Anastasiya V. Frolkova

The maximum capabilities of the process of rectification separation of multicomponent mixtures depend on the features of the structure of the liquid–vapor equilibrium diagram, in particular on the presence of internal dividing surfaces in the diagram. In this paper, we investigate the patterns of formation of the structure of separatric surfaces of maximum dimension for systems of different chemical nature. For systems with the same deviations, when azeotropes relative to components of the same component are nodal points, an approach to determining the number of saddle-shaped azeotropes of the first and (n – 2)-th orders and, accordingly, the number of internal separatric manifolds, is developed. The proposed approach is illustrated and validated using model systems and industrial mixtures as examples. The expediency of using one of the types of separation (first, second, intermediate) depending on the number and structure of internal separator surfaces is shown. The research presented in the article is aimed at developing the fundamental theory of thermodynamics of heterogeneous systems in terms of studying the structures of phase diagrams and the mechanisms of their formation using thermodynamic–topological analysis within the framework of the general concept of the scientific school of Professor Leonid Antonovich Serafimov, Doctor of Technical Sciences.

Objectives . When developing separation flowsheets for liquid mixtures, preference is often given to a specific process or flowsheet. Although alternative separation variants are sometimes considered, these tend to be based on a single-phase process, usually distillation. And while review papers on the specifics of implementing a particular separation technique exist, these mainly focus on the specific process of extractive distillation, combination of distillation and splitting processes, and extraction. Moreover, studies comparing the separation flowsheets of mixtures of different physicochemical nature based on different processes and special methods are fragmentary. This study presents a comparative analysis of the processes and methods of liquid mixtures separation based on a critical review of the literature and the authors’ own research results. Methods . The study is based on the critical analysis of literature and mathematical modeling of phase equilibria using local composition equations via freely distributed software packages. Results . Specific liquid mixture separation methods, including combining various processes in one flowsheet (including hybrid technologies), are compared in terms of their advantages and disadvantages. Conclusions . Promising areas of further research in the field of synthesis of organic mixtures separation flowsheets through the use of various separation processes and methods are identified. The effectiveness of the various processes (extraction, splitting, special distillation techniques) is estimated at different stages of different number of components mixtures separation. A comparative analysis of extractive and heteroazeotropic distillation processes when separating mixtures of different initial composition highlights the areas of energy advantage of each process. The effectiveness of the flowsheets is estimated by combining extraction with other processes, depending on the stage of extractant regeneration.

The present study explores methodologies for investigating the structure of the vapor–liquid equilibrium diagram of multicomponent systems. This investigation serves as a foundation for the predesign of distillation process flowsheets. A thorough analysis is conducted to assess the merits and limitations of existing methodologies, highlighting the efficacy of employing diverse techniques contingent on the system’s phase behavior specificity (e.g., the presence of one (two) singular points and internal separatrix manifolds). A group of systems that demonstrate the same deviations from ideality (in the absence of saddle-type ternary azeotropes) is identified. For these systems, it is possible to analyze the diagram structure based on the minimum amount of available information (i.e., boiling points of components and azeotropes). The proposed approach does not necessitate geometric construction of the concentration simplex, its scan, or individual components of the system. The proposed technique for analyzing the diagram structure of multicomponent systems is illustrated on the example of three industrial mixtures comprising different components.

Структурный анализ фазовой диаграммы и оценка возможности ректификации многокомпонентных смесей Структурный анализ фазовой диаграммы и оценка возможности ректификации многокомпонентных смесей

The paper shows the expediency of supplementing the balance simplex method by calculating the number of free variables of separation flowsheets containing recycle flows. The need to determine and set the free variables that provide lower energy consumption when calculating the material balance of flowsheets with recycling is justified. The problem of material balance multivariance is illustrated, and ways to solve it are shown with the example of separation flowsheets for two ternary mixtures: n-butanol + water + toluene and n-butanol + butyl acetate + water. Separation flowsheets containing three distillation columns and a liquid–liquid separator are proposed for both systems. The dependence of the recycle flow values and the energy consumption of distillation columns and separation flowsheets on the selection and setting of values of free variables in solving the balance problem is shown. The dependence of energy consumption on the composition of the original mixture is studied for an n-butanol + butyl acetate + water system. Recommendations for setting free variables for flowsheets of the separation of ternary mixtures with three binary (and one ternary) azeotropes are formulated. The technique of highlighting the region of separation flowsheet operability is illustrated. The column operating parameters that ensure the production of products of a given quality with minimal energy consumption are determined. It is shown that with the incorrect selection and setting of variables (during balance task solvation), the energy consumption for mixture separation can be overestimated by more than 40%.

The article is devoted to improving the separation technology of the methanol + water + methyl methacrylate mixture. Several alternative variants are proposed: separations based on the application of auto-extractive distillation and a combination of distillation and splitting process. The separation schemes are aimed at separating all components in pure form and increasing the yield of methyl methacrylate. A computational experiment is carried out to determine the operating parameters of the columns to ensure the production of substances of a given quality. The most energy-efficient scheme is based on the use of auto-extractive distillation and a combination of distillation with splitting process.

The phase equilibrium in an acetonitrile + water + cyclohexene + chloroform system was studied at 101.3 kPa. A prediction regarding the internal structure of the composition tetrahedron (presence/absence of one/two internal singular points) was made using thermodynamic modeling in AspenPlus V.10.0. The existence of two internal quaternary azeotropes (of node type with a minimum boiling point and of saddle type) was confirmed as a result of a full-scale experiment. Thermodynamic-topological analysis of the structure of phase equilibrium diagrams was carried out to confirm the correctness of the diagram construction.

Маслов М.А., Соломонов В.А., Фролкова А.К.//2023

Статья посвящена разработке технологии регенерации растворителей производства капролактама из смеси, содержащей н-бутанол, амилол, циклогексанон, циклогексанол, а также изоамилол и циклопентанон в примесных количествах. Для исследования фазового равновесия и процесса разделения выбран вычислительный эксперимент с использованием AspenPlus V.10.0. Параметры уравнения Non Random Two Liquid позволяют воспроизводить данные парожидкостного равновесия и азеотропные свойства системы с относительной ошибкой, не превышающей 5%. Разделение смеси обычной ректификацией затруднительно, что вызвано наличием трех бинарных азеотропов, а также трех пар компонентов, характеризующихся близкими летучестями. При уменьшении давления наблюдается усложнение структуры фазовой диаграммы из-за появления новых азеотропов. Предложена технологическая схема регенерации растворителей, основанная на использовании непрерывной ректификации. Схема содержит пять колонн. На первом этапе предполагается предварительное фракционирование смеси (режим промежуточного заданного разделения в первой колонне) с полным выделением в кубе циклогексанона и циклогексанола (для разделения данной пары используется ректификация при пониженном давлении, в дистилляте - смеси бутанола и амилола с примесными компонентами. Для очистки бутанола и амилола от примесей предложена экстрактивная ректификация с этиленгликолем. В присутствии последнего повышается летучесть бутанола по отношению к другим компонентам. Четвертая колонна предназначена для регенерации разделяющего агента. Отделение амилола предусмотрено в кубе пятой колонны. Определены статические параметры работы колонн (число тарелок, тарелка питания, флегмовое число, соотношение количеств исходной смеси и разделяющего агента), отвечающие минимальным энергозатратам и обеспечивающие получение веществ товарного качества. Для цитирования: Фролкова А.В., Фролкова А.К. Разработка технологии разделения спиртовой смеси растворителей. Изв. вузов. Химия и хим. технология. 2023. Т. 66. Вып. 1. С. 93-98. DOI: 10.6060/ivkkt.20236601.6670.