Adsorption of Volatile Organic Compounds

Adsorption of Volatile Organic CompoundsADSORPTION OF explosive ORGANIC COMPOUNDS ON DIFFERENT TIMBER SPECIESMarco Vasconcelos1, Nereida Cordeiro1,2*ABSTRACTDue to the wellness issues associated to VOC, this work aims to study the surface assimilation of these compounds onto flavourlands, in tack together to improve blood tone of voice. For this task, rearward bumble chromatography (IGC) was utilise to characterize mount properties (surface vigor, specific scanty animation and enthalpy of adsorption). Dispersive theatrical role of the surface null (SD) ranged from 39.95 to 43.81 mJ/m2, check to Amburana and courbaril respectively. lily-livered Pine shows lavishlyer value of the specific deliver push button of adsorption (Gs), indicating a higher(prenominal) number/ talent of polar sprightly sites. On the opposite hand, the enthalpy of adsorption baffle (Hs) dont go in agreement with Gs, believably collectible to its temperature-dependence. That said, the Hs determine guide a prefatory surface and Amburana establishes stronger interactions with polar probes while Yellow Pine establishes stronger interactions with cyclohexane. Additionally, the thermodynamic wages effect was guessd on these samples, being observe bedarity in Yellow Pine, Grapia and Brazilian burnt sienna. The set up was analogous betwixt the different species, indicating a equal adsorption weapon.Keywords reverse Gas Chromatography, Surface Properties, Wood Fibers, Volatile Organic Compounds, thermodynamic recompense effect1. INTRODUCTIONVolatile organic compounds (VOC) are organic compounds produced in industries, motor vehicles, power plants, etc. They are usually distinguished by boiling temperatures under 250C, at standard atmospheric pressure (1 atm), and with high vapor pressures, surpassing 0.5 kPa at 25C (Dobre, Prvulescu, Iavorschi, Stroescu, Stoica, 2014). The aforesaid(prenominal) compounds apply harmful impact on human health, such as eye and throat irritation, damage to the liver, central nervous system and carcinogenic effects, repayable to prolonged exposure (Das, Gaur, Verma, 2004). Therefore, reducing the VOC concentration on the air is an important task in order to improve air quality and avoid health issues.Wood fibers consist in both lifeless and living cells, being at a macroscopic level make within a layer of xylene, in the wood. From the chemical point of view, consists generally in cellulose, followed by hemicellulose and lignin. Due to the hydrogen bonds established by the hydroxyl group groups of cellulose of the surface, it affects strongly on the properties of the material, such as hydrophobicity and therefore its reactivity (Hodzic, Shanks, 2014). more or less 80.5% of the wood fibers are used in the paper industry and more or less 17% for wood fibers modification ( compounds Kazayawoko, Balatinecz, Romansky, 1997 Adusumali, Reifferscheid, Weber, Roeder, Sixta, Gindl, 2006 Cao, Hu, Liu, 2008).In this work, Inverse float Chromatography (IGC) was used to characterize the surface properties (surface brawniness, specific free energy and enthalpy of adsorption) of Amburana, Yellow Pine, Grapia, Courbaril and Brazilian Mahogany to evaluate the adsorption of some VOC (Chloroform, cyclohexane, ethyl radical acetate, benzine and methylbenzene). Additionally, the thermodynamic compensation effect was analyse to investigate the appliance of thermodynamic adsorption on the different samples examine.2. MATERIALS AND METHODS2.1 MaterialsMethane (99.99% purity) was used an inert course credit probe and the carrier gas utilized was helium (99.99% purity), both supplied by Air Liquide Company. The probe scraps were supplied by SigmaAldrich with GC grade (99% purity).2.2 iGC analysisiGC measurements were carried out, at least, in duplicate, on a commercial inverse gas chromatograph (Surface Measurements Systems, London, UK) fitted out(p) with a flame ionization (FID), thermal cond uctivity (TCD) and mass spectrometer (MS) detectors. Standard glass silanized (dymethyldichlorosilane Repelcote BDH, UK) columns with 0.4 cm ID and 30 cm in continuance were used.About 1.5 g of step sawdust mesh 40-60 was packed by just tapping for 10 min. The columns, with the samples, were pre-treated for 2h at 343 K and 10 ml/min of beat period rate, to clear up the impurities adsorbed on the surface and 