Sulfonated char from waste tire rubber used as strong acid catalyst for biodiesel production

A new acid catalyst based in a carbonaceous solid was functionalized using sulfuric acid as source of SO3H acid groups. This carbon‐based material prepared by the pyrolysis of waste tire rubber was used either as catalyst or as catalytic support. The pyrolysis process was performed with a flow of N2 at relatively low temperature to obtain a mesoporous carbon and achieve an effective sulfonation. The sulfonation method of carbon obtained from tire rubber was through direct immersion into concentrated H2SO4 under reflux. The mesoporous solids were characterized by several analytic techniques including an elemental analysis derived from scanning electronic microscopy (SEM). These ones indicated the presence of polycyclic disordered carbon plates in the carbonaceous structure with a low surface area and wide pores that provided many surface acid sites. The high catalytic activity and stability of this catalyst is related to the acid site density of Bronsted acid sites and to its homogeneous distribution. The hydrophobicity presented by this material favorably prevented hydration of hydrophilic OH and SO3H functional groups. The transesterification and esterification of waste oil under sub‐critical methanol mainly in the presence of sulfonated char were achieved. Hence, it was required shorter times, low temperature and significantly, a low amount of methanol compared to other studies. © 2016 American Institute of Chemical Engineers Environ Prog, 36: 619–626, 2017