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Biodiesel is obtained from vegetable oil or animal fat and is a renewable fuel. It involves a chemical process and can be used as either direct substitute, extender or as an additive to fossil diesel fuel in compression ignition engines. It is an extremely environmentally friendly source which can help in easing the pressure off the non-renewable sources of energy.
The biodiesels are made from vegetable oils for example soy and corn. It is a clean fuel, since it doesn't contain petroleum and other toxic substances and has fairly cost effective preparation. It is thus, helpful in reducing the carbon footprint and prevents global warming. Environmental Protection Agency (EPA) has passed this renewable source of energy as a clean and non polluting fuel and has accredited it to meet the standards of California Air Resources Board (CARB).
Methanol and chemical processes that separates glycerin and methyl esters from fats or vegetable oils are used to prepare biodiesel. Glycerin being a common byproduct is used ensuring optimum utilization and cost effective production.
Its only demerit lies in the fact that crops require substantial time and investment thus making biodiesal a bit expensive from petrol. However that demerit is adequately offset by the fact that it is an environment friendly fuel.
Biodiesel is an alternative liquid biofuel. It is an important source of renewable energy as it plays an important role in various sectors of industrial growth and is cost effective.
The production of biodiesel or alkyl esters can be carried out in a number of ways. The three basic established methods are introduced below:
Base catalyzed transesterification of the oil
Direct acid catalyzed esterification of the oil with methanol.
Conversion of the oil to fatty acids, and then to Alkyl esters with acid catalysis.
The major production of the alkyl esters is carried out with the base catalyzed reaction because of following reasons:
Low temp. around (150 F) and press (20 psi) .
High conversion (98%) with min reaction time.
Direct conversion to methyl ester involving no intermediate steps.
Expensive materials of construction are not required.
The general process is depicted below. A fat or oil is reacted with an alcohol,
The basic steps for production of biodiesel are as follows:
Determination and treatment of free fatty acids
The feedstock ie waste vegetable oil is first filtered to remove dirt and other non-oil material. Water is thus removed since it initiates the hydrolysis of triglycerides; hence it gives salts of the fatty acids (soaps). Therefore it doesnt undergo the process of transesterification to give biodiesel.
Determination And Treatment Of Free Fatty Acids
Sample of pure feedstock oil isÂ titratedÂ with a standardized base solution to evaluate the concentration of free fatty acids (carboxylic acids) which is contained in vegetable oil sample. Esterification of diesel oil is thus carried out, which is turned into biodiesel henceforth. Once esterified, the bound glycerides are removed, typically through neutralization.
Products of the reaction include biodiesel and byproducts like soap, glycerin, excess of alcohol, and traces of water. The biodiesel produced is thus required to be separated from the other byproducts.
The density of glycerin is found to be greater than of biodiesel. Hence this particular property of glycerin is used to filter the bulk of the glycerin byproduct. Residual methanol is removed through the process of distillation and reused. Soaps are converted or reused as acids.
Triglycerides (1) are reacted with an alcohol such as ethanol (2) to give ethyl esters of fatty acids (3) and glycerol (4):
Reaction proceeds exceedingly slow or at worst it doesn't take place at all. Acid, basis and heat are generally used to catalyse theÂ reaction to proceed more quickly. 99% biodiesel is produced through virgin vegetable oils by the process of base-catalyzed technique. It is the most economical and optimum process.
Natural oils are preferably used in this process, the alkyl groups of the triglyceride are not necessarily the same. Following reaction distinguishes it:
R1, R2, R3Â :Â AlkylÂ group.
Triglyceride is reacted with alcohol in presence of catalyst (NaOH,Â KOH, or Alkoxides).This is done primarily in production of biodiesel to estimate amount of alkaline needed to completely neutralize any free fatty acid present which more or less ensures 100% transesterification.
There are three basic methods to biodiesel production:
Base catalyzed transesterification of the oil
Acid catalyzed transesterification of the oil
Conversion of the oil to its fatty acids and then to biodiesel.
Most of the biodiesel produced today is done with the base catalyzed reaction. This catalyst gets divided into glycerin and biodiesel.Â
The catalyst generally used is sodium hydroxide or potassium hydroxide dissolved in methyl alcohol. Reaction mix is kept above the boiling point of alcohol in contention. Time that is prescribed is around 1 to 8 hrs.
Degussa has developed a special catalyst Sodium Methylate which is widely used for biodiesel production. During production process, 30 % sodium methylate solution in methanol is used to manage the reaction of the oil to biodiesel and glycerol. One tonne of raw material may need around 17 -18 kgs of catalyst. Methyl ester and glycerol are separated at the end.
