Тепловые эффекты фазовых и химических процессов в многокомпонентной системе с химическим взаимодействием тема диссертации и автореферата по ВАК РФ 02.00.04, кандидат наук Голикова Александра Дмитриевна

• Голикова Александра Дмитриевна
• кандидат наук
• 2021

Оглавление диссертации кандидат наук Голикова Александра Дмитриевна

Введение

Глава 1. Литературный обзор

1.1. Химическое равновесие в системе уксусная кислота - этиловый спирт - этилацетат

- вода

1.2. Фазовые равновесия в системе уксусная кислота - этиловый спирт - этилацетат -вода

1.3. Термохимические характеристики

Глава 2. Методики исследования

2.1. Очистка реактивов

2.2. Методика газохроматографического анализа

2.2.1. Экспериментальное определение химического равновесия

2.2.2. Экспериментальное определение равновесия жидкость-жидкость

2.3. Методика количественного анализа с применением метода ядерного магнитного резонанса

2.4. Методика анализа методом изотермического титрования

2.5. Методики калориметрических измерений

2.5.1. Экспериментальное определение теплот смешения

2.5.2. Экспериментальное определение теплоты химической реакции

2.5.3. Экспериментальное исследование растворимости методом калориметрии

Глава 3. Исследование растворимости и критических состояний в системе уксусная кислота - этиловый спирт - этилацетат - вода и ее подсистемах при изотермических условиях

Глава 4. Исследование химического равновесия

Глава 5. О равновесии жидкость - пар в системе уксусная кислота - этиловый спирт -этилацетат - вода

Глава 6. Исследование термохимических характеристик

6.1. Оценка влияния теплоты реакции на результаты калориметрических измерений

6.2. Избыточные энтальпии в системе уксусная кислота - этиловый спирт - этилацетат

- вода

6.2.1. Теплоты смешения в бинарных системах уксусная кислота - этиловый спирт этиловый спирт - вода, уксусная кислота - этилацетат, уксусная кислота - вода

6.2.2. Теплоты смешения в четверной системе уксусная кислота - этиловый спирт -этилацетат - вода

6.3. Теплота этерификации

Заключение

Благодарности

Список публикаций по теме исследования

Список литературы

Введение

Введение диссертации (часть автореферата) на тему «Тепловые эффекты фазовых и химических процессов в многокомпонентной системе с химическим взаимодействием»

Актуальность работы

Гетерогенные флюидные системы с химическим взаимодействием компонентов являются известными и перспективными экспериментальными объектами, с ними связан и широкий круг актуальных задач, на решение которых направлены их исследования. Интерес к системам с химическим взаимодействием компонентов в последние десятилетия обусловил появление работ конкретной технологической значимости, среди которых следует выделить направления в области реакционной ректификации и экстракции. Задачи организации указанных процессов прямо связаны с современными задачами энерго- и ресурсосберегающих экологически чистых технологий. Действительно, совмещение процессов разделения и синтеза дает возможность достичь высокого энергосбережения и степени конверсии реагентов, например, в процессах основного органического синтеза, что, в свою очередь, создает возможности безотходного экологически чистого производства при включении в него совмещенных реакционно-массообменных процессов, которыми являются указанные выше реакционная ректификация и экстракция. Вместе с тем, технологическая значимость исследований определила и основной акцент в экспериментальных работах, связанный преимущественно с относительно традиционным изучением фазовых и химических равновесий, то есть составов сосуществующих равновесных фаз, в том числе, при различных температурах.

В связи с этим следует отметить значимость полной термодинамической характеристики гетерогенных систем с химическим взаимодействием, которая должна включать сведения о тепловых эффектах как фазовых, так и химических процессов. Очевидно, что соответствующие данные не менее важны для синтеза технологических схем процессов разделения, синтеза и совмещенных процессов, например, в отношении их энергетической оценки и планирования. Особую значимость для химической технологии и фундаментальных проблем термодинамики имеют корректные термохимические данные в случае протекания одновременных фазовых и химических процессов: задачи разделения тепловых эффектов смешения и химических реакций являются, безусловно, нетривиальными. Этим сложным задачам посвящено достаточно ограниченное число современных исследований, хотя экспериментальная информация о термохимических характеристиках многокомпонентных систем с химическим взаимодействием необходима не только для развития соответствующих баз данных, но и для понимания природы протекающих процессов. Это дополнительно определяет как элементы новизны, так и актуальность диссертационного исследования. В работе поставлены задачи комплексного исследования тепловых эффектов в многокомпонентной системе с химическим взаимодействием веществ на примере технологически значимой системы с реакцией синтеза этилацетата. В то же время, многие выводы работы распространяются и на общие закономерности термохимического поведения многокомпонентных (четырехкомпонентных) систем с химической реакцией.

Цель и задачи работы

Основной целью диссертационной работы являлось комплексное экспериментальное исследование тепловых эффектов в многокомпонентной системе с химической реакцией, растворимости компонентов, критических фаз, химического равновесия и особенностей одновременного фазового и химического равновесия. Кроме того, цели работы включали

термодинамический анализ и моделирование, расчеты термодинамических параметров на основе полученных данных. Исследования фазового и химического равновесий проводились при разных температурах, что дало возможность комплексного описания диаграммы состояния системы при политермических условиях. Непосредственным объектом экспериментального исследования являлась система с реакциями синтеза и гидролиза этилацетата (уксусная кислота - этиловый спирт - этилацетат - вода). Выбор системы также определялся ее известной практической значимостью, экспериментальные данные должны иметь значение для дизайна оптимальных энерго- и ресурсосберегающих схем технологических процессов синтеза сложных эфиров карбоновых кислот. Наконец, цели работы включали фундаментальные задачи развития баз данных о термохимических свойствах многокомпонентных систем с химическими реакциями, включая топологию термодинамических поверхностей химически реагирующих смесей.

Методы исследования

В работе были использованы следующе методы исследования: газохроматографический анализ, метод изотермического титрования, калориметрические методы измерений, метод ядерного магнитного резонанса, метод титрования по Карлу-Фишеру, термодинамическое моделирование и расчеты.

Научная новизна работы:

• Получены детальные экспериментальные данные об избыточных энтальпиях в бинарных системах уксусная кислота - этиловый спирт, этиловый спирт - вода, уксусная кислота -этилацетат, уксусная кислота - вода при 313.15 К

• Получены данные о теплотах смешения в четверной системе уксусная кислота - этиловый спирт - этилацетат - вода 313.15 К

• Получены данные о химическом равновесии в системе с реакцией синтеза этилацетата при 313.15

• Получены данные о теплоте реакции синтеза этилацетата при 313.15 К с применением разработанной методики, позволяющей учитывать совокупность тепловых эффектов, сопровождающих процесс смешения и синтеза

• Получены новые детальные экспериментальные данные о растворимости в системе уксусная кислота - этиловый спирт - этилацетат - вода и ее бинарных и тройных подсистемах при 313.15 К

• Экспериментально установлен ход критических кривых в концентрационным тетраэдре четверной системы для температур 323.15 и 333.15 К

• Проведен анализ особенностей структур диаграмм для полученных термохимических и фазовых характеристик, включая многообразия химического равновесия, избыточных энтальпий, растворимости и критических состояний, а также результаты модельных расчетов (по групповой модели ЦВДГАС). В частности, установлено, что при данных температурах поверхности расслаивания и химического равновесия не пересекаются в концентрационном пространстве .

Практическая значимость работы:

Новые экспериментальные данные являются развитием базы данных о термохимических свойствах, о равновесии жидких фаз и критических состояниях многокомпонентных системах с

химической реакцией. Полученные результаты необходимы для реализации процессов синтеза этилацетата, включая реакционно-массообменные процессы. Для предсказательных расчетов и практической корреляции термохимических данных могут быть непосредственно использованы результаты моделирования. Результаты анализа поведения расслаивающихся химически реагирующих смесей, эволюция структуры диаграмм поверхностей растворимости и химического равновесия могут быть использованы для оптимизации реакционно -массообменных процессов (реакция, совмещенная с экстракцией ).

Положения, выносимые на защиту:

• Экспериментальные данные о теплотах смешения в бинарных системах уксусная кислота -этиловый спирт, этиловый спирт - вода, уксусная кислота - этилацетат, уксусная кислота -вода при 313.15 К

• Результаты экспериментального исследования избыточных энтальпий в система уксусная кислота - этиловый спирт - этилацетат - вода при 313.15 К

• Экспериментальные и расчетные данные о теплоте химической реакции в системе уксусная кислота - этиловый спирт - этилацетат - вода 313.15 К, методика экспериментов

• Экспериментальные данные о растворимости в системе уксусная кислота - этиловый спирт -этилацетат - вода, ее бинарных и тройных подсистемах (313.15, 323.15 и 333.15 К)

• Результаты экспериментального исследования химического равновесия в системе уксусная кислота - этиловый спирт - этилацетат - вода при 313.13 К, расчетные данные о равновесии при 313.15, 323.15 К.

• Результаты экспериментального исследования критических состояний: критических точек и кривых при политермических условиях

• Результаты анализа топологических особенностей структуры диаграмм химического равновесия и растворимости системы, в том числе, с одновременными фазовым и химическим равновесиями, критическими многообразиями.

