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Understanding liquid-liquid dispersions - turns out an easy way for me to understand process engineering is through my stomach...

Published on 03 June 2021

Understanding liquid-liquid dispersions - turns out an easy way for me to understand process engineering is through my stomach...

Kate GoldbergBy Kate Goldberg, Head of Marketing

It's safe to say that I am not technically minded. In a company that predominantly employs highly skilled, specialist engineers who solve complex projects for our clients, I'm definitely not the first person you'd turn to in order to double-check a calculation. My time is mostly spent trying to understand our client's wants and needs. In short, once said calculation is completed, I'll be the person asking what value the answer offers to our clients.

Needless to say, a lot of my time is spent talking to my colleagues to understand the benefits of the solutions we provide. Because in all honesty, that's what I'm really interested in.

One such colleague, Gustavo Padron, has recently been in Toulouse at the MIXING 16 conference, presenting some of the work developed through BHR Group's Fluid Mixing Processes research consortia, FMP.  

He presented a poster, which showed in detail the approach he and the team undertook to analyse the effect of impeller type on drop size in liquid-liquid dispersions. As a novice, this might as well be in a different language. Therefore, David Brown, who heads up our Process team very kindly took some time to explain the work in a way that I would understand.

As ever, I started with the why question. Why do the project? What's the point? How will it benefit the client? (I can be quite demanding). To answer the question in a way that someone without extensive experience in chemical engineering could understand, David keenly tapped into a subject that I'd be quite happy to talk about all day - food.

If you’ve ever struggled to make your own mayonnaise, you might have wondered how manufacturers achieve that perfect consistency.

Droplet size (in this case, olive oil) is one of the most important parameters to control in a liquid-liquid dispersion or emulsion - it’s the way to maintain the creamy consistency.

If the droplets of olive oil are processed to make them smaller it will make the dispersion smoother and more stable – because who wants lumpy, separated mayonnaise? 

This is something that BHR Group#s chemical engineers work on a lot, as it is a critically important process for many of our FMP members in the food and personal care industries. It’s (relatively) easy making it in a jar in the kitchen, but how about making 2000 litre batches, or even continuously manufacturing tonnes per hour?

So if you're scaling up from kitchen to production, you really need to get the mixing right.

Mixers are often sold as either “high shear” or “low shear”.

It is generally accepted that "high shear" impellers mix very intensely and are the first choice for generating small droplets and hence smooth and stable emulsions. Conversely, the "low shear" impellers are seen as having a much more gentle action and so do not deliver the same results. 

What  BHR Group’s work shows is that if you put the same power into each type of mixer, the low shear designs can actually make smaller droplets.

This innovative research has turned our understanding of the difference between low and "high shear" on its head. We now understand that this is to do with the maximum local intensity of mixing for the different impeller types. This insight enables engineers to select the most appropriate impellers for their processes and can therefore reduce production time and so save money.

It took me a bit of time to understand it, but I'm fully on board (who wouldn't be if you can measurably save time and money?) Unfortunately for my waistline, I'm also thinking of something nice to eat, featuring, of course, some creamy mayonnaise...