Dense Inorganic Polymer Membranes

The resulting membranes exhibit very good separation properties. For example, the separation factors for the gaseous mixtures of 10%S02/90%N2 and 10%H2S/90%CH4 

Pnlvrilflzflngs. Another organometallic polymer which has the potential for being an inorganic membrane material is polysilazane. There is indication that this family of Si-and N-based inorganic polymers has been studied as a membrane material [Johnson and Lamoreaux, 1989] but no detail information is available. 

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Zeolite/polymer mixed-matrix membranes can be fabricated into dense film, asymmetric flat sheet, or asymmetric hollow fiber. Similar to commercial polymer membranes, mixed-matrix membranes need to have an asymmetric membrane geometry with a thin selective skin layer on a porous support layer to be commercially viable. The skin layer should be made from a zeohte/polymer mixed-matrix material to provide the membrane high selectivity, but the non-selective porous support layer can be made from the zeohte/polymer mixed-matrix material, a pure polymer membrane material, or an inorganic membrane material. 

Dense inorganic or metallic membranes for gas separation are usually ion-conducting materials, while membranes with carriers are polymers or supported liquid membranes (SLM). For transport through these materials, different flux equations should be applied. Figure 4.2 sums up and generalizes the various types of transport, which may take place in gas-separation membranes [21]. 

The application of polymer membranes is generally limited to temperatures below 475 K and to the separation of mixtures that are chemically inert. Otherwise, membranes made of inorganic materials can be used. These include mainly microp-orous ceramics, metals, and carbon, and dense metals, such as palladium, that allow the selective diffusion of very small molecules such as hydrogen and helium. 

RO membranes eonsist of two layers, (i) a thin dense top polymer layer and (ii) a porous sublayer, which gives support to the top layer and inereases the mechanical stability of the membrane. These membranes have been effeetively used for water desalination with a very high rejection (sometimes over 99%) of the low moleeular mass compounds (inorganic salts or small organic molecules) (Velizarov et al., 2004). However, there are some drawbacks for RO treatment, which include (i) lack of dissolved minerals in the treated water, (ii) low rejection of neutral molecules and (iii) high energy consumption (Mondal et al., 2013). 

In dense stmctures there is no intentional void space with dimensions much larger than the atomic building blocks. Zeolites that may have a large stmctural void space in their crystal stmcture are generally not considered dense stmctures. Dense membranes generally have an ideal selectivity in which only one species is transported. The separative layer in supported polymer membranes is also considered dense, even though it may not be 100% selective for one component. In dense inorganic membrane transport, molecules such as H2 and O2 are converted at the surface into (smaller) atomic, ionic, and/or... 

Membranes are classified as organic or inorganic, taking into account the material used for their syntheses porous or dense, based on the porosity of the material applied and symmetric and asymmetric for a membrane made of a single porous or dense material or for a membrane made of a porous support and a dense end, respectively [16,64], We are fundamentally interested here in asymmetric inorganic membranes made of a porous end to bring mechanical stability to the membrane and made of alumina, silica, carbon, zeolites, and other materials, and a dense end to give selectivity to the membrane (see Chapter 10). However, we also analyze the performance of porous polymers. 

Membranes can be classified [2] according to the driving force (concentration or pressure difference) that causes the flow of the permeate through the membrane, or to the material(s) they consist of (organic polymers or inorganic materials). For both type of materials the membrane can be dense or porous. 

Extensively studied is oxygen permeation through dense ceramic membranes (e.g. perovskhes). Temperatures > 600 °C are applied. Here, oxygen splits at the surface and is transited as 0 . Porous membranes include porous polymer films (cellulosics, polyamides) as well as amorphous inorganic materials (alumina, silica). 

Most applications of GP use dense membranes of cellulose acetates and polysulfones. For high-temperature applications where polymers cannot be used, membranes of glass, carbon, and inorganic oxides are available, but they are limited in their selectivity. Almost all large-scale applications of GP use spiral-wound or hollow-fiber modules, because of their high packing density. 

The parameters and consequently the efficiency of PV strongly depends on the properties of the membrane material. Common membrane materials are various dense polymers and microporous inorganic membranes (zeolithes, silica,. ..) either with hydrophilic or organophilic character. Furthermore composite membranes offer the possibility to combine different materials for the dense active layer and the porous support layer. Besides membrane material fluid hydrodynamics influences the efficiency of separation. The pressure drop especially on the permeate side reduces the driving force of the most permeating components. 

The general procedure to fabricate dense MMM is as follows i) preparation of homogeneous polymer/inorganic filler/solvent mixture, ii) casting the solution on a smooth plate, iii) evaporation of the solvent, and sometimes iv) annealing the membrane at high temperatures to remove the residual solvent. 

Many efforts have been made in the design and fabrication of controlled organic/inorganic composites with novel properties, which include chemical, optical, electrical, biological, and mechanical properties [84-87]. For these hybrid systems, phase separation occurs naturally based on the fact that they are composed of two materials with totally different chemical characteristics [88,89]. MMMs are fabricated from polymer matrix and inorganic particles for improvement polymeric membrane properties. Dispersed particles in polymeric matrix are categorized in two groups porous and dense (non-porous) particles [90]. 

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