There are scores of promising technologies under development that can reduce energy consumption or capture carbon in fields including biotech, computer science, nanotechnology, materials science, and more. Not all will prove feasible, but with a little funding and nurturing, many could help solve the planet’s grand challenge.
One such solution is emerging from new approaches to industrial separation processes. At MIT’s Department of Chemical Engineering, Professor Zachary Smith is working on new polymeric membranes that can greatly reduce energy use in chemical separations. He’s also conducting longer range research into enhancing polymeric membranes with nanoscale metal-organic frameworks (MOFs).
Smith often consults with industry experts who share insights on separations technologies. With the Paris climate agreement of 2015 so far holding together, despite the retreat by the U.S., the chemical and petrochemical industries where Smith is primarily focused is starting to feel the pressure to reduce emissions. The industry is also looking to reduce costs. The heating and cooling towers used for separations require considerable energy, and are expensive to build and maintain.
Industrial processes used in the chemical and petrochemical industries alone consume from a quarter to a third of the total energy in the U.S., and separations account for about half of that, says Smith. About half the energy consumption from separations comes from distillation, a process that requires extreme heat, or in the case of cryogenic distillation, even more energy-hungry extreme cooling.
The most demanding separations require size selectively between molecules of only a fraction of an angstrom. To address this challenge, the Smith Lab is attempting to add nanoscale features and chemical functionality to polymers to achieve finer-grained separations. The new materials can “soak up one type of molecule and reject another,” says Smith.
While the Smith Lab has found success with many of these techniques, achieving the flux required for high-volume applications is still a challenge. The problem is complicated by the fact that there are more than 200 different types of distillation separation processes used by the chemical and petrochemical industry. Yet this can also be an advantage when trying to introduce a new technology — researchers can look for a niche instead of attempting to change the industry overnight.
Due to their small size and weight, membranes are already being used on airplanes to separate nitrogen from air. The nitrogen is then used to coat the fuel tank to avoid explosions like the one that brought down TWA Flight 800 in 1996. Membranes have also been used for carbon dioxide removal at remote natural gas wells, and have found a niche in a few larger petrochemical applications such as hydrogen removal.
Smith aims to expand into applications that typically use cryogenic distillation towers, which require immense energy to produce extreme cold. In the petrochemical industry, these include ethylene-ethane, nitrogen-methane, and air separations. Many plastic consumer products are made of ethylene, so reducing energy costs in fabrication could generate huge benefits.
Other potential applications for polymer membranes include “finding other ways to remove CO2 from nitrogen or methane or separating different types of paraffins or chemical feedstocks,” says Smith.
Smith is also experimenting with adding MOFs to polymers. MOFs, which are formed by linking together a metal ions or metal clusters with an organic linker, may not only solve the hydrocarbon problem, but the entropic disorder issue as well.
A similar application for MOFs would be storing hydrogen or natural gas for fueling a car. “Using a porous material in your fuel tank would let you hold more hydrogen or methane,” says Smith.
Smith cautions that MOF research could take decades before it achieves fruition. His lab’s polymer research, however, is much further along, with commercial solutions expected in the next five to 10 years.
“It could be a real game changer,” he says.