BIODIESEL
Submitted by: Rhea Wallang
Subject: Chemistry
Class: BSc. 6th Semester
Roll no.: 536 (S1701352)
INTRODUCTION
The generally and most widely used source of energy (contributes 80% of the world’s
energy needs) and the fuel we use on a daily basis are fossil fuels. These are carbonbased energy sources like coal, oil and natural gas and are considered non-renewable
resources as they are not easily regenerated. They are utilized most abundantly and are
most vital in the transportation sector, especially causing a great demand for Diesel and
Gasoline. The real expense of these fuels are rather greater than it’s mere cost, as they
impact not only our health and wellbeing, but also deplete and degrade our
environment.
Coal
Crude Oil
Natural Gas
A summary of the main aspects of their impact on the environment are given below:
•
Emissions: Fossil fuels emit harmful air pollutants long before they’re burned. Toxic
air pollutants are released from active oil and gas wells and from transport and
processing facilities. These include benzene (C6H5
) and formaldehyde (CH2O
), which are both carcinogenic and harmful in nature.
•
Global Warming: When oil, coal, and gas, are burnt, it is not just energy production
that is met, but also large quantities of Carbon dioxide (CO2
) is produced.
Oxygen (O2) reacts with glucose (C6H12O6) to produce water and CO2. The following
chemical equation describes the chemical process:
6 O2 + C6H12O6 —————> 6 H2O + 6 CO2 + Energy
Carbon emissions trap heat in the atmosphere resulting in the greenhouse effect
which subsequently leads to depletion of the ozone and climate change.
•
Land and water degradation: Apart from the obvious adverse effects of these fuels,
the extraction and transportation process itself, poses a great threat to it’s
surroundings.
It is for these reasons, and in attempts to overcome the persisting energy crisis,
various initiatives have been taken to substitute these fuels with cleaner, more
sustainable alternative for current and future utilization.
Biodiesel as one promising alternative to fossil fuel for diesel engines has become
increasingly important due to environmental consequences of petroleum-fuelled diesel
engines and the decreasing petroleum resources. Biodiesel can be produced by
chemically combining any natural oil or fat with an alcohol such as methanol or ethanol.
Research on biodiesel has shown that the fuel made by vegetable oil can be used
properly on diesel engines. Similarities between the combustion properties of biodiesel
and petroleum-derived diesel have made the former one of the most promising
renewable and sustainable fuels.
BRIEF HISTORY OF DISCOVERY
Biodiesel was first developed by German inventor Rudolph Diesel. Early
experimenters on vegetable oil fuels included the French government and Dr. Diesel
himself, who envisioned that pure vegetable oils could power early diesel engines for
agriculture in remote areas of the world, where petroleum was not available at the time.
Due to the widespread availability and low cost of petroleum diesel fuel, vegetable
oil-based fuels gained little attention, except in times of high oil prices and shortages.
World War II and the oil crisis of the 1970’s saw brief interest in using vegetable oils to
fuel diesel engines. Unfortunately, the newer diesel engine designs could not run on
traditional vegetable oils, due to the much higher viscosity of vegetable oil compared to
petroleum diesel fuel. A way was needed to lower the viscosity of vegetable oils to a
point where they could be burned properly in the diesel engine. Many methods had
been proposed to perform this task, including pyrolysis, blending with solvents, and
even emulsifying the fuel with water or alcohols, none of which have provided a suitable
solution.
It was a Belgian inventor in who first proposed using transesterification to convert
vegetable oils into fatty acid alkyl esters and use them as a diesel fuel replacement. The
process of transesterification converts vegetable oil into three smaller molecules which
are much less viscous and easy to burn in a diesel engine. The transesterification
reaction is the basis for the production of modern biodiesel, which is the trade name for
fatty acid methyl esters. In the early 1980s concerns over the environment, energy
security, and agricultural overproduction once again brought the use of vegetable oils
to the forefront, this time with transesterification as the preferred method of producing
such fuel replacements.