Апробация работы

Публикации: по материалу диссертации опубликовано 35 работ, из них 7 статей в международных журналах (первого и второго квартиля), индексируемых в Scopus и Web of Science, 28 тезисов докладов на международных и российских конференциях. Диссертационное исследование было поддержано грантами:

• Грант РФФИ, 19-03-00375, исполнитель: «Применение методов неравновесной термодинамики для решения теоретических задач химической технологии: устойчивость многокомпонентных систем, фазовое и мембранное разделение, реакционно-массообменные процессы»

• Грант РФФИ, 18-33-20138, исполнитель: «Фазовые, химические и мембранные процессы в биотопливных системах: синтез и разделение»

• Грант РФФИ, 12.15.452.2016, исполнитель: «Разработка термодинамического подхода к исследованию реакционно - массообменных процессов в системах c реакцией этерификации»

• Грант РФФИ, 15-03-02131, исполнитель: «Тепловые эффекты и термохимические характеристики реакционно - массообменных процессов»

• Грант РФФИ, 12.15.807.2013, исполнитель: «Химические и фазовые процессы в окрестности критического состояния гетерогенных систем с химическим взаимодействием»

• НИР СПбГУ (темплан), исполнитель: «Термодинамическое и кинетическое исследование процессов в гетерогенных системах и функциональных материалах»

Личный вклад автора заключался в активном участии при обсуждении и постановке задач, планировании и проведении экспериментов и анализе полученных данных о теплотах смешения и теплоте химической реакции в системе уксусная кислота - этиловый спирт -этилацетат - вода, химическом равновесии и растворимости в системе с реакцией синтеза этилацетата, термодинамическом моделировании и обобщении полученных результатов, подготовке докладов и публикаций.

Глава 1. Литературный обзор

Несмотря на указанную выше практическую значимость систем с химическим взаимодействием компонентов, можно отметить определенный акцент в исследованиях совмещенных равновесий в жидкофазных расслаивающихся системах. Имеются в виду детальные фундаментальные исследования концентрационных соотношений - составов фаз и химически равновесных составов - в полном (или достаточно полном) концентрационном интервале химически реагирующих смесей. Это можно объяснить, с одной стороны, относительно трудоемкими соответствующими экспериментами, с другой - прикладной направленностью этих работ, см., например, [1-4] Абсолютное большинство исследований при этом связано не с относительно простыми тройными смесями, а с многокомпонентными системами. Литературные данные даже о химическом равновесии в тройных гомогенных жидких смесях очень ограничены. Можно отметить, например, работу Хайнца и Веревкина о химическом равновесии (и одновременном равновесии жидкость-пар) в системе с реакцией синтеза метилкумилового эфира [5]. Подчеркнем, что проведенный нами анализ был направлен, в первую очередь, на расслаивающиеся жидкие смеси с химическими реакциями. Даже в этом случае можно выделить определенный класс систем, для которых имеются данные, достаточные для последовательного термодинамического анализа. Абсолютное большинство исследований - это системы с реакцией синтеза сложных эфиров:

Alcohol (R) + Acid ( R2) = Water (R3) + Ester ( R4), расслоение в которых, в первую очередь, определяется ограниченной растворимостью воды и эфира. Система с реакцией система этилацетата является классическим примером такого рода, причем, как указывалось во Введении, ее свойства во многом типичны для расслаивающихся жидких смесей с химическими реакциями (химическими равновесиями). Ниже рассмотрим основные данные о химическом и фазовом равновесии в данной системе, а также данные о ее термохимических свойствах.

1.1. Химическое равновесие в системе уксусная кислота - этиловый спирт - этилацетат -вода

Этилацетат - одно из наиболее важных химических веществ, имеющее широкий спектр промышленного применения, например, в качестве растворителя, при производстве красок, клеящих материалов, ароматизаторов и других областях. Ежегодное производство этилацетата составляет около 1,2 млн. тонн [1]. Традиционный способ синтеза основан на кислотно-катализируемой этерификации уксусной кислоты этанолом. Применяемый в промышленности процесс реакционной ректификации - совмещенный процесс «синтез + ректификационное выделение» позволяет значительно повысить выход конечного продукта и уменьшить энергозатраты [2-4]. Перспективность метода определила появление значительного числа экспериментальных и теоретических работ, касающихся применения реакционной ректификации при производстве этилацетата, например [6-12], а также работ, посвященных исследованию фазовых и химических равновесий, включая их моделирование, например, [1315]. Некоторые работы посвящены только исследованию реакции синтеза этилацетата: например, авторы [16] изучали эту реакцию в паровой фазе при 519.15-559.15 K и атмосферном давлении. Отметим, что в настоящее время база данных о фазовых и химических равновесиях в системе с реакцией синтеза этилацетата довольно обширна, поэтому, кроме указанных выше источников, мы ограничимся ссылками на обзорные работы [13,17]. Обращает на себя внимание существенное различие результатов разных авторов при определении константы химического равновесия реакции синтеза-гидролиза этилацетата. Точность определения термодинамической константы химического равновесия, Ka,

! = П !!, (1)

где ai - активность реагента i, vi - соответствующие стехиометрические коэффициенты, в значительной степени зависит от выбранной области составов, для которых проводится расчет указанной константы. Напомним, что термодинамическая константа имеет единственное определенное значение для всей системы, всех равновесных концентраций, при фиксированных температуре и давлении. Например, по данным работ [18,19], в случае системы с реакцией синтеза бутилацетата расчет по экспериментальным данным для составов в области, близкой к 0.005 мольных долей одного из компонентов (0.005 - обычное значение ошибки эксперимента) приводит к значительному росту погрешности в определении Ka.

Во избежание большого разброса значений Ka приходится в расчете константы использовать набор данных об области химического равновесия, где концентрации компонентов достаточно велики. К сожалению, данные о химическом равновесии в системе с реакцией синтеза этилацетата представленные разными авторами, не только существенно отличаются, но и весьма ограничены. Приведем некоторые примеры.

В 1928 году Cántelo и Billinger изучили химическое равновесие в системе уксусная кислоты -этанол - этилацетат - вода при 351.15 K и представили значение константы химического равновесия, 3.7. [20]. Хотя авторы указывали, что определяется термодинамическая константа, проведенный впоследствии анализ их данных показывает, что в действительности они представили данные для так называемой "концентрационной" константы:

К = П , (2)

где xi - мольная доля компонента i, !1 - стехиометрический коэффициент компонента i, значение которой, как известно, зависит от концентрации, в отличие от термодинамической константы Ka. Связь между Ka и Kx определяется следующим соотношением

! = !*П г?1, (3)

где yi - коэффициент активности компонента i. Отметим, что данные о «концентрационной» (или «эмпирической») константе химического равновесия имеют определенное значение для характеристики концентрационного смещения химического равновесия в практических задачах, но в этом случае надо давать не единственное усредненное значение, а приводить зависимость Kx от состава (см., например, [21-23]. Некоторые авторы определяли константу химического равновесия для фиксированного количества исходных реагентов, а именно, они изучали эквивалентные смеси чистых исходных веществ с различными катализаторами [21,22,24]. В связи с тем, что промышленное получение этилацетата проводится при высоких температурах и в газовой фазе (один из вариантов синтеза) этерификация этанола уксусной кислотой еще в ранних работах интенсивно изучались при указанных условиях [16,21,22,24,25]. Например данные о химическом равновесии в работе [24] получены при 423.15 K, 428.15 K и 473.15 K, а в работе [25] при 373.15K и 443.15K. Hawes и Kabel в своей работе [25] отметили, что при исследовании реакции этерификации в паровой фазе, необходимо учитывать дополнительные реакции: образование диэтилового эфира и этилена.

Промышленная значимость этилацетата определила и большое число работ, посвященных определению константы химического равновесия реакции синтеза этилацетата и ее температурному смещению. Тем не менее, соответствующие данные несколько противоречивы. Авторы статьи [26] представили данные о равновесии жидкость - пар и о химическом равновесии в системе уксусная кислота - этиловый спирт - этилацетат - вода при атмосферном давлении. Так как фазовому равновесию по данным [26] отвечает температурный интервал 345.15- 384.15 K, значение Ka не может быть отнесено к определенной температуре, и авторы представили значение Ka = 13.4 как усредненную константу химического равновесия. В указанной работе представлен также анализ имеющихся (на тот момент) литературных данных о Ka: эти данные существенно отличаются друг от друга. Авторы указали, что значение, полученное в их исследовании (Ka = 13.4), является наиболее надежным для рассматриваемого температурного диапазона. Позже это значение константы было использовано в других работах при вычислении равновесия жидкость - пар и химического равновесия, например, в статьях Peres Cisneros и соавторов [27] или Campanella и Mandagaran [28]. В более поздней работе [11] авторы использовали другое значение Ka = 25 и получили хорошо согласованные теоритические и экспериментальные данные о реакционной ректификации этилацетата в широком диапазоне температур (338.15 - 383.15 K). Новые данные о значении константы Ka были также представлены авторами Bernatova, Aim и Wichterle в статье [29]: усредненное значение термодинамической константы химического равновесия равно 5.5 при 348.15 K (среднее для концентрационной области). Другие значения константы Ka были получены Smith и Van Ness (Ka = 0.25) [30] и Dean (Ka = 10.2) [31]. Подобные различия в значении Ka были отмечены многими авторами. В частности, Okasinski и Doherty указали, что небольшие изменения в значении константы приводят к существенным изменениям в топологии фазовых диаграмм [32]. Некоторые исследования, касающиеся химического и фазовых равновесий в системе с реакцией синтеза этилацетата обсуждаются также в обзорных статьях [13,17,33].

