Selective adsorption in ultrasound assisted oxidative desulfurization process with nano-engineered adsorbents: mechanism and characterization

UnrestrictedThis thesis describes the use of alumina powders as solid adsorbents for a scale up system of deep desulfurization of liquid fossil fuels and application of functionalized carbon nanotubes (CNTs) for fabricating miniature reactors for fuel cell reformers.; Stringent emission regulations and the growing environmental awareness have raised the demand for ultra deep desulfurization technologies for protecting public health and welfare. The existing desulfurization techniques need to be optimized and fresh approaches are needed to reach very low sulfur content in fossil fuels. The application of selective solid adsorbents is an important phase in novel desulfurization techniques. The existing ultrasound assisted oxidative desulfurization (UAOD) process has been improved for practical use by replacing solvent extraction by solid adsorption units. Therefore the advantages of both oxidative and adsorptivedesulfurization have been put together for an enhanced continuous system to reach 99% sulfur removal effciency. A scale up test with 1 bpd showed promising results for industrial application of the system with expansion capabilities to produce ultra low sulfur fuel (ULSF) for mobile units.; This research work focuses on identifying suitable adsorbents for sulfur removal in diesel fuel and jet fuel. The results support the selective nature of adsorbents. Chromatograms from sulfur chemiluminescence detector (GC-SCD) and pulsed flame photometric detector (GC-PFPD) after the adsorption process of UAOD evaluate the efficiency and selectivity of the process on fuels with no detrimental effects on distillation profile of diesel and jet fuels. Images from scanning electron microscopy (SEM) and results of x-ray diffraction (XRD), laser diffraction particle size analyzer, and small angle neutron scattering (SANS) for different phases of alumina; clarify the characteristics of the adsorbents. High adsorption capacities were obtained due to high conversion rate of the UAOD process. Close to 13 mg of sulfur was removed per gram of alumina in marine gas oil (MGO) that indicates the optimized process without the use of composite adsorbents. Composites of alumina doped with a transition metal have shown problem for regeneration; however the alumina sample that was used in this study is capable of maintaining its capacity for more than 98% after heating up to 550°C for regeneration. The heat treating ofalumina for recovery eliminates the use of organic solvents for removing the adsorbates with very low loss in adsorption capacity. The resulting clean fuel very well meets the new emission control standards.; Adsorption studies were carried out to find the effect of pore size and surface area of each adsorbent. Amorphous acidic alumina shows promising results as an adsorbent in the improved UAOD process. An isotherm model was derived for dibenzothiophene sulfone (DBTO2) as a model compound to predict and calculate the adsorption of organic sulfur compounds by alumina. The Langmuir-Freundlich model covers a wide range of sulfur concentrations (5 to 700 ppmw).; Nano-engineered self assembled adsorbents were studied in form of CNTs and porous anodic alumina (alumite) as an alternative to conventional adsorbents. Nanofabricated adsorbents in fuel reformers have high potential applications in fuel cells and portable desulfurization units. Nanotubes of carbon have shown high selectivity among the most refractory sulfur compounds of diesel (e.g. 4,6-dimethyldibenzothiophene); therefore the assembly of functionalized CNT onalumina membrane that is used as templates is of interest. The high surface area of carbon structures enhances the design of a cartridge for miniature desulfurization kits. Adsorption of DBTO2 on single wall carbon nanotubes (SWNTs) was characterized with Raman spectroscopy in ambient temperature and atmospheric pressure. Epoxidation of SWNTs provides sidewall functionalized active sites for adsorption and subsequent reactivity. Infrared (IR) spectroscopy identified peaks related to selective adsorption of DBTO2 to nanotube surface with oxygen moeities. Images of the SWNT layer on alumina membranes were produced by vertical scanning interferometer (VSI) and atomic force microscopy (AFM) to measure the nanotube diameters and thickness of the layer atop of membrane. Molecular manufacturing has been discussed for scale up purposes in nanotechnology