Membranes and Membrane Processes

MRS Bulletin ◽  
1999 ◽  
Vol 24 (3) ◽  
pp. 19-22 ◽  
Author(s):  
Vasilis N. Burganos
Keyword(s):  
Membrane Separation ◽  
Transport Coefficients ◽  
Electrical Potential ◽  
Artificial Organs ◽  
Energy Storage And Conversion ◽  
Electrical Potential Difference ◽  
Catalytic Reactors ◽  
Membrane Processes ◽  
Separation Science ◽  
Structural And Functional Properties

Membrane separation science has enjoyed tremendous progress since the first synthesis of membranes almost 40 years ago, which was driven by strong technological needs and commercial expectations. As a result, the range of successful applications of membranes and membrane processes is continuously broadening. An additional change lies in the nature of membranes, which is now extended to include liquid and gaseous materials, biological or synthetic. Membranes are understood to be thin barriers between two phases through which transport can take place under the action of a driving force, typically a pressure difference and generally a chemical or electrical potential difference.An attempt at functional classification of membranes would have to include diverse categories such as gas separation, pervaporation, reverse osmosis, micro- and ultrafiltration, and biomedical separations. The dominant application of membranes is certainly the separation of mixed phases or fluids, homogeneous or heterogeneous. Separation of a mixture can be achieved if the difference in the transport coefficients of the components of interest is sufficiently large. Membranes can also be used in applications other than separation targeting: They can be employed in catalytic reactors, energy storage and conversion systems, as key components of artificial organs, as supports for electrodes, or even to control the rate of release of both useful and dangerous species.In order to meet the requirements posed by the aforementioned applications, membranes must combine several structural and functional properties.

Separation of Biologically Active Compounds by Membrane Operations

2017 ◽  
Vol 23 (2) ◽  
pp. 218-230 ◽  
Author(s):  
Xiaoying Zhu ◽  
Renbi Bai
Keyword(s):  
Energy Consumption ◽  
Bioactive Compounds ◽  
Membrane Fouling ◽  
Membrane Separation ◽  
Separation Efficiency ◽  
High Energy ◽  
Separation Processes ◽  
Membrane Processes ◽  
Separation Technology ◽  
Pressure Driven

Background: Bioactive compounds from various natural sources have been attracting more and more attention, owing to their broad diversity of functionalities and availabilities. However, many of the bioactive compounds often exist at an extremely low concentration in a mixture so that massive harvesting is needed to obtain sufficient amounts for their practical usage. Thus, effective fractionation or separation technologies are essential for the screening and production of the bioactive compound products. The applicatons of conventional processes such as extraction, distillation and lyophilisation, etc. may be tedious, have high energy consumption or cause denature or degradation of the bioactive compounds. Membrane separation processes operate at ambient temperature, without the need for heating and therefore with less energy consumption. The “cold” separation technology also prevents the possible degradation of the bioactive compounds. The separation process is mainly physical and both fractions (permeate and retentate) of the membrane processes may be recovered. Thus, using membrane separation technology is a promising approach to concentrate and separate bioactive compounds. Methods: A comprehensive survey of membrane operations used for the separation of bioactive compounds is conducted. The available and established membrane separation processes are introduced and reviewed. Results: The most frequently used membrane processes are the pressure driven ones, including microfiltration (MF), ultrafiltration (UF) and nanofiltration (NF). They are applied either individually as a single sieve or in combination as an integrated membrane array to meet the different requirements in the separation of bioactive compounds. Other new membrane processes with multiple functions have also been developed and employed for the separation or fractionation of bioactive compounds. The hybrid electrodialysis (ED)-UF membrane process, for example has been used to provide a solution for the separation of biomolecules with similar molecular weights but different surface electrical properties. In contrast, the affinity membrane technology is shown to have the advantages of increasing the separation efficiency at low operational pressures through selectively adsorbing bioactive compounds during the filtration process. Conclusion: Individual membranes or membrane arrays are effectively used to separate bioactive compounds or achieve multiple fractionation of them with different molecule weights or sizes. Pressure driven membrane processes are highly efficient and widely used. Membrane fouling, especially irreversible organic and biological fouling, is the inevitable problem. Multifunctional membranes and affinity membranes provide the possibility of effectively separating bioactive compounds that are similar in sizes but different in other physical and chemical properties. Surface modification methods are of great potential to increase membrane separation efficiency as well as reduce the problem of membrane fouling. Developing membranes and optimizing the operational parameters specifically for the applications of separation of various bioactive compounds should be taken as an important part of ongoing or future membrane research in this field.

