HEAT AND MASS TRANSFER IN THE ADSORBENT BED OF AN ADSORPTION HEAT PUMP

The heat and mass transfer equations governing an adsorbent bed in an adsorption heat pump and the mass balance equation for the adsorbent particles in the adsorbent bed were solved numerically to simulate the cycle of a basic adsorption heat pump, which includes isobaric adsorption, isosteric heating, isobaric desorption, and isosteric cooling processes. The finite difference method was used to solve the set of governing equations, which are highly nonlinear and coupled. The pressures of the evaporator and condenser were 2 and 20 kPa, respectively, and the regeneration temperature of the bed was 403 K. Changes in the temperature, adsorptive pressure, and adsorbate concentration in the adsorbent bed at different steps of the cycle were determined. The basic simulated cycle is presented in a Clausius-Clapeyron diagram, which illustrates the changes in average pressure and temperature of the adsorbent bed throughout the cycle. The results of the simulation indicated that the most time-consuming processes in the adsorption heat pump cycle were isobaric adsorption and isobaric desorption. The high thermal resistance of the bed slows down heat transfer, prolonging adsorption and desorption processes.     

Equilibrium and kinetics of vancomycin adsorption on polymeric adsorbent

Isolation step of vancomycin, a glycopeptide antibiotic, is usually done from fermentation broth filtrate, while its adsorption directly from the whole broth could rationalize the process. The equilibrium and kinetics of vancomycin adsorption from broth supernatant, diluted and whole broth on polymeric adsorbent was studied in this work. Experimental equilibrium data was correlated with Sips, Langmuir, Freundlich, and linear adsorption isotherms. Agreement between measured and regressed data for the first three mentioned models did not vary much and was relatively high. The maximum adsorbed amount for supernatant was higher than for fermentation broths because mycelium particles blocked adsorbent surface. Liquid film mass transfer studies showed that external mass transfer resistance could have been neglected. Diffusion of vancomycin inside adsorbent particles was acknowledged using a nonstructural, homogenous surface diffusion and bidisperse pore models. Model simulations indicated that kinetics of the process could be improved by using smaller adsorbent particles. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Adsorption characteristics of benzene on electrospun‐derived porous carbon nanofibers

The adsorption properties of polyacrylonitrile (PAN) carbon nanofibers fabricated by using an electrospinning route were assessed for their applicability as a novel alternative adsorbent. Commercial fiber, A–10, was chosen for comparison. Nitrogen adsorption/desorption isotherms and gravimetric techniques were used to examine the porous structure, adsorption equilibrium, kinetics, and the energetic heterogeneity of the prepared adsorbent. The nitrogen adsorption and desorption isotherms showed that PAN carbon nanofibers are highly microporous with small amounts of mesoporous regions. The equilibrium data of benzene was obtained at three different temperatures (343.15, 383.15, and 423.15) K with pressures up to 4 kPa. The data correlated successfully with the Toth isotherm equation. In addition, by using this isotherm model, the adsorption affinity and isosteric enthalpy of adsorption were determined. The results of the isosteric enthalpy of adsorption and adsorption energy distribution tests/equations revealed that although PAN carbon nanofibers have a heterogeneous surface, they seem to be more homogeneous than commercial carbon fibers. Moreover, the mass transfer and thermal desorption results showed that shallow pores contained within PAN carbon nanofibers may be effective adsorbents for removing toxic compounds. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2454–2462, 2006     

SCALE ANALYSIS AND PARAMETRIC STUDY OF TRANSIENT HEAT/MASS TRANSFER IN THE PRESENCE OF NONPOROUS SOLID ADSORPTION

A transient, two-dimensional theoretical analysis of combined heat and mass transfer in the presence of adsorption/desorption is developed to study the fundamentals of heat and mass transfer dynamics. A parallel-plate rectangular channel is used as a model system. Appropriate surface boundary conditions for heat and mass transfer and adsorption/desorption interactions are formulated. A scale analysis of the governing equations is performed in order to identify the dimensionless physical parameters governing the process and to obtain the order-of-magnitude estimates for characteristic time constants of the system dynamics. Predictions of the scale analysis are validated against the results of the parametric study obtained through the numerical solutions of the governing equations. The findings demonstrate that the scale analysis is a very powerful analytical tool which allows one to evaluate the effects of different process parameters on heat and mass transfer dynamics in the presence of adsorption without performing the exhaustive numerical calculations.     

