L7: Solid Liquid Extraction and flocullation Flashcards
What is the main objective of flocculation in bioprocessing?
To aggregate cells or cell debris, increasing particle size to improve centrifugation or filtration.
What are the two primary mechanisms by which flocculation occurs?
Neutralizing charges on particles and bridging particles together.
Why is flocculation often necessary after cell disruption?
To remove cell debris efficiently, reduce contaminants, and improve downstream processing.
What two forces affect colloid particles in suspension?
Electrostatic repulsion and Van der Waals attraction.
Why are most bioparticles in solution negatively charged?
Due to their surface charge properties, which necessitate charge neutralization for aggregation.
What are the main types of flocculants used in bioprocessing?
Metallic salts (e.g., aluminum and iron salts) and poly-ionic polymers.
What is the role of charge neutralization in flocculation?
It reduces surface charges, allowing particles to aggregate via Van der Waals forces.
What are the disadvantages of using high concentrations of salts for flocculation?
High salt concentrations can complicate subsequent downstream processes.
What is polymer bridging in flocculation?
Poly-ionic polymers form bridges between adjacent particles, facilitating aggregation.
How do monovalent, divalent, and trivalent ions differ in flocculation effectiveness?
They require ratios of 1000:10:1 relative to the solute to achieve aggregation.
What contaminants can flocculation remove from cell homogenates?
DNA, RNA, lipids, colloidal proteins, and other solids.
What are the main advantages of borax as a flocculant?
Selectively removes carbohydrates, is cheap and safe, and allows online operations with minimal protein loss.
What are the disadvantages of using borax in flocculation?
Limited applicability and inability to remove non-carbohydrate solids like lipids and nucleic acids.
How does polyethyleneimine (PEI) function as a flocculant?
It removes RNA, DNA, lipids, and colloidal proteins but is hard to remove and can foul chromatography columns
Why is borax-PEI sequential treatment preferred over simultaneous application?
High solids content makes simultaneous treatment impractical for centrifugation.
What are the steps in solid-liquid extraction (leaching)?
Solvent extracts the compound from a solid, followed by filtration and possible precipitation.
What factors influence mass transfer in solid-liquid extraction?
Molecule size, solvent type, temperature, and the solid’s porous structure.
Why is multi-stage extraction often necessary in solid-liquid extraction?
To improve yield and purity of the extracted product.
What are the most commonly used organic solvents in solid-liquid extraction?
Halogenated solvents (e.g., chloroform) and non-halogenated solvents (e.g., ethanol, acetone)
How is precipitation used to recover solutes after solid-liquid extraction?
By natural settling, lowering temperature, or adding an antisolvent to reduce solubility.
What are the benefits of green solvents like Deep Eutectic Solvents and Ionic Liquids?
They are biodegradable, non-toxic, and reduce solvent and energy consumption.
What are Deep Eutectic Solvents (DESs), and how are they formed?
They are mixtures of hydrogen bond donors and acceptors, tunable for polarity and cheap to synthesize.
What distinguishes Natural Deep Eutectic Solvents (NADESs) from traditional DESs?
NADESs are derived from natural compounds like terpenes and fatty acids, making them non-toxic and plant-based.
Why are green solvents considered the future of solvent extraction?
They improve sustainability by reducing toxicity, enhancing biodegradability, and integrating unit operations.
