In the chemical and the petrochemical industries, separating molecules in an energy-efficient way is one of the most important challenges. Overall, the separation processes account for around 40% of the energy consumed in the petrochemical industry, and reducing this can help addressing anthropogenic carbon emissions.
One of the most important products in the petrochemical industry is propylene, which is widely used in fibers, foams, plastics etc. Purifying propylene almost always requires separating it from propane. Currently, this is done by cryogenic distillation, where the two gases are liquefied by being cooled to sub-zero temperatures. This gives the propylene-propane separation process a very large energy footprint.
A solution is to use “metal-organic frameworks” (MOF’s). These are porous, crystalline polymers made of metal nodes that are linked together by organic ligands. The pores in their molecular structure allow MOFs to capture molecules so efficiently that they are now prime candidates in carbon-capture research.
In terms of separating molecules, MOF-based membranes are among the highest performers and can carry out the propylene-propane separation at ambient temperature. One MOF called ZIF-8 (zeolitic imidazolium frameworks-8), allows propylene to diffuse through its pores 125 times more efficiently than propane at 30oC, offering high selectivity without the need for sub-zero temperatures.
thumbnail courtesy of phys.org