Academic literature on the topic 'Carbon, Activated – Absorption and adsorption – Mathematical models'

The proposed mathematical model covered in this paper includes the most important parameters associated with the rates of adsorption and desorption. Also, partial pressure is included since it is an important factor that affects rates of adsorption and desorption. The study focuses on the effects of the constant rates on adsorption of pollutant concentrations for benzene, nickel, cadmium, and copper using modified active carbon. When the rate constant of adsorption decreases, the pollutant concentration will also decrease, yielding high acceptable evidence of the logic of the proposed mathematical model. Also, the proposed model is compared with experimental data and other models to give good outcomes with high accuracy.

The use of powdered activated carbon in combination with ultrafiltration membranes is attracting increasing interest for the removal of organic compounds in drinking water treatment. The overall adsorption efficiency of this hybrid membrane process strongly depends on the reactor configuration and its operating conditions. Identification of the operating conditions yielding optimum carbon performance can be facilitated by the use of mathematical models describing the adsorption process. In this study, the effect of various designs and operating parameters on the efficiency of the adsorption process is discussed using an adsorption model previously developed and verified by the authors. This discussion includes the effect of filtration time, membrane reactor volume, carbon dosing procedure, carbon dose and carbon particle size on the adsorption removal of two selected micropollutants and dissolved organic matter.

The use of powdered activated carbon in combination with ultrafiltration membranes is attracting increasing interest for the removal of organic micropollutants in drinking water treatment. The overall adsorption efficiency of this hybrid treatment process strongly depends on the reactor configuration and its operating conditions. Identification of the operating conditions yielding optimum carbon performance can be facilitated by the use of mathematical models describing the adsorption process. In this study, the effect of various design and operating parameters on the efficiency of the adsorption process is discussed using an adsorption model previously developed and verified by the authors. This discussion includes the effect of filtration time, membrane reactor volume, carbon dosing procedure, and the effect of dosing the carbon in reactors installed in series upstream of the membrane reactor.

Research on metal adsorption isotherms with activated carbon oil palm empty fruit bunches in liquid waste. Oil palm empty fruit bunches are used as adsorbent for metal absorption. Oil palm empty fruit bunches are prepared at 105O C for 24 hours to get a constant weight then are characterized by SEM. Oil palm empty fruit bunches are heated at temperatures (400O C – 700O C) to get activated carbon. Re-characterization using SEM at optimum conditions shows that the pore surface is expanding. Then with a batch method for metal absorption (Cu, Pb, Hg) and analyzed using AAS. The most common absorption of activated carbon of oil palm empty fruit bunches is Cu (II). Based on the Langmuir and Freundlich R2 models close to 1, which means that multi-layer adsorption occurs.

Granular Activated Carbon (GAC) adsorption is an effective treatment technology for the removal of Synthetic Organic Chemicals (SOCs) from drinking water supplies. This treatment process can be expensive if not properly designed. Application of mathematical models is an attractive method to evaluate the impact of process variables on process design and performance. In this study, a mathematical modeling methodology incorporating the pore and surface diffusion model (PSDM) is proposed for known mixtures in fixed-bed adsorbers. Thermodynamic correlations for estimation of equilibrium parameters and empirical correlations for estimation of mass transfer parameters are presented. The PSDM was successfully compared to a 6-component mixture for empty bed contact times (EBCTs) of 2.4, 4.9, and 9.56 minutes.

A new approach for the evaluation of activated carbon adsorption characteristics in the treatment of water contaminated by toxic organic compounds is presented. It is based on direct determination of the toxicity in the treated water, as opposed to actual chemical analysis of their constituents. The MicrotoxR bioassay, based upon measurement of bacterial bioluminescence, was utilized for this purpose. The suitability of this approach was judged by applying values of residual toxicities, obtained during batch adsorption experiments with mixtures of pure chemicals and industrial wastes, to traditional mathematical models. The Freundlich model was found to describe accurately adsorption isotherms derived from balances of residual toxicities, as well as from residual concentrations of specific chemicals. This approach allows a fast, convenient assessment of selective toxicant adsorption, alleviating the need for complex analytical methods.

