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This project studied the upcycling of the ‘waste’ in the paper industry - paper sludge to bio-based aromatics (benzene, toluene, and xylenes, bio-BTX) via a chemocatalytic conversion approach, namely catalytic pyrolysis. Three commercial catalysts including H-ZSM-5 zeolite, USY-based E-Cat, and Pt/Al2O3-based catalyst were employed and the paper sludge provided by consortium partner (Alucha Work B.V.) was tested. Catalytic pyrolysis of paper sludge were performed on two types of reactor systems, namely milligram-scale tandem micro-reactor and gram-scale downer-fixed bed reactor. The tandem micro-reactor enables quick screening of the catalysts and fingerprinting. It is interesting to see that fast pyrolysis of paper sludge without using a catalyst could produce styrene. When using a catalyst, a BTX yield of ca. 8.7 wt.% (based on dry organic fraction) could be obtained over an H-ZSM-5 catalyst. The downer-fixed bed reactor enables motoring the catalyst deactivation with the time on stream (for catalyst life-time) and during the reaction-regeneration cycles (for catalyst renderability). The three catalysts were tested for 5 reaction-regeneration cycles. The collected products including gases, liquids, and solids are being analyzed by a variety of methods such as elemental analysis, GC×GC-MS, KF, GPC, TAN for qualification and quantification and also the mass and carbon balances. The fresh, spent (after 1 and 5 reuses) and regenerated (after 1 and 5 regenerations) catalysts are being characterized by various techniques such as BET, XRD, pyridine-IR, NH3-TPD, and TGA, to correlate the catalyst performance and deactivation with the catalyst characteristics (e.g., textural property, crystallinity, acidity, and coking). These information will be discussed in detail in the final report of this project.
Paper sludge contains papermaking mineral additives and fibers, which could be reused or recycled, thus enhancing the circularity. One of the promising technologies is the fast pyrolysis of paper sludge, which is capable of recovering > 99 wt.% of the fine minerals in the paper sludge and also affording a bio-liquid. The fine minerals (e.g., ‘circular’ CaCO3) can be reused as filler in consumer products thereby reducing the required primary resources. However, the bio-liquid has a lower quality compared to fossil fuels, and only a limited application, e.g., for heat generation, has been applied. This could be significantly improved by catalytic upgrading of the fast pyrolysis vapor, known as an ex-situ catalytic pyrolysis approach. We have recently found that a high-quality bio-oil (mainly ‘bio-based’ paraffins and low-molecular-weight aromatics, carbon yield of 21%, and HHV of 41.1 MJ kg-1) was produced (Chem. Eng. J., 420 (2021), 129714). Nevertheless, catalyst deactivation occurred after a few hours’ of reaction. As such, catalyst stability and regenerability are of research interest and also of high relevance for industrial implementation. This project aims to study the potential of the add-on catalytic upgrading step to the industrial fast pyrolysis of paper sludge process. One important performance metric for sustainable catalysis in the industry is the level of catalyst consumption (kgcat tprod-1) for catalytic pyrolysis of paper sludge. Another important research topic is to establish the correlation between yield and selectivity of the bio-chemicals and the catalyst characteristics. For this, different types of catalysts (e.g., FCC-type E-Cat) will be tested and several reaction-regeneration cycles will be performed. These studies will determine under which conditions catalytic fast pyrolysis of paper sludge is technically and economically viable.