Sulfur Removal from Low‐Sulfur Gasoline and Diesel Fuel by Metal‐Organic Frameworks

Abstract

Several materials in the class of metal-organic frameworks (MOF) were investigated to determine their sorption characteristics for sulfur compounds from fuels. The materials were tested using different model oils and common fuels such as low-sulfur gasoline or diesel fuel at room temperature and ambient pressure. Thiophene and tetrahydrothiophene (THT) were chosen as model substances. Total-sulfur concentrations in the model oils ranged from 30 mg/kg (S from thiophene) to 9 mg/kg (S from tetrahydrothiophene) as determined by elementary analysis. Initial sulfur contents of 8 mg/kg and 10 mg/kg were identified for lowsulfur gasoline and for diesel fuel, respectively, by analysis of the common liquid fuels. Most of the MOF materials examined were not suitable for use as sulfur adsorbers. However, a high efficiency for sulfur removal from fuels and model oils was noticed for a special copper-containing MOF (copper benzene-1,3,5-tricarboxylate, Cu-BTC-MOF). By use of this material, 78 wt % of the sulfur content was removed from thiophene containing model oils and an even higher decrease of up to 86 wt % was obtained for THT-based model oils. Moreover, the sulfur content of low-sulfur gasoline was reduced to 6.5 mg/kg, which represented a decrease of more than 22 %. The sulfur level in diesel fuel was reduced by an extent of 13 wt %. Time-resolved measurements demonstrated that the sulfur-sorption mainly occurs in the first 60 min after contact with the adsorbent, so that the total time span of the desulfurization process can be limited to 1 h. Therefore, this material seems to be highly suitable for sulfur reduction in commercial fuels in order to meet regulatory requirements and demands for automotive exhaust catalysis-systems or exhaust gas sensors. IntroductionThe reduction in the level of sulfur compounds in commercial gasoline and diesel fuels is a major concern of the petrol, automotive and power generation industries. This aim is a necessity not only to meet regulatory requirements but also to enhance the life-time of exhaust gas aftertreatment systems and sensors or fuel cell components. Consequently, there is an increasing demand for ultra-low sulfur fuels (preferably down to 0.1 ppmw S ) [1].As a legal guideline, the European Union has mandated the reduction of sulfur levels (S-levels) in gasoline and diesel fuels to 10 mg/kg S (10 ppmw S ) by 2009 (directive 2003/17/EC). In addition, S-levels in diesel fuel for traction engines and heating purposes was reduced from the original value of 2000 mg/kg to 1000 mg/kg in 2008 [2]. Analog regulations of the federal government of the US and the EPA (U.S. Environmental Protection Agency) are proposing the implementation of ultralow sulfur diesel fuel with 15 ppmw S for 2010 [3, 4]. Similar to the EU proposals, the German government has also enacted the introduction of sulfur-free fuel (with a maximum tolerable level of sulfur of 10 mg/kg) in 2009 (Order 10. BImSchV) [5]. In order to meet these worldwide demands, oil refiners have been endeavoring to promote sulfur r...

Adsorptive desulfurization with metal-organic frameworks: A density functional theory investigation

“…Sabine Achmann et al [14] reported that MOF-199 has a very high efficiency for sulfur removal from low-sulfur model oils and fuels, it shows both the highest 6 sorption rates and the fastest sorption characteristics. It was proposed that the smaller pores in MOF-199 provide a better stabilization of the Cu-adsorbed sulfur compound by Van-der-Waals forces, and therefore leads to its outstanding sulfur removal performance.…”

Graphene oxide/mixed metal oxide hybrid materials for enhanced adsorption desulfurization of liquid hydrocarbon fuels

“…In the latter case, the organosulfur compounds are adsorbed as unchanged molecular species on the surface, simplifying the regeneration and cycling of the adsorbent. A range of adsorbent materials are currently under study, including zeolites, [21] metal organic frameworks (MOF), [22] mixed metal oxides, [18] activated carbon, [23], [24] and molecularly imprinted polymers. [25] In general, the development of a scalable adsorbent composed of inexpensive materials, but possessing a large capacity and the ability to regenerate for a significant number of cycles, would be ideal for continuous operation in a desulfurization unit.…”

Low-temperature loading of Cu+ species over porous metal-organic frameworks (MOFs) and adsorptive desulfurization with Cu+-loaded MOFs

“…Recently, MOF-type materials have also been investigated for the adsorptive removal of hazardous materials such as benzene [30,31] and dyes [32,33]. Sulfur-containing compounds have also been adsorbed/removed with MOFs both in liquid [34][35][36][37][38][39][40] and gas phases [41,42]. A few important factors, such as coordinatively unsaturated sites (CUS or open metal sites) [34], pore functionalities [42], and acid-base interactions [38,39] have been suggested for the efficient adsorptive removal of sulfurcontaining compounds with MOFs.…”