Energy & Fuels最新文献

The highly complex nature of wood pyrolysis bio-oils, which contain thousands of distinct molecular species with varying ionization efficiencies, poses a significant challenge for characterization by direct-infusion high-resolution mass spectrometry. This study presents a novel method combining high-performance liquid chromatography (HPLC) with 21 Tesla Fourier transform ion cyclotron resonance mass spectrometry (21T FT-ICR MS) for detailed molecular characterization of bio-oils within the scope of negative-ion ESI. The HPLC method is optimized to separate polyfunctional oxygen-containing molecules using a polymeric stationary phase with dimethylaminopropyl functionalities, and a methanol–water eluent with dimethylamine. The acidic compounds in bio-oils equilibrate between the DEA-containing mobile phase and the stationary phase, facilitating efficient gradient elution of oxygen-rich species. Coupling online HPLC with 21T FT-ICR MS revealed ∼3,000 additional monoisotopic O_x molecular formulas compared to direct-infusion FT-ICR MS. Newly detected compounds exhibited higher H/C ratios and a wider range of oxygen content, characteristic of low-molecular-weight carbohydrates and species with a composition that resembles biomass. The method enabled the detection of carbohydrate-like species (O/C ≈ 1, H/C ≈ 2) and highly aromatic compounds (H/C < 0.6, O/C < 0.3) that were undetectable via direct infusion. Early eluting, methanol-soluble species showed higher H/C ratios (∼1.5 to 2.0) and oxygen content consistent with lignin oligomers, while later-eluting compounds exhibited increased aromaticity, with compositions typical of condensed aromatic species. Advanced data processing using a Python-based, PyC2MC, software package further revealed compositional trends aligned with the solubility of bio-oils. Despite the overlap between LC–MS and direct infusion MS, single ion chromatograms revealed distinct elution patterns for identical molecular formulas, providing insights into potential isomeric diversity that are not accessible through direct infusion analyses. These findings demonstrate the enhanced molecular-level characterization achieved by HPLC-FT-ICR MS, providing key insights into the intricate composition of bio-oils and their potential for energy applications. The proposed approach provides a unique perspective on isomeric diversity and the distribution of functional groups, laying the groundwork for understanding the molecular basis of reactivity and upgrading potential in bio-oils. As the developed method targets the separation and characterization of polyfunctional oxygen-containing species, it can also be applied to dissolved/natural organic matter, photo-oxidation products, and emerging contaminants, e.g., water-soluble species leaching from materials like asphalt and petroleum-based road sealants.

The current plastic value chain is highly linear, leading to large amounts of waste plastics that harm the environment and human health. Recycling is required, and among the options, catalytic pyrolysis is particularly suited to convert polyolefin-rich plastic waste into useful chemicals such as benzene, toluene, and xylene (BTX). In this paper, we demonstrate ex situ catalytic pyrolysis of polypropylene in a continuous double-fluidized-bed reactor to produce BTX. The optimal pyrolysis temperature in the first fluidized-bed reactor was 550 °C, giving a BTX yield of 22.3 wt % (based on PP input). Lowering the nitrogen flow rate and the use of smaller catalyst particle sizes favor BTX formation. Our novel reactor concept showed good operational stability at longer times on stream (TOS, 10 h). Catalyst activity was slightly reduced during TOS, as is evident from a small decrease in BTX yields. Detailed catalyst characterization studies showed that coke formation is the main reason for catalyst deactivation. In addition, chemoselectivity was also a function of TOS and the selectivity to benzene and toluene decreased, while higher amounts of xylenes were formed.

The current plastic value chain is highly linear, leading to large amounts of waste plastics that harm the environment and human health. Recycling is required, and among the options, catalytic pyrolysis is particularly suited to convert polyolefin-rich plastic waste into useful chemicals such as benzene, toluene, and xylene (BTX). In this paper, we demonstrate ex situ catalytic pyrolysis of polypropylene in a continuous double-fluidized-bed reactor to produce BTX. The optimal pyrolysis temperature in the first fluidized-bed reactor was 550 °C, giving a BTX yield of 22.3 wt % (based on PP input). Lowering the nitrogen flow rate and the use of smaller catalyst particle sizes favor BTX formation. Our novel reactor concept showed good operational stability at longer times on stream (TOS, 10 h). Catalyst activity was slightly reduced during TOS, as is evident from a small decrease in BTX yields. Detailed catalyst characterization studies showed that coke formation is the main reason for catalyst deactivation. In addition, chemoselectivity was also a function of TOS and the selectivity to benzene and toluene decreased, while higher amounts of xylenes were formed.

