Membranes For Separation Applications Research Articles

Separations Using Zeolite Membranes

This overview describes some of the main features of the use of zeolite membranes for separation applications. Four different types of separations are considered: separation of non-adsorbing compounds, of organic molecules, of permanent gases from vapors, and of water (or polar molecules) from organic (or non-polar) species. Several factors, such as the limiting pore size and pore size distribution, surface diffusion, capillary condensation, shape selectivity and molecular sieving, contribute to the separations observed However, in most of the high selectivity separations reported in the literature, preferential adsorption is the dominant characteristic. In this case, the adsorption of one component in the mixture is stronger and this blocks or hinders the passage of the other components through the membrane pores.

Membrane degumming of crude soybean and rapeseed oils

AbstractMembrane separation in edible oil processing is a potential area for energy savings. However, technical and operating‐cost‐related barriers have impeded the successful application of membrane separation in food processing. Studies were undertaken with soybean and rapeseed oils in a magnetically stirred flat‐membrane batch cell with two types of composite polymeric membranes at 3 MPa pressure and at a constant temperature of 40°C. The membranes were NTGS‐1100 and NTGS‐2100, and used silicon as the active layer and polysulfone and polyimide as support layers, respectively. The membrane selectively rejected phospholipids, the content being less than 240 mg/kg in the permeate without any pretreatment or dilution of crude oil with organic solvent. Long‐term studies up to 97 days with soybean oil at two different pressures, 2 and 3 MPa, showed that the rejection of phosphatides was above 96% in most permeates. The permeate flux remained nearly constant but must be improved.

Complete anaerobic digestion of activated sludge by combining membrane separation and alkaline heat post-treatment

The objective of this laboratory study was to improve the particulate solids decomposition of activated sludge by combining solids-liquid separation and post-treatment to anaerobic digestion. The application of membrane separation has been shown to enhance the anaerobic biodegradability of sewage sludge. In this study, an anaerobic membrane digester with a volume of 51 and UF membrane of 177 cm2 was operated at 35 °C and a HRT of 30 days without considerable sludge wastage. For the first 83 days, the membrane digester was operated without post-treatment. For the succeeding 41 days the membrane digester was combined with alkaline heat post-treatment. This was done by taking out 50 ml per day of the digester sludge, post-treating it under the condition of 0.1M NaOH and 175 °C for 1hr, and returning it to the digester. The particulate solids decomposition percentage averaged for each operating phase was 61% without the post-treatment and about 100% with the post-treatment. These results indicate that the post-treatment was able to selectively destroy unbiodegradable components of the lab-cultivated activated sludge. In addition, because the feed activated sludge can be concentrated in the membrane digester, the post-treatment requires less volume to be treated than pre-treatment. On the other hands, the operation and application of this post-treatment combined process are limited by the allowable digester sludge level imposed by the membrane separation. The problem to be solved is the deterioration of membrane permeate quality and methane production efficiency.

Poly(3-alkylthiophene) membranes for gas separation

The separation of gases is a commercial process conducted primarily via cryogenic distillation. An alternative method involves the use of solvent cast polymer membranes. Unlike distillation, membrane processes are energy efficient, easy to scale-up, and require only electrical energy in their operation. Current membrane separation applications include oxygen or nitrogen enrichment of air, the separation of carbon dioxide from natural gases, and the recovery of hydrogen from refinery and purge streams. In our laboratory, gas separation membranes are being developed based on conducting, soluble and processable polymers such as poly(3-n-alkylthiophene)s. The chemistry of these membranes is being altered by changing the R group (e.g. octyl, dodecyl), the oxidation state, and by incorporating zeolites and molecular sieves to facilitate gas transport. An important aspect of this project concerns establishing the relationship(s) between the structure of poly(3-alkylthiophene) membranes and their bulk properties, specifically permeabilities and selectivities for various gases. It is anticipated that this understanding will help to elucidate the mechanism by which gas separation occurs in these membranes.

