1,720,984 research outputs found
Effect of the Fill Duration on the Aerobic Biodegradation of 3-CP in a Sequencing Batch Reactor
No full textRimozione dell’arsenico mediante processo di scambio ionico in presenza di anioni competitivi
No full textIon Exchange Processes for Arsenic Removal from Solutions with High Sulfate Concentrations: Breakthrough and Regeneration Tests
No full textDesign criteria for ion exchange process for arsenic removal from groundwater and surface water.
No full textCharacterization of natural and anthropogenic phenolic compounds in soils
No full textThis chapter provides a review of the most updated state of the art on both extraction and detection methods of soil phenols and treatment of soils contaminated by phenols. The presence of natural phenolic compounds in soils is due to the biochemical degradation and transformation of organic substances. However, there is an increasing presence in soils of phenolics due to anthropogenic activities
Ion exchange equilibria of arsenic in the presence of high sulfate and nitrate concentration
Full text linkThe aim of this work was to develop a quantitative description of the ion exchange equilibria of arsenic on a strong anionic resin, in the presence of nitrates and sulphates. First, the ion exchange equilibrium data of As(V) and NO3- on a strong anionic resin in chloride form were obtained and described with a model based on the mass action law. Namely, assuming ideal behaviour for both solution and resin phase, the thermodynamic constant of the As(V)/Cl- and NO3-/Cl- ion exchange equilibria were estimated by fitting of experimental data. Then, these equilibrium constants were used to predict the ion exchange behaviour of the ternary system As(V)/NO3-/Cl-, providing a rather good agreement with experimental results. The ion exchange equilibria involving sulphate ions were also studied, showing,a very high affinity to the resin phase. This behaviour did not allow a quantitative robust modelling of the equilibrium pattern. The results discussed in this paper represent a first step toward the development of a comprehensive modelling of the ion exchange process for the removal of As(V) from surface and groundwater in the presence of competitive, naturally occurring anions
Measurement of the dimerization equilibrium constants of enantiomers
No full textThe formation of homochiral and heterochiral dimers in solutions of enantiomers causes a number of remarkable phenomena, such as the enantiomeric enrichment of nonracemic mixtures on achiral chromatographic columns when chiral monomers and dimers exhibit different retention behavior. In this work, such effects on optical rotation and UV absorbance are analyzed theoretically and experimentally. In particular, it is demonstrated how optical rotation measurements can be used to estimate the dimerization equilibrium constants. It is shown how significant this is for polarimeter calibration, as well as for the determination of enantiomer concentrations in process streams, when optical rotation and UV absorbance measurements are combined. All experimental measurements refer to the enantiomers of the chiral 2,2'-dihydroxy-1,1'-binaphthyl in chloroform, at a temperature of 23 degreesC. The measured values of its dimerization equilibrium constants are 1.3 +/- 0.5 and 3.1 +/- 1.0 L/mol for the formation of homochiral and of heterochiral dimers, respectively
Vapor-phase SMB adsorptive separation of linear/nonlinear paraffins
No full textThe separation of various mixtures of the C-5-C-6 paraffin fraction is considered, being an important stage of the process aimed to gasoline octane enhancement. The separation is carried out in a six-port vapor phase SMB pilot plant operated at 448 K and 350 kPa, using n-heptane as desorbent and 5A-zeolite as adsorbent. The experimental runs deal with the separation of both a binary mixture (70% isopentane and 30% n-pentane) and a multicomponent C-5-C-6 stream. The results of these experiments illustrate the role and the effect of the different operating parameters on the process performance and demonstrate the possibility of achieving high performance separation. Moreover, they nicely assess the reliability of the known criteria for selecting robust and optimal operating conditions for SMB units
Design of Optimal Operating-conditions of Simulated Moving-bed Adsorptive Separation Units
No full textThe design of the optimal operating conditions for simulated moving bed (SMB) adsorptive separation units is considered. A procedure for the a priori selection of the operating conditions to achieve an assigned separation requirement is developed in the frame of equilibrium theory for the equivalent four section countercurrent unit, using a model where the adsorption equilibria are described through the constant selectivity stoichiometric model, while both mass transfer resistance and axial dispersion are neglected. The space of the operating parameters, i.e. the mass now rate ratios m(j), is divided in regions with different separation regimes. Curves at constant outlets purity and recovery are drawn in the (m(2),m(3)) plane. The introduction of three performance parameters, desorbent requirement, adsorbent requirement, and productivity, allows the development of a procedure for the design of optimal operating conditions. This procedure is completed, accounting for the effect of the switching time on the separation performances, with a detailed model of the SMB unit, considering both axial dispersion and mass transfer resistance. This result constitutes a useful tool for determining the range of operating conditions to achieve an assigned separation requirement and then for selecting the optimal operating condition within this range
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