Sources of the Alkanes | 烷烃的来源

📚 Sources of the Alkanes | 烷烃的来源

Alkanes are the simplest family of organic compounds, consisting only of carbon and hydrogen atoms joined by single covalent bonds. They are chiefly obtained from natural gas and crude oil, but can also be produced from coal and renewable biogas. This article reviews the main natural and industrial sources of alkanes, with emphasis on the processes used to separate and convert them.

烷烃是最简单的有机化合物家族，仅由碳和氢原子通过单共价键连接而成。它们主要来自天然气和原油，但也可以从煤和可再生沼气中制得。本文回顾烷烃的主要天然与工业来源，重点介绍用于分离和转化烷烃的工艺。

1. What Are Alkanes and Why Their Sources Matter | 什么是烷烃以及其来源为何重要

Alkanes are saturated hydrocarbons with the general formula CₙH₂ₙ₊₂. Each carbon atom forms four single covalent bonds, so only C–C and C–H single bonds are present. Methane (CH₄), ethane (C₂H₆), propane (C₃H₈) and butane (C₄H₁₀) are the smallest members of the family.

烷烃是通式为 CₙH₂ₙ₊₂ 的饱和烃。每个碳原子形成四个单共价键，因此分子中只存在 C–C 和 C–H 单键。甲烷（CH₄）、乙烷（C₂H₆）、丙烷（C₃H₈）和丁烷（C₄H₁₀）是该家族中最小的成员。

Alkanes are the main components of natural gas and petroleum fractions. They are used as fuels for heating, electricity generation and transport, and also serve as chemical feedstocks for plastics, solvents, hydrogen and many other important products.

烷烃是天然气和石油馏分的主要成分。它们用作供暖、发电和交通运输的燃料，同时也作为塑料、溶剂、氢气及许多其他重要产品的化学原料。

Because most alkanes come from non-renewable fossil resources, understanding their sources is central to evaluating energy security, industrial chemistry and environmental impact.

由于大多数烷烃来自不可再生的化石资源，理解其来源对于评估能源安全、工业化学和环境影响至关重要。

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2. Natural Gas as a Direct Source of Methane | 天然气作为甲烷的直接来源

Natural gas is a fossil fuel trapped in porous rock layers, often located above crude oil deposits or dissolved in the oil itself. It consists mainly of methane, CH₄, typically 70–90% by volume, with smaller amounts of ethane, propane and butane, as well as non-hydrocarbon impurities such as CO₂, N₂ and H₂S.

天然气是一种储存在多孔岩层中的化石燃料，通常位于原油矿床上方或溶解在原油中。其主要成分是甲烷 CH₄，通常占体积的 70–90%，还含有少量乙烷、丙烷和丁烷，以及 CO₂、N₂ 和 H₂S 等非烃杂质。

Methane from natural gas can be burned directly for heating, cooking and electricity generation. It is also separated and purified for use as a chemical feedstock, for example in the manufacture of hydrogen and methanol.

来自天然气的甲烷可以直接燃烧用于取暖、烹饪和发电。它也可以被分离和提纯，用作化学原料，例如用于制造氢气和甲醇。

When natural gas is processed, propane and butane are recovered as liquefied petroleum gas, LPG. These gases can be compressed into liquid form for convenient storage and transport, making them useful in areas without a piped gas supply.

天然气加工过程中可回收丙烷和丁烷，作为液化石油气（LPG）。这些气体可被压缩成液态以便储存和运输，在没有管道供气的地区非常实用。

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3. Formation and Composition of Crude Oil | 原油的形成与组成

Crude oil is a complex liquid mixture of hydrocarbons, mostly alkanes and cycloalkanes, formed from the remains of tiny marine organisms such as plankton that settled on the seabed millions of years ago.

原油是一种复杂的液态烃混合物，主要包含烷烃和环烷烃，由数百万年前沉积在海床上的浮游生物等微小海洋生物遗骸形成。

Over long periods, these organic remains were buried under layers of sediment. High pressure, moderate heat and the absence of oxygen caused anaerobic decomposition and chemical changes, converting the organic material into crude oil and natural gas.

