Integration of MFI Zeolite Membranes in the Light Gasoline Isomerisation Process

L. Bournay,A. Baudot

doi:10.2516/ogst/2009073

Abstract

Tests aiming at separating normal pentane from a light gasoline isomerate through a MFI zeolite composite membrane were carried out. The performances of this membrane sample were studied as a function of total hydrocarbon pressure upstream of the membrane as well as the temperature. Maximal permeate flux, close to 2 kg/m2.h, was observed at 250°C - 2 bar total hydrocarbon pressure. The normal pentane weight fraction was more than threefold higher in the permeate than in the feed. In a second step, a fully heat-integrated light gasoline isomerisation process loop integrating a MFI zeolite membrane-based separation was simulated and optimised. Integration of MFI zeolite membranes in this process proved to be valuable only if their cost is lower than 1000 EURO/m2.

Highlights

For more than fifteen years regulations have imposed increasingly tight limitations on the content in gasoline of aromatic octane number boosters produced by the reforming of straight-run gasoline
– experimental evaluation of the performances of a MFI zeolite membrane synthesised at IFP: a series of tests was carried out to separate mixtures of paraffins in the vapour phase containing 25% by weight of normal pentane on a laboratory scale on MFI-type zeolite membranes manufactured at IFP
The molecular sieving properties of the zeolite layer are clearly illustrated in the previous figure: the flux of the linear compound was four orders of magnitude greater than that of the branched compound, whereas the driving force inducing the transfer of material across the membrane was half that of normal pentane

Summary

Introduction

For more than fifteen years regulations have imposed increasingly tight limitations on the content in gasoline of aromatic octane number boosters produced by the reforming of straight-run gasoline (alkanes). The more conventional solution consists of fractionating the output stream from the isomerisation reactor through a continuous distillation column (a deisohexaniser or DIH), into three effluents:. – a sidestream, mainly containing unconverted normal hexane and the monobranched paraffins with 6 carbon atoms. This stream is recycled to the isomerisation unit;. – the bottom stream, containing the heaviest alkanes (paraffins) with 7 carbon atoms and naphthenes (cyclic paraffins) with 6 carbon atoms, with a RON of 82, is sent directly to the gasoline pool;

Methods

Results

Conclusion