The subject content and development trends of chemical engineering

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:) It is an engineering discipline that studies the common laws of chemical and physical processes carried out in the production of the chemical industry and other process industries. These industries include the petroleum refining industry, metallurgy industry, building materials industry, food industry, papermaking industry, and others. Starting from basic raw materials such as oil, coal, natural gas, salt, limestone, other ores, as well as food, timber, water, and air, they use chemical or physical processes to alter the composition, properties, and state of these materials, thereby turning them into a variety of high-value products such as steel, iron, aluminum, pulp, and so on. A chemical process refers to a situation in which substances undergo chemical changes; for example, the production of high-octane gasoline is a chemical reaction process. Physical processes refer to changes in the composition, properties, state, and energy of matter that occur without chemical reactions; for example, crude oil is separated through distillation to produce products such as gasoline, diesel, and kerosene. As for other fields such as ore smelting, fuel combustion, biological fermentation, leather manufacturing, seawater desalination, etc., although the forms of these processes vary, they can all be broken down into the aforementioned chemical and physical processes. In fact, chemical processes often occur simultaneously with physical processes. For example, catalytic cracking is a typical chemical process, but it is accompanied by heating, cooling, and separation; moreover, during the reaction, flow, heat transfer, and mass transfer also occur. All these processes can be studied through chemical engineering, so that their patterns can be understood and explained; they can then be applied to the development, design, and operation of production processes and equipment in order to optimize them and improve efficiency. A common feature of the above industrial productions is that, from the laboratory to industrial production, especially large-scale production, the issue of scaling up the equipment must be addressed. An important way to increase production scale and improve economic efficiency is the scaling up of facilities, in order to save on investments, reduce consumption, minimize land use, and cut labor costs. However, certain parameters that can be achieved in large-scale devices are usually lower than those obtained from small-scale tests, as the scaling up of the device leads to changes in the factors and conditions related to physical processes such as material flow, heat transfer, and mass transfer. This effect, which originates from the amplification process, has long been generally referred to as the “amplification effect”; it encompasses the influence of many identified and unidentified physical factors (or engineering factors). An important task in chemical engineering is to study the effects of engineering factors on processes and devices, particularly those effects that occur during scale-up, in order to address issues related to the theory and methods of process development, device design, and operation. It is based on the principles of physics, chemistry, and mathematics, and makes extensive use of various experimental methods in conjunction with them to solve problems in industrial production. Subject Content: Chemical engineering includes,,,,,,,, process dynamics and control, among other aspects. Unit operations: The physical processes involved in the production of various chemical products can be reduced to a limited number of basic processes, such as heat transfer (heating and cooling), distillation, absorption, evaporation, extraction, crystallization, drying, etc. These basic processes are called unit operations. Research on unit operations yields common results that can be used to guide the production of various products and the design of chemical processing equipment. At the beginning of the 20th century, although understanding of chemical engineering was limited to unit operations, a brand new field was established, and chemical engineers who pursued new types of careers emerged. These chemical engineers differ from previous workers in the chemical industry; they have received training in the specialized field of chemical engineering, which enables them to make the design, manufacturing, and operational control of chemical production processes and equipment more efficient. To this day, the study of various unit operations retains great theoretical significance and practical value. Moreover, to meet new technical requirements, new unit operations continue to emerge and be incorporated gradually. Chemical Reaction Engineering: Chemical reactions are a core aspect of chemical manufacturing; they determine the yield of products and have a significant impact on production costs. Nevertheless, its complexity hindered systematic research on it in the early stages. Until the mid-20th century, building on the research findings regarding unit operations and mass transfer processes, several common issues were identified in various reaction processes such as oxidation, reduction, nitration, and sulfonation, including those related to conditions within the reactor and the stability of the reactor. The study of these problems, as well as their various effects on reaction kinetics, has given rise to a new branch of science; this in turn has enriched and developed the content and methods of chemical engineering. The transfer process is the common foundation of unit operations and reaction engineering. The physical processes that take place in various unit operation equipment and reaction vessels are nothing more than three types of transfer: , and . For example, fluid transport based on momentum transfer, gas flow distribution in reactors ； Operations based on heat transfer, such as the removal of heat of polymerization in the polymerization reactor; operations based on mass transfer, such as the diffusion of reactants and products within the catalyst. In some processes, two or more types of transfer phenomena occur simultaneously, such as moisture addition and removal in gases. As a branch of chemical engineering, transfer processes focus on studying the rates of these three types of transfer as well as their interrelationships, thereby linking together phenomena that are essentially similar but exhibit different forms. Chemical thermodynamics also serves as the theoretical foundation for unit operations and reaction engineering; it studies the direction and limits of transfer processes, providing the basic data needed for process