Fractional Distillation of Crude Oil | 原油的分馏

📚 Fractional Distillation of Crude Oil | 原油的分馏

Crude oil is one of the most important natural resources on Earth. It is the source of many everyday fuels and materials, from petrol and diesel to plastics and roads. This article explores the process of fractional distillation, a key method used to separate crude oil into useful components. This topic is essential for Edexcel IGCSE Science students, as it appears frequently in examination questions.

原油是地球上最重要的自然资源之一。它是许多日常燃料和材料的来源，从汽油、柴油到塑料和道路。本文将探讨分馏这一关键方法，它用于将原油分离成有用的成分。对于爱德思 IGCSE 科学的学生来说，这一话题至关重要，因为它经常出现在考试题目中。

1. What is Crude Oil? | 什么是原油？

Crude oil, also called petroleum, is a dark, sticky liquid found deep underground. It was formed over millions of years from the remains of tiny marine organisms, such as plankton, that were buried under layers of sediment. High temperature and pressure slowly changed these remains into the mixture we call crude oil.

原油，也称为石油，是一种深色、粘稠的液体，存在于深层地下。它是由微小的海洋生物（如浮游生物）的遗骸在数百万年间形成的，这些遗骸被埋在沉积层下面。高温和高压慢慢将这些遗骸转化为我们称之为原油的混合物。

Crude oil is a mixture of hundreds of different chemical compounds. Most of them are hydrocarbons – molecules made only of carbon and hydrogen atoms. The simplest hydrocarbons are called alkanes, which have the general formula CₙH₂ₙ₊₂.

原油是数百种不同化合物的混合物。其中大多数是碳氢化合物——只由碳原子和氢原子组成的分子。最简单的碳氢化合物称为烷烃，其通式为 CₙH₂ₙ₊₂。

2. Why Does Crude Oil Need to Be Separated? | 为什么需要分离原油？

Crude oil as a whole is not very useful. It cannot be used directly as a fuel in cars, planes, or ships because it burns too easily and produces harmful smoke. Different hydrocarbons have very different properties and uses. Some are small and light, such as methane, which is a gas at room temperature. Others are large and heavy, such as bitumen, which is a solid. To make full use of crude oil, we must separate it into fractions – mixtures of hydrocarbons with similar boiling points.

原油作为一个整体并不是非常有用。它不能直接用作汽车、飞机或船舶的燃料，因为它燃烧太容易，并产生有害的烟雾。不同的碳氢化合物具有截然不同的性质和用途。有些是小的轻的，例如甲烷，它在室温下是气体。其他的是大的重的，例如沥青，它是固体。为了充分利用原油，我们必须将其分离成馏分——具有相似沸点的碳氢化合物混合物。

Fractional distillation is the process that achieves this separation. It is based on one simple idea: different hydrocarbons boil at different temperatures. Smaller molecules have lower boiling points, while larger molecules have higher boiling points.

分馏就是实现这种分离的过程。它基于一个简单的原理：不同的碳氢化合物在不同的温度下沸腾。较小的分子沸点较低，而较大的分子沸点较高。

3. The Fractionating Column | 分馏塔

In an oil refinery, crude oil is heated to a very high temperature (about 400 °C) and turned into a hot vapour. This vapour is then pumped into the bottom of a tall fractionating column. The column is hotter at the bottom and cooler at the top, with a temperature gradient.

在炼油厂中，原油被加热到非常高的温度（约 400 °C）并变成高温蒸气。然后这种蒸气被泵入高耸分馏塔的底部。塔的底部较热，顶部较冷，存在温度梯度。

The fractionating column is not a simple tube. It contains many horizontal trays or plates. Each tray has small holes or caps that allow vapour to rise through them. These trays help improve the separation by allowing vapour and liquid to mix and reach equilibrium.

分馏塔不是一根简单的管子。它包含许多水平托盘或塔板。每个塔板有小孔或泡罩，使蒸气可以通过它们上升。这些塔板通过使蒸气和液体混合并达到平衡，有助于改善分离效果。

The fractionating column separates crude oil into fractions by the difference in boiling points.

分馏塔利用沸点差异将原油分离成不同馏分。

4. How Fractional Distillation Works | 分馏的工作原理

When the hot vapour enters the column, it begins to cool. The hydrocarbons with the highest boiling points condense first, at the bottom where the temperature is high. As the vapour travels further up, it cools more, and hydrocarbons with lower and lower boiling points condense at different heights. In this way, different fractions are collected at different levels of the column.

