【F1】
Petroleum is the largest source of liquid fuel, and, in spite of attempts to develop synthetic fuels, and the continued use of solid fuels, world consumption of petroleum products is about four times greater now than in 1940.
Crude petroleum oil from different oilfields is never exactly identical in composition. Although all petroleum is composed essentially of a number of hydrocarbons, they are present in varying proportions in each deposit, and the properties of each deposit have to be evaluated.【F2】
Samples are subjected to a series of tests in the laboratory, the object of which is largely to determine the correct processing methods to be adopted in each case.
Petroleum is not normally used today in the crude state.【F3】
The mixture of oils of which it is composed must be separated out into a number of products such as petrol, aviation spirit, kerosene, diesel oils and lubricants, all of which have special purpose.
The main method of separation used, in refineries is fractional distillation, although further processing is normally required to produce marketable petroleum products. The different hydrocarbons present in petroleum have different boiling temperatures, and the fractions can therefore be isolated according to their boiling temperatures. Petrol, for instance, is a mixture of the lower-boiling hydrocarbons, with boiling temperatures ranging from 100℃ to 400℃. Diesel oils on the other hand have boiling temperatures of upwards of 400℃.
【F4】
Distillation was originally carried out in batch—stills and, although this is still done for special purposes, the development of the pipe—still has revolutionized refinery processes, since it allows continuous vaporization and rectification of the fractions.
The pipe-still consists of a bricok-lined furnace, in which is fitted a battery of tubes, through which the crude oil is pumped. The oil is heated, and petrol vaporization occurs. The oil then enters the fractionating tower, where it is distilled by coming into contact with condensed vapor which has previously been evolved from the still. Fractions of different boiling ranges are drawn off at different points in the tower, or, in some plants, in a series of towers, each one distilling successively heavier fractions.
【F5】
The heavier distillates, such as gas oil, undergo various other processes, of which the most important is known as cracking.
In this process, they are heated to a temperature of about 550℃, as a result of which the heavier molecules are broken up, lighter oils such as petrol being produced. Catalytic cracking, in which silicon compounds are used as catalysts to aid the process of decomposition, gives higher octane petrols. These are widely used as motorcar fuels, since the high octane value reduces the tendency of the fuel to detonation.
【答案解析】解析：句子中出现了两个表示列举的词汇，第一个是such as，而第二个先行词processes之后有which引导的非限定性定语从句。一方面可以理解这个定语从句限定先行词，另一方面通过关系代词之后的the most important判断词部分是对processes的一个列举。因此在处理句子时，应采用重译法，即译为“其最重要的是……”。distillate“精华，蒸馏物“；undergo“经历，遭受，忍受”；cracking“破裂，裂化”。