Introduction
Ethanol (CH3CH2OH) can be used as a fuel source, or as a fuel additive for use in combustion motors. This report will discuss whether it is cheaper, greener, or cleaner compared to fuel containing only petrol.
Research Question
As a fuel or as a fuel extender, is ethanol that is produced from biomass “cheaper, cleaner and greener” than other liquid fuels used in cars?
Chemical Background
Cheaper, Greener, Cleaner
In this report, “Cheaper” will relate to the price of each fuel, “Cleaner”, the chemicals that are produced through all stages of chemical reactions, and “greener”, the fuels effect on the environment.
Biofuels (1)
Biofuels are fuels produced from biological materials. (2) At this stage there are only four generations of biofuels. (3)
First generation: Biofuels produced from food sources (Animal Fats, Starch, Sugar, Etc.) (4)
Second: Biofuels produced from waste food sources (Seed crops, Grass, Waste Vegetable Oil, Etc.) (4)
Third: Biofuel produced from algae. (4)
Fourth: Biofuels produced from specially engineered biomass with potentially lower cellulosic breakdown barriers or higher energy yields. (5)
Ethanol
Ethanol is produced from any biomass containing large quantities of sugar, starch or cellulose. These components are fermented,
Glucose: C6H12O6
When fermented (using enzymes) glucose forms ethanol and carbon dioxide.
C6H12O6(aq) 2C2H5OH(l) + 2CO2 (6)
Reactions in a car engine
Combustion engines contain a chemical reaction, where Fuel and Air react in conditions of high temperature and pressure. The products of this reaction vary with the reactants, as shown underneath these combustion reactions. (7)
Petrol: 2C8H18 (l) + 25O2 (g) 16CO2 (g) + 18H2O (l) (ΔH = 4834 kJ/mol of octane)
Ethanol: C2H5OH (l) + 3O2 (g) 2CO2 (g) + 3H2O (l) (ΔH = 1371kJ/mol of Ethanol)
Ethanol
No burn
Volatile Organic Chemicals (Unburnt Hydrocarbons)
Complete Combustion
CO2 (greenhouse gas)
Incomplete combustion
CO or C
Octane
Sulphur contaminants
SOx (Primary Pollutant)
+H2O forms acid rain (secondary pollutant)
Air (O2, N2)
NOx (Primary Pollutant)
Ozone, Photo Chemical Smog (Secondary Pollutants)
Discussion
Greener
Ethanol is considerably “greener” to produce then regular petrol. Unlike petrol, it’s a renewable resource, being created using biological materials. Whilst the hydrocarbons found in petrol are sourced from unrenewable fossil fuels, the hydrocarbons found in bioethanol’s are produced from renewable biological material, either from food stocks or waste material. The process of retrieving crude oil to produce petrol can cause large amounts of damage to the environment, where the biomass used to produce ethanol is usually waste product, with almost no environmental damage. (8)
Research has been undertaken to allow CO2 to be used in photoelectrocatalytic reactors, to form Hydrocarbons using the CO2 and hydrogen, with catalysts to assist the reaction. This process is proving difficult to create reliable, consistent results, and is an unfinished technology at this time. (9) (10) (11)
Ethanol is produced by fermenting glucose. This process also produces CO2.
C6H12O6(aq) (ferment with enzymes) 2C2H5OH(l) + 2CO2(g)
Whilst producing ethanol from biomass is a much greener source of fuel then petrol, it must be considered that this fuel is essentially being produced using a potential food source. (12) (13)Whilst this may have been the case when biofuels were a relatively new concept, the technology has improved to a stage where other sources can be used. Second, third, and fourth generation biofuels are produced using waste food sources, algae, and specifically engineered biomass respectively. (4) (5) (14)
Cheaper
To find which one of the fuels is cheaper, the joules (of energy)/litres (of fuel) will be compared with the price of the fuels. (15) (16)
Petrol: 2C8H18 + 25O2 16CO2 + 18H2O (ΔH = 4834 kJ/mol of octane) 1mol=114.23g
Petrol:
Petrol=137.7 c/L
Ethanol: C2H5OH (l) + 3O2 (g)
