Effects of adsorption kinetics and surface heterogeneity on band spreading in perfusion chromatography—a network model analysis

A network model was used to simulate the band-spreading of an eluting solute from a perfusive column under retained conditions. The computer experiments were carried out over a wide range of Peclet numbers. The effects of pore size distribution (PSD), pore inter-connectivity and linear adsorption/desorption kinetics were taken into account in the simulations. Surface heterogeneity effects were also discussed. Among these parameters investigated, adsorption/desorption kinetics was the most important parameter, which influenced the transit-time moments and, in turn, the band-spreading as well as band-tailing results significantly over the whole range of Peclet numbers investigated. In addition, pore inter-connectivity and PSD also play an important role in determining the band-spreading results. However, their effects are only important in the molecular diffusion- and convection-controlled regimes. Under strongly retained conditions, contribution of hydrodynamics can be neglected. Furthermore, surface energetic heterogeneity resulting from the wide pore size distributions could exacerbate both band spreading and band tailing; the effects on band tailing being more significant than those on band spreading.     

亲和层析介质非特异性吸附的定量表征研究

针对亲和层析介质的非特异性吸附,基于脉冲响应法,建立了定量表征方法。以牛血清白蛋白、酵母发酵液和CHO细胞培养液作为典型杂质,考察了四种蛋白A亲和层析介质和两种基质微球,在不同pH和盐浓度条件下非特异性吸附。发现介质和基质对杂质均有不同程度的吸附,在酸性条件下非特异性吸附相对较强。对于不同料液,存在不同的杂质吸附机制,可通过静电、疏水作用或两者共同作用结合。两种介质和基质的比较结果表明,琼脂糖基介质的非特异性吸附主要依赖其基质微球与杂质间相互作用,而聚甲基丙烯酸酯基介质对杂质的吸附作用强于其基质微球。结果表明,本文建立的非特异性吸附定量表征方法切实可行,可用于量化表征介质非特异性吸附,探究相关作用机制,为介质研发提供新的分析方法和依据。     

Separation of palm carotene from crude palm oil by adsorption chromatography with a synthetic polymer adsorbent

Palm carotene was successfully concentrated from crude palm oil by a single-stage chromatographic process on a synthetic porous polymer. Carotene was concentrated to about 10⁵ ppm solution, which is about 160 times the original concentration in crude palm oil. Carotene recovery varied from 40 to 65% depending upon chromatographic conditions. The fatty acid composition of the palm oil did not change during the carotene recovery process, and the carotene composition was also almost the same as that in palm oil. Adsorption isotherms of the adsorbent differed from other adsorbents. This new recovery method for palm carotene may be suitable as an edible palm oil pretreatment process due to its efficient mass recovery of a valuable bioresource.     

Effect of ultrasound on liquid phase adsorption of azeotropic and non-azeotropic mixture

Relative adsorption experiments of azeotropic and non-azeotropic mixture were separately conducted at constant temperature with and without the presence of ultrasound. The ultrasound wave was applied at a frequency of 21 kHz with 25% amplitude at atmospheric pressure. The adsorption of azeotropic and non-azeotropic mixture was analysed using monolayer adsorption theory and at lower liquid equilibrium concentration it followed a Langmuir type of equation. The adsorptive capacity of azeotropic and non-azeotropic mixtures on activated carbon was found to decrease but the selectivity was increased. The result also showed that the azeotropic point of relative adsorption was noticeably moved due to the ultrasound effect.     

Molecular simulation of hydrogen adsorption in organic zeolite

The adsorption of molecular hydrogen on model zeolites has been simulated employing Grand Canonical Monte Carlo (GCMC) procedure. The effects of cation type, available volume, surface area, temperature, pressure and pre-adsorbed organics such as benzene on the hydrogen uptake are analyzed. The hydrogen adsorption can be affected mainly by the available volume and surface area per g-zeolite at the same temperature and pressure. Increase of temperature results in the decrease of sorption intensity and capacity. The adsorption capacity correlates well with the pressure with high linearity at room temperature. Adsorption is lowered by the pre-adsorbed benzene molecule. The orientation and the number of benzene molecule in zeolite affect the adsorption capacity. The organic zeolite with larger available volume shows larger adsorption capacity.     