OSMOTIC INHIBITION OF THE NATRIFERIC RESPONSE OF THE TOAD URINARY BLADDER TO VASOPRESSIN

1975 ◽  
Vol 67 (1) ◽  
pp. 119-125
Author(s):  
P. J. BENTLEY
Keyword(s):  
Urinary Bladder ◽  
Water Movement ◽  
Short Circuit ◽  
Electrical Potential ◽  
Short Circuit Current ◽  
Toad Bladder ◽  
Toad Urinary Bladder ◽  
Electrical Potential Difference ◽  
Osmotic Gradient

SUMMARY The electrical potential difference and short-circuit current (scc, reflecting active transmural sodium transport) across the toad urinary bladder in vitro was unaffected by the presence of hypo-osmotic solutions bathing the mucosal (urinary) surface, providing that the transmural flow of water was small. Vasopressin increased the scc across the toad bladder (the natriferic response), but this stimulation was considerably reduced in the presence of a hypo-osmotic solution on the mucosal side, conditions under which water transfer across the membrane was also increased. This inhibition of the natriferic response did not depend on the direction of the water movement, for if the osmotic gradient was the opposite way to that which normally occurs, the response to vasopressin was still reduced. The natriferic response to cyclic AMP was also inhibited in the presence of an osmotic gradient. Aldosterone increased the scc and Na+ transport across the toad bladder but this response was not changed when an osmotic gradient was present. The physiological implications of these observations and the possible mechanisms involved are discussed.

Reversal of glibenclamide and voltage block of an epithelial KATP channel

1996 ◽  
Vol 271 (4) ◽  
pp. C1122-C1130 ◽  
Author(s):  
O. Mayorga-Wark ◽  
W. P. Dubinsky ◽  
S. G. Schultz
Keyword(s):  
Hydrophobic Interactions ◽  
Basolateral Membrane ◽  
Electrical Potential ◽  
Membrane Vesicles ◽  
Voltage Gating ◽  
Electrical Potential Difference ◽  
Outer Solution ◽  
Channel Inhibition ◽  
K Concentration ◽  
Voltage Gate

K+ channels present in basolateral membrane vesicles isolated from Necturus maculosa small intestinal cells and reconstituted into planar phospholipid bilayers are inhibited by MgATP and sulfonylurea derivatives, such as tolbutamide and glibenclamide, when these agents are added to the solution bathing the inner mouth of the channel. In addition, these channels possess an intrinsic "voltage gate" and are blocked when the electrical potential difference across the channel is oriented so that the inner solution is electrically positive with respect to the outer solution. We now show that increasing the concentration of permeant ions such as K+ or Rb+ in the outer solution reverses channel inhibition resulting from the addition of 50 microM glibenclamide to the inner solution and also inhibits intrinsic voltage gating; these effects are not elicited by increasing the concentrations of the relatively impermeant ions, Na+ or choline, in the outer solution. Furthermore, increasing the K+ concentration in the outer solution in the absence of glibenclamide inhibits voltage gating, and, under these conditions, the subsequent addition of glibenclamide to the inner solution is ineffective. These results are consistent with a model in which the voltage gate is an open-channel blocker whose action is directly reversed by elevating the external concentration of relatively permeant cations and where the action of glibenclamide is to stabilize the inactivated state of the channel, possibly through hydrophobic interactions.

