Unit 4 Sources of Chemicals-2_化学工程与工艺专业英语音频资料_免费在线阅读收听下载

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2 Organic Compounds
In contrast to inorganic chemicals which, as we have already, are derived from many different sources, the multitude of commercially important organic compounds are essentially derived from a single source. Nowadays in excess of 99% (by tonnage) of all organic chemicals is obtained from crude oil (petroleum) and natural gas via petrochemicals process. This is a very interesting situation-one which has changed over the years and will change again in the future-because technically these same chemicals could be obtained from the raw materials or sources. Thus, aliphatic compounds, in particular, may be produced via ethanol, which is obtained by fermentation of carbohydrates. Aromatic compounds on the other hand are isolated from coal-tar, which is by-product in the carbonization of coal. Animal and vegetable oils and fats are a more such a stearic (octadecanoic) acid, CH3(CH2)16CO2H, and long-chain alcohols such as lauryl alcohol (dodecanol), CH3(CH2)11OH.

The formation of fossil fuels, i.e. oil, gas and coal reserves, takes millions of years and once used they cannot be replaced. They are therefore referred to as non-renewable resources. This contrasts with carbohydrates which being derived from plants, can be replaced relatively quickly. A popular source is sugar-cane-once a crop has been harvested and the ground cleared, new material may be planted and harvested, certainly in less than one year. Carbohydrates are therefore described as renewable resources. The total annual production of dry plant materials has been estimated as 2*1011 tones.
Fossil fuels-natural gas, crude oil and coal- are used primarily as energy sources and not as sources of organic chemicals. For instance various petroleum fractions are used as gas for domestic cooking and heating, petrol or gasoline for automobiled, and heavy fuel oil for heating buildings or generating steam for industrial processes. Typically only around 8% of a barrel of crude oil is used in chemical manufacture. The following figures demonstrate why the chemicals industry can compete with fuel -or energy-using industries for the crude oil.

Clearly alternative energy sources to fossil fuels are now available if we have the will to use them, and we can confidently expect other alternatives to become available in the net too distant future. It is therefore essential that we retain our precious oil supplies for chemicals production. The interesting, and salutory, to note that as early as 1894 Mendeleyev (the Russian chemist who developed the Periodic Table) reported to his government that “oli was too valuable a resource to be burned and should be preserved as a source of chemicals”.

Unit 4 Sources of Chemicals-2

Unit 4 Sources of Chemicals-2

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