Effect of temperature on the removal of lead(II) by adsorption on China clay and wollastonite

The removal of Pb(II) from aqueous solution by adsorption on china clay and wollastonite is an attractive process. The amount of Pb(II) removed by adsorption is highly dependent on the temperature of the adsorbate solution and favours low temperature. The equilibrium times were noted, i.e. 90 min for china clay and 120 min for wollastonite. The various rate parameters of the adsorption process have been determined at different temperatures. The activation energies were determined and found to be ?5.345 kJ mol^?1 and ?8.730 kJ mol^?1 for Pb(II)-china clay and Pb(II)-wollastonite systems, respectively. The adsorption isotherm was measured experimentally at various temperatures. The negative values of enthalpy change (ΔH = ?77.95 kJ mol^?1 and ?16.40 kJ mol^?1 for china clay and wollastonite, respectively) indicate the exothermic nature of the adsorption processes for both systems. The isosteric heats of the adsorption process have been determined at various surface coverages of the adsorbents used. The various thermodynamic parameters have been calculated to elucidate the mechanism involved in the adsorption process.     

Effects of ionic strength and pH on the adsorption equilibria of lysozyme on ion exchangers

The effects of ionic strength and pH on adsorption of lysozyme to three strong cation exchangers have been studied. Adsorption equilibrium data obtained using the batch techniques corresponded well to the Langmuir isotherm. Ionic strength had a considerable influence on the isotherms. In all cases, the maximum binding capacity of the three exchangers decreased while the apparent dissociation constant increased with increasing ionic strength. The maximum binding capacity also decreased while the apparent dissociation constant was not significantly affected by an increase in pH. It was found that the three exchangers exhibited different levels of binding capacity under identical solution conditions. This was shown to be caused by variation in the arrangement and distribution of charged groups. However, the ion-exchange matrix had little effect on the apparent dissociation constant.     

迎头色谱法测定人参皂苷Rg1和Re的吸附量

制备色谱分离条件优化的基础是吸附等温线的测定及保留时间的预测。本文以人参皂甙Rg₁、Re为研究对象，用色谱单柱制备了人参粗粉中的人参皂甙Rg₁、Re,以迎头法测定了人参皂甙Rg₁、Re在C₁₈球形固定相中的吸附等温线，在竞争Langmuir模型基础上确定了吸附参数G和b，并应用非线性色谱理论的结果预测了人参皂甙Re的保留时间，上述结果与实验值进行了比较，平均相对误差为3.68%。在实验中发现了运用竞争Langmuir模型进行拟合的一些问题并进行了讨论。     

Effect of adsorption characteristics of a modified cellulase on indigo backstaining

The effect of limited proteolysis (digestion) of a commercial cellulase preparation (Ecostone^® L350) on backstaining with indigo was investigated. The influence of protease (papain) concentration on limited proteolysis of cellulase preparation was studied, applying different ratios of papain/cellulase (w/w). Changes in adsorption on Avicel cellulose of the non‐digested compared with the papain‐digested Ecostone^® L350 were examined using the Langmuir adsorption isotherm. The non‐digested Ecostone^® L350 exhibited stronger interaction to Avicel cellulose compared with the digested form, while the maximum efficiency of cellulase adsorption to Avicel cellulose decreased after digestion. When papain‐digested Ecostone^® L350 was applied on cotton fabrics during the dyeing procedure with indigo, a reduction of indigo backstaining was obtained compared with the non‐digested Ecostone^® L350. Copyright © 2004 Society of Chemical Industry     

Feasibility of reactive chromatography for the production of 2-phenyl ethyl acetate

Reactive chromatography is a novel process intensification option when the progress of a reaction is hampered by reversibility (e.g., esterification and acetalization). In this work, we study its feasibility for the production of 2-phenyl ethyl acetate (PEAct) by esterification of 2-phenyl ethyl alcohol with acetic acid using Amberlyst-15 as a catalyst/adsorbent. The reaction kinetics is investigated in a laboratory batch reactor by varying various parameters such as agitation speed, temperature, feed molar ratio, catalyst loading, and particle size, and a Langmuir Hinshelwood kinetic model is proposed. The reaction is then studied in a fixed-bed chromatographic reactor (FBCR). Non-reactive binary adsorption experiments are performed in the same setup to estimate the corresponding parameters of the Langmuir adsorption isotherm. The experimentally observed reactive breakthrough curves in FBCR reveal that RC is a promising process option for the production of PEAct. Furthermore, it is shown that the FBCR model, which uses kinetics and isotherms developed in this work, explains the reactive breakthrough curves and the regeneration performance reasonably well. The work reported here forms a base for the design of a simulated moving-bed reactor that may be used for large-scale production.     

