External Mass‐Transfer Rate in Fixed‐Bed Adsorption

1985 ◽  
Vol 111 (6) ◽  
pp. 891-905 ◽  
Author(s):  
Paul V. Roberts ◽  
Peter Cornel ◽  
R. Scott Summers
Keyword(s):  
Mass Transfer ◽  
Transfer Rate ◽  
Mass Transfer Rate ◽  
Fixed Bed ◽  
External Mass Transfer ◽  
Fixed Bed Adsorption

Mechanisms by Which Pentane and Hexane Adsorb on Silica Gel

1966 ◽  
Vol 6 (02) ◽  
pp. 166-174 ◽  
Author(s):  
H.O. McLeod ◽  
J.M. Campbell
Keyword(s):  
Mass Transfer ◽  
Silica Gel ◽  
Transfer Rate ◽  
Mass Transfer Rate ◽  
Fixed Bed ◽  
Transfer Coefficients ◽  
Constant Length ◽  
Adsorbate Concentration ◽  
Transfer Zone ◽  
Effluent Curve

Abstract Data analysis of pentane and hexane adsorption from natural gas in a fixed bed of silica gel shows that constant length mass transfer zones form, the curvature of the adsorption isotherm controls the growth of the mass transfer zone and surface diffusion of molecules inside the silica gel particle controls the mass transfer rate. Curvature of the hexane isotherm is more than the curvature of the pentane isotherm. Because of this curvature the hexane adsorption zones reached a constant length. In contrast, the pentane adsorption zones were always increasing in length during each run. A procedure was developed to obtain correct mass transfer coefficients using effluent curve slopes. These transfer coefficients increase with the amount of hydrocarbon adsorbed on the silica gel particle. The characteristic shape of the hexane effluent curves also show that molecular diffusion inside the silica gel particle controls the adsorption rate of pentane and hexane. Introduction The purpose of this study was to determine the mechanisms that control the dynamic adsorption of hydrocarbons from a natural gas onto silica gel. Before one can deal effectively with multicomponent adsorption, the transfer mechanisms by which a single hydrocarbon component is adsorbed from the gas stream must be defined. Two principal investigations of this system have been published and indicate that diffusion through the gas around the particle controls the adsorption rate. Some of the experimental observations in each study either do not support this transfer mechanism or are inconsistent with the mathematical model used in analysis. In this study surface diffusion of molecules inside the particle controls the mass transfer rate of pentane and hexane. This mechanism is indicated by the effluent curve shape for a constant length transfer zone and by the variation of the mass transfer coefficient with concentration of the adsorbed hydrocarbon. THEORY AND DEFINITIONS-MATHEMATICAL MODELS Mathematical solutions for the isothermal adsorption of a trace component from a carrier gas are derived from three relationships: the mass balance or continuity equation, the equilibrium relationship between the gas and solid phases, and a mass transfer rate equation. The transfer rate is proportional to the adsorbate concentration gradient within either the gas or solid phase. Mathematical solutions of these equations usually give the adsorbate concentration as a function of time and distance from the bed inlet. That part of the bed in which the adsorbate concentration changes from a maximum to a minimum value is called the transfer zone. This transfer zone is directly related to a plot of the effluent concentration vs time which has a characteristic S-shape. This general shape is determined by the continuity equation and occurs in many processes of diffusional transfer. EQUILIBRIUM ADSORPTION ISOTHERMS Different mathematical models of fixed bed adsorption occur mainly because different equilibrium adsorption isotherms are assumed. Eq. 1 describes the amount of hydrocarbon adsorbed as a function of the amount of hydrocarbon in the gas phase at a constant temperature: ........................................(1) There are two main models which describe the separation of a trace component in a fixed bed. Model A assumes a linear isotherm (r = 1); Model B assumes a favorably curved isotherm (r is less than 1). SPEJ P. 166ˆ

Effect of ozonation on preloading of background organic matter in granular activated carbon filters

1997 ◽  
Vol 35 (7) ◽  
pp. 295-302 ◽  
Author(s):  
Ervin Orlandini ◽  
Tsegaye G. Gebereselassie ◽  
Joop C. Kruithof ◽  
Jan C. Schippers
Keyword(s):  
Mass Transfer ◽  
Organic Matter ◽  
Activated Carbon ◽  
Adsorption Capacity ◽  
Transfer Rate ◽  
Mass Transfer Rate ◽  
Fixed Bed ◽  
Granular Activated Carbon ◽  
River Rhine ◽  
Homogeneous Surface

Background Organic Matter (BOM) preloading is adsorption of BOM onto Granular Activated Carbon (GAC) prior to the adsorption of target compounds, such as pesticides and other organic micropollutants (e.g. atrazine). BOM preloading is commonly found to speed up the breakthrough of target compounds during GAC filtration. Ozonation of GAC filter influent may be expected to lower BOM preloading, because it results in less adsorbable and more biodegradable BOM compounds. Short Fixed Bed (SFB) tests with virgin and preloaded GAC, performed within this study, confirmed that preloading of BOM present in pretreated river Rhine water speeds up the breakthrough of atrazine in GAC filters. BOM preloading was found to lower equilibrium adsorption capacity of GAC for atrazine, and to slow down both external and internal mass transfer rate of atrazine on/into GAC. Adsorption capacity of (crushed) GAC was determined from atrazine adsorption isotherms, while mass transfer rate coefficients were determined by fitting the Homogeneous Surface Diffusion model to the breakthrough of atrazine in the SFB tests. More pronounced BOM preloading was found in the GAC filter receiving non-ozonated influent than in its ozonated counterpart. Biodegradation of ozonated BOM was shown to lower BOM preloading in GAC filters.