Таким образом, данные о химическом равновесии реакции синтеза этилацетата и температурном смещении требуют дополнительного анализа, что определило необходимость проведения соответствующих экспериментальных исследований в диссертационной работе.

1.2. Фазовые равновесия в системе уксусная кислота - этиловый спирт - этилацетат -вода

Не меньшее число работ посвящено исследованию фазовых равновесий в системе уксусная кислота - этанол - этилацетат - вода. Достаточно подробные современные обзоры представлены в статьях [13,17], поэтому далее ограничимся некоторыми избранными работами, включая исследования составляющих подсистем. В частности, равновесие жидкость - пар экспериментально изучено в работе [34]; эти данные вполне согласуются с результатами других авторов [35,36]. В работе [37] получены экспериментальные данные только для бинарных подсистем этанол - уксусная кислота, этилацетат - вода и этанол-вода (при 50 кПа и атмосферном давлении). Теоретическое рассмотрение термодинамических свойств и описание топологической структуры фазовых диаграмм четверной системы изложено в [38]. Описание равновесия жидкость - жидкость в системе уксусная кислота - этанол - этилацетат - вода (при 101,3 и 200 кПа) с помощью модели UNIFAC представлено в [39].

Используя различные модели, авторы работы [26] предложили новый алгоритм расчета одновременного фазового и химического равновесий для реакционных систем. Результаты расчетов для системы уксусная кислота- этанол-этилацетат-вода сопоставлены с расчетами, представленными в [40]. Термодинамическая согласованность экспериментальных данных для системы с реакцией синтеза этилацетата обсуждается в [41]. Авторы работы [42] провели моделирование фазовых равновесий с использованием уравнений Маргулеса и Вильсона. Моделирование на основе групповой модели ASOG (Analytical Solution of Groups) проведено в работе [43].

Анализ литературных данных показывает, что имеются многочисленные работы по моделированию равновесия жидкость - пар в системе уксусная кислота - этанол - вода -этилацетат (как и химического равновесия). Меньшее число работ посвящено данным о растворимости и равновесию жидких фаз. Поэтому в настоящей работе проводилось экспериментальное исследование растворимости и равновесия жидкость-жидкость, их температурного смещения в системе с реакцией синтеза этилацетата в политермических условиях (313.15 K, 323.15 K, 333.15 K).

1.3. Термохимические характеристики

Анализ литературы показывает, что термохимические свойства системы уксусная кислота - этиловый спирт - этилацетат - вода и ее подсистем изучены мало, а имеющиеся данные не структурированы. Некоторые работы приведены в Таблице 1.

Таблица 1 Литературные источники включающие данные о молярной избыточной энтальпии в бинарных и тройных подсистемах четверной системы уксусная кислота -этиловый спирт - этилацетат - вода

Система Температура Давление Литературный

T, K P, кПа. источник

298.15 атмосферное давление [12]

Уксусная кислота + этанол 292.15 - 299.15 - [44]

323.15 1548 [9]

- - [45]

Уксусная кислота + этилацетат 292.15 - 299.15 - [44]

323.15 1548 [9]

- - [45]

296.15-298.15 - [46]

Уксусная кислота + вода 290.15; 293.15; 298.15; 303.15; 313.15 - [47]

298 100 [48]

363.15 1548 [9]

Этанол + этилацетат 413.15 1307

298.15 - [49]

298.15; 305.15 - [50]

298.15 - [51]

352.15; 350.15 - [52]

298.15; 300.15; 307.15 - [53]

298.15 - [54]

298.15K - [55]

298.15K - [56]

Этанол + вода 298.15 - [57]

333.15 1824

363.15 1203 [9]

383.15 1500

298.15K - [58]

298.15; 323.15; 331.15; [59]

343.15; 363.15; 383.15

Этилацетат + вода 298.15 - [60]

353.15 1272 [9]

Уксусная кислота + этанол + этилацетат 298.15 100 [48]

292.15 - 300.15 - [44]

- - [45]

В некоторых приведенных работах также представлены данные, полученные при расчете по уравнению Редлиха - Кистера [46,47,60] и Вильсона [50]. В публикациях [49,51,54,59] приведены корреляционные коэффициенты. Отметим, что подобный «непрямой» расчет избыточной молярной энтальпии на основе данных о равновесиях представляет собой достаточно трудоемкую задачу (см., например, [61]).

Бинарные системы уксусная кислота - вода, уксусная кислота - этилацетат, этанол -вода и этанол - этилацетат представлены в Таблице 1 только как химически инертные подсистемы в четверной системе с химическим взаимодействием. Остальные подсистемы представленные в таблице являются реакционными (мы используем, для краткости, подобный термин, как аналог терминов «геасйуе» или «геасй^» в англоязычной литературе), в них возможно протекание химической реакции этерификации или гидролиза эфира. Очевидно, что в подобных случаях экспериментальное определение величин теплот смешения требует учета теплового эффекта реакции, что, в общем случае, существенно осложняет эксперименты и их корректную трактовку. Вместе с тем, можно использовать тот факт, что в отсутствие катализатора реакция синтеза этилацетата (как и других эфиров) практически заторможена, ее скорость невелика. Соответственно, тепловым эффектом именно реакции (в отсутствие катализа) можно пренебречь, что облегчает экспериментальное изучение избыточных молярных энтальпий. Можно полагать, что в большинстве случаев, указанное возможное протекание химической реакции (точнее, ее крайне низкая скорость), не вносит погрешность в определение избыточных молярных энтальпий. Это подтверждается, в частности, результатами исследований [62-65], в которых приведены доказательства незначительного влияния энтальпии реакции на эксперименты по определению теплоты смешения в системе с реакцией синтеза пропилацетата. Подобный анализ и экспериментальное исследование проводилось и в настоящей работе (представлены в разделе 7.1 диссертации).

Независимое (от избыточной молярной энтальпии) определение теплоты химической реакции дает важнейшую информацию для общей термодинамической базы данных. Тем не менее, в литературе только несколько работ посвящено данным о теплоте реакций этерификации/гидролиза в системе уксусная кислота - этиловый спирт - этилацетат - вода. Возможно, это связано с распространенными взглядами, начиная с Бертло, на возможность пренебрежения тепловыми эффектами реакции этерификации, по крайней мере, для технологических целей. Например, в учебнике Н. Н. Лебедева [66] «Химия и технология основного органического и нефтехимического синтеза» при обсуждении общих деталей о взаимодействия одноатомных спиртов с карбоновыми кислотами автор утверждает что химическая реакция этерификации протекает практически без тепловых эффектов (ДН=0). Тем не менее, в ряде случаев, эти данные приводятся, в том числе, как вспомогательные данные для решения других термохимических задач. Например, в работе 'Ле^ и Waldron [67] проводилось экспериментальное определение энтальпии гидролиза моноцикличесих лактонов. В ходе исследования определялись также энтальпии образования этиловых эфиров н-алкановых кислот: эти данные использованы для оценки энергии деформации в лактонах (связанной с замещением карбоксилатных групп). В результате были получены и экспериментальные значения энтальпии гидролиза этилацетата, ДНьул-о1=3,86±0,14 кДж/моль. Wadsб и соавторы [68] также проводили калориметрические исследования реакции гидролиза нескольких эфиров уксусной кислоты, в том числе этилацетата. В статье представлено значение энтальпии гидролиза этилацетата, ДНьу(^о1=3,72±0,16 кДж/моль для 298.15 К. Это значение вполне согласуется с данными работы [67]. Еще одно близкое по величине значение энтальпии реакции

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SAINT PETERSBURG STATE UNIVERSITY

Manuscript copyright

Alexandra D. Golikova

HEAT EFFECTS OF PHASE AND CHEMICAL PROCESSES IN A MULTICOMPONENT SYSTEM WITH CHEMICAL INTERACTION

02.00.04 - Physical Chemistry

Thesis submitted in conformity with the requirements for the degree of

Candidate of Chemical Sciences

Translation from Russian

Thesis supervisor: Doctor of Chemical Sciences, Professor

Alexander M. Toikka

Saint Petersburg 2020

Introduction............................................................................................................................................3

Chapter 1. Literature review.................................................................................................................6

1.1. Chemical equilibrium in the system acetic acid-ethanol-ethyl acetate-water........................6

1.2. Phase equilibria in the system acetic acid-ethanol-ethyl acetate-water.................................8

1.3. Thermochemical characteristics................................................................................................8

Chapter 2. Research methods..............................................................................................................11

2.1. Purification reagents.................................................................................................................11

2.2. Gas chromatographic method analysis...................................................................................12

