Keywords: industrial flow chart; Case analysis; interpret
China Library Classification Number: G427 Document Identification Number: A
Article number:1992-7711(2012)16-073-2.
The starting point for solving industrial process problems is the same as other problems. First of all, we must understand the problem, which is extremely difficult, and the difficulty lies in reading ability. I can read and understand the topic, and the answer is almost out! Read the stem carefully, investigate the meaning of the question, clarify the scope, pay attention to the limitations given by the stem, and lay the groundwork for solving the problem. Examining questions includes information before, during and after looking at the picture. Don't forget the problem-solving requirements, because understanding the problem-solving requirements: first, it can prevent irrelevant answers, and second, it can get important enlightenment from the problem-solving requirements, which can't be ignored. Therefore, the content and scope of the first-instance topic, the direction of the second-instance topic, and the additional requirements of the third-instance topic must be met. Specific to the industrial flow chart, the title is "recognize the flow chart", clarify the purpose of the process flow, and figure out what it wants and how to do it; Pay attention to the direction of the arrow: the arrow enters the feed (reactant), the arrow exits the product (including the main product and by-product), and the returned arrow is generally the "recovered" substance; Master the law of process problems, that is, main products of main line, by-products of branch line, and return to circulation.
The key to solving process problems is to "extract useful information". Some information is in the flow chart, and some information can only be understood by combining the problems in the topic. You should boldly skip information or problems you don't understand, which may be interference information unrelated to solving the problem. However, teachers should not comment on such problems at ordinary times, which is opportunistic and not conducive to improving students' ability to solve such process problems.
The problem to be solved in solving process problems is to find out what the experts think, and in fact it is often the idea of the proposer. Hua et al. wrote in the section of General Chemistry Principles 15.6 Preparation of Inorganic Substances: "Chemical preparation is a challenge to any chemist and any era, and any major successful preparation scheme is the crystallization of wisdom obtained by human beings through hard exploration. When designing a preparation experiment, we should not only consider whether the reaction can occur (thermodynamic criterion), but also consider whether the reaction rate and reaction conditions are easy to realize (kinetic criterion). In addition, factors such as preparation cost, raw material price and environmental protection should be considered, and even practical problems such as storage and transportation of raw materials and safety of preparation process should be considered. "
Then, according to the expert's thinking, the following questions are considered in combination with the topic: (1) Solve the production principle of transforming raw materials into products. (2) Control the reaction conditions, such as temperature and pH value. (3) removing all impurities and purifying the product. (4) Improve output and productivity. (5) Reduce pollution and consider "green chemistry" production. (6) The source of raw materials should consider both the richness and the cost, which is economical and applicable. (7) The process is simple and feasible.
Let's take the title of the college entrance examination in Jiangsu in recent years as an example to talk about how to interpret the industrial flow chart.
Example:1(In 2009, Jiangsu VolumeNo. 16, Jiangsu Examination InstructionsNo. 12,No.16,No. 17 have the same method asNo. 10. ) The original question is:
Potassium sulfate, potassium persulfate and iron oxide red pigment were produced with potassium chloride and ferrous sulfate as raw materials, and the comprehensive utilization rate of raw materials was high. The main process is as follows:
ferrous sulfate
Solution reaction Ⅰ Ⅰ NH4CO3 solution CO2(g) filtration reaction Ⅱ dilute H2SO4CO2(g) reaction Ⅲ ⅲKCl filtration K2SO4(s)NH4Cl solution reaction Ⅳ (NH4) 2SO8 solution N2(g)feco 2(s)fe2o 3(s) calcination in air.
(1) Before reaction I, it is necessary to add (filled with letters) to FeSO4 solution to remove Fe3+ in the solution.
A. zinc powder b, iron filings c, potassium iodide solution d H2
(2) The reaction temperature of reaction I should be controlled below 35℃ for the following purposes.
(3) In industrial production, a certain amount of alcohol solvent is often added in the process of reaction III, with the purpose of.
(4) Reaction IV is often used to produce (NH4)2S2O8 (ammonium persulfate) by electrolysis. Inert electrodes are used in electrolysis, and the electrode reaction on the anode can be expressed as.
The suspicious source of reading this question is: Liu Xiaohong et al. prepared potassium sulfate and iron oxide red from ferrous sulfate in September 2000. Chemical reaction and technology, 16 (5) 295 ~ 300.
As can be seen from the flow chart, the chemical reactants of reaction I are FeSO4 and NH4HCO3, the obvious products are FeCO3 and CO2, and the invisible products should be (NH4)2SO4, why not NH4HSO4? First, in order to improve the utilization rate of raw materials (FeSO4 here) in real industrial production, it is required that NH 4 CO 3 is excessive, and NH 4 SO 4 can continue to react with NH 4 CO 3. Secondly, if NH4HSO4 is generated and the equation cannot be balanced, then according to the flow chart, the chemical equation of reaction I can be written as FeSO4+2nh4CO3 = FeCO3 ↓+(NH4) 2SO4+H2O+CO2 ↑.
The filtrate of this reaction should be (NH4)2SO4 and excess NH4HCO3, so the chemical equation of reaction II is
2 NH 4h co 3+h2so 4 =(NH4)2so 4+2H2O+2co 2↑
Therefore, the solution obtained from reaction II should be (NH4)2SO4 and excess H2SO4 generated from reactions I and II. Divide the mixed solution into two parts according to the flow chart. One part is used for reaction III, and the other part is used for reaction IV. According to the flow chart, the following reaction is suggested in reaction III: 2KCl+(NH4)2SO4=K2SO4↓+2NH4Cl.
According to middle school knowledge, this double decomposition reaction can't happen. But this is actual industrial production. Since it is used in industry, it shows that this reaction really happened. As can be seen from the flow chart, K2SO4 precipitate and NH4Cl solution are formed. There is an idea in it: "Practice is the only criterion for testing truth" and "Experiment is the highest court of chemistry". The discipline background of chemistry itself is that when doing practical scientific research, we must first have experimental facts, then sum up the empirical laws (only summary, not absolute truth) to form a theory, and then use the laws to guide new experiments. When the experimental facts conflict with the original theory, the facts must be put in the first place. That is, positivism-the view that chemical conclusions come from chemical experiments (chemical production). Some scholars call it "the idea of experimental verification". With this idea, we might as well press this reaction first. Further reading, it is not difficult to get the answer from the following question (3). The reason is that a certain amount of alcohol solvent is added, which reduces the solubility of K2SO4 and makes the reaction proceed in the positive direction. In fact, if the examinee can transfer knowledge, it is not difficult to think of Experiment 2-2 (P42, People's Education Edition, 2007) in Textbook 3: adding ammonia water to copper sulfate solution until the precipitation disappears, and then adding less polar ethanol solvent, blue crystals will precipitate (actually, it is tetramine copper sulfate monohydrate, and the reason why heating concentration method cannot be used is that ammonia gas escapes when heating, which will precipitate solid basic copper carbonate). Much like this experiment, this problem can be solved smoothly. Students may also ask, which substances will alcohol reduce solubility? Will the solubility of KCl, (NH4)2SO4 and NH4Cl decrease in this reaction? Although this question is worth studying, it is unclear and does not affect the answer to this question. If necessary, please refer to: Zhang Xingfa et al. Phase diagram analysis of potassium sulfate prepared by double decomposition of potassium chloride and ammonium sulfate [J]. Journal of Hefei University of Technology (Natural Science Edition), Vol. 27,No. 10,184 ~186.