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PhD project

Summary

Logo TesiThe utilization of hydride materials has been demonstrated to be an important approach in many fields of science, and particularly, in separation processes. In this work, activated carbon was used to obtain composite membranes. They offer the potential of combine the simple utilization of polymers with the functional properties of carbon materials. Nevertheless, the incorporation of the activated carbon responds also to a second objective: the production of enzymatic membrane reactors by taking advantage of its adsorption capability. Therefore it is possible to obtain a single unit which carries out two processes: separation and reaction. This is process intensification, which is one of the main research trends.

In the first stage, polysulfone membranes were synthesized by immersion precipitation. Firstly, the effect of its concentration in the polymeric mixture was studied. Secondly, the type of solvent was also investigated. When the best conditions of these variables were encountered, the effect of the composition of the coagulation bath was deeply studied. The characterization included methods as the scanning electron microscopy (SEM), the force atomic microscopy, the experimental related to solid exclusion and the contact angle. Membranes were also mechanical characterized by strain-stress tests. Results demonstrated that with the variation of the coagulation bath it is possible to obtain a wide range of membrane morphologies with a cut-off range from 25 to 700 kDa (measured with dextrans). The SEM is one of the most versatile method because allows to characterize morphologically almost all the membrane surface, in a quick and simple way. But the results obtained are qualitative, and in this work, a software (IFME®) was developed to obtain quantitative results, quickly and systematically. Related to the experimental, the global performance of membranes depends also on the module design: a wrong design could imply a non-adequate flux flow over the membrane, which facilitates the phenomena of fouling and polarization that reduces the permeate flow. For this reason, several modules were considered, used and also simulated with computational fluid dynamics, and in those necessary cases, were also optimized.

The second stage consisted on the synthesis and characterization of composite membranes by adding activated carbon (same techniques). Two types of composite membranes were obtained. A single-layered one, which the activated carbon was added to the polymeric solution at the beginning of the process and, therefore, a homogeneous film and membrane were obtained, and a two-layered one. The activated carbon was added over the surface of the film obtained before immersing it in the coagulation bath, and therefore, producing the membrane. Results showed that the addition of the carbon did not modify the morphology of the membranes and therefore, their separation capability, but it added functionality to the membrane.

The last stage of the work consisted on the synthesis of two types of EMR. The first one contained a solid enzyme which was immobilized between two membrane layers (without chemical bind). The second one contained an enzymatic liquid complex with was bounded directly to the activated carbon and by using an ion metal (IMAC technique). Related to this second type of enzyme, two different EMR configurations were obtained: a single-layered one (adding the complex to the polymeric mixture) and two-layered one (adding the complex over the obtained film before producing the membrane). All the configurations demonstrated a successfully immobilization of the enzyme and also proper reactivity results (a good equilibrium between the kinetics of the reaction and the membrane flux was achieved). The monolayer enzymatic membrane reactor was the one which showed best overall results, since the desired reaction products could be obtained, the separation capability of the membrane was not altered, the system is also valid for diffusive processes and the system is very compact.

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