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.

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.

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.