These catalysts are marketed in ready to use form by Degussa. The catalyst are added directly from storage tank to the production process and can be used in facilities having a an annual capacity of around 50k to 100k tones.
The basic advantage of use of Degussa Catalyst is that high glycerol yield having satisfactory quality is produced at very optimum costs. Around 2/3 of reputed biodiesel facilities are designed to cater to this special catalyst.
Potassium methylate, is also used for making biodiesel from old cooking fat.
The Base Catalysed Method
Base Catalyzed Transesterification Of Oil
The basic advantage of this process is that it requires low temp. and pressure and the reaction time is minimum with no intermediate compounds formed..
The process is carried out by mixing of biodiesel and catalyst. The catalyst is mixed with the agitator, the resulting mix is then charged in a closed reaction container. Oil or fat is subsequently added in required portions into the mixture. Sealed container should ensure no evaporation.
About 1 to 8 hours of reaction time is required for biodiesel production. The levels of alcohol and water are monitored closely to maintain right proportions. On completion of the reaction, biodiesel is separated from excess glycerin and methanol which are the byproducts of the reaction.
Base-Catalysed Transesterification Mechanism
A strong deprotonating base is required (like KOH, NaOH, Sodium methoxide),to mix with alcohol to make disperse the solid catalyst into oil. A dry ROH is required. This is because any moisture will initiate saponification. This would lead to formation of soaps and consumption of base.
The alcohol mixture is then dissolved in the triglyceride. Alkyl group on the triglyceride is replaced in a number of steps depicted below:
Polarized attraction |
RO- ----------------> C=O
Tetrahedral intermediate is formed. It has a negative charge on carbonyl oxygen.
RO-C-O- (pair of electrons)
DiacylglycerolÂ forming the ester is pushed and the electrons thereby fall back.
At the carbonyl group RO group gets attached through this mechanism.
The reaction mechanism has a few demerits,. RO-Â has to attack where there is a +ve charge density, ie on C=O.MeO- is efficient because of its small size.As the chain of RO- increases in length, due to the phenomena called stearic hindrance, its effectiveness decreases considerably , as the reaction rate decreases. Thus due to this very reason we prefer using short chained alcohols like methanol, ethanol to increase the reaction rate.
Acid Catalyzed Transesterification Of Oil Process For Production of Biodiesel
The reaction kinetics of acid-catalyzed transesterification of waste frying oil in excess methanol to form fatty acid methyl esters (FAME), for possible use as biodiesel have been studied in recent times. Rate of mixing, feed composition (molar ratio oil: methanol: acid) and temperature were independent variables.
There was no significant difference in the yield of FAME when the rate of mixing was in the turbulent range 100 to 600Â rpm. The oil : methanol : acid molar ratios and the temperature were the most significant factors affecting the yield of FAME. At 70Â Â°C with oil : methanol : acid molar ratios of 1:245:3.8, and at 80Â Â°C with oil : methanol : acid molar ratios in the range 1:74:1.9-1:245:3.8, the transesterification was essentially a pseudo-first-order reaction as a result of the large excess of methanol which drove the reaction to completion (99Â±1% at 4Â h). In the presence of the large excess of methanol, free fatty acids present in the waste oil were very rapidly converted to methyl esters in the first few minutes under the above conditions. Little or no monoglycerides were detected during the course of the reaction, and diglycerides present in the initial waste oil were rapidly converted to FAME.
The reaction is as follows:
Some of the industrially superior methods being used are discussed below:
BATCH PROCESS IN PROGRESS(DISPLAYED ABOVE)
There are many methods for biodiesel production. Some of them include the batch method, supercritical method, ultrasonic and the latest microwave method. These have been discussed in the following paras:
Batch Process: In this process, agitator is used to dissolve alcohol. The alcohol catalyst mixture is then charged into a closed reaction vessel and the bio-lipid is added. Here after try to maintain a closed atmosphere to avoid any leakage.
Super Critical Method: This is a continuous catalyst-free process for trans-esterification using supercritical methanol at very high temperatures and pressures. The 'oil' and 'methanol' being in single phase ensure the reaction occurs almost instantaneously. The process can tolerate water in the feedstock, as the free fatty acids are converted to methyl esters instead of soap, so a wide variety of feed stocks can be used, but energy costs of production are more or less similar to catalytic method.
