Lecture 16

Starch, Cellulose and Lignocellulose: Starch:

carbohydrate consisting of a large number of glucose units connected linearly by chemical bonds. This polysaccharide is produced by all green plants as energy storage in the plant body. It is the most important carbohydrate in the human diet and is contained in staple food crops such as potatoes, wheat, maize (corn), rice, yum, and cassava. Cellulose is an organic compound with the formula (C6H10O5) n, a polysaccharide consisting of a linear chain of several hundred to over ten thousand glucoses. It is the major structural component of cell walls in plants and green algae. All plant cells have a primary cell wall, in which cellulose is the important structural component (an organic compound). Some plant cells (like xylem cells in woody plants) have secondary deposits of lignified cellulose which provides additional strength to the cell. This deposit (or layer) is also known as secondary cell wall. This secondary cell wall contains lots of lignin, a special chemical that conveys mechanical strength. 03.

Bioethanol, Cellulosic ethanol and Lignocellulosic ethanol:

Bioethonal is an alcohol made by fermenting the sugar components of plant materials. For the first-generation of biofuels, it is made mostly from sugar and starch crops (e.g. the edible part of rice or corn plants). In the second-generation of biofuels, it can be produced using plant celluloses and cell walls. Both cellulose and lignocellulose are essentially sugars (polysaccharides). If we can break them into simple glucoses, we can generate ethanol from them. Cellulosic ethanol is a biofuel produced from grasses or other plant parts that are rich in cellulose; they are not from edible parts of plants (sugar starches). Lignocellulosic ethanol is a biofuel produced mainly from plant materials such as wood debris and twigs that are rich in lignocelluloses (see definition above). Lignocellulosic biomass, in the form of wood fuel, has a long history as a source of energy for humans. All woody plants (e.g., poplar, pine, megaflora, willows trees) are good sources of lignified celluloses. The biggest challenge for both cellulosic and lignocellulosic ethanol production is that the sugars necessary for fermentation are trapped inside the cellulose and lignocellulose, which is resistant to degradation. 04.

Biogas:

It is produced by the process of anaerobic digestion of organic materials by microbes that can survive without oxygen. These kinds of microbes are also known as anaerobes. It contains methane (CH4), which can be combustible under oxygen and produce water and carbon dioxide. 06.

Oilgae:

It is the oil produced from algae which is used as a fuel, also known as algae biofuel. It belongs to the third generation biofuel. Algae are low-input, high-yield feedstock to produce biofuels. We can directly extract crude oils from algae as biodiesels, and we also can use algae's biomass to generate bioethanol through fermentation processes

Biodiesel:

It refers to vegetable oils or animal fat-based diesel fuels that consist of long-chain esters. The long-chain ester is generated through chemical reactions between an acid and an alcohol. Biodiesel is typically made by chemically reacting lipids (e.g., vegetable oils, animal fats or greases) with an alcohol. 05.

Lipids:

Lipids include waxes, fats, oils, steroids, fat-soluble vitamins, among others. The common feature among lipids is that they are hydrophobic (i.e., lipids are small molecules insoluble in water, but soluble in non-polar solvents). They serve important biological functions such as storage and provision of energy, structural components of cell membranes and so on. The building blocks of fats and oils are glycerol and fatty acids. 02.