Multicomponent sorption kinetics of ethane and propane in activated carbon: simultaneous adsorption

Extensive experimental data of binary adsorption kinetics of ethane and propane onto Ajax activated carbon are collected by using a 'differential adsorption bed' over a range of particle sizes and shapes, bulk concentrations and temperatures. A multicomponent model incorporating macropore, surface and micropore diffusion mechanisms recently proposed by Hu and Do (Chem Eng Sci (in press)) is used to predict the binary adsorption dynamic data by using information of single-component isotherms and dynamics. The multicomponent adsorption equilibrium is calculated by using the ideal adsorbed solution theory (IAST), with the single-component isotherm described by a Unilan equation. The model is found to describe the binary adsorption kinetics well and in particular it accurately predicts the degree of the overshoot of the fast-diffusing/less-strongly adsorbed species.     

Ternary desorption and displacement kinetics of gases in activated carbon

Both desorption and displacement kinetic experimental data of gases in activated carbon are presented in this article for ternary systems of ethane, propane and n-butane. Experiments are carried out under various temperatures, particle sizes and shapes. The collected data are compared with the predictions obtained from a multicomponent heterogeneous diffusion model proposed by Hu and Do (AIChE J (1993) 39 1628) using single-component equilibrium and mass transfer parameters.     

Modeling of thermal cracking kinetics—II: Cracking of iso-butane,of n-butane and of mixtures ethane—propane—n-butane

Molecular reaction schemes for the pyrolysis of isobutane and normal butane were derived from experimental products distributions, radical mechanisms and thermodynamic principles. The associated parameters were estimated by non linear regression using a Marquardt routine for the minimization of a suitable objective function. The discrimination between the rival models was based on physical criteria, statistical tests and the closeness of fit. The prediction of the product distributions of the cracking of binary mixtures of normal and isobutane, n-butane and ethane, n-butane and propane and the ternary mixtures of n-butane, propane and ethane was based upon a model obtained from the superposition of the models for single component cracking.     

Multicomponent sorption kinetics of hydrocarbons in activated carbon: Simultaneous desorption and displacement

Binary desorption and displacement kinetics of ethane and propane in Ajax activated carbon are studied in this paper to further understand the multicomponent adsorption of light hydrocarbons onto activated carbon. The experimental data are collected using a differential adsorption bed over a range of temperatures, bulk concentration combinations, particle sizes and shapes. A macropore, surface and micropore diffusion (MSMD) model recently proposed by Hu and Do (Chem Eng Sci (1993) 48 1317) is used in the analysis of experimental data. This model takes into account the concentration dependency of the surface diffusivity. Both diffusions of free and adsorbed species are allowed for in the theory. The adsorbed species are assumed to diffuse in the particle as well as in the microparticle (grain) coordinates. An imaginary gas-phase concentration concept is used to calculate the local diffusion flux of the adsorbed species inside the microparticle. The local multicomponent adsorption equilibrium at any point within the particle is calculated using the ideal adsorbed solution theory (IAST), with the single-component adsorption equilibrium data described by a Unilan equation.     

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.     

Adsorption and desorption kinetics for hydrophilic and hydrophobic vapors on activated carbon

Adsorption dynamics are of fundamental importance in applications of adsorbents in real situations. The adsorption/desorption characteristics of a series of adsorbates, with varying hydrophilic/hydrophobic and structural characteristics, for activated carbon BAX950, were investigated for temperatures in the range 288-323 K. These data provide a comprehensive kinetic study of adsorption/desorption for an activated carbon. The results are discussed in relation to the adsorbent pore structure and functional group concentration, adsorptive structure and adsorption mechanism. The study provides evidence for a compensation effect where activation energy and ln(pre-exponential factor) parameters obtained from the Arrhenius equation exhibit a linear correlation.     

