Olefin Separations

Olefin Separation. Olefin-containing streams are separated either by the OlefinSiv process (Union Carbide Corp.) separating / -butenes from isobutenes in the vapor phase, or the Olex process (Universal Oil Product) a Hquid-phase process. 

Extraction Solvent. Dimethyl sulfoxide is immiscible with alkanes but is a good solvent for most unsaturated and polar compounds. Thus, it can be used to separate olefins from paraffins (93). It is used in the Institute Fransais du Pntrole (IFF) process for extracting aromatic hydrocarbons from refinery streams (94). It is also used in the analytical procedure for determining polynuclear hydrocarbons in food additives (qv) of petroleum origin (95). 

Olex A version of the Sorbex process for separating olefins from paraffins in wide-boiling mixtures. It can be used for hydrocarbons in the range C6 - C20. Based on the selective adsorption of olefins in a zeolite and their subsequent recovery by displacement with a liquid at a different boiling point. Mainly used for extracting Cn - C14 olefins from the Pacol... 

Olefin Separation. U.O.P. s Olex Process. U.O.P. s other hydrocarbon separation process developed recently—i.e., the Olex process—is used to separate olefins from a feedstock containing olefins and paraffins. The zeolite adsorbent used, according to patent literature 29, 30), is a synthetic faujasite with 1-40 wt % of at least one cation selected from groups I A, IIA, IB, and IIB. The Olex process is also believed to use the same simulated moving-bed operation in liquid phase as U.O.P. s other hydrocarbon separation processes—i.e., the Molex and Parex processes. 

The fluidized reactor system is similar to that of a refineiy FCC unit and consists of riser reactor, regenerator vessel, air compression, catalyst handling, flue-gas handling and feed and effluent heat recovery. Using this reactor system with continuous catalyst regeneration allows higher operating temperatures than with fixed-bed reactors so that paraffins, as well as olefins, are converted. The conversion of paraffins allows substantial quantities of paraffins in the feedstream and recycle of unconverted feed without need to separate olefins and paraffins. 

Since it is often troublesome to indirectly introduce conjugated double bonds in hydrocarbon chains starting from polymers containing separated olefinic unsaturations, the possibility of building up macromolecules possessing conjugated diene systems in a sin e step is of interest. 

Anisotropic cellulose ester fibers (useful for reverse osmosis) with a dense skin and porous substructure were employed as supports for Immobilizing aqueous AgN03 solutions for separating olefins from paraffins ( ). However, these authors did not operate under any significant AP conditions, primarily to reduce membrane liquid loss under positive applied pressure differential. 

Dimethyl sulfoxide is a favored solvent for displacement reactions in synthetic chemistry. The rates of reaction in DMSO are many times faster than in an alcohol or aqueous medium [6]. Dimethyl sulfoxide is the solvent of choice in reactions where proton (hydrogen atom) removal is the rate determining step. Reactions of this type include olefin isomerizations and reactions where an elimination process produces an olefin. Another application that uses DMSO is its use as an extraction solvent to separate olefins from saturated paraffins [7]. Several binary and ternary solvent systems containing DMSO and an amine (e.g., methylamine), sulfur trioxide, carbon disulfide/ amine, or sulfur trioxide/ammonia are used to dissolve cellulose, and act as spinning baths for the production of cellulose fibers [8,9]. Organic fungicides, insecticides, and herbicides are readily soluble in DMSO. Dimethyl sulfoxide is used to remove polymer residues from polymerization reactors. 

The sorbent that forms a 7r-complexation bond with molecules of a targeted component in a mixture is named 7r-complexation sorbent. The r-complexation bond is a type of weak and reversible chemical bond, the same type that binds oxygen to hemoglobin in our blood. This type of sorbent has been developed in the past decade, largely in the author s laboratory. Because they have shown a tremendous potential for a number of important applications in separation and purification, they are discussed separately in Chapter 8. This chapter also presents their applications for olefin/paraffin separations, olefin purification (by removal of dienes to <1 ppm, separation of CO, as well as aromatics from aliphatics. The particularly promising application of 7r-complexation sorbents for sulfur removal from transportation fuels (gasoline, diesel, and jet fuels) is discussed in Chapter 10. 

As one very striking example of the capabilities of the high-temperature gradient HPLC system, the separation of random ethyleneA inyl acetate copolymers is presented in Fig. 23. On silica gel as the stationary phase and using decaline-cyclo-hexanone as the eluent, full separation of copolymers of different compositions was achieved. In addition, the homopolymers PE and PVAc were well separated from the copolymers. This was the first time that a chromatographic system was available that separates olefin copolymers irrespective of crystallinity and solubiUty over the entire range of compositions. Namely, the mobile phase components used are solvents for both PE and PVAc. The non-polar solvent, decalin, supports adsorption of PVAc on the silica gel, while the polar solvent, cyclohexanone, enables desorption and elution of the adsorbed polymer sample firom the column [155]. 

Olefins bind preferentially to silver ions. Supercritical fluid chromatography with silver-impregnated columns has therefore been employed to separate olefins from saturates and aromatics in the same sample [85]. Once the olefins have been isolated, they can be analyzed by conventional GC-MS to determine the distribution of various carbon numbers and isomers. In the analysis, the aromatics, olefins, and saturates are resolved by SEC as three separate peaks. With careful switching between the two SEC columns to elute one fraction at a time through the septum into an unmodified GC-MS injection port, the fraction is trapped cryogenically on the GC column head. The trapped fraction is analyzed by GC-MS prior to subsequent fractions being introduced onto the injector [86]. Figure 14 shows the GC-MS profiles of the three different SEC fractions. All analyses were performed on one 10- xl injection and data taken into the same data file with all three instruments under the control of the MS data station. 

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