Biodesulfurization of Dibenzothiophene and Its Alkylated Derivatives in a Two-Phase Bubble Column Bioreactor by Resting Cells of Rhodococcus erythropolis IGTS8

George Prasoulas,Konstantinos Vavitsas,Styliani Kalantzi,Dimitris G Hatzinikolaou,Chrysovalantis Templis,Nikolaos Papayannakos,Konstantinos Dimos,Panayiotis Glekas,Diomi Mamma,Dimitris Kekos,Stamatis Sarris

doi:10.3390/pr9112064

George Prasoulas, Konstantinos Vavitsas + Show 9 more

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https://doi.org/10.3390/pr9112064

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Abstract

Biodesulfurization (BDS) is considered a complementary technology to the traditional hydrodesulfurization treatment for the removal of recalcitrant sulfur compounds from petroleum products. BDS was investigated in a bubble column bioreactor using two-phase media. The effects of various process parameters, such as biocatalyst age and concentration, organic fraction percentage (OFP), and type of sulfur compound—namely, dibenzothiophene (DBT), 4-methyldibenzothiophene (4-MDBT), 4,6-dimethyldibenzothiophene (4,6-DMDBT), and 4,6-diethyldibenzothiophene (4,6-DEDBT)—were evaluated, using resting cells of Rhodococcus erythropolis IGTS8. Cells derived from the beginning of the exponential growth phase of the bacterium exhibited the highest biodesulfurization efficiency and rate. The biocatalyst performed better in an OFP of 50% v/v. The extent of DBT desulfurization was dependent on cell concentration, with the desulfurization rate reaching its maximum at intermediate cell concentrations. A new semi-empirical model for the biphasic BDS was developed, based on the overall Michaelis-Menten kinetics and taking into consideration the deactivation of the biocatalyst over time, as well as the underlying mass transfer phenomena. The model fitted experimental data on DBT consumption and 2-hydroxibyphenyl (2-HBP) accumulation in the organic phase for various initial DBT concentrations and different organosulfur compounds. For constant OFP and biocatalyst concentration, the most important parameter that affects BDS efficiency seems to be biocatalyst deactivation, while the phenomenon is controlled by the affinities of biodesulfurizing enzymes for the different organosulfur compounds. Thus, desulfurization efficiency decreased with increasing initial DBT concentration, and in inverse proportion to increases in the carbon number of alkyl substituent groups.

Highlights

Sulfur is the third most abundant heteroatom in crude oil, in which sulfur contents vary from 0.05% to 10% (w/w)
R. erythropolis IGTS8 was grown in a 20 L bioreactor using dimethyl sulfoxide (DMSO) as a sulfur source and glycerol as a carbon source in order to acquire the cells for the subsequent step of BDS with resting cells
For R. erythropolis IGTS8, DMSO has been reported as a sulfur substrate that does not repress the expression of desulfurization enzymes [1]

Summary

Introduction

Sulfur is the third most abundant heteroatom in crude oil, in which sulfur contents vary from 0.05% to 10% (w/w). 2 of 19environ most chemically recalcitrant sulfur compounds in oil products, and are potential mental pollutants, since upon combustion they are transformed into sulfur oxides (SOxs)—the principal cause of acid rain [1]. Environmental regulations concerning the sulfur contentpollutants, of motorsince fuelsupon havecombustion become increasingly stringent insulfur an effort to reduce environmental they are transformed into oxides (SOxs)—the principal acidEU rain [1].taken. 2012,ofthe has firm action to reduceconcerning the sulfurthe content o sulfur content fuels have become increasingly stringent in an effort to reduce SOx marine fuels of viamotor the Sulphur Directive [2]. HDS is based on the pas Currently, the conventional technology used in oil refineries for reducing the sulfur sage of hydrogen through the petroleum fractions at elevated pressures and temperatures content in petroleum products is hydrodesulfurization (HDS).

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