Synthesis of flowsheets for extractive distillation of azeotropic mixtures

Abstract

Separation of end fractions of given compositions from azeotropic mixtures is complicated by thermodynamic and topological constraints, which can be surmounted using the principle of redistribution of concentration fields between separation regions [1][2][3]. This principle can be implemented using homogeneous and heterogeneous (involving extraction, adsorption, absorption, and chemical and other separation techniques) separation systems. In homogeneous systems, distillation can be designed so that, at one of the steps, an azeotropic fraction is isolated, which is then separated by special methods. If this fraction contains two or more components, one can use extractive distillation or separation of the azeotropic mixture at different pressures. If the fraction contains more than two components, separation can be performed by methods using the curvature of the separating manifold [3,4]. Previously [2, 5], a general approach to synthesizing flowsheets for distillation of multicomponent nonideal (including azeotropic) mixtures was put forward, which is based on the concept of a distillation region. Later [6][7][8], some approaches to synthesizing flowsheets for distillation of multicomponent mixtures containing a single binary azeotrope were proposed, which use separation of an azeotropic mixture at different pressures.Note that, in practice, thermodynamic and topological constraints on separation of end fractions of given compositions are most often surmounted by using extractive distillation. However, conventional extractive distillation methods are highly energy-intensive. Therefore, it is topical to develop and use optimal energy-saving technologies. This problem is solved in several steps: structural optimization of a flowsheet, optimization of the operating parameters of distillation columns, design optimization of flowsheet elements. Since distillation is irreversible, its thermodynamic efficiency depends on the process path-a set of flowsheets or distillation trajectories. To date, approaches to synthesizing extractive distillation flowsheets have been developed obviously insufficiently. This question was considered only in few works. For example, a number of systems of different structures for separation of multicomponent azeotropic mixtures were proposed [9]. Certain technological solutions for distillation of an Abstract -An algorithm for synthesizing extractive distillation flowsheets for separation of complex ternary azeotropic mixtures with different vapor-liquid equilibrium patterns is proposed.

Application of the partially thermally coupled distillation flowsheets for the extractive distillation of ternary azeotropic mixtures

“…1), which were A c c e p t e d M a n u s c r i p t 5 obtained by Ivanova et al 24 for ternary azeotropic mixture separations. The schemes in Fig.…”

“…The five extractive distillation flowsheets were generated for the separation of ternary azeotropic mixtures with the heavy boiling entrainer. Their feasibility was evaluated 24 for all types of VLE diagrams in accordance with the Serafimov classification 38 .…”

“…1a-1e). The flowsheet feasibility conditions have been formulated by Ivanova et al 24 as follows: the initial ternary mixture must be separated into the pure components, the entrainer recycles must be presented and encircled at least two columns, the entrainer must be introduced only in the column where azeotropic components are separated.…”

“…Ivanova et al 24 have presented the algorithm of the extractive distillation flowsheet syntheses for the separation of multicomponent azeotropic mixtures. The algorithm combines the method of distillation flowsheet graph transformations with the thermodynamic-topological analysis of the vapor-liquid equilibrium (VLE) diagrams 38 .…”

Energy‐Saving Hydrocarbon Distillation with Coupled Heat and Material Flows

“…Earlier, it has been found by Ivanova et al 51 that only three conventional ED flowsheets are feasible in the case of VLE diagram type 3.1.0‐1a with direct residue curve directions (Figs. 12 a, 13 a, and 14 a).…”