The population of the world is increasing and the non renewable energy sources are fast depleting, there is a need to focus on alternate fuel. Biofuel is the best alternate fuel being focused. Of all the possible biofuel crops grown in the United States, perhaps the most attractive is Panicum virgatum, otherwise known as switchgrass. Perennial switchgrass is being evaluated as cellulosic bioenergy crops. Two major concerns have been the net energy efficiency and economic feasibility of switchgrass. Analyses is based on data from research plots and estimated inputs. It managed switchgrass as a biomass energy crop in field trials of 39 ha (1 ha = 10,000 m2) on marginal cropland on 10 farms across the mid- continent U.S. to determine net energy and economic costs based on known farm inputs and harvested yields.
In this report, we summarize the agricultural energy input costs, biomass yield, estimated ethanol output, greenhouse gas emissions, and net energy results. Annual biomass yields of established fields averaged 5.2 -11.1 Mg·haË†1 with a resulting average estimated net energy yield (NEY) of 60 GJ·haË†1·yË†1. Estimated average greenhouse gas (GHG) emissions from cellulosic ethanol derived from switchgrass were 94% lower than estimated GHG from gasoline. This is a baseline study available for switchgrass production in 2000 and 2001. Improved genetics and agronomics may further enhance energy sustainability and biofuel yield of switchgrass. Ethanol production from switchgrass is termed as BIOFOOLISH.
Switchgrass is one of these perennial grasses with scientific name Panicum virgatum. It is an ideal biomass energy source because of its moderate to high productivity, stand longevity, high moisture and nutrient use efficiency and adaptability to most agricultural regions in North America. Switchgrass produced 540% more renewable than nonrenewable energy consumed. Switchgrass can be densified into pelletized biofuel and used for space heating purpose with a close couple gasifier pellet stove.
Characteristic of a switchgrass as a biomass crop :
1.Low cost of establishment, because produces seeds
2. It is cold tolerant
3. High yield potential with low water and fertiliser inputs
4. Wide geographic adaptation
Switchgrass consists of long roots which can penetrate through the soil and make use of deep underground water and hence it can be also grown in drought. It grows upto 10 feet height and entire plant including roots can be used to produce ethanol.
USES OF SWITCHGRASS:
1.Paper pulp production: The fibre characterization of switchgrass revealed that it can be easily pulped by soda process and the pulp contains fibre with wide distribution of fibre length and are long and slender.It is believed that switchgrass can replace 15-20% of the hardwood pulp in the production of paper.
2. Fibre reinforced composites: Low cost fibre reinforced composites obtained from switchgrass were found to have mechanical strength and properties suitable applications in housing construction materials, furniture and automotive parts. Car manufacturer FORD started using these fibres in the interior door panels of several of their cars.
3. Switchgrass pellets: It can be palletized (fig 4) for use as a fuel in stove and household heating and also in space heating. These pellets have a potential to reduce fuel heating cost and green house gas emission by approximately 30% and 90% respectively compared to heating oil systems.
4. Electricity production: The switchgrass is mixed with the coal feedstock, replacing 10-12% of the coal normally used. This mixture is burnt in the boiler to produce electricity. This electricity used for battery powered vehicles would deliver an average of 80%more miles of transportation per acre of crops compared to internal combustion vehicle could only travel about 9,000 miles.
5.Biodegradable plastic: Plastics made from plant starch and soy protein have been used as an alternative to petroleum-based plastics. This organic polymer is a flexible and moldable plastic that can be used to make products such as grocery bags, soda bottles, disposable razors, and flatware. When discarded, the plastic is degraded into water and carbon dioxide by naturally occurring bacteria in the soil.
6. Biofuel production: It is the main use of switchgrass and is discussed briefly in this paper. As much as 96 gallons of ethanol can be produced from each ton of dry switchgrass.
PRODUCTION OF ETHANOL FROM SWITCHGRASS:
The basic steps for large scale production of ethanol from switchgrass are: microbial fermentation of sugars, distillation and dehydration. Prior to fermentation, switchgrass require Saccharification of carbohydrates.
Saccharification is also called Enzyme Hydrolysis, means to hydrolyse the carbohydrates such as starch,cellulose into sugar.During saccharification of liquefied starch, dextrin are broken down to glucose and maltodextrins. When maltodextrins are saccharified by further hydrolysis using glucoamylase or fungal alpha-amylase, a variety of sweeteners(high maltose), 55-70 (high conversion syrup).The sugar thus obtained is subjected to fermentation.
