Desulfurization Of Liquid Hydrocarbon Fuels Research Articles

Light-Enhanced Oxidative Adsorption Desulfurization of Diesel Fuel over TiO2–ZrO2 Mixed Oxides

This study explored a new method for the adsorptive desulfurization of liquid hydrocarbon fuels called “light-enhanced oxidative adsorption desulfurization (LEOADS)”, which combines the photo-oxidation of aromatic sulfur compounds with the adsorption of oxidized-sulfur compounds over an adsorbent. The LEOADS of dibenzothiophene in real diesel fuel (DBT/diesel) was conducted in a batch system under UV–vis irradiation at ambient conditions using air as an oxidant. The desulfurization performance of DBT decreased in the order of TiO2–ZrO2 ≫ TiO2-CeO2 > TiO2 ≈ ZrO2. Introducing simultaneous light irradiation together with an adsorption process using TiO2–ZrO2 can dramatically improve the sulfur uptake by 9-fold (5.2 mg-S/g-A) compared to one-step adsorptive desulfurization (0.6 mg-S/g-A) and by 1.4-fold compared to two-step photo-oxidative desulfurization (3.8 mg-S/g-A). Light and TiO2–ZrO2 play important roles in the LEOADS: Light enhanced peroxide generation and the TiO2–ZrO2 promoted the oxidation of DBT to DBTO2 with the in situ generated peroxide. X-ray diffraction, UV–vis spectroscopy, N2-adsorption desorption, and scanning electron microscopy techniques were used for the characterization of the materials.

Desulfurization of Liquid Hydrocarbon Fuels with Microporous and Mesoporous Materials: Metal-Organic Frameworks, Zeolites, and Mesoporous Silicas

This review discusses potential microporous and mesoporous materials that can address the issue of sulfur reduction via adsorptive desulfurization (ADS) with a focus on liquid fuels. During the transition to cleaner energy sources in the face of climate change, liquid fossil fuels will likely continue to provide a significant share of the world’s energy demand. Fossil fuels possess a substantial amount of deleterious sulfur compounds that reduce the efficiency of energy production, damage the environment, and harm human health. There has recently been a large push to address these challenges that sulfur presents. ADS is one of the most promising techniques to reduce the sulfur content of liquid fuels in a cost-effective manner. The three key materials that have attracted a great deal of attention for their application in ADS are metal-organic frameworks (MOFs), zeolites, and mesoporous silicas. These materials have emerged as potential candidates for ADS because of their high surface area, tunable structure, and advantageous porosity. Research interest has been generated around finding unique approaches to modify these materials that increase their selectivity, stability, adsorption capacity, and reusability. A deeper mechanistic understanding of the adsorption of various sulfur compounds on these novel materials has been pursued experimentally and with the aid of models. This review seeks to discuss the recent advances made surrounding the most promising ADS materials while providing an outlook on where advancements still need to be made.

Desulfurization of liquid hydrocarbon fuels via Cu 2 O catalyzed photo-oxidation coupled with liquid–liquid extraction

Abstract By combining the photochemical reaction and liquid–liquid extraction (PODS), we studied desulfurization of model fuel and FCC gasoline. The effects of air flow, illumination time, extractants, volume ratios of extractant/fuel, and catalyst amounts on the desulfurization process of PODS were analyzed in detail. Under the conditions with the air as oxidant (150 ml·min − 1 ), the mixture of DMF–water as extractant (the volume ratio of extractant/oil of 0.5) and photo-irradiation time of 2 h, the sulfur removal rate reached only 42.63% and 39.54% for the model and FCC gasoline, respectively. Under the same conditions, the sulfur removal rate increased significantly up to 79% for gasoline in the presence of Cu 2 O catalyst (2 g·L − 1 ). The results suggest that the PODS combined with a Cu 2 O catalyst seems to be a promising alternative for sulfur removal of gasoline.

Design and fabrication of nanoporous adsorbents for the removal of aromatic sulfur compounds

Traditional and recently emerged nanoporous adsorbents for deep desulfurization of liquid hydrocarbon fuels are summarized.

