Abstract: The rapid pyrolysis chars of an Inner Mongolia (Neimeng) lignite were prepared in a drop tube furnace, and the coal char gasification experiments with CO2 were conducted using a high-frequency induction furnace. The characteristics of char structure evolution during gasification were studied. Results show that as the reaction proceeds, the graphitization degree of gasified chars increases, but it is far less than the degree of natural graphite. The specific surface area firstly increases and then decreases with char conversion, while the average pore size has an opposite trend overall. The particle size of gasified chars gradually increases with conversion in the early stage, and the particle size of gasified chars increases when the conversion exceeds 74%, which could be ascribed to the cohesion of some particles in the later stage of gasification.
Abstract: The effects of temperature (850-1 150℃) and particle size (<60, 505, 950, 1 515 and 2 000 μm) on the gasification of Shenmu coal char with CO2 were investigated by using thermogravimetric apparatus (TGA) under atmospheric pressure. Three kinetic models of volumetric, shrinking core and random pore were applied to validate the experimental results, which illustrates that the random pore model can accurately predict the conversion rate for coal char gasification. Thiele modulus and effectiveness factor were determined on the basis of the intrinsic kinetic rate at 850-1 000℃; a comparison between calculated and experimental effective factors suggests that the calculated effective factor can give a quantitative estimation of the effect of internal diffusion on the initial stage of gasification, but cannot describe the whole gasification process.
Abstract: The coal char gasification experiments with Na2CO3 as catalyst was investigated on TGA. The pore structure and apparent structure evolution characteristics of char were studied by scanning electron microscopy and pore structure and specific surface area analyzer. The influence of temperature (650-800℃), gasification agent (steam, CO2) and sodium carbonate loadings (Na+ loading amounts 2.2%, 4.4%, 6.6%) on the gasification reactivity of Shenfu bituminous coal (SF) and Zunyi anthracite (ZY) were investigated. The results show that the loading of Na2CO3 stimulates the development of pore structure in pyrolysis process. In the atmosphere of CO2, there was a saturated catalyst capacity for SF and excessive catalyst loading could block internal pore structure of coal, leading to the decrease of gasification reactivity. ZY gasification reactivity increases with catalyst loading, and both SF and ZY gasification reactivity increase with the increase of temperature. In the atmosphere of steam, both SF and ZY gasification reactivity increase with the rise of catalyst loading and temperature. Na2CO3 is favorable for the decrease of reaction temperature and activation energy under the desired gasification rate.
Abstract: Xiangyang coal with low ash fusion temperature (AFT) and Jincheng coal with high AFT were used to prepare the blending samples. The influence of Xiangyang coal addition on AFT of Jincheng coal was explored by XRF, SEM, DSC, XRD, and ternary phase diagram analysis. The results show that blending coal can reduce the AFT effectively. The AFT of blending coal is lowered significantly when the adding amount of Xiangyang coal is lower than 24%. Whereas, when the adding amount is between 24% and 40%, AFT of the mixed coal has a slight change and the ash flow temperature is below 1 400℃. A series of chemical reactions among ash composition of mixed coal occur at 1 000-1 200℃, mainly including formation of high melting point compound (mullite) from SiO2 with A12O3, and that of low melting point compounds (anorthite and hercynite) from the reactions between mullite and CaO or Fe2O3. The above reactions mainly cause the changes of ash fusion temperature in blending coal. Based on BP neural network, a prediction model of ash fusion temperature was built. It is proved that the prediction average accuracy by BP neural network is higher than 99%, which is better than that of a previous empirical formula. Furthermore, analysis by thermodynamics software (HSC 5.0) shows that mullite prefers to react with CaO rather than Fe2O3.
