HDS Technology

The present chapter will review the present state of the art and challenges in the ultradeep desulfurization of natural gas, gasoline, jet fuel, diesel, reformate, and syngas from coal gasifier by HDS, selective adsorption, solvent absorption, and ODS, respectively. 

There are many methods for the desulfurization of nature gas, which can be classified into dry desulfurization, wet desulfurization, and catalytic adsorption. In the dry desulfurization, some solid sorbents, such as iron oxide, zinc oxide, activated carbon (AC), zeolites, and molecular sieves, are used. In wet desulfurization method, liquid-phase chemical/physical solvent absorption systems are usually used for scrubbing H2S amine-based processes are subject to equipment corrosion, foaming, amine-solution degradation, and evaporation, and require extensive wastewater treatment. As a result, this sulfur removal technology is complex and capital intensive,44 although the processes are still employed widely in the industry. The desulfurization of coal gasification gas will be reviewed in detail in Section 5.5. In the catalytic-adsorption method, the sulfur compounds are transformed into H2S by catalytic HDS or into elemental sulfur or SOx by selective catalytic oxidation (SCO), and then, the reformed H2S and SOx are removed by the subsequent adsorption. 

For large-scale hydrogen production from natural gas, currently, HDS is invariably the preferred method of sulfur removal. In this process, the natural gas is mixed with a small quantity of the added hydrogen and passed over a catalyst bed.6 The typical HDS catalyst is either Co-Mo/A1203 or Ni Mo/Al203. The organic sulfur is reduced to H2S and hydrocarbon by reaction of the following kind  

Because the sulfur compounds in natural gas are nonaromatic and of low molecular weight, HDS can be performed at lower H2 partial pressures, 1-lOkPa, and temperatures of 200-300 °C depending on the catalyst and the sulfur specia-tion.46 Zinc oxide adsorption capacities for H2S in industrial applications are reported to be high, typically 150-200 mg-S/g sorbent.47 

In comparison with the diesel desulfurization, it is not very difficult to remove sulfur from gasoline by HDS technology. The challenges to the refinery for gasoline deep desulfurization are to meet the new EPA Tier II regulations on sulfur contents (2006-2010) and aromatic contents, and still produce high-octane gasoline in a profitable manner. 

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Current progress in HDS via improvement of conventional catalysts, reactors, and processes or development of new catalysts, reactors, and processes has allowed the refining industry to be able to produce the low-sulfur fuels to meet the new EPA regulation. However, the current HDS technology is still difficult or costly to produce the ultraclean liquid hydrocarbon fuels for fuel cell applications. Adsorptive desulfurization and ODS are two promising alterable technologies for ultradeep desulfurization of hydrocarbons fuels for fuel cell applications. 

The current widely used method for desulfurization is HDS technology, which is a high-pressure and high-temperature catalytic process. This means that the HDS... 

Nonetheless, ultimately EBC was unsuccessful in commercializing the technology. This can be attributed to a lack of obtaining shutdown economics in comparison with HDS, continuous improvements in HDS technology, and reluctance on the part of refiners to introduce such novel technology at a scale relevant to the industry. 

Zybell [7] also described some HD technology packages for meeting low emissions and fuel consumption, but mainly in the context of fuel injection technology. His slopes of fuel consumption versus NOx are not as steep as shown in Figs. 1.3 and 1.4, so his minimum cost range is in the 3-5 g/kW-h NOx range. However, when fuel injection pressure is increased from 1,800 to 2,400 bar, the fluid consumption drops about 0.6 % and the minimum calibration shifts to... 

Because of the current limitations in HDS technology, Whitehurst et al, suggested alternative approaches listed below ... 

Catalysis based HDS technology -Conventional HDS -HDS with fuel specification recovery -HDS by advanced reactor design -HDS by advanced catalysis... 

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