Organic desorption from carbon—II. The effect of solvent in the desorption of phenol from wet carbon

The desorption of phenol from active carbon was studied using cyclic and continuous flow desorbers. A wide difference in desorption capabilities was shown among ten solvents. The system employed was complex, with water being present in addition to phenol on the carbon. An attempt to correlate the desorption data with the physical properties of the phenol and solvent and regular solution theory is made. A thermodynamic approach using the linear free energy—enthalpy relationship produced a reasonable correlation of the heat of formation of the phenol—solvent hydrogen bond with the desorption data. This indicates that the desorption of the phenol from carbon in this complex system is dependent upon the ability of the solvent to form hydrogen bonds with the phenol.     

Hygrothermal absorption and desorption of deep underground hydropower station envelopes

The heat and moisture environment of hydropower stations underground plants will directly affect the useful life and safe running of electromechanical devices. Engineers need to calculate the transient heat and moisture loads due to the storage and transport of heat and moisture in the porous cavern envelopes. In order to avoid complex dynamic calculations and save design time, this paper gives monthly mean hygrothermal absorption and desorption indexes and regression formulas of limestone envelopes with no-lining. These indexes are obtained by means of numerical calculation method based on the air temperature and moisture fluctuation ranges controlled by air-conditioning systems and hygrothermal parameters of cavern envelop. And then, validity and reliability of hygrothermal absorption and desorption indexes are verified by using monitored data of main plants in Dachaoshan and Jiangkou hydropower stations in China. The results show that the heat and moisture indexes can be applied in real project design and operation management.     

Phenanthrene desorption from soil in the presence of bacterial extracellular polymer: observations and model predictions of dynamic behavior

The extracellular polymer produced by a bacterium isolated from soil was employed in laboratory studies of desorption of a model polynuelear aromatic hydrocarbon (PAH), phenanthrene. The experimental results show that the selected extracellular polymer enhances the extent of release of soil-bound phenanthrene. A kinetic model was developed as an aid in interpreting the alterations in phenanthrene desorption resulting from polymer addition. The model employs a statistical gamma (gamma) distribution to describe spectrum of rate constants for transfer of phenanthrene from soil to water, and assumes instantaneous binding of phenanthrene to polymer and of polymer to the test soil. The relevant distribution coefficients and statistical parameters of the gamma distribution needed for the model were evaluated in independent experiments. Using these measured parameters, the model provides a satisfactory independent prediction of phenanthrene release from soil to aqueous phase at two test polymer concentrations, 50 mg TOC/L and 100 mg TOC/L. The success of the independent model predictions suggests a mechanism for the influence of extracellular polymer on phenanthrene desorption. The intrinsic, soil-specific, rate constants for solid to solution transfer of phenanthrene do not appear to be changed by bacterial polymer. Instead, polymer binding of phenanthrene in solution results in an increase in driving force for desorption by decreasing the solution concentration of the free, unbound, PAH molecule.     

The importance of organic matter distribution and extract soil:solution ratio on the desorption of heavy metals from soils

The lability (mobility and bioavailability) of metals varies significantly with soil properties for similar total soil metal concentrations. We studied desorption of Cu, Ni and Zn, from 15 diverse, unamended soils. These studies included evaluation of the effects of soil:solution extraction ratio and the roles of soil properties on metal desorption. Dcsorption was examined for each metal by computing distribution coefficients (Kd) for each metal in each soil where Kd = [M]soil/[M]solution, Results from soil:solution ratio studies demonstrated that Kd values for the metals tended to increase with increasing soil:solution ratio. This result also held true for distribution of soil organic matter (SOM). Because the soil:solution ratio has a significant effect on measured metal distributions, we selected a high soil:solution ratio to more closely approach natural soil conditions. Copper showed strong affinity to operationally defined dissolved organic matter (DOM). In this study, DOM was operationally defined based on the total organic carbon (TOC) content in 0.45-microm or 0.22-microm filtrates of the extracts. The Kd of Cu correlated linearly (r2 = 0.91) with the Kd of organic matter (Kd-om) where the Kd-om is equal to SOM as measured by Walkley-Black wet combustion and converted to total carbon (TC) by a factor of 0.59. These values representing solid phase TC were then divided by soluble organic carbon as measured by TOC analysis (DOM). The conversion factor of 0.59 was employed in order to construct Kd-om values based on solid phase carbon and solution phase carbon. SOM plays a significant role in the fate of Cu in soil systems. Soil-solution distribution of Ni and Zn, as well as the activity of free Cu2+, were closely related to SOM, but not to DOM. Kd values for Ni, Zn and free Cu2+ in a particular soil were divided by the SOM content in the same soil. This normalization of the Kd values for Ni, Zn, and free Cu2+ to the SOM content resulted in significant improvements in the linear relationships between non-normalized Kd values and soil pH. The semi-empirical normalized regression equations can be used to predict the solubility of Ni and Zn and the activity of free Cu2+ as a function of pH.     

