Abstract: Effect of acid treatment on specific surface area, sulfur forms and their transformation during pyrolysis of Yima coal were investigated by XANES technique. Results show that the specific surface area of acid-treated coals is higher than that of raw coal due to removal of some mosaic minerals in coal matrix and opening of some pores. Most of the minerals and inorganic sulfur are removed by the acid treatment, the relative percentages of sulfide, sulfoxide and sulfone in YMN are higher than that of YMR and YMD due to the higher oxidability of HNO3. Sulfur forms on the coal surface are more modified than that in the coal bulk by the acid treatment. The release amount of sulfur-containing gases during pyrolysis of acid-treated coals decreases, but the accumulated release yields increase due to removal of most alkaline minerals and the relative increase of thermally decomposable sulfur forms in coal. The main sulfur forms show a more even distribution in acid-treated coal chars due to the inter-conversions between different sulfur forms during pyrolysis. HCl-HF-HNO3 process could remove most of the minerals and inorganic sulfur, and change distribution of sulfur forms, which provides a suitable guidance for utilization of high ash, pyrite-rich high-sulfur coals.
Abstract: Forms and distribution of sulfur in pulverzied Jincheng coal were analyzed, and their influence on ash fusion temperature (AFT) was studied. With the float-sink method, the whole coal was separated into four density fractions, i.e. < 1.6, 1.6-1.7, 1.7-2.0 and >2.0 g/cm3. The distribution of sulfur content and their forms were analyzed. SO3 content and AFT of the coal samples ashed at 450, 815, 1000, and 1300℃ were determined. XRF and XRD were used to reveal the mechanism. The results show that sulfur in pulverized Jincheng coal is not evenly distributed in different density fractions, mainly concentrated in >2.0 g/cm3. With increase of the density, content of organic sulfur decreases rapidly, while those of sulphate sulfur and pyrite increase significantly. With increasing ashing temperature, sulfur contents in the whole coal and density fractions decrease. At 450℃, 87% sulfur is vaporized and at 1300℃ almost all sulfur is vaporized. Different density fraction shows different AFT, with >2.0 g/cm3 having the lowest AFT. Besides, AFT of >2.0 g/cm3 increases with rising ashing temperature. Mechanism study shows that the differentiation of AFT in different density fraction can be attributed to their chemical composition. The increase of AFT of >2.0 g/cm3 with ashing temperature is mainly due to sulfur SO3 content in the ash residual.
Abstract: Based on the possible effect of limestone on composition and structure of coal chars during underground coal gasification (UCG), gasification of lignite by steam with different dosages of limestone of 0-30% (mass fraction) was performed in a simulated UCG test system. The composition, specific surface area (SBET) as well as pore structure properties, microcrystal structure and surface functional groups of the obtained residual chars were examined by low-temperature nitrogen adsorption, XRD and FT-IR, etc. The results show that composition of coal char is significantly influenced by limestone. Limestone contributes to development of micro-pore toward meso-pore, increases SBET and total pore volume (vt) of residual chars. When dosage of limestone increases from 0 to 30%, the SBET of residual chars increases by 21.91%, and the ratio of meso-pore volume to total pore volume rises percentage points of 21.49. XRD analysis shows that the presence of calcium destroys aromatic structure of coal char, increases both degree of disorder and interplanar spacing (d002), and inhibits graphitization tendency of coal char. FT-IR analysis indicates that hydroxyl group of residual chars is reduced with the presence of limestone.
Abstract: A thorough theoretical exploration of microscopic mechanism for effect of sodium (Na) on nitric oxide (NO) heterogeneous reduction by char was performed based on density functional theory with consideration of London dispersion interaction. Calculation results show that the Na atom could migrate at edge of char and prefers to be incorporated into a five-atom ring forming a pentagon with 174.2 kJ/mol released. A strong electrostatic attraction between the Na atom and carbon atoms at the edge is found by reduced density gradient analysis. Electrons transfer from the Na atom to char, resulting in electron rearrangement on char. It is the most stable mode for adsorption of the first NO molecule when O atom in NO molecule is adjacent to the Na atom. The doping of Na could promote adsorption of the first NO molecule, but has little effect on that of the second NO molecule. The intrinsic reaction coordinate calculations and Mayer bond order analyses suggest that the Na atom affects heterogeneous reduction through "oxidized-reduced" cycle via "combination-separation" with the O atom. Desorption of N2 molecule is the rate-determining step in the whole reaction channel. The canonical variational theory was used for kinetic analyses, considering the tunneling effect along the reaction coordinate with Wigner method. It is found that the reaction is accelerated by doping Na atom. Although the addition of Na would not significantly reduce activation energy of the rate-determining step, but would increase activation sites at the edge of char.
