Selective Absorption of Methane by Ionic Liquids (SAMIL) - Phase 2 Demonstration in a Packed Bed Reactor

An alternative approach to high temperature oxidation of ventilation air methane (VAM) is the separation of VAM from the ventilation air. A separation process allows for the capture of VAM at temperatures significantly less than the autoignition temperature of lean air-methane mixtures. Hence, existing safety concerns with connecting high temperature abatement processes to ventilation systems can be eliminated.  Separation processes investigated in the past included adsorption, absorption and membrane techniques.  This project, which is a continuation of project C27008, focuses on the absorption of methane in ionic liquids using a rotating packed bed reactor. This project was a key step in the transition from the fundamental chemistry investigations already completed in project C27008, to the demonstration of the process in an appropriate reactor.

The primary aim of the project was to demonstrate the absorption of VAM in ionic liquids using a rotating packed bed, focussing on:

• Understanding the influence of operating parameters such as temperature, ionic liquid viscosity, residence time, bed surface area, and rotational speed;
• Determining mass transfer models for the absorption of gas in ionic liquids in rotating packed beds Determining the absorption and desorption rates of methane in ionic liquids;
• Evaluating the performance of ionic liquids and conducting a preliminary feasibility assessment of absorption in packed beds;

To demonstrate the absorption of methane in a rotating packed bed, the following tasks were undertaken:

• Design and construction of a rotating packed bed experimental apparatus for methane absorption.
• An experimental program which investigated the influence of operating parameters such as temperature, ionic liquid viscosity, residence time, bed surface area, and rotational speed on the absorption of methane.
• Calculation of mass transfer rates for the absorption of methane in ionic liquids.
• Desorption experiments to determine the concentration of the absorbed gas.

The key findings for the project were:

• Overall assessment: from a technical standpoint a rotating packed bed is a suitable technology for the absorption of VAM using ionic liquids

• Methane was selectively absorbed from air at low concentrations and low pressures

• Methane absorption increased with increasing reactor volume

• Methane absorption was significantly influenced by the rotating packed bed parameters of packing material and rotational speed

Assessing the applicability of rotating packed beds to large scale VAM abatement requires the process to be undertaken on a continuous absorption/desorption basis. This would allow for the derivation of scaleup rules and an analysis of the levelised cost of abatement to be completed. Comparisons with traditional packed bed reactors operating at similar conditions would be beneficial.