Evaluation of Sodium Chloride Crystallization in Membrane Distillation Crystallization Applied to Water Desalination

Abstract

-Crystallization in a Direct Contact Membrane Distillation (DCMD) process was studied both theoretically and experimentally. A mathematical model was proposed in order to predict the transmembrane flux in DCMD. The model fitted well experimental data for the system NaCl-H2O from undersaturated to supersaturated conditions in a specially designed crystallization setup at a bench scale. It was found that higher transmembrane fluxes induce higher temperature and concentration polarizations, as well as higher supersaturation in the vicinity of the solution-vapor interface. In this region, the supersaturation ratio largely exceeded the metastable limit for NaCl crystallization for the whole range of transmembrane fluxes of 0.37 to 1.54 kg/ (m 2 h), implying that heterogeneous primary nucleation occurred close to such interface either in solution or on the membrane surface. Solids formed in solution accounted for 14 to 36% of the total solids, whereas solid formed on the membrane surface (fouling) was responsible for 6 to 19%. The remaining solids deposited on other surfaces such as in pumps and pipe fittings. It was also discovered that, by increasing the supersaturation ratio, heterogeneous nucleation in solution increased and on the membrane surface decreased. Heterogeneous nuclei in solution grew in size both by a molecular mechanism and by agglomeration. Single crystals were cubic shaped with well-formed edges and dominant size of about 40 µm whereas agglomerates were about 240 µm in size. The approach developed here may be applied to understanding crystallization phenomena in Membrane Distillation Crystallization (MDC) processes of any scale.

Slippery for scaling resistance in membrane distillation: A novel porous micropillared superhydrophobic surface

“…However, similar to other membranes, MD membranes are prone to fouling, scaling and membrane wetting (Tijing, Woo et al 2015), which will lead to deteriorated performance. For high salt solutions, in particular when the concentration of salt approaches saturation, scaling becomes the most serious problem (Ji, Curcio et al 2010, Gryta 2011, Edwie and Chung 2013, Chen, Lu et al 2014, Hickenbottom and Cath 2014, Nariyoshi, Pantoja et al 2016, Bouchrit, Boubakri et al 2017, Jiang, Tuo et al 2017, Tang, Iddya et al 2017, Julian, Ye et al 2018, Zou, Dong et al 2018. Crystals attached to the membrane surface alter surface wettability (e.g.…”

“…When treating 18 wt.% NaCl brine in direct contact membrane distillation (DCMD), a critical size of 25 µm was found for the crystals on the PVDF membrane surface, which acted as initial growth sites and led to the full membrane coverage (Chen, Lu et al 2014). Single NaCl crystals of 40 µm were also reported in a membrane distillation-crystallization (MDC) process, where about 9 to16% of the total crystals were on the membrane surface and the piping (Nariyoshi, Pantoja et al 2016). Scaling often occurred when the feed reached saturation (Bouchrit, Boubakri et al 2015, Gryta 2016, Bouchrit, Boubakri et al 2017).…”

Influence of Polyvinylidene Fluoride Polymorphs in Membrane-Assisted Crystallization: NaCl Crystals Nucleation and Growth

“…The metastable limit for NaCl, i.e., the supersaturation ratio limit for spontaneous crystal formation (primary nucleation) is S = 1.0025. [48] All the molecular details of the models realised are reported in Table 1. The SPC/E model [49] was used for water; the ion parameters were those of the OPLS force field; [50,51] the force field parameters of the PVDF polymer developed by Byutner and Smith [52] were utilized with all pair interactions consisted of Lennard-Jones (LJ) (Table 2) and Coulombic terms.…”

Modeling and Simulation of a Vacuum Membrane Distillation Plant Coupled With Solar Energy and Using Helical Hollow Fibers

“…The first configuration is the direct contact membrane distillation (DCMD). For the DCMD, the cooling solution is in direct contact with the permeate side of the membrane (Andrjesdóttir et al, 2013;Nakoa et al, 2016;Nariyoshi et al, 2016). The air gap membrane distillation (AGMD) is the second configuration.…”