Membrane Crystallization of Sodium Carbonate for Carbon Dioxide Recovery: Effect of Impurities on the Crystal Morphology

Abstract

Membrane contactors have been proposed as an advanced tool for CO2 capture from flue gases by absorption in alkaline solutions. However, regeneration of the alkaline reagent and further CO2 sequestration are pending issues. In this paper, membrane-assisted crystallization is proposed for crystallizing Na2CO3, which allows its reuse, after CO2 absorption from flue gases. Due to the presence of compounds other than CO2 in flue gases (i.e., SO2, NO x ), other compounds (Na2SO4 and NaNO3) may interfere with Na2CO3 crystallization. This was evaluated by measuring the flux through the membrane and the morphology, crystallography, and purity of the crystals. Furthermore, the presence of NaCl possibly transferred from the osmotic solution to the feed solution was evaluated. The experimental results indicate that the presence of impurities decreases the flux through the membrane due to the decrease of water activity, although there is no influence on the overall mass transfer coefficient. The presence of Na2SO4 affected the morphology of the Na2CO3 crystals while NaNO3 and NaCl had no apparent effect on the crystalline products. It was confirmed that Na2CO3·10H2O was formed during the crystallization. Moreover, the purity of Na2CO3 crystals reaches up to ca. 99.5%. Membrane-assisted crystallization was concluded to be feasible in recovering CO2 as a carbonate salt, which can possibly be reused in the industry.

Enhanced performance of a biomimetic membrane for Na2CO3 crystallization in the scenario of CO2 capture

“…This induced an increase of the osmotic pressure in the draw solute but a decline of the osmotic pressure in the feed liquor, enhancing the driving force for water transport across the membrane. than that in previous studies [26,35]. This impressive performance of the AIM 60 FO membrane in terms of water transport is promising for application in membrane crystallization.…”

“…PRO mode FO mode ♦ Na 2 CO 3 ⋅10H 2 O Fig. 11 XRD patterns of the obtained crystals from different operating modes Additionally, crystals obtained with the AIM FO membrane crystallizer have the same polymorphism as the crystals generated in previous work [26,35], reflecting the fact that the obtained crystals were formed under similar thermodynamic conditions, namely, <30% Na 2 CO 3 mother liquor at room temperature [26]. Theoretically, the crystalline structure of Na 2 CO 3 crystal in aqueous solution is mainly influenced by the temperature and the concentration of Na 2 CO 3 in the mother liquid, as the evident from the phase diagram for the thermodynamic formation of Na 2 CO 3 [58].…”

“…The properties of crystal samples were characterized by ion chromatography, microscopy, X-ray diffraction (XRD), and total water fraction (TWF), as described elsewhere [26,35].…”

“…Luis et al [25] demonstrated that osmotic membrane distillation has the potential for production of Na 2 CO 3 ·10H 2 O crystals from CO 2 -rich solutions for closing the loop of CO 2 sequestration. Ye et al [26] further investigated the effect of inorganic impurities on the Na 2 CO 3 crystallization in view of a realistic scenario of CO 2 capture, demonstrating that crystals with ca. 99.5% 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 5 purity can be obtained with the exclusion of co-crystals of impurities.…”

“…However, osmotic membrane distillation, with an inherently low driving force (arising from the transmembrane vapor pressure gradient), fails to provide high mass transfer: ca. 0.09 to 0.18 kg·m -2 ·h -1 at room temperature [25][26][27]. To promote the mass transfer through hydrophobic membranes, thermally assisted membrane distillation is an interesting solution at elevated temperatures [19,28,29].…”