脉冲-应答技术测定传递与吸附系数和动力学系数

本文运用脉冲-应答技术,在不同温度和不同流速条件下测定了糠醛在BHK-1催化剂上的传递与吸附系数和加氢反应速率常数.依据修正过的Kubin-Kucera气-固相传质-维扩散模型,采用比较准确的Fourier分析法处理实验结果,并通过最优化计算求得了E、D_e、K_f、k_a、K_a、K_r,等6个参数.     

Adsorption equilibrium constants of methyl oleate and methyl linoleate in vapor phase on supported copper and nickel catalysts

Adsorption equilibrium constants for methyl oleate and methyl linoleate in vapor phase on supported copper and nickel catalysts have been determined using the technique of pulse gas chromatography. The results are discussed in relation to selectivity in fat hydrogenation. Notation: A, column cross-section, m₂ ; a_n,b_n, nth Fourier coefficients; c, concentration of adsorbate in bulk flow, mol/m³ ; c^* = c/ ∫ ₀ ^∞ cdt, normalized concentration of adsorbate in bulk flow; C_i, concentration of adsorbate in catalyst pores, mol/m³ ; c_a, concentration of adsorbate on catalyst surface, mol/kg; c_TOT, active area of catalyst as measured by hydrogen adsorption, mol/kg; D_e, effective diffusion coefficient of adsorbate in catalyst, m²/s; D_ea, axial dispersion coefficient based on void cross-section, m²/s; h_n, nth coefficient in Hermite polynomial expansion; H_n nth Hermite polynomial; ΔH_A, adsorption enthalpy, kJ/mol; ΔH_vap , heat of vaporization, kJ/moll; k_a, adsorption rate constant, m³/kgs;K_A, adsorption equilibrium constant, m³/kg; K₀ , preexponential factor defined in Eqn. 8, m³/kg; k_f, mass transfer coefficient, m/s; L, bed length, m; q, flow rate, m³/s; R, particle radius, m; R_g, gas constant; t, time, s; T, temperature, K; T_F, period of Fourier expansion, s; u = q/A, linear velocity, m/s; z, length coordinate in packed column, m. Greek symbols: δ(t), Dirac delta function; ∈_B, void fraction of bed; ∈_-p, particle void fraction, ρ_rp, particle density, kg/m³ ; ξ, radial coordinate in particle, m; μ₁, first absolute moment, μ₂, second central moment.     

Application of ethylenediamine hydroxypropyl tamarind fruit shell as adsorbent to remove Eriochrome black T from aqueous solutions – Kinetic and equilibrium studies

Ethylenediamine Hydroxypropyl Tamarind Fruit Shell (EDAHP-TFS) was synthesized to remove Eriochrome Black T (EBT) from aqueous solutions. Maximum adsorption occurred at pH 2.0 and equilibrium time 2 h. Adsorption increased with increase in initial concentration and temperature. Adsorption kinetics obeyed the pseudo-second-order model and indicates a partial ion exchange, followed by the complexation mechanism. Lower E^# (4.48 kJ/mol) represents film diffusion as the rate-limiting step. EBT removal followed the Sips isotherm model with a maximum adsorption capacity of 0.237 mmol/g at 30ºC. Isosteric heat of adsorption (ΔH_i) decreased with increase in surface loading, indicating heterogeneous adsorption sites. Desorption studies were carried out and 96.4% recovery was achieved at pH 11.0.     

DETERMINATION OF ADSORPTION AND KINETIC PARAMETERS FOR SYNTHESIS OF ISOBUTYL ACETATE CATALYZED BY AMBERLITE IR-122

In the present study, the kinetics of esterification of acetic acid with isobutanol was studied by using Amberlite IR-122 as an acid catalyst. Experiments were carried out in a stirred batch reactor in dioxane at different temperatures (323 to 348 K) under atmospheric pressure. The equilibrium constant was found to be constant as 4 in the temperatures ranging from 323 to 367 K. The possible mechanism of reaction was mathematically treated using the theories of the Eley-Rideal model based on inhibition by water and isobutanol on the resins. The reaction rate constants and the adsorption coefficients for isobutanol and water were determined from the experimental data at the same temperature intervals. Furthermore, the activation energy of the esterification reaction was found to be 50.5 kJ/mol. The heat of adsorption for isobutanol and water was also calculated as ? 50.9 kJ/mol and ? 18.9 kJ/mol, respectively.     

用单颗粒色谱法测定颗粒内的各种速率参数——(Ⅱ)CO变换反应动力学参数的测定

运用统计矩理论推导出催化剂颗粒内气体吸附常数、有效扩散系数和反应速率常数与实验矩之间的关联式.在常压及高至340℃的温度下,用常规的热导池鉴定器测定了Co在B110催化剂中的有效扩散系数、吸附平衡常数以及变换反应CO十H_2O=H_2十CO_2的反应速度常数.它为化学反应工程基础研究提供了一种新型的、有效实用的实验技术.     

