THE COKING PROPERTIES AND STATES OF AN INDUSTRIAL W-Ni USED CATALYST

PASCA, ESR and Microreactor, have been used to study the states and properties of coking deposits on catalyst. The results indicate that the C exists as three types of states on catalyst surface. The first and second types of carbon are the main reason of the catalyst deactivation, but the third type has a promoting role in n-C_7 hydrocracking reaction. The S_s-C interacts strongly with catalyst, forming metal-carbon-support interaction (MCSI).

Preparation and coking properties of coal maceral concentrates

The concentrates with different maceral contents were obtained from Kailuan coking coals with different coal ranks(Ro;ranvarying from 0.88%to 1.73%)by float–sink separation in lab.Then these concentrates were characterized by proximate analysis,ultimate analysis,petrography analysis and coking index determination.The results show that the vitrinite is characterized as nature of lower carbon content,higher hydrogen content,higher volatile matter and stronger caking property compared to inertinite.The relationships between variation rate of volatile matter and maximum volatile matter and coal ranks are identified,and a linear model is developed for fast determination of the maceral contents.Compared to inertinite-rich concentrate,the blending ratio of vitrinite-rich concentrate is increased by 13%,which is considered to be a potential technique based on maceral separation for expanding the coking coal resources.

Characteristics of Preheating Combustion of Power Coal with High Coking Properties

Yankuang coal with the high coking property is difficult to use through direct combustion.The main purpose of this paper is to study the combustion characteristics and NO_(x)emissions of this type of coal using preheating combustion technology.The experimental results show that after the pulverized coal is preheated,the char residue characteristic is significantly reduced from 5 to 1.During the preheating process,the preheating temperature is stable at about 910°C,and the particle size of char after preheating is reduced,and the pore structure and specific surface areas are increased.The combustion temperature of preheated fuel is stable at around 1100℃,and the combustion efficiency can reach more than 99%under different conditions.Changing the structure of the secondary air nozzles during the preheating combustion process can influence the characteristics of NO_(x)emissions.The NO_(x)emission of the central nozzle is about 112 mg/Nm~(3)lower than that of the annular nozzle.Changing the tertiary air distribution modes can reduce the final NO_(x)emissions to 215 mg/Nm~3(@6%O_2),and the corresponding conversion ratio of fuel N to the final NO_(x)is 4.2%.The results of this experiment prove that the Yankuang coal can achieve stable combustion by preheating combustion technology,and this proposed a new way for the utilization of Yankuang coal.

Coking properties of thermal soluble constituents of coals by N-methyl-2-pyrrolidone solvent

Four types of coals, KL, XB, ZS and GD with different coal ranks, were dissolved with the organic solvent N-methyl-2- pyrrolidone at 350 ℃ and around 3.0 MPa pressure to obtain thermal soluble constituents （TSCs）. The yield, component and maceral group were investigated as well as their coking properties, including caking index and thermoplasticity. The results indicated that the yields of the four coals were of the following order： KL 〉 XB 〉 ZS 〉 GD. Based on the yield and the vitrinite content, coals were ranked from high to low. The ash contents of TSCs were significantly less than that of raw coals, and the TSCs contain more light components, leading to an increase in volatile matter. The patterns of Fourier transform infrared spectroscopy indicated that carbonyl was enriched in TSCs. Regarding the maceral group, TSCs were mainly composed of vitrinite which is the main reactive material and converts into binder phase in cokemaking process. Higher caking index values and fluidity were obtained in TSCs compared with the raw coals. The coking experiments with different amounts of TSCs addition were carried out. The results demonstrated that the proper TSCs addition could enhance the coke strength due to its high caking index and good fluidity.

Effects of surface chemical properties of activated coke on selective catalytic reduction of NO with NH_3 over commercial coal-based activated coke

Surface chemical properties of typical commercial coal-based activated cokes were characterized by Xray photoelectron spectroscopy(XPS) and acid-base titration, and then the influence of surface chemical properties on catalytic performance of activated cokes of NO reduction with NH3 was investigated in a fixed-bed quartz micro reactor at 150 ℃. The results indicate that the selective catalytic reduction(SCR) activity of activated cokes with the increase of its surface acidic sites and oxygen content,obviously, a correlation between catalytic activity and surface acidic sites content by titration has higher linearity than catalytic activity and surface oxygen content by XPS. While basic sites content by acid-base titration have not correlation with SCR activity. It has been proposed that surface basic sites content measured by titration may not be on adjacent of acidic surface oxides and then cannot form of NO2-like species, thus the reaction of reduction of NO with NH3 have been retarded.

