Distillation: Distillation and Che- 396 Senior Design Essay

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Distillation

Senior Design CHE 396
Andreas Linninger

Innovative Solutions
Michael Redel
Alycia Novoa
Tanya Goldina
Michelle Englert

CHE-396 Senior Design

(Distillation)

Table of Contents

Introduction

3

Flowsheet

4

Limitations

5

Applicability

6

Theory

7

Case Study___________________________________________________24
Alternatives

288

References

309

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CHE-396 Senior Design

(Distillation)

Introduction

This report examines the distillation process. This will enable the reader to understand the necessary components along with distillation calculations. Distillation is a process that separates two or more components into an overhead distillate and bottoms. The bottoms product is almost exclusively liquid, while the distillate may be liquid or a vapor or both.

The separation process requires three things. First, a second phase must be formed so that both liquid and vapor phases are present and can contact each other on each stage within a separation column. Secondly, the components have different volatilities so that they will partition between the two phases to different extent. Lastly, the two phases can be separated by gravity or other mechanical means. Distillation differs from absorption and stripping in that the second phase is created by thermal means (Seader, 1998).

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CHE-396 Senior Design

(Distillation)

Flowsheet

The distillation column contains one feed stream and two product streams. The feed contains a mole percent of the light component, ZF. The product stream exiting the top has a composition of XD of the light component. The product stream leaving the bottom contains a composition of Xb of the light component. The column is broken in two sections. The top section is referred to as the rectifying section. The bottom section is known as the stripping section.

The top product stream passes through a total condenser. This effectively condenses all of the vapor distillate to liquid. The bottom product stream uses a partial reboiler. This allows for the input of energy into our column.

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CHE-396 Senior Design

(Distillation)

Limitations
• Azeotropes: An azeotrope is a liquid mixture which when vaporized produces the same composition as the liquid. If the mixture is azeotropic, then more advanced types of separation must be considered. More information on azeotropes maybe found in Douglas, Section 7.3.
• Solids: If the material to be separated is high in solids, or contains tars or resins that could plug or foul a continuous unit, then a batch separation should be considered (Perry’ 1997). s, • Optimum Pressure (King, 1980):
1. Vacuum operation: Use of a vacuum should be considered for heatsensitive compounds or polymerizable materials. Vacuum is usually not used unless required, e.g., a low bottoms temperature is needed to avoid thermal decomposition.
2. Distillation column is above atmospheric pressure: Column shell should be thicker to withstand pressure of the column.
3. If the column pressure required to accomplish overhead condensation with
2
cooling water is less than 250 lb/in , then the column pressure should give

an average temperature driving force of 5-15*C in the overhead condenser. 4. If the column pressure required accomplishing overhead condensation with cooling water is greater than 250 lb/in2, then consider an alternative of using a refrigerant on the overhead and running the column at a lower pressure. 5

CHE-396 Senior Design

(Distillation)

• Optimum Temperature Differences in Reboilers and Condensers (King,
1980):
1. Reboiler temperatures should be kept low enough to avoid bottoms degradation and/or fouling.
2. Common temperature differences used for heat exchange across reboilers and condensers are shown in the following table:

Temp, K
Condenser:
Refrigeration
Cooling Water
Pressurized Fluid
Boiling Water
Air
Reboiler:…