当高温蒸气进入塔内时，它开始冷却。沸点最高的碳氢化合物首先在温度较高的底部冷凝。随着蒸气进一步上升，它冷却得更多，沸点越来越低的碳氢化合物在不同高度冷凝。这样，不同的馏分在塔的不同高度被收集。

Each fraction is a mixture of hydrocarbons that have a narrow range of boiling points. For example, the gasoline fraction collected near the top contains molecules with 5 to 10 carbon atoms per molecule, while the diesel fraction collected lower down contains molecules with 15 to 20 carbon atoms.

每个馏分都是沸点范围较窄的碳氢化合物混合物。例如，在靠近顶部收集的汽油馏分包含每个分子含有 5 到 10 个碳原子的分子，而在较低处收集的柴油馏分包含含有 15 到 20 个碳原子的分子。

Position in column	Temperature	What condenses
Bottom	Hot (~400 °C)	Long-chain hydrocarbons (bitumen, fuel oil)
Middle	Warm (~200-300 °C)	Medium-chain hydrocarbons (diesel, kerosene)
Top	Cool (~20-150 °C)	Short-chain hydrocarbons (gasoline, refinery gases)

5. The Temperature Gradient | 温度梯度

The column is designed so that the bottom is very hot and the top is cooler. Usually, the column is heated at the bottom and has an outlet at the top for gases that do not condense. The temperature gradient is created naturally: the hot vapour from below warms the lower trays, while the upper trays lose heat to the surroundings.

塔的设计使底部非常热，顶部较冷。通常，塔在底部加热，并在顶部设有出口，用于不冷凝的气体。温度梯度是自然产生的：来自下方的热蒸气加热下层塔板，而上层塔板则向周围环境散失热量。

This gradient is essential because each fraction has a specific range of boiling points. If a hydrocarbon’s boiling point is equal to the temperature at a certain tray, it will condense there. If it has a lower boiling point, it will remain a vapour and continue rising; if it has a higher boiling point, it will have condensed below.

这种梯度至关重要，因为每种馏分都有特定的沸点范围。如果一种碳氢化合物的沸点等于某个塔板的温度，它就会在那里冷凝。如果其沸点较低，它将继续保持蒸气状态并上升；如果其沸点较高，它将在下面已经冷凝。

6. Fractions and Their Uses | 馏分及其用途

Each fraction collected from the column has its own set of uses. Here is a summary of the main fractions, their boiling point ranges, and their common applications:

从塔中收集的每个馏分都有其自身的用途。以下是主要馏分、沸点范围及其常见应用的总结：

Refinery gases (bottled gas) – Boiling point: < 40 °C – Used as fuel for heating and cooking (e.g., propane and butane).
Gasoline (petrol) – Boiling point: 40-110 °C – Used as fuel for cars.
Naphtha – Boiling point: 110-180 °C – Used as a chemical feedstock to make plastics and other products.
Kerosene (paraffin) – Boiling point: 180-250 °C – Used as jet fuel and for heating.
Diesel oil – Boiling point: 250-340 °C – Used as fuel for lorries, buses, and some cars.
Fuel oil – Boiling point: 340-400 °C – Used as fuel for ships and power stations.
Bitumen – Boiling point: > 400 °C – Used for roads and roofing materials.

Notice that the fractions at the top are lighter, more volatile, and burn more easily. The fractions at the bottom are heavier, more viscous, and have higher boiling points.

注意，顶部的馏分更轻、更易挥发、更易燃。底部的馏分更重、更粘稠，沸点更高。

7. Comparing Fractions: Properties | 比较馏分：性质

The properties of a hydrocarbon fraction depend on the size of its molecules. In general, as the number of carbon atoms in a hydrocarbon increases:

碳氢化合物馏分的性质取决于其分子的大小。一般来说，随着碳氢化合物中碳原子数的增加：

Boiling point increases – Larger molecules have stronger intermolecular forces, so more energy is needed to break them apart.
Viscosity increases – The liquid becomes thicker and flows less easily.
Flammability decreases – Larger molecules are less likely to ignite because they are less volatile.
Volatility decreases – They evaporate less easily.
Colour darkens – Heavy fractions are often darker in colour.

