NITROGEN FIXATION — LOP 219 



Chemical Co., the operating pressure being only about one-half that 

 which is used in Germany. 



The Haber process consists, briefly, in passing a mixture of 1 

 volume of nitrogen and 3 volumes of hydrogen (the constituents of 

 ammonia) at a pressure of from 100 to 200 atmospheres over a suit- 

 able catalyzer at a temperature of some 900° to 1,000° F. The nitro- 

 gen and hydrogen will then combine and form ammonia according 

 to the reaction : N 2 -f 3H 2 =2NH 8 . 



A single passage of the gas mixture through the catalytic cham- 

 ber causes a conversion of about G to 8 per cent (by volume) of the 

 nitrogen-hydrogen mixture to ammonia, this being recovered either 

 by refrigeration and condensation to anhydrous ammonia or by ab- 

 sorption in water to aqua ammonia, which can again be converted 

 into gaseous form by distillation. The unconverted nitrogen and 

 hydrogen mixture, still under the above pressure, is replenished with 

 a fresh gas mixture corresponding to the separated ammonia, after 

 which it is reheated and returned to the catalytic chamber, thus re- 

 peating the cycle. 



Besides the mechanical difficulties due to the high pressures at 

 which the process is operated, the solution of the very complicated 

 chemical problems which are involved has required an enormous 

 amount of experimental and research work. It is absolutely essen- 

 tial that the two gases, nitrogen and hydrogen be in a very pure 

 state, as even minute quantities of impurities such as carbon mon- 

 oxide will be poisonous to the catalytic material and the two gases 

 will refuse to combine, or do so at a very reduced rate. It is this 

 preparation and purification of the nitrogen and hydrogen, and espe- 

 cially the latter, which comprises the chief items of cost in the Haber 

 process. 



The problem of providing a durable and suitable catalyst has also 

 been a difficult one. The reaction when the two gases combine to 

 form ammonia can only take place in the presence of what is known 

 as " catalytic " metals. A catalyst, therefore, is simply a substance 

 which promotes the union of two elements with each other, without 

 itself entering into the combination. 



Water is naturally the source from which hydrogen is produced, 

 either chemically or by electrolysis. In the former method, water 

 gas is first generated in a gas producer in the ordinary way by pass- 

 ing steam over incandescent coke. This gas consists of one-half 

 volume of hydrogen, the other one-half being chiefly carbon monox- 

 ide, as seen from the following equation : C-{-H 2 0=CO-f-H 2 . 



In order to remove this carbon monoxide it is found desirable 

 to convert it into carbon dioxide, which can readily be separated 

 by water scrubbing at a pressure of around 25 to 30 atmospheres. 



