溶剂在高分子膜中传递现象研究的进展

溶剂在高分子膜中吸收和解吸的传递机理非常复杂,对其传递过程的研究有助于膜分离过程的开发、膜材料的选择。本文对溶剂在高分子膜中传递现象研究的进展作简要介绍。     

Adaptive Neuro-Fuzzy inference system analysis on sorption studies of strontium and cesium cations onto a novel impregnated nano-zeolite

In this research, a novel impregnated nano-zeolite (NAASMS-Z) was synthesized and characterized using different characterization techniques. Excellent properties, such as high specific surface area (~502.77 m²/g), low pore size (~8.92 Å) and the existence of numerous functional groups caused the efficient elimination of Sr²⁺ and Cs⁺ cations from aquatic systems. The sorption performance of the nano-particles was enhanced by impregnation up to 60% in the aquatic media. The kinetic study indicated that the elimination process of both the concerned cations is controlled by external film mass transfer through the boundary within the first 30 min then controlled by intra-particle diffusion. The sorption equilibrium data suggested that the sorption process occurs on the heterogeneous sorbent surface. Parameters affecting the elimination of Sr²⁺ and Cs⁺ from a single metal sorption system, such as pH, initial contaminant concentration (C_i) and contact time (t), were investigated and optimized. A predictive model based on an Adaptive Neuro-Fuzzy Inference system (ANFIS) analysis was applied to evaluate the experimental parameters affecting the elimination of Sr²⁺ and Cs⁺ cations from aquatic system. A Mamdani-type FIS was employed to justify a collection of 16 rules (If-Then format) by means of centroid membership functions. The suggested fuzzy model revealed high predictive concert with high correlation coefficient (R²) and satisfactory deviation from the experimental data, affirming its appropriateness to predict Sr²⁺ and Cs⁺ elimination efficacy from the studied system. Rooted in experimental data and statistical analysis, the synthetized material was effective for treating contaminated aquatic solutions containing Sr²⁺ and Cs⁺ cations.     

Degradation of soil-sorbed trichloroethylene by stabilized zero valent iron nanoparticles: effects of sorption, surfactants, and natural organic matter

Zero valent iron (ZVI) nanoparticles have been studied extensively for degradation of chlorinated solvents in the aqueous phase, and have been tested for in-situ remediation of contaminated soil and groundwater. However, little is known about its effectiveness for degrading soil-sorbed contaminants. This work studied reductive dechlorination of trichloroethylene (TCE) sorbed in two model soils (a potting soil and Smith Farm soil) using carboxymethyl cellulose (CMC) stabilized Fe-Pd bimetallic nanoparticles. Effects of sorption, surfactants and dissolved organic matter (DOC) were determined through batch kinetic experiments. While the nanoparticles can effectively degrade soil-sorbed TCE, the TCE degradation rate was strongly limited by desorption kinetics, especially for the potting soil which has a higher organic matter content of 8.2%. Under otherwise identical conditions, ∼44% of TCE sorbed in the potting soil was degraded in 30 h, compared to ∼82% for Smith Farm soil (organic matter content = 0.7%). DOC from the potting soil was found to inhibit TCE degradation. The presence of the extracted SOM at 40 ppm and 350 ppm as TOC reduced the degradation rate by 34% and 67%, respectively. Four prototype surfactants were tested for their effects on TCE desorption and degradation rates, including two anionic surfactants known as SDS (sodium dodecyl sulfate) and SDBS (sodium dodecyl benzene sulfonate), a cationic surfactant hexadecyltrimethylammonium (HDTMA) bromide, and a non-ionic surfactant Tween 80. All four surfactants were observed to enhance TCE desorption at concentrations below or above the critical micelle concentration (cmc), with the anionic surfactant SDS being most effective. Based on the pseudo-first-order reaction rate law, the presence of 1×cmc SDS increased the reaction rate by a factor of 2.5 when the nanoparticles were used for degrading TCE in a water solution. SDS was effective for enhancing degradation of TCE sorbed in Smith Farm soil, the presence of SDS at sub-cmc increased TCE degraded by ∼10%. However, effect of SDS on degradation of TCE in the potting soil was more complex. The presence of SDS at sub-cmc decreased TCE degradation by 5%, but increased degradation by 5% when SDS dosage was raised to 5×cmc. The opposing effects were attributed to combined effects of SDS on TCE desorption and degradation, release of soil organic matter and nanoparticle aggregation. The findings strongly suggest that effect of soil sorption on the effectiveness of Fe-Pd nanoparticles must be taken into account in process design, and soil organic content plays an important role in the overall degradation rate and in the effectiveness of surfactant uses.     

DRYING OF WASTE SLUDGES IN A FLUIDIZED BED DRYER WITH A MIXER

Sludge wastes are a very attractive source of many valuable compounds such as nitrogen, phosphorus and organic matter. One of the interesting methods of sludge utilization is dewatering and drying. In this paper some problems of drying of two types of sludge wastes of different form and origin are presented. One of the sludges—a brewery by-product— contains spent grain suspension of brewer's yeast and diatomaceous earth. The second one is a by-product of a biotechnological process which contains mainly lime, protein, many microelements and some microorganisms. Moisture content of both sludges is about 65-70% w/w. The laboratory experiments of sludge drying in the fluidized bed dryer with a mixer, fluidized bed hydrodynamics, and the effects and advantages of sludge drying are shown.     

