Types of Biofuel

8/10/2019 Types of Biofuel

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Types of Biofuel

Biofuels, like fossil fuels, come in a number of forms and meet a number of different energy needs. The class of

biofuels is subdivided into two generations, each of which contains a number of different fuels that will be explored inthis article.

First Generation Biofuels

First generation biofuels are made from sugar, starch, or vegetable oil. They differ from second generation biofuels

in that their feedstock (the plant or algal material from which they are generated) is not sustainable/green or, if used

in large quantity, would have a large impact on the food supply. First generation biofuels are the original biofuels

and constitute the majority of biofuels currently in use.

Second Generation BiofuelsSecond generation biofuels are greener in that they are made from sustainable feedstock. In this use, the term

sustainable is defined by the availability of the feedstock, the impact of its use on greenhouse gas emissions, its

impact on biodiversity, and its impact on land use (water, food supply, etc.). At this point, most second generation

fuels are underdevelopment and not widely available for use.

Biofuel Table

This table breaks biofuels down by generation and then explores their uses, energy densities, and greenhouse gas

impacts. Specific biofuels from the table are selected for further exploration on subsequent pages.


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CO2

Solid Biofuels

Wood

Dried plants

Bagasse

Manure

Seeds

Everything

from wood and

sawdust togarbage,

agriculturalwaste, manure

By Type

16-21

10-16

10

10-15

15

By Type

1.9

1.8

1.3

N/A

N/A

This category

includes a very

wide variety ofmaterials. Manure

has lowCO2emissions,but high nitrate

emissions.

Second Generation

Cellulosic

ethanol

Usually made

from wood,grass, or

inedible partsof plants

Algae - based

biofuels

Multiple

different fuels

made fromalgae

Can be used to

produce any of the

fuels above, as wellas jet fuel

See specific

fuels above

More expensive,

but may yield 10-

100X more fuelper unit area than

other biofuels

Biohydrogen Made from

algae breakingdown water.

Hydrogen

compressed to 700times atmospheric

pressure has energy

density of

123

Does not have

anygreenhouse

effect.

Used in place of

the hydrogenproduced from

fossil fuels

Methanol Inedible plantmatter

19.7 1.37 More toxic andless energy dense

than ethanol

Dimethylfuran Made from

fructose foundin fruits and

some

vegetables

33.7 Energy density

close to that ofgasoline. Toxic to

respiratory tract

and nervous

systemFischer-Tropsch

Biodiesel

Waste from

paper and pulp

manufacturing

37.8 2.85 Process is just an

elaborate

chemical reactionthat makes

hydrocarbon from

carbon monoxideand hydrogen


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Bioalcohols

The use of alcohol as a fuel is not a new concept. Henry Ford originally planned for his cars to run on ethanol, but the

value of alcohol for drinking made it more expensive for use as a fuel than the newly discovered petroleum. The first

four alcohols, (in order of carbon content) methanol, ethanol, propanol, and butanol, are of greatest interest for fuel

use as their chemical properties make them useful in internal combustion engines.

Fuel Economy and Octane

One of the problems with alcohols is that they have lower energy densities than gasoline. The chart below illustrates

the differences.

Fuel Energy Density(megajoules/liter) Average Octane (AKI rating/RON)

Gasoline ~33 85-96/90-105

Methanol ~16 98.65/108.7

Ethanol ~20 99.5/108.6

Propanol ~24 108/118Butanol ~30 97/103

AKI - Anti-Knock Index: This octane rating is used in countries like Canada and the United States.

RON - Research Octane Number: This octane rating is used in Australia and most of Europe

The chart above also reveals average octane numbers for each fuel. Besides reducing knock, higher octane values

are indicative of a fuel that burns slowly. In general, the slower a fuel burns, the more efficient it is to extract energy

from it. Thus, a higher octane also reveals a more energy efficient fuel. The fact that alcohols have higher octane

values than gasoline helps to offset some of the difference in energy density. The net result is that the loss of fuel

economy (how far a car can travel on a volume of fuel) is not as drastic as it would be if the octane numbers were the

same.

Biological Production versus Refining

It is true that any of the alcohols above can be generated from fossil fuels. However, it is easier and more efficient to

derive these products from biomass or even carbon dioxide and water than to refine petroleum. It is also the case that

petroleum-derived alcohols tend to be less pure (ethanol is contaminated with methanol for instance) and often

cannot be purified through simple distillation.

Methanol

Methanol is closely related to methane. In fact, there is only one atom different between these two chemicals

(Oxygen shown in blue, carbon in black, hydrogen in red).


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Methane Methanol

Though these molecules are remarkably similar, their properties could not be more different. To begin, methane is a

gas at standard temperature and pressure. Methanol, on the other hand, is a liquid. Methane has an energy density

of 55 MJ/kg while methanol has an energy density of only 23 MJ/kg at best. Burning methane produces twice the

amount of carbon dioxide per kilogram as burning methanol does (2.74 kg CO2/kg methane versus 1.37 for

methanol).

How can two molecules that are so similar act so different? The answer is in the oxygen atom. This highly

electronegative atom (that means it like electrons) changes the structure of the bonds so much that the overall

reaction energy for the molecule is changed. Of course, losing energy is not the only consideration. Methane makes a

poor fuel because it is a gas, which makes it difficult to transport. On the other hand, methane isn't toxic, while

methanol will cause blindness or even death in small quantities. Perhaps there is a better alcohol that has the positive

properties of methane and methanol, with fewer of the negative properties.

