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Experimental study and mathematical modeling of sorption and desorption of volatile organic contaminants on soil.

机译：土壤中挥发性有机污染物吸附和解吸的实验研究和数学模型。

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摘要

The adsorption equilibria of various volatile organic contaminants on EPA standard soil were measured by a dynamic response technique based on frontal analysis chromatography. The adsorption isotherms were BET type II isotherms, which indicate multilayer adsorption in the pores. The magnitude of the calculated heats of adsorption confirmed that the adsorption was physical adsorption. It was also shown that adsorption of relatively non-polar organics took place uniformly on the available external surface area whereas water adsorption was much greater probably due to the polar nature of water molecules that allows them access to the internal clay layers and/or capillary condensation.;As moisture is always present in the natural soil environment, the effect of humidity on organics' adsorption was assessed by measuring the sorption equilibria of toluene and chlorobenzene at different relative humidity levels. The sorption isotherms at low relative humidity were BET type II isotherms whereas at high relative humidities, they exhibited a type III behavior. In all cases, the presence of humidity reduced the organic uptake on soil. At high relative humidity and low organic relative vapor concentration, there was almost complete suppression of organic adsorption. At high organic relative vapor concentration, there was competitive adsorption of water and organic.;The shape of the desorption profile was very much linked to the shape of the adsorption isotherms and showed a two-step behavior. The first step corresponded to the desorption of the multilayers and the second step to the monolayer desorption. This last step was the rate-limiting step for the overall decontamination process. It was shown that using a water-saturated gas stream improved greatly the organic removal rates by accelerating the monolayer desorption.;A model was proposed to simulate breakthrough curves and desorption profiles, assuming local equilibrium between the pore gas phase and the solid phase and an axially-dispersed flow pattern. The sensitive parameters of the model were the axial dispersion coefficient and the adsorption equilibrium. The local equilibrium assumption gave good results which proved that there was no slow diffusion necessitating the consideration of a kinetic/retardation term.
机译：通过基于正面分析色谱的动态响应技术，测量了EPA标准土壤上各种挥发性有机污染物的吸附平衡。吸附等温线为BET II型等温线，表明孔隙中存在多层吸附。计算出的吸附热的大小证实了吸附是物理吸附。还显示出相对非极性有机物的吸附均匀地分布在可用的外表面上，而水的吸附则更大，这可能是由于水分子的极性所致，从而使它们能够进入内部粘土层和/或毛细管凝结。由于天然土壤环境中总是存在水分，因此通过测量甲苯和氯苯在不同相对湿度水平下的吸附平衡来评估湿度对有机物吸附的影响。在较低的相对湿度下的吸附等温线为BET II型等温线，而在较高的相对湿度下则表现出III型行为。在所有情况下，湿度的存在都会减少土壤对有机物的吸收。在较高的相对湿度和较低的有机相对蒸气浓度下，几乎完全抑制了有机吸附。在较高的有机相对蒸气浓度下，水和有机物之间存在竞争性吸附。解吸曲线的形状与吸附等温线的形状密切相关，并表现出两步行为。第一步对应于多层的解吸，第二步对应于单层的解吸。最后一步是整个净化过程的限速步骤。结果表明，使用水饱和气流通过加速单层解吸可以大大提高有机去除率。;提出了一个模型来模拟穿透曲线和解吸曲线，并假设孔隙气相和固相之间存在局部平衡，并且轴向分散的流型。该模型的敏感参数是轴向分散系数和吸附平衡。局部平衡假设给出了良好的结果，证明没有缓慢的扩散，因此需要考虑动力学/延迟项。

著录项

  • 作者

    Thibaud, Catherine.;

  • 作者单位

    Texas A&M University.;

  • 授予单位 Texas A&M University.;
  • 学科 Chemical engineering.;Environmental science.
  • 学位 Ph.D.
  • 年度 1993
  • 页码 183 p.
  • 总页数 183
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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