Gema Ruiz

Parallelism and differences of pervaporation and vacuum membrane distillation in the removal of VOCs from aqueous streams

In this work two gas–liquid separation processes, pervaporation (PV) and vacuum membrane distillation (VMD), have been compared in their application to the separation of chloroform–water mixtures. After selection of the adequate separation membrane the comparison of the PV and VMD should be based on the kinetics and selectivity towards the desired compound. The kinetic models and parameters previously reported by the authors (A.M. Urtiaga, E.D. Gorri, J.K. Beasley, I. Ortiz, J Membr Sci 156 (1999) 275–291 and A.M. Urtiaga, G. Ruiz, I. Ortiz, J Membr Sci 165 (2000) 99–110) for the separation of chloroform from aqueous solutions in the range of concentrations 200<C<2000 mg/l, temperature 5<T<44°C and flowrate 140<Re<1400 have been used to compare the mass transfer flux and selectivity in both separation processes. The use of hollow fiber membranes of polydimethylsiloxane in the PV system and microporous polypropylene in the VMD process resulted in the same rate of removal in both systems under the simulated conditions. Particularly, the PV system offered the uppermost selectivity, providing a high concentration of chloroform in the permeate.

Monosaccharide production in an acid sulfite process: kinetic modeling.

Spent sulfite liquor is a lignocellulosic waste obtained after the sulfite pulping process. It is mainly formed by sugars and lignosulfonates which are isolated from the pulp during the cooking process. The current work investigates the kinetic modeling of the sulfite process from a biorefinery point of view since monosaccharides present in the spent liquor can be used as a raw material in further biorefinery processes to produce other value-added products. Kinetic parameters of carbohydrate degradation have been determined following sugar and inhibitors from wood to spent liquor, using laboratory scale reactors and different temperatures, 130, 140 and 150 °C. Three types of reaction schemes were developed. Kinetic parameters were obtained for each one using first and n order reactions, using Aspen Custom Modeler. Results show that the best temperature to be used in the process is 130 °C, giving the maximum sugar conversion, 33.91 mol% and obtaining 13.81 mol% of decomposition products.