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Advances and Challenges in Low‐Temperature Upcycling of Waste Polyolefins via Tandem Catalysis
Abstract Polyolefin waste is the largest polymer waste stream that could potentially serve as an advantageous hydrocarbon feedstock. Upcycling polyolefins poses significant challenges due to their inherent kinetic and thermodynamic stability. Traditional methods, such as thermal and catalytic cracking, are straightforward but require temperatures exceeding 400 °C for complete conversion because of thermodynamic constraints. We summarize and critically compare recent advances in upgrading spent polyolefins and model reactants via kinetic (and thermodynamic) coupling of the endothermic C─C bond cleavage of polyolefins with exothermic reactions including hydrogenation, hydrogenolysis, metathesis, cyclization, oxidation, and alkylation. These approaches enable complete conversion to desired products at low temperatures (<300 °C). The goal is to identify challenges and possible pathways for catalytic conversions that minimize energy and carbon footprints.
50-kWth methane/air chemical looping combustion tests with commercially prepared CuO-Fe 2 O 3 -alumina oxygen carrier with two different techniques
CuO-Fe 2 O 3 /alumina oxygen carriers were manufactured using two different techniques (i.e., spray drying and wet granulation). The spray drying method produced porous, spherical particles in the range of 100–200 µm. The wet granulation, or tumbling method, produced particles in the range of 200–600 µm. Both batches of material showed good gas conversion and particle durability during tests in NETL’s 50-kWth chemical looping circulating fluidized bed combustor unit at 700–900 °C. No agglomeration was observed, even though the oxygen carrier had a high CuO concentration (30%). The particle losses with 200–600 µm batch were significantly lower than that with the 100–200 µm batch. The oxygen carrier materials in the 200–600 µm range were circulated for approximately 3.1 days in the target temperature range (700–850 °C) and a total of approximately 40 h of chemical looping combustion testing was conducted during that time. The average fuel reactor temperatures ranged from 760 to 815 °C for the chemical looping combustion test periods, and the average air reactor temperature ranged from 840 to 915 °C. The fuel conversion from natural gas to CO 2 ranged from 50 to 80%. Approximately 1.6 h of continuous operation was achieved with no gas preheat and no natural gas augmented heating. During this test period, the average fuel reactor temperature ranged from 780 to 825 °C, the air reactor temperature ranged from 930 to 960 °C, and the natural gas to CO 2 conversion ranged from 50 to 65%. Finally, analysis of the oxygen carrier after the test indicated that there were no significant changes in the particle size or the surface morphology.
Inhibitory Effect of Furanic and Phenolic Compounds on Exoelectrogenesis in a Microbial Electrolysis Cell Bioanode
Furanic and phenolic compounds are 20 lignocellulose-derived compounds known to inhibit to H2- and ethanol- producing microorganisms in dark fermentation. Bioelectrochemical conversion of furanic and phenolic compounds to electricity or H2 has recently been demonstrated as a productive method to use these compounds. However, potential inhibitory effect of furanic and phenolic compounds on exoelectrogenesis in bioelectrochemical systems is not well understood. This study systematically investigated the inhibitory effect of furfural (FF), 5-hydroxymethylfurfural (HMF), syringic acid (SA), vanillic acid (VA), and 4-hydroxybenzoic acid (HBA) on exoelectrogenesis in the bioanode of a microbial electrolysis cell. A mixture of these five compounds at an increasing initial total concentration from 0.8 to 8.0 g/L resulted in current decrease up to 91%. The observed inhibition primarily affected exoelectrogenesis, instead of non-exoelectrogenic biotransformation pathways (e.g., fermentation) of the five compounds. Furthermore, the parent compounds at a high concentration, as opposed to their biotransformation products, were responsible for the observed inhibition. Tests with individual compounds show that all five parent compounds contributed to the observed inhibition by the mixture. The IC50 (concentration resulting in 50% current decrease) was estimated as 2.7 g/L for FF, 3.0 g/L for HMF, 1.9 g/L for SA, 2.1 g/L for VA and 2.0 g/L for HBA. Nevertheless, these compounds below their non-inhibitory concentrations jointly resulted in significant inhibition as a mixture. Catechol and phenol, which were persistent biotransformation products of the mixture, inhibited exoelectrogens at high concentrations, but to a lesser extent than the parent compounds. Recovery of exoelectrogenesis from inhibition by all compounds was observed, except for catechol, which resulted in irreversible inhibition. The reversibility of inhibition, as well as the observed difference in recovery rates, suggest different modes of exoelectrogenesis inhibition, related to the hydrophobicity of the inhibiting compounds.