Abstract: The structural characteristics and differences of coal tar and petroleum C7-asphaltenes were studied, such as chemical composition, functional groups and molecular structure, using nuclear magnetic resonance (NMR), small angle X-ray scattering (SAXS), X-ray photoelectron spectroscopy (XPS), improved B-L method and other methods. Furthermore, the association behavior and aggregation size of two different types of asphaltenes as well as the hydrogen bonds and acidic-basic interaction were analyzed by asphaltenes solubility parameters in polar solvents. The experiment results showed that the coal tar asphaltenes (CT-asp) was mainly composed of less aromatic rings with more short alkyl branched chains and possessed a high aromaticity degree. The higher content oxygen heteroatoms of CT-asp were mostly presented as aromatic ether bonds and phenolic hydroxyl groups. The aromatic nucleus size and the average relative molecular weight of petroleum asphaltenes (M-asp) were larger than that of CT-asp. The M-asp consisted primarily of more aromatic rings with more long alkyl branched chains and possessed a low aromaticity degree. The association and aggregation degree between CT-asp and M-asp was associated with the amount of substance ratio (nCT-asp/nM-asp) and their molecular structure characteristics. The association force of two types mainly was the hydrogen bonds and the acidic-basic interaction from heteroatomic functional groups.
Abstract: In order to understand the pyrolysis process and sulfur transformation property of high sulfur petroleum coke at high temperature, the pyrolysis experiment of Qingdao high sulfur petroleum coke at high temperature (900-1500℃) was carried out in a high temperature fixed bed. The release rule of pyrolysis gas and the evolution of physical pore structure and chemical characteristics of coke during pyrolysis were investigated. At the same time, the content and existing mode of sulfur in the samples before and after pyrolysis were studied. The results show that with the increase in pyrolysis temperature, the content of H2 in the pyrolysis gas of petroleum coke increases gradually; the content of CO changes little; while the content of CH4 and CO2 decreases gradually. Moreover, as the pyrolysis temperature is increased, the specific surface area and average porosity of pyrolysis coke increase; the surface morphology of particles is less affected; the content of amorphous carbon in petroleum coke reduces; and the order and graphitization degree of microcrystalline structure increase gradually. However, with the increase in pyrolysis temperature, the gasification activity of pyrolysis coke is first decreased and then increased, with the minimum value around 1100℃. It is found that the sulfur release rate in high sulfur petroleum coke pyrolysis at 1500℃ reaches 81.34%, and only a small amount of organic sulfur in the form of mercaptans and thiophene rings is retained in solid.
Abstract: A molecular modeling study based on density functional theory (DFT) and transition state theory (TST) was performed to investigate the effect of Na on the NO heterogeneous reduction by char; zero point energy correction was considered and the transition states was confirmed by frequency analysis. The results show that Na can effectively promote the adsorption of first NO molecule on to the char. The presence of Na cannot change the reaction steps, but reduce the activation energies of rate-determining steps from 121.04 kJ/mol to 100.62 kJ/mol. Moreover, the presence of Na can increase the pre-exponential factors as well as the reaction rate, meaning more active sites and enhanced catalytic performance of char in NO reduction.
Abstract: Zeolitic imidazolate frameworks (ZIF-8) were synthesized by solvothermal method. Used as precursor, ZIF-8 was decomposed into nanoparticles ZnO at different pyrolysis temperature in air atmosphere. The composition, structure and crystal size of ZnO were characterized by XRD, TEM, XPS, and Raman methods. The ZnO nanoparticles were coupled with HZSM-5 to form bifunctional catalysts. The catalytic performances of bifunctional catalysts in the syngas conversion were investigated in a fixed-bed tubular reactor. The results demonstrate that the pyrolysis temperature has an important influence on the particle size of ZnO. The temperature affects the rate of grain formation. High temperature promotes the aggregation of ZnO. The ZnO grain size by changing the temperature plays a role in changing the product distribution. When the pyrolysis temperature is near or below 450℃, carbon-coated ZnO nanoparticles are obtained, and the ZnO grain size is less than 20 nm. The carbon-coated ZnO coupled with HZSM-5 catalyzes syngas mainly into dimethyl ether (DME). When the temperature is higher than 450℃, pure phase ZnO nanoparticles are obtained, and the ZnO grain size is larger than 20 nm. The pure ZnO coupled with HZSM-5 catalyzes syngas mainly into hydrocarbons. Obviously, the coupling modes of ZnO and HZSM-5 have a significant effect on the product selectivity of bifunctional catalysts.
