Abstract: Asphaltenes including asphaltene and preasphaltene (PAA) are the important products of the direct coal liquefaction process, whose structure and property are essential for the high-efficiency liquefaction and the subsequent utilization. The structure and property of PAA are closely related to the liquefaction conditions. Therefore, in this work, the effects of liquefaction temperature, residence time, pressure, and the ratio of solvent to coal on the structure and property of PAA obtained from mild liquefaction of Hami coal (named as HMPAA), were investigated in a batch autoclave with tetrahydronaphthalene as solvent. The structure features of HMPAA obtained under different conditions were characterized by elemental analysis, infrared spectroscopy and solid-state 13C-NMR. Thermal reactivity of HMPAA and the evolution curves of gas product during pyrolysis were analyzed by TG-MS. The results showed that the yield of HMPAA increased with decreasing reaction temperature, increasing pressure, decreasing residence time and increasing the ratio of solvent to coal. The highest HMPAA yield was 35.0% at 340 ℃, 3 MPa, residence time of 1 h, and the ratio of solvent to coal of 2∶1. The carbon structure of HMPAA consisted of aliphatic carbon and aromatic carbon, while the latter accounted for about 80%. Increasing liquefaction temperature was favorable to the formation of HMPAA with higher aromaticity. The aromatic condensation degree of HMPAA increased with extended residence time. The aromaticity and aromatic condensation degree of HMPAA decreased with the increase of the ratio of solvent to coal. The liquefaction pressures examined in this work had little effect on the structure and property of HMPAA. The pyrolysis of HMPAA started at about 250 ℃ and the peak temperature of maximum weight loss was between 400 ℃ and 500 ℃, and the final weight loss was over 40%. The thermal reactivity of HMPAA increased with decreasing liquefaction temperature and increasing the ratio of solvent to coal, and the change of pressure had little effect on the thermal reactivity of HMPAA.
Abstract: In this paper, the variation of pore structure of three typical coal chars with the gasification temperature and its effect on subsequent gasification reaction were studied by means of drop tube furnace (DTF) and thermogravimetric analyzer (TG). The results show that the pore structure parameter of coal char increases with the increase of temperature, which characterizes the shrinkage and closure of pores at high temperature. The local decrease of pore structure parameter near the ash melting point indicates the blockage and cover of pore structure caused by ash melting at high temperature. The growth ratio is defined as the ratio of the difference between the maximum gasification reaction rate and the initial reaction rate to the initial reaction rate. When the pore structure parameter is greater than 2, there is a linear relationship between the growth ratio and the pore structure parameter, and the growth ratio increases with the increase of the pore structure parameter. When the pore structure parameter is less than 2, the relationship between the growth ratio and the pore structure parameter is not obvious. The experimental results also show that the high content of alkali metals has a great effect on the gasification rate, which makes it difficult to accurately fit the experimental data curve with the existing model, and the value of the growth ratio can not be affected by it. It is feasible to couple the growth ratio to the gasification model to improve the robustness of the model.
Abstract: Char gasification reactivity plays a vital role in the design of a gasifier. In this paper, a series of char were prepared by pyrolysis at 900−1100 ℃ in a fluidized bed and a drop tube reactor with a lignite as the sample, and the physico-chemical structure and CO2 gasification reactivity of chars were studied by X-ray diffractometer (XRD), Raman spectrometer, static physical adsorption instrument and fixed-bed reactor. The results showed that the gasification reactivity of char in the fluidized bed and drop tube reactors mainly depended on its chemical structure. In the two reactors, as pyrolysis temperature increased, the polycondensation reactions of char deepened, resulting in the increasing crystalline size (aromatic sheet stacking height Lc, average diameter La) and larger ring to smaller ring ratio $ {I_{\rm{D}}}/{I_{({{\rm{G}}_{\rm{r}}}{\rm{ + }}{{\rm{V}}_{\rm{r}}}{\rm{ + }}{{\rm{V}}_{\rm{1}}})}} $ of char. Therefore, the gasification reactivity of char decreased with increasing pyrolysis temperature. Compared with in the drop tube reactor, the crystalline size and larger ring to smaller ring ratio $ {I_{\rm{D}}}/{I_{({{\rm{G}}_{\rm{r}}}{\rm{ + }}{{\rm{V}}_{\rm{r}}}{\rm{ + }}{{\rm{V}}_{\rm{1}}})}} $ of char in the fluidized bed reactor were lower at the same pyrolysis temperature, and their variations with increasing pyrolysis temperature were smaller, resulting in the lower gasification reactivity of char and the smaller change of gasification reactivity of char with increasing pyrolysis temperature. Those were mainly due to the long residence time of char and strong interactions of char and volatiles in the fluidized bed reactor, deepening the degree of polycondensation reaction of char.
