Development of Hydrophobic Coal-Fly-Ash-Based Ceramic Membrane for Vacuum Membrane Distillation

Abstract

Membrane distillation is an emerging separation technology with a high separation factor in water desalination. Ceramic membranes are increasingly used in membrane distillation because of high thermal and chemical stabilities. Coal fly ash is a promising ceramic membrane material with low thermal conductivity. In this study, three hydrophobic coal-fly-ash-based ceramic membranes were prepared for saline water desalination. The performances of different membranes in membrane distillation were compared. The effects of membrane pore size on permeate flux and salt rejection were researched. The coal-fly-ash-based membrane showed both a higher permeate flux and a higher salt rejection than the alumina membrane. As a result, using coal fly ash as the material for membrane fabrication can effectively increase the performance when applied to MD. Increasing the membrane pore size improved the permeate flux, but reduced the salt rejection. When the mean pore size increased from 0.15 μm to 1.57 μm, the water flux rose from 5.15 L·m−2·h−1 to 19.72 L·m−2·h−1, but the initial salt rejection was reduced from 99.95% to 99.87%. The hydrophobic coal-fly-ash-based membrane with a mean pore size of 0.18 μm exhibited a water flux of 9.54 L·m−2·h−1 and a salt rejection of higher than 98.36% in membrane distillation.

Application of coal fly ash based ceramic membranes in wastewater treatment: A sustainable alternative to commercial materials

“…Ceramic particles can be held together using binders such as polyvinyl alcohol [ [79] , [80] , [81] ], sodium metasilicate [ 82 , 83 ], carboxymethyl cellulose (CMC) [ 84 ], and others. The settling of the powder particles is prevented by the use of dispersants like sodium hexametaphosphate [ 34 ], sodium carbonate, and boric acid [ 82 ]. In order to make synthetic membranes more flexible, glycerine is mostly utilized as a plasticizer.…”

“… Ceramic membrane Fabrication method Additives Characteristic of the synthesized material Ref. Hydrophobic Coal-Fly-Ash-Based Ceramic Membrane Extrusion sodium hexametaphosphate of the suspension served as a dispersant and the PVA acted as a binder Increased pore size from 0.15 μm to 1.57 μm, the water flux rose [ 34 ] Highly porous whisker-structured mullite ceramic membranes Uniaxial pressing MoO 3 as a single sintering additive Organic binder polyvinyl alcohol Open porosity showed a significant increase from 41.65 ± 0.13 % to 58.14 ± 0.15 % as the MoO3 content increased from 0 to 20 wt%, accompanied by a decrease in shrinkage and pore size in the absence of any pore-forming agent [ 103 ] Coal fly ash based multipurpose ultrafiltration membrane Uniaxial pressing – The membrane porosity-39.8 % hydraulic pore radius - 41 nm. The membrane pure water flux increased from 2.09 to 11.31 m 3 /m 2 sec as the applied pressure increased from 69 to 483 kPa.…”

“…Surface wettability has an impact on how membranes are utilized, with hydrophilic membranes frequently employed in water filtration and hydrophobic membranes excellent for membrane distillation [ 153 ]. For instance, Zhang et al [ 34 ] fabricated hydrophobic coal fly ash based ceramic membrane for desalination. The membrane showed excellent water flux and higher salt rejection compared to aluminium based ceramic membranes.…”

“…The membrane showed excellent water flux and higher salt rejection compared to aluminium based ceramic membranes. Surface geometrical structure or surface free energy can be modified to alter the wettability of membrane surfaces [ 34 , 106 , 154 ]. Zhang et al [ 80 ] studied the effect of changing wettability of the surface of a coal fly ash based ceramic membrane.…”

“…Ceramic membranes can successfully eliminate various pollutants from wastewater through processes such as size exclusion, adsorption, and electrostatic repulsion. The efficiency of separating pollutants in wastewater using ceramic membranes depends on factors such as the membrane's pore volume, pore size, size distribution, and surface chemistry [ 34 ].…”