Assignment 2: Describe different ways to split a mixture of benzene and methanol into its components using two phase system separation.

University Of MauritiusBEng (Hons) Chemical and Environmental Engineering - E400Chemistry and Basic Engineering CHE 1001Y (3)

Assignment 2:Describe different ways to split a mixture of benzene and methanol into its components using two phase system separation.Tutor: Dr. D. SurroopName: Fanilo Antra Tia RazafindralamboIndex number: 1312636

Table of Contents2Introduction23General Information33.1Comparison between Methanol and benzene34Techniques of separation44.1Separation based on density44.2Separations Based on a Change of state44.3Separations Based on a Partitioning Between Phases55References7

Introduction

Recent advances in analytical chemistry are characterized by great progress towards more powerful methods of separation, equaling in significance the great forward strides made in instrumental methods of determination. It is important for an analyst to split the mixture into its components to analyze it. Various techniques are used to separate different types of mixtures but the methods of separation depend mostly on the properties of the components. Here, we are dealing with a benzene-methanol mixture so it is important to know their properties and attributes before attempting to separate them.General InformationComparison between Methanol and benzene

Table a. resumes important attributes of benzene and methanol that will be considered the splitting techniques described in this document.PropertiesBenzeneMethanol

ColorColorlessColorless

Boiling Point/C80.164.6

Density(at 20C)/g/mL0.8790.791

PolarityNon-polarPolar

VolatilityHighLow

Solubility in water (g of solute per mL of water)0.0018Totally soluble

Table a. Comparing benzene and methanolThe table shows that benzene and methanol are both liquids at 20C.Figure 1 Light refraction of benzene (above) and water (below).

Benzene is a non-polar, molecule whereas methanol is, this also makes the two liquids immiscible. That is, the two components form 2 distinct layers, or phases, to develop a heterogeneous mixture. Benzene is very volatile as well, due to the absence of bonding between its molecules but Van der Waal forces of attraction.Benzene should be handled with extreme caution as it is a powerful skin irritant, a carcinogen and a mutagen. It is also a flammable liquid hence a dangerous fire hazard. (New Jersey Department of Health, 2008)Methanol is polar because of the O-H group attached to it. This gives the alcohol a high boiling point and is also the reason why it is completely soluble in water, it forms Hydrogen bonds with the water molecules.Figure 1 shows exactly how the benzene-methanol mixture would appear except that benzene would set down at the bottom below methanol due to its higher density.It is with this dissimilarity that we proceed to our first method of separation.

Techniques of separationSeparation based on density

i. DecantationDecantation is a technique used to separate the components of a mixture by the difference in their densities.Immiscible liquids, such as benzene and methanol can be separated by using a separating funnel (Figure 2). The mixture is put into a separating funnel, shaken and allowed to settle. Benzene and from two separate layer. The liquid with higher density, in this case benzene, forms the lower layer. Remove the stopper and open the tap after standing. The benzene runs out through the tap. The methanol remains in the funnel and can be run out into another beaker.Figure 2. A separating funnel

This method is a simple separation to implement since it requires no special equipment, but obtaining a complete separation and a totally clear liquid can takes a long time, especially when the difference in density is not large enough.Separations Based on a Change of state

i. Azeotropic distillationWhen we attempt to distill the mixture directly, the mixture will boil at a constant temperature but will not change its composition. This is because the component ratio of unvaporized solution is equal to that of the vaporized solution. Mixtures that behave this way are termed azeotropes.Azeotropes cannot be distilled by straight distillation but only by azeotropic distillation. A standard distillation apparatus is used during the process. In general, a substance called entrainer is added to the mixture to affect the volatility of one of the azeotrope elements. The substance added is relatively non-volatile compared with the components to be separated, and it is therefore fed continuously near the top of the column. In this case, water can be used as entrainer.

