Abstract: Two different ranks of coals (Ximeng lignite, L and Xishan bituminous coal, B) and biomass (cornstalk, C) were selected to investigate effects of heating rate and pressure on structure and oxidation reactivity of chars from pyrolysis. The chars were prepared in a two-step pressurized fixed bed reactor at 900℃ from slow pyrolysis and fast pyrolysis under a range of pressures (0.1-2.0 MPa), which were marked as SC and FC, respectively. Specific surface area, surface morphology, and aromaticity of chars were characterized. Isothermal thermogravimetry was performed to study oxidation reactivity of chars. Results indicate that the char yields of three samples are distinctly varied and pyrolysis pressure and heating rate influence them through different residence time and diffusion rate of volatiles varying with different raw materials. The yields of chars from fast pyrolysis are all lower than those from slow pyrolysis and they increase slightly with increasing pyrolysis pressure from atmospheric pressure to 2.0 MPa. The specific surface areas of L-FC and B-FC are larger than that of L-SC and B-SC. However, the specific surface area of C-FC is smaller than that of C-SC. The morphology of FC is all rougher than that of SC. The aromaticity of B-SC is higher than that of B-FC, while that of L-SC and C-SC is lower than that of L-FC and C-FC derived from pressurized pyrolysis. The evolution of char structure at low heating rate and high pressure results generally in poor reactivity of char. The reactivity of cornstalk char is much higher than that of coal char, which should be correlated to the dispersion and concentration of inorganic matters in the char which is affected by heating rate and pressure.
Abstract: Crucible cokes were obtained by co-carbonization of Zhongwei lean coal as main coking coal and thermal extract from Datong long-flame coal as additive. The degree of regularization on anisotropic structure (DRAS) of coke was obtained by quantitative calculation of optical tissue from polarized microscopy. The crystallite size (Lc), aromatic condensation (La) and degree of graphitization (g) have been quantitative calculated by combination of XRD and curve-fitted method. Furthermore, Raman spectrum and curve-fitted method have been used to obtain content of ideal graphite microcrystalline of coke. The quantitative analysis of optical micro-component on obtained cokes shows that addition of thermal extract from Datong long-flame coal has a significant influence on optical micro-component of coke. There is good consistency on DRAS and microcrystalline parameters, which is calculated by the method of polarized microscopy and XRD and Raman spectrum, respectively. Moreover, the micro-strength index of coke is highly correlated with its microstructure.
Abstract: The nitrate solution of K+, Ca2+ and Fe3+ was used to treat Hefeng demineralized coal (DC) separately. The weight loss and gas evolution of coal samples were studied by thermogravimetric analyzer. It is found that the total weight loss of treated coal samples decreases, while the concentration of CO2 and H2 increases for treated samples. Then the distribution variation of products during the pyrolysis process of treated coal samples were investigated in a fixed bed reactor together with the analyses of elemental analysis, FT-IR, simulated distillation and GC-MS. The results indicate that the char and gas yields of treated coal samples rise, while the tar yields decline. The unsaturation and condensation of corresponded char samples exhibit a decreasing tendency. Under the action of these metal components, the percentage of light component in the tar increases, especially by 22.4% due to the effect of iron species. GC-MS analysis exhibits that long chain alkanes occupy about 70% of the total relatively, leading to the high content of heavy component in tar, which can be catalytically cracked by K and Fe species.
Abstract: The potassium fixation ability and ash fusibility in gasification of corn stalk coke blended with coal ash were studied in CO2 atmosphere using a tube reactor. The ash samples were analyzed by inductively coupled plasma atomic emission spectrometer (ICP-AES), X-ray diffraction (XRD) and ash-melting point measuring device. The results show that coal ash has a certain ability of fixing potassium in the biomass ash as the reference of kaolin and the potassium retention ratio (PRR) increases when adding more coal ash. On the other hand, ash fusion temperatures (AFTs) of the blended ash increase by adding the coal ash, compared with the biomass ash. XRD patterns show that the reaction between alumina/silica compounds in coal ash and potassium that volatilized into the gas phase and existed in slag phase leads to formation of potassium aluminosilicates(KAlSi3O8, KAlSi2O6 and KAlSiO4), which are high melting point compounds. It confirms that coal ash is a potential additive for not only fixing potassium, but also increasing the ash fusion temperatures of easy-to-slagging biomass.
Abstract: Cat-1, Cat-2, Cat-3 and Cat-4 catalysts were synthesized via different preparation methods that are incipient wetness, impregnation-precipitation and mechanochemical method (carriers from market and homemade for comparison), and then characterized by BET, H2-TPR, XRD, XPS and NH3-TPD. The cracking behavior of toluene and pyrene (3%, mass fraction) (coal tar model compounds) were investigated to evaluate the catalytic performance of the stated catalysts. The catalyst characterization showed that the pore size of all the catalysts belonged to mesoporous range, and Cat-4 catalyst exhibited higher ordered mesoporous and larger surface area than others, up to 235 m2/g. Besides, the peak area of NiAl2O4 spinel reached up to the highest value of 85.2%. The dispersion of Ni in the reduced Cat-4 was the highest and its particle size was the lowest value, about 10.0 nm. Which means that there are more active sites. The catalytic performance results showed that the cracking rate of pyrene varied little for other catalysts, except for Cat-1, but the lowest carbon deposition of 10.84% was obtained under the action of Cat-4, while the carbon deposition of Cat-1, Cat-2 and Cat-3 increased by 35.0%, 74.7% and 45.7% respectively compared with that of Cat-4. Thus, Cat-4 prepared by mechanochemical method is more suitable for the cracking of toluene and pyrene system because of highest BET surface area, which is favorable for the dispersion of active component, and at the same time, the highest content of NiAl2O4 can inhibit the formation of carbon.