Ethanol

Ethanol is standard drinking alcohol, so we know it isn't poisonous. Already we're off to a better start than methanol. It

also has a higher energy density than methanol and is still a liquid, which makes it an attractive alternative. Ethanol is

only one atom different than ethane. Like methane and methanol, the differences between these molecules aredrastic.


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Ethane

Ethanol

Ethanol is a common additive to fuels in many countries. Globally, the average ethanol content in petrol is roughly

5.4%, though some countries supply 25% or even 100% ethanol for vehicle fuel. The world's largest producers of

ethanol are the United States and Brazil. In the U.S., petrol contains an average of 10% ethanol. In Brazil, petrol has

a minimum of 25% ethanol by law and as many as 17.3 million vehicles use 100% ethanol (called neat ethanol) as a

fuel.

Ethanol has some benefits as a fuel or as a fuel additive. First, because it has a higher octane number than ethane

and even many of the larger hydrocarbons, ethanol can be used to boost the octane of a fuel. Beyond that, it burns

cleaner than most hydrocarbon fuels and, if created from biomass rather than petroleum, contains little or no

contamination to damage vehicle parts or lead to smog.

The drawbacks to ethanol as a fuel, however, have prevented its widespread adoption. First of all, it takes about 1.5

times more ethanol than gasoline to get the same energy. That means you need a fuel tank 1.5 times larger if you

want to travel the same distance on ethanol that you do on gasoline. Another problem with ethanol is that it is

corrosive to the rubbers used in the gaskets and fuel delivery lines of older vehicles. A reformulation of rubber was

necessary to ensure that these components do not fail in modern cars, particularly those running on 100% ethanol.

Finally, ethanol absorbs water from the environment, which dilutes its concentration and makes it impossible to ship it

through pipelines.


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So, ethanol isn't the optimal standalone fuel, but it does seem to make for a great fuel additive. In addition, some

inventive individuals have found ways to combine ethanol and gasoline combustion to improve fuel economy by up to

30%. At the Massachusetts Institute of Technology, the use of high compression engines that mix gasoline and

ethanol (each stored separately onboard) to combat knock during high engine loads has led to a car that is 30% more

fuel efficient than a standard gasoline engine and which avoids the high costs associated with diesel and hybrid

technology. Though ethanol may never be a standalone fuel, its potential as a fuel supplement appears high so longas we remain a petroleum-based society.

Propanol

Propanol is the forgotten alcohol fuel, but for good reason. Propanol is the most difficult and expensive alcohol to

produce. Because its energy gains over ethanol are minimal, the large scale production and use of this fuel is hard to

justify.

Propanol is not without its uses, however. The major use, at least in the automotive segment, comes from the drying

properties of 2-propanol, which is better known as isopropyl alcohol or rubbing alcohol. It is known as a gas dryer, but

2-propanol actually keeps water in solution with gasoline, thereby preventing it from freezing in gas lines. You canalso buy isopropyl alcohol in spray cans to de-ice your windshield.

Butanol

Butanol is more similar to gasoline than ethanol or methanol. This similarity is a consequence of its longer

hydrocarbon chain, which means there is more carbon in relation to the single oxygen and thus the molecule is less

polar. The diagram below shows only one version of butanol. Because there are four carbons, there are four possible

structures to butanol.

Butane


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n-Butanol

The similarity of butanol to gasoline means that it can be used in a standard vehicle without the need for

modifications. Also, because of its size, butanol has an energy density similar to that of gasoline. In fact, butanol is so

close to gasoline in energy content that its octane rating nearly makes up for the difference in energy density. In other

words, a liter of butanol will get your car about as far as a liter of gasoline, with the difference only being about 10%. It

is also true that butanol only produces about 2.03 kg of carbon dioxide per kilogram of butanol while gasoline

produces 3.3 kg of carbon dioxide per kilogram of gasoline.

With all of these advantages the natural question is why has butanol not replaced gasoline? The answer is three-fold.

First, butanol actually produces more carbon dioxide than what arises just from burning it. The reason for this

discrepancy is that producing the biomass, harvesting it, and processing it all requires energy which releases CO2.

This input of energy needed just to produce butanol as raises questions about how efficient biofuels are, a topic

addressed in detail in another article. Right now there is a great deal of research into using algae to produce butanol.

Tulane University is leading the charge in this are as well as in the use of bacteria to produce butanol from cellulose.

The second reason that butanol has not replaced gasoline is that its health effects are not well understood. It is

thought to behave similar to ethanol in the human body, but further research into its effects, especially when burned

as a fuel, are required before it is considered safe.

Finally, butanol has not replaced gasoline because it is very difficult to produce. Until recently, butanol was not

considered a viable biofuels because it tended to kill the organisms that produce it before they were able to create it

in any great quantity. In order to prevent this, butanol has to be removed from solution as it is made. Until 2012, the

removal of butanol away from the organisms producing it was an energy intensive and expensive process. Research

out of the University of Illinois, however, may make the process simpler and allow for the efficient production of larger

quantities of butanol. It remains to be seen how effective this process is on larger scales, but it may pave the way for

butnaol to replace gasoline in the near future.


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Understanding Carbon Dioxide and Carbon Fuels

In the sections above, mention is given to the amount of carbon dioxide that each alcohol produces and this is

compared to the carbon dioxide production of an equivalent amount of the fossil fuel that most closely resembles,

structurally, the alcohol. Comparing carbon dioxide in this way, however, can be misleading.

A better way to compare carbon dioxide production is in terms of energy produced per kilogram of carbon dioxide

expelled. This is a better example because even though a quantity of ethanol produces less carbon dioxide than the

same quantity of gasoline, it also produces less energy. The result is that it is necessary to burn more of the alcohol

to get the same amount of energy as the fossil fuel. The chart below contains a few examples that help to clarify the

point.