2.2.1. Experimental determination of chemical equilibrium 12

2.2.2. Experimental determination of the liquid-liquid equilibrium 12

2.3. The technique of quantitative analysis using the method of nuclear magnetic resonance . 12

2.4. Cloud-point technique...............................................................................................................15

2.5. Methods of calorimetric measurements..................................................................................17

2.5.1. Experimental determination of the heats of mixing17

2.5.2. Experimental determination of the heat of a chemical reaction 18

2.5.3. Experimental research of solubility by calorimetric analysis 19

Chapter 3. Solubility and critical states for the quaternary system acetic acid-ethanol-ethyl acetate-water at isothermal conditions..............................................................................................21

Chapter 4. The study of chemical equilibrium..................................................................................46

Chapter 5. On the liquid-vapor equilibrium in the system acetic acid-ethanol-ethyl acetate-water ................................................................................................................................................................55

Chapter 6. The study thermochemical characteristics.....................................................................65

6.1. Evaluation of the effect of reaction heat on the results of calorimetric measurements......65

6.2. Excess enthalpy in the system acetic acid-ethanol-ethyl acetate-water................................66

6.2.1. Heats of mixing in binary systems acetic acid-ethanol, ethanol-water, acetic acid-ethyl acetate, acetic acid-water 66

6.2.2. Heat of mixing in the quaternary system acetic acid-ethanol-ethyl acetate-water. 73

6.3. Heat of reaction of esterification..............................................................................................76

Conclusions...........................................................................................................................................79

Acknowledgements...............................................................................................................................80

List of publications on the research topic..........................................................................................81

Bibliography.........................................................................................................................................85

Introduction

Heterogeneous fluid systems with chemical interaction of components are well-known and promising experimental objects. They are associated with a wide range of topical issues. In recent decades, the interest in systems with chemical interaction of components has led to the emergence of works of specific technological significance. Among these works we should highlight areas in the field of reaction rectification and extraction. The tasks of organizing these processes are directly related to the modern tasks of saving energy and resources, as well as developing environmentally friendly technologies. Indeed, the combination of separation and synthesis processes makes it possible to achieve high energy savings and the degree of conversion of reagents, for example in processes of basic organic synthesis. It creates the possibility of waste-free and environmentally friendly production when it includes combined reaction-mass transfer processes or reaction rectification and extraction. At the same time, the technological significance of the research has also determined the main focus in experimental work, which is mainly associated with the relatively traditional study of phase and chemical equilibria, including the compositions of coexisting equilibrium phases, investigated at different temperatures also.

In this regard, we should note the importance of a complete thermodynamic characterization of heterogeneous systems with chemical interaction. It should include information about the thermal effects of both phase and chemical processes. It is obvious that the relevant data is equally important for the synthesis of technological schemes for separation, synthesis, and combined processes, for example in relation to their energy assessment and planning. Correct thermochemical data in the case of simultaneous phase and chemical processes are of particular importance for chemical technology and fundamental problems of thermodynamics: the problems of separating the thermal effects of mixing and chemical reactions are non-trivial. A fairly limited number of modern studies are devoted to these complex problems, although experimental information on the thermochemical characteristics of multicomponent systems with chemical interaction is necessary not only for the development of appropriate databases, but also for understanding the nature of the processes. This additionally determines both the novelty elements and the relevance of the dissertation research. The paper sets the tasks of a comprehensive study of thermal effects in a multicomponent system with chemical interaction of substances on the example of a technologically significant system with the reaction of ethyl acetate synthesis. At the same time, many conclusions of the work extend to General laws of thermochemical behavior of multicomponent (four-component) systems with a chemical reaction.

Objectives

The main purpose of the thesis is complex experimentation research thermal effects in multicomponent system with chemical reaction, solubility of components, critical phases, chemical equilibrium and features of simultaneous phase and chemical equilibrium.

In addition, the goal of the work included thermodynamic analysis and modeling, calculations of thermodynamic parameters based on the data obtained.

Investigations of phase and chemical equilibrium were carried out at different temperatures, which made it possible to complex describe the state diagram of the system in polythermal conditions. The object of the experimental study was a system with ethyl acetate synthesis reaction (acetic acid -ethyl alcohol - ethyl acetate - water).

The choice of the system was also determined by its known practical importance. The experimental data are important for the design of optimal energy and resource-saving schemes of technological processes for the synthesis of esters of carboxylic acids.

Finally, the objectives of the work included the fundamental tasks of developing databases about thermochemical properties of multicomponent systems with chemical reactions, including the topology of the thermodynamic surfaces of chemically reacting mixtures.

Method of research:

The following research methods were used in the work: gas chromatographic analysis, isothermal titration method, calorimetric measurement methods, nuclear magnetic resonance method, KarlFischer titration method, thermodynamic modeling, and calculations.

Novelty of scientific work:

• Detailed experimental data on excess enthalpies in binary systems acetic acid - ethyl alcohol, ethyl alcohol - water, acetic acid - ethyl acetate, acetic acid - water at 313.15 K were obtained

• Data on the heats of mixing in the quaternary system acetic acid - ethanol - ethyl acetate - water 313.15 K were obtained

• Data on the chemical equilibrium in the system with the reaction of ethyl acetate synthesis at 313.15 K were obtained

• There were obtained data on the heat of reaction for the synthesis of ethyl acetate at 313.15 K using the developed technique that allows to take into account the totality of thermal effects accompanying the mixing and synthesis process.

• There were obtained new detailed experimental data on the solubility in the system acetic acid -ethanol - ethyl acetate - water and its binary and ternary subsystems at 313.15 K

• The course of critical curves in the concentration tetrahedron of the quaternary system was experimentally established for temperatures of 323.15 and 333.15 K

• Structural features of the diagrams of the obtained thermochemical and phase characteristics were analyzed, including various chemical equilibria, excess enthalpies, solubility, critical states and model calculations (based on the model of the UNIFAC group).

Practical significance of the work:

New experimental data are the development of a database on thermochemical properties, liquid phase equilibrium, and critical States of multicomponent systems with a chemical reaction. The results obtained are necessary for the implementation of ethyl acetate synthesis processes, including reaction-mass transfer processes. Simulation results can be directly used for predictive calculations and practical correlation of thermochemical data. The results of the analysis of the behavior of stratified chemically reacting mixtures and the evolution of the structure of the solubility and chemical equilibrium surface diagrams can be used to optimize reaction - mass transfer processes (reaction combined with extraction ).

The statements and results put forward for defense

• Experimental data on mixing heats in binary systems acetic acid-ethanol, ethyl alcohol-water, acetic acid-ethyl acetate, acetic acid-water at 313.15 K

• Results of an experimental study of excess enthalpy in the system acetic acid-ethanol-ethyl acetate-water at 313.15 K

• Experimental and calculated data on the heat of the chemical reaction in the system acetic acid-ethyl alcohol-ethyl acetate-water 313.15 K, experimental methodology

• Experimental data on solubility in the acetic acid - ethanol-ethyl acetate - water system, its binary and triple subsystems (313.15, 323.15 and 333.15 K)

• Results of an experimental study of the chemical equilibrium in the system acetic acid-ethanol-ethyl acetate-water at 313.13 K, calculated data on the equilibrium at 313.15, 323.15 K

• Results of experimental study of critical states: critical points and curves under polythermal conditions

• Results of analysis of topological features of the structure of chemical equilibrium and solubility diagrams of the system, including those with simultaneous phase and chemical equilibria and critical manifolds

Approbation of the research

Publications: 35 papers have been published on the dissertation material, including 7 articles in international journals (first and second quartile) indexed in Scopus and Web of Science, 28 abstracts at international and russian conferences. The dissertation research was supported by grants:

• Grant RFBR, 19-03-00375, executor: «Application of the methods of non-equilibrium thermodynamics for the solution of theoretical problems of chemical engineering: stability of multicomponent systems, phase and membrane separation, reaction and mass transfer processes»

• Grant RFBR,, 18-33-20138, executor: «Phase, chemical and membrane processes in biofuel systems: synthesis and separation»

• Grant RFBR,, 12.15.452.2016, executor: «Development of a thermodynamic approach of coupled processes investigation in systems with esterification reaction»

• Grant RFBR,, 15-03-02131, executor: «Heat effects and thermochemical features of reaction - masstransfer processes»

• Grant RFBR,, 12.15.807.2013, executor: «Chemical and phase processes in the vicinity of critical state of heterogeneous systems with chemical interaction»

• Research Work of St. Petersburg state University, executor: «Thermodynamic and kinetic study of processes in heterogeneous systems and functional materials»

Personal contribution of the author

The author's personal contribution consisted in active participation in the discussion and setting of tasks. Planning and conducting experiments. Analysis of the obtained data on the mixing heat and the heat of the chemical reaction in the acetic acid - ethanol-ethyl acetate - water system. Analysis of data on chemical equilibrium and solubility in a system with an ethyl acetate synthesis reaction. Conducting thermodynamic modeling and summarizing the results, preparing reports and publications.

