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  3. 【F1】Petroleum is the largest source of liquid fuel, and, in spite of attempts to develop synthetic fuels, and the continued use

【F1】Petroleum is the largest source of liquid fuel, and, in spite of attempts to develop synthetic fuels, and the continued use

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问题     【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.
【F4】
选项
答案蒸馏原先是在间歇性蒸馏器进行的。虽然为特殊需要仍沿用这种形式的蒸馏，可是管式精馏器的发展却改进了精炼工艺；这是因为管式精馏器可连续蒸发，并能分馏出馏出液。
解析 该句子第一部分的被动语态部分可以沿用原句的表达。而第二部分是由although引导的让步状语从句的主从复合句，其中还含有一个since引导的原因状语从句。让步状语从句中的代词this所指代的是“之前提到的蒸馏形式”，因此应译为“这种形式的蒸馏”。而原因状语从句中的代词it在翻译为汉语时也须增译为“管式精馏器”。distillation“蒸馏，蒸馏法，蒸馏物”；refinery“精炼厂；提炼厂；炼油厂”；vaporization“汽化器，喷雾器，蒸馏器”；rectification"纠正，整顿，精馏，恢复”；fraction“小部分，片断，分数”。
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