Bio ethanol which is commonly known as ethanol fuel is simply ethanol liquid which forms a major component of alcoholic beverages. In precise terms ethanol fuel is a water-free, high octane alcohol produced from fermentation of sugar or starch. In its purest form it is a colourless clear liquid with a mild characteristic odour. In chemical terms ethanol is produced during fermentation of glucose (a simple sugar), producing carbon dioxide as a by-product which can later be used for again producing glucose, the reaction being:
C6H12O6 ——> 2 C2H5OH + 2 CO2 + heat
Other simple sugar fructose also undergoes similar reaction as glucose to produce ethanol. Both these sugars are produced in abundance in plants during the photosynthesis reaction which helps ethanol in being a fuel which can be easily obtained from various plants all around the globe. There are complex compounds too which are strings of these simple sugars and by breaking them down can be used to produce ethanol. Starch and cellulose, easily available in plants, are strings of glucose, whereas one of the most common substances present in a household-sucrose i.e. table sugar-is strings of glucose bonded with fructose. Another method to produce ethanol is through industrial addition of water (H20) to an ethylene (ethene) molecule in presence of an acid catalyst which increases rate of reaction:
C2H4 + H2O ——> C2H5OH
Since the ethylene is obtained from petroleum by steam cracking, the increasing prices of petroleum have made this process lose out on popularity amongst bio ethanol producers.
What are the sources for bio ethanol?
There are many crops which serve as a feedstock for production of bio ethanol. A few examples amongst the huge list are- sugarcane, maize, barley, hemp, potatoes, sweet potatoes, sunflower, fruits, molasses, corn, wheat, straw, cotton and switch grass. Other biomasses and cellulose waste can also be used a feedstock for bio ethanol making it a fuel which has a huge base for source. The first generation of bio ethanol fuel uses only small part of the plant as a feedstock.
New second generation types of processes have started utilising more of the plant by converting cellulose to ethanol using enzymes and yeast fermentation. Apart from this new method an even more modern method of obtaining ethanol is being developed in many places where algae’s are used as the source for feedstock. It has been observed that algae themselves naturally produce ethanol while growing in sunlight; hence there is no need to harvest the algae and kill it. A new process which produces a new variant of bio fuel called cellulosic ethanol is further reducing the cost of production of ethanol through crops like corn and maize as this method uses the non-edible parts of a plant like wood and grass to produce bio fuels.
Ethanol as a fuel blend
Ethanol’s main use is as a motor fuel and is easily used in petrol engines by creating its blends by mixing it with conventional petrol. There are mainly two types of ethanol blends- E10 and E85. The E10 blend is a mixture of 10% ethanol and 90% petrol, and is the most common fuel blend in the Australian continent. The E85 blend comprises of85% ethanol and 15% of unleaded petrol. The cleaner E85 blend has been in wide use in Brazil and United States of America for many years. Due to E85 being a cleaner blend and Australian government pushing for more eco-friendly fuels, the E85 blend is slowly becoming popular in Australia too. The E85 blend can be used only in Flexible Fuel Vehicles (FFVs) which can run with a maximum of 85% ethanol content in the fuel, although most unleaded petrol run cars have been approved by manufacturers to run E10 blend of ethanol with petrol.
Why is bio ethanol advantageous?
Apart from the environment related benefits of bio ethanol, there are so many other benefits of bio ethanol over petrol that even motor-racing teams have started using ethanol blends to improve the performance of their speed machines.
Ethanol fuel is also used as rocket fuel for lightweight aircrafts. The higher compression ratio of a purely ethanol run engine makes it better for power output and increased fuel economy, due to the better torque output than petrol engines. The higher octane rating helps ethanol gain over petrol due to higher thermal efficiency.
Environmentally ethanol is a very good source of fuel to replace petrol due to lesser emissions. Pure bio ethanol has complete nearly complete combustion which results is almost no release of the harmful carbon monoxide hence ethanol blends are being advised in places with huge carbon monoxide concentration.
Apart from lesser carbon emissions, the other reason why ethanol is so green is because the products of combustion of ethanol can again be utilised to produce glucose which is a source for bio ethanol. All the components of the 3 reactions involving production and use of bio ethanol- production of glucose through photosynthesis, production of ethanol through fermentation and combustion of ethanol-are recycled again and again and, except for a few wastage during the process, the only components that remain in the final summed reaction are sunlight (which is abundant) and the heat generated during combustion. This makes ethanol an almost perfect fuel in terms of chemical reaction.
What are bio ethanol’s disadvantages?
On theory bio ethanol seems almost perfect but on practice it has many operational problems. One of the main problems of bio ethanol during production is the huge tracts of land required to produce the feedstock thus affecting the biodiversity of a place. Due to better prices for ethanol fuel, farmers who were previously growing crops for food have shifted to ethanol thus burdening the granaries in various places, hence starting the fuel vs. food debate.
There are various problems which ethanol faces as a fuel in current generation petrol engines. One major problem is that its energy per unit is lower than petrol hence, more ethanol is needed to produce same energy as petrol. In cold conditions ethanol is unable to develop enough vapour pressure to evaporate hence making it unable to start a cold engine. Thus in cold conditions, drivers are advised to use blends with lesser concentration of ethanol.
Due to the water absorbing property of ethanol, the water absorbed reduces the fuel value of the bio ethanol thus ethanol blends have to be kept in airtight containers. Some researches show that growing the feedstock and transporting and other manufacturing processes reduce the ‘green’ nature of bio ethanol, and hence it is facing stifling competition from electric run cars on being more environment friendly.
How does the future look for bio ethanol?
Although it has limitations and many rivals, bio ethanol seems to have a bright future as a replacement for petrol. This future has been strengthened by the continuous research done to produce bio ethanol is cheaper, easier and more environment friendly ways. Many countries have started trusting this fuel, even though it has a few limitations, due to the ultimate positive effect it has on the environment of having lesser carbon emissions compared to the similar petrol.
Countries such as USA and Brazil have shown a lot of faith in this fuel due to the abundance of feedstock available for its production and it will continue to increase. The main reason why bio ethanol has a brighter future in running vehicles over electric power is because the technology can be easily made with a few modifications to the present machines. With ever increasing research done on algae and cellulose ethanol, bio ethanol will stay in news for good reasons for many generations to come.