A solid acid catalyst that can keep high activity and stability is necessary when low cost feedstocks are
utilized for biodiesel synthesis because the reaction medium contains a large amount of water. Three
solid acid catalysts were prepared by the sulfonation of carbonized vegetable oil asphalt and petroleum
asphalt. The structure of these catalysts was characterized by a variety of techniques. A new process that
used the coupling of the reaction and separation was employed, which greatly improved the conversion
of cottonseed oil (triglyceride) and free fatty acids (FFA) when a model waste oil feedstock was used. The
vegetable oil asphalt-based catalyst showed the highest catalytic activity. This was due to the high density
and stability of its acid sites, its loose irregular network, its hydrophobicity that prevented the hydration
of –OH species, and large pores that provided more acid sites for the reactants.