吸附热预测吸附等温线

实验测定了N2 在沸石分子筛、C2 H6 在活性炭、CO2 在硅胶上的吸附等温线 ,研究用Clausius Clapeyron方程求得等量吸附热、再利用所得的吸附热预测其它温度的吸附等温线数据的方法。将吸附热预测的等温线与实验值及插值法内插得到的吸附等温线数据进行了比较 ,结果表明吸附热预测值与实验值吻合较好。此外还对文献数据利用等量吸附热预测较高压力 ( 65 0kPa)下的等温线 ,均与文献中的实验值一致。为吸附工业操作需要不同温度下的等温线数据和吸附过程的模拟与设计提供了简便、准确的计算方法     

Characteristics of as-prepared biochar derived from catalytic pyrolysis within moderate-temperature ionic liquid for CO2 uptake

A promising biochar as solid adsorbent for CO₂ uptake was prepared by the catalytic pyrolysis of coconut shell in moderate-temperature ionic liquid (IL). Then, it was characterized by means of SEM, EDS, BPEA, BET, NLDFT, FTIR, and TG-DSC, and a mechanism interpretation of the porous biochar formation was conducted. In addition, the adsorption characteristics of CO₂ on the as-prepared biochar, such as adsorption capacity, adsorption potential, isosteric heat, and static selectivity at different adsorption temperatures and pressures, were systematically evaluated. The results indicated that the as-prepared biochar exhibited an adequate CO₂ adsorption with a capacity of 4.5 mmol/g at 273 K and 100 kPa. Then, a significant number of slit-like pores were revealed to exist on the as-prepared biochar with a peak pore size between a range of 0.6 nm-2 nm. The porous structure formation was ascribed to the release of carbon-, hydrogen-, oxygen-, sulphur-, and nitrogen-containing compounds during biochar preparation. Meanwhile, both the adsorption potential and isosteric heat of the CO₂ uptake under the tested conditions decreased with an increase in the adsorption capacity, which ranged from 33 kJ/mol-21 kJ/mol and 23 kJ/mol-7 kJ/mol, respectively. Therefore, the isosteric heat could be considered as a piecewise function of adsorption capacity. In addition, the molar ratios of CO₂ over N₂ adsorbed under the tested conditions were above 11 and were accompanied by molar ratio peaks of 26 at 273 K and 19 at 298 K, respectively. Moreover, an interesting phenomenon occurred: the static adsorptive selectivity of CO₂ over N₂ first increased and then decreased and there was an increase in the adsorption pressure at the tested adsorption temperatures.     

吸附制冷用复合吸附剂的吸附等温线推算

用真空重力法测定了水和乙醇在自制复合吸附剂上的吸附等温线。采用由微孔填充理论导出的吸附平衡方程对所测得的等温线进行了拟合,计算相应的吸附热;对用Clausius Clapeyron方程推算吸附等温线的方法进行了讨论,并推算有关吸附等温线。结果表明:水在自制复合吸附剂M1 0001和M1 9906上平衡吸附量的推算值与实测值之间的相对误差<10%;乙醇在自制复合吸附剂上的推算误差<15%。给出了推算等温线和获得等压线的简便方法。     

温度-压力-吸附方程在计算煤岩等量吸附焓的应用

用鄂尔多斯盆地的长焰煤、肥煤、瘦煤和贫煤4个煤样的系列等温吸附实验数据来验证一个温度-压力-吸附方程,并探讨等量吸附时吸附平衡压力与温度之间的函数关系。用克劳修斯-克拉佩龙方程求等量吸附焓。提出单位等量吸附焓的概念及计算方法。结果表明：煤样等量吸附焓为负值,证实吸附过程是个放热过程;对于同一煤样,单位等量吸附焓随吸附量的增加而下降是由于吸附介质表面的能量不均匀性所造成。正因为吸附过程是个放热过程,所以吸附先发生在能量较高的位置上,以便放出更多能量;在相等吸附温度和压力条件下,高阶煤有较大的单位等量吸附焓,必有较大的吸附量。同时高阶煤吸附量随着吸附温度的升高而快速衰减,而中低阶煤吸附量衰减却没有那么明显。     

