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.
more »
« less
Clay-catalyzed in situ pyrolysis of cherry pits for upgraded biofuels and heterogeneous adsorbents as recoverable by-products
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.
more »
« less
- NSF-PAR ID:
- 10345035
- Date Published:
- Journal Name:
- Biomass Conversion and Biorefinery
- ISSN:
- 2190-6815
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
more » « less
Abstract Cotton gin waste (CGW) is produced in large quantities (1–1.5 × 106metric ton/year) in the Texas High Plains (THP), one of the largest cotton-producing regions in the USA. We examined locally supplied CGW for soil amendment as biochar (CGW-BC) with a view toward rainfed cropping systems, which will likely become increasingly necessary due to declines in groundwater availability for irrigation. Sixteen unique biochar samples were produced under varying conditions of time, temperature, and post-processing wash in a muffle furnace. We performed material characterization on the biochar. We then incubated CGW-BC samples that seemed favorable for increasing the water holding capacity increase for 10 days with local, rainfed, clay loam soil. We found that increasing the pyrolysis time and temperature decreased the biochar yield but only up to 40 min. Beyond 40 min, the yield did not decrease further. Additionally, the majority of mass loss occurred during pyrolysis and not during crush-sieving or postproduction washes. CGW-BC produced at higher temperatures and for longer times had greater thermal stability. This interesting aspect of thermal stability, which did not always follow strict time‒temperature trends, may be because cotton gin waste is a heterogeneous material. We found that the addition of acid decreases the mineral content while lowering the thermal stability of lower temperature (450 °C) biochars. Regarding the CGW-BC surface area, we found that higher temperatures generally increase the micropore surface area. Using a GAB isotherm, water vapor surface area did not correlate with the highest WHC when water was added to the soil. In fact, biochar, which was pyrolyzed in less time at a lower temperature and with the use of acid washing, better held the water in soil-biochar mixtures. The measurements suggested that CGW-BC could be a valuable soil amendment that could increase the WHC without adversely increasing the pH. Our initial investigation revealed how scaled-up production of CGW-BC for soils might be economically and sustainably pursued for use in rainfed cropping, deficit irrigation, or ranchlands.
-
null (Ed.)Biochar’s ability to amend and remediate agricultural soil has been a growing interest, though the energy expenses from high-temperature pyrolysis deter the product’s use. Therefore, it is urgent to improve the pyrolysis efficiency while ensuring the quality of produced biochar. The present study utilized three types of feedstock (i.e., switchgrass, biosolid, and water oak leaves) to produce biochar via conventional slow pyrolysis and microwave pyrolysis at different temperature/energy input. The produced biochar was characterized and comprehensively compared in terms of their physiochemical properties (e.g., surface functionality, elemental composition, and thermal stability). It was discovered that microwave-mediated biochar was more resistant to thermal decomposition, indicated by a higher production yield, yet more diverse surface functional groups were preserved than slow pyrolysis-derived biochar. A nutrient (NO3-N) adsorption isotherm study displayed that microwave-mediated biochar exhibited greater adsorption (13.3 mg g−1) than that of slow pyrolysis-derived biochar (3.1 mg g−1), proving its potential for future applications. Results suggested that microwaves pyrolysis is a promising method for biochar production.more » « less
-
In this study, we systematically investigated the effects of thermal air oxidation on the properties of biomass-derived BC made at carbonization temperatures (HTTs) of 300–700 ˚C. BC produced by including air in the carbonization step was found to have a low surface area and underdeveloped pore structure. Substantial changes of BC were observed after post-pyrolysis thermal air oxidation (PPAO). Well-carbonized BC samples made anoxically at relatively high HTTs (600 and 700 ˚C) showed, after PPAO, significant increases in N2 BET surface area (SA) (up to 700 times), porosity (< 60 Å) (up to 95 times), and adsorptivity (up to 120 times) of neutral organic species including two triazine herbicides and one natural estrogen. Partially carbonized BC made at a lower HTT (300 or 400 ˚C) showed moderate increases in these properties after PPAO, but a large increase in the intensity of Fourier transform infrared spectroscopy bands corresponding to various oxygen-containing functional groups. Well-carbonized BC samples, on the other hand, were deficient in surface oxygen functionality even after the PPAO treatment. Adsorption of the test organic compounds on BC generally trended with BET SA when it was less than 300 m2/g, but BET SA was poorly predictive of adsorption when it was greater than 300 m2/g. Overall, our results suggest that thermal reactions between molecular oxygen and BC 1) increase surface oxygen functionality more effectively for low-HTT than for high-HTT BC samples; 2) increase SA and porosity (< 60 Å) especially for high-HTT BC samples; and 3) create new adsorption sites and/or relieve steric restriction of organic molecules to micropores, thereby enhancing the adsorptivity of BC. These results will prove useful not only for understanding the fate of environmental BC but also in devising strategies for improving the practical performance of the engineered form of BC (i.e., biochar).more » « less
-
Transforming the organic fraction of municipal solid waste (OFMSW) into biochar to reduce fugitive landfill emissions and control organic micropollutants (OMP) during landfill leachate treatment could provide a new circular economy organics diversion approach. However, research on landfill leachate treatment under consistent, representative conditions with biochar derived from the wide range of OFMSW components is needed. Further, the competitive nature of leachate dissolved organic matter (DOM) for biochar adsorption sites has not been examined. To this end, biochars were produced from seven diverse OFMSW types and batch tested using two representative organic contaminants. To evaluate leachate DOM impact on OMP removal and fouling mitigation with biochar enhancement methods, experiments were performed with three background matrices (deionized water, synthetic leachate, real leachate) and two enhancement methods (ash-pretreatment, double-heating). Since evaluating all possible OFMSW feedstock combinations is infeasible, fundamental relationships between individual feedstocks and biochar properties were evaluated. Overall, biochar performance varied substantially; the dose to achieve a given target removal spanned an order of magnitude between the OFMSW feedstocks. Also, the presence of leachate DOM more negatively impacted the performance of all biochars relative to the benchmark adsorbent activated carbon. Finally, the enhancement methods altered biochar pore structure by increasing micropore and slightly decreasing non-micropore surface areas, resulting in improved adsorption capacity (by 23 to 93%). By providing the basis for a low-cost, enhanced leachate treatment method, this study could incentivize a novel organics diversion approach that reduces climate change impacts, harvests energy from waste, and reduces landfill air emissions.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1007/s13399-022-02921-3
