1,721,178 research outputs found
Electrochemical treatment as a pre-oxidative step for algae removal using Chlorella vulgaris as a model organism and BDD anodes
No full textAn experimental work is presented in this paper on the inactivation of algae through electrochemical treatment. A green algae (Chlorella vulgaris) was adopted as a model. A commercial filter-press electrochemical reactor (Electro MP-Cell), equipped with a boron doped diamond (BDD) anode and a stainless steel cathode, was used to perform the electrolysis. The cell was inserted in a hydraulic circuit and used in either a closed loop, as a recirculating batch reactor, or in the continuous mode. The effects of current density and hydrodynamics were studied, as well as the formation of active chlorine and other chloride oxidation products. Active chlorine concentrations on the order of 0.3 mmol dm(-3) were obtained when algae were not present in the initial solution (batch experiments) or in the feed (continuous experiments). In the presence of algae, the value was 0.03 mmol dm(-3). The highest values were measured with i = 75 A cm(-2) and flow conditions corresponding to a Reynolds number of 100 (batch experiments) or a hydraulic residence time of 4 min (continuous experiments). The process led to the total inactivation of algae when 100 mg dm(-3) of chlorides was present in the solution, which is a typical value for natural waters. The results indicated that, under the adopted conditions, the prevailing mechanism was inactivation by means of long-life oxidants electrogenerated. A simple model of continuous stirred tank reactors (CSTRs) in-series was adopted to account for the non-ideal flow conditions in the continuous experiments, which was able to interpret the data under all the conditions tested. (C) 2013 Elsevier B.V. All rights reserved. RI Mascia, Michele/D-8080-2011; Vacca, Annalisa/D-8073-2011 OI Mascia, Michele/0000-0001-9733-9008; Vacca, Annalisa/0000-0003-3795-986
Cubic-to-Tetragonal Phase Transitions in Ag-Cu Nanorods
Full text linkMolecular dynamics simulations have been used to investigate the structural behavior of nanorods with square cross section. The nanorods consist of pure Ag and Cu phases or of three Ag and Cu domains in the sequence Ag-Cu-Ag or Cu-Ag-Cu. Ag and Cu domains are separated by coherent interfaces. Depending on the side length and the size of individual domains, Ag and Cu can undergo a transition from the usual face-centered cubic structure to a body-centered tetragonal one. Such transition can involve the whole nanorod, or only the Ag domains. In the latter case, the transition is accompanied by a loss of coherency at the Ag-Cu interfaces, with a consequent release of elastic energy. The observed behaviors are connected with the stresses developed at the nanorod surfaces
Optimal Distillation Sequence For The Separation of a N-Paraffin Mixture Under Industrial Constraints: a Case Study
No full textEffect of surface equilibria on the electrokinetic behaviour of Pb and Cd ions in kaolinite
No full textBACKGROUND: Electrokinetic remediation of fine-grained soils polluted by heavy metals is affected by the equilibria between dissolved and sorbed ions; pH can also influence the surface equilibria. Geochemical models which describe the behaviour of different surface sites and their interactions with heavy metal ions have to be considered for a good mathematical representation of an electrokinetic process. RESULTS: Cd2+ and Pb2+ sorption isotherms were performed at different pH values using kaolinite as sorbent. Electrokinetic tests were performed with samples of kaolinite spiked with Cd2+ and Pb2+ at 0.7 and 2Vcm-1: the concentration profiles were obtained experimentally at different treatment times. The pH in the compartments was conditioned by acetate buffer. On the basis of the experimental results, a numerical model was formulated to simulate ion transport under an electric field combining the diffusion-advection equations with a two-sites geochemical model taking into account ion exchange and surface complexation of the metal ions, as well as the protonation-deprotonation reactions of the surface sites. CONCLUSIONS: The process was effective for cadmium removal, while a strong dependence on pH was observed for lead removal. The model allowed prediction of time/space profiles in solid and liquid phase: a good agreement with the experimental data was obtained under all the conditions adopted
Energy saving in a crude distillation unit by a preflash implementation
No full textAfter the 70s energy crisis the revamping of plants designed before this date is very attractive for improving energy recovery and lowering operation costs. A typical case is the oil refinery plant where an intensive usage of energy takes place and is a promising case for the application of energy saving solutions. In this work we focused our attention to an industrial crude oil distillation unit, evaluating the possibility to modify the feed conditions by installing a preflash drum or a preflash plate column. Real data plant were collected to obtain a reliable simulation of the unit by means of the software package Aspen Plus 13.0. To characterize the crude oil fed the TBP curve was used. The results obtained were compared with the plant data in terms of flow rate and product quality utilizing the ASTM D-86 curves and a good agreement was obtained. According to the specialized literature the preflash drum/column was placed at the end of the pre-heat train, just before the column furnace. The furnace is the bottleneck of the plant and with both the preflash devices it is possible to lower its energy consumption. However the energy reduction is associated to the decrease of one kind of distillates (light or middle). The choice of the best preflash device was made according to the production asset of the plant. (C) 2008 Elsevier Ltd. All rights reserved
Partial feed and product withdrawal for the SMB separation of a glucose-fructose mixture
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Recovery of polyphenols from olive oil mill wastewaters by a chromatographic process: design and simulation
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