Choose how you work — type your answers below or write in your book.
IQ4Lesson 10 of 2345 minOrganic Chemistry
Production of Alcohols
Ethanol is simultaneously the world's most consumed psychoactive substance, a major industrial solvent, a fuel additive, and a feedstock for dozens of other chemicals — and it can be made three completely different ways, each with different feedstocks, conditions, costs, and environmental footprints.
🏭
Printable worksheet
Download this lesson's worksheet
Use the PDF for classwork, homework or revision. It includes key ideas, activities, questions, an extend task and success-criteria proof.
In 2023, Brazil produced approximately 35 billion litres of ethanol from sugar cane — almost entirely by fermentation. At the same time, chemical plants in Europe and Asia produced ethanol from ethene and steam over a phosphoric acid catalyst in high-pressure reactors. Both processes make identical molecules of CH₃CH₂OH. The Brazilian factory runs at 35°C with yeast in giant vats. The European plant runs at 300°C and 65 atmospheres of pressure with stainless steel vessels.
Before you read on, write down: Which method do you think produces higher-purity ethanol? Which costs more to run? Which is more sustainable? You will return to evaluate each prediction at the end of the lesson.
You met alkene hydration in L06 as a reaction type — now you examine it as an industrial process, which means thinking about equilibrium, yield, scale, and the economic context that determines whether this reaction is worth running at all.
The hydration of ethene to produce ethanol is one of the most important industrial organic reactions in the world:
CH₂=CH₂ + H₂O ⇌ CH₃CH₂OH
The reaction is reversible — written with ⇌, not →. At equilibrium, both the forward reaction (hydration → ethanol) and the reverse reaction (dehydration → ethene + steam) occur simultaneously.
Conditions Chosen to Maximise Yield — Le Chatelier's Principle
HIGH PRESSURE (~65 atm): The left side has 2 moles of gas (ethene + steam); the right side has effectively 0 moles of gas (ethanol condenses as liquid). Increasing pressure shifts equilibrium to the side with fewer gas moles — the right side — increasing ethanol yield.
TEMPERATURE (~300°C): The forward reaction is exothermic. Lower temperature would favour the forward direction and increase yield. However, lower temperature also means slower rate and lower throughput. 300°C is a rate-vs-yield compromise — not optimal for yield, but acceptable for rate. (Same trade-off as the Haber process for ammonia.)
H₃PO₄ CATALYST: Speeds up attainment of equilibrium without shifting the equilibrium position. More ethanol is produced faster per unit time.
RECYCLE LOOP: Single-pass conversion is only ~5% — most ethene does not react in one pass. Unreacted ethene is separated from the product stream, recycled, and passed through again. This continuous recycling achieves high overall yield despite low single-pass conversion.
Must Do: Write ⇌ not → for the hydration equation. Using → implies complete conversion and tells the marker you don't understand that this is an equilibrium reaction. The ⇌ signals that you know conditions (high pressure, catalyst, temperature) are chosen to maximise yield within equilibrium constraints.
Common Error: "High temperature is used to increase ethanol yield." This is wrong for an exothermic reaction. High temperature shifts the exothermic equilibrium LEFT (Le Chatelier — opposes heating by favouring the endothermic reverse reaction), which DECREASES yield. 300°C is a rate compromise, not a yield-maximising choice. Distinguish rate effects from equilibrium effects.
Insight: The H₃PO₄ catalyst is not dissolved in the reaction mixture — it is absorbed onto solid silica and acts as a heterogeneous catalyst. Gaseous reactants flow over the solid catalyst surface. This continuous-flow design allows the catalyst to stay in the reactor while ethanol vapour flows out and is condensed downstream. Such reactors can operate without stopping for weeks or months.
Exam TipFor organic chemistry questions, draw full structural formulas showing all atoms and bonds — condensed or skeletal formulas alone may lose marks in HSC extended-response questions.
