Hydrocarbons from water, separation

This publication provides several examples of the use of solid-phase extractions for separating analytes from their matrices. Some of the examples included are caffeine from coffee, polyaromatic hydrocarbons from water, parabens from cosmetics, chlorinated pesticides from water, and steroids from hydrocortisone creams. Extracted analytes maybe determined quantitatively by gas (GC) or liquid chromatography (LG). 

The VPS overhead consists of steam, inerts, condensable and non-condensable hydrocarbons. The condensables result from low boiling material present in the reduced crude feed and from entrainment of liquid from the VPS top tray. The noncondensables result from cracking at the high temperatures employed in the VPS. Inerts result from leakage of air into the evacuated system. Steam and condensable hydrocarbons are condensed using an overhead water-cooled condenser. The distillate drum serves to separate inerts and non-condensables from condensate, as well as liquid hydrocarbons from water. Vacuum is maintained in the VPS using steam jet ejectors. 

The drum is provided with a drawoff boot of nominal 6(X) mm diameter by 900 mm in height, with a separate steam coil fabricated from 25 mm pipe. Normally it is not necessary to withdraw hydrocarbon and water separately, and the pumpout pump takes suction from the bottom of the boot. The LL(CO)A is located as close as possible to the top of the boot to ensure that the pump is shutdown before losing suction. 

Leoni [366] observed that in the extraction preconcentration of organochlo-rine insecticides and PCB s from surface and coastal waters in the presence of other pollutants such as oil, surface active substances, etc., the results obtained with an absorption column of Tenax-Celite are equivalent to those obtained with the continuous liquid-liquid extraction technique. For non-saline waters that contain solids in suspension that absorb pesticides, it may be necessary to filter the water before extraction with Tenax and then to extract the suspended solids separately. Analyses of river and estuarine sea waters, filtered before extraction, showed the effectiveness of Tenax, and the extracts obtained for pesticide analysis prove to be much less contaminated by interfering substances than corresponding extracts obtained by the liquid-liquid technique. Leoni et al. [365] showed that for the extraction of organic micro pollutants such as pesticides and aromatic polycyclic hydrocarbons from waters, the recoveries of these substances from unpolluted waters (mineral and potable waters) when added at the level of 1 xg/l averaged 90%. 

The SFC Oleofiltration system separates hydrocarbons from water. The technology combines a vertical-fin coalescing unit and a patented, amine-coated, oleophilic granule filtration system (the Oleofilter) into one system that can, according to the vendor, separate mechanical emulsions of hydrocarbons in water that are not treatable by conventional oil/water separators. The Oleofilter can also separate many chemical emulsions and reduce the concentrations of dissolved hydrocarbons. The technology is not commercially available. 

WATER-AIR EQUILIBRATION. McAuliffe (6) introduced a multiple phase equilibrium procedure for the qualitative separation of hydrocarbons from water-soluble organic compounds. For n-alkanes, more than 99% were found to partition in the gas phase after two equilibrations with equal volumes of gas and aqueous solution. Cycloalkanes require three equilibrations to be essentially completely removed, and oxygen-containing organic compounds (e.g., alcohols, aldehydes, ketones, and acids) remain in the aqueous layer. Thus, after equilibration with equal volumes of gas, an immediate clue is given regarding the identification of the compound. More details of this technique can be found in Chapter 7. 

In multiphase flow metering, it is usually required to distinguish hydrocarbon from water. If the liquid phase is "oil continuous," the water fraction can be determined by dielectric constant measurement at microwave frequencies because the dielectric constant of dry hydrocarbon is on the order of 2 to 4 and that of water is 82. Naturally, density measurement can also distinguish water from oil. The next requirement is to distinguish the flow of liquid from the flow of gas in a system where the two will try to separate and travel at different velocities. Cross-correlation by nuclear techniques can measure the density of the stream twice (a short vertical distance apart) and correlate the fluctuations in density with time to determine velocity. Multiphase flow metering is a new and evolving technology,... 

Demulsifiers aid in the separation of fuel from water. Normally, hydrocarbons and water separate rapidly and cleanly. But if the fuel contains polar compounds that behave like surfactants and if free water is present, the fuel and water can form a stable emulsion. Any operation that subjects the mixture to high shear forces, like pumping the fuel, can stabilize the emulsion. Demulsifiers are surfactants which can destabilize the emulsions and allow the fuel and water phases to separate. Demulsifiers are used in concentrations of up to 30 ppm. 

Waste material snch as tank bottoms from crude oil storage tanks constitute a large percentage of refinery solid waste and pose a particularly difficult disposal problem due to the presence of heavy metals. Tank bottoms are comprised of heavy hydrocarbons, solids, water, rust, and scale. Minimization of tank bottoms is carried ont most cost-effectively through careful separation of the oil and water remaining in the tank bottom. Filters and centrifuges can also be used to recover the oil for recycling. 

Fig. 3.1 outlines the liquefaction of air. Air is filtered to remove particulates and then compressed to 77 psi. An oxidation chamber converts traces of hydrocarbons into carbon dioxide and water. The air is then passed through a water separator, which gets some of the water out. A heat exchanger cools the sample down to very low temperatures, causing solid water and carbon dioxide to be separated from the main components. 

Thermal distillation is a process that uses heat to volatilize hydrocarbons and water from contaminated media. The volatiles are later condensed and separated, leaving only reduced-volume solids suitable for landfilling. 

The QED Environmental Systems Ferret in-well separator removes hydrocarbons from ground-water. QED Environmental Systems, Inc., has regional distributors of its Ferret in-well separator from whom the product is commercially available. 

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