MohammadAbu]HossAINI,MikioKuMITAl, YoshimasaMIcHIGAMI2andShigeruMoRIl IGra血α'eScノZooノqノノV、"ralScje"Ceα"d7bcノ!"o〃gy, Kα"αZuWaU"jverSj[ybKakⅨ"'α-"1αcノzj,Kα"αZawa-Sノ、j, バカjkawa920-II92,〃pα〃 zE'Zyjm""ze"'αノP、/eajo〃助gj"eerj"gCe"'eM(ZJ"αZawaUmlノ巴応j(y, KaAcw1a-"1αcノZj,j、"αzawa-shj,ノs/liAawa920-ノノ92,"pα〃 K2ywords:AdsorptionChromium(VI),UsedBlackTbaLeaves,KineticAnalysis,RateConstant KineticinvestigatiomswerecarriedouttoevaluatetheapplicabiIityofusedblackteaIeaves(UBTLs) asalow-costadsorbenttOtheremovalofchromium(Ⅵ)fromaqueOussoIutions・Theeffectsofvarious thekineticstudyontheremovaIofCr(VI)byUBTLs Thepredictionoftheadsorptionrateforagivensystemisthemostimportantparameterforadsorberdesignwithadsorbateresidencetime,ultimatelycontroI-1edbythekineticsoftheadsorptionsystem(Eligweej aL,1999). Variousresearchershavedescribedtheorderof adsorptivereactionofmetalionsinaqueoussystem usingdifferentkineticmodels、Theadsorptionsof ReceivedonOctoberl2,2004Correspondenceconcerningthis articleshouldbeaddressedtoSMori(E-mailaddress: smori@しkanazawa-u・ac.』p).
Dynamic characteristics of Cr(VI) sorption on used black tea leaves (UBTLs) as a low-cost adsorbent are studied. Batch experiments were conducted to evaluate the effects of Cr(VI) concentration, solution pH and temperature on the removal process. Both of adsorption and reduction, involved in the process, are affected by the processing parameters. The adsorption kinetics is described successfully using pseudo-second order rate equation and the rate constant decreases with increasing the initial concentration of Cr(VI) up to 150 mg/L (for 0.1 g/L UBTLs) then becomes slow. Experimental and calculated kinetic data for equilibrium are well expressed by Langmuir isotherm. The solution pH has a profound effect on the adsorption rate. The rate constant increases linearly with an increase in temperature, and the low value of activation energy of adsorption, 16.3 kJ/mol, indicates that Cr(VI) is easily adsorbed on UBTLs. The maximum Cr(VI) adsorptive conditions, with a minimum reduction, were achieved from the dynamics of operational parameters: the initial Cr(VI) concentration <150 mg/L (for 0.1 g/L UBTLs); the initial solution pH = 1.54-2.00 and the processing temperature <50 • C, for the possibility of its practical application.
There is an increasing demand of air filters with a high collection performance, i.e., high collection efficiency and low pressure drop, for the application to indoor air cleaning. Air filters consisting of nanofibers have attracted great interests since they may have a low pressure drop because of slip flow effect and high collection efficiency due to interception. Although various nanofiber filters are available on the market, their collection performance is not as high as expected by the conventional filtration theory because non-uniform packing of fibers plays a significant role. In the present work, the collection performance of nanofiber (780 nm) and microfiber (11.2 µm) mixed filters with various mixing fractions was studied in order to maximize the quality factor of filter, q F , as a function of mixing fraction of nanofibers. The collection performance of mixed fiber filters was predicted by using theoretical equations reported by Bao et al. (1998) for bimodal distribution of fibers. As a result, it was found that the mixed fiber filters had a uniform fiber packing compared to laminated filters and that the collection efficiency was well predicted by introducing the inhomogeneity factor calculated for the filter consisting of two distinct fiber sizes. Furthermore, we found that the mixed fiber filter with the nanofiber mixing fraction of 5% in mass had the highest quality factor.
The slip flow effect is often brought out to explain the reduction in pressure drop for nanofiber filters. Kirsch et al. (1973) studied the slip flow effect on the pressure drop of fibrous filters consisting of micron fibers, and proposed an empirical equation to predict the dependence of the dimensionless drag, F, on the Knudsen number, Kn, with considering non-uniformity of fiber packing. However, their empirical equation was derived based on the experiments with filters consisting of micron fibers so that the empirical equation is not yet verified for nanofiber filters. In the present work, we used various commercially available nanofiber filters with various physical properties, and the pressure drop was measured at low pressures in order to examine the validity of the empirical equation. As a result, we found that the empirical equation is valid even for nanofiber filters with a large inhomogeneity factor at a large Kn up to 20.
A new adsorbent coating for the adsorber unit of an adsorption heat pump made of hybrid, organic-inorganic microfibres was prepared and characterized. Different coatings were obtained by the electrospinning of polyvinylpyrrolidone (PVP) solutions added with different quantities of tetraethyl orthosilicate (TEOS). PVP is a polymer with water adsorption capability and the TEOS addition allowed to increase the thermal stability of microfibres. The aim, indeed, was to preserve the polymeric structure of microfibres in order to obtain coatings with high flexibility and mechanical strength. The results demonstrated that TEOS concentrations in the range of 5-13 wt.% produced microfibre coatings of non-woven textile structure with both good water affinity and good thermal stability. SEM images of coatings showed that the deposited microfibre layers have both a high surface area and a high permeability representing a significant advantage in adsorption systems.Coatings 2019, 9, 443 2 of 12 and silica tetrahedra that form a crystalline nanoporous structure with hydrophilic behavior [14,15]. Although zeolites are the ideal adsorbing solid for the elevated thermal stability, their use in adsorption systems is limited by the high regeneration temperatures. The desorption of water vapor from the zeolite porosity requires temperatures above 300 • C for the complete material dehydration [16,17]. The ideal exploitation of this technology, indeed, is the coupling with low temperature heat sources (T < 150 • C), like solar thermal panels or waste combustion fumes [11,18]. For such a reason, other adsorbing materials have been proposed and sometimes used in solid sorption applications, like silica gel, alumino-phosphour zeotypes (AlPO and SAPO), and metalorganic frameworks (MOF). AlPO and SAPO are interesting for their high adsorption capacity, their good structural stability, and low regeneration temperatures but they are difficult to find on the market and costly [19,20]. MOF are new adsorbing materials with large water capacity and low regeneration temperatures, but their structural stability is still an open issue and they are expensive and difficult to find in large quantities [21,22]. Among others, silica gel is the adsorbent most used in commercial adsorption chillers mainly for its low cost and large availability on the market although it shows a lower water adsorption capacity and problems of morphological and thermal stability [22][23][24][25].Over the years, the scientific community has focused not only on the development of the porous material but also on the engineering of the absorber, the heat exchanger module where the adsorbent material is located. In order to reduce heat transfer resistances, the porous material distribution around the heat exchanger surfaces is very important. Zeolites and silica gel are generally used in form of granules or powder and the simplest and most used solution is to fill the free space between the fins of the heat exchanger with the adsorbent granules. In this case, however, the poor co...
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