Modeling of adsorption process establishes mathematical relationship between the interacting process variables and process optimization is important in determining the values of factors for which the response is at maximum. In this paper, response surface methodology was employed for the modeling and optimization of adsorption of phenol onto rice husk activated carbon. Among the action variables considered are activated carbon pretreatment temperature, adsorbent dosage, and initial concentration of phenol, while the response variables are removal efficiency and adsorption capacity. Regression analysis was used to analyze the models developed. The outcome of this research showed that 99.79% and 99.81% of the variations in removal efficiency and adsorption capacity, respectively, are attributed to the three process variables considered, that is, pretreatment temperature, adsorbent dosage, and initial phenol concentration. Therefore, the models can be used to predict the interaction of the process variables. Optimization tests showed that the optimum operating conditions for the adsorption process occurred at initial solute concentration of 40.61 mg/L, pretreatment temperature of 441.46°C, adsorbent dosage 4 g, adsorption capacity of 0.9595 mg/g, and removal efficiency of 97.16%. These optimum operating conditions were experimentally validated.

An attempt was made to study the potential of rice husk as an alternative cheap precursor for activated carbon to remove Ni2+ from aqueous solution. Rice husk was treated chemically (with NaOH) and physically (carbonization) to prepare rice husk based activated carbon (RHAC). The textural properties of RHAC, i.e. surface area (255 m2/g) and pore volume (0.17 cm2/g), were determined by N2 adsorption using Brunauer-Emmett-Teller (BET) surface analyzer. RHAC was also characterized for its morphology and its elemental compositions. The adsorption studies for the removal of Ni2+ from aqueous solution were carried out using different dosage of RHAC as adsorbent as a function of varied contact time. The concentration of Ni2+ was determined by atomic absorption spectrometer (AAS). The results obtained from adsorption studies indicate good potential of rice husk as a cheap precursor to produce activated carbon for the removal of Ni2+ from aqueous solution. The equilibrium data from adsorption studies fitted well the of Langmuir and Freundlich isotherm models.

Response surface methodology (RSM) was utilized to optimize the best adsorbent conditions on Malachite Green in wastewater by the activated carbon which has been prepared from grapefruit peel with potassium hydroxide activating. Built on single-factor experiment, adsorbent dosage, pH, initial MG concentration and temperature were chosen as influencing factors during adsorption. The experimental mathematical model was arranged according to central composite design (CCD). The results shown that the best conditions were pH 9, initial MG concentration of 2000 mg/L, 1 g/L dosage of KAC and 40°C. Maximum absorption was 1944.35 mg/L.

Heat actuated adsorption heat pumps offer the opportunity to improve overall energy efficiency in waste heat applications by eliminating shaft work requirements accompanying vapor compression cycles. The coefficient of performance (COP) in adsorption heat pumps is generally low. The objective of this thesis is to model the adsorption system to gain critical insight into how its performance can be improved. Because adsorption heat pumps are intermittent devices, which induce cooling by adsorbing refrigerant in a sorption bed heat/mass exchanger, transient models must be used to predict performance. In this thesis, such models are developed at the adsorbent particle level, heat/mass exchanger component level and system level. Adsorption heat pump modeling is a coupled heat and mass transfer problem. Intra-particle mass transfer resistance and sorption bed heat transfer resistance are shown to be significant, but for very fine particle sizes, inter-particle resistance may also be important. The diameter of the adsorbent particle in a packed bed is optimized to balance inter- and intra-particle resistances and improve sorption rate. In the literature, the linear driving force (LDF) approximation for intra-particle mass transfer is commonly used in place of the Fickian diffusion equation to reduce computation time; however, it is shown that the error in uptake prediction associated with the LDF depends on the working pair, half-cycle time, adsorbent particle radius, and operating temperatures at hand. Different methods for enhancing sorption bed heat/mass transfer have been proposed in the literature including the use of binders, adsorbent compacting, and complex extended surface geometries. To maintain high reliability, the simple, robust annular-finned-tube geometry with packed adsorbent is specified in this work. The effects of tube diameter, fin pitch and fin height on thermal conductance, metal/adsorbent mass ratio and COP are studied. As one might expect, many closely spaced fins, or high fin density, yields high thermal conductance; however, it is found that the increased inert metal mass associated with the high fin density diminishes COP. It is also found that thin adsorbent layers with low effective conduction resistance lead to high thermal conductance. As adsorbent layer thickness decreases, the relative importance of tube-side convective resistance rises, so mini-channel sized tubes are used. After selecting the proper tube geometry, an overall thermal conductance is calculated for use in a lumped-parameter sorption bed simulation. To evaluate the accuracy of the lumped-parameter approach, a distributed parameter sorption bed simulation is developed for comparison. Using the finite difference method, the distributed parameter model is used to track temperature and refrigerant distributions in the finned tube and adsorbent layer. The distributed-parameter tube model is shown to be in agreement with the lumped-parameter model, thus independently verifying the overall UA calculation and the lumped-parameter sorption bed model. After evaluating the accuracy of the lumped-parameter model, it is used to develop a system-level heat pump simulation. This simulation is used to investigate a non-recuperative two-bed heat pump containing activated carbon fiber-ethanol and silica gel-water working pairs. The two-bed configuration is investigated because it yields a desirable compromise between the number of components (heat exchangers, pumps, valves, etc.) and steady cooling rate. For non-recuperative two-bed adsorption heat pumps, the average COP prediction in the literature is 0.39 for experiments and 0.44 for models. It is important to improve the COP in mobile waste heat applications because without high COP, the available waste heat during startup or idle may be insufficient to deliver the desired cooling duty. In this thesis, a COP of 0.53 is predicted for the non-recuperative, silica gel-water chiller. If thermal energy recovery is incorporated into the cycle, a COP as high as 0.64 is predicted for a 90, 35 and 7.0°C source, ambient and average evaporator temperature, respectively. The improvement in COP over heat pumps appearing in the literature is attributed to the adsorbent particle size optimization and careful selection of sorption bed heat exchanger geometry.

