Effect of pretreatment and adsorption conditions on gas adsorption by supported metal catalysts

The influence of pretreatment and adsorption conditions on the adsorption of oxygen and hydrogen on supported Pt and Rh catalysts has been studied. It has been found that reduction conditions (temperature and time) and subsequent out gassing conditions influence the amount of gas adsorbed. Oxygen and hydrogen uptakes measured in a static system were significantly different than those measured in a dynamic system. Reproducible adsorption uptakes can be obtained by careful control of pretreatment and adsorption conditions.     

Statistical condensation adsorption isotherms of gas molecules adsorbed on porous adsorbents, surface monolayer adsorption isotherms and hysteresis phenomena

Condensation adsorption isotherms of type IV (or V) according to BDDT classification on porous adsorbents composed of one or two groups of adsorption sites are derived statistically. When Β_c1 (or Β_c2) is less than unity, the isotherm becomes type IV, and when it is greater than unity, the isotherm becomes type V. It is understood that the negative sign(-) of the additional adsorption energy, q, in the nth layer in deriving those theoretical isotherms plays a decisive role on the horizontally flat approach to the axis of the isotherm near the saturation vapor pressure. The values of the surface area can be calculated easily. The pore radii of all the adsorbents which we have obtained by using the derived isotherms with respect to the appropriately selected experimental data agree with those obtained by using the Kelvin equation. Many surface mono-layer adsorption isotherms are obtained in the process of deriving the various adsorption isotherms. From them we can learn that the surface sites are not adsorbed completely even near the saturated vapor pressure, and we can find the range of error by comparing them with v_ms of the BET equation. We could mention through judging the results of a great deal of the experimental isotherm data of types IV and V that “the cause of hysteresis phenomena of the condensation adsorption-desorption of gases is originated from the deviation from the thermodynamically reversible adsorption-desorption process in the condensation adsorption-desorption of gases”.     

酸预处理对活性炭吸附有机物的影响

无论是在工业用水还是生活饮用水的处理中,活性炭都是一种常规的去除有机物的方法.但活性炭在使用前如何进行预处理却无相关的研究资料,作者将水处理中常用的5种活性炭,包括果壳炭、椰壳炭、煤质炭进行酸预处理对比,试验证实,酸预处理后可以提高活性炭对水中有机物的吸附性能.     

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     

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。     

地下水反渗透除盐预处理工艺的优化

地下水基本没有悬浮物,污染指数SDI低,比较适宜做反渗透的水源,但硬度高,容易引起反渗透膜结垢,故地下水反渗透除盐,预处理的重点是防止膜表面结垢。软化法预处理操作繁琐,设备复杂,讨论了在地下水中加入阻垢剂防止反渗透膜表面结垢的方法,结果表明此法有效可行。     

Calculation of single adsorption isotherms from gravimetrically measured binary gas mixture adsorption isotherms on activated carbon at high pressures

A method is developed for the calculation of single-component adsorption isotherms from gravimetrically measured binary gas mixture adsorption isotherms at high pressures, at two temperatures and for different mole fractions of the gas phase. The adsorption of nitrogen/methane on active carbon Norit R1 is taken as an experimental example.     

VOCs在MAC上吸附等温线的测定与拟合

大气中挥发性有机物（VOCs）所造成的污染严重地危害人体健康,引起了社会公众和政府的高度重视,研究高效的VOCs治理技术已是一个刻不容缓的课题.本文主要研究用微电磁天平在线测定20、60、90、140℃时甲苯、丁醇和乙酸乙酯在蜂窝状活性炭MAC上的吸附等温线,并用Langmuir、Freundlich、Langmuir-Freundlich、DR和Toth方程对吸附实验等温线进行了拟合.结果表明,MAC对3种VOCs都有比较大的吸附容量,是一种有效的治理VOCs的方法;无论在低浓度下还是在高浓度下,Toth方程都能够很好地拟合甲苯、丁醇和乙酸乙酯在MAC上的吸附等温线,相对误差不超过±6％.     

