📚 IGCSE Edexcel Science: Manufacturing Ethanol & Its Uses | 乙醇的制取与用途
Ethanol (C₂H₅OH) is one of the most important organic compounds in everyday life and industry. In the Edexcel IGCSE Science (Double Award) and Chemistry specifications, you need to understand its structure, how it is made by two distinct methods, and why it is such a versatile substance. This article unpacks every assessment point, giving you a clear, bilingual revision path.
乙醇（C₂H₅OH）是日常生活和工业中最重要的有机化合物之一。在爱德思 IGCSE 科学（双奖）和化学大纲中，你需要掌握它的结构、通过两种不同方法制取的途径，以及为什么它是一种用途广泛的物质。本文将逐一剖析每个考点，为你提供清晰的双语复习路径。
1. Introduction to Ethanol | 乙醇简介
Ethanol belongs to the alcohol homologous series, with the general formula CₙH₂ₙ₊₁OH. It contains two carbon atoms, a hydroxyl (–OH) functional group, and the rest of the molecule is a hydrocarbon chain. Ethanol is a colourless, volatile liquid that mixes completely with water and has a characteristic smell. It is the alcohol found in drinks, but the same chemical is also used as a solvent, a fuel, and a chemical feedstock.
乙醇属于醇类同系物，通式为 CₙH₂ₙ₊₁OH。它含有两个碳原子、一个羟基（–OH）官能团，其余部分是一个烃链。乙醇是一种无色、易挥发的液体，与水完全混溶，并具有特殊气味。它是饮品中含有的酒精，但同样的化学品也被用作溶剂、燃料和化工原料。
2. Structural Formula and Key Properties | 结构式与主要性质
Ethanol can be represented by its molecular formula C₂H₅OH, or by the displayed formula showing all atoms and bonds. The hydroxyl group is responsible for its solubility in water – hydrogen bonds form between ethanol and water molecules. Key physical properties include a boiling point of 78 °C, a melting point of –114 °C, and a density of about 0.789 g/cm³. Ethanol is highly flammable and burns with a clean, pale blue flame.
乙醇可以用分子式 C₂H₅OH 表示，也可以用展示所有原子和键的显示式表示。羟基是其溶于水的原因——乙醇和水分子之间形成氢键。关键的物理性质包括沸点 78 °C、熔点 –114 °C、密度约 0.789 g/cm³。乙醇高度易燃，燃烧时产生干净的淡蓝色火焰。
3. Why Two Manufacturing Methods? | 为什么有两种制取方法？
Edexcel IGCSE requires you to describe two different routes to ethanol: fermentation of sugars, and direct hydration of ethene. Fermentation is a biological process that uses renewable resources, while hydration of ethene comes from the petrochemical industry and uses a non-renewable raw material. Comparing these methods allows us to discuss sustainability, cost, and purity of the product.
爱德思 IGCSE 要求你描述乙醇的两种不同制取途径：糖类的发酵，以及乙烯的直接水化。发酵是利用可再生资源的生物过程，而乙烯水化来自石化工业，使用不可再生的原料。比较这两种方法可以讨论可持续性、成本和产品的纯度。
4. Manufacture of Ethanol by Fermentation | 通过发酵制取乙醇
Fermentation converts a carbohydrate source, typically glucose (C₆H₁₂O₆), into ethanol and carbon dioxide using enzymes in yeast. The yeast provides the enzyme zymase, which catalyses the reaction under anaerobic conditions. The process is carried out in an aqueous solution at an optimum temperature between 25 °C and 37 °C. If the temperature is too high, the enzymes denature; if too low, the rate is too slow. A thick paste or 'mash' of crushed plant material (sugar cane, maize, or other starch sources) is often used, with the starch first broken down into sugars.
