[PDF] Emulsion Processing - Homogenization

1 Emulsion Formation, Stability, and Rheology

Coalescence This refers to the process of thinning and disruption of the liquid film between the droplets with the result of fusion of two or more droplets into larger ones The limiting case for coalescence is the complete separation of the emulsion into two distinct liquid phases The driving force for coalescence is the surface or film

Emulsions –Part 2

coalescence is not a single stage process but comprises at least four elementary steps: • contact at a distance that allows aattractive interaction, • the drainage of the continuous phase film between the drops, • the rupture of the film, • the collapse of the droplets nowadays aggregation processes

Emulsion Processing - Homogenization

Disruption Coalescence 12 Factors Affecting Droplet Size: Emulsifier Concentration 0 2 0 4 0 6 0 8 1 1 2 1 4 0 0 2 0 4 0 6 0 8 Once the emulsifier concentration

Emulsions - Max Planck Society

This makes an emulsion very prone to coalescence processes which lead to a decrease in ∆A and subsequently in ∆W The conclusion is straightforward that ultimate stability against coalescence processes is only achieved if s approaches zero ∆ =σ⋅∆W A The increase in the energy of an emulsion compared to the non-

LECITHINS - Cargill

to prevent water coalescence during heating, while keeping spattering to a minimum In gravies, soups and sauces, lecithin’s stabilizing, emulsifying and dispersion properties can help create the consistent, smooth textures consumers expect It can also be used as a release agent, serving as a nonstick barrier between foods and contact surfaces

Tack CoatBest Practices

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CHAPTER 11 EMULSION BREAKING

active agent or neutralization of the charged oil droplet 2 Flocculation: This is agglomeration of the neutralized droplets into large, separable globules Traditionally, sulfuric acid has been used in oily waste treatment plants as the first step in emulsion breaking Acid converts the carboxyl ion in surfactants to

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agent systems through middleware that complies with the FIPA specifications and through a set of graphical tools that supports the debugging and deployment phases The agent platform can be distributed across machines (which do not even need to share the same operating system) and the configuration can be controlled via a remote GUI

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Emulsion Processing

- Homogenization -

Jochen Weiss

Principle of Emulsion Formation

Oil Water

Primary

HomogenizationSecondary

Homogenization

EI Q BT /R9 18 Tf

0 1.00187 -1 0 485.16 348 Tm

[(P r e m i x 2

Emulsion Processing:

Homogenizers

Oil Water

Homogenizer

Homogenization is a unit operation using a class of processing equipment referred to as homogenizersthat are geared towards reducing the size of droplets in liquid-liquid dispersions 3

Physiochemical Processes Occurring During

Homogenization

Rapid adsorption:Stable dropletsSlow adsorption:Coalescence

Droplet

Deformation

Disruption

Continuous

phase

Dispersed

phaseEmulsifier

I. Pre-

homogenizationII. HomogenizationIII. Stabilization 4 The order of ingredient addition and homogenization may have a large impact on product properties (A) (B)

General Homogenization Options

5

Homogenization:

Process Parameters

■Energy density-minimum droplet size achievable■Energy efficiency-heat losses-manufacturing costs■Volume Flow Rates-throughput -production time■Product rheology-limitations -materials that can be homogenized

6

The Physics of Droplet Disruption

•Maintaining Force. Drop shape maintenance forces (Laplace Pressure) •Disruptive Force. Drop disruption is due to drop-surface applied tangential stresses

•Weber-Number (We): The ratio between drop disrupting and drop maintaining forces, drop disruption occurs only above a critical Weber number

-We < We crit or t br< t br,crit droplet deformation -We > We crit or t br> t br,crit droplet disruption

•Deformation Time. Droplets must be exposed to tangential stresses for a sufficient amount of time

1 21 1 4

cp r r d 4 c d Wep ,d br crit c t pητ=

Key Parameter:

Energy Density E

v • The volume specific energy input or the energy density E vcan simply be calculated from the power consumption and the volume flow rate • The mean droplet diameter may often be empirically related to the energy density, IF, all other parameters are kept constant!