Prediction of mixed-gas adsorption equilibria from pure component adsorption isotherms

Using only a single binary interaction parameter per adsorbate-adsorbate pair, the adsorption nonrandom two-liquid theory successfully correlates binary gas adsorption experimental data and predicts multicomponent gas adsorption equilibria. This work estimates the binary adsorbate–adsorbate interaction parameters from pure component isotherms and shows very promising agreement with the binary interaction parameters identified from regression of binary gas adsorption data. The results support the feasibility to predict binary and multicomponent gas adsorption equilibria from pure component isotherms for various adsorbents including silica gel, activated carbon, zeolites, and metal–organic frameworks.     

Analysis of some adsorption isotherms on calcium silicate hydrates

Tricalcium silicate was hydrated in suspension at a water/solid ratio (w/s) of 9 and as a paste at a w/s of 0.7. Water contents after outgassing at room temperature were 23–25% for the suspension hydrates and 19–20% for the pastes. Outgassing was standardised so that subsequent increases in BET nitrogen surface area were small even when the pumping time was doubled. Nitrogen adsorption isotherms were similar for both types of product except for the greater volume of mesopores in the suspension hydrates filled at relative pressures greater than ca 0.9_p0(r_p > 100 ǎ). Electron microscopy suggested that the additional uptake of nitrogen involved capillary condensation between bundles of fibrils. Adsorption at low relative pressures would have occurred principally between the fibrils which were of the order of 20 ǎ thick. Pore sizes could be seen to extend continuously from the mesopore to micropore range and the fact that all the isotherms contained a hysteresis loop closing with an abrupt desorption at ca0.44p0 was regarded as a property of liquid nitrogen rather than as an indication of the pore size distribution. A more quantitative indication of the pore size range present was obtained using the α_s method with standard data for Fransil (silica). Plots for pastes were similar to those for suspension hydrates indicating a similar texture accessible to nitrogen in the pastes at the high w/s used. In order to characterise further the surface of the hydrates argon and carbon dioxide adsorptions were determined and the data compared using the Frenkel–Halsey–Hill equation.     

Rate equations and isotherms for two adsorption models

The rate equations and isotherms for two adsorption models have been formulated and discussed. The rate equations obtained have been compared to those of pseudo-first-order model and pseudo-second-order model, respectively. Calculated results indicated that the rate equations of single site model and dual site model could be approximated by those of pseudo-first-order model and pseudo-second-order model, respectively, in a limited ranges of the values of , K*and t*. The adsorption isotherm of single site model has been found to be the same as that of Langmuir type.     

NaOH预处理对香菇废弃物镉吸附性能的影响

为得到一种高效、廉价的生物吸附剂,采用NaOH对香菇废弃物进行预处理。研究了吸附时间、pH和镉初始浓度对香菇废弃物NaOH处理前后镉吸附性能的影响。结果表明,香菇粉NaOH处理前后对镉吸附的最适宜pH值范围不变均为6~7,平衡吸附时间均为1 h。当镉初始浓度从10 mg/L增加到60 mg/L,两种香菇对镉的吸附量线性增加,继续增加镉浓度(60~100 mg/L),未处理香菇对镉的吸附量不再增加(2.82 mg/g),NaOH处理香菇则继续增加至12.50 mg/g,但未达到饱和;伪二级动力学模型拟合香菇废弃物NaOH处理前后吸附镉的动力学过程结果良好,相关系数R~2分别为0.999 8和0.999 9;Langmuir模型和Freundlich模型均能较好的拟合两种香菇对镉的等温吸附热力学过程;NaOH处理香菇粉对镉的理论最大吸附量q_m13.78 mg/g,是未处理前q_m(2.832 mg/g)的约4.4倍。红外光谱分析表明,香菇吸附镉的过程中,香菇细胞壁上的N—H、C—H及O—H官能团发挥了作用,而NaOH处理活化了这些官能团,提高了对镉的吸附容量。     

Correlation of adsorption isotherms of hydrocarbon gases on activated carbon

A single curve of the adsorbate volume W in the adsorbed phase versus the reduced adsorption potential φ correlates adsorption isotherms of saturated hydrocarbons of low molecular weight (viz. ethane, propane, and n-butane) at pressures from 0.034 to 10 mm Hg on Columbia 4LXC activated carbon at 25 and 30°C. This correlation is based on the Polanyi-Dubinin adsorption potential theory and the use of the Peng. Robinson equation of state to calculate thermodynamic properties. This correlation can be represented analytically by expanding the logarithm of W in terms of a quadratic polynomial in φ.     

