Estimation of Selectivity on Nickel Dithiolene in Olefin Separation
Advancing the chemical engineering fundamentals
Thermodynamics (T2-1P)
Keywords: Olefins, Nickel dithiolene, Selectivity
The transition metal dithiolene complex can reversibly and selectively react with simple aliphatic olefins under mild conditions, without being poisoned by many impurities such as hydrogen, carbon monoxide, acetylene, hydrogen sulfide, and so forth. On account of the specific structures of olefin complexes may make influences on this reaction, a theoretical estimation of the olefin-structure-induced effects is performed by means of density functional theory in the present work. The reactions of nickel dithiolene with olefins of ethylene, propylene, 1-butylene, 2-trans-butylene, 2-cis-butylene, 1-hexene, 3-trans-hexene and 3-cis-hexene are considered.
The complete optimizations of all stagnation points and corresponding frequency calculations are performed for all reactions. It is shown that the reaction of complexing nickel dithiolene with olefin is a two-step process, and the first step is the rate-determining step because the activation energy of the first step is greater than that of the second step. Most of the bond lengths of the transition states, intermediates and products will become longer, while most of the bond angles will become smaller, as the number of carbon atoms in olefins increases. Moreover, the activation energies of the first and second step will increase, and the reaction rates will decrease with increasing the number of carbon atoms in olefins, while the equilibrium constant will rapidly decrease from 12.12 to 0.0007. It is demonstrated that the reaction between the nickel dithiolene and olefins is sensitive to the number of carbon atoms in olefins. Olefins with more carbon atoms will block the reaction, and decrease the production rate. This is beneficial to separate the olefins with less carbon atoms, e.g. ethylene and propylene, from those with relatively more carbon atoms. Notably, in case of olefins with trans- and cis-structures, the reaction between nickel dithiolene and trans-structure olefin will be much easier and faster to occur than cis-structure olefin will be. This work may be of some significance for estimating the reaction rate and production rate in olefin separation.
Presented Monday 17, 13:30 to 15:00, in session Thermodynamics (T2-1P).
