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(CENG101)[2009](s)midterm~1021^_10020.pdf
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DEPARTMENT OF CHEMICAL ENGINEERING
Hong Kong University of Science and Technology
Mid-term Exam - Spring Semester 2009/2010



CENG 101 C Chemical Process Principles
Thursday, 26 March 2009, Time: 15:00 C 18:00 LTG



Instructions to Students

1. Write your NAME and COURSE CODE on each answer book and this question sheet.

2. The percentage marks are shown with each question.

3. Start each question on a new page and number all pages.

4. You can use books or notes.

5. Calculator is permitted.

6. Read questions carefully.

7. Return examination QUESTION SHEETS together with your answers.












1.
Desalination of seawater to produce water suitable for human consumption and/or agricultural uses is a vital operation in many parts of the world. The salt content is sea water is typically about 3.50wt%, mainly NaCl. For an ideal desalination unit, salt and water are separated perfectly. In reality, if 80.0% water can be recovered, the process is already acceptable. If 5000 kg/h of seawater is processed, find the flowrates of desalinated water and salty stream for an ideal desalination unit, and also for a realistic desalination unit. (20 marks)







2.
One option of seawater desalination is to use freezing technology. The slowly formed ice is almost pure water. The slush (mixture of ice and liquid) can be separated to harvest ice which can be subsequently melted to produce water. In order to keep the salt content of the desalinated water low, the harvested ice is usually washed by the purified water before it is melted. The used washing water is recycled back to the feeding line. Draw the process flow diagram and label each stream. (10 marks)



3.
Titanium oxide (TiO2) is by far the most widely used pigment in white paint. Specifications for the white pigment powder used in paint making require that 70.0wt%TiO2, 5.00wt% ZnO, and 25.0 wt% SiO2. The powders make 45.0% of paint, the rest is latex. The density of paint so made is 4000. kg/m3. The making of the paint starts early in the morning, 8:00am, and ends at 5:00pm in the afternoon. The paint made is stored in a container tank for packaging that starts at noon and ends at 5:00pm also. The consumption rate of TiO2 is 100.0 kg/h. It is required that at 5:00pm, all the paint made is also packaged. Find the paint packaging rate in liters/min. (5 marks). What is the volume of paint in the storage tank at 3:00pm? (5 marks).









4.
We wish to react acetylene (C2H2) and hydrogen chloride (HCl) to produce vinylchloride (C2H3Cl), which is used to manufacture polyvinylchloride (PVC):


C2H2 + HCl = C2H3Cl (desired reaction) (1)

We wish to minimize the subsequent reaction of vinylchloride to dichloroethane:

C2H3Cl + HCl = C2H4Cl2 (undesired reaction) (2)

Consider the three process schemes diagramed below. All compositions are in