New zeolite separates ethane from ethylene

A NEW zeolite that can separate ethane from ethylene could “significantly” reduce the amount of energy and emissions needed for the ethylene production process.

Pure ethylene is vital for many chemical and plastic manufacturing processes, but it has very similar properties to ethane, making them difficult to separate. Generally, this is achieved using cryogenic distillation, which is energy intensive. Many alternatives so far investigated are not selective enough or too sensitive to contamination. Researchers from ExxonMobil and the Instituto de Tecnologia Quimica (ITQ) in Valencia, Spain, say that using their new zeolite is highly selective and could reduce the energy needed for ethylene and ethane separation by 25%.

The new material, ITQ-55, which has been patented, is based on silica and has what the researchers describe as a unique flexible pore structure. It has very high selectivity for ethylene at ambient temperature. The ‘cages’ within the zeolite framework are heart-shaped and connected by flexible, elongated pore openings. The slightly flatter ethylene molecules are able to diffuse into the pores, while the more cylindrical ethane molecules cannot.

“ITQ-55 is a very interesting material whose unique combination of pore dimension, topology, flexibility and chemical composition results in a highly stable and inert material that is able to adsorb ethylene and filter out ethane,” said ITQ chemistry professor Avelino Corma.

The researchers say that the new material could additionally provide insights into designing other materials which could be used as adsorbents or as membranes for other gas separation processes in chemical manufacturing.

Vijay Swarup, vice president of research and development at ExxonMobil Research and Engineering Company said that the research is “another great example of collaboration between industry and a university that is focused on driving solutions for improving energy efficiency and reducing carbon emissions from industrial processes.”

The collaborative research is part of ongoing efforts by ExxonMobil to improve industrial efficiency and reduce the environmental impact of its operations. Chemical plants currently account for 8% of the world’s energy needs, and this is predicted to rise to 15% by 2040. More research will be necessary to commercialise the technology, including incorporating the zeolite into a membrane and developing other gas separation materials.

“Our ultimate goal of actually replacing cryogenic distillation is a long-term challenge that will require many more years of research and testing, in and out of the lab,” said Gary Casty, section head for catalysis at ExxonMobil Research and Engineering Company. “Our next steps will focus on better understanding the full potential of this new zeolite material.”

Science doi.org/gck9cq