2h at the measurement conditions. After pre-treatment, pulsation injections were carried out with a 0.25 l gas loop. The iGC system was fully change with purpose written control software (SMS iGC Controller v1.3) and data were analyzed using iGC Standard v1.3 and Advanced Analysis Software v1.21. The presented results are the amount of the determine obtained for each sample with a standard deviation peanut than 5%.Measurements of the dispersive interaction were made with n-alkanes (n-decane, n-nonane, n-octane, n-heptane and n-hexane) at 298 K, at 0% RH. The carrier ga s (Helium) work rate was 10 ml/min. To acid-base studies cyclohexane, benzene, chloroform, toluene and ethyl acetate were used at 0% RH. Heat of sorption measurements were through with the polar probes at 298 K, 0% RH, and 10 ml/min head for the hills rate.3. RESULTS AND DISCUSSION3.1 Dispersive component of the surface tensityThe solventsorption properties of the tinctures were studied at infinite dilution condition in order to remove the interactions mingled with the probe molecules adsorbed at the surface of the samples. The methane injection allows the calculation of the dead time and subtracts it to the retention time in order to obtain the retention bulk (Thielmann, 2004). The corrected net retention volume VN is effrontery bywhere Vd is the brisk phase hold-up volume (called dead volume), and VR the thrifty retention volume. The 0 superscript indicates a correction for the column pressure drop given by jwhere where T is the column temperature, F is the exit flow rat e at 1 atm and 273.15K, tR is the retention time and t0 is the mobile phase hold-up time.The dispersive component of the surface energy, as well as the specific free energy of sorption, was measured with dispersive and acid-base probe molecules. The apprisal between the retention volume and free energy of sorption GS is given by the following equationG0S = RTln VR0 + Kwhere R is the gas constant and K is the De Boer or Kemball/Rideal constant depending on the chosen pen state (De Boer, 1953 Kemball Rideal, 1946). Moreover, G0S is related to the energy of adhesion WA (between probe molecule and truehearted) by the equationG0S = NAaWAwhere a is the cross sectional area of the adsorbate and NA the Avogadro constant. According to Fowkes (1964), the dispersive contribution of the work of adhesion WA is given byWA = 2(SDLD)1/2with SD and LD as the surface tension of the adsorbent and the adsorbate respectively. Combining the equations aboveThus, the dispersive component of the surfac e tension (SD) value could be calculated based on the patchs of RT lnV0R vs a(LD)1/2 for the adsorption of n-alkane probes, as illustrated in see 1. Good unidimensional correlations (0.9991-0.9996) were obtained for the n-alkane serial for all samples analyzed. The calculated SD value are given in confuse 1 and show very similar results between the different calibre species. The surface energy ranged from 39.95 to 43.81 mJ/m2, corresponding to Amburana and Courbaril respectively. These value are similar to those reported by Kazayawoko, Balatinecz, Romansky (1997) and Shu, Xu, JinWei, BaoLi (2007) for wood flour (35.6 mJ/m2 at 323K) and ashtree wood repast (36.52 mJ/ m2 at 323K) respectively. Gouveia, Cordeiro and conjuring trick (2011) reported various lignocellulosic fibres (flax, hemp, kenaf, century plant, agave hybrid pineapple, and sisal), with SD values ranged from 37.17 to 51.37 mJ/ m2 (at 298K).In the same article aforementioned, its also explained that variations in the SD values can be due to the different composition, growing conditions of the fibers and method of extraction. The latter(prenominal) is justified due to the fibers being usually covered by a layer of wax, and may interfere with elutant-fiber interactions. When removed during the method of extraction its evaluate to change drastically the surface energy.3.2 Polar probes sorption studiesA far-flung approaching to the Lewis acid/base surface interactions can provide break dance perceptive of the chemical-physical properties of the timber surfaces. The presence of acid and base active agent sites on the surfaces increases the possibility of specific intermolecular interactions with solvents and some others compounds.The specific free energy of sorption, Gs was rigid by the distance between the alkane line and the points