Abstract: A series of hierarchical Hβ zeolites were prepared by using NaOH post-treatment methods, viz., desilication under alkaline conditions; the effect of NaOH concentration on the catalytic performance of hierarchical Hβ zeolites in the pyrolysis of lignin was investigated. The results illustrated that with the increase of NaOH concentration up to 0.2 mol/L, the amount of mesopores in the hierarchical Hβ zeolites is increased, accompanying with a significant increase in the yield of liquid products for the lignin pyrolysis over Hβ zeolites. By the alkaline treatment with a NaOH concentration lower than 0.5 mol/L, the microporous structure of hierarchical Hβ zeolites remains basically intact and over them a good deoxidation effect is observed for the lignin pyrolysis; the product is mainly composed of aromatic hydrocarbons and the yield of oxygenates is always less than 3%. However, if the NaOH concentration for post-treatment is further increased to 1 mol/L, the microporous structure of Hβ zeolites is substantially destroyed, leading to a decrease in the yield of liquid products for lignin pyrolysis as well as a poor deoxidization effect.
Abstract: Al2O3 supported KNO3 (KNO3/Al2O3) catalyst was prepared and characterized by XRD, DRIFT, nitrogen adsorption, ICP and basicity titration. The catalytic performance of KNO3/Al2O3 in the transesterification of soybean oil with methanol for biodiesel production was investigated; especially, the nature of active species and deactivation behavior during the reaction was considered. The results illustrate that KNO3 on the surface of Al2O3 is completely decomposed after calcination at 873 K, forming potassium aluminate. During the transesterification reaction, aluminate as the active species in KNO3/Al2O3 is gradually dissolved out, which is responsible for the high catalytic activity of KNO3/Al2O3. The biodiesel and glycerol products formed have a great influence on the catalyst activity and the catalyst deactivation is mainly ascribed to the saponification of biodiesel with the active species.
Abstract: The direct, nonoxidative conversion of methane to aromatics and hydrogen is a challenging research topic in the field of C1 chemistry due to the high carbon-atom utilization efficiency, zero CO2 emissions and short process flow. In the present paper, the advance of methane dehydroaromatization (MDA) is reviewed based on the research works of our group and the pertinent literatures from 2013 to 2017. The reaction mechanism and coking formation for the MDA process, the catalyst modification and regeneration, the application of the membrane reactor, as well as the non-Mo-based catalyst system were considered, the future prospect was given for the MDA reaction.
Abstract: Mesoporous ZSM-5 (MFI), MCM-22 (MWW), ZSM-22 (TON) and SSZ-13 (CHA) zeolites were obtained by TEAOH and NaOH solution treatment. Under the following operating conditions:t=480℃, p=0.1 MPa, m(methanol):m(H2O)=1:1 and WHSV (methanol)=1.5 h-1, the catalytic properties of four mesoporous zeolites with different topologies were investigated in the methanol to propylene (MTP) reaction. The fresh and spent samples after 2 h were characterized with XRD, nitrogen adsorption experiments, NH3-TPD, TG, UV-Rama and GC-MS techniques. It demonstrated that both zeolites exist mesopores after treated by alkali. The mesoporous T-ZSM-5 zeolite had the highest lifetime; the lifetime of T-MCM-22 zeolite with was secondary and deactivation rate was slow; The N-ZSM-22 with one-dimensional channel structure and N-SSZ-13 zeolite with 8-member ring channels both deactivated rapidly. Due to the difference of topology structure and diffusion performance, their coke contents after 2 h increased in the order:T-ZSM-5 < N-ZSM-22 < T-MCM-22 < N-SSZ-13. Moreover, the molecular weight of soluble coke increased with the increasing of coke contents, changed from pentamethylbenzene to polycyclic aromatic hydrocarbons, such as phenanthrene and pyrene.
Abstract: Density functional theory calculations were used to investigate CO2 adsorption behaviors on Fetet1-and Feoct2-terminated surface of Fe3O4 (111). The results indicated that on the Fetet1-terminated surface, the linear CO2 is favored at 1/5 monolayer (ML), whereas the bent CO2 bonded to surface O, i.e. carbonate structure, becomes possible at higher coverage. On the Feoct2-terminated surface, the bent CO2 is favored; both carbonate and carboxylate structure are formed at both 1/6 and 1/3 ML. Meanwhile, the Fetet1-terminated Fe3O4(111) surface has weak coverage effects, whereas the Feoct2-terminated Fe3O4(111) surface has strong coverage effects; the Feoct2-terminated surface is thermodynamically more favorable than the Fetet1-terminated surface for CO2 adsorption.