Abstract: The catalytic performance of zeolites in industry can often be enhanced by modification with transition metals and Ni is one of the most widely used transition metals for the hydrogenation and dehydrogenation catalysts. In this work, the structure and acid properties of Ni-modified HAl-ZSM-12 zeolites were investigated by the dispersion corrected periodic density functional theory. The results indicate that single Ni atoms can reduce the H atoms in the zeolites into H2 molecule, whereas the Ni clusters like Ni2 cannot. The quantity of Brønsted acid sites may decrease after the modification with single Ni atoms; the Ni atoms in the zeolites are oxidized and work as strong Lewis acid sites, which may weaken the Lewis acidity of Al3+. After modification with Ni, the Ni-modified ZSM-12 displays greater ability to adsorb hydrogen molecules. The adsorbed hydrogen molecules are dissociated to negatively charged H atoms, which do not function as Brønsted acid sites. Due to the transfer of electron from the Ni atoms to the pre-adsorbed H atoms, as revealed by the adsorption energy of NH3, the pre-adsorption of hydrogen on the Ni-modified ZSM-12 zeolites can enhance the Lewis acidity.
Abstract: Methanol conversion to olefins (MTO) catalyzed by zeolite catalysts is a typical diffusion dominated reaction process. In this paper, the diffusion behavior of several typical product molecules (ethylene/ethane, propylene/propane, benzene) on a HZSM-5 zeolite was systematically studied by using Frequency Response method. The results show that the mass transfer regularity of the product molecules have been successfully determined by the Frequency Response method. It is confirmed that the diffusion rates of C2 and C3 hydrocarbon molecules within the HZSM -5 micropores are similar, but the effects of the surface resistance are different. So, the C2 molecules can freely go in and out of the channels of the HZSM-5 zeolite, while the diffusion of C3 molecules is significantly affected by the channel diffusion limitation. In addition, the diffusion rate of benzene molecules is observably lower than that of C2 and C3 molecules, and the resistant effects of benzene molecules caused by the zeolite crystal surface are not serious. The conclusions obtained in this study can be used to explain the product selectivity of MTO reaction over HZSM-5 zeolites and the coking mechanism of the catalyst, and provide the mass transfer theoretical guidance for the preparation of the MTO catalysts with excellent performance.
Abstract: Silicon carbide supported copper oxide (CuO/SiC) catalysts were prepared by wet impregnation method and characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS); their catalytic performance in the selective catalytic reduction of NOx with NH3 at low temperature was investigated with a mimic flue gas. The results indicate that the catalytic performance of CuO/SiC in the selective catalytic reduction NO with NH3 is related to the loading of copper oxide and reaction temperature. The CuO/SiC catalyst with a CuO loading of 5% exhibits high activity at low temperature, where SO2 shows slightly inhibition upon the NO reduction activity; the NO reduction reaction over CuO/SiC may take place between the adsorbed ammonia and the gaseous or weakly adsorbed NO. Such CuO/SiC catalysts may provide a new choice for the practical removal of NOx in industry.
Abstract: A series of Cu-Mn/SAPO-34 catalysts with different mass ratios of Cu to Mn were prepared by impregnation method. The influence of Cu and Mn loading on the denitrification performance was investigated in a fixed-bed reactor. XRD, NH3-TPD, H2-TPR, XPS were used to characterize and analyze the catalysts. The results show that the bimetallic modified Cu-Mn/SAPO-34 have excellent catalytic activity and broad active temperature window. Especially, the Cu-Mn/SAPO-34/1:4 catalyst with a Cu/Mn mass ratio of 1:4 has the widest active temperature window, its denitrification rates could reach 85.39% at 250℃, 96% at 300-400℃, and up to 90% at 450℃. Cu and Mn species are highly dispersed on the surface of the catalyst and do not change the crystal structure of SAPO-34. Co-doping of Cu and Mn promotes the transformation of Cu2+ to Cu+, increases the ratio of Mn4+ to Mn3+, improves the activity at low temperature and promotes the catalytic reaction. Cu-Mn/SAPO-34/1:4 catalyst has rich acid sites, good redox performance and resistance to SO2 and H2O, which can improve the activity and stability of the catalysts.