analysis and design. Therefore, the disciplinary branches of chemical engineering can also be divided into two levels: unit operations and reaction engineering are more directly oriented toward industrial practice, while transport processes and chemical thermodynamics support the first two branches from a fundamental research perspective. These two levels enable a close integration of theory and practice. As production scales expand and large amounts of resources and energy are consumed, issues that were not considered important earlier are gradually becoming more prominent. For example, energy utilization issues and design and operation optimization problems are very important in large-scale production. Since the various process units in a chemical process influence and restrict one another, it is essential to consider the chemical process as an integrated system and establish the concept of overall optimization. As a result, the discipline of systems engineering developed rapidly within chemical engineering, achieving significant results and giving rise to chemical engineering systems engineering. It is the product of combining systems engineering methods with the two disciplinary fields of unit operations and chemical reaction engineering. To maintain rational and optimized operations, the dynamic characteristics of processes and control methods are also important aspects of chemical engineering. Objects and methods of research: The objects of study in chemical engineering are usually very complex, as evidenced by the following: ① The complexity of the process itself: it involves both chemical and physical aspects, and these often occur simultaneously, influencing each other. ②Complexity of the system: it includes both fluids (gases and liquids) and solids, with multiple phases often coexisting. Fluid properties can vary significantly, such as low viscosity and high viscosity, as well as Newtonian and non-Newtonian behavior. Sometimes, significant changes in physical properties occur during the process, such as the transition of the reactant system from low viscosity to high viscosity during polymerization. ③The complexity of boundaries in fluid flow: The varying geometries of equipment such as trays, impellers, and baffles, as well as the diverse shapes of fillers, result in complex flow boundaries that are difficult to determine and describe. Research methods in chemical engineering: Due to these characteristics of the objects of study in chemical engineering, analytical methods often fail to be effective in chemical engineering research. This also led to the development of its own research methods (chemical engineering research methods), some of which were not original but were adapted from other fields. Early research methods: The main approach in the early days of chemical engineering was to explore the laws of scaling up through multi-level, progressively scaled-up experiments. This empirical approach is costly, time-consuming, and inefficient, and people have been striving to get rid of this situation. But to this day, for some particularly complex processes about which very little is known, one still has to turn to this method, or partially to it. In the research methods of the early 20th century, a commonly used approach was to reduce the numerous variables that influence a process, through similar transformations or dimensionless analysis, into a smaller number of dimensionless groups. Model experiments were then designed to determine the relationships among these groups of numbers. Using these two methods to summarize the experimental results is very effective. For reaction processes, step-by-step empirical methods have been used for a long time. Since it is impossible to satisfy both geometric similarity and physical quantity similarity while meeting the conditions of chemical similarity, the approach of using dimensionless groups to relate experimental results in order to obtain the laws governing the reaction process becomes ineffective. Research methods after the 1950s were not widely applied in the field of chemical reaction engineering until that decade. The impact of this method spread to other branches of chemical engineering, leading to an innovation in research methods. But even with this approach, experimental work remains crucial; fundamental data must be obtained through experiments, models need to be validated through experiments, model parameters have to be determined experimentally, and the reliability of models must be verified through experiments. The foundation of various chemical engineering research methods is experimental work, and regardless of the method used, efforts should be made to ensure that the experiments are effective, reliable, and straightforward to carry out. Various theories, methods, and the use of computers are all aimed at enabling experimental work to reveal the laws governing phenomena more effectively, while saving time, labor, and costs. In the application of the aforementioned methods, the concepts of process decomposition (breaking down a complex process into two or several simpler processes), process simplification (ignoring minor factors in a more complex process in order to simplify it using simpler processes), and process integration (combining the separately processed components back together after they have been broken down) are reflected in various ways. Important role: The scale of modern industrial production often requires that a single facility have an annual output of hundreds of thousands of tons or more. These devices inevitably face numerous engineering challenges, and even a slight drop in performance can result in significant financial losses. Advances in science and technology are constantly creating new products and new processes. However, these new products must rely on engineering methods to be produced industrially, and new processes must be economically and technically viable in order to replace the existing ones. The issues of scaling up the aforementioned devices and the industrialization of new products and new processes all fall within the scope of chemical engineering research. The important role of chemical engineering in the national economy is quite evident. For example, harmful components such as sulfur and nitrogen oxides in large amounts of flue gas are removed before release. After meeting the requirements in the laboratory, to achieve the purification of large volumes of flue gas on an industrial scale, it is necessary to consider the economic viability and feasibility of such large-scale purification, and the focus is quite different from that of laboratory research. In chemical manufacturing as well, highly pure products are required as raw materials; for