Screening of Deep Eutectic Solvents as Green Solvents for the Purification of Diesel

Abstract

The oil and gas industry has been under great strain in the last decade with the increase in energy demand and restrictive quality control. Diesel is one of the major products from refining crude oil that had no exception to this strain. The pretreatment of diesel from aromatics is usually achieved via hydrogenation at very high temperature and pressure, which is an energy-intensive process and releases harmful emissions to the equipment, workers, and environment. Many alternative methods have been investigated, and one of the most promising is Liquid-Liquid Extraction (LLE). Such potential candidates for fuel dearomatization are deep eutectic solvents (DESs), which are considered novel ‘green' solvents, mainly due to having negligible vapor pressure, low flammability, and being very tailorable. In this study, DESs were screened for their capability to extract aromatics (e.g. toluene) S-containing aromatics (e.g. thiophene) and N-containing aromatics (e.g. pyridine) from n alkanes using COnductor like Screening MOdel for Real Solvents (COSMO-RS). A total of 69 DESs were screened and their performance index values were calculated. The DESs were evaluated at different HBA:HBD molar ratios; 1:2, 1:3, 1:4 and 1:5. Then, each DES was presented with the molar ratio at which each DES had their highest performance index. The highest performing DESs were acid-based or urea-based DESs. Nonetheless, most of these DESs were hypothetical combinations, or had a corrosive or reactive nature, and thus were excluded. The final selection fell on methyltriphenylphosphonium bromide: triethylene glycol (MTPB:TEG) (1:4), which had an extraction efficiency of 21.9, 72.8, and 54.5% for toluene, quinoline, and thiophene, respectively, in a single extraction stage. The extraction efficiency of MTPB:TEG (1:4), was experimentally validated and found to be 8.9, 87.4, and 29.4% for toluene, quinoline, and thiophene, respectively. Furthermore, the DES regeneration was tested using two different approaches: (1) DES washing via anti-solvent (water or diethyl ether), and (2) back extraction using n-heptane. It was found that diethyl ether reacted with the DES, so it was excluded. Water washing and back-extraction have successfully removed all toluene and thiophene. Regarding quinoline, back-extraction with n-heptane reduced the quinoline from 22.80 to 16.78wt%. While, water washing remarkably reduced quinoline to 0.88wt%.

Date of Award	Jun 2021
Original language	American English