Techno-Economic and Life Cycle Assessment of Chemical Recycling and Upcycling of Mixed Plastics Waste Containing Poly-vinyl-chloride
Developing technologies that completely remove chlorine from plastic waste can allow its chemical recycling and upcycling with catalytic methods. Here, this study compares eight processes involving different dechlorination methods (absorption columns, adsorption in beds of zeolites, catalytic dechlorination, and dissolution in ionic liquids) and chemical conversion technologies (incineration, pyrolysis, hydrogenolysis) to upgrade mixed plastics waste to various products (e.g., electricity, fuels, virgin polymers, and lubricant oil). The analysis determines that the absorption of chlorine in columns with basic aqueous solutions is limited to plastics waste with PVC concentrations below 0.1%. Dissolution in ionic liquids is not cost-competitive. On the contrary, two-step processes with catalytic dechlorination followed by thermochemical catalytic depolymerization, either pyrolysis or hydrogenolysis, significantly improve process economics and emissions. The most economically viable alternative is hydrogenolysis for producing lubricants, while the technology with the lowest global warming potential is chemical recycling via catalytic pyrolysis.
Dynamic control and quantification of active sites on ceria for CO activation and hydrogenation
Ceria (CeO 2 ) is a widely used oxide catalyst, yet the nature of its active sites remains elusive. This study combines model and powder catalyst studies to elucidate the structure-activity relationships in ceria-catalyzed CO activation and hydrogenation. Well-defined ceria clusters are synthesized on planar CeO 2 (111) and exhibit dynamic and tunable ranges of Ce coordination numbers, which enhance their interaction with CO. Reduced ceria clusters (e.g., Ce 3 O 3 ) bind CO strongly and facilitate its dissociation, while near-stoichiometric clusters (e.g., Ce 3 O 7 ) adsorb CO weakly and promote oxidation via carbonate formation. Unlike planar ceria surfaces, supported ceria clusters exhibit dynamic properties and enhanced catalytic activity, that mimic those of powder ceria catalysts. Insight from model studies provide a method to quantify active sites on powder ceria and guide further optimization of ceria catalysts for syngas conversion. This work marks a leap toward model-guided catalyst design and highlights the importance of site-specific catalysis.
Quantum-Cutting Luminescent Coatings for High-Efficiency, Low-Cost Solar Cells (Final Technical Report)
The objective of the project is to optimize the deposition and post-deposition annealing conditions of quantum-cutting materials to enable coatings with high photoluminescence quantum yields and optimal absorption onset. These coatings will be integrated with commercial solar photovoltaic cells to enable improved power conversion efficiency, and the quantum-cutting cell stability will be ensured using industry-standard packaging methods.
Upgrading of Raw Coal and Coal Waste for Coal-Derived Graphene Process
Conference presentation at 47th International Technical Conference on Clean Energy (Clearwater Clean Energy Conference), Clearwater, Florida, July 23–27, 2023. The University of North Dakota Energy & Environmental Research Center (EERC) conducted a laboratory-scale coal-derived graphene (CDG) project focused on developing a technological process for making graphite from four U.S. domestic coals and coal wastes. Coal and coal waste preprocessing methods were developed and applied to clean and upgrade the coal precursors prior to graphitization and subsequent conversion to graphene products. Carbonization and graphitization of these preprocessed coals and coal wastes has produced graphite, which was used to make graphene oxide (GO) and reduced graphene oxide (rGO). Graphene quantum dots (GQDs) were also made from the raw and upgraded coal precursors.
Controlling metabolism by substrate cofeeding
The disclosure provides methods using mixed substrate cofeeding for bioproduct synthesis, which enables faster, more efficient, and higher yield carbon conversion in various organisms.
Apparatus and methods of detecting transient discharge modes and/or closed loop control of pulsed systems and method employing same
A system and method for differentiating between different modes of pulsed electrical discharges via of an amplitude to time (ATC) conversion circuit is described. A bipolar ATC circuit is used to add together the positive and negative portions of an attenuated and filtered signal derived either from the voltage or current of a pulse. Alternatively, a unipolar ATC circuit may be employed. The resulting processed signal is compared against a reference voltage to generate an output signal that is active for the amount of time that the processed signal exceeds the reference voltage. Discharge mode is determined based on three factors: did a pulse occur, if a pulse occurred when did the pulse start relative to the original pulse event, and what is the duty cycle of the pulse. Subsequent pulse generated may be controlled accordingly.
