Fouling interface

When bubbles accumulate at the steam-water interface, dissolved solids pass into the post-boiler steam section, and this carryover contaminates the steam and causes fouling of the system. Where the foam-... 

A comparison of the products of AP hydrolysis of HQDP (HQ), PP, and 1-NP using cyclic voltammetry revealed that HQ produced well-defined peaks, and that the oxidation of HQ is reversible. More importantly, no apparent passivation of the electrode surface was observed even at high millimolar concentrations after 50 scans. Following a series of investigations, this non-fouling nature of HQ was attributed to the non-accumulation of its oxidation products on the electrode surface and the good diffusional properties of HQ at the electrode-solution interface. Another positive feature of HQDP as a substrate for AP is a tenfold greater oxidation current response of HQ compared to those obtained in the presence of PP or 1-NP. Overall, HQDP provides a suitable and attractive alternative substrate system for AP in the development of amperometric immunosensors. 

Cross-flow filtration systems utilize high liquid axial velocities to generate shear at the liquid-membrane interface. Shear is necessary to maintain acceptable permeate fluxes, especially with concentrated catalyst slurries. The degree of catalyst deposition on the filter membrane or membrane fouling is a function of the shear stress at the surface and particle convection with the permeate flow.16 Membrane surface fouling also depends on many application-specific variables, such as particle size in the retentate, viscosity of the permeate, axial velocity, and the transmembrane pressure. All of these variables can influence the degree of deposition of particles within the filter membrane, and thus decrease the effective pore size of the membrane. 

This raises the question of whether diffusion plays a role in the kinetics of slurry polymerization. Certainly there is no limitation across the gas-liquid interface doubling the catalyst also doubles the polymer yield, but increasing the stirring rate does nothing. Diffusion through the polymer particle is a more troubling issue. There are times when the polymerization clearly becomes diffusion limited, or fouled, due to solvation of the polymer, but this is rarely a problem if the temperature is kept down and the molecular weight up. 

Divert the solvent front from the HPLC column, containing salts and unretained material, to waste instead of the mass spectrometer in order to minimize fouling of the LC/MS interface. 

Since APCI and ESI interfaces operate at atmospheric pressure and do not depend upon vacuum pumps to remove solvent vapor, they are compatible with a wide range of HPLC flow rates. HPLC methods that have been developed using conventional detectors such as UV/VIS, IR, or fluorescence are usually transferable to LC/MS systems without adjustment. However, the solvent system should contain only volatile solvents, buffers, or ion-pair agents to reduce fouling of the mass spectrometer ion source. In the case of chlorophyll solvent systems, isocratic and gradient combinations of methanol, acetonitrile, water, acetone, and/or ethyl acetate have been used for APCI or ESI LC/MS. Unlike continuous-flow FAB/LSIMS, no sample matrix is necessary. 

The main disadvantages of contactors are related to the nature of the membrane interface. The membrane acts as an additional barrier to transport between the two phases that can slow the rate of separation. Over time, the membranes can foul, reducing the permeation rate further, or develop leaks, allowing direct mixing of the two phases. Finally, the polymeric membranes are necessarily thin (to maximize their permeation rate) and consequently cannot withstand large pressure differences across the membrane or exposure to harsh solvents and chemicals. In many industrial settings, this lack of robustness prohibits the use of membrane contactors. 

At the inlet the flow is almost linear and a vertical interface between the two fluids exists [135], For this reason, fouling of the inlet is predicted and this agrees with the experimental findings. 

Mass-transport limitations are common to all processes involving mass transfer at interfaces, and membranes are not an exception. This problem can be extremely important both for situations where the transport of solvent through the membrane is faster and preferential when compared with the transport of solute(s) - which happens with membrane filtration processes such as microfiltration and ultrafiltration - as well as with processes where the flux of solute(s) is preferential, as happens in organophilic pervaporation. In the first case, the concentration of solute builds up near the membrane interface, while in the second case a depletion of solute occurs. In both situations the performance of the system is affected negatively (1) solute accumulation leads, ultimately, to a loss of selectivity for solute rejection, promotes conditions for membrane fouling and local increase of osmotic pressure difference, which impacts on solvent flux (2) solute depletion at the membrane surface diminishes the driving force for solute transport, which impacts on solute flux and, ultimately, on the overall process selectivity towards the transport of that specific solute. 

Ho CC, Zydney AL (2000), A combined pore blockage and cake filtration model for protein fouling during microfiltration, J. Colloid Interface Sci. 232 389-399. 

The processes developed initially were based essentially on liquid-liquid extraction techniques, but the chemical problems encountered in the treatment of irradiated Pu/Al targets (e.g. considerable interface fouling in the extractors and formation of stable emulsions) and the intensification of safety requirements led to use of extraction chromatographic techniques. 

Can fouling be reduced by maintaining a higher shear rate at the interface ... 

---