Diesel plays an important role particularly in the Industrial Economy of a country. This fuel plays a vital role in the transport sector. The demand for this fuel increases with growth of economy of a country. Since Auto sector is one of the principal user, much of the attention has been in this area. So an alternate fuel which is competitive on price, environmentally friendlier and readily available has been on the wish list of many countries.
Biofuels and bioenergy are identified as the solutions that will relieve us from the current dependence on fossil fuels. There are several initiatives in this direction with multi pronged research and activities in making biodiesel as an alternative (1).
Biodiesel is often referred to as vegetable oil or animal fat, and this is a misnomer. It is alkyl esters produced by a transesterification reaction between fat or oil and with an alcohol. Methanol is the most commonly used alcohol for transesterification for it reacts easily and is inexpensive compared to other alcohols. Also a mixture of Biodiesel and petroleum diesel is loosely referred to as Bio diesel, which again is not totally correct. It is to be mentioned as Biodiesel blend (1).
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Biodiesel is an interesting alternative energy resource. Whether they can substitute our current fossil fuel demands as a viable, large scale energy source, is a moot point. Since it is likely that biodiesel can play a significant role in future energy consumption, it is important that both pros and cons are analyzed extensively.
This is the issue for which an answer will be attempted in this section.
Biodiesel has lot of advantages and benefits, but flip side issues exist as well. This article provides insight into the several (perceived) disadvantages of biodiesel, and also the concerns that have been encountered while using them.
While Biodiesel has been in use for several decades, their usage became and has been insignificant, since crude oil began to be extracted at a low cost. However with the depletion of Fossil Fuel happening, the Biodiesel has slowly crept back into prominence and their share is slowly moving up.
Biologically produced oils can be used in diesel engines. Biologically produced fuels can be produced from various wastes and common crops. This can be viewed as an advantage and as disadvantage too. Valuable land gets used up and so is food of many. Segregating Bio wastes is currently a tricky operation since source segregation of waste is yet to be implemented successfully.
While Europe principally derives Bio diesel from rapeseed, the United States use Soybean as feedstock for Biodiesel production. Palm oil and Jatropha are feedstock which are popular and gaining ground. So the feed stock depends on crops which can be grown easily in a particular area and no one crop can be used or termed as The crop for production of biodiesel (1).
The disadvantages of Biodiesel appear to be too many, perhaps due to the fact that usage of Biodiesel has just about caught up the attention and people have started looking at it more closely. These disadvantages are likely to reduce with increased research and they are likely to be addressed and solved.
In the following write up, the disadvantages are discussed and the research measures in key areas are also discussed.
THE MAJOR DISADVANTAGES OF BIODIESEL
A major factor preventing the extensive usage of biodiesel is cost. The feedstock costs for biodiesel is high compared to the cost of petroleum diesel. This results in the cost of biodiesel being higher than petroleum diesel fuel. Additionally, transportation costs are far higher for biodiesel because the transportation infrastructure for biodiesel is yet to mature.
The cost of biodiesel consists of following major components:
the cost of the feedstock, the cost of the biodiesel, the price of glycerol by-product, and availability of biodiesel (2).
We will examine some of these components.
? Cost of the Feedstock
The cost of the feedstock varies from one season to the next. It also varies from one crop to the other, depending on supply and demand. The wide fluctuation of the feedstock has impact on the final cost, which swings accordingly.
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? Cost of Biodiesel
Since biodiesel is not yet available on pipeline network, almost all deliveries are made by surface transport. This cost of surface transportation, forms a significant portion of the final product cost.
? Long term storage stability of biodiesel
It is very critical that research analyses carried out by various researchers are studied for the long term storage of the Biodiesel. During long term storage Bio-Diesel is likely to deteriorate and consequently wastage occurs.
? NOx and Other Exhaust Emissions
Biodiesel causes more NOx emissions than conventional diesel fuel. For example in case of B100, NOx production increase is by 13%. When using a B20 blend, NOx emission is increased by mere 2% (3).
