Vacuum membrane distillation: Experiments and modeling (original) (raw)
Related papers
Extraction of organic components from aqueous streams by vacuum membrane distillation
Journal of Membrane Science, 1993
The removal of volatrle organic compounds from aqueous streams by vacuum membrane distrllatlon (VMD) has been analyzed. VMD is an evaporation process which takes place through microporous hydrophobrc membranes; at low pressure the mass transfer through the membrane is generally domrnated by the Knudsen mechanism, while the process selectivity is essentially determined by the hquldvapor equrhbrium condrtlons existing at the mterface. Dilute aqueous mmtures containmg ethanol or methylterbutyl ether have been expenmentally mvestigated, in a wide range of operating conditions. The role of concentration-polarixation phenomena on the separation factor was also mvestrgated. A detailed model of the transport phenomena involved in the process is developed and compared with the expenmental data. A VMD system IS finally designed for the purification of waste waters and the related treatment costs are evaluated.
Separation and Purification Technology, 2001
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,
Pollutants removal from wastewaters through membrane distillation
Desalination, 2005
The Sweeping Gas Membrane Distillation process is considered for the treatment of wastewaters containing volatile organic compounds such as acetone and ethanol. The separation technique is based on the use of microporous hydrophobic membranes under conditions of non wettability, in which the membrane separates an aqueous phase from a stripping gas. A wide experimental investigation is performed to study the role of temperature, composition and flow rate of the liquid phase and the influence of the sweeping gas flow rate. Performances of flat PTFE membranes are studied in the case in which dry nitrogen is used as stripping agent. Liquid feed flow rate as well as nitrogen flow rate are identified as the major design quantities since they greatly affect the separation efficiency. A simplified mathematical model is developed to describe multicomponent mass transfer in the gas phases, in which a pseudo-binary diffusion approach is assumed; molecular diffusion is considered as the prevailing transport mechanism through the membrane. The results obtained are compared with the experiments and the validity range of the model is defined.
Air gap membrane distillation technique (AGMD) was applied for removal of ethanol, butanol and acetone–butanol–ethanol mixture from water. The influence of various parameters (feed temperature, cooling wall temperature) on pure water transport in AGMD was determined and the efficiency of organic solvents removal from water through two porous membranes (PTFE and PP) was investigated in the detail. Selectivity of organic components recovery did not change significantly with an increase of feed temperature from 41 °C to 63 °C in case of AGMD applied for ethanol and butanol recovery, however significantly higher fluxes were obtained at higher feed temperature. Slightly higher fluxes were obtained during experiments performed with PTFE membrane comparing with PP one. It was found that both PTFE and PP membranes are wetted during AGMD process of water–butanol feed mixture if organic concentration exceeds 2.5 wt% (PTFE) and 1 wt% (PP) at 63 °C feed temperature. This fact limits the possibility of wider AGMD application in organic solvent recovery. The comparison of the efficiency of AGMD with the efficiency of thermopervaporation (TPV) was also performed. In case of 1 wt% ethanol feed mixture it was found that AGMD seems to be more suitable due to higher process separation index value (PSI in the range of 6 kg m À 2 h À 1) than in the case of TPV (PSI in the range of 3 kg m À 2 h À 1). On the contrary, in the case of water–butanol or water–ABE systems TPV is much more efficient method for organics recovery from aqueous mixtures than AGMD. In contact with 3 wt% ABE mixture PSI is equal to 28 and 9 kg m À 2 h À 1 for TPV and AGMD processes, respectively.
