Polar contaminant

Supercritical CO2 has also beea tested as a solveat for the removal of organic contaminants from sod. At 60°C and 41.4 MPa (6,000 psi), more than 95% of contaminants, such as diesel fuel and polychlotinated biphenyls (PCBs), may be removed from sod samples (77). Supercritical CO2 can also extract from sod the foUowiag hydrocarbons, polyaromatic hydrocarbons, chlotinated hydrocarbons, phenols, chlotinated phenols, and many pesticides (qv) and herbicides (qv). Sometimes a cosolvent is required for extracting the more polar contaminants (78). 

A significant problem is the dehydrocoupling reaction, which proceeds only at low yields per pass and is accompanied by rapid deactivation of the catalyst. The metathesis step, although chemically feasible, requires that polar contaminants resulting from partial oxidation be removed so that they will not deactivate the metathesis catalyst. In addition, apparendy both cis- and /ra/ j -stilbenes are obtained consequendy, a means of converting the unreactive i j -stilbene to the more reactive trans isomer must also be provided, thus complicating the process. 

Particularly polar contaminants may associate with polymeric humic components of soil, water, and sediment. Their biodegradation then depends on the degree to which these processes are reversible and the contaminants become accessible to microorganisms (bioavailable). This is especially significant after weathering (aging), even for nonpolar compounds. 

Due to their unique surface-active properties, surfactants possess the capacity to remobilize non-polar contaminants, such as polycyclic aromatic hydrocarbons or heavy metals, which have accumulated in... 

The partition of different lipids between two immiscible solvents (countercurrent distribution) is useful for crude fractionation of lipid classes with greatly differing polarities. Repeated extractions in a carefully chosen solvent pair increase the effectiveness of the separation but in practice mixtures of lipids are still found in each fraction. A petroleum ether-ethanol-water system can be used to remove polar contaminants (into the alcoholic phase) when interest lies in the subsequent analysis of neutral glycerides, which may be recovered from the ether phase. Carbon... 

A simulated moving bed system has been proposed for the production of p-cresol from mixtures of cresol isomers even derived from coal tar [52]. Neuzil et al. give details of the development of the adsorbent and desorbent system reviewing balancing mass transfer issues with selechvity [53]. The desorbent for the cresol system is 1-pentanol. For these Hquid adsorptive systems where highly polar molecules are adsorbed and desorbed with polar desorbents, the tolerance of the system for trace polar contaminants is higher because the feed and desorbent can more easily exchange with them on the surface of the zeolites. 

Non-polar and moderately polar solutes generally present the least difficulty, and these extracts are amenable to reversed phase partition chromatography followed by final purification of separated fractions by adsorption chromatography. Reversed phase chromatography is a practical first step because it is effective for a very wide range of compounds, and secondly because it has less tendency to be "fouled" by irreversible absorption of highly polar contaminants. 

One aspect of cleaning that can save considerable time and energy is remembering that like dissolves like. Polar solvents can dissolve polar contamination far more effectively than can nonpolar solvents. In addition, proper selection of solvent material can avoid damaging the object you want to clean as well as preventing the introduction of possibly hazardous materials. For example, say you have a plastic container with a stick-on label which, after it is removed, leaves a sticky,... 

Polar solvents, such as the alcohols and ketones, are useful for the removal of polar contaminants, but also attach to adsorbed sites and thereby limit the amount of area available for undesirable materials. Thus, final rinses with polar hydrocarbons can be very beneficial. 

Halocarbons, a class of polar solvents, are hydrocarbons with an attached halogen. There are commonly three types of halocarbon solvents those based on chlorine, fluorine, and a combination of the two. They are all powerful degreasing materials and can be particularly effective in removing polar contaminants from glass. The chlorofluorocarbons are currently under review because they cause environmental damage to the ozone layer.1... 

This solvent system is convenient to separate less polar contaminants such as tert-butyl acetate or unchanged di-tert-butyl dicarbonate. 

