25 Search Results

Chloroaluminate ionic liquid catalyzes the disproportionation of alkanes, a reaction readily initiated by carbenium-ion precursors such as tert-butyl chloride, resulting in equimolar amounts of isobutane and methylpentanes. The carbenium ion-AlCl4- ion-pairs stabilized by the ionic liquid are the key intermediates in two distinctive kinetic phases, i.e., a transi-ent phase (0-5 minutes) and a steady-state phase (after 5 minutes). The transient phase constitutes the majority of iso-pentane conversion and is governed by the initial carbenium ion concentration. In the steady-state phase, disproportiona-tion occurs at a considerably lower rate, affected by the carbenium ion concentration, the concentration of the ionic liq-uid, andmore » the reaction temperature. The formation of olefins observed in the 1H NMR spectra of the reacting substrates, along with the DFT calculations, suggests that dehydrochlorination of active carbenium ion-pairs reduces their concentra-tion, decreasing, in turn, the reaction rate. Kinetic modeling indicates that the transient phase is significantly controlled by the hydride transfer (kHT) and the dehydrochlorination rate constants (kDC), while the steady-state phase is additional-ly influenced by the hydrochlorination rate constant (k–DC). The overall activation energy of the reaction at the steady state, expressed as Ea,steady-state = Ea,HT – Ea,DC + Ea,–DC, was 54 kJ/mol. The reaction mechanism and the kinetics highlight the potential of Lewis acid-catalyzed conversions of hydrocarbons under remarkably mild conditions.« less

Converting high-performing powder catalysts from the laboratory reactor scale into effective extruded catalysts at the industrial scale remains a hurdle for advancing sustainable catalytic processes, such as the conversion of biogenic syngas into high octane gasoline. Recently, a process-intensified syngas-to-hydrocarbons (STH) reaction in a single reactor under relatively mild conditions (220–250 ºC, 0.75–2.0 MPa) was reported, enabled by the development of a dimethyl ether (DME) homologation catalyst, Cu-modified H-BEA (Cu/BEA) zeolite. In this study, we explore approaches for synthesizing engineered Cu/BEA catalysts for use in the STH reaction to retain the high performance observed with the powder catalyst. We demonstratemore » that changes to the order of manufacturing steps (i.e., Cu deposition, alumina binder addition, and extrusion) result in observable changes to key active sites (Brønsted acid sites and zeolitic Cu⁺ species), and ultimately, catalyst performance. When the Cu precursor was added directly to BEA before extrusion, both types of active sites were stabilized, preserving the activity of the powder catalyst. However, when the Cu precursor was added after extrusion, the resulting Cu species were mobile, destabilizing Brønsted acid sites and leading to near-zero activity.« less

Catalytic fast pyrolysis (CFP) is a promising strategy for producing hydrocarbon transportation fuels from biomass feedstocks. However, catalyst development is needed to increase bio-oil yields and enhance process economics. In this work, we demonstrate how post synthetic modification of formed ZSM-5 with phosphorus shifts CFP selectivity from coke and light gases toward the desired bio-oil product. Microscale experiments demonstrated reduced coke production relative to unmodified ZSM-5 and identified an optimal P loading. Extensive catalyst characterization revealed that P interacted with Al sites to reduce the acid site density, with preferential binding to the strongest acid sites. Insights from the microscalemore » experiments were leveraged to produce kilogram quantities of formed P-ZSM-5 for evaluation in a larger semi-integrated process. These experiments generated liters of bio-oil that was hydrotreated and fractionated into gasoline, diesel, and jet cuts. The phosphorus-modified ZSM-5 improved CFP bio-oil yield, resulting in an 11% relative increase in the carbon yield from biomass to aviation fuel and a 14% decrease in the minimum fuel selling price. These results highlight the impact targeted changes in catalyst acidity, achieved by adding 2.5 wt % P, can have on the carbon efficiency and feasibility of fuel production from biomass feedstocks.« less

