Influence of chemical thermodynamics on production

. Examples of Chemical Thermodynamics from Life to Production 3 Feng Xin, Ji, Liang (State Key Laboratory of Material Chemical Engineering, Nanjing University of Technology, Jiangsu 2 10009) [Abstract] Vivid examples are a good medicine to change the boring and abstract situation of chemical thermodynamics. This paper lists several examples of "from life to production" closely related to the principle of thermodynamics, so as to stimulate students' interest and make them realize the charm of chemical thermodynamics. [Keywords:] chemical thermodynamics; Examples; PVT real estate; Partial molar property; Practical Energy Saving and Emission Reduction Practical Engineering Thermodynamics Feng Xin, Ji Huihui and Qian Hongliang Abstract: Chemical thermodynamics is a course that students generally feel abstract and difficult to understand. However, vividexampleswillexcitethem. This paper lists many examples closely related to life production, lists students' interests and helps them understand the characteristics of chemical engineering thermodynamics. Practical examples; Partial molar property of pVTproperty; As we all know, chemical thermodynamics is the essence of chemical engineering. However, this course is boring and difficult to learn, and abstract concepts and complicated formulas often make many students daunting. Understanding is a necessary stage leading to true knowledge. [2] The author believes that vivid examples are a good medicine to change this situation. Considering that students have no perceptual knowledge of production, the course teaching should try to use the example of "production from life" and design it carefully. It is not easy to make up vivid examples, which is also the biggest distress of front-line teachers. This article would like to share with you many examples collected by the author. Perhaps they are not mature and accurate enough, but I hope more teachers will join the team and let more people enjoy his wisdom and achievements. 1. pVT properties of fluids Critical temperature Tc is one of the most important and common basic concepts in process safety. So the author always focuses on this knowledge point when designing pVT examples. Relationship between PVT behavior of 1 and composition selection of liquefied gas. Liquefied gas is an ideal gas fuel. The requirement of household liquefied gas is to turn it into liquid after pressurization and store it in a high-pressure steel cylinder, and then turn on the pressure reducing valve to burn and vaporize it. At present, six substances as shown in table 1 are candidate gases for liquefied gas components. (1) Please select 2 4 components of liquefied gas according to the storage and use requirements of liquefied gas. (2) Please explain the following phenomenon: In winter, sometimes there is a lot of liquid in the cylinder but it cannot be ignited. Table 1 combustion value Tc, pc and normal boiling point Tb[3] substance Tc, ℃pc, atmTb,℃, KJ/ G methane-82.5545.36-161.4555.6 ethane 32. 1848.08-88.6552.0 propane 96.591.98-42. N-hexane 234.4 29.80 68.75 48.4 solution: (1) Draw p2T diagram according to the range of candidate components Tc and pc of liquefied gas, as shown in figure 1. Figure 1 case 1 p2T diagram of candidate components of liquefied gas assumes that the kitchen room temperature is 10 ~ 40℃ and the pressure is 1atm. As can be seen from figure 1, methane is always a gas at room temperature. If the temperature of methane does not drop below Tc, that is, -82.55℃, no matter how high the pressure is applied, it cannot be liquefied-so methane is not suitable as a liquefied gas component; The Tc of ethane is 32. 18℃. Once it exceeds 32. 18℃ in summer, the pressure rise will cause explosion-so ethane is not suitable as a liquefied gas component. N-hexane is a liquid at room temperature and does not need to be compressed, but its normal boiling point Tb is 68.75℃. No matter spring, summer, autumn and winter, it will not vaporize when the pressure reducing valve is opened. N-pentane can be liquefied at room temperature, but it can't be gasified in most seasons. Therefore, only propane and n-butane meet the requirements. (2) Most liquefied gases will contain a small amount of C5 and C6 components such as pentane, so the room temperature is low in winter, and higher alkanes such as pentane cannot be gasified, resulting in residual liquid. Example 2 Relationship between 2pVT behavior and compressed natural gas as a new fuel for automobiles. With the rising price of gasoline, natural gas, which is both economical and environmentally friendly, has become a new fuel for automobile engines, and more and more buses and taxis are burning natural gas (mainly methane). In order to make the unit gas