Therefore to meet the statutory emission requirement, engine manufacturers will use both blended biodiesel and also treat of exhaust to reduce NOx emissions.
This is also possible because of low sulphur levels in biodiesel fuels and exhaust gas treatment technologies are readily available.
There are several studies which found increased nitrous oxide (NOx) emissions with higher concentrations of biodiesel (4).
? Lower energy content
Biodiesel fuels contain about 12.5% less energy per unit of weight than petroleum diesel fuel (37,215 kJ/ kg vs. 42,565 kJ/kg). However, due to higher density of Biodiesel, the energy content per unit of volume is only 8% less. The result is that, the fuel economy of diesel engine run with biodiesel is slightly less than an engine powered by petroleum diesel fuel.
Power loss in engine operation occurs due to energy content of neat Biodiesel being lower than that of petroleum based diesel.
Biodiesel is generally blended with petroleum fuel to minimize the power loss. (Blends are designated as Bxx, where "xx" is the percentage of biodiesel in the blend. The current popularly accepted blend is a B5 blend (5% biodiesel and 95% diesel fuel) .Several other blends are also in the race for popularity (5).
? Viscosity of Biodiesel
A major disadvantage of biodiesel is its higher viscosity. Viscosity of biodiesel is approximately 1.5 times higher than that of fossil diesel. Fuel may thicken at lower temperatures and does not flow properly and affects the performance of fuel lines, pumps and injectors. Viscosity also adversely affects quality of atomization and combustion as well as engine wears (3).
Because of this higher viscosity, fuel pumping difficulty is encountered in Diesel engines. This results in increase in fuel consumption too, indirectly. If one takes into consideration the higher cost of production compared to petro-diesel, this increase in fuel consumption contributes adversely to the overall cost of biodiesel when considered as an alternative to petro-diesel (3).
? Cold Weather
The cloud point is much higher for biodiesel than that of diesel fuel. This results in the biodiesel fuel not working in the engine as well as petro diesel fuel, particularly at lower temperatures. Additives are generally used to reduce the cloud point of biodiesel fuel. The cold-weather properties of biodiesel can also be improved by using a lower level blend of biodiesel fuel (i.e., B5 instead of B20) (3).
Besides at low temperatures, Biodiesel Fuel is likely to thicken and gel because of its low cloud point. Tanks need to be kept heated in the winter (6).
? Material Compatibility
Biodiesel fuel reacts aggressively with some plastics and some metals. Nylon, Teflon, and Viton are however acceptable. Non-ferrous metals, such as copper and zinc, react with biodiesel fuel causing precipitation. This is a concern, since some of these are used as material of construction in components of fuel tanks, transfer lines, pump diaphragms, seals etc. (3).
Biodiesel is a solvent and this creates problems. The biodisesel dissolves existing residues in used fuel tanks and carries them to the fuel system and clogs them. So in existing tanks before switching over to bio diesel thorough cleaning is mandatory (3).
? Storage and use
Blending of biodiesel is not effective if the temperature of either fuel is below 4 C. Low temperatures adversely impact mixing of petroleum diesel fuel.
Biodiesel has high flash point and hence is not considered flammable. However the fuel is considered combustible. This is not the case for a low-level blend. Blends of biodiesel are to be handled in the same way as petroleum diesel fuel. This makes it expensive, since flammables are to be handled much more carefully from the safety point of view. Additional equipment to address this aspect on safety is another reason for the price increase (7).
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The oxidative stability of biodiesel fuel is a major issue during long term storage of biodiesel fuel. The iodine number is commonly used in estimating the oxidative stability of the fuel before addition of stabilizers. Biodiesel fuels can be stored up to 6 months without any major problem. For storage beyond this period, antioxidants are to be added to enhance stability. Otherwise biodiesel is likely to form gums and sediments which are likely to clog filters or deposits on fuel components, including fuel pumps and injectors.