Abstract: The fluxing mechanism of rice straw for Jincheng anthracite with high ash fusion temperatures was investigated under weak reducing atmosphere by CaO-Al2O3-SiO2 ternary phase diagram, X-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive X-ray spectrometry (SEM-EDX). The fusion temperatures of blended ash decrease, and the content of basic oxide CaO, Na2O and K2O increases with increment of rice straw addition. The slagging index Rb/a is between 0.20 and 0.69. The fluid temperature (FT) declines to 1 369℃ by adding 20% rice straw, which could satisfy requirement of liquid slag discharge for gasifier. The addition of rice straw reduces the initial temperature and increases the occurrences proportion and probability of liquid phase in the ash. The formation of crystal albite with low melting point and eutectics formed from anorthite, quartz and mullite lead the decrease of ash fusion temperatures.
Abstract: The effect of Fe on structure of unreacted residues from combustion of demineralized Shengli lignite at ignition temperature was studied. TGA was adopted to investigate the ignition temperature of demineralized and Fe adding lignite, which were combusted at ignition temperature in quartz tube reactor to attain solid unreacted residues. The structure properties of lignite and the unreacted residues were investigated by FT-IR, XPS, XRD, and Raman spectra to study influence of Fe on the combustion reaction. The results indicate that adding of Fe lowers the ignition temperature of demineralized Shengli lignite, especially when the adding amount was 3.50%. The FT-IR of solid unreacted residues demonstrates that the adding of Fe has no obvious effect on functional groups of unreacted residues, suggesting that the functional groups are not the main factors to affect he combustion performance. The Fe adding accelerates the decrease of carbon-oxygen structure of SL+ during combustion and causes the reduced aromaticity and graphitization degree of unreacted residues, and favors the increase in alkyl side chain and crystal structure defects, indicating that the Fe adding promotes the changes in carbon-oxygen structure during combustion and restrains graphitized transformation of unreacted residues.
Abstract: Adsorbent-decorated Fe2O3/Al2O3 as oxygen carrier (OC) was proposed for restraining the emission of chloride, sulfide and heavy metals during the chemical-looping combustion process of gaseous or solid fuels. Three adsorbents (K2O, Na2O and CaO) were selected for decorating these OC particles. First, the raw Fe2O3/Al2O3 and three adsorbent-decorated Fe2O3/Al2O3 were reduced by synthesis gas and then the oxidation kinetics of four reduced OCs (raw FeO/Al2O3 and three adsorbent-decorated FeO/Al2O3) were investigated by using thermogravimetric analysis (TGA) technique in air atmosphere at four temperatures (850, 875, 900 and 925℃). It was found that the translation of FeO to Fe2O3 can be described by the phase boundary-controlled (contracting cylinder) model, and the apparent activation energy (E) was calculated to be 13.71, 20.21, 21.62 and 24.20 kJ/mol for raw FeO/Al2O3, K2O-decorated FeO/Al2O3, Na2O-decorated FeO/Al2O3 and CaO-decorated FeO/Al2O3, respectively. Last, the reaction mechanism was evaluated through comparing the calculated data from the obtained kinetic parameters and the experimental results, which demonstrated the reliability of the phase boundary-controlled (contracting cylinder) model.
Abstract: The release of NOx precursors (NH3, HCN and HNCO) in the pyrolysis of two nitrogen-rich biomass materials, viz., soybean straw (SBS) and fiberboard (FB), were investigated by thermogravimetric-Fourier transform infrared spectroscopy (TG-FTIR, for slow pyrolysis) and horizontal tubular reactor-X-ray photoelectron spectroscopy (HTR-XPS, for rapid pyrolysis); the effects of final temperature, heating rate and nitrogen form in biomass on the release characteristic were considered. The results indicate that the evolution pathway is related to the form of nitrogen in biomass; nitrogen in SBS (SBS-N) is mainly converted to NH3 during the secondary cracking reaction, whereas nitrogen in FB (FB-N) is transformed to NH3, HCN (rapid) and HNCO (slow) during the primary pyrolysis reaction. Nitrogen in biomass (fuel-N) is inclined to convert to nitrogen in char (char-N) at low temperature and to nitrogen in tar (tar-N) or NOx precursors at high temperature (>600℃), which suggests that a pyrolysis temperature below 600℃ can suppress the release of NOx precursors. SBS-N and FB-N are characterized by protein and amide, respectively, which are partly converted to pyrrolic-N and pyridinic-N in char, forming preferably NH3 and HCN, respectively.