Solubility can also be enhanced by the presence of other compounds. This phenomenon is caused by one or more compounds acting as solubility enhancers for other compounds present on a surface. This phenomenon is sometimes called the local cosolvent effect. A typical method of enhancing contaminant solubility is through the addition of a small amount of secondary solvent to the SCF cleaning system. Alcohols are commonly used in this manner to increase solubilities of more polar contaminants. However, more subtle local cosolvent effects have been observed. Perhaps a classic example was first reported by Kumik and Reid. In their study, they observed that the solubilities of both naphthalene and benzoic acid in supercritical CO2 were enhanced by 107% and 280%, respectively, when both species were present. It has also been shown that there needs to be enough of a secondary component present in solution about the local contaminant environment to enhance the solubility of another compound, This example demonstrated that an excess of phenanthrene promoted the solubility of anthracene in supercritical COj, but since anthracene was only present in very small quantities, it did not help to enhance the overall solubility of phenanthrene. A... 

A 28.9 Clear 1 = 231.5 A = 0.720 Acylglycerols Acylglycerols Polar contamination Contamination Good 95%... 

B 27.9 Light yellow 1=231.5 A =0.667 No acylglycerols No acylglycerols Polar contamination OK Poor 70%... 

The ACM and PCM tests were developed and patented by Libra Laboratories (USA). Oil Process Systems of Allentown, PA also known as Mir-Oil, owns the patent and distribution rights for the testing devices. The ACM test measures alkaline contaminant materials, which include soaps. The PCM measures polar contaminant materials (accumulated polar compounds). These tests provide results that could be used at the restaurants. However, the test units are relatively expensive and the restaurants tend to avoid using them after the initial introduction of the device. 

In commercial polyethylene operations, poisons may enter the process as trace (ppm) contaminants in ethylene, comonomer, hydrogen (CTA), nitrogen (used as inert gas), solvents and other raw materials. These poisons reduce catalyst activity. Most damaging are oxygen and water. However, CO, CO, alcohols, acetylenics, dienes, sulfur-containing compounds and other protic and polar contaminants can also lower catalyst performance. With the exception of CO, aluminum alkyls react with contaminants converting them to alkylaluminum derivatives that are less harmful to catalyst performance. Illustrative reactions of contaminants with triethylaluminum are provided in eq 4.9-4.11 ... 

It seems likely that the dominant artefacts are produced by linearly polarized contaminants in the incident circularly polarized beam, with different azimuths in the right and left phases. Hug noticed that, if the intensities of the linearly polarized contaminants in the two phases are identical, a twin-lens collection system comprising two identical collection optics with their axes in the xy plane and inclined at 45° to the y axis will eliminate the spurious intensity difference. For the collection optic with its axis at + 45° to the y axis, the incident azimuth is effectively 0 — 45°, whereas... 

The measurement of interfacial tension (ASTM D-971, ASTM D-2285) between oil and water is a sensitive method for determining traces of polar contaminants, including products of oil oxidation, and minimum values will sometimes be found in insulating oil specifications. The test is frequently... 

Design of the separation. It is well known that gradients can improve apparent resolution in chromatography (1). The use of a gradient in a separation such as that shown in Figure 6a would be ideal in that adequate clearance of the polar contaminants could... 

Heberer Th, Schmidt-Baumler K, Stan H-J (1998) Occurrence and distribution of organic contaminants in the aquatic system in Berlin. Part I Drug residues and other polar contaminants in Berlin surface and groundwater. Acta Hydrochim Hydrobiol 26, 272-278. 

Silica processing utilizes a chemically inert synthetic amorphous silica adsorbent with an affinity for polar contaminants. The surface area, porosity, and moisture content of the silica adsorbents provide them with the capability of removing soaps, phospholipids, sulfur compounds, and trace metals from edible oils. The function of the moisture is to hold the pores open and aid in the attraction of polar contaminants. Several different options are offered for the use of silica adsorbents. The simplest option adds... 

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