Temperature-Driven Transition from Knudsen Diffusion to Viscous Flow in a Macroporous Ceramic Membrane

The main objective of this work was to investigate the removal of boron from processed geothermal waters (i.e., after energy production) in lab-scale tests using ceramic ultrafiltration membranes. The impacts of membrane operating pressure, feed water pH and temperature and membrane pore size on boron rejections were determined. Three different single-channel tubular ceramic membrane modules with average pore sizes of 4 nm, 10 nm and 1 kD were tested. Fine-UF ceramic membrane with 4 nm pore size provided higher boron and salt rejections than the other two tested membranes. Increasing pH from 8.8 to 10.5 did not enhance boron rejections. Operating pressure around 8 bar was found to be optimum in terms of flux values and boron and salt rejections for the 4 nm pore-sized membrane. The results indicated that ceramic ultrafiltration membranes can only partially (around 25-30%) remove boron from geothermal waters. Once much lower pore-sized nanofiltration or brackish water reverse osmosis type ceramic membranes are available, they may be used for the desalination of processed geothermal waters since ceramic membranes are resistant to extreme conditions. Ceramic fine-UF membranes can also be used as a pre-treatment stage prior to polymeric brackish water reverse osmosis processes in desalination of geothermal waters.

Experimental study of water recovery from flue gas using hollow micro–nano porous ceramic composite membranes

Simulation study of using macroporous ceramic membrane to recover waste heat and water from flue gas

Summary: The aim of the study was to investigate the variation in total surface area, porosity, pore size, Knudsen and surface diffusion coefficients, gas permeability and selectivity before and after the application of sol‐gel process to porous ceramic membrane in order to determine the effect of pore modification. In this study, three different sol‐gel process were applied to the ceramic support separately; one was the silica sol‐gel process which was applied to increase porosity, others were silica‐sol dip coating and silica‐sol processing methods which were applied to decrease pore size. As a result of this, total surface area, pore size and porosity of ceramic support and membranes were determined by using BET instrument. In addition to this, Knudsen and surface diffusion coefficients were also calculated. After then, ceramic support and membranes were exposed to gas permeation experiments by using the CO2 gas with different flow rates. Gas permeability and selectivity of those membranes were measured according to the data obtained. Thus, pore surface area, porosity, pore size and Knudsen diffusion coefficient of membrane treated with silica sol‐gel process increased while total surface area was decreasing. Therefore, permeability of ceramic support and membrane treated with silica sol‐gel process increased, and selectivity decreased with increasing the gas flow rate. Also, surface area, porosity, pore size, permeability, selectivity, Knudsen and surface diffusion coefficients of membranes treated with silica‐sol dip coating and silica‐sol processing methods were determined. As a result of this, porosity, pore size, Knudsen and surface diffusion coefficients decreased, total surface area increased in both methods. However, viscous flow and Knudsen flow permeability were detected as a consequence of gas permeability test and Knudsen flow was found to be a dominant transport mechanism in addition to surface diffusive flow owing to the small pore diameter in both methods. It was observed that silica‐sol processing method had lower pore diameter and higher surface diffusion coefficient than silica‐sol dip coating method.

Study on the performance of CO2 capture from flue gas with ceramic and PTFE membrane contactors

In this work, a ceramic membrane tube with a pore size of 1 μm was used to conduct experimental research on moisture and waste heat recovery from flue gas. The length, inner/outer diameter, and porosity were 800 mm, 8/12 mm, and 27.2%, respectively. In the experiments, the flue gas, which was artificially prepared, flowed on the shell side of membrane module. The water coolant passed through the membrane counter-currently with the gas. The effects of flue gas flow rate, flue gas temperature, water coolant flux, and water coolant temperature on the membrane recovery performance were analyzed. The results indicated that, upon increasing the flue gas flow rate and its temperature, both the amount of recycled water and the recovered heat increased. The amount of recycled water, recycled water rate, recovered heat, and heat recovery rate all decreased as the water coolant temperature increased. When the water coolant temperature exceeded 30 °C, the amount of recycled water dropped sharply. The maximum amounts of recycled water, recovered heat, and total heat transfer coefficient were 2.93 kg/(m2·h), 3.63 kW/m2, and 224.3 W/(m2·K), respectively.

