CONTEXT

One of the main advantages of membrane processes compared to other separations is the ability to work under steady conditions, without any separate regeneration step. Nevertheless, unique separation performances can be achieved in some cases when a transient regime is applied under specific cyclic conditions. Nevertheless, since the pioneer study of the cyclic membrane-based process was explored in 1971, it has been shown that this former design of cyclic processes cannot be competitive with respect to classical steady operations due to the unavoidable drawbacks of the recovery ratio and complicated valve operations. Based on a novel design, a dedicated patented cyclic process offers the opportunity to achieve  a competitive recovery ratio while the unique performance on purity is conserved. The design has been validated for gas separations but it can be also applicable for liquid separations

TECHNICAL DESCRIPTION

A classical hollow fiber module is used as the core of the process. 4 or 5 automatic valves are placed around the module in order to control the flow directions. Two options are available according to the operation complexity.  By optimising the valve opening durations and the downstream/upstream volume ratio γ, different production performances can be attained.

BENEFITS

Assuming that a binary mixture {O₂,  CO₂} with α = 6 is separated, two flows’ purities at the outlet between the novel design and classical steady operations (_{– – – –} for cross flow pattern and …… for perfectly stirred pattern) are compared in the left figure. In the case of the sidestream option, the downstream flow is recycled at a composition close to the feed one by chosing judiciously valve opening durations.
The advantage of the novel design is highlighted: both flows at the outlet can be enhanced on their values if the volume ratio γ is large enough. Moreover, the separation efficiency can be further improved by adopting the sidestream option.

INDUSTRIAL APPLICATIONS

This innovation could be very helpful for binary gas separation where both components are valuable. For example, the application for separating rare gases might be of great interest. Furthermore, since the innovation produces a rather pure gas at a high recovery ratio, it can also be used for massive gas production, such as producing oxygen enriched gas from air separation.

DEVELOPMENT STAGE

The design was first validated by simulation and optimization studies. Recently, one experimental validation of the basic option based on air separation by a commercial PPO membrane was performed and gave solid support to the design proposed.

For further information, please contact us (Ref 04593-01)