Impulse Response Analysis for Adsorption of Ethyl Acetate on Activated Carbon in Supercritical Carbon Dioxide

Abstract

Adsorption equilibria and mass transport properties for ethyl acetate on activated carbon have been evaluated in the presence of supercritical carbon dioxide by means of the impulse response technique. A two-column system, one for dissolving solute and one for adsorption, was used to evaluate the phenomena purely in the adsorption column. The adsorption equilibrium constant was larger for higher temperature and lower pressure. The apparent heat of adsorption calculated from the temperature dependence of the adsorption equilibrium constant was 30–40 kJ/mol. The intraparticle effective diffusivity was larger for higher temperature and lower pressure. The Peclet number that relates to the axial dispersion coefficient was 0.08–0.39. These estimated parameters are in good agreement with those obtained from desorption measurements reported in the literature.     

DYNAMIC ANALYSIS OF SORPTION OF VOLATILE ORGANIC COMPOUNDS IN WATER

Chlorinated and brominated volatile organic compounds are among the groundwater pollutants creating major environmental problems. In this study, dynamic behavior of certain volatile organic compounds in water was investigated by using a novel moment technique. Adsorption equilibrium constant and the penetration length of tracers were evaluated by the first absolute and the second central moment expressions derived for a pulse-response system. In order to obtain adsorption equilibrium constant and penetration length, pulse-response experiments were carried out with different tracers in a one-sided adsorption cell at 30°C. The adsorption equilibrium constants at the gas-water interface were calculated for 1,2-dichloroethane, 1,1,1-trichloroethane, and carbon tetrachloride. This study showed that the adsorption equilibrium constant and the penetration length values could be successfully evaluated using the one-sided adsorption cell moment technique. The adsorption equilibrium constant for 1,2-dichloroethane, 1,1,1-trichloroethane, and carbon tetrachloride were found to be 0.30, 0.49, and 0.54 cm³/cm², respectively.     

Microcalorimetric studies of ammonia adsorption on γ-Al2O3, HNa-Y zeolite,and H-mordenite

The acidities of-Al₂O₃, HNa-Y zeolite, and H-mordenite have been examined by microcalorimetric measurements of ammonia adsorption at 423 K. The differential heat of adsorption on -Al₂O₃ decreases continuously with ammonia coverage from an initial value of 165 kJ/ mol at low coverages to a value of 70 kJ/mol at higher coverages. The differential heat of adsorption on HNa-Y zeolite shows similar behavior, with a plateau of nearly constant heat at 115 kJ/mol. H-mordenite exhibits a nearly constant heat of adsorption equal to 155 kJ/mol. The results from these microcalorimetric measurements are in agreement with thermogravimetric and temperature-programmed desorption results collected at higher temperatures. Adsorbed ammonia has sufficient mobility at 423 K to equilibrate with the catalyst surface on the time scale of microcalorimetric measurements, and these measurements provide an effective method for quantifying acid site distributions of solid-acid catalysts.     

Kinetic studies on the esterification of free fatty acids in jatropha oil

Kinetic studies have been carried out on the esterification of free fatty acids (FFAs) in jatropha oil with methanol in the presence of sulphuric acid catalyst at 5 and 10 wt% concentrations relative to free fatty acids (0.4–0.8 wt% relative to oil) and methanol–FFA mole ratios ranging from 20:1 to 80:1. It has been found that a 60:1 methanol–FFA mole ratio and 5 wt% catalyst at 60°C and 500 rpm or above provided a final acid value lower than 1 mg KOH/g oil within 60 min. A kinetic model has been proposed with second‐order kinetics for both the forward and backward reactions. The effect of temperature on the reaction rate constants and equilibrium constant has been determined using Arrhenius and von't Hoff equations, respectively. The heat of reaction was found to be ?11.102 kJ/mol.     

Pulse Chromatographic Studies of Adsorption of CO2, CH4, and N2 Using Amine Functionalized Polystyrene Adsorbents

Adsorption of CO₂, CH₄, and N₂ was investigated using pulse concentration chromatography on polystyrene functionalized by covalently attached diethanolamine, dimethylamine, imidazole, and N-methyl piperazine. The adsorption equilibrium constants at different temperatures were estimated by fitting the experimental chromatograms into a non-linear equilibrium dispersive chromatography model using gPROMS. Axial dispersion was found to be the controlling mechanism for dispersion of the chromatograms. The heat of adsorption and corresponding equilibrium selectivities were determined from the adsorption equilibrium constants. The imidazole based adsorbent showed the highest affinity for CO₂.     