run a longer mileage, the natural gas filling station needs to compress the natural gas of 0.2MPa and 10℃ transported by pipeline into the gas storage tank to make compressed natural gas with a pressure of 20MPa. Because the refrigeration effect of the compressor is poor in summer, the gas temperature is 15℃ in winter and 45℃ in summer. It is known that the volume of the gas storage tank is 70L, and each kilogram of methane can travel 17km. Q: (1) If the compressed natural gas at 20 MPa, 15℃ is regarded as an ideal gas, compared with RK equation of state, is the mileage of a can of compressed natural gas calculated by it more or less, and how many kilometers is the difference? (winter). Can compressed natural gas be used as ideal gas at this time? (2) How many kilometers can a can of natural gas travel if the natural gas with 0.2MPa and 10℃ transported from the pipeline is directly loaded into the gas storage tank without compression? (3) In order to drive a longer mileage, can the compressed natural gas be changed into liquefied natural gas by increasing the pressure when other conditions remain unchanged? Any good suggestions? (4) According to the taxi driver, "the mileage of the same can of compressed natural gas is shorter in summer than in winter". Why? Please explain the reason and estimate how much it costs to drive 300 kilometers a day in summer than in winter. A can of compressed natural gas is around 50 yuan. The necessary data can be assumed by yourself). Solution: (1) ① v = rt p =1.198×10-4m3 can be obtained from the ideal gas state equation? mol- 1； N=V total V = 584.5438+0mol；; Mileage s ideal = 584.3/kloc-0 /×16×10-3×17 =158.93km ② According to RK equation, V=0.0000980m3? The total mileage of Mol- 1 n=V is: SRK = 714.29×16×13×17 =194.29 km vs. (2) mol- 1； N= V, and the total V = 3.63mol = 3.63x16x10-3x17 = 0.987km.. Therefore, the natural gas transported by pipeline, as automobile fuel, must be compressed into high-pressure natural gas by compressor to have practical significance. (3) no. Because "other conditions are constant" means that the temperature is constant. From the example of 1, it can be seen that when the temperature is about 10℃ and greater than Tc, no matter how much pressure is applied, it cannot be liquefied. Therefore, it is only necessary to reduce its temperature to below -82.55℃ and then pressurize it. Theoretically, when the temperature drops to -82.55℃, it is possible to liquefy under pressure, but the pressure is extremely high at 4.60MPa. According to the p2V2T relation of fluid, the lower the temperature, the lower the required pressure, so in fact, the temperature of liquefied natural gas often drops to-162℃, so that it can become liquid under normal pressure. (4)① According to (1), when the winter temperature is 15℃, the cost per kilometer is 50 194.29 = 0.257 yuan; ② When the summer temperature is 45℃ by the same method, the cost per kilometer is 50 163.94 =0.305 yuan. Therefore, if you drive 300 kilometers every day, the cost in summer is 300×(0.305-0.257)= 14.4 yuan/day. Spend more in a quarter 1300 yuan. This is because V∝T, when the temperature rises in summer, the molar volume V of gas increases. Because the total volume of the gas storage tank is fixed, the mole number n=V total /V of the loaded compressed natural gas becomes smaller, and the driving mileage decreases accordingly. So the mileage of the same tank of oil is shorter in summer than in winter. The pressure of automobile tires is related to the temperature of the air in the tires. When the air temperature in the fetus is 25℃, the pressure gauge shows 2 10kPa. If the volume of the tire is 0.025m3, what should the pressure gauge show when the air in the tire rises to 50℃ in summer? For the safe use of tires, it is necessary to restore the original pressure of tires. How much air will be released from the tire at this time? Suppose the atmospheric pressure is 100kPa and the composition of air is 21wt% O2; 79 wt% N2. [4] Please give the idea of solving the problem. Solution: See the solution in Figure 2. It should be noted that if the pressure gauge shows 2 10kPa, the actual pressure should be 2 10+ 100 (local atmospheric pressure) =3 10kPa. Figure 2, Example 3, 44 examples of chemical thermodynamics from life to production: (1) 25℃, V65438. mol- 1； N1= 0.025/0.0079854 = 3.13mol (2) When the air in the fetus rises to 50℃ in summer, the pressure gauge should display 336.15-100 = 236./kloc-. (3) at 50℃, V3=0.00866m3? mol- 1； N3 = 0.025/0.00866 = 2.887 mol, so 3. 