燃料化学学报最新文献

To provide some useful suggestions to the operation of circulating fluidized bed (CFB) gasifier, the effect of gasification temperature, residence time and agent on the release and transformation of sodium was studied by using a fixed bed reactor combined with Factsage software. The results indicated that gasification temperature was the significant factor to the release and transformation of sodium. For the promoting effect of sodium release, it was ascribed to the intense of sodium volatilization and competitive reaction between lime and meta-kaolin. Meanwhile, the high temperature promoted the formation of nepheline and slag. The threshold temperature of latter was near 950 °C. It was interesting to find that the release of sodium could be divided into two stages: coal pyrolysis and char gasification. In coal pyrolysis, part of organic and water-soluble sodium was released. The remainder either combined with char structure, or reacted with minerals. In char gasification, sodium, combined with char structure, was released along with char gasification. Due to the decrease of melting temperature and the formation of NaOH, steam showed a promoting effect on the sodium release. Oppositely, oxygen and nitrogen presented an inhibiting effect. The former was ascribed to the formation of Na₂SO₄, while the latter was caused by the chemical binding and physical wrapping effect of char.

With carbon dots (CDs) as the reducing agent and support, a PdAg/CDs composite catalyst was prepared by simple light reduction method. The results of XRD, TEM, FT-IR and XPS characterization indicate that the PdAg/CDs composite has an average particle size of about 10.45 nm, where Pd and Ag exist on the surface of CDs mainly in the alloy form of zero valence. The catalytic performance of the PdAg/CDs composite was evaluated in the hydrogenolysis of glucose in water. The results illustrate that the PdAg/CDs composite catalyst is highly active in the glucose hydrogenolysis; after reaction for 3 h under 140 °C, 4 MPa of initial H₂ pressure, 100 mg of glucose and 25 mg of catalyst, the conversion of glucose is 68.85% and the yield of acetol reaches 8.36%.

Fast pyrolysis of biomass is an effective way for biomass conversion and utilization. However, the pyrolysis temperature is usually high because it is a non-catalytic process, resulting in the complicated composition of bio-oil and difficulty to control. Aiming to explore in-situ catalysis in this paper, the fast pyrolysis of lignin, cellulose, corncob and pine wood powder was studied using ZnCl₂ as the catalyst. The activation energies of non-catalytic pyrolysis and catalytic pyrolysis were obtained based on kinetic fitting of their thermal gravimetric curves. The variation in pyrolysis oil composition was analyzed. It was found that ZnCl₂ in situ catalysis could not only significantly reduce the pyrolysis temperature, but also simplify the resultant bio-oil composition. Even under pyrolysis temperature as low as 350 °C, fast pyrolysis of pine wood powder could achieve a yield of 47% of bio-oil, which was predominantly composed of the derivatives of cellulose and hemicellulose. ZnCl₂ in situ catalysis could significantly decrease the activation energy of cellulose cracking from 304.78 to 112.46 kJ/mol, but has little effect on that of lignin. The carbon residue from ZnCl₂-catalyzed pyrolysis was further carbonized at 600 °C, affording activated carbon with adsorption capacity of phenol up to 165 mg/g. The research work provides guidance and reference for the development of in-situ catalytic pyrolysis technology with high efficiency.

The chemical looping gasification (CLG) kinetics of biochars with calcium ferrite as oxygen carriers and the effects of different kinds of calcium ferrite and biochars were investigated by TGA. The properties of biochars and calcium ferrite were analyzed by XRD, SEM, BET, etc. The Škvára-Šesták method was used to determine the kinetic mechanism function. The results show that the reduction reaction rate and the oxygen carrying capacity of oxygen carriers follow the sequence: Ca₂Fe₂O₅ > CaFe₂O₄ > Fe₂O₃, and CaFe₂O₄ > Ca₂Fe₂O₅ > Fe₂O₃, respectively. The oxygen carriers can be completely reduced to Fe and CaO by biochar. The activation energy of CaFe₂O₄ reduction is in the range of 167.44–600.83 kJ/mol; and the activation energy of Ca₂Fe₂O₅ reduction is in the range of 413.62–583.51 kJ/mol. The CaFe₃O₅ generated during the reduction of CaFe₂O₄ may have a negative influence on the lattice oxygen diffusion. The reduction of CaFe₂O₄ can be divided into two stages: when the conversion degree α is less than 0.15, the CaFe₂O₄ is reduced to Ca₂Fe₂O₅ following the random nucleation and nuclei growth model; when α is greater than 0.15, Ca₂Fe₂O₅ is further reduced to CaO and Fe following the 3-D diffusion mechanism. The mechanism function of the reduction of Ca₂Fe₂O₅ is the same as that of the second stage of CaFe₂O₄ reduction.

Supported cobalt catalysts (Co@C-ZnZrO₂ and Co/ZnZrO₂) were prepared through a metal-organic frameworks (MOFs)-mediated synthesis strategy. The influence of MOFs pyrolysis on the structure and Fischer-Tropsch synthesis performance of supported cobalt catalysts was investigated. The crystalline phase and microstructure of supported cobalt catalysts were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), N₂ adsorption-desorption and X-ray photoelectron spectroscopy (XPS). The Co/ZnZrO₂ showed the CO conversion of 18.1% and the C₅₊ selectivity of 77.4%, whereas the Co@C-ZnZrO₂ exhibited the CO conversion of 8.5% and the C₅₊ selectivity of 35.2%. The excellent CO conversion for Co/ZnZrO₂ was attributed to the more exposure of active Co sites. Meanwhile, the activity of Co sites on Co@C-ZnZrO₂ catalyst was restricted by the carbon layer, suppressing the adsorption and activation of syngas on Co sites.

