Cellulosic ethanol-it can be a major source of sustainable energy?
Cellulose is the fiber contained in leaves, stems, and stalks of plants and trees, the most abundant organic compound on earth. Unlike corn and sugar, the plants now used to make most ethanol, cellulose is not used for food, and it can be grown in all parts of the world. Many feedstocks including corn cobs, wheat straw, woody biomass, and municipal waste are readily available, and it is estimated that cellulosic ethanol will reduce CO2 emissions by 90% compared to petroleum-based fuels.
What is cellulosic ethanol?
Cellulosic ethanol is a biofuel produced from tough plant stems, leaves and trunks instead of supple starch. It is expected to be less expensive and more energy-efficient than today’s ethanol because it can be made from low-cost feedstocks, including sawdust, forest thinnings, waste paper, grasses, and farm residues (corn stalks, wheat straw, and rice straw). Switchgrass and other perennial grasses are particularly considered to be promising sources of cellulosic ethanol. Perennial grasses are less expensive to produce because they don’t have to be replanted each year. Fast-growing woody crops, such as poplar and willow, are also attractive options because of harvesting and storage advantages.
How to make cellulosic ethanol?
The first step in production is transporting the plants to the refinery. There are two primary pathways to produce cellulosic ethanol : biochemical and thermochemical. The biochemical process involves a pretreatment to release hemicellulose sugars followed by hydrolysis to break cellulose into sugars. Sugars are fermented into ethanol and lignin is recovered and used to produce energy to power the process. The thermochemical conversion process involves adding heat and chemicals to a biomass feedstock to produce syngas, which is a mixture of carbon monoxide and hydrogen. Syngas is mixed with a catalyst and reformed into ethanol and other liquid co-products.
What are the advantages of cellulosic ethanol?
From farm to car, cellulosic ethanol releases less greenhouse gas than gasoline and corn ethanol. Cellulosic biomass is more available than corn or any other source of ethanol, or for that matter, any existing source of fuel. When done wisely, cellulosic ethanol production can get rid of waste and make fuel.
Concerns about cellulosic ethanol
If you’re going to produce biofuel from biomass on a very large scale, where is the land to grow it? Some groups envision switchgrass spreading over the country like a weed and charge that energy crops will compete with food crops. However, it depends on our management. Food and cellulosic biomass can come from the same plant, corn is food and the stalks are cellulosic biomass. Using yard waste to make ethanol requires no new land.
Producing fuel ethanol from abundantly-available cellulose biomass offers an important opportunity to sustainably produce alternative transportation fuels and we have to continuously develop production technologies in order that bioethanol could become a viable and efficient economic choice as a transportation fuel that also reduces greenhouse gas emissions.