Experimental and mechanistic study on chemical looping combustion of caking coal

Under high-temperature batch fluidized bed conditions and by employing juye coal as the raw material,the present study determined the effects of the bed material,temperature,OC/C ratio,steam flow and oxygen carrier cycle on the chemical looping combustion of coal.In addition,the variations taking place in the surface functional groups of coal under different reaction times were investigated,and the variations achieved by the gas released under the pyrolysis and combustion of Juye coal were analyzed.As revealed from the results,the carbon conversion ratio and rate were elevated significantly,and the volume fraction of the outlet CO_(2)remained more than 92%under the oxygen carriers.The optimized reaction conditions to achieve the chemical looping combustion of Juye coal consisted of a temperature of 900℃,an OC/C ratio of 2,as well as a steam flow rate of 0.5 g·min^(-1).When the coal was undergoing the chemical looping combustion,volatiles primarily originated from the pyrolysis of aliphatic-CH_(3)and-CH_(2),and CO and H_(2)were largely generated from the gasification of aromatic carbon.In the CLC process,H_(2)O and CO_(2)began to separate out at 270℃,CH4 and tar began to precipitate at 370℃,and the amount of CO_(2)was continuously elevated with the rise of the temperature.

Characteristics of reactivity and structures of palm kernel shell (PKS) biochar during CO_2/H_2O mixture gasification

Palm kernel shell(PKS)biochars with different levels of carbon conversion were initially prepared using a tube furnace,after which the reactivity of each sample was assessed with a thermogravimetric analyzer under a CO_2 atmosphere.The pore structure and carbon ordering of each biochar also examined,employing a surface area analyzer and a Raman spectroscopy.Thermogravimetric results showed that the gasification index R_sof the PKS biochar decreased from 0.0305 min^(-1) at carbon conversion(x)=20% to 0.0278 min^(-1)at x=40%.The expansion of micropores was the dominant process during the pore structure evolution,ad mesopores with sizes ranging from 6 to 20,48 to 50 nm were primarily generated during gasification under a CO_2/H_2O mixture.The proportion of amorphous carbon in the PKS biochar decreased significantly as x increased,suggesting that the proportion of ordered carbon was increased during the CO_2/H_2O mixed gasification.A significantly reduced total reaction time was observed when employing a CO_2/intermittent H_2O process along with an 83.46% reduction in the steam feed,compared with the amount required using a CO_2/H_2O atmosphere.

Performance of anaerobic fluidized bed microbial fuel cell with different porous anodes

Anode materials were used to construct microbial fuel cells(MFCs),and the characteristics of the anodes were important for successful applied performance of the MFCs.Via the cyclic voltammetry(CV)method,the experiments showed that 5 wt%multiwalled carbon nanotubes(MWNTs)were optimal for the PANI/MWNT film anodes prepared using 24 polymerization cycles.The maximum output voltage of the PANI/MWNT film anodes reached 967.7 mV with a power density of 286.63 mW·m-2.Stable output voltages of 860 mV,850 mV,and870 mV were achieved when the anaerobic fluidized bed microbial fuel cell(AFBMFC)anodes consisted of carbon cloth with carbon black on one side,copper foam and carbon brushes,respectively.Pretreatment of the anodes before starting the AFBMFC by immersion in a stirred bacterial fluid significantly shortened the AFBMFC startup time.After the AFBMFC was continuously run,the anode surfaces generated active microbial catalytic material.

The effect of the Ce content on the oxidative dehydrogenation of propane over CrOy-CeO2/γ-Al2O3 catalysts

A series of CrOy(17.5 wt%)-CeO2(X wt%)/γ-Al2O3 catalysts(X=0,0.5,2,5,8)with various Ce contentswere prepared by a wetness impregnation method and were applied to the dehydrogenation of propane to propylene at 550℃ and 0.1 MPa.The prepared catalysts were characterized by BET,H2-TPR,O2-TPD,XPS,XRD,SEM-EDS and Raman spectroscopy.Among the prepared catalysts,the 17.5Cr-2Ce/Al catalyst with the largest amount of lattice oxygen exhibited the best catalytic performance for the dehydrogenation of propane to propylene with lattice oxygen.The decreased presence of oxygen defects and reducibility were the factors responsible for the improved dehydrogenation activity of the catalysts.The CeO2 layer could inhibit the evolution of lattice oxygen(O2^−)to electrophilic oxygen species(O2^−),and the oxygen defects on the catalyst surfacewere reduced.The inhibited lattice oxygen evolution prevented the deep oxidation of propane or propylene,the average COx selectivity decreased from 24.41%(17.5Cr/Al)to 5.71%(17.5Cr-2Ce/Al),and the average propylene selectivity increased from 60.15%(17.5Cr/Al)to 85.05%(17.5Cr-2Ce/Al).

