A numerical and experimental study of the monocomponent and multicomponent adsorption and desorption of BTX compounds (benzene, toluene, and o-xylene) in a batch reactor and fixed-bed column was carried out in aqueous solution at 23 °C, using coconut shell activated carbon as the adsorbent. The monocomponent Langmuir isotherm model best represented the experimental results (average R 2 = 0.9952) and the multicomponent Langmuir model, using the multicomponent parameters, represented the multicomponent data obtained in a fixed-bed column better than the monocomponent model. The equations which describe the phenomenology were discretized using the Finite Volumes Method with the WUDS and CDS formulations. The results for the monocomponent breakthrough curves obtained through simulation showed good agreement when compared with the experimental data (maximum error of 11.52%). For the monocomponent breakthrough curves the greatest deviation was observed for the compound which had the least affinity for the solid phase (benzene). The best results for the desorption of the BTX compounds from the adsorbent were obtained using ethanol as the desorbent solvent, and the average removal percentages in three cycles of regeneration in the column were 90% for benzene, 82% for toluene, and 78% for o-xylene.

An experimental and numerical study of the individual and competitive adsorption of BTX compounds (benzene, toluene, and o-xylene) in aqueous solution was carried out in a fixed-bed column filled with activated carbon. The equations of transport were discretized using the finite volumes method and an algorithm was implemented in the Fortran programming language. The results obtained in all cases showed that o-xylene is the contaminant which is most competitive for the active site of the adsorbent, and over time it is able to desorb the compounds which have a lower affinity and adsorb to the free active sites. The result is that the local concentration of the weakly adsorbed component in the fluid phase is higher and surpasses the dimensionless concentration. This finding appeared to be related to the Biot number. As the Biot number increased the rate of competitive adsorption decreased, and the form of the breakthrough curves is flat with a lower breakpoint. This is due to the low intraparticle resistance and also the reduced contact time required to reach saturation.

The adsorption of benzene, toluene, and o-xylene (BTX) in monocomponent and multicomponent aqueous solutions onto activated carbon was studied in a batch reactor at 23 °C for wastewater reuse. The kinetics and thermodynamic equilibrium parameters were obtained for all compounds, where the competitiveness for the active site of adsorption was investigated. The results showed that the order of monocomponent adsorption of these three contaminants is o-xylene > toluene > benzene, and in the multicomponent mixture o-xylene is the most competitive contaminant for the active site of adsorption. The adsorption kinetics were fitted to the homogeneous diffusion model, giving linear correlation coefficients higher than 0.96. The Langmuir isotherm provided the best fit with the monocomponent experimental data. In this study, the multicomponent mixture isotherms were obtained and compared to the models found in the literature.

The adsorption of aqueous solutions of BTEX (benzene, B; toluene, T; ethyl benzene, E; and xylenes, X) on hydrophobically modified zeolite was investigated. Multicomponent kinetics and equilibrium studies were carried out using a batch system. Furthermore, a mathematical model was studied that considers the mass transfer kinetics in a fixed-bed adsorption system. The influences of external mass transfer as well as the constant adsorption equilibrium and intraparticle diffusion resistance on breakthrough curves were evaluated. The adsorption kinetics was adjusted to the homogeneous diffusion model. The breakthrough times of the BTEX compounds increased with an increase in the bed height of the adsorbent and decreased with an increase in the flow. The mathematical model and numerical methodology that were applied represented the data of the present adsorption process with good accuracy.

2015): Multielement adsorption of metal ions using Tururi fibers (Manicaria Saccifera): experiments, mathematical modeling and numerical simulation, Desalination and Water Treatment, A B S T R A C TA numerical and experimental study of the multielement adsorption of Cd 2+ , Cu 2+ , Ni 2+ , and Pb 2+ metal ions in batch and column system were carried out in aqueous solution using Tururi fibers as adsorbent. The kinetics and thermodynamic equilibrium parameters were studied. The adsorption kinetics was fitted to the homogeneous diffusion model and the results showed good linear correlation coefficients. Furthermore, a mathematical model was built to describe the mass transfer kinetics for fixed bed column tests. The effects of constant adsorption equilibrium, external mass transfer, and intraparticle diffusion resistance on breakthrough curves were studied. The equations which describe the phenomenology were discretized using the finite volumes method with the weight upstream differencing scheme and central difference scheme formulations. The results for the breakthrough curves obtained through simulation showed good agreement compared with the experimental data.

No abstract

RESUMO -A remoção de compostos orgânicos voláteis como benzeno, tolueno e xilenos (BTX) do efluente da indústria petroquímica é de interesse considerável, devido o alto grau de toxicidade destes compostos. Investigações na remoção da maioria dos grupos de hidrocarbonetos por adsorção tem focado em compostos individuais; entretanto no efluente da indústria petroquímica existe uma mistura de compostos tóxicos a serem removidos. Assim, neste trabalho, foi realizado o estudo da adsorção dos compostos BTX em coluna de leito fixo a fim de investigar a competitividade por sítio ativo entre os contaminantes, utilizando-se como adsorvente o carvão ativado de casca de coco. Os resultados mostraram que dos três contaminantes estudados o o-xileno foi o mais competitivo pelo sítio ativo, sendo que depois de um certo tempo ele consegue expulsar os compostos mais fracamente adsorvidos no topo da coluna e adsorver nos sítios ativos livres. Palavras-chave:Adsorção Multicomponente, Competitividade, BTX. INTRODUÇÃOA contaminação de recursos naturais, especificamente os hídricos, tem levado à maior conscientização da população para a necessidade da preservação do meio ambiente. É notório que o lançamento de efluentes não tratados ou que não seguem os limites impostos pela legislação ambiental, aumentou nas últimas décadas com impactos eutróficos severos sobre a fauna, flora e nos próprios seres humanos (Luz, 2013).Diante disso nota-se que nas últimas décadas a preocupação e a conscientização, por parte dos governos e população do planeta, têm aumentado. Prova disso são os encontros de cúpulas governamentais e de movimentos sociais para discutir os problemas ambientais que afetam o planeta. Um destes encontros mais recente é a Rio + 20, que em um documento de acordo entre Área temática: Engenharia das Separações e Termodinâmica 1

-Hexavalent chromium has toxic and carcinogenic effects and is often found contaminating in surface waters. In the present study, coconut shell charcoal (CSC) thermally and chemically activated with acetic acid was used for the removal of Cr(VI) from aqueous solutions. The increase in temperature reduced the adsorption capacity, indicating exothermic adsorption. Adsorption kinetics was best analyzed for pseudo-second order model exhibited the best correlation coefficient (R 2 = 0.99) and proved the most efficient in describing the adsorption rate. The Langmuir-Freundlich isotherm demonstrated the best fit to the experimental data (R 2 = 0.99) to describe the adsorption equilibrium of Cr(VI) at different temperatures. The ∆G° value was negative, which confirms the viability and spontaneity of the adsorption process. The present findings demonstrate that CSC thermally and chemically activated with acetic acid proved efficient and can be used for the treatment of waters containing Cr(VI).