Polymeric adsorption

A number of papers have appeared on the removal of heavy metals in the effluents of dyestuff and textile mill plants. The methods used were coagulation (320—324), polymeric adsorption (325), ultrafiltration (326,327), carbon adsorption (328,329), electrochemical (330), and incineration and landfiU (331). Of interest is the removal of these heavy metals, especiaUy copper by chelation using trimercaptotria2ine (332) and reactive dyed jute or sawdust (333). 

Pyridine. Pyridine and its methyl substituted derivatives (picolines and lutidines) were found to polymerize electrochemically and, under certain circumstances, catalytically. This behavior was not expected because usually pyridine undergoes electrophilic substitution and addition slowly, behaving like a deactivated benzene ring. The interaction of pyridine with a Ni(100) surface did not indicate any catalytic polymerization. Adsorption of pyridine below 200 K resulted in pyridine adsorbing with the ring parallel to the surface. The infrared spectrum of pyridine adsorbed at 200 K showed no evidence of either ring vibrations or CH stretches (Figure 5). Desorption of molecular pyridine occurred at 250 K, and above 300 K pyridine underwent a... 

To overcome problems with VX, a reaction with silver fluoride impregnated on a filter in front of the adsorption tube has been applied. The fluoride converts VX to the more volatile ethyl methylphos-phonofluoridate (CAS 673-97-2), which is more amenable to GC (37). In an alternative approach, adsorption tubes can be extracted with a suitable solvent such as ethyl acetate or acetone (chlorinated solvents may dissolve the polymeric adsorption material). This offers the advantage of a repeat analysis. To compensate for the loss of sensitivity, compared with thermodesorption, on-column... 

Polymeric adsorption resins — A series of polymeric adsorbents has recently been developed that can adsorb hydrocarbons from aqueous systems. They derive their adsorptive properties from a combination of macroreticular porosity, pore size distribution, high surface area, and the aliphatic nature of their structure. Adsorbent resins can produce water containing less than 1 ppm oil. 

Sato, T. Ruch, R. Stabilization of Colloidal Dispersions by Polymeric Adsorption Surfactant Science Series Marcel Dekker, Inc. New York, 1980 Vol. IV. 

Equation 15.16 describes cracking of the aliphatic part of the feedstock, i.e., detachment of the aliphatic fragments from the heavy residue. The reactive centers of polymerization/adsorption formed as a result of cracking cause the decrease in the concentration of the aliphatic component C that can be potentially converted to the cracking product. This reduction on the potential product yield is described by Equation 15.17. It is assumed that the polymerized (or adsorbed) products are radiation resistant and do not further participate in the cracking reactions. Equation 15.18 describes accumulation and disappearance of the long-living radicals R. ... 

Browne, T.E., and Cohen, Y., Polymer-grafted silica A screening system for polymeric adsorption resin development, Ind. Eng. Chem. Res., 32(4), 716-725 (1993). 

Dolan and Edwards [386] calculated the steric interaction free energy per unit area, for two polymeric adsorption monolayers (Fig. 28b) in a theta solvent as a function of the film thickness, h ... 

The second detergent function is to prevent formation of varnishes that come from polymerization of deposits on hot surfaces of the cylinder and the piston. Finally, by adsorption on metallic surfaces, these compounds have anti-corrosion effects. 

Protein adsorption has been studied with a variety of techniques such as ellipsome-try [107,108], ESCA [109], surface forces measurements [102], total internal reflection fluorescence (TIRE) [103,110], electron microscopy [111], and electrokinetic measurement of latex particles [112,113] and capillaries [114], The TIRE technique has recently been adapted to observe surface diffusion [106] and orientation [IIS] in adsorbed layers. These experiments point toward the significant influence of the protein-surface interaction on the adsorption characteristics [105,108,110]. A very important interaction is due to the hydrophobic interaction between parts of the protein and polymeric surfaces [18], although often electrostatic interactions are also influential [ 116]. Protein desorption can be affected by altering the pH [117] or by the introduction of a complexing agent [118]. 

After reviewing various earlier explanations for an adsorption maximum, Trogus, Schechter, and Wade [244] proposed perhaps the most satisfactory one so far (see also Ref. 243). Qualitatively, an adsorption maximum can occur if the surfactant consists of at least two species (which can be closely related) what is necessary is that species 2 (say) preferentially forms micelles (has a lower CMC) relative to species 1 and also adsorbs more strongly. The adsorbed state may also consist of aggregates or hemi-micelles, and even for a pure component the situation can be complex (see Section XI-6 for recent AFM evidence of surface micelle formation and [246] for polymeric surface micelles). Similar adsorption maxima found in adsorption of nonionic surfactants can be attributed to polydispersity in the surfactant chain lengths [247], Surface-active impuri-... 

Figure Bl.19.13. (a) Tliree STM images of a Pt(l 11) surface covered witli hydrocarbon species generated by exposure to propene. Images taken in constant-height mode. (A) after adsorption at room temperature. The propylidyne (=C-CH2-CH2) species that fomied was too mobile on the surface to be visible. The surface looks similar to that of the clean surface. Terraces ( 10 mn wide) and monatomic steps are the only visible features. (B) After heating the adsorbed propylidyne to 550 K, clusters fonn by polymerization of the C H...

