From Atoms to Materials

Snapshot Hydrocarbons of smaller molecular sizes condense at higher levels, and are collected. Hydrocarbons of very small molecular sizes do not condense. They are collected at the top. lower temperature higher temperature crude oil Crude oil is heated to about 400 °C in a furnace. Hydrocarbons of larger molecular sizes condense at lower levels, and are collected. Hydrocarbons of very large molecular sizes do not vaporize. They sink to the bottom and are collected. fractionating tower Fig. 13.33 An oil refinery oil refinery 煉油廠 furnace 熔爐 fractionating tower 分餾塔 Uses of crude oil fractions Each crude oil fraction is a mixture of hydrocarbons within a certain boiling point range. These hydrocarbons have similar molecular sizes and properties. Different fractions of crude oil can be used separately for different purposes. Fig. 13.34 on the next page shows their uses. C Industrial fractional distillation Large-scale fractional distillation of crude oil is carried out in an oil refinery*. There, crude oil is first heated to about 400 °C in a furnace*, so that most hydrocarbons become vapour. The heated crude oil then enters a fractionating tower*. In the fractionating tower, hydrocarbons that do not vaporize flow to the bottom. Hydrocarbons that have vaporized rise to different levels, depending on their boiling points. Then they condense at different levels of the tower. As a result, hydrocarbons of similar boiling points are collected in the same fraction. 13 From Atoms to Materials 87 © United Prime Educational Publishing (HK) Limited 2024 All rights reserved; no part of this publication may be reproduced, photocopied, recorded or otherwise, without the prior written permission of the Publisher. Sample