Carbon foam prepared by pyrolysis of olive stones under steam

The experimental conditions for the pyrolysis of olive stones to produce a swelling of the particle and eventually the formation of carbon foam are described and discussed. The greatest expansion of the material occurred when 200-300 g of precursor, in the presence of steam at a pressure of 1 MPa, is introduced into a 1000 ml stainless steel reactor placed inside a sand-bath furnace previously heated to 500 °C. In a few minutes the pyrolysis begins and this exothermic process leads to a more rapid pyrolysis. A relationship between heating rate and degree of foaming for the resulting char is observed. The carbon foam obtained exhibits a low density, 0.2-0.3 g/cm³, due to the presence of meso and macropores, mainly those of size larger than 1 μm. A mechanism is suggested to explain the formation of the foam as a combination of a softening of the precursor and a fragmentation of the biopolymers to produce a “melt”. A fast increase in temperature reduces the viscosity of the “melt” and facilitates the fragmentation to volatiles, responsible for the swelling of the particles and the formation of the foam.