Uptake of Fluoride by Al3+ Pretreated Low‐Silica Synthetic Zeolites: Adsorption Equilibrium and Rate Studies

Abstract

The removal of fluoride from single component aqueous solution using Al³⁺‐ pretreated low‐silica synthetic zeolites (Al‐Na‐HUD, Al‐HUD, Al‐F9, and Al‐A4) was studied. The effects of adsorbent mass, initial solution pH, and initial concentration on fluoride removal in a batch system were evaluated. Equilibrium data were simulated using simple isotherms such as the Freundlich (F), Langmuir‐Freundlich (LF), Redlich‐Peterson (RP) and Dubinin‐Radushkevitch (DR) isotherms. From the DR model, initial pH effects and desorption studies, it was considered that the fluoride adsorption onto the zeolites proceeded by ion‐exchange or chemisorption mechanism. In interpreting the kinetic results, reaction kinetics (using Elovich equation) and mass transfer processes (both external mass transfer and intraparticle diffusion) were considered. Equilibrium and kinetic results of fluoride adsorption onto the adsorbents demonstrated the following order of performance: Al‐Na‐HUD>Al‐F9> Al‐HUD>Al‐A4.     

超声波应用于吸附/脱附过程的研究进展

从热力学和动力学两方面介绍了近年来超声波应用于吸附/脱附过程的研究结果。比较了非超声波/超声波作用下吸附等温线的变化,分析了超声波强度、频率、第三组分的加入等因素对吸附/脱附相平衡影响;以及非超声波/超声波作用下吸附/脱附动力学的变化,并对温度、超声功率、初始浓度和颗粒大小等因素对吸附/脱附速率的影响及其原因进行分析。     

Modeling separation of proteins by inert core adsorbent in a batch adsorber

Adsorption/desorption kinetics of protein on the binding ligand of inert core adsorbent in a batch adsorber is analyzed theoretically for Langmuir isotherm coupled with the intraparticle diffusion and film mass transfer resistances. For the two limiting cases of Langmuir isotherm, there are analytical solutions. New analytical solutions are derived for Henry isotherm, and the analytical solution of shrinking core model is recommended for rectangular isotherm. The effects of the inert core radius, equilibrium constant, intraparticle diffusion and film mass transfer resistances on the time evolution of bulk concentration and particle radial profiles were investigated. The applicable range of the analytical solution with rectangular isotherm is given. A new method to estimate both film mass transfer coefficient, k_f, and effective pore diffusivity, D_pe, from a single bulk concentration-time curve in batch adsorber is given and tested with literature data for the adsorption of BSA on CB-6AS inert core adsorbent.     

Systematic investigation of SO2 adsorption and desorption by porous powdered activated coke: Interaction between adsorption temperature and desorption energy consumption

Porous carbon materials have been widely used for the removal of SO₂ from flue gas. The main objective of this work is to clarify the effects of adsorption temperature on SO₂ adsorption and desorption energy consumption. Coal-based porous powdered activated coke (PPAC) prepared in the drop-tube reactor was used in this study. The N₂ adsorption measurements and Fourier transform infrared spectrometer analysis show that PPAC exhibits a developed pore structure and rich functional groups. The experimental results show that with a decrease in adsorption temperature in the range of 50–150?℃, the adsorption capacity of SO₂ increases linearly; meanwhile, the adsorption capacity of H₂O increases, resulting in the increase in desorption energy consumption per unit mass of adsorbent. The processes of SO₂ and H₂O desorption were determined by the temperature-programmed desorption test, and the desorption energies for each species were calculated. Considering the energy consumption per unit of desorption and the total amount of adsorbent, the optimal adsorption temperature yielding the minimum total energy consumption of regeneration is calculated. This study systematically demonstrates the effect of adsorption temperature on the adsorption–desorption process, providing a basis for energy saving and emission reduction in desulfurization system design.     

The Comparison of Operating Time between Batchwise and Columnwise Adsorption

Abstract

The performance of separation processes for batchwise and columnwise adsorption with rectangular isotherms was compared. Experiments were carried out for the ion-exchange system of sodium hydroxide aqueous solution and MR-type cation exchange resin. The operating time was compared based on adsorption efficiencies with respect to the recovery of the solute and the utilization of adsorbent. Batchwise adsorption often required a shorter time than columnwise adsorption. The batchwise operation was more advantageous for greater mass transfer rate, larger adsorbent particles, and a shorter column.     

Amine modified mesocellular siliceous foam (MCF) as a sorbent for CO2

Adsorption is considered a promising method for carbon capture. CO₂ adsorbents take a variety of forms - but one approach is to fill mesoporous substrates with a polymeric CO₂ selective sorbent. SBA-15 and mesocellular siliceous foam (MCF) are high pore volume, high surface area ordered mesoporous materials for which modification with amine should result in high capacity, highly selective adsorbents. SBA-15 and MCF were separately loaded with approximately one pore volume equivalent of linear polyethyleneimine (PEI) (M_w = 2500) or branched PEI (M_n = 1200). CO₂ adsorption/desorption isotherms under dry CO₂ were obtained at 75, 105 and 115 °C. The CO₂ adsorption/desorption kinetics were improved with temperature, though the CO₂ capacities generally decreased. The adsorption capacity for MCF loaded with branched PEI at 105 and 115 °C were 151 and 133 mg/g adsorbent, respectively (in 50% CO₂/Ar, 20 min adsorption time). These are significantly higher than the adsorption capacity observed for SBA-15 loaded with branched PEI under same conditions, which were 107 and 83 mg/g adsorbent, respectively. Thus the results indicate that, on a unit mass basis, amine modified MCF's are potentially better adsorbents than amine modified SBA-15 for CO₂ capture at modestly elevated temperature in a vacuum swing adsorption process.     

