Biodesulphurization of gasoline by Rhodococcus erythropolis supported on polyvinyl alcohol

A new biodesulphurization (BDS) method has been considered using Rhodococcus erythropolis supported on polyvinyl alcohol (PVA) for BDS of thiophene as a gasoline sulphur model compound in n-hexane as the solvent, subsequently this biocatalyst has been applied to BDS of gasoline samples. The obtained results according to UV-Spectrophotometer analysis at 240 nm showed that 97·41% of thiophene at the optimum condition of primary concentration 80 mg l^-1 , pH = 7, by 0·1 g of biocatalyst in 30°C and after 20 h of contact time has been degraded. These optimum conditions have been applied to gasoline BDS and the biodegradation of gasoline thiophenic compounds have been investigated by gas chromatography-mass spectrometry (GC-MS). According to GC-MS, thiophene and its 2-methyl, 3-methyl and 2- ethyl derivatives had acceptable biodegradation efficiencies of about 26·67, 21·03, 23·62% respectively. Also, benzothiophene that has been detected in a gasoline sample had 38·89% biodegradation efficiency at optimum conditions, so biomodification of PVA by R. erythropolis produces biocatalysts with an active metabolism that facilitates the interaction of bacterial strain with gasoline thiophenic compounds. The morphology and surface functional groups of supported R. erythropolis on PVA have been investigated by scanning electron microscope (SEM) and FT-IR spectroscopy respectively. SEM images suggest some regular layered shape for the supported bacteria. FT-IR spectra indicate a desirable interaction between bacterial cells and polymer supports. Also, the recovery of biocatalyst has been investigated and after three times of using in BDS activity, its biocatalytic ability had no significant decreases.

The biomodification of polyvinyl alcohol by Rhodococcus erythropolis described herein produces a new biocatalyst which can be used for significantly reducing the thiophenic compounds of gasoline and other fossil fuels. The immobilization process is to increase the biodegradation efficiency of cells and accelerating the biodesulphurization process.