METHODS OF PREPARATION
There are several methods of preparation of Biodiesel, the most common of which
would be the transesterification due to low cost and reliable and fast but depending on
the raw material used, it may sometimes not be the preferred method. The various
methods of preparation are as follows:
1. Transesterification Process:
Transesterification process, as showed is a conventional method of biodiesel
production. In transesterification reaction, homogeneous catalysts (alkali or acid) or
heterogeneous catalysts can be used. The catalysts split the oil into glycerin and
biodiesel and they could make production easier and faster.
In this method, fatty acid alkyl esters are produced by the reaction of triglycerides
with an alcohol, especially ethanol or methanol, in the presence of alkali, acid or enzyme
catalyst etc. The sodium hydroxide or potassium hydroxide, which is dissolved in
alcohol, is generally used as catalyst in transesterification reaction. The products of the
reaction are fatty acid methyl esters (FAMEs), which is the biodiesel, and glycerin.
Ethanol can be also used as alcohol instead of methanol. If ethanol is used, fatty acid
ethyl ester (FAEE) is produced as product but methanol is preferred due to lower cost.
Mechanism:
A) Basic Catalysis
Alkali-catalyzed transesterification proceeds much time faster than that catalyzed by
an acid and it is the one most used commercially. The most commonly used alkali
catalysts are NaOH, CH3ONa, and KOH.
Step 1: The formation of an alkoxide, which is a strong nucleophile that attacks the
electrophilic Carbon in a carbonyl group of the triglyceride.
Step 2: The attack turns the carbonyl into a tetrahedral intermediate.
Step 3: The tetrahedral carbon is separated from the intermediate to form an alkyl ester
Step 4: De-protonation of catalyst regenerates the alkali, whereas the proton is attached
to a diglyceride anion as shown . Catalyst can reacts with another alcohol
molecule and the mechanism is repeated until the catalyst reacts once again
with an alcohol molecule to produce glycerol and alkyl esters
B) Acid Catalysis
For acid-catalyzed systems, sulfuric acid has been the most investigated catalyst, but
other acids, such as HCl, BF3, H3PO4, and organic sulfonic acids, have also been used by
different researchers.
Step 1: Protonation of the carbonyl group is the first stage
Step 2: A carbocation is then formed.
Step 3: The carbocation undergoes a nucleophilic attack. Alcohol is attached to the
tetrahedral intermediate
Step 4: A new ester is obtained by glycerol elimination and catalyst regeneration. The
carbocation formed in step II is highly reactive by which water must be avoided
during reaction because this molecule can act as a nucleophile and form
carboxylic acids, which is a competitive reaction
In these homogeneous catalyzed reactions, separation of catalyst from the reaction
mixture is hard and expensive. Large amounts of water is used to separate catalyst and
product and undesired by-product formation such as glycerin can be seen. The reaction
lasts very long and energy consumption may be very high, thus, new processes such as
supercritical process, microwave assisted method and ultrasound assisted method have
recently been developed.
2. Supercritical process:
Supercritical method is one of the novel methods in biodiesel production. Biodiesel
production can be easily achieved by supercritical process without catalysts. A
supercritical fluid is any substance at a temperature and pressure above its critical point.
It can diffuse through solids like a gas, and dissolve materials like a liquid. These fluids
are environment-friendly and economic. Generally, water, carbon dioxide and alcohol
are used as supercritical fluids.
In the study of this method, rapeseed oil was converted to methyl esters with
supercritical methanol (molar ratio of methanol to rapeseed oil: 42 to 1) at temperature
of 350°C in 240 s. The methyl ester yield of the supercritical methanol method was
higher than those obtained in the conventional method with a basic catalyst. Liquid
methanol is a polar solvent and has hydrogen bonding between OH oxygen and OH
hydrogen to form methanol clusters, but supercritical methanol has a hydrophobic
nature with a lower dielectric constant, so non-polar triglycerides can be well solvated
with supercritical methanol to form a single phase oil/methanol mixture. For this reason,
the oil to methyl ester conversion rate was found to increase dramatically in the
supercritical state.