13-2.887 = 0.243 mol of air is released. Second, the partial molar nature Partial molar nature is a relatively abstract concept, and it is difficult to give examples. The following two examples are metaphors of interaction between people. Example 4 J.M.Prausnitz, the most famous authority on thermodynamics in the world today, a winner of the American Presidential Award, an academician of the American Academy of Sciences and a professor of chemical engineering at the University of California, Berkeley, described it this way: [5] The interaction between molecules is usually very special. In this case, it is a pity that it is impossible to predict (even approximately predict) the properties of the mixture with the properties of pure components. This is not surprising if we consider the following far-fetched analogy. Imagine that there is a sociologist in Russia. He carefully studies the behavior of Russians. After observing them for a few years, he knows them like the back of his hand. Then he went to China and made a similar thorough study of China people. So with this knowledge, can he predict the behavior of the society formed by the arbitrary mixing of Russians and China people? Probably impossible. This analogy is very extreme, but it can remind us that molecules are not inert particles that move blindly in space. On the contrary, they are complex "individuals" and their "personality" is very sensitive to the environment. China has a saying: "Men and women work together tirelessly"! There will be interaction between boys and girls, and their behavior when they are alone cannot be used to describe the behavior of boys and girls when they are together, that is, "the strength of boys and girls together ≠ the strength of boys and girls". Henry's Law Example 6 The Reaction of the Mountain and Henry's Law Because the pressure on the mountain is very small, the partial pressure of oxygen in the atmosphere pO2=p? O2( 1) in Y air and dissolved oxygen in blood are: pO2=kO2x O2 (2) in blood. According to the formula (1), since the proportion of oxygen in the atmosphere is constant to keep O2 = 2 1wt% in Y air, when the total pressure on the mountain becomes smaller (at an altitude of 3000m, X O2 in the blood becomes smaller, and the brain reacts at high altitude due to lack of oxygen. Example 7 Hyperbaric oxygen chamber and Henry's Law Hyperbaric oxygen therapy is a treatment method that patients are placed in a treatment chamber above 1.4atm and intermittently inhaled 100wt% oxygen. The principle is the same as in Example 6. On the one hand, the total pressure P increases, on the other hand, O2 in Y air increases, both of which increase pO2. According to formula (2), O2 in X blood increases with the increase of pO2 in hyperbaric oxygen chamber, which is 72,265,438+0 times, so that the brain tissue can be fully supplied with oxygen. Table 2 explains Example 8: Air is cheaper and nontoxic than CO2. Why can't it be used to make soda and sparkling champagne? [6] Table 2 Henry constants of various gases dissolved in water at 25℃ [6] Gas H/bar gas H/bar gas H/ Bar acetylene 1350 ethane 30600 hydrogen sulfide 550 air 72950 ethylene1kloc-0/550 methane 4 1850 carbon dioxide. Example 9 of energy saving and emission reduction Chongqing Changfeng Chemical Plant suffered a continuous loss of 15 years, and made a profit of 20 million yuan for half a year by relying on scientific and technological innovation, realizing a qualitative leap from huge loss to huge profit. [7] Solution: Sort the chemical reaction heat and process waste heat in each production process of the whole plant. The heat production process and heat utilization process of each production device are integrated in linkage, and the heat production process and heat utilization process of different devices are integrated across devices, so that both heat supply and demand sides not only have the same quantity, but also match the quality, and strive to replace low-grade waste heat with higher-quality energy. Without coal-fired boilers, the factory saves coal-fired costs100000 yuan every year. The utilization of cold energy of liquefied natural gas (LNG) has become a hot project of circular economy. Liquefied natural gas has the characteristics of high calorific value and little pollution. In the process of use, a lot of heat energy must be consumed to convert it into normal temperature natural gas. The usual practice is to use seawater as a heat source. If the temperature of the returned seawater is reduced by 5℃, it will take about 654.38+200 million m3 of seawater to gasify 3 million tons of LNG every year. If a 30,000 m3/hr air separation plant is built by using its cold energy, the annual output of oxygen will be 286,000 tons, and the output value will exceed 200 million yuan. Compared with the traditional air separation device for producing liquid products, this device can save 50%-60% electricity and 70%-90% water due to the effective recycling of cold energy in LNG. (Continued from page 66) 5 4 The situation