Developments in destructive and non-destructive pathways for selective desulfurizations in oil-biorefining processes

Biocatalytic desulfurization is still not a commercial technology, but conceptual engineering and sensitivity analyses have shown that the approach is very promising. The purpose of this paper is to investigate further some aspects of the biodesulphurization pathways, discussing the non-destructive pathway with the well-known Rhodococcus rhodochrous IGTS8. Findings revealed byproducts, such as 2'-hydroxybiphenyl (HBP), sulfite and sulfate, obtained by the desulfurization of dibenzothiophene (DBT), to exert an inhibiting effect. The results suggest that IGTS8 may follow two different metabolic pathways in stationary-growth-phase cells or under growing conditions. The first pathway is characterized by oxidative steps, which convert DBT to DBT sulfoxide and to DBT sulfone. The sulfone is transformed to 2-(2'-hydroxyphenyl)benzene sulfinate and then to HBP and sulfite by a sulfinic acid hydrolase. In the second pathway the sulfone is further oxidized to 2-(2'-hydroxyphenyl)benzene sulfonate and then to HBP and sulfate by a sulfonic acid hydrolase. Experiments using benzene sulfonic acid suggest that the sulfonic acid hydrolase is an induced enzyme.