Thermodynamics Interaction Studies Solids, Liquids and Gases 2011 Part 3 pot

Thermodynamic Aspects of Precipitation Efficiency 89 the removal of microphysical effects of ice clouds barely impacts local atmospheric cooling on 5 June and it decreases local atmospheric cooling on 6 June, the decreases in stratiform rainfall are associated with the slowdown in transport of hydrometeor concentration from convective regions to raining stratiform regions. As a result, the decreases in stratiform rainfall lead to the decreases in PEH from CNIR to CNIM. On 7 June, the elimination of microphysical effects of ice clouds increases PEWV through the weakened water vapor divergence and increases PEH through the weakened local atmospheric cooling. 7. Conclusions Precipitation efficiency can be well defined through diagnostic surface rainfall budgets. From thermally related surface rainfall budget, precipitation efficiency associated with heat processes (PEH) is first defined in this study as the ratio of surface rain rate and the rainfall source from heat and cloud budgets. Precipitation efficiency associated with water vapor processes (PEWV) was defined by Sui et al. (2007) as the ratio of surface rain rate to the rainfall source from water vapor and cloud budgets. In this study, both precipitation efficiencies and their responses to effects of ice clouds are investigated through an analysis of sensitivity cloud-resolving modeling data of a pre-summer heavy rainfall event over southern China during June 2008. The major results include:  The calculations of model domain mean simulation data show that PEH is lower than PEWV because heat divergence contributes more to surface rainfall than water vapor convergence does. Precipitation efficiencies are lower during the decay phase than during the development of rainfall. PEH is generally lower than PEWV over convective regions, whereas it is generally higher than PEWV over raining stratiform regions. Precipitation efficiencies increase as surface rain rate increases.  PEWV has different responses to radiative effects of ice clouds during the different stages of the rainfall event. The exclusion of Microphysical effects of ice clouds generally decreases PEWV in the calculations of model domain mean simulation data, whereas it generally increases PEWV over raining regions.  The exclusion of radiative effects of ice clouds generally decreases PEH. The removal of microphysical effects of ice clouds generally decreases PEH except that it increases PEH over convective regions.  Effects of ice clouds on precipitation efficiencies can be explained by the analysis of surface rainfall budgets. The changes in PEWV are mainly associated with the changes in local atmospheric moistening and transport of hydrometeor concentration from convective regions to raining stratiform regions during the life span of pre- summer heavy rainfall event and the change in water vapor divergence on 7 June. The changes in PEH are mainly related to the changes in local atmospheric cooling and radiative cooling and transport of hydrometeor concentration from convective regions to raining stratiform regions during the life span of pre-summer heavy rainfall event. 8. Acknowledgment The authors thank W K. Tao at NASA/GSFC for his cloud resolving model, and Dr. N. Sun at I. M. Systems Group, Inc. for technical assistance to access NCEP/GDAS data. This study Thermodynamics – Interaction Studies – Solids, Liquids and Gases 90 is supported by the National Key Basic Research and Development Project of China under Grant No. 2011CB403405, the National Natural Science Foundation of China under Grant No. 41075039, the Chinese Special Scientific Research Project for Public Interest under Grant No. GYHY200806009, and the Qinglan Project of Jiangsu Province of China under Grant No. 2009. 9. References Auer, A. H. Jr. & Marwitz, J. D. 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Thermodynamics – Interaction Studies – Solids, Liquids and Gases 94 Yoshizaki, M. (1986) Numerical simulations of tropical squall-line clusters: Two- dimensional model. Journal of Meteorological Society of Japan, Vol.64, No.4, (August 1986), pp. 469-491, ISSN 0026-1165. 