Thoughts on the 2008 Chemical Engineering Examination and Several Exam Questions

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Thoughts on the 2008 Registered Chemical Engineer Examination and Several Exam Questions 1. Time allocation for the exam and scores for each question: The national examination for registered chemical engineers in survey and design is held over 2 days. The first day is dedicated to knowledge tests, while the second day is for case studies. Each day consists of 3 hours in the morning and 3 hours in the afternoon. On the first day, there are conceptual questions; 70 questions in total, with 40 single-choice questions worth 1 point each, and 30 multiple-choice questions worth 2 points each. Scores from both mornings and afternoons are combined, with a total score of 200 points for the exam. 　　The second day consists of case analysis questions; 25 questions must be answered in the morning and 25 in the afternoon, with each question worth 2 points. The scores from the morning and afternoon sessions are combined, giving a total score of 100 points for the exam. 2. Examination subjects: 1) Material and energy balance 2) Thermodynamic processes 3) Fluid flow processes 4) Heat transfer processes 5) Mass transfer processes 6) Chemical reaction kinetics 7) Chemical process design 8) Design of chemical process systems 9) Engineering economic analysis 10) Project management in chemical engineering. 3. Overview of this year’s exam questions: The professional knowledge questions (both parts) had a somewhat unusual format; especially the multiple-choice questions were difficult to answer even with reference to textbooks. A notable feature of this year’s exam questions is that they require you to choose the incorrect answer. Under professional knowledge, Chapters 9 on engineering economic analysis and Chapter 10 on chemical engineering project management contain a large number of questions; therefore, compared to the morning session, there is more time available in the afternoon. For professional knowledge exams, one needs to hurry up in order to finish all the questions. Of course, they are multiple-choice questions; you can mark the answers on the card at the end. I work on the problems slowly; I usually finish a set only 15 minutes early, and there are still many questions I don’t manage to complete. The amount of calculation required is quite substantial. In the questions related to professional knowledge, there are also many questions concerning the Code for Fire Protection Design of Petrochemical Enterprises GB 50160-92 (1999 edition) as well as system layout. Professional Cases (Part 1): The exam questions involve a large amount of calculation, and they are poorly formulated; most of the questions involve unit conversions, which takes a lot of time! The questions in the professional case study (Part 2) were well-designed, but the amount of calculation required was large and time pressure was high; it was much better than the morning session. Regarding the professional case studies (part 1 and part 2), the exam questions this year focused more on pump installation height, distillation, chemical reaction engineering, and heat transfer; absorption and crystallization were covered less frequently. 4. Exam tips: Ø Start with the easier questions – those that can be answered without referring to books, as this will help save time ； Ø Accumulate knowledge about fire protection regulations and layout practices on a regular basis, and allocate more time before the exams to work on practice questions from TianDa as well as those provided by survey and design firms; in short, do as many practice problems as possible ； Ø It is recommended to bring plenty of reference books for the professional knowledge exam on the first day, while for the professional case study exam on the second day, it is sufficient to carry lightweight materials such as principles of chemical engineering, professional review books, and practice questions. (The exam time is limited, so try not to consult the book.) Ø For professional case calculation questions that require writing out the calculation steps, remember to keep the steps as concise as possible – this will help save time!) 5. Reference books: The Tianjin University edition of \"Review Tutorial for the Professional Examination of Certified Chemical Engineers\", as well as the chapters on reactors in the \"Chemical Process Design Manual\" – these should be studied carefully. Also, the Tianjin University edition of \"Principles of Chemical Engineering\", practice test questions, and GB 50160-92 (1999 version), the Code for Fire Protection Design of Petrochemical Enterprises. There are also books related to system layout. 6. Professional knowledge aspects (exam questions that can be memorized): 1) Effects on processing capacity when the catalyst in a reactor is increased, or when the space velocity is raised (there is also a similar question in professional case studies). 2) During the adiabatic free expansion of an ideal gas, the correct changes in its internal energy and enthalpy are (A) A. ΔU=0, ΔH=0 B. ΔU>0, ΔH>0 C. ΔU=0, ΔH≠0 D. ΔU>0, ΔH>0 Solution: Since no work is done, W=0, and it is adiabatic, so Q=0. The answer for this process is therefore A. 7 Professional Case Studies (the calculation problems from the second day): 1) Regarding the calculation of the number of orifices in the F1 float valve, the densities of the gas and liquid as well as their volumetric flow rates are provided (formulas can be found in principles of chemical engineering). 2) For a saturated aqueous solution of NaHCO3 at 60°C, 2000 Kg of this solution is cooled to 20°C; determine how much solute will precipitate At 60°C, the solubility of NaHCO3 in water is 16.4 g of NaHCO3 per 100 g of H2O; at 20°C, it is 9.6 g of NaHCO3 per 100 g of H2O. 3) The composition of the final mixture resulting from the chlorination of benzene (in mass percentage, the same below) is 39% benzyl chloride, 1% dichlorobenzene, and 60% benzene. The standard enthalpies of formation for these substances are as follows: benzene: 49.061 kJ/mol, chlorobenzene: –52.17 kJ/mol, dichlorobenzene: –53.05 kJ/mol, hydrogen chloride: –92.36 kJ/mol. The heat released by 1 ton of benzene during the reaction is approximately (C). (It’s from Tianjin University’s Practice Test 2; in the actual exam, it was given as 10 tons of benzene.) A. 788 kJ B. 78,369.0 kJ C. 788,700 kJ D. 89,418.68 kJ C. The correct answer is C. Solution: The chemical reaction equations are as follows: C6H6 + Cl2 → C6H5Cl + HCl; C6H6 + 2Cl2 → C6H4Cl2 + 2HCl. The relative molecular masses are: C6H6 = 78, C6H5Cl = 112.5, C6H4Cl2 = 147. For calculations, 100 kg of reactants is taken as the basis, while for heat calculations, 1,000 kg of benzene is used.

(1) Material balance calculation: In 100 kg of the reaction mixture, there are 60 kg of C6H6, 39 kg of C6H5Cl, and 1 kg of C6H4Cl2. The amount of benzene consumed to produce chlorobenzene is…; the amount consumed to produce dichlorobenzene is…; the amount of unreacted benzene is W0 = 60 kg. Therefore, the total amount of benzene required to produce 100 kg of the mixture is W = W0 + W1 + W2 = 27.04 + 0.53 + 60 = 87.57 kg. From 1 ton of benzene, 1,000/0.8757 = 1,142 kg of reaction mixture can be obtained. Of this, 1,142×0.39 = 445.4 kg is chlorobenzene, 1,142×0.01 = 11.4 kg is dichlorobenzene, and 1,142×0.6 = 685.2 kg is benzene.

(2) Heat calculation: The enthalpy change for the reaction is = –52.17 + (–92.36) – 49.063 = 193.593 kJ/mol. Another value for the enthalpy change is = –286.83 kJ/mol. Thus, the heat released when 1 ton of benzene is chlorinated is Q = 193.593 × (445.4/112.5) × 1000 + 286.83 × 11.4 × (1000/147) = 788,700 kJ per ton of benzene. I hope this information is useful for those preparing for the registration as chemical engineers.