Industrial Chemistry

Part IV 

Biodiesel2011

BiodieselHomegrown Fuel Solution

Overview Biodiesel Background & Advantages Making Biodiesel, Glycerin Separation,

washing issues Chemistry of the process Demo: Canola Oil Biodiesel properties (double bond

location), viscosity, Cetane number, cloud point)

Biodiesel Challenges (Gelling, additives,..) Possible Lesson Plans: Energy efficiency,

Vehicle comparison

What is biodiesel?What are its uses?How is it made? Pros and cons.Environmental impact

What is Biodiesel?

Biodiesel is a cleaner alternative to petrodiesel.

It is a processed fuel made from biological sources.

Biodiesel is renewable.Biodiesel is a mixture of alkyl esters of

fatty acids .

Biodiesel can be used in existing Diesel EnginesBiodiesel can be used in any diesel engine. Biodiesel can also be used as a heating fuel in

domestic and commercial boilers.

Production

Biodiesel can be made from triglycerides which are available in many different forms such as:Virgin oils (canola, soybean)Waste vegetable oils (WVO)Animal fats (lard, tallow)

Production:What is a triglyceride?

Vegetable oils are triglyceride esters of fatty acids with chain length generally from 12-24 carbons.

They are made from glycerol and “free” fatty acids

The R groups in the picture represent fatty acid chains, possibly of different lengths.

C

C

C

OH

OH

OH

H

H

H

H

H

Glycerol

O

O-

CH3

a ‘free’ fatty acid

a triglyceride

The production of biodiesel generally starts with one of three different techniques:Base catalyzed transesterification of triglyceride

with alcoholDirect acid catalyzed esterification of the

triglyceride with methanolConversion of the triglyceride to fatty acids, and

then to alkyl esters with acid catalystA base catalyzed transesterification of the oil with an

alcohol is the preferred method as it produces higher yields at lower temperatures.

The base catalyzed production of biodiesel usually follows these steps:Catalyst-alcohol mixingPurificationReactionSeparationRemoval of alcoholWash

Production: Catalyst-alcohol mixing

At this step the catalyst (NaOH or KOH) is dissolved in the alcohol (methanol). This is then thoroughly mixed.

PurificationThe purification step is used when WVO is

used. This is to clean the WVO of dirt, food remains, and anything else that should not be in the oil.

Water and free fatty acids are also removed from the oil.

The water is dried with a drying agent like magnesium sulfate. The free fatty acids are neutralized with base.

Reaction

The oil of choice is now added into a reaction vessel with the catalyst/alcohol (NaOH/CH3OH) mix. This mixture is kept at a temperature just above the boiling point of methanol.

This reaction then takes place

C

C

C

O

O

O

C

C

C

O

O

O

R2

R1

R3

H

H

H

H

H

+ CH3OH

NaOH

CH3OC

O

R1CR2O

CH3

O+

CR3O

CH3

O+ + C C C

OHOHOH

H

H H H

H

BIODIESEL Glycerin

Triglyceride

Methanol3

CH2OOR1 catalyst CH2OH| |CHOOR2 + 3CH3OH 3CH3OORx + CHOH| |CH2OOR3 CH2OHTriglyceride 3 Methanols Biodiesel Glycerin

R1, R2, and R3 are fatty acid alkyl groups (could be different, or the same), and depend on the type of oil. The fatty acids involved determine the final properties of the biodiesel (cetane number, cold flow properties, etc.)

Cetane is a colorless, liquid hydrocarbon (a molecule from the alkane series) that ignites easily under compression.

For this reason, it was given a base rating of 100, and is used as standard measure of the performance of compression ignition fuels, such as diesel fuel and biodiesel. All the sundry hydrocarbon constituents of diesel fuel are measured and indexed to cetane's base 100 rating.

Cetane and Cetane number

Cetane Number

is a measure of the ignition quality of a diesel fuel.  It is often mistaken as a measure of fuel quality.  Cetane number is actually a measure of a fuel's ignition delay.  This is the time period between the start of injection and start of combustion (ignition) for the fuel.  In a particular diesel engine, higher cetane fuels will have shorter ignition delay periods than lower cetane fuels.

Cloud Point:

Cloud point is the temperature where the fuel becomes cloudy. Microcrystals are beginning to form. The crystals are waxes. In biodiesel fuel, it is biowax, in diesel it is paraffin wax. When the crystals get large enough they settle to the bottom of the tank.

The fuel will become cloudier and thicker as the temperature is lowered, until the gel point is reached.  Filter clogging becomes a problem between the cloud and gel points.

Gel Point: is the temperature at which the fuel freezes solid and can no longer be pumped

As the fuel is warmed up, enough of it will melt so that it can be poured again- this is the ungel point.  However, many of the waxes will remain in solid form.  It can look like crystals, pellets, or amorphous.  Most of this wax will be loosely packed at the bottom of the barrel.  In order to completely remelt or redissolve the waxes, the fuel has to be warmed up to the remix temperature.  The other option is to only use the liquid fuel from the top of the barrel. 

The lowest temperature at which an oil or other liquid will pour under given conditions.

Pour Point

Flash point

The flash point of a fuel is the temperature at which the vapour given off will ignite when an external

flame is applied under standardized conditions . It is defined to minimize fire risk during normal storage and handling

Separation

After the completion of the reaction we will have a methyl ester (the biodiesel) phase and a glycerin phase.

The glycerin phase is much more dense than the biodiesel phase so it can be removed by gravity filtration or by centrifuge.

Both phases will have methanol still in them. This excess should be extracted from each phase by distillation.

The biodiesel is then sometimes washed with warm water to clean the alkyl esters of any possible catalysts that remain or soaps that were produced.

The biodiesel is then dried, and stored until it is put to use.

Wash

Pros and Cons of Biodiesel

Pros

Carbon Neutral Non-toxic Can be neat or can be a mixture Higher flashpoint than petrodiesel Can prolong engine life Burns more efficiently than petrodiesel RENEWABLE

Cons

It is currently more expensive than petrodiesel

Can deteriorate tubes and hoses in older model vehicles

May cause filter blockage in low temperatures

Pros and Cons of Biodiesel

After Glycerin removal, biodiesel now just needs to be cleaned/purified before use: