• 멤브레인
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• 제7권2호
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• pp.57-64
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• 1997

새로운 분리공정으로서 Membrane Distillation(MD)에 대하여 고찰하였다. 정밀여과에서 이용되고 있는 소수성막이 MD공정에 적합한 막소재가 된다. MD는 고온보다는 완화된 온도에서 100%에 가까운 선택도를 가지면서 기존의 수처리 공정을 간소화시킬 수 있는 가능성이 있다. MD는 막표면의 기공에서 층기-액체간의 상분리가 일어나는 분리원리를 이용한다. 공급액 및 투과액의 온도, 조성, 막의 젖음현상, 열 및 물질전달이 MD의 선택도와 플럭스를 결정할 수 있다.

• 한국유체기계학회 논문집
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• 제17권2호
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• pp.30-34
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• 2014

Membrane distillation (MD) is a thermal driven separation process in which separation a hydrophobic membrane is a barrier for the liquid phase, letting the vapor phase pass through the membrane pores. Therefore, a porous and hydrophobic membrane should be used in membrane distillation. MD cannot work if water penetrates into the pores of the membrane (membrane wetting). Accordingly, it is necessary to prevent wetting of MD membranes and to remove water inside the pores of the wetted membranes if possible. In this context, our study aimed to develop methods to recover wetted membranes in MD processes. Poly-vinylidene fluoride (PVDF) membranes were used in this study. A laboratory-scale direct contact MD (DCMD) system was used to examine the effect of operating parameters on wetting. For dewetting the wetted membranes, specific techniques including the use of high temperature air were applied. The performances of the membranes before and after dewetting were compared in terms of flux, salt rejection and liquid entry pressure(LEP). The surface morphology of dewetted membrane was confirmed by scanning electron microscope (SEM).

• 상하수도학회지
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• 제30권3호
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• pp.343-350
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• 2016

Membrane distillation (MD) is a novel separation process that have drawn attention as an affordable alternative to conventional desalination processes. However, membrane fouling and pore wetting are issues to be addressed prior to widespread application of MD. In this study, the influence of ultrasonic irradiation on fouling and wetting of MD membranes was investigated for better understanding of the MD process. Experiments were carried out using a direct contact membrane distillation apparatus Colloidal silica was used as a model foulants in a synthetic seawater (35,000 mg/L NaCl solution). A vibrator was directed attached to membrane module to generate ultrasonic waves from 25 kHz (the highest energy) to 75 kHz (the lowest energy). Flux and TDS for the distillate water were continuously monitored. Results suggested that ultrasonic irradiation is effective to retard flux decline due to fouling only in the early stage of the MD operation. Moreover, wetting occurred by a long-term application of ultrasonic rradiation at 75 kHz. These results suggest that the conditions for ultrasonic irradiation should be carefully optimized to maximize fouling control and minimize pore wetting.

• Environmental Engineering Research
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• 제24권2호
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• pp.347-353
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• 2019

Although membrane distillation (MD) has great promise for desalination of saline water sources, it is crucial to improve its thermal efficiency to reduce the operating cost. Accordingly, this study intended to examine the thermal energy efficiency of MD modules in a pilot scale system. Two different modules of hollow fiber membranes were compared in direct contact MD mode. One of them was made of polypropylene with the effective membrane area of $2.6m^2$ and the other was made of polyvinylidene fluoride with the effective membrane area of $7.6m^2$. The influence of operation parameters, including the temperatures of feed and distillate, feed flow rate, and distillate flow rate on the flux, recovery, and performance ratio (PR), was investigated. Results showed that the two MD membranes showed different flux and PR values even under similar conditions. Moreover, both flow rate and temperature difference between feed and distillate significantly affect the PR values. These results suggest that the operating conditions for MD should be determined by considering the module properties.

• 상하수도학회지
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• 제30권4호
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• pp.441-447
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• 2016

Development of shale gas has drawn increasing attention since it is one of promising alternative energy resources. However, contamination of groundwater and surface water during the extraction of shale gas is becoming a serious environmental issues, which brings the needs to treat wastewater generated from hydraulic fracking. In this study, the feasibility of membrane distillation (MD) for the treatment of shale gas wastewater was investigated using a laboratory scale experimental setup. Flat-sheet MD membranes were used to treat produced water from a shale gas well in the United States. Different configurations such as direct contact MD (DCMD) and air gap MD (AGMD) were compared in terms of flux and fouling propensity. The foulants on the surface of the membranes were examined. The results suggest that MD can treat the shale gas produced water containing more than 200,000 mg/L of total dissolved solids, which is impossible by other technologies such as reverse osmosis (RO) and forward osmosis (FO). In this study, we investigated the possibility of processing and characterization of shale gas produce wastewater using membrane distillation. Laboratory scale membrane distillation experimental device was developed. It was compared the flat-sheet direct contact membrane distillation and flat-sheet air gap membrane distillation. AGMD flux in lower than the flux of DCMD, it was expected that the contamination caused by organic matters.

