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This study uses precipitation, soil moisture and evapotranspiration data as independent variables to predict future soil moisture in the Xilingol grassland of Inner Mongolia, China, while keeping the grazing strategy unchanged. Firstly, the data with anomalous values in the obtained dataset were differenced, and the soil moisture data for different depths were split to build a multi-group ARIMA prediction model. The reliability of the model was determined to obtain the soil moisture in grassland at different depths from 2022 to 2023. Through this study, we have added VAR to the ARIMA model to improve the limitations of predicting future soil moisture based on a single variable and to improve the accuracy of soil moisture prediction, thus providing some theoretical support for the ecological restoration and sustainable development of grasslands.

A comprehensive overview is presented to summarize the research works since 1982 on oxidative coupling of methane (OCM), a complex reaction network combining heterogeneous and homogeneous reaction steps. Fundamentals on reaction mechanisms and thermodynamics have revealed that the OCM process is highly exothermic and its C2+ selectivity and yield is critical in evaluating its commercial viability. Catalytic strategies have been put to enhance C2+ selectivity, improve C2+ yield and lower reaction temperature. The catalyst Mn-Na2WO4/SiO2 enables methane activation at a temperature of 800 °C and simultaneously a high C2+ selectivity of 70–80%, while the nanowire and La2O3-based catalysts enable to lower the reaction temperature to 200–300 °C and 500 °C, respectively. Reaction engineering aspects have also been dealt in many investigations in order to make the process technically feasible. Particularly, research works on reaction kinetics, reactor selection and reactor operating mode choice have been addressed. Intermediate cooling and distributed oxygen feed have been integrated into a multi-stage adiabatic fixed-bed reactor system to suppress the side oxidation reactions and improve the performance of the catalysts towards CH4 conversion and C2+ yield. This review paper proposes employing a circulating reactor system coupled with catalyst fine particles but having little internal diffusion resistance to maximize one-pass C2+ selectivity and yield of the OCM reaction and evaluate its industrial application potential.

CeO2 nanorods (CeO2-nrs), CeO2 nanocubes (CeO2-ncs) and CeO2 nanopolyhedrons (CeO2-nps) were prepared by hydrothermal method and then NiO crystallites were deposited on these supports by precipitation-deposition, respectively. The physic-chemical properties of Ni/CeO2 catalysts were characterized and performances for carbon dioxide methanation reaction were tested. The Ni/CeO2-nrs sample shows well metal dispersion and high concentration of oxygen vacancy, which leads to the high catalytic activity for CO2 methanation. Especially at 300 °C, the CO2 conversion could reach 60%. Further analysis reveals that the content of oxygen vacancy has a positive correlation with the surface area of catalyst. The largest surface area results in the most of oxygen vacancy on the Ni/CeO2-nrs catalyst, and then a large amount of CO2 could be activated at low temperatures. Meanwhile, large surface area facilitates the dispersion of active metals, and improves the degree of H2 activation. The combined effect results in the promotion of catalytic activity for CO2 methanation at low temperatures. CeO2 nanorods (CeO2-nrs), CeO2 nanocubes (CeO2-ncs) and CeO2 nanopolyhedrons (CeO2-nps) supported Ni catalysts were prepared. These catalysts ware tested for CO2 methanation and further characterized by BET, XPS, TEM, H2-TPR and TPD. The results showed that the content of oxygen vacancy has positive correlation with the specific surface area of catalyst.

Fuel conversion and clean energy reaction systems involve a variety of catalytic and non-catalytic gas-solid thermochemical reactions. A good understanding of the correct reaction mechanism and kinetics, as well as the profiles of reaction products, is of great significance to the development, design, and operation of such reaction systems. The micro fluidized bed reaction analysis provides an efficient and reliable method to acquire this essential information with low capital and operating costs, low energy consumption and enhanced safety. This paper provides an overview of the system and its characteristics for the micro fluidized bed reaction analyzer that has been well proven to be a reliable new approach as well as an instrument for characterizing various gas-solid thermochemical reactions.

