Regulation Of Pore Structure Of Coal-based Granular Activated Carbon Prepared By Briquetting Method

The expanding application fields and increasing production scale for activated carbon require the physical properties such as particle size, strength, density of activated carbon to be enhanced. In terms of preparation technics, coal based granular activated carbons can be divided into three types as coal crushing activated carbon, columnar activated carbon and briquetted activated carbon. Now preparing activated carbon by briquetting method is the priority for briquetted activated carbon keeps the excellent mechanical properties, stable adsorption capacity and adjustable porosity.The application value of activated carbon(AC) roots in the strong adsorption capacity. However, the variety of molecular size for different adsorbates demands activated carbon with coordinate pore structure, which determines the adsorption capacity of AC for the adsorbates. Thus, the question comes that how to regulate the pore structure of AC to improve its application value. By now, research on regulation methods of pore structure of AC is in process but hasn't been combined with preparation technique of briquetted activated carbon. The effects of coal rank, coal blending, additive, carbonization and activation processes on porosity of briquetted activated carbon is not clarified.In this paper, coals of different ranks including lignite, subbituminous coals and anthracite were chosen to be the raw materials for the preparation of coal-based activated carbon by briquetting method. The pyrolysis reactivity and gasification reactivity of the coals or coal-based granules were evaluated by thermo-gravimetric Analysis(TGA). The microcrystalline structure and minerals of the chars were analyzed by X-Ray Diffraction(XRD). The magenetic properties of the briquetted activated carbon were tested by vibrating sample magnetometer(VSM). The porosity of the briquetted activated carbons was characterized by N2 adsorption-desorption isotherms. The effects of coal ranks, coal blending, additives and activation conditions on the pore structure of activated carbons were investigated. And their mechanisms were discussed.The main contents of this paper conclude: 1) Pore structure of briquetted AC from coals of different ranks; 2) Additivity of pore structural parameters of briquetted AC from blending coals; 3) Relationship between crystalline structure of char(precursor) and porosity of briquetted AC; 4) Effects of FeCl3 addition on the porosity and magnetic properties of briquetted AC.The main conclusions of this paper are as following:1) Coals of different ranks are transformed into chars with different crystalline structure and mineral componsitions.The higher the coalification degree(Cdaf) of coal, the higher the graphitization degree(G) of char, leading to lower gasification reactivity. The Ca- and Fe- minerals in the char improve the gasification reactivity and generate higer burn-off.The specific surface area SBET and average pore size da increases and decreases with the rising Cdaf, respectively. The high ash content in the raw coal reduces SBET, while Ca- and Fe- minerals are helpful to mesopore development.2) There is a certain additivity between process parameters(charring yield, YG and burn-off, B) and pore structural parameters of briquetted AC from blending coals.For arbitrary coal blend, the relative error(?) between fitted values and experimental values of CY or B is small than 6%.The the relative error(?) between fitted values and experimental values of pore structural parameters of AC from blend of non-caking coals is small than 10%, with overlapped pore size distribution.However, while caking coal participates in the blend, ? may reach 25%, and the fitted and experimental pore size distributions differ from each other.3) In the preparation of briquetted AC from coal blend, the coal nature or the mass ratio of coals determines the porosity and the path of pore development while the activation conditions affect the degree of pore development. The parameters affecting B and Iodine value E are in a descending order: activation temperature T > activation time t> steam flow rate q.4) Increasing carboniziton heating rate and KOH addition reduces the graphitization degree(G) of char, improving gasification reactivity and leading to higher burn-off. However, briquetted AC from char of higher G value obtains larger SBET and pore volume at the same burn-off. In another word,more pores generate in the char of higher G value while the burn-offs are the same.5) Adding acidic FeCl3 solution into the raw coal powder endows activated carbon magnetic properties and affects pore structure. The different methods of addition results in the following different effects.Ion exchange method doesn't introduce any Fe3+ into low rank bituminous coal but reduces the contents of original Fe- and Ca- minerals in the chars for acid dissolution. This process is disadvantageous to the development of pore structure and magnetic properties of activated carbon.The effects of adding FeCl3 by mixing method and impregnation method are similar: Fe is formed from FeCl3 in carbonization process and affects the pyrolysis of coal based granulars: the weight loss rate is increased before 350?, but decreased between 350? and 600?. For Datong coal, the graphitization degree of char is decreased and the gasification reactivity is enhanced. For Lingwu coal, the graphitization degree of char is also decreased while the gasification reactivity is weakened because original Fe- and Ca- minerals dissolve in the acidic Fe Cl3 solution. Micropore volume and surface area of activated carbon are increased under the same activation conditions. The mixing method and impregnation method can effectively improve the magnetic properties of activated carbon.