Charging and separation behavior of gluten–starch mixtures assessed with a custom-built electrostatic separator

• A custom-built separator allowed well-defined charging & separation experiments.
• Particle–particle interactions play important role in charging & separating mixture.
• Dispersibility of powders is crucial for effective electrostatic separation.
• Separation improved at low particle concentrations and high electric field strength.

Electrostatic separation is a novel and sustainable process for dry separation of food ingredients. To establish guidelines for electrostatic separation, well-defined charging and separation experiments of model mixtures prepared from wheat gluten and starch were carried out. For this a custom-built bench-scale electrostatic separator was developed. Charging behavior of mixtures improved with decreasing particle concentration and increasing gas flow rate, which was similar compared to charging behavior of single materials. However, the charge of mixtures was not simply the sum of the charge of single materials because particle–particle interactions also largely influence the charging. Separation efficiencies for mixtures were found lower than could be expected on the basis of behavior of single materials in the equipment. This was attributed to formation of agglomerates by particles having opposite charge, which was further confirmed by the observation that dispersibility of the mixtures was poorer than for the single materials. Agglomeration of particles during electrostatic separation can be minimized by using high gas flow velocity, low feed dosing and higher field strength.