• Energy Research

Abstract Heavy components (molecular weight > 200 Da) in bio-oil affect the thermal conversion of bio-oil significantly. The inherent alkali/alkaline earth metal species (AAEMs) in biomass affect the formation of heavy components in bio-oil due to its catalytic effects. In order to investigate the effects of AAEMs on the formation of heavy components in bio-oil during biomass pyrolysis, the heavy components in bio-oil were characterized with the Fourier transform ion cyclotron resonance mass (FT-ICR MS) spectrometer and the ultraviolet fluorescence (UV-F) spectroscopy. The roles of K and Ca were also investigated. The results showed that AAEMs promoted the breakage of active oxygen-containing functional groups in heavy phenolics and inhibited their formation during pyrolysis, as well as the formation of heavy carbohydrates. The total content of heavy components decreased due to the catalytic effects of AAEMs. The catalytic effects of K on the decomposition of large molecular weight compounds (> 500 Da) in heavy components were stronger than those of Ca. K increased the content of single ring aromatic components in bio-oil for 1.5 times, while Ca decreased the content of the 2–3 rings aromatic components in bio-oil for more than 50%, compared to the bio-oil generated from the pyrolysis without AAEMs.

Abstract The evolution mechanism and energy conversion of volatile in low-rank coal with pyrolysis temperatures still remain uncertain. The experimental results on gas products and light tar pyrolyzed from Shenfu coal at various pyrolysis temperatures reflect the complex correlation between volatiles and coal structure affected by temperatures. Thermodynamic competitive evolution towards CO from oxygen-containing structures are analyzed by density functional theory. The formation mechanisms of polycyclic aromatic hydrocarbons (PAHs) from by-product cyclopentadienyl through Diels-Alder reaction and C–H β-scission are confirmed at the CBS-QB3//M06–2X/def2-TZVP level of theory. Kinetic rate coefficients of the rate-limiting step are computed. Thermodynamic and kinetic calculation results indicate that phenols pyrolysis have to cross a higher energy barrier. Moreover, cyclopentadienyl thermodynamically tends to form indene at 645 °C, while forming PAHs such as naphthalene, even fluorene, phenanthrene, and anthracene at 855 °C, which is consistent with the experimental results. A hydrogen-rich environment can kinetically facilitate the formation of PAHs.

Abstract The electrochemical method has emerged as a novel option for bio-oil upgrading due to the advantages of having mild reaction conditions, control convenience and carbon neutrality. Bio-oil is easy to form coke even at low current densities during electrochemical upgrades of bio-oil. Unveiling the coke evolution during the electrochemical processing of bio-oil is essential to enable both oil-to-material and oil-to-fuel strategies. Here, we investigate the coke formation behaviors during the electrochemical processing of bio-oil. The coke comes primarily from the polymerization of aromatic components. The reaction time and current density have a promoting effect on the coke yields. The current density has an accelerating influence on the morphological evolution of the coke. The O-containing groups increases slightly with the increasing reaction time and current density. The large to small ring ratio of the coke is similar under different reaction time and current densities. The potential applications as carbon materials of the coke formed from bio-oil via electrochemical polymerization are discussed based on its physical morphology and chemical structure.

Abstract Pyrolysis of waste tires is a promising way to cost-efficiently produce high value limonene, but the reaction characteristics and mechanisms of limonene under pressurized pyrolysis are unclear to date. This study aims to investigate the effects of residence time and pressure on limonene conversion during waste tire pyrolysis. The yields of limonene increased significantly with a decrease of residence time during high pressure pyrolysis. At a pressure of 1.0 MPa, the yield of limonene increases by 20 % as the residence time decreases from 60 s to 15 s, while limonene concentration in TDO (tire-derived-oil) increases to 35.10 wt.%. On the other hand, the pressure has a positive effect on limonene production. The yield of limonene at 1.0 MPa is approximately 1.7 times larger than that of 0.1 MPa at a residence time of 30 s. Based on Spearman correlation analysis, the mechanisms of limonene conversion at pressurized pyrolysis were studied. Longer residence time means limonene undergoes more secondary reactions to be degraded to aromatic rings such as xylene and trimethylbenzene. However, the higher N2 partial pressure during pyrolysis suppressed the decomposition of limonene, producing TDO with high limonene concentration. Therefore, methods of reducing residence time and increasing pressures promote yield and concentration of limonene in the aspect of inhibiting decomposition, which provides references for improvement in limonene production by waste tire pyrolysis.

