Temperature drop of feed liquid during pervaporation

Heat transfer during pervaporation through a membrane module of silicone-rubber microtubes was studied for ammonia/water and ethanol/water feeds. The temperature drops of the feed mixture were measured as a function of flow rate, concentration and permeate side pressure. A model calculation with a vapor-phase driving force was compared with the data. The vapor permeability of the permeate components needed in the model were independently measured using an original measurement method with a differential transformer. The present simple model for heat and mass transfer during pervaporation proved to be applicable to the theoretical calculation for a membrane module of pervaporation to be used as a heat-transfer unit.     

Nature of flow on sweeping gas membrane distillation

The process of sweeping gas membrane distillation (SGMD), with the liquid feed and the sweeping gas counterflowing in a plate and frame membrane module, has been studied. A theoretical model, which was presented in a previous paper and permitted to obtain the temperature profiles inside the fluid phases, has been developed in order to analyse the physical nature of the transmembrane water flux. Two porous hydrophobic membranes have been studied in different experimental conditions. The influence of some relevant parameters, such as the inlet and outlet temperatures or the circulation velocities of the fluids, has been studied. The experimental results have been analysed according to the model and the conclusion is that the water transport takes place, apparently, via a combined Knudsen and molecular diffusive flow mechanism. From the temperature profiles, a local temperature polarisation coefficient may be defined. From this local value, an overall one for the whole system is then defined. The new theoretical predictions have been applied to the obtained results and the accordance may be considered good.     

Fast response filter module with plug flow of filtrate for on-line sampling from submerged cultures of filamentous fungi

Automatic and accurate sampling is both convenient and sometimes necessary to obtain detailed information about cell cultures. We developed an autoclavable sampling system in which culture broth was pumped through an ultrafiltration cross-flow module with a novel filtrate collecting principle and a novel regulation of filter back pressure. Filtrate was collected from equal membrane filter areas through holes connected to channels with an even length to the collecting point, resulting in a near plug flow of filtrate and a reduction in the response time to 1 min (98% of full signal of the tracer molecule glucose). Constant pressure difference (0.3 bar) across the membrane filter (30 kDa cutoff value) and prevention of leakage was obtained by squeezing the tubing with culture broth between two flexible spring steel plates fixed at one corner (filtrate flow 1 ml min⁻¹). The large contact area allowed the tubing to open the passage more when pressure increased. Using this design of sampling system, the metabolite profiles of Aspergillus niger wild type and a phosphofructokinase overexpressing strain (three times wild type) were concluded to be indistinguishable by detailed monitoring of fast transients of substrates and products in batch culture and glucose pulse experiments. The combination of the fast response filter module and prevention of high pressure peaks with the flexible resistance to flow enables long-term (>5 days) and automatic monitoring of cultures of filamentous fungi or other microorganisms with fast changes in extracellular concentrations.     

Evaluation of ODS-AQ stationary phase for use in capillary electrochromatography

The aim of this study was to evaluate the applicability of ODS-AQ packing material as a stationary phase in capillary electrochromatography (CEC). The electroosmotic flow created on an ODS-AQ stationary phase was measured at different mobile phase compositions and at different column temperatures. It was observed that the electroosmotic flow generated in the column increased by 50% when the temperature of the system was raised from 20 degrees C to 60 degrees C, while all other conditions were kept constant. The electroosmotic flow produced by the ODS-AQ stationary phase was found to be comparable to the flow generated in a column packed with Nucleosil bare-silica material. In addition, a set of polar compounds (D-lysergic acid diethylamide derivatives) was utilized to determine the influence of temperature and mobile phase composition on their chromatographic behavior on an ODS-AQ stationary phase in a CEC mode. A linear relationship between the solute retention factor and column temperatures was seen over the temperature range studied (20 degrees C to 60 degrees C). A quadratic function was used to describe the changes in the solute retention factors with variation of acetonitrile concentration in the mobile phase.     

Estimation of the diffusion coefficient of water evolved during the non-isothermal dehydration of Australian sedimentary opal

The dehydration of an opal specimen was investigated by thermogravimetric analysis (TG) in powder and bulk forms. The change in geometry resulted in a significant difference in the temperature range in which dehydration occurred with peak temperatures in the differential TG (DTG) curve for the hand ground opal at 203°C and for the bulk opal at 340°C. This difference was attributed to time taken for diffusion of free water in the bulk opal to the specimen surface prior to evolution as a registered mass loss. A model was proposed to account for the diffusion of water and was used to estimate the diffusion coefficient.     

