Membranes as support

Yang, Q., Chung, T.S., Xiao, Y.C. and Wang, K.Y. (2007) The development of chemically modified P84Co-polyimide membranes as supported liquid... 

The in situ membrane growth technique cannot be applied using the zeolite-based ceramic porous membrane as support, under hydrothermal conditions in a solution containing sodium hydroxide. The high pH conditions will cause membrane amorphization and lead to final dissolution. Therefore, we tried to synthesize an aluminophosphate zeolite such as AlP04-5 [105] over a zeolite porous ceramic membrane. For the synthesis of the AlP04-5-zeolite-based porous membrane composite, the in situ membrane growth technique [7,13,22] was chosen. Then, the support, that is, the zeolite-based porous ceramic membrane, was placed in contact with the synthesis mixture and, subsequently, subjected to a hydrothermal synthesis process [18]. The batch preparation was as follows [106] ... 

The most demanding support requirements are those for ultra thin micro-porous gas separation membranes, which are currently being developed in several research organisations worldwide including ECN (Petten, the Netherlands). In principle, a mesoporous Knudsen or UP membrane can serve as support for these membranes if the defect density in the substrate surface, i.e. the mesoporous layer, is low enough. Indeed, the quality of the Knudsen or UF membrane as support for a microporous gas separation membrane should be higher than is usually needed for the UF or Knudsen function [4]. This means that not every mesoporous ceramic membrane is a suitable support for micro-porous or dense amorphous gas separation membranes. 

Some researchers have also used nitrocellulose filters as liquid membrane supports. Mochizuki and Forster (5) used this material as a support for hemoglobin solutions to study the facilitated transport of O2 and CO. Enns (6) used the same support for studying the facilitated transport of CO2 using aqueous solutions of carbonic anhydrase. Donaldson and Quinn (7) utilized both nitrocellulose filters and cross-linked protein membranes as supports to investigate CO2 facilitated transport using enzymatically active liquid membranes. 

In bench-scale tests, using hoUow-fiber membrane as support and a carrier concentration of 2 M the ethylene permeance was 4.6 X 10 barrer/cm with an ethylene partial pressure of 65 psia, while the selectivity C2H4/C2H6 was about 240. Same tests were carried out for separation of propylene from propane. The selectivity obtained was greater than 100 but this result was confirmed only at bench scale. In fact, in the large pilot system, the selectivity and flux dechned over some weeks due to loss of solvent and carrier and to the necessity of remove hydrogen from the feed gas to prevent reduction of Ag f carrier. Despite the result, this remains the first study on the use of facilitated transport membrane for gas separations on a pilot scale. 

The use of nanofiltration membranes as supporting membranes have been also reported [28]. In this case, direct filtration of ionic liquids through the nanofiltration membrane was not possible at a gas pressure up to 7 bars. The ionic liquids with cations associated with straight or branched hydrocarbon chains were easily absorbed into the polymeric membrane allowing the nanoporous structure saturated with the ionic liquids. 

Since then, a number of papers have been published on this type of membrane [93-96]. Along with the use of ion exchange membranes as supports, yet another approach to overcome the previously mentioned limitations was developed by introducing carriers directly into polymer membranes [60,97,98]. These FSC membranes have carriers covalently bonded to the polymer backbone hence, the carriers have restricted mobility but are favorable when stability is considered. It is obvious that the diffusivity (and thus permeability) in an FSC membrane is lower than that of a mobile carrier membrane. The diffusivity of a swollen FSC membrane should however show diffusivities between that of a mobile and a fixed carrier. 

Another interesting application explored for track-etched membranes is for the synthesis of nanoparticles by simply passing molecules from one side of the membrane and precipitating the molecules at the other side of membrane. Here, a PCTE was attached on an AAO nanoporous membrane as supporting substrate (Figure 20.26). Chitosan was... 

Electrospun polymeric membranes have been investigated for CBD applications for some time (81-83). Early materials lacked the flexibihty and durabihty required in many protective systems, and efforts did not sufficiently address the issue of production. Current advances in the area of modehng electrospim membranes (84,85), elastomeric membranes (86), and effective use of electrospim membranes as supports for reactive nanoparticles could assist in the imderstanding and application of this class of materials in chem./bio defense. The recommendation is to focus on projects that specifically address the... 

Hashemi, P Abolghasemi, M. M. Preparation of a novel optical sensor for low pH values using agarose membranes as support. Sens. Actuators, B 2006, B115,49-53. 

Figure 11.8 Membrane as support of the biofilm in a solid-state fermentation process. Adapted from Wang and Chen (2009).

Facilitated Transport by Mobile Carrier Membranes with Ion Exchange Membrane as Supports. 

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