A comparison of isotherm and kinetic models for binary-solute adsorption to affinity membranes

Single-solute isotherms for pepsin (EC 3.4.23.1) and chymosin (EC 3.4.23.4) adsorption to affinity membranes were fitted using five of the most popular isotherm models. It was found that the single-solute Langmuir isotherm was the best two-parameter model, although the three-parameter models gave even better fitting. Experimental binary-solute adsorption isotherms were compared with four different types of binary-solute Langmuir models using the single-solute parameters. The results showed that the difference in the saturation capacities affected the adsorption equilibrium. Furthermore, three types of binary-solute Langmuir models were converted into the kinetic form and used to calculate the association rate constants of pepsin and chymosin from experimental data. The best-fitted rate constant values were found to be identical for different kinetic models. However, the model predictions of association curves were significantly influenced when the values of association rate constants were changed.     

Relationship between breakthrough curve and adsorption isotherm of Ca(Ⅱ) imprinted chitosan microspheres for metal adsorption

In this work, an equilibrium-dispersion model was successfully established to describe the breakthrough performance of Ca(II) imprinted chitosan (Ca(II)-CS) microspheres packed column for metal adsorption, and the assumptions of Langmuir isotherms and axial dispersion controlled mass transfer process were confirmed. The axial dispersion coefficient in Ca(II)-CS microspheres packed column was found to be almost proportional to the linear velocity and fit for prediction through single breakthrough test. Sensitivity analysis for breakthrough curve indicated the axial dispersion coefficient as well as Langmuir coefficient was sensitive variable for deep removal requirement. The retrieval of the adsorption isotherms of Ca(II)-CS microspheres from breakthrough curve was fulfilled by model ing calibration. A strategy based on the correlation between adsorption isotherms and breakthrough performance was further proposed to simplify the column adsorption design using absorbents with smal/uniform size and fast adsorption kinetics like Ca(II)-CS microspheres to cut down the gap between lab and industry.     

Experimental and theoretical study of methane adsorption on granular activated carbons

The experimental and theoretical study of methane adsorption on granular activated carbons is presented. The adsorption data are modeled by various isotherm equations. Toth equation is found to have the best fit. The isosteric heat decreases with loading and increases weakly with temperature, which is an indication of heterogeneity of the methane and granular activated carbon system. Using optimized parameters from Toth equation, a novel procedure is developed to calculate the integral heat of adsorption, which is the total amount of isosteric heat of adsorption at a given temperature and pressure during the adsorption process. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

The applicability of the numerical algorithm for the evaluation of isosteric heat of adsorption

The calculation of isosteric enthalpy from an adsorption equation, and the comparison of theoretical enthalpy plot with the values measured calorimetrically is the fundamental condition for the verification of the correctness of an adsorption model. However, sometimes it is very difficult to get a simple analytical form of adsorption heat equation i.e. the isosteric heat of adsorption cannot be easily calculated from the thermodynamic van’t Hoff relation. For such cases we propose the new numerical algorithm. The applicability of the algorithm is checked out for two cases of the D’Arcy and Watt water adsorption isotherm equations. It is shown that the algorithm can be successfully applied for the thermodynamic verification of arbitrarily chosen adsorption isotherm equation, even possessing complicated form that disables simple analytical derivation of the heat formula.     

Multicomponent adsorption isotherm modeling using thermodynamically inconsistent and consistent models

In this work, the multicomponent adsorption modeling of the experimental adsorption data of ternary system consisting of nitrobenzene (NI), phenol (PH) and aniline (AN) onto granulated activated carbon (GAC) was performed. The Redlich–Peterson and Freundlich isotherm models provided better fitting of the single component experimental data than the Langmuir isotherm model. The adsorption preference of GAC was found to be: NI > PH > AN. The ternary adsorption equilibrium data were analyzed by using thermodynamically consistent and inconsistent isotherm models as well as an artificial neural network model. Modified Redlich–Peterson and LeVan–Vermeulen models, and real adsorbed solution theory model provided satisfactory fit of the ternary system. Levenberg–Marquardt back-propagation or scaled conjugate gradient back-propagation algorithm with two neurons, either logsig or tansig transfer function in the hidden layer, and purelin transfer function in output layer were found to be the best network and gave an excellent prediction of experimental data.     