Effects of dissolved organic matter from the rhizosphere of the hyperaccumulator Sedum alfredii on sorption of zinc and cadmium by different soils

Pot experiments were conducted to investigate the changes of the dissolved organic matter (DOM) in the rhizosphere of hyperaccumulating ecotype (HE) and non-hyperaccumulating ecotype (NHE) of Sedum alfredii and its effects on Zn and Cd sorption by soils. After planted with HE, soil pH in the rhizosphere reduced by 0.5-0.6 units which is consistent with the increase of DOM. The hydrophilic fractions (51%) in DOM from the rhizosphere of HE (HE-DOM) was much greater than NHE-DOM (35%). In the presence of HE-DOM, Zn and Cd sorption capacity decreased markedly in the following order: calcareous clay loam > neutral clay loam > acidic silty clay. The sorption isotherms could be well described by the Freundlich equation (R² > 0.95), and the partition coefficient (K) in the presence of HE-DOM was decreased by 30.7-68.8% for Zn and 20.3-59.2% for Cd, as compared to NHE-DOM. An increase in HE-DOM concentration significantly reduced the sorption and increased the desorption of Zn and Cd by three soils. DOM derived from the rhizosphere of the hyperaccumulating ecotype of S. alfredii could significantly reduce metal sorption and increase its mobility through the formation of soluble DOM-metal complexes.     

Predicting moisture state of timber members in a continuously varying climate

A prerequisite for a sensible estimate of moisture induced stresses in timber members is an accurate prediction of the members’ moisture states during their service life. There are, however, an infinite number of possible moisture states for an arbitrary timber member in a natural varying climate. The naturally varying humidity is possible to describe as harmonic cycles, with different periods, superimposed. This work presents realizations of envelop curves over the possible moisture states in a timber member for some carefully chosen harmonic humidity variations. The calculations, on which the realizations were made, are based on a fully coupled transport model including a model for the influential sorption hysteresis of wood. A format containing required information suitable for assessing the “moisture” action on timber members is proposed. In addition it is illustrated how a model of high complexity and nonlinearity renders results with large degree of consistency. Large moisture gradients in a timber member are detected when variations of the humidity are frequent (daily period) and with large amplitude at high humidity levels. Overall and complete moisture changes of structural timber members with normal dimensions are found for members subjected to varying humidity with long (annual) periods. A timber member’s initial moisture state in relation to the ambient humidity can have a significant influence on both moisture gradients and overall moisture change of the member.     

Separation of IPA/water mixtures by pervaporation: sorption and pervaporation results

Homogeneous membranes were prepared by blending polyvinyl alcohol (PVA) with polyacrylic acid (PAA) and furthermore the blend membrane is cross-linked covalently through an ester linkage formation between a hydroxyl group of PVA and carboxyl group of PAA. These membranes were evaluated for separation of azeotropic isopropyl alcohol (IPA)/water mixtures by pervaporation, that is, a vacuum applying membrane process. The overall and preferential sorption of IPA/water mixtures in cross-linked membranes were determined to investigate the influence of PVA/PAA ratio and of liquid mixture composition. Pervaporation characteristics were also determined as a function of PVA/PAA ratio and of the feed mixture composition. With increasing PAA content in the membranes, solubilities and fluxes decreased and selectivities increased. Because of polarity, water permeated preferentially through the membranes. Sorption results showed the same tendency as pervaporation results.     

A Study of the Limitations to Spray Dryer Outlet Performance

The concept of the product moisture locus was tested in this work using a pilot-scale modified Niro spray dryer (diameter 0.8 m, height 2 m), where the residence time of the particles inside this spray dryer is lower compared with larger industrial spray dryers. The moisture contents of skim milk powder produced from spray drying skim milk (solids content 8.8% w/v) at different operating conditions, namely different swirl vane angles (0°, 25°, 30°), inlet air temperatures (170°C, 200°C, 230°C) and process fluid flowrates (1.4 kg h^-1, 1.6 kg h^-1, 1.8 kg h^-1), were compared with the predicted equilibrium moisture contents. In addition, the residence time of the particles was also increased in the spray dryer by decreasing the inlet air mass flowrate from 0.016 to 0.013 kg s^-1. The outlet moisture contents of the skim milk powder for all the 23 runs carried out in this work were within 0.4% of the equilibrium values. Thus, the skim milk powder particles were in close equilibrium with the gas inside the drying chamber. These equilibrium limitations are confirmed by other literature data (Boonyai, P. Comparative Evaluation of Soymilk Drying in a Spray Dryer and Spouted Bed of Inert Particles. M.Sc. Thesis. Asian Institute of Technology: Bangkok, Thailand, 2000; 90 pp; Harvie, D.J.E.; Langrish, T.A.G.; Fletcher, D.F. A computational fluid dynamics study of a tall-form spray dryer. Trans IChemE 2002, in press). The use of this finding to predict spray dryer performance is demonstrated by mass and energy balance calculations.     

锝在格列土上的吸附研究

用静态实验法研究了锝在格列土上的吸附行为，考察了葡萄糖，ＮａＯＨ和腐殖酸对锝在格列土上吸附比（Ｒｄ）的影响，结果表明，格列土比一般地表土（砂土，凝灰岩土等）对锝有更大的吸附比，微生物活动能够阻滞锝的迁移，腐殖酸对吸附的影响不大，ＮａＯＨ可以增加格列土锝的阻滞能力。