Unit 10 - Biofuels and Bio-Derived Chemicals Flashcards
Why are liquid hydrocarbons used as fuels?
They have a very high energy content.
They are easy to store and pump into engines.
They can be transported easily in pipelines.
Currently, they are cheap.
What are the problems with using liquid hydrocarbons as fuels?
Oil reserves are becoming depleted.
Lots of oil comes from politically unstable or conflict zones.
The fuels emit carbon dioxide when combusted as well as other forms of pollution.
What are the benefits of using biofuels for transport?
Improves energy security and reduces the impact of climate change.
EU directives introduce a binding target of 10% share of renewable energy in transport by 2020 and this includes biofuels.
What is the concept of biofuels?
Plants photosynthesise which converts the Sun’s energy into biomass.
Biomass is converted to biofuel.
Burning biofuel releases the stored energy.
What are the problems with biofuels?
Plants need more than sunlight to grow (land, fresh water, fertilisers)
Nitrate fertiliser can release N2O which is a powerful greenhouse gas.
Plants do not necessarily grow all year round.
Biomass contains large amounts of water which needs to be removed.
Food vs. fuel debate - Mexican Tortilla Riots 2007.
What is an approach of making biofuels?
Fischer Tropsch Process where the biomass is broken down into syngas.
(CH2O)n → nCO + nH2
The syngas can then be reacted under a catalyst to make hydrocarbons.
This is a very energy intensive process.
Where has gas-to-liquid Fischer Tropsch been used?
Shell use it in Qatar with gas that would have been flared to make 4% of the world’s diesel.
How can biofuel be used for Fischer Tropsch?
It can be fed directly into existing Fischer Tropsch plants provided that sulphur residues are removed first (stops the catalyst becoming poisoned).
How else can biofuels be made?
By converting biomass directly into biofuels.
Fats and oils from seeds can be converted to biodiesel and cars can run directly on this.
Fermentation of starch and cellulose to bioethanol which can be blended with petrol.
Food waste can be converted into jet fuel.
What is the equation for making biofuels?
Triglycerides are reacted with methanol under sodium hydroxide to make glycerol and fatty acid methyl esters.
This process is called transesterification.
What are some problems with making biodiesel?
Lots of glycerol that is wasted.
Loss of habitat and biodiversity.
Carbon dioxide can be emitted from cleared forests.
Oils can be used for higher value products or food.
What is the problem with bioethanol?
Limited to 5% in Europe although 10% (E10) is becoming more common. In the USA 85% ethanol is used and in Brazil, 100% ethanol is used.
Ethanol has a lower energy content than petrol and can absorb water.
How is bioethanol made?
Through fermentation.
After the fermentation, the ethanol needs to be separated from the water. Separation by distillation is preferred but other separation methods are being developed. Significant improvements are needed as sometimes more energy is being put in than is made from the ethanol.
What is first generation bioethanol technology?
Using sugar and corn to make bioethanol.
What is second generation bioethanol technology?
Using ligno-cellulosics which improves energy efficiency.
