A significant amount of the light olefins produced during the refining of crude oil is used as refinery fuel. As natural gas supplies in North America decline, the need to conserve and recover these olefins will become critical. Cost-effective separation technologies will be required that can withstand the harsh operating environment of a petroleum refinery. In addition to traditional refinery and olefin plant applications, paraffin dehydrogenation units for the production of olefins from natural gas liquids (NGL) have recently been brought on stream. Recent federal regulations mandate that hydrocarbon emissions from refineries and chemical plants be reduced to low levels. To reduce the economic penalty of environmental compliance, low-cost hydrocarbon separation technologies are required. For streams containing a mixture of paraffinic and olefinic material, economic and process considerations may dictate that the olefin be recovered and recycled. A review of traditional and nontraditional technologies for the separation of light olefins and paraffins is presented. The technologies addressed range from conventional low-temperature distillation to chemical complexation using copper and silver ions.

Olefin/paraffin separation technology: a review

Weak attractive interactions between closed shell metal ions have been increasingly studied in the last few years and are generally designated as metallophilic interactions. They are best evidenced in the solid state where structural data obtained by X-ray diffraction provide precise information about the distance between the metals involved. The strength of such metal–metal interactions has been compared to that of hydrogen bonding (ca. 7–11 kcal mol−1) and is clearly sufficient to bring about novel bonding and structural features and confer interesting physical properties such as luminescence, polychromism, magnetism or one-dimensional electrical conductivity. The Cu(I)–Cu(I), Ag(I)–Ag(I) and Au(I)–Au(I) interactions have been increasingly observed and the latter have certainly been the most studied. Early qualitative analyses of the aurophilic attraction focused on Au–Au bonding originating from 6s, 6p and 5d orbital mixing. Numerous theoretical studies on metallophilic interactions continue to be carried out at various levels of sophistication which take into account relativistic and correlation effects to describe these van der Waals-type interactions. In this critical review, we would like to focus on the synthesis and structures of heterometallic clusters of the transition metals in which intra- rather than intermolecular d10–d10 interactions are at work, in order to limit the role of packing effects. We wish to provide the reader with a comparative overview of the metal core structures resulting from or favoring metallophilic interactions but do not intend to provide a comprehensive coverage of the literature. We will first examine heterometallic clusters displaying homometallic and then heterometallic d10–d10 interactions. Although the focus of this review is on d10–d10 interactions involving metals from the group 11, we shall also briefly examine for comparison some complexes displaying intramolecular d10–d10 interactions involving metals from other groups (188 references).

/pdf/intramolecular-d10-d10-interactions-in-heterometallic-581tky0doc.pdf

Intramolecular d10–d10 interactions in heterometallic clusters of the transition metals

The Transition Metal Coordination Chemistry of Hemilabile Ligands

Monolayer dispersed AgNO3 on silica gel was prepared by thermal dispersion. This sorbent exhibited superior adsorption properties for olefin/parafin separations by selective adsorption of olefins through π-complexation. This sorbent, along with Ag+ ion-exchanged resin, was subjected to simulation studies for olefin/parafin separations by pressure-swing adsorption. Kinetic separations (due to differences in olefin/parafin diffusivities) using zeolite 4A and molecular-sieve carbon were also studied, Using 50/50 mixtures of C2 H4/C2 H6 and C3H6/C3H8, separations using these sorbents were compared directly based on olefin product purity, recoveiy, and throughput. The monolayer AgNO3/SiO2 sorbent showed superior separation results for C3H4/C3H8, and the Ag+-exchanged resin showed best results for C2H4/C2H6. In both cases, over 99% product purities could be obtained at reasonably high recoveries and throughputs. For C3H6/C3H6 separation on AgNO3/SiO2, multiplicity of cyclic steady states were observed within certain regions of feed and purge velocities. within these regions, two stable cyclic steady states were reached starting ffom different initial-bed conditions while all operating conditions were identical.