Fuel Energy Density(MJ/kg)

Carbon Dioxide

production (kg/kg)

Carbon Dioxide

production (MJ/kg)

Carbon Dioxide*

(kg/Equivalent)

Methanol ~21 1.37 ~15 ~3.6

Methane ~55 2.74 ~20 N/A

Ethanol ~24.5 1.91 ~13 ~4.05

Ethane 52 2.93 ~18 N/AButanol 36 2.37 ~15 ~3.02

Gasoline ~46 3.30 ~14 N/A

* This measure compares an alcohol to its closest hydrocarbon equivalent. The value of carbon produced is arrived atby determining how many kilograms of alcohol are needed to derive the same amount of energy as the hydrocarbon.

This number is multiplied by the CO2production in kg/kg to determine how many kilograms carbon dioxide areproduced for when energy production is kept the same.

What the chart above tells us is that alcohols, no matter how they are produced, are not likely to be viable alternatives

to fossil fuels until they start to get larger. In other words, methanol and ethanol are not great fuel sources because

they produce more carbon dioxide than their equivalent hydrocarbons for the same amount of energy. Butanol,

however, begins to show a difference. Butanol produces LESS carbon dioxide than gasoline for the same amount of

energy. If humans can overcome the challenges of producing butanol in large quantity and avoid impact on the food

chain, then it may become a viable alternative to hydrocarbon fuels.

Long Chain Alcohols

The information in the chart above naturally brings about the question of why scientists don't just produce longer

chain alcohols (5 or more carbons) and use those as fuel. Part of the answer to that question is related to the food

supply as discussed in other articles. The other part relates to chemistry. Synthesizing long-chain alcohols is not

easy. In fact, five carbon alcohols (called pentanols or amyl alcohols) are the longest scientists have been able to

produce. Recently, however, a method of genetic engineering has revealed that bacteria may be the key to producing

long-chain alcohols, which hold even more benefit and have greater energy densities than butanol.

In the short term, alcohol fuels will not replace hydrocarbon fuels. They will, however, be important additives to fuels

for the foreseeable future. If science continues to progress and the problem of compromising the food chain can be

solved, then alcohol fuels may provide an excellent alternative to fossil fuels that allow us to better balance how much

carbon dioxide we put into the atmosphere with how much plants remove.


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Aviation Biofuel

Fuels like methanol and ethanol are not practical for aviation because they have very low energy densities. Planes

would either be severely limited in their range or would not be able to take off thanks to the weight of the fuel they

would need to carry. Aviation fuel has an energy density of 42 to 50 MG/kg, which is roughly the same as gasoline. In

order for biofuels to compete with fossil fuels, they need to pack more punch.

Standard Aviation Fuel

To understand what an aviation biofuel needs to be, it is important to understand what makes current aviation fuels

practical. This chart lists the major properties that are required of a fuel that will be used in planes and helicopters.

Important Properties of

Aviation FuelsHigh Quality

Does Not Freeze

Low Risk of Explosion

High Octane

Few Contaminants

The engines that are found in aircraft come in two types: turbines and piston engines. Each requires a different kind

of fuel and so the various aviation fuels will be discussed here briefly. The production of both of these fuels focuses

on providing high power outputs and stable performance under the demands of flight. Of critical importance is water.

Water in aviation fuel can freeze and cause lines to clog at higher altitudes. This is one of the reasons that alcohols,

which tend to attract water, are not useful as aviation fuels. Cold weather performance is the most important factor in

aviation fuel besides energy density.

Avgas

This is short for aviation gasoline and it is used in standard piston-engine aircraft (propellers). Its major difference

from gasoline is that it is less prone to explosion, has a higher octane, and won't freeze at the low temperatures of

higher altitudes. Avgas is generally being replaced by other aviation fuels. Avgas has an energy density of about 45

MG/kg.

Jet Fuel

Jet fuel is similar in many ways to kerosene and comes in two basic types: Jet A and Jet B (there are others, but we

don't consider them here). Jet A fuel is designed for use in turbine engines. It is designed to rest explosion by having

an autoignition temperature of 210 degrees Celsius. Jet A is subdivided into Jet A and Jet A-1. The major difference

between these fuels is freezing point. Jet A fuel freezes at -40 Celsius while Jet A-1 freezes at -47 Celsius. Jet A-1 is


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used much more commonly than Jet A. The energy densities of these two fuels are nearly identical at about 43

MJ/kg.

Jet B fuel is lighter than Jet A, which means it is more prone to evaporation and thus more prone to explosion. Its

major use is for cold climates where its freezing point of -60 Celsius gives it a major advantage. Jet B has an energy

density of about 43 MJ/kg.

Uses of Aviation Biofuel

Despite the challenges, aviation biofuels have seen some use starting in 2008. The first flight, which was undertaken

by Virgin Atlantic, used a blend of 20% biofuels. This was followed by 50-50 blends through 2012. Then in October

2012, 100% biofuels was used by the National Research Council in Canada to power a Dassault Falcon 20.

Production of Aviation Biofuel

In all cases above the aviation biofuels were no different, chemically, from standard fossil fuels. It is the case that

direct alcohols cannot be used as aviation fuel because they freeze easily and have low energy densities. However,

alcohols can be converted to kerosene, which is the basis for all aviation fuels.

