Azeotrope super

As ammonia oxidation technology developed, it became possible to produce aqueous weak nitric acid of super-azeotropic composition, typically 69-73 wt% HNO3. Such acid is theoretically distillable to higher concentration in one step. At the same time, acid of azeotropic composition is returned to the plant absorbers the higher the weak acid concentration, the lower is the recycle of azeotrope. 

An important point is that for most uses concerned with chemical production, the acid must be concentrated above its azeotropic point to greater than 95%(wt). Conversely, the commercial manufacture of ammonium nitrate uses nitric acid below its azeotropic point in the range 50-65%(wt). If the stronger chemical grade is to be produced, additional process equipment appropriate to super-azeotropic distillation is required. 

Many new developments have occurred over the last 20 years, as discussed in Section 1.2.3, particularly for the production of strong nitric acid ( > 90% by weight). Strong nitric acid production employs the technique of super-azeotropic distillation to concentrate weaker acid beyond theazeotropic point (68% by weight). However, it is not necessary to discuss this technology further because the market... 

For many purposes the commercial reagent-grade DMF, dried with molecular sieves, can be used DMF decomposes on distillation at atmospheric pressure. The most convenient way to purify DMF is probably to let it pass through a column [358] of alumina (e.g., ICN Alumina N-Super I). Other methods involve drying (CUSO4 [367], which also removes amines), azeotropic distillation with benzene, or percolation through molecular sieves [368] followed by fractional distillation at reduced pressure. DMF is difficult to obtain in an anhydrous form, but for most purposes a small water content is not critical. An impurity of A-methylformamide may act as a proton donor or otherwise interfere in the follow-up reactions [369]. DMF should be stored in the dark under nitrogen. The different purification methods have been compared and discussed [370]. 

The acetalization of benzaldehyde with 1,3-propanediol has been examined in the presence of 1 mol% of a fluorous super-Br0nsted acid, 13 or 8, at azeotropic reflux in cyclohexane with the removal of water for 3 h [Eq. (6)]. Both solid acids are soluble in cyclohexane under reflux conditions, and promote the reaction well to give the desired acetal in good yields. Post-reaction, 13 has been recovered in 96% yield by precipitation at room temperature. However, 13 can not be recovered in the same manner. Besides this acetalization, 8 is also effective as a fluorous catalyst for the acylation of l-menthol with benzoic anhydride [Eq. (7)] and esterification of 3-phenylpropionic acid in methanol [Eq. (8)] [11]. 

Types rv and I are of partieular interest in representing behavior exploited in super-critieal extraction. There are many more possible classes and subclasses, especially where azeotropic behavior variations are involved, as discussed in the works of Rowlinson and King. More on the phase behavior applicable to dense gases can be found in reviews ... 

The isobutylene is then dried by azeotropic distillation and purified in a super-firactionating distillation column to reduce the butenes to less than 1000 ppm. Note that if water is not removed it will cause icing in the feed chillers and this will lead to a poor reactor service factor. 

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