Concentration of nitric acid or separation of other mixtures forming azeotrope by extractive distillation uses process heat for heating feed and recycled, very concentrated extractant

In 75-99.9% nitric acid (I) production from dilute (impure) (I) by rectifying 45-70% (I), using circulating extractant (II), the (I) feed (IA) is heated to a boiling liquid, vapor-liquid mixture or separate vapor and liquid with (part) of the heat content of all process streams; >= 50% of (IA) is pre-mixed with 0.1-60% (concentrated) (I); indirect heating is used for rectification; and a very concentrated (II) feed is used to minimize the amount circulating and maximize dilution. Production of 75-99.9% nitric acid (I) from dilute, optionally impure (I), involves rectification of 45-70% (I) under pressure, at atmospheric pressure and/or in vacuo in contact with a liquid extractant (II) to prevent the formation of a HNO3-water azeotrope, condensing the concentrated (I) vapor and recovering concentrated (I); and also reconcentrating (II) and recycling it to extractive rectification. The novel features are that: (i) the heat content of the process streams in the entire process is used partly or largely; (ii) the (I) to be concentrated is fed to extractive distillation as boiling liquid, vapor-liquid mixture or separate vapor and liquid, using this heat; (iii) >= 50% of the amount to be rectified is mixed with 0.1-60% HNO3, preferably concentrated (I), before rectification; (iv) the energy required for rectification is supplied (mainly) by indirect heating; and (v) the (II) fed to rectification in as concentrated a form as possible, to minimize the amount of circulating extractant and, at the same, maximize the dilution of (II) discharged from rectification. Independent claims are also included for: (a) the plant used in this process; (b) a process for producing a concentrated product fraction from a liquid mixture forming azeotrope(s) by extractive rectification in the same way, especially for separating highly concentrated volatile products from dilute aqueous mixtures or for separating mixtures of organic compounds. Verfahren zur Herstellung einer Salpetersäure einer Konzentration von 75 bis 99,9% aus einer verdünnteren Salpetersäure, bei dem man eine Salpetersäure einer Konzentration von etwa 45 bis 70% im Kontakt mit einem flüssigen Extraktionsmittel zur Verhinderung der Bildung eines Salpetersäure-Wasser-Azeotrops rektifiziert, die Dämpfe der konzentrierten Salpetersäure kondensiert und eine konzentrierte Salpetersäure gewinnt und bei dem man außerdem das Extraktionsmittel unter Rückkonzentrierung aufarbeitet und in die Extraktivrektifikation zurückführt,