Production of kerosene from biomass can occur in several different ways. Research into the use of biological

organisms is ongoing and not yet viable. Current conversion processes take the form chemical cracking and

gasification, which are energy intensive and do not represent viable solutions to the large-scale production of

biofuels. At this point, aviation biofuel is more of a research curiosity than a practical consideration.

Biomass Feedstock

Where the biomass for producing aviation fuel comes from plays large part in how environmentally friendly thesefuels are. Both the type of plant used and the location in which it is grown are important.

Several studies have shown that using arid or former agricultural land to produce biofuels feedstock can reduce

greenhouse gas emissions. Plants like Jatropha or algae can be grown in these settings and are under investigation

for use as feedstock. A study from the Yale School of Forestry has shown, however, that using natural woodland to

grown these plants (that is cutting down existing forest to create land for growing plants) will INCREASE greenhouse

gas emissions over the use of fossil fuels.

To get an idea of just how much land would be needed to meet current demands for aviation fuel, let's consider the

following graph, which shows the land areas needed if a particular feedstock is to fully replace fossil fuels in aviation

and compares those to well-known land masses.


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The graph above demonstrates something fantastic. Each year, 809,000 square kilometers of corn are planted, which

is a land area roughly twice as large as the U.S. state of Montana. If Jatropha were used exclusively to create

aviation fuel, 2.7 million square kilometers would be needed to meet current demand. Said another way, about 36%

of the land area of Australia would be need to grow enough of the plant Jatropha. It is easy to see that this could have

tremendous impact on land use and the food chain.

Note that algae require much less area than most other plants, which is why it is of interest to researchers. It is worth

nothing, however, that little is known about what kind of impact this would have on local and global ecosystems. A

great deal more needs to be learned about biofuel production before it becomes viable.


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Biodiesel and Green Diesel

The terms biodiesel and green diesel are easy to confuse and often are. Both of these products are refined from

vegetable oil (and occasionally animal fat). What sets these two diesel fuels apart are the processes used to produce

them and the end product that results.

Biodiesel is produced by reacting triglycerides with alcohol to produce fatty acid esters as well as glycerol, which is a

byproduct. This chemical reaction is referred to as transesterification. It produces biodiesel, which is about 9% less

energy dense than petro diesel. Biodiesel requires that engines be modified so that damage to rings, fuel lines, and

other rubber components.

Green diesel is produced through a refining process, rather than through a chemical reaction. The result is that green

diesel is chemically identical to petro diesel, except that it does not contain sulfur. Green diesel is nothing more than

renewable diesel fuel. It is not necessarily green in the sense that it protects against global warming. It is "greener"

than standard diesel though because it reduces particulate emissions as well as odor. Green diesel will run in any

engine without modification.

Production of Biodiesel

The production of green diesel is, in many ways, no different from the production of petrol diesel. Both go through a

refining process to yield a fuel at the end. In other words, producing green or petrol diesel is more about separating

the components of interest from the rest of the material than about changing the fundamental properties of the

feedstock. Biodiesel, on the hand, is all about chemically altering the feedstock.

There are actually several processes for producing biodiesel that include batch processing, supercritical processing,

ultrasonic processing, and microprocessing. Though vastly different in application, each of these procedures has the

same outcome; the transesterification of triglycerides.

Triglycerides are a type of biological molecule common in plants and animals. They are made up of three atoms,

oxygen, carbon, and hydrogen. They look something like this.


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The part in red is called glycerol and the three black chains are each fatty acids. So, a triglyceride molecule is made

up of one glycerol and three fatty acid molecules. The fatty acid chains are very similar to hydrocarbons, so scientists

use processes to break off the glycerol and release the fatty acids. This process is called transesterification and it

produces an ester (actually three, one for each fatty acid). An ester looks like this:

The red part is referred to as the "R group" and can be any length from one carbon up. Biodiesel also contains fatty

acid alcohols, which look like the following.

The process of transesterification also produces glycerol, a type of alcohol, as a byproduct. For every metric ton

(tone) of biodiesel that is produced, 100 kilograms of is produced. Glycerol looks like the following.


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Biodiesel Properties and Cetane Rating

The esters in biodiesel are superior to petrol diesel in centane rating, which is similar to octane rating for gasoline.

The cetane rating is a measure of how well a fuel combusts under compression ignition. This is different from octane,

which measure combustion under spark combustion. What is the difference?

In spark combustion, an electric spark (from a spark plug), is used to ignite a fuel. This is similar to putting a flame to

a can of gasoline. Compression ignition works differently. In this process, a gas is compressed to well above

atmospheric pressure. Compressing a gas causes its temperature to increase because pressure and temperature are

related by one of the three gas laws as follows:

This law tells us that pressure is inversely related to temperature. In other words, if we raise the pressure, then we

also raise the temperature so that the equation P/T remains a constant. In diesel engines, the pressure is increased

to the point that temperature rises above the combustion point of the fuel, causing ignition. That is to say, no spark is

needed in a diesel engine. A standard petrol engine usually has a compression ratio of about 10:1. A diesel engine

will have a compression ratio that ranges from 14:1 to 18:1.

So, cetane rating tells us how well a fuel burns under the conditions found in a diesel engine and can basically be

thought of as a quality rating. The rating is based off of an alkane called cetane, which has the formula C 16H24. With

this fuel, the time between fuel being injected into the cylinder and ignition is 2.407 milliseconds, which gets a cetane

rating of 100. The longer ignition takes, the lower the cetane number will be.

Cetane number is not the only property of biodiesel that is of interest. Biodiesel is liquid, usually yellow to dark brown,

and has a high boiling point. Of most importance, biodiesel has no sulfur content.

