1st Year • ER20-11T

Pharmaceutics (ER20-11T): Unit 3 - Mixing & Filtration Technology

Compiled by Pharmacist365 Academic Council

Unit 3 • ER20-11T

Mixing, Homogenization & Filtration

Pharmacy Council of India (PCI) ER-2020 Standard Lecture Notes

1. Liquid and Powder Mixing Principles

Mixing is defined as an operation in which two or more distinct components are treated so that each unit (particle, molecule) of one component lies as nearly as possible adjacent to a unit of each of the other components.

Types of Pharmaceutical Mixtures:

Positive Mixtures: Form spontaneously with complete miscibility (e.g. alcohol and water, true solutions).

Negative Mixtures: Thermodynamically unstable; separate unless continuous external energy or stabilizers are added (e.g. emulsions, suspensions).

Neutral Mixtures: Static equilibrium without tendency to mix spontaneously or separate easily (e.g. pastes, toothpastes, ointments).

2. Filtration Theory & Mathematical Formulation

The rate of filtration through a porous bed of solid particles is governed by Darcy's Law:

$$\frac{dV}{dt} = \frac{K \cdot A \cdot \Delta P}{\eta \cdot L}$$

Where:

$dV/dt$ = Rate of filtration (volume per unit time)
$K$ = Permeability coefficient of the cake
$A$ = Surface area of the filter bed
$\Delta P$ = Pressure drop across the filter
$\eta$ = Viscosity of the liquid filtrate
$L$ = Thickness of the filter cake

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