Influence of CaO and HZSM-5 on oxygen migration in Chlorella vulgaris polysaccharide pyrolysis

With polysaccharides of Chlorella pyrenoidosa as the raw material,the effects of CaO and HZSM-5 on the yield of bio-oil and the oxygen content in each phase in the pyrolysis of Chlorella vulgaris polysaccharides(CVP),which occurred in a tube furnace at 600℃,were comprehensively investigated.The reaction path of deoxidation was also analyzed by TG,GC and GC-MS.The GC-MS analysis of liquids showed that liquids from the pyrolysis of chlorella polysaccharides included a range of light oxygenated compounds(e.g.,furans,ketones and phenols),and the oxygen content of furan compounds decreased significantly with CaO and HZSM-5.Compared with the direct pyrolysis of polysaccharides(CVP),the catalytic pyrolysis contributed to the decrease in the oxygen content of organic components by 7.32%and 5.76%.The GC analysis showed that there was a remarkable downtrend in the release of oxygen-containing gas(CO and CO_(2)),and the emission of CO_(2) decreased from 53.11%to 32.92%.The results of the thermogravimetric analysis indicated that the reaction paths of deoxidation in the pyrolysis process of polysaccharides(CVP)with CaO and HZSM-5 varied from those of the direct pyrolysis process:the catalytic pyrolysis with HZSM-5 promoted the conversion of carbohydrate from furans to aromatics over strong acid sites,which was consistent with previous studies;CaO not only acted as a catalyst but also participated in the reaction to change the reaction paths.All results and findings can help to further understand the thermochemical utilization of CPP for bio-oil.

Cotton stalk activated carbon-supported Co-Ce-B nanoparticles as efficient catalysts for hydrogen generation through hydrolysis of sodium borohydride

Porous cotton stalk activated carbons(CSAC)were prepared by phosphoric acid activation of cotton stalks in a fluidized bed.The CSAC-supported Co-B and Co-Ce-B catalysts were prepared by the impregnation-chemical reduction method.The samples were characterized by the nitrogen adsorption,XRD,FTIR and TEM measurements.The effects of the sodium borohydride(NaBH_(4))and sodium hydroxide(NaOH)concentrations,reaction temperature and recyclability on the rate of NaBH_(4)hydrolysis over the CSAC-supported Co-Ce-B catalysts were systematically investigated.The results showed that the agglomeration of the Co-Ce-B nanoclusters on the CSAC support surface was significantly reduced with the introduction of cerium.The CSAC-supported Co-Ce-B catalyst exhibited superior catalytic activity and the average hydrogen generation rate was 16.42 L min^(−1)g^(−1)Co at 25℃,which is higher than the most reported cobalt-based catalysts.The catalytic hydrolysis of NaBH_(4)was zero order with respect to the NaBH_(4)concentration,and the hydrogen generation rate decreased with the increase in the NaOH concentration.The activation energy of the hydrogen generation reaction on the prepared catalyst was estimated to be 48.22 kJ mol^(−1).A kinetic rate equation was also proposed.

CaSO_4载氧体-煤化学链气化过程气化剂的影响（英文）

The chemical looping gasification uses an oxygen carrier for solid fuel gasification by supplying insufficient lattice oxygen. The effect of gasifying medium on the coal chemical looping gasification with Ca SO4 as oxygen carrier is investigated in this paper. The thermodynamical analysis indicates that the addition of steam and CO2 into the system can reduce the reaction temperature, at which the concentration of syngas reaches its maximum value.Experimental result in thermogravimetric analyzer and a fixed-bed reactor shows that the mixture sample goes through three stages, drying stage, pyrolysis stage and chemical looping gasification stage, with the temperature for three different gaseous media. The peak fitting and isoconversional methods are used to determine the reaction mechanism of the complex reactions in the chemical looping gasification process. It demonstrates that the gasifying medium(steam or CO2) boosts the chemical looping process by reducing the activation energy in the overall reaction and gasification reactions of coal char. However, the mechanism using steam as the gasifying medium differs from that using CO2. With steam as the gasifying medium, parallel reactions occur in the beginning stage, followed by a limiting stage shifting from a kinetic to a diffusion regime. It is opposite to the reaction mechanism with CO2 as the gasifying medium.