1,721,000 research outputs found
Photocatalytic ozonation for a sustainable aquaculture: A long-term test in a seawater aquarium
No full textA long-term test at a laboratory scale with a closed system (a coral reef aquarium)has been carried out to study the potentialities of photocatalytic ozonation and photocatalysis for the removal of noxious organic compounds in recirculating systems (aquaria and recirculating aquaculture systems)working with a minimum make up of new water. Attention has been focused not only on the depuration capabilities but also on possible negative phenomena, some of which could become apparent only at long times. After having tuned the system by setting appropriate operating conditions and procedures, positive results were obtained. In particular, it was observed that the alternation of photocatalytic ozonation with photocatalysis with definite cycle allowed to severely limit the presence of the organic compounds, which otherwise could accumulate in the system, and at the same time to control the formation of bromate, the ozonation side-product of main concern. In addition, the values of other parameters, which are important for water quality, remained at satisfactory values. It was also verified that the prepared photocatalytic films maintained a good photocatalytic activity even after several months of utilization in seawater. These results demonstrate that photocatalytic ozonation is a good candidate for water purification in recirculating systems in view of sustainable aquaculture
Green synthesis of bromine by TiO2 heterogeneous photocatalysis and/or ozone: A kinetic study
No full textElemental bromine is an industrially relevant compound traditionally produced from bromide ions by using chlorine as the oxidizing agent. Problems related to transportation and handling of the corrosive, expensive and toxic chlorine make green synthetic alternatives highly desirable. In this paper the green synthesis of bromine from bromide in aqueous solutions under mild conditions by means of TiO2 photocatalysis and/or ozonation has been investigated from a kinetic point of view. The ozonation in the absence of the photocatalyst follows a first order kinetic with respect to both ozone and bromide. The kinetics of the reactions in the presence of the photocatalyst has been described by means of a Langmuir-Hinshelwood type model and the values of the kinetic constants and of the apparent adsorption constants have been determined. The results obtained constitute the basis for practical applications of this green and novel bromine synthesis and can be used for future reactor engineering and scale up of the process
Heat and mass transfer boundary layers in radial creeping flow
No full textHeat and mass transfer in radial flow between two parallel disks are analysed. This kind of problem is sometimes encountered in chemical engineering and we faced this situation in membrane separation processes in which the fluid is fed into the center of the cell and flows towards zones at higher radii. In the examined case heat and/or mass are exchanged across one of the two surfaces which confine the flow region. An analysis of the transport phenomena of such a geometry is performed by resorting to two different mathematical models. As a result the concentration and/or temperature profiles, the transport coefficients and the influence of the relevant dimensionless groups are obtained. The capability of the models to predict the experimental behavior of the vacuum membrane distillation process is demonstrated. © 1994
Green synthesis of vanillin: Pervaporation and dialysis for process intensification in a membrane reactor
Full text linkIn the present work, two different membrane processes (pervaporation and dialysis) are compared in view of their utilization in a membrane reactor, where vanillin, which is probably the most important aroma of the food industry, is synthesized in a green and sustainable way. The utilized precursor (ferulic acid, which is possibly a natural product from agricultural wastes) is partially oxidized (photocatalytically or biologically) and the product is continuously recovered from the reacting solution by the membrane process to avoid its degradation. It is observed that pervaporation is much more selective towards vanillin than dialysis, but the permeate flux of dialysis is much higher. Furthermore, dialysis can work also at lower temperatures and can be used to continuously restore the consumed substrate into the reacting mixture. A mathematical model of the integrated process (reaction combined with membrane separation) reproduces quite satisfactorily the experimental results and can be used for the analysis and the design of the process
A Collection of Chemical Reaction Engineering Solutions in Photocatalysis
No full textThere are problems in photocatalysis that researchers cannot disregard in a rigorous study of photocatalytic systems. The purpose of the present work is to show how chemical reaction engineering can answers to the previous questions, thus helping scientists to face researches on photocatalysis more successfull and consistent
Process for the production of bromine
No full textA process for the preparation of molecular bromine, by means of advanced oxidation processes or their combination is disclose
Photocatalytic Ozonation: from Science to Aquaculture Applications
No full textDemographic growth and management of water and food resources are probably the most challenging issues of the coming years. In this scenario, intensive aquacultura will be increasingly important in the near futur
A dialysis photocatalytic reactor for the green production of Vanillin
Full text linkIn the present work, dialysis was used to recover vanillin while being produced by partial photocatalytic oxidation of ferulic acid in an aqueous solution at ambient temperature. The relatively high value of the permeate flux through a dense polyether-block amide membrane allowed continuously extracting vanillin from the reacting solution, thus avoiding its successive oxidation. The rate of vanillin formation was improved, compared to other reactor configurations, because intermediate compounds permeated from the reacting solution and did not hinder the reaction, while ferulic acid permeated in the opposite direction to partially replenish the reactor with the substrate. The photocatalytic membrane reactor obtained by the effective coupling of dialysis with the photocatalytic reaction improved the production yield. For instance, with the utilized experimental set up, the total amount of vanillin produced after 5 h in the membrane reactor was more than one-third higher than in the photocatalytic reactor without dialysis. The results obtained with a mathematical model agree with the experimentally observed behavior. The model allowed estimating vanillin diffusivity in the membrane and showed that concentration polarization might limit the process
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