Chelsea Wieland
Chem 160
4-14-14
The Good Money Laundering People rarely stop to think where their money comes from. Few minds reach back beyond the hands of the cashier, bank, or boss. However, the average banknote has a lifespan of one to three years, during which the bill is exchanged numerous times between people.1 Human contact and the stresses of the currency life eventually send them to be replaced by the 150 billion new banknotes produced annually worldwide. The problem arises in the costliness of reproducing the 60-80% of bills that are rejected and disposing of the old currency.2 The average cost of producing a group of 1,000 bills adds up to be about sixty-five dollars. Taking into consideration the varying costs of different denominations, the bill replacements add up to be $10 billion annually. The government must then remedy the problem of having the remaining 150,000 tons of bills of which to dispose.3 Research and developing methods have been investigated in order to prolong the life of the average banknote, thus suppressing the accumulating cost of making and disposing of money. Supercritical carbon dioxide has been used to extract damaging molecules through cleaning in other biotechnology applications, removing grease and other contaminants from high performance technology, and even as another version of dry cleaning. This supercritical fluid has been proven to dissolve molecules more efficiently with the smallest of changes in pressure and temperature, which is exhibited in its critical point of 304.25 Kelvin and 72.9 atmospheres.3 Past applications of supercritical CO2 have led researchers to believe that similar techniques could be used to clean banknotes. Research has determined that the main reason of deterioration of banknotes originates from the sebum that gets left behind by those who touch the bills.4 Sebum is an oily substance that comes from the sebaceous glands of the skin.1 Though composed mostly of water, there is a small fraction of the sebum that is comprised of solids such as fatty acids, lipids, carboxylic acids, and triglycerides. Once the water of the finger prints evaporates, the almost solid finger prints are left behind on the bill.1 The sebum goes through an oxidation process that begins with the decomposition of the triglycerides into glycerin and fatty acids. The double bonds of the unsaturated fatty acids are then oxidized into carbonic acids. Then the oxidation process begins, thus resulting in a yellow-brown color. This change of color allows scientists to test for the amount of sebum, or soil, that is present through measuring the absorbance of light with a spectrophotometer.4 The use of a spectrophotometer allows the scientist to determine if the supercritical CO2 (SCCO2) was successful in cleaning the bill. Being supercritical means that the CO2can exist in both the gas and liquid phases. Efficient recovery is achieved through the coexistence of these states after the extraction of the contaminating compounds. Scientists maintain the pressure and temperature at the supercritical point and manipulate the solvent to behave as organic solvents such as chloroform and methylene chloride. 5 The SCCO2 is non-polar; however, a polar organic co-solvent can be an addition to the cleaning process in cases where the goal is to subtract other polar compounds, such as sebum.6 The cleaning mechanism used in experiments is composed of aluminum and clear acrylic windows in order to allow visual observation. It is furnished with a CO2 pump in order to allow a continuous flow of the cleaner in and out of the chamber even after being pressurized. The sebum is thus constantly being dissolved and carried out of the cell. Past experiments using the supercritical CO2 have found that the procedure was successful in that it was able to remove the sebum, while also leaving costly security features such as holograms, threads, lenticular arrays, watermarks, ultraviolent emission inks, fibers, magnetic inks, and capacitive structure intact.3 Though not utilized on a large scale, supercritical CO2was able to clean even bills that were stacked in groups of one hundred. This application will prove to be useful due to the fact that most banks bundle their money in such arrangements for practicality. The CO2will also do some deep cleaning of the bills. When researchers closely examined the bills, they realized that oxidized sebum was able to soak into the bill itself and did not solely rest on the surface. The whole process is able to solubilize 70%-100% of the sebum in and on the bill. Colonies of bacteria, such as micrococcus luetus and yeast, were found on soiled bills pre- CO2 treatment and absent after being put in the chamber. Although the CO2will not keep the bills clean forever, diminishing the amount of bacteria occasionally would help prevent the spread of disease.3 Further results of the CO2 treatment showed that weight was extracted from the bill due to the loss of the solid sebum. Another discovery was that holograms and security threads were not harmed, except in one national currency where the problem could be resolved simply by changing the composition of the adhesive combining the two types of threads. Though it is possible for the SCCO2 to damage certain types of inks, it was also discovered that there are inks already being used that demonstrate a resiliency factor. Other parts of the bill that remained undamaged were the magnetic inks that only the central bank machines can recognize. Due to the fact that they are made of inorganic oxide, they were not carried away by the SCCO2 treatment. Porosity is another factor that affects the life of a banknote and is manifested in the bending, folding, and crumpling that leads to limpness. An important thought to be examined is if the SCCO2 will cause the bill to become more porous. By forcing argon gas through the bill scientists can determine how many and how big the holes are in the bills. Though some change was exhibited–the bills became more porous–it was determined that not enough effect was made to discount the mechanism of cleaning.3 The use of SCCO2 in cleaning money has not been expanded in the real world to actually help decrease the amount of bills taken out of circulation. Further money and research is needed to discover the practicality of cleaning a larger volume of 100,000 notes or more in a 200 liter system of SCCO2 treatment.3 It is important for the government to realize that though it will take money to develop a practical mechanism for cleaning the money, much more money will be saved. Cleaning methods still need to be improved upon and the lack of knowledge on the matter leads to labor intensive, time consuming, and expensive experiments that need more funding to continue. A more empirical method of creating soiled banknotes needs to be examined and funded in order for future experiments to appear when changes in the compositions of the bills are made. In order for experiments to be made that do not require the use of bills from actual circulation, money needs to be put into the development for a way to mechanically deteriorate banknotes for further testing. Despite the fact that this research does not appear to be immediately life-changing like some other developments, it has the potential to help alleviate some of the financial stress that the government is feeling by making their currency good as new. By putting money into the research being done on cleaning money, the results will yield currency that is fit for circulation for a longer time period, thus saving on the cost in the long run of creating more replacement banknotes and alleviating the environmental concern of dealing with discarding old bills.2

References 1. Balke, P. New Soiling Test Method: Anti-Dirty Fingers. De Nederlandsche Bank [Online] 2009. 2. Morin, M. Scientist Experiment with Money Laundering. http://articles.latimes.com/2014/jan/08/science/la-sci-sn-scientists-launder-dirty-money-20140108 (accessed 2/20/14), part of Los Angeles Times. http://www.latimes.com/ (accessed 2/20/14). 3. Lawandy, N.M.; Smuk, A. Y. Supercritical Fluid Cleaning of Banknotes. Ind. Eng. Chem. Res.[Online] 2013, 53, 530-540. 4. Balke, P. From Fit to Unfit: How Banknotes become Soiled. De Nederlandsche Bank [Online] 2011. 5. Beasley, S. Supercritical CO2. http://www.appliedseparations.com/supercritical-co2 (accessed 4/11/14), part of Applied Separations. http://www.appliedseparations.com/ (accessed 4/11/14). 6. Picardo, M.; Ottaviani, M. Sebaceous gland lipids. Dermatoendocrinol [Online] 2009, 1, 68-71.