Hydrogen plays a vital role in renewable energy systems and has a significant environmental impact. Storing hydrogen in underground geological formations offers an efficient and safe solution to balance production and consumption. However, due to hydrogen’s unique properties, there is a risk of leakage through the caprock of underground aquifers, potentially causing serious issues such as groundwater contamination, reduced storage efficiency, and explosion hazards. This study employs numerical simulations to investigate hydrogen leakage from caprock during underground storage, focusing on key parameters. These parameters include injection and production rates, cycle duration, hydrogen molecular diffusion, aquifer pressure, injection and production depths, well types, aquifer dip angle, caprock permeability, and capillary entry pressure. By examining these factors, the study provides an in-depth comprehensive analysis of hydrogen leakage from aquifers, addressing a critical gap in existing research. The results indicate that a significant amount of the total injected hydrogen leaks into the caprock after eight years of injection and storage cycles. This leakage can have significant environmental and economic impacts. The study also reveals that caprock permeability is crucial in influencing hydrogen leakage with higher permeability leading to increased leakage rates. Moreover, vertical caprock permeability has a more pronounced effect on leakage rates than horizontal permeability. Additionally, factors such as aquifer pressure, aquifer dip angle, injection and production depths, and hydrogen injection duration contribute to a higher hydrogen leakage from the caprock. The findings underscore the importance of carefully selecting underground hydrogen storage sites to mitigate the potential risks of hydrogen leakage.

The electrochemical nitrogen reduction reaction (NRR) is emerging as a sustainable and carbon-free ammonia production approach under mild conditions, but it is highly dependent on the activity of the electrocatalyst material. Nevertheless, the availability of active sites on electrocatalysts for N₂ adsorption and activation limits the overall NRR performance. Herein, active site generation with defect engineering strategy is employed to explore selenium vacancy-rich transition metal dichalcogenides ex-MoSe₂ and ex-WSe₂ toward NRR. Thick-layered bulk MoSe₂ and WSe₂ are converted to selenium vacancy-rich few-layered nanosheets on chemical exfoliation. Highly promising electrocatalytic activity is witnessed for both materials. Typically, ex-MoSe₂ exhibited an NH₃ yield rate of 15.86 μg mg_cat^–1 h^–1 and a Faradaic efficiency of 9.39% at −0.9 V vs Ag/AgCl in 0.1 M Na₂SO₄ electrolyte of pH = 7. Moreover, validation of the true ammonia production with the elimination of probable contamination is done via feeding gas purification, control experiments, and isotope labeling experiments. Importantly, density functional theory calculations exhibit selenium vacancy as a favorable active site for N₂ adsorption and activation for efficient NRR and strongly support the experimental findings.

This study explores the synergistic effects of Tween 80 surfactant combined with monoethanolamine (MEA) and sodium carbonate (Na₂CO₃) alkalis to reduce interfacial tension, alter wettability, and enhance emulsification for improved enhanced oil recovery under optimal salinity conditions. Experimental results reveal that MEA and Na₂CO₃ comparably improve the interfacial tension (IFT) reduction and wettability alteration capabilities of surfactant solutions. However, MEA demonstrates a superior performance in stabilizing oil–water emulsions with smaller droplet sizes and lower corrosion potential. The IFT of crude oil in water was significantly reduced from 29.8 to 0.222 mN/m using Tween 80 at CMC, and further decreased to 0.0075 mN/m with the addition of 0.75 wt % MEA at an optimal salinity of 1.5 wt % NaCl. This pronounced reduction confirms the synergistic effect between the surfactant and organic alkali, providing a favorable balance of hydrophilic and lipophilic interactions at the oil–water interface. Microscopic analysis revealed that the MEA-surfactant system produced emulsion droplets with an average radius of 5.8 μm, significantly smaller than the 10.4 μm droplets observed with Na₂CO₃, contributing to greater emulsion stability. Additionally, MEA was found to exhibit 57.5% lower corrosiveness on mild steel compared with Na₂CO₃, highlighting its operational advantages for long-term field applications. Core flooding experiments revealed that a surfactant-alkali slug containing MEA and Tween 80 at optimal salinity achieved a 32.37% OOIP recovery, surpassing the 29.40% OOIP recovery from a Na₂CO₃ and surfactant slug. The higher viscosity of MEA-based surfactant-stabilized emulsions improves both macroscopic sweep efficiency and displacement efficiency, leading to improved oil recovery. The combination of Tween 80 and MEA optimizes enhanced oil recovery (EOR) efficiency, reduces equipment corrosion, and enhances sustainability, offering a cost-effective, ecofriendly solution for long-term oil recovery operations.

To promote the chemical recycling of polyethylene terephthalate (PET), its valorization by hydrocracking was investigated. To ease the implementation at large-scale of this valorization route, the PET was coprocessed with vacuum gasoil (VGO), which is a benchmark feed of the industrial hydrocracking unit (10 and 90 wt %, respectively) and hydrocracked using a PtPd/HY catalyst. Furthermore, the suitability of using PETs of different natures and origins to produce fuel-assimilable streams was assessed. Specifically, one virgin, one commercial, and one mechanically recycled PETs were used, analyzing the differences in the conversion, yields of product fractions (dry gas, liquefied petroleum gases, naphtha, and light cycle oil), and composition of naphtha and light cycle oil fractions, given their possible interest of being used in the formulation of automotive fuels. The reaction runs were performed in a batch reactor under the following conditions: 80 bar, 420 °C, 120 min, and a catalyst/feed mass ratio of 10 g_catalyst g_feed^–1. The modified and degraded plastics were more easily converted into liquid hydrocarbons within the naphtha and LCO fractions with contents of isoparaffins between 45 and 50 wt %. From the composition of the liquid products, the possible hydrocracking pathways of the PET-derived molecules were evaluated.

