Biofuels Lecture – Key Concepts

Flashcards covering the major ideas, processes and implications of biofuels, ethanol, biodiesel and related emerging technologies discussed in the lecture.

What primary motivation drives the search for alternative fuels such as biofuels?

The desire to lower carbon footprints while maintaining energy-dependent lifestyles for transport, heating and power.

Name the three main categories of energy sources mentioned, apart from emerging technologies.

Fossil fuels (coal, oil, gas), renewables (wind, solar, hydro) and biofuels.

By how much has atmospheric CO₂ risen since pre-industrial times?

From about 280 ppm to over 420 ppm, with most of the rise in the last 100 years.

Which BP scenario targets the most aggressive reduction in carbon emissions?

The Net Zero scenario.

List two key strategies proposed for lowering the climate impact of energy use.

Reducing fossil-fuel consumption and increasing the use of renewables (including biofuels and green hydrogen).

What portion of global liquid-fuel use do biofuels currently represent?

Roughly 5–10 %, varying by country.

Give two reasons liquid fuels remain attractive despite electrification trends.

High energy density and an existing refuelling/handling infrastructure.

Why is Australia considered to have a liquid-fuel sovereign risk?

It refines less than 10 % of its own liquid fuels and relies heavily on imports, mainly from Singapore.

Define a biofuel.

A fuel whose carbon is recently captured from biomass via photosynthesis rather than ancient fossil carbon.

What are the three main feedstock categories for ethanol production?

Fermentable sugars (e.g., cane juice, molasses), hydrolysed starches (e.g., corn, wheat) and lignocellulosic biomass.

What molecule produced by yeast fermentation of glucose serves as a liquid biofuel?

Ethanol.

Which blend percentages of ethanol and petrol are most common in Australia?

E5 to E10.

Why does adding ethanol to gasoline generally lower carbon-monoxide emissions?

Ethanol contains oxygen, promoting more complete combustion.

What property of ethanol gives it an octane rating above 100?

Its ability to allow higher compression before auto-ignition in internal-combustion engines.

At what composition does ethanol-water distillation form an azeotrope, requiring a secondary drying step?

About 96 % ethanol and 4 % water.

What post-distillation method is commonly used to obtain anhydrous ethanol?

Molecular sieving (often using zeolite beds).

What does the acronym EROEI stand for?

Energy Returned On Energy Invested.

In the context of biofuels, what does a high EROEI indicate?

That the fuel yields significantly more usable energy than was consumed to produce it.

What is the chemical abbreviation FAME in biodiesel production?

Fatty Acid Methyl Ester.

Which two reactants are combined in transesterification to turn triglycerides into biodiesel?

A vegetable (or waste) oil and methanol, usually with a catalyst such as NaOH.

What valuable by-product is formed alongside biodiesel in transesterification?

Glycerol.

Give one advantage of biodiesel over conventional diesel regarding emissions.

Lower particulate and carbon-monoxide emissions.

What blending levels of biodiesel are typically acceptable in standard diesel engines without modification?

B10 or B20 (10 % or 20 % biodiesel).

What environmental issue arose from increased demand for vegetable-oil feedstocks for biodiesel?

Deforestation for large-scale palm-oil plantations in Indonesia and Malaysia.

Distinguish first-gen, second-gen and third-gen biofuels by feedstock type.

1st gen uses food crops (sugars, starches, edible oils); 2nd gen uses non-food wastes & residues (lignocellulose, used oil); 3rd gen uses non-arable resources like microalgae.

Provide an example feedstock for first-generation ethanol.

Corn starch (in the US) or sugar-cane juice (in Brazil).

Provide an example feedstock for second-generation ethanol.

Bagasse (fibrous residue of sugar cane) or timber-processing waste.

Which enzymes are industrially used to hydrolyse starch into fermentable glucose?

α-Amylase (e.g., Termamyl) and glucoamylase (e.g., AMG).

In cellulose breakdown for second-generation ethanol, what major challenge increases cost?

Pretreatment and enzymatic hydrolysis needed to make cellulose accessible and remove fermentation inhibitors.

Name the three Australian bioethanol plants mentioned and their primary feedstocks.

Shoalhaven Starches (Nowra, wheat starch), Dalby Bio-Refinery (sorghum) and Sarina Distillery (molasses).

What concept explains how biofuels can be close to carbon-neutral?

Their carbon cycle is closed: CO₂ released on combustion roughly equals CO₂ captured during recent photosynthesis.

What term describes the high energy content per volume that makes liquid fuels convenient?

Energy density.

Compared with gasoline, how does ethanol’s volumetric energy density differ?

Ethanol’s energy density is significantly lower, so blends deliver slightly less energy per litre.

What is the typical reaction equation for yeast fermentation of glucose to ethanol called?

The Gay-Lussac equation.

Which transport sectors currently rely most on liquid biofuels?

Road transport and, increasingly, marine and aviation sectors (via blends).

What Australian facility converts market food waste into biogas through anaerobic digestion?

EarthPower near Rosehill, Western Sydney.

List two products, besides energy, that EarthPower harvests from its digestion process.

Fertiliser from digested sludge and treated wastewater.

What historical fermentation process produces acetone, butanol and ethanol?

The ABE (Acetone-Butanol-Ethanol) process.

Why is biobutanol attractive compared with ethanol as a fuel?

Higher energy density and better compatibility/miscibility with gasoline.

What is “green hydrogen”?

Hydrogen produced without fossil fuels, e.g., by water electrolysis using renewable power or by fermentation pathways.

What Sydney-based company engineers E. coli to produce hydrogen biologically?

Hydgene.

What catalyst alternative to caustic soda can reduce soap formation in biodiesel manufacture?

Immobilised lipase enzymes.

Why can straight vegetable oil be problematic in diesel engines, especially in cold climates?

High viscosity and tendency to gel.

What advantage do diesel engines have over petrol engines regarding biodiesel use?

They tolerate higher blends and even straight biodiesel with minimal modification.

Name one non-edible oil crop investigated for biodiesel that can grow on marginal land.

Jatropha curcas.

What problem does the azeotrope in ethanol production pose, and how is it solved industrially?

Distillation stalls at 96 % ethanol; molecular sieves or other dehydration methods remove the remaining water.

Which exhaust pollutants are generally reduced when ethanol is blended into petrol?

Carbon monoxide (CO) and nitrogen oxides (NOx).

How does the MIT “carbon counter” graph compare vehicle types?

It plots lifecycle GHG emissions against total cost of ownership for petrol, diesel, hybrid, electric and fuel-cell cars.

What proportion of petroleum’s original energy typically remains after refining and distribution to the customer?

About two-thirds; roughly one-third is consumed in refining and distribution.

Summarise the key benefit of using lignocellulosic feedstocks for biofuel production.

They do not compete with food crops and can yield more energy from the same plant biomass.