Chapter 1. Literature review

Despite the practical significance of systems with chemical interaction of components, we can note a certain emphasis in the research of combined equilibria in liquid-phase with limited miscibility systems. These are detailed fundamental studies of phase compositions and chemical equilibrium compositions in the full concentration range of chemically reacting mixtures. These are on the one hand complex experiments, on the other hand applied value, see, for example, [1-4] Most of the research is related to multi-component systems that are difficult to study. Literature data even on chemical equilibrium in ternary homogeneous liquid mixtures are limited. For example, the work of Heinz and Verevkin on chemical equilibrium and simultaneous liquid-vapor equilibrium in a system with a methylcumyl ether synthesis reaction [5]. Our analysis was primarily aimed at liquid mixtures with limited miscibility and chemical reactions.. In this case, we can distinguish a certain class of systems for which there is sufficient data for a consistent thermodynamic analysis. Most studies are systems with the reaction of synthesis of esters:

Alcohol (R) + Acid (R2) = Water (R3) + Ester (R4), The limited miscibility in these mixtures is determined by the limited solubility of water and ether. A system with an ethyl acetate synthesis reaction is a classic example of this type of systems. Moreover, as indicated in the introduction, its properties are characteristic of liquid mixtures with limited miscibility and chemical reactions (chemical equilibria). Then we will consider the basic data on the chemical and phase equilibrium in this system, as well as data on its thermochemical properties.

1.1. Chemical equilibrium in the system acetic acid-ethanol-ethyl acetate-water

Ethyl acetate is one of the most important chemicals widely used as a solvent in various industries for producing of paints, inks, adhesives, and fragrances, with annual global production around 1.2 million tons [1]. Conventional way of ethyl acetate production is based on acid-catalyzed esterification of acetic acid with ethanol. Usually, the industrial synthesis is combined with the separation. Such coupled process as reactive distillation (RD) allows one to get a significant improvement of the degree of reactant conversion. [2-4]. There are many experimental and theoretical works concerning the application of RD for ethyl acetate production, e.g. [6-12]. The design of this process demands special knowledge on phase and chemical equilibria (CE) [13-15]. Some works are devoted only to the study of the reaction of ethyl acetate synthesis: for example, the authors [16] studied this reaction in the vapor phase at 519.15-559.15 K and atmospheric pressure. In present time the database on thermodynamic properties and phase transitions in the system with ethyl acetate synthesis reaction is quite extensive , so in addition to the above sources, we will limit ourselves to references to review works [13,17]. There is a significant difference in the results of different authors in determining the chemical equilibrium constant of the synthesis-hydrolysis of ethyl acetate Ka,

! = П ^, (1)

where ai - activity of species i, vi - stoichiometric coefficients respectively. The accuracy of determination of Ka on the base of Eq. (1) strongly depends on the initial data set, first of all from the composition area. The thermodynamic constant has a single definite value for the entire system, for all equilibrium concentrations, at a fixed temperature and pressure. For example, according to [18,19], in the case of a system with a butyl acetate synthesis reaction, the calculation based on experimental data

for compositions in the region close to 0.005 mole fractions of one of the components (0.005 is the usual experimental error value) leads to a significant increase in the error in determining Ka. To avoid this problem the Ka values could be calculated from the whole data set for the surface of chemical equilibrium where concentrations of all species are large enough. The determination of Ka requires detailed and reliable data on CE compositions. Unfortunately, the data on the chemical equilibrium in a system with an ethyl acetate synthesis reaction presented by different authors vary significantly and are very limited. There are some examples.

In 1928 Cantelo and Billinger studied a chemical equilibrium in acetic acid - ethanol - ethyl acetate -water system at 351.15 K and presented the value of the constant of CE, 3.7 [20]. Authors have considered a thermodynamic constant but in fact they presented the data for "concentration" constant:

K = n , (2)

where xi - molar fraction of species i, v1 - stoichiometric coefficient of species i. The data on Kx have well-known practical importance but depend on composition, opposite to thermodynamic constant Ka:

! = !*n !!, (3)

where yi - activity coefficient of species i. Data on the "concentration" (or "empirical") constant of chemical equilibrium have a certain value in practical problems, but in this case it is necessary to give the dependence of Kx on the composition, but not the only average value , see e.g. [21-23]. Moreover some authors determined constant of CE for fixed amount of initial substances only: mixtures of exactly equivalent amounts of pure initial substances with different catalysts in papers [21,22,24]. Due to the fact that industrial production of ethyl acetate is carried out at high temperatures and in the gas phase (one of the synthesis methods), etherification of ethanol with acetic acid was intensively studied in early works under these conditions [16,21,22,24,25]. For example the data on CE in paper [24] are related to 423.1 K, 428.1 K and 473.1 K, in work [25] to 373.15 K and 443.15 K. Hawes and Kabel also pointed out that for vapor phase esterification the additional reactions should be taken into account: formation of diethyl ether and ethylene [25].

The industrial significance of ethyl acetate has also been determined by a large number of works devoted to determining the chemical equilibrium constant of the ethyl acetate synthesis reaction and its temperature shift. However, the relevant data is somewhat contradictory. Kang et al. studied the vapor-liquid equilibria (VLE) with CE in the system acetic acid - ethanol - ethyl acetate - water at atmospheric pressure [26]. Accordingly, the Ka values are not related to constant temperature: the temperature of quaternary VLE varies from 345.85 K to 384.55 K. Nevertheless, authors present the Ka value as an average CE constant, 13.4: authors proposed that Ka is independent of temperature since the heat of reaction is small. Kang et al. also presented a short analysis of available data on Ka that are significantly differ one from another and pointed out that their Ka value, 13.4, is most reliable for considered temperature range. Later, this value has been used by some authors for computation of VLE and CE, e.g. by Peres Cisneros et al. [27] or Campanella and Mandagaran [28]. On the other hand Kenig et al. used the value Ka = 25 and obtained the reliable chemical equilibrium surface in the system acetic acid - ethanol - ethyl acetate - water in work [11]. Recently a new data on Ka were reported by Bernatova, Aim and Wichterle: the average value of the chemical equilibrium constant is 5.5 at 348.15 K. [29]. Other data were reported by Smith and Van Ness (Ka = 0.25) [30] and Dean (Ka = 10.2) [31]. These differences in Ka value were pointed out by many authors. For example, Okasinski and Doherty used Ka for the computation of phase diagrams and indicated a substantial amount of uncertainty in the value of the reaction equilibrium constant [32]. Some other studies concerning CE

and phase equilibria in the system with ethyl acetate synthesis reaction are discussed in review papers [13,17,33].

Thus, the data on the chemical equilibrium of the ethyl acetate synthesis reaction and the temperature shift require additional analysis, which determined the need for appropriate experimental studies in the dissertation work.

1.2. Phase equilibria in the system acetic acid-ethanol-ethyl acetate-water

A number of papers are also devoted to the study of phase equilibria in the acetic acid - ethanol

- ethyl acetate - water system. Fairly detailed modern reviews are presented in the articles [13,17]. Therefore, we will limit ourselves to some chosen works, including studies of the constituent subsystems. VLE was experimentally studied by Calvar et al. [34]; these results are in agreement with the data of other authors [35,36]. The paper's experimental data sets [37] include only data for binary sub-systems ethanol-acetic acid, ethyl acetate-water and ethanol-water (at 50 kPa and atmospheric pressure). Theoretical consideration of thermodynamic properties and description of the topological structure of the quaternary system are reported in [38]. The description of liquid-liquid equilibria (LLE) in acetic acid-ethanol-ethyl acetate-water system (at 101.3 and 200 kPa) with the help of UNIFAC model are presented in [39].

Using various models, Kang et al. [26] proposed new algorithms for calculating simultaneous chemical and phase equilibrium for reactive systems. The calculation results for the acetic acid-ethanol-ethyl acetate-water system were compared with calculations made by Pérez Cisneros et al. [40]. The thermodynamic coherence of experimental data for the quaternary system with ethyl acetate synthesis reaction is discussed in [41]. The authors of [42] considers the results of modeling equilibria in this system using Margules and Wilson equations. Simulation on the base of a group model (ASOG, Analytical Solutions of Groups) is described in [43].

Analysis of literature data shows that there are numerous papers on the modeling of VLE and chemical equilibrium in acetic acid-ethanol-water-ethyl acetate system. In contrast, the data sets on LLE and solubility are limited. Accordingly, the aim of our work was the experimental study of solubility and LLE in this system under isothermal conditions (313.15 K, 323.15 K, 333.15 K).

1.3. Thermochemical characteristics

Our analysis of the literature data showed that the thermochemical properties of the acetic acid

- ethyl alcohol - ethyl acetate - water system and its subsystems are limited, and the available data are not structured. Some works are shown in Table 1.

Table 1 Literary sources on excess molar enthalpy data for binary and ternary subsystems of the quaternary system acetic acid - ethyl acetate - ethanol - water

Systems Temperature Pressure Literature

T, K P, kPa.

