Preparation And Application Of Coal Fly Ash-based Ceramic Composite Membranes For Membrane Distillation

Membrane distillation(MD)is an emerging water treatment technology with high separation factor.Ceramic membrane is widely used in membrane distillation because of its high thermal and chemical stability.At present,ceramic membranes used in membrane distillation are mainly made of alumina with high thermal conductivity,while membrane materials with low thermal conductivity can effectively increase thermal resistance in membrane distillation process and improve separation performance.Coal fly ash(CFA),as a ceramic membrane material with low thermal conductivity,is rarely used in membrane distillation research.In this study,coal fly ash was used as the raw material to prepare ceramic composite membrane,and its performance modulation and optimization was conducted to improve its separation performance in membrane distillation application,and the performance in vacuum membrane distillation process was compared with alumina ceramic membrane,and the effect of pore size of coal fly ash-based ceramic membrane on the separation performance was analyzed.The results show that when pH=4 and the concentration of dispersant PAA is 40 g/L,the dispersion stability of the suspension is the best.The pore size of the ceramic composite membrane prepared by using it as coating liquid is the best.The mean pore size of the membrane is 0.26 μm,the maximum pore size is 0.35 μm,and the proportion of most probable pore size is 59.05%.When the number of coating times increases,the separation layer of composite film is denser,the pore size is smaller,and the pure water flux of composite membrane is smaller.The results of vacuum membrane distillation showed that the permeation flux of hydrophobic ceramic membrane increased with the increase of liquid flow rate at a constant temperature,but its upward trend decreased gradually,and the salt rejection of NaCl solution remained almost unchanged.When the flow rate of material liquid was constant,the permeation flux of hydrophobic ceramic membrane increased with the increase of temperature,but the salt rejection decreased.The performance of coal fly ash-based ceramic membrane is better than that of alumina ceramic membrane.With the increase of mean pore size of coal fly ash-based ceramic membrane,the permeation flux of the membrane increases,but the salt rejection decreases.Considering the permeation flux,salt rejection and hydrophobic stability,the coal fly ash-based ceramic membrane with mean pore size of 0.18 μm has the best performance in membrane distillation process.Its permeation flux is 9.54 L·m-2·h-1,and the salt rejection is higher than 98.36%.