巨正则系综Monte Carlo方法模拟甲烷在活性炭孔中的吸附存储

用巨正则系综MonteCarlo方法模拟了甲烷在活性炭孔中的吸附行为 .在此模拟中 ,甲烷分子采用单点LJ球型分子模型 ,狭缝活性炭孔墙采用 1 0 4 3模型 .在低温时 (T =74 0 5K) ,模拟并观察到了甲烷分子在狭缝活性炭孔中的吸附、脱附以及毛细凝聚现象 ,得到了吸附等温线和孔中流体的局部密度轮廓图 .同时 ,把所得的数据与Jiang、Rhykerd和Gubbins的模拟结果进行了比较 ,结果表明 ,模拟方法是正确的 .在此基础上 ,进一步模拟了常温下 (T =30 0K)甲烷分子在狭缝活性炭孔中的吸附存储行为 ,得到了常温下甲烷在不同孔宽活性炭孔中的吸附等温线、有效存储量随压力变化的图像以及有效存储量随孔宽变化的图像 ,并求出了狭缝孔吸附存储甲烷的最佳孔宽和合理的吸附压力 .     

Adsorption and desorption kinetics in activated carbon

Modelling of fixed bed adsorption and desorption kinetics for gas separation and purification is based on the correct representation of mass transport mechanisms on the single-pellet scale. In the case of adsorption it is commonly assumed that pore mass transport within the adsorbent particle is rate limiting. It has been questioned whether this is also true for desorption. Here the exchange step between the adsorbed state on the solid surface and the mobile state within the pore fluid was considered as being the dominant kinetic resistance. Therefore, experimental and theoretical investigations of single component adsorption and desorption of water vapour, n-hexane, cyclohexane and tetrachloroethylene on single pellets of activated carbon were performed. From the results it can be concluded that for most cases of physical gas-phase adsorption as well as desorption the overall kinetics is controlled by mass transport within the pore system of the adsorbent. The exchange step between the adsorbed phase and the fluid phase happens infinitely fast justifying the assumption of adsorption equilibrium at every position along the pellet radius.     

氮吸附法表征多孔材料的孔结构

采用低温氮吸附法表征了具有不同孔结构的碳纳米管、碳分子筛、活性炭、分子筛和石墨化炭黑等多孔材料的孔径分布。氮吸附一脱附等温线利用康塔公司NOVA3000在相对压力0．001-1范围内测定。五种材料的比表面积在100-1000m2／g之间。低压下的吸附等温线和高压下的脱附等温线分别用HK方法和BJH方法解析,结果表明:五种多孔材料既含有发达的微孔,又含有一定数量的中孔。孔径大小及其分布的细微信息在色谱采样中能够预测吸附剂的吸附性能,也是新型多孔材料开发的关键。     

活性炭吸附焦化纯苯中CS2的机理分析

对活性炭吸附焦化纯苯中CS2的吸附机理进行了初步探讨。用Freundlich方程关联出吸附等温线，并求出吸附热，结果表明吸附热较低，即吸附过程属典型的物理吸附。CS2在活性炭上的吸附动力学行为可用Elovich方程进行描述，传质系数在进料流速为1 mL／min时最大，与动态吸附试验结果一致。     

Pd(II) ion adsorption onto emulsion gel beads in a fixed bed

We developed previously an emulsion gel adsorbent for improved metal adsorption. This study focuses on a continuous adsorption–desorption process of metal ions from a solution onto emulsion gel beads using the fixed-bed method. The monodisperse millimeter-sized emulsion gel beads, a polymeric hydrogel containing randomly distributed oil microdroplets of di-n-hexylsulfide as an extractant, were prepared using an automatic production method combining sedimentation polymerization and two-fluid atomization. The isotherms and the kinetics for Pd(II) adsorption were investigated. A continuous adsorption–desorption process was successfully demonstrated, and the breakthrough curve was successfully predicted by a mathematical analysis.     

ISOTHERMAL AND NON-ISOTHERMAL MULTICOMPONENT ADSORPTION KINETICS

The model equations in the relaxation form for the multicomponent kinetics of isothermal and non-isothermal adsorption, taking into account all major distinctive features of the interphase heat and mass exchange inside porous grains and at their surface (see points 1 to 4 below) for P (“pore”) and S (“solid”) models of mass transfer within porous grains of the adsorbent, have been obtained.

