solution

In the present study, potential of green nanoemulsions in the removal of Congo red (CR) from aqueous solution was investigated. Nanoemulsions were prepared by low energy emulsification technique using ethyl acetate (EA), Triton-X100, ethylene glycol (EG), and water. Nanoemulsions were characterized for thermodynamic stability, self-nanoemulsification efficiency, droplet size, polydispersity, viscosity, refractive index, and transmittance. Adsorption studies were carried out for contact time of 10, 15, and 20 min. The influence of contact time and EA & Triton-X100/EG concentrations on droplet size, viscosity, and % CR removal was also investigated. It was observed that droplet size, viscosity, and % CR removal were significantly influenced by EA and Triton-X100/EG concentrations. However, contact time had negligible/little impact on % CR removal. Based on the lowest droplet size (14.3 nm), lowest viscosity (11.4 cp), and highest % CR removal efficiency (91.6%), the nanoemulsion F7 containing 5% w/w of EA, 33.3% w/w of Triton-X100, 16.7% w/w of EG, and 45% w/w of water was optimized as the best formulation for the removal of CR from its bulk aqueous solution. These results indicated the potential of green nanoemulsions in the removal of toxic dyes such as CR from its aqueous solution via liquid-liquid adsorption.     

Removal of Reactive Red 198 from aqueous solution by combined method multi-walled carbon nanotubes and zero-valent iron:Equilibrium,kinetics, and thermodynamic

Dyes often include toxic,carcinogenic compounds and are harmful to humans' health.Therefore,removal of dyes from textile industry wastewater is essential.The present study aimed to evaluate the efficiency of the combination of zero valent iron(ZVI) powder and multi-walled carbon nanotubes(MWCNTs) in the removal of Reactive Red 198(RR198) dye from aqueous solution.This applied research was performed in a batch system in the laboratory scale.This study investigated the effect of various factors influencing dye removal,including contact time,p H,adsorbent dose,iron powder dose,initial dye concentration,and temperature.The equilibrium adsorption data were analyzed using three common adsorption models:Langmuir,Freundlich and Temkin.Besides,kinetic and thermodynamic parameters were used to establish the adsorption mechanism.The results showed,in pH =3,contact time = 100 min,ZVI dose = 5000 mg·L~(-1),and MWCNTs dose = 600 mg·L~(-1)in 100 mg·L~(-1)dye concentration,the adsorption efficiency increased to 99.16%.Also,adsorption kinetics was best described by the pseudo-second-order model.Equilibrium data fitted well with the Freundlich isotherm(R2= 0.99).The negative values of ΔG0and the positive value of ΔH0(91.76) indicate that the RR198 adsorption process is spontaneous and endothermic.According to the results,the combination of MWCNTs and ZVI was highly efficient in the removal of azo dyes.     

Removal of Cr(III) in the fixed bed column and batch reactors using as adsorbent zeolite NaX

In this work, the uptake capacity of Cr(III) ions in NaX zeolite was investigated. The experiments were carried out in continuous and batch systems at . The batch isotherm evidenced an irreversible shape with a maximum chromium uptake of 3.61 meq/g. The column experiments were carried out at pH=3.5, with a flow rate of 9 ml/min and an average particle size of 0.180 mm. The dynamic system provided a distinct ion-exchange mechanism, which generated a favorable isotherm with a chromium uptake of 3.27 meq/g. A mathematical model was also applied to represent the dynamics of the sorption of the column. The model considered the axial dispersion in the column and the intraparticle diffusion as the rate-controlling step. The dynamic isotherm was successfully modeled by the Freundlich equation and the mathematical model described well the experimental dynamic data for the feed concentrations from 0.3 up to 3.0 meq/g.     

Removal and recovery of heavy metal ions in fixed and semi-fluidized beds

Uptakes of heavy metal ions such as Pb²⁺ and Ni²⁺ were studied experimentally in fixed and semifluidized beds packed with a strong cation exchange resin, Amberlite 200. Single and binary aqueous solutions of lead and nickel ions were passed through ion exchange columns, and the exit concentrations were measured to get the breakthrough behavior of the ions. From the exit concentration profiles, the breakthrough time and the ion exchange capacity were evaluated. After removal of heavy metal ions from binary solution of lead and nickel ions until the breakthrough time, two metal ions were recovered by precipitation and resolubilization of lead. In this paper, the recovery yield and separation efficiency are rigorously discussed.     

Use of CaCl2 modified bentonite for removal of Congo red dye from aqueous solutions

CaCl₂ modified bentonite (BCa²⁺), a clean and cost-effective adsorbent with a basal spacing of 15.43 Å, was prepared for the removal of Congo red dye from water. It was effective for the removal of Congo red with a high adsorption capacity, and the adsorption was favored over a broad pH range (5-10). The pseudo-second-order kinetic model provided the best correlation of the experimental data. Adsorption isotherms indicated that sorption took place at specific homogeneous sites within the adsorbent. Furthermore, BCa²⁺ showed higher sorption capacity compared with other common materials used as adsorbents for Congo red dye. The results showed that BCa²⁺ could be employed as a low-cost material for the removal of Congo red from aqueous solutions.     

Removal of methyl violet from aqueous solution using a stevensite-rich clay from Morocco

An inexpensive and easily available Moroccan natural clay, called locally Ghassoul, was employed for adsorption of methyl violet, a cationic dye, in aqueous solution. The experiments were carried out in a batch system to optimize various experimental parameters such as pH, initial dye concentration, contact time, temperature and ionic strength. The experimental data can be well represented by Langmuir and Freundlich models. The Langmuir monolayer adsorption capacity was estimated as 625 mg/g at 298. Kinetic analyses showed that the adsorption rates were more accurately represented by a pseudo second-order model. Intraparticle diffusion process was identified as the main mechanism controlling the rate of the dye sorption. In addition, various thermodynamic activation parameters, such as Gibbs free energy, enthalpy, entropy and the activation energy were calculated. The adsorption process was found to be a spontaneous and endothermic process. The obtained results confirmed the applicability of this clay as an efficient and economical adsorbent for cationic dyes from contaminated water.     

Removal of Basic Red 46 dye from aqueous solution by adsorption and photocatalysis: equilibrium,isotherms, kinetics,and thermodynamic studies

ABSTRACT

In this study, the main objective is the elimination of Basic Red 46 dye by coupling two processes, adsorption on activated clay followed by photocatalysis over ZnO as photocatalyst. The adsorption was investigated under different conditions of pH, adsorbent dose, dye concentrations, and temperature. The best adsorption yield occurs at neutral pH ~ 7 within 60 min with an uptake percentage of 97% for a concentration of 25 mg/L and a dose of 0.5 g/L. The results at equilibrium were successfully described by the Langmuir model with an adsorption capacity of 175 mg/g. To investigate the mechanism of dye adsorption characteristic, the adsorption constants were determined using pseudo first order, pseudo second-order and intraparticle diffusion model. It was found that the Basic Red 46 dye adsorption is well described by the pseudo second-order kinetic. The second part of this work was dedicated to the photodegradation onto ZnO under solar irradiation of the residual BR 46 concentration, remained after adsorption. For the remaining concentrations, the removal yields reach 100% under.