Modeling of the hygrothermal absorption and desorption for underground building envelopes

The hygrothermal storage characteristics of an underground building envelope have discernible effects on the heat and humidity of the indoor environment. To predict the hygrothermal storage capacity, it is necessary to accurately calculate the transient heat and moisture flux through the envelope. This paper describes the development of a new hygrothermal model described with relative humidity and temperature based on the results of existing researches. The moisture model fully states actual moisture transfer process involving both vapor diffusion and liquid water migration in porous building envelopes. Verified using the results calculated by the mathematical model of Mendes et al., the new hygrothermal model can accurately predict the heat and moisture transfer of building envelopes. Hygrothermal absorption and desorption of three types of common underground building envelopes in Chengdu region in China are analyzed by using the new model. The results show that the hygrothermal absorption and desorption of underground building envelopes must be considered when the heat and moisture environment is controlled by HVAC. Taking account of these factors can reduce air-conditioning equipment capacity and save running energy.     

调湿材料吸放湿性能的测试方法

建立了调湿材料吸放湿过程的热湿传递耦合方程,在周期性热湿作用边界条件下对耦合方程进行变换分析,得出其理论解。研究了封闭空间内调湿材料在周期性热湿作用下的吸放湿特性,结果表明空气含湿量波动振幅与温度波动振幅之比值为一复常数,其模值能表示材料吸放湿能力大小,初相位能表示材料吸放湿应答性快慢,从而引出了测试调湿材料吸放湿性能的方法———封闭箱热作用法。利用该方法测试了硅胶板、混凝土板和夯土板的吸放湿性能,验证了该方法的有效性,结果显示硅胶板的吸放湿性能最好,混凝土板最差;得出了调湿材料在封闭箱中的吸放湿规律,即空气温度升高时材料放湿,空气温度下降时材料吸湿,可根据空气绝对湿度曲线判断材料吸放湿性能的好坏。     

Partitioning and desorption behavior of polycyclic aromatic hydrocarbons from disparate sources

Contaminated sediments pose a unique challenge for risk assessment or remediation because the overlying water column may transport contaminants offsite or to ecological receptors. This research compares the behavior of polycyclic aromatic hydrocarbons (PAHs) on marine sediments from two sites. The first site was affected by shipping activities and the second was impacted by a creosote seep. Organic carbon:water partitioning coefficients (Koc values) were measured with three solutions. Desorption was measured using Tenax beads. PAHs from the ship channel had lower Koc values than those from the creosote facility. For example, the average logKoc value of ship channel pyrene was significantly lower than that of creosote facility pyrene (4.39 +/- 0.35 and 5.29 +/- 0.09, respectively, when tested in 5 mM calcium chloride). These results were consistent with the greater desorption of pyrene, phenanthrene and benzo(a)pyrene from the ship channel than from the creosote facility sediments. Organic compound desorption from sediments can be considered to be a two-stage process, with a labile fraction that desorbs quickly and a refractory fraction that desorbs much more slowly. In both sediments, more than 75% of the benzo(a)pyrene was found to have partitioned into the refractory phase. The amounts of phenanthrene and pyrene that partitioned into the refractory phase were lower. Linear correlations of logKoc with log(CR/CL) (where CR and CL are the fractions of the compound in the refractory and labile phases, respectively, at time zero) showed that partitioning measurements made with the US EPA's Toxicity Characteristic Leaching Procedure fluid (US EPA, 1996) most closely matched predictions of desorption behavior. The data imply that with a larger data set, it may be possible to relate simple partitioning measurements to desorption behavior. Partitioning measurements were used to predict water concentrations. Despite having higher concentrations of carcinogenic PAHs [cPAHs, the seven PAHs categorized by the US EPA (2004) as class B2 carcinogens], creosote facility sediments were predicted to produce lower aqueous concentrations of cPAHs. These results indicate that both sediment and contaminant characteristics will impact contaminant release from sediments.     

