Abstract
Highly efficient Si3N4 ceramic planar membrane for water desalination process using membrane distillation was prepared by the dual-layer phase inversion tape casting and sintering method. In comparison with typical phase inversion tape casting method, the green tape was formed using Si3N4 slurry on the top and graphite slurry on the bottom. After consuming away the graphite structure, a ceramic membrane consisting of a two-layered structure (skin and finger-like layers) was obtained. The skin layer was relatively tight, and thus could act as a functional layer for separation, while the finger-like layer contained straight open pores with a diameter of 100 μm, acting as a support with low transport resistance. For comparison, typical Si3N4 ceramic membrane was fabricated by phase inversion technique without graphite substrate, resulting in a three-layered structure (skin, finger-like, and sponge layers). After membrane modification from hydrophilic to hydrophobic with polymer derived nanoparticle method, the water desalination performance of the membranes was tested using the sweeping gas membrane distillation (SGMD) with different NaCl feed solutions. With the increase of salt content from 4 to 12 wt%, the water flux decreased slightly while rejection rate maintained over 99.99%. Comparing with typical three-layered Si3N4 membrane, an excellent water flux enhancement of over 83% was resulted and the rejection rate remained over 99.99%.
Highlights
Clean water demand has been one of the most serious global problems during last decade [1,2]
These kinds of membranes retained the hydrophobicity under harsh conditions and exhibited satisfactory long-term stability, which are proposing the application of ceramic membrane in membrane distillation [17]
The skin layer has remained as the functional layer which decreases the water vapor transfer resistance and increases permeate flux in sweeping gas membrane distillation (SGMD)
Summary
Clean water demand has been one of the most serious global problems during last decade [1,2]. Inorganic modifiers were used for ceramic membrane modification to achieve hydrophobic structure. These kinds of membranes retained the hydrophobicity under harsh conditions and exhibited satisfactory long-term stability, which are proposing the application of ceramic membrane in membrane distillation [17]. In our last few works, phase inversion tape casting method has been investigated for preparation of porous ceramic membrane to enhance the mass transfer. The typical three-layered hydrophobic Si3N4 ceramic membrane consists of skin layer, vertical finger-like voids, and sponge-like region [17,18]. Sponge layer in conventional three-layered membrane structure is considered as an obstacle against gas transmission which is restricting their application in MD process. The Si3N4 membrane showed satisfying water desalination performance, wherein emerging its potential for practical applications
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