164 research outputs found
Solubility of benzene in copolymer aqueous solutions for the design of gas absorption unit operations
No full textIn this work, an amphiphilic block copolymer (ABC) aqueous solution is proposed as innovative green liquid for benzene recovery from polluted gas. This ABC has been selected among four commercially available copolymers, two thermosensitive ABC containing poly-ethylene oxide and poly-propylene oxide blocks-Pluronic (R) L62 and Pluronic (R) P123 - one non-thermosensitive ABC - poly(vinyl pyrrolidone)-polystyrene (PVP-PS) and one non-ionic surfactant - polyoxyethylene sorbitol monooleate (Tween 80 (R)). For each copolymer aqueous solution, benzene Henry's constant (H) has been experimentally calculated and the effects of temperature (4-90 degrees C) and copolymer concentration (4-20%) have been investigated. Experimental results at 20 degrees C and 4% copolymer concentration showed that the H values are in the range 50-280 atm, with a ranking PVP-PS 1100 atm) has been measured in P123 aqueous solution at 90 degrees C, corresponding to its critical point (i.e. phase separation and no micelles presence). As a result of its benzene H values, the P123 aqueous solution was found to be the most promising liquid for benzene recovery among those investigated, being effective for both operations of gas absorption (at low temperature) and solvent regeneration by thermal stripping (at high temperature)
Sustainability Indicators for Materials and Processes
No full textThe concept of sustainability is nowadays employed to compare manufacturing processes or to define the correct path for material selection. Sometimes, this concept is only partially defined, including just low costs, profit maximization and/or CO2 emission reduction. Actually, a process or material can be defined as sustainable only if an objective function related to the economic, environmental and social impacts is simultaneously maximized. To this aim, it is necessary to define appropriate and specific sustainability indicators (i.e., values related to the economic, social and environmental aspects of a process or material under analysis). These indicators come about from simple calculations, and they are defined in terms of percentages and represented and compared using radar diagrams. Then, a process or specific material is identified by an objective function (i.e., the area included by the polygon that links the scores reported on the diagram). The scope of this representation of data is to individuate the major weaknesses of the process/material, proposing methods of optimization and trying to maximize the objective function in the retrieved diagram. This work aims to propose a general and simple method to calculate sustainability indicators on the basis of specific definitions related to a given process/material. To highlight the potential of this calculation and comparison instrument, two case studies are proposed: the first aims at comparing processes for the production of energy, while the second aims at driving the choice of manufacturing material. The selected indicators and adopted algorithm allowed for the identification of hydroelectric and eolic as the most sustainable processes for energy production; for materials, the results strictly depended on the assumptions made regarding favorable mechanical properties
A modelling analysis of PCE/TCE mixture adsorption based on Ideal Adsorbed Solution Theory
No full textFor a proper design of multicomponent adsorption systems, the availability of reliable adsorption models is paramount. In this work, an experimental and modelling analysis of PCE/TCE adsorption, aimed at investigating adsorption capacities in a binary system, is carried out. All the experimental tests are conducted at constant pH and temperature. The analyte concentration is varied over a wide range in order to cover as much as possible real cases that could lead to different adsorption behaviours and, consequently, to different modelling results.
Experimental data show that the PCE adsorption capacity does not depend on TCE presence, and the equilibrium final conditions are not related to different analyte adsorption rates.
The equilibrium adsorption data are analyzed by using different adsorption models, namely Langmuir multicomponent, Ideal Adsorbed Solution Theory (IAST) and Predictive Real Adsorbed Solution Theory (PRAST) models. The Langmuir model provides the worst data prediction since its basic hypotheses do not reflect the physical behaviour of the system.
