This post is based on my article from the September 2007 issue of Biomass Magazine. The information in this article may no longer reflect the current state of the research projects described or current thinking about any scientific issues discussed.
I find the system of federal laboratories to be fascinating. Often derided as “pork” they provide industry an invaluable resource for conceiving, testing and implementing technologies that are beyond the capabilities of most private companies. William Proxmire, a Wisconsin Democrat, did tremendous damage with his Golden Fleece Award which he used to attack what he saw as wasteful government spending. However, it seems he never bothered to check the science behind the odd-sounding and oftentimes inaccurate descriptions of the projects he attacked. This is a troublesome trend that continues even today as presidential candidate John McCain derided genetic research to monitor bear populations as “paternity tests.”
This article highlights work by the Department of Energy that uses in interesting property of light and matter to determine the composition of biomass and its suitability for biofuel production. No doubt the discovery of Raman scattering could have been derided by the budget cutters of the 1920s as “shining lights at stuff to see what happens.” But in the hands of scientists, it promises to be a powerful tool that could allow biofuel producers to have as much control over their feedstocks as fine vintners.
Emily Smith compares Raman imaging to a vintner measuring the sugar content of his or her grapes to find the perfect moment when they will make the finest wine. The spectrographic technique allows Smith to peer inside the cells of biomass and measure the type and amount of various chemical constituents.
Smith is a research associate at the U.S. DOE’s Ames (Iowa) Laboratory. Her work with Raman imaging is part of a team effort to develop biomass feedstocks optimized to produce cellulosic ethanol and other products. She also works in the chemistry department at Iowa State University in Ames, Iowa.
The Raman effect was discovered in the 1920s when Indian scientist Chandrasekhara Venkata Raman found that a tiny portion of light scattered off a surface had a slightly different wavelength than the original light source. In fact, it was altered by the chemical composition of the sample being illuminated. A spectroscope allows researchers to measure the difference in wavelength precisely, giving them a picture of the chemical makeup of the sample. “We send high-powered light from a laser source onto our sample and that light interacts with that sample, and there are subtle changes in the property of light after it interacts with the sample,” Smith explains. “Those subtle changes are what we use to measure the composition of our material.”
Plant tissue is complicated. While it contains the feedstocks for energy and chemical production, it also contains material that isn’t as valuable. “We are interested in the cellulose, hemicellulose and lignin, and we can look for the changes in the light that we get when those materials are present,” Smith says.
One advantage of Smith’s technique is that it requires little material for testing. “There are other techniques that can do our analysis,” Smith says. “We can take a sample from a plant that is growing in the field, and because it is such a small sample, we are not going to destroy the plant. In addition, our analysis is fairly quick. Some of the other technologies require extraction steps and some processing steps. Our technique allows us to just take that plant sample, put it in our instrument and look at it.”
Smith is working with Iowa State University agronomy professor Ken Moore, who will be providing her with plant material samples. She plans to screen several biofuel plant stocks for cellulosic ethanol production, such as switchgrass, Miscanthus (a subtropical perennial grass that can grow 13 feet high), corn, and poplar and willow trees. Smith says her goal is to analyze plant composition under different environmental conditions. “I’ve done some reading, and it seems like the amount of water the plant material gets can affect lignin levels particularly,” she says. “So in one season where it might be drier, you might want to harvest your material at different times for optimal composition so you get the highest ethanol yield.”
Right now, Raman imaging is primarily a research tool. However, Smith believes that as the biomass industry grows, it could be adapted to measure plant growth in the field, allowing growers to know the best time to harvest their biomass for the most efficient production. “While it is not at that stage yet, it is something we hope for in the future,” Smith says. “It is feasible that we could develop an instrument that we could give to someone in the field who is not necessarily trained in spectroscopy or as a chemist and do this analysis.”