A highly efficient uranium grabber derived from acrylic fiber for extracting uranium from seawater
Acrylic fiber can be chemically converted to an am- idoxime and carboxylate containing chelating adsorbent for extraction of uranium from seawater. At an optimized ratio of amidoxime:carboxylate, the chelating fiber in real seawater shows a higher uranium, shorter saturation time and lower vanadium adsorption capacity relative to similar high-surface area chelating fibers developed recently using a radiation-induced grafting method. This simple and low-cost synthesis method can be scaled up to mass produce the chelating fiber for recovering metals from aquatic environments including production of uranium from seawater.
Microwave resonance enhanced CO 2 reduction using biochar
The conventional process for CO 2 conversion requires high energy and expensive catalysts, and shows poor product selectivity. Here, in this study, we address these challenges by investigating an environmentally friendly method for CO production through the variable frequency microwave-driven CO 2 Boudouard reaction over biochar. We hypothesized that tuning the microwave frequency to align with the dielectric properties of biochar, and thereby induce a resonance effect, could significantly enhance reaction efficiency. Experiments were conducted to explore the effect of microwave frequency on CO 2 conversion efficiency in the variable frequency microwave reactor operating within a frequency range of 2430–6000 MHz. Results reveal a significant resonance effect at 4225 MHz resulting in an outstanding CO 2 conversion of 96.3%, in sharp contrast to the complete absence of conversion observed at the conventional 2450 MHz. The resonance frequency not only facilitated exceptional conversion but also remarkably improved energy efficiency, yielding a productivity of 1427.5 µmol/kJ of CO. This represents a remarkable 474-fold increase compared to electrical heating. Furthermore, continuous microwave irradiation at this optimized frequency demonstrated remarkable stability and induced substantial enhancements in the pore structure and surface area of biochar. This innovative approach provides promising insights into sustainable and efficient CO production processes.
Influence of propylene glycol/nitrates ratio on microwave-assisted combustion synthesis of CuO-ZnO-Al2O3 nanocatalyst: Structural and catalytic properties toward hydrogen production from methanol
Highlights: • Applicability of propylene glycol in synthesis of CuO/ZnO/Al{sub 2}O{sub 3} via combustion method. • Addressing the influence of fuel to nitrates ratio on catalytic properties and performance. • Synthesis of stable and active CuO/ZnO/Al{sub 2}O{sub 3} nanocatalyst in methanol to hydrogen. • Achievement of complete conversion at 260 °C by choosing appropriate amount of fuel. • Decrease of CO production by applying suitable fuel/nitrates ratio. - Abstract: A series of CuO-ZnO-Al{sub 2}O{sub 3} nanocatalysts were fabricated by microwave-assisted combustion method to investigate the role of propylene glycol/nitrates ratio. XRD, FESEM, FTIR, EDX, BET and TG techniques were applied to study the physicochemical properties of prepared nanocatalysts. It was found that increasing of fuel/nitrates ratio decreased the specific surface area due to incomplete combustion reaction. TG and FTIR results proved that some combustion residuals such as nitrate species and propylene glycol remained in fabricated samples and their amount increased by increasing of fuel/nitrates ratio. Also, higher dispersion of CuO crystallites as the major active sites of steam methanol reforming achieved by CZA(PG/N = 1). So, it reached the complete conversion of methanol at lower temperature compared to the other samples. The synthesized sample with propylene glycol to nitrates ratio of 1 showed high stability during 1200 min. Moreover, the deactivation study was performed on best and worst synthesized nanocatalysts.
Nitrogen doped carbon quantum dots as a green luminescent sensitizer to functionalize ZnO nanoparticles for enhanced photovoltaic conversion devices
Highlights: • Hydrothermal synthesis for highly green luminescent nitrogen doped carbon quantum dots (NCQDs) was proposed. • ZnO NPs were prepared by CTAB assisted low temperature reaction method. • High green luminescence was observed from NCQDs. • NCQDs are applied as light harvesting material in ZnO photoanodes. • Enhanced photoconversion efficiency was observed with NCQDs. - Abstract: A simple and facile hydrothermal approach for the synthesis of highly green luminescent nitrogen doped carbon quantum dots (NCQDs) is reported. The prepared NCQDs show narrow size distribution of 2–3 nm, abundant surface functional groups and good water solubility. To showcase the potential of these NCQDs as a solar light harvesting material, we designed NCQDs sensitized ZnO nanoparticles based photoanodes for photovoltaic solar cells. As a result, NCQDs sensitized ZnO photoanodes exhibited 75% higher photoconversion efficiency when compared to that of bare ZnO photoanodes. The characterization and optical properties of NCQDs sensitized ZnO photoanodes is also discussed.
