Preparation Of New Carbon Materials From Coal Hydroliquefaction Residue

Preparation of high specific area activated carbons (ACs) from high sulphur occurringcoal hydroliquefaction residue (CLR) is presented in this thesis. The CLR sample was treatedby oxidizing with KNO₃ followed by chemical activation with KOH. During oxidizingprocess of CLR powder, effects of KNO₃ content on formation of suitable carbide wereinvestigated at present. It has been shown that the most suitable conditions for carbidepreparation are as follows: at temperature of 400℃, with a content of oxidant of 10 % basedon mass of residue added, and in a 30 min of heating time. During the process of activationwith KOH, effects of carbonization temperature, alkali/carbon ratio, activation temperatureand activation time on the yield and the pore structure of the prepared ACs were investigatedthrough a series of experiments. The extensive study indicates that the optimum technologicalsteps are as follows: carbonization temperature-600℃for 60 min, impregnation ratio ofalkali/carbon-2.5:1, activation temperature-800℃with holding time being 90 rain. Theseconditions lead to 34 % yield of the activated carbon. Furthermore, the activated carbonprepared under the optimum conditions was characterizedby nitrogen adsorption at 77 K. Thespecific surface area, micropore volume and total pore volume of the activated carbon were1940 m²/g, 0.62 cm³/g and 1.06 cm³/g, respectively. The activated carbon has a narrowdistribution of micropore with diameter less than 1 nm. At last, the mechanism of formationof the prepared ACs is given in this paper. Results show that the treatment of preoxidationand chemical activation is a key step for the production of carbon materals. Because of thedifferent decomposing degree, KNO³ and KOH can play important role in the differenttemperature zone during heating treatment.In addition, activated carbon prepared under the optimum conditions has been used inadsorption. The adsorption capacity of activated carbon for benzene and thiophene in modeloil is much higher than that of the commercial activated carbon under the same conditions,implying that the activated carbons are of potential as adsorbent.Carbon nanotubes (CNTs) in large quantities also have been successfully obtained withCLR as the starting carbon source by the DC arc discharge technique. The synthesized CNTswere also characterized by Scanning electron microscopy (SEM), Transmission electronmicroscopy (TEM), High resolution transmission electron microscopy (HRTEM) and X-raydiffraction (XRD). The results showed that large quantities of straight CNTs with high degree of graphitization were obtained. The synthesized CNTs range in length from tens ofnanometers to several micrometres and the outer diameters of the CNTs are estimated to be ca.120 nm and the inner diameters of the CNTs are about 80 nm. In addition, the mineral mattersespecially the pyrite and pyrrhotite in the residue may also play an important role in theformation process of CNTs.