On a New Mechanism for Separating two Components in a Stationary Flow through Mesopores

Harald Morgner

doi:10.4236/ajac.2011.25070

Abstract

When simulating the behavior of fluids in a stationary flow through mesopores we have observed a phenomenon that may prove useful in some cases as basis for separating fluid components. The scheme works at constant temperature which makes it energy efficient as are other schemes like (molecular) sieves or chromatography. Sieves rely on differences in molecular size and chromatography on different affinity of components to the solid material of the ‘packing’. The scheme presented here may sometimes complement the established techniques in that it is based on a different mechanism. The fluids to be separated can have the same molecular size and the same affinity to solid material they are in contact with. The only requirement for the scheme to work is that the miscibility behavior varies somewhat with pressure or density. From literature it is known that virtually any mixture reacts on strong variations of pressure. Even a mixture that behaves almost ideally at ambient pressure will show slight deviations from ideal miscibility when exposed to extreme pressure. The strong differences in pressure are not created by external means but by exploiting the spontaneous behavior of fluids in mesopores. If the experiment is designed correctly, strong pressure gradients show up in mesopores that are far beyond any gradient that could be established by technical means. Our simulations are carried out for situations where pressure inside the pores varies between a few hundred bar positive pressure and a few hundred bar negative pressure while the pressure in the gas phase outside the pores amounts to ca.170 mbar.

Highlights

It is common knowledge that the vapor of a fluid may condense in mesopores even if the pressure of the gas reservoir is below the saturation pressure at the given temperature
Sieves rely on differences in molecular size and chromatography on different affinity of components to the solid material of the ‘packing’
The fluids to be separated can have the same molecular size and the same affinity to solid material they are in contact with

Summary

Introduction

It is common knowledge that the vapor of a fluid may condense in mesopores even if the pressure of the gas reservoir is below the saturation pressure at the given temperature. The boundary conditions were chosen so as to bring the system into a state pertaining to the curve of states COS( ), i.e. to create a liquid in the pore Such a system is studied experimentally and by simulation with equal pressure in both gas reservoirs. The fluid flows through the system, leaving the structure of the liquid phase in the pore unaffected This stationary state remains stable over a range of pressure differences between both gas reservoirs [5], cf Figure 2. The interesting aspect of the strategy found here is the notion that the two components can well have very similar properties and even mix ideally at ambient pressure Even if both components have identical interaction with the pore wall the separation still takes place. We will see that introducing the skimmer is not detrimental to the separation power of the scheme

Remarks on the Simulation Technique

M grad v

Extending the Range of Parameters Compared to Previous Results

Summary and Outlook