corresponding to the Gs value of polar probes (Gamble, Leane, Olusanmi, Tobyn, Supuk, 2012).Gs = RTln(VN) RTln(VNref)The Gs values are given in put off 2 an d represented in Figure 2. Chloroform was used as an acid probe on this work. The values ranged from 0.53 to 2.50 kJ/mol, corresponding to Brazilian Mahogany and Yellow Pine respectively. Based on the results obtained, the Gs values of Chloroform decrease in the following order Pine Grapia Courbaril Amburana Mahogany. This observation indicates that Yellow Pine may have a higher quantity/energy of active sites with basic character compared to the other fibers.A similar order was spy on Cyclohexane, indicating that Yellow Pine exponent also have a higher quantity/energy of active sites with apolar character. Although, the same order is not observed in SD, since that for the surface energy were used n-alkanes and due to the shape of cyclohexane and consequent different steric hindrance, it provide have different interactions with the surface. On the other hand, Brazilian Mahogany shows the lowest Gs values for the overall probes, indicating a lower quantity/energy of active sit es.Ethyl acetate was used as a basic probe in Amburana, Yellow Pine and Courbaril. The interaction of this probe, alongside chloroform, with the timber surface indicates the presence of both acidic and basic sites on the solid surface.3.3 Heat of sorption measurementsIn the infinite dilution region, where the isotherm is analogue, VN should be measured at a range of column temperatures and ln(VN/T) plotted vs. 1/T, which yields the heat of sorption Hs according to (Conder Young, 1979)To determine the enthalpies of sorption (HS) of the VOCs in the timber species, the specific retention volume (VN) was measured at different temperatures (293 to 298K) and the retention diagrams ln VN vs 1/T were plotted (Fig. 3-7). virtually of VOCs couldnt be used in some of the timber species because the retention time was too low to make accurate calculations due to the peak overlap.The Hs values are given in dodge 3, determined at three different temperatures. Good linear correlations (0.99) wer e obtained for the probes used, as shown in Figures 3-7. In this work, the Hs values for the basic probes (Ethyl acetate Higher DN/AN*) were lower than the Hs values for the acid probes (Chloroform Lower DN/AN*), indicating a basic character of the solid surface. Cordeiro, Mendona, Pothan and Varma (2012) and Gouveia, Cordeiro and John (2011) observed the same basic character in macro and nanobanana fibers, flax, hemp, kenaf, agave, agave hybrid pineapple, and sisal.For chloroform, the Hs values decreased in the following order Amburana Brazilian Mahogany Grapia Courbaril Yellow Pine. At first sight it indicates that Amburana establishes stronger interactions with the surface, compared with the other timbers. On the other hand, Yellow Pine establishes the weakest interactions with chloroform. A similar order was also observed for cyclohexane, for the exception of Yellow Pine, that shows the highest Hs value for this probe.The results dont go in agreement with the ones obtained f rom the specific free energy of adsorption study, probably due to the fact that the temperature might influence the Gs values and therefore it might mislead to incorrect conclusions. Thus, the Hs values will give a better insight of which timber is advised (or not) to remove VOC from the atmosphere since it already have in account the temperature. Being said, the results indicate that for polar probes Amburana have stronger interactions while for apolar probes Yellow Pine have stronger interactions.3.4 second of Sorption calculationThe linear dependence between HS and SS is called Thermodynamic Compensation act. Normally, stronger intermolecular interactions (related to HS) result in less degrees of freedom of the elutant, leading into a greater order of the system, decreasing the haphazardness of the system (Liu L., Guo Q-X., 2001). The entropy of sorption was instantly calculated according toFigure 8 represents the entropy-enthalpy correlation, being only observed on Yellow P ine, Grapia and Brazilian Mahogany. All three dependences are linear and almost parallel, with a slope between 2.7910-3 and 3.7310-3 K-1. Therefore, these three samples follow the forward equation. According to Korolev A. et al., (2011), a similar