Development, Integration and Optimization of a Membrane Separation Process to reduce the Energy Demand in Super-Critical-CO2 Extraction-Processes

Introduction

The extraction with supercritical fluids (SCE) as solvents allows the environment- and product-gentle separation of valuable materials for many separation problems. The SCE is successfully used as separation process in the following industries: environmental technology, food technology, polymer chemistry, pharmaceuticals and petrochemicals. Because of its many favorably features carbon dioxide (CO2) is frequently used as a solvent in SCE processes. The critical point of carbon dioxide (31°C, 74 bar) is highly acceptable for natural substances.

In conventional processes the extract is obtained by the expansion from supercritical extraction conditions to subcritical pressures. In this expansion the CO2 loses much of its energy, and therefore it has to be brought back to supercritical extraction conditions for the next cycle by supplying compression work.

The relatively high amount of energy is the reason why this promising separation process has not made the big breakthrough for many application areas yet.

Scope of our Research Work

Therefore, the scope of our research is the development, integration and optimization of a membrane separation process included in the CO2 cycle under supercritical conditions. The idea is not to remove the extracted compound by expansion of the CO2, but by an integrated membrane separation process. As a result, the energy consumption would be significantly reduced and the whole process would be more environmentally friendly and more cost-effective.

Own investigations and the investigations of other groups, however, show that conventional organic polymer membranes are not stable under the conditions of supercritical CO2. Membranes having a ceramic structure, however, are stable under these conditions, according to previous knowledge.

With these investigations, a new field for the membrane technology is opened. Our Pilot-Plant is extended by a membrane separation process for applications of the extraction with supercritical CO2.