02
Substitution of Haloalkanes — Making Alcohols from Halides
Haloalkanes are the most versatile building blocks in organic synthesis — and one of their most important transformations is nucleophilic substitution with hydroxide ion, which converts a C–X bond directly into a C–OH bond without needing a double bond at all.
When a haloalkane is heated with aqueous NaOH or KOH, the halogen is replaced by a hydroxyl group. This is nucleophilic substitution — OH⁻ acts as a nucleophile and replaces the halogen (which leaves as halide X⁻).
R–X + NaOH(aq) → R–OH + NaX
Worked Equations
Haloalkane
Equation
Product
bromoethane
CH₃CH₂Br + NaOH(aq) → CH₃CH₂OH + NaBr
ethanol
2-bromopropane
CH₃CHBrCH₃ + NaOH(aq) → CH₃CHOHCH₃ + NaBr
propan-2-ol
2-bromo-2-methylpropane
(CH₃)₃CBr + NaOH(aq) → (CH₃)₃COH + NaBr
2-methylpropan-2-ol
Key Features
(1) Aqueous NaOH: The hydroxide must be aqueous (dissolved in water) to give substitution. If NaOH is in ethanol (alcoholic NaOH), elimination occurs instead — producing an alkene.
(2) Reflux: Heating increases rate. Reflux prevents volatile haloalkane and alcohol vapours from escaping — condensed vapours drip back into the flask, keeping reactants in contact and improving yield.
(3) Halide leaving group reactivity:
R–I (fastest)›R–Br›R–Cl (slowest)
C–I bonds are weakest and most easily broken; C–Cl bonds are strongest. Iodoalkanes react fastest.
Conditions — Haloalkane Substitution to Alcohol
Reagent
NaOH(aq) or KOH(aq) — aqueous hydroxide (NOT alcoholic)
Must Do: The word AQUEOUS in "NaOH(aq)" is critical — it determines the reaction type. Aqueous NaOH → substitution → alcohol. Alcoholic NaOH (NaOH dissolved in ethanol) → elimination → alkene. This is one of the most commonly tested condition-based questions in Module 7. Always check: aqueous or alcoholic?
Common Error: Writing the product side as "R–OH + Na + X" as if NaOH splits into separate Na and X products. The correct product is NaX (sodium halide salt) — Na⁺ and X⁻ combine. The equation must balance: one NaOH consumed, one NaX produced. Writing Na + X separately shows a misunderstanding of ionic compound formation.
Reflux apparatus for haloalkane substitution — condenser returns volatile reactants to the flask, preventing loss and improving yield
03
Fermentation — Biological Production of Ethanol
Fermentation is the oldest chemical process humans have used deliberately — and it works because yeast cells contain an enzyme (zymase) that catalyses the conversion of glucose to ethanol under conditions impossible to replicate in an industrial pressure reactor.
Fermentation is the biological conversion of glucose to ethanol and carbon dioxide, catalysed by the enzyme zymase found in yeast cells:
Optimal for enzyme activity. <15°C = too slow. >45°C = enzyme denatures.
🚫
Anaerobic
No oxygen. With O₂, yeast respires aerobically → CO₂ + H₂O, not ethanol.
🍞
Yeast (zymase)
Enzyme catalyst. Not consumed overall, but reproduces and dies in vessel.
Maximum ethanol concentration: ~15%. When ethanol reaches ~15%, it becomes toxic to yeast cells and fermentation stops — regardless of remaining glucose. Spirits (40%) require fractional distillation of the fermented liquid.
Feedstock: Any sugar or starch — sugar cane, sugar beet, corn, wheat, barley, cassava. Starch must first be hydrolysed to glucose by amylase enzymes before zymase can act.
