Membrane distillation of concentrated brines—Role of water activities in the evaluation of driving force

Membrane distillation crystallisation (MDC) can be used to recover crystalline products from solutions. MDC of a concentrated solution of magnesium sulphate of 375 g/l was investigated. It was found that the MDC of epsomite was achievable at a feed temperature of only 33 °C and a distillate temperature of approximately 17 °C. The orthorhombic crystals were formed at a growth rate of 1.6 × 10−8 m s−1. The transmembrane flux was then measured for the membrane distillation (MD) of two concentrated solutions of mixed electrolytes, MgSO4 and NaCl with concentrations of 225 and 225 g/l, respectively, for one mix; and 275 and 137.5 g/l, respectively, for the other mix. For the mixtures of salts, only sodium chloride was precipitated while magnesium sulphate remained in solution but increased in concentration. The geochemical equilibrium speciation program, PHRQPITZ, was used to determine solution activities. These results were verified by experimental vapour pressure values determined by dynamic vapour–liquid equilibrium (VLE) experiments to calculate the vapour pressures of the solution (and hence driving force) at each stage during the distillation. The accountability of water activities showed how the trend of decreasing flux fitted with that of the driving force for the distillation process. When operated in batch concentration mode the flux and driving force showed a constant initial rise (due to stabilisation of temperature and concentration profiles and fluid dynamics inside the module) after which it plateaus off before rapidly declining. Preliminary computer modelling has demonstrated how the understanding of membrane distillation processes can be improved by being able to predict driving forces.

[1]  Mohamed Khayet,et al.  Theoretical and experimental studies on desalination using the sweeping gas membrane distillation method , 2003 .

[2]  Enrico Drioli,et al.  Integrated system for recovery of CaCO3, NaCl and MgSO4·7H2O from nanofiltration retentate , 2004 .

[3]  Giulio C. Sarti,et al.  Extraction of organic components from aqueous streams by vacuum membrane distillation , 1993 .

[4]  Giulio C. Sarti,et al.  Low energy cost desalination processes using hydrophobic membranes , 1985 .

[5]  Enrico Drioli,et al.  Energetic and exergetic analysis of an integrated membrane desalination system , 1999 .

[6]  Noam Lior,et al.  Membrane-distillation desalination: Status and potential , 2005 .

[7]  S.-I. Andersson,et al.  Design and field tests of a new membrane distillation desalination process , 1985 .

[8]  Enrico Drioli,et al.  Membrane distillation : An experimental study , 1985 .

[9]  Joachim Ulrich,et al.  Crystallization kinetics of epsomite influenced by pH-value and impurities ☆ , 2002 .

[10]  Shoji Kimura,et al.  Transport phenomena in membrane distillation , 1987 .

[11]  D. Ramjugernath,et al.  Phase equilibrium properties of binary systems with diacetyl from a computer controlled vapour–liquid equilibrium still , 2001 .

[12]  S. T. Hsu,et al.  Seawater desalination by direct contact membrane distillation , 2002 .

[13]  Benjamin S. Sparrow,et al.  Empirical equations for the thermodynamic properties of aqueous sodium chloride , 2003 .

[14]  Marcel Mulder,et al.  Basic Principles of Membrane Technology , 1991 .

[15]  Fawzi Banat,et al.  Theoretical and experimental study in membrane distillation , 1994 .

[16]  Jiban Podder,et al.  Habit modification of epsomite in the presence of urea , 2003 .

[17]  Enrico Drioli,et al.  A new membrane-based crystallization technique: tests on lysozyme , 2003 .

[18]  M.H.V. Mulder,et al.  Wetting criteria for the applicability of membrane distillation , 1987 .

[19]  J. David Raal,et al.  Phase equilibria : measurement and computation , 1998 .

[20]  Yonglie Wu,et al.  An experimental study on membrane distillation-crystallization for treating waste water in taurine production☆ , 1991 .

[21]  Enrico Drioli,et al.  Direct contact membrane distillation: modelling and concentration experiments , 2000 .

[22]  M. Tomaszewska,et al.  Concentration of the extraction fluid from sulfuric acid treatment of phosphogypsum by membrane distillation , 1993 .

[23]  Enrico Drioli,et al.  Membrane distillataion in the treatment of aqueous solutions , 1987 .

[24]  M. Menon Protein charge ladders: a new technique for studying electrostatic interactions in ultrafiltration systems , 2001 .

[25]  Enrico Drioli,et al.  Theoretical and Experimental Study on Membrane Distillation in the Concentration of Orange Juice , 1994 .

[26]  David L. Parkhurst,et al.  A computer program incorporating Pitzer's equations for calculation of geochemical reactions in brines , 1988 .

[27]  K. Pitzer,et al.  Thermodynamics of electrolytes. II. Activity and osmotic coefficients for strong electrolytes with one or both ions univalent , 1973 .

[28]  Giulio C. Sarti,et al.  Separation of liquid mixtures by membrane distillation , 1989 .

[29]  Sudjito,et al.  Desalination by solar heated membrane distillation , 1991 .

[30]  Shoji Kimura,et al.  Experiments on sea water desalination by membrane distillation , 1988 .

[31]  Zhi-Kang Xu,et al.  Microporous polypropylene and polyethylene hollow fiber membranes. Part 3. Experimental studies on membrane distillation for desalination , 2003 .

[32]  Roland Wimmerstedt,et al.  Membrane distillation - a theoretical study of evaporation through microporous membranes , 1985 .

[33]  Anthony G. Fane,et al.  Membrane distillation crystallization of concentrated salts—flux and crystal formation , 2005 .

[34]  Marek Gryta,et al.  CONCENTRATION OF NaCl SOLUTION BY MEMBRANE DISTILLATION INTEGRATED WITH CRYSTALLIZATION , 2002 .

[35]  K. Smolders,et al.  Terminology for Membrane Distillation , 1989 .

[36]  W. T. Lindsay,et al.  Thermodynamics of sodium chloride solutions at high temperatures , 1972 .

[37]  Anthony G. Fane,et al.  Heat and mass transfer in membrane distillation , 1987 .

[38]  Antoni W. Morawski,et al.  Membrane distillation of NaCl solution containing natural organic matter , 2001 .