Polymer film will promote industrial separation technology upgrade

HC Plastics News: Many promising technologies are currently being developed to reduce energy consumption or to acquire carbon in areas such as biotechnology, computer science, nanotechnology, and materials science. While not everything will prove to be viable, but with a little funding and training, many people can help solve the planet's enormous challenges.

One such solution is emerging from new methods of industrial separation processes. At the Department of Chemical Engineering at the Massachusetts Institute of Technology, Professor Zachary Smith is working on new polymer membranes that can greatly reduce energy use in chemical separations. He is also conducting more in-depth research to improve the performance of nanoscale metal organic frameworks (MOFs) polymer membranes.

JosephRMares (1924) Zachary Smith, Assistant Professor of Chemical Engineering Career Development. Source: DavidSella

“We not only produce and analyze materials based on the fundamentals of transportation, thermodynamics and reactivity, but we have begun to use this knowledge to create models and design new separation performance materials that have never been achieved before,” Smith said. . “Thinking carefully, from the laboratory to mass production and its impact on society, this is exciting.”

Smith often interacts with industry experts who have insights into separation techniques. Although the United States has withdrawn from the Paris Climate Agreement of 2015, the agreement has remained legally effective so far. The chemical and petrochemical industries that Smith is primarily concerned with are beginning to feel the pressure to reduce emissions. Heating and cooling towers for separation require considerable energy and are expensive to construct and maintain, so the industry is also looking for ways to reduce costs.

Smith said that the industrial production process in the chemical and petrochemical industries consumes between one-quarter and one-third of the total US energy, while industrial separation accounts for half of the energy consumption. About half of the separated energy comes from rectification, a process that requires extremely high heat, or in the case of cryogenic distillation, or even more energy-intensive extreme cooling.

“It takes a lot of energy to boil and re-boiling the mixture, and it's less efficient because it requires a phase change,” Smith said. “Membrane separation technology avoids these phase changes and uses less energy. The polymers can be defect-free, and you can cast them to be selective enough to cover a 100-nanometer thick film on a football field.”

However, there are still many difficulties. Membrane separation is only used for a small portion of the industrial gas separation process because polymer membranes are "usually inefficient and do not match the distillation performance," Smith said. “Current membranes do not provide sufficient throughput (called flux) for high volume applications, and their chemical and physical properties are unstable when using more aggressive feed streams.”

Most of these performance problems are caused by the phenomenon that the polymer tends to be amorphous or entropy chaotic. "Polymers are easy to process to form useful geometries, but the distance a molecule can move through a polymer film changes over time," Smith said. “It is difficult to control the free volume inside the porous state.”

The most stringent optional separation size is only a fraction of an angstrom. To meet this challenge, Smith Labs is trying to add nanoscale features and chemical functions to the polymer to achieve finer-grained separation. Smith said, "New materials can 'absorb one molecule and reject another.'"

To create a higher throughput and higher selectivity polymer film, Smith's team is reacting the new polymer and template ordered structure developed by the Massachusetts Institute of Technology laboratory into a traditional disordered amorphous polymer. As he explained, “Then we use a nano-sized pocket for post-synthesis processing to form a diffusion path.”

Although Smith Labs has succeeded in many technologies, the throughput required to achieve high-volume applications remains a challenge. The problem is complicated by the fact that the chemical and petrochemical industries use more than 200 different types of distillation separation processes. However, this is also an advantage. When introducing new technologies, researchers can look for niches instead of trying to change the industry overnight.

"We are looking for the most influential goals," Smith said. “Our membrane technology has a small footprint so you can use them in remote areas or on offshore oil platforms.”

Due to the small size and light weight of the membrane, membranes have been used on the aircraft to separate nitrogen from the air. Nitrogen gas was then used in the oil tank to avoid bursting. In remote natural gas wells, membranes have also been used to remove carbon dioxide and have found suitable locations in some of the larger petrochemical applications, such as hydrogen removal.

Smith's goal is to expand to the equipment of the cryogenic distillation column, which requires huge amounts of energy to produce extreme cooling. In the petrochemical industry, separation of ethylene-ethane, nitrogen-methane and air is included. Many plastic consumer products are made from ethylene, so reducing energy costs in the manufacturing process can bring huge benefits.

“By cryogenic distillation, it is not only necessary to separate molecules of similar size and similar thermodynamic properties,” Smith said. “The height of the distillation column can reach 200 or 300 feet, and the flow rate is very high, so the cost of separation can be as high as several billion dollars. And the energy required for an operating system at -120 degrees Celsius is huge.

Other potential applications for polymer films include "finding other methods to remove carbon dioxide from nitrogen or methane or to separate different types of paraffin or chemical materials," Smith said.

Carbon capture and storage is also a potential application. He said: "If there is an economic driving force for carbon dioxide capture today, then the carbon capture will be the maximum amount of membrane multiplied by 10 times. We can make a sponge-like material that absorbs carbon dioxide and effectively separate it so that Press it and store it underground."

One challenge when using polymeric membranes in gas separation is that the polymers are typically made from hydrocarbons. Smith said: "If your polymer contains the same type of hydrocarbons, the polymer you are trying to separate will swell, dissolve or lose separation. We want to introduce non-hydrocarbon components such as fluorine into the polymer. In order to make the membrane interact better with the hydrocarbon-based mixture."

Smith is also trying to add MOFs (metal organic framework compounds) to polymers. MOFs formed by linking metal ions or metal clusters to an organic linker can not only solve the hydrocarbon problem, but also solve the entropy disorder problem.

"MOFs materials allow you to form one, two, or permanently porous three-dimensional crystal structures," Smith said. “A teaspoon of MOFs has as much internal surface area as a football field, so you can consider the inner surface of functionalized MOFs to selectively bind or reject certain molecules, or you can define the shape and geometry of the holes to allow one molecule to pass. The other was rejected."

Unlike polymers, MOFs generally do not change shape, so pores remain more durable over time. In addition, Smith said: "They do not degrade through the aging process like some polymers. The challenge we face is how to incorporate crystalline materials into processes that can be made into thin films. One approach we are taking is to disperse MOFs as nanoparticles. In the polymer, this allows you to take full advantage of the efficiency and productivity of MOFs while maintaining MOFs."

One potential advantage of introducing MOFs to enhance polymer membranes is process enhancement: bundling different separation or catalytic processes in one step to achieve higher efficiencies. Smith can say: "You can consider combining a MOFs material that separates the gas mixture and allows the mixture to undergo a catalytic reaction at the same time. Some MOFs can also act as crosslinkers, rather than using polymers that are directly crosslinked together. You can disperse Establishing a connection between MOFs particles in the polymer matrix will create more stability for separation."

Due to their porous nature, MOFs may be used to "capture hydrogen, methane, and even in some cases to capture carbon dioxide."

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