4 Comparison of the Thermodynamic Parameters Estimation for the Adsorption Process of the Metals from Liquid Phase on Activated Carbons Svetlana Lyubchik, Andrey Lyubchik, Olena Lygina, Sergiy Lyubchik and Isabel Fonseca REQUIMTE, Faculdade Ciência e Tecnologia, Universidade Nova de Lisboa Quinta de Torre, Campus da Caparica, 2829-516 Caparica Portugal 1. Introduction Over the past decades investigation of the adsorption process on activated carbons has confirmed their great potential for industrial wastewater purification from toxic and heavy metals. This chapter is focused on the adsorption of Cr (III) in high-capacity solid adsorbents such as activated carbons. There are abundant publications on heavy metal adsorption on activated carbons with different oxygen functionalities covering wide-range conditions (solution pH, ionic strength, initial sorbate concentrations, carbon loading and etc. (Brigatti et al., 2000; Carrott et al., 1997; Li et al., 2011; Lyubchik et al., 2008; Tikhonova et al., 2008; Kołodyńska, 2010; Anirudhan & Radhakrishnan, 2011). Although much has been accomplished in this area, less attention has been given to the kinetics, thermodynamics and temperature dependence of the adsorption process, which is still under continuing debates (Ramesh et al., 2007; Myers, 2004). The principal problem in interpretation of solution adsorption studies lies in the relatively low comparability of the data obtained by different research groups. These are due to the differences in the nature of the carbons, conditions of the adsorption processes and the chosen methodology of the metals adsorption analysis. Furthermore, the adsorption from the solution is much more complex than that from the gas phase. In general, the molecules attachment to the solid surface by adsorption is a broad subject (Myers, 2004). Therefore, only complex investigation of the metal ions/carbon surfaces interaction at the aqueous-solid interface can help to understand the metals adsorption mechanism, which is an important point in optimization of the conditions of their removal by activated carbons (Anirudhan & Radhakrishnan, 2008; Argun et al., 2007; Aydin & Aksoy, 2009; Ramesh et al., 2007; Liu et al., 2004). Particularly, thermodynamics has the remarkable ability to connect seemingly unrelated properties (Myers, 2004). The most important application of thermodynamics is the calculation of equilibrium between phases of the adsorption process profile. The basis for thermodynamic calculations is the adsorption isotherm, which gives the amount of the metals adsorbed in the porous structure as a function of the amount at equilibrium in the solutions. Whether the adsorption isotherm has been experimentally determined, the data points must be fitted with analytical equations for interpolation, extrapolation, and for the calculation of thermodynamic properties by numerical integration or differentiation (Myers, 2004; Ruthven, 1984). Thermodynamics – Interaction Studies – Solids, Liquids and Gases 96 It has to be noted, that the thermodynamics applies only to equilibrium adsorption isotherms. The equilibrium of heavy metals adsorption on activated carbons is still in its infancy due to the complexity of operating mechanisms of metal ions binding to carbon with ion exchange, complexation, and surface adsorption as the prevalent ones (Brown et al., 2000). Furthermore, these processes are strongly affected by the pH of the aqueous solution (Liu et. al., 2004; Chen and Lin, 2001; Brigatti et al., 2000). The influence of pH is generally attributed to the variation, with pH, in the relative distribution of the metal and carbon surface species, in their charge and proton balance (Csobán et al., 1998; Kratochvil and Volesky, 1998). Therefore, the equilibrium constants of each type of the species on each type of the activated sites are very important for the controlling of metals ions capture by activated carbons (Carrott et al., 1997; Chen & Lin, 2001). Another area of the debates is an optimum contact time to reach the adsorption equilibrium and, once again, regardless of the solution pHs, the differences in metal ions speciation, adsorbents charge and potential, complicate the overall process and make a comparison of the results of a metals capture by activated carbons difficult. The majority of studies on the sorption kinetics have revealed a two-step behaviour of the adsorption systems (Brigatti et al., 2000; Csobán et al., 1998; Raji et al., 1998) with fast initial uptake and much slower gradual uptake afterwards, which might take days even months (et al., 2000; Csobán et al., 1998; Raji et al., 1998; Kumar et al., 2000; Ajmal et al., 2001; Lakatos et al., 2002; Chakir et al., 2002; Leist et al., 2000; Csobán & Joó, 1999). Some of the authors reported the optimum contact time of minutes (Kumar et al., 2000; Ajmal et al., 2001), whereas, at the other extreme, that of hundred hours (Brigatti et al., 2000; Lakatos et al., 2002) for equilibrium to be attained; and the average values reported for the heavy metal binding were of 1–5 hours (Csobán et al., 1998; Raji et al., 1998; Chakir et al., 2002; Leist et al., 2000; Csobán and Joó, 1999). It has been also stressed that adsorption thermodynamics is drastically affected by the equilibrium pH of the solutions. Regardless of the equilibrium pH, adsorption of the heavy metals by a single adsorbent could be completed in a quite different contact time (Carrott et al., 1997; Lalvani et al., 1998; Farias et al., 2002; Perez-Candela et al., 1995). Taking into account that equilibration of metal ions uptake by activated carbons depends on the equilibrium pH, authors agreed (Lyubchik et al., 2003) with the statement (Carrott et al., 1997) that it would be appropriate to express adsorption results in terms of the final solution pH. However, this practice is not widely used by the investigators. Due to the prolonged time is needed to accomplish thermodynamic equilibrium conditions, the adsorption experiments are often carried out under pseudo-equilibrium condition, when the actual time is chosen either to accomplish the rapid adsorption step or, rather arbitrary, to ensure that the saturation level of the carbon is reached (Kumar et al., 2000). However, once again, the adsorption models are all valid only and, therefore, applicable only to complete equilibration. The study presented herein is part of the work aimed the exploration of the mechanism of Cr (III) adsorption on activated carbons associated with varying of surface oxygen functionality and porous texture. The mechanism of chromium adsorption was investigated through a series of equilibrium and kinetic experiments under varying pH, temperature, initial chromium concentration, carbon loading for wide-ranging carbons of different surface properties (i.e. texture and surface groups) (Lyubchik et al., 2004; Lyubchik et al., 2005; Lyubchik et al., 2008); and particular objective of the current study is evaluation of the thermodynamics (entropy, enthalpy, free energy) parameters of the adsorption process in the system “Cr (III) – activated carbon”. Comparison of the Thermodynamic Parameters Estimation for the Adsorption Process of the Metals from Liquid Phase on Activated Carbons 97 Thermodynamics were evaluated through a series of the equilibrium experiments under varying temperature, initial chromium concentration, carbon loading for two sets of the commercial activated carbons and their oxidised by post-chemical treatment forms with different texture and surface functionality. This approach served the dual purpose: i) gained deep insight into various carbon’s structural characteristics and their effect on thermodynamics of the Cr (III) adsorption; and ii) gained insight, which often very difficult or impossible to obtain by other mean, into equilibrium of the Cr (III) adsorption on activated carbon. The thermodynamics parameters were evaluated using both the thermodynamic equilibrium constants and the Langmuir, Freundlich and BET constants. The obtained data on thermodynamic parameters were compared, when it was possible. 2. Experimental 2.1 Materials Two commercially available activated charcoals GR MERCK 2518 and GAC Norit 1240 Plus (A– 10128) were chosen as adsorbents. The activated carbons were used as supplied (parent carbons) and after their oxidative post treatments. Chemical treatment aimed at introduction of the surface oxygen functional groups on the carbon surface. In some conditions, the chemical treatments also changed the carbons porous texture. 