Kaolin as a raw material for mesoporous support was firstly modified by calcination, acid treatment, and then was used to prepare nickel catalysts. The amount of alumina which was activated in kaolin during thermal treatment and then leached out in the acid was different. XRD pattern of the kaolin calcined at 600 °C or 900 °C exhibited only the diffraction peaks for amorphous silica and quartz while that calcined at 1100 °C showed obvious peaks for γ-Al2O3. Therefore, the nickel-based catalysts exhibited different physic-chemical properties. Atmospheric syngas methanation over the catalysts clarified an activity order of CA-1100 > CA-900 > CA-1400 > CA-600 > KA ≈ 0 at temperatures of 350–650 °C and a space velocity of 120 L·g−1·h−1. Metallic nickel with small diameter which has medium interaction with the modified kaolin and is well dispersed on the support would have reasonably good activity and carbon-resistance for syngas methanation.

The key challenge for CO2 methanation, an eight-electron process under kinetic limitation, relies on the design of non-noble metal catalysts so as to achieve high activity at low reaction temperatures. In this work, four Ni-based catalysts with different supports were prepared and tested for CO2 methanation at 250–550 °C in a fixed bed quartz reactor and further characterized to reveal the structure–function relationship. The Ni-based catalysts followed an activity order of Ni/CeO2 > Ni/Al2O3 > Ni/TiO2 > Ni/ZrO2, especially at temperatures lower than 350 °C. H2-TPR and TPD results indicated that the interaction between nickel and support was strong and the metallic nickel was well dispersed in the Ni/Al2O3 catalyst, while more amount of CO2 was adsorbed on the weak basic sites in the Ni/CeO2 catalyst. By establishing the correlation between the catalytic performance and the catalyst structure, it was found that the Ni nanoparticles and basic support serve as H2 and CO2 active centers respectively and cooperatively catalyze CO2 methanation, resulting in high low-temperature reaction activity. High CO2 conversion was achieved over Ni/CeO2 catalyst at 300 °C for its high H2 uptake on Ni nanoparticles and high CO2 adsorption capacity on the support with weak basic sites and cooperatively to catalyze CO2 methanation.

Thermochemical conversions are pathways for the utilization of biomass to produce a variety of value-added energy and chemical products. For the development of novel thermochemical conversion technologies, an accurate understanding of the reaction performance and kinetics is essential. Given the diversity of the thermal analysis techniques, it is necessary to understand the features and limitations of the reactors, ensuring that the selected thermal analysis reactor meets the specific need for reaction characterization. This paper provides a critical overview of the thermal analysis reactors based on the following perspectives: 1) gas flow conditions in the reactor, 2) particle’s external and internal heat and mass transfer limitations, 3) heating rate, 4) temperature distribution, 5) nascent char production and reaction, 6) liquid feeding and atomization, 7) simultaneous sampling and analyzing of bed materials, and 8) reacting atmosphere change. Finally, prospects and future research directions in the development of thermal analysis techniques are proposed.

We have for the first time investigated the gas-solid fluidization behavior in size-reduced beds called micro fluidized bed (Liu. X et al. Chem. Eng. J., 2008, 137: 302–307), but up to now there is not yet any clear definition for the micro fluidized beds (MFBs). This study intends to characterize MFBs in terms of gas back-mixing. The residence time distribution (RTD) and extent of back-mixing of gas were investigated in beds with inner diameters of up to 21 mm for particles of FCC, glass beads and silica sand. The RTD curves of gas, shown as E(t) versus time t, in such beds were determined on the basis of axial dispersion model to obtain the mean residence time t ¯ , variance σt2 and peak height of a given E(t) curve. In terms of these parameters the degree of gas back-mixing and its variation were evaluated with respect to particles, bed diameter (D), superficial gas velocity (Ug) and static particle bed height (Hs). It was found that the RTD of gas is subject to a unique correlation between the height of E(t) peak and the variance σt2, which makes it clear that the gas flow in an MFB has limited gas dispersion and is highly approaching to a plug flow if σt2 is below 0.25 or the height of E(t) peak is larger than 1.0. This refers to the feature that is most desired for an MFB and can thus be the criterion for defining MFB.

