Separation Unit Operations You Didn’t Learn about in School

Wednesday, June 12, 2013, 2:00pm-3:30pm CDT

Session Chair & Co-Chair:

  • Kevin Joback, Molecular Knowledge Systems, Inc.
  • David Raab

Session Description:

The ingredients for most chemical products must be separated from a reaction mixture or natural source. The most commonly chosen separation process is distillation. But for many chemicals, distillation is not a choice. Mixtures containing chemicals that are heat sensitive, highly viscous or nonvolatile must be separated by other processes. Some of these other separation processes include crystallization, freeze drying, filtration and flotation. Often separating agents, such as solvents, flocculants, or nucleators, are needed. The talks in this session will discuss the guidelines for the selection and design of such separation processes and show examples demonstrating their advantages and disadvantages. 


Scale-Up Droplet to Production Spray DryerNzinga Turner, GEA Process Engineering Inc.
Commercial Evaporator Types – An OverviewJohn Micheli, Middough
Tips and Tools for Solution Crystallization Process DesignPaul Larsen, The Dow Chemical Company

Scale-Up Droplet to Production Spray Dryer

Nzinga Turner, GEA Process Engineering Inc.

Spray Drying has been the chosen technology for discrete particle production dating back to the early 1900’s. Computational Fluid Dynamics (CFD) is one of the developments utilized to better understand the behaviors of various products processed in spray dryers. With the extensive research using CFD there was a gap regarding the effects of heated gas on the atomized droplets in the chamber. Recently this gap was filled by the development of the Drying Kinetics Analyzer (DKA). The DKA opens the doors to visually evaluate the drying process of a single droplet.

Now with the data gathered in DKA analysis can be utilized with CFD modeling in designing new spray drying processes and improve existing installations.

In this presentation we will discuss our ability to examine how an individual particle dries and how varying conditions can impact the final powder morphology and properties. This allows the spray dryer to produce a “custom particle” through adjustment of spray drying parameters determined by DKA. For example, some might want a strong particle not easily damaged during transport; others might require a lightweight powder that dissolves easily. Use of DKA can determine if a given feed will dry into hollow spheres, shriveled particles, “doughnut” shape, etc., and how to design the drying process and equipment to attain a certain type of particle.

Commercial Evaporator Types – An Overview

John Micheli, Middough

Generally, most Unit Operations courses in Chemical Engineering curricula cover basics in fluids, heat transfer, and distillation very well, but the average engineer upon graduation may find that he or she has to deal with a unit operation that was in their text books but was never covered or discussed in class.  Evaporators for removing water or other solvents from solutions are such operations that are used in numerous chemical, pulp & paper, food, agricultural, power, and waste treatment applications.  Evaporators are available in different types and may be configured in many ways to increase steam efficiency. This presentation summarizes the various evaporator types and basic configurations available for different process needs.

Tips and Tools for Solution Crystallization Process Design

Paul Larsen, The Dow Chemical Company

Crystallization from solution is a common unit operation for separating chemical species and producing solids with specific properties. Effective design and scale-up of crystallization requires an understanding of solid-liquid phase behavior and the kinetics of particle formation. In this talk, I will present a workflow for developing crystallization processes and provide guidance on appropriate experimental, analytical, and modeling tools for effective design and scale-up. The workflow includes the following steps:

  1. Define the product. The crystal structure, purity, size and shape impact the product performance and ease of processing or formulation. Key tools for defining and characterizing the solid form include X-ray diffraction, TGA (for solvates or hydrates), DSC, Raman and infrared spectroscopy, and optical microscopy. High throughput experimental methods are useful for identifying potential solid forms.
  2. Select a solvent. The solvent impacts both the phase behavior and crystallization kinetics and therefore affects the process yield, throughput, and product properties. The solvent should be selected not only on the basis of solubility but also based on the solvent’s impact on particle formation. Environmental, health, and safety concerns must be considered as well. Solvent databases, solubility modeling tools, high throughput experimental methods, and heuristics based on crystal structure are useful for solvent selection.
  3. Characterize the phase diagram. The phase diagram dictates the mode of operation and defines the operational window to avoid excessive nucleation, formation of undesired solid forms, and liquid-liquid phase splitting (oiling out). Tools such as OLI Analyzer Studio, SLEEKTM, and DynoChem® are useful for prediction and regression of complex phase behavior.
  4. Select mode of operation and mode of initiation. The mode of operation (cooling, evaporative, antisolvent, reactive) impacts yield, scalability, and operability. The impact is difficult to predict so various modes and configurations should be tested experimentally. Furthermore, crystallization is a path-dependent process: the end result depends on the starting conditions. The method by which crystallization is initiated, therefore, impacts process variability and controllability. Alternative methods for initiating crystallization include primary nucleation; seeding; sonication; and conditioning/digestion.
  5. Determine operating conditions. Operating rates and mixing conditions determine the supersaturation trajectory in the phase diagram, thus influencing the relative rates of nucleation, growth, and agglomeration that control the evolution of the particle population. Experiments at the 1-L scale using in situ analytical tools such as turbidity probes, FBRM, ATR-FTIR, Raman, and video imaging are helpful for assessing the impact of operating rates on the end-product properties. The Bourne protocol is a useful experimental design methodology for assessing the relative importance of macro-, meso-, and micro-mixing.

I will illustrate the application of this workflow using case studies from crystallization process development work at The Dow Chemical Company.