Separations Based on a Partitioning Between Phases

a. Solvent ExtractionSolvent extraction or Liquid-liquid extraction is a technique in which a solution (usually aqueous) is brought into contact with a second solvent (usually organic), essentially immiscible with the last, in order to bring about a transfer of one or more solute into the second solvent. In the case of a benzene-methanol mixture, we are dealing with organic solutes, the extraction system will, therefore, involve immiscible organic solvents rather than the aqueous-organic type of extraction. A simple separating funnel can be used for extractions.Choice of solvent1. A high distribution ratio for the solute and a low distribution ratio for undesirable impurities.1. Low solubility in the aqueous phase.1. Sufficiently low viscosity and sufficient density difference from the aqueous phase to avoid the formation of emulsions.1. Low toxicity and flammability.1. Ease of recovery of solute from the solvent for subsequent analytical processing. Thus the b.p. of the solvent and the ease of stripping by chemical reagents merit attention when a choice is possible.Here are some solvents that can be used in this process:a. Ether (Ethyl Ether-very flammable)b. Methylbenzenec. Chloroformd. Tetrachloromethanee. Water ExtractionIt can be accomplished in either a batch operation or a continuous operation.Batch: Extracting the solute from one immiscible layer by simply shaking the two layers until equilibrium is attained. Then the layers are allowed to settle and separated.Batch extraction offers some advantages:1. simple and easy 1. must be repeated several times1. separations readily obtainable1. constant temperatureFor most complete extraction, the best results are obtained by a relatively large number of extractions with small amounts of solvent.Continuous: Continuous extraction makes use of a continuous flow of immiscible solvent through the solution or a countercurrent flow of both phases.Spent solvent is stripped and recycled.

StrippingStripping is the removal of extracted solute from the organic phase for further preparation for detailed analysis.If the solvent is volatile (e.g. diethyl ether) the simplest procedure is to add a small volume of water and evaporate the solvent on a water bath. Care should be taken to avoid loss of solute during the evaporation.It must be pointed out that from the safety point of view, the most dangerous step in extraction procedures is the stripping of volatile solvents by evaporation.

References1. Agency, U. S. E. P., 2014. EPA. [Online] Available at: http://www.epa.gov/otaq/regs/toxics/airtox1b.pdf[Accessed 1 February 2014].2. Anon., 2004. Millipore. [Online] Available at: http://www.biomanufacturing.org/protein_cash/articles/Purification_Liquid_Chromatography.pdf [Accessed 1 February 2014].3. Anon., n.d. Methanex. [Online] Available at: http://www.methanol.org/Technical-Information/Resources/Technical-Information/Physical-Properties-of-Pure-Methanol.aspx[Accessed 1 February 2014].4. Freiser, G. H. M. a. H., 1957. Solvent extraction in Analytical Chemistry. United States of America: John Wiley & Sons, Inc.5. Harker, J. F. R. a. J. H., 1955. Particle Technology and Separation Processes. 2nd ed. Oxford: Butterworth-Heinemann.6. Health, N. J. D. o., 2008. The Official Website for The State Of New Jersey. [Online] Available at: http://nj.gov/health/eoh/rtkweb/documents/fs/0197.pdf[Accessed 3 February 2014].7. John R. Dean, Alan M. Jones, David Holmes, Rob Reed, Jonathan Weyers, Allan Jones, 2002. Practical skills in chemistry. Edinburgh Gate: Pearson Education Limited.8. Renge, V. C., 2013. International Journal for Chemical and Physical Science. [Online] Available at: http://www.ijcps.org/issue7/P2.pdf[Accessed 3 February 2014].9. Richardson, J. M. C. a. J. F., 2005. Chemical Engineering Design. 6th ed. Linacre House, Jordan Hill, Oxford: Elsevier Butterworth-Heinemann.10. Vogel, A. I., 1989. A Textbook of quantitative analytical chemistry. 5th ed. Burnt Mill, Harlow: Longman Group UK Ltd.

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