The study proposed an isotopes-tagging method for investigation of reactions under the atmosphere of product gas. To illustrate this method, the calcination kinetics of calcium carbonate Ca13CO3 in CO2 atmospheres were investigated by monitoring 13CO2 produced using a micro fluidized bed reaction analyzer (MFBRA). The results demonstrated that the presence of CO2 in the reaction atmosphere increases the apparent activation energy. The increase in the apparent activation energy is, however, significantly overestimated by the TGA because of the excessive suppression by stagnated product gas inside the sample crucible. Comparatively, the results from the MFBRA are due primarily to the thermal equilibrium limitation, because the gas diffusion in the MFBRA is essentially eliminated. It is thus concluded that the MFBRA is quite capable of acquiring the real kinetics of reactions in such inhibitory atmospheres. atmosphere.

Selective photocatalytic oxidation of alcohols into value-added aldehydes or ketones is a promising alternative for alcohol oxidation concerning the mild reaction conditions and the controllable selectivity. To increase the activity, defective Bi2WO6 with abundant oxygen vacancies (OVs) was synthesized via substitution of W by Ta. The resulting Ta-doped Bi2WO6 loaded with Pt nanoparticles as co-catalyst efficiently converted aromatic and aliphatic alcohols into the corresponding carbonyl compounds with high selectivity (>99%) in aqueous solution under visible-light irradiation and anaerobic conditions, with equivalent H2 as a coupled product. The optimal amount of benzyl alcohol converted by the Ta-doped catalyst was two times higher than that of the undoped catalyst. Surface OVs were found to favor the dissociative adsorption of the alcohols and to prolong the life time of the charge carriers. More importantly, isotopic labelling experiments confirmed that over Pt-loaded pristine undoped Bi2WO6, the coupled H2 product results from water reduction, while over Pt-loaded Ta-doped Bi2WO6, the produced H2 originates from benzyl alcohol, implying that benzyl alcohol can be photo-oxidized via a complete dehydrogenation pathway. Thus, enriched surface OVs in photocatalysts can activate α-C-H bonds in alcohols, boosting the photocatalytic oxidation performance.

Micro fluidized bed (MFB) reactor offers a good way to determine the intrinsic kinetics of some reactions. For catalytic decomposition of methane (CMD), the hydrogen production rate appears much hi...

The measurement and analysis of reaction behavior, kinetics quantification, and mechanism clarification for gas–solid reactions are essential to the research and development of process technologies in fields of chemical engineering, energy production, mineral processing, etc. By far, different approaches and instruments have been applied for gas–solid reaction analysis and measurement, but a recent development appears distinctive because of its use of a micro fluidized bed (MFB) in implementing the so-called isothermal differential analysis of gas–solid reactions at the Institute of Process Engineering, Chinese Academy of Sciences (CAS). Systematic work has been reported on hydrodynamic studies in MFBs and the standardized development as well as its utilization of the so-called micro fluidized bed reaction analyzer (MFBRA) for investigating various particle-involved reactions, such as pyrolysis, combustion, gasification, reduction, catalysis, absorption, etc. The obtained results well demonstrated the dis...

Improving distribution uniformity of spent catalyst and adding horizontal baffles are two effective measures to improve the regeneration performance of a fluid catalytic cracking (FCC) unit. In this study, an industrial coaxial compact FCC regenerator is simulated using a Eulerian- Lagrangian multi-phase particle in cell (MP-PIC) method. By using the energy-minimization multi-scale (EMMS) drag model based on turbulent flow regime, the MP-PIC simulation predicts the typical solids fraction profile which is in good agreement with industrial data. The Crosser grid (a typical horizontal baffle) is successfully constructed with the help of “virtual baffles” in simulation. The simulation results show that, after adding Crosser grid (a new horizontal fluidized bed baffle by our group), the bed height increases slightly, the lateral mal-distribution index of solids decreases and the descending flux of spent catalysts decreases significantly. The distribution uniformity of spent catalyst distribution along the bed cross section is more uniform when spent catalyst particles are distributed more uniformly. The presence of gas cushion beneath the Crosser grid allows it to act as a pseudo gas distributor, eliminating gas channeling and decreasing zones of low fluidization quality. The rising bubbles are absorbed by the gas cushion and new small bubbles are generated above the Crosser grid, thereby strengthening the gas–solid contact. The guiding vanes of Crosser grid accelerate the lateral movement of particles. The Crosser grid also proves its stronger suppression on the axial back-mixing of solids.