The performance and emissions for a downscaled single-cylinder 2-stroke crosshead engine were determined for a very low sulfur fuel oil (VLSFO) when blended with 10 wt.% fast pyrolysis (FP) or hydrothermal liquefaction (HTL) bio-intermediates. The FP and HTL oils were derived from biomass and were observed to contain lower molecular weight (MW) hydrocarbons than neat VLSFO (which was evaluated as a baseline comparison). The addition of either biofuel reduced the overall viscosity of the VLSFO. Aging tests at 50, 90, and 120°C showed that the dynamic viscosity of VLSFO increased with exposure time up to two weeks. Similar trends weremore » observed for the FP and HTL blends, but a pronounced spike in viscosity occurred for these fuels during the early period of exposure. None of the viscosity increases exceeded the operational limits of fuel system pumps. Engine performance studies were conducted under low, medium and high load operational settings. The relative performance of the test fuels was highly dependent on operating condition. In general, the engine results for the three test fuels were similar, but modest improvements in brake thermal efficiency and brake specific fuel consumption were observed, which may be attributed to the heightened reactivity of low molecular weight fraction of the FP and HTL oils.« less

Polyolefins and their chlorinated derivatives such as polyvinyl chloride (PVC) are among the most prevalent plastics in global production and waste streams. Traditional waste-to-energy methods such as incineration and pyrolysis, as well as most chemical upcycling methods for PVC utilization, require thorough, high-temperature dechlorination to prevent the release of toxic chlorinated compounds. Here, we present here a strategy for upgrading discarded PVC into chlorine-free fuel range hydrocarbons and hydrogen chloride in a single-stage process catalyzed by chloroaluminate ionic liquids. This approach offsets endothermic dechlorination and carbon-carbon bond cleavage with exothermic alkylation and hydrogen transfer by isobutane or isopentane in amore » low-temperature tandem process. The light isoalkanes are available from refinery processes and partly from recycling of the product stream. This process is suitable for handling real-world mixed and contaminated PVC and polyolefin waste streams.« less

Wet air oxidation (WAO) offers an effective method for treating waste streams, converting pollutants into benign substances, and holds significant potential for processing the aqueous product from the hydrothermal liquefaction (HTL-AP) of wet wastes, a promising renewable fuel technology. Here, we conducted a comprehensive study of the WAO of HTL-AP from four different wet wastes. Through continuous testing under various conditions, we produced samples with different chemical oxygen demand (COD) levels, enhancing understanding of reaction parameters necessary for substantial COD reduction (>95%). Chemical analysis revealed that alcohols and ketones in the HTL-AP rapidly oxidized to acetic acid through aldehyde intermediates,more » while acetic acid, other carboxylic acids, and phenols oxidized relatively slowly. The light N-containing compounds were found to exhibit a change in concentration only after the whole sample reaches an 80% COD reduction, indicating their refractory nature under applied conditions. Energy released in the WAO reaction was calculated, and anaerobic toxicity assay demonstrated that WAO treatment enhanced methane production kinetics due to reduced inhibitory effects, suggesting partial oxidative transformation of inhibitory compounds into less toxic derivatives. These findings provide insights into designing effective WAO processes for valorizing HTL aqueous products, addressing key barriers to HTL process commercialization.« less