发酵是利用酵母中的酶，将碳水化合物来源（通常为葡萄糖 C₆H₁₂O₆）转化为乙醇和二氧化碳。酵母提供酒化酶，在厌氧条件下催化该反应。该过程在水溶液中进行，最佳温度在 25 °C 至 37 °C 之间。温度过高会使酶变性；温度过低则速率太慢。通常使用碾碎的植物原料（甘蔗、玉米或其他淀粉来源）制成浓浆，其中的淀粉先被分解为糖类。
5. The Fermentation Equation and Key Conditions | 发酵的方程式与关键条件
C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂
The balanced equation shows that one mole of glucose produces two moles of ethanol and two moles of carbon dioxide. The reaction is exothermic overall. Once the ethanol concentration reaches about 10–15%, the yeast becomes inactive, and the mixture must be distilled to obtain a higher concentration. Fractional distillation can produce ethanol of around 96% purity.
配平方程显示，一摩尔葡萄糖生成两摩尔乙醇和两摩尔二氧化碳。该反应总体放热。当乙醇浓度达到约 10–15% 时，酵母失活，必须通过蒸馏获得更高浓度。分馏可以制得纯度约 96% 的乙醇。
6. Manufacture of Ethanol by Hydration of Ethene | 通过乙烯水化制取乙醇
Ethene (C₂H₄) is obtained from crude oil or natural gas by cracking. It is mixed with steam and passed over a phosphoric acid catalyst (H₃PO₄) absorbed onto a solid silicon dioxide support. The reaction takes place at a high temperature of about 300 °C and a high pressure of around 60–70 atm. This is an addition reaction where water adds across the double bond, producing ethanol only in one step:
乙烯（C₂H₄）通过裂解从原油或天然气中获得。它与水蒸气混合后，通过负载在固体二氧化硅载体上的磷酸催化剂（H₃PO₄）。反应在约 300 °C 的高温和约 60–70 个大气压的高压下进行。这是一个加成反应，水加成到双键上，一步生成乙醇：
C₂H₄ + H₂O ⇌ C₂H₅OH
The reaction is reversible, so unreacted ethene and steam are recycled to improve yield. The product stream is cooled and ethanol condenses out. This method gives a very high purity of ethanol, typically above 99%, and produces no carbon dioxide as a direct by-product.
该反应是可逆的，因此未反应的乙烯和水蒸气被循环利用以提高产率。产物气流冷却后，乙醇冷凝分离。此方法可获得极高纯度的乙醇，通常超过 99%，且不直接产生二氧化碳作为副产物。
7. Comparing Fermentation and Hydration | 发酵与水化方法的比较
| Feature | Fermentation 发酵 | Hydration of Ethene 乙烯水化 |
|---|---|---|
| Raw material | Renewable (sugar cane, maize) | Non-renewable (crude oil) |
| Type of process | Batch process, slow | Continuous process, fast |
| Temperature | 25–37 °C | ~300 °C |
| Pressure | Atmospheric | 60–70 atm |
| Catalyst | Yeast (enzyme zymase) | Phosphoric acid |
| Purity after first stage | ~10–15%, needs distillation | >99%, very pure |
| Greenhouse gas emission | CO₂ released, but carbon neutral overall | No direct CO₂, but fossil fuel use |
From an environmental viewpoint, fermentation is often described as carbon‑neutral because the CO₂ released was absorbed by the plants during photosynthesis. However, the distillation step requires energy, which may reduce this benefit. Hydration of ethene is energy‑intensive and depends on finite fossil fuels, though it is very efficient in terms of atom economy.
从环境角度看，发酵通常被描述为碳中和的，因为释放的 CO₂ 是植物在光合作用中吸收的。但蒸馏步骤需要能量，这可能削弱这一优势。乙烯水化能耗较高且依赖有限的化石燃料，但原子经济性很高。
8. Uses of Ethanol as a Solvent | 乙醇作为溶剂的用途
Ethanol is an excellent solvent for many organic compounds, including fats, oils, resins, and perfumes. Because it is less toxic than many industrial solvents and miscible with water, it is widely used in medicines (cough syrups, antiseptics), cosmetics (perfumes, deodorants), and cleaning products. In the laboratory, ethanol is a common solvent for chromatography and for recrystallisation.