Conditions — Fermentation
Reagent
Glucose solution (C₆H₁₂O₆ in water)
Catalyst
Yeast (enzyme zymase — biological catalyst)
Temperature
~35°C (enzyme optimum)
Atmosphere
Anaerobic (no oxygen / air excluded)
Equipment
Sealed fermentation vessel (vented to release CO₂)
Arrow
→ (goes essentially to completion, stops at ~15% ethanol)
Must Do: Three conditions are always required: (1) temperature ~35°C; (2) anaerobic (no oxygen / air excluded); (3) yeast or zymase enzyme. The most commonly omitted condition is anaerobic. Without anaerobic conditions, yeast respires aerobically and produces CO₂ + H₂O instead of ethanol — no ethanol at all.
Common Error: Writing C₆H₁₂O₆ → C₂H₅OH + CO₂ without coefficients — this is unbalanced. The balanced equation requires coefficient 2 on both products: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂. An unbalanced equation loses marks even if the rest of the answer is correct.
Insight: The CO₂ produced in fermentation is not always waste. In beer and sparkling wine, CO₂ is retained to carbonate the drink. In bread-making, CO₂ bubbles are trapped by gluten proteins, causing dough to rise. The same equation — the same two products — underlies beer, wine, spirits, and artisan bread. What changes is only whether the CO₂ is captured or released.
Comparing the Three Methods — Feedstock, Yield & Sustainability
Choosing between hydration, haloalkane substitution, and fermentation is not a chemistry question — it is an engineering, economic, and environmental question that chemistry informs but does not answer alone.
Rate: hydration > substitution > fermentation. Hydration is continuous industrial; fermentation is slow batch.
Purity: hydration gives highest purity; fermentation gives lowest (15% — must distil to get concentrated product).
Sustainability: fermentation wins on renewable feedstock — plant biomass grown using solar energy; net CO₂ near zero for the growth phase. Hydration and substitution both depend on fossil fuel feedstocks.
Energy: fermentation at 35°C = low energy input. Hydration at 300°C + 65 atm = very high energy and infrastructure cost.
Simplicity: fermentation requires no high-pressure vessels, viable at small scale. Hydration requires sophisticated industrial infrastructure.
Must Do — HSC Comparison Questions: Structure your response as explicitly paired comparisons, not as separate descriptions. Marks go to COMPARATIVE statements: "fermentation is slower than hydration because…" — not "fermentation is slow" and "hydration is fast" in isolation. Use comparison language: faster/slower, higher/lower, more/less renewable.
Common Error: Writing "fermentation is better than hydration because it is renewable." This earns one mark but ignores trade-offs: fermentation is slower, produces lower-purity ethanol requiring energy-intensive distillation, and cannot supply full global industrial demand. HSC evaluation questions require you to acknowledge both advantages AND limitations of each method. One-sided answers are penalised.
⚠️ Common Misconceptions — Alcohol Production
✗
"Higher temperature increases ethanol yield in alkene hydration." Wrong — the forward reaction is exothermic. Higher temperature favours the reverse (endothermic) reaction by Le Chatelier, DECREASING yield. 300°C is chosen for rate, not yield.
✗
"Fermentation is always more sustainable than hydration." Oversimplified — distillation of low-purity fermented ethanol consumes significant energy, and large-scale fermentation requires land clearing, irrigation, and may compete with food crops. Context matters.
✗
"NaOH always gives substitution with haloalkanes." Only aqueous NaOH gives substitution (→ alcohol). Alcoholic NaOH gives elimination (→ alkene). The solvent determines the product.
✗
"Fermentation equation: C₆H₁₂O₆ → C₂H₅OH + CO₂ (no coefficients)." Unbalanced — must be C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂. Missing coefficients always lose marks.
Worked Examples
Example 1Straightforward
Writing Balanced Equations for All Three Production Methods
Problem: Write balanced equations for the production of ethanol using: (a) hydration of ethene; (b) substitution of bromoethane with NaOH; (c) fermentation of glucose. State the conditions for each.