Adsorption of reaction species on raney nickel for slurry-phase hydrogenation of p-nitrotoluene

Adsorption of hydrogen, p-nitrotoluene, p-toluidine and water on Raney nickel from their methanol solutions has been investigated under catalytic conditions. The isotherms of reversible adsorption of hydrogen are linear and the estimated heat of adsorption is 28.9 kJ mol^?1. The amount of hydrogen held irreversibly on the catalyst is very large as compared to that adsorbed reversibly. The isotherms of adsorption of p-nitrotoluene, p-toluidine and water have different shapes (viz. types H3, S1 and L3 respectively). Among the reaction species, p-toluidine is not adsorbed on the catalyst at low concentrations (< 0.8 mmol cm^?3).     

MTBE synthesis in a novel riser simulator

MTBE synthesis, from methanol and iso-butylene, is studied in a novel Riser Simulator using a ZSM-5 catalyst. Conditions selected for the operation of the Riser Simulator unit are as follows: 1-5 catalyst/reactant ratios, 80 to 160°C temperatures, 1.09 methanol/iso-butylene mol ratio, 25 to 34 kPa methanol partial pressures and 10 to 120 s reaction times. Injection of methanol, with enough time for the methanol to reach adsorption equilibrium, followed by an isobuty-lene injection is found to be the best operating mode to achieve 100% iso-butylene selectivity toward MTBE with 4 to 6.8% isobutylene conversions. With the gathered experimental data, a reaction rate model based on the Rideal-Eley kinetic model is successfully developed.     

Chromatographic Analysis of Limonene and Linalool on Silica Gel in Supercritical Carbon Dioxide

ABSTRACT

Adsorption behavior of limonene and linalool, which are respectively the principal constituents of terpene and oxygenated compounds in citrus oil, on silica gel in the presence of supercritical carbon dioxide was analyzed by the tracer response method. In this study a two-column system was used to eliminate the effect of nonideal behavior at the sample injection. Adsorption equilibria and mass transport properties were evaluated by means of the moment method at pressures of 8.8–23.5 MPa and temperatures of 313–333 K. The adsorption equilibrium constant was larger for higher temperature and lower pressure when linalool was selectively adsorbed on silica gel. The apparent heat of adsorption ranged from –20 to 230 kj/mol. The Peclet number and the ratio of intraparticle effective diffusivity to molecular diffusivity were 0.013–0.257 and 0.002–0.716, respectively.     

Adsorption of pigments and free fatty acids from shea butter on activated Cameroonian clays

Adsorption of pigments and free fatty acids from shea butter on acid‐activated Cameroonian local clays was investigated. The adsorption of the pigments was followed by the reduction of the absorbance of the shea butter at 295 nm. The kinetic study revealed that both the temperature at which the experiment was performed and the degree of activation of the clays influence the time of contact required to reach adsorption equilibrium of the pigments and the amount of pigments adsorbed. Thus, at 90 °C, the time required was 30 min for the clays activated with 0.5 M (A0.5M) and 1.0 M solutions (A1M) of sulphuric acid, and 45 min for the clay activated with a 2.0 M solution (A2M) of sulphuric acid. At 80 °C, the adsorption equilibrium was reached after 45 min for clays A0.5M and A1M, and 60 min for clay A2M. At 65 °C, the contact time to reach adsorption equilibrium was longer than 75 min for all the adsorbents used. At 90 °C, the amount of pigments adsorbed at equilibrium by clay A2M was about two thirds of that adsorbed by clay A0.5M, and one half of the amount adsorbed by clay A1M. For each adsorbent, the amount of pigment adsorbed decreased with temperature. A1M was the most efficient local clay for the adsorption of shea butter pigments and compared favourably with the industrial clay used as reference. The same evolution was observed with the adsorption of free fatty acids on different clays. The contact time needed for the elimination of peroxides was 40 min for all the clays used. The most efficient adsorbents for the adsorption of the pigments and free fatty acids were also the ones that gave the best results in the elimination of peroxides. The energy of activation for the adsorption of the pigments, as determined by the adsorption kinetic model of Brimberg, were 61 ± 9 kJ/mol, 73 ± 11 kJ/mol, 67 ± 10 kJ/mol, and 47 ± 7 kJ/mol for the industrial adsorbent (EN) and clays A0.5M, A1M and A2M, respectively. These values of activation energies indicate that the shea butter pigments are chemisorbed on acid‐activated clays. It was found that the adsorption isotherms follow the Freundlich equation.     

