An investigation of solubility of aliquat 336 in different extracted solutions

A major concern in solvent extraction processes is the loss of extractant into the aqueous phase due to its slight solubility in the aqueous phase. Similarly, in membrane extraction processes, extractant loss through extractant leakage from the membrane into the aqueous phase is also a concern. Several published membrane extraction studies using Aliquat 336 as the extractant, have expressed this concern, but none has studied extractant leakage quantitatively. It is the authors’ opinion that the extractant leakage should be considered as a technical parameter of a membrane. In our laboratory active progress has been made in using Aliquat 336 ‘entangled’ into the polymer membranes to remove heavy metal ions from wastewater samples. In this work, we studied the loss of Aliquat 336 from the point of view of its solubility in aqueous solutions. The results showed that the solubilities of Aliquat 336 in an aqueous phase acidified with 2 M HCl is about 0.1 g/100 m/ of the solution. This figure provides a useful guideline for evaluating the leakage of the Aliquat 336 extractant from the membranes.

Polypyrrole-coated electrospun nanofibre membranes for recovery of Au(III) from aqueous solution

In this paper, for the first time, polypyrrole-coated electrospun nanofibre mats have been used as separation membranes to electrolessly recover Au from aqueous [Au(III)Cl₄]− solutions, based on a continuous-flow membrane separation process. With a [Au(III)Cl₄]− solution passing through the nanofibre membrane, the Au(III) ions were converted into elemental Au. The gold recovered was deposited on the nanofibre membranes in the form of Au particles, as confirmed by EDX and XPS measurements. It has been found that the polypyrrole-coated electrospun nanofibres are good candidate membrane material for the recovery of Au, and the recovery efficiency is affected by the membrane thickness, the permeate flux rate and the initial [Au(III)Cl₄]− concentration.

Problems in seawater industrial desalination processes and potential sustainable solutions: a review

Seawater desalination has significantly developed towards membrane technology than phase change process during last decade. Seawater reverse osmosis (SWRO) in general is the most familiar process due to higher water recovery and lower energy consumption compared to other available desalination processes. Despite major advancements in SWRO technology, desalination industry is still facing significant amount of practical issues. Therefore, the potentials and problems faced by current SWRO industries and essential study areas are discussed in this review for the benefit of desalination industry. It is important to consider all the following five components in SWRO process i.e. (1) intake (2) pre-treatment (3) high pressure pumping (4) membrane separation (performance of membranes and brine disposal) and (5) product quality. Development of higher corrosion resistant piping materials or coating materials, valves, and pumps is believed to be in higher research demand. Furthermore, brine management, that includes brine disposal and resource recovery need further attention. Pre-treatment sludge management and reduced cleaning in place flush volume will reduce the capital costs associated with evaporation ponds and the maintenance costs associated with disposal and transportation reducing the unit cost of water. © 2013 Springer Science+Business Media Dordrecht.

Electrospun fibrous membranes with super-large-strain electric superhydrophobicity

Large-strain elastic superhydrophobicity is highly desirable for its enhanced use performance and functional reliability in mechanically dynamic environments, but remains challenging to develop. Here we have, for the first time, proven that an elastic fibrous membrane after surface hydrophobization can maintain superhydrophobicity during one-directional (uniaxial) stretching to a strain as high as 1500% and two-direction (biaxial) stretching to a strain up to 700%. The fibrous membrane can withstand at least 1,000 cycles of repeated stretching without losing the superhydrophobicity. Stretching slightly increases the membrane air permeability and reduces water breakthrough pressure. It is highly stable in acid and base environments. Such a permeable, highly-elastic superhydrophobic membrane may open up novel applications in membrane separation, healthcare, functional textile and energy fields.

A novel class of gas separation membrane based on organic ionic plastic crystals

The first use of organic ionic plastic crystals (OIPCs) as CO2 separation membranes is reported. The novel OIPC/PVDF nanofiber composites show CO2/N2 ideal selectivities of 30 at 35 °C. The dependence of gas permeability on the thermal phase of the plastic crystals is discussed.

A novel polymer membrane for extraction applications

In this study, a new type of Aliquat 336/PVC membrane has been made for extraction experiments. This new membrane is capable of holding more Aliquat 336 than previously developed extraction membranes, hence overcoming a major problem that has confronted many researchers for a long time. The new membrane has been used to investigate the rate of extraction for the Cd(II) ion in 2.0 M HCl solution and the effect of membrane thickness on the rate of extraction. The experimental results have shown this new membrane has a promising future in relevant industrial applications. A new method is also used in this study to qualitatively identify the oily substance on the surface of membrane after the extraction experiment was completed. This oily substance has been found to be Aliquat 336.

