Purification, olefin-diene

Pressure injection bismuth nanowires, 175-177 experimental setup, 174 nanowire fabrication, 173-177 template requirements, 175 Washburn equation, 174-175 Pressure swing adsorption, adsorption, 80 Protein microtube-mediated synthesis, nanostructured materials, 15-16 Purification, olefin-diene, 117... 

D. Olefin-Diene Separation and Purification, Aromatic and Aliphatics Separation, and Acetylene Separation... 

A series of conjugated polyenes capped with chromophores and containing an androstane spacer were synthesized by Wittig or Wittig-type olefinations from epi-androsterone 5150. For example, vinyl carboxaldehyde 52, prepared from 51 in 60% yield as shown in equation 32, was treated with 9-anthrylmethylphosphonium bromide and n-butyllithium to give diene 53. Exocyclic diene 53 was subsequently oxidized to vinyl carboxaldehyde 54. The androsterone vinyl aldehyde intermediate could either be treated with a tetraphenylporphyrinpolyenyl phosphonium ylide, or, as shown below, the phosphonium salt of the androsterone (55) could be reacted with TPP polyeneal 56. The desired all-(E) isomer, 57, was obtained from the ( )/(Z)-isomeric mixture by chromatographic purification. 

Sorbents and separations based on 7r-complexation have also found use in other possible applications. Ag+ ion-exchanged X or Y zeolites showed an excellent capability for purification of olefins by removing trace amounts of corresponding dienes. This has been demonstrated for the butadiene/butene system (Padin, Yang, and Munson, 1999). 

Based on the principles of n-complexation, we have already developed a number of new sorbents for a number of applications. These include sorbents for (a) olefin/paraffin separations [9-12], (b) diene/olefin separation or purification (i.e., removal of trace amounts of dienes from olefins) [13], and (c) aromatics/aliphatics separation and purification (i.e., removal of trace amounts of aromatics from aliphatics [14]. Throughout this work, we have used molecular orbital calculations to obtain a basic understanding for the bonding between the sorbates and sorbent surfaces, and further, to develop a methodology for predicting and designing n-complexation sorbents for targeted molecules (e.g. Ref 11). 

Isobutane and light olefins are the desired hydrocarbon feeds. Unfortunately, impurities such as acetylenes, dienes, sulfur- and oxygen-containing hydrocarbons, cyclopentene, and water are also often present. Purification of the feeds is expensive, but is sometimes cost-effective as a means of reducing the buildup in the acids of conjunct polymers. Dry hydrocarbon feeds are preferred, especially with HE. The water transfers to the HE and is a concern relative to metal corrosion. Solid adsorbents are often used for drying of feedstocks. 

For the reasons above, the w-complexation sorbents hold a tremendous potential for future applications in purification, some of which will be inclnded for discnssion. The removal of dienes from olefins by AgY and CuY has already been demonstrated and applied in the field (Padin et al., 2001). Other promising applications inclnde ... 

Sorbents based on TT-complexation for olefin purification have been developed recently in the author s laboratory (Padin et al., 1999 Jayaraman et al., 2001 Padin et al., 2001 Takahashi et al., 2001a and 2001b). AgY and Cu(l)Y are the best sorbents. Although only vapor phase isotherms are reported in the literature cited above, these sorbents have been demonstrated successfully for the liquid-phase feeds in the field. Diene impurities below 1 ppm can be readily achieved. The isotherms are shown in Figures 8.12 and 8.13, for 1,3-butadiene and 1-butene. 

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. 

The removal of acetylenes and dienes from steam-cracked olefins is a critical step in purification. Selective hydrogenation processes and catalysts have become more important as worldwide olefin production has increased in 1999 to more than 90 million tormes of ethylene and almost 50 million tonnes of propylene. Demand for better catalysts with improved selectivity and longer operating cycles has grown as larger plants are built. Tighter product specifications have also been imposed now that more of the olefins produced are being converted to polyolefins. 

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