Microfibrillated Cellulose and High-value Chemicals from Orange Peel Residues

Recent studies have applied orange peel waste for the extraction of essential oil and pectin but neglected the cellulosic residues. This thesis presents a sustainable approach for the production of microfibrillated cellulose (MFC) and high-value chemicals from depectinated orange peel residue (DOPR) in the context of a zero-waste orange peel biorefinery. The methodology applied was based on an acid-free hydrothermal microwave treatment of DOPR undertaken at several temperatures (120–220 °C). This valorisation approach formed two fractions: a solid fraction, giving MFC, and a hydrolysate, which was potentially rich in pectin and other molecules. To evaluate the green and sustainable credentials of the process, energy efficiency calculations, E-factor and green star metrics were carried out. MFC was successfully characterised as a nanostructured material with properties highly dependent on the treatment temperature. MFC produced at 120 °C presented excellent hydrogel formation and improved rheological performance against conventional food rheology modifiers. The hydrolysate produced residual pectin, lignin microparticles, sugars, soluble organic acids and furans. The process greenness assessment showed that microwave can be up to 50% more economic than conventional heating, and solvent use in MFC work-up has major role in the environmental impact of the process. In conclusion, the presented valorisation of orange peel cellulosic residues confirmed its potential as a valuable bioresource for the production of bio-based materials with tunable properties and numerous potential applications, as well as other high-value chemicals which can be further explored.