Fixed-Bed Column Adsorption Modeling of MnO4- Ions from Acidic Aqueous Solutions on Activated Carbons Prepared with the Biomass

Activated carbons calcined at 400˚C and 600˚C (AC-400 and AC-600), prepared using palm nuts, collected in the town of Franceville in Gabon, were used to study the dynamic adsorption of MnO4- ions in acidic media on fixed bed column and on the kinetic modeling of experimental data of breakthrough curves of MnO4- ions obtained. Results on the adsorption of MnO4- ions in fixed-bed dynamics obtained on AC-400 and AC-600 adsorbents beds indicated that the AC-400 bed appears to be the most efficient in removing MnO4- ions in acidic media. Indeed, the adsorbed amounts, the adsorbed capacities at saturation and the elimination percentage of MnO4- ions obtained with AC-400 (31.24 mg;52.06 mg·g-1 and 41.65% respectively) were higher compared to those obtained with AC-600 (9.87 mg;16.45 mg·g-1 and 17.79% respectively). The breakthrough curves kinetic modeling revealed that the Thomas model and the pseudo-first-order kinetic model were the most suitable models to describe the adsorption of MnO4- ions on adsorbents studied in our experimental conditions. The results of the intraparticle diffusion model showed that intraparticle diffusion was involved in the adsorption mechanism of MnO4- ions on investigated adsorbents and was not the limiting step and the only process controlling MnO4- ions adsorption. In contrast to AC-400, the intraparticle diffusion on AC-600 bed plays an important role in the adsorption mechanism of MnO4- ions.

Adsorption dynamics of ethane from air in structured fixed beds with different microfibrous composites

Adsorption dynamics of ethane in two granular fixed beds and structured fixed beds with microfibrous composites was studied.5A zeolite membrane 5A/PSSF(paper-like sintered stainless steel fiber)and microfibrous entrapped activated carbon(MEAC)composites were prepared by wet layup papermaking/sintering technique and in-situ hydrothermal method.Microfibrous composites were characterized by X-ray diffraction,scanning electron microscopy and N2 adsorption/desorption.Structured fixed beds were designed by filling granular adsorbents(5A zeolite or activated carbon)and microfibrous composites at the inlet and outlet of the beds,respectively.Effects of flow rate,bed height and structure on the breakthrough curves were investigated.The length of unused bed(LUB)was determined,and Yoon–Nelson model was used to fit the breakthrough curves.The experimental results showed ethane was effectively adsorbed on the granular adsorbents and microfibrous composites.Both composites could decrease the LUB values and enhance bed utilization.All breakthrough curves fitted well to Yoon–Nelson model,with correlation coefficient exceeding 0.89.The adsorption rate of ethane could be improved in the structured fixed beds,which showed an enhanced mass transfer efficiency for ethane adsorption.LUB values of structured fixed beds with 5A/PSSF composites were larger,the bed utilization values were lower,and the adsorption rate constants were higher than those with MEAC composites under the same conditions.

Chemically activated carbon nanofibers for adsorptive removal of bisphenol-A:Batch adsorption and breakthrough curve study

Activated carbon nanofibers(ACNFs)with small diameter can significantly increase the accessibility of intra pores and accelerate adsorption of molecules from water.In this study,ACNFs were made by blending K_(2)CO_(3)or ZnCl_(2)as the activating agent into the polyacrylonitrile(PAN)in dimethylformamide solution for electrospinning prior to pyrolysis.Bisphenol-A(BPA),an endocrine disruption pollutant,is widely applied in the production of polycarbonate plastics and epoxy resins.Accordingly,BPA is often used as a model contaminant commonly removed via adsorption.Batch adsorption studies were used to evaluate the kinetics and adsorption capacity of the ACNFs.Redlich-Peterson(R-P)and Langmuir models were found to fit the isotherm of BPA adsorption better than Freundlich model,showing the homogeneous nature of the PAN originated ACNFs.The adsorption kinetics was better described by the pseudo second-order model than that by the pseudo first-order model.The fitting by intraparticle diffusion model indicates the adsorption of BPA onto ACNFs is mainly controlled by pore diffusion.High pH value and ionic strength reduced BPA adsorption from aqueous solution.The breakthrough curves studied in two different fixed bed systems(cross flow bed system and packed flow bed system)confirmed the scalability of BPA removal by ACNFs in dynamic adsorption processes.The modified dose-response model predicted well the fixed-bed outlet concentration profiles.