Ru/C-catalyzed polyethylene (PE) and hydrocarbon hydrogenolysis under quasi-supercritical fluid of isopentane was kinetically and mechanistically investigated. PE hydrogenolysis with C–C and C–H cleavage showed zeroth order, suggesting strong adsorption of hydrocarbons. PE yielded broad product distribution of heavy (C_21–40) and diesel-range (C_11–20) hydrocarbons in the primary step of hydrogenolysis due to stochastic C–C cleavage over Ru surface. Catalytic hydrogenolysis of n-hexadecane, squalane, and light hydrocarbons such as n-pentane, iso-pentane, and n-hexane further described C–C cleavage reactivity between primary and secondary carbons, i.e., ¹C–²C and ²C–²C, which has an order of magnitude higher hydrogenolysis rate than that involving a tertiary carbon.more » The PE saturated Ru surface and lower C–C cleavage reactivity of tertiary carbon in iso-pentane, therefore, imited sovlent conversion during hydrogenolysis, whereas leading to selective PE conversion. Using hexadecane, we observed comparable hydrogenolysis rates between H₂ and D₂ (k_H/k_D ~ 1), indicating the kinetically relevant step of C–C cleavage with facilitating C–H cleavage and rehydrogenation. However, the normal kinetic isotope effect between hexadecane and deuterated hexadecane (k_C16H34/k_C16D34 ~ 5) revealed that the dehydrogenation, i.e., C–H cleavage, can be kinetically involved in the hydrogenolysis kinetic. By considering the 8-fold lower H-D exchange rate with deuterated hexadecane compared to n-hexadecane, the lower rate for hydrogenolysis and H-D exchange with deuterated hexadecane can be attributed to the C–D bond dissociation energy being 3 kJ/mol higher than that of the C–H bond. Increasing H₂ pressure favors internal C–C bond cleavage over terminal one. This minimizes the formation of lower hydrocarbons, particularly methane. However, the increase in H₂ pressure increases the coverage of adsorbed hydrogen on the Ru particles due to competitive adsorption of H₂ and polyethylene, which, in turn, reduces the polyethylene conversion rates.« less

Yttrium-modified dealuminated Betazeolite (Y-BEA) represents a type of Lewis acid zeolite that has gained attention for its potential to efficiently catalyze the conversion of biomass-derived oxygenates. The structure of the Y active sites and their dynamics during biomass conversion reactions, which normally involve substantial amounts of water, necessitate thorough investigation for the rational design of more active and stable catalysts. Here, we conducted a study where a series of Y-BEA catalysts with different yttrium loadings (1–7 wt.%) were subjected to hydrothermal treatment (450 °C, 20% water) and investigated for their structural and catalytic activity changes through a combination of multiplemore » characterizations and kinetic measurements. The number of acid sites of Y-BEA decreased without a change in acid strength following the hydrothermal treatment, which was confirmed by the results of acid site titration, infrared spectroscopy of probe molecules, and kinetic measurements for probe reactions (acetone aldol condensation). Structural analysis using X-ray diffraction (XRD), specific surface area measurement, X-ray absorption spectroscopy (XAS), and X-ray photoelectron spectroscopy (XPS) demonstrated that both the zeolite structure and the isolation status of the Y site remain intact after hydrothermal treatment. Further, the Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) spectra, thermogravimetric analysis (TGA), and operando ¹H and ²⁹Si magic-angle spinning (MAS) nuclear magnetic resonance (NMR) revealed the dehydroxylation of Y-BEA induced by hydration-rearrangement-condensation restructuring during the high-temperature steam treatment. Dehydroxylation affects the structure of Y sites by reducing their vicinal silanol sites. In conclusion, this conversion of Lewis acidic Y sites into nonacidic sites is the primary factor behind the change in acid site quantity and catalytic activity on Y-BEA.« less

Bioethanol to middle distillate technologies have offered a unique solution to produce renewable aviation fuel for decarbonizing the hard-to-electrify sectors. Here, we have developed the series of bimetallic Cu- and rare earth-containing (RE) Beta zeolite catalysts that yield high C₃₊ alkene selectivity from ethanol upgrading (>80% selectivity at ~100% conversion, 623 K). The formation rates of butene isomers to C₅₊ alkenes are linearly correlated with the strength of Lewis acidic RE identity, which follows the sequence of Yb₁₂/Beta >Y₇/Beta > Gd₁₂/Beta > Ce₁₀/Beta > La₁₂/Beta. Rate measurements indicate that the RE selection plays the vital role in altering the ratemore » of the key competitive reactions within the ethanol-to-alkenes reaction network, namely C₄ alcohol dehydration and C-C chain growth, which dictate alkene product distributions. Finally, these findings indicate a feasible and promising method for tailoring alkene product distributions from ethanol upgrading, which is of notable significance to the generation of renewable middle distillates.« less