Remarkable Progress Made in BIT in the Research of Pervaporation Separation Membrane


Recently, Lihao Xu, a doctoral student in the School of Chemistry and Chemical Engineering, BIT, published a research paper titled "An advanced necklace-like metal organic framework with an ultrahighly continuous structure in the membrane for" in the top international journal Journal of Materials Chemistry A as the first author. "superior butanol/water separation" research paper. Beijing Institute of Technology is the only communication unit, and Professor Zhao Zhiping from the Advanced Functional Membrane and Membrane Process Team of the School of Chemistry and Chemical Engineering is the author of the address book. This research acquired fund from the key project of the National Natural Science Foundation of China (21736001).

The carbon dioxide produced during the production and use of biofuels (ethanol, butanol, etc.) is absorbed by the equivalent amount of biomass growth photosynthesis, which can make the cycle of carbon dioxide. The production process covers three major steps: the hydrolysis of biomass to sugar (reducing sugar and xylose), the fermentation of sugar to alcohol, and the separation of alcohol-water. Among the three steps, the product alcohol of the fermentation step is for yeast (a biological enzyme that converts sugar into alcohol is produced). This activity has an inhibitory effect, which makes the fermentation efficiency low and the production cycle long. Due to this, in recent years, scientists the coupling process of pervaporation (PV) membrane separation and biological fermentation to separate alcohol in real time have been studied so that the fermentation system maintains a lower alcohol concentration, thereby maintaining the biological activity of yeast. Besides, compared with traditional distillation, PV membrane separation can save energy by 35-65%, and the coupling process has obvious effects of high efficiency and energy saving. The key to this process lies in high-performance separation membranes, but traditional polymer PV separation membranes that preferentially permeate organics, their permeation selectivity cannot meet actual needs.

Generally, there is a trade-off effect between membrane permeability and selectivity. During the past years, mixed matrix membranes have attracted attention because of their advantages in combining organic and inorganic materials. The "selective molecular permeation channel" dominated by the filling matrix is one of the important challenges facing the field of separation membrane preparation. On how to make full use of the effectiveness of the nano-hybrid matrix to break the "trade-off" game effect, Professor Zhao Zhiping’s team conducted an in-depth study and put forward a priority for the construction of relatively continuous small molecules with metal organic framework (MOF) materials in membrane Dissolve-permeate channel" solution strategy.



Figure 1. The design principle, preparation, structure and application of "MOF Necklace"

Inspired by the pearl necklace, "MOF Boy" designed and produced a novel "MOF Necklace" as a gift for his loved girl. The team first prepared a polypyrrole nanotube (PPy nanotube) using methyl orange as a template, and then induced ZIF-8 to nucleate and grow on the outer wall of the PPy nanotube, which generated a special "necklace-like" highly continuous MOF structure (ZIF-8 @PPy), ZIF-8 crystal particles crystal plane window holes "butt" to form a relatively continuous molecular channel, PPy nanotube provides a continuous and rapid diffusion channel for guest molecules in the tube while piercing the MOF crystal particles. Furthermore, the researchers introduced this novel "MOF necklace" into polydimethylsiloxane (PDMS) to prepare a high-performance mixed matrix film. Through measuring the free volume of the membrane material, combined with molecular dynamics simulation, the dissolution-diffusion behavior of the five molecular transport channels (Figure 2) of the guest molecules in the membrane was analyzed. Interestingly, the "Small World" formed at the interface of ZIF-8 and PPy nanotube can effectively inhibit the continuous transmission of water molecules without changing the inherent structure of ZIF-8, by which the membrane Permeation selectivity for butanol molecules has been improved.


Figure 2. The built of five molecular selective permeation channels in the membrane and the analysis of the dissolution-diffusion mechanism

The researchers found that the "MOF Necklace" has displayed good dispersibility in the membrane, and the membrane separation performance is better than the PV membrane reported at this stage in the world. This highly continuous "MOF Necklace" provides a new way for the creation of mixed matrix membranes. Besides, the full play of its effectiveness in the membrane also provides the possibility for the industrial preparation of high-performance PV membranes.