Abstract: The NO emission characteristics of bituminous coal/semi-coke blends were investigated in an electrical-heating circulating fluidized bed. Meanwhile, the distribution and occurrence forms of N element in fuels were also analyzed in order to enhance the understanding of NO emission characteristics. The results indicated that the volatile-N and char-N in Shenhua bituminous coal (BC) accounted for 53.85% and 46.15%, respectively, and the majority of N in semi-coke (SC) was char-N. During the combustion, the volatile-N released quickly and was easy to be reduced in the dense-phase zone, whilst the char-N released relatively slowly. Hence, the NO emission concentration of SC was obviously higher than that of BC. After blending SC with BC, the NO emission decreased with the SC blending ratio, and the interactions between component fuels could suppress the NO emission as well. The NO emission of SC and BC showed the opposite variation tendencies with the combustion temperature, and it increased with the temperature for blends with 40% and 80% BC. Besides, the NO emission of BC, SC and their blends all increased with the excessive air coefficient and primary air ratio.
Abstract: PbCl2 emitted from coal-fired power plants is of great concern due to its extreme toxicity and global migration and accumulation. Unburned carbon is considered as a promising adsorbent for effective PbCl2 removal. However, existing models of unburned carbon do not reflect the structure of carbon defects on the surface of actual unburned carbon. Therefore, it is of great practical importance to develop a defective unburned carbon model. In addition, the carbon model is not deep enough for the adsorption of PbCl2, and the reaction mechanism is not clear. This greatly hinders the development of efficient adsorbents. In order to reveal the adsorption mechanism of PbCl2 on the surface of defective unburned carbon, the adsorption process of PbCl2 on different defective unburned carbon surfaces was systematically investigated by using density functional theory (DFT). The results show that the defective adsorption sites are the best sites for PbCl2 adsorption.
Abstract: Developing the oxygen carriers with large oxygen carrying capacity, high reactivity, and strong cycle stability is one of the research focuses in the chemical looping combustion technology. In this study, the effect of spinel-structured K3FeO4 on the reactivity of Fe-based oxygen carrier was investigated based on the density functional theory involving the electronic structural properties such as the density of states, adsorption energy, and activation energy. The results show that when the K3FeO4 is loaded on the α-Fe2O3(001) surface, the microscopic electronic structure of α-Fe2O3(001) surface is changed, the Fe–O bond on the surface is elongated, the O-p orbital electrons transition to a higher energy level, and the electron activity of oxygen atom is improved. The energy barriers of CO reaction with the surface lattice oxygen show a decreasing trend at the three lattice oxygen sites after the loading of K3FeO4 which can improve the activity of surface oxygen atoms and make the breakage of Fe–O bond via elongation easier with less energy required. In addition, CO can bond with the more active oxygen atom in K3FeO4, and also can combine with the O2 atom to form a new C–O bond, by which CO is adsorbed on the surface in the form of bidentate carbonate that can be decomposed and released as CO2.
