Nanocomposites and Hybrid Materials for Adsorptive Desulfurization

1. Introduction

Fossil fuels are the main source of energy worldwide; crude oil, which occurs naturally and comprises of several organic components (such as diesel, gasoline, jet fuels, kerosene etc.), serves as the major source of energy in the world. Crude oils are usually classified based on density and sulfur content. The lighter the crude oil the better its value and the lower the sulfur content in crude oil the better its profitability. Sulfur is the main important hetero-element found in crude oil and has the most significant effect on refining. It poisons catalyst, corrode refining equipment, and combustion of the products of sulfur from automobiles impair the emission control technology designed to meet the nitrogen oxides (NOx) and particulate emission standards which leads to environmental pollution. It contributes to the deterioration of air quality and affects public health and the ecosystem. The maximum allowable sulfur content in highway diesel fuel in the US was 15 ppmw in 2006 and it will be less than 10 ppmw by 2017. Sulfur compounds found in crude oil are divided into aliphatic (mercaptans, sulfides, disulfides) and aromatic refractory group (thiophenes derivatives). The methods in use for the removal of sulfur compounds in fuels are either pre-combustion techniques or the post combustion techniques. The pre-combustion techniques are the best methods and they involve the decomposition of sulfur compounds, removal of the compounds without decomposition and final separation of the compounds followed by decomposition (Babich et al., 2003). The conventional method used by refineries for the removal of sulfur from the fuel is hydrodesulphurization (HDS) (Bej 2004). It is efficient in the removal of most aliphatic sulfur compounds from fuels e.g. thiols. However, it is not efficient in the removal of aromatic refractory sulfur compounds e.g. thiophene derivatives (dibenzothiophene (DBT) and 4, 6 dimethyl dibenzothiophene (DMDBT)) which are the least reactive and pose more serious danger to the environment. In addition, it requires high temperature, pressure and high dosage of catalyst before achieving the desired objective which is uneconomical (Ali et al., 2006).