Solvent regeneration of activated carbon

Nineteen solvents were evaluated in batch tests involving the desorption of a representative organic adsorbate (phenol) from activated carbon. Three of the better solvents which also possess complete miscibility with water (acetone, dimethylformamide, methanol) were tested further in fixed-bed runs. The effects of solvent temperature and solvent flow rate on phenol desorption were evaluated. In addition, the recovery of phenol adsorption capacity by an activated carbon bed operated cyclically using a sequence of phenol adsorption, desorption with methanol, and rinsing with water was determined. It was found that solvent temperature and flow rate are not critical variables. Solvent volume and type were the most important factors in phenol desorption. A modest volume of methanol restored 88% of the fixed-bed adsorption capacity for phenol after 1 regeneration, and the capacity essentially leveled off after 5 regenerations at a value of 81% of the capacity of fresh carbon. Methanol regeneration is effective, easy to perform and offers convenient solvent recovery. Thus, it is an attractive alternative to thermal regeneration methods.     

Predicting the rate and extent of cadmium and copper desorption from soils in the presence of bacterial extracellular polymer

The movement of cationic transition metals through the subsurface is strongly retarded by sorption to the porous media. However, dissolved organic ligands can compete with soil surfaces by providing binding sites for metals in solution. An extracellular polymer produced by a bacterium isolated from soil was used in this study to observe and model the influence of a naturally occurring ligand on the release of adsorbed metals from two test soils. Experimental results show that the presence of dissolved extracellular polymer enhanced the rate and extent of desorptive release of soil-bound cadmium and copper. A kinetic model that uses a gamma distribution of rate constants to account for the physical and chemical heterogeneity of the soil matrix was employed to describe the release of cadmium and copper in batch experiments. Model parameters describing soil, metal and extracellular polymer interactions were obtained through separate experiments. With these parameters the model successfully predicted the influence of dissolved polymer on the rate and extent of release of cadmium and copper from soil in independent batch experiments. These results suggest that the presence of natural metal-binding ligands such as bacterial extracellular polymers can act to increase the driving force for desorption by lowering the aqueous concentration of free unbound metals in solution.     

Study of the desorption of linuron from soils to water enhanced by the addition of an anionic surfactant to soil-water system

The influence of the addition of the anionic surfactant sodium dodecyl sulphate (SDS) to the soil-water-linuron system in the herbicide desorption from soils with different organic matter (OM) content to water have been studied. SDS was used at critical micelle concentrations (cmc) of 0.75, 1.50, 5 and 10. The adsorption-desorption isotherms of linuron in aqueous medium and in SDS solutions at concentration of 0.75 cmc fitted the Freundlich adsorption equation for all the soils studied. When the SDS concentration was 1.50 cmc only the desorption isotherms for the soils with OM content < or = 5.40% fit this equation and was not fulfilled by any of the soils when the SDS concentration was 5 or 10 cmc. All the desorption isotherms displayed hysteresis, the hysteresis coefficients of the desorption isotherms in SDS solutions always being lower than those of the desorption isotherms in water. The efficiency coefficients, defined as the relationship between the percentages of linuron desorbed in SDS solution and the percentages of linuron desorbed in water, range from 1.02 to 2.41 in the soil with the lowest OM content, and from 1.91 to 17.1 in the soil with the highest OM content. The results obtained indicate the enhancement of linuron desorption by the addition of SDS surfactant to soil-water system. The efficiency of SDS is seen as from surfactant concentrations below the cmc and varies with the surfactant concentration and with the soil OM content.     

Sorption and desorption of pyridine-clay in aqueous solution

Sterile, radiochemical procedures were applied in a study of the cationic exchange processes occurring during pyridine sorption onto highly-purified sodium kaolinite and sodium montmorillonite particulates of colloidal dimensions. Sodium desorption is directly related to increased protonation. Hydrogen ion exchange dominates at pH < 3. Maximum pyridium sorption occurs at pH 4.0–5.5. At pH > 7.0 neither pyridium nor hydrogen exchange occurs. Previously sorbed pyridium desorbs from the clays as a function of time and solution pH with maximum desorption at pH 1 and 11 and minimum near pH = pK_a = 5.25. Pyridine desorption is much slower than sorption at comparable pH and clay:organic ratio. The extent of desorption is also directly related to the number of stages and/or the volume of solution. Particulate charge, zeta potential, changes are greatest between pH 1–4 with coagulation and charge reversal at pH ≅ 2 if the pyridine concentration is < cation exchange capacity, CEC. Pyridine concentration in excess of CEC induces coagulation through the “cage effect”.     

