医学博士英语统一考试之后，即将迎来各院校的考博英语初试，英语考试的备考，参考历年真题是一个很重要的备考过程，今天新东方在线小编给大家整理了西南交通大学2012年考博英语真题，帮助大家更好的备考，考博英语考试，一起来看看吧!
Petroleum products, such as gasoline, kerosene, home heating oil, residual fuel oil, and lubricating oils, come from one source----crude oil found below the earth’s surface, as well as under large bodes of water, from a few hundred feet below the surface to as deep as 25,000 feet into the earth’s interior. Sometime crude oil is secured by drilling a hole through the earth, but more dry holes are drilled than those producing oil. Pressure at the source or pumping forces crude oil to the surface. Crude oil wells flow at varying rates, from ten to thousands of barrels per hour. Petroleum products are always measured in 42-gallon barrels.
Petroleum products vary greatly in physical appearance: thin or thick, transparent or opaque, but their chemical composition is made up of only two elements: carbon and hydrogen, which form compounds called hydrocarbons. Other chemical elements found in union with the hydrocarbons are few and are classified as impurities. Trace elements are also found but these are of such minute quantities that they are disregarded. The combination of carbon and hydrogen forms many thousands of compounds which are possible because of the various positions and joinings of these two atoms in the hydrocarbon molecule.
The various petroleum products are refined from the crude oil by heating and condensing the vapors. These products are the so-called light oils, such as gasoline, kerosene, and distillate oil. The residue remaining after the light oils are distilled is known as heavy or residual fuel oil and is used mostly for burning under boilers. Additional complicated refining process rearranges the chemical structure of the hydrocarbons to produce other products, some of which are used to upgrade and increase the octane rating of various types of gasoline.
56. Name at least 6 petroleum products.
57. Why is it possible that the chemical composition of various petroleum products is made up of only two elements: carbon and hydrogen?
58. Why are trace elements disregarded when the chemical composition of petroleum products is concerned?
59. How is gasoline refined from crude oil?
60. To increase the octane rating of gasoline, what refining process is needed?