化工专业英语-unit 7

N2 +3H2 2NH3
In principle the reaction between hydrogen and nitrogen is easy; it is exothermic (放热的) and the equilibrium（平衡） lies to the right （在…右边） at low temperatures. Unfortunately, nature has bestowed（给予）dinitrogen with an inconveniently strong triple（三
atmospheric pressure（大气压） and ambient temperature（环境温度，
常温）; despite a hundred years of effort, the chemical industry still needs high temperatures and pressures of hundreds of atmospheres to do the same job.
N 2 +3H 2 2NH3
The Haber Process for Ammonia Synthesis
Introduction. All methods for making ammonia are basically finetuned （调整了的）versions（版本） of the process developed by Haber, Nernst and Bosch in Germany just before the First World War.
Raw materials. The process requires several inputs: energy, nitrogen and hydrogen. Nitrogen is easy to extract from air, but hydrogen is another problem. Originally it was derived from coal via coke which can be used as a raw material (basically a source of carbon) in steam reforming(蒸汽重整), where steam is reacted with carbon to give hydrogen, carbon monoxide and carbon dioxide. Now natural gas （天然气）(mainly methane) is used instead, though other hydrocarbons from oil can also be used. Ammonia plants always include hydrogen-producing plants linked directly to the production of ammonia.
Special English
For Chemical Engineering & Process
unit 7
Ammonia, Nitric Acid and Urea
By Ding Ming-jie By Zhao Ya-qi Department of Chemical Engineering
Department of August 2009 Engineering In Chemical
Prior to reforming reactions（变换/重整反应）, sulphurcontaining compounds （含硫化合物）must be removed from the hydrocarbon feedstock（给料） as they poison both the reforming catalysts and the Haber catalysts. The first desulphurization（脱硫） stage involves a cobalt-molybdenum（钴－钼） catalyst, which hydrogenates（使与氢化合） all sulphur-containing compounds to hydrogen sulfide（硫化氢）. This can then be removed by reaction with zinc（锌） oxide (to give zinc sulfide and water). The major reforming reactions are typified（代表，表示） by the following reactions of methane (which occur over nickel-based catalysts at about 750℃): CH4+H2O→CO+3H2 CH4+2H2O→CO2+4H2 Synthesis gas
Guiding questions
Do you know the amount of energy consumed in ammonia process every year? When was the Haber process for ammonia synthesis developed? Can you list the major uses of ammonia? How many stages are involved in the conversion of ammonia to nitric acid? What are the main raw materials for urea?
倍的） bond, enabling the molecule to thumb its nose at（嗤之以鼻）
thermodynamics（热力学）.
In scientific terms the molecule is kinetically（在动力学上） inert （惰性的）, and rather severe reaction conditions （苛刻反应条件） are necessary to get reactions to proceed at a respectable rate. A major source of “fixed”“ (meaning, paradoxically（荒谬地）, “usefully reactive”) nitrogen in nature is lightning, where the intense heat is sufficient（足够的） to create nitrogen oxides from nitrogen and oxygen. To get a respectable（相当的，可敬的） yield of ammonia in a chemical plant we need to use a catalyst. What Haber discovered — and it won him a Nobel prize（诺贝尔奖） ― was that some iron compounds were acceptable catalysts. Even with such catalysts extreme pressures (up to 600 atmospheres in early processes) and temperatures (perhaps 400℃) are necessary.
Biological fixation also uses a catalyst which contains molybdenum（钼） (or vanadium（钒）) and iron embedded（植入的， 深入的） in a very large protein, the detailed structure of which eluded（躲避） chemists until late 1992. How it works is still not understood in detail.
பைடு நூலகம்
technologists has been unable to（不能够） find an easy alternative to
this. Leguminous plants（豆类植物） can take nitrogen from the air and convert it into ammonia and ammonium-containing products at
Contents
Prelude The Haber Process for Ammonia Synthesis Nitric Acid Urea
Prelude
Dinitrogen makes up（占，弥补） more than three-quarters of the air we breathe, but it is not readily available(可利用的，有用的) for further chemical use. Biological transformation（生物转化） of nitrogen into useful chemicals is embarrassing (令人为难的/困难的) for the chemical industry, since all the effort of all the industry’s
Pressure drives the equilibrium forward, as four molecules of gas are being transformed into two. Higher temperatures, however, drive the equilibrium the wrong way, though they do make the reaction faster, chosen conditions must be a compromise (妥协，折衷) that gives an acceptable conversion at a reasonable speed. The precise choice will depend on other economic factors and the details of the catalyst. Modern plants have tended to （趋向于）operate at lower pressures and higher temperatures (recycling unconverted material) than the nearer-ideal early plants, since the capital and energy costs （资金和能量耗费）have become more significant.