Main factors affecting transesterification via supercritical process are the effect of temperature,
pressure and effect of molar ratio between alcohol and oil sample. Of which, temperature is
the most important factor in all parameters and affects the transesterification under
supercritical condition.
Fig. Biodiesel production by continuous supercritical alcohol process
Advantages of supercritical process are the shorter reaction time, easier purification
of products and more efficient reaction.
3. Microwave assisted process
Microwave process can be explained for the biodiesel production with
transesterification reaction: the oil, methanol, and base catalyst contain both polar and
ionic components. Microwaves activate the smallest degree of variance of polar
molecules and ions, leading to molecular friction, and therefore the initiation of
chemical reactions is possible because the energy interacts with the sample on a
molecular level, very efficient and rapid heating can be obtained in microwave heating.
Since the energy is interacting with the molecules at a very fast rate, the molecules do
not have time to relax and the heat generated can be for short times and much greater
than the overall recorded temperature of the bulk reaction mixture. There is
instantaneous localized superheating in microwave heating and the bulk temperature
may not be an accurate measure of the temperature at which the actual reaction is
taking place
Fig. Microwave assisted transesterification process shematic diagram
When the reaction is carried out under microwaves, transesterification is efficiently
accelerated in a short reaction time. As a result, a drastic reduction in the quantity of byproducts and a short separation time are obtained and high yields of highly pure
products. The only great drawbacks of this process are that it may not be easily scalable
from laboratory small-scale synthesis to industrial production and also the safety aspect
of this synthesis.
4. Ultrasound assisted process:
Ultrasonic waves are energy application of sound waves which is vibrated more than
20,000 per second. In another words, it can be defined as the sound waves beyond
human hearing limit. Ultrasonic irradiation has three effects according to the
investigators.
i.
First one is rapid movement of fluids caused by a variation of sonic pressure. It
causes solvent compression and rarefaction cycles
ii.
The second and the most important one is cavitation. If a large negative
pressure gradient is applied to the liquid, the liquid will break down and
cavities (cavitation bubbles) will be created. At high ultrasonic intensities, a
small cavity may grow rapidly through inertial effects. The formation and
collapse of micro bubbles are responsible for most of the significant chemical
effects and the major factor responsible for reaction speed.
iii.
The last effect of ultrasound is acoustic streaming mixing.
Ultrasonic mixing is an effective mixing method to achieve a better mixing and
enchancing liquid–liquid mass transfer and is responsible for increased yield. Vigorous
mixing increases the contact area between oil and alcohol phases with producing
smaller droplets than conventional stirring.
Cavitation effects increase mass and heat transfer in the medium and hence increase
the reaction rate and yield and also provides the necessary activation energy for
initiating transesterification reaction.
Fig. Scheme of biodiesel production process via ultrasound assisted method
Ultrasonic assisted transesterification of oil presents some advantages compared to
conventional stirring methods such as reducing reaction time, increase the chemical
reaction speed and decrease molar ratio and methanol, increase yield and conversion.
Ultrasound irradiation reduces the reaction time compared to conventional stirring
operation. Ultrasonic irradiation method enabled to reduce the reaction time by 30
minutes or more in production from various vegetable oils, thus, proving to be a
promising method of synthesis.
APPLICATIONS OF BIOSIESEL
Although Biodiesel is most popularly used as an alternative fuel for automotives, but
as a biofuel itself, it is an energy source that can be employed in many other industries
while also proving an environmental aid. Some of it’s uses are Listed below:
1) Automotive diesel engines:
The engine performance fuelled with biodiesel is crucial for the application of
biodiesel. Biodiesel raises the cetane number of the fuel and improves fuel lubricity. A
higher cetane number means the engine is easier to start and reduces ignition delay.
Diesel engines depend on the lubricity of the fuel to prevent moving parts from wearing
prematurely. Improved lubricity reduces friction within the moving parts, avoiding
additional wear. A primary advantage of biodiesel is that it can improve the lubricity of
the fuel at blend levels as low as 1%.