Abstract: Ni-Sm/SiC (Ni:9%, Sm:5%) catalysts were prepared by a hydrothermal route for carbon dioxide reforming of methane. The catalysts were characterized by XRD, BET, ICP, H2-TPR, TG-DTA and TEM. The catalytic performance, influence of different nickel precursors and carbon deposition in the CO2 reforming of CH4 were investigated. The results suggested that the Ni-Sm/SiC catalysts prepared by a hydrothermal route showed excellent catalytic activity, stability and good coke resistance. Different nickel precursors nearly had no impact on the performance of the catalysts.
Abstract: Citric acid hold great promise to improve the Mo-based catalyst performance for hydrogenation reaction applications. MoO3/CeO2-Al2O3 catalysts were prepared by impregnation method with adding citric acid into CeO2-Al2O3 composite supports and tested for sulfur resistant methanation. The syngas methanation activity increased with the increase of citric acid additive amount, and CO conversion could reach up 60% when the molar ratio of citric acid to Ce was 3. The prepared catalysts were characterized by BET, H2-TPR, XRD and XPS. The increased catalytic performance was mainly attributed to the increased amount of Ce species on the surface of catalysts which could decreased the interaction force between MoO3 and CeO2-Al2O3 supports. Additionally, the increased specific surface of CeO2-Al2O3 composite support was also in favor of catalytic performance.
Abstract: A series of cerium modified Silicalite-1 molecular sieves were prepared by incipient wetness impregnation and used as the catalysts in the conversion of methanol to propene (MTP). The cerium modified Silicalite-1 catalysts were characterized by X-ray diffraction (XRD), N2 sorption, pyridine adsorption Fourier transform infrared spectroscopy (Py-FTIR) and temperature-programmed desorption of NH3 (NH3-TPD); their catalytic performance in MTP was evaluated in a continuous flow fixed-bed micro-reactor at atmospheric pressure and 450℃, with a methanol weight hourly space velocity (WHSV) of 9.6 h-1. The results showed that Silicalite-1 exhibits superior catalytic performance in MTP in terms of catalytic stability and selectivity to propene, in comparison with the HZSM-5 zeolite with a SiO2/Al2O3 molar ratio of 200. The introduction of Ce can effectively adjust the acid properties and pore structure of Silicalite-1; modification with an appropriate concentration of Ce can reduce the amount of strong acid sites and then enhance the catalytic performance of Silicalite-1 in MTP. Over the cerium modified Silicalite-1 with a CeO2 content of 5.0%, the selectivity to propene is increased from 31.9% to 38.2% and the catalytic lifetime is extended from 51 to 72 h, in comparison with those over the parent Silicalite-1.
Abstract: Mg-Co and Mg-Mn-Co composite oxides with different compositions were prepared by sol-gel method for N2O catalytic decomposition in the presence of oxygen. Of Mg-Mn-Co catalysts, the one with higher activity was impregnated by K2CO3 solution to make K-modified catalyst. These catalysts were characterized by X-ray diffraction(XRD), nitrogen physisorption (BET), scanning electron microscopy(SEM), temperature-programmed reduction of hydrogen(H2-TPR), and temperature-programmed desorption of oxygen(O2-TPD). The effect of preparation parameters such as compositions and potassium loadings on their catalytic activity has been investigated. The results show that K-modified catalysts exhibit better activity and higher resistance towards water in contrast to un-modified catalyst due to the weakness of surface metal-oxygen bonds. Among these catalysts, 0.02K/MgMn0.2Co1.8O4 is the most active, over which 97% and 60% conversions of N2O can be reached at 400℃ after continuous running for 50 h under the atmosphere of oxygen-alone and oxygen-steam together, respectively. When the steam is switched off, the catalytic activity of 0.02K/MgMn0.2Co1.8O4 can be restored to large extent, indicating the good water-resistance of K-modified catalyst.
