Microchannel Processing: A Novel Approach to Making Emulsions

Jun 1, 2011 | Contact Author | By: Mark Grace, Velocys Inc. and Larry Plonsker, Chemical Network Associates
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Title: Microchannel Processing: A Novel Approach to Making Emulsions
microchannel emulsificationx particle sizex stabilityx shearx energy consumptionx
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Keywords: microchannel emulsification | particle size | stability | shear | energy consumption

Abstract: In the present article, microchannel emulsification is explored as a process method that precisely adds a dispersed phase into a continuous phase through an engineered dispersion plate. This approach is shown to produce emulsions with smaller droplets having tighter size distributions than conventional means, which leads to stable products with the limited need, if any, for surfactants.

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M Grace and L Plonsker, Microchannel Processing: A Novel Approach to Making Emulsions, Cosm & Toil 126(6) 446 (2011)

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Emulsions, i.e., mixtures of immiscible liquids, are the cornerstone of the personal care and cosmetics industries. In the form of hand lotions, shampoos, shaving creams, sunscreens and more, they enable a wide variety of ingredients to be quickly and conveniently delivered to hair and skin. However, despite their ubiquity, many possible ingredients experience significant changes in physical properties under high shear conditions, such as in traditional emulsification equipment. For example, many large molecules, both natural and synthetic, are non-Newtonian fluids. By definition, these fluids change their rheological properties under shear conditions. Examples include solutions of cornstarch and xanthan gum.

Traditionally, emulsions are formed under high shear conditions using static mixers, ultrasound devices, homogenizers or rotor/stator mixers but due to the limitations of these mixing technologies, compositions and processing conditions are typically over-designed to ensure product requirements are met. This results in the use, and often overuse, of chemical surfactants, the over-shearing sensitive materials, and high energy consumption. As an alternative, the authors propose the method of microchannel emulsification to enhance process control, thus enabling the introduction of new products to the market.

Microchannel Emulsification

Emulsification is one of the many applications of microchannel process technology. This technology platform is based on performing process unit operations in very small channels rather than large vessels. Microchannel technology holds many parallels with microelectronics, which revolutionized the computer industry by shrinking processing hardware while improving performance. The result was processing equipment that is much smaller, less costly and more efficient. To date, microchannel technology has been applied to the production of biofuels as well as various petrochemical processes.1

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Figure 1. Schematic of a microchannel emulsifier

Figure 1. Schematic of a microchannel emulsifier

In microchannel emulsification, droplets as small as 1 micron or less are formed one at a time by pushing the dispersed phase of a traditional o/w or w/o emulsion system into a continuous phase through a specially designed porous dispersion plate (see Figure 1).

Figure 2. Microchannel emulsification evaluation setup

Figure 2. Microchannel emulsification evaluation setup

To test the ability of the microchannel process technology to form stable emulsions with even particle size distribution, a simple o/w shea butter hand lotion was formulated (see Formula 1) and put through the device (see Figure 2) equipped with heat exchangers and compatible pumps that feed the formula phases in a steady, controlled manner.

Figure 3. Shea butter hand cream formulation made by microchannel and conventional means

Figure 3. Shea butter hand cream formulation made by microchannel and conventional means

As seen in Figure 3, the emulsions resulting from the microchannel device exhibited a narrow, single peak droplet size distribution, while the conventionally mixed emulsions had a wider, double peak distribution.

Figure 4. Droplet size comparison for example hand lotion formulation with varying flow rates

Figure 4. Droplet size comparison for example hand lotion formulation with varying flow rates; legend: 190 mL/min (red); 380 mL/min (green); 770 mL/min (blue)

Legend: 190 mL/min (red); 380 mL/min (green); 770 mL/min (blue)

Figure 5. Droplet size comparison for example hand lotion with varying dispersion plates

Figure 5. Droplet size comparison for example hand lotion with varying dispersion plates

Legend: 1µm pore plate (red); 40 µm pore plate (green)

Figure 6. Droplet size comparison of example hand lotion with in-line cooling

Figure 6. Droplet size comparison of example hand lotion with in-line cooling

Legend: 75°C (red), 45°C (green)

Formula 1. Example hand lotion formulation

Stearic Acid (Emersol 132NF, Cognis) 3.0% w/w
Glyceryl Monostearate 3.0
Mineral Oil (and) Lanolin Derivative  10.00
Acetulan  1.0
Sweet Almond Oil 3.5
Shea Butter 2.0
Water (aqua) 72.0
TEA 1.0
Propylene Glycol 4.5
  100.00

 

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