/pdf/olefin-paraffin-separations-by-adsorption-p-complexation-vs-247phrw7s7.pdf

Olefin/paraffin separations by adsorption: π-Complexation vs. kinetic separation

New adsorbents for olefin paraffin separation are synthesized by effective dispersion of Ag(I) and Cu(I) cations on substrates with hydrocarbon-phobic surfaces. These cations bind olefin molecules by a {pi}-complexation bond, a weak chemical bond. Ethane/ethylene and propane/propylene separations are considered. Cation exchange resins and CuCl/{gamma}-Al{sub 2}O{sub 3} are effective substrates. On the Ag(I) resin at 25 C and 1 atm, the equilibrium adsorption ratio for C{sub 2} H{sub 4}/C{sub 2}H{sub 6} = 9.2 and C{sub 2}H{sub 4} capacity = 1.15 mmol/g; the corresponding values for C{sub 3}H{sub 6}/C{sub 3}H{sub 8} = 10.4 and C{sub 3}H{sub 6} capacity = 1.29 mmol/g. The CuCl/{gamma}-Al{sub 2}O{sub 3} sorbent shows equally promising results. The sorption rates are pore-diffusion-controlled and rapid. The olefin selectivity, capacity, and rates are much higher than all previous attempts and are suitable for applications in cyclic adsorption processes. The equilibrium data are correlated with an isotherm equation that accounts for both physical adsorption and {pi}-complexation with energy, heterogeneity, using only two true fitting parameters. Molecular orbital calculations using a C{sub 6}H{sub 5}SO{sub 3}{sup {minus}} substrate indicate that the {pi}-complexation bond is contributed mainly by the donation of olefin {pi}-bond electrons to the empty s-orbital of the metal, while the d-{pi}*more » back donation contributes only 16%. Moreover, the relative order of the heats of adsorption is correctly predicted.« less

New sorbents for olefin/paraffin separations by adsorption via π ‐complexation

Separation d'olefines en C 2 -C 5 , de paraffines possedant le meme nombre de carbones et d'α-olefines lineaires, d'olefines internes et ramifiees possedant le meme nombre de carbones. Importance de la force complexante du solvant (α-methyl styrene) lors de la decomplexation. Effet de l'encombrement sterique de la double liaison de l'olefine

Olefin separations via complexation with cuprous diketonate

Depending on the nature of the ligands and the reaction conditions, phosphine substituted copper(I) halides (L"CuX) can react with Fe(CO)a′ to form either trinuclear CuzFe derivatives or the novel lO-atom Cu6Fe4(CO)f5 Cluster anion.

Mixed copper/iron clusters. The preparation and structures of [(Ph3P)2Cu]2Fe(CO)4 and [(diphos)2Cu]2Cu6Fe4(CO)16

Bimetallic complexes containing copper. The crystal structures of (tmed)CuMo(CO)3(.eta.5-C5H5) and [(C6H5)3P]3CuV(CO)6

Cristallisation dans le groupe C2/c avec a=20,630, b=5,004 et c=13,410 A, β=97,42°, Z=8. Affinement jusqu'a R=0,045. Coordination tetraedrique autour des atomes Cu. La structure generale consiste en chaines infinies de cycles a 8 chainons joints par des gorupes de trois atomes Cu−O−S

Preparation of copper(I) carbonyl complexes derived from sulfonic acids. Crystal structure of carbonylcopper ethanesulfonate (Cu(CO)C2H5SO3)

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Olefin separations via complexation with cuprous diketonate

Mixed copper/iron clusters. The preparation and structures of [(Ph3P)2Cu]2Fe(CO)4 and [(diphos)2Cu]2Cu6Fe4(CO)16

Mixed copper/iron clusters. The preparation and structures of [(Ph3P)2Cu]2Fe(CO)4 and [(diphos)2Cu]2Cu6Fe4(CO)16

Bimetallic complexes containing copper. The crystal structures of (tmed)CuMo(CO)3(.eta.5-C5H5) and [(C6H5)3P]3CuV(CO)6

Preparation of copper(I) carbonyl complexes derived from sulfonic acids. Crystal structure of carbonylcopper ethanesulfonate (Cu(CO)C2H5SO3)