Process design and intensification of

multicomponent azeotropes special

distillation separation via molecular
simulation and system optimization
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panelChunliang Liu, Jianhui Zhong, Ranran Wei, Jiuxu Ruan, Kaicong Wang, Zha
oyou Zhu, Yinglong Wang, Limei Zhong
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ABSTRACT
This work provides an overview of distillation processes, including process design
for different distillation processes, selection of entrainers for special distillation
processes, system integration and intensification of distillation processes,
optimization of process parameters for distillation processes and recent research
progress in dynamic control strategies. Firstly, the feasibility of using
thermodynamic topological theories such as residual curve, phase equilibrium line
and distillation boundary line to analyze different separation regions is discussed,
and the rationality of distillation process design is discussed by using its feasibility.
Secondly, the application of molecular simulation methods such as molecular
dynamics simulation and quantum chemical calculation in the screening of
entrainer is discussed for the extractive distillation process. The thermal coupling
mechanism of different distillation processes is used to explore the process of
different process intensifications. Next, a mixed integer nonlinear optimization
strategy for the distillation process based on different algorithms is introduced.
Finally, the improvement of dynamic control strategies for different distillation
processes in recent years is summarized. This work focuses on the application of
process intensification and system optimization in the design of distillation
process, and analyzes the challenges, prospects, and development trends of
distillation technology in the separation of multicomponent azeotropes.

Introduction
In the chemical industry, many mixtures consist of multiple components, some of
which have very close boiling points [1]. This makes traditional single-component
rectification separation very difficult or even impossible. These highly complex
mixtures can be efficiently separated into pure components by means of
multivariate azeotrope separation and purification. By separating components
close to the boiling point, impurities are removed, resulting in a purer product [2].
This is especially important for the pharmaceutical and food industries, where
purity is critical to the safety and efficacy of drugs and foods. As a common and
important separation technique, distillation plays an irreplaceable role in the
chemical industry. By utilizing the differences in boiling points of different
components, rectification can achieve efficient separation and purification of
various mixtures and is widely used in petrochemical, pharmaceutical, food and
chemical fields [3]. With the continuous development of science and technology,
the optimization and innovation of the distillation process are also carried out
continuously.
For the multivariate azeotropic system, it cannot be separated by the conventional
distillation process, and it is often separated and purified by special rectification.
Special distillation can be divided into azeotropic distillation, reactive distillation,
membrane distillation, extractive distillation, pressure swing distillation, and other
methods [4]. Azeotropic distillation is a rectification process carried out at
atmospheric pressure for the separation of two or more components that are close
to or completely azeotropic. This is done by adding auxiliary agents or changing
operating conditions, adjusting the temperature and pressure of the system so that
the azeotropic components in the liquid mixture undergoes material transfer,
thereby achieving their separation [5]. Reactive distillation is a separation
technique that combines chemical reactions with the rectification process. By
introducing the reactants into the rectification column, the reaction and separation
are carried out simultaneously by utilizing the difference in vapor–liquid equilibrium
of different components. Membrane distillation is an emerging low-cost and high-
energy membrane separation technology that uses hydrophobic microporous
membranes as the mass transfer driving force for membrane separation. It
realizes the selective separation of the feed through the difference of the affinity of
each component, and the mass transfer resistance. Compared with traditional
distillation technology, membrane separation technology has the advantages of
high efficiency and high selectivity. It should be noted that in the application
process of membrane separation technology, the process design needs to be
carried out according to the specific mixture composition and separation
requirements, and the solvent selection and operating conditions are reasonably
matched to obtain the best separation effect [6]. Pressure-swing distillation
achieves separation by changing the operating pressure and adjusting the balance
of components between the liquid and gas phases. The principle of extractive
distillation is to use the selective affinity between the extractant and the target
components to achieve separation. In the distillation column, the extractant enters
the top of the column, mixes with the raw material, and extracts the target
component from the raw material through selective interaction with the target
component. Then, at the bottom of the tower, by changing the temperature,
pressure, or other operating conditions, the separation of the target component
and the extractant is achieved so as to obtain the pure target substance [7]. For
the separation of azeotropes, it is very important to choose a suitable separation
process. A good process can significantly reduce the energy consumption of the
process and greatly improve the efficiency of separation. This manuscript mainly
reviews how the two most common distillation methods in industry, such as
extractive distillation and pressure swing distillation, are designed. For extractive
distillation, the appropriate extractant is not only related to the separation of
azeotropes or near-azeotropes, but also closely related to economic and
environmental benefits [8]. But how to choose the most suitable separation solvent
from thousands of solvents? This manuscript introduces the enormous role
molecular simulations play in screening solvents. Molecular simulations can
evaluate and predict the interaction strength, selectivity, and performance of
compounds. By combining experimental data and molecular simulation results, the
process of extractant screening can be accelerated, reducing experimental cost
and time. The application of molecular modeling to extractant screening can
provide an understanding of molecular-level interactions, which can aid in the
design and optimization of more efficient and sustainable extraction processes [9].
The world energy distribution is that 21%, 28%, 19%, and 32% of the world's total
energy consumption are commercial, transportation, residential and industrial,
according to the report of Sholl and Lively [10]. The energy consumption in the
separation process accounts for about 45% to 55% of the total energy
consumption in the industry. Because of its simple operation and easy control,
distillation is the most widely used industrial method for separating liquid
mixtures in many chemical and other industries, such as perfume and
pharmaceutical processing, and the energy consumption of the distillation process
is approximately 49% of the total separation process. Distillation is the most widely
used separation technology, but due to the complexity of working conditions and
mixture properties, there are still problems of low separation efficiency and large
energy consumption [11,12]. The optimization of distillation process operation
parameters is a method to achieve energy saving and consumption reduction by
optimizing the parameters to make the process reach the optimal operation state
based on the determined distillation sequence and equipment structure [[13], [14],
[15]]. It is of great significance for the separation and purification of organic matter,
green energy conservation, and directly affects the final quality and cost
advantages of products [16]. With the proposal and promotion of the concept of
sustainable development, the standards for comprehensive utilization of resources
and environmental governance are more stringent, posing new challenges to
separation of science and technology and providing good opportunities for the
emergence and development of advanced separation science and technology [17].
In the chemical production process, the operation performance and control ability
of the device are the keys to safe and stable production. With the change of time,
the operation of the device has uncertainty and complexity, and the steady-state
model cannot deal with these problems. In order to meet the performance
requirements of factories, it is an inevitable trend to develop dynamic control
technology. From the perspective of economy and safety, robust dynamic control
is of great significance to the production and development of chemical industry
[18,19]. Research on effective control strategies of distillation process is an
important part of distillation design to ensure strong control performance in the
face of inevitable interference [[20], [21], [22]].
The distillation process has always played a key role in the separation of
azeotropes. We cover the latest developments in many aspects of distillation
technology, including distillation process design, extractant screening for extractive
distillation, distillation process enhancement mechanisms, distillation process
parameter optimization, and process dynamic control strategies. First, the design
rules of different distillation processes are expounded, and the specifications that
need to be paid attention to in distillation design are explained in detail for the
processes of extractive distillation and pressure swing distillation; secondly,
considering that the most important step in the design process of extractive
distillation is the selection of extractant, we have deeply studied the application of
quantum chemical calculations and molecular dynamics simulations in screening
suitable entrainers; thirdly, we investigated the strengthening mechanism of the
distillation process through coupling mechanisms such as thermal integration;
based on two optimization algorithms, the optimization method of process
parameters in the distillation process was studied; we also summarized the latest
progress in dynamic control strategies for different distillation processes. This
study explores the challenges, foregrounds, and opportunities of multicomponent
azeotrope separation and distillation technology. Table 1 summarizes some
representative research achievements in recent years.
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Section snippets
Process Design for Distillation Process
The process design of a distillation process needs to consider several aspects to
ensure effective separation and efficient operation. Firstly, a comprehensive
property analysis of the components in the mixture to be separated is required,
including boiling point, relative volatility, density, solubility, etc., which helps to
determine the appropriate operating conditions and design parameters [32].
Simultaneous thermodynamic analysis is the key to the design of the distillation
process. These

