Percorrer por autor "Silva, Viviana"
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- Batch and continuous studies for ethyl lactate synthesis in a pervaporation membrane reactorPublication . Pereira, Carla; Silva, Viviana; Pinho, Simão; Rodrigues, AlírioPervaporation process using commercial silica water selective membranes was evaluated to contribute for the ethyl lactate process intensification by continuous pervaporation membrane reactor. Preliminary studies were performed in order to assess the existence of membrane defects and mass transfer limitations, studying the influence of feed pressure and flowrate, respectively. After, in the absence of mass transfer limitations, membrane performance was evaluated experimentally, at different composition and temperature measuring the flux and selectivity of each species in binary mixtures (water/ethanol, water/ethyl lactate and water/lactic acid). Thus, species permeances were obtained for each experiment and correlated in order to account for the effect of temperature and feed composition. Permeances of ethanol and ethyl lactate depend solely on the temperature, following an Arrhenius equation; for water, its permeance follows a modified Arrhenius equation taking into account also the dependence on the feed water content. Mathematical models, considering concentration and temperature polarization, and nonisothermal effects as well, were developed and applied to analyze the performance of batch pervaporation and continuous pervaporation membrane reactor, in both isothermal and non-isothermal conditions. The PVMR with five membranes in series, operating at 70 ◦C, leads to 98% of lactic acid conversion and 96% of ethyl lactate purity.
- Ethyl lactate synthesis using A15 resin as catalyst/adsorbent: kinetic and absorption studiesPublication . Pereira, Carla; Pinho, Simão; Silva, Viviana; Rodrigues, Alírio
- Thermodynamic equilibrium and reaction kinetics for the esterification of lactic acid with ethanol catalyzed by acid ion-exchange resinPublication . Pereira, Carla; Pinho, Simão; Silva, Viviana; Rodrigues, AlírioThe heterogeneous catalysis of lactic acid (88 wt %) esterification with ethanol in the presence of Amberlyst 15-wet was studied for catalyst loading of 1.2-3.9 wt %, initial molar ratio of reactants of 1.1-2.8, and temperature from 50 to 90 °C. In this work a methodology based on the UNIQUAC model was developed to determine the thermodynamic equilibrium constant since in the literature there is inconsistency concerning the temperature dependence of the thermodynamic equilibrium constant. A simplified Langmuir-Hinshelwood kinetic model was used to predict the experimental data. The proposed rate law is r ) kc(aEthaLa - aELaW/ K)/(1 + KEthaEth + KWaW)2; the kinetic parameters are the preexponential factor, kc,0 ) 2.70 107 molâg-1âmin-1, and the activation energy, Ea ) 49.98 kJ/mol. The equilibrium reaction constant is K ) 19.35 exp(-515.13/T (K)) with reaction enthalpy 4.28 kJ/mol. The model reasonably predicts the kinetic experimental data, and it will be very useful to apply to the design and optimization of industrial hybrid reactive separation processes.