Abstract: Fuel desulfurization is an appealing topic for the chemical industry since severe environmental regulations regarding SO2 emissions have been legislated in many countries. In order to reduce the amount of sulfur-containing compounds in fuels, responsible for high SOx emission levels, a green chemistry approach is compulsory. In this paper, vanadium salen and salophen complexes were used in the oxidation of a model aromatic sulfide, such as dibenzothiophene (DBT), in the presence of H2O2 as green oxidant. The oxidative process was successfully coupled with the extraction of the oxidized compounds by ionic liquids. The system resulted highly selective for sulfide oxidation, showing poor reactivity toward the oxidation of alkenes and allowing a significant reduction of S content in a model benzine. To note, the use of microwave in place of standard heating allowed to obtain 98% of DBT oxidation and almost complete sulfur extraction in the model fuel in 1000 s. For these reasons, this system was considered an easy, rapid and clean process to achieve fuel desulfurization.
Abstract: Combined with molecular imprinting technology, a novel surface molecularly imprinted polymer material MOF@SMIP was prepared, using MOF199 used as matrix, dibenzothiophene (DBT) as template molecule and methacrylic acid (MAA) as functional monomer. The structure and morphology were characterized by SEM, BET, FT-IR, etc. The adsorption behavior was evaluated using a simulated oil sample. The adsorption equilibrium time was 1.5 h. The MOF@SMIP adsorption capacity for DBT (130.73 mg/g) was higher than that for the MOF199 (37.79 mg/g), while the MOF@SMIP adsorption capacity (57.13 mg/g) was comparable to the MOF@NIP adsorption capacity. The obvious advantage is that the imprint factor fimp is 2.29. Adsorption behavior follows the pseudo-first-order kinetic model, indicating that the adsorption is primarily a physical process. The selective adsorption experiments showed that the MOF@SMIP exhibited a higher affinity for the target molecule DBT than the structural analog benzothiophene (BT) and biphenyl. The relative selection coefficient k' of the adsorbed DBT to the interferent BT and biphenyl was 2.55 and 2.14, respectively.
Abstract: The main objective of this paper was to characterize the voltammetric profiles of the Pt/C, Pt/C-ATO, Pd/C and Pd/C-ATO electrocatalysts and study their catalytic activities for methane oxidation in an acidic electrolyte at 25℃ and in a direct methane proton exchange membrane fuel cell at 80℃. The electrocatalysts prepared also were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The diffractograms of the Pt/C and Pt/C-ATO electrocatalysts show four peaks associated with Pt face-centered cubic (fcc) structure, and the diffractograms of Pd/C and Pd/C-ATO show four peaks associated with Pd face-centered cubic (fcc) structure. For Pt/C-ATO and Pd/C-ATO, characteristic peaks of cassiterite (SnO2) phase are observed, which are associated with Sb-doped SnO2 (ATO) used as supports for electrocatalysts. Cyclic voltammograms (CV) of all electrocatalysts after adsorption of methane show that there is a current increase during the anodic scan. However, this effect is more pronounced for Pt/C-ATO and Pd/C-ATO. This process is related to the oxidation of the adsorbed species through the bifunctional mechanism, where ATO provides oxygenated species for the oxidation of CO or HCO intermediates adsorbed in Pt or Pd sites. From in situ ATR-FTIR (Attenuated Total Reflectance-Fourier Transform Infrared) experiments for all electrocatalysts prepared the formation of HCO or CO intermediates are observed, which indicates the production of carbon dioxide. Polarization curves at 80℃ in a direct methane fuel cell (DMEFC) show that Pd/C and Pt/C electroacatalysts have superior performance to Pd/C-ATO and Pt/C-ATO in methane oxidation.
Abstract: g-C3N4 nanosheet was obtained from the precursors melamine and BiOBr nanosheets was synthesized from the raw materials Bi(NO3)3·5H2O and KBr. The two-dimensional g-C3N4/BiOBr heterojunction was synthesized by hydrothermal method. The intimated interface and suitable crystal facets of g-C3N4 and BiOBr were favorable the combination of this two photocatalysts, resulting in enhancing the visible-light photocatalytic activity. The phase structure, optical absorption property as well as composition and structure of as-prepared materials were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet-visible diffuse reflection spectroscopy (DRS) and photoluminescence emission spectroscopy. The potential mechanisms of constructing two-dimensional g-C3N4/BiOBr heterojunction were revealed. The photocatalytic activity of as-synthesized photocatalysts was evaluated by photocatalytic degradation of RhB under visible light (λ>420 nm) irradiation. Results show that the as-synthesized heterojunctions can significantly enhance photocatalytic activity in comparison with pure g-C3N4 and BiOBr. The mechanisms of enhanced photocatalytic performance were explained.
Supervisor：Chinese Academy of Sciences
Sponsors by：Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences Chinese Chemical Society