NaOH预处理对香菇废弃物镉吸附性能的影响

为得到一种高效、廉价的生物吸附剂,采用NaOH对香菇废弃物进行预处理。研究了吸附时间、pH和镉初始浓度对香菇废弃物NaOH处理前后镉吸附性能的影响。结果表明,香菇粉NaOH处理前后对镉吸附的最适宜pH值范围不变均为6⁷,平衡吸附时间均为1 h。当镉初始浓度从10 mg/L增加到60 mg/L,两种香菇对镉的吸附量线性增加,继续增加镉浓度(607,平衡吸附时间均为1 h。当镉初始浓度从10 mg/L增加到60 mg/L,两种香菇对镉的吸附量线性增加,继续增加镉浓度(60¹00 mg/L),未处理香菇对镉的吸附量不再增加(2.82 mg/g),NaOH处理香菇则继续增加至12.50 mg/g,但未达到饱和;伪二级动力学模型拟合香菇废弃物NaOH处理前后吸附镉的动力学过程结果良好,相关系数R100 mg/L),未处理香菇对镉的吸附量不再增加(2.82 mg/g),NaOH处理香菇则继续增加至12.50 mg/g,但未达到饱和;伪二级动力学模型拟合香菇废弃物NaOH处理前后吸附镉的动力学过程结果良好,相关系数R²分别为0.999 8和0.999 9;Langmuir模型和Freundlich模型均能较好的拟合两种香菇对镉的等温吸附热力学过程;NaOH处理香菇粉对镉的理论最大吸附量q_m13.78 mg/g,是未处理前q_m(2.832 mg/g)的约4.4倍。红外光谱分析表明,香菇吸附镉的过程中,香菇细胞壁上的N—H、C—H及O—H官能团发挥了作用,而NaOH处理活化了这些官能团,提高了对镉的吸附容量。     

Prediction of binary component isotherms for adsorption on heterogeneous surfaces

The adsorption of three basic dyes onto peat has been studied as single and bisolute equilibrium isotherms. The Freundlich equilibrium isotherm, suitable for heterogeneous adsorption systems has been selected to describe the single component data. Furthermore, the extended Freundlich formula for binary systems has been used to describe binary system equilibrium. A very good agreement is obtained between experiment and theory. The dyes under investigation are: Basic Blue 3, Basic Red 22 and Basic Yellow 21 in their single phases and binary solutions, respectively, all onto peat.     

On the form of adsorption isotherms for substitutional adsorption of molecules of different sizes

Adsorption from solution occurs by solvent displacement in the interphase. When the adsorbate differs appreciably in size from the previously adsorbed solvent, the relative size factor (x) of adsorbate and solvent determines (a) the form of the relation for free energy of adsorption and (b) the form of the configurational function in terms of fractional coverage θ or site fraction X. Various types of isotherms that have been proposed for this situation are critically compared in relation to the statistics of the solvent-lattice replacement process that occurs in adsorption, eg, of organic substances at electrodes. It is concluded that the correct configurational term to be used when x > 1 is θ/e^x?1 (1 ?θ)^x. Using this term in an equilibrium adsorption isotherm then allows standard free energies of adsorption and derived quantities to be properly calculated from experimental coverage or surface excess measurements.It is shown that it is strictly incorrect to refer to an isotherm containing the configurational term θ/x(1 ?θ)^x as the “Flory—Huggins isotherm,” since Flory—Huggins statistics leads to an isotherm having a different form for the configurational term, viz that containing e^x?1, as above.For adsorption of molecules for which x > 1, failure to include the size factor term in the isotherm leads to errors in the evaluation of any interaction effects in the adsorption behaviour.     

On selection of standard states in adsorption isotherms

The question of choice of appropriate standard states for adsorbed phases at electrode interfaces is reviewed and examined in relation to solvent displacement and the Langmuir and Flory-Huggins types of adsorption isotherms. Comparison with the situation for gas/solid adsorption is made. Standard potentials for electrochemisorption are considered for electrochemical isotherms with and without interaction/heterogeneity terms.     

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.