Abstract
REWAMP – Effective Recycling of Cellulosic Waste from the Paper Industry Funded by the European Union – NextGenerationEU, National Recovery and Resilience Plan (NRRP), Mission 4 “Education and Research”, PRIN 2022 PNRR Among the major challenges identified by Horizon Europe is the development of innovative technologies supporting the transition towards a circular economy. Paper represents one of the most successful examples of circularity, with a recycling rate exceeding 70% in Europe. However, paper fibres cannot be recycled indefinitely, generating increasing quantities of waste streams from paper production and recycling. These residues represent a promising feedstock for advanced biorefineries. The REWAMP (Effective Recycling of Cellulosic Waste from Paper Industry) project aimed to develop an integrated and sustainable strategy for the valorisation of pulp and paper mill sludge (PPMS), transforming waste into valuable chemicals, materials and energy. The project investigated two complementary waste fractions: (i) primary paper sludge, rich in partially depolymerised cellulose, and (ii) biological sludge, containing lignin and other complex organic compounds. The overall objective was to demonstrate how the paper industry can become a virtuous model of circular economy through innovative catalytic technologies and sustainability-oriented process design. The project involved the University of Milan (coordinator), the University of Bologna and the University of Turin. Main Scientific Results A wide range of heterogeneous catalysts based on abundant and non-critical metals, mainly nickel and tungsten, were successfully designed, synthesized and tested for the conversion of cellulose-derived waste into value-added chemicals. Different catalyst architectures were developed using commercial activated carbons, alumina and biochars directly produced from paper mill sludge. Particular attention was devoted to the production of biochar-derived catalytic materials, allowing waste generated by the paper industry to be reused within the same valorisation process. This approach represents a concrete example of circular economy, where waste streams become functional materials for new production cycles. The project demonstrated that the nature of the support strongly influences catalyst performance, stability and product selectivity. Acid-functionalized biochars proved particularly promising, leading to the unexpected formation of tungsten phosphide phases that showed significant catalytic activity. Advanced characterization techniques, including electron microscopy, X-ray diffraction, UV-Vis and infrared spectroscopy, enabled a detailed understanding of the relationships between catalyst structure, surface acidity, metal dispersion and catalytic behaviour. These investigations provided fundamental knowledge for the rational design of more efficient catalysts for biomass conversion. One of the most significant achievements of REWAMP was the efficient conversion of cellulose-rich waste streams into industrially relevant bio-based chemicals through catalytic hydrogenation and hydrogenolysis processes. Optimized nickel–tungsten catalysts showed excellent performances in the transformation of cellulose into polyols, particularly ethylene glycol (EG), a strategic building block widely used in polyester manufacturing and other chemical industries. Following the optimization of catalyst composition and reaction conditions, ethylene glycol yields above 54–55 wt% were achieved from cellulose, representing highly competitive results compared with state-of-the-art literature. The catalysts also maintained satisfactory activity over five consecutive reaction cycles, demonstrating promising stability and potential for future industrial implementation. The catalytic systems were successfully applied not only to cellulose but also to other cellulosic substrates, including cotton waste and starch. Particularly noteworthy were the results obtained with cotton, a highly crystalline material that is generally difficult to convert. In parallel, hydrothermal treatment of paper sludge generated two valuable fractions: i) a solid hydrochar that can be further transformed into catalyst supports, and ii) a liquid fraction rich in platform molecules such as furfural and 5-hydroxymethylfurfural (HMF). The project further demonstrated that furfural can be selectively converted into high-value chemicals including cyclopentanone, γ-valerolactone and pentanediols, all of which are important intermediates for the chemical, polymer and bio-based industries. These results confirm the possibility of achieving a nearly complete valorisation of paper mill sludge, maximizing the recovery of carbon and minimizing waste generation. In addition to conventional hydrogenation processes, REWAMP explored catalytic transfer hydrogenation using renewable hydrogen donors such as isopropanol, avoiding the direct use of gaseous hydrogen and enabling safer and potentially more sustainable operating conditions. Continuous-flow catalytic systems were developed and optimized, demonstrating the feasibility of producing valuable products from biomass-derived molecules under industrially relevant conditions. Copper-based catalysts modified with cobalt showed particularly promising selectivity towards pentanediols, important bio-based monomers for advanced materials. One of the most innovative outcomes of the project was the direct valorisation of the polyol mixtures obtained from cellulose conversion. The mixture, composed mainly of ethylene glycol together with propanediols, butanediols, glycerol and sorbitol, was successfully employed to synthesize new semi-aromatic polyesters through conventional polymerisation routes. The resulting materials showed good compatibility with commercial polybutylene terephthalate (PBT) and promising thermal and mechanical properties. Current developments include the production of films and packaging materials incorporating antioxidant molecules, opening potential applications in sustainable food packaging and bio-based plastics. Environmental Sustainability Assessment A comprehensive Life Cycle Assessment (LCA) was performed to evaluate the environmental sustainability of the proposed valorisation pathways. Six different scenarios were analysed, comparing conventional catalyst supports with waste-derived biochar, implementation of renewable electricity integration, and the diversion of a fraction of the sludge into the other. The results clearly demonstrated the environmental advantages of the integration of renewable energy and recycled biochar in the REWAMP approach. The major environmental hotspots are the production of hydrogen (38% of the global warming impact and 40% of the energy demand in the baseline scenario) and the catalyst precursor (51% of the contribution to water consumption). The most advanced scenario, combining the valorisation of both primary and secondary sludges through biochar production and catalyst manufacturing, achieved substantial reductions in greenhouse gas emissions, water consumption and cumulative energy demand. Compared with the current graphene-based benchmark scenario, the biochar-based system reduced global warming impacts from approximately 28 kg CO₂-equivalent to less than 6 kg CO₂-equivalent per kilogram of sludge valorised, the energy demand decreased from more than 500 MJ to nearly 130 MJ, and the water consumption decreased from 690 L to 150 L. Further improvements were obtained when renewable electricity was considered. Further reduction in the system's environmental impact could be achieved by extending the catalyst's service life, operating at lower temperatures, and producing the hydrogen required for the cellulose valorisation process from more sustainable sources such as biomass or electrolysis. The Multi-Criteria Analysis (MCA) compared the REWAMP system with conventional waste-management routes such as landfilling and waste-to-energy incineration, evaluating their environmental, economic, and social impacts through a quantitative analysis of various qualitative impact categories. By integrating environmental, economic and social indicators, the analysis identified REWAMP as the most sustainable option, achieving the highest overall score compared with waste-to-energy and landfilling. This result is mainly due to the high scores obtained by the REWAMP system in criteria such as circularity, product value, government incentives, indirect employment, and social acceptability. The study confirmed that transforming paper sludge into chemicals, catalyst supports and advanced materials can generate environmental benefits while simultaneously creating economic value and new industrial opportunities.
Project details
Unibo Team Leader: Stefania Albonetti
Unibo involved Department/s:
Dipartimento di Chimica Industriale "Toso Montanari"
Coordinator:
Università degli Studi di MILANO(Italy)
Total Unibo Contribution: Euro (EUR) 101.750,00
Project Duration in months: 24
Start Date:
30/11/2023
End Date:
29/11/2025