Dynamic adsorption of Xe on a fixed-bed adsorber at 77 K

In designing a fixed-bed adsorber, it is vital to understand dynamic adsorption properties of the unit. Temperature is an important effect on adsorbent performance, as the dynamic adsorption coefficients tend to increase with decreasing temperature. To minimize the volume of the fixed-bed adsorber, the dynamic adsorption characteristics of Xe were studied at 77 K by employing a variety of adsorbents under different operational conditions. The carbon molecular sieve performed better than that of activated carbon. Both operational conditions and the presence of gaseous impurities were found to affect the adsorption properties.

Photodegradation of Methylene Blue in a Batch Fixed Bed Photoreactor Using Activated Carbon Fibers Supported TiO2 Photocatalyst

A batch fixed bed photoreactor,using felt-form activated carbon fibers(ACF)supported TiO2 photocatalyst(TiO2/ACF),was developed to carry out photocatalytic degradation of methylene blue(MB)solution.The effects of TiO2 particle size,loaded TiO2 amount,initial MB concentration,airflow rate and successive run on the decomposition rate were investigated.The results showed that photodegradation process followed a pseudo-first-order reaction kinetic law.The apparent first-order reaction constant kapp was larger than 0.047 min- 1 with half reaction time t1/2 shorter than 15 min,which was comparable to reported data using suspended Degussa P-25 TiO2 particles.The high degradation rate was mainly attributed to adsorption of MB molecules onto the surface of TiO2/ACF.The photocatalytic efficiency still remained nearly 90%after 12 successive runs,showing that successive usage of the designed photoreactor was possible.The synergic enhancement effect in combination of adsorption with ACF and photodegradation with TiO2 was proved by comparing MB removal rates in the successive degradation and adsorption runs,respectively.

STUDIES ON THE DYNAMIC COMPETITIVE ADSORPTION OF ORGANIC VAPORS ON THE ACTIVATED CARBON FIBERS ACTIVATED WITH PHOSPHORIC ACID

The dynamic competitive adsorption behaviors of different binary organic vapor mixtures on ACF-Ps under different operation conditions were investigated by gas chromatography in this paper. The studied mixtures included benzene/toluene, toluene/xylene, benzene/isopropylbenzene, ethyl acetate/toluene and benzene/ethyl acetate. Experimental results show that various ACF-Ps, as with ACF-W, can remove both vapors in binary vapor mixtures with over 99% of removal efficiency before the breakthrough point of the more weakly adsorbed vapor. In dynamic competitive adsorption, the more weakly adsorbed vapor not only penetrates early, but also will be displaced and desorbed consequently by stronger adsorbate and therefore produces a rolling up in the breakthrough curve. The ACF-Ps prepared at different temperatures have somewhat different adsorption selectivity. The feed concentration ratio of vapors, the length/diameter ratio and the thick of bed have effect on competitive adsorption. The competitive adsorption ability of a vapor is mainly related to its boiling point. Usually, the higher the boiling point, the stronger the vapor adsorbed on ACF-P.