However, the quantity of Pa produced in this manner is much less than the amount (more than 100 g) that has been isolated from the natural source. The methods for the recovery of protactinium include coprecipitation, solvent extraction, ion exchange, and volatility procedures. AH of these, however, are rendered difficult by the extreme tendency of protactinium(V) to form polymeric coUoidal particles composed of ionic species. These caimot be removed from aqueous media by solvent extraction losses may occur by adsorption to containers and protactinium may be adsorbed by any precipitate present. 

Polymeric cation-exchange resins are also used in the separation of fmctose from glucose. The UOP Sarex process has employed both 2eohtic and polymeric resin adsorbents for the production of high fmctose com symp (HFCS). The operating characteristics of these two adsorbents are substantially different and have been compared in terms of fundamental characteristics such as capacity, selectivity, and adsorption kinetics (51). 

Adsorption systems employing molecular sieves are available for feed gases having low acid gas concentrations. Another option is based on the use of polymeric, semipermeable membranes which rely on the higher solubiHties and diffusion rates of carbon dioxide and hydrogen sulfide in the polymeric material relative to methane for membrane selectivity and separation of the various constituents. Membrane units have been designed that are effective at small and medium flow rates for the bulk removal of carbon dioxide. 

PMMA-impregnated sol—gel-derived siUca gels have also been examined (54). Long-wave uv illumination was employed in addition to benzoyl peroxide for PMMA polymerization. This method prohibited the degradation of the siUca xerogel from moisture adsorption and desorption. Overall the material behaved more like bulk PMMA than bulk siUca, with the exception of hardness. 

Pharmaceutical. Ion-exchange resins are useful in both the production of pharmaceuticals (qv) and the oral adrninistration of medicine (32). Antibiotics (qv), such as streptomycin [57-92-17, neomycin [1404-04-2] (33), and cephalosporin C [61-24-5] (34), which are produced by fermentation, are recovered, concentrated, and purified by adsorption on ion-exchange resins, or polymeric adsorbents. Impurities are removed from other types of pharmaceutical products in a similar manner. Resins serve as catalysts in the manufacture of intermediate chemicals. 

During Stages II and III the average concentration of radicals within the particle determines the rate of polymerization. To solve for n, the fate of a given radical was balanced across the possible adsorption, desorption, and termination events. Initially a solution was provided for three physically limiting cases. Subsequentiy, n was solved for expHcitiy without limitation using a generating function to solve the Smith-Ewart recursion formula (29). This analysis for the case of very slow rates of radical desorption was improved on (30), and later radical readsorption was accounted for and the Smith-Ewart recursion formula solved via the method of continuous fractions (31). 

Incorporation of less than a stoichiometric amount of alkyl sulfonamides of copper phthalocyanines into copper phthalocyanine improves the pigment s properties in rotogravure inks (67). Monomeric and polymeric phthalocyanine derivatives with basic substituents adsorb strongly to the pigment surface and promote the adsorption of binder molecules (68—72). 

High quahty SAMs of alkyltrichlorosilane derivatives are not simple to produce, mainly because of the need to carefully control the amount of water in solution (126,143,144). Whereas incomplete monolayers are formed in the absence of water (127,128), excess water results in facile polymerization in solution and polysiloxane deposition of the surface (133). Extraction of surface moisture, followed by OTS hydrolysis and subsequent surface adsorption, may be the mechanism of SAM formation (145). A moisture quantity of 0.15 mg/100 mL solvent has been suggested as the optimum condition for the formation of closely packed monolayers. X-ray photoelectron spectroscopy (xps) studies confirm the complete surface reaction of the —SiCl groups, upon the formation of a complete SAM (146). Infrared spectroscopy has been used to provide direct evidence for the hiU hydrolysis of methylchlorosilanes to methylsdanoles at the soHd/gas interface, by surface water on a hydrated siUca (147). 

New areas in adsorption technology include carbonaceous and polymeric resins (3). Based on synthetic organic polymer materials, these resins may find special uses where compound selectivity is important, low effluent concentrations are required, carbon regeneration is impractical, or the waste to be treated contains high levels of inorganic dissolved soHds. 

Table 8. Adsorption Capacity of Amberlite XAD-4 Polymeric Resin ...

A gas chromatographic determination of benzotrichloride and related compounds ia the work environment, after adsorption on a polymeric adsorbant and desorption with CCl has been reported (61). Trace amounts of benzyl chloride, benzal chloride, and benzotrichloride ia environmental samples can be analyzed by Method 8120 of EPA ManualSW-846 with modifications (62). 

In secondary operations, where chemicals are injected into hydrocarbon formations in conjunction with a chemical flooding process, polyamines are used to reduce the loss of injected chemicals to the formation by adsorption and precipitation (312). TEPA and other ethyleneamines are used with water-soluble polymeric thickeners in water—flood petroleum recovery operations to stabilize viscosity, mobiUty, and pH while imparting resistance to hydrolysis (313). 

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