On the conceptual design of the hybrid nanofiltration/distillation process in the production of alcohol-free beers

Abstract

In this paper, the conceptual design of a hybrid process consisting of a dealcoholization task via nanofiltration followed by a permeate valorization task via distillation is deeply investigated for the case of a lager beer. To this end, we resorted to conceptual models of each task. The conceptual model of the nanofiltration task, which is built from experiments al lab scale with the membrane NF99 HF (Alfa Laval, Sweden), allows the proper modeling of the three consecutive sub-tasks in which the process is divided; namely, pre-concentration, constant volume diafiltration, and re-dilution. Estimation of the overall permeation coefficient and the variation of the osmotic pressure difference throughout the pre-concentration stage are key in the model development. For the scaling-up of the membrane unit, the pressure loss issue is taken into account. The result of this task is a beer with an alcohol content below 0.5% by volume. For the conceptual modeling of the distillation task, a pinch-based method is adopted to allow a proper estimation of the minimum energy demand of the task, with feasible separations constrained by the presence of the azeotrope ethanol-water. This task is divided into two consecutive sub-tasks. In the first stage the alcohol is recovered as an ethanol-water mixture to be used for on-site Gin production by operating the rectifier in constant distillate composition mode (and thus at variable reflux ratio). In the second stage, operated at a constant reflux ratio, both the second cut, which is recycled to the next batch, and the water-rich content in the still at the end of the distillation step, which is recycled to the subsequent nanofiltration stage, are obtained. Economic and environmental performance of the hybrid process is compared with that of a case base with both units operating as standalone processes. In the latter case, the water-rich content in the still at the end of the distillation step is treated in a biological treatment plant on-site. Applied to an annual production of 720 000 L of alcohol-free beer, the total cost of the standalone variant was 193 600 US$/year while the cost of the hybrid process was 205 500 US$/year; that is, 6.2% higher. On the other hand, and according to the life cycle assessment carried out, the Hybrid process has a lower environmental load. Results analyzed as a whole indicate the appropriateness of the Hybrid process.