example, it is often necessary that the impurity content in the precursor monomers be at the level of a few parts per million (ppm). For laboratory work, this is not necessarily difficult, and small experiments do not require economic metrics for purification. However, requiring large-scale production facilities to achieve this with low consumption and using simple and feasible equipment is a completely different challenge. The resolution of such problems depends on the study of unit operations. If the optimal temperature, concentration, and reaction time are determined in the experimental reactor, satisfactory results are obtained. During the amplification process, due to the uneven flow, the residence time (reaction time) of the material in the reactor becomes uneven, deviating from the optimal reaction time. Due to the heat of reaction, the temperature unevenness that occurs in large-scale devices as a result of heat transfer limitations causes the reaction temperature to deviate from the optimal temperature. Uneven temperature inevitably leads to uneven concentration. These effects cause a decrease in efficiency in large-scale devices, an increase in product costs, and may even render them devoid of industrial value, making them unsuitable for use in production. This example illustrates the role and significance of research in chemical reaction engineering. Another example is industrial production, where heating and cooling are sometimes required to meet the needs of various processes. In the laboratory, energy consumption metrics are not important, but in large-scale production, proper utilization of heat must be taken into account; heating and cooling should be matched as much as possible, and low-grade thermal energy should be utilized to the fullest extent. How to make rational use of heat and how to properly arrange numerous devices are issues that cannot be resolved through experimental methods; rather, they are addressed through the study of chemical process engineering. The above cases illustrate the urgent need for chemical engineering knowledge as production scales up. The achievements of chemical engineering have enabled these problems to be solved to a considerable extent. Development Direction: Chemical engineering is faced with new challenges and new issues, and the process of addressing these new issues will inevitably lead to the development of the field of chemical engineering. Its scope of research and application prospects have far exceeded its original meaning. Chemical engineering is developing in two directions: on the one hand, as the discipline matures, it continues to advance in terms of depth ； On the other hand, there is a continuous penetration into new fields, with the aim of researching and solving new problems in those fields. In terms of the in-depth development of this discipline, in order to gain a thorough understanding of the laws governing these processes, systematic and in-depth research is conducted on the transfer mechanisms of multiphase systems, highly viscous fluids, and non-Newtonian fluids that are commonly encountered in chemical engineering. These studies not only help solve problems in traditional research fields but also contribute to understanding emerging topics such as blood flow in the human body. The study of multiple steady-state stability problems in the reaction process is not only necessary for reactor design and operation, but also represents a contribution to the research on the stability of nonlinear systems from another perspective. To make the design of large-scale devices faster and more reliable, various physical property parameters of materials, thermodynamic parameters and thermochemical parameters, as well as phase equilibrium and chemical equilibrium data were studied, thereby promoting a closer integration of chemical engineering thermodynamics with practical applications. In terms of research methods, mathematical modeling techniques continue to improve. Complementing these are methods such as experimental design, data processing, model selection and identification, as well as model parameter estimation, which are based on statistical theory and information theory. To carry out process simulation and multi-scenario calculations, various computer simulation systems have been developed, model libraries and databases have been established, and the approach has evolved from steady-state simulation to dynamic simulation required for process control. Penetration into new fields is an objective necessity as well as a driving force for the development of disciplines. Historically, chemical engineering has developed through the development and optimization of various new processes, driven by the scaling up of facilities in fields such as inorganic chemicals and petrochemicals, including technologies for large-scale radial and catalytic cracking. In addressing the treatment of multi-component reactant systems in petroleum processing, a lumped kinetic approach was developed, which in turn can be used for such treatments. As it penetrated the materials industry, the application of principles from chemical engineering to polymerization processes emerged, and research on the transfer properties of highly viscous systems became a topic with practical applications. With the advancement of biotechnology, techniques such as ultrafiltration have emerged to address issues like those in bioreactors and the separation of biological agents. The energy shortage has led to increased attention being paid to the use of low-temperature heat sources, giving rise to new types. To protect the environment as well as to exploit marine resources, there is a need to develop separation techniques for low-concentration mixtures, which has led to the emergence of new separation methods such as foam separation. By applying the principles and methods of chemical engineering to the study of physiological processes in the human body, such as the distribution of drugs within the body, as well as to the development of artificial organs, a new field of research known as biomedical engineering has emerged. To explore the laws governing processes under the influence of centrifugal force fields, electric fields, magnetic fields, etc., field-induced chemical engineering emerged. The principles of chemical engineering are even applied to the study of the fabrication of high-purity electronic devices, jet technology, and other areas. In other words, outside the field of chemical manufacturing, wherever there are reaction processes or transfer processes that are significant, chemical engineering can find applications in almost all such situations. This understanding reflects the current landscape of chemical engineering.