Energy input

homogenized volume vv v E P E Pt

V V= = =&( )

1,2 b v x C E 8

How Droplets Are Disrupted:

Flow Situations in Homogenizers

Elongational

FlowRotational

FlowSimple Shear

Flow

Flow profiles are complex based on geometry of homogenizer. Flow may be laminar (rotational, simple shear, elongation) or

turbulent. 9

Simple Deformation Scenarios For Liquid-

Liquid DispersionsRotation of

whole droplet

Circulation of

fluid within dropletElongation of droplet

Disruption of

droplet "Neck"

Formation

Increased Exertion of Stress Due to Superimposed Flow Profile 10

Role of Emulsifiers in Emulsion

Formation and Stabilization

Stabilization

Formation

Rapidly adsorbLower interfacial tensionFacilitate breakup Generate repulsive forcesForm resistant membranePrevent Coalescence 11

Optimum Emulsifier Characteristics for

Emulsion Formation

• Objective: to generate small stable droplets - Rapid adsorption - Lower interfacial Tension - Form protective membrane

Disruption Coalescence

12

Factors Affecting Droplet Size:

Emulsifier Concentration

0.20.40.60.811.21.4

0 0.2 0.4 0.6 0.8

Once the emulsifier

concentration exceeds a certain level the droplet size depends on the energy input of the homogenizer.

Corn O/W emulsion - Pandolfe (1995)

Fixed Homogenization

Conditions (1000 psi)

Emulsifier/Oil

Mean Droplet Diameter [μm]

Factors Affecting Droplet Size:

Emulsifier Type

012345

0 5 10 15

FastSlowInsufficientDenaturation

Depends on:

Emulsifier Type Emulsifier Conc.Solution Conditions Mechanical Device

Mean Droplet Diameter [μm]

E [MJm

-3]

Characterizing Emulsifier Efficiency During

Homogenization• Maximum amount of oil that can be homogenized by fixed amount of emulsifier using standardized conditions (homogenization, pH, I, T)

- EAI (g oil / g emulsifier) - Emulsifier activity index

• Minimum amount of emulsifier required to achieve a given droplet size using standardized conditions (φ, homogenization, pH, I, T)

- c min (g emulsifier / g oil) • Minimum droplet size that can be achieved by homogenization - r min (μm) 15

HomogenizersHigh Speed Blender

High Pressure Homogenizers

Colloid Mill

High Shear Dispersers

Ultrasonic Disruptor

Membrane Homogenizers

16

Homogenizers:

A General Overview (I)

17

Homogenizers:

A General Overview (II)

I. High Speed Blenders

• Low volume specific energy input (energy density) • Energy input highly distributed in the stirred vessel (regions of low and high shear) • Blender geometry and rotational speed are the prime parameters turbulent flows preferred. • Broad particle size distribution, large particles • Need to avoid air incorporation to avoid foam formation • Fairly inexpensive usually used for premix production 19

II. High Pressure Homogenizer (HPH)

• Most common used homogenizer in the food industry (milk, cream etc.) • Disruptive energy comes from relaxation of high pressure build up across homogenization valve • Pressures typically range from 50 to

500 bar (microfluidizer up to 1600 bar)

• Homogenization valve geometry of key importance influences flow profile • Homogenization may be single or multiple stage

Shear, Turbulent &

Cavitation Forces

20

Physical Process Inside the Homogenization

Valve

• On entering the homogenization valve, the flow speed greatly increases pressure drops (Bernoulli) to reach the vapor pressure

p

Dat point A

• Since p

Dis lower than the external pressure p

A cavitation and two phase fluid flow

• Pressure signal transduction in multi-phase flows is slower than in single phase flow equilibration with external pressure occurs late (close to exit)

• Sudden pressure jump leads to collapse of cavitational bubbles and the flow reverts to a one-phase flow

• Droplet disruption is therefore due to - Laminar and turbulent flow at entrance of valve (a)quotesdbs_dbs6.pdfusesText_12