Abstract: C5 and C7 asphaltene were separated from paraffin base Yumen atmospheric residue and naphthene base Merey atmospheric residue by n-pentane and n-heptane respectively using the method of SARA. The structure parameters and functional groups analyzed and characterized systematically by VPO, 1H-NMR, FT-IR and elemental analysis, in order to comparative studied the differences in asphaltene structure of different residues and asphaltene obtained by different precipitants. The results showed that there was consistent in the functional groups of different asphaltenes basically, but there was some differences in the unit structure of different asphaltene. Yumen paraffinic asphaltenes had significantly higher molecular weight, smaller HAU/CA value and higher condensation degree than Merey naphthenic asphaltenes. With the increase of carbon chain of precipitants, the yield (the yield of n-heptane asphaltene was about 80% of n-pentane for the some feedstook) and the H/C of asphaltene decreased, the molecular weight of asphaltene increased. C7 asphaltenes had higher aromatic carbon ratio ($ f $A) and more structure units than C5 asphaltene. More saturated structure existed in various asphaltenes and the saturate carbon fraction was about 0.5.
Abstract: A series of nFe(III)Ox/ZnO photocatalysts with different Fe contents was prepared by impregnation method, and the samples were characterized by XRD, N2 physisorption, TEM, XPS, UV-vis and PL. It was found that by changing the concentration of Fe species in the impregnation solution, the Fe content in the final sample could be properly adjusted. Within the scope of this work, the loading of Fe does not cause significant changes in the phase, morphology, and porous structure of the ZnO support. However, the electronic state of the catalyst surface was altered considerably, with more O-vacancies were introduced. Fe species enhanced the separation of photo-induced electron-hole pairs, which was responsible to improve the performance of photocatalytic CH4 conversion. Through the optimization of solvent volume, H2O2 concentration and reaction time, the 0.1Fe(III)Ox/ZnO sample showed the best performance over which the yield and selectivity of liquid oxidation products (CH3OH, CH3OOH, HCHO) was 5443 μmol/(gcat·h) and 99%, respectively. Based on radical quenching experiments, it was found that the ·${{\rm{O}}_2^-} $ radicals derived from H2O2 played a major role for the activation of CH4 to ·CH3.
Abstract: CO2 electrocatalytic reduction to synthesize highly value-added fuels provides a sustainable path for CO2 conversion and utilization. Nevertheless, the development of electrocatalysts with high catalytic activity and product selectivity remains a major challenge. In this work, copper-doped FeS2 catalysts (CuxFe1−xS2) were prepared for CO2 electrochemical reduction. The physicochemical properties of the catalysts were studied by XRD, XPS, SEM and other characterization analysis methods. Experimental results show that Cu doping can control the size of the catalyst nanosheets and inhibit the oxidation of FeS2 in the air. Cu0.33Fe0.67S2 shows better catalytic activity for CO2 electrocatalytic reduction than FeS2. In the potential range of (−1.5) − (−1.6) V vs. RHE, the total efficiency of carbon-containing products of CO2 electrocatalytic reduction is 50.8% and its current density is 23.8 mA/cm2, which increases by 71.2% compared with FeS2 catalyst. The Faradaic efficiency of Cu0.09Fe0.91S2 to produce C3H6 at −1.3 V vs. RHE is 21.8%, which is significantly higher than the value reported in the current literature. Thus, CuxFe1−xS2 is regarded as an excellent electrocatalyst for CO2 reduction.
