Pretreatment of Asphaltenes as Precursors for Carbon Fiber Production

Abstract

Oilsands bitumen produced from Alberta, Canada contains 14–20 wt.% n-pentane insoluble asphaltenes. Separation of asphaltenes from the bitumen by solvent deasphalting has the benefit of improving the properties of the deasphalted oil compared to the bitumen, for example, by decreasing its viscosity and increasing its hydrogen-to-carbon ratio. Due to the low hydrogen-to-carbon ratio and high aromatic content of the asphaltenes, the asphaltenes fraction potentially is a good feedstock for carbon fiber production. The processing path for converting asphaltenes to carbon fibers involves the following steps. First, melt-spinning is used to convert the asphaltenes into fibrous form. Then the precursor fibers are oxidatively stabilized to render them infusible for the final carbonation step, during which the fibers are subjected to high temperatures, up to 1500 °C, in an inert atmosphere. When using asphaltenes as a precursor for carbon fibers production, the production process can benefit from pretreatment of the asphaltenes to increase its softening point temperature. Low softening point is undesirable as it can lead to a lengthy stabilization process as well as potential fusing of the fibers during stabilization and carbonization steps. In this study, industrially pentane solvent deasphalted asphaltenes was pretreated in three ways to increase its softening point temperature: (i) solvent deasphalting / solvent extraction with n-pentane and n-heptane as solvent (ii) autoxidation and (iii) halogenation/dehalogenation. From this investigation, it was found that all three treatments were effective in increasing the softening point. Additionally, all three pretreatments were also effective in improving the melt spin productivity during the melt-spinning process. One exception was noted, namely, when removing the n-heptane soluble materials by rigorous solvent deasphalting, it did not improve melt spin productivity.