Numerical simulation of low-concentration CO_(2) adsorption on fixed bed using finite element analysis

Accurately predicting distributions of concentration and temperature field in fixed-bed column is essential for designing adsorption processes.In this study,a two-dimensional(2D),axisymmetric,nonisothermal,dynamic adsorption model was established by coupling equations of mass,momentum and energy balance,and solved by finite element analysis.The simulation breakthrough curves fit well with the low-concentration CO_(2) adsorption experimental data,indicating the reliability of the established model.The distributions of concentration and temperature field in the column for CO_(2) adsorption and separation from CO_(2)/N_(2) were obtained.The sensitivity analysis of the adsorption conditions shows that the operation parameters such as feed flow rate,feed concentration,pellet size,and column height-to-diameter ratio produce a significant effect on the dynamic adsorption performance.The multi-physics coupled 2D axisymmetric model could provide a theoretical foundation and guidance for designing CO_(2) fixed-bed adsorption and separation processes,which could be extended to other mixed gases as well.

Adsorption of Reactive Dyes on Activated Carbon Developed from <i>Enteromorpha prolifera</i>

Activated carbon was prepared from Enteromorpha prolifera by zinc chloride activation. The adsorption behaviors of three reactive dyes (Reactive Red 23, Reactive Blue 171 and Reactive Blue 4) onto this biomass activated carbon were investigated in batch systems. The experimental findings showed that the removal efficiencies of three dyes onto activated carbon were maximum at the initial solution pH of 4.5 - 6.0. Thermodynamic studies suggested that adsorption reaction was an endothermic and spontaneous process. Adsorption isotherm of the three dyes obeyed Freundlich isotherm modal. Dye adsorption capacities of activated carbon were 59.88, 71.94 and 131.93 mg·g?1 for RR23, RB171 and RB4 at 27?C, respectively. Second-order kinetic models fitted better to the equilibrium data of three dyes. The adsorption process on activated carbon was mainly controlled by intraparticle diffusion mechanism.

Modeling the Adsorption Kinetics of Activated Carbon for Oil Vapor Recovery and Applications

Oil Vapor recovery is a critical process in downstream chemical industries, in oil and gas industries and in environmental protection. For that purpose, highly-efficient absorbent materials for vapor recovery are in high demand and their associated adsorption kinetics is of great importance for their performance. As oil vapor consists of multiple components with different physical and chemical properties, modeling the overall adsorption kinetics of activated carbon for multi-component oil vapor is essentially valuable for industrial applications. In this work, we developed a comprehensive model of multi-component gas adsorption kinetics on activated carbon in a packed-bed reactor and numerically solved the model by the finite element method. The predictions from the model are all in the reasonable range indicating good validity of the model. Some dimensionless parameters are also derived to further investigate the prediction results.

Characterization of P-nitrophenol Adsorption Kinetic Properties in Batch and Fixed Bed Adsorbers

P-nitrophenol（PNP） adsorption in batch and fixed bed adsorbers was studied. The homogeneous surface diffusion model（HSDM） based on external mass transfer and intraparticle surface diffusion was used to describe the adsorption kinetics for PNP in stirred batch adsorber at various initial concentrations and activated carbon dosages. The fixed bed model considering both external and internal mass transfer resistances as well as axial dispersion with non-linear isotherm was utilized to predict the fixed bed breakthrough curves for PNP adsorption under the conditions of different flow rates and inlet concentrations. The equilibrium parameters and surface diffusivity（Ds） were obtained from separate experiments in batch adsorber. The obtained value of Ds is 4.187×1012 m2/s. The external film mass transfer coefficient（kf） and axial dispersion coefficient（DL） were estimated by the correlations of Goeuret and Wike-Chang. The Biot number determined by HSDM indicated that the adsorption rate of PNP onto activated carbon in stirred batch was controlled by intraparticle diffusion and film mass transfer. A sensitivity analysis was carried out and showed that the fixed bed model calculations were sensitive to Ds and kf, but insensitive to DL. The sensitivity analysis and Biot number both confirm that intraparticle diffusion and film mass transfer are the controlling mass transfer mechanism in fixed bed adsorption system.