2.1.1 Surface modification Commercial activated charcoals GR MERCK 2518 and GAC Norit 1240 Plus (A– 10128) have been subjected to the post-chemical treatment with 1 М nitric acid at boiling temperature during 6 h. The oxidized materials, were subsequently washed with distilled water until neutral media, and dried in an oven at 110 0 C for 24 h. 2.1.2 Surface characterization The textural characterization of the carbon samples was based on nitrogen adsorption isotherms at 77K. These experiments were carried out with Surface Area & Porosimetry Analyzer, Micromeritics ASAP 2010 apparatus. Prior to the adsorption testing, the samples were outgassing at 240 0 C for 24 h under a pressure of 10 -3 Pa. The apparent surface areas were determined from the adsorption isotherms using the BET equation; the Dubinin- Raduskhevich and B.J.H. methods were applied respectively to determine the micro- and mesopores volume. The oxidation treatment resulted in reduction of the apparent surface area with mesopores formation (Table 1). The carbon’s point zero charge (pH PZC values) were obtained by acid–base titration (Sontheimer, 1988). pH PZC decreases when the carbon surface is treated with nitric acid (Table 1). The parent carbons and their oxidized forms were characterized by elemental and proximate analyses using an Automatic CHNS-O Elemental Analyzer and a Flash EATM 1112 (Table 2). The oxygen content significantly increases when the carbon surface is treated with nitric acid. The carbon surface was also characterized by temperature-programmed desorption with a Micromeritics TPD/TPR 2900 equipment. A quartz microreactor was connected to a mass spectrometer set up (Fisons MD800) for continuous analysis of gases evolved in a MID (multiple ion detection) mode. Surface oxygen groups on carbon materials decomposed Thermodynamics – Interaction Studies – Solids, Liquids and Gases 98 upon heating by releasing CO and CO 2 at different temperatures (Table 3). The assignment of the TPD peaks to the specifics surface groups was based on the data published in the literature (Figueiredo, 1999). Thus, a CO 2 peak results from decomposition of the carboxylic acid groups at low temperatures (below 400 0 C), or lactones at high temperatures (650 0 C); carboxylic anhydrous decompose as CO and CO 2 at the same temperature (around 650 0 C). Ether (700 0 C), phenol (600-700 0 C) and carbonyls/quinones (700-980 0 C) decompose as CO. The treatment by nitric acid resulted in an increase in carboxylic acids and anhydrous carboxylic, lactones and phenol groups. Carbons S BET , (m 2 / g ) V total , (cm 3 / g ) V micro , (cm 3 / g ) S meso , (m 2 / g ) S micro , (m 2 / g ) pH PZC Merck_ initial 755 0.33 0.31 41 714 7.02 Merck_1 M HNO 3 1017 0.59 0.55 40 977 3.41 Norit_initial 770 0.40 0.32 41 729 6.92 Norit_1 M HNO 3 945 0.43 0.41 72 873 4.41 Table 1. Textural and surface characteristics of the studied activated carbons. Carbons Proximate analysis (wt %) Elemental analysis (wt %) Moisture Volatile Ash C H N O Norit_initial 3.9 6.7 2.8 95.2 0.40 0.48 3.90 Norit_1M HNO 3 1.8 7.9 2.0 87.9 0.60 2.60 8.90 Merck_initial 2.0 9.1 3.2 92.8 0.25 0.40 6.50 Merck_1M HNO 3 1.7 12.8 2.0 86.3 0.30 0.54 12.80 Table 2. Proximate and elemental analyses of the studied activated carbons Carbons Oxygen evolved, (g/100g) CO 2 CO CO/CO 2 Norit_initial 0.49 1.18 2.41 Norit_1M HNO 3 3.18 5.94 1.86 Merck_initial 0.44 1.15 2.61 Merck_1M HNO 3 3.05 18.7 6.22 Table 3. Surface oxygen functionality of the studied activated carbons All chemicals used were of an analytical grade. Salt Cr 2 (SO 4 ) 2 OH 2 , which is used in the tanning industry, was used as a sources of trivalent chromium. Metal standard was prepared by dissolution of Cr (III) salt in pure water, which was first deionized and then doubly distilled. The initial pH of the resulting Cr (III) solution was 3.2. The chromium solution was always freshly prepared and used within a day in order to avoid its aging. [...]... 2.5448 1.01750.5 632 0.5651 2. 639 2 0,9 636 5. 635 0 2.2412 0.1245 0.9680 4.1 034 0.97950.8566 0.2990 3. 8750 0,9745 5.2799 0 .35 09 0.4684 0. 534 4 0.5419 22. 033 6 31 .7875 15.4698 12.76 23 0.67 93 0.8272 0.8058 0. 832 7 -1.0185 -0,0954 0.9644 0.1022 1.25500.9641 0 .35 25 9. 535 3 0.7945 3. 1000 -0. 139 9 -0.2946 0.9701 28.9194 2.62280 .30 15 0.2 937 3. 2066 0.9727 4 .39 25 -0 .34 38 -0 .34 43 0.9677 9.7227 1.69420.7065 0.2 134 2.7445 0.9672... pH3.2 Merck 75.9 837 0.9795 10.6608 0.7 836 0.9641 0.1197 9.1498 138 .7455 0.52 53 3.9487 0.05080.9608 0.1092 3. 