Abstract This work aimed to evaluate the detailed chemical structures of the asphaltenes in the tetrahydrofuran-microwave-extracted portions from two Chinese coals, namely, Shenfu and Zhundong coal (SF, ZD) and to clarify their characteristics on chemical composition at molecular level. Based on the analyses of diffuse reflectance Fourier transform infrared spectroscopy (DRIFT) and Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS), the detailed chemical structure of a series of basic and non-basic nitrogen- and oxygen-containing class species in the asphaltenes were clarified. The results revealed that condensed nitrogen-containing alkylaromatic structures with amidogens (1–3) were the main structure units in N 4 O y (y = 0–2) class species due to the high double bond equivalent (DBE) values for both the asphaltene from SF (A SF ) and the asphaltene from ZD (A ZD ). Acidic O 2 –O 7 class species with two or three aromatic rings were the main structure units, among which O 4 and O 2 class species had the highest relative abundances (RAs) in A SF and A ZD , respectively. Acidic oxygen-containing components in A ZD had narrower range of DBE and carbon number and mainly consisted of aromatic structure units with two rings. On the contrary, the average DBE values of O 4 –O 7 class species in A SF had positive relationship with oxygen atom number which could be attributed to the introduction of phenol groups. The results provided more detailed information on the structural characteristics of polar and aromatic-rich components of mobile phase in coal.

Abstract Fe-modified Ni/Al2O3 catalysts with Fe/Ni molar ratios of 0, 0.5, 1 and 2 were prepared to promote the co-production of H2 and carbon nanotubes (CNTs) during steam reforming of toluene as a tar model compound. After the addition of Fe, toluene conversion increased from 55.1% of Ni/Al2O3 to 73.6% of F1N1A (Fe/Ni ratio of 1), and H2 yield over F1N1A reached the maximum of more than 2000 mmol/(g-cata). Multi-walled carbon nanotubes with average diameter of 10–30 nm were generated and follow tip-growth mechanism. Compared with Ni/Al2O3, the addition of Fe remarkably increased the amount and quality of CNTs which had longer length and less tortuosity. These dual promoting effects on H2 and CNTs after the addition of Fe were attributed to the strong interaction between Ni and Fe in Fe-Ni alloy. Fe-Ni alloy had the high activity for the decomposition performance of toluene and H2O to generate more H2 and intermediates for improving the reforming reaction. Meanwhile, the high catalytic decomposition activity supplied more carbon species and the formation of Fe-Ni alloy enhanced the generation of metal carbide for promoting CNTs growth. Besides, the deposition of amorphous carbon was suppressed and the interaction between Ni particle and catalyst support was weakened after the addition of Fe, which kept the activity of catalyst and promoted the tip-growth of CNTs.

Abstract Substituted polycyclic aromatic hydrocarbons released from sewage sludge pyrolysis bring the concern of the clean utilization for the waste. Herein, the roles of calcium oxide on the release of these compounds, especially the heavy ones containing nitrogen and oxygen atoms were investigated. The results showed that calcium oxide significantly decreased light substituted polycyclic aromatic hydrocarbons in the volatiles from 450 to 850 °C and showed obvious inhibitory effects on the formation of heavy substituted polycyclic aromatic hydrocarbons at 850 °C. To understand the impact mechanisms, pyrolysis experiments of sludge model compounds lipid, protein and polysaccharides were conducted. It was found that calcium oxide could catalyze or react with all three components to decrease the content of light substituted polycyclic aromatic hydrocarbons. Heavy oxygen-containing aromatics in sludge derived volatiles mainly resulted from polysaccharides and protein, and they considerably decreased after mixing with calcium oxide. Oxygen-containing aromatics content in the lipid derived volatiles, however, would increase due to polymerization reactions. The decreasing release of nitrogen substituted polycyclic aromatic hydrocarbons from sludge could be attributed to the synergy effects of CaO and other minerals or the effects of CaO on the interaction between protein and other organics.