The effects of silicon oxide additive on the transformation characteristics of sodium and sulfur in coal ash under atmospheric and elevated pressure were investigated in this study. The results indicated that silicon oxide additive significantly inhibited the release of sodium under high pressure. The sodium content in ash with 4% of silicon oxide additive was 3.5% at 0.1 MPa, which was higher than that without additive. However, the sodium content increased to 5.4% without additive and 6.9% with 4% additive at 4 MPa, respectively. The sodium mainly existed in the forms of NaAlSiO₄ and NaAlSi₃O₈ at 0.1 MPa, and the content of NaAlSiO₄ increased with increasing additive dosage, which weakened the agglomeration of ash. The decomposition of low melting point mineral CaSO₄ was inhibited at 4 MPa, and the formation of Na₆Ca₂Al₆Si₆O₂₄(SO₄)₂ from NaAlSiO₄ and CaSO₄ was promoted significantly with increasing additive dosage. Furthermore, the inhibition mechanism of sodium and sulfur released from coal ash by silicon oxide under high pressure was proposed.

The fluorescence characteristics of coal macerals can be used as one of the indexes to evaluate the properties of coking coal. In this work, a single-wavelength laser with a wavelength of 360 nm was used as the excitation source to excite the surface of particulate block under a polarizing microscope. Effect of excitation time on fluorescence characteristics of the macerals was studied. The relationship between spontaneous fluorescence intensity and the excitation time of each maceral of six kinds of coking coals show that the fluorescence characteristics of coal macerals are related to the type and metamorphism of coal. The excitation time has a certain effect on the fluorescence parameters of the macerals. By comparing the relative fluorescence intensity values under different excitation times, it is found that the mean relative fluorescence intensity within 15 s can be used as an optical parameter to characterize the structure and metamorphic grade of different macerals. The essence of this method is to express movement of electrons in outer layer of nucleus by macroscopic fluorescence spectrum and relative fluorescence intensity of the initial state value and simplify microscopic complexity into macroscopic and numerical form generally accepted.

Highly efficient and environmentally friendly utilization of coal gasification slag is a hot research subject in the coal chemical industry at present. The preparation of activated carbon with a flotation refined carbon from gasification slag, a long flame coal, a high temperature coal tar containing 70% asphalt and an active agent in proper proportion was carried out. The influence of activation temperature and time on the surface properties and compressive strength of the produced activated carbon was investigated in a tube furnace. The oxygen functional group, pore structure and absorption performance of the produced activated carbon were characterized by FT-IR, N₂ adsorption-desorption, SEM and iodine adsorption. The COD removal from biochemical waste water by the produced activated carbon was verified. The results show that the key factors for the effective formation and expansion of pore are the suitable activation temperature and time for the floatation refined carbon from gasification slag as the feedstock. The activated carbon prepared by carbonization at 550 °C for 30 min and steam activation at 950 °C for 2 h exhibits a crisscross morphology of organic carbon components and minerals. The surface area, pore capacity and average pore diameter are 566 m²/g, 0.5611 mL/g and 5.1 nm, respectively, with the characteristics of a concentrated pore distribution and a certain quantity of mesopore. Both iodine value (650 mg/g) and methylene blue value (128 mg/g) meet the requirements of the Chinese standard “Technical Specifications and Test Methods of Activated Carbon for Purification of Industrial Wastewater”. The COD in biochemical waste water treated by the activated carbon for 60 min with a solid-to-liquid ratio of 0.6 g/L can be reduced to lower than 30 mg/L, meeting the B class water quality of the Chinese standard “Integrated Discharge Standard of Water Pollutants” (DB11/307—2013).

In this study, the thermal degradation mechanism of avermectin (AVM) was analyzed via experiments and density functional theory calculations (DFT). The experimental results of AVMD pyrolysis indicated that the removal rate of AVM residues reached peak value of 99.88% above 250 °C. The main product of AVM pyrolysis was alcohols. Based on the C–O bonds breaking, four potential degradation pathways were proposed. The findings of the calculations were in agreement with those of the experiments. These results provide theoretical and empirical guidance for the development of safe antibiotic disposal technology.

An efficient dehydrogenation catalyst is crucial for the application of ammonia borane (NH₃BH₃, AB) as a solid chemical hydrogen storage material. In this work, a kind of nitrogen-doped rice husk activated carbon (N-RHC) was prepared by roasting melamine and rice husk at high temperature under nitrogen atmosphere. With N-RHC as the support, the rice husk-based carbon supported ruthenium catalyst (Ru/N-RHC) was prepared through impregnation with the RuCl₃ solution and its catalytic performance in the hydrolysis of ammonia borane to produce hydrogen was investigated. The results indicate that the Ru/N-RHC catalyst with a Ru loading of 5% performs excellently in the hydrolysis of ammonia borane; the reaction turnover frequency (TOF) reaches 83.71 min⁻¹ and the apparent activation energy decreases from 88.9 to 64.9 kJ/mol under light irradiation. In addition, the hydrogen production rate is positively correlated with the content of ammonia borane and catalyst.