How to understand chemical industry?

1.1 Chemistry is a fundamental discipline that deals with the modification of substances at the molecular level. As a basic subject, the main body of its research is the law and principle of material change. In addition to physical chemistry is the study of abstract and macroscopic concepts, through physical experiments and statistical mathematics and other tools established disciplines; Inorganic chemistry and organic chemistry are both disciplines that study the mechanism and law of molecule formation. There is also a discipline called analytical chemistry, which is a tool - when we cannot directly observe the structure of molecules with tools such as a microscope, we will use some properties of matter under energy to "observe" the microscopic structure into a macroscopic state that can be quantified or qualitative to a certain extent. 

1.2 Chemical engineering is an engineering discipline, or an applied discipline. It's absolutely different from chemistry. 

1.2.1 Chemical industry is not only to learn chemistry, but also to learn physics, they are the tools of chemical industry, which is more inclined to apply the properties of molecules and substances - here the properties include chemical properties and physical properties - to achieve a certain purpose than to study the properties of molecules themselves. In chemical engineering, physical properties are just as important as chemical properties, if not more so. For chemical workers, we often say that the four major chemistry: inorganic chemistry, organic chemistry, analytical chemistry and physical chemistry are all courses that must be studied, but in practical applications, the first three will have more professional chemical researchers to provide professional guidance for chemical workers, and physical chemistry is an important tool and research object for chemical workers. As mentioned above, physical chemistry is a discipline that studies abstract and macroscopic concepts and is established through physical experiments and statistical mathematics and other tools. Chemical industry pays more attention to macroscopic phenomena and physical experiments, as well as scientific statistical mathematical methods. 

1.2.2 The chemical industry is the work of the craftsman - creator To make a perhaps inappropriate metaphor, the chemist is the expert in asking questions, more in the image of the "scientist", who is constantly asking the world why and proving it. Chemical people are more of a creator, and each of their research or practice is accompanied by a clear purpose - creating value, that is, producing. Scientists have a kind of achievement called "failure", their efforts can tell others that a thing is objectively impossible, which can reduce the detours of others, and is also a kind of value creation. However, chemical workers cannot bear "failure", because the meaning of failure is that they cannot get products that meet the quality requirements, such products are just like a failed painting or low-quality clothing. Can't produce any economic value. 

1.2.3 Chemical engineering is a complex study As a chemical engineer, maybe you do not need to master all the disciplines involved in chemical production, but you must understand them and master the language of dialogue with their experts - laws and regulations, drawings, professional terms, such as: chemistry (reaction mechanism, material safety properties); Machinery (feasibility of producing the necessary power equipment and means of process modification); Pressure vessels (necessary for the production of static equipment); Instruments (necessary tools for observing the state of materials); Electrical appliances (the basis of instrument function and power operation); Construction (structure and location of plant installations); Materials (equipment in contact with materials needs to choose materials that meet the temperature and corrosion of the materials, and can be processed into the shape required for production); Pipeline valves (mainly related to the calculation of fluid mechanics and structural mechanics, the characteristics and selection of pipe fittings); Metrology (involving the use of instruments to detect whether reliable, whether recognized by the customer); Analysis (involves observing the microscopic state of materials and the quality of products); Packaging (which is essential for the safe transportation of materials, safe storage and ensuring the quality of materials); Technical economics (calculation of costs and benefits); Mathematics (tools of analysis and statistics); Safety..... Of course, your compulsory course "chemical engineering" needs continuous improvement. Whether in actual production or scientific research, chemical people are acting as a hub role, information from various departments is gathered to you, for a common purpose, you need to fully communicate with people in each industry, understand his reasons, and tell others when they ask you for help - personally, this is the charm of chemical industry. It's one of the reasons I've stayed in this industry for five years. "What are the main technologies that distinguish chemical engineering from civil, mechanical, electronic, electrical and other engineering disciplines?"

 2, chemical industry is the study of "three transmission and one opposite" discipline, three transmission refers to "momentum transfer", "mass transfer", "heat transfer", one refers to reaction engineering. 

