Lecture Notes 7

Lecture Notes 7 - Scopes sec 1.3 (principles of column...

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Unformatted text preview: Scopes sec 1.3 (principles of column chromatography) and Belter ch 6 (adsorption) Adsorption vs Chromatography Column Adsorption/desorption (full binding) Adsorption: captures a product from a feed stream by binding it to an adsorbent (resin) in the column Desorption: then releases product into a new stream introduced to the column Load soln volume > col volume Regarded as an isolation step can concentrate the product Column Chromatography (partial binding) Separates solutes by differences in their migration speeds in a column with a mobile phase (buffer) flowing through it High resolution possible: can remove impurities similar to the product Load soln (injection) volume << col volume Regarded as a purification step - does not concentrate the product QUESTION 1 migration speed A small volume containing a mixture of three solutes, 1, 2, and 3, is injected into the inlet of a packed column and then a steady flow of mobile phase is fed into the column. Inside the column, each solute molecule begins to interact with the resin as described below: the dynamic equilibrium between solute 1 and the resin has 20 % of it adsorbed and 80 % of it in the mobile phase; 80 % of solute 2 is adsorbed, 20 % is in the mobile phase; 99 % of solute 3 is adsorbed, 1 % is in the mobile phase; After the mobile phase front has passed through the column and just reached the column exit, where is each solute? A : 1 2 3 B : 3 2 1 C : 3 2 1 D : 1 2 3 col inlet col outlet ANS 1= B A : 1 2 3 B : 3 2 1 C : 3 2 1 D : 1 2 3 col inlet col outlet Whenever a solute molecule is adsorbed (or even simply inside the resin bead) it is not advancing through the column. The fraction of time it is adsorbed equals the fraction of its mass that is adsorbed. Likewise, the fraction of time a solute is in the mobile phase equals the fraction of its total mass in that phase. For ex, 20 % of solute Bs mass is in the mobile phase at any moment, so it is moving at 20 % of the speed of the mobile phase. When the mobile phase front has reached the column exit, solute B has travelled only 20 % of that distance. The Isotherm Graph y , solute conc dissolved in liquid (mass solute / vol liquid ) q , solute conc bound to resin (mass solute/ vol resin ) Typical resin volume basis is the packed volume or settled volume. Sometimes use mass solute/ mass resin QUES 2- Interpreting isotherms y eq q eq In a batch process, resin is added to a tank holding a solution and some of the solute is adsorbed from the solution onto the resin. The isotherm graph shows the conc of the solute in the solution, y eq , and on the adsorbent, q eq , after equilibrium is reached....
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Lecture Notes 7 - Scopes sec 1.3 (principles of column...

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