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Biofuels produced via thermochemical conversions of waste biomass could be sustainable alternatives to fossil fuels but currently require costly downstream upgrading to be used in existing infrastructure. In this work, we explore how a low-cost, abundant clay mineral, bentonite, could serve as an in situ heterogeneous catalyst for two different thermochemical conversion processes: pyrolysis and hydrothermal carbonization (HTC). Avocado pits were combined with 20 wt% bentonite clay and were pyrolyzed at 600 °C and hydrothermally carbonized at 250 °C, commonly used conditions across the literature. During pyrolysis, bentonite clay promoted Diels–Alder reactions that transformed furans to aromatic compounds, which decreased the bio-oil oxygen content and produced a fuel closer to being suitable for existing infrastructure. The HTC bio-oil without the clay catalyst contained 100% furans, mainly 5-methylfurfural, but in the presence of the clay, approximately 25% of the bio-oil was transformed to 2-methyl-2-cyclopentenone, thereby adding two hydrogen atoms and removing one oxygen. The use of clay in both processes decreased the relative oxygen content of the bio-oils. Proximate analysis of the resulting chars showed an increase in fixed carbon (FC) and a decrease in volatile matter (VM) with clay inclusion. By containing more FC, the HTC-derived char may be more stable than pyrolysis-derived char for environmental applications. The addition of bentonite clay to both processes did not produce significantly different bio-oil yields, such that by adding a clay catalyst, a more valuable bio-oil was produced without reducing the amount of bio-oil recovered.
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Carbon is Carbon: Translating Lessons from Coal Chemistry to Biomass Valorization
Without substantial government subsidies, the integrated biorefineries producing sustainable aviation fuels, and the airlines industry’s touts of carbon reduction, wouldn’t be profitable. The thermochemical processes that convert waste to biofuels – pyrolysis, gasification, hydrothermal processing – are each uniquely suited to varying biomasses. Yet they all suffer from similar issues. First, the products are difficult to separate, and the biocrudes are unstable and require substantial downstream upgrading for use as a drop-in fuel. Second, the solid residues of these processes are of low value, though they could be upgraded to fuels and sustainable materials. Finally, capturing the fugitive carbon in the so-called process wastes could shift such carbon upcycling from economic liability to viability. We will demonstrate that it is possible to approach these three problems as simultaneous opportunities. While the thermochemical conversion pathways and separation techniques we design are for biomass conversions, they all leverage fundamental knowledge that pioneers in coal science – notably Prof. Eric Suuberg – developed over the past several decades. Together we may dare to say: petroleum paved the way for holistic carbonaceous waste valorization.
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- Award ID(s):
- 2305505
- PAR ID:
- 10540997
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Format(s):
- Medium: X
- Location:
- Denver, CO
- Sponsoring Org:
- National Science Foundation
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