Of note, diesel engines do not use lubricant. Instead, they rely on the fuel, which is more oil-like than gasoline, to

lubricate the pistons and reduce friction with the cylinder wall. Biodiesel is a better lubricant than low-sulfur diesel,

though not quite as good as standard diesel (which is being phased out due to pollution).

Gelling and Low Temperatures

One of the things that determines the temperature at which a molecule freezes is polarity. The more polar a molecule

is, the easier it is for it to form a repeating crystal structure and become solid. Biodiesel, because it contains oxygen,

is more polar than standard diesel and thus more prone to freezing. Though the fuel usually does not freeze solid, it

does develop small crystals. This is referred to as gelling.


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Biodiesel will begin to gel at temperatures as high as 16 degrees Celsius depending on the feedstock used in its

production. The best feedstock in terms of gelling is canola oil, which produces biodiesel that gels at -10 degrees

Celsius. Petro diesel usually gels at -15 to -19 degrees Celsius.

Engine Impact

Like other biofuels, biodiesel cannot be used in standard diesel engines. The alcohol content and different structure

of biodiesel means that it can react with the rubbers used in standard engines and cause them to dry and crack. This

leads to leaks and engine failure. The solution is to use different rubbers, which is the case with newer diesel

engines.

Fuel Economy, Greenhouse Gases, and Acid Rain

Diesel engines are "lean burn" engines, which means they have more air in the combustion chamber than needed to

complete the reaction. This means they use less fuel to go the same distance than a gasoline engine. Biodiesel

usually offers about 9% less energy density than standard diesel, which reduces the distance traveled on a given

quantity of fuel. However, these engines are still more efficient than gasoline engines and provide better distance for

a given quantity of fuel.

By burning less fuel per distance, diesel engines also produce less greenhouse gas emissions. Even though a

burning the same quantity of diesel fuel will yield MORE CO2than an equivalent amount of gasoline, the increased

fuel economy more than offsets this. A diesel engine will produce 10-20% less greenhouse gas than the same sized

gasoline engine. Overall, the EPA estimates that biofuels reduce greenhouse gas emissions by 57% compared to

diesel.

The down side to diesel is that it produces more nitrogen compounds, which means more acid rain. This is actually

made worse by using biodiesel because the inevitable contamination with biologic material means there is more

nitrogen present in biodiesel. Counterbalancing the production of acid rain from nitrogen compounds is the lack of

sulfur in biodiesel. This means there is less sulfuric acid produced by biodiesel.

Feedstock

As usual, feedstock and where it is grown can make or break biodiesel. Though most biodiesel is currently made from

waste vegetable oil or processed corn, there is research into algae, pongamia, Jatropha, Fungi, and used coffee

grounds. Algae presents the best situation as it would not result in land-use changes, would not replace or impact a

food crop, and is economical. What is even more appealing is that it may be possible to grow algae on ponds in

wastewater treatment facilities, making it possible to improve water quality while also producing fuel.


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Biogas

Unlike the other biofuels mentioned so far, biogas is a gas and not a liquid. It is produced from the anaerobic (without

oxygen) breakdown of organic matter that can include anything ranging from manure to sewage to plant material and

even crops. It is given the generic name biogas because it is composed of several different chemicals.

The Chemicals in Biogas

The main chemical of interest in biogas is methane, which typically constitutes half of the mixture. The rest of the gas

includes carbon dioxide, water, oxygen, hydrogen, nitrogen, and often a small amount of hydrogen sulfide. The

presence of many of these other chemicals can be eliminated through refinement, processing, and through controlled

production procedures.

Production

Biogas is produced through the use of bacteria or other microorganisms that digest and degrade organic matter.

These bacteria work only in oxygen-free (anaerobic) environments and participate in fermentation reactions similar to

those used in the production of beer or wine.

Most biogas is produced from wastewater treatment facilities or from landfills. In these facilities, the process of

fermentation is carefully monitored to ensure that methane constitutes at least 50% of the gas produced. At times,

concentrations can reach as high as 75%. The methane is then refined and purified, often on site, before being used.

Often, the produced fuel is either used directly on site for energy generation or is pumped into a pipeline for

distribution. Biogas can also be compressed and transported by truck.

Environmental ImpactOther biofuels run into the question of land-use and how growing feedstock on virgin soil can actually lead to a

carbon debt that takes centuries to pay off. Biogas is different because it is often made directly from animal waste,

which has many environmental benefits.

First of all, manure and sewage have one major problem, which is that they contain high amounts of nitrogen. When

left to decompose in the presence of oxygen, this nitrogen is converted to nitrogen dioxide with is 310 times more

effective at trapping heat in the atmosphere than carbon dioxide. In fact, methane itself is 21 times more effective at

trapping heat than carbon dioxide. So, biogas helps in two ways. To start, by converting waste to methane in

anaerobic conditions, the production of nitrogen dioxide is avoided altogether. On top of the reduction in nitrogen

dioxide is the fact that methane is never released. Because it is burned as a fuel, it produces only carbon dioxide and

water (ideally), which means that the impact on global warming is greatly reduced by refining animal waste into

biogas.

In North America, using all available animal waste (including landfills and sewage) would produce electricity to meet

about 3% of energy needs. Thought of another way, one cow produces enough methane to power a 100 watt light

bulb for a day and there are roughly 100,000,000 cattle in the United States (which is only about 1/3 of the

280,000,000 in India).


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Technological Investment

The largest investor in biogas technology is Germany with nearly 6,000 plants producing nearly 2.3 GW of electrical

power. This investment is part of Germany's push for energy independence and greener technology.

