The effect of different promoters on activity and selectivity of Lewis-acidic chloroaluminate ionic liquid catalysts was studied for isobutane/2-butene alkylation. When tert-butyl halides are used as promoters, the active species of the alkylation reaction, which is the tertbutyl cation, is directly generated whereas upon catalysis with Brønsted-acid supported ionic liquids, this species is indirectly provided through a hydride shift between protonated 2-butene and isobutane. Experimental results both from batch and continuously operated liquid phase alkylation reactors indicate, that tert-butyl halides are able to speed up the reaction rate significantly and shift the C 8 -selectivity towards the desired high-octane trimethylpentanes (TMPs). However, secondary reactions like oligomerization and cracking could not be suppressed by the use of this additives and high deactivation rates in continuous opperation were observed. Suggestions are made, how the product composition is effected by the additive and how the promoted IL-catalyst system is deactivated with time on stream.
Acidic ionic liquids (IL) are attractive alternative
catalysts in refinery alkylation of i-paraffins with light olefins,
but the intrinsic kinetics and influence of mass transfer on the effective
kinetics in this biphasic system is still unknown. Solubility measurements
were conducted (largely with neutral, nonacidic ILs) using mixtures
of i-hexane/2-hexene and i-pentane/2-pentene, respectively, to determine
the Nernst partition coefficient and thus the maximum concentration
of olefins and paraffins in the IL. Thereafter, kinetic studies were
carried out both in a stirred and nonstirred batch reactor using i-hexane/1-hexene
and i-pentane/1-pentene. In the static system, the concentration profile
of the particular olefin in the organic phase was measured. The experimental
results are in good agreement with the simulation based on the interplay
of the chemical reaction in the ionic liquid as well as of the external
and internal mass transfer to the interface and into the IL. The effective
reaction rate of alkylation is proportional to the interfacial surface
area between organic and IL phase: The intrinsic chemical reaction
is very fast which leads to a strong mass transfer limitation of the
olefin into the IL phase. Hence, the effectiveness (compared to utilization
of the entire IL phase) is very low, and the alkylation reaction takes
place in a very thin layer with a thickness of only around 5 μm.
Perfluorierte Polymere gehören mit zu den stabilsten organischen Verbindungen, sowohl hinsichtlich der chemischen Resistenz als auch der thermischen Beständigkeit. Aufgrund der Langlebigkeit und der sehr unterschiedlichen Einsatzgebiete von Fluorpolymeren existieren zurzeit keine nachhaltigen Recycling-Konzepte.In
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