Acid heterogeneous catalysis in supercritical media : application to isobutane alkylation by light olefins
Sustainable process-product development & green chemistry
SCF as Solvent Substitutes (T1-8P)
Keywords: supercritical, alkylation
Acid heterogeneous catalysis in supercritical media : application to isobutane alkylation by light olefins
Maxime Montillet1, Denis Guillaume1, Nadine Essayem2
1Institut Français du Pétrole-Lyon BP3 69390 -Vernaison- France
2 Institut de Recherche sur la Catalyse, 2Av Albert Einstein 69626 -Villeurbanne- France
Introduction
The specific properties of supercritical fluids near and above the critical point are the subject of intensive researches and developments in separation processes, material synthesis and also for application to chemical reactions. In the case of heterogeneous reactions, supercritical media are expected to improve the extraction of products from the catalytic surface. This is due to their enhanced transfer properties resulting from a high density and diffusivity combined to a low viscosity (Baiker, 1999).
Objectives of the study
This study aims to understand and elucidate the phenomena which promote the reactions in heterogeneous catalysis and to differenciate physical and chemical effects due to the presence of supercritical phase, during the reaction.
The reaction of isobutane alkylation by olefins seems to be well adapted to demonstrate the supercritical fluid contribution in heterogeneous catalysis.
The alkylation process is used in the refining industry to produce gazoline of a high octane number, using highly corrosive and toxic liquid acid catalyst (HF, H2SO4). The replacement by a solid catalyst has not been industrialized up to now. Indeed, rapid deactivation takes place due to heavier products formation. In the literature, earlier studies have reported the enhancement of the catalyst lifetime in supercritical media (Subramaniam, 2000).
Experimentation conditions
Supercritical alkylation was performed with excess isobutane with addition of a solvent. The reaction was carried out in a continuous flow type fixed bed reactor. Liquid reactants and solvent was fed by mean of two HPLC pumps and the supercritical phase was reached within the reactor by tuning the pressure and the temperature. The reaction products were analysed on-line, in gas phase by two GC equipment.
Results
The use of a solvent with low critical temperature (like carbon dioxide or ethane), allowed to perform the reaction at equivalent temperature in supercritical media (with solvent) and in liquid phase (without solvent). Experiments, using butene or propylene as olefin, confirmed the enhanced activity and longevity of the catalyst (β-zeolite) in supercritical media as regard to the liquid phase. However in those conditions, the supercritical media doesn’t seem to have chemical effect (kinetic and mecanism pathway).
References
[1] A.Baiker, Supercritical fluids in heterogeneous catalysis, chem.rev.99 (1999) 453-473.
[2] B.Subramaniam, Enhancing the stability of porous catalysts with supercritical reaction media, Applied catalysis A: General 212 (2000) 199-213.
Presented Monday 17, 13:30 to 15:00, in session SCF as Solvent Substitutes (T1-8P).
