Environmental, Energetic and Economic Evaluation of Implementing a Supercritical Fluid-Based Nanocellulose Production Process in a Sugarcane Biorefinery

Abstract

Nanocellulose, which is a disintegration product of plant cellulose, has recently come to public attention because of its great mechanical properties combined with renewability and biodegradability. From an environmental point-of-view, nanocellulose has shown potential for applications in drinking water filtration, catalytic degradation of organic pollutants, etc. Nanocellulose prepared from renewable and biodegradable lignocellulosic materials is only considered green and environment-friendly when its obtaining method is also environmentally friendly. Thus, this procedure should be done by means of an eco-friendly multistep procedure. Towards this direction in this study, nanocelulose production that uses supercritical fluid-based processes for cellulose separation, e.g. supercritical CO₂ explosion or organosolv assisted by CO₂, were compared with conventional steam explosion and organosolv processes in terms of environmental, energetic and economic aspects using commercial simulator Aspen Plus. In addition, the implementation of nanocelulose production as part of an ethanol production process from lignocellulosic materials was also investigated. The results showed that the production of nanocellulose from the lignocellulosic residue of the ethanol production through enzymatic hydrolysis is very promising. On the other hand, this more economically attractive process design was when explosion-based methods (i.g. SO₂-catalized steam explosion and supercritical CO₂ explosion) were used during cellulose separation step. It was determined that over 95% of the energy needs for cellulose disintegration during nanocellulose production process come from heating requirements. However, it was also found that this latter step can be self sufficient in terms of energy usage when the undisintegrated cellulose is used as fuel into an energy generation system. It was estimated that a combined heat and power boiler can produce a heat surplus of 365 kWh, which can be redirected to the lignocellulosic biomass fractionation, enzymatic hydrolysis and/or ethanol production processes, thus reducing the overall energy requirement. In terms of environmental aspects, three environmental indicators were examined. The CO₂ emissions per kg of nanocellulose produced was found to be acceptable as it is, but the chemicals/water usage should be re-examined, as their requirements were deemed higher than the desirable.