Pervaporation of ethanol-water solutions using commercially available pervaporation membranes
Date
2024-03
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Stellenbosch : Stellenbosch University
Abstract
ENGLISH ABSTRACT: Pervaporation can be used for the recovery of bioethanol from fermentation broths. Most previous studies focused on laboratory-synthesized membranes and the OFAT approach has generally been used to investigate the influence of operating variables. In this study, pervaporation of ethanol-water solutions is investigated using commercial membranes (Pervap 4060 and Pervatech) and key operating parameters and their effects on pervaporation performance are identified. First, a laboratory-scale pervaporation unit was set up and validated in terms of repeatability of results and comparison with results reported. From repeated runs, coefficient of variance values for total and ethanol flux were 2.8% and 8%, respectively, indicating that the results were reproducible. Furthermore, the results obtained were comparable to those reported by the membrane manufacturer and in literature. The second phase of this study involved investigating the effects of key operating parameters on pervaporation performance. The parameters were feed temperature (40 - 60℃), feed flow (7 - 15 litre/min), and feed concentration (5 - 15 mass%). An increase in feed temperature and concentration caused an increase in flux, while feed flow did not have a notable effect. Generally, ethanol selectivity decreased with an increase in feed temperature and concentration and increased slightly with an increase in feed flow rate. In the third stage, an empirical model was developed using a 3-level central composite design was performed. Based on experimental data, a second-order model was developed using Statistica software. The developed flux model had a good accuracy; however, the selectivity model did not fit the experimental data well. Nevertheless, suggested optimum values were identified as: 60℃ feed temperature and 15 mass% EtOH feed concentration, with a predicted total flux of 3.52 kg/(m2h) and ethanol flux of 1.63 kg/(m2h). Possible limitations of pervaporation performance at high feed ethanol concentrations were investigated during the fourth phase of this study. Experiments were performed at increasing feed concentrations up to 75 mass% EtOH. A notable increase in ethanol and total flux were observed with an increase in feed concentration from 1 to 75 mass% EtOH. Conversely, a considerable decrease in the selectivity was observed. This indicates that the Pervap 4060 membrane is ethanol-selective at low ethanol concentrations in the feed. In the fifth stage of this study, the effects of membrane type on pervaporation performance were investigated. The pervaporation performance of commercial membranes, Pervap 4060 and Pervatech PDMS, were compared over a range of feed https://scholar.sun.ac.za iii concentrations (5 - 75 mass% EtOH). The pervaporation separation index (PSI) combines flux and selectivity data and was used to compare overall efficiency. The average PSI values of the Pervap 4060 and Pervatech PDMS membranes were 12 and 25 kg/(m2h), respectively. PSI values of the Pervatech membrane were higher than that of the Pervap 4060 membrane, indicating that the Pervatech membrane may be more efficient for ethanol recovery
AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.
AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.
Description
Thesis (MEng)--Stellenbosch University, 2024.