Electrochemical Desulfurization Of Coal Basic Research

A number of coal cleaning methods have been developed,which range from simple crushing and pulverizing to reduce inorganic sulfur,to extensive chemical treatment to reduce inorganic sulfur and a part of organic sulfur.However,an effective and economic process to remove finely disseminated inorganic sulfur and organic sulfur remains to be found.Recently, electrochemical desulfurization,as an economic,lower cost and milder sulfur removal method, has received more attention.Usually,the high sulfur coal was electrolyzed in a diaphragm cell in order to eliminate the sulfur in coal.The anode is a large-area and expensive Pt foil electrode.In the process of desulfurization,the membrane was easily plugged.So a small-area platinum anode or large-area graphite was used to study the electrochemical cleaning of coal in a cell without membrane in this thesis.The effects of electrolytic conditions including potential,temperature,time,kinds and the concentration of catalysts,concentration of coal as well as forms of sulfur in coal on the rate of desulfurization were studied.According to the relationship between the rate of desulfurization and electrolytic conditions,the math models of desulfurization of coal-derived pyrite and pyrite in coal were established in use of chemical kinetic and thermodynamic principles.Then,the reactions of desulfurization were postulated by means of some necessary analytic methods such as XPS,XRD,FT-IR and TG.At last,the influence of electrolysis on the organic matter of coal was also examined.The main results of this thesis are summarized as follows:(1)The effects of electrolytic conditions on desulfurization in acid or alkaline media in the cell without membranes were studied.Under the selective conditions,over 63 percent of total sulfur,60 percent of organic sulfur,I00 percent of inorganic sulfur and a part of ash content can be removed.(2)By means of the concept of electrocatalysts,the effect of catalysts on the desulfurization in acid media was studied.The experimental results show that Mn³⁺is better than Fe³⁺as an electrocatalysts for desulfurization and the rate of desulfurization is related to the kinds and concentration of catalysts,electrolytic temperature,time and so on.If Mn³⁺is selected as the catalyst for desulfurization,the 100 percent of inorganic sulfur and a part of organic sulfur can be removed under these conditions:the room temperature(298K),8h,smallarea Pt electrode as anode,10 percent of H₂SO₄.(3)It is the first time to study the desulfurization of coal-derived pyrite by electrolysis. When MnSO₄ was used as the catalyst,100 percent of pyrite can be oxidized into SO₄^2- and Fe³⁺at 298K and other selective electrolytic conditions and no pollutant is emitted. Therefore the electrolysis may be a better method by which pyrite can be oxidized into useful products than common pyritic utilization ways.(4)By aid of law of chemical thermodynamics and new analytic instntrnents,the mechanism of desulfurization of coal in acid or alkaline media was investigated.In alkaline media,the pyritic sulfur is oxidized into SO₄^2-,Fe(OH)₂,Fe(OH)₃,and organic sulfur into sulfone or sulfoxide by the active oxygen from anode surface.Then sulfone or sulfoxide can be eliminated by hydrolysis in alkaline media.In acid media,the pyritic sulfur can be oxidized into SO₄^2-and Fe³⁺by Mn³⁺or Fe³⁺from anode surface,While organic sulfur can react with Mn³⁺or Fe³⁺and a part of them can be oxidized into sulfone or sulfoxide.At last sulfone or sulfoxide is leached into solutions by hydrolysis.(5)By means of chemical kinetic principles,the desulfurization math models of coalderived pyrite and pyrite in coal were established.(a)the desulfurization model of coal-derived pyriteThis model is a shrinking core model.By this model,the apparent activity calculated is 7.89KJ/mol.(b)The desulfurization model of pyrite in coalThe pyrite in coal can be divided into the 'high reactive' pyrite and 'low reactive' pyrite.So the relation between the kinetic equation of desulfurization according to Langmuir-Hinshelwood approach is as follow:By this model,the apparent activity calculated is 10.44KJ/mol.(6)The influence of electrolysis on the organic matter of coal was studied.It is limited if the rate of organic sulfur removal is not high.Otherwise the influence of electrolysis on the organic matter of coal is strengthened and the yield of cleaning coal becomes lower.