Carbon Dioxide/Methane Separation by Adsorption on Sepiolite

In this work, the use of sepiolite for the removal of carbon dioxide from a carbon dioxide/methane mixture by a pressure swing adsorption （PSA） process has been researched. Adsorption equilibrium and kinetics have been measured in a fixed-bed, and the adsorption equilibrium parameters of carbon dioxide and methane on sepiolite have been obtained. A model based on the LDF approximation has been employed to simulate the fixed-bed kinetics, using the Langmuir equation to describe the adsorption equilibrium isotherm. The functioning of a PSA cycle for separating carbon dioxide/methane mixtures using sepiolite as adsorbent has also been studied. The experimental results were compared with the ones predicted by the model adapted to a PSA system. Methane with purity higher than 97% can be obtained from feeds containing carbon dioxide with concentrations ranging from 34% to 56% with the proposed PSA cycle. These results suggest that sepiolite is an adsorbent with good properties for its employment in a PSA cycle for carbon dioxide removal from landfill gases.

Continuous flow removal of acid fuchsine by dielectric barrier discharge plasma water bed enhanced by activated carbon adsorption

Continuous processes which allow for large amount of wastewater to be treated to meet drainage standards while reducing treatment time and energy consumption are urgently needed. In this study, a dielectric barrier discharge plasma water bed system was designed and then coupled with granular activated carbon (GAC) adsorption to rapidly remove acid fuchsine (AF) with high efficiency. Effects of feeding gases, treatment time and initial concentration of AF on removal efficiency were investigated. Results showed that compared to the N2 and air plasmas treatments, O2 plasma processing was most effective for AF degradation due to the strong oxidation ability of generated activated species, especially the OH radicals. The addition of GAC significantly enhanced the removal efficiency of AF in aqueous solution and shorten the required time by 50%. The effect was attributed to the ability of porous carbon to trap and concentrate the dye, increasing the time dye molecules were exposed to the plasma discharge zone, and to enhance the production of OH radicals on/in GAC to boost the degradation of dyes by plasma as well as in situ regenerate the exhausted GAC. The study offers a new opportunity for continuous effective remediation of wastewater contaminated with organic dyes using plasma technologies.

Breakthrough CO_2 adsorption in bio-based activated carbons

In this work, the effects of different methods of activation on CO2 adsorption performance of activated carbon were studied. Activated carbons were prepared from biochar, obtained from fast pyrolysis of white wood, using three different activation methods of steam activation, CO2 activation and Potassium hydroxide（KOH） activation. CO2 adsorption behavior of the produced activated carbons was studied in a fixed-bed reactor set-up at atmospheric pressure, temperature range of 25–65°C and inlet CO2 concentration range of10–30 mol% in He to determine the effects of the surface area, porosity and surface chemistry on adsorption capacity of the samples. Characterization of the micropore and mesopore texture was carried out using N2 and CO2 adsorption at 77 and 273 K, respectively.Central composite design was used to evaluate the combined effects of temperature and concentration of CO2 on the adsorption behavior of the adsorbents. The KOH activated carbon with a total micropore volume of 0.62 cm3/g and surface area of 1400 m2/g had the highest CO2 adsorption capacity of 1.8 mol/kg due to its microporous structure and high surface area under the optimized experimental conditions of 30 mol% CO2 and 25°C. The performance of the adsorbents in multi-cyclic adsorption process was also assessed and the adsorption capacity of KOH and CO2 activated carbons remained remarkably stable after50 cycles with low temperature（160°C） regeneration.