The reduction kinetics of Brazilian hematite by CO is investigated in a Micro Fluidized Bed Reaction Analyzer (MFBRA) using an analyzing method based on Johnson-Mehl-Avrami (JMA) model at temperatures of 973 K (700 °C), 1023 K (750 °C), 1073 K (800 °C), and 1123 K (850 °C). The solid products at different reduction stages are evaluated by SEM/EDS and XRD technologies. Results indicate that the reduction process is better to be discussed in terms of a parallel reaction model that consists of the reactions of hematite to wustite and wustite to iron, rather than a stepwise route. Meanwhile, the controlling mechanism of the reduction process is found to vary with temperature and the degree of conversion. The overall process is controlled by the gas–solid reaction occurring at the iron/wustite interface in the initial stages, and then is limited by the nucleation of wustite, and finally shifts to diffusion control. Moreover, the reactions of hematite to wustite and wustite to iron take place simultaneously but with different time dependences, and the apparent activation energies of hematite to wustite and wustite to iron are determined as 83.61 and 80.40 KJ/mol, respectively.

A micro spouted bed reactor was designed to implement the real-time analysis of fast reactions like biomass pyrolysis. The release characteristics of major gas components from pyrolysis, such as H2, CO, CO2, and CH4, were online recorded and comprehensively analyzed to get the generation kinetics. With the increase of pyrolysis temperature, the reaction time gradually decreased, and the recorded reaction-completion time was 3 s at 1173 K, which was much shorter than the results in literature. The calculated activation energy (E) for the formation of H2, CH4, CO, and CO2 were about 44.24, 27.46, 23.35, and 15.94 kJ/mol, respectively. They were more or less high than those obtained in a micro fluidized bed with the same inner diameter. By comparing with the researches in literature, it well demonstrated that the micro spouted bed granted unique heat and mass transfer, low gas back-mixing, and good feasibility in the measurement of fast reaction characterization.

Gas-solid micro fluidized beds have unique characteristics such as bed pressure drop overshoot, delayed minimum and bubbling/slugging but advanced turbulent fluidization, as well as negligible gas back-mixing. The data covering a wide range of operating conditions reported by various researchers are summarized, and analyzed in an effort to gain in-depth understanding about these characteristics. Based on the analysis, an approximate quantitative criterion to distinguish micro and macro fluidized beds is proposed, and the boundaries between non-fluidizable and fluidizable zones are defined. In micro fluidized beds, gas-solid flow can be situated in particulate, bubbling, slugging and turbulent fluidization regimes based on superficial gas velocity, ratios of D t / d p and H s / D t . Hydrodynamic characteristics of these flow regimes are discussed, and the correlations for U mf , U mb , U ms , and U c are developed based on analysis of experimental data. Finally, generalized fluidization maps applicable to micro fluidized beds are proposed based on the developed correlations. Through the analysis, some uncertainties and even contradictories among the reported data are identified, which would guild future studies to bring the micro fluidized bed technology forward.

The physiochemical properties of chars produced by coal pyrolysis in a laboratory-scale fluidized bed reactor with a continuous coal feed and char discharge at temperatures of 750 to 980 degrees C under N-2-based atmospheres containing O-2, H-2, CO, CH4, and CO2 were studied. The specific surface area of the char was found to decrease with increasing pyrolysis temperature. The interlayer spacing of the char also decreased, while the average stacking height and carbon crystal size increased at higher temperatures, suggesting that the char generated at high temperatures had a highly ordered structure. The char obtained using an ER value of 0.064 exhibited the highest specific surface area and oxidation reactivity. Relatively high O-2 concentrations degraded the pore structure of the char, decreasing the surface area. The char produced in an atmosphere incorporating H-2 showed a more condensed crystalline structure and consequently had lower oxidation reactivity. (C) 2015 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.orgilicenses/by-nc-nd/4.0/).