在漫长的时间里，这些有机遗骸被沉积物层层掩埋。高压、中等温度以及缺氧环境引发了厌氧分解和化学变化，将有机物质转化为原油和天然气。

Crude oil contains alkane molecules with widely varying chain lengths, from C₁ to C₅₀ or more. The exact composition depends on the geological source and history of the deposit.

原油中含有碳链长度差异很大的烷烃分子，从 C₁ 到 C₅₀ 甚至更长。具体组成取决于原油的地质来源和形成历史。

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4. Fractional Distillation of Crude Oil | 原油的分馏

Crude oil cannot be used directly because it is a mixture with a very wide range of boiling points. It is separated into useful fractions by fractional distillation in a tall fractionating tower.

原油不能直接使用，因为它是沸点范围很宽的混合物。工业上通过在高大的分馏塔中进行分馏，将其分离为有用的馏分。

First, crude oil is heated in a furnace to about 350–400 °C, vaporising most of it. The hot vapour enters the fractionating tower, where the temperature decreases from the bottom to the top.

首先，原油在炉中加热到约 350–400 °C，使大部分组分汽化。热蒸气进入分馏塔，塔内温度从下到上逐渐降低。

As the vapour rises, different fractions condense when the temperature falls below their boiling point ranges. Small, short-chain alkanes with weak van der Waals forces condense near the top; large, long-chain alkanes with stronger intermolecular forces condense lower down.

蒸气上升时，不同馏分在温度低于其沸点范围时冷凝。碳链短、范德华力弱的小分子烷烃在塔顶附近冷凝；碳链长、分子间作用力强的大分子烷烃在较低位置冷凝。

Fractional distillation is a physical separation process, not a chemical reaction. No covalent bonds are broken, and the fractions are still mixtures of alkanes, but they have narrower boiling point ranges and more useful properties.

分馏是一种物理分离过程，而不是化学反应。没有共价键断裂，各馏分仍然是烷烃混合物，但其沸点范围更窄，性质更适合实际应用。

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5. Main Alkane Fractions and Their Uses | 主要烷烃馏分及其用途

The main fractions obtained from crude oil include refinery gas, petrol/gasoline, naphtha, kerosene, diesel oil, lubricating oil and bitumen. Each fraction is used for different purposes according to its boiling point range and viscosity.

从原油中得到的主要馏分包括炼厂气、汽油/车用汽油、石脑油、煤油、柴油、润滑油和沥青。每种馏分根据其沸点范围和黏度用于不同用途。

Refinery gas, containing C₁–C₄ alkanes, is used as a fuel on site or processed into LPG. Petrol or gasoline, with approximately C₅–C₁₀ alkanes, is blended for use in spark-ignition car engines.

炼厂气含有 C₁–C₄ 烷烃，可在炼厂内用作燃料或加工成液化石油气。汽油约含 C₅–C₁₀ 烷烃，调配后用于火花点火式汽车发动机。

Kerosene, C₁₀–C₁₆, is used as aviation fuel and for domestic heating. Diesel oil, C₁₄–C₂₀, is used in diesel engines. The heaviest fractions provide lubricating oils, waxes and bitumen for road surfaces.

煤油为 C₁₀–C₁₆，用作航空燃料和家庭取暖。柴油为 C₁₄–C₂₀，用于柴油发动机。最重的馏分用于生产润滑油、石蜡和铺路沥青。

In most markets, the demand for petrol and diesel is greater than the supply obtained directly from fractional distillation. This mismatch is corrected by converting heavy fractions into smaller alkanes and alkenes through cracking.

在大多数市场中，汽油和柴油的需求量大于分馏直接得到的供应量。通过裂化将重馏分转化为较小的烷烃和烯烃，可以弥补这一供需差距。

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6. Cracking: Increasing the Supply of Smaller Alkanes | 裂化：增加较小烷烃的供应

Cracking is the process of breaking large alkane molecules into smaller alkanes and alkenes. It

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