Great Lakes Bioenergy Research Center

Transcription

What is cellulose and how is it used to make ethanol? When plants grow, they synthesize a variety of different compounds. Carbohydrates are the most common. There are many different forms of carbohydrates stored inside each plant. Examples include sugars, which are abundant in fruits, starch, which is found in storage organs like potatoes, and cellulose, which is found in all plant organs, including leaves, fruits, and stems. Every plant, from grasses to trees, has cellulose. It is the most abundant organic compound on Earth. This cellulose is part of plant cell walls, which give the plant structure and protection. Cellulose contains high energy sugars called glucose, which could be broken down and transformed into biofuels like ethanol. This ethanol could be used to replace gasoline in your car. Just breaking down the plants' cellulose into sugars seems simple enough. So why are scientists having difficulty transforming cellulose into ethanol? To understand this problem, scientists start by looking at the structure of cellulose. Cellulose is actually made of building blocks of glucose, a simple sugar. In plants, these building blocks are linked together into long chains inside the cell walls. These glucose chains are found in a complex web of other sugars, like hemicellulose, and a structural material called lignin. This web protects and supports the high energy sugars. Because the cellulose is so tangled with hemicellulose and lignin, it is difficult to separate it out of the plant material for conversion into ethanol. So how do scientists solve this problem and turn this tangled mess of cellulose into ethanol? First, the plant material is chopped up into smaller pieces to be roughly the same size. Then, scientists much detangle the plant material in a process called "pretreatment," using heat or chemicals. This exposes the plant cell walls and loosens the cellulose from the lignins and the hemicelluloses. After pretreatment, enzymes are used to chope the cellulosic chains of glucose apart into individual sugars. Next, the glucose sugars are fermented in large tanks by microbes like yeast or E.coli. The microbes can eat sugars and release ethanol as a waste product. Then, the ethanol product is recovered and sent to the gas station for use in vehicles. Right now, these steps are costly and time consuming. But scientists are working to make the whole process less expensive and more efficient, so that one day, ethanol produced from cellulose can rule the road. GLBRC, Great Lakes Bioenergy Research Center Starring Plant Material Glucose Cellulose Hemicellulose Lignin Enzymes Microbes Ethanol Scientists