O alto custo do carvão ativado tem motivado a busca por materiais adsorvedores de baixo custo, como os subprodutos industriais. Neste sentido, o uso dos subprodutos industriais de xisto: finos de xisto (XC), xisto retortado (XR) e xisto retortado com pneus (XRP), proveniente do processo PETROSIX/PETROBRAS, e o catalisador exaurido (CAT), da unidade de FCC (Craqueamento Catalítico em Leito Fluidizado), foram caracterizados e utilizados neste trabalho na adsorção de compostos orgânicos de efluente líquido industrial. O objetivo geral deste estudo é modelar matematicamente o processo de adsorção de compostos orgânicos em xisto, catalisador exaurido de FCC e carvão ativado em pó, utilizando o modelo HSDM (Modelo de Difusão por Superfície Homogênea), e o comportamento hidráulico do sistema adsorvedor. A caracterização estrutural e química de várias amostras de xisto (finos de xisto, xisto retortado e xisto retortado com pneus) e do catalisador exaurido de FCC, além do desenvolvimento de um modelo computacional para a simulação do processo de adsorção são contribuições adicionais ao trabalho. Os resultados de caracterização dos adsorventes de xisto mostram que estes materiais são basicamente macroporosos e com área superficial em torno de 0,51 a 3,36 2 . 1 m g , além de apresentarem as mesmas estruturas cristalinas, e micrografias características dos argilominerais. Já o adsorvente CAT mostrou-se formado basicamente por faujasita, sílica e alumina, apresentando-se na forma de grânulos esféricos, irregulares e microporosos, com área superficial característica de materiais zeolíticos (148 e 155 2 . 1 m g ). Os ensaios de adsorção realizados nos efluentes sintéticos e industriais (Fenólico e Petroquímico) mostraram que existe potencial de aplicação dos subprodutos industriais de xisto e CAT na remoção de compostos orgânicos (corantes, fenóis e COT) destes efluentes. Os resultados das simulações obtidos do modelo proposto mostraram que o tratamento unicamente por adsorção em xisto ou CAT, tendo em vista os padrões ambientais de descarte de efluente (resolução CONAMA 357), é inviável. Isto por que a quantidade de adsorvente requerida é muito elevada. Entretanto, tais adsorventes podem ser utilizados na redução da carga orgânica de ambos os efluentes. Por questões de transporte, é indicado que cada subproduto industrial seja utilizado na própria indústria que lhe deu origem. Ou seja, o CAT é indicado para o tratamento do efluente Petroquímico e os adsorventes de xisto para o Fenólico.
The high cost of the activated carbon has motivated the search of low cost adsorbents such as industrial by-products. In this sense, the use of industrial by-products of oil shale: Oil Shale (XC), Pirolized Oil Shale (XR) and Pirolized Oil Shale with Tires (XRP), from PETROSIX/PETROBRAS, and the spent catalyst (CAT), from FCC (Fluid Catalytic Cracking) unit were characterized and used in this work in the adsorption of organics compounds of industrial liquid effluent. The main contribution of this thesis is to propose a mathematical model to the adsorption process of organic compounds in oil shale, spent catalyst of FCC and powdered activated carbon. This model is based on HSDM (Homogeneous Surface Diffusion Model) model and on the hydraulic behavior of the adsorbent system. Other contribution is the structural and chemical characterization of several samples of oil shale (oil shale, Pirolized oil shale and Pirolized oil shale with Tires) and of the spent catalyst of FCC. A computational model to simulate the adsorption process of these materials is also developed and can be considered an additional contribution of this work. Experimental and simulated results allow characterization of the oil shale adsorbent as basically macroporous and with superficial area about 0.51 to 3.36 m2.g-1. In addition, they present the same crystal structures and clay micrografies characteristics. The adsorbent CAT is composed basically by Faujasite, silica and alumina. They present spherical beads, irregular forms and micropores, with superficial area characteristics of zeolitic materials (148 and 155 m2.g-1). The adsorption tests realized in the synthetic and industrial effluents (Phenolic and Petrochemical) showed the potential of application of the industrial by-products of oil shale and CAT in the removal of organics compounds (dyes, Phenol and COT) of these effluents. In respect of environmental standards to effluents disposal (CONAMA resolution 357), simulations results, obtained with the proposed model, has demonstrated that the use of only oil shale or CAT is not viable, because the high quantity of adsorbents required. However, such adsorbents can be used in the reduction of organic loads in both effluents, when combined with other processes. Each adsorbent showed be used where it is produced because of transportation cost. The CAT is indicated for the treatment of Petrochemical effluent while the others adsorbents may be applied in the phenolic effluent treatment.