柠檬酸改性球形活性炭对氨气吸附性能的影响

以沥青基球形活性炭为载体,采用等体积浸渍法将不同浓度的柠檬酸负载到活性炭孔隙内。通过固定床动态吸附装置评价柠檬酸改性活性炭对氨气吸附性能的影响。采用扫描电子显微镜、X射线衍射仪、傅里叶变换红外光谱和氮气吸脱附对改性前后活性炭的理化特性进行表征分析。结果表明,当柠檬酸负载量为60%(质量分数)时,改性活性炭对氨气的吸附性能最佳,氨气防护时间为194min,单位活性炭的氨气吸附容量为42.8mg/mL(66.8mg/g),是未改性活性炭吸附容量的24倍;吸附剂的总比表面积和孔体积以及pH都随着柠檬酸负载量的增加不断减小,其中微孔的比表面积和孔体积与柠檬酸负载量的相关系数R2分别为0.9944和0.9842;柠檬酸的利用率随着负载量的增加不断减少,氨气与柠檬酸反应生成柠檬酸铵,产物主要沉积在微孔内,微孔对氨气吸附至关重要。

Tuning porosity of coal-derived activated carbons for CO_(2) adsorption

A simple method was developed to tune the porosity of coal-derived activated carbons,which provided a model adsorbent system to investigate the volumetric CO_(2)adsorption performance.Specifically,the method involved the variation of the activation temperature in a K2CO3 induced chemical activation process which could yield activated carbons with defined microporous(<2 nm,including ultra-microporous<1 nm)and meso-microporous structures.CO_(2)adsorption isotherms revealed that the microporous activated carbon has the highest measured CO_(2)adsorption capacity(6.0 mmol∙g^(–1)at 0℃and 4.1 mmol∙g^(-1)at 25℃),whilst ultra-microporous activated carbon with a high packing density exhibited the highest normalized capacity with respect to packing volume(1.8 mmol∙cm−3 at 0℃and 1.3 mmol∙cm^(–3)at 25℃),which is significant.Both experimental correlation analysis and molecular dynamics simulation demonstrated that(i)volumetric CO_(2)adsorption capacity is directly proportional to the ultra-micropore volume,and(ii)an increase in micropore sizes is beneficial to improve the volumetric capacity,but may lead a low CO_(2)adsorption density and thus low pore space utilization efficiency.The adsorption experiments on the activated carbons established the criterion for designing CO_(2)adsorbents with high volumetric adsorption capacity.

熔盐改性氧化镁吸附剂制备及固定床低浓度CO_(2)吸附捕集

针对吸附法捕集烟道气CO_(2)成本和能耗较高问题,研究采用六水氯化镁和碳酸氢钠通过沉淀法制备碱式碳酸镁并煅烧制得氧化镁粉体,再通过硝酸钠和碳酸钠浸渍改性并成型为(Na NO_(3))_(0.1)-Mg O和(Na NO_(3))_(0.1)(Na_(2)CO_(3))_(0.05)-Mg O颗粒状吸附剂。采用X射线衍射等表征手段对两种吸附剂颗粒微观结构进行分析,并结合热重实验评估了CO_(2)吸附/解吸动力学和循环稳定性。进行了硝酸钠/碳酸钠改性氧化镁吸附剂颗粒填充床低浓度CO_(2)气体的吸附解吸实验研究,分析了氧化镁表面负载的硝酸盐和碳酸盐对低浓度CO_(2)条件下捕集的强化作用。结果表明,在300℃左右,硝酸钠能够在氧化镁表面形成熔盐层,显著强化了CO_(2)吸附性能;硝酸钠熔盐层内存在CO_(2)扩散阻力,需要一定的CO_(2)分压作为通过熔盐层所需的传质推动力,进而降低了低浓度CO_(2)吸附量;碳酸钠的添加可降低CO_(2)通过熔盐层所需的传质推动力,提高低浓度CO_(2)吸附量。

某电子工业园区污水处理厂工程设计

针对某电子工业园区污水处理厂进水水质特性,采用粗格栅及进水泵房-细格栅及沉砂池-调节池(含事故池)-混凝初沉池-水解酸化池-厌氧-多级好氧缺氧生物池-二沉池-高效沉淀池-反硝化深床滤池-活性炭(焦)吸附流化床-氧化铝吸附滤池-接触消毒工艺,并针对难降解COD、氟化物等问题,设计了保证率高且切换灵活的运行模式,介绍了工艺流程、主要设计参数及运行效果。污水处理厂出水可以稳定达到《地表水环境质量标准》(GB3838-2002)Ⅲ类标准。

