problem_1

Problem Set #1

Due Thursday, February 3

Flowsheets and Chemical Processes

Read Chapters 1-3 from Felder and Rousseau. Chapter 2 should be mostly review, and Chapter 3 contains many definitions of terms that will be used over the semester.

1. The ammonia synthesis reaction discussed in class is actually reversible. The reaction rate is faster (smaller reactor needed) at high temperature, but the equilibrium limits conversion at high temperatures. You've covered liquid-phase equilibria in Chemistry courses, and we'll use the same ideas for gas-phase reactions too. We can control both the total pressure (Pt) and temperature (T) in the plant. For a stoichiometric mixture of H₂ and N₂, it can be shown that the fraction of N₂ converted to ammonia is given by f in the equation:

K_eq = (2f)^2 (4-2f)^2 / 3^3 (1-f)^4 P^2 ,
where K_eq(T) = 4.4 x 10^-11 exp( 11100/T(K) ) atm^-2

a) Solve for f by reducing this equation to a 2nd order polynomial in f, by taking the square root of both sides, and then using the quadratic equation.
b) Using a spreadsheet or other computer tool to avoid the tedious calculations, calculate the maximum conversion allowed by the equilibrium at 1 atmosphere total pressure and temperatures between 300 and 1000 K.
c) Repeat the calculations for 50 and 100 atm total pressures. Show the equilibrium conversions in an appropriately-labeled graph.

2. The ammonia synthesis process described in class differs from current industrial practice in several ways. Use a page or less (typed) to describe several significant modifications. Comment on how the changes might improve the process. Include a sketch or drawing of the process.

3. There's a lot of information out there besides the textbook and my lectures. Investigate and report on one of the Top 50 chemicals off the C&E News handout. To see which one you are assigned, use the 6th and 7th digits of your UW ID number (subtract 50 if your number ends in 51 or above). Give the overall reaction, general flowsheet, and a paragraph-to-page of discussion of the most interesting aspects of this process. Be sure to mention by-products or other species that are needed but do not show in the overall reaction.

[If you don't have the 1990 Top-50 chemicals handout, then choose either methanol, acetone, or isopropanol as your chemical.] [For these last two problems, properly cite your information source. Felder&Rousseau is not a good book for process flowsheet information, so you will need to look into some of the other reserve books at the libraries. Type your answers to these "description" problems, using subscripts, spell-checking, etc. as available in MS Word or other word processing programs. See us or your favorite computer consultant at CAE right away if you have problems with this.]

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