The IAST model does not provide a satisfactory prediction of binary data except for low liquid concentration levels, as it underestimates the PCE adsorption capacity and overestimates ICE. It follows that when the solid coverage increases, the PCE-TCE mixture behaviour is not ideal. Finally, the PRAST model, here developed for liquid systems for the first time, is considered in order to take into account a non-ideal system by including activity coefficients. The PRAST model provides a very good prediction of PCE adsorption experimental data but it is not useful to predict ICE adsorption data, its performance being even worse than IAST. The inability of the model to correctly predict both isotherms simultaneously lies in the particular type of non-ideality of the system itself, as shown by experimental data
A Real Adsorbed Solution Theory model for competitive multicomponent liquid adsorption onto granular activated carbon
No full textIn this work, a new Real Adsorbed Solution Theory (RAST) model, for competitive multicomponent adsorption equilibrium correlation in liquid systems has been developed. The model is derived from Ideal Adsorbed Solution Theory; in its formulation it explicitly takes into account the non-ideal behavior shown by most of the adsorption systems. The occurrence of interactions among adsorbed molecules is accounted for by the introduction of activity coefficients, as a function of sorbates adsorption capacity and spreading pressure. These coefficients are experimentally evaluated through multicomponent adsorption isotherms determination, also considering single-compound adsorption isotherm parameters in the model formulation. The RAST model was tested on the experimental results of tetrachloroethylene/trichloroethylene (PCE/TCE) binary mixtures adsorption, obtained at constant temperature and different concentration ratio of the two compounds. This model, with the experimental determination of activity coefficients, allowed an accurate description of PCE/TCE binary adsorption experimental data, thus being a reliable instrument for the design of industrial adsorption equipment for wastewater containing a mixture of pollutants
Desorption of arsenic from exhaust activated carbons used for water purification
No full textThis work aims to the analysis of arsenic desorption from an exhaust activated carbon used for the purification of a natural water. This last was used to mimic the properties of common groundwater or drinking water. Different low-cost and harmless eluting solutions were considered, including distilled water, natural water, saline (NaCl, CaCl2 and NaNO3) and basic (NaOH) solutions. Experimental results showed that, for 1 g of activated carbon with arsenic loading close to the maximum value available for the model natural water (omega approximate to 0.1 mg/g), it is possible to recover more than 80% of the arsenic using 20 ml of 0.1 M sodium chloride solution. A temperature variation within 20 and 40 degrees C has scarce effect on desorption efficiency. A comparison between desorption data and adsorption isotherms data suggests that arsenic adsorption is actually a reversible process. Therefore, it is virtually possible to increase arsenic recovery efficiency close to 100% by increasing the NaCl concentration or the volume of the desorption solution, but a preliminary cost benefit analysis lead to consider a NaCl 0.1 M solution as an optimal solution for practical application
Theoretical investigation of the solubility of some antiemetic drugs
No full textA theoretical study using density functional theory (DFT) is carried out to compare and explain the observed solubility of four antiemetic molecules, namely chlorpromazine, haloperidol, ondansetron and metoclopramide.The COSMO-RS (conductor-like screening model for real solvents) method is used to study the interaction between hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs) of the antiemetic drugs, and their molecular interactions with water (dipole moments, interaction and solvation energies). In addition, the AIM (Atoms in Molecules) method is used to deeply study the hydrogen bonding interaction of the antiemetic drug which was found the most soluble in water, namely the metoclopramide. In fact, results show that atom O42 makes two H-bonds with two different water-oxygen atoms (BCP59 and BCP60). One of them, have another H-bond (BCP62) with the hydrogen H27. This study confirms that two of the three H-bonds with water are more stable than the intramolecular interaction between O9 and H27 (BCP1). These H-bonds are likely responsible of the highest solubility of metoclopramide
Fixed-bed adsorption of trichloroethylene onto activated carbon
No full textThe present work deals with the study of the adsorption of Trichloroethylene (TCE) onto a commercial
granular activated carbon (GAC). Thermodynamic (batch) and dynamic (fixed-bed column) tests were
carried out, under a wide range of operating conditions. In particular, adsorption isotherms were
preliminary determined to support the investigation on a fixed-bed column at lab-scale. The main fluid
dynamic and physical parameters such as flow rate, TCE concentration and GAC particle size were
investigated.
Experimental data on fixed-bed column show that an increase in TCE initial concentration and, more
markedly, an increase in flow rate lead to a shorter breakpoint time. In fact, the breakthrough curves
become steeper as a consequence of higher velocity that enhances the external mass transport.