In addition, under certain climatic conditions, biological growth (such as algae), happens in the fuel. To stop this, biocide can be added. Water contamination, if avoided greatly helps in reduction of this biological growth in the fuel (7).
To understand this stability issue, the oxidation stability study has to necessarily be conducted for a period of at least 12 months, at regular intervals; samples are to be taken to measure the following physicochemical quality parameters.
The following are the principal parameters which are pointers in this direction of long term storage.
? Peroxide value (PV)
This influences Cetane Number (CN), specified in the fuel standard. Increasing the Peroxide Value increases the Cetane Number, an effect that likely reduce ignition delay time ( Knothe, 2002 ) (8).
? Acid value (AV)
The acid number increases with an increase in peroxides because the esters first oxidize to form peroxides which then undergo complex reactions, including a split into more reactive aldehydes which further oxidizes into acids (8).
? Viscosity (m)
Oxidation of ethyl ester begins with build-up of peroxides; viscosity starts to increase only after the peroxides reach a certain level. During long storage the viscosity of ethyl esters increases owing to the formation of oxidized polymeric compounds. This leads to the formation of gums and sediments and these clog filters (8).
? Iodine value (IV)
The lack of correlation between oxidative stability as well as other properties of biodiesel and iodine value had been noted previously by other researchers ( Knothe, 2002;Knothe and Dunn, 2003; Schober and Mittelbach, 2007 ) (8).
For the success of Biodiesel as an alternative, this storage is an essential issue to be tackled and solved however this is very time consuming.
CURRENT RESEARCH INITIATIVES TO COUNTER DISADVANTAGES OF EXISTING BIODIESEL PRODUCTS
There are several barriers or disadvantages to the development and eventual large scale commercialisation of biodiesel production from the currently used feedstock.
The major disadvantages can be broadly classified as technological, cost including feedstock, supply chain and storage. Several research initiatives aim at reducing these barriers.
Presently, Production costs are uncertain and vary with the type of feedstock and their availability. The major non-technical barriers are land availability and its effective usage. In some cases fertility of land suffers depletion, resulting in poor subsequent yields.
Feedstock selection ranging from soybean, rapeseed to palm oil and jatropha have been steps in improvement based on the ENERGY CONTENT and cost. Several advancements have been achieved, through research, in solving Technological barriers; a few are Catalyst recovery, improvement of long term Storage by oxidation stability through anti oxidants etc. (9).
Similarly, Viscosity which has been a major issue is also being tackled, since it is several times greater than the normal diesel fuel. Problems appear in the engine after prolonged operation. Blending with normal Diesel fuel, micro-emulsification with methanol or ethanol has been a simple solution; considerable experiments are being conducted in approaching this problem.
Usage of solid catalyst is another area of research for improvement
Genetic engineering could play a vital role in viscosity reduction. Acetyl glycerides, or acTAGs posses low viscosity and could be a boon. "The lower viscosity acTAGs could therefore be useful as a direct-use biofuel for many diesel engines." Several such ongoing research programs are on and could perhaps arrive at an answer in the years to come (10).
While these Technical solutions through multi pronged research activities have been progressing, non technical barriers do not allow the current Biodiesel technology to acquire a leadership role against the conventional Diesel. With the currently identified feed stock, the land availability for future expansion to meet the increased Biodiesel demand, poses a major question.
Therefore research initiatives have begun in the direction of identifying a feedstock with higher energy content and consequently that which does not require large space.
The one such feedstock showing great promise is Algae and several research programs are on to use this as a source for Biodiesel.
Algae s are one of the fastest-growing plants in the world and can be grown in open ponds, photo-bioreactors and closed systems. Different species of algae are available and are suited for different types of fuel. Algae grow almost everywhere, sewage or salt water, and do not require fertile land (which is required by food crops) and almost 50% of their weight is oil." (11).
