CHALLENGES OF LIGNOCELLULOSIC ETHANOL TECHNOLOGIES

Energy consumption has increased steadily over the last century with the tremendous growth of world population and the industrialization of many countries. Fossil fuel, especially petroleum oil, has been the major resource to meet the increased energy demand worldwide. The limited crude oil supply and reserve will be exhausted in the near future if petroleum oil consumption continues to increase at its current rate. In addition, combustion of fossil fuel has resulted in a release of huge amount of carbon dioxide to the atmosphere, causing global climate change. Because the current world economy depends on petroleum oil, consequences of inadequate oil availability could be severe. There is also an urgent call to reduce carbon dioxide emission to the atmosphere to protect the environment. There is great interest in exploring renewable energy sources. Ethanol supplies a significant percentage of the total energy resource in Brazil and US. However, substantially increasing ethanol production using the current sugarcane- or cornstarch-based technologies is not practical because of the completion for the limited arable land against food and feed production. Lignocellulosic materials such as wood, grasses, and agricultural residues are abundant in most regions of the world. They can be grown in marginal land or waste materials from food or feed production. However, there are major challenges for the commercialization of the lignocellulosic ethanol technologies. First of all, almost all lignocellulosic materials have compact structures that are resistant to conversion, so pretreatment is usually necessary. Secondly, cellulase enzyme is a key to successful conversion of cellulose and hemicelluloses into fermentable sugars, but the enzymes are quite expensive to produce and a significant cost in lignocellulosic ethanol production. Another major challenge is to efficiently utilize the lignocellulosic materials, especially the hemicelluloses and lignin. Perspectives of overcoming these challenges will be presented in the lecture.