1002_Progress in membrane crystallization

ESEL Paper Review_20141002
By Hong Guo
Mail: hongguo@gist.ac.kr
Phone: (+82) (0)10 82276568
1, Title and Author
Title: Progress in membrane crystallization
Journal: Current Opinion in Chemical Engineering
Enrico Drioli 2,3, Gianluca Di Profilo 1 and Efrem Curcio 2
1 Institute on Membrane Technology (ITM), Italian National Research Council (CNR), Via P. Bucci CUBO 17/C, 87030 Arcavacata di Rende(CS), Italy
2 Department of Chemical Engineering and Materials, University of Calabria, Via P. Bucci CUBO 44/A, 87030 Arcavacata di Rende (CS), Italy
3 Hanyang University, WCU Energy Engineering Department, Seongdong-gu, Seoul 133-791, South Korea
2. Summary of Paper
? MCr is an innovative concept combining membrane technology and crystallization process, able to promote crystals nucleation and growth in a well-controlled pathway, starting from undersaturated solutions.
? The porous topography of the membrane surface and the existence of chemical functionalities in the polymer chain act together as promoter of heterogeneous nucleation at supersaturation levels that would not be adequate for spontaneous nucleation in the bulk of the solution. The extension of the MCr concept to antisolvent crystallization is a real opportunity to extend the advantages of this technology for the crystallization of heat-sensitive molecules.
3. Results
? In MCr a solution containing a nonvolatile solute, which is likely to be crystalized is in contact, by means of a porous membrane, with the distillate side.
? When the membrane is prevented to be wet from the liquid phases in such a way that the operating hydrostatic pressure is below the Liquid Entry Pressure (LEP), no mass transfer occurs through the porous structure in liquid phase, but the two contacted subsystems are subjected to mass interexchange in vapor phase.
? The membrane in MC r does not act as sieving barrier for the selective transport of specific components, but as physical support able to generate and to sustain a controlled a controlled supersaturated environment in which crystals can nucleate and grow.
? Depending on the chemical?physical properties of the membrane and on the process parameters (temperature, concentration, flow rate, etc.), the solvent evaporation rate, and hence super saturation degree and super saturation rate, might be regulated very precisely
? The effect would be the control of the nucleation and growth rate by choosing a broad set of available kinetic trajectories in the thermodynamic phase diagram, that are not readily achievable in conventional crystallization methods, and which would lead to the production of specific crystalline morphologies and structures
? Crystallizing solution is in direct contact with the membrane surface, therefore a solute?membrane interaction is likely to occur, depending on the fluid dynamic regime.
? Main results that might be obtained integrating MCr to concentrate NF and/or RO retentate (Figure 3) are:
- The reduction of the huge amount of brine.
- The enhancement of the overall water recovery factor.
- The production of valuable crystalline products (like NaCl, MgSO47H2O, LiCl, etc.).
? MCr is an efficient instrument to improve seawater desalination processes by approaching zero liquid discharges and valuable solid product recovery.
? A membrane distillation?crystallization bench-scale plant operating on synthetic seawater RO brine, reached a water recovery greater than 90%, with a concomitant reduction in volumetric waste discharged to the environment
? MCr operations were stable over 100 hours as a result of a careful control of super saturation, polarization phenomena, nucleation process, and hydrodynamics.
? Analogous investigations carried out on RO brines from natural seawater were affected by the presence of dissolved organic matter, showing a 20% reduction of the amount of salt crystallized, and an 8% decrease of the transmembrane flux.
? Growth rate of sodium chloride crystals generated from natural RO brines was 15?23% lower than those measured for NaCl crystals grown from artificial concentrates.
4. Contribution:
This research studies management strategies under the review of the future view of the MCr process application for high salinity water treatment and membrane characteristics of the MCr process. It would be greatly helpful for the future studies.
5. Contact (Mail address): e.drioli@itm.cnr.it
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