Fouling surface effect

Fouling Salt formation can build-up on the catalyst surface effectively limiting accessibility. Ammonium bisulfate can form at low temperatures. This foulant can be removed by increasing temperature and is considered a temporary poison. 

Compounds containing sulfur and cyanide become a potential source of air pollution when treated with this system. A caustic scrubber may be required to capture the combustion products of these compounds if sulfur and cyanide levels are high enough to exceed health and safety or applicable air quality standards. Metals that are not particularly volatile are not likely to be treated effectively by the TDS. Plastic materials are not recommended for treatment since their decomposition products could cause plugging or foul surfaces. 

The deleterious effect of water vapor was speculated to be due to its inhibition of carbon formation freeing the metal surface for interaction by H2S. Thus, sulfur poisoning of nickel at high temperature (above 673 K) may be more representative of a carbon-fouled surface, whereas at low temperatures it may be more characteristic of the clean metal surface. Again, this needs to be confirmed by direct measurements of carbon and sulfur adsorption. For Ni/Al203 and Ni/ZrOz the extent of sulfur deactivation was about fiftyfold at 673 K at 523 K the extent of deactivation was about 1000-fold. However, for Raney Ni the extent of sulfur deactivation was tenfold higher at 673 K than at 523 K this difference in behavior also needs confirmation and explanation. 

Particles of different attributes, such as characteristic surface or charge, need to be investigated to be able to predict treatment performance. The impact of particle content on fouling of tight membranes is not clear in the literature, but it is generally assumed that p>articles play a major role in fouling. These effects need to be understood prior to optimising membrane pretreatment. 

Chemical additives can hold the fouling deposit in suspension, by reducing their tendency to stick, and by weakening their bond to the surface. However, sometimes, chemical additives can contribute to fouling. The effectiveness of this method may depend on the match between chemical additives, chemical components of process streams, and conditions under which an exchanger operates. For example, a certain additive may work well with asphaltene but not wax deposits. In same cases, chemical additives can also poison catalysts or adsorbents. 

Electrodeless conductivity is a technicjue for measuring the conductance of a solution using the electrical inductance principle at low frequencies. This method does not use contacting electrodes thereby eliminating maintenance and other errors due to surface effects created by coatings and fouling. The measurement enjoys widespread acceptance in the chemical process industries. Its history and a review of the literature have been presented here. 

Negative results of protein adsorption, such as membrane fouling, thromboembolitic effects of implants, deffects of contact lens and others have been considered and some ways to reduce undesirable processes are given. To remove these difficulties it is useful to use low energetic surfaces of optimal surface energy with well water saturated surfaces, to avoid essential contributions of electrostatic interactions between the surfaces of protein and adsorbent, as well as conditions inducing denaturation of proteins in a solution. Materials with pre-adsorbed HSA, or a mixture of HSA and vitamin C are useful especially for biocompatibility improving. 

Peptoids represent mimics of natural peptides, whose residues are chemically bonded to the nitrogen instead of the a-carbon atoms. This modification makes them more stable in contrast to peptides. In general, peptoides and peptides have proven themselves as effective non-fouling surface coatings, even for more than five months. ... 

Benefits of this system include its potential for practical application due to the enhanced stability. Disadvantages include those inherent in any SLM including the potential for fouling of membrane pores due to surface effects. Also, solvents and macrocycles must be rather hydrophobic for optimal membrane function (64). 

Fouling of the pH sensor may occur in solutions containing surface-active constituents that coat the electrode surface and may result in sluggish response and drift of the pH reading. Prolonged measurements in blood, sludges, and various industrial process materials and wastes can cause such drift. Therefore, it is necessary to clean the membrane mechanically or chemically at intervals that are consistent with the magnitude of the effect and the precision of the results requited. 

Commonly used heat-transfer surfaces are internal coils and external jackets. Coils are particularly suitable for low viscosity Hquids in combination with turbine impellers, but are unsuitable with process Hquids that foul. Jackets are more effective when using close-clearance impellers for high viscosity fluids. For jacketed vessels, wall baffles should be used with turbines if the fluid viscosity is less than 5 Pa-s (50 P). For vessels equipped with cods, wall baffles should be used if the clear space between turns is at least twice the outside diameter of the cod tubing and the fluid viscosity is less than 1 Pa-s (10... 

Only trace amounts of side-chain chlorinated products are formed with suitably active catalysts. It is usually desirable to remove reactive chlorides prior to fractionation in order to niinimi2e the risk of equipment corrosion. The separation of o- and -chlorotoluenes by fractionation requires a high efficiency, isomer-separation column. The small amount of y -chlorotoluene formed in the chlorination cannot be separated by fractionation and remains in the -isomer fraction. The toluene feed should be essentially free of paraffinic impurities that may produce high boiling residues that foul heat-transfer surfaces. Trace water contamination has no effect on product composition. Steel can be used as constmction material for catalyst systems containing iron. However, glass-lined equipment is usually preferred and must be used with other catalyst systems. 

Work in connection with desahnation of seawater has shown that specially modified surfaces can have a profound effect on heat-transfer coefficients in evaporators. Figure 11-26 (Alexander and Hoffman, Oak Ridge National Laboratory TM-2203) compares overall coefficients for some of these surfaces when boiling fresh water in 0.051-m (2-in) tubes 2.44-m (8-ft) long at atmospheric pressure in both upflow and downflow. The area basis used was the nominal outside area. Tube 20 was a smooth 0.0016-m- (0.062-in-) wall aluminum brass tube that had accumulated about 6 years of fouhng in seawater service and exhibited a fouling resistance of about (2.6)(10 ) (m s K)/ J [0.00015 (fF -h-°F)/Btu]. Tube 23 was a clean aluminum tube with 20 spiral corrugations of 0.0032-m (lA-in) radius on a 0.254-m (10 -in)... 

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