Oxygen separation methods

Nitrogen Enriched Air occurs as a colorless gas. It is produced from air in situ by physical separation methods. It contains not less than 90% and not more than 99% nitrogen, by volume. The remaining components are noble gases and, primarily, oxygen. 

On the other hand, analysis for sulfur and oxygen shows that in the polyaromatic/polar fractions, of an av mol wt of 490, 6.8% sulfur and 2. 6% oxygen represent on the average 1.04 sulfur atoms and nearly 0.7 oxygen atoms per molecule. The material is therefore essentially heterocyclic in character. The nitrogen contents of the fractions were also comparable, suggesting that in the class separation method most of the... 

The occurrence of isotopes among the 83 most abun-dantelements is widespread, but separation methods are complicated and costly. Twenty-one elements have no isotopes, each consisting of only one kind of atom (see note below). The remaining 62 natural elements have from 2 to 10 isotopes each. There are 287 different isotopic species in nature noteworthy among them are oxygen-17, carbon-14, uranium-235, cobalt-60, and strontium-90, all but the first being radioactive. 

Extraction of the cadmium-iodide complex from iodide-H2S04 solutions with oxygen-containing solvents (e.g., mesityl oxide, 2-ethyl-1-butanol) is a selective recommended separation method (e.g., from zinc) [1-3]. The iodide complex of cadmium can also be extracted with high molecular weight amines in xylene [4], TBP in benzene [5], and with tetra-n-butylammonium iodide in CHCI3 [6]. 

Gas separation membrane technologies are extensively used in industry. Typical applications include carbon dioxide separation from various gas streams, production of oxygen enriched air, hydrogen recovery from a variety of refinery and petrochemical streams, olefin separation such as ethylene-ethane or propylene-propane mixtures. However, membrane separation methods often do not allow reaching needed levels of performance and selectivity. Polymeric membrane materials with relatively high selectivities used so far show generally low permeabilities, which is referred to as trade-off or upper bound relationship for specific gas pairs [1]. 

For this work they chose several types of base stocks—some were raffinates from solvent extraction and therefore contained different percentages of aromatics and some were blends of white oils (of near-zero aromatic content) with added quantities of aromatic fractions separated from bright stocks. Oxidations were performed at a number of temperatures with and without added metals (metallic iron and copper to simulate wear metals) and were followed by the oxygen uptake method. Their overall conclusion was that aromatics did indeed inhibit oxidation, whether metals were present or not, and that the effect with their samples exhibited a maximum at about 5% aromatics content. Figure 5.4 illustrates this phenomenon, with measurements of the time for uptake of 1800 ml of oxygen per 100 ml of sample. It can be seen that the reaction rate at zero and 8% aromatics is twice as fast as at 5% (times vary by a factor of two). It was clear that aromatics contained these naturally occurring inhibitors, but this work was unable to shine any light on just what these inhibitors were. 

This concept of optimum aromaticity and the role of sulfur compounds as inhibitors were further established by a study by Bum and Greig (British Petroleum) of the oxidation of solvent extracted base stocks.18 They chose samples from a North African (Sahara) and three Middle East (Iran, Abu Dhabi, and Kuwait) crudes. The aromatic + heterocyclic (A + II) and paraffin + naphthene (P + N) components were separated by alumina chromatography from each base stock (Table 5.9 includes their composition and sulfur contents) and recombined in several ratios and the resistance of the blends to oxidation measured by the oxygen uptake method. 

During process synthesis, in the distribution of chemicals, a key question involves whether it is preferable to remove 1-butene and 1,3-butadiene before or after the reaction operation. In this example, distillation is considered, although other separation methods normally are evaluated as well. It should be noted that recently MTBE was found to contaminate ground water and, thus, in most locations is no longer the preferred source of oxygen. 

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