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

A series of mixed metal oxides (MMOs) adsorbents (MgAl-, CuAl- and CoAl-MMOs) were supported on graphene oxide (GO) through in-situ precipitation of layered double hydroxides (LDHs) onto exfoliated GO, followed by thermal conversion. The study shows that GO is an excellent support for the LDH-derived MMOs due to matching geometry and charge complementarity, resulting in a strong hybrid effect, evidenced by significantly enhanced adsorption performance for the commercially important removal of heavy thiophenic compounds from hydrocarbons. Fundamental liquid-phase adsorption characteristics of the MMO/GO hybrids are quantified in terms of adsorption equilibrium isotherms, selectivity and adsorbent regenerability. Upon incorporation of as little as 5wt% GO into the MMO material, the organosulfur uptake was increased by up to 170%, the recycling stability was markedly improved and pronounced selectivity for thiophenic organosulfurs over sulfur-free aromatic hydrocarbons was observed.

Density Functional Theory Study on the Role of Ceria Addition in TixCe1–xO2 Adsorbents for Thiophene Adsorption

A TixCe1–xO2-based material has been reported as a potential adsorbent for ultradeep adsorptive desulfurization of liquid hydrocarbon fuels. To understand the roles of TiO2 and CeO2 in the adsorbent, density functional theory (DFT) calculations examined the energetics of adsorption site formation and corresponding thiophene adsorption energies on surfaces of TiO2 anatase, CeO2, and Ce-doped anatase. Compared with pure anatase surfaces, thiophene binds more strongly to Ce-doped anatase surfaces. O-rich sites (with activated O2) bind strongly to thiophene, but the formation of the O-rich sites is favored only on higher energy surfaces such as anatase (001) and ceria (100). The formation of a TixCe1–xO2 mixed surface decreases the relative surface formation energy of anatase (001), and thus a greater fraction of the (001) facet could be exposed on the adsorbent. Ceria may also act as an oxygen storage reservoir, providing oxygen for the formation of O-rich sites that strongly adsorb thiophenic species.

Density functional theory study on adsorption of thiophene on TiO 2 anatase (0 0 1) surfaces

In order to develop a fundamental understanding of the adsorption mechanism of thiophenic compounds on TiO 2-based adsorbents for ultra-deep desulfurization of liquid hydrocarbon fuels, a density functional theory (DFT) study was conducted on the adsorption of thiophene over the TiO 2 anatase (0 0 1) surface. The perfect, O-poor (with oxygen vacancies), and O-rich (with activated O 2 on the surface) anatase (0 0 1) surfaces were built, and the interaction of thiophene molecule with these surfaces was examined. The adsorption configuration and adsorption energy on the different surfaces and sites were estimated. The results showed that thiophene may be adsorbed on both the perfect and O-poor surfaces through an interaction between the Ti cations on the surface and the S atom in thiophene, whereas on the O-rich surface through an interaction of the activated O atoms (the dissociatively or associatively adsorbed O 2) on the surface with the S atom in thiophene to form a sulfone-like surface species. The adsorption of thiophene on the O-rich surface is significantly stronger than adsorption on the perfect and O-poor surfaces on the basis of the calculated adsorption energies. The results indicate that the activated O 2 on the TiO 2 anatase (0 0 1) surface may play an important role in the adsorption desulfurization over the TiO 2-based adsorbents, and increased concentration of the activated O 2 on the surface may result in improvement of the adsorption capacity of the adsorbents.

A novel method for oxidative desulfurization of liquid hydrocarbon fuels based on catalytic oxidation using molecular oxygen coupled with selective adsorption

The present study explored a novel oxidative desulfurization (ODS) method of liquid hydrocarbon fuels, which combines a catalytic oxidation step of the sulfur compounds directly in the presence of molecular oxygen and an adsorption step of the oxidation-treated fuel over activated carbon. The ODS of a model jet fuel and a real jet fuel (JP-8) was conducted in a batch system at ambient conditions. It was found that the oxidation in the presence of molecular oxygen with Fe(III) salts was able to convert the thiophenic compounds in the fuel to the corresponding sulfone and/or sulfoxide compounds at 25°C. The oxidation reactivity of the sulfur compounds decreases in the order of 2-methylbenzothiophene>5-methylbenzothiophene>benzothiophene≫dibenzothiophene. The alkyl benzothiophenes with more alkyl substituents have higher oxidation reactivity. In real JP-8 fuel, 2,3-dimethylbenzothiophene was found to be the most refractory sulfur compound to be oxidized. The catalytic oxidation of the sulfur compounds to form the corresponding sulfones and/or sulfoxides improved significantly the adsorptivity of the sulfur compounds on activated carbon, because the activated carbon has higher adsorptive affinity for the sulfones and sulfoxides than thiophenic compounds due to the higher polarity of the former. The remarkable advantages of the developed ODS method are that the ODS can be run in the presence of O2 at ambient condition without using peroxides and aqueous solvent and thus without involving the biphasic oil–aqueous-solution system.