Temperature dependence of local density augmentation for acetophenone N,N,N',N'-tetramethylbenzidine exciplex in supercritical water

Local density augmentation around exciplex between acetophenone and N,N,N',N'-tetramethylbenzidine in supercritical water was measured by observing the peak shift of transient absorption spectrum at temperatures from 380 to 410 degrees C and at pressures from 6 to 37 MPa. Large local density augmentation was observed at lower solvent densities. Local density augmentation was evaluated by the excess density, which was defined as the difference between local density and bulk density, and the density enhancement factor, which was defined by the ratio of the local density to the bulk density. The number of solvating molecules was estimated with a Langmuir adsorption model. The excess density was found to exhibit a maximum at approximately 0.15 g cm(-3), which decreased with increasing temperature. The density enhancement factor was found to decrease with increasing temperature; however, its value was much greater than unity at 410 degrees C, which provides evidence that exciplex-water interactions still exist at these conditions. The temperature dependence of local density augmentation around the exciplex in supercritical water was comparable with that in supercritical carbon dioxide, which suggests that the ratios of the solute-solvent and solvent-solvent interactions are comparable between these two systems.     

Diffusioosmotic flows in slit nanochannels

Diffusioosmotic flows of electrolyte solutions in slit nanochannels with homogeneous surface charges induced by electrolyte concentration gradients in the absence of externally applied pressure gradients and potential differences are investigated theoretically. A continuum mathematical model consisting of the strongly coupled Nernst-Planck equations for the ionic species' concentrations, the Poisson equation for the electric potential in the electrolyte solution, and the Navier-Stokes equations for the flow field is numerically solved simultaneously. The induced diffusioosmotic flow through the nanochannel is computed as functions of the externally imposed concentration gradient, the concentration of the electrolyte solution, and the surface charge density along the walls of the nanochannel. With the externally applied electrolyte concentration gradient, a strongly spatially dependent electric field and pressure gradient are induced within the nanochannel that, in turn, generate a spatially dependent diffusioosmotic flow. The diffusioosmotic flow is opposite to the applied concentration gradient for a relatively low bulk electrolyte concentration. However, the electrolyte solution flows from one end of the nanochannel with a higher electrolyte concentration to the other end with a lower electrolyte concentration when the bulk electrolyte concentration is relatively high. There is an optimal concentration gradient under which the flow rate attains the maximum. The induced flow is enhanced with the increase in the fixed surface charge along the wall of the nanochannel for a relatively low bulk electrolyte concentration.     

Transport of gaseous mixtures through membranes

Thermoosmosis of ternary mixtures of oxygen, nitrogen, and carbon dioxide across a porous unglazed membrane has been studied, The thermoosmotic pressure difference, ΔP, created by a temperature difference, ΔT, has been measured at various mean temperatures and pressures. Experimental data have been interpreted in the light of non-equilibrium thermodynamics of irreversible processes and the dusty gas model of Mason. Heats of transport for the mixtures, Q^★, have been estimated from the measured values of pressure difference and temperature difference. It is found that the heat of transport of mixtures is independent of the mean temperature and temperature difference as was found in earlier studies on multicomponent mixtures.     

Study on a novel antifouling polyamide–urea reverse osmosis composite membrane (ICIC–MPD): III. Analysis of membrane electrical properties

In this study, the electrical properties of the new polyamide–urea (ICIC–MPD) reverse osmosis composite membrane were analyzed via two self-made test cells. The electrical potential difference across membrane was measured via a perpendicular flow through mode potential difference measurement cell, and the electrical conductivity of membrane was tested by a tangential flow across mode conductivity measurement cell. Both streaming potential coefficient and gap between the upward and downward curves were determined by the plot of electrical potential difference versus up-loading and down-loading external pressure difference at both sides of membrane. It was found that pH of electrolyte solution has strong impact on streaming potential coefficient and electrical conductivity due to the dissociation of COOH group and protonation of NH₂ group of the active layer of ICIC–MPD membrane. It was also observed that both concentration of monomer 5-isocyanato-isophthaloyl chloride (ICIC) in the organic phase and contact time of organic phase with aqueous phase play an important role in salt rejection rate, gap between curves and electrical conductivity of the prepared ICIC–MPD membrane, and experimental results indicate that salt rejection rate of ICIC–MPD membrane is closely correlated to gap between curves at either polymerization condition. In addition, the effects of fouling behaviors on electrical potential difference and electrical conductivity of membrane were also discussed.     

A novel high-temperature (360 degrees C)/high-pressure (30 MPa) flow system for online sample digestion applied to ICP spectrometry

A flow injection sample digestion system has been developed comprising an indirectly electrically heated Pt/Ir capillary. Such a capillary allows reaction temperatures of up to 360 degrees C and pressures of up to 30 MPa (300 bar) and withstands concentrated acids. This temperature is 130 degrees C to 160 degrees C higher compared to the operating temperatures of microwave heated flow systems. A combination of an ultrasonic nebulizer and membrane desolvator serves as an interface between the flow digestion system and an ICP/AES spectrometer. The membrane desolvator removes interfering gaseous digestion products so effectively before the sample stream enters the plasma that the measured residual carbon concentration falls in the region of the detection limit of ICP/OES measurements. Sewage sludge samples were digested using nitric acid and the elemental traces online determined. The detection limits related to the original dry substances amount to the lower microg/g range.     