Abstract: Microwave-assisted heating method was used to rapidly prepare three-dimensional hollow nickel-cobalt hydroxide (Ni-Co LDH) by using zeolite dimethyl imidazolium cobalt (ZIF-67) as template and cobalt source. The effect of microwave reaction time on the morphology and electrochemical properties of the materials was investigated. X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and specific surface and aperture analyzer (BET) were used to investigate the effect of microwave reaction time on the structure and morphology of the samples. The electrochemical properties of Ni-Co LDH electrode materials were analyzed by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). The results showed that the electrochemical properties of Ni-Co LDH-15 min electrode were the best. The specific capacitance was 2371.0 F/g at 0.5 A/g. The Ni-Co LDH-15 min also possessed excellent capacity retention of 78.5% when the current density increased by 20 times. An asymmetric supercapacitor (Ni-Co LDH//AC) was assembled by using Ni-Co LDH as the positive electrode and AC as the negative electrode. The Ni-Co LDH//AC device delivered a high energy density of 19.17 W·h/kg at the power density of 448.05 W/kg. Furthermore, the capacitance retention rate still maintained 88.7% after 5000 cycles. These results showed that Ni-Co LDH was a kind of electrode material for supercapacitor with excellent electrochemical performance and practical application potential.
Abstract: The capture and utilization of carbon dioxide (CO2) have attracted much attention in recent years; in particular, the direct hydrogenation of CO2 to light aromatics has been considered as a potential route to produce high value-added chemicals. However, it is still a big challenge to adjust the aromatic distribution and achieve a high selectivity to the targeted products. In this work, a bifunctional catalyst that combines the Cu-modified Fe3O4 and the chain-like ZSM-5 zeolite is used for the hydrogenation of CO2 to light aromatics. The catalyst components were characterized by XRD, SEM, TEM, ICP-AES, Py-IR and N2 adsorption-desorption; the effect of acid density and length-to-diameter ratio (b-axis/ a-axis) of zeolite moiety on the selectivity and distribution of aromatic products was then investigated. The results indicate that the chain-like ZSM-5 zeolite moiety with high acid density and appropriate length-to-diameter ratio can promote the C–C coupling for CO2 hydrogenation and inhibit the formation of CH4, which can improve the selectivity to aromatics and the space time yield (STY) of toluene.
Abstract: A series of iron sulfide catalysts were prepared by pre-sulfidation at different temperatures and different hydrogen partial pressures, and their catalytic naphthalene hydrogenation activities were studied under 5 MPa 1% H2S-H2 atmosphere at 360 ℃. By means of XRD, MES, SEM-EDS, ICP and GC-MS, the effect of hydrogen on the pre-sulfidation process at different temperatures was studied. The results show that the introduction of hydrogen during the pre-sulfidation process facilitates the transfer of sulfur, thereby promoting the sulfidation. The effect of hydrogen is different at different pre-sulfidation temperatures. When pre-sulfidation at 50 ℃, the introduction of hydrogen can be beneficial to the transfer of sulfur, which increases the catalytic activity, but a lot of elemental Fe and elemental S can still be observed at this temperature; when pre-sulfidation at 150 ℃, the catalytic activity is the best. The content of zero-valent Fe decreases and no pure S is observed. With the increase of hydrogen partial pressure, the hydrogenation conversion of naphthalene increases from 60.6% to 69.1%. When pre-sulfidation at 300 ℃, the catalytic activity decreases with the introduction of hydrogen. Hydrogen reduces the sulfur on the catalyst surface to low valence state and crystalline Fe3O4 is observed inside the catalyst particles, which is not conducive to the transfer of sulfur.
Abstract: ZSM-5@Beta core-shell molecular sieve was prepared by dynamic hydrothermal synthesis method using ZSM-5 adhered Beta seed crystals as the core phase, and polydiallyl dimethyl ammonium chloride (PDDA) was used as a coupling agent to adhere Beta seed crystals on the surface of ZSM-5. The structure and physical properties of composite molecular sieves were characterized by XRD, N2 adsorption-desorption, SEM, TEM, ICP, NH3-TPD and Py-FTIR. The catalytic performance of composite molecular sieves for alkylation of 2-methylnaphthalene (2-MN) with methanol was investigated. The results showed that ZSM-5@Beta composite molecular sieve prepared by this method had a core-shell structure, and the particle size was about 500 nm. Compared with mechanically mixed binary molecular sieve, core-shell molecular sieve had higher specific surface area and external surface area, lower acid strength and stronger acid center density. Through the construction of core-shell interface and hierarchical porous, the catalytic activity was improved by shell phase Beta molecular sieve with 12-membered ring channel, and the catalytic selectivity was improved by core phase ZSM-5 molecular sieve with 10-membered ring channel in the alkylation reaction of 2-MN with methanol. The 2,6-/2,7-DMN ratio in the products reached 1.35, and the yield of 2,6-DMN reached 4.29%.
