Development of Eco-friendly, Low-energy Organic Solvent Separation Membranes

KAIST Research Team, No Need for Heat or Large-Scale Plants

When separating mixed chemical substances during petroleum and pharmaceutical production, distillation methods that utilize differences in boiling points are typically used. However, these methods require a lot of energy, emit carbon dioxide, and necessitate large-scale plants. A domestic research team has developed an ultra-high-performance nanomembrane for organic solvent purification that can create a highly efficient separation process without consuming energy.

KAIST (Korea Advanced Institute of Science and Technology, President Kwang Hyung Lee) announced on the 3rd that Professor Min-Ki Choi’s research team from the Department of Bio and Chemical Engineering developed a two-dimensional porous carbon-based ultra-high-performance nanofiltration membrane for organic solvent purification.

Figure 1. Schematic diagram of bottom-up fabrication of two-dimensional microporous carbon using zeolite.

Image source: Provided by KAIST

Unlike distillation, membrane separation technology enables selective permeation simply by applying pressure and can effectively remove particles larger than organic solvents. In particular, since heat is not applied, it can reduce the energy and costs required in the process and eliminate the risk of chemical alteration of high-value-added products during heating.

To develop a high-performance membrane, the research team synthesized a two-dimensional micro-porous carbon material and developed a technology to manufacture it into a membrane. Graphene, a representative two-dimensional carbon material, is thin, stable, and mechanically strong, making it an ideal membrane material. However, due to its densely packed carbon atoms, it does not allow any substances to pass through. Attempts have been made to create additional pores for membrane use, but there remain technical challenges in drilling uniformly sized micro-pores at high density.

The research team synthesized a two-dimensional micro-porous carbon material for membranes by using zeolite, a crystalline aluminosilicate material with micro-pores smaller than 2 nanometers (nm), as a template. Most zeolites have a three-dimensional interconnected micro-pore structure, but some have a two-dimensional pore connectivity structure, which particularly provides enough space for continuous carbon frameworks to grow.

Figure 2. Schematic diagram of organic solvent nanofiltration using a two-dimensional micro-porous carbon separation membrane.

Image courtesy of KAIST

The team succeeded in synthesizing a plate-shaped two-dimensional carbon material by filling carbon inside the zeolite with this two-dimensional pore connectivity structure and then selectively dissolving only the zeolite. The synthesized carbon has a skeletal structure that replicates the micro-pore structure of the original zeolite, with extremely uniform-sized micro-pores densely arranged in a honeycomb pattern. The pore density is tens of times higher than that of previously reported porous graphene.

The researchers stacked the synthesized two-dimensional carbon sheets to produce a thin membrane. When applied to organic solvent nanofiltration, the membrane effectively filtered out organic solutes larger than the carbon sheet pores while allowing smaller organic solvents to pass freely, resulting in high-purity organic solvents. In particular, due to the high pore density, this membrane exhibited dramatically higher organic solvent permeability compared to existing membranes, making it highly suitable for large-scale organic solvent purification.

Professor Choi, who led the research, said, "The synthesis method of two-dimensional porous carbon with ultra-high-density, extremely uniform-sized micro-pores is a new concept that has never been reported worldwide," adding, "It is expected to be applicable not only to membranes but also to various fields such as electrochemical energy storage devices like batteries and capacitors, as well as chemical sensors."

The research results were published on February 10 in the international journal Science Advances (paper title: Bottom-up synthesis of two-dimensional carbon with vertically aligned ordered micropores for ultrafast nanofiltration).

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