Fuel Processing Technology最新文献

The development of highly effective bifunctional catalysts for n-hexadecane hydroisomerization is still essential to produce second-generation biodiesel. Herein, a Pt-Pd/ZSM-22-G (abbreviated as Pt-Pd/Z22-G) bimetallic catalyst was prepared by employing a room temperature electron reduction (RTER) method with glow discharge as the electron source. As a contrast, a series of Pt/Z22-H, Pd/Z22-H and Pt-Pd/Z22-H catalysts were prepared by the conventional hydrogen reduction method. The Pt-Pd/Z22-G catalyst reveals more exposed metal sites, larger C_Me/C_H+ values and an enhanced distribution of Pt-Pd(111) facets compared with the Pt/Z22-H, Pd/Z22-H and Pt-Pd/Z22-H catalysts. These modifications are originated from the stronger electron interactions and the smaller metal nanoparticles because of the effects of highly energetic reducing electrons. The n-hexadecane hydroisomerization results show that the iso-hexadecane yield over the Pt-Pd/Z22-G catalyst is 82.9%, which is the highest among four investigated catalysts in this work. This phenomenon occurs because more exposed Pt-Pd(111) facets and larger C_Me/C_H+ ratios are beneficial for the adsorption and hydrogenation of iso-alkene intermediates at metal sites to increase the iso-alkanes yield based on density functional theory (DFT) calculations. Furthermore, the iso-alkanes yield over the Pt-Pd/Z22-G catalyst also keeps steady after long-term tests for 120 h because of the limited metal aggregation and carbon deposition.

This paper proposes a new method of pulverized coal gasification using high-temperature tertiary air in a cement precalciner, in which an external hanging gasifier is added nearby. A full-scale model is established and simulated for the entrained flow gasifier. During the gasification process, the global reaction mechanism is used to model the release and reactions of volatiles from pulverized coal, and a particle surface reaction model is employed to calculate the fixed carbon content. The mechanism by which reducing gas reacts with NO is also considered. The results of the velocity, temperature, gas composition, NO_x emissions, calorific value, volatile conversion ratio and char burnout ratio, are achieved in the simulation. The results show that the volatile conversion ratios were close to 100%, and the carbon conversion ratios ranged from 27.97% to 62.76% among all the tested conditions. The concentrations of NO at the outlet of the gasifier were 109, 98, 75, 91, 87, 76, and 90 mg/m³ separately in 7 conditions. These values are significantly lower than those of complete combustion. However, the addition of raw meal had the best temperature control effect, leading to a significant decrease in thermal NO_x production and no side effects on the stability of the production line.

The additivation of solid biofuels has proven to be an effective method for reducing total particulate matter (TPM) and carbon monoxide (CO) emissions, as well as for reducing ash-related problems related to, e.g., fouling and slagging. During the combustion with additives, potassium (K) released from the solid biofuels is bound into temperature-stable compounds, thus preventing the formation of inorganic (i.e., K-based) TPM. Simultaneously by reducing K in the gas phase, the inhibition of gas-phase oxidation (e.g., CO oxidation) due to interference of K within the existing radical pool is hindered. Particularly kaolin, an aluminum-silicate-based additive has proven effective in reducing not only TPM but also CO emissions. The mitigation effects on CO emissions have previously been reported mostly in a subordinate role and explanations are given in the form of hypotheses. In this study, seven additives (i.e., kaolin, kaolinite, meta-kaolinite, aluminum hydroxide, muscovite, muscovite coated with titanium dioxide and kalsilite, each at 0.3 wt%_a.r.) were investigated during wood pellet combustion in a small-scale furnace (7.8 kW). For both CO and TPM emissions, kaolin proved to be most effective (i.e., −52% CO, −49% TPM), followed by muscovite, kaolinite, TiO₂ coated muscovite, aluminum hydroxide, and meta-kaolinite.

