Density and rheology of acid suspensions of peanut waste in different conditions: An engineering basis for bioethanol production

• Thermophysical properties were necessary to the correct design of unit operations.
• Suspensions of peanut waste have had their rheological behavior determined.
• Rheological parameters and density were modeled.
• The pH did not affect the suspension thermophysical properties.
• Farris effect was observed in more concentrated suspensions.

The current world-wide energetic situation implies in researches about new resources and technologies capable of producing biofuels, such as the peanut processing residues. To design operations associated to bioethanol processing, understanding material properties, as density and rheology, is necessary. In this study, peanut shells were firstly chemically characterized, showing 37.1% cellulose, 33.4% hemicellulose and 15.0% lignin. Aqueous acid suspensions of powdered peanut shell were prepared and their physical properties were determined. Rheological parameters and density could be correlated with solid content and temperature by exponential and quadratic equations, respectively, while pH did not present significant effect on these parameters. Dilute suspensions showed Newtonian behavior, but at concentration above 8% (w/w) of solids, a non-Newtonian behavior was observed, showing yield stress and shear thinning. By evaluating the relative viscosity behavior with increasing solids concentration, Farris effect was also evidenced in suspensions above 8% of solids due to the presence of fine particles. Such result indicates the possibility of processing peanut shells for biofuel production in solids concentration higher than 10%, without a significant influence on viscosity.

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