Membrane performance characterization

Despite improvement to synthesis methods used it is known that all membranes possess unavoidable defects due to intercrystalline porosity, which are formed during membrane growth [7, 8]. The goal of many characterization techniques is to determine the size and concentration of such defects and evaluate how their presence affects membrane performance. 

The membrane performance for separations is characterized by the flux of a feed component across the membrane. This flux can be expressed as a quantity called the permeability (P), which is a pressure- and thickness-normalized flux of a given component. The separation of a feed mixture is achieved by a membrane material that permits a faster permeation rate for one component (i.e., higher permeability) over that of another component. The efficiency of the membrane in enriching a component over another component in the permeate stream can be expressed as a quantity called selectivity or separation factor. Selectivity (0 can be defined as the ratio of the permeabilities of the feed components across the membrane (i.e., a/b = Ta/Tb, where A and B are the two components). The permeability and selectivity of a membrane are material properties of the membrane material itself, and thus these properties are ideally constant with feed pressure, flow rate and other process conditions. However, permeability and selectivity are both temperature-dependent... 

A.G. Boricha and Z. Murthy, Acrylonitrile butadiene styrene/chitosan blend membranes Preparation, characterization and performance for the separation of heavy metals, J. Membr. Sci., 339(l-2) 239-249, September 2009. 

Permporometry. Permporometry is based on the well known phenomenon of capillary condensation of liquids in mesopores. It is a collection of techniques that characterize the interconnecting active pores of a mesoporous membrane as-is and nondestiuctively using a gas and a liquid or using two liquids. The former is called gas-liquid permporometry [Eyraud, 1986 Cuperus et al., 1992b] and the latter liquid-liquid permporometry [Capanneli et al., 1983 Munari et al., 1989]. The "active" pores are those pores that actually determine the membrane performance. 

In liquid filtration using micro-, ultra-, and nanofiltration porous membranes, the driving force for transport is a pressure gradient. Solvent permeability and separation selectivity are the two main factors characterizing membrane performance. Convective flux is predominant with macroporous and mesoporous membrane strucmres, the selectivity being controlled by a... 

Membranes need to be characterized to ascertain which may be used for a certain separation or class of separations (13). Membrane characterization is to measure structural membrane properties, such as pore size, pore size distribution, free volume, and crystallinity to membrane-separation properties. It helps gather information for predicting membrane performance for a given application. 

C. Guizard, C. Mouchet, R. Vacassy, X. Bouisson and V. Thoraval, Zirconia nanofiltration membranes II. Performance of the membranes, dynamic characterization with model solutes, in preparation. 

Information about the porous support layer rather than the skin layer. The techniques used by these authors, as well as those reviewed by Pusch and Welch (21), provide valuable Insight Into the mechanism of membrane formation and thus may assist membrane scientists In developing better membranes. However, many of these techniques do not characterize the membrane under the conditions of application for example, the ultrafiltration membranes (23,24) are dried prior to gas sorption studies and microscopy. Therefore, caution must be exercised In Interpreting the results of these characterization methods and relating them to membrane performance and transport mechanisms. 

The PEC-1000 membrane of Toray Industries, Inc., has been described by Kurihara et al (21). This membrane was characterized as a thin-film composite type made by an acid catalyzed polymerization on the surface. Membrane performance reported for seawater tests was 99.9 percent TDS rejection at fluxes of 5.0 to 7.4 gfd (8.3 to 12.3 L/sq m/hr) when tested with 3.5 percent synthetic seawater at 800 psi (5516 kPascals). The membrane was stable in 1500-hour tests in spiral-wrap elements and exhibited stability in a temperature range of 25 to 55°C and in a pH range from 1 to 13. High organic rejections were reported for the PEC-1000 membrane rejection of dimethylformamide from a 10 percent solution was 95 percent and similar tests with dimethylsulfoxide showed 96 percent rejection. The composition and conditions for preparation of PEC-1000 membrane is not disclosed in Reference 21. Apparently it is a dip-cast membrane related to compositions described by Kurihara, Watanaba and Inoue in Reference 18. 

The CCRO concept has not been proven in practice thus, an objective of the present work was to demonstrate the process concept experimentally. Various RO membranes were characterized to determine if their use for ethanol enrichment by CCRO would be more energy-efficient than by distillation, and to identify membrane characteristics that affect the performance of the process. 

A new high performance module, Daicel HemoFresh (a registered trademark) for hemofiltration, is characterized by both superior membrane performance and good blood compatibility. It is now being confirmed clinically that this module is superior to other hemofilters so far available with regard to UFR, permeation of undesirable solutes, clotting, hemolysis and the amount of blood left behind in the module. 

A majority of commonly used inorganic membranes are composites consisting of a thin separation barrier on porous support (e.g., Membralox zirconia and alumina membrane products). Inorganic MF and UF membranes are characterized by their narrow pore size distributions. This allows the description of their separative performance in terms of their true pore diameter rather than MW CO value which can vary with operating conditions. This can be advantageous in comparing the relative separation performance of two different membranes independent of the operating conditions. MF membranes, in addition, can be characterized by their bubble point pressures. Due to their superior mechanical resistance bubble point measurements can be extended to smaller diameter MF membranes (0.1 or 0.2 pm) which may have bubble point pressure in excess of 10 bar with water. 

