Extraction and valorization of cellulose from municipal and industrial waste biomass

Cellulose is the most abundant organic polymer on the planet. Due to its properties, such as biocompatibility, biodegradability, thermal and chemical stability has been used in many applications. Cellulose can be obtained from biomass waste without exposing the food and feed supplies, forests, and biodiversity in the world. This thesis investigates the valorisation of lignocellulosic biomass waste: industrial paper sludge, municipal sewage sludge and agricultural corn stover as a potential source of carbohydrates, mainly cellulose, which can be converted into value-added molecules. At the same time, this work follows the concept of circular economy for biomass waste. Paper industry generates large amounts of dried sludge (40 and 50 kg) per ton of paper produced. The cellulose contained in the residual sludge can be reused or converted into other materials. The first study realised in this thesis evaluates the influence of commercial and cheap phosphonium-based ionic liquid on cellulose separation from industrial paper mill wastewater dried sludge. The ionic liquid demonstrated potential for cellulose recovery from industrial paper sludge as well as ability to dissolve ashes from paper sludge. Additional study realised on industrial paper mill wastewater dried sludge aimed at characterization of paper sludge by standard methods; cellulose recovery by phosphonium and imidazolium based ionic liquids, and characterization of recovered cellulose. As a result of this study, both ionic liquids were able to recover the cellulose of the sludge (~100%). The ratio sludge: ionic liquid had only a low influence on the recovery. Phosphonium ionic liquid was able to clean better the cellulose, eliminating a major quantity of ashes. Imidazolium ionic liquid was able to leave a minor quantity of initial proteins in the cellulose. However, improvement of the performances of the ionic liquids is necessary to allow a scale-up of the technology. Since the recovery of cellulose from industrial paper sludge was feasible with ionic liquids, the optimization study about cellulose recovery was realised from the other type of sludge, municipal primary sewage sludge. The influence on amounts of carbohydrates, proteins and ashes was investigated based on three independent factors: temperature of dissolution; time of dissolution and sludge: ionic liquid ratio. The ionic liquid, tetrakis (hydroxymethyl) phosphonium chloride, [P(CH2OH)4]Cl, allowed the recovery of all cellulose, although it was not able to completely clean the cellulose. 36% of ashes and 51% of the proteins remained in the recovered cellulose. The experimental design did not manage to optimize the operative conditions of the process. All examined conditions were able to recover maximal values of cellulose. Experiments realised at 60℃ for 13 h and with ratio of dry sludge: ionic liquid 1 g:12 ml allowed the recovery of high quantities of cellulose, the best removal of ashes but still maintaining high amounts of proteins in the recovered cellulose. In recent years the dissolution of lignocellulosic biomass in ionic liquid has drawn a great attention. Ionic liquids are used as green replacement for harmful volatile organic solvents due to their non-volatile character, excellent chemical and thermal stability. One classical example of lignocellulosic biomass is corn stover, which basically consists of cellulose, hemicellulose, lignin and ash. The use of designed ionic liquids with improved reusing capabilities was evaluated to recover the cellulose from corn stover. The ionic liquids were synthesized during the research stay at QUILL group (Queen’s University Ionic Liquid Laboratories) in Belfast. Two imidazolium-based ionic liquids, able to bring hydrophobic and hydrophilic (hexane/water) solvents together as stable microemulsions and three phosphonium-based ionic liquids were evaluated for the recovery of cellulose. The experiments were carried out under mild conditions. The ionic liquids showed the ability to break cell walls and extract cellulose from the corn stover. Tetrabutylphosphonium 2-ethylhexanoate [P4444][EH] was the ionic liquid able to extract the highest quantity of the available cellulose (84%) while imidazolium-based ionic liquids can be considered as easily recovered due to their abilities to form microemulsions and being separated. Finally, the thesis also investigates the valorisation of cellulose recovered from WWTP sludge to added value levulinic acid with a Bronsted acidic ionic liquid. The recovered the cellulose from the urban and industrial sludge was bleached to decrease the content of ash and proteins still presented. Then, the bleached cellulose was used to produce levulinic acid through a hydrothermal catalysed process. The results demonstrate that both types of sludge can be used as precursors to obtain value-added chemicals. However, direct conversion of the sludge gave very low yield of levulinic acid. This suggests that the recovery of cellulose is an essential step in production of value-added molecules.