沸点升高 – 较大的分子具有更强的分子间作用力，因此需要更多能量将它们分开。

粘度增加 – 液体变得更稠，流动更困难。

可燃性降低 – 较大的分子不易点燃，因为它们不易挥发。

挥发性降低 – 它们不容易蒸发。

颜色变深 – 重质馏分通常颜色较深。

These trends are a direct consequence of the molecular size, which determines the strength of the intermolecular forces. This is a common exam question.

这些趋势是分子大小的直接结果，分子大小决定了分子间作用力的强度。这是一个常见的考试问题。

8. Cracking: Making More Useful Fractions | 裂化：制造更有用的馏分

Fractional distillation does not produce enough of the most useful fractions, such as gasoline and kerosene. There is usually a surplus of the heavier fractions, like fuel oil and bitumen. To solve this problem, refineries use a process called cracking.

分馏不能生产足够的最有用的馏分，如汽油和煤油。通常较重馏分（如燃料油和沥青）会过剩。为了解决这个问题，炼油厂使用一种称为裂化的过程。

Cracking involves breaking large hydrocarbon molecules into smaller ones. This is done by heating the long-chain molecules to a high temperature in the presence of a catalyst (catalytic cracking). The process produces a mixture of alkanes and alkenes. Alkenes are unsaturated hydrocarbons containing a double bond, and they are valuable raw materials for making plastics.

裂化涉及将大的碳氢化合物分子分解成较小的分子。这是通过在催化剂存在下将长链分子加热到高温来完成的（催化裂化）。该过程产生烷烃和烯烃的混合物。烯烃是含有双键的不饱和碳氢化合物，是制造塑料的有价值的原料。

CₙH₂ₙ₊₂ → CₘH₂ₘ₊₂ + CₓH₂ₓ (where m + x = n)

For example, the cracking of decane (C₁₀H₂₂) can produce octane (C₈H₁₈) and ethene (C₂H₄).

例如，癸烷（C₁₀H₂₂）的裂化可产生辛烷（C₈H₁₈）和乙烯（C₂H₄）。

C₁₀H₂₂ → C₈H₁₈ + C₂H₄

9. Environmental Impact and Alternatives | 环境影响与替代方案

Burning fossil fuels like the fractions of crude oil releases carbon dioxide, a greenhouse gas that contributes to climate change. Burning also produces pollutants such as sulfur dioxide and nitrogen oxides, which cause acid rain, and particulates that harm health. For this reason, there is a global effort to find cleaner alternatives.

燃烧化石燃料（如原油的馏分）会释放二氧化碳，这是一种导致气候变化的温室气体。燃烧还会产生污染物，如二氧化硫和氮氧化物，它们会导致酸雨，以及危害健康的颗粒物。因此，全球都在努力寻找更清洁的替代品。

However, crude oil still plays a huge role in modern life. Not only is it used for fuels, but it is also the raw material for plastics, medicines, and many other products. Even as we move towards renewable energy, we still rely on chemical feedstocks from oil. Understanding fractional distillation and its products is therefore not just an academic exercise – it is essential for understanding how our world works.

然而，原油在现代生活中仍然扮演着重要角色。它不仅用于燃料，还是塑料、药品和许多其他产品的原料。即使我们走向可再生能源，我们仍然依赖来自石油的化学原料。因此，理解分馏及其产物不仅仅是学术练习——它对于理解我们的世界如何运作至关重要。

10. Exam Tips and Summary | 考试提示与总结

When answering exam questions on fractional distillation, remember these key points:

在回答关于分馏的考试问题时，请记住以下要点：

Crude oil is a mixture of hydrocarbons; it is separated into fractions.
The separation is based on differences in boiling points.
The fractionating column is hot at the bottom and cool at the top.
Large-chain hydrocarbons condense near the bottom; small-chain hydrocarbons condense near the top.
Shorter molecules have lower boiling points and are more volatile.
Fractions include refinery gases, gasoline, naphtha, kerosene, diesel, fuel oil, and bitumen.
Cracking converts heavy fractions into lighter, more useful ones.

原油是碳氢化合物的混合物；它被分离成馏分。

分离基于沸点的差异。

分馏塔底部热、顶部冷。

长链碳氢化合物在底部附近冷凝；短链碳氢化合物在顶部附近冷凝。

较短的分子沸点更低，更易挥发。

馏分包括炼厂气、汽油、石脑油、煤油、柴油、燃料油和沥青。

裂化将重质馏分转化为较轻、更有用的馏分。Published by TutorHao | IGCSE Science Revision Series | aleveler.com

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Fractional Distillation of Crude Oil | 原油的分馏