1
Part (a) — Alkene Hydration:
Equation: CH₂=CH₂ + H₂O ⇌ CH₃CH₂OH
Note: reversible arrow (⇌) — this is an equilibrium reaction.
Conditions: H₂O (steam), H₃PO₄ catalyst, ~300°C, ~65 atm.
2
Part (b) — Haloalkane Substitution:
Equation: CH₃CH₂Br + NaOH(aq) → CH₃CH₂OH + NaBr
Note: single arrow (→) — substitution goes essentially to completion.
Conditions: NaOH(aq) [aqueous], heat under reflux.
3
Part (c) — Fermentation:
Equation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂
Balance check: Left — 6C, 12H, 6O. Right — 4C+12H+2O + 2C+4O = 6C, 12H, 6O ✓
Conditions: yeast (zymase enzyme), ~35°C, anaerobic (no oxygen).
Explaining Equilibrium Considerations in Alkene Hydration
Problem: The industrial hydration of ethene operates at ~300°C and ~65 atm with a H₃PO₄ catalyst. Single-pass conversion is only ~5%. (a) Explain why high pressure is used. (b) Explain why 300°C is a compromise. (c) Explain how low single-pass conversion is managed without sacrificing overall yield.
1
(a) High pressure:
Equation: CH₂=CH₂ + H₂O ⇌ CH₃CH₂OH
Left side: 2 moles of gas (ethene + steam). Right side: 0 moles of gas (ethanol condenses as liquid).
By Le Chatelier's Principle: increasing pressure shifts equilibrium to the side with fewer moles of gas — the right side (products). ∴ High pressure increases ethanol yield.
2
(b) 300°C as rate-yield compromise:
The forward reaction is exothermic. By Le Chatelier, DECREASING temperature favours the exothermic direction → shifts equilibrium right → increases ethanol yield.
However, lower temperature also means slower reaction rate and lower throughput.
300°C gives a rate fast enough for continuous industrial production while still achieving an acceptable (if not maximum) equilibrium yield. This is a kinetics-vs-thermodynamics compromise, analogous to the Haber process.
3
(c) Managing low single-pass conversion:
After each pass through the reactor, the exit stream contains mostly unreacted ethene + small amounts of ethanol. The ethanol is condensed and separated. Unreacted ethene is recycled — pumped back to the reactor inlet and passed through again.
This continuous recycling achieves high overall yield despite only ~5% conversion per pass. Almost all ethene is eventually converted across multiple passes.
Answer:
(a) High pressure (65 atm) favours the side with fewer gas moles (right side) — Le Chatelier — increasing ethanol yield.
(b) Lower temperature would increase yield (exothermic forward reaction) but would slow the rate unacceptably. 300°C is a kinetics-thermodynamics compromise.
(c) Unreacted ethene is separated from the product stream and recycled to the reactor inlet — continuous recycling achieves high overall yield despite low single-pass conversion.
Example 3Extended Response
Evaluating Production Methods — Brazil vs. Germany (7 marks)
Problem: Brazil produces ethanol almost exclusively by fermentation of sugar cane; Germany produces industrial ethanol by catalytic hydration of ethene. (a) Write balanced equations for both processes with all conditions. (b) Explain why fermentation is preferred in Brazil. (c) Explain why hydration is preferred in Germany for industrial use. (d) Evaluate the claim: "Fermentation is always the more sustainable choice."
(b) Fermentation preferred in Brazil:
Brazil has abundant agricultural land for sugar cane — a renewable, photosynthetically produced glucose source. Fermentation requires no high-pressure infrastructure, operates at 35°C (low energy input), and is near-carbon-neutral (CO₂ released during fermentation is offset by CO₂ absorbed during sugar cane growth). The resulting ethanol is used as car fuel, reducing fossil fuel import dependence. Brazil's warm climate enables continuous sugar cane cultivation year-round.