The analysis of the macromolecular structure and morphology in coal during oxidation is the basis to explore the mechanism of spontaneous combustion. To explore the evolutionary rules of coal macromolecular structure during oxidation, Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), and Raman Spectroscopy (Raman) were employed to analyze the coal samples with different oxidation degrees. The results revealed that the oxidation action led to the decrease of the aliphatic structures and aromatic hydroxyl groups in coal, while promoting the formation of oxygen-containing functional groups and aromatic structures. It also led to a relative increase of free hydroxyl groups linked to hydrogen bonds. The aromatic layer spacing (d₀₀₂) decreased with increasing oxidation degree, while the microcrystal stacking height (L_c), the aromatic layer diameter (L_a), the average number of crystal stacking layers (n) generally increased. It indicated that small aromatic ring molecules in coal could undergo continuous polymerization during oxidation to form a single aromatic layer structure. The variation of Raman spectrum parameters exhibited a consistent decreasing trend in W_D/W_G, I_D/I_G, A_D/A_G, and A_(GR+SL)/A_G value, indicating an increase in the vibration of sp² hybridization carbon atoms within the lattice structure of coal. Conversely, P_G-D, A_S/A_D and A_(GR+VL+VR)/A_D value increased overall, suggesting that small aromatic rings decreased in content during oxidation while polymerizing into larger aromatic rings. The coal structure underwent a brief stage of disordered evolution during oxidation, followed by removal of impurity structures and condensation of aromatic structures due to increasing oxidation temperatures, ultimately leading to a highly ordered crystalline state. The oxidation process significantly influenced the development of coal's aromatic structure, particularly in less metamorphic coal. The research findings provide a theoretical basis for analyzing the underlying mechanism behind spontaneous combustion induced by coal oxidation.

This paper investigates the impact of ammonia (NH₃) kinetics on the ignition mechanism of dimethyl ether (DME), a topic minimally addressed in existing literature, by utilizing a hypothetical NH₃ representative species with identical thermodynamic properties and atomic mass to actual NH₃, yet remaining inert during reactions, thereby distinguishing the kinetic effects from thermal and dilution influences. Kinetic analysis via zero-dimensional (0D) idealized reactor calculations shows that DME ignition in the ammonia-air atmosphere is still primarily governed by peroxy kinetics, yet ammonia kinetics significantly modify the ignition reaction pathways of DME. Specifically, during the low-temperature oxidation preparation stage, ammonia oxidation yields nitrogen-containing species that (e.g., NO₂, NO, NH₂), through CN reactions, reduce the flux in the keto-hydroperoxides (KET) formation pathway in DME. The NH₃ oxidation pathway also competes for OH radicals, which disfavors DME ignition. The rapid decomposition of KET during the low-temperature heat release (LTHR) stage emits a substantial amount of OH radicals, increasing temperature and causing the shift from chain branching to chain propagation pathways in DME oxidation, leading to significant CH₂O production and decreased reaction reactivity. This shift also promotes the hydrogen‑oxygen reaction mechanism, transitioning the controlling mechanism from the KET mechanism to the hydrogen peroxide (H₂O₂)-loop mechanism. The LTHR stage further enhances CN reactions in the CH₃ pathway, favoring NO production and increasing the flux of NO and HO₂ reactions releasing OH radicals. Moreover, the ammonia oxidation pathway, characterized by HO₂ radical consumption and concurrent OH radical and H₂O₂ generation, significantly influences the H₂O₂-loop system, resulting in a diminished reaction flux in the H → HO₂ → H₂O₂ mechanism during the thermal ignition preparation stage. In summary, these findings underscore the significance of CN interactions in the NH₃/DME ignition process and highlight the necessity of considering CN interactions in mixed fuels between ammonia and other high-reactivity fuels (e.g., diesel with higher carbon atoms), for accurate ignition prediction.

Developing highly efficient single-atom catalysts (SACs) for electrocatalytic carbon dioxide reduction reaction (CO₂RR) is a promising approach to promoting carbon neutrality. However, challenges such as low activity, selectivity and high costs hinder industrial scaling, attributed to the lack of innate activity or insufficient transition metal (TM) active site density in current catalysts. Therefore, the focus of CO₂RR research remains on developing SACs with intrinsic catalytic activity, high TM coverage and cost-effectiveness. This study presents the design of carbon-based materials with ultra-high TM coverage (TM₂C₁₂) (TM = Mo, Ru, Rh, W, Re, Os and Ir) as electrocatalyst SACs for CO₂RR using density functional theory calculations. Among these materials, W₂C₁₂ (W represents tungsten) demonstrates superior selectivity and catalytic activity for CO₂RR to carbon monoxide (CO) products with overpotentials of 0.45 V and a W coverage of up to 71.84 wt%. To further enhance its catalytic activity, non-metallic (NM) coordination modification (NM = B, N, O, P doping and C vacancy) was explored on W₂C₁₂. The results indicate that N-doped W₂C₁₂ (N-W₂C₁₂) can significantly improve selectivity and catalytic activity, achieving an extremely low overpotential of 0.34 V. This research offers valuable insights into designing SACs with high activity, selectivity and stability for CO₂RR and other catalytic reactions.