of communication and coordination of examples from life to production in chemical thermodynamics must be broken, and it is imperative to establish process-oriented management mechanism and coordination mechanism to realize process management. (4) Continuously and permanently improve the system "improvement" is not a once-and-for-all job. The change of environment requires us to continuously improve the existing workflow. Never think that "we have achieved the optimization of workflow so far, and the current state can stand the test in a certain period of time!" Because this kind of thinking will only make us slack off, thus relaxing the vigilance of finding potential problems in the work process. Process improvement should always be carried out, so that our system can be in an efficient state. (Text Editor: Wu Wenshui) References: [1] Wang Yingluo. Industrial engineering [M]. Xi 'an: Machinery Industry Press, 1996.5. [2] Liu Guangdi. Quality management [M]. Beijing: Tsinghua University Publishing House, 1996.2. 【3】W？ Walker. Human resource strategy [M]. Beijing: Renmin University of China Press, 200 1.4. [4] Fan Yun. Management [M]. Xi an: Shaanxi People's Publishing House, 200 1.8. [5] Zhao Tao. Found Deming [M]. Beijing: Beijing University of Technology Press. In addition, using LNG cold energy to develop circular economy and expand tourism resources. For example, the "Ice and Snow World" project is to transport the cold energy in the process of LNG gasification to the ice and snow world heat exchange station through refrigerant, and use the cold energy in different functional areas of the ice and snow tourism world to provide cold energy for ski resorts, skating rinks, hotels and other steps, so as to realize the comprehensive utilization of LNG cold energy. This will not only allow citizens to enjoy skating and skiing in summer, but also effectively control the damage caused by a lot of cold energy to the environment. V. Examples of Refrigeration and Heating 1 1 Rode Technology for Freezing Soil of Qinghai-Tibet Railway. Of the newly-built110 km line of Qinghai-Tibet Railway, 550 km will pass through the frozen soil area. Frozen soil is a kind of soil medium which is extremely sensitive to temperature. In winter, frozen soil expands violently with the decrease of temperature under negative temperature, pushing the upper subgrade and pavement; In summer, the frozen soil melts with the increase of temperature, and the subgrade settles after the volume decreases. This periodic change often leads to the collapse, subsidence, deformation and rupture of subgrade and pavement. Nowadays, the hot rod technology erected every 15 meters has solved the frozen soil problem. Hot rod (also known as coreless gravity heat pipe and thermosyphon) is an efficient heat conduction device, 7 meters long, 5 meters below subgrade and 2 meters above ground. The whole stick can is filled with liquid ammonia. When the subgrade temperature rises, liquid ammonia is heated and gasified, and rises to the upper end of the hot rod. The heat is conducted into the air through the heat sink, and the gaseous ammonia is cooled into liquid ammonia, and then sinks into the bottom of the rod. In this way, the hot rod is equivalent to a permanent natural refrigerator, which continuously discharges the heat in the frozen soil layer and makes it permanently frozen. Einstein said: Although most theories of physics will change with time, thermodynamics is universal and eternal. [5] Chemical thermodynamics is boring and abstract, but we believe that through hard work, students can see the essence of science through familiar phenomena, and then students will definitely appreciate the happiness brought by the charm of chemical thermodynamics! Because "it is pleasant to know the nature of things!" (Text Editor: Wu Wenshui) References: [1] Feng Xin, Student-centered teaching reform of Chemical Thermodynamics [J]. Chemistry Higher Education, 2006, (4):30234. [2] Zhang Chuting. Science curriculum reform [J]. china university teaching, 2004, (. Editor gu. Chemical Thermodynamics (2nd Edition) [M], Beijing: Chemical Industry Press, 200 1.2952297. [4] Younoussa. Singlin, Michael. Boles. Thermodynamics: General Method (6th Edition) [m]. McGraw-Hill, 2006. 1592 160. [5] Prausnitz et al., Lu Xiaohua Liu Honglai. Molecular thermodynamics of fluid phase equilibrium (third edition) [M]. Beijing: Chemical Industry Press, 2006.5000500505 Trans. Lu Xiaohua et al. Introduction to Chemical Thermodynamics (7th Edition) [M]. Beijing: Chemical Industry Press, 2008. 2 1822 19.[7] Deng. From Huge Losses to Huge Profits —— On-the-spot record of scientific and technological innovation in Chongqing Changfeng Chemical Plant [N]. China chemical industry news, 200010001.888686866616.