乙醇是许多有机化合物的优良溶剂，包括脂肪、油脂、树脂和香料。由于它的毒性比许多工业溶剂低，且与水混溶，它被广泛用于药品（止咳糖浆、消毒剂）、化妆品（香水、除臭剂）和清洁产品中。在实验室中，乙醇是色谱法和重结晶的常用溶剂。
9. Ethanol as a Fuel and Biofuel | 乙醇作为燃料和生物燃料
Ethanol can be burned in internal combustion engines, either pure or blended with petrol (gasohol). The complete combustion of ethanol yields carbon dioxide and water, and releases about 30 MJ/kg of energy. The equation is:
乙醇可在内燃机中燃烧，既可使用纯品，也可与汽油混合（乙醇汽油）。乙醇完全燃烧生成二氧化碳和水，释放约 30 MJ/kg 的能量。方程式为：
C₂H₅OH + 3 O₂ → 2 CO₂ + 3 H₂O
Bioethanol produced by fermentation is considered a renewable biofuel. Many countries blend ethanol with petrol to reduce dependence on crude oil and lower net carbon emissions. However, growing crops for fuel can compete with food production, creating an ethical debate.
通过发酵生产的生物乙醇被视为一种可再生生物燃料。许多国家将乙醇与汽油混合，以减少对原油的依赖并降低净碳排放。然而，为了燃料而种植作物可能与粮食生产竞争，引发伦理争议。
10. Ethanol in Alcoholic Drinks | 乙醇与酒精饮料
Ethanol is the psychoactive ingredient in beer, wine, and spirits. Beverage ethanol derives entirely from fermentation of sugars in grains, grapes, or other fruit. The alcohol content varies: beer typically 3–7% ABV (alcohol by volume), wine 9–16%, and spirits 35–50% after distillation. Governments usually impose heavy taxes and regulations because excessive consumption causes health and social problems.
乙醇是啤酒、葡萄酒和烈酒中的精神活性成分。饮料乙醇完全源自谷物、葡萄或其他水果中糖分的发酵。酒精含量各异：啤酒通常酒精体积分数 3–7%，葡萄酒 9–16%，蒸馏后的烈酒 35–50%。政府通常征收重税并严格监管，因为过量消费会引发健康和社会问题。
11. Quick Revision Checklist | 快速复习清单
- Recall the molecular and structural formula of ethanol, and identify the –OH functional group. 记忆乙醇的分子式和结构式，识别–OH官能团。
- Write balanced equations for fermentation and hydration. 书写发酵和水化反应的配平方程式。
- State the conditions (temperature, catalyst, pressure, raw materials) for both processes. 列出两种方法的条件（温度、催化剂、压力、原料）。
- Compare the two manufacturing routes in terms of renewability, purity, speed, and environmental impact. 从可再生性、纯度、速度和环境影响上比较两种制取途径。
- Describe at least three uses of ethanol: solvent, fuel/biofuel, and alcoholic drinks. 描述乙醇的至少三种用途：溶剂、燃料/生物燃料和酒精饮料。
- Explain why fermentation is a carbon‑neutral process in principle. 解释为什么从原理上发酵是碳中和的过程。
12. Exam-Style Questions to Practise | 应考型题目练习
1. Ethanol can be made by fermentation and by the hydration of ethene. Give one advantage and one disadvantage of each method. (4 marks)
2. Write a balanced equation for the complete combustion of ethanol. (2 marks)
3. Explain why the production of bioethanol from sugar cane can be described as carbon neutral. (3 marks)
4. Suggest why fermentation is carried out in a sealed container, but not completely filled. (2 marks)
1. 乙醇可通过发酵和乙烯水化制取。分别给出每种方法的一个优点和一个缺点。（4 分）
2. 写出乙醇完全燃烧的配平方程式。（2 分）
3. 解释为什么以甘蔗为原料生产生物乙醇可被称为碳中和。（3 分）
4. 说明为什么发酵在密闭容器中进行，但容器不完全装满。（2 分）
Work through these questions with the mark scheme in mind. For method comparisons, always link your answer to practical consequences: energy use, sustainability, purity levels, and cost.
在答题时，要紧扣评分方案。进行方法比较时，一定要将你的答案与实际结果联系起来：能源消耗、可持续性、纯度水平和成本。
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