This Small Business Innovation Research (SBIR) Phase I project proposes to demonstrate the feasibility of a new type of advanced hydrodesulfurization (HDS) catalyst for deep desulfurization purposes. Specifically, metal nanoparticles supported on zinc oxide nanowires are proposed for creating higher performance, reactive adsorbent type HDS catalysts. HDS is a process used for the removal of sulfur from hydrocarbon fuels. In this process, fuels are treated with hydrogen gas in the presence of a catalyst. The environmental regulations are continuously pushing down the sulfur levels allowed in transportation fuels and will continue to lower the limits much below 10 ppm in future. Also, low sulfur concentrations are desirable for various fuel cell and refinery technologies where presence of small amounts of sulfur can poison the catalysts. The current, traditional HDS catalysts are efficient in removing the sulfur to levels down to around 20 ppm and leaves behind difficult-to-remove thiophenic sulfur compounds. In this project, an advanced catalyst and a scalable and cost-effective manufacturing is proposed that can accomplish deep desulfurization for lowering sulfur levels down well below 5 ppm.
The broader/ commercial potential of this project will be improved air quality and energy/cost savings for the nation from improved durability of fuel cell and several refining technologies. The project's other outcome will also include new manufacturing technologies for advanced catalyst materials which is crucial for both the nation and the state of Kentucky to be globally competitive in terms of energy technologies. The catalyst materials using ZnO nanowire supports will also find applications beyond deep hydro-desulfurization such as C1-C4 alcohol production using syngas, and steam reforming of methanol. The market size for the proposed catalysts is estimated to exceed $1B considering the number of application areas.
Sulfur compounds in the fuels contribute to emissions of SO2 and sulfate particulate matter. Sulfur in fuel degrades the catalytic converter which results in NOx and SOx emissions and cause acid rain. Sulfur must be removed in any catalytic process because it poisons/deactivates the catalyst. Stringent government laws have forced researchers both in academia and industry to focus on developing better process in order to bring down the sulfur levels to less than 10 ppm. In the US and Canada, the maximum limit for sulfur in on-road diesel is 15 ppm whereas in Europe it is 10 ppm. Governments in developing countries such as India, Mexico, and China are also imposing low sulfur regulations which has increased the demand for ultra-deep desulfurization catalysts. The conventional hydro-desulfurization (HDS) process utilizes alumina supported cobalt or nickel molybdenum catalysts and operate at 350-3900C, and pressures between 60 and 90 bar. Using the conventional HDS, it is very difficult to bring sulfur levels down to less than 15 ppm and even more so, with sulfur level at less than 5 ppm in the final product. Currently, industry uses a modified HDS catalyst and reaction conditions to achieve a sulfur level of 15 ppm. Even after conventional treatment, the sulfur levels are too high for sulfur-sensitive applications like fuel cells and further chemical processing. Also, it is becoming difficult for refiners to meet the growing demand for ultra-low sulfur diesel (ULSD). All these factors have necessitated the need for better catalysts and processes. In the SBIR Phase I project titled "Advanced Hydrodesulfurization Catalysts", AdEM demonstrated a high performance catalyst AdeSulfurTM with ultra-deep desulfurization of fuels. The catalyst is designed using a reactive adsorption concept involving active metal loaded nanowire based materials. Successful testing included desulfurization of diesel and kerosene to remove sulfur species. The four main technological outcomes from the project are: (a) a new catalyst product AdeSulfurTM;(b) a new "dry" process for catalyst manufacturing; (c) large scale production of nanowire based materials; and (d) fundamental understanding of the deep hydrodesulfurization process and catalyst properties. (a) A new catalyst product, AdeSulfurTM: Several gram scale quantities of AdeSulfurTM extrudates comprising of Ni cluster decorated Zinc Oxide nanowire powder was produced. Catalysts were packed in a packed bed reactor and tested using fuels like diesel, kerosene and gasoline, with sulfur concentrations as high as 200 ppm. The feed contained difficult to remove sulfur compounds such as 4-methyldibenzothiophene (MDBT), 4,6-Dimethyldibenzothiophene (DMDBT). Testing was done at temperatures lower than 300 C and pressures lower than 30 bar in the presence of hydrogen flow. The results showed that the activity of the catalyst was high resulting in removal of sulfur from fuels down to 1 ppm or lower at liquid hourly space velocities of > 2.2/hr. Testing conducted over two hundred hour period showed the existence of such high activity towards deep desulfurization. AdEM's catalyst has also shown to be active towards hydrogenation of aromatics at moderate reaction conditions. In comparison to the state of the art in HDS, the conditions used for desulfurization (pressure, temperature and liquid space velocity) are similar or better than the industry standards. Both desulfurization and aromatics hydrogenation are critical for an improved fuel quality. The active catalytic site is determined to be super Ni rich NixZny phase which remained essentially sulfur free in our tests to date. (b) A new "dry" process for catalyst manufacturing: Demonstrated a new process for loading ZnO NW powder with nanoscale clusters of NiO or NiO+MoOx using a dry approach that shows promise in improving dispersion, minimizing process time and solvent usage and thus final cost. The traditionally used wet chemical approaches have sustainability issues, i.e. the waste water reclamation could present sustainability and cost issues. (c) Large scale production of nanowire based materials: There is no commercially available process for producing nanowire based materials in bulk quantities for catalyst applications. AdEM investigated and developed a process and a reactor, and demonstrated a 50-150 gram batch runs over 1.5 hour. Bulk nanowire powder was produced and used for developing AdeSulfurTM, as well as sending samples to potential strategic partners. (d) Fundamental understanding of the deep desulfurization process and catalyst: A number of preliminary studies were conducted to understand both the hydrodesulfurization process and catalyst activity. The mechanical properties of the catalyst extrudates show industrially acceptable crush strength values (~1.5 lbf/mm). In addition, preliminary data shows feasibility of regeneration of the catalyst using air at atmospheric pressure and 510oC. In a comparative study, the activity of the catalyst made using the commercially available zinc oxide powder does not have the high activity as that of the AdeSulfurTM catalyst using AdEM's nanowire powders.