M. Tech. Engineering Chemical.
Aims to investigate how the addition of impurities in a CO2 stream affects the adsorption capacity of CO2 on South African coals. To achieve this aim, the following objectives were carried out. 1. To measure the adsorption isotherms and adsorption capacities of pure CO2 and flue gas mixtures on various South African coals under in-seam conditions including pressures up to 88 bar and isothermal temperature of 35 º%x;C; 2. To evaluate the effects of coal rank on the adsorption isotherms and adsorption capacities of pure CO2 and flue gas mixtures; 3. To do a comparative study to evaluate the effects of CO2 impurities on the adsorption capacity of pure CO2 on coal; 4. To study the degree of preferential sorption of the individual flue gas mixtures components on coal; 5. To determine the suitability of the Langmuir, Freundlich, and Temkin adsorption isotherm models in representing pure CO2 adsorption onto coal; and 6. To determine the suitability of Extended Langmuir (EL) adsorption models in representing the flue gas mixture adsorption onto coal.

An experimental and numerical modeling investigation was conducted to study interactions between microbial dynamics and transport processes in variably saturated porous media. These interactions are important in a variety of applied problems such as water and wastewater treatment, bioremediation, and oil-field recovery operations. These processes and interactions also have great ecological significance, with global scale implications for carbon cycling in the environment and the related issue of climate change. Experiments were conducted under variably saturated flow conditions in columns and 2D light-transmission chambers packed with translucent quartz sand. A bioluminescent Pseudomonas fluorescens bacterium was utilized in the experiments and bioluminescence was used as a non-destructive measure of bacterial density and distribution. In the column experiments, pressure heads increased (became less negative) at all measured depths, but significant changes in apparent volumetric water contents were only observed in the upper 5 cm of the columns. Permeability was reduced by a factor of 40 within one week during growth on glucose. In the chamber experiments, aqueous-phase saturations decreased by 7-9% in the region of primary colonization and the capillary fringe dropped by 5 cm during the 6-day experiment. The colonized region expanded laterally by 15 cm and upward against the flow by about 7-8 cm. The desaturation phenomenon resulted in increased lateral spreading of solutes around the colonized region. A numerical model was developed and used to help interpret the experimental data. Water flow was modeled using the single-phase Richards equation. Solute and bacterial transport, cell growth, substrate consumption, and gas diffusion were modeled using advection-dispersion-reaction equations. Observed changes in saturations and pressure heads were reproduced approximately using fluid-media scaling to represent an apparent surface-tension lowering effect, which was assumed to be due to sorption of cells and/or biosurfactants at gas-liquid interfaces. Microbial dynamics, and substrate and oxygen consumption were represented using first-order reversible kinetics for cell attachment/detachment, and dual Monod-type kinetics for cell growth and substrate and oxygen consumption. Reasonably good matches were obtained between the observed and simulated results.
Graduation date: 2003