Membranes are characterized by structure and function that is, vfaat they are and how they perform. The most significant primary structural properties of a membrane are its chemical nature including the presence of charged species at the molecular level, its microcrystalline structure at the microcrystalline level, and on the collodial level its pore statistics such as pore size distribution and density, and degree of asymmetry (11) (12). 

MTBE synthesis from /-butanol and methanol in a membrane reactor has been reported by Salomon et al. [2.453]. Hydrophilic zeolite membranes (mordenite or NaA) were employed to selectively remove water from the reaction atmosphere during the gas-phase synthesis of MTBE. This reaction was carried out over a bed of Amberlyst 15 catalyst packed in the inside of a zeolite tubular membrane. Prior to reaction, the zeolite membranes were characterized by measuring their performance in the separation of the equilibrium mixture containing water, methanol, /-butanol, MTBE, and isobutene. The results obtained with zeolite membrane reactors were compared with those of a fixed-bed reactor (FBR) under the same operating conditions. MTBE yields obtained with the PBMR at 334 K reached 67.6 %, under conditions, where the equilibrium value without product removal (FBR) would be 60.9%. 

Membrane separation of gaseous small molecules through dense (non-porous) polymeric membranes occurs because of differences in solubility and diffusivity, while membrane performance is characterized by permeability and selectivity. The permeability of component i. Pi, is defined as the product of the diffusion and solubility coefficients (A and Si, respectively) (Eq. (9-13)). 

Once the membranes were characterized to guarantee a structural integrity and well performance on fluid and pressure conditions [9]. Saucedo-Rivalcoba et al. directed their research to the use of hybrid keratin-polyurethane membranes to remove... 

He X, Hagg MB. StructuraL kinetic and performance characterization of hollow fiber carbon membranes. J Membr Sci 2012 390-391 23-31. 

In order to obtain oscillated backflushing and enhanced membrane performance, the design of the pressure waveform is crucial. The pressure waveform can be characterized by the minimum and maximum pressure, the duration of the negative pressure and the positive pressure, and the pulsation frequency. Figure 10.28 shows four typical pressure waveforms studied by Li [50]. Wave type 1 has a long steady-pressure phase and a short negative pulsation. Wave type 2 has an approximate sinusoidal form with smooth variation of the pressure. Wave type 3 is approximately square shaped and wave type 4 had a shortened sinusoidal disturbance. Figure 10.29 shows the cake resistance reduction results as a function of the minimum TMP obtained by Li and Bertram [49] for pulsatile flow filtration with the four... 

It is essential that the feedwater to the membrane system be well characterized. This allows operational changes in membrane performance to be better nnderstood bnt also allows potential foulants to be recognized. Data on the chemical, physical, radiological, and biological properties of the feed stream are required. The basic information required will include, but is not limited to, the range of the following ... 

Electrochemical performance of ion-exchange membranes is characterized by transport numbers, selectivity and specific selectivity. The ion transport number (h) is the fraction of the electric current carried by specific ion type ... 

Characterization of the membrane surface It should be emphasized that the properties of the membrane surface strongly affect membrane performance. Contact angle is often used as a measure of surface hydrophilicity or hydrophobicity. X-ray photoelectron spectroscopy (XPS) provides the data on atomic compositions at the membrane surface. Recently, attentions have been focused on the nodular structure as well as the roughness at the membrane surface that can be measured by atomic force microscopy (AFM). 

Therefore, an attempt will be made in this chapter to find some relationships between the surface characterization parameters obtained by AFM and the membrane performance data. Most obviously, the pore size and the pore size distribution will have a direct influence on the selectivity and the permeation rate of NF, UF, and MF membranes, where pores are most visible. 

Finally, in Chap. 8, attempts are made to correlate the AFM parameters, such as nodule and pore sizes, to the membrane performance data. Membranes used for a variety of membrane processes, including reverse osmosis, nanofiltration, ultrafiltration, microfiltration, gas and vapor separation, pervaporation, and other membrane separation processes, are covered in this chapter. AFM parameters are also correlated to membrane biofouhng. This chapter also includes appUcations of AFM to characterize biomedical materials, including artificial organs cind drug release. 

Mansourpanah, Y, Madaeni, S.S., Rahimpour, A., Farhadian, A. and Taheri, A.H. 2009. Formation of appropriate sites on nanofiltration membrane surface for binding TiOj photo-catalyst Performance, characterization, and fouling-resistant capability,... 

In this chapter, the experimental details of the SMM synthesis and characterization as well as the membrane preparation, characterization, and testing are thoroughly described in the following examples. Moreover, the effects of the SMM type on the membrane morphology as well as its performance were clearly identified. Furthermore, the performance of the newly developed membranes was compared to a commercial PTFE membrane in terms of the permeate water flux and the separation factor. 

This chapter has provided a range of mathematical models that can be used to characterize the effects of minor components on membrane performance. However, the quantity of good experimental data that can be used to fit these models remains quite limited. Good characterization of membrane performance in both pre-combustion and post-combustion flue gases will require accurate experimentally based determination of parameters such as Flory-Huggins interaction parameters, Langmuir constants and plasticization potentials. 

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