Dependence of critical condition in liquid chromatography on the pore size of column substrates

The dependence of critical condition in liquid chromatography on the pore size of column substrates was investigated by Lattice Monte Carlo simulations. In the current study, the pore was modeled by a square channel and polymer chains were modeled by both the random walk (RW) and the self-avoiding walk (SAW) models. When the polymer chains were modeled by the RW model, the critical conditions in the square channels with different channel widths remained the same as the critical condition on a single surface if the special edge effect was eliminated. For the SAW chain, the shift of critical condition with the square channel width was still observed even when the special edge effect of square channel was eliminated. This confirms the results reported in our earlier study (Macromolecules 2004, 37, 10073-10078) that the critical condition in square channel pore shifts as pore width decreases. Since the square channel pore is a better representation of the actual pore shapes in a liquid chromatography column than the slit pore, the current study confirms that the shift in critical condition with pore size is a true phenomenon. A recent experimental study also confirms the shift (J. Polym. Sci. Polym. Phys. 2009, 47, 2533-2540).     

氯丙酸改性壳聚糖对Hg~(2+)的吸附性能研究

研究了改性壳聚糖对重金属Hg2+的吸附特性,包括吸附动力学和吸附等温式,且研究了pH、反应时间对其吸附性能的影响.结果表明:羧乙基壳聚糖对Hg2+的吸附在不同温度下符合Freundlich和Langmuir吸附等温式,吸附过程动力学适合二级反应.当pH为4～6,吸附时间为180 min时,羧乙基壳聚糖对Hg2+有较高吸附效果.     

The effect of number of pressure equalization steps on the performance of pressure swing adsorption process

Cycle sequence has an important effect on the performance of pressure swing adsorption (PSA) processes. Pressure equalization steps influence significantly the purity and recovery of product, and therefore, may be properly designed to improve the performance of PSA processes. Open literature lacks of a systematic study on the effect of cycle sequence design on the performance of a specific PSA process as a controlling parameter. In this work, the results of recent studies on different cycle schedule design strategies have been used as a basis for comparing various cycle schedules (proposed by the authors of this work) on the performance of a six-bed PSA process for hydrogen purification. Three different cycle sequences have been designed, the pressure equalization and idle steps consisting the main controlling parameters. Simulation results showed that designs with more pressure equalization steps result in higher product recovery and those with less pressure equalization steps result in higher product purity. The proper performance of a PSA process is a tradeoff between product recovery and product purity. In this view, a target function has been developed that enables us to lump the latter performance parameters into one function for comparing the performance of the different cycles employed.     

Study of the CO2 adsorption isotherms on El Hicha clay by statistical physics treatment: microscopic and macroscopic investigation

ABSTRACT

CO₂ introduction in deep aquifers based on adsorption phenomena represents geological tanks that reduce CO₂ emission. Thus, investigating carbon dioxide adsorption on rocks is becoming more interesting. In our work, carbon dioxide adsorption on El Hicha clay is extensively studied. Experimental data for CO₂ adsorption on this clay are given for the first time. All the corresponding parameters are simulated and interpreted using the multilayer model with two interaction energies. The effect of the key parameters involved in the adequate model on the isotherm curves are thus elucidated and interpreted. The formulation of this model is based on statistical physic formalism. Several hypotheses involving some physicochemical parameters which describe perfectly the adsorption process are used.

The characteristic parameters of the adsorption isotherm such as the number of carbon dioxide molecules per site (n), the receptor site densities (N_M), the number of adsorbed layers (N_L) and the energetic parameters (-ε₁) and (-ε₂) are estimated for the studied systems by a nonlinear least square regression. These parameters are discussed and interpreted considering their temperature dependence. In order to provide new macroscopic interpretations of adsorption mechanisms, three thermodynamic functions are also determined such as the entropy, the internal energy and the free enthalpy of Gibbs from experimental data. Thus, we prove theoretically and experimentally that CO₂ adsorption on El Hicha clay is feasible, spontaneous and exothermic in nature.     

Effect of surface properties of activated carbons on surfactant adsorption kinetics

This research investigates the adsorption properties of three activated carbons (AC) derived from coconut, coal, and wood origin. A linear relationship exists between the number of water molecules adsorbed onto each AC and the oxygen content determined elemental analysis and XPS. An inverse linear relationship exists between the plateau amount of dodecanoic acid anionic surfactant and the oxygen content on the surface of ACs. The surface charge on each AC’s surface had a linear relationship with the plateau amount of dodecanoic acid. A plug-flow heterogeneous surface diffusion model (PFHSDM) for a fixed-bed adsorption process was developed to describe the adsorption kinetics in a fixed-bed column. The model represents axially dispersed plug-flow, external mass transfer, adsorption equilibrium on the fluid-particle interface, and intraparticle diffusion. The larger molecular dimension of the dodecanoic acid as a more hydrophobic entity than octanoic acid led to a faster external mass transfer rate but a slower surface diffusion rate as estimated from the PFHSDM. The interaction between the organic moiety of surfactant and the AC surface chemistry such as surface oxygen content and surface charge contributes to the adsorption performance in both to the adsorption equilibrium and kinetics.     

