Science & Research

Affiliated prof. finds bill cleaning method

Staff Writer
Wednesday, January 22, 2014

Carbon dioxide may soon become a key player in the financial industry. Over the past six months, Nabil Lawandy, an affiliated professor of engineering and physics, and his former graduate student Andrei Smuk PhD ’00, have used a derivative of carbon dioxide to effectively clean paper money without damaging the security aspects or mechanical integrity of the bills.

Now CEO of both of his self-founded corporations — Solaris Nanosciences and Spectra Systems — Lawandy said the cleaning process is “basically a way of extending the life of a bank note.” When people touch bills, they leave sebum, an oil from the skin, behind. Sebum left on the money then reacts with the air causing its discoloration, and build-ups of sebum make it difficult for machines to process bills.

An accumulation of sebum renders a bill liable for removal from circulation, Lawandy said. Each year the federal government must replace and reprint 150 billion bills because of the accumulation of sebum or from “limpness,” Lawandy said.

Lawandy’s knowledge of this expense, combined with prior work experience at NASA gave him the tools to develop a way to clean paper bills and save the government money. He and Smuk published a paper detailing their methods in the Industrial and Engineering Chemistry Research journal last month.

The cleaning process they invented uses carbon dioxide in the supercritical fluid state to clean sebum from the bills. A supercritical fluid simultaneously exhibits properties of a liquid and a gas under certain temperature and pressure conditions, giving it the density of a liquid but the behavior of a gas, Lawandy said. Carbon dioxide exhibits these properties under “conditions that are like a hot summer day in Providence, but at 340 times the pressure,” he said.

When dirty bills are placed in supercritical carbon dioxide, the sebum dissolves and the clean bill is removed from the substance.

Additionally, because supercritical carbon dioxide has different chemical properties from those of normal cleaning agents, it does not remove or damage any security features on the bills, Lawandy said.

The cleaning process takes about an hour to complete, but bills can be processed in stacks making the process efficient, Lawandy added.

While the method does not guarantee a bill’s cleanliness for life, it does allow dirty notes to be recycled rather than disposed, reducing the amount of waste from money that would otherwise be shredded or burned, Lawandy said. Moreover, the cleaning process does not affect the strength of the bill itself and can theoretically be completed a limitless number of times.

While the federal government may not adopt the money-cleaning process right away, , Lawandy is working with two central banks in the United States that have agreed to implement his cleaning process. The machinery will be delivered to them in the next week, he said, adding that he hopes other banks will try the new process as well.

The use of this system on a large scale would be economical. Processes that require high pressure are not expensive to complete and use equipment that rarely needs replaced, Lawandy said.

The outstanding cost would be for labor,  though no special training would be needed to operate the machinery, Lawandy said.  Despite the benefits of the new money-cleaning method, Lawandy said he does not “think the U.S. will be an early adapter.” One reason for this is because by reducing the reprinting of new bills, the suppliers of paper and ink are hurt, he said.

Smaller countries, such as those that outsource to print their money, may implement the process more quickly, Lawandy said.

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