Active electrolyte transport in mammalian buccal mucosa

1988 ◽  
Vol 255 (3) ◽  
pp. G286-G291 ◽  
Author(s):  
R. C. Orlando ◽  
N. A. Tobey ◽  
V. J. Schreiner ◽  
R. D. Readling
Keyword(s):  
Buccal Mucosa ◽  
Short Circuit ◽  
Basolateral Membrane ◽  
Electrical Potential ◽  
Short Circuit Current ◽  
Electrolyte Transport ◽  
Electrical Potential Difference ◽  
Ussing Chambers ◽  
Net Fluxes

The transmural electrical potential difference (PD) was measured in vivo across the buccal mucosa of humans and experimental animals. Mean PD was -31 +/- 2 mV in humans, -34 +/- 2 mV in dogs, -39 +/- 2 mV in rabbits, and -18 +/- 1 mV in hamsters. The mechanisms responsible for this PD were explored in Ussing chambers using dog buccal mucosa. After equilibration, mean PD was -16 +/- 2 mV, short-circuit current (Isc) was 15 +/- 1 microA/cm2, and resistance was 1,090 +/- 100 omega.cm2, the latter indicating an electrically "tight" tissue. Fluxes of [14C]mannitol, a marker of paracellular permeability, varied directly with tissue conductance. The net fluxes of 22Na and 36Cl were +0.21 +/- 0.05 and -0.04 +/- 0.02 mueq/h.cm2, respectively, but only the Na+ flux differed significantly from zero. Isc was reduced by luminal amiloride, serosal ouabain, or by reducing luminal Na+ below 20 mM. This indicated that the Isc was determined primarily by active Na+ absorption and that Na+ traverses the apical membrane at least partly through amiloride-sensitive channels and exits across the basolateral membrane through Na+-K+-ATPase activity. We conclude that buccal mucosa is capable of active electrolyte transport and that this capacity contributes to generation of the buccal PD in vivo.

Effects of flow rate and potassium intake on distal tubular potassium transfer

1975 ◽  
Vol 228 (4) ◽  
pp. 1249-1261 ◽  
Author(s):  
RN Khuri ◽  
WN Strieder ◽  
G Giebisch
Keyword(s):  
Flow Rate ◽  
Electrical Potential ◽  
Isotonic Saline ◽  
Distal Tubule ◽  
Sodium Reabsorption ◽  
Electrical Potential Difference ◽  
High Potassium ◽  
Flow Rates ◽  
Potassium Intake ◽  
Potassium Secretion

Potassium transport was studied across proximal and distal tubular epithelium in rats on a normal, low- and high-potassium intake during progressive loading with isotonic saline (150 mM) or a moderately hypersomotic urea (200 mM) sodium chloride (100 mM) solution. Free-flow micropuncture and recollection techniques were used during the development of diruesis and tubular fluid (TF) analyzed for inulin-14C, potassium (K) and sodium (Na). Tubular puncture sites were localized by neoprene filling and microdissection. During the large increase in tubular flow rates (10 times): 1) fractional potassium reabsorption fell along the proximal tubule, 2) TFk along the distal tubule remained constant and independent of flow rate in control and high-k rats; thus, net potassium secretion increased in proportion to and was limited by flow rate. 3) In low-K rats TF k fell; with increasing flow rates distal K secretion was not effectively stimulated. 4) Distal tubular sodium reabsorption increased in all animals with flow rate, but tubular Na-K exchange ratios varied greatly. It is suggested that whenever sodium delivery stimulates distal tubular potassium secretion it does so by 1) increasing volume distal tubular potasssium secretion and by 2) augmenting the transepithelial electrical potential difference (lumen negative).

scholarly journals Микроволновая вольт-импедансная спектроскопия полупроводников

2020 ◽  
Vol 90 (11) ◽  
pp. 1944
Author(s):  
А.Н. Резник ◽  
Н.В. Востоков ◽  
Н.К. Вдовичева ◽  
В.И. Шашкин
Keyword(s):  
Electrical Potential ◽  
Complex Impedance ◽  
Impedance Spectrum ◽  
Antenna System ◽  
Electrical Potential Difference ◽  
Complex Impedance Spectrum ◽  
Homogeneous Sample ◽  
Semiconductor Interface ◽  
Constant Bias ◽  
Central Disk