Additionally, research has shown that emissions for 100% biodiesel (B100) are 74%
lower than those from petroleum diesel
2) Railway usage:
The potential of biodiesel application on rail transport for reducing the dependence
on using the non-renewable diesel fuel and improving the environmental characteristics
of the locomotive have been considered. The technique of comparative research
concerning fuels on the rheostat and through operational tests has been offered. The
methods of measuring harmful emissions with exhaust gases and the use of existing
methods of controlling the fuel consumption have been developed.
3) Aviation fuel:
A large number of studies conducted in Russia and abroad have been devoted to the
development of low-emission gas turbine engines for aircraft and power stations . When
using biofuel, the emission of smoke, solid carbon, carbon monoxide, sulfur and total
carbon dioxide is decreased. It is economically feasible and can be mixed in any
proportion with conventional jet fuel so as to not require the creation of an alternative
ground fuel-supply infrastructure and adjustment of aircraft engines.
4) Heating oil
The environmental benefits of biodiesel in producing bioheat are significant. First,
depending on the blend level, biodiesel lowers the carbon content of heating oil.
Secondly, biodiesel is made from renewable, organic sources such as the oil from soy
beans and used cooking oils. The heating oil industry have also committed to
introducing higher blends of biodiesel into the heating oil marketplace and these
organization are conducting ongoing research on higher percentage blends of biodiesel
in heating oil.
5) Use in electrical energy generators
Biofuels are derived from biomass—that is, plant material or animal waste. Biomass
crops provide an environmentally friendly fuel source for generating electrical energy.
Generation powerplant, fuelled by biomass uses conventional steam turbine electricity
generating plant as used in coal fired power stations with modifications to the
combustion chamber and fuel handling systems to handle the bulkier fuel.
Because of the poor energy conversion efficiencies of biomass fuels, practical
generating systems often employ co-firing with coal to achieve reasonable utilisation of
the generating plant.
ADVANTAGES AND DRAWBACKS OF BIODIESEL
Advantages:
•
Produced from Renewable Resources: Biodiesel is a renewable energy
source unlike other petroleum products that will vanish in years to come. Since it is
made from animal and vegetable fat, it can be produced on demand and also
causes less pollution than petroleum diesel.
•
More Health Benefits: Air pollution cause more deaths and diseases than any other
form of pollution. Pollutants from gasoline engines when released in the air,
form smog and make thousands of people sick every year. Biodiesel produce less toxic
pollutants than other petroleum products.
•
Cost efficient: As of now, biofuels cost the same in the market as gasoline does.
However, the overall cost-benefit of using them is much higher. They are cleaner fuels,
which means they produce less emission by reducing the amount of suspended particles
in the air. This reduces the cost of healthcare products.
•
Durability of diesel engines: There is also no need for engine conversion. This
keeps the engine running for longer, requires less maintenance and brings down overall
pollution check costs. It can be used in 100% (B100) or in blends with petroleum diesel.
e.g. B20 is called 20% blend of biodiesel with 80% diesel fuel. It improves engine
lubrication and increases engine life since it is virtually sulphur free.
•
Better Fuel Economy: Vehicles that run on biodiesel achieve 30% fuel economy
than petroleum based diesel engines which means it makes fewer trips to gas stations
and run more miles per gallon.
•
Less Greenhouse Gas Emissions: Fossil fuels when burnt release greenhouse
gases like carbon dioxide in the atmosphere that raises the temperature and causes
global warming. To protect the environment from further heating up, many people have
adopted the use of biofuels. Experts believe that using biodiesel instead of petroleum
diesel can reduce greenhouse gases up to 78%.
•
Biodegradable and Non-Toxic: When Biofuels are burnt, they produce
significantly less carbon output and few pollutants. As compared to petroleum diesel,
biodiesel produces less soot (particulate matter), carbon monoxide, unburned
hydrocarbons, and sulfur dioxide. Flashpoint for biodiesel is higher than 150°C whereas
the same is about 52°C for petroleum diesel, which makes it less combustible. It is
therefore safe to handle, store and transport.
Disadvantages:
•
Variation in Quality of Biodiesel: Biodiesel is made from variety of biofuel crops.
