synthesis of biofuels

what is a biofuel?

any fuel derived from biomass which includes plant material and animal waste

why are biofuels called a renewable energy source?

because their feedstock material can be replenished readily

what are the advantages of biofuels?

• renewable

• produce less greenhouse gas emissions compared to fossil fuels

• reduces dependence on fossil fuels

what are the disadvantages of biofuels?

• some have economic and environmental costs associated with refining

• expanding biofuel production may compete with land needed for food crops

what is an enzyme?

a biomolecule that acts as a catalyst to speed up specific chemical reactions within living organisms

what is a catalyst?

a substance that increases reaction rate by providing alternative reaction pathway with lower activation energy

how does a catalyst work?

allows greater proportion of reactant particles to have energy greater than activation energy

how do enzymes work?

1. substrate molecule collides with enzyme and binds to its active site. active site has complementary shape to substrate

2. enzyme undergoes conformational change which strains substrate’s bonds, providing lower activation energy

3. enzymes provide optimal environment

4. substrate is converted into products. enzyme releases products and returns to original conformation

what is denaturation?

when an enzyme’s folded structure is altered due to various factors, losing its catalytic activity

how does temperature cause enzyme denaturation?

high temperatures disrupt intermolecular forces that maintain enzyme’s shape. enzyme loses its functional 3D structure, rendering its active site ineffective.

how does pH denature enzymes?

altered pH affects charges on amino acids, disrupting enzyme’s folding pattern

what is the hydration method of producing ethanol?

mixture of steam and ethene produced and passed over bed of silica particles coated with phosphoric acid

explain the pressure conditions of the hydration method of producing ethanol

• high pressure of 6000-7000kPa used

• there are fewer number of moles on products side so high pressure will favour formation of products

explain the temperature conditions of the hydration method of producing ethanol

• moderate temperature of 300ºC used

• this is an exothermic reaction so although a high temperature favours higher reaction rate, leads to lower yield of ethanol

why is it important to use a 1:0.6 ratio of ethanol to water during hydration process?

to ensure that water is the limiting reagent, preventing dilution and washing away of phosphoric acid

describe the process of producing ethanol using fermentation of biomass

1. sucrose sugars hydrolysed using enzyme called invertase to produce simple sugars such as glucose and fructose

2. fermentation occurs and simple sugars converted into ethanol molecules using enzyme zymase

what are the reaction conditions for the production of ethanol by fermentation?

• molasses as feedstock must be diluted prior to use

• air is excluded to allow yeast to respire anaerobically so glucose is converted into ethanol and not carbon dioxide/water

• ethanol concentration kept below 14% as it can poison yeast, causing fermentation to cease

what is biodiesel?

renewable biofuel derived from biological sources of triglyceride. consists of long chain fatty acid esters and usually made from triglycerides

what pre treatment needs to occur for the base catalysed method of producing biodiesel?

• biomass pre treated by filtering off unwanted material and removing water

• as sodium hydroxide is used as the catalyst, the presence of any water will lead to soap formation

• free fatty acid content kept below 4%

what are the reaction conditions for the base catalysed method of producing biodiesel?

• catalyst: KOH or NaOH

• temperature: 60ºC

• conducted in sealed vessel to prevent loss of methanol

• methanol reacted with triglycerides in 3:1 ratio (>6:1 for high yield)

• byproduct is glycerol which forms separate, bottom layer

how is the lipase catalysed method different from base catalysed?

uses lipase as catalyst instead of NaOH

what are the advantages of the lipase catalysed method of producing biodiesel?

• conducted at milder temperature and pH to not denature enzymes

• treatment of FFA’s not needed as they are all converted simultaneously

• no NaOH or KOH means no soap formation

• lower temperature means lower energy demand

• no basic products means environmentally safer

what are the disadvantages of the lipase catalysed method of producing biodiesel?

• very slow and higher amount of enzyme required

• lipase catalyst fairly expensive

• difficult to liberate lipase from reaction mixture so fresh batch must be used each time

• if methanol or glycerol concentration too high it will inhabit activity of enzyme. methanol must be added gradually