Selection of Entrainer for Distillation Process

For the most commonly used extractive distillation process, the choice of
extractant plays a crucial role in the success and efficiency of the extractive
distillation process. The extractant is the medium that mixes with the raw materials
and interacts with the target components in extractive distillation. They have the
ability to specifically interact with target components, thereby enabling selective
extraction and separation of target components. Therefore, careful consideration
needs to be
Intensification process of heat integration
distillation
In process intensification, heat integration process, and intermediate reboiler
process are commonly used energy integration technologies to improve energy
utilization efficiency and reduce energy consumption. Thermal integration includes
two parts: full thermal integration and partial thermal integration. Full thermal
integration refers to achieving maximum recovery and reuse of heat in the
process. By transferring heat from a high-temperature fluid to a low-temperature
fluid, energy is fully

Process Parameter Optimization of Distillation

Process
With the continuous extension of the scale of chemical engineering research
problems, more decision variables are included in the synthesis and optimization
of chemical processes, multiple optimization objective functions are introduced,
and the operation variables (continuous variables) and design variables (discrete
variables) are simultaneously optimized, thus increasing the complexity of the
problem, which makes it difficult for deterministic algorithms to solve such
problems efficiently.

Dynamic Control of Distillation Process

Many pieces of equipment in the petrochemical industry rely on control systems to
make the equipment run stably. In the petrochemical industry, control can be used
to control the adjustment of PH value of the acid base and the automatic
instrument control of the ethylene plant for the production of propylene,
butanediolene, and ethylene [167]. Many pieces of equipment in the petrochemical
industry rely on proportional integral differentiation (PID) control system to make
the equipment run

Conclusions
In this study, the latest research progress in process design, entrainer selection,
process integration, optimization, and dynamic control strategy of distillation
separation of multicomponent azeotropes is reviewed. Distillation technology has
always occupied a very important position in the field of azeotrope separation.
Optimal process design can achieve efficient separation while reducing economic
costs and environmental impact. The emergence of process simulation software
greatly

Declaration of Interest
 The authors declare that they have no known competing financial interests or
personal relationships that could have appeared to influence the work reported in
this paper.

CRediT Authorship Contribution Statement

Chunliang Liu: Conceptualization, Data curation, Software, Writing – original draft.
Jianhui Zhong: Investigation, Software. Ranran Wei: Conceptualization. Jiuxu
Ruan: Conceptualization. Kaicong Wang: Writing – review and editing. Zhaoyou
Zhu: Supervision. Yinglong Wang: Writing – original draft, Writing – review and
editing. Limei Zhong: Resources.

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