3
(c) Hydration preferred in Germany:
Germany has sophisticated petrochemical infrastructure — ethene is available from oil refinery cracking. Catalytic hydration produces high-purity ethanol (~95%) continuously at large scale — suitable for industrial solvents, pharmaceutical manufacturing, and chemical synthesis where strict purity is required. The process has far higher throughput than fermentation. Fermentation's slow rate and low purity (requiring energy-intensive distillation) make it less competitive for high-volume industrial applications in a high-wage economy with existing large-scale infrastructure.
4
(d) Evaluation of the claim: Arguments FOR (fermentation more sustainable): renewable feedstock; lower energy requirement (35°C vs 300°C + 65 atm); near-carbon-neutral when plant growth is accounted for; no fossil fuel dependence. Arguments AGAINST (claim is oversimplified): fermentation produces only ~15% ethanol — purification to industrial grade requires fractional distillation consuming significant energy. Large-scale fermentation requires clearing land for biomass crops, potentially involving deforestation, habitat loss, and food-vs-fuel competition. Water consumption for irrigation is very high. Conclusion: Fermentation has genuine sustainability advantages in many contexts. However, it is not universally "better" — net sustainability depends on feedstock, land use, water use, energy source for distillation, and local infrastructure. The claim is too absolute.
Model Answer Summary:
(a) Equations with conditions as above.
(b) Fermentation in Brazil: renewable agricultural feedstock, low energy/infrastructure, near-carbon-neutral, reduces import dependence.
(c) Hydration in Germany: ethene from refinery cracking, high purity, high throughput, no distillation needed for industrial-grade concentration.
(d) Partially correct but oversimplified. Fermentation has genuine sustainability advantages but distillation energy cost, land use, water use, and food-vs-fuel trade-offs mean it is not automatically "more sustainable" in every context.
Each equation below contains an error in the arrow notation or equation balance. Identify and correct each one.
CH₂=CH₂ + H₂O → CH₃CH₂OH (industrial ethanol)
CH₃Br + NaOH(aq) ⇌ CH₃OH + NaBr
C₆H₁₂O₆ → C₂H₅OH + CO₂ (fermentation)
Activity B
Conditions Matching — Which Method?
For each set of conditions below, identify which method of alcohol production is being described and write the balanced equation:
Yeast, 35°C, sealed vessel, no oxygen
H₃PO₄ catalyst, 300°C, 65 atm, steam
KOH(aq), round-bottom flask, reflux condenser, heating mantle, 1-bromopropane as starting material
Check Your Understanding
Question 1. A student reacts 1-chloropropane with aqueous NaOH under reflux. Which product is formed and what is the reaction type?
APropene + NaCl — elimination reaction
BPropan-1-ol + NaCl — nucleophilic substitution
CPropan-2-ol + NaCl — nucleophilic substitution
DPropan-1-ol + NaCl — addition reaction
Question 2. In the industrial production of ethanol by alkene hydration, single-pass conversion is approximately 5%. Which combination correctly explains how high overall yield is still achieved?
AUsing excess ethene forces the equilibrium fully to the right in a single pass
BThe H₃PO₄ catalyst converts all ethene to ethanol at 300°C
CUnreacted ethene is separated from the product stream and recycled to the reactor, achieving high overall conversion across multiple passes
DHigh temperature at 300°C shifts the equilibrium fully to the product side
Question 3. Which set of conditions correctly describes fermentation of glucose to produce ethanol?
AGlucose solution, H₃PO₄ catalyst, ~300°C, high pressure, aerobic
CFermentation requires lower temperatures than hydration but produces lower purity ethanol, requiring distillation for industrial-grade product
DHaloalkane substitution requires high pressure conditions to achieve acceptable yield
Question 5. The industrial hydration of ethene is described as operating at a rate-yield compromise temperature. Which statement best explains this?