Behind Germany, the United States, the United Kingdom, India, and China are all major producers of biogas.

Coincidentally, the U.S., India, and China constitute three of the four largest cattle-owning nations in the world with

the fourth (second by ranking) being Brazil.


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Syngas

Syngas is the short name for a gasification product known as synthesis gas. It s a mixture of hydrogen, carbon

monoxide, and carbon dioxide that used as an intermediate in processing synthetic petroleum and as a potential

intermediate in the conversion of certain biomass in fuel. To understand what syngas is, one must first understand

what gasification is.

Gasification

Gasification is a thermochemical process that converts organic carbon into carbon monoxide, hydrogen, and carbon

dioxide. The process is carried out at high temperatures (>700 C) in a controlled environment. Usually, a specific

mixture of oxygen or steam is injected into the reaction chamber. The key to this process in the combustion does not

occur.

The point of gasification to convert carbon compounds into syngas, which tends to burn more efficiently than the

original fuel because it burns at higher temperatures. Syngas can be burned directly or it can be used to produceethanol and hydrogen. It can also be processed into other synthetic fuels through a process known as the Fischer-

Tropsch process. Biomass can be converted to biofuel via gasification.

The gasification of biomass has historically resulted in low yields. Recently, the University of Minnesota developed a

metal catalyst, which reduces the reaction time for biomass by a factor of 100. It also allows the process to be carried

out autothermically, which means no exogenous heat need be applied. The catalyst therefore greatly improves the

efficiency of biomass gasification.

Uses of Syngas

The primary use of syngas is in the production of other fuels, namely methanol, and diesel fuel. In industrial setting

such as steel milling and petroleum refining, large amounts of waste gas are produced. Rather than vent these toxic

gases into the atmosphere, they are captured and used to produce syngas. Doing so not only benefits the

environment, but the products derived can be sold or used in cogeneration facilities, both of which can help to make

plants more profitable.

The production of diesel fuel relies on the Fischer-Tropsch process, which is a series of chemical reactions that

converts carbon monoxide and hydrogen into liquid hydrocarbon. In most cases, methane from landfills acts as the

feedstock for producing diesel fuel. This is technically considered biodiesel because it is not derived from fossil fuels.

A novel use of syngas is to directly power hydrogen fuel cells. Hydrogen is simply captured from the gas and refined

for use in fuel cells. Of course, this process tends to defeat the zero emissions aim of fuel cells and so is not widelyused outside of research settings.

Syngas can also be used for the production of:

Hydrogen

Nitrogen

Ammonia


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Carbon Monoxide

Carbon Dioxide

Steam

Minerals and Solids

Sulfur

Whether the above products can be derived from synthesis gas depends upon the original feedstock. Though

synthesis gas need only contain hydrogen and carbon monoxide, it frequently contains other components as well.

Syngas can be burned directly in internal combustion engines, but, if it is to be used directly, is often burned in an

integrated gasification combined cycle where heat is captured for electricity, but waste heat for space or water

heating.

Syngas Fermentation

Microbial fermentation of syngas can be used to develop fuels and chemicals. Most notably, syngas fermentation can

produce:

Ethanol

Butanol

Acetic Acid

Butyric Acid

Methane

The benefit of fermentation is the it is simpler and takes place a lower temperatures than chemical conversion. Oddly

enough, biologic fermentation can also tolerate high levels of sulfur, making it ideal for use in steel factories and

power plants that burn coal. In general, the process is simpler because it does not require careful control of reaction

conditions or specific quantities of CO and hydrogen. The biggest disadvantage is that it is low throughput, whichmeans that it takes a long time.

Syngas Reactions

1. Stock + Air Low Energy Syngas Burned in IC engines or used to generate heat/power.

2. Stock + Steam Medium Energy Gas IC engines or used to heat/power generation.

3. Stock + Oxygen Medium Energy Gas Pipeline energy or chemicals like methanol, ammonia & gasoline.

4. Stock + Heat Char or Oil Oil used to produce pyrolysis oil

Ultimately, the stock provided is less important than the process it is subjected to so long as the stock has a high

carbon content. Thus, the reactions above work as well with biofuel stock as they do with fossil fuel stock. Biofuels

like Switchgrass and other lignocellulose feedstock are highly amenable to syngas production.


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Biomass and Syngas

The basic biomass gasification reaction is as follows:

C6H12O6 + O2 + H2O CO + CO2 + H2 + other compounds

(other compounds result from contaminants like sulfur, nitrogen, etc.)

It is estimated that as much as 1.2 billion dry tones of biomass could be available for conversion to syngas by 2050.

This would result in about 21 quadrillion BTU/year of energy, which is well above the 16 quadrillion BTU/year used in

transport and roughly 21% of the total 98 billion BTU of energy used each year in the United States.

Now, biomass can be converted via biological mechanisms as well, so what are the advantages of using

thermochemical conversion via syngas to convert biomass? First, gasification is fast, taking minutes compared to

days or weeks for biochemical conversion. Second, gasification is able to extract more energy from the biomass and

this is its primary advantage. The reason it can extract more energy is that it can convert carbon stored in lignin (the

tough part of plants often found in stems and trunks) into usable products. At this point, gasification of biomass (otherthan crops like corn and soybean) is more efficient than biochemical conversion. In particular, the gasification of

waste such as corn stalks, corn cobs, and other agricultural byproducts is highly efficient and ultimately can improve

the energy yield per acre of first generation biofuels.


