Progress with Solids Takes Shape

Particles pose unique challenges — their size, size distribution, shape, cohesiveness and other attributes can dramatically affect how they act. So, a good grasp of particle properties often is key to successful processing. Fortunately, new research initiatives and technologies will help engineers get a much firmer grip.

One such initiative is the Engineering Research Center (ERC) for Structured Organic Particulate Systems based at Rutgers University, Piscataway, N.J. Freeman Technology, Malvern, U.K., a particle analysis and characterization expert and developer of the FT4 powder rheometer (www.ChemicalProcessing.com/articles/2009/095.html), is the latest company to join the ERC.

As part of this initiative, Freeman has installed FT4s at Rutgers, New Jersey Institute of Technology, Newark, N.J., and Purdue University, West Lafayette, Ind., to do studies on particle formation and functionalization.

There are two major goals here: to develop new methods for controlled-size particle formation that can be effectively scaled to the manufacturing level; and to control and optimize physicochemical properties of materials such as size, shape and stability through systematic functionalization. Both goals require development of requisite characterization techniques for effective measurement of critical particle properties and process monitoring.

Overall, the plan is to replace empirical methods currently used in the processing industries with a predictive framework for science-based product and process development.

Real-World Relevance
The aim of this and the company's own research, according to Reg Freeman, managing director, is to be able to describe and predict the various behavior modes of powders that occur in everyday processing.

Consistent Results

Figure 1. Sample conditioning ensures high reproducibility for accurate measurement using FT4 rheometer.
Source: Freeman Technology.
 

Underpinning this is the company's conditioning process, which ensures that the packing condition of a powder sample is reproducible for testing. Repeatability (on a specific instrument and with a particular operator) and reproducibility (for any instrument/operator around the world) is very important and impossible to achieve without a conditioning process, he says.

"For example, a single light tap when placing a sample onto a work surface would cause flow energy to increase by typically 30%. Conditioning removes such an effect and also ensures that the operator's methodology for loading the sample, etc., does not affect the measured result," he notes.

The Freeman approach is to provide high reproducibility and sensitivity of measurement for all types of powder behavior. The FT4 powder rheometer (Figure 1) gives dynamic flowability measurement and determines bulk properties including compressibility, permeability and bulk density.

"The subject is challenging due to the inherent complexity of powder flow and the difficulty of predicting flow behavior in real processing environments. Much research is being done by companies and universities worldwide and we have collaborative projects with some of these as well as with other instrumentation companies like Malvern Instruments," Freeman adds.

Understanding powder behavior can be daunting but a pragmatic approach can be very effective, says Freeman. It involves making good use of process experience most companies already have.

"The process plant will have been a major investment and often is used to manufacture or process various formulations, whether making bulk material, filling bags or making tablets or capsules. Process engineers will know which materials process efficiently and which are problematic — prone to stoppages and quality issues. Our perspective is that with the FT4 it is now possible to understand why some powders process well and others do not. The benefits of this are that stoppages can be reduced or eliminated and, importantly, new formulations can have properties that suit the plant. This approach works for whole process lines as well as for individual items of plant such as a hopper, feeder or granulator."

European Initiative
BASF, Ludwigshafen, Germany, also is focusing on DEM technology. "BASF Engineering is a partner of the European research program 'PARDEM [particle DEM],' intending to validate the method and parameters for simulation purposes," notes spokeswoman Laura-Rebecca Janz.

Nanoparticle Analysis

Figure 2. Increase in nanoscale applications is boosting demand for specialized devices such as the Zetasizer.
Source: Malvern Instruments.

Particles and granular solids constitute more than 75% of all raw materials used by industry, according to a European Union (EU) study. Attempts to improve processing via simulations based on classical continuum theory and standard numerical methods and design tools can't always succeed because they can't treat materials as assemblages of discrete objects.

A promising interdisciplinary alternative is DEM, which follows in detail the motion and interaction of particle assemblies. While already established in academia, the method as yet can't handle realistic particle systems of industrial relevance.

The overarching aim of the PARDEM project is to provide high quality training to a group of young researchers to foster multidisciplinary and mutli-industry use of DEM for granular processes. Part of the EU-funded Framework 7 Marie Curie Initial Training Network, it runs from 2009–2013 and currently involves 15 research projects across Europe. The EU has earmarked nearly €5 billion for research within different Marie Curie priority areas.