Journal of The Energy Institute最新文献

Coking is a major issue in catalytic pyrolysis of biomass over zeolite catalysts. Using oxidative gas might mitigate formation of carbonaceous deposits. This was verified herein by catalytic pyrolysis of lignin with different oxygen concentrations (0 %, 3 %, 6 %, 9 % and 12 %) in carrier gas using ZSM-5 as the catalyst at 600 °C. The results indicated that the O₂ introduced oxidized both volatiles and biochar, reducing bio-oil yield from 29.2 to 20.7 % and biochar yield from 56.8 to 53.7 % with increasing O₂ concentration from 0 to 12 %. Oxidation of intermediates in “hydrocarbon pool” on surface of catalyst decreased the yield of BTX from 11.5 % in inert gas to 6.1–8.0 % and also other aromatics with 1 or 2 benzene rings. The aromatics with rigid polycyclic aromatic structures were more resistant towards oxidation. However, toluene, xylene, and other aromatic hydrocarbons or phenolics with side chains were more prone to be oxidized, abundance of which decreased more significantly at high O₂ concentrations. Such results were also observed in catalytic pyrolysis of guaiacol or vanillin. The benefit of using O₂ was diminished formation of coke and/or precursors of coke over ZSM-5. Characterization of reaction intermediates in catalytic pyrolysis of lignin with in-situ IR showed that O₂ presence remarkably decreased the abundance of aliphatic intermediates containing –OH, -C-H and C=O through oxidation reactions and also interrupted aromatization organics in both coke and biochar.

Biodegradable plastics are increasingly utilized due to environmental concerns but are typically disposed of together with conventional plastics. Valuable chemicals could be recovered from waste plastics by chemical recycling, but the mixing of different types of waste plastic affects the efficiency of the process. In this study, high-value chemicals were produced from a mixture of polyolefins and biodegradable polylactide by single and stepwise pyrolysis processes. The pyrolysis of polyolefins yielded fuel-like hydrocarbons, and the pyrolysis of polylactide yielded lactide and lactic acid. In the stepwise process, oxygenated compounds were only produced in the low-temperature step, and fuel-like hydrocarbons produced in the high-temperature step were not contaminated by oxygenated compounds. The influence of different catalysts on yields was investigated in the single-step and stepwise processes. The yield and selectivity of each product were significantly influenced by the type of catalyst and the composition of the plastic feedstock. Using a mixed feedstock of polyolefins and polylactide, low-temperature pyrolysis with a zeolite LTA catalyst favored the formation of lactide and lactic acid, while diesel-range hydrocarbons were obtained in the second step at a higher temperature. Aromatic and gasoline-range hydrocarbons were preferably produced from the single-step pyrolysis of polyolefins with spent FCC catalyst.

Minerals, as a secondary component, have a significant influence on the structure and thermal reactivity of coal. In order to further clarify the effect of minerals on the structure and thermal conversion of Hefeng sub-bituminous coal (HSBC) from Xinjiang, the mineral removal of HSBC was investigated. In this paper, acid-washing treatment was used to remove minerals from HSBC. The ash composition, mineral composition, and chemical structure of HSBC and its acid-washed coals were analyzed by X-ray fluorescence spectroscopy (XRF), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). Their pyrolysis characteristics and pyrolysis products were examined by thermogravimetric infrared gas chromatography/mass spectrometry (TG-FTIR-GC/MS). Acid-washing pretreatment not only significantly alters the mineral composition of the coal, but also destroys its organic structure, resulting in decreased coal stability. Especially, hydrofluoric acid (HF), as well as hydrochloric acid and hydrofluoric acid (HCl–HF) stepwise acid-washing treatment. In addition, the pretreatment effectively increased the weight loss during coal pyrolysis by destroying the organic structure of the coal and improving the pyrolysis reactivity of coal. The pretreatment inhibits the generation of CO₂ by changing the form of oxygen-containing functional groups in coal, allowing more oxygen-containing functional groups to migrate into coal tar, thereby promoting the formation of phenols, aromatics and alkanes, and improving the quality of coal tar.

The effects of butanol blending to Jet A on soot formation characteristics are investigated on a laminar coflow liquid burner with a butanol volume ratio of 0–80 %. With the increase of the butanol blending ratio, the flame liftoff gradually increases, but the flame height and flame brightness gradually decrease. The laser-induced incandescence (LII) signal of soot develops from the two wings to the axis, meanwhile, the sooting area becomes smaller. The addition of butanol does not alter the distribution shape of polycyclic aromatic hydrocarbons (PAHs), which exhibit high concentrations on the wings and maintains the shape of a "hollow cone". With the increase in the butanol blending ratio, the LII-soot and LIF-PAH signals at different heights all decreased, and the peak and average signals of soot and PAH decreased nearly linearly. A new butanol-Jet A mechanism including PAH formation is established. The simulation results show that the formation of A1 mainly comes from propylbenzene (PBZ) in Jet A, and the degree of decreases of the maximum mole fraction of A4 is consistent with the decrease in the volume fraction of Jet A, suggesting that addition of butanol results in reduced content of Jet A and the dilution of PBZ reduces the formation of PAH, ultimately leading to the reduction of soot.

In this study, it is targeted to examine the efficiency of metal supported MCM-41 catalysts on the liquid product yield from pyrolysis process of apricot kernel shell selected as a biomass and to characterize the pyrolysis liquids. In the non-catalytic pyrolysis experiments, the maximum liquid yield is obtained as 21.41 % at 500 °C. At the determined optimum condition, catalytic pyrolysis process of the biomass sample is performed with metal supported MCM-41 catalysts synthesized by sonochemical method (metal: aluminium, cobalt, iron) at different ratios to biomass (1 and 2 wt %). The pyrolysis procedures of apricot kernel shell are carried out in a tubular fixed-bed reactor at different pyrolysis temperatures. The use of catalysts improved both the liquid product (tar) yield and tar quality in respect to the calorific value, the distribution of hydrocarbons and the elimination of oxygenated groups. The results revealed that all metal-supported MCM-41 catalysts, especially the Fe-MCM-41 catalyst ratio of 2, showed an excellent catalytic ability for thermal conversion of biomass. In the catalytic pyrolysis experiments carried out at 500 °C, 75.84 % conversion to liquid and gaseous products was obtained using 2 % Fe-MCM-41 catalyst, and the calorific value of the liquid product obtained was determined as 40.96 MJ/kg. The functional group analyses in the structure of the liquid products are characterized using FT-IR spectroscopy, and the distributions of the aliphatic/aromatic fractions of the liquid products are characterized using GC-MS technique. The H/C ratio of the liquid product obtained from catalytic pyrolysis is between light and heavy petroleum products and also has lower oxygen content and higher calorific value, indicating the potential of metal-supported MCM-41 catalyst for renewable hydrocarbon production from apricot kernel shell.

Ammonia blending in diesel is an efficient combustion strategy that overcomes the combustion resistance of ammonia while maintaining high engine adaptability. A smaller and accurate chemical kinetic mechanism is crucial for exploring the application of ammonia/diesel in engine. This study, based on the stepwise validation and optimization mechanisms, developed a novel ammonia/diesel mechanism comprising 130 species and 772 reactions. The mechanism was validated through kinetic verification for ammonia, n-dodecane, diesel and ammonia/diesel fuel. For profound understanding of the low-temperature autoignition chemistry of ammonia/diesel, applying this mechanism construct precise CFD models in RCCI optical engine. The results indicate that this mechanism can accurately capture ignition under high AER, wide working conditions, and low-temperature conditions. In the kinetic analysis, the C–N interaction reaction, particularly C₂H₄+NH₂=C₂H₃+NH₃, plays a crucial role in predicting the IDT of ammonia/diesel. In addition, NH2 undergoes deoxygenation reaction with HO2, converting inactive radicals HO2 into OH active radicals, enhances the reactivity of ammonia/diesel under low-temperature conditions. Applying the mechanism to CFD models, the model accurately predicts the pressure and heat release rate in RCCI optical engine, capturing the phenomenon of the high-temperature flame rapidly spreading towards the low-temperature regions in the cylinder. The research on this mechanism can construct accurate CFD model for optimizing efficient and clean combustion simulations of ammonia/diesel.

The formation of nitrogen-containing species during char gasification is crucial for emission of nitrogenous pollutants. In this work, the detailed nitrogen migration mechanism during char gasification is studied. Density functional theory (DFT) coupled with ReaxFF MD methods are used to conduct an in-depth analysis on the intrinsic reaction mechanism during Char(N) and steam interaction. DFT results show that orbital electrons of carbon atoms on char surface are driven towards nitrogen atoms by nitrogen functional groups. The electron density of adjacent carbon atoms is weakened, which has a positive charge. Orbital electron properties show that the band energy gaps of three Char(N) models are 3.063 eV, 1.092 eV and 3.328 eV, indicating the reactivity order for three Char(N) models is as follows: Char(N)-2＞Char(N)-1＞Char(N)-3. DFT calculation indicates that the interaction between Char(N) and steam reduces unsaturated carbon atoms and lower the char decomposition activity, which will inhibit the yield of HCN. In contrast, through hydrogen transfer reactions, nitrogen atoms are easily combined with hydrogen atoms, which is more conducive to the formation of ammonia. ReaxFF MD modeling proves that HCN is the main product for Char(N) decomposition under inert atmosphere. Under steam atmosphere, nitrogen atoms in char are more likely to be converted into amino products. The induction of steam provides a large number of active hydrogen radicals, which is able to attack the nitrogen atoms of char and form N–H bonds, thus promoting the formation of ammonia.

