Organic Solvent nanofiltration (OSN) or Solvent Resistance Nanofiltration (SRNF) is a vivid emerging field in membrane technology. It offers the process chemist an a-thermal separation tool, alternative to energy-intensive distillation, evaporation or other classical separation methods.

The first win: catalyst recovery using OSN membranes

Homogeneous organometallic catalysis has evolved into being a mature technique. It is often an indispensable and reliable method to synthesize molecular entities produced by pharmaceutical and fine-chemical industries. Although efficient, these catalyst complexes can be expensive and difficult to remove after reaction.

Therefore, in industrial applications emphasis is placed upon increasing catalyst turnover numbers (TON) and catalyst recovery. Strategies to increase catalyst TON are often based either on increasing their stability or reaction rate. Another strategy is to develop catalyst recycling methods since resource recovery is seen as one of the key elements of sustainable chemistry.

In recent years there has been an increasing industrial interest in solvent based separations using membranes which are stable to organic solvents, due in part to the non-thermal, hence mild and energy efficient nature of the technique. OSN membrane technology is seen as a technical and economically viable solution for recovery of precious metals from a solution.

One step beyond: Continuous processing by combining tailored catalysts with tailored membranes

By increasing the TON of a catalyst using optimized catalyst designs coupled to tailored membrane technology one can go one step further. VITOs patented FunMem® technology allows for a functional membrane surface, opening up the possibility of designing the membrane surface and the catalyst ligands to achieve the desired rejection profile and reaction performance.

Moreover, the functional groups at the surface of the membrane reduce the fouling behavior of the membrane, hence high and constant fluxes can be maintained throughout the reaction. These high and constant fluxes are necessary to evolve from batch reactions to continuous flow reactions.

By judicious choice of the N-heterocyclic carbene Pd complexes we have been able to successfully carry out continuous-flow synthesis methodologies and applied these in a continuous synthesis-separation process (in-line). In this process the membrane retains the catalyst in such efficient way that the catalyst is recycled into the model Suzuki cross-coupling reaction used to demonstrate the principle, resulting in significantly enhanced catalyst TON’s.

Read the full research paper

'Synthesis of Pd Complexes Containing Tailed NHC Ligands and Their Use in a Semicontinuous Membrane-Assisted Suzuki Cross-Coupling Process'.

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