Load-Dependent Soft-Switching Method of Half-Bridge Current Doubler for High-Voltage Point-of-Load Converter in Data Center Power Supplies
With the increased cloud computing and digital information storage, the energy requirement of data centers keeps increasing. A high-voltage point of load (HV POL) with an input series output parallel structure is proposed to convert 400 to 1 VDC within a single stage to increase the power conversion efficiency. The symmetrical controlled half-bridge current doubler is selected as the converter topology in the HV POL. A load-dependent soft-switching method has been proposed with an auxiliary circuit that includes inductor, diode, and MOSFETs so that the hard-switching issue of typical symmetrical controlled half-bridge converters is resolved. The operation principles of the proposed soft-switching half-bridge current doubler have been analyzed in detail. Then, the necessity of adjusting the timing with the loading in the proposed method is analyzed based on losses, and a controller is designed to realize the load-dependent operation. A lossless RCD current sensing method is used to sense the output inductor current value in the proposed load-dependent operation. In conclusion, experimental efficiency of a hardware prototype is provided to show that the proposed method can increase the converter's efficiency in both heavy- and light-load conditions.
Development of a scalable, robust electrocatalytic technology for conversion of CO 2 to formic acid via microstructured materials
This project was funded by the Bioenergy Engineering for Product Synthesis (BEEPS) program under the Funding Opportunity Announcement (FOA) DE-FOA-0001916 Topic Area 5 “Rewiring Carbon Utilization”. This FOA sought projects that would electrocatalytically reduce CO 2 to a carbon intermediate and then upconvert to a multi-carbon product or fuel via non-photosynthetic biological system engineering. The project sought to combine the expertise of OCO Chem, whose chief scientist had previously developed an efficient electrocatalytic reactor for conversion of CO 2 to formate with potential to scale, Montana State University investigators who had recently patented a method for laterally grading membranes with the potential of improving reactant distribution and more uniform efficiency across membrane-based reactors, and University of South Florida which had recently discovered a novel C-C bond forming reaction not known to naturally occur in biological systems and which uses C1 substrates and circumvents the central microbial metabolism.
Hydrogen and methoxy coadsorption in the computation of the catalytic conversion of methanol on the ceria (111) surface
Methanol decomposition to formaldehyde catalyzed by the ceria (111) surface has been investigated using the DFT + U method. Our results rationalize experimental temperature programmed desorption experiments on the fully oxidized surface. Particular attention has been paid to the model correctness of methoxy with coadsorbed hydrogen on the surface. This issue has been raised by the experimental observation of water desorption at low temperature removing hydrogen from the system. Our investigation also includes hydrogen diffusion as a means of hydrogen removal. We find that the presence of methoxy reduces the reaction energy for water formation considerably. In addition, the preference of the electron to locate at the methoxy oxygen results in a dehydrated surface that does not contain Ce 3+ ions, despite the existence of a vacancy.
Scalable and Tunable Carbide-Phosphide Composite Catalyst System for the Thermochemical Conversion of Biomass
We have prepared composite materials of hexagonal nickel phosphide and molybdenum carbide (Mo2C) utilizing a simple and scalable two-stage synthesis method comprised of carbothermic reduction followed by hydrothermal incubation. We observe the monophasic hexagonal phosphide Ni2P in the composite at low phosphide-to-carbide (P:C) ratios. Upon increasing the proportion of P:C, the carbide surface becomes saturated, and we detect the emergence of a second hexagonal nickel phosphide phase (Ni5P4) upon annealing. We demonstrate that vapor-phase upgrading (VPU) of whole biomass via catalytic fast pyrolysis is achievable using the composite material as a catalyst, and we monitor the resulting product slates using pyrolysis gas chromatography/mass spectrometry. Our analysis of the product vapors indicates that variation of the P:C molar ratio in the composite material affords product slates of varying complexity and composition, which is indicated by the number of products and their relative proportions in the product slate. Our results demonstrate that targeted vapor product composition can be obtained, which can potentially be utilized to tune the composition of the bio-oil downstream.