Unit 4 - Chemical Synthesis (Fuel Cells)

Question 1

Biodiesel

Answer 1

Biodiesel is a fuel derived from vegetable oils and fats with a similar combustion properties to regular petroleoum diesel fuel

Question 2

Process of Biodiesel

Answer 2

Biodiesel can be produced from oil-yielding crops including soybean, canola, sunflower.
It is biodegradeable and non-toxic and combustion produces signficantly fewer emission than petroleum based diesel.
Process to convert oils to biodiesel is called tranesterfication

Question 3

Biodiesels Structure

Answer 3

Biodiesel is a mixture of organic compounds called esters.
Esters are produced by the tranesterification of tryglycerides conatined in vegatable or animal or fats and oils with short-chain alcohols.

Question 4

Short-Chain Alcohols used in Biodiesel

Answer 4

Typically ethanol is the most common alcohol used due to its low cost. However, high yields 98% can be achieved using methanol
Reaction can be catalysed using acids and bases

Question 5

Manufacture from Fats and Oils

Answer 5

In the tranesterification process, the triglyceride, which is an ester composed of a triglyceride structure with the long chain fatty acids, is reacted with short-chain alcohols to produce a different esters.
Usually the methyl or ethyl ester

Question 6

Biodiesels relation to fatty acids

Answer 6

Biodiesels are sometimes referred to as fatty acid esters because carboxylic acids with relatively long hydrocarbon chains are referred to as fatty acids

Question 7

Comparison of petrodiesel and biodiesel

Answer 7

• Petrodiesel produced up to 10% more energy than biodiesel (this is offset by the fact that biodiesel turns up more smoothly and effectively)
• Biodiesel have a higher viscosity than petrodiesel. Biodiesel does not flow as easily along fuel line and through filters
• In low temps, biodiesel can lose its ability to flow, or worse still, it can solidify. The cloud point is a measure of performance at low temperature (temp at which small crystals can start to form)

Question 8

Forces of Biodiesel

Answer 8

Strong intermolecular forces of biodiesel increase it melting and viscosity (dipole-dipole)
Hydroscopic - water is more attracted to

Question 9

Ethanol - Hydration of Ethene

Answer 9

Ethanol can be formed by either a substitution reaction involving a haloethane, or the acid-catalysed reacting of ethene with water.
Since the substitution reaction of the haloalkae involved a slow catalaytic reaction with water and completed with elimination of the halide, ethanol is produced industrially by addition reaction of steam and ethene.

Question 10

Fermentation of Gluecose

Answer 10

Alternatively, the ethanol can be produced by the fermentation of carbohydrates usually in the form of gluecose.
Process depends on the presence of enzymes by yeasts that catalyse the conversion of gluecose to ethanol and CO2 according to:
C6H12O6 —–> 2C2H5OH + 2CO2

Question 11

Fuel Cells

Answer 11

A fuel cell is a type of galvanic cell that generates electricty from redox reactions quietly efficiently and with almost no pollution

Question 12

Galvanic Cells vs Fuel Cells

Answer 12

Unlike the regular galvanic cells, fuel cells do not run down or need recharging
A key difference between a fuel cell and a primary or secondary cell is that reactions are not stored in the fuel cell but must be continously supplied
Fuel cells incorporate the vision where hydrogen will become the main source of energy

Question 13

Fuel Cell Design

Answer 13

There is two intlets
Hydrogen gas inlet and oxygen gas inlet
The hydrogen outlet is near the anode and next to the porous anode
The oxygen gas in near the cathode and next to the porous cathode
The electrolyte solution is within the cathode and anode, it carries ions from one electrode to another
There is a water outlert
Anode (-)
Cathode (+)

Question 14

Two conditions of a Fuel Cell

Answer 14

Acidic and Alkaline Conditions

Question 15

Hydrogen Cells under Alkaline Conditions - The Anode

Answer 15

An alkaline fuel cell can use potassium hydroxide solution as the electrolyte and the cell is operated at 250 degrees celsius

At the anode (negative electrode), hydrogen gas (‘the fuel’) is oxidised by reacting with hydroxide ions from the electrolyte

The catalyst incorporated in the anode increases the rate of oxidation of the hydrogen gas. Platnium metal is commonly used as a catalyst at this electrode

H2 (g) + 2OH- —> 2H2O + 2e-

Question 16

Hydrogen Cells under Alkaline Conditions - The Cathode

Answer 16

At the cathode (positive electrode), oxygen gas is reduced.

The cathode catalyst, which increase the rate of reduction half-reaction, can be made from different material such as nickel powder or nanomaterial

O2 (g) + 2H2O (l) + 4e- ——-> 4OH- (aq)

Overall equation is:
2H2 (g) + O2 —> 2H2O

Each cell produces 1 volt