Minimizing carbon monoxide (CO) emissions from the combustion of solid biofuels is essential to improve thermo-chemical conversion efficiencies and avoid impact on human health. This review focuses on the formation mechanisms and subsequent oxidation of CO within the combustion process; for this, the different phases of biomass combustion (i.e., heating up, pyrolysis, gasification, and homogeneous gas-phase oxidation) are considered separately. The comprehensive analysis shows that CO emissions can be mitigated by fuel-related measures (e.g., washing and leaching to eliminate K components) as well as by (mineral) additivation of the fuel to repress the K-release by binding it in temperature-stable components within the ash. Furthermore, the addition of sulfur results in the sulfation of critical K-compounds to less corrosive and non-radical interfering compounds.

Lignin, as a renewable energy source, has attracted much attention due to its high valorization potential. Due to the complex composition of lignin, vanillin, an important intermediate of lignin, was chosen as a model compound in this study. The study examined the influence of the HZSM-5 molecular sieve on the quality of pyrolysis oils during the catalytic pyrolysis of vanillin at 600 °C using a horizontal tube furnace and Py-GC/MS analysis. The results revealed that the HZSM-5 catalyst significantly increased the yields of toluene, guaiacol, and 4-hydroxyisophthalaldehyde by 2.49 %, 19.26 %, and 1.8 %, respectively, whereas reducing the contents of phenol and 3,4-dimethoxyphenol by 6.01 % and 3.79 %, respectively. These findings indicate that the HZSM-5 molecular sieve effectively improves the quality of pyrolysis oils during the catalytic pyrolysis of vanillin. The evolution of the main functional groups in the pyrolysis of vanillin was analyzed using an in situ diffuse reflectance infrared Fourier transform spectroscopy. The addition of HZSM-5 promoted the cleavage of oxygen-containing functional groups and the generation of aromatic hydrocarbons during the pyrolysis of vanillin. Furthermore, the pyrolysis reaction pathways of vanillin were simulated under the B3LYP/6-311 g (d, p) basis set using the density functional theory. The acidic sites of HZSM-5 interacted with vanillin via the hydrogen bonds that affected the energy barriers of the pyrolysis reaction pathways of vanillin. HZSM-5 inhibited the generation of phenol and 3,4-dimethoxyphenol by increasing the energy barriers by 32.95 and 31.03 kJ/mol, respectively; however, HZSM-5 promoted toluene production by decreasing the energy barrier by 37.38 kJ/mol. The effects of HZSM-5 on the products in the simulation results were consistent with the experimental results.

In recent years, diesel vehicles have made a considerable contribution to the total emissions of vehicle pollutants. In view of stringent emission regulations, it is meaningful to look for clean, renewable and sustainable fuels and the correct utilization technology. One effective approach is application of diesel and alcohols dual fuel (DADF) engines, which can achieve the maximum substitution of alcohols to diesel without requirement for mutual solution and meanwhile reduce the emissions of major pollutants. In this study, three combustion modes of DADF engine are firstly introduced and comparatively analyzed, and then the combustion and emission characteristics of DADF engine are compared with those of pure diesel engine, and finally, the effects of alcohol injection strategy, substitution ratio and type of pilot fuel on the combustion and emission characteristics of DADF engine are summarized. The results show that the DADF engine can reduce both particulate matter (PM) and nitrogen oxides (NOx) emissions in conventional dual fuel (CDF) mode, especially under high load conditions; compared to the CDF mode, the engine has a longer ignition delay (ID) and poorer combustion stability in reaction controlled compression ignition (RCCI) mode, with a significant reduction in NOx and soot emissions and an increase in hydrocarbon (HC) and carbon monoxide (CO) emissions; compared to a pure diesel engine, the DADF engine has increased maximum cylinder pressure (Pmax), heat release ratio (HRR) and ID, shortened combustion duration (CD), increased HC and CO emissions, but reduced soot emissions; the combustion process of the engine is also improved when biodiesel and polyoxymethylene dimethyl ether (PODE) are used as pilot fuels.