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Solid Biofuels

The term solid biofuel can be a bit misleading because many people associate biofuels with advanced refining and

chemical processes. In fact, a biofuels can be any renewable, biological material used as fuel. With that definition, it

becomes clear that things like wood, sawdust, leaves, and even dried animal dung all constitute biofuels. In fact, solid

biofuels are how humans have been heating themselves and their food since the dawn of...well...humans!

Production

There is no production necessary for a solid biofuels in most cases because it is often in a convenient form. On the

other hand, sawdust and wood chips are not so convenient and so they are often put through a process known as

densifying. All this means is that the biomass is compressed into a form that is easier to handle or is mixed with

some sort of bonding agent (tar for instance or tree sap) to hold it together for easier transport, storage, and use.

Pellets and bricks are common densified forms of solid biomass.

Environmental Impact

Studies have shown that solid biofuels create less environmental impact than doe solid fossil fuels like coal. The

United States Department of Energy has studied the impact of both biomass and fossil fuels on global warming over

the lifecycle of an electrical generating facility. When all aspects are taken into account, using biofuels rather than

coal, even when the carbon from burning the coal is sequestered, leads to a 148% reduction in the global warming

potential for the power plant.

On the reverse side of the environmental equation, raw biomass is known to emit a number of particulates as well as

polycyclic aromatic hydrocarbons (PAHs). Burning solid biomass directly contributes to reduction in air quality, often

to a greater degree than oil or other hydrocarbons. Burning animal waste creates more dioxin and chlorophenol

pollutants than burning wood does. This is particularly harmful when it is burned indoors without venting.

PAHs are well-known carcinogens having the potential to damage DNA and cause birth defects. Dioxins are

derivatives of PAHs and are known to be highly toxic to fish and wildlife. A dioxin level as low as 0.5

micrograms/kilogram (about 0.0000005% by mass) are lethal to some species. Chlorophenol is also an aromatic

compound. It is commonly used in pesticides, herbicides, and disinfectants. It is one of the primary components of

mothballs. Chlorophenol is less toxic than the above compounds, with lethal doses in the range of 600

milligrams/kilogram or about 50% by mass. Long-term exposure to relatively high levels can lead to damage to red

blood cells and to the immune system.

Wood

Wood constitutes the majority of biomass that is burned for fuel and comes in the forms firewood, charcoal, chips,

pellets, and sawdust. The use of wood as a fuel for cooking, heating, and other applications dates back to well before

humans when Neanderthals were the predominant species of hominid. In fact, the most troubling aspect of using

wood as a fuel is generating the spark to start the fire. Otherwise, wood is readily available, abundant, and can even

be collected from the ground if cutting tools are not available. Today, wood is even used in some electric generating

applications.


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Wood is reasonably energy dense. Hardwoods have an energy density of around 14-15 MJ/kg if burned with 100%

efficiency. As with any fuel, however, the efficiency tends to be lower. Wood is actually more efficient than many

fuels, with about 70% of the energy content (10 MJ/kg) recoverable on average.

The downside to wood is pollution. Not only does it produce more carbon dioxide than fuels like methane, it also

produces other pollutants like soot, smoke, and PAHs. Research has lead to stoves that burn at extremely hightemperatures (over 600 degrees Celsius). Temperatures this high actually allow the smoke itself to burn, which

reduces emissions.

Animal Dung

More than 2 billion people across the planet burn dried animal dung for energy. Its benefits are that it is cheap, can

be found in areas were wood is scarce, is renewable, and contains a reasonable amount of energy. Cow dung, for

instance, is about 50% methane and 30% carbon dioxide by mass when converted into biogas. Of course, burning it

directly is a different matter and less energy can be extracted. Cow dung has an energy density of approximately 12

MJ/kg if burned with 100% efficiency.

Unfortunately, burning animal dung efficiently is even more difficult than burning wood efficiently. It also produces a

number of pollutants and is a major health hazard in countries where it is burned indoors with limited ventilation.

Animal dung tends to have much higher levels of dioxins and chlorophenols as explained above.

Municipal Waste

Otherwise known as rubbish, garbage, or refuse, this biofuel includes pretty much everything that humans discard on

a daily basis. In general, this waste is not directly burned, but rather is converted through a number of different

processes into useable, cleaner fuels.

Methane can be harvested from landfills through a process known as landfill gas capture. Waste can also be

gasified directly at high temperatures and with controlled concentrations of oxygen and steam to produce syngas.

Finally, waste can be put through a process known as pyrolysis. In this reaction, decomposition is enhanced though

the application of higher temperatures and anaerobic conditions. This is the process used to make char, which is

similar to charcoal. Finally, waste can be burned directly, which is generally not allowed in most developed nations as

it produces large amounts of pollutants and toxic gases.

Energy Crops

The last major category of solid biofuel includes crops grown explicitly for burning. Though some people include the

conversion of these crops to biofuels, they are no longer solid at that point and so are not included in this discussion.

Most crops grown for direct combustion are woody. In most cases, these crops are dried and converted to pellets for

easy transport. They are then burned either alone or in cogeneration plants where they are combined with other fuels.

Many home heating burners use pellets. Crops that are grown for conversion to liquid biofuel generally have high oil

content or produce lipid, which can be converted into various liquid fuels. Crops grown for direct combustion include

switchgrass and elephant grass, though both are also converted to ethanol in some settings


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Advanced Biofuels

The term "advanced biofuel" is a bit misleading because any biofuel can be advanced as long as it is made from

sustainable feedstock. The definition of a sustainable feedstock is not well developed, but in general, a feedstock is

considered sustainable if it:

Is available in large enough quantity to meet a reasonable proportion of our energy demands;

Has a limited impact on greenhouse gas emissions. This is a tough criteria as the impact a feedstock has

varies depending the land it is grown on, the fertilizers used, etc.;

Does not have an impact on biodiversity. In other words, it won't lead to an ecological problem like super-

pests and it is not so invasive so as to choke off native organisms;

Does not result in major land use changes. This, of course, goes back to the impact the fuel will have on

greenhouse gas emissions, but also evaluates its impact on food crops.

