Extraction Of Naphthalene From Pitch Spheres For The Preparation Of Spherical Activated Carbons

Pitch-based spherical activated carbon (PSAC) has been widely used as ideal adsorbent in the fields of oral medications, blood purification, catalyst carrier, military protective equipment, chromatographic column supporter and so on, mainly due to its superior physiochemical properties, such as high mechanical strength, large specific surface area, good spherical degree, smooth surface and excellent adsorption performance. Naphthalene is one of key raw materials, which is added into the high-softening-point pitch to increase the fluidity, allowing the formation of pitch spheres via an emulsion sphering method. The obtained pitch spheres were further extracted to remove the naphthalene and others small organic molecules, recovering the softening point of the pitch. This extraction step is the key for the successful oxidation stability and carbonization/activation process. However, the extraction solvent, generally N-hexane, is very expensive and very volatile, making the extraction being one of core cost-controlled steps for the preparation of PSAC. To lower the cost and broaden the applications of PSAC, developing a new cost-effective extraction solvent is highly necessary.In this work, we successfully employed methanol as a low cost, relatively green solvent for the extraction of naphthalene from the pitch spheres. The influences of process conditions, such as extraction temperature, stirring rate and extraction time on methanol extraction kinetics were investigated in comparison to the N-hexane extraction. The results confirmed that the extraction efficiency of methanol was almost the same with the n-hexane. The highest extraction rate with methanol was achieved as63.67%at the temperature of30℃and the stirring rate of27rpm. The extraction equilibrium time is generally within24h.The as-extracted pitch spheres were further treated by the pre-oxidation, carbonization and activation. The results showed that the oxidation and carbonization yields, surface appearance and element content of the pitch spheres were similar regardless of the extraction process. The PSAC extracted by methanol and N-hexane had almost same total volume. However, the methanol-extracted samples exhibited significantly larger micropore size and contained considerable mesopores with pore size of2-3nm. Moreover, the methanol-extracted samples showed higher strength. Our encouraging results demonstrated that methanol is a suitable solvent instead of the n-hexane for the extraction of naphthalene.