Fouling agent

There are situations where thermal oxidation may be preferred over catalytic oxidation for exhaust streams that contain significant amounts of catalyst poisons and/or fouling agents, thermal oxidation may be the only technically feasible control where extremely high VOC destmction efficiencies of difficult to control VOC species are required, thermal oxidation may attain higher performance and for relatively rich VOC waste gas streams, ie, having >20 25% lower explosive limit (LEL), the gas stream s explosive properties and the potential for catalyst overheating may require the addition of dilution air to the waste gas stream (12). 

Downhole turbine motors are sensitive to fouling agents in the mud therefore, when running a turbine motor steps must be taken to provide particle-free drilling mud. 

Tin has been used in smokeless propints as an anti-barrel fouling agent (Refs 2 3), and in electrically functioned pyrot delay compns for millisecond delays to space expl action in mining operations (until fused, the delay compns contg the Sn alloys are electrically non-conductive)... 

Catalysts can be regenerated, that is, the performance of deactivated catalysts can be improved by regeneration. That is, when the catalyst activity and/or selectivity is reduced during operation, a particular treatment allows the proper activity and/or selectivity of the catalysts to be restored [7], Deactivation is produced by inhibition, fouling, or sintering, and all of these can be reversed, by the removal of poisons, or fouling agents, like coke, or by the re-dispersion of the active species [8], The reproducibility of a catalyst is related to the consistency of its properties in different sets of production lots [7],... 

Fouling agents act in quantities equivalent to several layers spread over the catalyst surface or to pore volume they may according to different cases, have a rapidly reversible, an only slowly reversible, or an irreversible effect. 

It follows that regeneration may consist of either (i) removal of IS sometimes poisons, most often inhibitors or fouling agents, e.g., coke (hydrogenation catalysts, e.g., selective hydrogenation of pyrolysis gasoline) or (ii) redispersion of the active species (platinum catalysts) or (iii) both (hydrodesulfurization or catalytic reforming catalysts). 

In essence, three criteria permit identification of the category (poison, inhibitor, fouling agent) to which IS belongs (see Table 1). 

As the quantity of fouling agents necessary to bring about a noticeable change in activity/sclcctivity is relatively large, characterization by methods other than catalytic activity measurements is useful. The rate of... 

Recently, supercritical fluids (c.g. CO2) have been proposed for removing coke and fouling agents. 

Dahl, B., Blanck, H. (1996) Toxic effects of the anti-fouling agent 1051 on Periphyton communities in coastal water microcosms. Marine Pollution Bulletin 32 342-350. 

Nystrom M., Ruohomaki K., and Kaipa L., Humic acid as a fouling agent in filtration. Desalination 106 1996 78-86. Kahsch-Korbutowicz M., Majewska-Nowak K., and Winnicki T., Analysis of membrane fouUng in the treatment of water solutions containing humic acids and mineral salts. Desalination 126 1999 179-185. 

Products used as stabilizers in PVC are distinguished by their respective alkyl groups octyl, butyl and methyl. The group comprises only mono- and di-organotin stabilizers which are to be differentiated from tri-organotin stabilizers like the very effective biocide (anti-fouling agent) tri-butyl tin. 

It may be possible to modify the membrane in such a way as to reduce or eliminate the binding of a fouling agent. These modifications can be tested empirically or screened theoretically if the nature of the foulant is known. 

---