Study On The Upgrading Of Shaanxi Coal By Catalytic Depolymerization

Pyrolysis is an important method for producing high value-added chemicals.However,the low tar yield and poor oil quality limit the industrialization process.Catalytic pyrolysis can change the activation energy of chemical bonds cleavage,and make more small molecules break from the coal structure under relatively mild conditions,and then improve the conversion rate of coal pyrolysis.However,during the traditional catalytic pyrolysis process,a large amount of catalysts are all needed,which would raise a host of problems such as high production cost,serious corrosion equipment and the difficult recovery of the catalyst.Based on this,a novel catalytic pyrolysis concept named as catalytic depolymerization is proposed by our team,in which the catalyst could be added into the coal structure with the help of the adjunct reagents and then more small molecules could be obtained by catalytic depolymerization the bridge bonds in the macromolecule structure of coal,thereby increasing the tar yield.In this study,a Shaanxi coal?SX?is selected.This type of coal is rich in reserves,low in price,and highly volatile.It is suitable as a raw material for pyrolysis.However,the total sulfur content of coal is 2.10%,which inorganic sulfur content 54.29%of the total sulfur.During the pyrolysis process most of the sulfur remains in char in a stable form,which is unfavorable to the environment and the use of char combustion and gasification.resulting in lower quality of char.The literature indicates that the physical floatation method has the advantages of conventional equipment,simple process,etc.,and can effectively reduce the content of inorganic sulfur in coal.Therefore,in this paper,before the pyrolysis of SX coal,it is necessary to preprocess with the use of different density of zinc chloride solution to reduce the sulfur content in coal samples.The desulfurization effects of zinc chloride solutions with different densities,the pyrolysis characteristics of upper coal,and the effect of catalysts on the SX coal and DE_1.4.4 coal?prepared when the density was 1.40 g/cm³?pyrolysis characteristics are investigated.Firstly,the effects of zinc chloride solutions with different densities on the yield of floating coal,and the removal effect of total sulphur and forms of sulfur in floatation are investigated.The results show that the yield of floating coal decreases with decreasing floatation density,When the density level is 1.6 g/cm³,the upper float coal(DE_1.6)yield is 92%,the upper float coal yield is 80%at 1.4g/cm³,and the upper float coal(DE_1.3)yield is 47%at 1.3 g/cm³.The total sulphur content of the floating coal decreases with decreasing floatation density,which is reduced from the 2.10%of SX raw coal to 1.31%for DE_1.6 coal,1.17%for DE_1.4coal,and 1.19%for DE_1.3 coal.Among them,sulfate sulfur is reduced from 0.16%of SX raw coal to 0.04%for DE_1.6 coal,0.04%for DE_1.4 coal,and 0.03%for DE_1.3coal.The pyrite sulfur decreased from 0.98%of the SX raw coal to 0.42%for DE_1.6 coal,0.27%for DE_1.4 coal,and 0.43%for DE_1.3 coal.The organic sulfur decreased from 0.96%of the SX raw coal to 0.85%for DE_1.6 coal,0.86%for DE_1.4coal,and 0.73%o for DE_1.3 coal.Secondly,the pyrolysis characteristics of floating coal at different densities are investigated.The results show that with the decrease of the floatation density,the yield of char decreased,while tar yield increased.The char yield decreased from 75.66%for SX coal to 73.78%for DE_1.6 coal,73.25%for DE_1.4 coal,and71.44%for DE_1.3 coal.The tar yield increased from 12.55%for SX coal to 12.77%for DE_1.6 coal,13.45%for DE_1.4 coal,and 15.07%for DE_1.3 coal.The floating coal getting from the low flotation density have higher vitrinite and inertinite content,and the aliphatic hydrocarbon functional groups in the floating coal are enriched.Finally,the SX coal and DE_1.4 coal are upgrading by the catalytic depolymerization.The results show that the SX coal and DE1.4 coal pyrolysis with the addition of CoCl₂ and Fe?NO₃?₃ catalysts have no obvious effect on tar yield,while FeCl₃ catalyst significantly increases tar yield.Combined with element analysis and thermogravimetric analyzer concluded that during the catalytic depolymerization of SX coal FeCl₃,CoCl₂ and Fe?NO₃?₃ catalysts facilitate the cracking of C_al-O and C_al-S bonds,during the catalytic depolymerization of DE_1.4 coal FeCl₃,CoCl₂ and Fe?NO₃?₃ catalysts facilitate the cracking of C_al-O bonds.