2.1 Heat transfer What is heat transfer, let me take two examples in life: 

2.1.1 Heating hot water, heating tap water through the gas stove to make hot water, is a process in life - the heat generated by combustion needs to be transferred to the hot water, resulting in the hot water heating results, which is the transfer of heat. As mentioned in 1

.2.2, chemical industry is a process with serious purpose, in this process, "production of hot water" is the purpose of this process, is the product. If we want the water to heat up faster, I can increase the temperature of the flame, because the rate of radiative heat transfer is positively related to the temperature difference. Heating water from 25 ° C to 35 ° C is faster than heating it from 85 ° C to 95 ° C, because the rate of heat transfer is proportional to the temperature difference between the hot and cold sources, which is Fourier's law. I can increase the heat transfer area and enhance the heat transfer area, which involves the engineering calculation of the heat transfer area. I can stir the hot water to make it more turbulent, so I can change the temperature distribution of the hot water in the kettle, using a physical model of the film theory. 

2.1.2 Why is the heating set at the lower side of the window instead of the upper side? This is based on the principle of heat convection. The hot air is lighter than the cold air, so it will naturally rise, while the cold air will naturally fall. The window is the gathering place of the cold air, and the falling cold air will be heated by the central heater, because compared with the hot air that does not flow, the heated and cold air will have a larger temperature difference between the cold and hot sources, and the heat transfer rate will be faster. The heated hot air moves upward, creating convection in the room. 

2.2 Mass transfer Mass transfer is more abstract than heat transfer. Let me use Coke as an example. There is carbon dioxide dissolved in coke, when the temperature is constant, close the bottle cap, stand the bottle, the bubble will become less or even disappear, this is because there is a gas-liquid phase equilibrium of carbon dioxide gas in Coke and air, when the temperature is fixed, there is an equilibrium concentration (including the concentration of carbon dioxide in Coke, called the liquid phase concentration; It is the concentration of carbon dioxide in the air above the bottle, called the vapor phase concentration, at which the rate at which the gas diffused from the cola into the air is the same as the rate at which the carbon dioxide in the air dissolves into the cola, this is the gas-liquid phase equilibrium, and the bubbles in this state will be reduced or even disappear. When we just screw on the cap, the gas phase concentration is lower than the equilibrium concentration, and the liquid phase concentration is higher than the equilibrium concentration, and as the gas molecules move between the two phases - from the liquid phase to the gas phase migration, that is, the bubble is generated, the gas phase concentration rises, the liquid phase concentration will first, and eventually the equilibrium. We open the bottle cap again, because the concentration of carbon dioxide measured inside the bottle cap is higher than that on the outside, under the action of this concentration gradient, carbon dioxide gas diffused into the air, resulting in a decrease in the concentration of carbon dioxide gas in the bottle, the balance is broken, and the bubble is restored. Here the process of "diffusion of carbon dioxide gas into the air under the action of this concentration gradient" is the mass transfer process. The main components of the gasoline used in our cars, C5 ~ C12 aliphatic hydrocarbons and naphthene, are the carbon dioxide in the cup of Coke, which is condensed after flying out of the distillation tower, and is refined and blended, and finally becomes the gasoline in the tank of the gas station. 

2.3 The part of momentum transfer is more abstract, which can be simply understood as the resistance to hinder fluid movement. The water pressure of the water pipe in the old building decreases with the years, because the internal garments of the galvanized pipe reduce the effective circulation inner diameter and increase the surface roughness, which strengthens the momentum transfer effect of the inner wall of the water pipe on the water, resulting in smaller water pressure.

 2.4 Reaction Engineering This is a discipline that studies micro reactions to macro reactions. Some reactions need to be carried out in heterogeneous phases. In addition to the dynamics of the reaction itself, the mass transfer and heat transfer in heterogeneous phases also affect the properties of the reaction, such as rate, conversion rate and by-product formation. This requires the use of some empirical formulas in this discipline to make predictions.