Adsorptive Desulfurization

Recently, great attention has been paid to the ambient temperature adsorption for removing sulfur compounds from natural gas, as the system is simple and is quick and easy to be started up. The major adsorbents that were used in the ambient temperature adsorption are AC-based and zeolite-based materials. The Osaka Gas mixed metal and metal oxide catalyst provides a low-temperature method of desulfurization. The catalysts (or adsorbents) is claimed to remove organic sulfur and H2S at room temperature.115 

Manufacturer Active Component Product Name Ave. DMS (ppmv) Ave. Total Sulfur (ppmv) Performance Index (ppmv) DMT Bed Volumes 

United Catalysts Inc. (Sud-Chemie) ZnO at 350 °C (no preceding CoMo catalyst bed or hydrogen addition) G-72E 1.5 6.7 668 

Norit Carbon with chromium and copper salts RGM-3 0.8 5.1 24,000 

Grace Davison Molecular sieve 13 x 10A pore) zeolite-X 554HP 0.8 4.4 110,376 

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The ultradeep desulfurization of the current infrastructure fuels has become a bottleneck in the production of H2 for fuel cell applications. It is urgent to develop a more efficient and environmentally friendly process and technology for the ultradeep desulfurization of the hydrocarbon fuels. Consequently, many approaches have been conducted in order to improve the conventional HDS process and to develop new alternative processes. These approaches include catalytic HDS with improved and new catalysts, reactor and/or process, adsorptive desulfurization,27 oxidative desulfurization (ODS), extractive desulfurization (EDS), and biodesulfurization (BDS) by using special bacteria and others. Some of these works were reviewed recently by Topsoe et al.,15 Whitehurst et al.,28 Kabe et al.,29 Cicero et al.,30 Babich and Moulijn,31 Dhar et al.,32 Song,33 Song and Ma,16,34 Bej et al.,35 Mochida and Choi,36 Hemandez-Maldonado and Yang,37,38 Hemandez-Maldonado et al.,39 Topsoe,40 Brunet et al.,41 Gupta et al.,42 and Ito and van Veen.43... 

Table 5.3. Adsorption Desulfurization Performance of Various Sorbents for Natural Gas4...

The Research Triangle Institute136 also reported a TReND process for adsorptive desulfurization of gasoline over a regenerable metal oxide sorbent in a transport... 

In the study of adsorptive desulfurization of a model diesel fuel over a nickel-based sorbent in a fixed-bed adsorption system at ambient temperature and atmosphere pressure, Kim et al.123 found that the direct interaction between the sulfur atom in the sulfur compounds and the surface nickel plays an important role, indicating that the supported nickel adsorbent is good for the selective removal of the sulfur compounds, which have no alkyl steric hindrance, from hydrocarbon streams. However, the sorption affinity of the alkyl DBTs with alkyl groups at 4- and/or 6-positions is reduced due to the steric hindrance. The sorption selectivity of the nickel-based sorbent for various compounds at room temperature increases in the order of Nap 1-MNap < 4,6-DMDBT < DBT < quinoline < indole, as shown in Figure 5.14.123... 

AC materials as porous materials with very high surface areas and large pore volume have been widely used in deodorization, decolorization, purification of drinking water, treatment of wastewater, and adsorption and separation of various organic and inorganic chemicals. Recently, some carbon materials have been reported for adsorptive desulfurization of liquid hydrocarbon fuels. 

Sano and coworkers reported an interesting work on adsorptive desulfurization of real gas oil over AC with surface area from 683 to 2972 m2/g.165 They found that using the AC materials can remove sulfur and nitrogen species from gas oil and the AC materials with the larger surface area and higher surface polarity have the better adsorptive performance. They also found that the adsorption pretreatment of gas oil over the AC material significantly improved the HDS performance of the gas oil. 

As shown above, since the different adsorbents may be suitable for separating different sulfur compounds from different hydrocarbon streams and some coexisting species, such as polyaromatic hydrocarbons and moisture, in hydrocarbon streams might inhibit the adsorption of sulfur compounds on the sorbent, a combination of two or more sorbents in an adsorptive desulfurization process might be more efficient for a practical ultradeep desulfurization process. 

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. 

A combination of multidesulfurization technologies together, such as HDS and ADS (adsorptive desulfurization), ODS and ADS, and solvent scrubbing and adsorption, has become a trend in research and development to achieve ultradeep desulfurization technology of the hydrocarbon fuels for environmental protection, hydrogen production, and fuel cell applications. 

Ma, X.L., Velu, S., and Song, C.S. Adsorptive desulfurization of diesel fuel over a metal sulfide-based adsorbent. Preprints of Papers—American Chemical Society, Division of Fuel Chemistry, 2003, 48, 522. 

The US company Mesoscopic Devices patented a method for an adsorptive desulfurization process with integrated regeneration in mobile fuel-cell systems... 

Redlich O., Peterson D.L. A useful adsorption isotherm. J. Phys. Chem., 1959 63 1024 1026. Selvavathi V., Chidambaram V., Meenakshisundaram A., Sairam B., Sivasankar B. Adsorptive desulfurization of diesel on activated carbon and nickel supported systems. Catdl. Today, 2009 141 99-102. 

Samadi-Maybodi A, Teymouri M, Vahid A, Miranbeigi A (2011) In situ incorporation of nickel nanoparticles into the mesopores of MCM-41 by memipulation of solvent-solute interaction and its activity toward adsorptive desulfurization of gas oil. J Hazeu d Mater 192 1667-1674... 

Figure 9. Breakthrough curves for the adsorptive desulfurization of a model diesel fuel containing 4,6-DMDBT at 60°C over Transition metal oxides supported on MCM-41 and activated carbon...

Adsorption Desulfurization Using Alumina Based Adsorbents... 

Desulfurization by adsorption is based on the ability of a sorbent to selectively adsorb sulfur compounds from fossil fuels. Based on the mechanism of the sulfur compound interaction with the sorbent, it can be divided into two groups adsorptive desulfurization and reactive adsorption desnlfnrization . Adsorptive desulfurization employs physical adsorption of snlfur compounds on the sorbent surface. Regeneration of the sorbent is usnally performed by flushing the spent sorbent with a desorbent, resulting in a high snlfur compound concentration flow. Reactive adsorption desulfurization is based on chemical interaction of the sulfur compounds and the sorbent. Sulfur is fixed in the sorbent, usually as sulfide, and the S-free hydrocarbon is released into the purified fuel stream. Regeneration of the spent sorbent results in sulfur elimination as H2S, S, SOx, or sulfur-compounds depending on the process applied [11]. 

During the past decade, several results have been published on the use of adsorption for liquid fuel desulfurization. Commercially available sorbents (i.e., zeolites, activated carbon, and activated alumina) were used in these studies [7,8,12-14]. However, it is reported that currently available commercial sorbents are not suitable for the adsorptive desulfurization [3]. 

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