Distillation azetropic

When secondary amines are heated with ketones or aldehydes in the presence of an acidic catalyst, a related condensation reaction occurs and can be driven to completion by removal of water by azetropic distillation or use of molecular sieves. The condensation product is a substituted vinylamine or enamine. 

Lonza S.p.A. Maleic anhydride Phthalic anhydride offgas Maleic anhydride recovery, dehydration and azetropic distillation 2 1987... 

The solution is distilled from a 250-ml. distillation flask, using boiling chips to avoid bumpii. The fraction boiling from 125 to 127°C is collected. The yield is about 90% based on the I3 used. The azetropic acid (57% HI) boils at 126°C (760 mm.), d 1.70. It fumes strongly in air. Aqueous HI solutions must be stored in dark, well-sealed flasks. It is advisable to seal the stor e flasks with paraffin. As a further precaution gainst oxidation, the air above the surface of the liquid may be displaced by an inert gas before sealii the flask. 

Besides the isomerization of olefins and the hydrogenation of aldehydes, the acetalization of the formed aldehydes is one of the most important reactions in the frametvork of hydroformylation (Scheme 5.68) [1, 2]. In general, the reaction of aldehydes with alcohols is mediated by Bronsted or Lewis acids. By removal of water (azetropic distillation, treatment with molecular sieves, or reaction with trialkyl formates), the equilibrium can be shifted in favor of the acetal. The back reaction takes place also due to the effect of acids but requires the presence... 

Besides the methods illustrated so far in this book, there are other ways for separating azeotropes. One way is to react the azeotrope away in a reactive distillation column to form other useful products. The design and control of various reactive distillations have been extensively studied in a recent book by Luyben and Yu. Another way commonly used in ethanol dehydration is to use the hybrid distillation-adsorption process. In this process, distillation is used to purify the mixture to a composition near the ethanol-water azetrope, and then an adsorption unit (e.g., molecular sieves) is used to adsorb the remaming water so that anhydrous ethanol can be obtained. The key technology in this process is the performance of the adsorbent material in removing water from the mixture and is beyond the scope of this book. 

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