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University of Bahrain College of Engineering Department of Chemical Engineering

(CHEG 413) Unit operation laboratory

Experiment 6Investigation the effects of a constant reflux ratio on product composition in batch distillation between ethanol and water

name Ahmed Sameer Faisal AlShowaikh Saeed sawar Faisal AlShowaikh

Id. number 20073435 20070590 20001791 20070590

task leader secretary Safety officer member

Supervised by: Dr. Fatma Marhoon expirement Date: 21/05/2012 Submission Date: 04/06/2012

Semester 2, 2011-20121

Abstract:Ethanol and water have different boiling points so they separated from each other by using batch distillation. The mole fraction of the components at the top and the bottom of the column was determined by using refractive indices calibration curve which is constructed at different ethanol and water volume percent. The column was operated at total reflux at the beginning of experiment until the ethanol evaporated then a 0.8 reflux ratio is specified in order to determine the effect of constant reflux ratio on product mole fraction. The refractive indices and the system temperatures were noted at every 10 minute interval for 1 hour. Then the system was simulated by using ASPEN PLUS software and the simulation results were compared with the experimental results. We obtain an error between 0.5% and 35%. We found that the mole fraction of light component increases with the time at the top of the column and decreases at the bottom. We recommended taking more points in the calibration curve in order to decrease the percentage of error.

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Table of ContentsAbstract ...................................................................................................................... 2 I.Introduction and Background ....................................................................................... 4 II.Theory ...................................................................................................................... 6 III.Industrial Applications ............................................................................................... 8 IV.Apparatus and Procedures ......................................................................................... 9 IV.1 Apparatus .......................................................................................................... 9 IV.2 Material ........................................................................................................ 10 IV.3 Procedure ........................................................................................................ 10 V.Results and disscusion.............................................................................................. 13 VI.Conclusions and Recommendations .......................................................................... 15 VII.References ............................................................................................................ 16 VIII.Appendices .......................................................................................................... 17 A. Raw Data............................................................................................................ 17 B. computer simulation ........................................................................................... 20 C. Nomenclature ..................................................................................................... 24

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I. Introduction and BackgroundDistillation is one of the oldest and still most common methods for both the purification and the identification of organic liquids. It is a physical process used to separate chemicals from a mixture by the difference in how easily they vaporize. As the mixture is heated, the temperature rises until it reaches the temperature of the lowest boiling substance in the mixture, while the other components of the mixture remain in their original phase in the mixture. The resultant hot vapor passes into a condenser and is converted to the liquid, which is then collected in a receiver flask. The other components of the mixture remain in their original phase until the most volatile substance has all boiled off. Only then does the temperature of the gas phase rises again until it reaches the boiling point of a second component in the mixture, and so on. Batch distillation is a type of distillation process. In batch distillation, a still is charged with a batch of feed mixture, which is then separated into its component fractions which are collected sequentially from most volatile to less volatile, with the bottoms (remaining least or nonvolatile fraction) removed at the end. The still can then be recharged and the process. Distillation is a fundamentally important process in both chemistry and industry. Distillation probably accounts for 90% of all separation processes in the chemical industry and is also a significant user of energy due to the necessary heating involved. Batch distillation is preferable rather than other types in a case of small scale and high purity production and in laboratory experiments. Batch distillation is usually used in the pharmaceutical industry and in wastewater treatment units. The first clear evidence of distillation comes from Greek alchemists working in Alexandria in the first century AD. Distilled water has been known since at least ca. 200 AD, when Alexander of Aphrodisias described the process. Arabs learned the process from the Egyptians and used it extensively in their chemical experiments. Early forms of distillation were batch processes using one vaporization and one condensation. Purity was improved by further distillation of the condensate. Greater volumes were processed by simply repeating the distillation. Chemists were reported to carry out as many as 500 to 600 distillations in order to obtain a pure compound In the early 19th century the basics of modern techniques including pre-heating and reflux were developed, particularly by the French, then in 1830 a British Patent was issued to Aeneas Coffey for a whiskey distillation column, which worked continuously and may be regarded as the archetype of modern petrochemical units. In 1877, Ernest Solvay was granted a U.S. Patent for a tray column for ammonia distillation and the same and subsequent years saw developments of this theme for oil and spirits. [1] In this experiment ethanol and water are separated from each other in batch distillation to accomplish the following Objectives:4

1. To calibrate a refractive index graph for distilled water-ethanol . 2. To perform batch distillation on a binary mixture using a sieve plate column. 3. To investigate the effects of a constant reflux ratio on product composition at top and bottom. 4. Compare your results with the theoretical ones from computer simulation. [2]

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II. Theory

Figure II-1: typical batch distillation configuration. In batch distillation a mixture of binary or multicomponents is charged to the column pot as shown in figure II-1. The feed is heated to a boiling point temperature of the lowest volatile component in order to separate it from other components. Vapor flows upwards in the rectifying column and condenses at the top. Usually, the entire condensate is initially returned to the column as reflux. In batch distillation the time, reflux ratio and the concentration of the products is the main factor thats control the efficiency of separation. Reflux ratio is the ratio of the returned liquid to the column to the distillate. When reflux ratio increases more liquid will contact with the vapor and therefore better separation is achived. There are three cases in batch distillation:

Figure II-2: configurations of Differential distillation at the left and batch rectification at the right.

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1- Differential distillation: in this case there is no reflux as shown in figure II-2 and all condensate is drawn from the condenser. 2- Binary batch rectification with constant distillate composition and variable reflux: in this case reflux ratio is varied to achieve a constant distillate composition that meets the specified purity. A complex control system is required, including a composition sensor on the distillate. 3- Binary batch rectification with constant reflux and variable distillate composition: this method is easier than pervious method because only flow seniors are required to control the reflux ratio. [3] For the third method instantaneous distillate and still bottoms compositions vary with time. The concentration of light component at the top of the column increases with time and the concentration of heavy component at the bottom decreases. Batch distillation is usually carried out in two steps: 1- Operating at total reflux ratio until the system reach steady state. 2- Operating at a desired reflux ratio.

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III.

Industrial Applications

The application of distillation can roughly be divided in four groups: laboratory scale, industrial distillation, distillation of herbs for perfumery and medicinal (herbal distillate), and food processing. The latter two are distinctively different from the former two in that in the processing of beverages, the distillation is not used as a true purification method but more to transfer all volatiles from the source materials to the distillate. Commercially, distillation has a number of applications. It is used to separate crude oil into more fractions for specific uses such as transport, power generation and heating. Water is distilled to remove impurities, such as salt from seawater. Air is distilled to separate its componentsnotably oxygen, nitrogen, and argon for industrial use. Distillation of fermented solutions has been used since ancient times to produce distilled beverages with higher alcohol content. The premises where distillation is carried