利用二维流体分子热力学模型计算气体混合物在固体界面的吸附等温线

结合流体混合规则,将之前建立的二维变阱宽方阱链流体分子热力学模型（SWCF-VR-2D）扩展至混合流体,并利用模型计算了甲烷/二氧化碳、甲烷/氮气和甲烷/乙烷等气体混合物在不同吸附剂上的吸附等温线。由于混合气体间的相互作用会使得混合气体的吸附不同于单一气体的吸附,通过调节气体与固体壁面间的相互作用参数ε_w以描述这种变化。调节能量参数后模型能满意计算混合气体的吸附等温线,总的平均偏差为5.06%。     

On the derivation of the state equation in models of adsorption from solution

A new procedure for the derivation of the equation of state in models of adsorption from solution is developed. Based on thermodynamics a simple relation between the surface pressure and the chemical potential of one reference solvent state is established, making the calculation of the state equation straightforward in cases where the chemical potentials of the adsorbed particles are known. The relation is applied to various lattice models for the derivation of their equation of state. The calculation of the state equation directly from the Helmholtz free energy of mixing of the surface layer and the bulk solution is also indicated.     

利用二维变阱宽方阱链流体分子热力学模型计算吸附等温线

以二维硬碟流体为参考,借助现代分子热力学研究方法建立了一个二维变阱宽方阱链流体的分子热力学模型(SWCF-VR-2D),并将建立的模型用于气体在固体界面吸附的关联计算中,获得了相应吸附质和吸附剂的模型参数。发现模型能满意再现氮气、甲烷、乙烷、乙烯等气体在硅胶、活性炭、沸石、金属有机骨架(MOF)等不同固体界面上的吸附等温线,总的平均绝对偏差为3.42%,其中能量参数ε _w反映了吸附剂与吸附质之间的相互作用大小。     

Sorption Characteristics of Whole Pistachio Nuts (Pistacia Vera L.)

ABSTRACT

Moisture sorption characteristics of whole pistachio nuts were investigated at 10, 20, and 30°C using the static method. The sorption isotherms exhibited hysteresis over the range of 0.10-0.80 water activity which was succesfully interpreted using BET, GAB, Oswin, Smith, Henderson, Chung-Pfost and Halsey mathematical models and from which the BET, GAB and Oswin models were found to give the best fit. Monolayer moisture content of pistachio nuts was determined from BET and GAB equations and the isosteric heat of sorption data were derived using Clausius-Clapeyron equation and presented in graphical form. The information generated can be utilized to optimize the packaging parameters for long term storage of pistachio nuts.     

Prediction of thermodynamic properties of aqueous electrolyte solutions using equation of state

In this study, a predictive model is presented for estimation of second order thermodynamic properties of electrolyte solutions. In order to provide a comprehensive understanding, the capability of modified electrolyte PC‐SAFT up to high pressure and temperature has been studied. In addition to the first order derivative thermodynamic properties, the Gibbs free energy, enthalpy and heat capacity of aqueous electrolyte solutions at infinite dilution are predicted. Using new methodology, the dielectric constant is modified to keep the pressure, temperature, and ionic strength dependency. Our results show that the Born term has a significant contribution on prediction of second order derivative properties. Meanwhile the impact of temperature‐dependent solution dielectric constant on standard state heat capacity is studied. Finally, the isobaric heat capacity at various salt concentrations is predicted without any adjustable parameters. The results of this work indicate an acceptable agreement with experimental data especially at high pressure and temperature. © 2017 American Institute of Chemical Engineers AIChE J, 2017     

氢在多壁碳纳米管上的等量吸附热

为说明氢在多壁碳纳米管(MWCNTs)上所受吸附作用的强弱,文中基于氢和77 K氮的吸附数据,比较了由非局域密度泛函理论(NDFT)、等量吸附线和归一化等温线线性化确定的等量吸附热。结果表明,氢在MWCNTs上等量吸附热随温度变化且表现出在弱的能量不均匀表面吸附的特点,平均值约为3—4 kJ/mol;由77 K氮吸附等温线确定的孔大小分布(PSD)和比表面积影响NDFT计算初始吸附时的精度;在吸附量和吸附温度都较低时,等量吸附线标绘结果与归一化等温线线性化方程确定的等量吸附热之间的偏差较小,在200—290 K温度区间则与ND-FT计算结果更为接近。然而,当温度大于310 K时,3种方法计算结果间的偏差较大。     