Abstract: In this paper, the iron-magnesium hydrotalcite-based catalysts with well dispersed noble metal for the lean NOx trap (LNT) were prepared by co-precipitation and impregnation methods. The effects of different calcination temperatures on the catalyst structure and the adsorption-reduction performance for NOx were investigated by analytical techniques. Results show that the crystalline structure of the catalysts remains stable when the calcination temperature is lower than 700℃. The sintering of the catalysts prepared and the conglobation of Pt particles appear on the catalyst surface after calcination at 800℃. With the increase in calcination temperature from 500 to 800℃, the desorption amounts of NOx increases after an initial decrease, while the corresponding peak temperature show a marginal change. DRIFTs results indicate that the adsorbed NOx species and the adsorption pathways over the catalyst after calcination at 800℃ differ from those at 500℃. The ratio of NH3/N2 released from the reduction of adsorbed NOx species over the catalyst calcinated at 800℃ decreases in comparison with those calcinated at lower temperatures, which is responsible for the decrease in the NOx conversion efficiency.
Abstract: The AgCeY-n adsorbents were successfully synthesized by microwave-assisted liquid ion exchange (AgCeY-1), hydrothermal ion exchange (AgCeY-2) and liquid phase ion exchange (AgCeY-3) methods with NaY (Si/Al ration=5.3) molecular sieve parent and characterized by XRD, BET, XPS and Py-FTIR analysis. With thiophene (TP) and benzothiophene (BT) as the model sulfides, and toluene and cyclohexene as the competition components, the effects of the preparation method on the adsorptive desulfurization properties of the as-prepared adsorbents were evaluated. The results show that the Ag and Ce species in AgCeY-n zeolites exist as Ag+ and Ce4+. The AgCeY-1 prepared via microwave-assisted liquid ion exchange method possesses the highest Ag+ and Ce4+ contents. In addition, it possesses the highest amounts of L and B acid. The adsorption selectivity to sulfur compounds follows the order:BT>TP. The effects of competition components on the sulfur removal with AgCeY-n zeolites follow the order:cyclohexene>toluene. Among the preparation methods tested,the microwave-assisted liquid ion exchange method takes the shortest time (20 min). The as-prepared AgCeY-1 adsorbent exhibits most satisfied performance of adsorption for all the model oils and a wonderful regeneration property. The removal ability for TP and BT of various adsorbents follows the order:AgCeY-1 >AgCeY-2 >AgCeY-3.
Abstract: A variety of TiO2-Al2O3 composite support were prepared using improved sol-gel method (SG), co-precipitation method (CP), surface precipitation (PR) and mechanical kneading method (ME), and the influence of preparation methods on their physical properties were investigated. The hydro-desulfurization activity of Co-Mo/TiO2-Al2O3-X catalysts prepared by impregnation method was studied. XRD, BET and SEM were used to characterize the composite support and the catalysts. Results show that the composite support prepared by SG method has uniform morphology with larger surface area, pore size and pore volume. And the monolayer or sub-monolayer of TiO2 existed in the γ-Al2O3. Under the reaction conditions of 3.0 MPa of hydrogen pressure, 280℃ of reaction temperature, 4 h of reaction time, 1.4 h-1 of the liquid space velocity and 600 of hydrogen to oil ratio, Co-Mo/TiO2-Al2O3 prepared by SG method has highest hydro-desulfurization activity, and the thiophene conversion rate reached 96.6%.
Supervisor：Chinese Academy of Sciences
Sponsors by：Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences Chinese Chemical Society