活性炭含水量对甲烷吸附量的影响

本文利用容积法测试了活性炭AX－21在不同含水量下对甲烷吸附量的影响。实验条件为温度298．15K、压力0－8MPa。分析了活性炭的不同含水量对甲烷吸附量的影响。以及干燥时间与AX－21含水量的变化关系,并对在吸附剂微孔中甲烷和水形成水合物的问题进行了探讨。     

Silica-supported tantalum clusters: catalysts for conversion of methane with n-butane to give ethane, propane, and pentanes

Si0₂-supported tantalum clusters were prepared by adsorption of the precursor Ta(CH₂Ph)₅ (Ph is phenyl) on the support followed by treatments in H₂ at 523, 623, and 723 K. The resultant clusters, had approximate average diameters of 0.3, 0.8, and 2 nm, as determined by extended X-ray absorption fine structure (EXAFS) spectroscopy. The samples were tested as catalysts for conversion of methane with n-butane in a once-through flow reactor operated at atmospheric pressure and 523 K, and EXAFS spectroscopy was used to characterize the used catalysts. The results show that (a) the catalysts are active for the conversion of methane with n-butane to give ethane, propane, and pentanes; (b) catalytic activity decreased to nearly zero over a time on stream of 22 h; (c) the catalyst incorporating the smallest clusters exhibited the highest initial activity and that incorporating the largest clusters exhibited the lowest activity; (d) each used catalyst contained clusters of approximately the same nuclearity as the respective fresh catalyst, but with Ta–Ta bond lengths approximately 0.17 ? longer than those found in the fresh catalysts. The data are consistent with catalysis by the supported clusters, and the product distributions are consistent with disproportionation of n-butane accompanied by the reaction of methane with propane to give other alkanes.     

Ternary adsorption kinetics of gases in activated carbon

Ternary adsorption kinetic experiments of ethane (light species), propane (intermediate species) and n-butane in activated carbon are collected under various concentration combinations, temperatures and particle sizes. The effects of these parameters on the ternary adsorption dynamics are investigated. All the experimental data are compared with the predictions by a multicomponent heterogeneous macropore, surface and micropore diffusion (HMSMD) model recently proposed by Hu and Do (AIChE J (1993) 39 1628) using only single-component equilibrium and mass transfer parameters. The model can accurately predict the adsorption rates of ethane, propane and n-butane, but a small error in the calculation of the adsorbed amount of propane at ternary equilibrium is observed.     

Equilibrium isotherms and adsorption heats analysis for ternary mixture of methane,ethane, and propane on 4A zeolite

Equilibrium isotherms were obtained experimentally and theoretically for adsorption of methane, ethane, and propane mixtures on 4A zeolite at 301 K. The experimental data were measured using constant volume method and analyzed by extended Langmuir, modified extended Langmuir, and extended Freundlich isotherm models. The best correlation was achieved with the extended Freundlich isotherm equation and the negative values for heats of adsorption indicate exothermic adsorption nature for these gases on 4A zeolite. The selectivity of 4A zeolite to adsorb gases was also studied with the observation that ethane was more selectively adsorbed than methane on 4A zeolite, while propane was less selectively adsorbed on this zeolite at the studied temperature. Also, it was found that an increase in initial partial pressure of ethane decreases the adsorbed amount of methane, while the increase in partial pressure of methane had no effect on adsorbed amount of ethane.     

The role of adsorbent pore size distribution in multicomponent adsorption on activated carbon

The impact of adsorbent pore size distribution (PSD) on adsorption mechanism for the multi solute system was evaluated in this study. Anoxic and oxic adsorption equilibrium for the single solute (phenol), binary solute (phenol/2-methylphenol) and ternary solute (phenol/2-methylphenol/2-ethylphenol) systems on one granular activated carbon (GAC) F400 and two types of activated carbon fibers (ACFs), namely, ACC-10 and ACC-15, were determined. F400 has a wide PSD, while ACC-10 and ACC-15 have narrow PSD and their critical pore diameters are 8.0 Å and 12.8 Å, respectively. In single solute adsorption, the increase of adsorptive capacity under oxic conditions as compared to anoxic ones was related to the PSD of the adsorbent. Binary solute adsorption on ACC-10 and ternary solute adsorption on ACC-15 indicated no impact of the presence of molecular oxygen on the adsorptive capacity and the adsorption isotherms were well predicted by the ideal adsorbed solution theory (IAST). Significant differences between oxic and anoxic isotherms were noticed for other multicomponent adsorption systems. The narrow PSD of ACFs was effective in hampering the oligomerization of phenolic compounds under oxic conditions. Such a phenomenon will provide accurate predictions of fixed bed adsorbers in water treatment systems.     

