Integrated valorization of paper mill wastes for the sustainable production of chemicals and energy

The great world production of paper and paperboard (more than 400 Mt/a) involves the production of significant amounts of waste streams. A cellulose-rich waste (CRW) and the inorganic-rich waste (IRW), supplied by the company Lucart Group, resulted particularly interesting for chemical and energy valorisation as an alternative to costly disposal. CRW, deriving from the converting step, has a content of glucan of 75 wt % but cannot be reused within the paper mill process, while IRW contains 70 wt % of CaCO3 and about 25 wt % of cellulose. Due to its high cellulose content, CRW was employed as substrate for the one pot acid-catalyzed conversion to ethyl levulinate (EL) using ethanol as reagent and reaction medium. The increasing interest towards EL is related to its outstanding characteristics: EL is a promising versatile biofuel which can be employed as bio-blendstock in both diesel and gasoline engines, and also an intermediate for the production of plasticizers, solvents and pharmaceuticals. The optimization of the ethanolysis process, performed in the presence of 1% sulphuric acid, allowed to reach EL yields of 45 mol%, an important achievement given the simplicity of the process involved. On the other hand, the IRW was employed in an oxy co-gasification process for energy recovery through the production of syngas adopting a downdraft fixed bed reactor with O2/H2O as gasifying agents. A blend of IRW and wood pellets in 1/5 wt/wt ratio was adopted as substrate. Notably, the co-gasification in the presence of IRW produced a syngas characterized by high hydrogen content (40 mol %) and CO (21 mol %). Moreover, tar compositional analysis revealed the presence of long-chain (C19-C39) and polyaromatic hydrocarbons. Finally, the ash characterisation evidenced the formation of good quality CaO deriving from CaCO3 decarbonisation, which can be exploited in the paper mill process itself in a circular economy perspective.