Thermodynamics of the process of adsorption of aliphatic amidpolyamine on cellulose

The subject of this research is the thermodynamics of the adsorption equilibrium of three types of bleached pulp in water solutions of aliphatic amidpolyamine—Lamid-1, (L-1) in concentrations from 0.03 to 0.50 g/L in a temperature interval of 0–60°C and the influence of pH of the environment on the adsorption process. It was established that with the increase of temperature the quantity of adsorbed L-1 decreases. The values of the heat of adsorption are negative, do not depend on the quantity of adsorbed L-1, and are of the order 111.7–14.7 kJ/mol. The values of the entropy of the entropy of adsorption are also negative and are of the order of 76.8 ÷ 84.5 J/mol?K. Adsorption equilibrium is described by ther adsorption isotherm of Langmuir. Optimum pH for lower concentrations of the solution is from 5 to 7. When the concentrations of the solution are higher (C ≧ 0.15 g/L) the process can also take place very satisfactorily in an alkaline environment.     

咪唑啉缓蚀剂合成工艺优化及吸附性能

以油酸、二乙烯三胺为原料,氧化钙为脱水剂,氯化苄为季铵化试剂,经酰胺化-环化、季铵化合成了新型咪唑啉季铵盐缓蚀剂,并对其吸附过程进行了研究.响应面法优化了油酸与二乙烯三胺摩尔比、环化时间和环化温度等合成关键工艺条件,采用红外光谱和可见光吸收光谱法分析产品结构,以动电位扫描极化曲线法评价缓蚀效果.以0.05mol油酸为基准,氧化钙0.10mol,氯化苄0.06mol,季铵化时间2.5h,季铵化温度55℃条件下,优化结果为:n(油酸):n(二乙烯三胺)为1:1.18,环化温度162.8℃,环化时间5.55h;在50℃缓蚀剂浓度200mg/L、15%盐酸溶液中缓蚀率可达94%;该缓蚀剂的吸附行为符合Langmuir 吸附等温式,为自发放热过程,50℃下吸附平衡常数为1.0277′10⁵L/mol,吉布斯自由能为-41.75kJ/mol,吸附热能为-54.07kJ/mol,熵值为-38.11J/(K·mol),属于以化学吸附为主的过程.与同类合成工艺相比较,环化温度明显降低,产物具有优异的缓蚀性能.     

活性炭对不锈钢酸洗废水中Cr3+和Fe3+的吸附特性

对颗粒活性炭吸附不锈钢酸洗废水中的Cr3+和Fe3+进行了研究. 结果表明,活性炭对Cr3+的饱和吸附量为4.546 mg/g,对Fe3+的饱和吸附量为40.76 mg/g,吸附平衡时间分别为90和60 min. 对吸附过程进行准一级、准二级动力学模型拟合,发现准二级模型拟合较好. 活性炭对Cr3+的吸附基本符合Langmuir和Freundlich等温吸附模型,而对Fe3+的吸附与BET吸附模型拟合较好,吸附Cr3+, Fe3+的活化能Ea分别为37.19和51.01 kJ/mol. 活性炭对Cr3+的吸附以化学吸附为主,而物理吸附则主导对Fe3+的吸附.     

Adsorption Isotherms,Kinetics, and Desorption of 1,2-Dichloroethane on Chromium-Based Metal Organic Framework MIL-101

Adsorption equilibrium and kinetics of 1,2-dichloroethane on a chromium-based metal-organic framework MIL-101 were studied. Desorption activation energies of 1,2-dichloroethane on the MIL-101 were measured using temperature program desorption (TPD) experiments. Results showed that the adsorption capacity of the MIL-101 for 1,2-dichloroethane is 19 mmol/g at 288 K, being much higher than those of some activated carbon, zeolite, and MWCNTs. The isotherms of 1,2-dichloroethane were well fitted by the Langmuir equation. The isosteric heat and diffusion coefficients of 1,2-dichloroethane adsorption on the MIL-101 were separately within the range of 42.0–61.6 kJ/mol and range of 0.854–2.246 × 10^?10 cm²/s. TPD spectra exhibited two types of adsorption sites on the MIL-101 with desorption activation energy of 48.6 and 87.6 kJ/mol separately. Multiple recycle runs of 1,2-dichloroethane adsorption-desorption at 298 K (10 mbar for adsorption and 0.05 mbar for desorption) showed the 1,2-dichloroethane adsorption on the MIL-101 is highly reversible, and desorption efficiency is up to 98.42%.     

凤鸣村腐植酸和活性褐煤对Cr(Ⅵ)离子的吸附等温式

研究了从凤鸣村褐煤中提取的腐植酸和活性褐煤对Cr (Ⅵ )离子的吸附 ,求出了Langmuir和Fre undlich方程的有关参数 ,结果表明 ,腐植酸对Cr(Ⅵ )离子吸附具有以化学吸附为主的Langmuir单分子吸附特征 ,活性褐煤对Cr(Ⅵ )离子吸附符合Freundlich方程。