Acetic acid + ethanol 298.15 standard pressure [12]

292.15 - 299.15 - [44]

323.15 1548 [9]

- - [45]

Acetic acid + ethyl acetate 292.15 - 299.15 - [44]

323.15 1548 [9]

- - [45]

Acetic acid + water 296.15-298.15 - [46]

290.15, 293.15, 298.15, 303.15, 313,15 - [47]

Ethanol + ethyl acetate 298 100 [48]

363.15 413.15 1548 1307 [9]

298.15 - [49]

298.15, 305.15 - [50]

298.15 - [51]

Ethanol + water 352.15, 350.15 - [52]

298.15, 300.15, 307.15 - [53]

298.15 - [54]

298.15K - [55]

298.15K - [56]

298.15 - [57]

333.15 363.15 383.15 1824 1203 1500 [9]

298.15K - [58]

298.15, 323.15, 331.15, 343.15, 363.15, 383.15 - [59]

Ethyl acetate + water 298.15 - [60]

353.15 1272 [9]

Acetic acid + ethanol+ ethyl acetate 298.15 100 [48]

292.15 - 300.15 - [44]

- - [45]

Some of the above reports also present data obtained by calculating the Redlich-Kister equation [46,47,60] and Wilson [50]. In the publications [49,51,54,59] correlation coefficients are given. Note

that such calculation of the excess molar enthalpy based on equilibrium data is a rather difficult task (see, for example, [61]).

In Table 1 binary systems acetic acid + water, acetic acid + ethyl acetate, ethanol + water and ethanol + ethyl acetate are non-reacting systems. Other binary and ternary subsystems are the mixtures with chemical reaction of esterification or ester hydrolysis. The experimental determination of the heats of mixing in reacting systems usually is complicated by simultaneous emission of heat of reaction. Nevertheless in the case of ethyl acetate synthesis reaction (and other esters) the study of excess molar enthalpies is simplified: the heat of reaction and the reaction rate in the absence of catalyst are small. Accordingly the determination of heats of mixing by regular calorimetric measurements does not connected with significant errors. For example, the evidence of the negligible influence of the reaction enthalpies in mixing experiments had been presented for the system with propyl acetate synthesis reaction in [62-65]. A similar analysis and experimental research was carried out in this paper (presented in section 7.1 of the dissertation).

The determination of the heat of a chemical reaction is the most important information for the General thermodynamic database. However, only a few works in the literature are devoted to data on the heat of esterification/hydrolysis reactions in the acetic acid - ethyl alcohol - ethyl acetate - water system. This may be due to widespread views, starting with Berthelot, that the thermal effects of the esterification reaction can be ignored, at least for technological purposes. For example, in the textbook by H. H. Lebedev [66], the author States that the chemical reaction of esterification proceeds practically without thermal effects (AH=0). However, in some cases, these data are provided, including as auxiliary data for solving other thermochemical problems. For example, Wiberg and Waldron [67] experimentally determined the enthalpy of hydrolysis of monocyclic lactones. In the course of the study, the enthalpies of formation of ethyl esters of n-alkanoic acids were also determined: these data were used to estimate the deformation energy in lactones (associated with the substitution of carboxylate groups). As a result, experimental values of the enthalpy of hydrolysis of ethyl acetate were obtained, AHhydxol=3,86±0,14 kJ mole-1. Wadso and co-authors [68] also conducted calorimetric studies of the hydrolysis reaction of several acetic acid esters, including ethyl acetate. The article presents the value of the enthalpy of hydrolysis of ethyl acetate, AHhydxol=3,72±0,16 kJ mole-1 at 298.15 K. This value is quite consistent with the work data [67]. Another value of the enthalpy of the ethyl acetate synthesis reaction is given in the dissertation work of Yuri. A. Pisarenko [69]: -3,72±0,2 kJ mole-1.

The literature analysis shows that data on the thermodynamic properties of multicomponent systems with chemical interaction of components are rather limited and new research and correction of the available data are necessary.

Chapter 2. Research methods

2.1. Purification reagents

All the reagents used in the work were thoroughly cleaned beforehand and their main physical and chemical parameters corresponded to the literature data.

Ethanol ("reagent" grade, Vekton, Russia) and ethyl acetate ("purified" grade, Vekton, Russia) were purified by distillation. Water was bidistilled. Acetic acid ("purified" grade, Vekton, Russia) was purified by two times rectification, with the presence of 98% sulphuric acid. Hydrochloric acid (36.5 wt%) - the reagent was used as a catalyst for the ethyl acetate esterification reaction in the study of chemical equilibrium. The purity of chemicals was verified chromatographically and in terms of refraction indexes and boil- ing points. All physico-chemical constants of pure substances were found to be in agreement with NIST Standard Reference Database

Physical and chemical characteristics of the purified substances in comparison with the literature data are presented in Table 2.

Table 2 Physical and chemical characteristics of reagents

Substance „20 !boil, K Resource

Acetic acid 1.3719±0.0003 390.95±0.2 [70]

1.3718 391.15 present work

Ethanol 1.3614±0.0003 351.5±0.2 [70]

1.3612 351.55 present work

Ethyl acetate 1.3724±0.0003 350.25±0.1 [70]

1,3726 350.25 present work

Water 1.3335±0.0013 373.15 [70]

1.3330 373.15 present work

It is known that due to the hygroscopicity of "absolute" ethyl alcohol, its use may cause some technical difficulties, in particular, incorrect concentration values may be obtained due to the absorption of water from the air. In our case, water is one of the components of the systems under study. we use an azeotropic ethanol-water mixture and introduce a correction for the water content (when preparing mixtures). This technique is used in many studies published in the world literature. However, in some cases, in calorimetric studies, it was necessary to use absolute (dehydrated) alcohol. To do this, the ethyl alcohol was drained using molecular sieves. KA 3A Zeolite with an input window diameter of 0.3 nm was used. The final product was controlled by titration using the Karl Fischer method. The final purity of "absolute" ethyl alcohol for calorimetric studies was 0.999 mass fraction.

In calorimetric studies, KU-2 cationite (Na-form) was used as a catalyst for esterification/hydrolysis reactions, which is an ion - exchange resin with functional sulfogroups and a styrene-divinylbenzene matrix (Lenreactive, Russia).

2.2. Gas chromatographic method analysis

2.2.1. Experimental determination of chemical equilibrium

The first stage of the CE experiment was carried out using gas chromatography (GC) analysis. In experiments to determine the chemical equilibrium, the compositions of the initial chemically non-equilibrium homogeneous solutions were chosen so that the concentrations of the final chemically equilibrium mixtures as fully as possible reflected the position of the chemical equilibrium surface in the concentration tetrahedron. Initial quaternary mixtures of known overall compositions were prepared in glass vessels (5 mL) by weight, using an analytical balance Shinko VIBRA HT-120CE (Japan) with the accuracy of 0.001 g. Hydrochloric acid was used as a catalyst in an amount of 0.003 mol fraction. After stirring, sealed vessels were placed in the liquid thermostat (303.15, 313.15 and 323.15 K). The temperature uncertainty was ±0.05 K.

The compositions of reacting mixtures were determined by GC analysis. The constancy of composition confirmed equilibration. The CE was reached in no longer than 3 days. A gas chromatograph ''Chromatec Crystal 5000.2'' (Russia) with thermal conductivity detector (TCD) and packed column Porapak R (1 m 9 3 mm i.d.) was used. The TCD was chosen because of the presence of water. The carrier gas was helium with the flow rate of 60 mL«min-1. Operating temperatures of column, vaporizing injector and TCD were 463.15, 503.15 and 513.15 K, respectively.

The method of internal standard and relative calibration were used to determine the compositions. Ethanol was accepted as a linking component. Uncertainty of the GC analyses is ±0.005 mol fraction. It should be noted that samples were kept in a thermostat during the experiment and sampling process in order to avoid violation of CE. The experiments were conducted in a transparent liquid thermostat for this purpose. The sample of each solution investigated after the reaching of CE was taken by a 1 p,L Hamilton chromatographic syringe and was analyzed by GC. The analysis of each sample was repeated 2-3 times. All samples were homogeneous during the experiment. All experiments were conducted at atmospheric pressure.

2.2.2. Experimental determination of the liquid-liquid equilibrium

Experiments to determine the liquid-liquid equilibrium were carried out only for the binary system ethyl acetate-water at 313.15 K. Binary mixtures with limited Miscibility of a certain composition were also prepared in glass vessels (volume ~5 ml) by weight method on analytical scales Shinko VIBRA HT-120CE with an accuracy of 0.001 g. Then the finished solution was mixed in a closed vessel and kept in a transparent liquid thermostat at a temperature of 313.15 K (±0.01 K) until the phase equilibrium occurred. Phase equilibrium was considered to have been reached after complete phase breakdown. As a rule, the time of equilibrium was about 100 minutes at 313.15 K.

After reaching equilibrium, samples of each phase were taken using a Hamilton chromatographic syringe (1 p,L) and analyzed on a gas chromatograph. Samples were analyzed 2-3 times for each phase. All experiments were also carried out at atmospheric pressure.

2.3. The technique of quantitative analysis using the method of nuclear magnetic resonance

The chemical equilibrium was additionally studied by JH NMR spectroscopy. All samples were analyzed using a 500 MHz Buker AVANCE III NMR spectrometer, equipped with a BBI probe head with inner coil for JH nuclei. The spectra were acquired with an acquisition time of 3 s, a relaxation

delay of 1 s, and a pulse with 30° flip angle. The 16 scans were accumulated. The spin-lattice NMR relaxation times T1 for all molecular groups of all compounds were measured. Observed T1 values are in range from 3 to 5 s. The relaxation delay was high enough for quantitative analysis of peak integrals since the relaxation times have close values and the flip angle of pulse is relatively small. The error introduced by saturation was below 1%. The processing of the acquired spectra was carried out using Bruker TopSpin software. The phase correction was done manually. Polynomial baseline correction was done automatically. The integration region of 250-500 Hz was chosen which is over 20 times wider than the linewidth of analyzed peak. The uncertainty of the determination of the peak areas introduced by the processing is estimated to be 3%.