Temperature and concentration polarization in membrane distillation of aqueous salt solutions

In this paper we have studied water transport in membrane distillation using a flat PTFE membrane. Experiments have been carried out with water and aqueous solutions of NaCl as feed. The effects of temperature and concentration polarization on the reduction of vapour pressure differences across the membrane with regard to the vapour pressure differences corresponding to the bulk phases which are separated by the membrane, are evaluated. A coefficient which measures this reduction has been introduced. This coefficient and the temperature polarization coefficient coincide when water is used as feed, but they are more and more different when the salt concentration of feed increases.The measured flux results and the calculated polarization results are discussed for different temperatures, recirculation rates and solution concentrations.     

Denaturing gradient-based two-dimensional gene mutation scanning in a polymer microfluidic network

An integrated two-dimensional (2-D) DNA separation platform, combining standard gel electrophoresis with temperature gradient gel electrophoresis (TGGE) on a polymer microfluidic chip, is reported. Rather than sequentially sampling DNA fragments eluted from standard gel electrophoresis, size-resolved fragments are simultaneously electrokinetically transferred into an array of orthogonal microchannels and screened for the presence of sequence heterogeneity by TGGE in a parallel and high throughput format. A bulk heater assembly is designed and employed to externally generate a temporal temperature gradient along an array of TGGE channels. Extensive finite element modeling is performed to determine the optimal geometries of the microfluidic network for minimizing analyte band dispersion caused by interconnected channels in the network. A pH-mediated on-chip analyte stacking strategy is employed prior to the parallel TGGE separations to further reduce additional band broadening acquired during the electrokinetic transfer of DNA fragments between the first and second separation dimensions. A comprehensive 2-D DNA separation is completed in less than 5 min for positive detection of single-nucleotide polymorphisms in multiplex PCR products that vary in size and sequence.     

Simulation of pressure swing adsorption modules having laminated structure

A mathematical model was formulated for the bulk separation of binary gas mixtures in micro-structured pressure swing adsorption (PSA) modules consisting of parallel channels lined with adsorbent. Axial and radial dispersion in the gas phase and mass transfer resistance in the adsorbent phase were taken into consideration. The partial differential equations governing the concentration profiles in the gas and adsorbent phases were solved by orthogonal collocation. The model enabled the prediction of the concentration profiles in both the gas and adsorbent phases (as a function of location and time), the product purity and the separation efficiency. The effects of model parameters and operating conditions on the module performance were investigated. Simulation of oxygen enrichment from air by molecular sieve 13X indicated that long modules with thin layers of adsorbent, narrow gas flow channel heights and large numbers of flow channels give the best separation.     

Nonequilibrium molecular dynamics simulation of water transport through carbon nanotube membranes at low pressure

Nonequilibrium molecular dynamics (NEMD) simulations are used to investigate pressure-driven water flow passing through carbon nanotube (CNT) membranes at low pressures (5.0 MPa) typical of real nanofiltration (NF) systems. The CNT membrane is modeled as a simplified NF membrane with smooth surfaces, and uniform straight pores of typical NF pore sizes. A NEMD simulation system is constructed to study the effects of the membrane structure (pores size and membrane thickness) on the pure water transport properties. All simulations are run under operating conditions (temperature and pressure difference) similar to a real NF processes. Simulation results are analyzed to obtain water flux, density, and velocity distributions along both the flow and radial directions. Results show that water flow through a CNT membrane under a pressure difference has the unique transport properties of very fast flow and a non-parabolic radial distribution of velocities which cannot be represented by the Hagen-Poiseuille or Navier-Stokes equations. Density distributions along radial and flow directions show that water molecules in the CNT form layers with an oscillatory density profile, and have a lower average density than in the bulk flow. The NEMD simulations provide direct access to dynamic aspects of water flow through a CNT membrane and give a view of the pressure-driven transport phenomena on a molecular scale.     

Numerical model of non-isothermal pervaporation in a rectangular channel

A numerical model of non-isothermal pervaporation was developed to investigate the development of the velocity, concentration and temperature fields in rectangular membrane module geometry. The model consists of the coupled Navier–Stokes equations to describe the flow field, the energy equation for the temperature field, and the species convection-diffusion equations for the concentration fields of the solution species. The coupled nonlinear transport equations were solved simultaneously for the velocity, temperature and concentration fields via a finite element approach. Simulation test cases for trichloroethylene/water, ethanol/water and iso-propanol/water pervaporation, under laminar flow conditions, revealed temperature drop axially along the module and orthogonal to the membrane surface. The nonlinear character of the concentration and temperature boundary-layers are most significant near the membrane surface. Estimation of the mass transfer coefficient assuming isothermal assumption conditions can significantly deviate from the non-isothermal predictions. For laminar conditions, predictions of the feed-side mass transfer coefficient converged to predictions from the classical Lévêque solution as the feed temperature approached the permeate temperature.     