Finally, a thorough modeling analysis of the fixed-bed column was carried out using a model that includes
axial dispersion and external-film diffusion followed by internal diffusion. A good accordance between
experimental data and model results was observed
Investigation of adsorption process of benzene and toluene on activated carbon by means of grand canonical ensemble
No full textIn this work, the performances of a commercial activated carbon (Filtrasorb 400, provided by Calgon) were experimentally tested for the adsorption of different aromatic compounds, i.e., toluene and benzene from synthetic groundwater. Batch adsorption tests were carried out at constant pH (8) and four different temperatures (10-50 degrees C). The experimental equilibrium adsorption data were fitted with a new statistical physics model named as 'multilayer model with saturation' and established through the grand canonical ensemble in statistical physics. The characteristic model parameters of the adsorption isotherm such as the number of benzene or toluene molecule(s) per site, n, the receptor site densities, N-M, the number of adsorbed layers (N-L) and the energetic parameter, (-epsilon(1)) and (-epsilon(2)), were estimated for the studied systems by a non-linear least square regression. These parameters were discussed and interpreted for their temperature dependence. The calculated thermodynamic parameters such as entropy, Gibbs free energy and internal energy from experimental data showed that the adsorption of benzene and toluene onto activated carbon Filtrasorb 400 was feasible, spontaneous and exothermic in nature
Mercury adsorption on granular activated carbon in aqueous solutions containing nitrates and chlorides
No full textAdsorption is an effective process to remove mercury from polluted waters. In spite of the great number of experiments on this subject, the assessment of the optimal working conditions for industrial processes is suffering the lack of reliable models to describe the main adsorption mechanisms. This paper presents a critical analysis of mercury adsorption on an activated carbon, based on the use of chemical speciation analysis to find out correlations between mercury adsorption and concentration of dissolved species. To support this analysis, a comprehensive experimental study on mercury adsorption at different mercury concentrations, temperatures and pH was carried out in model aqueous solutions. This study pointed out that mercury capture occurs mainly through adsorption of cationic species, the adsorption of anions being significant only for basic pH. Furthermore, it was shown that HgOH+ and Hg2+ are captured to a higher extent than HgCl+, but their adsorption is more sensitive to solution pH. Tests on the effect of temperature in a range from 10 to 55 degrees C showed a peculiar non-monotonic trend for mercury solution containing chlorides. The chemical speciation and the assumption of adsorption exothermicity allow describing this experimental finding without considering the occurrence of different adsorption mechanisms at different temperature
Interpretation of single and competitive adsorption of cadmium and zinc on activated carbon using monolayer and exclusive extended monolayer models
No full textIn this work, a modeling analysis based on experimental tests of cadmium/zinc adsorption, in both single-compound and binary systems, was carried out. All the experimental tests were conducted at constant pH (around neutrality) and temperature (20 A degrees C). The experimental results showed that the zinc adsorption capacity was higher than that of cadmium and it does not depend on cadmium presence in binary system. Conversely, cadmium adsorption is affected by zinc presence. In order to provide good understanding of the adsorption process, two statistical physics models were proposed. A monolayer and exclusive extended monolayer models were applied to interpret the single-compound and binary adsorption isotherms of zinc and cadmium on activated carbon. Based on these models, the modeling analysis demonstrated that zinc is dominant in solution and more favorably adsorbed on activated carbon surface. For instance, in single-compound systems, the number of ions bound per each receptor site was n (Zn2+) = 2.12 > n (Cd2+) = 0.98. Thus, the receptor sites of activated carbon are more selective for Zn2+ than for Cd2+. Moreover, the determination of adsorption energy through the adopted models confirmed that zinc is more favored for adsorption in single-compound system (adsorption energies equal to 12.12 and 7.12 kJ/mol for Zn and Cd, respectively) and its adsorption energy does not depend on the cadmium presence in binary system. Finally, the adsorption energy values suggested that single-compound and binary adsorption of zinc and cadmium is a physisorption
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