4681 23. 7812 0.6158 3. 2485 0. 135 10.94 43 0.1164 -16.8765 4.2890 0.67 73 4.2274 0.17480.8825 0.0997 -9 .33 69 Langmuir constants T, 0C 22 30 40 50 22 30 40 50 22 30 40 50 22 30 40 50 R2 Initial 0.7671 Initial 0.7921 Initial 0.7711 Initial 0.7 730 1M 0.9877 HNO3 1M 0.9606 HNO3 1M 0.9042 HNO3 1M 0.94 03. .. 0.94 03 HNO3 Initial 0.9728 Initial 0.9411 Initial 0.8679 Initial 0.9576 1M 0.9728 HNO3 1M 0.9688 HNO3 1M 0.9810 HNO3 1M 0.9827 HNO3 qmax, mmol/g 0.1290 0.2617 0 .33 32 0 .30 27 107 Equlibrium constants R2 Kd 0.0945 0.1976 0.2040 0.1677 4.701 6.688 5.445 4.754 -3. 7564 -0.0466 0.9898 5. 438 6 1.07560.9214 0 .35 25 3. 1462 0,9 630 3. 936 1 2 .34 53 0.1021 0.9595 4.7 632 1.2 235 0.6241 0 .31 64 2.5019 0.9717 4.70 63 2.1961... 0.2 134 2.7445 0.9672 5.0415 -0. 438 9 -0.2106 0.9588 9. 438 7 1.64540.7 735 0.1910 2.7281 0.9860 4.62 23 Fixed [Carbon] = 4 g/l, pH3.2 Merck 84.5720 0.9752 1.1620 0.06150.9670 0.0689 10.40 93 0.0667 3. 1676 0 .39 85 0.9868 3. 1705 0. 836 20.9746 0.4179 2 .33 40 0.9701 5 2972 Norit 28.0 537 0.9792 3. 2751 0 .37 480.9786 0.1157 9.5029 0.1740 3. 2 031 0.9891 0.2496 1. 538 40.9817 0.1720 8.0 431 0.9758 4.7848 22 Initial 0.9915... 1. 538 40.9817 0.1720 8.0 431 0.9758 4.7848 22 Initial 0.9915 0.1159 1M 22 0.9661 1.0690 HNO3 22 Initial 0.9716 0.2756 1M 22 0.9851 0.5617 HNO3 0.8277 Norit 3. 7895 0.10170.9 436 3. 7895 0.18200.99 73 2.1710 0. 236 00.9899 1. 933 3 0. 232 00.9854 0.1 931 9.7116 0,1412 3. 5450 0.4087 176.2481 0. 234 5 5.0420 0.4127 130 .32 93 0.1845 3. 9250 0.4020 148.4 132 0.0945 4.6290 Table 4 Parameters of the Cr(III) adsorption on studied activated... 12) and was plotted against the adsorbate concentration at the adsorbent surface [Cr III]eql, as shown in Fig 13 114 Thermodynamics – Interaction Studies – Solids, Liquids and Gases Fig 8 Plots of Langmuir (KF); Freundlich (KF), BET (KBET) and thermodynamic equilibrium constants (Kd) vs temperature for the adsorption of Cr(III) on parent Norit () and Merck () and modified by 1M HNO3 Norit (▲) and. .. attributed to the combined chemical-physical adsorption processes Fig 13 Plot of isosteric heating (ΔHx) as a function of the amount adsorbed of the parent Norit () and Merck () activated carbons and their oxidized by1M HNO3 Norit (▲) and 1M HNO3 Merck() forms 118 Thermodynamics – Interaction Studies – Solids, Liquids and Gases 3. 4 General remarks It should be stressed, however, that the interpretation... activated carbon at () – 22; () – 30 ; () – 40 and () – 50 0C On the other hand, Langmuir, Freundlich and BET constants showed similar variation with temperature (Fig 8 (I), (II) and (III)), and hence were also used to calculate the thermodynamic parameters (compare the R2 for different calculations, Table 5) 112 Thermodynamics – Interaction Studies – Solids, Liquids and Gases Table 5 Thermodynamic parameters... Christmann, 2010) 100 Thermodynamics – Interaction Studies – Solids, Liquids and Gases Since the adsorptive and the adsorbent often undergo a chemical reactions, the chemical and physical properties of the adsorbate is not always just the sum of the individual properties of the adsorptive and the adsorbent, and often represents a phase with new properties (Christmann, 2010) When the adsorbent and adsorptive... () – 40 and () – 50 0C 106 Thermodynamics – Interaction Studies – Solids, Liquids and Gases Fig 3 Isotherms of the Cr (III) adsorption on initial Merck activated carbon at different temperatures: () – 22; () – 30 ; () – 40 and () – 50 0C Fig 4 Isotherms of the Cr(III) adsorption on initial Norit activated carbon at different temperatures: () – 22; () – 30 ; () – 40 and () – 50 0C Comparison . 9. 535 3 0.7945 3. 1000 30 1M HNO 3 0.9688 -0. 139 9 -0.2946 0.9701 28.9194 2.62280 .30 15 0.2 937 3. 2066 0.9727 4 .39 25 40 1M HNO 3 0.9810 -0 .34 38 -0 .34 43 0.967 7 9.7227 1.69420.7065 0.2 134 . 0.987 7 -3. 7564 -0.0466 0.9898 5. 438 6 1.07560.9214 0 .35 25 3. 1462 0,9 630 3. 936 1 30 1M HNO 3 0.9606 2 .34 53 0.1021 0.9595 4.7 632 1.2 235 0.6241 0 .31 64 2.5019 0.9717 4.70 63 40 1M HNO 3 0.9042 2.1961 0.2201. 0.7711 0 .33 32 23. 7812 0.6158 3. 2485 0. 135 10.94 43 0.1164 -16.8765 0.2040 5.445 50 Initial 0.7 730 0 .30 27 4.2890 0.67 73 4.2274 0.17480.8825 0.0997 -9 .33 69 0.1677 4.754 22 1M HNO 3 0.987 7 -3. 7564