AHigher temperature increases both equilibrium yield and reaction rate, so 300°C is chosen to maximise both simultaneously
BLower pressure would increase ethanol yield but is not used because it would decrease the reaction rate
CThe H₃PO₄ catalyst increases equilibrium yield but only functions above 300°C
DHigher temperature increases reaction rate but shifts the exothermic equilibrium towards reactants, decreasing yield — 300°C balances these competing effects
Revisit Your Initial Thinking
Look back at what you wrote in the Think First section. What has changed? What did you get right? What surprised you?
Short Answer Questions
Question 64 marks
Write a balanced equation for the fermentation of glucose to produce ethanol. State all three conditions required for fermentation, and explain why each condition is necessary.
Question 75 marks
The industrial hydration of ethene is carried out at ~300°C, ~65 atm, with a H₃PO₄ catalyst. Using Le Chatelier's Principle, explain: (a) why high pressure is used rather than atmospheric pressure; (b) why 300°C is described as a compromise temperature and not the temperature that maximises ethanol yield.
Question 86 marks
Brazil produces most of its transport fuel ethanol by fermentation of sugar cane, while Germany produces most of its industrial ethanol by catalytic hydration of ethene. Evaluate which method is more sustainable for large-scale ethanol production, considering feedstock, energy, purity, and land use.
Multiple Choice Answers
Q1 — B: Propan-1-ol + NaCl — nucleophilic substitution.
1-chloropropane (CH₃CH₂CH₂Cl) + NaOH(aq) → CH₃CH₂CH₂OH (propan-1-ol) + NaCl. Nucleophilic substitution — OH⁻ replaces Cl on the same carbon (C1), giving propan-1-ol. Propan-2-ol (C) would require -OH to move to C2, which does not happen in simple substitution. Propene (A) forms with alcoholic NaOH (elimination), not aqueous NaOH.
Q2 — C: Unreacted ethene is recycled.
The low 5% single-pass conversion is compensated by continuous recycling of unreacted ethene back to the reactor inlet. Over many passes, almost all ethene is converted. A is wrong — excess ethene shifts equilibrium slightly right but cannot achieve full conversion per pass. D is wrong — 300°C is a rate compromise; higher temperature shifts the exothermic equilibrium LEFT (away from products), decreasing yield.
Q3 — B: Glucose solution, yeast (zymase enzyme), ~35°C, anaerobic.
Fermentation requires all three: yeast (zymase), ~35°C (enzyme optimum), and anaerobic conditions (no oxygen). D is the most dangerous distractor — adding excess oxygen causes aerobic respiration (→ CO₂ + H₂O), not increased ethanol. A describes alkene hydration conditions applied incorrectly to fermentation.
Q4 — C: Fermentation lower temperature, lower purity.
Fermentation operates at ~35°C (lower than hydration's ~300°C) but produces only ~15% ethanol (much lower purity than hydration's ~95%). Purification by fractional distillation is required for industrial-grade product. A is wrong (hydration gives higher purity). B is wrong — the feedstocks are the reverse: fermentation uses renewable plant biomass, hydration uses non-renewable ethene from crude oil.
Q5 — D: Higher temperature increases rate but decreases yield for exothermic reaction.
The forward hydration reaction is exothermic. By Le Chatelier, higher temperature shifts the equilibrium LEFT (favours endothermic reverse), decreasing ethanol yield. However, higher temperature increases reaction rate. 300°C is chosen to balance these opposing effects — fast enough rate for industrial viability, acceptable (not maximum) yield. A is incorrect — higher temperature does NOT increase equilibrium yield for an exothermic reaction.