Recent developments in carbon nanotube membranes for water purification and gas separation

Carbon nanotubes (CNTs) are nanoscale cylinders of graphene with exceptional properties such as high mechanical strength, high aspect ratio and large specific surface area. To exploit these properties for membranes, macroscopic structures need to be designed with controlled porosity and pore size. This manuscript reviews recent progress on two such structures: (i) CNT Bucky-papers, a non-woven, paper like structure of randomly entangled CNTs, and (ii) isoporous CNT membranes, where the hollow CNT interior acts as a membrane pore. The construction of these two types of membranes will be discussed, characterization and permeance results compared, and some promising applications presented.

Evidence of changes in membrane pore characteristics due to filtration of dye bath liquors

This study was carried out to investigate the treatment of various salt solutions and synthetic dye bath liquors by nanofiltration using Nanomax-50 membrane in a stirred cell with 150 mL working volume. Donnan exclusion was compared by filtering salts with monovalent and divalent cations and anions. This was done by comparing three salts including sodium chloride (NaCl), calcium chloride (CaCl2) and sodium sulphate (Na2SO4). The rejection order determined was Na2SO4>NaCl>CaCl2 which is typical of a negatively charged membrane where Donnan and steric exclusion play an important role in separation. Studies on the flux and rejection characteristics of sodium sulphate were undertaken for concentrations ranging from 10 to 40 gl−1 thereby replicating actual dye bath salt concentrations. Synthetic dye bath liquors were prepared using acidic dye (Acid Green 25) at a fixed concentration of 100 mgl−1 with 10 and 15 gl−1 of sodium sulphate solutions. While, the results showed evidence of flux decline due to increased resistance and decreased transmembrane pressure, pore enlargement occurred after the filtration experiments with sodium sulphate solutions greater than 20 gl−1. Pore enlargement was even more prominent in the two synthetic dye bath liquors filtered. Pore enlargement was determined by observing the pure water flux before and after filtering sodium sulphate solutions or dye bath liquors. An increase in pore diameter of 58 and 94 %was estimated when dye bath liquors containing 10 and 15 gl−1 of sodium sulphate, respectively were filtered through the membrane. The following equation was derived in estimating the pore enlargement, where de1 and de2 are the apparent diameter of membrane pore sizes before and after filtration of salt solutions or dye bath liquors and Rm1 and Rm2 are the membrane resistance of pure water flux before and after filtration of salt solutions or dye bath liquors. These results have important implications for the application of nanofiltration technology to textile wastewater treatment and reuse.

Highly stable external short-circuit-assisted oxygen ionic transport membrane reactor for carbon dioxide reduction coupled with methane partial oxidation

A membrane reactor allows for simultaneous separation and reaction, and thus, can play a good role to produce value-added chemicals. In this work, we demonstrated such a membrane reactor based on fluorite oxide samarium-doped ceria (SDC) using an external short-circuit concept for oxygen permeation. The fluorite phase was employed to impart its high structural stability, while its limited electronic conductivity was overcome by the application of an external short circuit to function the SDC membrane for oxygen transport. On one side of the membrane, i.e., feed side, carbon dioxide decomposition into carbon monoxide and oxygen was carried out with the aid of a Pt or Ag catalyst. The resultant oxygen was concurrently depleted on the membrane surface and transported to the other side of the membrane, favorably shifting this equilibrium-limited reaction to the product side. The transported oxygen on the permeate side with the aid of a GdNi/Al2O3 catalyst was then consumed by the reaction with methane to form syngas, i.e., carbon monoxide and hydrogen. As such, the required driving force for gas transport through the membrane can be sustained by coupling two different reactions in one membrane reactor, whose stability to withstand these different gases at high temperatures is attained in this paper. We also examined the effect of the membrane thickness, oxygen ionic transport rate, and CO2 and CH4 flow rates to the membrane reactor performance. More importantly, here, we proved the feasibility of a highly stable membrane reactor based on an external short circuit as evidenced by achieving the constant performance in CO selectivity, CH4 conversion, CO2 conversion, and O2 flux during 100 h of operation and unaltered membrane structure after this operation together with the coking resistance.