May 2014 Labnotes

NETL-Boston Scientific Coronary Stent Alloy Applications Expand

One of Boston-Scientific Corporation’s coronary stents deployed in a tube representing the blood vessel. One of Boston-Scientific Corporation’s coronary stents deployed in a tube representing the blood vessel.

A coronary stent is a small, self-expanding metal mesh tube that is surgically implanted in heart disease patients to open narrowed arteries and allow blood to flow freely. In 2010, Boston Scientific Corporation, Inc. introduced a platinum/chromium coronary stent series made of a novel austenitic stainless steel formulation jointly developed with NETL. The platinum included in the alloy gives the stent high radiopacity—visibility under x-ray scanning. Better visibility means greater ease and precision in placement of stents in patients’ blood vessels. In addition, the greater yield strength of the alloy allowed the stent’s designers at Boston Scientific to make a thinner, more flexible stent that is more easily threaded through the winding path of the artery without doing damage along the way. This has allowed the stents to be deployed in much smaller vessels in and around the heart.

Over the past few years, the NETL- Boston Scientific research team captured several prestigious awards for the alloy: a 2011 R&D 100 Award, given by R&D Magazine to recognize the 100 most technologically significant products entering the marketplace each year; a technology transfer award for “Outstanding Commercialization Success” from the Federal Laboratory Consortium for Technology Transfer, and the U.S. Secretary of Energy’s Achievement Award. It has also been nominated for the United States Patent Office’s Presidential Medal for Innovation in 2013 and American Society for Materials’ Engineering Materials Achievement Award in 2014.

2.	Expanded coronary stent, showing structure.Expanded coronary stent, showing structure.

Boston Scientific has now received CE Mark approval for the REBEL™ Platinum Chromium Coronary Stent System, joining the existing PROMUS® Element™, ION™, OMEGA™, and Premier™ Stent Systems based on the NETL- Boston Scientific alloy. CE marking is a mandatory conformity marking for certain products sold within the European Economic Area (EEA). With this approval, the stents can be marketed in most European countries, as well as in areas of Africa and the Middle East.

Developed to expand their platinum-chromium alloy customized architecture family of stents, the REBEL™ Stent System offers physicians the same stent platform as the Premier™ line of drug-eluting stents (DES), but without the Everolimus drug.  The new system allows surgeons to treat patients who are not candidates for DES therapy, and the stents feature low recoil, which is particularly important for patients treated with bare metal stents.

The platinum/chromium coronary stent series has become the leading stent platform in the world. Total sales since introduction have exceeded $6 billion. Boston Scientific has a 25 percent share of the market in the U.S. and believes that this addition will significantly expand their market share. The company is hoping for FDA approval of this series of stents by next year.


Surface Science: Cleaning up Syngas to Reach Efficiency Goals

In a demonstration test, almost 100% of the mercury was removed from flue gas that flowed through a bed of NETL’s palladium-based sorbent.In a demonstration test, almost 100% of the mercury was removed from flue gas that flowed through a bed of NETL’s palladium-based sorbent.

Coal gasification is a promising technology for the use of coal in a clean and efficient manner.  While a conventional subcritical pulverized coal (PC) power plant has a typical plant efficiency of about 35%, an integrated gasification combined cycle (IGCC) power plant can have a plant efficiency from 38 to 41%.  Synthesis gas (syngas), the product of gasification, can be burned for electricity, converted to synthetic fuels, or processed to recover hydrogen.  But first it must be cleaned of trace contaminants such as mercury (Hg), arsenic (As), and selenium (Se).  Palladium (Pd), one of the platinum-group metals, excels at adsorbing these contaminants, but is a rare and expensive material.  NETL is studying the way Pd interacts with syngas contaminants in order to develop cheaper sorbents that can yield a cleaner syngas product.

Dr. Evan Granite of NETL’s Office of Research and Development (ORD) describes one approach to understanding sorbent chemistries, “Sorbents are often treated as a black art.  People try different things without having good information about surface chemistry.”  In contrast, his research team is trying to understand exactly what is happening at the surfaces of the materials that are interacting to maximize the performance of sorbents used to clean syngas. 

Warm Gas Clean-Up research group: Dr. Evan Granite, Dr. Karen Uffalussy, Dennis Stanko, Michael Hajduk, Dr. Elliot Roth.Warm Gas Clean-Up research group: Dr. Evan Granite, Dr. Karen Uffalussy, Dennis Stanko, Michael Hajduk, Dr. Elliot Roth.

Success enables the team to optimize results using the smallest amount of Pd, and perhaps in the future, materials less expensive than Pd. Early research at ORD into the use of Pd for syngas cleanup screened a variety of pure metal powders in the laboratory for their ability to adsorb mercury from mixtures of the gases that make up syngas – nitrogen, hydrogen, carbon monoxide, and carbon dioxide.  Palladium performed well from the start at warm gas temperatures.  Less expensive palladium-alumina sorbent materials were also created and analyzed to better understand their ability to adsorb contaminants from syngas.

One result of these tests was the discovery that arsenic and mercury interact with the sorbent in different ways; mercury capture is better at lower temperatures (204 °C), and arsenic adsorption improves at higher temperatures (up to 371 °C). The design of a clean-up system for syngas from an IGCC plant will be affected by this discovery, perhaps by including adsorption beds with variable temperature.

Micro-analysis images showing sorbent beads coated with arsenic.  Palladium analysis is shown on the left and arsenic analysis on the right.  Both elements use the same color scale; red areas are highest in the element analyzed and black and blue areas are lowest.Micro-analysis images showing sorbent beads coated with arsenic. Palladium analysis is shown on the left and arsenic analysis on the right. Both elements use the same color scale; red areas are highest in the element analyzed and black and blue areas are lowest.

The sorbents developed at NETL were selected in 2008 as one of the 100 most technologically significant products to enter the marketplace in the previous year, and the patented technology is licensed to Johnson Matthey to extend the work to larger scales. Laboratory tests required only 10 milligram quantities of the sorbents per experiment; Johnson Matthey has manufactured much larger amounts of the sorbents and supplied them for use in pilot-scale testing at the Southern Company’s National Carbon Capture Center.  These tests are conducted under real-world conditions using syngas from coal gasification, which contains tars, moisture, and parts per million quantities of Hg, As, and Se.  The syngas is treated by passing it through a packed bed of the Pd-alumina sorbent.  Test results have been very good, indicating that the NETL-developed sorbent removes up to 100% of the contaminants.

Understanding surface chemistry is the key to developing effective sorbents.  All of this will help DOE reach its goals for producing electricity cleanly from coal with the smallest increase in cost of electricity.  This work helps meet those goals, says Granite, “…because we’re trying to develop cheaper sorbents for trace contaminant removal.  That’s an immediate goal that impacts the bigger goals.”

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