Pervaporative recovery of aroma compounds in the production of non-alcoholic beers: Incorporation of different condensation strategies into the conceptual design of the process

Abstract

The study carried out in the present work focused on the conceptual design of the aroma recovery stage of from a lager beer by pervaporation with a PDMS membrane taking into account the condensation step. First, using laboratory-scale experiments, the performance of the Pervatech PDMS membrane was measured in terms of aroma recovery, ratio of higher alcohols to esters (A/E ratio), ethanol flux and overall flux for different operating conditions. In addition, model was obtained that adequately characterized the fluxes through the membrane as a function of temperature and permeate pressure. This model allowed estimating the membrane area requirements for different operating conditions. Secondly, the possibility of using two partial condensers in the condensation stage to approximate the A/E ratio of a lager beer was explored through simulations. Influence of operating conditions and presence of CO2 and air on values for the A/E ratio, the overall fractional recovery of aroma compounds and the economics of the process were modeled. Both the case of mixing condensates obtained from the two condensers and that of an optimal combination of condensates were taken into account in order to approximate the A/E ratio of the lager beer. The best alternative for this variant was the one corresponding to the operating conditions of 30 °C temperature and a pressure of 2.13 kPa for the pervaporation stage, with two partial condensers in series operating at −5 °C and −46 °C, respectively. In this way, two condensates would be obtained which, when combined in a 0.43/1 ratio for subsequent reincorporation into the dealcoholized beer, would result in a product maintaining the (A/E) ratio of the original beer. Under these conditions, a recovery of 14.1% of aromas would be achieved with a total cost of 0.1070 USD/L. Finally, the state-of-the-art alternative consisting of two total condensers condensers in parallel working out of phase was also considered. Results indicate that, if properly designed, the A/E ratio obtained at lab scale level would coincide with that achieved after total condensation and thus, the adjustability of the ratio of higher alcohols to esters would decrease with respect to that achieved when partial condensers are used. Although the use of a total condenser results in more expensive designs, this alternative is very advantageous in terms of overall aroma recovery and process feasibility. From the results obtained, the importance of developing conceptual models that make use of both experimental runs of the aroma recovery process at laboratory scale and simulations of the condensation process from parameters corresponding to the vapour-liquid equilibrium of the multi-component system can be deduced.