First for isothermal and non-isothermal kinetics in the mixed kinetics region of mass and heat exchange in the absence natural mutual diffusion and natural thermal-diffusion the essential influence effective mutual diffusion and effective thermal-diffusion is shown.

Recommendations on the use of model equations of adsorption kinetics for describing isothermal and non-isothermal adsorption dynamics of multicomponent mixtures in the inner-diffusion and mixed (outer- and inner-diffusion) kinetic region of heat and mass exchange are made.     

改性蒙脱石吸附亚甲蓝的研究

取钠型蒙脱石和钙型蒙脱石,经铜离子交换反应使其改性。研究改性前后蒙脱石吸附亚甲蓝的能力及其受温度、介质pH值和离子强度的影响,并就吸附等温线和相关热力学参数进行分析。结果表明：不论是钠型还是钙型蒙脱石,经铜离子处理后,二者吸附亚甲蓝的能力均有所下降,但改性钠型蒙脱石下降的幅度要大于改性钙型蒙脱石;介质pH值和离子强度对蒙脱石和改性蒙脱石吸附性能的影响有差异,而吸附温度对各吸附剂吸附性能的影响程度则相近;改性蒙脱石和蒙脱石吸附亚甲蓝的等温线均能较好的符合BET和Langmuir等温方程,在298．15K下,其吸附过程均为热力学自发过程。     

Ordered mesoporous carbons with various pore sizes: Preparation and naphthalene adsorption performance

Ordered mesoporous carbons (OMCs) with tunable pores were synthesized by a soft-template method with F127 as a template and boric acid as a pore regulator agent. The prepared samples were characterized by small-angle X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and N₂ adsorption–desorption. The results show that the OMCs had well ordered, two-dimensional (2D) hexagonal structures and the pore sizes were finely tunable in the range 3.4–4.7 nm when boric acid was used as the pore regulator agent. The adsorption experiments showed that the OMCs had a strong adsorption affinity to naphthalene and the maximum adsorption amount was shown to reach up to 303.2 mg/g. Furthermore, the mesopore volume between 2 and 3.5 nm of OMCs was crucial to the adsorption capacity, and OMCs with pore sizes of 2–3.5 nm were much more favorable for the naphthalene adsorption process. The adsorption isotherms of naphthalene on OMCs matched well with the Langmuir adsorption isotherm. Theoretical studies showed that the adsorption kinetics of naphthalene on OMCs accounted well for the use of the Langmuir adsorption kinetics equation. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

ATMOSPHERIC FREEZE-DRYING PART 2 : MODELLING DRYING KINETICS USING ADSORPTION ISOTHERMS

This paper describes the modelling of atmospheric pressure freeze-drying using a fluidized bed of adsorbent. The original feature of this modelling, based on a model of the “Uniformly Retreating Ice Front” type, is the coupling of the laws of heat and mass transfer as well as the introduction into the model of adsorbent sorption isotherms. The model which describes dehydration kinetics has been validated further to experiments on potatoes. The working parameters of the facility were optimized thanks to the model. This new freeze-drying process may well be useful for small freeze-dried products dried at a temperature close to their melting point.     

蛋白质的膨胀床吸附过程穿透模型分析

引　言膨胀床吸附技术是近十几年来出现的一种新型生物分离模式 .该技术集细胞碎片清除、料液浓缩和蛋白质纯化等步骤于一身 ,大大提高了目标产物收率 ,降低了纯化时间和费用 .自 1993年Streamline系列膨胀床吸附介质和装置问世以来 ,国外已有不少利用膨胀床吸附技术提取蛋白质的报道[1,2 ] .已有研究表明 ,料液特性、吸附剂粒径等对膨胀床的流体力学特性和蛋白质在膨胀床内的吸附行为有着不同程度的影响[3～ 5] .考察这些影响因素有助于加深对膨胀床层析行为的理解 ,指导膨胀床层析的优化设计 .然而 ,由于膨胀床层析过程的复杂性 ,众多因素相互作用 ,某一参数的改变往往引起操作参数的系统性变化 ,因此实验条件下考察单一参数的改变对膨胀床层析过程的影响是不现实的[5,6 ] .　　　前期研究表明 ,对不同黏度的缓冲液 ,穿透模型能够较准确的预测蛋白质的穿透行为 .因此 ,本研究在前期研究的基础上[4 ,7] ,利用穿透模型分析了膨胀床吸附过程的质量传递和流体力学特1　穿透模型该模型假设[4 ,5] :①吸附剂颗粒为球形 ,有均一的尺寸和密度 ,离子交换基团均匀地分布在颗粒内部 ;②床内径向不存在浓度梯度 ;...