"High oil species of microalgae cultured in growth optimized conditions of photo-bioreactors have the potential to yield 19,000 57,000 l of microalgal oil per acre per year. The yield of oil from algae is many time over the yield from the best-performing plant/vegetable oils." (11)
Besides, Microalgae are not only fast-growing with an appetite for carbon dioxide, which makes it more environmentally friendly. Green house gases which have drawn the global attention are likely to get diminished with this. Current research is focused on microalgae to produce biodiesel from algal oil (11).
"Cost of producing microalgal biodiesel can be reduced substantially by using a biorefinery based production strategy, improving capabilities of microalgae through genetic engineering and advances in engineering of photo-bioreactors (11).
Producing biodiesel from algae is being looked upon as the most efficient and environment friendly option to produce biodiesel fuel. Conversion of Algal-oil into biodiesel is as easy as obtaining oil from land-based crops. The key issue is in identifying an algal strain with a high lipid content, high growth rate and cost-effective cultivation system (i.e. type of photobioreactor) that is best suited to that strain. Photo bioreactors currently are not cost effective but eventually prices are likely to fall once standardisation comes into effect and large scale requirement are likely to have a positive impact in further bringing down the prices.
During growth phase, Algae consume carbon dioxide and this could be used to capture CO2 from industrial sources where they are let out into atmosphere (11).
The possibility of using genetically modified system could further enhance the attractiveness to use Algae as the future feedstock for biodiesel.
One other major area of current research interest is growing Algae off Shore in the ocean and converting into Biodiesel. If this becomes successful, fertile landmass will be used for more productive application, of providing food for the hungry. Though it may appear to be advantageous to countries with vast shoreline, the prices are likely to drop because of the mass production, which will make it globally attractive.
Biodiesel definitely offers several advantages to be considered as an effective alternative to the petroleum based Diesel. However, currently the number of disadvantages far outnumbers the advantages particularly on the technical aspects. The result is that the commercial viability also gets affected. Hence the successful utilisation of Biodiesel is not to the proportion it should be. Therefore the future success of Bio diesel as an alternative fuel has to wait till the shortcomings are effectively resolved.
The current major concerns on the two major aspects, Technical and commercial, which affect the acceptability of Biodiesel, can be listed as follow
The Biodiesel production process is currently shifting from homogeneous to heterogeneous which use solid catalysts to achieve high yield. This process is clean and product separation is easier, but is not economical.
The raw material contains free fatty acid and moisture and must be sufficiently controlled but this is a very challenging task.
Higher fuel consumption is expected with biodiesel due to relatively lower energy content which makes it more expensive.
Biodiesel has a major shortcoming in its cold flow properties particularly in cold environments. This means additional gadgets thus making it unattractive on final price.
Storage problems due to biological changes and the alcohol content in biodiesel which attack certain rubber components still are major concerns. Biodiesel, with high-level NOx emission due to its high oxygen content, is still offering a technical challenge to the experts. (1)
Many of the above problems can be addressed, while some others cannot be, at least now. Issues concerning toxic emissions could possibly be taken care of by innovative designs and technology. The two issues that appear quite daunting are:
(a) Land Availability for Feedstock
Biodiesels from conventional bio-feedstock to replace today s petro products completely, it will take almost the entire cultivable area of Earth; yields cannot be increased to that level in the next few years.
This is being addressed by identifying higher yield feedstock such as palm oil or Jatropha oil.
(b) Ecological Concerns
Large-scale cultivation of these feedstocks can result in massive ecological damage such as cutting down of the rainforests (12).
The one area where considerable focus is being done is to look at Algae as a source, which will save deforestation. Besides, the yield is also very high compared to the traditional oil crops (12).
The eventual use of Biodiesel is in the hands of various Governments and business houses to pump in huge resources into research to tackle the above mentioned shortcomings and to finally achieve a greener world (13).
As of now it appears biodiesel can replace Petroleum diesel only to a small level but creep up eventually to have a healthier share.