ormic acid (FA) and acetic acid (AA), as the simplest organic acids, are pivotal platform chemicals. Distillation-based water/acid separation requires large energy expenditure, thus leading to a significant carbon footprint. Separation using membranes is identified to be a low-carbon technology.
Metal-organic frameworks (MOFs) bring tremendous opportunities for membrane separation. The MIL-53 material derived from the aluminum-based carboxylic acid coordination unit is a typical high-stability MOF material. However, the preparation of highly compact MIL-53 membranes for acid/water separation is still a challenging issue.
The researchers reported a continuous layer of ZnAl-CO3 Layered Double Hydroxide (LDH) nanoflakes on an alumina support as a template triggered a chemical self-conversion to a MOF membrane [MIL-53 (Al)], with approximately 8 hexagonal lattices (LDH) traded for 1 orthorhombic lattice (MIL-53) according to two-dimensional topologic simulation.
The MIL-53 membrane can realize nearly complete dewatering from formic acid and acetic acid solutions, respectively, and maintain stability in a continuous pervaporation over 200 h. Noteworthily, MIL-53 membranes enable a complete separation of water from its azeotropic acid (~70/30 FA/water), with the water content reaching 98.5% in the permeant.  This is the first success in directly applying a pure MOF membrane to such a corrosive chemical environment (lowest pH value of 0.81). The energy consumption is saved by up to 77% when compared with traditional distillation.
This work was supported by the National Natural Science Foundation of China and Youth Innovation Promotion Association of Chinese Academy of Science.

The article links:https://onlinelibrary.wiley.com/doi/10.1002/anie.202302181