活性炭吸附乙烷的应用条件研究

乙烷是动力学直径较小的非极性分子,传统吸附剂对它的吸附能力较弱,因此采用吸附法回收乙烷时,吸附材料的选择和应用条件的设定至关重要。通过分析4种活性炭的孔道结构、物相组成和乙烷吸附能力,筛选出具有较强乙烷吸附能力的吸附剂,并研究了应用条件改变对吸附床层吸附乙烷的影响关系。结果表明,具有大比表面积和孔径在1~4 nm之间的AC-1具有优异的乙烷吸附性能。应用条件优化实验表明:浓度、流速、温度和压力均能影响床层对乙烷的吸附性能,增加入口浓度或进料流速有利于提升床层的吸附速率,降低吸附温度或增加吸附压力有利于延长床层的穿透时间。

Numerical simulations and comparative analysis of two- and three-dimensional circulating fluidized bed reactors for CO2 capture

Carbon dioxide(CO2),the main gas emitted from fossil burning,is the primary contributor to global warming.Circulating fluidized bed reactor(CFBR)is proved as an energy-efficient method for post-combustion CO2 capture.The numerical simulation by computational fluid dynamics(CFD)is believed as a promising tool to study CO2 adsorption process in CFBR.Although three-dimensional(3D)simulations were proved to have better predicting performance with the experimental results,two-dimensional(2D)simulations have been widely reported for qualitative and quantitative studies on gas-solid behavior in CFBR for its higher computational efficiency recently.However,the discrepancies between 2D and 3D simulations have rarely been evaluated by detailed study.Considering that the differences between the 2D and 3D simulations will vary substantially with the changes of independent operating conditions,it is beneficial to lower computational costs to clarify the effects of dimensionality on the numerical CO2 adsorption runs under various operating conditions.In this work,the comparative analysis for CO2 adsorption in 2D and 3D simulations was conducted to enlighten the effects of dimensionality on the hydrodynamics and reaction behaviors,in which the separation rate,species distribution and hydrodynamic characteristics were comparatively studied for both model frames.With both accuracy and computational costs considered,the viable suggestions were provided in selecting appropriate model frame for the studies on optimization of operating conditions,which directly affect the capture and energy efficiencies of cyclic CO2 capture process in CFBR.

活性炭对酚醛类化工废水深度处理的动态吸附性能研究

为活性炭应用于酚醛类化工废水深度处理,研究了活性炭对此类废水中有机物的动态吸附性能以及氮的去除。通过动态吸附试验,选出吸附效果最佳的活性炭,研究其对废水中有机物的等温吸附和动力学,并利用比表面积(BET)测试法和傅里叶红外光谱(FTIR)表征技术分析活性炭表面特征,同时探讨不同因素对吸附的影响,再以床厚服务时间(Bed-Depth-Service Time, BDST)模型对动态试验数据进行线性拟合分析。结果表明:椰壳炭吸附效果最好,朗格缪尔(Langmuir)吸附等温线模型和拟二级动力学模型可以较好地描述其动态吸附行为;吸附过程中粒子内扩散并不是唯一的限速步骤,有机物的吸附主要发生在边界层扩散阶段;根据椰壳炭孔状结构的变化说明吸附主要发生在微孔区;—OH、—COOH、C=C等官能团能与有机物相互反应,主要涉及氢键、π-π相互作用、静电引力;含氮化合物会与有机物产生竞争吸附,影响其吸附量;BDST模型不仅可以有效描述吸附床高度与穿透时间之间的关系,而且能够准确地预测新的操作条件下的有机物穿透时间,误差均小于5%。