Removal of Dienes from Olefins

For purification, the undesired component or impurity is present at a low concentration or partial pressure. It is important that a significant amount of the 

The purification of 1-hexene by removal of 1,5-hexadiene by AgY was also tested by vapor phase adsorption isotherms. The data in Fignre 8.14. show the good capacity of the w-complexation sorbent for the removal of hexadiene at low concentrations. 

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Removal of dienes from olefins (to oxides TT-complexation sorbents such as Cu(I)Y,... 

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 ... 

CH3 storage H3 storage N3/CH3 separation CO3 adsorption CO removal from (to <10 ppm) NO removal Removal of dienes from olefins (to <1 ppm) Super-activated carbon and activated carbon fibers Carbon nanotubes Clinoptilolite, Sr-ETS-4 MCM-41-polyethylenimine composite 7t-Complexation sorbents such as CuCl/y-Al O, CuY, and AgY Fe-Mn-li oxides, Fe-Mn-Zr oxides, Cu-Mn oxides tc-Complexation sorbents such as Cu(I) and AgY... 

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). 

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 stated above, olefin metathesis is in principle reversible, because all steps of the catalytic cycle are reversible. In preparatively useful transformations, the equilibrium is shifted to one side. This is most commonly achieved by removal of a volatile alkene, mostly ethene, from the reaction mixture. An obvious and well-established way to classify olefin metathesis reactions is depicted in Scheme 2. Depending on the structure of the olefin, metathesis may occur either inter- or intramolecularly. Intermolecular metathesis of two alkenes is called cross metathesis (CM) (if the two alkenes are identical, as in the case of the Phillips triolefin process, the term self metathesis is sometimes used). The intermolecular metathesis of an a,co-diene leads to polymeric structures and ethene this mode of metathesis is called acyclic diene metathesis (ADMET). Intramolecular metathesis of these substrates gives cycloalkenes and ethene (ring-closing metathesis, RCM) the reverse reaction is the cleavage of a cyclo-... 

The stream from the cryogenic unit which is rich in C /C-olefins can be fractionated and selectively hydrogenated (to remov traces of dienes) to yield the pure olefins. Common uses of propene are the production of polypropylene, acrylonitrile, cumene etc. Butene can be catalytically dehydrogenated to butadiene which is used in the production of synthetic rubbers. 

Hydroformylation of Other Lower Olefins and Dienes - Lower olefins such as 1-butene or 1,3-butadiene are hydroformylated with acceptable rates using Rh/tppts catalysts according to the RCH/RP process. Hoechst AG Werk Ruhrchemie has developed an attractive new process350 for the hydroformylation of raffinate II, a mixture of 1-butene, cis- and /rbutane derived from the C4 stream of naphtha crackers (after removal of 1,3-butadiene... 

Removal of 1,3-butadiene by selective hydrogenation from industrial olefin feedstocks before hydroformylation or polymerization is an important process in preventing catalyst deactivation. Amorphous Cu70Zr3o exhibits an excellent ability to do this (152). At 348 K a mixture of butenes containing 3% 1,3-butadiene could be converted to a diene-free product with only 1.63% butane. This catalyst also hydrogenates 1,3-butadiene in ethene with a selectivity of 95% with no hydrogenation of ethene. 

Olefins lower than C5 or C6 are removed by means of a stabilization column. The other two columns are then used to separate the C6-C9, C10-Ci3 cuts at the top and Cj4-Cis cut at the bottom. The olefins produced are not as pure as those resulting from the oligomerization of ethylene. They contain small amounts of dienes and cyclic compounds. 

Dienes can undergo olefin metathesis reactions of two types (i) intermolecular, and (ii) intramolecular, as illustrated by the reactions of hexa-1,5-diene and octa-1,7-diene, respectively, eqns. (1) and (2). If necessary, reaction can be driven from left to right by the removal of ethene. 

The (S)-lactone acid 1, obtained from L-glutamic acid by nitrous acid deamination, was converted to the acid chloride, then treated with excess diazomethane followed by hydrogen iodide to yield the keto-lactone 2. Amidation occurred quantitatively to give the partially racemized amide 3, which was purified by repeated recrystallizations. The vicinal diol resulting from reaction with excess methylmagnesium iodide was protected as the acetonide 4. An isomeric mixture of olefins (Z , 26 74) was obtained from the subsequent Wittig reaction. Reduction followed by separation on silver nitrate coated silica gel gave the (Z)-and ( )-alcohols in 20% (6) and 61% (5) yield, respectively. Conversion of the (S)-( )-alcohol (5) to the chloride then afforded the thioether (7) on reaction with sodium phenylsulfide. The thio ether anion was formed by treatment with n-butyllithium. Alkylation with the allylic chloride" (8), followed by removal of sulfur, then yielded the diene 9, which was converted in several steps to (/ ) (-t-)-10,11 -epoxy famesol. 

Based on the empirical results/ X-ray-diffraction data/ and solution-phase NMR experiments/ a transition state model (6) has been advanced to explain the observed enantioselectivity. The presence of an ortho substituent in the A arylmaleimide reactant directs aluminum coordination to occur with the lone pair of electrons anti to the nitrogen atom. A 3,5-dimethylphenyl moiety present on the ethylenediamine framework blocks one face of the dienophile, resulting in approach of the diene from the backside. A considerable amount of spectroscopic evidence, most notably that obtained fromNOE (nuclear Overhauser effect) experiments, has been accumulated to support this model. A -arylmaleimide derivatives that lack an ortho substituent and other dienophiles (e.g., maleic anhydride) can coordinate to the aluminum catalyst in alternative modes such that the reactive olefin is far removed from the chiral environment of the ligand scaffold, thereby resulting in cycloaddition reactions that exhibit little or no enantioselectivity. 

In the early studies of nonenantioselective hydrogenation it has been found that b/s-monophosphine Ir complexes give stable trans-solvate dihydrides 1 upon removal of the coordinated diene from a precatalyst. These solvate dihydrides were found to be capable of exchanging one or two of their solvent molecules for olefins yielding dihydride olefin complexes 2 or 3, respectively which were characterized at -80°C, Equation 1.1.354,355... 

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