Bioadsorbent Hura Crepitans for the removal of phenol from solution

The use of Hura crepitans (sandbox tree) seed as a biomass adsorbent was studied for the removal of phenol from aqueous solutions before extraction (HC) and after extraction (EHC) with hexane and methanol. The surface chemistry of HC and EHC was characterized by using the Boehm titration and pH drift while the removal of phenol from solution was monitored by using high performance liquid chromatography (HPLC). Decrease in the pH of solutions led to a significant increase in the adsorption capacity of HC and EHC. The linear regression of the experimental data showed that the Freundlich model fitted well with the values of adsorption capacity equal to 121 mmol/g for HC and 85 mmol/g for EHC, and the pseudo-second order kinetic model best described the adsorption process for HC and EHC. The experimental data indicated that the seed of Hura crepitans could be effectively used as an adsorbent for the removal of phenol from aqueous solutions.     

Slow and very slow desorption of organic compounds from sediment: influence of sorbate planarity

The kinetics of desorption of in situ chlorobenzenes, PAHs, and PCBs from four different sediments was studied employing Tenax beads as an infinite sink for sorbates. Rate constants for slow desorption were 2.9+/-0.4 x 10(-2) x h(-1), irrespective of the extent of sorbate planarity. Rate constants for very slow desorption were 2.1+/-0.5 x 10(-4) and 6.7+/-1.4 x 10(-4) x h(-1) for planar and non-planar compounds, respectively. Comparison with literature data suggests a priori estimates for rate constants for slow desorption to be 3 x 10(-2) x h(-1), and to be 2 x 10(-4) and 7 x 10(-4) x h(-1) for very slow desorption of planar and non-planar compounds, respectively. The ratio between the fractions in the very slowly desorbing domain and the rapidly desorbing domain was 15-38 for planar compounds which is higher than for non-planar compounds for which the ratio was 2.8-5.2. The ratio between the fractions in the slowly desorbing domain and the rapidly desorbing domain was 1.3-1.8 and independent of the sorbate planarity. The difference in influence of sorbate planarity on the very slowly desorbing domain as compared to the slowly desorbing domain points to different environments for the slowly and the very slowly desorbing fractions.     

Evaluation of surfactants/cosolvents for desorption/solubilization of Phenanthrene in clayey soils

Throughout the USA, numerous sites exist where the soils have been contaminated by polycyclic aromatic hydrocarbons (PAHs). These compounds may be toxic, mutagenic and/or carcinogenic, so these sites threaten human health and the environment and prompt remediation is warranted. In situ flushing with surfactants/cosolvents has shown promise for treating PAH‐contaminated soils that are uniform and possess a high permeability, but the efficiency of this process is severely limited when heterogeneous and/or low permeability soils are present. For these difficult situations, electrokinetically enhanced in situ flushing offers great potential, but this method is highly dependent on the type of purging agent that is used. Thus, in this laboratory investigation, batch desorption experiments were conducted to evaluate different surfactants/cosolvent solutions for use in electrokinetically enhanced in situ flushing. The surfactants/cosolvents were evaluated on their ability to desorb and solubilize phenanthrene, a representative PAH, from two widely varying clayey soil types. The soils were artificially contaminated at four PAH concentrations, and batch tests were conducted using six different surfactant/cosolvent solutions. The results indicated that phenanthrene was more strongly bound to the soil with the higher organic content, and the surfactants with a higher hydrophile – lipophile balance number (HLB) caused greater PAH desorption and solubilization. Furthermore, the surfactant solutions performed better when they were used at a higher concentration. Compared to the cosolvent solution or a combined mixture of the cosolvent and surfactant solutions, greater desorption and solubilization of the contaminant occurred when the surfactant solution was used by itself.     

封闭体系中煤体升温解吸的热力学特性研究

气体在煤中吸附解吸取决于其压力和温度,气体解吸量随温度升高和压力降低而有所增加。在封闭体系中,温度升高造成煤体解吸量增加,并引起体系压力变大,但同时抑制解吸。吸附态气体和游离态气体相互转化时,伴有能量交换。为研究煤体升温吸附/解吸的热力学特性,依据实际气体状态方程、玻尔兹曼能量分布理论以及两能态模型,得到了吸附热的数学表达式,并在物理实验基础上加以验证。实验结果表明:封闭体系内温度升高,升温促进解吸和加压促进吸附同时作用直至动态平衡,其中温度对解吸的促进作用要强于压力对解吸的抑制作用,体系整体表现为解吸作用;两能态模型能较准确地反映吸附热与温度和压力的变化关系,且吸附热是温度和压力的函数,其值与初始平衡条件有关,初始压力越大,吸附热越小,解吸时间越短,更易达到平衡。     