An analytical equation of state for water and alkanols

An analytical equation of state extended from statistical associating fluid theory (SAFT) is modified to describe the thermodynamic properties of fluids with high polarity such as water and alkanols up to the region close to the critical point. Five terms are used in the equation of state: the term for hard convex body, the term for dispersion energy, the term for the chain formation of hard convex body, the term for the change of the dispersion energy because of chain formation, and the term for dipole-dipole interaction. This equation of state is still called SAFT-CP (across critical points). Six fluids water, methanol, ethanol, 1-propanol, 1-butanol and 1-pentanol are used as examples. The new equation of state reproduces saturated pressures and densities in vapor-liquid equilibrium, critical properties (as temperature, pressure and density), and densities in the one-phase region with rational accuracies. The comparison of the calculated critical exponent β with the experimental one for methanol shows the improvement up to the region only with 20 K difference of temperature to the critical point. The result coincides with the estimation of the critical region on the basis of Ginzburg number and also with the available opinion that crossover methods and renormalization theories are necessary in the near-critical region.     

颗粒分布对吸附热变换器内传热传质的影响

采用直接接触法提高吸附热变换器内的传热传质速率,回收热水直接生成过热蒸汽。对蒸汽生成过程进行数值建模,耦合质量、能量和动量方程。气液固的三相计算被合理简化成两个由一个移动水-气界面连接的两相区域计算。模拟研究填充床内的沸石颗粒分布如松散-密集型和密集-松散型对蒸汽生成的影响。两种填充床生成蒸汽的总质量相同。密集-松散型生成蒸汽的时间短,但生成速率快。密集-松散型生成蒸汽与入水的时间比值为58.8%,生成的蒸汽均保持在峰值,最高温度达249℃,系统整体温升达139℃,而松散-密集型生成的蒸汽仅有1/3保持在峰值。密集-松散型出口处与水-气液面产生蒸汽的质量比值大,表明该床层的颗粒分布更有利于蒸汽的快速通过。     

Generalization of thermodynamic Langmuir isotherm for mixed-gas adsorption equilibria

This work presents a comprehensive thermodynamic model for both pure component isotherms and mixed-gas adsorption equilibria. A generalization of thermodynamic Langmuir isotherm, the proposed model assumes competitive adsorption of multiple adsorbates on adsorbent surface for mixed-gas adsorption equilibria, and it applies an area-based adsorption nonrandom two-liquid activity coefficient model in the activity coefficient calculations for the adsorbate phase. The resulting generalized Langmuir isotherm properly captures both surface loading dependence and adsorbate phase composition dependence for mixed-gas adsorption equilibria. The model is validated with accurate representations of gas adsorption equilibrium data for varieties of unary, binary, and ternary gas systems. The model results are further compared with those calculated from extended Langmuir isotherm and Ideal Adsorbed Solution Theory.     

Statistical modeling of adsorption isotherm of potassium on aza[7]helicene-coated gold electrode attached to quartz crystal microbalance

ABSTRACT

A chemically coated piezoelectric sensor has been used for the determination in liquid phase of the adsorption isotherm of potassium. A thin film of aza[7]helicene was attached to the surface of a gold electrode of a quartz crystal microbalance using spin coating method.

Statistical physics formalism was applied to elucidate the adsorption mechanism of potassium onto coated electrode by aza[7]helicene. The simulation results showed that a monolayer adsorption occurs with the number of potassium per site about 1 and the adsorption energy is less than 30 kJ.mol^?1, characteristic of physical adsorption.

The statistical model was used to investigate three thermodynamic potentials such as the entropy, the free enthalpy, and the internal energy. It is found that the adsorption took place with releasing energy, such behavior confirms the exothermic character of the adsorption process.