バイオテクノロジーへの膜の応用 バイオセパレーションにおける膜分離

Membrane separations are widely used in bioseparation processes. Bioseparation processes consist of the following four processes, that is, cell harvesting/removal of cell debris, concentration, purification and polishing. In these separation processes microfiltration (MF) is used in removal of cells or cell debris, ultrafiltration (UF) in concentration of biomaterials of high molecular weight and biomass, reverse osmosis (RO) including nanofiltration (NF) in concentration of organic acid, amino acid and saccharide, and electrodialysis (ED) in desalting. Besides the conventional applications mentioned above, more sophisticated membranes, membrane modules and equipments are developed and utilized. In this report the following topics are reviewed ; 1) the rotating membranes and their filtration performances in the separation of cells or cell debris, 2) the hybrid membrane separation of cell debris combined with centrifuge, 3) application of adsorptive membranes for affinity separation and membrane chromatography, 4) pervaporation of aroma compounds and 5) membrane extraction.

Recovering CO 2 and N 2 from combustion exhaust gas use membrane technology

Recovering CO 2 and N 2 from combustion exhaust gas use membrane technology

Microporous SiO2 and SiO2/MOx (M=Ti, Zr, Al) for ceramic membrane applications: A microstructural study of the sol-stage and the consolidated state

Microporous SiO2 and SiO2/MO2 (M=Ti, Zr, Al; 10 mol% MOx) materials for gas separation membrane applications have been prepared from polymeric sols. Characterization of these sols with SAXS showed that the mean fractal dimension of the SiO2 sols is 1.3–1.4 with a radius of gyration of approximately 2.5 nm. The dried and calcined films are microporous and the pore size distribution was bimodal with maxima at diameters of 0.5 nm and 0.75 nm. For the SiO2/TiO2, SiO2/ZrO2 and SiO2/Al2O3 systems, much milder reaction conditions proved to be necessary to obtain sols with comparable fractal dimensions due to the high reactivity of the Ti/Zr/Al-alkoxides. Microporous supported membranes with molecular sieve-like gas transport properties can be prepared from a relatively wide range of sol structures: from polymers too small to characterize with SAXS to structures with fractal dimensions: 1<df<2.04.

An integrated electrochemical reaction and supported liquid membrane approach to recycling

Abstract The application of membrane separation integrated into an electrochemical technique for recycling of industrial effluent containing dissolved chromium is presented. Hexavalent chromium, produced by the anodic oxidation of Cr(III) in an undivided electrochemical batch reactor equipped with membrane separation, is extracted into a strip phase by a solvent loaded microporous flat sheet polypropylene membrane containing Aliquat 336. This process is compared with oxidation carried out in a divided and an undivided cell without membrane separation.

Feasibility Study of the Application of Membrane Separation in CO2 Removal from Flue Gases.

燃焼排ガスの二酸化炭素除去への膜分離法の適用を, コンピューターシミュレーションにより検討した.操作方式として, 通常の1段分離 (SSP), 連続膜塔 (CMC) および単純2段カスケード (TSC) を選び, 膜分離の目標として, CO2純度90%, 回収率60%を設定した.分離膜に要求される選択性は, SSPでは210, 循環率 (RR) =2のCMCでは70, RR=3のCMCでは44, TSCでは24と算定された.検討した中で, TSC操作での所要動力が最も大きく石油発電力の15.6%に相当したが, SSP操作ではTSCでの所要動力の38%にすぎなかった。濃縮ガスをさらに液化するとした時の回収CO2量当たりの必要全エネルギー [kWh・kmol-1-CO2] は, TSCで28.0, CMC (RR=3) で 26.9, CMC (RR=2) で22.9そしてSSPで14.9と見積られた.3種の膜分離法と液化法の複合プロセスは, 化学吸収法と液化法の複合プロセスより運転エネルギー面で優位にある.

