Liquid-phase isobutane alkylation with butenes over aluminum chloride complexes synthesized in situ from activated aluminum and tert-butyl chloride

Abstract

The liquid-phase interaction between isobutane and butenes at 303 K and 2.5–3.0 MPa has been investigated using activated aluminum (Al*)-tert-butyl chloride (TBC) model system (TBC: Al* = 0.35−4 mol/mol). It has been demonstrated by attenuated total reflection FT-IR (ATR-FT-IR) spectroscopy that the catalytically active aluminum chloride complexes forming in situ in the hydrocarbon medium vary in composition. Alkylation as such takes place at equimolar proportions of the reactants (TBC: Al* = 1: 1) and butenes feed 1mass flow rate of 5 h−1 per gram of Al*. According to ATR-FT-IR data, the most abundant aluminum complexes resulting under these conditions are the AlCl4− and Al2Cl7− ions and, probably, the molecular complex AlCl3 · sec-C4H9Cl. In a fourfold excess of TBC over Al* at butenes mass feed rate of 2.5 h−1, isobutane undergoes self-alkylation. In this case, the Al2Cl7− ion is not detected and the most abundant complexes are AlCl4−, Al3Cl10− and the molecular species AlCl3 · tert-C4H9Cl. It is hypothesized that the Al2Cl7− ion plays the key role in the liquid-phase alkylation of isobutane with butenes.