Abstract: In order to study the catalytic oxidation process of carbon black over La0.7Sr0.3CoO3-δ perovskite catalyst, two different contact modes of the catalyst and carbon black were designed, namely intimate contact and loose contact, and used to observe the reaction behavior. The results showed that the tig (light-off temperature) of carbon black decreased by 89.5 and 157.4℃ under intimate contact conditions compared with the loose contact and no catalyst contact conditions. Meanwhile, as the ratio of catalyst/carbon black increased, the tig, tm (maximum conversion temperature) and tf (burn-up temperature) of the carbon black all shifted to the low temperature, indicating that the catalyst had good catalytic performance for carbon black oxidation.
Abstract: In this study, TiO2, TiZr and TiSn supports were prepared using co-precipitation method, and MnTi, MnTiZr, and MnTiSn catalysts with MnO2 content of 10%were prepared by the wet impregnation method. BET, XRD, H2-TPR, FT-IR, and XPS were employed to characterize the prepared samples. The Hg0 removal performance tests over the three catalysts were conducted in a fixed-bed reactor apparatus. The results indicated that the Hg0 removal performance of MnTiZr and MnTiSn catalysts was better than that of MnTi catalyst in the temperature range of 100-300℃. This could be attributed to the introduction of Sn and Zr, which increased the specific surface area of the catalyst, improved the low-temperature redox performance of the catalyst, and elevate the number of acid sites, the high valence manganese ions concentration and O* content on the catalyst surface. The mercury removal efficiency of the MnTiSn catalyst was higher than that of MnTiZr catalyst at reaction temperature of 150-300℃, which could be ascribed to the higher redox performance of the MnTiSn catalyst and more content of the high valence manganese ions, O*, and surface acid sites on its surface. During the removal of Hg0 in flue gas by MnTiZr and MnTiSn catalysts, active ingredients on the catalyst surface such as high-valence manganese ions and O* were consumed and participated in the reaction of Hg0 oxidation to Hg2+. And the consumed amount of active ingredients on the surface of MnTiSn catalyst was more than that on the MnTiZr catalyst.
Abstract: The adsorption and desorption behaviors of n-hexane, toluene and ethyl acetate on activated carbon, 5A, NaY, 13X, ZSM-5 (SiO2/Al2O3=27, 300), Hβ and MCM-41 at different temperatures were investigated by chromatography method and thermogravimetry (TG).And the adsorption thermodynamic parameters (ΔH, ΔS and ΔG) were calculated based on the results obtained by inverse gas chromatography, by which, the interactions between adsorbent and VOC molecules were elucidated. In addition, the adsorption mechanisms of VOC molecules on molecular sieves were confirmed based on FT-IR results. There are two modes of spontaneous adsorption involving physical and chemical adsorptions. The physical adsorption strength is dependent on the pore size distribution of the adsorbent and the molecular diameter of the adsorbate, while the chemical adsorption strength is associated with the Si/Al ratio of the molecular sieve, the cations of Ca2+, Na+, H+, and the dipole moment of the adsorbate molecules. Meanwhile, the presence of strong chemical adsorption makes desorption temperature up to 200℃.
Abstract: The texture and surface chemistry of carbon nanotubes before and after chemical treatment using ZnCl2, KOH and HNO3 were determined by scanning electronic microscope, X-ray diffraction, N2 adsorption, and Boehm titration; and the effect of adsorptive conditions (contact time, initial concentration and temperature) on phenol removal and the thermodynamic and kinetic behavior and adsorption mechanism were investigated by tests and data fitting with three kinetic models (pseudo-first order, pseudo-second order and the Elovich kinetic equations) as well as thermodynamic equation. The results show that the treatment by HNO3, ZnCl2 or KOH less changes the BET surface area of carbon nanotubes, but obviously changes the surface chemical property. Specifically, the treatment by HNO3 obviously enhances surface acidic groups and slightly increases basic groups, whereas the treatment by ZnCl2 or KOH greatly decreases surface carboxyl groups and lactonic groups but obviously increases surface basic groups, which affects the phenol removal by carbon nanotubes. It is found that the phenol removal by carbon nanotubes treated with ZnCl2 or KOH increases due to a decrease in surface carboxyl groups of carbon nanotubes, but HNO3 treatment slightly reduces the phenol removal possibly because the adsorption is influenced by both structure and surface chemical property. Moreover, the adsorption of phenol by carbon nanotubes is spontaneous, exothermic and physically controlled, and the adsorption process of phenol by carbon nanotubes complies with the pseudo-second order equation.
Supervisor：Chinese Academy of Sciences
Sponsors by：Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences Chinese Chemical Society