slope indicates similar adsorption mechanism on the samples studied on this work. Since all the samples have similar composition, it was expected the same adsorption mechanism between them.4. CONCLUSIONIGC was used to evaluate different surface properties, namely surface energy, specific free energy and enthalpy of adsorption. The SD values were measured at 298K and ranged from 39.95 to 43.81 mJ/m2. These variations between results are due to different composition, growing conditions and method of extraction.The results dont go in agreement between enthalpy of adsorption and the specific free energy of adsorption probably due to the influence of the temperature on the Gs. In Yellow Pine were observed higher Gs values for chloroform and cy clohexane compared to the other fibers, indicating a higher quantity/energy of active sites with basic and apolar character. In Amburana, Yellow Pine and Courbaril, the basic probes showed lower Hs values compared to acid Hs values, indicating a basic character. The same was observed on other fibers found in literature. Amburana establishes stronger interactions with Chloroform while Yellow Pine establishes stronger interaction with cyclohexane, compared to the other timber species.The Thermodynamic Compensation Effect was only observed in Yellow Pine, Grapia and Brazilian Mahogany, with linear fits almost parallel. The slope ranged between 2.7910-3 and 3.7310-3 K-1. Similar slopes indicate similar adsorption mechanism, which makes sense due to similar composition.ACKNOWLEDGEMENTReferencesAdusumali R-B, Reifferscheid M, Weber H, Roeder T, Sixta H, Gindl W. Mechanical properties of regenerated cellulose fibres for composites. Macromolecular Symposia 2006, 244 11925.Cao S., Hu B., Liu H. Synthesis of pH-responsive crosslinked polystyrene-co-(maleic sodium anhydride) and cellulose composite hydrogel nanofibers by electrospinning. Polymer International 2009, 58 545551.Cordeiro N., Gouveia C., John M. J. Investigation of surface properties of physico-chemically special natural fibers using inverse gas chromatography. Industrial Crops and Products 2011, 33 108115.Cordeiro, N., Mendona, C., Pothan, L. A., Varma, A. observe surface properties evolution of thermochemically modified cellulose nanofibres from banana pseudo-stem. Carbohydrate Polymers 2012, 88, 125131.De Boer, J.H., 1953. The moral force Character of Chemisorption, 2nd Ed., Clarendon Press, Oxford.Gamble J., Leane M., Olusanmi D., Tobyn M., Supuk E., Khoo J., Naderi M., 2012, Surface energy analysis as a tool to probe the surface energy characteristics of micronized materials A compare with inverse gas chromatography International Journal of Pharmaceutics 422 238-244Kemball C., Rideal, E.K. The Adsor ption of vapors on Mercury. I. Non-Polar Substances. 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Chichester John Wiley Sons Ltd.TABLE CAPTIONSTable 1 Dispersive component of the surface tension (SD).Table 2 Specific free energy of sorption (GS).Table 3 heat content of sorption (HS).Table 4 second of sorption (SS).Table 1Table 2Table 3Table 4FIGURE CAPTIONSFigure 1 Energy of adsorption vs a(DL)1/2 for n-alkanes on the timbers (Amburana, Grapia, Courbaril, Brazilian Mahogany and Yellow Pine) surface at 298K and 0%RH.Figure 2 Specific free energy of the adsorption (Gs) of Chloroform and Cyclohexane onto samples analyzed at 298K.Figure 3 Enthalpy of sorption plot and linear fits for cyclohexane, chloroform and ethyl acetate measurement on Amburana timber surface 293-298K, at 0 % RH and 10ml/min.Figure 4 Enthalpy of sorption plot and linear fits for cyclohexane, chloroform and ethyl acetate measurement on Yellow Pine timber surface 293-298K, at 0 % RH and 10ml/min.Figure 5 Enthalpy of sorption plot and linear fits for cyc lohexane, chloroform and benzene measurement on Grapia timber surface 293-298K, at 0 % RH and 10ml/min.Figure 6 Enthalpy of sorption plot and linear fits for cyclohexane, chloroform and ethyl acetate measurement on Courbaril timber surface 293-298K, at 0 % RH and 10ml/min.Figure 7 Enthalpy of sorption plot and linear fits for cyclohexane, chloroform and toluene measurement on Brazilian Mahogany timber surface 293-298K, at 0 % RH and 10ml/min.Figure 8 Entropy-enthalpy compensation effect on Yellow Pine, Grapia and Brazilian Mahogany.Figure 1Figure 2Figure 3Figure 4Figure 5Figure 6Figure 7Figure 8