midterm postlab unit op2.pptx

7/29/2019 midterm postlab unit op2.pptx

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ION EXCHANGE

CHROMATOGRAPHY


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CHROMATOGRAPHY

The word chromatography literally means

colorwriting

Chromatography is a technique for separating

mixtures into their components in order to

analyze, identify, purify, and/or quantify the

mixture or components.


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Chromatography is used by scientists to:

Analyzeexamine a mixture, its components, andtheir relations to one another

Identify determine the identity of a mixture orcomponents based on known components

Purify separate components in order to isolate oneof interest for further study

Quantify determine the amount of the a mixtureand/or the components present in the sample


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Components of Chromatography

1) Matrix (or stationary phase) usually an

inert solid or gel and may be associated with

various moieties, which interact with the

analyte(s) of interest.

2) Mobile phase usually a liquid or a gas, is

used to transport the analytes through the

stationary phase.


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PRINCIPLE: Ion Exchange Chromatography relies on the

reversible exchange of ions in solution with ionselectrostatically bound to an insoluble support

media.

There can be two types of functional groups

covalently attached to the support beads. These arecalled

1) Anion exchangers (resin with positive functional

groups) - negatively charged molecules are attractedto a positively charged solid support.

2) Cation exchangers (resin with negative

functional groups) - positively charged molecules are

attracted to a negatively charged solid support.


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ION EXCHANGE RESIN

An ion exchange resin or ion exchange

polymer is an insoluble matrix (or support

structure) normally in the form of small beads,

usually white or yellowish, fabricated from an

organic polymer substrates.

The material has highly developed structure of

pores on the surface which are sites witheasily trapped and released ions.


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The trapping of ions takes place only with

simultaneous releasing of other ions; thus the

process is called ION EXCHANGE.


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SELECTIVITY/AFFINITY OF IONS The degree to which the exchange takes place is

limited by the preference the resin exhibits for the

ion in solution. Consequently, the use of the resins exchange

capacity will be limited unless the selectivity for theion in solution is far greater than for the

exchangeable ion attached to the resin.Generally, ions with higher valence, greater atomic

weights and smaller radii are said to have a greateraffinity for (be preferred by) ION EXCHANGE resins.Relative affinities of common ions are:

Ag+ > Cs+ > K+ > Na+ > Li+

Ba+2 > Sr+2 > Ca+2 > Mg+2

I- > NO3- > CN- -> HSO4

- > NO2- > Cl- >HCO3

-


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Those substances with high affinities can

continue to load to higher concentrations onthe resins by displacing other previously

exchanged potentially regulated ions with

lower relative affinities. This is referred asCHROMATOGRAPHIC PEAKING.


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RESIN REGENERATION

When the capacity of the resin is exhausted, it

is necessary to regenerate the resin using a

saturated solution to restore the capacity of

the resin and return the resin to its initial

condition. Brine, or sodium chloride solution,

is most the commonly used regenerant,

although others, such as strong acids(hydrochloric acid, sulfuric acid) or strong

bases (sodium hydroxide) may also be used.


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Regeneration Procedure. After the feed solution

is processed to the extent that the resin becomes

exhausted and cannot accomplish any further ionexchange, the resin must be regenerated.,

Regeneration employs the following basic steps:

1. The column is backwashed to remove

suspended solids collected by the bed during the

service cycle and to eliminate channels that may

have formed during this cycle. The back- washflow fluidizes the bed. releases trapped particles.

and reorients the resin particles according to size.


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During backwash the larger, denser particles willaccumulate at the base and the particle size will

decrease moving up the column. This distributionyields a good hydraulic flow pattern and resistance tofouling by suspended solids.

2) The resin bed is brought in contact with the

regenerant solution.3) The resin bed is subjected to a fast rinse that

removes the last traces of the regenerant

solution and ensures good flowcharacteristics.

4) The column is returned to service.


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BATCH AND COLUMN EXCHANGE SYSTEMS

Ion exchange processing can be accomplished byeither a BATCH METHOD or a

COLUMN/CONTINUOUS METHOD.

1) BATCH METHOD

The resin and solution are mixed in a batch tank,

the exchange is allowed to come to equilibrium,

then the resin is separated from solution

Fundamental concept involved is ChemicalEquilibrium k (assign: Recall calculations

involving chemical equilibrium)


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2) CONTINUOUS/COLUMN METHOD

Continuous ion exchange processes areusually of the down-flow and packed-bed

column type

Passing a solution through a columncontaining a bed of exchange resin is

analogous to treating the solution in an

infinite series of batch tanks


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The primary residual generated by ion

exchange processes is the SPENT

REGENERANT. The spent regenerant will have

very high total dissolved solids (TDS)concentrations, as it will include all of the ions

removed by the resin as well as the excess

regenerant ions


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In water treatment, it is primarily used for softening where

calcium and magnesium ions are removed from water


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PAPER CHROMATOGRAPHY


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Paper chromatography is the technique inwhich the separation of an unknown

substance is mainly carried out by the flow of

solvents on the specially designed

chromatographic paper.

Paper chromatography is an analytical

method technique for separating and

identifying mixtures that are or can be

colored, especially pigments.


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A few categories of pigments are listed below

along with their characteristic range of colors.


