Research On Preparation Of Granular Activated Carbon For Sugar Refining And Decolorizing

Granular activated carbon is hard, dustless and easily regenerated, therefore ithas been paid much attention in refining sugar.The activated carbon was made from Lingwu bituminous coal, Guizhou lean coal,bagasse and additives in this study. The preparation process is under the followingprocedures: extruding, carbonization and steam activation. An orthogonal experimentmethod was employed to research the optimum preparation conditions. At the sametime, the influence of coal type, blending ratio of coal and additives on carameldecolorizing rate and hardness of the resulted activated carbon was studied. Theresults show that the optimum preparation conditions of the activated carbon are thatthe ratio of Lingwu bituminous coal to Guizhou lean coal is8:2, the bagasseproportion is20%, the additive Aproportion is8%, the additive B proportion is1.5%,the carbonization temperature is550℃, the activation temperature is930℃and theignition loss rate is70%. The caramel decolorizing rate and hardness of the activatedcarbon at the conditions are97.44%and37.43%, respectively. Conditions, which theproportion of Guizhou lean coal is not more than40%of the total coal, the additive Ais between5%and8%and the additive B is less than1.5%, are in favor of highdecolorizing ability and high hardness. Adding some caking bituminous coals such ascoking coal isbeneficial to the hardness, but it is not conducive to the improvement ofdecolorizing ability.Nitrogen adsorption method and mercury intrusion method were used to studythe pore structure of the activated carbon. By the nitrogen adsorption data analysis,the caramel decolorizing rate of activated carbon is independent of specific surfacearea and total pore volume, but it has great relevance to the pore size distribution(PSD). Most apertures of activated carbon are in the range of0.6nm to1.4nm and2.8nm to4nm. The caramel decolorizing rate has significant linear negativecorrelation with the pore volume of apertures between0.61nm to0.79nm, and thevalue of R2is0.782; when the apertures are more than1.42nm, they begin to havepositive correlation. Reducing pores of the apertures between0.61nm to0.79nm andmaking them to larger pole diameter help to make the activated carbon with gooddecolorizing ability.By the mercury intrusion data analysis, the greater the total volume and theporosity, the higher the caramel decolorizing rate is. Most macroporous apertures of the activated carbon are in the range of1μm to4μm and70μm to170μm, and theaverage pore diameter of the activated carbon with high caramel decolorizing rate isabout3μm. More pores of the apertures between2μm to18μm, especially the pores ofthe apertures between2μm to4μm in the activated carbon help to enhance thedecolorizing rate.There are many functional groups measured by FT-IR such as alcohols, phenols,esters, quinones, carboxylic acid, benzene ring structure and fat species groups on thesurface of the activated carbon. With the improvement of caramel decolorizing rate ofactivated carbon, the species of surface functional groups on activated carbon will notobviously change, but the quantity and function of surface oxygen containingfunctional groups on the activated carbon can be increased and strengthened.