水中丙酮在活性炭上吸附平衡与动力学研究

研究了水中丙酮在活性炭上的吸附平衡与动力学曲线,对在20、30、40℃下的吸附等温线用Freundich方程拟合,得出了满意的结果。选择合适的实验条件,在消除了外膜阻力的条件下,表明颗粒内扩散中的表面扩散占主要地位,考察了初始浓度、温度、活性炭粒径等因素对丙酮吸附的影响,并用间歇搅拌槽吸附的表面扩散模型拟合出扩散时间常数。     

沥青/树脂基活性炭的制备及其吸脱附性能研究

以高软化点煤沥青、热塑性酚醛树脂为原料,在机械混合条件下,制备出比表面积大、吸脱附时间短、机械强度高的沥青/树脂基活性炭。通过偏光显微镜(OM)、N2物理吸脱附、TEM及苯的静态吸脱附实验对不同复合比沥青/树脂基复合颗粒进行对比研究。实验结果表明:沥青基活性炭吸脱附时间短,酚醛树脂基活性炭的静态饱和吸附值大、机械强度高;而沥青/树脂基活性炭则兼具沥青基活性炭与酚醛树脂基活性炭的优点,在机械强度为6.5 N(CP/PF-50/50)、静态苯吸附值达到472 mg/g时,仅需60 min进行脱附。结构及性质变化的原因在于:两种前躯体分子结构的不同导致两者在高温煅烧过程中由于所受热应力的不同而产生一定程度的界面剥离,进而形成一定量的孔道结构。     

ZL50活性炭吸附脱除二氧化硫的吸附动力学模型(英文)

A semi-empirical adsorption kinetic model was proposed with the time compensation method to describe the chemisorption of SO2 in flue gas by carbon adsorbents for flue gas purification. The change in adsorption capacity and adsorption rate with time at different water vapor concentrations and different SO2 concentrations was studied. The model was in good agreement with experimental data. The surface reaction was probably the rate controlling step in the early stage for SO2 adsorption by ZL50 activated carbon. The parameters m and n in the nth order adsorption kinetic model were related to the magnitude of the time compensation and adsorption driving force, respectively. The change of parameter n with water vapor concentrations and sulfur dioxide concentrations was studied and some physical implications were given. The sum of square errors was less than 1.0 and the average absolute percentage deviations ranged from 0.5 to 3.2. The kinetic model was compared with other models in the literature.     

烟梗基活性炭的优化制备及对苯酚吸附动力学

为了优化制备烟梗基活性炭,经Minitab软件设计2~3全因素正交实验.比表面积作为活性炭制备的评价指标。通过微孔材料吸附仪和SEM表征活性炭;采用间歇吸附实验探索苯酚在活性炭上吸附特性和机理。由结果可知影响活性炭制备的最主要因素为ZnCl_2质量分数,且活性炭制备最佳条件为:活化温度500℃,ZnCl_2质量分数为30%,活化时间0.2 h。最佳条件下制备的活性炭比表面积为1 036 m~2/g,介孔占比68.9%。拟二级能更好地描述活性炭对苯酚的动力学吸附,Freundlich和Langmuir 2种模型均能很好描述活性炭对苯酚的等温吸附。制备活性炭3个主因素间的交互作用既不利于活性炭制备,同时也增加耗能,活性炭的孔结构一定程度上决定其吸附速率和能力,丰富的孔结构更利于吸附。