Importance of Structural and Chemical Heterogeneity of Activated Carbon Surfaces for Adsorption of Dibenzothiophene

The performance of various activated carbons obtained from different carbon precursors (i.e., plastic waste, coal, and wood) as adsorbents for the desulfurization of liquid hydrocarbon fuels was evaluated. To increase surface heterogeneity, the carbon surface was modified by oxidation with ammonium persulfate. The results showed the importance of activated carbon pore sizes and surface chemistry for the adsorption of dibenzothiophene (DBT) from liquid phase. Adsorption of DBT on activated carbons is governed by two types of contributions: physical and chemical interactions. The former include dispersive interactions in the microporous network of the carbons. While the volume of micropores governs the amount physisorbed, mesopores control the kinetics of the process. On the other hand, introduction of surface functional groups enhances the performance of the activated carbons as a result of specific interactions between the acidic centers of the carbon and the basic structure of DBT molecule as well as sulfur-sulfur interactions.

Dynamics of removal of organosulfur compounds from diesel by adsorption on carbon aerogels for fuel cell applications

Carbon aerogels (CAs) were investigated as adsorbents for the desulfurization of liquid hydrocarbon fuels for fuel cell applications. Synthetic mixtures of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) in n-hexadecane (n-HD) were used as models for sulfur contaminated diesel fuel. Carbon aerogels were found to have good adsorption capacity for both DBT and 4,6-DMDBT. Both the thermodynamics and dynamics of adsorption were investigated by the measurement of adsorption isotherms and concentration decay curves in batch mode. A theoretical model was developed to describe the dynamics of adsorption of both DBT and 4,6-DMDBT on CAs from model diesel and it was found to represent the experimental data fairly well. The model takes into account pore diffusion and assumes local equilibrium within the pores. The tortuosities of 22nm pore diameter CA and 4nm pore diameter CA were found to be 3.5 and 4.0, respectively. For the latter, a restrictiveness factor had to be included due to the closeness of the size of the solute, DBT, to the pore size. The simulations indicated that the particle diameter and the pore size of the carbon aerogel adsorbent were critical parameters in design of large-scale fixed-bed adsorbers for sulfur removal.

Ultra-deep Desulfurization of Liquid Hydrocarbon Fuels: Chemistry and Process

Recently, ultra-deep desulfurization of liquid hydrocarbon fuels is becoming very important worldwide not only because of the heightened interest for cleaner air and thus increasingly stringent environmental regulations for fuel sulfur content, but also because of the great need for making ultra-low-sulfur fuels used in hydrocarbon fuel process for fuel cell applications. This article is a selective review on chemistry and process concerning the ultra-deep desulfurization of liquid hydrocarbon fuels. The principles and problems for the existing hydrodesulfurization processes and the challenges, concepts, advantages, and disadvantages of various new approaches are discussed, including (1) sulfur compounds in liquid hydrocarbon fuels; (2) Reactivity and mechanistic aspect of various sulfur compounds; (3) Challenges in ultra-deep desulfurization processes; (4) Approaches to ultra-deep desulfurization process.

Removal of Dibenzothiophene from Model Diesel by Adsorption on Carbon Aerogels for Fuel Cell Applications

Carbon aerogels (CAs) were studied as adsorbents for the desulfurization of liquid hydrocarbon fuels for fuel cell applications. A synthetic mixture of dibenzothiophene (DBT) and n-hexadecane (n-HD) was used as a model for sulfur contaminated diesel fuel. Carbon aerogels with two different average pore sizes (4 and 22 nm) were synthesized, characterized, and tested for adsorption of DBT at ambient temperature and atmospheric pressure. The approach-to-equilibrium was monitored, and adsorption isotherms were measured. The CA with the larger average pore size had a higher sulfur adsorption rate and a higher capacity for DBT. The isotherms were best represented by the Freundlich model. According to the Langmuir isotherm, the adsorption capacities of the 4 nm CA and 22 nm CA were 11.2 and 15.1 mg S/g dry CA, respectively. The CAs were found to selectively adsorb DBT over naphthalene, which is a chemically similar but non-sulfur containing organic compound, when both are present in solution. However, the presence of naphthalene slightly reduced the amount of DBT adsorbed.