Design and characterization of macroporous alumina membranes for passive samplers of water contaminants

The non-uniformity of pore size and pore distribution of the current hemodialysis membrane results in low efficiency of uremic solute removal as well as the loss of albumin. By using nano technology, an anodic alumina membrane (ceramic membrane) with self-organized nano-pore structure was produced. The objective of this study was to investigate the correlation between various anodization conditions and the pore characteristics of the ceramic membrane as a potential use in artificial kidney / hemodialysis. An aluminum thin film was oxidized in two electrolytes consisting of 3% and 5% sulfuric acid and 2.7% oxalic acid. The applied voltages were 12.5, 15, 17.5 and 20 (V) for sulfuric acid and 20, 30, 40 and 50 (V) for oxalic acid. Pore size and porosity were determined by analyzing scanning electron microscopy (SEM) images and hydraulic conductivity was measured. Pore size increased linearly with voltage. Acid concentration affected pore formation but not pore size and pore distribution. Hydraulic conductivity of the ceramic membrane was higher than that of polymer dialysis membrane. The optimal formation conditions for self-organized nano-pore structure of ceramic membrane were 12.5–17.5V in 3–5% sulfuric acid at 0 °C. These conditions produced ceramic membranes with pores of ~ 10 nm diameter. Conclusion: Anodic alumina technology reliably produced in quantity structures with pore sizes in the 10–50 nm diameter range. Because of more uniform pore size, high porosity, high hydraulic conductivity and resistance to high temperature, the ceramic membrane has potential for future application as a hemodialysis membrane.

Influence of hydrophobization conditions and ceramic membranes pore size on their properties in vacuum membrane distillation of water–organic solvent mixtures

In this study, the water recovery performance from flue gas with ceramic membrane tubes of different pore sizes 30, 50, and 200 nm was experimentally studied. The effects of flue gas temperature, flue gas flow rate, water coolant temperature, and water coolant flow rate on the water recovery performance were analyzed. In addition, in the experimental study of SO2 permeability, the pH of the water coolant inlet and outlet was measured using a pH meter to analyze the SO2 permeability of ceramic membranes during the water recovery process. The results show that the water recovery performance of the 50 nm pore size ceramic membrane is better than that of the other two types of ceramic membrane in most cases. The maximum amount of reclaimed water and the highest water recovery rate are 4.82 kg/(m2·h) and 80.3%, respectively. Under the same SO2 concentration condition, the SO2 permeation flux of the 30 nm pore size ceramic membrane is smallest, and that of the 200 nm membrane is the largest. When the SO2/N2 mixed gas flow rate is 6 L/min, the SO2 permeation flux of the 30 and 200 nm membranes is 0.407 and 0.635 mmol/(m2·h), respectively. The ceramic membrane with smaller pore size can block more SO2 permeation, while the ceramic membrane with larger pore size can remove SO2 better.

The purpose of this study was to investigate membrane fouling caused by microalgal cells in submerged membrane systems consisting of polymeric and ceramic microfiltration membranes. In this study, one polymeric (flat-sheet, pore size: 0.2 um) and two ceramic (flat-sheet, pore size: 0.2 um and cylindrical, pore size: 1 um) membranes were used. Physical cleaning was performed with water and air to determine the potential for reversible and irreversible membrane fouling. The study results showed that substantial irreversible membrane fouling (after four filtration cycles, irreversible fouling degree 27% (cleaning with water) and 38% (cleaning with air)) occurs in the polymeric membrane. In cleaning studies performed using water and air on ceramic membranes, it was observed that compressed air was more effective (recovery rate: 87-91%) for membrane cleaning. The harvesting performance of the membranes was examined through critical flux experiments. The critical flux values for polymeric membrane with a pore size of 0.20 um and ceramic membranes with a pore size of 0.20 um and 1 um were <=95 L/m2hour, <=70 L/m2hour and <=55 L/m2hour, respectively. It was determined that critical flux varies depending on the membrane material and the pore size. To obtain more information on membrane fouling caused by microalgal cells, the characterization of the fouled polymeric membrane was performed. This study concluded that ceramic membranes with a pore size of 0.2-1 um in the submerged membrane system could be efficiently used for microalgae harvesting by cleaning the membrane with compressed air at regular intervals.

Chitosan based ceramic ultrafiltration membrane: Preparation, characterization and application to remove Hg(II) and As(III) using polymer enhanced ultrafiltration

One step co-sintering synthesis of gradient ceramic microfiltration membrane with mullite/alumina whisker bi-layer for high permeability oil-in-water emulsion treatment

A theoretical analysis on pore size change of porous ceramic membranes after modification

Fabrication and characterization of TiO2/ZrO2 ceramic membranes for nanofiltration