As a major means of reducing carbon emissions and achieving the carbon-zero target, CO₂ geological storage has been widely applied in depleted oil or gas reservoirs for enhanced oil recovery. However, during CO₂ injection and long-term geological storage, the carbonation-induced corrosion of the cement sheath is the main threat as CO₂ may leakage from the well to atmosphere. In this study, G-grade oil well cement was placed in different CO₂ corrosion environments to investigate the effects of the CO₂ pressure and water saturation on long-term cement corrosion. Mechanical and pore permeability properties, as well as changes in the microstructure and composition, were analyzed using uniaxial compression, X-ray diffraction, mercury intrusion porosimetry, and scanning electron microscopy testing methods, respectively. Specially, nuclear magnetic resonance (NMR) technology was used to evaluate the pore changes in cement during the CO₂ corrosion. Results showed that wet-phase corrosion facilitated the occurrence of carbonation reactions and the migration of corrosive medium and products. Moreover, the microstructure and composition of the CO₂-corroded cement exhibited different characteristics at different stages of corrosion. The T₂ spectrum curve indicated that the degree of CO₂ corrosion of cement was related to the diffusion rate of the CO₂. When the pressure was low, CO₂ was difficult to penetrate deep into the cement, resulting in the smallest change in the NMR curve area under dry-phase CO₂ corrosion conditions at 5 MPa. This study employed nuclear magnetic technology to further analyze the mechanism of CO₂ corrosion on oil well cement at the microscopic level. It will contribute to a deeper understanding of the mechanism of CO₂ corrosion of cement and lay a theoretical analysis foundation for practical engineering applications of cement in CO₂ geological storage and enhanced oil recovery.

Lacustrine fine-grained sedimentary rocks exhibit various lithofacies types and strong multiscale heterogeneity, encouraging us to investigate multistage characteristics of the panoramic pore-microfracture evolution process and potential triggering mechanisms of continental shale reservoirs. We present new results here from organic geochemistry analysis, X-ray diffraction, total organic carbon (TOC) analysis, the R₀ test, rock pyrolysis analysis, field emission scanning electron microscopy, low-pressure CO₂ and N₂ adsorption, high-pressure mercury injection (MIP), nuclear magnetic resonance (NMR), and spontaneous imbibition tests. First, we conducted thermal simulation experiments using low-mature shale samples with an R₀ value of 0.67%, aiming to innovatively unravel the entire dynamic evolution process of the micropore-fracture system in continental shales. Multitemperature thermal simulation investigations on naturally low-mature shale samples show that (1) the extensively developed interparticle pores and microfractures are conducive to the formation of complex and heterogeneous pore-fracture network systems. (2) The multistage evolution process of the pore-fracture system in continental shale reservoirs is triggered by differential hydrocarbon generation potential of maceral components, clay mineral transformation, and catalysis processes. (3) Four stages of the pore-fracture system evolution of the shale reservoir were identified, respectively occurring in R₀ ≤ 0.9, 0.9% < R₀ ≤ 1.6, 1.6% < R₀ ≤ 3.0%, and R₀ > 3.0%. This study laid a foundation for future research into differential diagenetic and reservoir-forming mechanisms of continental shale reservoirs, offering new insights into accurate prediction and comprehensive evaluation of the lacustrine shale gas “sweet spot”.

In this study, the autoignition of oxygen-enriched ammonia diffusion flames under gas turbine-like conditions is investigated using two-dimensional (2D) direct numerical simulation (DNS) and carefully designed zero-dimensional (0D) simulations with a detailed reaction mechanism. Three oxygen concentrations (25, 30, and 35%) are considered in the oxidizer stream, and the air (21% of oxygen) condition is also calculated as a reference. The zero-dimensional calculations indicate that there is a “most-reactive mixture fraction” (Z_MR) independent of the oxygen concentration for the autoignition of oxygen-enriched ammonia flame, which is still valid in the 2D-DNSs. The autoignition process in the turbulent mixing layer could be divided into inert mixing, preignition, and postignition stages. As the oxygen concentration increases, the periods of inert mixing and preignition sages are shortened, resulting in earlier autoignition. The ignition kernels are located at regions of the mixture fraction value of the Z_MR and low scalar dissipation rates (SDR). As the oxygen concentration increases, autoignition kernels could form at a higher SDR, indicating enhanced combustion stability. NH and NH₂ can be regarded as suitable candidates for marking the heat release rate (HRR) of oxygen-enriched ammonia flames. NO formation is enhanced as the oxygen concentration increases, which is because both the NO production (thermal, HNO, and NH_i) and consumption (N₂O) pathways are enhanced with increasing oxygen concentration; the increment in production is more significant than that in consumption.