Theoretical study of simultaneous water and VOCs adsorption and desorption in a silica gel rotor

One-dimensional partial differential equations were used to model the simultaneous water and VOC (Volatile Organic Compound) adsorption and desorption in a silica gel rotor which was recommended for indoor air cleaning. The interaction among VOCs and moisture in the adsorption and desorption process was neglected in the model as the concentrations of VOC pollutants in typical indoor environment were much lower than that of moisture and the adsorbed VOCs occupied only a minor portion of adsorption capacity of the rotor. Consequently VOC transfer was coupled with heat and moisture transfer only by the temperatures of the rotor and the air stream. The VOC transfer equations were solved by discretizing them into explicit up-wind finite differential equations. The model was validated with experimental data. The calculated results suggested that the regeneration time designed for dehumidification may be prolonged to allow complete removal of the VOC pollutants from the rotor. The regeneration temperature designed for dehumidification provides considerable efficiency for indoor air cleaning. The application of the model in estimating the cleaning capacity of the rotor for VOC pollutants was demonstrated. PRACTICAL IMPLICATIONS: Silica gel rotors, usually used to dehumidify air, were found to be effective to remove VOCs by experiments recently. But the removal characteristics of VOCs are different from that of moisture. Therefore, the rotor structure and operating parameters for dehumidification needs to be optimized for the use of removing moisture and VOCs. This paper gives a way for the optimization.     

生土建筑围护结构表面吸放湿过程实验研究

陕南地区的生土建筑是一种独特的民居建筑 .为了定量地研究生土建筑室内热湿环境 ,确定生土建筑围护结构表面吸放湿过程质交换系数是一项基础工作 .建筑围护结构表面的热湿迁移过程是一个典型的边界层内的流动、传热和传质过程 ,该过程的微分控制方程比较复杂 ,求解困难 .首次实验研究了生土建筑材料的等温吸放湿过程 ,提出了生土建筑围护结构表面质交换系数实验测试方法 ,实测分析计算结果与利用对流质交换相似关系计算得到的表面质交换系数比较吻合 .本研究为定量地分析生土建筑室内热湿环境奠定了科学基础     

考虑温度影响下煤层气解吸渗流规律试验研究

通过不同温度条件下煤层气渗透率、渗流量测定的试验,研究了温度条件下煤层气渗透率、渗流量的影响因素,得到考虑温度情况下的煤层气解吸渗流规律。利用三维应力条件下煤样吸附解吸试验系统,在三轴渗透仪中加入温度控制系统,测定煤样在温度、围压、轴压和孔隙压力的不同组合情况下的渗透率和渗流量。结果表明,在相同围压、轴压和孔隙压力情况下,煤样渗透率随温度的增加而减少;不同温度条件下,渗透率随孔隙压力的增加均以指数形式递增。在相同围压、轴压和孔隙压力情况下,等温解吸时,煤样渗流量随温度的增加而减少;升温解吸时,煤样20℃吸附、升温至40℃解吸时渗流量比20℃吸附、20℃解吸时明显增加;等温或升温情况下,渗流量随孔隙压力增加均呈现非线性递增关系。这一规律对煤层气热采方式的选择具有重要指导意义。     

建筑内表面吸放湿过程对室内环境和空调负荷影响的仿真研究

提出了一个考虑室内表面材料吸放湿过程的建筑热湿过程简化模型,介绍了对室内空气湿度及空调负荷的仿真分析。仿真结果表明,室内表面材料吸放湿过程有明显的降低湿度变化幅度的作用,对潜热负荷的影响较大     

Dynamic and static adsorption and desorption of Hg(II) ions on chitosan membranes and spheres

The adsorption and desorption of Hg(II) ions was studied using static and dynamic methods, employing membranes and spheres of chitosan as the adsorbent. The quantity of adsorption was influenced by chitosan crosslinking and by the adsorbent shape. The Langmuir model was applied to fit the experimental equilibrium data. Glutaraldehyde-crosslinked membranes presented a lower desorption capacity, when compared to natural membranes, but could be regenerated for use in successive cycles. Dynamic adsorption experiments suggested that the adsorption capacity depended mainly on adsorbent geometry, due to differences between surface area to mass ratio and initial concentration of Hg(II) ions. The adsorption capacity determined by the dynamic method was 65% and 77% for membranes and spheres, respectively of the value obtained static method results. A process combining dynamic adsorption and static desorption can be used to concentrate the Hg(II) ions by a factor of nearly seven (7x), when compared to the initially treated volume.