The CE was also studied by 1H NMR spectroscopy. All samples were analyzed using a 500 MHz Buker AVANCE III NMR spectrometer, equipped with a BBI probe head with inner coil for 1H nuclei. The spectra were acquired with an acquisition time of 3 s, a relaxation delay of 1 s, and a pulse with 30° flip angle; 16 scans were accumulated. The spin-lattice NMR relaxation times T1 for all molecular groups of all compounds were measured. Observed T1 values are in range from 3 to 5 s. The relaxation delay was high enough for quantitative analysis of peak integrals since the relaxation times have close values and the flip angle of pulse is relatively small. The error introduced by saturation was below 1%. The processing of the acquired spectra was carried out using Bruker TopSpin software. The phase correction was done manually. Polynomial baseline correction was done automatically. The integration region of 250-500 Hz was chosen, which is over 20 times wider than the linewidths of analyzed peaks. The uncertainty of the determination of the peak areas introduced by the processing is estimated to be 3%.

The assignment of signals for studied system was done using the NMR chemical shifts of water, acetic acid, ethanol and ethyl acetate were tabulated in ref. [71]. The esterification reaction cause small changes in chemical shifts: for acetic acid the CH3 resonance at 2.08 ppm shifts to 2.07 ppm for CH3CO group of ethyl acetate; methyl 1.17 ppm and methylene 3.65 ppm resonances of ethanol shift to 1.24 ppm and 4.14 ppm, respectively, in ethyl acetate. In quaternary system of these compounds the chemical shifts also change due to mutual influence of components on electronic environment of their molecular groups. It is clearly seen on Fig. 1 that linewidths are such that peaks of (area D) CH3 of acetic acid and CH3CO of ethyl acetate and also (area E) CH3 of ethanol and second CH3 group of ethyl acetate could not be separated, while methylene resonances are well resolved (areas D and C). As a result, to determine the values of peak areas for each specific group, it is necessary to take into account all the areas selected on the spectrum: A, B, C, D, and E. (see Fig. 1). Thus the five parameters that are equal to the areas of abovementioned regions could be extracted from each spectrum. The derivation of formulas connecting these parameters to molar fractions of solution components is presented below.

5 4 3 2 1 0 [ppm]

Figure 1 Typical NMR spectrum of the mixture acetic acid-ethyl alcohol-ethyl acetate-water

The region A (Fig. 1) contain peaks from all OH groups of all compounds in the system; regions B and C contain peaks from CH2 groups of ethyl acetate and ethanol, respectively; region D contain peaks from CH3 groups of ethyl acetate and acetic acid; and finally region E contain peaks from CH3 groups of ethyl acetate and ethanol. These regions have areas SA SB, Sc, SD and SE, respectively. Each area is proportional to the sum of areas of peaks St of individual compounds. The area of peak St is equal

Si = CNj m , (4)

to the product of number of molecules of j-th compound Nj, the number of chemically equivalent protons in molecule n corresponding to this peak and spectrometer specific constant C.

For the methylene group n is equal to 2, for methyl group - to 3, for OH of acetic acid and ethanol to 1 and for OH of water - to 2.The area of !-th region thus is the sum of several peak areas from different compounds (assuming that only peaks for same molecular groups could be overlapped):

Si = CNini + CN2ni + ••• (5)

By introducing the constant C' = CNtot, where Ntot is the total number of all molecules of all compounds in solution, one can express the area of ! -th region via the molar fractions Xj of compounds, which have peaks in this region:

Sk = C' ^m + C' m + - = C'x.m + C'x2nt + - (6)

! Ntot Ntot 1 1 1 ! 1 W

By combining the expressions for areas of all regions and the condition, that sum of all molar fractions is equal to 1, we obtain a system of equations for unknown molar fractions Xj and constant C'. For the system acetic acid - ethanol - ethyl acetate — water the equations are written in following way:

rSA = C '( xEtOH + XAcO$ + 2! 'XH20

SB = 2 C xEt0Ac

S! = 'XEtOH (7)

SD = 3 C XXAcOH + XEtOAc) SE = 3 C '(XEtOH + XEtOAc) ,.1 = !h20 + XEtOH + XAcOH + XEtOAc

This system contains one unnecessary equation that should be eliminated, because only five variables are unknown. We suggest neglecting the equation with area of region with smallest value of integral, since it introduces greater experimental uncertainty than other regions. After the analysis of spectra (see Fig. 1) we decided to eliminate equation for region B containing peak of CH2 group of ethyl acetate.

Finally, molar fractions of compounds in system acetic acid - ethanol - ethyl acetate — water could be found from areas of regions using following formulas:

x

3 Sr

EtOH

!

EtOAc

X

AcOH

KXH20

!E + !D + 3!!

: 2Se - 3Sc

!E + !D + 3!!

-2Se + 2 SD + 3 Sc

!E + !D + 3!!

! 3Sr + 3 Sa

(8)

Sr + Sn + 3Sa

Using Eq. (8) we have obtained the molar fractions for compounds in quaternary system acetic acid -ethanol - ethyl acetate — water, which were compared to values obtained by gas chromatography. The twenty test compositions were analyzed both by NMR and GC. The deviations do not exceed the experimental uncertainty of methods.

The approach described above is applicable for any system with sufficient number of separate regions. A system of equations similar to Eq. (7) can be written for such a system taking into account the peculiarities of it's composition. Data using the NMR method are published in the works [72,73].

2.4. Cloud-point technique

Cloud-point technique was used to study solubility and critical phenomena in the acetic acid -ethyl alcohol - ethyl acetate - water system at 313.15 K, 323.15 K and 333.15 K. A special installation was designed for this purpose Fig. 2.

Figure 2 Installation for Cloud-point technique 1-transparent thermostat; 2-magnetic stirrer; 3-flask; 4-microburette; 5-thermometer

Binary or ternary mixtures of known overall composition within the homogeneous region were prepared by gravimetric method in round-bottomed flask (100 ml) using analytical balance Shinko VIBRA HT-120CE (Japan) with an accuracy of 0.001 g. Initial compositions were chosen so that experimental points were placed on the same distance on the bimodal surface.

Titration was performed in liquid thermostat at continuous stirring by magnetic stir bar. Bidistilled water as a titrant was added to initial mixtures using 2 ml microburette. Accuracy of titrant volume measurement was estimated to be 0.05 ml. Turbidity of the solution to be titrated persisting during at least 2 min was considered to be a final point of titration. Taking into account a volume of mixtures (20-50 ml) and volume of titrant drop (0.02 ml) accuracy of concentration determination was estimated to be 0.001 mole percent. Taking into consideration another possible factors affecting on accuracy (such as purity of chemicals, thermostatic control uncertainty and others) maximum error of an experimental data was appreciable to be ±0.002 mole fraction of the component. Next, the molar fractions of all the components of the solution were calculated. Taking into account the experimental temperature (on average 293.15 K), the following water density value d425 = 0.9971 g/ml was used [74].

2.5. Methods of calorimetric measurements

2.5.1. Experimental determination of the heats of mixing

The method for determining excess enthalpy met the accepted requirements of thermochemical studies and was similar to the procedures described in detail earlier in the works [75,63]. Below we give a brief description of the method and its features.

Excess molar enthalpies have been measured with the C80 calorimeter (Setaram Instrumentation, France, 2010) Research Park at St. Petersburg University « Thermogravimetric and Calorimetric Research Centre». The C80 calorimeter is a calorimetric chamber which is adapted to a reversal fitting, capable of 180° rotations. This automatism allows enhancing the mixing of liquids.

Within the calorimetric block there are two Platinum probes: a Pt100 Platinum probe is to measure the calorimetric sample temperature, and another probe, a Pt200 Platinum one, is to control the temperature of the block. The uncertainty in the temperature is less than 0.05 K.

For our studies we have used membrane mixing cells. It looks like a cylindrical body with two compartments, which are isolated from each other with a membrane. One substance is placed in the lower compartment (2.5 ml), the other in the upper compartment (3.5 ml). A sharp-edged impeller, connected to a command rod, movable along the central shaft of the cell and the cell well, is used to break the membrane in order to mix the substances.

A Sartorius MSU225S analytical balance (precision ±0.1 mg) has been used to weight the pure component masses. The uncertainties in the mole fractions were less than 0.0002. Two substances under the study have been loaded into the compartments of the cell separated with the aluminum membrane. The measurement and reference cells have been loaded identically. Then the cells have been introduced into the calorimeter. The temperature of the C80 calorimeter has been stabilized at the required set point. The temperature and heat flow signals have been being kept stable during at least 30 min. Mixing has been initiated via lowering the command rod of the measurement cell and breaking the separation membrane. Then the rod has been returned to an initial state. After the end of the experiment displayed by thermal stability, the correction on rod movements has been done, i.e. the rod has been lowered and raised one more time. Integration of the heat flow peaks yields the excess enthalpy.