Efficient Ethanol Separation from Water Using Vacuum Membrane Distillation
Egyptian Journal of Chemistry, 2023
This work presents an investigation into the efficiency of ethanol separation from water using vacuum membrane distillation (VMD). The study explores the influence of variables such as feed flow rate, initial ethanol concentration, and temperature on the performance of the distillation process. The polyvinylidene fluoride (PVDF) membrane was utilized due to its desirable properties such as high thermal stability, chemical resistance, and excellent mechanical properties. The results showed that the feed temperature had the greatest impact on the permeation flux. The permeate flux and ethanol flux increased with increasing initial ethanol concentration, while the separation factor decreased. Increasing the feed flow rate also resulted in increased permeate flux, ethanol flux, and separation factor. The study provides valuable insights into the optimization of the VMD process for efficient ethanol-water separation. The findings could potentially contribute to the development of more sustainable and efficient separation processes in the industry.
CT y F - Ciencia, Tecnologia y Futuro
En este trabajo se planteó un modelo matemático para la transferencia de masa y energía durante la etapa de separación de etanol utilizando destilación con membranas al vacío. Este modelo es uno de los pocos propuestos para el estudio de la separación de etanol por destilación con membranas al vacío; solo Soni, Abildskov, Jonsson y Gani (2008) han propuesto un modelo de mayor complejidad que el del presente estudio. El modelo matemático fue validado utilizando cuatro casos de estudio reportados en la literatura. El modelo permite predecir satisfactoriamente los resultados experimentales para condiciones de operación que se encuentren entre 20 - 70ºC, con 0.25 - 5% p/p de etanol en la alimentación, presiones de 2000 - 6000 Pa y Reynolds entre 50 y 2700. Este modelo permitió realizar el análisis de la influencia de parámetros de operación y de diferentes tipos de membranas sobre variables de respuesta como flux de etanol, flux de agua y fracción de etanol en el permeado, utilizando la...
Ethanol Separation from an Ethanol–Water Solution Using Vacuum Membrane Distillation
Membranes
The vacuum membrane distillation (VMD) process was applied to separate ethanol from a simulated ethanol–water solution using a commercial polytetrafluoroethylene (PTFE) membrane. The presence of ethanol in the ethanol–water solution with a 2 wt.% ethanol concentration at a temperature above 40 °C during the MD process may result in membrane failure due to an increase in the chance of the PTFE membrane wetting at high temperatures. Therefore, the operating temperature in this study was not higher than 35 °C, with an initial ethanol concentration up to 10 wt.%. This work focuses on optimizing the VMD operating parameters using the Taguchi technique based on an analysis of variance (ANOVA). It was found that the feed temperature was the most-affected parameter, leading to a significant increase in the permeation flux of the PTFE membrane. Our results also showed that the permeate flux was reported at about 24.145 kg/m2·h, with a separation factor of 8.6 of the permeate under the operat...
Theoretical Assessment of Dilute Acetone Removal from Aqueous Streams by Membrane Distillation
Separation Science and Technology, 1999
The removal of dilute acetone from aqueous streams by air-gap membrane distillation is theoretically assessed. A combined heat and mass transfer model that includes temperature and concentration polarization effects as well as temperature and concentration variation along the module length is employed to predict the flux and selectivity of acetone under the relevant process operating conditions. Three mass transfer solutions are heeded in the model: the exact Stefan-Maxwell, the approximate Stefan-Maxwell, and the Fickian binary solution. Although, behaviorally, the three solutions exhibit the same trends, quantitatively some differences exist between the Fickian-based solution on the one hand and the Stefan-Maxwell solutions on the other hand. The exact and approximate solutions of the Stefan-Maxwell equation showed a similar capability in predicting the process achievement under all process conditions. Predictions showed that acetone selectivity and flux were strongly dependent on feed conditions and air-gap width.
Membrane distillation: A comprehensive review
Desalination
Membrane Distillation (MD) is a thermally-driven separation process, in which only vapour molecules transfer through a microporous hydrophobic membrane. The driving force in the MD process is the vapour pressure difference induced by the temperature difference across the hydrophobic membrane. This process has various applications, such as desalination, wastewater treatment and in the food industry. This review addresses membrane characteristics, membrane-related heat and mass transfer concepts, fouling and the effects of operating condition. State of the art research results in these different areas will be presented and discussed.