Comparison of CO2 Emissions for Biodiesel and Petroleum Diesel

Table 1and Figure 1summarize CO2 flows from the total life cycles of biodiesel and petroleum diesel and the total CO2 released at the tailpipe for each fuel. The dominant source of CO2 for both the petroleum diesel and the biodiesel life cycles is the combustion of fuel in the bus. For petroleum diesel, CO2 emitted from the tailpipe represents 86.54% of the total CO2 emitted across the entire life cycle of the fuel. Most remaining CO2 comes from emissions at the oil refinery, which contribute 9.6% of the total CO2 emissions. For biodiesel, 84.43% of the CO2 emissions occur at the tailpipe. The remaining CO2 comes almost equally from soybean agriculture, soybean crushing, and soy oil conversion to biodiesel. Figure 2 shows the effect of biodiesel blend levels on CO2 emissions.

Figure 1: Comparison of Net CO2 Life Cycle Emissions for Petroleum Diesel and Biodiesel Blends*

*Net CO2 calculated by setting biomass CO2 emissions from the tailpipe to zero.

Table 1: Tailpipe Contribution to Total Life Cycle CO2 form Petroleum Diesel and Bio diesel (g CO2/ bhp- h)

Figure 2: Effect of Biodiesel Blend Level on CO2 Emissions

At the tailpipe, biodiesel (most of which is renewable) emits 4.7% more CO2 than petroleum diesel. The nonrenewable portion comes from the methanol. Biodiesel generates 573.96 g/bhp-h compared to 548.02 g/bhp-h for petroleum diesel. The higher CO2 levels result from more complete combustion and the concomitant reductions in other carbon-containing tailpipe emissions. As Figure 1 shows, the overall life cycle emissions of CO2 from B100 are 78.45% lower than those of petroleum diesel. The reduction is a direct result o  carbon recycling in soybean plants. B20 reduces net CO2 emissions by 15.66%.

Understanding Coal and Petroleum

Man's quest for sources of energy is inexhaustible. Early man depended mainly on muscular energy and later began to use wind and flowing water as sources of energy. He learned the art of making and controlling fire. Fire became his source of light at night. He used fire for warmth and realized that cooked food tastes better than raw food. As civilization advanced, man started using fire in making weapons, pottery etc. Today, with the progress in science and technology, fuels have become indispensable to man.

Fossil fuels are energy-rich, combustible forms of carbon or compounds of carbon formed by the decomposition of biomass buried under the Earth over millions of years. It is a black mineral of plant origin which is chemically, a complex mixture of elemental carbon, compounds of carbon containing hydrogen, oxygen, nitrogen and sulphur. Petroleum is a dark, viscous, foul smelling liquid, a mixture of solid, liquid and gaseous hydrocarbons with traces of salt, rock particles and water.

Liquefied Petroleum Gas, LPG is butane with small quantities of ethane and propane. These gases can be liquefied under pressure and bottled in cylinders. By itself LPG is odorless. On leakage, it is toxic if inhaled. It also forms an explosive mixture with air. LPG can be hazardous if handled carelessly. A strong smelling compound, ethyl mercaptan is added to detect the leakage of LPG. The composition of natural gas is chiefly methane (>90%) with traces of ethane and propane. In countries, where coal is easily available as compared to the rapidly depleting petroleum and natural gas, it is possible to avert the energy crisis by preparing petroleum and natural gas artificially.

With Man's ever increasing need for energy, he has been using fossil fuels indiscriminately. In the process, harmful materials contributing to air pollution are being produced. Organic chemistry is a branch of chemistry that deals with the study of compounds of hydrogen and carbon (hydrocarbons) and their derivatives. There is existence of innumerable organic compounds. Properties of organic compounds are distinctly different from those of inorganic compounds. Catenation, the single most important property of carbon, is defined as the property of atoms of the same kind to covalently link with one another to form linear chains, branched chains or rings.

Hydrocarbons are compounds containing only hydrogen and carbon. They form an important class of organic compounds. Several organic compounds are derived from hydrocarbons. Therefore, they are also referred to as parent compounds. Nomenclature is the system of naming. With the existence of innumerable compounds of carbon, it has become necessary to follow a universal, rational system of naming. Such a system has been evolved by International union of pure and applied chemistry (IUPAC). By following this system, we can eliminate the confusion that arises due to usage of common names or trivial names. Isomers are compounds having the same molecular formula but different properties due to different structural arrangement of atoms in their molecules. Homologous series is a series of organic compounds having the same general formula, arranged in an ascending order of their molecular masses.

Alkanes are saturated hydrocarbons having only single bonds between the carbon atoms of their molecules. The general formula of alkanes is CnH2n+2. Alkanes are called paraffins because of their low reactivity (in Latin paraffin means- less reactivity). Methane forms an explosive mixture with air and is therefore dangerous. Methane being insoluble in water is convenient and safer to collect by the downward displacement of water. Biogas is a clean and efficient fuel. It is a mixture of methane (CH4), carbon dioxide (CO2), hydrogen (H2) and hydrogen sulphide (H2S).

Alkenes are unsaturated compounds having the general formula CnH2n. Ethene is a colourless gas with a sweetish odor. It is insoluble in water and soluble in organic solvents. It causes unconsciousness when inhaled. Alkynes are unsaturated hydrocarbons with the general formula CnH2n-2. They are the most reactive as compared to alkenes and alkanes.   (ArticlesBase SC #1161579)