The world's energy requirement is rising continuously due to an increase in the global population and demand for better quality of life. Fossil fuels are non-renewable, and their consumption poses global warming. Biomass-derived fuels are sustainable alternatives to fossil fuels as they are originated from renewable feedstocks. The present study investigates the production of biocrude from hydrothermal liquefaction of Canadian agricultural straws at identical conditions. Further, barley straw is found to be promising; therefore, hydrothermal liquefaction process parameters are varied for barley straw to maximize the biocrude yield with lower oxygen content. At optimum reaction conditions, the existence of carboxylic acids, phenols, aldehydes, and ketones is identified in the produced biocrude. Further, the recyclability study of the aqueous phase is attempted to explore the possibility of reusing this phase. The physicochemical characteristics of the biocrude (main product) and by-products (hydrochar, non-condensable gases, and aqueous phase) are also studied to identify the suitable areas of applications. The present experimental study demonstrates a detailed understanding of the liquefaction behavior of Canadian barley straw for biocrude production with an immense potential to co-refine in the existing petroleum refineries.

One-step transesterification between ethylene carbonate (EC) and ethanol (EtOH) can effectively prevent the formation of azeotropes in the synthesis of diethyl carbonate (DEC) / ethyl methyl carbonate (EMC). However, owing to the influence of volume and electronic effects of EtOH molecules, the catalytic activity is insufficient. In this study, we propose an on-line synthesis technique for catalysts and prepare a unique heterogeneous alkali catalyst, PS-(NR₃OH)EG. This technique simplifies the catalyst preparation process and protects it from exposure to water and carbon dioxide in the air. The active sites of PS-(NR₃OH)EG are derived from the product ethylene glycol (EG). PS-(NR₃OH)EG exhibits excellent catalytic performance in promoting EC and EtOH transesterification. The physicochemical properties of PS-(NR₃OH)EG are analysed, and the reaction conditions are optimized. The results indicate that PS-(NR₃OH)EG has superior catalytic activity and stability compared to the similar previously reported catalysts. Notably, after continuous reaction in a fixed-bed reactor for 500 h, PS-(NR₃OH)EG maintain its initial catalytic activity. This study provides theoretical and experimental guidance for catalyst preparation and transesterification reaction process design.

The limited solubility of lignin in commonly used solvents poses a challenge for its depolymerization into high-value monomers. This paper investigates the solubility of alkali lignin in water, methanol, ethanol, acetone, 1,4-dioxane, and their binary solution, and examines their impact on lignin depolymerization. The distribution of depolymerization products was correlated with the chemical structure changes in various solvent. Among the solvents tested, water-acetone mixtures demonstrated exceptional solubility for alkali lignin (95.24%) and provide the highest yield of bio-oil and phenolic monomers. The enhanced solubility of guaiacol units in acetone, combined with the addition of water in the co-solvent system dramatically improved the solubility of alkali lignin. Moreover, formic acid donated hydrogen protons to facilitate lignin depolymerization and prevented the repolymerization of unstable intermediates. Optimal reaction conditions were achieved at 300 °C for 120 mins using a mixed solvent composed of water, acetone, and formic acid in a ratio of 5:5:1 (v/v/v), corresponding to the highest yield of bio-oil with 81.45 wt%, the lowest yield of residue with 6.20 wt%, and a phenolic monomer content of 57.48%. Furthermore, this co-solvent system revealed satisfactory adaptability for converting various lignin into phenolic monomers.

The self-sintering of green petroleum coke (GPC) is an important method for the synthesis of high-strength graphite blocks owing to its relatively short production cycle. However, the volatilization of small molecular components in GPC inevitably results in the generation of pores and microcracks which seriously deteriorates the mechanical performance of carbon blocks. Herein, we report a facile quinoline-assisted composition regulation approach to prepare high mechanical strength carbon blocks using GPC as the starting material. Quinoline exhibits three major functions. Firstly, unideal organic volatiles can be effectively removed via quinoline extraction, thereby inhibiting the generation of pores and microcracks. Secondly, the presence of quinoline can promote the polymerization of aryl compounds due to its easy formation of free radicals. Thirdly, the interactions between the graphite layers are enhanced by the polarization of the aromatic rings, which clearly improves the mechanical performance of the carbon blocks. As a result, the obtained carbon block GPC/QI-17-C demonstrates an apparent density of 1.56 g·cm⁻³, flexural strength of 39.61 MPa and compressive strength of 136.98 MPa, which are 1.16, 3.39 and 4.53 times that of pristine GPC counterparts, respectively.