Interviews with Leading Engineers: Q&A with Eric Maynard

This is the third interview (in a series of five) of selected speakers for AIChE's upcoming Northeast Regional Conference at the Chem Show in November. I'm Michelle Bryner (MB), one of the newest editors of CEP. You can learn a bit more about me here. I was excited to be able to interview Eric Maynard (EM), senior consultant at Jenike & Johanson, about his upcoming course on blending and segregation. MB: What challenges do chemical engineers face when developing blending systems? EM: The biggest challenge is that in most cases, mixing and blending remains an art and not a science. In the absence of a scientific approach to choosing the blending equipment and the appropriate operating conditions, engineers often rely on prior operating history. If the company or engineering team has always used a ribbon blender, for example, they will continue to use that type of blender even if it is not optimal for their process. If they're using excessive mix time, which increases cycle time, or they're using excessive energy, they still will stick with using that prior history because that's what they've always done.

Eric Maynard, senior consultant at Jenike & Johanson

Secondly, in engineering curricula in the U.S. -- for mechanical, civil, and chemical engineers -- you usually don't learn about mixing/blending equipment and their selection for a particular process. You may learn about fluid mixers and continuous stirred reactors and tanks, but as for solids mixing, you're often reliant upon vendors and their knowledge or reliant upon other personnel in a plant who have been through the process before -- the school of hard knocks. In fact, many chemical engineers will overrun their blenders. For example, an engineer may run the blender at 1,000 rotations because that's the way it's always been done, when really they just need to turn, let's say, 300 rotations. It comes back to education and whether it's in a college setting or in a conference like the Chem Show, you want to make sure that the attendees understand the ramifications of their actions with blending. We can take a lot of art out of it and put the science back in. MB: How will your course address these challenges? EM: We thoroughly cover the basic technology of mixers and blenders. They're synonymously thought of as the same but in fact mixing and blending can be dissimilar processes. Blending is often when you're combining multiple streams together in a gentle action, whereas mixing could be with a single component, you may have a salt material that has a range of particle size and you need to thoroughly mix that salt usually with higher speed and more agitation. Mixing and blending can be different, and we define that in the course. We define the basic mechanisms of mixing and blending, which are diffusive blending, convective blending, and high-shear blending; go through each of those mechanisms and then most importantly we tie those mechanisms in to types of blenders, both batch and continuous. We also go through the different blender types and we help people understand the challenges that they might face. For instance, instead of using 1,000 rotations at 15 rpm on a tumble blender because that's how it's always been done, we show how to get a uniform blend without being so dependent on speed but rather looking at the number of rotations. And we bring a lot of science back into why that occurs and how you can overblend a material or how you may underblend a material having the incorrect mixer selected for an application. We go into a lot of the mechanics, the types of blenders, and then also how to sample the powders that are being blended so that you can define quantitatively the uniformity of the material, whether it be by particle size or chemical nature. We're really addressing those challenges that result from viewing blending as an art and we give the science behind. We also bring our experience from working on blending for 30 years and our course is very unbiased because Jenike & Johanson doesn't sell blenders; we're just engineers who have designed these systems, operated these systems, and we know what works in industry and what doesn't work. MB: Will you give a real-world example of how your course material could be applied? EM: Before I answer your question, I want to bring up a point that I haven't mentioned yet that ties into the example. Another topic we discuss in the course is that of post-blend handling. Many in industry -- food, pharmaceuticals, chemicals, specialty chemicals -- will focus on the blender doing a good job and that's not a bad focus to have. But at Jenike & Johanson, we also focus on the post-blender handling steps because no matter how well you blend a material, each time you transfer it out of a blender and through a chute or into a bin, for instance, you could induce particle separation and demix the material the blender just mixed. In our course, we cover segregation, the different types of segregation that can occur, and how you can mitigate or solve problems associated with that. For a real world example for a chemical engineer, I would say that knowledge of mixing and blending, sampling, and segregation process, which I cover thoroughly in the course, is absolutely vital when you're blending toxic additives with excipients for the pharmaceuticals industry. Imagine you're a chemical engineer dealing with a cytotoxic drug. Inefficient blending (either in the blender or segregation after blending) of the active ingredient with the inactives, including sugar, starch, and cellulose, could result in tablets with a high concentration of the active ingredient. If someone were to take that super-potent tablet, it could literally be a life-and-death situation. MB: What is timely about the topics that will be discussed in your blending and segregation course? EM: Too much emphasis for years has been placed on sampling in the blender to prove uniformity of the final product. That's very dangerous, because no matter how good a blending job you do in a blender or mixer, when you transfer that powder through additional process steps, there's a propensity for the material to segregate. That being said, in the blending and segregation course, we talk about something called stratified sampling. What's timely about this topic is that a group, which includes Jenike & Johanson, academia, the pharmaceuticals industry, and the U.S. Food and Drug Administration (FDA), is currently working to devise stratified-sampling protocols. We've submitted a draft proposal to the FDA that would require pharmaceutical companies to sample at each point of transfer during the process, as the powder moves from the blender to a drum, to a bin, and so on. MB: When do you expect these protocols to roll out? In the next five years? EM: Absolutely. A draft guidance is already being utilized by most pharma manufacturers. This is something, in my opinion, that is going to be fully adopted and I don't think that industry is going to resist it too much because certainly they want to make sure they are selling and issuing safe products to consumers. And many of the manufacturers heavily involved in the science, whether it's the formulation scientists or the manufacturing engineers, are very confident that they can work through issues of segregation and flow to make sure that the customer is receiving a safe, viable product. See the complete program for AIChE's Northeast Regional Conference at the Chem Show. Register to attend