Coordination Polymers and Polymer Nanofibers for Effective Adsorptive Desulfurization

Desulfurization of fuel oils is an essential process employed in petroleum refineries to reduce the sulfur content to levels mandated for environmental protection. Hydrodesulfurization (HDS), which is currently being employed, is limited in treating refractory organosulfur compounds and only reduces the sulfur content in fuels to a range of 200-500 ppmS. In this chapter, several scientific and technological advances reported in the literature for the desulfurization of fuels are reviewed and discussed. Amongst these techniques, oxidative desulfurization (ODS) and adsorptive desulfurization (ADS) are proposed as additional steps to complement HDS in meeting the mandated ultra-low sulfur levels (10 ppmS). In the ODS technique, refractory organosulfur compounds are oxidized to organosulfones, followed by solvent extraction or adsorption of the organosulfones. The chemistry involved in the development and fabrication of sulfur/sulfone responsive adsorbents is also discussed. The use of molecular imprinted polymers (MIPs) and coordination polymers (CPs) for the selective adsorption of organosulfone compounds (in ODS) and/or organosulfur (in ADS) offers various properties such as imprinting effect, hydrogen bonding, π-π interactions, van der Waals forces, π-complexation, and electrostatic interactions. CPs, in particular metal organic frameworks (MOFs), have been reported to possess suitable features to overcome most of these challenges associated with adsorptive ultra-deep desulfurization when design strategies to achieve good selectivity are strictly followed. Matching the sizes of the cavities to the critical dimensions of the sulfur containing compounds (SCCs), using suitable metal centres which allow for coordinative interaction with the SCCs and using linkers with suitable functionality as to enhance specific interaction (dispersion forces) with the SCCs were considered to be pivotal features to prioritize. The prospects for the use of MIPs and CPs for future industrial applications in desulfurization are envisaged.

Environmental Concerns and the Importance of Desulfurization

The increased utilization of fossil fuels and subsequent industrialization in most of the world has led to a remarkable increase in the atmospheric sulfur compounds concentrations. Pollution released by the use of petroleum-based fuels contributes immensely to the deterioration of air quality despite regulatory and technological advances in place. SOx, NOx, and particulate matter are constantly emitted to the environment which affects public health, ecosystem, and general wellbeing of the people living mostly in urban areas. Sulfur dioxide, which is the immediate sulfur compound found in the lower atmosphere after combustion of fuels, has a major role to play in the formation of acid rain, smog formation, and particulate aerosols. Each of these formations affects the healthy living of animals, plants, soils, water, and the general ecosystem. This chapter discusses the environmental issues of sulfur.

Advances in Carbon-Based Nanocomposites for Deep Adsorptive Desulfurization

The ultra-low sulfur diesel (ULSD) is required to comply with stricter government policy on low sulfur content of transportation fuels. Better knowledge of the different factors that concern deep desulfurization of fuels is necessary to achieve ultra-low sulfur content and cheaper way of producing ULSD. Both the capital and operating cost of the adsorptive desulfurization process is cheaper compare to the conventional hydroprocessing. In the future, the need to produce more volume of fuels with very low sulphur content from low-grade feedstocks like heavy oil and light cycle oil in order to meet up with the global demand for sulphur-free fuels is pertinent. Several on-going researches are pointing to the use of adsorbents for removal of sulfur compounds from hydrocarbon refining stream. In this chapter, varieties of carbon nanomaterials suitable for adsorptive desulfurization are discussed. If the active lifetime, where the capacity of the adsorbents are adequate, the approach is practically feasible for commercial application.

Nanomaterials and Nanocomposites for Adsorptive Desulfurization

Desulfurization (removal of S compounds) of fuels is an important research topic in recent years. Several techniques have been reported to remove the sulfur-containing compounds in fuels. One of these techniques is adsorptive desulfurization (removal based on chemisorption and physisorption), which has received much attention because of low energy consumption and facile operation condition. This chapter discusses the methods employed under this technique and the types of nanocomposites and hybrid materials (adsorbents) that have been investigated as potential adsorbents. The strategies to enhance sulfur adsorption capacity and main challenges will be discussed.

Advanced Desulfurization Technologies and Mechanisms

This chapter describes different desulfurization technologies used for the removal of sulfur from petroleum products or from refined products. These technologies include hydrodesulfurization and non-hydrodesulphurization such as extractive desulphurization, adsorptive desulfurization, precipitative desulphurization, oxidative desulphurization, and desulfurization by membranes. Types of reactors including batch and fixed bed reactors are discussed. The chapter also highlights some of the common mechanism to explain the desulphurization process.

Polyoxometalates-Based Nanocatalysts and Their Efficiency for Production of Sulfur-Free Diesel

Polyoxometalates have been demonstrated to be efficient catalysts for the activation of oxidants in desulfurization processes. Successful results on desulfurization using polyoxometalates and hydrogen peroxide to desulfurize model oils and liquid fuels were reported and can be found in the literature. The desulfurization is an actual subject with notable interest for refineries and fuel cost, and consequently, it is important to focus the scientific community to work in desulfurization technology in order to develop catalytic systems based on polyoxometalates capable to be reused, stable, efficient, and selective. Therefore, the main goal is the design of heterogeneous polyoxometalate based catalysts. This chapter pretends to inform the research society about the scientific directions that have been taken using heterogeneous polyoxometalate catalysts in oxidative desulfurization of simulated and real liquid fuels. In addition, future perspectives are proposed to cover the actual needs of this area.

The Relation of Ni/ZnO Nano Structures With Properties of Reactive Adsorption Desulfurization

Ni/ZnO nano-sorbent systems have been extensively used in the reactive adsorption desulfurization (RADS) of gasoline steams, especially in China, to meet the more rigorous regulation on the sulfur content. The apparent advantage of RADS is that most of the olefins are kept in the product with low consumption of hydrogen and little loss of octane. The authors discussed in this chapter the relation of catalytic properties with components and structures of Ni/ZnO sorbent. Based on detailed characterization and reaction results, they revealed the dynamic change of Ni/ZnO sorbents during RADS, the mechanisms of desulfurization, and the sulfur transfer and sulfur adsorption. Apart from the RADS of Ni/ZnO nano-sorbent for cleaner gasoline production, they also presented other potential applications.

Advances in the Reduction of the Costs Inherent to Fossil Fuel Biodesulfurization Towards Its Potential Industrial Applications

The biodesulfurization (BDS) process consists of the use of microorganisms for the removal of sulfur from fossil fuels. Through BDS it is possible to treat most of the organosulfur compounds recalcitrant to the conventional hydrodesulfurization (HDS), the petroleum industry's solution, at mild operating conditions, without the need for molecular hydrogen or metal catalysts. This technique results in lower emissions, smaller residue production, and less energy consumption, which makes BDS an eco-friendly process that can complement HDS making it more efficient. BDS has been extensively studied and much is already known about the process. Clearly, BDS presents advantages as a complementary technique to HDS; however, its commercial use has been delayed by several limitations both upstream and downstream the process. This study will comprehensively review and discuss key issues, like reduction of the BDS costs, advances, and/or challenges for a competitive BDS towards its potential industrial application aiming ultra-low sulfur fuels.