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Some plant pigments you may be familiar withthat are of current interest in nutritional andpharmaceutical research are listed below


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Performing a paper chromatography

experiment is basically a three-step process:

1) application/treating of the sample

2) "developing" the chromatogram by

allowing the mobile phase to move up the

paper, and

3) calculating Rfvalues


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R Value

The retention factor (R) may be defined as theratio of the distance traveled by the substance

to the distance traveled by the solvent.

distance traveled by substance from application point

distance traveled by solvent from application point

It represents the movement or migration of

solute relative to the solvent

Rf=


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PIGMENT VISIBLE RF VALUE

Carotene Yellow 0.98

Alpha Carotene Yellow Orange 0.97

Xanthopyll Yellow 0.86

Beta Carotene Yellow Orange 0.94

Xanthophyll Red 0.8

Lycopene Yellow Orange Red 0.81

Phaeophytin Dark Gray 0.67

Leutein Yellow Brown 0.75


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Phaeophytin Light Gray 0.6

Violaxathin Yellow Brown 0.66

Xanthophyll Yellow 0.5

Neoxathin Yellow Brown 0.28

Chlorophyll Light Blue Green 0.48

Chlorophyll Dark Blue Green 0.46

Chlorophyll Light Yellow Green 0.30

Chlorophyll Dark Yellow Green 0.25


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USES OF PAPER CHROMATOGRAPHYPathology and Forensic

SciencePaper chromatography is useful inthe field of forensic science, forinvestigation of crime. This isbecause this process can besuccessfully carried out even with

very small quantities of material.Samples from crime scenes arecollected to be analyzed andidentified, using this technique.

Used in DNA and RNA

fingerprinting. Pathologicallaboratories use paperchromatography to detect thepresence of alcohol or chemicals inblood.


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Qualitative Analysis

Paper chromatography is one ofthe methods of qualitativeanalysis, to analyze or separatethe different constituents of amixture. It is a useful tool forseparating polar as well as

nonpolar solutes. Pharmaceuticalcompanies use this technique toanalyze the different compoundsin drugs.

Used in the testing ofantibiotics and determining thepollutants in water.


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GAS ABSORPTION PRESSURE DROP

MEASUREMENT


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Packed towers are vertical columns filled with

suitable packing and normally operate

countercurrently.

Liquid enters the top of the column and is

distributed over the top of the column packing

via nozzles or distributor plates. Liquid flows

downward while contacting with the vaporphase.

PACKED TOWER/COLUMN


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The liquid flows downward through thepacking against the pressure and the flowinggas phase because the liquid is appreciablydenser than the gas and so is pulled down bygravity.

If we keep the flow rate of either liquid or gasconstant and increase the flow rate of theother phase, we will eventually come to alimiting condition in which counter-currentflow cannot be maintained. This limitingcondition is called FLOODING.

Internal packing provides a large surface area for two


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Internal packing provides a large surface area for two-phase contact and facilitates transfer of materialsbetween phases.


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You can also consult p. 570 of McCabe and Smith 7 th edition for more information


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ANALYSIS OF PRESSURE DROP IN

PACKED COLUMNS As the flow rate of liquid or gas is increased

through a packed column of constant

diameter, the pressure drop per foot of

packing increases.

The pressure drop is greater than that in dry

packing, because the liquid in the towerreduces the space available for gas flow.


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When the packing is dry, the line obtained is

straight and has a slope of about 1.8. The

pressure drop therefore increases with the 1.8power of the velocity.

If the packing is irrigated with a constant flow

of liquid, the relationship between pressuredrop and gas flow rate initially follows a line

parallel to that of the dry column.


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With a dry packing (i.e. no liquid flow, L = 0),

pressure drop increases as gas velocityincreases according to the linear relationship

as shown by line a-a

With liquid flowing in the column, thepackings now become wetted (irrigated). Part

of void volume in the packings now filled with

liquid, thereby reducing the cross-sectional

area available for gas flow.


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For a constant liquid flow (say L = 5000),

at low to moderate gas velocity G; the

pressure drop characteristics is similar to that

of dry packings, i.e. section b-c of the plot isstill straight on log-log plot. Up to this point,

there is an orderly trickling of the liquid down

the packings. There is no observable liquidbeing trapped among the packings (no liquid

hold-up).


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As the gas velocity is increased further, thepressure drop increased. Some liquid startedto be retained in the packings. When point c is

reached, the quantity of liquid retained in thepacked bed increases significantly. There isa change in slope of the line at point c aspressure drop increases more rapidly with

G.Point c is known as the loading point, asliquid starts to accumulate (load) in thepackings.


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From point c to d to e, there is a sharp

increase in pressure drop at higher G: there is

a greater amount of liquid hold-up, a gradual

filling of the packing voids with liquid (startingat the bottom of the column), and the column

is slowly "drowned" in the liquid.


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At point e, there is another sharp change in

the slope. At this point the entire column is

filled liquid and the gas now has to bubble

through the liquid in the packing voids. Thegas pressure drop is now very high. Point e is

known as the flooding point. The gas velocity

at this point is known as the flooding velocity(limiting velocity)


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Points to Note

At constant liquid rate, gas pressure dropincreases with gas velocity.

t constant gas velocity, the gas pressure drop ishigher at larger liquid rate.

Each liquid rate has its own loading and flooding

points.At higher liquid rate, the loading and floodingpoints occur at lower gas pressure drop.

Operation of a gas absorption column is not

practical above the loading point. For optimumdesign, the recommended gas velocity is 1/2 ofthe flooding velocity.

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midterm postlab unit op2.pptx