Researchers are finding unusual ways to cut the production cost for ethylene, the raw material for polyethylene.
Cracking naphtha from crude oil is an important ethylene production route. However, this reaction also makes ethane at levels of about 6 to 10 percent of the output. Separating the two petrochemicals is necessary before the ethylene can be used to make PE. Normally, this separation is energy intensive as it involves cryogenic distillation at about -100° C.
A research team based in the University of Texas at San Antonio has developed a technique that separates ethylene from ethane at a fraction of the energy cost normally used in cryogenic distillation.
UTSA professor Banglin Chen and colleagues found a way to trap ethane from the mixture to yield a stream of 99.99 percent pure ethylene.
In their paper recently published in Science the researchers say the separation "is an important, challenging and energy-intensive process."
The team used a microporous framework of a metal-organic compound to adsorb the ethane. Earlier research with this approach involved adsorbing the ethylene onto the compound but this requires an extra step to desorb ethylene from the metal-organic framework. With the new technique that extra desorption step can be avoided because the ethane is "pinned down" by the MOF while purified ethylene passes through the MOF bed. Next, the ethane is desorbed from the MOF bed which is then ready for another cycle. The new method requires about 40 percent less energy than the previous desorption technique.
"Without the fundamental understanding of the mechanism, no one would believe our results," Chen said in a telephone interview with Plastics News.
Chen and researchers used an iron peroxide organic compound to create the MOF. The ingredients for the compound are readily available.
Chen said it is too early to predict how commercially relevant the discovery is but he is enthusiastic about its potential.
"Certainly it will be useful," Chen told Plastics News.
The cost of raw materials for the MOF is reasonable and the iron-peroxide MOF is relatively stable.
"But it will take time," he added. Researchers would need to scale up the process to commercial scale and the MOF structure could be tweaked for higher efficiency.
An industry expert said his company is actively examining MOFs and other ethylene/ethane separation methods such as selective membranes.
"We support it but there is a long way to go," said Tony Go, chief engineer for ExxonMobil Chemical Co.'s transformational technology platform. Issues such as durability of the MOF in the presence of contaminants need closer scrutiny, Go told Plastics News.
Chen led a team that included UTSA postdoctoral researchers Libo Li and Rui-Biao Lin, and researchers in China, the Netherlands and the U.S. National Institute of Standards and Technology. The research was supported by funding from the Welch Foundation, one of the largest private funding sources for basic chemical research in Texas.