Kinetics Study of Reduction / Sulfidation of ZnO and Zinc Titanate Powders in a Drop-Tube Furnace
The reaction kinetics of fine particles of zinc oxide and zinc titanate with H2S were studied using a drop-tube furnace in order to test the potential of the sorbent injection hot-gas desulfurization process. Fine ZnO sorbent particles with diameter smaller than 50 tm were sulfided with H2S and/or reduced with H2 in a laminar flow reactor over the temperature range of 620-910 C. The reacted sorbent particles were separated from gas and size-classified using a cascade impactor and an absolute filter. Sulfidation conversion was measured by thermo-gravimetric analyses and compared for different particle sizes and reaction conditions. Other sorbents such as zinc titanate, metallic zinc, and ZnO with different porosity were also tested and compared. In the experiments of the reduction of ZnO without H2S, it was deduced from the change of size distribution of particles that a significant amount of Zn was formed and vaporized. On the other hand, the presence of H2S suppressed the change of size distribution of particles. This suggests that H2S suppresses the reduction of ZnO by rapid surface sulfidation and/or that gaseous Zn reacts with H2S immediately and forms fine particles of ZnS, most of which deposit onto the original particle surface. Formation and vaporization of elemental Zn from zinc titanate sorbents was slower than from zinc oxide with and without H2S. Surface reaction rate of ZnO and zinc titanate sulfidation was obtained and a reaction model for a single particle was formulated and compared with experimental results in the drop-tube furnace. Thesis Supervisors: Professor Maria Flytzani-Stephanopoulos Professor Adel F. Sarofim
Detailed studies of novel regenerable sorbents for high-temperature coal gas desulfurization: Final report
The novel sorbent systems considered in this program are bulk mixed oxides of copper, aluminum and iron, as well as zinc and titanium oxide mixtures capable of removing H/sub 2/S from a level of 0.5--1.0 mol % in coal-derived gases down to a few parts per million, ppM(v). The latter sorbents were examined up to 650/degree/C (1200/degree/F), which is the operating temperature of molten carbonate fuel cells (MCFC), primarily in regard to stabilization of ZnO against reductive metallation (and vaporization). Both types of sorbent systems also address another application, namely, Integrated Gasification Combined Cycle (IGCC) power generation where the hot coal gas (after removal of contaminants) is used to drive a gas turbine. The CuO-based sorbents are developed for an extended range of operating temperatures (up to 1500/degree/F). Objectives were to (1) examine reduction stabilization effects imparted on CuO and ZnO by additives such as Al/sub 2/O/sub 3/ and TiO/sub 2/, respectively; (2) prepare different sorbent compositions in porous granular form, and test them under similar conditions of sulfidation-regeneration in a lab-scale quartz reaction system; (3) evaluate and select most promising sorbents on the basis of performance stability, H/sub 2/S removal efficiency, sulfur capacity, and regeneration characteristics; (4) prepare selectedmore » sorbents in the form of 1/8'' extrusions combining suitable pore structure and good mechanical strength; and (5) carry out cyclic sulfidation-regeneration tests with selected sorbent extrusions at 650/degree/C and examine the structural stability and performance regenerability of sorbents after extended use. 32 refs., 59 figs., 26 tabs.« less
Exopolysaccharide biosynthesis and related enzyme activities of the medicinal fungus, Ganoderma lucidum, grown on lactose in a bioreactor
Exopolysaccharide (EPS) production and biosynthesis were studied in Ganoderma lucidum, a fungus used in traditional Chinese medicine, grown with lactose in a bioreactor. β-Galactosidase activity, which implies the existence of a lactose permease system, was induced by lactose. Lactose feeding also increased α-phosphoglucomutase activity and EPS accumulation but decreased phosphoglucose isomerase activity and lactate concentration in the culture broth. A maximum cell density of 22 g l−1 and EPS at 1.25 g l−1 were obtained in fed-batch bioreactor culture.