(563k) Extractive Denitrogenation and Desulfurization of Crude Oil Using Deep Eutectic Solvents

Hydrotreatment is the established method in the industry for removal of aromatics and heteroaromatics from crude oil. Conventionally, hydrotreatment is conducted at relatively high pressure (⁓ 3.5 - 7 MPa) and temperature (⁓ 573 – 673 K) resulting in an expensive and energy-consuming process. Moreover, it suffers from high hydrogen consumption and low removal efficiency for some heteroaromatics (i.e. S- and N-containing aromatic) due to steric hindrance. Aiming to reduce the energy requirements, hydrogen consumption and improve the efficiency of this separation, liquid-liquid extraction is proposed. The main objective of this work was to selectively remove the sulfur- and nitrogen-containing aromatics from crude oil using a highly selective solvent as an extractive agent. This allows the removal of (S- and N-containing) heteroaromatic compounds from crude oil at milder conditions (near atmospheric) and without any hydrogen consumption, making the process much more energy- and cost-effective. Deep eutectic solvents (DESs) are proposed as an extractive agent for this application. DESs are analogus to ionic liquids in terms of low volatility and tuneability of physiochemical properties, however, being easier to make from low-cost starting material and more environmentally benign.

Building on the literature finding, phosphonium-based DESs were selected for the removal of S- and N-containing aromatic from crude oil “represented by n-alkanes”. Next, solubility measurements of S- and N-containing aromatics and n-alkanes in DESs were carried out to examine the suitability of the DESs for this extraction. Then, the single stage liquid-liquid equilibrium data of {n-alkane + heteroaromatic + DES} systems were determined at 298 K and atmospheric pressure. The experimental LLE data were correlated using the nonrandom two-liquid thermodynamic model. Also, the solute distribution ratios and the selectivities were calculated from the experimental LLE data and compared to the relevant literature. It was found that the DESs are potential solvents for extractive desulfurization processes.