ADSORPTION AND DESORPTION DYNAMICS OF SULPHUR DIOXIDE ON A SINGLE LARGE ACTIVATED CARBON PARTICLE

A single particle sorption model based on dual diffusion processes (pore diffusion and diffusion of adsorbed species) with equilibrium (Freundlich isotherm) between the macropore fluid phase and the sorbed phase was developed. The model was fitted to experimentally determined adsorption and desorption of SO₂ on large (0.2 cm radius) activated carbon particles over a range of temperatures and SO₂ concentrations. The model fitted the experimental data well and typical extracted values of the macropore and surface diffusivities were D_P = 0.038 cm²/s and D_s = 1.0 × 10^-5cm²/s at 25°C. The value of macropore diffusivity gave a macropore tortuosity factor of 8.0, whilst the temperature dependence of the surface diffusivity gave an activation energy of 5.0 kJ/mole.     

MODELLING OF THE INTERACTION OF NITROGEN DIOXIDE WITH ACTIVATED CARBON II. KINETICS OF REACTION WITH PORE EVOLUTION

Adsorption of nitrogen dioxide on activated carbon is found to be followed by reaction with the carbon surface at temperatures higher than 373 K. The dynamics of the nitrogen dioxide reaction with the carbon are measured gravimetrically over the temperature range 423-623 K. At small particle sizes (0.014 cm radius) the overall gasification kinetics are controlled by the surface reaction step, and are first order in nitrogen dioxide concentration. Using the random pore model to describe the evolution of reaction surface with porosity, the experimental data are fitted by a kinetic control gasification model, giving an activation energy of 86.2 kJ/mole.     

DIFFUSION COEFFICIENTS OF CARBON DIOXIDE WITHIN TYPE 13X ZEOLITE PARTICLES

The self-diffusion processes of CO₂ in a single particle of commercial type 13X zeolite have been studied by a new sorption rate method using a constant volume, variable pressure system. Experiments were carried out at 303.2 and 343.2 K. An inverse analysis of experimental uptake curves based on a macropore and micropore series diffusion model was performed to determine effective diffusion coefficients for both macropore and micropore diffusion simultaneously. Knudsen diffusion occurs within the macropore and the micropore diffusion coefficients having values of the order 10^-15-10^-14 m²/s, which are slightly greater than the previously reported micropore diffusion coefficients of type 5A zeolite crystals.     

DIFFUSION COEFFICIENTS OF CARBON DIOXIDE WITHIN TYPE 13X ZEOLITE PARTICLES

The self-diffusion processes of CO₂ in a single particle of commercial type 13X zeolite have been studied by a new sorption rate method using a constant volume, variable pressure system. Experiments were carried out at 303.2 and 343.2 K. An inverse analysis of experimental uptake curves based on a macropore and micropore series diffusion model was performed to determine effective diffusion coefficients for both macropore and micropore diffusion simultaneously. Knudsen diffusion occurs within the macropore and the micropore diffusion coefficients having values of the order 10^?15–10^?14 m²/s, which are slightly greater than the previously reported micropore diffusion coefficients of type 5A zeolite crystals.     

GOLD ADSORPTION ON ACTIVATED CARBON AND THE EFFECT OF SUSPENDED SOLIDS AND DISSOLVED SILICON DIOXIDE

The use of gold adsorption by activated carbon has recently become widespread on South African gold mines. This has caused a great deal of interest in the kinetics of gold adsorption onto activated carbon. However, almost all previous work has been done using clear solutions. In practice the gold adsorption occurs from a slurry containing fine ground rock particles and possibly a number of other metals in solution as well as organics which may poison the carbon. As the next step in the understanding of the gold adsorption process, this work assesses the impact of a fine solid suspension on the gold adsorption kinetics. This is found to significantly reduce the adsorption rate of gold cyanide (Au(CN)2¯) by G210 activated carbon in completely mixed batch adsorbers. The relative effects of solid particle size and mixing intensity on the adsorption rate are investigated. Batch adsorption rate experiments are performed with clear solutions, and with solutions containing 20% (m/m) fine suspended solid material, agitated at impeller speeds of 200 and 300 r.p.m. with an initial gold cyanide concentration of = 10 p.p.m. Equilibrium isotherms for gold cyanide, gold cyanide/glass particles and dissolved silicon on G210 activated carbon were determined. The batch adsorption kinetics of gold cyanide from clear solutions were successfully modelled using the Homogeneous Surface Diffusion Model of Crittenden & Weber (1978). The adsorption of gold cyanide from clear solutions was found to be characterized by intra-particle diffusion rate control, limited by a finite film mass transfer rate at low gold loadings. When fine suspended solids are present it is shown that blinding of the carbon macropores is the likely cause of the reduced adsorption rate. Although the solids used were artificial in the sense that these would not be present in this form in an industrial operation, it was felt that using solids from an operating mine would introduce complications in addition to the specific effects this paper addresses.     

基于酚醛树脂的超高比表面积中孔活性炭的研究

以酚醛树指为原料,氢氧化钾为活化剂,制备酚醛树脂基超高比表面积活性炭。采用正交实验考查了制备工艺中炭化温度,碱炭比,活化温度和活化时间对活性炭吸附性能的影响,确定了超高比表面积活性炭的制备最佳工艺。利用TG—DTA对热解过程中树脂的炭化活化行为进行了探讨;通过N2-BET对活性炭比表面积和孔结构进行了表征,并简单分析了成孔机理。结果表明：炭化温度400℃,碱炭比为5：1,活化温度为750℃,活化时间为100min时,制备的酚醛树脂基活性炭比表面积为3013m^2·g^-1,孔容1．609ml／g,平均孔径2．135nm,亚甲基蓝吸附值为592mg·g^-1。     

A STUDY OF H2SO4 FORMATION IN THE PROCESS OF SIMULTANEOUS SORPTION OF SO2, O2 AND H2O ONTO A SINGLE CARBON PARTICLE

A mathematical model to describe simultaneous sorption of SO₂, O₂ and H₂O in an activated carbon particle is presented in this paper. The competition for active sites of these species is taken into account by a modified Langmuir-type isotherm, which incorporates the competition of the immobile reaction product phase, H₂SO₄. Simulations of the model are presented in terms of transient micropore filling of reactant species and product H₂SO₄. The simulation results show that the multicomponent interactions play an important role in the sorption process. Fast diffusing species like O₂ and H₂O instantaneously adsorb in the micropore volume of the sorbent. In the course of simultaneous adsorption and reaction of all species in the micropore, a rollup phenomenon on the transient behavior of fast diffusing species could occur, i.e. the micropore loading of these gaseous species can overshoot the final equilibrium level. The simulation results of H₂SO₄ micropore loading are found to agree reasonably well with the experimental data.     

电化学方法研究碳钢高温水体系中的氢扩散和渗透

本文应用Devanathan渗透装置的原理,设计了一套能用于测量碳钢-高温水体系中氢在碳钢中的扩散和渗透的实验装置,找出了该装置用于测量的最佳工作参数,并用该装置测量了373—473K下氢在碳钢中的扩散系数和扩散速率,讨论了氢在碳钢上还原的机理。