Abstract: The adsorption and dissociation of hydrogen sulfide (H2S) molecule on Pt or Pt4 cluster doped graphene with different vacancy (VG), as well as their geometric and electronic structures have been investigated by density functional theory (DFT). It has found that H2S and H atom are weakly adsorbed on Pt/Pt4-VG, while HS and S atom are strongly chemisorbed on different surfaces. By using climbing nudged elastic band method (CI-NEB), three elementary processes have been studied: (I) H2S(gas)→H2S(ads); (II) H2S(ads)→HS(ads) + H(ads); (III) HS(ads) → H(ads)+ S(ads). The energy barriers to break the first H–S bond in H2S on four different surfaces (Pt-MVG, Pt-DVG, Pt4-MVG, Pt4-DVG) are 1.69, 0.52, 0.01 and 0.24 eV respectively. In contrast, the energy barriers to break the second H–S bond in HS are 2.34, 1.08, 0.81 and 1.12 eV respectively. It is suggested that the control step of the complete dissociation of H2S is the second H–S bond rupture process. The trend shown in this study reveals that single Pt atom doped defected graphene is favored for adsorption of H2S, but is disadvantage for dissociation. Pt cluster doped defected graphene with bigger vacancy can successfully adsorb and easily eliminate H2S molecule, which is expected to be the ideal material for the adsorption and dissociation.
Abstract: A series of TiO2-supported V-W bimetallic catalysts were prepared by incipient wetness impregnation method. The effects of V/W ratios on the catalytic combustion performance for chlorobenzene were investigated. The results showed that proper W doping (5V5W-Ti and 3V7W-Ti) improved the catalytic combustion activity of chlorobenzene and the selectivity of HCl. In combination with BET, XRD, XPS, H2-TPR, NH3-TPD and Py-FTIR characterizations, it indicated that higher activity for chlorobenzene oxidation was attributed to the high dispersion of the active species and the abundant surface adsorbed oxygen. In addition, moderate doping of W significantly enhanced the surface acidity of catalysts, especially strong acids and Brønsted acids, and thus improved the selectivity to HCl in the products.
Abstract: Pyrolysis char was prepared from high sulfur and iron content textile dyeing sludge. The combined states of S and Fe in the samples before and after pyrolysis and the removal characteristics of Hg0 by pyrolysis char were studied. The performance of Hg0 removal was improved by air oxidation and ZnCl2 impregnation. The results showed that S in sludge was divided into sulfate, sulfide, and organic sulfur. Fe existed as Fe3+ and Fe2+ compounds. After pyrolysis, inorganic sulfur was transferred to organic sulfur and Fe3+ was transferred to Fe2+. Most S and Fe were retained in pyrolysis char and some formed pyrrhotite (Fe1−xS). The specific surface area of raw char was small and had a certain Hg0 removal capacity, dominated by chemical adsorption. When the air oxidation time was controlled within 12 h, the Hg0 adsorption capacity of pyrolysis char at high temperature (≥600 ℃) was increased by more than 46%. During pyrolysis of ZnCl2 impregnated sludge, more S was fixed in pyrolysis char to generate ZnS. The Hg0 adsorption capacity of ZnCl2 modified char pyrolyzed at 600 ℃ reached 28.71 μg/g in 30 min. With air oxidation, the Hg0 removal efficiency was further improved. After oxidation for 12 h, the Hg0 adsorption capacity was 43.75 μg/g.
Supervisor：Chinese Academy of Sciences
Sponsors by：Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences Chinese Chemical Society