We have tested experimentally the proposed method of microwave volt-impedance spectroscopy of semiconductors. The method allows to determine the local values of the semiconductor electrophysical parameters. The studies were performed on a homogeneous single-crystal GaAs wafer with a concentric antenna system formed on its surface. The resolution is determined by the diameter of the antenna central disk, which was amounted a = 12, 27, 57 μm. A constant bias voltage of 0 ≤ U ≤ 5 V was applied between the contact pads of the antennas. The complex impedance spectrum Z (f, U) of each antenna was measured using a Cascade Microtech probe station in the frequency range f = 0.1 - 10 GHz. The electrophysical characteristics of the semiconductor were determined from Z(f, U) spectra by the inverse problem solving. We have established the n-type for our semiconductor and determined the electrical potential difference on the metal-semiconductor interface. We have found as well the electron concentration, mobility and conductivity. Measurements of the same parameters by Hall four-probe method (giving the surface averaging) showed good mutual agreement of the results for the homogeneous sample under study.

Membrane processes

2017 ◽  
Vol 2 (12) ◽  
Author(s):  
Katarzyna Staszak
Keyword(s):  
Twentieth Century ◽  
Water Treatment ◽  
Industrial Application ◽  
Membrane Separation ◽  
Separation Process ◽  
Pulp And Paper ◽  
Transmembrane Pressure ◽  
Permeate Flux ◽  
Calculation Methods ◽  
Membrane Processes

Abstract The membrane processes have played important role in the industrial separation process. These technologies can be found in all industrial areas such as food, beverages, metallurgy, pulp and paper, textile, pharmaceutical, automotive, biotechnology and chemical industry, as well as in water treatment for domestic and industrial application. Although these processes are known since twentieth century, there are still many studies that focus on the testing of new membranes’ materials and determining of conditions for optimal selectivity, i. e. the optimum transmembrane pressure (TMP) or permeate flux to minimize fouling. Moreover the researchers proposed some calculation methods to predict the membrane processes properties. In this article, the laboratory scale experiments of membrane separation techniques, as well their validation by calculation methods are presented. Because membrane is the “heart” of the process, experimental and computational methods for its characterization are also described.

The Ionic Relations of Artemia Salina (L.)

1969 ◽  
Vol 51 (3) ◽  
pp. 739-757
Author(s):  
P. G. SMITH
Keyword(s):  
Sea Water ◽  
Electrical Potential ◽  
Artemia Salina ◽  
Electrical Potential Difference ◽  
External Concentration ◽  
Sodium Efflux ◽  
Exchange Diffusion ◽  
Similar Shape ◽  
Diffusional Permeability ◽  
Free Media

I. The effects of different external media on the sodium and chloride efflux in Artemia salina, the brine shrimp, have been observed, using animals acclimatized to sea water. In sea water, both sodium and chloride fluxes across the epithelium are approximately 7,000 pmole cm.-2 sec.-1. 2. Sodium efflux drops markedly in sodium-free media, and chloride efflux falls in chloride-free media; the two effects are independent, and are not due to changes in external osmolarity. 3. The decreases in sodium efflux can be explained by changes in electrical potential difference and diffusional permeability; exchange diffusion of sodium does not occur. 4. Approximately 70% of the chloride efflux is due to exchange diffusion, and most of the remainder is due to active transport. 5. It is shown that graphs of ion efflux against external concentration which can be fitted by a Michaelis-Menten equation do not constitute evidence for the presence of exchange diffusion; graphs of similar shape can be obtained if the flux is simply diffusional. 6. The drinking rate, determined from the rate of uptake of 131I-polyvinylpyr-rolidone, is 36 pl. sec.-1, or 2.0% body weight hr.-1. 7. The diffusional influx of water is 240 pl. sec.-1.

Sign in / Sign up

Export Citation Format

Share Document