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.
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The reaction is as follows:
Where is the para for the third type of process - Conversion of the oil to its fatty acids and then to biodiesel
Some of the industrially superior methods being used are discussed below:
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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, catalyst is initially 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. The reaction mixture is made sure is above B.P. of alcohol. The reactions take a long time then both the resultant biodiesel and by product glycerin are allowed to settle down.
Super Critical Method (PLEASE PUT ALL OTHER METHODS IN THIS FORMAT) 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.
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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.
The importance of biodiesel as a renewable and economically viable alternative to fossil diesel for applications in compression ignition (CI) engines has led to intense research in the field over the last two decades. This is predominantly due to the depletion of petroleum resources, and increasing awareness of environmental and health impacts from the combustion of fossil diesel. Biodiesel is favoured over other biofuels because of its compatibility with present day CI engines, with no further adjustments required to the core engine configurations when used in either neat or blended forms. Studies conducted to date on various CI engines fuelled with varying biodiesel types and blends under numerous test cycles have shown that key tailpipe pollutants, such as carbon monoxide, aromatics, sulphur oxides, unburnt hydrocarbons and particulate matters are potentially reduced. The effects of biodiesel on nitrogen oxides emission require further tests and validations.
The improvement in most of the diesel emission species comes with a trade-off in a reduction of brake power and an increase in fuel consumption. Biodiesel's lubricating properties are generally better than those of its fossil diesel counterpart, which result in an increased engine life. These substantial differences in engine-out responses between biodiesel and fossil diesel combustion are mainly attributed to the physical properties and chemical composition of the fuels. Despite the purported benefits, widespread adoption of biodiesel usage in CI engines is hindered by outstanding technical challenges, such as low temperature inoperability, storage instabilities, in-cylinder carbon deposition and fuel line corrosion. It is imperative that these issues are addressed appropriately to ensure that long-term biodiesel usage in CI engines does not negatively affect the overall engine durability. Possible solutions range from biodiesel fuel reformulation through feedstock choice and production technique, to the simple addition of fuel additives. This calls for a more strategic and comprehensive research effort internationally, with an overarching approach for co-coordinating sustainable exploitation and utilization of biodiesel.
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This review examines the combustion quality, exhaust emissions and tribological impacts of biodiesel on CI engines, with specific focus on the influence of biodiesel's physico-chemical properties. Ongoing efforts in mitigating problems related to engine operations due to biodiesel usage are addressed. Present day biodiesel production methods and emerging trends are also identified, with specific focus on the conventional transesterification process wherein factors affecting its yield are discussed.