Study On Biodesulfurization Characteristics Of Immobilized Resting Cells And Modeling

Biodesulfurization (BDS) plays an important role in dealing with environment issues. Operated under ambient temperature and pressure and removing heterocyclic sulfur compounds such as DBT and DBT derivatives, BDS is expected to be a complement and a promising alternative to the conventional hydrodesulfuration (HDS) for deep desulfurization. Immobilization makes cells maintain their distribution and improves their stability; prevents cells from leaking out and makes ease separation of biocatalyst from the treated fuels; prolongs the life-time of biocatalyst. Promoting the application of BDS, cell immobilization is becoming a focus of BDS research.In this paper, immobilization of Gordonia sp. WQ-01A resting cells was studied. The effects of immobilization conditions on biodesulfurization were investigated. Microstructure of alginate gel beads was observed by SEM and the biodesulfurization characteristics between immobilized cells and resting cells was compared in water phase. The results showed that the optimum immobilization condition is: bacteria is cultivated at 30℃for 36 hours after activation twice; the concentration of carrier, sodium alginate (SA), is 4% (w/v) and the ratio of cells (g) to SA (mL) is 1:20 with the 3% (w/v)calcium chloride as the precipitator under 4℃. Besides, it is better to preserve immobilized cells in physiological saline solution under 4℃. When the initial concentration of DBT is 0.25 mM, the maximal desulfurization rate of immobilized cells reaches above 97% while that of resting cells is only 53.6%. Moreover, compared to resting cells, immobilized cells have stronger adaptability to different conditions and are less affected by substrate inhibition. Through reactivation, immobilized cells can be used more than three times, the lifetime exceeds 360 hours.Batch DBT biodesulfurization in the oil-water-immobilization system was conducted. A mathematical model was developed to simulate the biodesulfurization process, which took into account the internal and external mass transfer resistances of DBT and oxygen and the intrinsic kinetics of bacteria. The good agreement between the model simulations and the experimental measurements of DBT concentration profiles validated the proposed model. Moreover, the time and radius courses of DBT and oxygen concentration profiles within the alginate gel beads were reasonably predicted by the proposed model.