This work evaluates stripper performance for CO₂ capture using seven potential solvent formulations and seven stripper configurations. Equilibrium and rate models were developed in Aspen Custom Modeler (ACM). The temperature approach on the hot side of the cross exchanger was varied between 5 - 10°C. The results show that operating the cross exchanger at a 5°C approach results in 12% energy savings for a 7m MEA rich solution of 0.563 mol/mol Alk and 90% CO₂ removal. For solvents with [Delta]H[subscript abs] < 60 kJ/gmol CO₂, stripping at 30 kPa is more attractive than stripping at 160 kPa. Normal pressure (160 kPa) favors solvents with high heats of desorption. The best solvent and process configuration, matrix with MDEA/PZ, offers 22% and 15% energy savings over the baseline and improved baseline, respectively, with stripping and compression to 10 MPa. The energy requirement for stripping and compression to 10 MPa is about 20 % of the power output from a 500 MW power plant with 90% CO2 removal. Rate model results show that a 'short and fat' stripper requires 7 to 15% less equivalent work than a 'tall and skinny' one. The optimum stripper design could be one that operates between 50% and 80% flood at the bottom. Stripping at 30 kPa and 160 kPa require 230 s and 115 s of effective packing volume to get an equivalent work 4% greater than the minimum. Stripping at 30 kPa with [Delta]T = 5°C was controlled by mass transfer with reaction in the boundary layer and diffusion (88% resistance at the rich end and 71% resistance at the lean end) and mass transfer with equilibrium reactions (84% resistance at the rich end and 74% resistance at the lean end) at 160 kPa. The model was validated with data obtained from pilot plant experiments at the University of Texas with 5m K⁺/2.5m PZ and 6.4m K⁺/1.6m PZ under normal pressure and vacuum conditions using Flexipac AQ Style 20 structured packing. Foaming was experienced during tests. The effective packing height was 5.09m for 5m K⁺/2.5m PZ and 6.47m for 6.4m K⁺/1.6m PZ.
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This paper compares the quantitative and qualitative performances of three different heat-activated cooling systems, e.g. a silica-gel water adsorption system, a LiBr-H2O absorption system, and a desiccant air system. Each of these systems can be utilized at relatively low heat source temperatures, but it is unclear which of these systems is best suited to what range of heat source temperature. Our study explores answers to this question by generating quantitative results comparing their relative thermal performance, i.e. COP and refrigeration capacity, and a qualitative comparison based on the size, maturity of technology, safe operation, etc. Each of these systems is assumed to work under the following operating conditions: a condensing temperature of 29 °C, an evaporating temperature of 19 °C, a hot water temperature range of 40-120 °C, and a hot water mass flow rate of 0.4 kg/sec. Individual mathematical models are developed for each system and numerically solved using different techniques. In order to provide a fair comparison between the fundamentally different systems, a UA (overall heat transfer coefficient multiplied by the heat transfer area) value of 1.0 kW/ °C is considered for the heat exchanger that transfers heat from the supplied hot water. Furthermore, to compare systems of similar size, the mass of silica gel in adsorption and desiccant system and mass of LiBr-H2O solution in absorption system were specified such that each system provides the same amount of refrigeration (8.0 kW) at a source temperature of 90 °C. It is found that the absorption and adsorption cooling systems have a higher refrigeration capacity at heat source temperatures below 90 °C, while the desiccant air system outperforms the others at temperatures above 90 °C.