Glycerol is an attractive bio-based platform chemical that can be converted to a variety of bio-based chemicals. We here report a catalytic co-conversion strategy where glycerol in combination with a second (bio-)feed (fatty acids, alcohols, alkanes) is used for the production of bio-based aromatics (BTX). Experiments were performed in a fixed bed reactor (10 g catalyst loading and WHSV of (co-)feed of 1 h-1) at 550 °C using a technical H-ZSM-5/Al2O3 catalyst. Synergistic effects of the co-feeding on the peak BTX carbon yield, product selectivity, total BTX productivity, catalyst life-time, and catalyst regenerability were observed and quantified. Best results were obtained for the co-conversion of glycerol and oleic acid (45/55 wt%), showing a peak BTX carbon yield of 26.7 C%. The distribution of C and H of the individual co-feeds in the BTX product was investigated using an integrated fast pyrolysis-GC-Orbitrap MS unit, showing that the aromatics are formed from both glycerol and the co-feed. The results of this study may be used to develop optimized co-feeding strategies for BTX formation. This journal is
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The catalytic conversion of oleic acid to aromatics (benzene, toluene, and xylenes, BTX) over a granular H-ZSM-5/Al2O3 catalyst (ϕ 1.2–1.8 mm, 10 g loading) was investigated in a continuous bench-scale fixed-bed reactor (10 g oleic acid h–1). A peak carbon yield of aromatics of 27.4% was obtained at a catalyst bed temperature of 550 °C and atmospheric pressure. BTX was the major aromatics formed (peak carbon yield was 22.7%), and a total BTX production of 1000 mg g–1 catalyst was achieved within a catalyst lifetime of 6.5 h for the fresh catalyst. The catalyst was deactivated due to severe coke deposition (ca. 22.1 wt % on the catalyst). The used catalyst was reactivated by an ex situ oxidative regeneration at 680 °C in air for 12 h. The regenerated catalyst was subsequently recycled, and in total, 7 cycles of reaction-regeneration were performed. A gradual decrease in the peak carbon yield of BTX was observed with reaction-regeneration cycles (e.g., to 16.3% for the catalyst regenerated for 6 times). However, the catalyst lifetime was remarkably prolonged (e.g., >24 h), leading to a significantly enhanced total BTX production (e.g., 3000 mg g–1 catalyst in 24 h). The fresh, used, and regenerated catalysts were characterized by N2 and Ar physisorption, XRD, HR-TEM-EDX, 27Al, and 29Si MAS ssNMR, NH3-TPD, TGA, and CHN elemental analysis. Negligible changes in textural properties, crystalline structure, and framework occurred after one reaction-regeneration cycle, except for a slight decrease in acidity. However, dealumination of the H-ZSM-5 framework was observed after 7 cycles of reaction-regeneration, leading to a decrease in microporosity, crystallinity, and acidity. Apparently, these changes are not detrimental for catalyst activity, and actually, the lifetime of the catalyst increases, rationalized by considering that coke formation rates are retarded when the acidity is reduced.
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The catalytic conversion of glycerol to aromatics (GTA, e.g., benzene, toluene, and xylenes, BTX) over a shaped H-ZSM-5/Al2O3 (60/40 wt%) catalyst was investigated in a continuous fixed-bed reactor to study the addition of the Al2O3 binder in the catalyst formulation on catalyst performance. The experiments were performed under N2 at 550 °C, a WHSV of glycerol (pure) of 1 h−1, and atmospheric pressure. The spent H-ZSM-5/Al2O3 catalysts were reused after an oxidative regeneration at 680 °C and in total 5 reaction-regeneration cycles were performed. Catalyst characterization studies show that the addition of the Al2O3 binder does not affect the surface area and crystallinity of the formulation, but increases the total pore volume (mesopores in particular) and total acidity (Lewis acidity in particular). The H-ZSM-5/Al2O3 (60/40 wt%) catalyst shows a considerably prolonged catalyst life-time (8.5 vs. 6.5 h for H-ZSM-5), resulting in a significant increase in the total BTX productivity (710 vs. 556 mg g−1 H-ZSM-5). Besides, the addition of the Al2O3 binder retards irreversible deactivation. For instance, after 3 regenerations, catalyst performance is comparable to the fresh one. However, after 4 regenerations, some irreversible catalyst deactivation occurs, associated with a reduction in total pore volume, crystallinity, and acidity (Brønsted acidity in particular), and meso-porosity of the Al2O3 binder. This study shows that both the stability and reusability of H-ZSM-5-based catalysts for GTA are remarkably enhanced when using a suitable binder.
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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.
