L7: Solid Liquid Extraction and flocullation

Question 1

What is the main objective of flocculation in bioprocessing?

Answer 1

To aggregate cells or cell debris, increasing particle size to improve centrifugation or filtration.

Question 2

What are the two primary mechanisms by which flocculation occurs?

Answer 2

Neutralizing charges on particles and bridging particles together.

Question 3

Why is flocculation often necessary after cell disruption?

Answer 3

To remove cell debris efficiently, reduce contaminants, and improve downstream processing.

Question 4

What two forces affect colloid particles in suspension?

Answer 4

Electrostatic repulsion and Van der Waals attraction.

Question 5

Why are most bioparticles in solution negatively charged?

Answer 5

Due to their surface charge properties, which necessitate charge neutralization for aggregation.

Question 6

What are the main types of flocculants used in bioprocessing?

Answer 6

Metallic salts (e.g., aluminum and iron salts) and poly-ionic polymers.

Question 7

What is the role of charge neutralization in flocculation?

Answer 7

It reduces surface charges, allowing particles to aggregate via Van der Waals forces.

Question 8

What are the disadvantages of using high concentrations of salts for flocculation?

Answer 8

High salt concentrations can complicate subsequent downstream processes.

Question 9

What is polymer bridging in flocculation?

Answer 9

Poly-ionic polymers form bridges between adjacent particles, facilitating aggregation.

Question 10

How do monovalent, divalent, and trivalent ions differ in flocculation effectiveness?

Answer 10

They require ratios of 1000:10:1 relative to the solute to achieve aggregation.

Question 11

What contaminants can flocculation remove from cell homogenates?

Answer 11

DNA, RNA, lipids, colloidal proteins, and other solids.

Question 12

What are the main advantages of borax as a flocculant?

Answer 12

Selectively removes carbohydrates, is cheap and safe, and allows online operations with minimal protein loss.

Question 13

What are the disadvantages of using borax in flocculation?

Answer 13

Limited applicability and inability to remove non-carbohydrate solids like lipids and nucleic acids.

Question 14

How does polyethyleneimine (PEI) function as a flocculant?

Answer 14

It removes RNA, DNA, lipids, and colloidal proteins but is hard to remove and can foul chromatography columns

Question 15

Why is borax-PEI sequential treatment preferred over simultaneous application?

Answer 15

High solids content makes simultaneous treatment impractical for centrifugation.

Question 16

What are the steps in solid-liquid extraction (leaching)?

Answer 16

Solvent extracts the compound from a solid, followed by filtration and possible precipitation.

Question 17

What factors influence mass transfer in solid-liquid extraction?

Answer 17

Molecule size, solvent type, temperature, and the solid’s porous structure.

Question 18

Why is multi-stage extraction often necessary in solid-liquid extraction?

Answer 18

To improve yield and purity of the extracted product.

Question 19

What are the most commonly used organic solvents in solid-liquid extraction?

Answer 19

Halogenated solvents (e.g., chloroform) and non-halogenated solvents (e.g., ethanol, acetone)

Question 20

How is precipitation used to recover solutes after solid-liquid extraction?

Answer 20

By natural settling, lowering temperature, or adding an antisolvent to reduce solubility.

Question 21

What are the benefits of green solvents like Deep Eutectic Solvents and Ionic Liquids?

Answer 21

They are biodegradable, non-toxic, and reduce solvent and energy consumption.

Question 22

What are Deep Eutectic Solvents (DESs), and how are they formed?

Answer 22

They are mixtures of hydrogen bond donors and acceptors, tunable for polarity and cheap to synthesize.

Question 23

What distinguishes Natural Deep Eutectic Solvents (NADESs) from traditional DESs?

Answer 23

NADESs are derived from natural compounds like terpenes and fatty acids, making them non-toxic and plant-based.

Question 24

Why are green solvents considered the future of solvent extraction?

Answer 24

They improve sustainability by reducing toxicity, enhancing biodegradability, and integrating unit operations.

Question 25

What is the overall purpose of flocculation and solid-liquid extraction in bioprocessing?

Answer 25

To efficiently aggregate and remove contaminants, extract bioproducts, and optimize downstream processing.