Determinations cinetiques par microcalorimetrie differentielle en programmation de temperature. III. Probleme de la non correspondance entre temperatures mesurees et constantes de vitesse

Rate constants of the free radical decomposition of AIBN have been determinated in different solvents using a differential scanning microcalorimeter at several temperature programmes. They seem to depend on the heating rate; but this is explained by the existence of a difference in temperature between the studied solution and the position at which θ is measured. At low heating rate, there is agreement between real and measured temperatures and, thus, fair correspondence between rate constants and temperatures observed.     

Experimental test of the Sydney Young equation for the presentation of distillation curves

The distillation (or boiling) curve of a complex fluid is a critically important indicator of the bulk behavior or response of the fluid. For this reason, the distillation curve, usually presented graphically as boiling temperature against volume fraction distilled, is often cited as a primary design and testing criterion for liquid fuels, lubricants and other important industrial fluids. Clearly, the boiling temperatures that is measured near ambient conditions during the course of a distillation curve determination depend upon the local atmospheric pressure. For this reason, the user community is accustomed to data presented with an adjustment of the temperatures to those that would be observed at a standard atmospheric pressure of 101.325 kPa, or standard atmospheric pressure of 1 atm. Typically, this is done with a simplified Sydney Young equation. This correction makes little difference to measurements done consistently in a particular laboratory, or when the atmospheric pressure varies little. The correction can be quite large when measurements are done in laboratories at different elevations, however. In this paper, we describe an evaluation of this correction. Specifically, we performed measurements of the distillation curve of a binary mixture of (n-decane + n-tetradecane) at three elevations (and, therefore three different values of atmospheric pressures, (70.06, 82.73, and 101.00) kPa). Comparisons are made between the raw and adjusted values, and recommendations are presented as to when the equation might be inadequate.     

A novel high-temperature (360 °C)/high-pressure (30 MPa) flow system for online sample digestion applied to ICP spectrometry

A flow injection sample digestion system has been developed comprising an indirectly electrically heated Pt/Ir capillary. Such a capillary allows reaction temperatures of up to 360?°C and pressures of up to 30 MPa (300 bar) and withstands concentrated acids. This temperature is 130?°C to 160?°C higher compared to the operating temperatures of microwave heated flow systems. A combination of an ultrasonic nebulizer and membrane desolvator serves as an interface between the flow digestion system and an ICP/AES spectrometer. The membrane desolvator removes interfering gaseous digestion products so effectively before the sample stream enters the plasma that the measured residual carbon concentration falls in the region of the detection limit of ICP/OES measurements. Sewage sludge samples were digested using nitric acid and the elemental traces online determined. The detection limits related to the original dry substances amount to the lower μg/g range.     

Dead-end ultrafiltration in hollow fiber modules: Module design and process simulation

Ultrafiltration in a hollow-fiber module operating with outside-in and dead-end flow at a constant flow rate was simulated using a model that takes into account the longitudinal pressure drops inside the fibers and within the fiber bundle. The model considers both the filtration phase during which the membrane is fouled by the formation of a filter cake and the backwash phase in which it is cleaned, so as to predict the net rate of production of the module during an operating cycle.The results show that there is a combination of packing density and fiber diameter that gives a maximum net flow rate. Furthermore, this model allows the influence of operating conditions and feed properties on the module performance to be estimated. This can be used to determine how operating parameters must be modified when there is a change in the feed properties.     

Effect of Size and Temperature on Water Dynamics inside Carbon Nano-Tubes Studied by Molecular Dynamics Simulation

Water transport inside carbon nano-tubes (CNTs) has attracted considerable attention due to its nano-fluidic properties, its importance in nonporous systems, and the wide range of applications in membrane desalination and biological medicine. Recent studies show an enhancement of water diffusion inside nano-channels depending on the size of the nano-confinement. However, the underlying mechanism of this enhancement is not well understood yet. In this study, we performed Molecular Dynamics (MD) simulations to study water flow inside CNT systems. The length of CNTs considered in this study is 20 nm, but their diameters vary from 1 to 10 nm. The simulations are conducted at temperatures ranging from 260 K to 320 K. We observe that water molecules are arranged into coaxial water tubular sheets. The number of these tubular sheets depends on the CNT size. Further analysis reveals that the diffusion of water molecules along the CNT axis deviates from the Arrhenius temperature dependence. The non-Arrhenius relationship results from a fragile liquid-like water component persisting at low temperatures with fragility higher than that of the bulk water.