Fermentation is a means for organisms to extract energy from their chemical environment. This diagram below shows a small section of an incredibly complex net of biochemical processes that go on in the cells that do the work of ethanol synthesis for us.
The reaction starts on the left hand side, with glucose. A series of enzyme-catalysed reactions that are common to both of these species converts each molecule o f glucose into two molecules of glyceraldehyde-3-phosphate. This molecule is converted to the carboxylic acid pyruvic acid, generating two molecules of adenosine triphosphate (ATP).The fermentation steps are the conversion of pyruvic acid to acetaldehyde, and then to ethanol. The hydrogen required for the conversion of acetaldehyde to ethanol is provided by nicotinamide adenine dinucleotide (NADH); the resulting hydrogen-deprived NAD+ is necessary to drive the covnersion of D-glyceraldehyde-3-phosphate to pyruvic acid, ensuring the cycle keeps turning around. The description above that the process of fermentation itself gives rise to carbon dioxide; this is captured by the ethanol manufacturers and used to prepare dry-ice for use in other industrial applications. This reaction is shown below.
For the ethanol to be usable as a fuel, water must be removed. Most of the water is removed by Distillation, by using steam, but the purity is limited to 95-96% due to the formation of a low-boiling water-ethanol azeotrope. The 95.6% m/m (96.5% v/v) ethanol, 4.4% m/m (3.5% v/v) water mixture may be used as a fuel alone, but unlike anhydrous ethanol, is immiscible in gasoline, so the water fraction is typically removed in further treatment in order to burn in combination with gasoline in gasoline engines.
There are basically three dehydration processes to remove the water from an azeotropic ethanol/water mixture. The first process, used in many early fuel ethanol plants, is called azeotropic distillation… Another early method, called extractive distillation. Both these methods need distillation. With increasing attention being paid to saving energy, many methods have been proposed that avoid distillation all together for dehydration. Of these methods, a third method has emerged and has been adopted by the majority of modern ethanol plants. This new process uses Molecular seives to remove water from fuel ethanol. In this process, ethanol vapor under pressure passes through a bed of molecular sieve beads. The bead’s pores are sized to allow absorption of water while excluding ethanol. After a period of time, the bed is regenerated under vacuum to remove the absorbed water. Two beds are used so that one is available to absorb water while the other is being regenerated. This dehydration technology can account for energy saving of 3,000 btus/gallon (840 kJ/l) compared to earlier azeotroic distillation. Ethanol has a lower energy content than gasoline. That means that about one-third more ethanol is required to travel the same distance as on gasoline. But other ethanol fuel characteristics, including a high octane rating, result in increased engine efficiency and performance.
ADVANTAGES OF SWITCHGRASS
1.CARBON NEUTRAL: Ethanol from switchgrass is aim to be carbon neutral or even carbon negative. the risk Switchgrass cycles and sequesters atmospheric CO2, thus reducing of global warming.
2.Biofuels produced from switchgrass offers 540 % more renewable energy than the non renewable energy used during its manufacture according to the study conducted by researchers.
3.The main advantage of switchgrass is that it can be grown on marginal cropland, so it would not be in competition with food crops on our best land.
4.Another advantage switchgrass has over other oil crops such has corn,sugarcane is that the entire plant and not the seed can be used to produce ethanol,leading to much higher yields per tone.
DISADVANTAGES OF BIOFOOLISH:
1.Biofooliosh results in deforestation as it needs to clear the virgin land to make room for biofuels.
2.It would require us to use 96% of the US land mass for biofuel just to power the current number of cars on the road. So it cannot replace fossil fuel, but can reduce the usage of fossil fuel.
3.Production of ethanol from switchgrass needs saccharification an extra process compared to sugarcane.
Switchgrass can reduce usage of fossil fuel but it cannot replace the fossil fuel.It also replaces a part of hardwood pulps in printing and writing papers.Due to itshigh bulk it will especially suitable for bulky printing papers.It can be adopted easily into the current farming techniques. A new report by US researchers has found that fast-growing “switchgrass produces 94%less green house gas compared to non renewable gassoline. But it has limited herbicide option especially during establishment.
There is no open, operating biorefinery in the Pacific North West at this time to convert cellulosic material from switchgrass into bioenergy but this will be coming in the future. It has yet to be introduced in developing countries. So it holds out the shimmering promise of one day producing vast quantities of fuel in “carbon neutral” fashion, absorbing as much carbon dioxide in growth as it releases when burned. DuPont Danisco Cellulosic Ethanol makes biofuel from switchgrass, but the environmental benefits are highly questionable.
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