For this problem, the feed is 60 mol% dimethyl ether (DME) and 40 mol% methanol. Assume that the equilibrium data provided are correct.

1. A feed of 200 kmol/h is flashed at 5 bar and 50°C. What are the liquid and vapor flowrates and the mole fractions in the vapor and liquid exit streams?

A feed of 200 kmol/h is to be fractionated to give a distillate containing 98 mol% dimethyl ether and a bottoms product containing 98 mol% methanol. The feed is 20% vapor and 80% liquid. There is a total condenser and a partial reboiler.

2. Determine the molar flowrates of the distillate and bottoms.

3. Calculate all internal flows for operation at a reflux ratio of 0.1.

4. In order to use cooling water in the condenser, assume that the DME must condense no lower than 55°C. Estimate the top pressure for this column.

5. In order to use low-pressure steam in the reboiler, the bottom temperature must be no higher than 148°C. Estimate the bottom pressure for this column.

6. Determine the diameter of a sieve tray tower with 18-in tray spacing to operate at 75% of flooding. The active tray area is 85% of the column area.

Determine the diameter both above and below the feed. There are six equilibrium stages with the feed on the third stage.

7. Assume that the tray efficiency is 42%. Estimate the maximum weir height for which trays can be designed to meet the pressure specifications.

8. Suppose you determine that the height to diameter ratio for this column exceeds 20, which is usually the maximum recommended value. Suggest at least one design change that would result in a height to diameter ratio smaller than 20. Explain the rationale for your suggestion and its consequences.

9. Determine the diameter of a packed tower to operate at 70% of flooding using 1.5-in, ceramic Berl saddles. Determine the diameter both above and below the feed.

10. Look up the behavior of the DME-methanol system. How would it impact the answers to this problem?

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Vapor Pressure Data In P* (bar) = A - DME Methanol Other Data DME Methanol B T(K) A 655 10.543 Liquid density (kg/m³) 788 12.8591 B 2623.14 4336.7 Viscosity (CP) 0.5 0.4