The other methods include the Ultra Shear and High Shear biodiesel production method, which uses up to three sets of rotor and stator which converts mechanical energy to high tip speed, high shear stress and high shearing frequencies. The droplet size range is expected in the low micrometer until sub-micrometer range after one pass.
These Ultra and High Shear mixers are used for the pre-treatment of crude vegetable oil or animal fats, for the trans-esterification and water wash process such as improved de-gumming, improved refining. They also facilitate faster bleaching, batch Biodiesel conversion, continuous Biodiesel conversion, semi continuous Biodiesel conversion and continuous water wash process.
The ultra shear mixers are used to rapidly and intimately blend the acid or water, allowing a continuous trans-esterification process. The inline or batch reactors allow production of biodiesel in batch mode. This d reduces production time considerably and volume of production is increased.
In ultrasonic reactor biodiesel production method, the ultrasonic waves cause the reaction mixture to produce and collapse bubbles constantly. The cavity simultaneously provides the mixing and heating required to carry out the trans-esterification process.
Hence the trans-esterification process can be run inline in this method, rather than using the time consuming batch processing. Industrial scale ultrasonic devices permit the industrial scale processing of several thousand barrels per day.
Presently research is being directed into using commercial microwave ovens for biodiesel production to provide the heat needed for the trans-esterification process. The microwaves are capable of providing very high temperatures. A nonstop flow process producing 6 liters/minute at a 99% conversion rate has been innovated and proved to consume only 25% of the energy required as incase of batch process.
Although it is still in its development stage, the microwave method has undoubtedly great potential to be a highly efficient, cost effective method for the biodiesel production commercially.
There have been various advances in production of biofuels. Various researches have been carried out which are aimed at better utilization of bio-fuels that are cost effective too.
Through various researches, aimed at better utilization and cost effectiveness, there have been numerous advances in biofuels. Syracuse University's Radhakrishna Sureshkumar, professor and chair of biomedical and chemical engineering in the L.C. Smith College of Engineering and Computer Science, and SU chemical engineering Ph.D. student Satvik Wani have discovered a process that is a promising stride toward achieving these three goals.
An algae discovered by Sureshkumar and Wani can be used in the production of bio fuels. These algae tend to grow faster by manipulating light particles through the use of nanobiotechnology. As highlighted in the August 2010 issue of Nature Magazine, accelerated photosynthesis will makes the algae grow faster with minimal changes in the ecological sources required.
A new bioreactor as developed by the SU team can enhance algae growth. This was accomplished by making use of nanoparticles, selectively scattering blue light which promote algae metabolism. The team was able to achieve 30 percent greater growth of an algae sample as compared to a control with the use of optimal combination and confined nanoparticle suspension configuration.
As per Sureshkumar, "Algae produce triglycerides, which consist of fatty acids and glycerin. The fatty acids can be turned into biodiesel while the glycerin is a valuable by-product, Molecular biologists are actively seeking ways to engineer optimal algae strains for biofuel production. Enhancing the phototropic growth rate of such optimal organisms translates to increased productivity in harvesting the feedstock".
A miniature reactor consisting of a Petri dish of a strain of green algae (Chlamydomonas reinhardtii) on top of another dish containing a suspension of silver nanoparticles, to serve backscattering blue light into algae culture was created for this process. By varying the concentration and size of the nanoparticle solution, the team discovered that they could manipulate the intensity and frequency of the light source, hence achieving an optimal wavelength for algae growth.
As per Sureshkumar, "Implementation of easily tunable wavelength specific backscattering on larger scales still remains a challenge, but its realization will have a substantial impact on the efficient harvesting of phototrophic microorganisms and reducing parasitic growth. Devices that can convert light not utilized by the algae into the useful blue spectral regime can also be envisioned."
Thus far, this is one of the first explorations into utilizing nanobiotechnology to promote microalgal growth. The acceleration in the growth enhancement of algae also had various advantages outside the area of biofuel production.
Advances in Biodiesels
There is abundant biomass present in low value agricultural commodities or processing wastes requiring proper disposal to avoid our pollution problem, for example, the corn refinery industry generates more than 10 million metric tones of corn byproducts that are currently of limited use and pose significant environmental problems. Similarly, there are 60 billion pounds of cheese whey generated annually in the dairy industry much of this byproduct has no economical use at the present time and requires costly disposal because of its high biological oxygen demand. These various forms of biomass are inexpensive feedstocks for hydrogen, chemicals and power grade alcohol fuel (butanol) production.
