The flow of two immiscible fluids was investigated in rectangular glass microchannels with equivalent diameters of 269 and 400 m. Deionised water, dyed toluene and hexane were selected as probe fluids. Flow patterns were obtained for Y-and T-junction of two micro-channels and monitored by a photo-camera. Volumetric velocities of water and organic phase varied between 1 and 6 ml/h. The formation mechanism of slug and parallel flow was studied and the mass transfer performances of two flow patterns were compared. The shape of the interface between the immiscible liquids was controlled by a competition between the viscous forces and the local interfacial tension. The flow patterns could be correlated with the mean Capillary and Reynolds numbers. The mass transfer coefficients for parallel and slug flow were determined using instantaneous neutralisation (acid-base) reaction. The two flow patterns showed the same global volumetric mass transfer coefficients in the range of 0. 2-0. 5 s −1 , being affected mainly by the base concentration in water for parallel flow and by the linear velocity in the case of the slug flow.

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Chemical batch processes are typically used for the production of speciality chemicals and pharmaceuticals. Due to the still growing importance of this type of processing, design methods are required that take into account the special requirements and constraints in the corresponding production facilities. We developed a method that optimizes the design of a single chemical process to be implemented in an existing multi-purpose batch plant, in which a well-defined set of equipment units is available for realizing this process. In the optimization, three objectives with different priorities are considered. A flexible metaheuristic algorithm, Tabu Search (TS), has been implemented to solve this multi-objective combinatorial non-linear problem. We started from a basic form of TS to determine the effectiveness of this version as well as establish the relative strengths and weaknesses of first level TS strategies. Our investigation includes a thorough examination of algorithm parameters and of implementation issues to identify algorithm settings that can handle the whole class of problems considered. Overall, we concluded that the basic form of TS-using fixed default settings-exhibits highly attractive performance features for solving the problems at hand. Moreover, comparison with a multi-start steepest descent algorithm shows that a basic TS approach conducts a global search more effectively. As illustrated by three case studies, the new method is well suited for identifying optimal designs of a chemical process to be implemented in an existing multi-purpose batch plant. The approach is particularly suited for considering multiple prioritized objectives and for enabling the use of external (e.g. commercial) batch process simulation software as a black-box model for the process evaluations.

This paper deals with the kinetic study of bulk free radical polymerization of styrene initiated with the commercial bifunctional initiator 2,5-dimethyl-2,5-bis(2-ethyl hexanoyl peroxy)hexane (Lupersol 256). The polymerization kinetics is investigated by DSC measurement for temperatures between 80 and 110ЊC and for initiator initial concentration from 0.115 up to 0.46 mol%. The experimental conversion and reaction rate are compared and discussed with the calculated values. For modeling the polymerization rate, a reaction scheme similar to the one given by Yoon and Choi (Polymer 1992;33(21):4582-4591) has been used and adapted. A detailed diffusional and semi-empirical model proposed by Chiu et al. (Macromolecules 1983;16(3):348-357) has been modified by Rouge (Etude de la polymérisation radicalaire du styrène initiée par un amorceur bifonctionnel dans un réacteur tubulaire à recyclage, Diploma work, DC, EPF, Lausanne, 1997) in order to describe these results. The model allows the description of the number molecular weight, but the polydispersity is underestimated for conversion higher than 70%. For temperature higher than 100ЊC, thermal initiation must be taken into account. The efficiency factor is found close to 1, but seems to decrease for temperatures above 100ЊC. ᭧

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Adsorption to a chelating resin is a method for recovering heavy metals from wastewater containing very light quantities of heavy metals ( B0.3 mol m − 3 , which approximately corresponds to 20 ppm). A thermodynamical study in a closed vessel showed that equilibrium is well represented by a Langmuir isotherm. Adsorption kinetics in a continuous stirred tank reactor were also conducted. Experiments were simulated by a global kinetics model comprising mass transfer in a liquid film around the resin particles, with diffusion through the pores and reaction on the adsorption sites. Kinetics has been found to be limited by film mass transfer for all metals studied (Cu 2 + , Ni 2 + , Co 2 + and Zn 2 + ). The mass transfer coefficient k L was found to be around 10 − 4 m s − 1 . Adsorption of heavy metals was then carried out at mini-pilot scale. Problems due to a decrease in particles mean radius during the adsorption prompted us to use a fluidized bed. It is also possible with this reactor to treat solutions containing suspended solids which would clog fixed beds. The decrease in particle radius (or increase in apparent density of the resin) produces a contraction of the fluidized bed: unloaded particles remain at the top of the bed and a density gradient appears throughout the column, leading to a stabilization of the fluidized bed. The measured phenomenon is well described by a liquid plug flow model with immobile resin in the column. As for the adsorption in the continuous stirred tank, the Langmuir model and the kinetics limited by film mass transfer were considered. The mass transfer coefficient k L was adjusted to a value around 10 − 5 m s − 1 .

The cost of treatment of the waste emanating from chemical production significantly contributes to the total production cost and should therefore be estimated as early as possible during process development. We developed a model that, taking the waste treatment facilities of an existing chemical plant as an example, calculates the cheapest feasible combination of treatment operations for a given waste stream that satisfies legal emission limits. A special feature of the software is that uncertainty in the waste stream composition and the separation efficiencies (e.g., in early process development phases) can easily be propagated through the model, leading to probability distributions of treatment cost and selected treatment paths. To demonstrate its capabilities, the model was applied to three waste streams. The results show that rather small variations in one or several input parameters might result in pronounced differences in treatment costs because certain treatment options become technically infeasible or emission limits are exceeded, thereby rendering a scenario legally noncompliant. The model also highlights recycling potentials and possible problems of waste streams that might best be resolved by modifying the chemical process.