Determination of the diffusion coefficients of organic solvents in polyepichlorohydrin: A comparative study of inverse gas chromatography and sorption methods

The diffusivity of organic solvents in polyepichlorohydrin was studied with two different experimental setups: inverse gas chromatography (IGC) with packed columns and sorption measurements in gravimetric experiments monitored in a Cahn electrobalance. The aim of this work was to test the possibility of solving an inherent problem in the data reduction of IGC measurements, that is, the necessity of characterizing the morphology of the polymer coated on the support (usually given in the so‐called geometric factor of the column). Temperatures between 35 and 65°C were used in the IGC experiments, whereas the sorption measurements were performed between 30 and 40°C. Glass beads were used as supports in IGC for obtaining data concerning the variation of the plate height with the average gas velocity, with which the use of the Van Deemter equation allowed the determination of the diffusion coefficient if the geometric factor was known. In the sorption experiments, the diffusion coefficients at different penetrant activities were directly measured. For their extrapolation within the same concentration range used for IGC (infinite dilution of the penetrant), the theoretical model of Vrentas and Duda was used. By a combination of sorption and IGC experiments, the geometric factor of an IGC column could be adjusted, and this allowed the determination of the diffusion parameters of any other solvent in the same column. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2216–2223, 2003     

吸附树脂极性的高效液相色谱法测定及表征

建立了测定及表征吸附树脂极性的高效液相色谱法。DA-201极性树脂、AB-8弱极性树脂和D-101非极性树脂分别填充高效液相色谱柱,以去离子水为流动相,葡聚糖为示踪剂,流速1.0 mL/min,柱温30℃,测定树脂的极性。结果表明,正丁醇、乙醇均可作为单一探针分子,流出顺序可定性表征吸附树脂极性:DA-201极性树脂AB-8弱极性树脂D-101非极性树脂;采用乙醇/甲醇作为探针分子组,通过相对极性法计算,得到3种吸附树脂的定量极性值:DA-201极性树脂极性值100,AB-8弱极性树脂极性值18,D-101非极性树脂极性值0,相对标准偏差(RSD)均小于1.50%。方法稳定可靠,可以有效表达吸附树脂的极性。     

Modeling of the Chromatographic Solvent Gradient Reversed Phase Purification of a Multicomponent Polypeptide Mixture

Abstract

A model for Calcitonin purification from an industrial peptide mixture using polymer‐based reversed phase columns was developed. Regressed competitive bi‐Langmuir isotherm parameters for pure calcitonin are strong functions of the eluent composition and were correlated to the overall Henry coefficient only. It is shown that, by keeping constant these correlations, the adsorption behavior of impurities can be predicted simply by estimating their Henry coefficient from the raw mixture. The same can be repeated with very good results when changing the stationary phase or the organic solvent in the eluent. In both cases, only the Henry coefficient must be re‐estimated from pulse injections.     

Effect of particle size on the adsorption and desorption properties of oxide nanoparticles

Using water molecules as a model adsorbing compound, the effect of particle size on the adsorption and desorption properties of porous oxide nanoparticles (NPs) was investigated at different temperatures. The moisture concentration on the surface of NPs was measured by monitoring the infrared spectra peaks corresponding to the stretching vibration of water molecules. A transient multilayer model was developed to represent the fundamental steps in the process. The thermal stability of adsorbed species and the strength of bonding to the surface were evaluated by determining the activation energies of various steps. The results indicate that the surface interaction parameters are both temperature and particle‐size‐dependent. Smaller NPs have a higher saturated surface concentration and a slower response to purging and desorption. As temperature decreases, NPs exhibit a higher saturated moisture concentration and are more prone to the adsorption of moisture and similar contaminants. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1502–1510, 2013     

焙烧条件对煤系高岭土吸附城市生活污水中有机物的影响

利用L16(45)正交试验考察了焙烧温度、焙烧时间、颗粒大小和硫酸浓度对煤系高岭土吸附城市生活污水中有机物的影响。结果表明当焙烧温度为700℃,焙烧时间为30 min,颗粒粒径为0.106 mm(150目)和硫酸质量分数为80%时,煤系高岭土对城市生活污水中有机物的吸附率达到最大值。