Steam reforming of acetic acid over Ni/biochar of low metal-loading:Involvement of biochar in tailoring reaction intermediates renders superior catalytic performance

Biochar is a reactive carrier as it may be partially gasified with steam in steam reforming,which could influence the formation of reaction intermediates and modify catalytic behaviors.Herein,the Ni/biochar as well as two comparative catalysts,Ni/Al_(2)O_(3) and Ni/SiO_(2),with low nickel loading(2%(mass))was conducted to probe involvement of the varied carriers in the steam reforming.The results indicated that the Ni/biochar performed excellent catalytic activity than Ni/SiO_(2) and Ni/Al_(2)O_(3),as the biochar carrier facilitated quick conversion of the -OH from dissociation of steam to gasify the oxygen-rich carbonaceous intermediates like C=O and C-O-C,resulting in low coverage while high exposure of nickel species for maintaining the superior catalytic performance.In converse,strong adsorption of aliphatic intermediates over Ni/Al_(2)O_(3) and Ni/SiO_(2) induced serious coking with polymeric coke as the main type(21.5%and 32.1%,respectively),which was significantly higher than that over Ni/biochar(3.9%).The coke over Ni/biochar was mainly aromatic or catalytic type with nanotube morphology and high crystallinity.The high resistivity of Ni/biochar towards coking was due to the balance between formation of coke and gasification of coke and partially biochar with steam,which created developed mesopores in spent Ni/biochar while the coke blocked pores in Ni/Al_(2)O_(3) and Ni/SiO_(2) catalysts.

Effect of carbon solution-loss reaction on properties of coke in blast furnace

The pore structure of coke under CO2 atmosphere was investigated by the carbon solution-loss reaction experiment.The results show that the pore size distribution of coke gradually changes from dispersion to relative concentration with the increase in carbon loss rate,but it tends to be dispersed again in the late stage of the reaction,and the pore volume and specific surface area also increase first and then decrease with the increase in carbon loss rate.Scanning electron microscopy results show that the evolution of coke pores is from the formation of micropores to the expansion of micropores,and finally the micropore and mesopores collapse to form a large number of string holes.The chemical bonds and functional groups of different reacted cokes were analyzed by Fourier-transform infrared spectroscopy.Furthermore,the microstructure of reacted cokes was analyzed by optical microscopy,and then the ordering of the affinity of different microstructures with CO2 was given.The volume hypothesis which was the theory about energy size of comminution was adopted to analyze the degradation behavior of reacted cokes.The breakage energy of reacted cokes was calculated by volume hypothesis,and the power consumption coefficient CK of different reacted cokes was determined by drum experiment,and then the degradation behavior of reacted cokes under different power consumptions was predicted.

Mg-Al-hydrotalcite with alkaline sites protects Ni/KIT-6 from formation of amorphous coke in glycerol steam reforming via tailoring reaction intermediates

During steam reforming,the performance of a catalyst and amount/property of coke are closely related to reaction intermediates reaching surface of a catalyst.Herein,modification of reaction intermediates by placing Mg-Al-hydrotalcite above Ni/KIT-6 catalyst in steam reforming of glycerol was conducted at 300 to 600°C.The results revealed that the catalytic activity of Ni/KIT-6 in the lower bed was enhanced with either Mg1-Al5-hydrotalcite(containing more acidic sites)or Mg5-Al1-hydrotalcite(containing more alkaline sites)as upper-layer catalyst.The in situ infrared characterization of steam reforming demonstrated that Mg-Al-hydrotalcite catalyzed the deoxygenation of glycerol,facilitating the reforming of the partially deoxygenated intermediates over Ni/KIT-6.Mg-Al-hydrotalcite as protective catalyst,however,did not protect the Ni/KIT-6 from formation of more coke.Nonetheless,this did not lead to further deactivation of Ni/KIT-6 while Mg5-Al1-hydrotalcite even substantially enhanced the catalytic stability,even though the coke was much more significant than that in the use of single Ni/KIT-6(52.7%vs.28.6%).The reason beneath this was change of the property of coke from more aliphatic to more aromatic.Mg5-Al1-hydrotalcite catalyzed dehydration of glycerol,producing dominantly reaction intermediates bearing C=C,which formed the catalytic coke of with carbon nanotube as the main form with smooth outer walls as well as higher aromaticity,C/H ratio,crystallinity,crystal carbon size,thermal stability,and resistivity toward oxidation on Ni/KIT-6 in the lower bed.In comparison,the abundance of acidic sites on Mg1-Al5-hydrotalcite catalyzed the formation of more oxygen-containing species,leading to the formation of carbon nanotubes of rough surface on Ni/KIT-6.