Free Convective Mass Transfer at Isosceles Triangular Surfaces of Varying Inclination

2003 ◽  
Vol 68 (11) ◽  
pp. 2080-2092 ◽  
Author(s):  
Martin Keppert ◽  
Josef Krýsa ◽  
Anthony A. Wragg
Keyword(s):  
Mass Transfer ◽  
Transfer Rate ◽  
Mass Transfer Rate ◽  
Mass Transfer Process ◽  
Sulfate Solution ◽  
Convective Mass Transfer ◽  
Varying Length ◽  
Inclined Surface ◽  
Vertical Case ◽  
Limiting Diffusion Current

The limiting diffusion current technique was used for investigation of free convective mass transfer at down-pointing up-facing isosceles triangular surfaces of varying length and inclination. As the mass transfer process, copper deposition from acidified copper(II) sulfate solution was used. It was found that the mass transfer rate increases with inclination from the vertical to the horizontal position and decreases with length of inclined surface. Correlation equations for 7 angles from 0 to 90° were found. The exponent in the ShL-RaL correlation ranged from 0.247 for the vertical case, indicating laminar flow, to 0.32 for inclinations of 60 to 90°, indicating mixed or turbulent flow. The general correlation ShL = 0.358(RaL sin θ)0.30 for the RaL sin θ range from 7 × 106 to 2 × 1011 and inclination range from 15 to 90° was obtained.

Distributed mass transfer rate for modelling the leaching of porous granular materials containing soluble pollutants

2000 ◽  
Vol 55 (7) ◽  
pp. 1257-1267 ◽  
Author(s):  
Tiruta-Barna Ligia ◽  
Barna Radu ◽  
Moszkowicz Pierre ◽  
Bae Hae-Ryong
Keyword(s):  
Mass Transfer ◽  
Granular Materials ◽  
Transfer Rate ◽  
Mass Transfer Rate

Enhancement of formic acid production from CO2 in formate dehydrogenase reaction using nanoparticles

RSC Advances ◽  
2016 ◽  
Vol 6 (111) ◽  
pp. 109978-109982 ◽  
Author(s):  
Young-Kee Kim ◽  
Sung-Yeob Lee ◽  
Byung-Keun Oh
Keyword(s):  
Mass Transfer ◽  
Formic Acid ◽  
Acid Production ◽  
Transfer Rate ◽  
Formate Dehydrogenase ◽  
Mass Transfer Rate ◽  
Liquid Mass ◽  
Dehydrogenase Reaction ◽  
Liquid Mass Transfer ◽  
Mesoporous Nanoparticles

In an enzyme process using a gas substrate, the enhanced gas liquid mass transfer rate of the gas substrate by methyl-functionalized mesoporous nanoparticles could improve the productivity.

STUDY OF EXTERNAL MASS TRANSFER DURING DRYING OF BERRY RAW MATERIALS TAKING INTO THE SHRINKAGE PHENOMENON

2019 ◽  
Author(s):  
А.В. АКУЛИЧ ◽  
Л.А. ГОСТИНЩИКОВА
Keyword(s):  
Mass Transfer ◽  
Energy Supply ◽  
Raw Materials ◽  
Mass Transfer Rate ◽  
Experimental Studies ◽  
Volume Shrinkage ◽  
External Mass Transfer ◽  
Transfer Coefficients ◽  
Ir Radiation ◽  
Criterial Equations

Исследованы закономерности внешнего массообмена при сушке ягодного сырья для различных способов энергоподвода. Установлено, что ягоды при сушке подвержены значительной объемной (72–81%) и линейной (35–43%) усадке, которую необходимо учитывать при расчете коэффициентов массоотдачи. Объекты исследования – ягоды черники, красной и черной смородины. Проведены экспериментальные исследования по сушке ягодного сырья при конвективном и конвективном с ИК-излучением способах энергоподвода. Исследования проведены при скорости сушильного агента хса1,2 м/с и температуре tса 70°С. Получены критериальные уравнения внешнего массоообмена при сушке ягод для периода постоянной скорости, учитывающие объемную усадку. Определено, что при сушке с конвективным энергоподводом объемная усадка при одном и том же значении критерия Рейнольдса оказывает на 12–20% большее влияние на интенсивность массоообмена для красной смородины по сравнению с черникой и черной смородиной. При сушке с конвективным энергоподводом, ИК-излучением и предварительным прокалыванием объемная усадка наиболее существенно влияет на массообмен для черной смородины, протекающий в 1,5–1,8 раза интенсивнее по сравнению с черникой и красной смородиной. Полученные критериальные уравнения могут быть использованы при расчете и проектировании установок для сушки ягодного сырья. The laws of external mass transfer during drying of berry raw materials for various methods of energy supply are investigated. It is established that the berries during drying are subject to significant volumetric (72–81%) and surface (35–43%) shrinkage, which must be taken into account when calculating the mass transfer coefficients. The objects of the study were various berries: blueberries, red and black currants. Experimental studies have been carried out on the drying of selected berries both in the case of convective and convective methods with IR radiation. Investigations were carried out at a drying agent velocity хса1,2 m/s and its temperature tca70°С. The criterion equations of external mass transfer during drying of berries for a period of constant speed, taking into account the volume shrinkage, are obtained. It was determined that during drying with convective energy supply, volume shrinkage with the same value of the Reynolds criterion on 12–20% has a greater effect on the mass transfer rate for red currants. When drying with convective energy supply, IR radiation and preliminary piercing, the volume shrinkage most significantly affects the mass transfer for black currants, which is 1,5–1,8 times more intense than blueberries and red currants. The obtained criterial equations can be used in the calculation and design of berries dryers.

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