Hollow carbon microparticles prepared from spray-dried particles of a lignin aqueous solution

Abstract

An approach for manufacturing hollow carbon microparticles of various morphologies has been developed. The approach includes spray drying of an aqueous solution of lignin and inorganic compounds to prepare composite microparticles, followed by heat treatment, washing, and drying. The morphology of the carbon microparticles is greatly affected by the inorganic compound used and the added fraction of the inorganic compound to lignin, although the kind of lignin and its molecular weight have little effect on the morphology. The weight yield of carbon microparticles to the original lignin content is about 40%. Typical morphologies of carbon microparticles are (1) very thin and flexible spherical hollow carbon microparticles prepared by addition of lithium carbonate, and (2) hollow and porous carbon microparticles obtained by using sodium metasilicate in which carbon beads of about 10 nm are connected in a highly branched structure. Spherical hollow carbon microparticles with a bulk density of 0.015 g cm^-3 are so flexible that their original spherical form is mostly recovered when returned to atmospheric pressure after compression at 100 MPa. The hollow and porous carbon microparticles obtained by heating at 1000 °C exhibit superior electrical conductivity compared with commercial conductive carbon nanoparticles, acetylene black and Ketjenblack.