Production of industrial butanol and acetone via fermentation, using Clostridia acetobutylicum, started in 1916, during World War I. Chime Wizemann, a student of Louis Pasture, isolated the microbe that made acetone. England approached the young microbiologist and asked for the rights to make acetone for cordite. Up until the 1920s acetone was the product sought, but for every pound of acetone fermented, two pounds of butanol were formed. A growing automotive paint industry turned the market around, and by 1927 butanol was primary and acetone became the byproduct.
The production of butanol by fermentation declined from the 1940s through the 1950s, mainly because the price of petrochemicals dropped below that of starch and sugar substrates such as corn and molasses. The labor intensive batch fermentation system's overhead combined with the low yields contributed to the situation. Fermentation-derived acetone and butanol production ceased in the late 1950s.
In the 1970s the primary focus for alternative fuels was on ethanol -- people were familiar with its production and did not realize that dehydration (a very energy-consuming step) was necessary in order to blend it with fossil fuels. Nor did we realize the difficulty of distribution, since ethanol cannot be transferred through the existing pipeline infrastructure. The selection of ethanol, a lower-grade, corrosive, hard-to-purify, dangerously explosive, and very evaporative alcohol is the result. Ethanol is still subsidized by the government, since it is not profitable enough to compete with gasoline. Over the past 30 years, however, the very energy-intensive ethanol process has not solved our fuel, power or clean-air requirements.
'Acetone butanol ethanol' fermentation by is a well known industrial fermentations. It is ranked 2nd to ethanol fermentation by yeast in its scale production.The actual fermentation,is very complicated, plus very difficult to control. ABE fermentation declined at a quick rate since the 1950s, and 99% butanol is produced via petrochemical routes.
In ABE fermentation, butyric, propionic, lactic and acetic acids are firstly produced by C. acetobutylicum, henceforth the pH drops which undergoes metabolic "butterfly" shift,as a result butanol, acetone and isopropanol are formed.
Conventional ABE fermentations involves butanol production from glucose that is low, taround 15 % and rarely exceeding 25%. Butanol production was limited by strong product inhibition. At a concentration of 1%,butanol can significantly inhibit cell growth and the fermentation process. Thus its concentration is below 1.3%.
During past 20 years, there have been many engineering attempts to improve the quality of butanol production in 'ABE fermentation', including processes like cell recycling and cell immobilization to enable an increase in cell density and reactor productivity,therby using extractive fermentation to minimize product inhibition.
The importance in the field of biodiesel technology has led to various viable replacements to fossil fuel for applications in C.I. engines has led to various researches in this field .
Our non renewable sources are fast depleting and thus in a scenario like today's there is a greater need to find renewable sources of energy that not only are eco friendly but cost effective too.There has been a spurge in research works in bio diesel production mainly because of the depletion of petroleum resources, and increase in awareness of environmental ,health impacts from the combustion of fossil diesel.
'Biodiesel' is preferred over other biofuels because of its compatibility with present day CI engines, as not many adjustments are required to make it compatible with present day C.I. engines. Studies performed to ensure C.I. engines Studies conducted till date on various CI engines that are fuelled with varying biodiesel blends under many test cycles have shown that key pollutants, such as carbon monoxide, sulphur oxides, unburnt hydrocarbons and particulate matters are potentially reduced.
The improvement in the 'diesel emission' species comes with a trade-off between reduction of brake power and substantial increase in fuel consumption. Biodiesel's has a very good lubricating property that is far better than fossil fuel in comparison, which invariably ensure increase in engine life.These prominent differences in engineout responses between biodiesel and fossil diesel combustion are decided by the physical properties and chemical composition of the fuels. Despite the stated benefits, universal use of biodiesel in CI engines is not a profitable proposition because of outstanding technical challenges, these include low temp. inoperability, storage instabilities, in-cylinder carbon deposition and also the fact the fuel might errode.
It is important that these problems are solved appropriately to make sure that long-term biodiesel usage in CI engines necessarily doesn't affect the durability of the engine.some of the solutions range from the biodiesel fuel reformulation as per feedstock choice and production technique, and also through the simple addition of fuel additives. This calls for a vehement intensive research internationally, with an 'overarching' approach for co-ordinating sustainable exploitation and utilisation of biodiesel. This review examines the combustion quality.
Exhaust emissions mainly like tribological impacts of biodiesel on CI engines, which specially focus on the influence of biodiesel's physico-chemical properties.The efforts in mitigating problems are related to engine operations due to biodiesel 'usage' must be addressed. Production methods that emerging at the present should be identified which specifically emphasize on the process where the yield is good like conventional transesterification process.
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