The door opens for inorganic membranes

Inorganic and hybrid membranes get nearer to commercialization

By By C. Kenna Amos,contributing editor

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Some companies certainly see the potential. Chevron, for instance, has been working with Koros since the mid-1990s on membranes for natural gas purification and oth-er uses, notes Steve Miller, senior consulting scientist with Chevron Energy Technology Co., Richmond, Calif. “The membranes we have been investigating have been primar-ily composites of zeolites or carbon molecular sieves within a polymer matrix, where the zeolite or sieve enhances the separation properties of the membrane beyond that of the polymer alone.”

While Miller didn’t reveal when commercialization will begin, he says this is “a promising approach for en-hancing the performance of polymer membranes.” It can help make membrane separation more competitive with alternative technologies for some separations, he believes.

(Polymer membranes are advancing in their own right, too. For example, as CP reported in November, polymer membranes with hour-glass-shaped pores reportedly provide significantly better performance for gas sepa-ration than do conventional membranes. The first industrial trial should occur within five years in Korea for CO2 re-moval from power-plant stack gas.)

Bold action needed

Now squarely on the commercialization path is collabora-tive research by Noble and Falconer. With support from Shell for the past four to five years, they’ve investigated SAPO-34 zeolite membranes to remove carbon dioxide from natural gas. “We have been able to improve produc-tivity — a technical term for permeance, the flux across the membrane divided by the driving force, which is the delta P [pressure] — by a factor of 10, while maintaining the selectivity at or near 100,” Noble says, noting that se-lectivity here means the ratio of CO2 permeance to meth-ane permeance. “That means less membrane is needed,” he adds. And, because of that finding, “Shell has indicated that they’re pursuing commercialization.”

Like Koros’ best guess for zeolite polymerics, Noble reckons it will be three to five years before industrial availability. “This would be the first commercial production and application of a gas-separation zeolite membrane,” he be-lieves. “[It] will make a big splash,” Noble hopes, because current polymeric gas-separation membranes are mature technology. For real progress, he says, “it’s going to have to be the introduction of new materials where the traditional polymeric membranes don’t work… [And] if this becomes commercial, then that gets people’s attention — and that means that economics and science are viable.”

However, getting gas-separation membranes to market will require cost-effective technology as well as indus-trial boldness, Koros suggests. He predicts “tremendous” growth in use of gas-separation membranes if membranes’ selectivity can be enhanced “especially in high-gas-volume areas of natural-gas sweetening and low-purity nitrogen production.” The key, he believes, will be “having people willing to take enough of a step, to say, ‘We’re going to try to ‘use membranes.’”

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