Researchers at King Abdullah University of Science and Technology (KAUST) have developed a process for fabricating polytriazole membranes with 10-nanometer-thin selective layers containing subnanometer channels. The membranes, with their ultrathin tunable selective layers, offer an innovative membrane development solution for energy-efficient crude oil fractionation.

The membranes are also advantageous for their low-carbon footprint properties and suitability to promote the circular carbon economy (CCE). A paper on the work is published in Science.

I've been working on polytriazole membranes for more than twenty years. In this paper, the approach was proposed by Dr. Stefan Chisca, research scientist in our lab. I'm always looking for polymers that can take challenges that are not possible with a very simple membrane.

—Dr. Suzana Nunes, KAUST professor of chemical and environmental science and engineering

Chisca specializes in developing polymers for membrane applications, with a focus on separation processes that involve minimal energy consumption. Before joining KAUST, Nunes led membrane research as the department head of Membranes for Sustainable Energy at Germany's Helmholtz Association.

While most commercially available membranes are built for water environments and room temperature, there's a unique challenge in developing stable membranes for harsher conditions characterized by elevated temperatures and a wide range of organic solvents and pH, such as the case for oil fractionation.

A crucial but highly energy-intensive and costly element common to chemical, pharmaceutical and petrochemical industries is the separation process required to purify solvents and chemicals, regulate solvent exchange, and manage catalysts. The most common separation techniques include distillation, adsorption, evaporation and extraction.

Membrane technology offers a low-carbon footprint alternative that is considered more sustainable. However, these industries find it difficult to replace conventional separation methods because they would need membranes to meet stringent mechanical and thermal stability requirements to prevent rapid physical aging and deterioration.

The environment is rough at temperatures of more than 100 degrees, and what you fractionate could dissolve your membrane.

—Dr. Suzana Nunes

Polytriazole membranes have proven to be better suitable for separating complex non-aqueous mixtures. The team synthesized polytriazole membranes through film casting and non-solvent-induced phase separation, followed by a simple thermal treatment step to induce chemical cross-linking. This converted the polymer into an asymmetric membrane with an ~10-nm selective layer showing excellent solvent permeability and selectivity.

The resulting membranes can enhance the concentration of hydrocarbons with fewer than 10 carbons. These membranes preferentially separate paraffin over aromatic components, making them suitable for integration in hybrid distillation systems for crude oil fractionation.

In order to better understand the membrane and solvent interactions, and also the chemical modification process through thermal treatment, Nunes' team worked with scientists at the KAUST Core Labs to fully characterize the membrane and oil itself. Different spectroscopic and microscopy methods were used to investigate the morphology of the membranes before and after crosslinking and follow the oil fractionation, resulting in the full characterization of properties.

Resources

• Stefan Chisca, Valentina-Elena Musteata, Wen Zhang, Serhii Vasylevskyi, Gheorghe Falca, Edy Abou-Hamad, Abdul-Hamid Emwas, Mustafa Altunkaya, Suzana P. Nunes (2022) “Polytriazole membranes with ultrathin tunable selective layer for crude oil fractionation” Science Vol 376, Issue 6597 pp. 1105-1110 doi: 10.1126/science.abm7686