Azeotrope rectification

SABAR [Strong acid by azeotropic rectification] A process for making nitric acid by the atmospheric oxidation of ammonia. The nitrous gases from the oxidation are absorbed in azeotropic nitric acid in the presence of oxygen under pressure ... 

As for the separation of trimethylchlorosilane (the boiling point is 57.3 °C) and silicon tetrachloride (the boiling point is 57.7 °C), this is a gruelling task, since they form an azeotropic mixture which cannot be separated by simple rectification. The separation can be achieved with the help of physical (azeotropic rectification) or chemical techniques (hydrolysis, etherification). 

As mentioned earlier in this chapter, the SABAR process absorbs nitrous gases in azeotropic nitric acid in the presence of oxygen and then makes strong acid by azeotropic rectification. Some of the key reactions in this process are illustrated by Eq. (9.15) and Eq. (9.16). 

The SABAR (Strong Acid By Azeotropic Rectification) process makes nitric acid by the atmospheric oxidation of ammonia. Davy McKee developed the process and built plants based on this technology from 1974 to 1986. 

In Davy McKee s Sabar process (Strong Acid By Azeotropic Rectification) the nitrous gases from the oxidation of nitrogen(ll) oxide are absorbed in azeotropic (ca. 68 to 69%) nitric acid in the presence of atmospheric oxygen (at 6 to 13 bar) and superazeotropic acid is formed ... 

Due to the total pressure dependency of the chemical potential, the equilibrium curves with their azeotrope points can be shifted by applying different pressures. Azeotrope rectification can be performed either in batch or in continuous mode. On a technical... 

Examples for the usage of azeotrope rectification on an industrial scale are ... 

The manufacture of concentrated nitric acid (98—99%) can be done by two methods, direct and indirect. The indirect method, mainly used in the United States, is performed industrially by two different systems, the sulfuric acid and magnesium nitrate processes. Both processes involve the dehydration of nitric acid with concentrated H2S04 or Mg(N03)2. The sulfuric acid process has acute corrosion problems. This process utilizes azeotropic rectification to produce concentrated nitric acid. 

The second involves the absorption of N02/N0 in concentrated HNO3 (Re action 3.17). This produces a superazeotropic acid which then is distilled to produce concentrated nitric acid. Examples of these processes are the Uhde CNA (concentrated nitric acid) process and Davy McKee s SABAR (Strong Acid By Azeotropic Rectification) process. 

For the separation of azeotropes or mixtures with relative volatilities that lie below about 1.4, which are difficult to separate, special distillation processes are available, such as two-pressure distillation and extractive and azeotropic rectification. 

Total miscibility with the mixture components at the operating temperature with extractive rectification, and with azeotropic rectification formation of a miscibility gap and a minimum-boiling azeotropic... 

In azeotropic rectification, the otherwise unwanted formation of an azeotrope is used to simplify the separation by distillation of a mixture with a narrow range of boiling points, or azeotropic mixtures. An auxiliary... 

Azeotropic rectification processes using adjuvants to form a homogeneous azeotrope are not of economic interest, since distillation is not easy. Therefore, other separation processes are employed. 

Other columns arrangements than those shown in Fig. 2-26 are possible in azeotropic rectification processes. The column arrangement and the locations of the outlets for the components of the mixture and the entrainer, depend on the state and behavior of the mixture. 

Examples of practical azeotropic rectification are listed in Table 2-7. 

Table 2-7. Examples of a practical azeotropic rectification process.

Separation of an isopropanol/water mixture by azeotropic rectification using toluolene, reduction of energy costs to 70% of these compared to conventional operation by means of a heat pump IPA Isopropanol P Power Q Heat flow... 

It should be noted that the dehydration of the ethanol by the azeotropic rectification requires considerable operational and energy expenses. Ethanol dehydration technologies using the adsorption on molecular sieves and evaporation through the membrane are less power consuming ones. However, the ethanol dehydration by the evaporation through the membrane requires significant capital investment and the smooth/uninterrupted operation of the factory. 

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