Despite the promise of waste-to-energy conversions, bio-oils produced via thermochemical techniques such as pyrolysis suf- fer from high viscosity and acidity, which render the oils unstable and corrosive. While pyrolysis biocrude can be upgraded downstream, the use of precious metal catalysts limits the economic feasibility of biomass to biofuel conversions. To address these economic limitations, the present work explores the use of clay minerals as inexpensive catalysts to upgrade bio-oils in situ. Cherry pits, a representative carbonaceous agro-industrial waste, were pyrolyzed at 600 °C for 1 h in the presence of a series of clay minerals. For some clays, the bio-oils produced from catalyzed pyrolysis exhibited lower oxygen and fatty acid content than bio-oil from non-catalyzed pyrolysis. The heterogeneous clay-cherry pit biochar mixtures had higher surface areas and surface chemistries with increased free and intermolecularly bonded hydroxyl groups relative to those of pure cherry pit biochar. However, adsorption studies using methylene blue as a model organic contaminant showed that these heterogenous chars had a decreased adsorption capacity, likely due to a loss of surface functional groups. The addition of clay materials to the pyrolysis stream yields a biocrude more amendable to downstream upgrading and a heterogeneous biochar-clay mixture capable of (though certainly not optimized for) adsorbing a model organic compound.
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Impact of Bentonite Clay on In Situ Pyrolysis vs. Hydrothermal Carbonization of Avocado Pit Biomass
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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- NSF-PAR ID:
- 10345032
- Date Published:
- Journal Name:
- Catalysts
- Volume:
- 12
- Issue:
- 6
- ISSN:
- 2073-4344
- Page Range / eLocation ID:
- 655
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)Biophysical cohesive particles in aquatic systems, such as extracellular polymeric substances (EPS) and clay minerals, play an important role in determining the transport of spilled oil contamination and its eventual fate, particularly given that suspended sediment and microbial activities are often prevalent and diverse in natural environments. A series of stirring jar tests have been conducted to understand the multiple structures characteristics of the oil-mineral aggregates (OMAs) and EPS-oil-mineral aggregates (EPS-OMAs). OMAs and EPS-OMAs have been successfully generated in the laboratory within artificial seawater using: Texas crude oil (Dynamic viscosity: 7.27 × 10 –3 Pa⋅s at 20°C), two natural clay minerals (Bentonite and Kaolin clay), and Xanthan gum powder (a proxy of natural EPS). A magnetic stirrer produced a homogeneous turbulent flow with a high turbulence level similar to that under natural breaking waves. High-resolution microscopy results show that EPS, kaolinite, and bentonite lead to distinguished oil floc structures because of the different stickiness character of EPS and mineral clay particles. With relatively low stickiness, kaolinite particles tend to attach to an oil droplets surface (droplet OMAs) and become dominant in small-sized flocs in the mixture sample. In contrast, the more cohesive bentonite particles stickiness could adsorb with oil droplets and are thus dominated by larger sized flocs. Biological EPS, with the highest stickiness, demonstrated that it could bond multiple small oil droplets and form a web structure trapping oil and minerals. Generally, adding EPS leads to flake/solid OMAs formation, and individual oil droplets are rarely observed. The inclusion of ESP within the matrix, also reduced the dependence of settling velocity on floc size and mineral type.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/catal12060655