This article investigates the necessary metal-support interaction in the Ni–Mg–Zr–La/Al2O3 catalyst for high-temperature syngas methanation through varying the calcination and reduction temperatures during catalyst preparation. Atmospheric syngas methanation was conducted continuously but at 823 K and 923 K alternatively. Raising the calcination temperature increased the interaction between the nickel and alumina support but lowered the surface area of the catalyst. The catalyst calcined at the higher temperature such as 1073 K exhibited the highest initial activity in spite of its least active sites. However, only those catalysts with moderate interaction, such as that calcined at 973 K, showed stable activity of methanation above 823 K. Too small surface area of the catalyst calcined at too high temperatures, such as 1073 K, would lead to serious aggregation of nickel particles and thus cause carbon deposition during methanation. Varying the reduction temperature for the catalyst demonstrated that the excessive reduction of the nickel species such as that reduced at 1073 K almost removed all the nickel aluminates to cause the catalyst to have low activity, quick nickel aggregation and carbon deposition. This further justified the claim that moderate metal-support interaction is necessary to ensure the high activity and stability of the Ni/Al2O3 catalyst for syngas methanation at high temperatures.

This study is devoted to investigating the potential of producing phenols via pyrolysis of lignin in black liquor (BL) by a fixed bed reactor at 350-550 degrees C. The chemicals in the pyrolysis liquid of both black liquor solid (BLS) and purified lignin (PL) from BL are mainly phenols including 4-methoxyphenol, 3,4-dimethoxyphenol, 2-methoxy-4-alkylphenols and alkylphenols. For pyrolysis of BLS, high temperature facilitated the breakage of methoxyl group(s). The highest liquid yield was 27 wt.% at 450 degrees C, and the content of phenols free of -OCH3 reached 55 wt.% in addition to a small amount of other phenols. The pyrolysis of PL with and without addition of alkali additives of NaOH and Na2CO3 at 450 degrees C verified that the alkali could promote the formation of phenols. The strong alkali of NaOH greatly promoted the production of phenols free of -OCH3, whereas the effect of Na2CO3 in this aspect was much less. Catalyzed by its self-contained alkalis, the pyrolysis of BLS had high contents of alkylphenols and phenol in the tar (organics). This shows the prospective for production of phenols from pyrolyzing black liquor, while the heating value of the pyrolysis residue was above 6300 kJ/kg to further support the cascade utilization of BLS. (C) 2014 Elsevier B.V. All rights reserved.

This study is devoted to investigating the effect of alkaline additives on lignin pyrolysis for producing phenols. The effects of different types and amounts of alkaline additives, i.e., 0-20 wt.% NaOH, KOH, Na2CO3 or K2CO3, on lignin pyrolysis were tested in a fixed bed reactor. The chemicals in the pyrolysis liquid from a commercial alkali lignin with and without alkaline additive were mainly phenols including 2-methoxy-phenol, 2,6-dimethoxy-phenol, alkyl-phenols (free of methoxyl group) and 2-methoxy-4-alkyl-phenols. More vanillin and dimethoxy-benzene appeared in the pyrolysis liquid of alkali lignin and lignin purified from black liquor, respectively. While carbonate additives facilitated the production of methxoy-phenols, more alkyl-phenols were formed with the hydroxide additives. Analysis showed that all the alkaline additives promoted the reactions of decarboxylation or decarbonylation and the removal of unsaturated alkyl branch chains. The strong alkalescence of NaOH and KOH facilitated more deoxygenation of methoxyl groups so that there were more phenols free of methoxyl groups. The pyrolysis of PL resulted in the liquid yields of up to 30 wt.% (dry base), and the content of phenols was above 80% in the liquid. (C) 2014 Elsevier B.V. All rights reserved.

Ni-char catalyst doped with different additives was used to catalytically upgrade coal pyrolysis tar in situ generated in a laboratory-scale dual-stage reactor. The additives including Fe, Mg, Ce, Zr were all beneficial to the catalytic activity for tar cracking. The best result of tar upgrading was achieved with Ce–Ni-char at a Ce-to-Ni molar ratio of 0.4. The upgrading test at 500 °C over a layer of such a catalyst (20% of the tested coal mass) increased the light tar (boiling point

Catalytic upgrading of coal pyrolysis tar was investigated in a dual-stage reactor over char and metal-impregnated char (Co-char, Ni-char, Cu-char, Zn-char). The catalytic upgrading caused the lower total tar yield and the higher non-condensable gas yield but the fraction of light tar (boiling point Ni-char > Cu-char > Zn-char, and over Ni-char the realized light tar yield and its content in the tar increased by 17.2% and 32.7%, respectively. The upgrading effect also lowered the contents of element N and S in the resulting tar by 45.6% and 43.5%, respectively. NH3-TPD clarified that the order in acidity of the char-based catalysts was the same as for the upgrading activity shown above. (C) 2014 Elsevier B.V. All rights reserved.

