biofuels

Why are biofuels needed?

Fossil fuels are limited and produce CO₂ emissions, driving demand for renewable alternatives — though biomass alone cannot supply total global energy demand

Why are biological systems better at energy conversion than human technology?

Biology has had ~3 billion years of evolution to develop microscopic, efficient energy interconversion using ATP, NADH/FADH₂, and ion gradients, whereas human technology (~100 years old) loses significant energy as heat

What are "drop-in" fuels?

Biofuels designed to be compatible with existing infrastructure (engines, seals, pipelines), which are built around current fossil fuel blends

What are first-generation biofuels and their limitations?

Bioethanol and biodiesel from food crops (maize, starch)

What is second-generation biofuel feedstock?

Lignocellulosic biomass (straw, grass, wood) — does not compete with food but is technologically difficult to process

What is third-generation biofuel production?

Direct photosynthetic production, e.g. using algae, avoiding biomass pre-treatment but facing major engineering challenges

What makes lignocellulose difficult to use as a feedstock?

It contains crystalline cellulose and degradation-resistant lignin, requires harsh pre-treatment (steam/high temp), and generates inhibitors like furfural, HMF, vanillin, and syringic acid

What is the fatty acid route to biofuels?

Glycolysis → acetyl-CoA → fatty acids → aldehyde → alkane (via decarbonylation) or alkene (via peroxide-dependent conversion)

What is the isoprenoid route to biofuels?

Isoprene units are assembled into naturally branched/cyclic hydrocarbons via terpene cyclases, suitable for diesel and jet fuel blends

How does enzyme engineering improve fatty acid chain length specificity?

Active site mutations (e.g. Ala → Phe) reduce the binding cavity, shifting enzyme preference toward shorter chains

How do terpene cyclases determine product outcome?

Active site geometry controls carbocation folding and cyclization

What are the three major engineering challenges in biofuel production?

(1) Feedstock conversion — using all sugars and tolerating inhibitors

(2) Light delivery in dense photosynthetic cultures;

(3) Metabolic stability — GM pathways are lost when not essential for survival

What properties does jet fuel specifically require?

C8–C16 hydrocarbons, branched and cyclic structures, high energy density, low freezing point, and seal compatibility

Why can biofuels not replace all fossil fuel use?

Global biomass is insufficient — even at 100% conversion efficiency, entire forests would be depleted rapidly

What is Botryococcus braunii and why is it limited?

An alga that produces oil-like hydrocarbons under high light/carbon and low nitrogen/phosphorus, but has poor scalability, difficult light delivery, and high infrastructure costs