biosurfactants and their use in upgrading petroleum vacuum distillation residue: a review

it has been known for years that microbial surface active agents have a wide range of applications not only in oil spill environment but also in many industries. their properties including: (i) changing surface active phenomena, such as lowering of surface and interfacial tensions, (ii) wetting and penetrating actions, (iii) spreading, (iv) hydrophylicity and hydrophobicity actions, (v) microbial growth enhancement, (vi) metal sequestration and (vii) anti-microbial action attract the biotechnologist’s attention to be substituted instead of synthetic ones. there are many advantages of biosurfacants in comparison with chemically synthesized counterparts like biodegradability, generally low toxicity, biocompatibility and digestibility, availability of cheap raw materials, acceptable production economics, use in environmental control, specificity and effectiveness at extreme temperatures, ph and salinity. hydrophobic petroleum hydrocarbons require solubilization before degradation by microbial cells. surfactants can increase the surface area of hydrophobic materials, such as oil spills in soil and water environment, thereby increasing their water solubility. hence, the presence of surfactants would increase biodegradation of complex hydrocarbons like asphaltenes and resins. increasing supply of heavy crude oils, bitumens, distillation vacuum residue in most of oil producing countries has increased the interest in transportation and conversion of the high-molecular weight fractions of these materials into refined fuels and petrochemicals and also the interest of conversion of heavy fraction of crude oil like vacuum distillation residue to more valuable components.