When the oil is extracted and converted to fuel using chemical process, the result can
vary in ability to produce power. In short, not all biofuel crops are same as amount of
vegetable oil may vary.
•
Limitation at low temperatures: These problems include improving the relatively
poor low-temperature properties of biodiesel as well as monitoring and maintaining
biodiesel quality against degradation during long-term storage (due to its unstable
double bond). Maintaining fuel quality during long-term storage is a concern for
biodiesel producers, marketers, and consumers.
•
Food Shortage: Since biofuels are made from animal and vegetable fat, more
demand for these products may raise prices for these products and create food crisis in
some countries. For e.g.: the production of biodiesel from corn may raise its demand
and it might become more expensive which may deprive poor people from having it.
•
Clogging in Engine: Biodiesel cleans dirt from the engine. This proves to be an
advantage of biofuels but the problem is that this dirt gets collected in fuel filter and
clogs it.
•
Regional Suitability: Some regions are not suitable for oil producing crops. The
most productive crops can’t be produced anywhere and they need to be transported to
the plants which increases the cost and amount of emission associated with the
production and transportation.
•
Monoculture: Monoculture refers to the practice of producing same crop over
and over again rather than producing different crops. While this results in fetching best
price for the farmer but it has some serious environmental drawbacks. When the same
crop is grown over large acres, the pest population may grow and it may go beyond
control. Without crop rotation, the nutrients of soil are not put back which may result in
soil erosion.
•
Fuel Distribution: Biodiesel is not distributed as widely as petroleum diesel. The
infrastructure still requires more boost so that it is adopted as most preferred way to run
engines.
•
Use of Petroleum Diesel to Produce Biodiesel: It requires much amount of energy
to produce biodiesel fuel from soy crops as energy is needed for sowing, fertilizing and
harvesting crops. Apart from that, raw material needs to be transported through trucks
which may consume some additional fuel. Some scientists believe that producing one
gallon of biofuel needs energy equivalent to several gallons of petroleum fuel.
CONCLUSION
To sum up all the above points, biodiesel, rich in vast raw materials, excellent in
dynamic properties, has received high attention. It’s production is set to rise drastically
in the coming years. Biodiesel offers the promise of numerous benefits related to energy
security, economics, expansion of the agriculture sector and reduction of pollutant
emission. Despite its many advantages as a renewable alternative fuel, biodiesel
presents a number of problems that must be resolved before it will be more attractive as
an alternative to petroleum diesel. These benefits of biodiesel will continue to ensure
that a substantial market exists for this attractive alternative to conventional petroleum
diesel fuel.
However despite all this, from a commercial standpoint, the traditional petroleum
industry may be more comfortable with non-ester renewable diesel fuels than with
biodiesel, which may present a substantial challenge to the widespread deployment of
biodiesel as an alternative fuel. All governments should correctly understand and handle
the relation between biofuel and unresolved issues, such food security, land use
changes, forest protection. If these issues mentioned above could be resolved properly,
it would be reasonable to believe that in the near future.
BIBLIOGRAPHY
E-books:
1.
Chemistry of Fossil Fuels and Biofuels by Harold H. Schobert
2.
Biodiesel: production and properties by Amit Shah
3.
Biodiesel Science and Technology: From Soil to Oil by Jan C. J. Bart, N Palmeri, and
Stefano Cavallaro
4.
Production of Biofuels and Chemicals with Ultrasound by Zhen Fang, Richard L.
Smith, Jr., Xinhua Qi
Articles:
1.
Agarwal, A.K. Biofuels (alcohols and biodiesel) applications as fuels for internal
combustion engines. Progress in Energy and Combustion Science 2007
2.
Shia, X.; Panga, X.; Mu, Y.; He, H.; Shuai, S.J.; Wang, J.X.; Chen, H.; Li, R.L. Emission
reduction potential of using ethanol–biodiesel–diesel fuel blend on a heavy-duty
diesel engine Atmospheric Environment 2006
3.
Ewing, M., Msangi, S.. Biofuels production in developing countries: assessing
tradeoffs in welfare and food security.