After heat flow and temperature stabilization, the similar actions have been done with the reference cell: in this case the values of the enthalpy have to be taken with a reversed sign. Thus measurements for each composition have been repeated at least two times.

Heat effects (J) were calculated by integrating the peaks of the heat flow signal (mW) over time in the Calisto program using a tangential-sigmoid baseline (Fig. 3.)

The method was verified by measuring the mixing heat in the standard n-hexane-cyclohexane system.

Figure 3 Example of a signal obtained on a C80 calorimeter and its processing in the Calisto program. (a mixture of acetic acid + ethyl alcohol)

Heat of mixing in the Quaternary systems were determined by mixing of two binary systems. In the lower part of the cell was placed a mixture of acetic acid-ethyl acetate, and in the upper part - a mixture of ethyl alcohol-water. Binary mixtures were prepared in such a way that the composition of the final Quaternary systems corresponded to the state of chemical equilibrium and the heat from the possible reaction would not introduce a significant error. The amounts of substances were calculated based on the chemical equilibrium of the ethyl acetate synthesis reaction at 313.15 K

The average error in determining the mixing heat, according to the results of test experiments, did not exceed 2 %.

2.5.2. Experimental determination of the heat of a chemical reaction

The method for determining the heat of a chemical reaction is similar to the method for measuring the heat of mixing.

Ion-exchange resin KU-2 was used as a catalyst for the esterification reaction. To get heat effects in the reacting system, the initial binary mixture of ethanol and acetic acid was prepared in molar ratio 1:1. Catalyst KU-2 was placed in the lower part of the membrane mixing cell, and the initial binary mixture was placed in the upper part of the cell. Mass ratio of the catalyst and the binary mixture was 1:20. To get heat effects in the reacting system, the initial binary mixture of ethanol and acetic acid was prepared in molar ratio 1:1. Catalyst KU-2 was placed in the lower part of the membrane mixing cell, and the initial binary mixture was placed in the upper part of the cell. Mass ratio of the catalyst and the binary mixture was 1:20. The experiment to determine the heat of a chemical reaction was carried out for an average of about 40 hours. After the experiment, the composition of the final chemically equilibrium mixture in each cell of the calorimeter was determined by NMR. An example of a thermogram obtained during the experimental determination of the heat of a chemical reaction is shown in the Fig. 4.

-30-

-35-

-40-

-150 5 10 15 20 25 30 35

Time (h)

Figure 4 Example of a thermogram: experimental determination of the heat of a chemical reaction

2.5.3. Experimental research of solubility by calorimetric analysis

The solubility in the ethyl acetate - water binary system was studied using the calorimetric titration method. The calorimeter NANO ITC 2G (TA Instrument) Research Park at St. Petersburg University « Thermogravimetric and Calorimetric Research Centre» was used for the experiment. The device consists of a measuring unit (located in a sealed case filled with dry nitrogen) and the buret assembly.

The buret assembly ensures that the titrant is accurately fed into the reaction vessel in specified portions at a specified time interval, while the reaction system is simultaneously stirred. A schematic representation of the measuring unit and the buret assembly is shown in Fig. 5.

5

Figure 5 Schematic representation Nano ITC 2G. 1 -buret assembly; 2 - TED-controlled block; 3 -Sample cell; 4 - Reference cell; 5 - Control heater

During the experiment, one of the components of the binary mixture, bidistilated water, in an amount of 1.4 ml was placed in the reference and reaction cell. Titration with ethyl acetate was performed with a 250 syringe installed in the buret assembly at a temperature of 313.15 K. Ethyl acetate was introduced in portions of 0.86 p,L at intervals of 1000 seconds with stirring at a speed of 300 rpm. The total duration of the experiment was 34-36 hours.

As a result of the experiment, thermograms were obtained that characterize the dependence of the heat flow on time (Fig. 6). The measurement error of the heat flow was 0.02 mW. To estimate the measurement error, idle experiments were performed: the error is about 3.6% for the minimum values of the heat flow.

Chapter 3. Solubility and critical states for the quaternary system acetic acid-ethanol-ethyl acetate-water at isothermal conditions

Solubility in the binary system ethyl acetate - water

Solubility in the ethyl acetate - water binary system was determined by several methods: gas chromatographic analysis, cloud-point technique and calorimetric analysis. All studies were conducted at a temperature of 313.15 K and atmospheric pressure.

Fig. 6 shows a thermogram obtained from a calorimetric study of the solubility of ethyl acetate in water.

Figure 6 Change in heat flow during water titration with ethyl acetate (313.15)

Fig. 6 shows first the process of dissolution of ethyl acetate in water, and then the process of delamination. The first part of the peaks (injections 1 - 88, concentration range 0 - 0.0175 mole fractions) relate to the exothermic process of dissolving ethyl acetate in water. All subsequent peaks respond to the endothermic splitting process.

Note that the integration of the heat flow allows you to simultaneously obtain data on the change in enthalpy for each injection of ethyl acetate. Numerical values were normalized to the amount of ethyl acetate per injection. The dependence of the enthalpy on the molar fractions of ethyl acetate in water is shown in Fig. 7. Experimental data on the solubility of ethyl acetate in water at 313.15 K obtained by the calorimetric method are shown in Table 3. Fig. 7 also shows data on solubility obtained by other methods (this work and literature data). All solubility values, including

those obtained by calorimetric titration, are in good agreement: the range of values is 0.0028 mol. fraction.

Figure 7 Dependence of the enthalpy change on the change in the concentration of ethyl acetate in the binary system at 313.15 K, comparison of data on the solubility of ethyl acetate in water obtained by different methods. Literature data [70]

This method of calorimetric titration was applied only to the study of the binary system, because of the complexity and duration of experiments, especially for the purpose of obtaining solubility data. At the same time, we note that this method allows not only to obtain solubility data, but, first of all, gives a detailed description of the thermochemical behavior of the system during the solubility-splitting processes. Let's take a closer look at some elements of the titration process. The first 34 injections (Fig. 6) correspond to the process of solubility ethyl acetate in water. The integral values of the corresponding peak areas, converted to kJ/mol, were extrapolated to zero concentration. Thus the values of the enthalpy of solubility of ethyl acetate in water were obtained, A!sol:

A!sol = 8,4

кДж

моль

The results are shown in Fig. 8.

10 9

o o o O

ju 6 o

£

X

<3

5

4

3

2

1

0 0

y = -166.53x + 8.3552 R2 = 0.44776

0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004 0.0045

mole fraction

Figure 8 Data on the thermal effect of dissolution of each injection of ethyl acetate, extrapolated to zero

Data on solubility in the binary system ethyl acetate - water at 313.15 K, obtained by different methods, are also presented in Table 3, and, additionally, in Fig. 9. colored dots indicate the concentration values corresponding to the splitting.

Table 3 Solubility in the ethyl acetate - water binary system at 313.15 K

Concentrations, mole fractions

Ethyl acetate Water

Cloud-point technique

0,819 0,181

0,016 0,984

Gas chromatography method

0,838 0,162

0,017 0,983

Calorimetric analysis

- -

0,015 0,985

Literature data [70]

0,844 0,156

0,014 0,986

Figure 9 Comparing data on solubility in the ethyl acetate — water binary system at 313.15 K obtained by different methods: calorimetric (red dot), titrimetric (yellow), and gas chromatographic (purple). Literature data [70] (green dot)

In the analysis of solubility at temperatures of 323.15 K and 333.15 K, the literature data on the ethyl acetate - water binary system were used in this work (Table 4).

Table 4 Literature data on liquid - liquid equilibrium in the ethyl acetate - water system [70]

T, K Concentrations, mole fractions

Water phase Organic phase

Ethyl acetate Water Ethyl acetate Water

323.15 K 0,014 0,986 0,774 0,226

333.15 K 0,013 0,987 0,759 0,241

Solubility in ternary systems acetic acid-ethyl acetate-water and ethanol-ethyl acetate-water at\ 313.15 K

When studying solubility in ternary component systems acetic acid - ethyl acetate - water and ethanol - ethyl acetate - water, binary mixtures of substances that are soluble in each other, namely alcohol - ether and acid-ether, were selected as initial solutions, which were titrated with bidistilled water at a constant temperature. That is, the initial homogeneous mixtures were titrated "for turbidity»: the compositions corresponding to the binodal curve were recorded at the moment when the solution became cloudy (visual observation), as a result of the formation of a new second phase. The compositions of binary mixtures were selected in such a way that the composition points obtained from the titration results were fairly evenly placed on the binodal.

The results obtained in determining the solubility in the system acetic acid-ethyl acetate-water and ethanol-ethyl acetate-water by isothermal titration at 313.15 K are presented in Table 5 and Table 6 and Table 6. Solubility curves based on experimental data are shown in Fig. 16 and 18. The data is published in the paper [76].

Table 5 Experimental data on solubility in the ternary component ethanol-water-ethyl acetate system at 313.15 K

Concentrations, mole fractions

Ethanol Ethyl acetate Water

0,155 0,204 0,641

0,132 0,130 0,737

0,165 0,258 0,578