Short Answer Sample Answers
Q6 — Fermentation equation and conditions (4 marks):
Equation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ [1 mark — must have coefficient 2 on both products]
Condition 1 — Yeast (zymase enzyme): biological catalyst that facilitates the multi-step conversion of glucose to ethanol; without it the reaction is too slow to be useful [1 mark]
Condition 2 — ~35°C: optimal temperature for enzyme activity; above ~45°C enzyme denatures and loses function; below ~15°C rate is too slow [1 mark]
Condition 3 — Anaerobic (no oxygen/air excluded): in the presence of oxygen, yeast undergoes aerobic respiration (→ CO₂ + H₂O) rather than fermentation; oxygen must be excluded for ethanol to be produced [1 mark]
Q7 — Le Chatelier pressure and temperature (5 marks):
(a) High pressure [2–3 marks]: Equation: CH₂=CH₂ + H₂O ⇌ CH₃CH₂OH. Left side: 2 moles of gas (ethene + steam). Right side: 0 moles of gas (ethanol condenses as liquid under process conditions). Le Chatelier's Principle: increasing pressure shifts equilibrium to the side with fewer moles of gas — the right side (products). ∴ High pressure increases the equilibrium yield of ethanol.
(b) Temperature compromise [2–3 marks]: Forward reaction is exothermic. By Le Chatelier, decreasing temperature favours the exothermic direction (forward), shifting equilibrium right and increasing yield. However, lower temperature also decreases reaction rate, reducing economic throughput. 300°C is a compromise — the rate is fast enough for continuous industrial production while still giving an acceptable equilibrium yield. The temperature that maximises yield would be much lower, but the reaction rate would be too slow to be economically viable. [Analogous to Haber process for NH₃ — award 1 bonus mark for this connection]
Q8 — Sustainability evaluation (6 marks): Arguments for fermentation being more sustainable: Uses renewable feedstock (plant biomass — sugar cane, corn); grown using solar energy and photosynthesis. Near-carbon-neutral — CO₂ released during fermentation is largely offset by CO₂ absorbed during plant growth. Operates at 35°C — very low energy input compared to 300°C + 65 atm for hydration. No dependence on declining fossil fuel reserves. [up to 3 marks] Arguments against fermentation being universally more sustainable: Produces only ~15% ethanol — must be distilled to reach industrial-grade concentrations; distillation is energy-intensive and erodes the sustainability advantage. Large-scale fermentation requires clearing land for biomass crops, potentially involving deforestation, habitat loss, and food-vs-fuel competition (corn for fuel vs food). Very high water consumption for crop irrigation. Slow batch process with high labour requirements at scale. [up to 3 marks] Conclusion: Fermentation has genuine sustainability advantages — particularly in countries with surplus agricultural land, warm climate, and renewable energy for distillation (e.g. Brazil). However, it is not universally more sustainable. The net outcome depends on land use, water availability, energy source for distillation, and scale. For high-volume industrial chemical production requiring high purity, hydration may have a lower overall environmental impact when land use and distillation energy are fully accounted for. [1 mark for qualified conclusion acknowledging context-dependence]
Revisit — Think First
Brazil vs. Germany — Were Your Predictions Right?
Return to your predictions. Check each one:
Higher-purity ethanol: Alkene hydration (industrial, Germany) produces ~95% purity directly from the reactor. Fermentation produces only ~15% — the Brazilian ethanol requires fractional distillation to reach fuel grade. If you predicted hydration, you were right.
Higher running cost: This is context-dependent, but alkene hydration requires 300°C and 65 atm pressure — enormous energy and infrastructure costs per unit of product. Fermentation at 35°C costs far less per batch energy-wise, though distillation adds cost. If you said hydration costs more to run in terms of energy and capital infrastructure, you were broadly right.
More sustainable: Fermentation has genuine sustainability advantages — renewable feedstock, low energy, near-carbon-neutral. But it's not a simple win: distillation energy, land clearing, and water use complicate the picture. The honest answer is "it depends on context" — which is exactly the kind of nuanced evaluation the HSC rewards in Band 6 responses.
⚔️
Boss Battle
Production of Alcohols
Put your knowledge of Production of Alcohols to the test. Answer correctly to deal damage — get it wrong and the boss hits back. Pool: lessons 1–10.