Effects Of Inorganic Components On Degradative Solvent Extraction Of Low-rank Coals

With the large consumption of high-quality coals and increasing attention to environmental protection,the efficient and clean upgrading utilization of low-rank coal has received more and more attention.Low-rank coal has significant advantages such as abundant reserves,shallow burial,easy mining,and good reactivity.But its high moisture content,high oxygen content,low carbon content,low calorific value and other shortcomings have severely restrict its effective utilization.Therefore,the development of efficient lowrank coal deoxygenation and dewatering upgrading technology is of great significance for the effective utilization of low-rank coal.Based on this situation,degradative solvent extraction of low-rank coal was proposed which could realize deoxygenation and dewatering of low-rank coal under mild conditions.This technology mainly uses organic solvents,such as 1-methylnaphthalene,to upgrade low-rank coals and obtain ash-free extracts.And the extracts has been widely used in fine chemicals,carbon materials and many other aspects.In this paper,firstly,the effects of water on the yields and physicochemical properties of degradative solvent extraction of low-rank coal was studied.Then the transformation characteristic of typical minerals during degradative solvent extraction was discussed.Finally,the effect of different forms of minerals on the degradative solvent extraction of low-rank coal was studied,which laid the foundation for the practical application of this upgrading technology.By investigating the effects of water on the degradative solvent extraction of low-rank coal,it was found that after drying treatment,the extraction yield of the low-rank coal was significantly reduced,mainly due to the difficulty of the solvent to enter the coal pore structure after the removal of water molecules.With the deoxygenation and decarboxylation reactions at higher temperatures,a large number of cross-linking reactions are occurred between coal molecules,thereby inhibiting degradative solvent extraction.The addition of water could promote the yield of the extraction product,mainly because the water participates in the degradative solvent extraction process,which increases the extraction yield.Elemental analysis,thermogravimetric analysis,FT-IR spectroscopy,and high-resolution solid nuclear magnetic resonance results showed that water had little effect on the physicochemical properties of solid products,which proved the wide application of this upgrading method.Through the research on the migration and transformation of typical minerals during the degradative solvent extraction,it was found that more than 93% of the K,Ca,Na and Mg in the raw coal were transferred to the extraction residue RD,and only a small amount was transferred to SL and DP.Therefore,ash is mainly concentrated in the extraction residue RD,while SL and DP are almost ash-free.Moreover,the Cu,Pb and Zn in SL were lower than 130 ?g/g.During the degradative solvent extraction process,only insoluble K and Ca are transferred to SL.SL contain water-soluble,acid-soluble and insoluble Na and Mg,and the proportion of water-soluble is the highest.In DP,Ca exist in insoluble form,K exist in acidsoluble and insoluble forms,and Na and Mg exist in water-soluble,acid-soluble,and insoluble forms,with the most was water-soluble form.The distribution of the ions in the RD is similar to that of the raw coal.This is mainly because the main carbon skeleton structure of the raw coal is retained in RD after degradative solvent extraction.After the water leaching or acid leaching treatment,the yields of degradative solvent extraction was promoted.The effect of water leaching treatment is small,while the effect of acid leaching treatment is more obvious.For Naomaohu coal and Huolinhe coal,after acid leaching,the total yield of SL and DP increased by 12.09% and 3.92% respectively,and the increase in DP yield was the main factor.Water leaching or acid leaching treatments hardly change the functional groups of SL and DP.The acid leaching treatment could affect the chemical structure of RD,mainly removing some ash components.The reason that the acid leaching treatment can significantly improve the extraction yield mainly comes from two factors.The first is that the acid leaching process can destroy the pore structure of the coal sample,making it loose,and reducing the resistance of the solvent to enter the coal structure.When the raw coal was used for degradative solvent extraction,the carboxyl groups between the coal molecules and the metal cation form a stable metal cross-linking bond that cannot be destroyed under the action of the solvent,resulting in a reduction in extraction yield.After leaching treatment,the active hydrogen ions replace the metal cations in the coal,breaking the metal cross-linking bonds in the coal,thereby improving the extraction yield.