Adsorbents fouling

When possible, adsorbent-fouling and -damaging components should be removed upstream of adsorber inlet. 

We used desorption of deactivated catalysts in vacuo at reaction temperatures into the ion source of a mass spectrometer as a method of examining desorbable intracrystalline fouling products. The method of dissolution of deactivated catalyst, followed by adsorbate analysis, that was reported by Venuto et al. (3, 4) was also used. The latter method gives composition and quantity of total adsorbate. The vacuum desorption technique provides information on the mobility—i.e., desorption dynamics, of desorbable (rather than total) adsorbed fouling products. 

A, 5A, and 13X zeoHtes are the predorninant adsorbents for CO2 removal by temperature-swing processes. The air fed to an air separation plant must be H2O- and C02-ftee to prevent fouling of heat exchangers at cryogenic temperatures 13X is typically used here. Another appHcation for 4A-type zeoHte is for CO2 removal from baseload and peak-shaving natural gas Hquefaction faciHties. 

Physica.1 Properties. Carbonyl sulfide [463-58-1] (carbon oxysulfide), COS, is a colorless gas that is odorless when pure however, it has been described as having a foul odor. Physical constants and thermodynamic properties are Hsted ia Table 1 (17,18). The vapor pressure has been fitted to an equation, and a detailed study has been made of the phase equiUbria of the carbonyl sulfide—propane system, which is important ia the purification of propane fuel (19,20). Carbonyl sulfide can be adsorbed on molecular sieves (qv) as a means for removal from propane (21). This approach has been compared to the use of various solvents and reagents (22). 

The normal regeneration temperature for siUca gel is 175°C. In hydrocarbon service, higher temperatures (225—275°C) are recommended to desorb heavy hydrocarbons, which tend to foul the adsorbent during prolonged use (see Silicon compounds). 

Second, most membrane materials adsorb proteins. Worse, the adsorption is membrane-material specific and is dependent on concentration, pH, ionic strength, temperature, and so on. Adsorption has two consequences it changes the membrane pore size because solutes are adsorbed near and in membrane pores and it removes protein from the permeate by adsorption in addition to that removed by sieving. Porter (op. cit., p. 160) gives an illustrative table for adsorption of Cytochrome C on materials used for UF membranes, with values ranging from 1 to 25 percent. Because of the adsorption effects, membranes are characterized only when clean. Fouling has a dramatic effect on membrane retention, as is explained in its own section below. 

Disinfection by-products (e.g., adsorbable organic halides such as trihalomethanes) are more than 50% decreased compared to equivalent chlorine treatments in standardized AOX test with STABREX3. In practice, disinfection by-products are decreased even further in STABREX applications because less oxidant is required to control the microbial fouling process compared to bromine or chlorine applications. 

Haines A process for recovering sulfur from natural gas, using a zeolite adsorbent. The hydrogen sulfide in the gas is adsorbed on the zeolite when the bed is saturated, hot sulfur dioxide is passed through it. The zeolite catalyzes the reaction between hydrogen sulfide and sulfur dioxide to fonn elemental sulfur, which sublimes out and is condensed. The process was invented by H. W. Haines in 1960 it was developed by Krell Associates and piloted in Canada from 1961 to 1962, but not commercialized because of problems caused by fouling of the zeolite with heavy hydrocarbons. 

Differential pulse voltammetry and electrochemical impedance have demonstrated that G, A, guanosine, and their oxidation products are electrostatically adsorbed on GC and GC(ox) surfaces [47,49]. The strength of adsorption of the DNA bases on the GC surface were found to be similar [49]. Strongly adsorbed G dimers were formed on GC between G and the adsorbed G oxidation products, which slowly cover and block the surface. The appHcation of ultrasound led to removal of the adsorbed species. The effect of this was mainly to enhance transport of electroactive species and to clean the electrode in situ, avoiding electrode fouling. 

Another attractive application of polymer brushes is directed toward a biointerface to tune the interaction of solid surfaces with biologically important materials such as proteins and biological cells. For example, it is important to prevent surface adsorption of proteins through nonspecific interactions, because the adsorbed protein often triggers a bio-fouling, e.g., the deposition of biological cells, bacteria and so on. In an effort to understand the process of protein adsorption, the interaction between proteins and brush surfaces has been modeled like the interaction with particles, the interaction with proteins is simplified into three generic modes. One is the primary adsorption. 

Polymer adsorbents No fouling problems Much more expensive Removal of organics... 

Most aliphatic amines and alcohols are considered to be nonelectroactive. The reason for this is that the product of the oxidation adsorbs to the electrode surface, fouling the electrode. Therefore, most reactions of these compounds at noble metal electrodes have been transient and not amenable to direct amperometric detection. In voltammetry experiments, electrodes are cleaned between experiments by electrochemical or chemical treatment to restore the electrode response. 

External fouling is caused by the formation of a cake layer of cells or other materials on the membrane surface, leading to a reduction in permeate flux (defined as the volume of permeate produced per time and membrane area). Internal fouling is caused mainly by proteins and particles smaller than membrane pores. Proteins and protein aggregates can adsorb or deposit at the pore entrance or inside the pores and cause pore blockage or narrowing, leading to increased hydraulic resistance (2). 

For reasons of fouling or deactivation, it may be desirable to be able to replace immobilized enzymes in time, and for this a programmable way of adsorption and release of enzymes would be very welcome. An example of this is the use of a 4nm thin polymer film that can be thermally switched between a hydrophilic (swollen) state at 20 °C and a more hydrophobic protein-adsorbing (collapsed) state at 48 °C, integrated into a micro hotplate with fast heating options so that a protein monolayer can be adsorbed and released within 1 s (Huber et al., 2003). 

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