Oxygen chemical diffusion in strontium doped lanthanum manganites

Abstract The chemical diffusion coefficient of oxygen in (La 0.79 Sr 0.20 )MnO 3−δ and (La 0.50 Sr 0.50 )MnO 3−δ was measured in a solid state electrochemical cell using the potentiostatic step method. In the temperature range between 700°C and 860°C, the chemical diffusion coefficient of oxygen in (La 0.79 Sr 0.20 )MnO 3−δ was found to be in the range of 10 −8 to 10 −6 cm 2 /s and also strongly dependent on the oxygen partial pressure between 0.21 atm and 10 −8 atm. For the case of the stoichiometric oxygen content, the activation energy for oxygen chemical diffusion in this material was determine to be about 70 kJ/mole. Similar measurements between 700°C and 840°C using samples of the composition (La 0.50 Sr 0.50 )MnO 3−δ yielded comparable diffusion coefficient values. Such rapid oxygen transport in these materials make them attractive for high temperature fuel cell electrode and gas separation membrane applications. They also exhibited unusually high values of the order of 10 3 to 10 4 for the thermodynamic enhancement factor indicative of narrow oxygen nonstoichiometry.

Adsorptive and Membrane Separations: A Bibliographical Guide (1985–1989)

This article provides a bibliography of published papers on selected topics concerned with adsorptive and membrane separations for the period 1985–1989. During this period rapid growth occurred in the number of papers published in these areas. The following topics are covered: Adsorptive separations: theory; design data; adsorbents; PSA and cyclic systems; systems and applications; liquid-phase adsorption. Membrane separations: membrane materials; membrane separation theory; membrane separation applications.

Temperature effects on gas permselection properties in hexafluoro aromatic polyimides

Abstract Temperature dependencies of gas permeabilities, solubilities, diffusivities, and selectivities for various gas pairs (He/CH 4 , CO 2 /CH 4 , O 2 /N 2 , and N 2 /CH 4 ) are reported for two hexafluoro-substituted aromatic polyimides prepared in our laboratory. The activation energies for gas permeation and diffusion, and the heats of sorption are also reported. These polyimides have exceptionally high permeabilities and permselectivities as compared to typical glassy polymers used in gas separation membrane applications. The temperature dependency of the permeabilities of all penetrants in these polyimides also is smaller than in other standard glassy polymers having more flexible backbones. The differences in activation energies between larger and smaller penetrants in these packing-disrupted rigid matrices, however, are more extreme than in standard glassy polymers, thereby causing a stronger temperature dependency of the permselectivity than for more flexible backbone glassy polymers.

Inorganic Membrane Technology

The objective of this program is to develop a variety of inorganic based high temperature separation membranes. Organic membranes are limited by temperature (<100/sup 0/C) and chemical environments, and are unsuitable for high temperature applications. The higher temperature stabilities of inorganic materials make them ideal candidates for high temperature membrane applications. Polymers with inorganic backbone structures, such as the polyphosphazenes, are being examined for mid-temperature membrane separation applications (100/sup 0/C - 350/sup 0/C). Metallic and ceramic membrane materials are being examined for high temperature separation applications (350/sup 0/C - 1000/sup 0/C). The liquid and gas membrane test systems developed for this program are described. Preliminary results on the separation properties of poly(bis(2,2,2 trifluoroethoxy)phosphazene) membranes are reported for dilute aqueous methanol, ethanol, isopropanol, and phenol feedstreams.

Evaluation of UF and RO in a cellulose saccharification process

Abstract The applications of membrane separation within the bioconversion of lignocellulosic materials to ethanol are studied, and this paper reports on cellulolytic enzyme recovery, and reduction of the product inhibition. The conversion of cellulose and hemicellulose to hexoses and pentoses is carried out in a laboratory scale UF-membrane reactor, and the sugars, which have an inhibiting effect on the enzymes, are continuously removed with the permeate. By optimizing the space velocity, the enzyme inhibition is minimized and the rate of hydrolysis is significantly increased. The recovery of the enzymes has also been investigated with regard to their mechanical stability and adsorption on the substrate. Prior to enzymatic hydrolysis, the raw material is subjected to a pretreatment to make the cellulose more accessible to the enzymes, and the effect of the pretreatment can easily be evaluated in the UF-membrane reactor. As a result of the continuous removal of products formed in the hydrolysis, the permeate has a low content of fermentable sugars, and to give the optimal conditions for the fermentation a concentration step is needed. Different RO-membranes are tested in a laboratory scale batch cell to be able to choose a membrane material, fit for filtration in larger modules.