It’s not only that Western countries are no longer want to rely on the Middle East for their fuel needs but the also the depletion, harmful effects of fossil fuels on our environment and Bioethanol is the solution to these problems.
Increasing demand for Energy for Transportation, Industry and heating is on the biggest challenges to the society in 21stcentury. The European Commission plans to substitute progressively 20% of conventional fossil fuels with alternative fuels in the transport sector by 2020. Similar approaches are being observed from the USA, Japan and Latin America.
Bioethanol is the largest player of renewable energy being produced in the USA by Strach and in Brazil by Sugar. This process uses the human and animal consumables but now researching are looking for new methods to produce Bioethanol by agriculture or forest residues called lignocellulosic material. Ethanol can be blended with petrol or used as neat alcohol in dedicated engines.
What is Bioethanol?
Bioethanol is an alcohol produced by the fermentation of sugars by microorganisms. Synthetically produced Bioethanol is obtained from the Petrochemical sources.
It can be utilised as a liquid fuel in internal combustion engines, either neat or in blends
with petroleum. Ethanol has a high octane rating (99), which is a measure of a fuel’s resistance to pre-ignition, meaning that internal combustion engines using ethanol can have a high compression ratio giving a higher power output per cycle. Regular petrol (gasoline) has an average octane rating of 88.
Additional uses of Bioethanol are ethanol gels (domestic cooking), fuel for electric power, in fuel cells (thermo-chemical action), in flueless fires and in power co-generation systems.
Advantages and Disadvantages of Bioethanol as Fuel
Pros
- Carbon Dioxide Neutral
- Reduced Dependence on Oil
- Allows Agricultural Diversification
- Clean Burning, Low Toxicity
- Higher Flash Points (better fire safety)
- Better Biodegradability
- Co-generation of Electricity
- Low GHG Emissions (~65% less than petrol)
Cons
- Food-to-Fuel is Unethical
- Economics Driven by Oil Price, which is Dynamic
- Un-sustainability of some Biomass Sources Unfavourable Energy Balances
- Inefficiency of Fermenting Microbes Hydroscopic Nature of Liquid
- Higher Fuel Consumption (c.f. petrol)
- Some Residues, Emissions may be Harmful
Bioethanol Production Process
The production of ethanol from natural sources such as plant biomass is considered an important renewable resource technology. It has multi-steps that are;
Biomass Harvesting
Biomass could be any plant material and obtained mostly from sugarcane, sorghum or corn. Harvesting is done through labours or mechanical means by hammermill or roller mill. This plant material is transported for milling.
Milling and Grinding
In this step, cutting and steeping of plant material are done for milling. Milling can be done by two methods.
- Wet Milling: Plant material is broken by heating and in the presence of sulfurous acid for 2 days, so by-products are formed.
- Dry Milling: This milling method is relatively simpler than another one. It produces fewer products than wet milling and it includes ethanol, carbon dioxide and dried distiller grain with solubles (DDGS).
Liquefaction
The grinded substance is heated at the temperature higher than 60°C to form a viscous suspension. The main aim of this step is to break the long chain of the starch molecule into shorter ones. Liquefaction requires a pH of 5.9-6.2. The enzymes that work in this step is α-amylases that act on internal glycosidic bonds and yield smaller chains.
Saccharification
The process of making ethanol is termed as saccharification. In this step, further hydrolysis takes place and glucose monomers are formed in the presence of an enzyme glucoamylases.
Fermentation
The chemical reaction of fermentation is where 1 mole of glucose yields 2 moles of ethanol and 2 moles of carbon dioxide. T
In this step, yeast Saccharomyces cerevisiae is added and the reaction occurs at 30-32°C for 2-3 days. 90-95% glucose is converted to ethanol.
Distillation
Ethanol is processed to increase the concentration of ethanol that is 12-15% only. In this process, components are separated from ethanol by heating in a specialized vessel. But both water and ethanol interact with each other due to the presence of –OH group in ethanol and form an azeotrope so we can not completely separate water from ethanol. Thus at the end of distillation, we have 95% ethanol pure.
Feedstock for Bioethanol Production
First Generation
The feedstock used to produce first generation bioethanol is directly from food crops. Corn, wheat, and sugar cane is the most commonly used first generation biofuel feedstock.
Corn
It is one of the primary sources of the world’s fuel ethanol. It is used because it is simple to convert corn starch to ethanol, also it can use other parts of plants like stalks & cobs to produce bioethanol. There is no need to have an infrastructure for plantation, harvesting and processing of corn as it is already present. But there is a problem that it is a staple food and use in biofuel has increased food prices worldwide, leading to hunger.
Sugarcane
World’s largest producer country of sugarcane is Brazil and hence used it for bioethanol feedstock. Unlike corn, sugar cane provides sugar rather than starch, which is more easily converted to alcohol. As corn requires heating and then fermentation, sugar cane requires only fermentation. It is advantageous as its yield is higher and also it is environmentally friendly and Carbon dioxide emissions can be 90% less. But the problem is only a few regions are suitable for its cultivation and also sugar cane is a food staple.
Second Generation
The second generation ethanol is a liquid fuel from non-food bio-materials such as biomass and bio-waste which includes agricultural wastes such as corn stover, sugarcane bagasse and also from wood, grasses or the non-edible parts of plants. The bioethanol production is from the lignocellulosic component of feedstock. Lignocellulosic material is abundantly present that is roughly 60 to 90 per cent of terrestrial biomass by weight. Also, it is not the source of food and feed requirement so this becomes key interest feedstock for bioethanol production. Bioethanol is chemically same whether it is produced from corn, sugarcane or cellulose, but there is the difference in production processes.
Third Generation
Fourth Generation
The feedstock used in fourth generation bioethanol production is derived from specially engineered plants or biomass that produces higher energy and pose very less barrier to cellulosic material breakdown and are able to grow on non-agricultural lands or water bodies.
Biomass crops have efficient ability to capture carbon, which is then converted into biofuel by applying techniques. The fuel that is produced is the renewable source and is carbon-negative. It provides the sustainable source of energy.