This study is devoted to investigating the continuous coal pyrolysis in a laboratory fluidized bed reactor that fed coal and discharged char continuously at temperatures of 750-980 degrees C and in N-2-base atmospheres containing O-2, H-2, CO, CH4 and CO2 at varied contents. The results showed that the designed continuous pyrolysis test provided a clear understanding of the coal pyrolysis behavior in various complex atmospheres free of and with O-2. The effect of adding H-2, CO, CH4 or CO2 into the atmosphere on the tar yield was related to the O-2 content in the atmosphere. Without O-2 in the atmosphere, adding H-2 and CO2 decreased the pyrolysis tar yield, but the tar yield was conversely higher with raising the CO and CH4 contents in the atmosphere. In O-2-containing atmospheres, the influence from varying the atmospheric gas composition on the product distribution and pyrolysis gas composition was closely related to the oxidation or gasification reactions occurring to char, tar and the tested gas. (C) 2012 Elsevier B.V. All rights reserved.

The effects of thermal pretreatment on pyrolysis behavior of Shengli lignite were investigated in a fixed bed reactor. In comparison with raw coal, the thermally pretreated coal has lower content of hydroxyl group and lower ratio of aromatic-H to aliphatic-H. The yield of pyrolysis water is lowered after thermal pretreatment in N 2 , N 2 +O 2 and CO 2 atmospheres. The pretreatment also causes a higher CO 2 content in pyrolysis gas, which thus lowers the heating value of the gas. Pretreating the coal in superheated steam raises the tar yield by 3–4 weight percentage points, and the composition of tar varies with the atmosphere and temperature of the pretreatment. The light fraction (with boiling points below 360°C) increased by 27 weight percentage points by pretreatment in 200°C -steam. The pretreatments at 200°C and 250°C in the mixture of steam and simulated flue gas elevate the light oil and phenol oil fractions in tar by 60 and 42 weight percentage points, respectively.

A coal gasification technology for producing middle caloric fuel gas using granular coal is urgently required in China considering the huge energy demand required for project development. This work demonstrated the dual-bed gasification technology on a pilot plant (1000 tons of coal/a) mainly consisting of a fluidized-bed gasifier and a pneumatic combustor using the coal with a particle size of less than 20 mm. Simulation was performed with Aspen Plus to investigate the feasibility of producing a middle caloric fuel gas. It was found that, with a bituminite powdered coal as fuel and air as the gasifying reagent, the pilot plant could operate steadily within a given duration of 16 h. At a gasifier temperature of 900 °C and combustor temperature of 980 °C, a fuel gas with 1680 kcal N−1 m−3 of high heating value (HHV) was produced at an equivalence ratio (ER) of 0.089 (defined as the ratio of the oxygen mole in air supplied in the gasifier to the oxygen mole needed for burning the fed coal completely). The h...

A novel gas solid Micro Fluidized Bed Reaction Analyzer (MFBRA) was developed to deduce reaction rates and kinetic parameters through measuring time-dependent composition changes of evolved gases from the reactions. Application of the MFBRA to the decomposition of CaCO(3) powder resulted in an apparent activation energy of 142.73 kJ/mol and a pre-exponential factor of 399,777 s(-1). This apparent activation energy was much lower than the thermogravimetry-measured value of 184.31 kJ/mol, demonstrating a quicker reaction in the MFBRA. This was further verified by CuO reduction in CO, as accelerated by the fast diffusion and high heating rate in the MFBRA. Measurement of pyrolysis of coal and biomass in MFBRA found that the reaction process was completed in about 10 s, a time much shorter than the literature-reported values in larger fluidized bed reactors. By monitoring the release of gas species from reactions at different temperatures, the MFBRA also allowed deeper insight into the mechanism of pyrolysis reactions. (C) 2010 American Institute of Chemical Engineers AIChE J, 56: 2905-2912, 2010