As you can see, the criteria are rather loosely defined. They act more as conceptual, qualitative criteria than as

quantitative metrics for making definitive decisions about the value of a biofuel. The lines between an advanced and a

traditional biofuel are blurred in the sense that a fuel that has limited energy density, but can be grown on arid land

and have little impact on greenhouse gas emissions is going to be highly valued despite its poor performance in the

first criteria above.

When considering how "advanced" a feedstock is, one must consider water impacts, pesticide residue, fertilizer use

and runoff, biodiversity, invasiveness, energy content, impact on food supply, impact on the climate, ease of

production, and economic return just to name a few. Despite these vast considerations, a few feedstock sources have

risen to the forefront of the investigation into sustainable biofuel.

Lignocelluloses

Lignocelluloses is a derivative of plant biomass that contains cellulose and lignin. Cellulose is the main structural

component of plant walls and is often found in algae as well. It is a tough polysaccharide (sugar) that can be

hundreds to thousands of glucose (sugar) units long. Lignin is an extremely complex chemical that fills the spaces

between cellulose molecules and helps to stiffen the walls of plants.

Lignocelluloses can be broken down into ethanol because it contains carbon, hydrogen, and oxygen. However, doing

so is not so easily accomplished. Over the years, scientists have developed a number of ways of producing ethanol

from lignocelluloses, but the processes are not particularly economical. As of 2007, a gallon of ethanol produced from

cellulose cost roughly U.S. $7/gallon compared to the $1-$3/gallon for ethanol produced from corn.

The benefits of using cellulose for a feedstock derive primarily from the fact that it is usually the leftover, inedible part

of crop plants. In other words, we are already producing a large abundance of this feedstock and are simply throwing

it away. Estimates put the annual production at around 323 million tons (British tons) in the U.S. alone. This quantity,

combined with the use of marginal agricultural land for growing cellulose crops, is enough to substitute for all

petroleum imports (though not all petroleum used) in the United States.

In addition to waste agricultural products, paper and other cellulose components make up roughly 70% of all landfill

waste. When these decompose, they produce methane gas, which is 21 times more potent as a warming gas than

carbon dioxide. So, converting this material to ethanol may have a very positive net environmental impact.


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Finally, lignocelluloses yield about 80% more energy than is consumed in growing the plant and converting it to

ethanol. This compares very favorably with corn, which yields only 26% more energy. The conversion rate is roughly

4-5 fold, meaning that energy invested in producing ethanol from lignocelluloses gives you 4-5 times more energy

than if it were invested into producing ethanol from corn. Estimates suggest that cellulosic ethanol could reduce

greenhouse gas emission over the long term by about 115%.

Jatropha

Jatropha is a type of flowering plant that, oddly enough, has never been fully domesticated. Despite this fact, the

plant has found use in a number of applications including land reclamation after oil contamination and as a decorative

addition to many gardens. What makes it interesting as a biofuel feedstock is that Jatropha is drought resistant, has

few pests, and produce seeds that contain 27 to 40% oil.

The oil from Jatropha can be refined into biodiesel and the leftover can be used as a solid biofuel or as a feedstock

for producing syngas. Because it is refined biodiesel and not chemically converted biodiesel, diesel from Jatropha

qualifies as "green diesel" and can be used in any standard diesel engine.

The major benefit of Jatropha is that it can grow in places where most other plants would die. This means it will not

threaten the world's food supply because it can be grown on land where food crops cannot survive. Unfortunately, the

plant does not produce many seeds (where the oil is found) in poor conditions and it turns out to need just as much

water and fertilizer as any other crop. Currently, research is being done into how Jatropha might be domesticated or

genetically altered to ensure that it produces oil even under harsh conditions.

The other problem with Jatropha may be the fact that it actually increases greenhouse gas emissions. Like any

biofuel, how and where Jatropha is planted impacts its overall greenhouse gas emissions. If it is planted on land that

contains other species, the potential carbon debt could take decades or even centuries to pay off. In recent years,

interest in Jatropha has dwindled as its need for more nutrient rich environments has undermined its initial appeal.

Camelina

Camelina is another type of flowering plant that produces seeds rich in oil. Like Jatropha, its seeds can contain up to

40% oil that is easily converted into biodiesel and even jet fuel. Camelina is a hardy plant and does well in water-

scarce environments. However, like Jatropha it may face potential problems from the fact that it might actually

increase greenhouse gas emissions, does not produce as well in dry environments as in wet, and uses nearly twice

the land to produce the same quantity of biofuel as Jatropha. Camelina is of interest to the United States Air Force as

a potential replacement for up to 50% of their jet fuel with biofuel by 2016.

Algae

Algae produce lipid, which is oil that can be converted into a number of different fuels including biodiesel, ethanol,

methanol, butanol, jet fuel, and others. Unlike the refining processes above, the process of converting lipid to fuel

requires chemical reactions that produce esters and alcohols. Algae-derived biofuels cannot be used in standard

engines because they can erode and damage the seals, gaskets, and lines made of rubber. Specialized rubber is

needed if algae-based biofuels are to be used in an internal combustion engine.


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Types of Biofuel

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