Isopropyl alcohol (IPA) is a key industrial solvent for the pharmaceuticals, electronics and fine chemicals sectors, among other uses, but methods for making IPA leave water-alcohol mixtures that need to be separated to achieve the purities required for industrial use. A team of researchers from KU Leuven (Belgium; www.kuleuven.be) and the University of Bath (U.K.; www.bath.ac.uk) was investigating lower-energy, lower-cost methods for effecting the separation of water from IPA and hit upon a graphite-based pervaporation membrane that accomplishes the task.
The membrane combines graphite oxide sheets with different characteristics to create an internal structure that allows water to pass while blocking bulkier molecules. “The main challenge is to design a structure where the channels are not too small, which would slow down the separation and require more energy, but also not too large, which would reduce the purity of the final product,” explains Lei Jiang, a researcher at KU Leuven. The new membrane combines both efficient and high-quality separation in a single structure, taking advantage of specific graphite properties to selectively transport water.
Source: KU Leuven/Bath
To construct the engineered nanoporous graphene oxide (GO) membranes, known as N-GOm, researchers co-assembled nanoporous graphene oxide (NPGO) and GO nanosheets. An interesting aspect of the membrane and one that is crucial to its function is that the NPGO is rich in hydrophilic sp3 carbon regions, while the GO nanosheets are rich in hydrophobic sp2 carbon domains.
The different sp2 – and sp3 -hybridized regions act cooperatively to form cavities in the membrane, as well as disordered stacking. “The sp3 domains induce water adsorption, while sp2 domains maintain alignment and mechanical rigidity” the researchers say. “This synergy enables a balanced structure with enhanced permeability and transport efficiency, essential for high-performance separation applications.” The complementary structural properties enable rapid and highly selective transport via densely packed sieving channels and interconnected internal pathways.
The new membrane efficiently removes water from a mixture containing 90% isopropanol and 10% water, explains Pengrui Jin, a leading investigator on the study, adding that the process is faster than existing techniques and requires less energy, because it doesn’t rely on heating. The thermal crosslinking rN-GOm membrane achieves a flux of 18.4 kg\·m–2·h–1, highlighting the potential for industrial solvent dehydration, the researchers say.
Details of the research were published in a recent issue of Nature Communications.