• Membrane and Water Treatment
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• 제11권5호
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• pp.363-374
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• 2020

Membrane distillation (MD) is a process used for water desalination. However, its commercialization is still hindered by its increased specific cost of production. In this work, several process configurations comprising Direct Contact and Permeate Gap distillation membrane units (PGMD/DCMD) were investigated to maximize the production rate and consequently reduce the specific water cost. The analysis was based on a cost model and an experimentally validated MD model. It was revealed that the best achievable water cost was approximately 5.1 $/㎥ with a production rate of 8000 ㎥/y. This cost can be further decreased to approximately 2 $/㎥ only if the heating and cooling energies are free of cost. Therefore, it is necessary to decrease the MD capital investment to produce pure water at economical prices.

• 상하수도학회지
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• 제32권4호
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• pp.301-307
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• 2018

Membrane distillation (MD) is a thermally driven desalination process with a hydrophobic membrane. MD process has been known to have a lower fouling potential compared to other pressure-based membrane desalination process (NF, RO). However, membrane fouling also occurs in MD process. In this study, the membrane fouling was observed in MD process according to the pre-treatment processes. The filtration and precipitation processes were applied as the pre-treatment to prevent the membrane fouling. The pore sizes of roughing filters were 0.4, 5, 10, 30, and $60{\mu}m$. The concentration of the coagulant was 1.2 mg/L as $FeCl_3$. The membrane fouling on MD membrane was successfully removed with both pre-treatment processes.

• Membrane and Water Treatment
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• 제2권1호
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• pp.1-24
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• 2011

The deficiency of clean water is a major global concern because all the living creatures rely on the drinkable water for survival. On top of this, abundant of clean water supply is also necessary for household, metropolitan inhabitants, industry, and agriculture. Among many purification processes, advances in low-energy membrane separation technology appear to be the most effective solution for water crisis because membranes have been widely recognized as one of the most direct and feasible approaches for clean water production. The aim of this article is to give an overview of (1) two new emerging membrane technologies for water reuse and desalination by forward osmosis (FO) and membrane distillation (MD), and (2) the molecular engineering and development of highly permeable hollow fiber membranes, with polyvinylidene fluoride (PVDF) and polybenzimidazole (PBI) as the main focuses for the aforementioned applications in National University of Singapore (NUS). This article presents the main results of membrane module design, separation performance, membrane characteristics, chemical modification and spinning conditions to produce novel hollow fiber membranes for FO and MD applications. As two potential solutions, MD and FO may be synergistically combined to form a hybrid system as a sustainable alternative technology for fresh water production.

• 멤브레인
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• 제25권3호
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• pp.216-222
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• 2015

막증류(membrane distillation, MD)용 분리막의 장기 내구성능에 영향을 미치는 인자인 소수성 분리막의 젖음 현상에 대한 평가 지표로 사용되는 액체투과압력(liquid entry pressure, LEP) 측정 방법을 최적화하였다. PE (polyethylene) 분리막 및 PVDF (polyvinylidene di-fluoride) 중공사 분리막의 LEP를 측정하기 위하여 20 wt%의 고농도 염수를 제조하여 원수로 사용하고 투과수의 전도도를 모니터링하였다. PE와 PVDF 중공사 분리막의 신뢰성 있는 LEP 측정을 위해서는 5 min 이상의 holing time을 두고 주입 압력을 증가시켜야 하며, 증류수 수조의 물량대비 분리막의 면적비 또한 $10m^2/m^3$ 이상으로 부여되어야 함을 확인하였다.

• Membrane and Water Treatment
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• 제13권5호
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• pp.235-243
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• 2022

The paper presents the effect of operating temperatures and flow rates on the distillate flux that can be obtained from a hydrophobic membrane having the characteristics: pore size of 0.15 ㎛; thickness of 130 ㎛; and 85% porosity. That membrane in the present investigation could be the direct contact (DCMD) or the air-gap membrane distillation (AGMD). To model numerically the membrane distillation processes, the two-dimensional computational fluid dynamic (CFD) is used for the DCMD and AGMD cases here. In this work, DCMD and AGMD models have been validated with the experimental data using different flows (Parallel and Counter-current flows) in non-steady-state situations. A good agreement is obtained between the present results and those of the experimental data in the literature. The new approach in the present numerical modeling has allowed examining effects of the nature of materials (Polyvinylidene fluoride (PVDF) polymers, copolymers, and blends) used on thermal properties. Moreover, the effect of the area surface of the membrane (0.021 to 3.15 ㎡) is investigated to explore both the laminar and the turbulent flow regimes. The obtained results found that copolymer P(VDF-TrFE) (80/20) is more effective than the other materials of membrane distillation (MD). The mass flux and thermal efficiency reach 193.5 (g/㎡s), and 83.29 % using turbulent flow and an effective area of 3.1 ㎡, respectively. The increase of feed inlet temperatures and its flow rate, with the reduction of cold temperatures and its flow rate are very effective for increasing distillate water flow in MD applications.