טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentCherniak Hadas
SubjectApproaches towards Photocatalytic Partial Oxidation
of Propane
DepartmentDepartment of Chemical Engineering
Supervisor Professor Yaron Paz


Abstract

Natural gas has become an abundant energy resource over the last century. It is commonly transported and distributed from its natural reservoirs for utilization as liquefied natural gas (LNG). The weak intermolecular interactions between the gas molecules are responsible for the high cost of liquefaction process, and eventually to the overall cost of LNG to the consumer. One possible way to decrease transportation costs is to convert natural gas into less volatile compounds, for example by partial-oxidation (at the expense of reducing the specific energy content of the fuel).

Photocatalysts, such as titanium dioxide and bismuth oxides, are known to oxidize organic compounds upon exposure to light. Utilizing OH radicals, formed on their surfaces upon exposure, they tend to mineralize the organics all the way to carbon dioxide and water.  

This work aimed at studying the possibility of arresting the photocatalytic oxidation of propane to yield partially oxidized products that still contain high energetic value. Several routes were examined: (1) working under oxygen-lean conditions (2) using photocatalysts with relatively low oxidation potential (3) tailoring the surface of the photocatalyst in a manner that will decrease the adsorptivity towards polar molecules and increase the adsorptivity towards non-polar molecules (4) utilizing the ability of ceria to reversibly release lattice oxygen. Along this line a variety of photocatalysts (BiOBr, BiOCOOH / BiOI, Bi2WO6, CeO2 and Ag3PO4) were prepared and characterized.

A closed-loop system was constructed, enabling to follow changes in the concentrations of propane, CO2, water and any other products by in-situ FTIR measurements. While a decrease in the concentration of propane in parallel to an increase in the concentration of CO2 and water was observed, no evidence for the presence of IR-active partial oxidation products was found, regardless of the type of photocatalyst that was used. Evidence for the dominant role of adsorption (most likely on the silica fiber mats used as substrates for the photocatalysts), together with mass-balance calculations proposed that partial oxidation products were indeed formed, but were not observed due to adsorption on the mats.