Adsorption and Ultrasound-Assisted Sorbent Regeneration

Abstract

This work was conducted for the department of Energy. In this work, we developed a class of new sorbents that were highly sulfur sepective and had high sulfur capacities. The study consisted of two sections. Development of the new sorbents is described in Section 1, and Section was a fundamental study, conducted for a better understanding for desulfurization of jet fuels. More details of the results are given blow separately for the two sections. Section 1: Desulfurization of Model Jet Fuels by Adsorption on Carbon-based Sorbents and Ultrasound-Assisted Sorbent RegenerationSeveral high-sulfur-capacity carbon-based adsorbents, CuCl/AC, PdCl 2 /AC, and Pd/AC (where AC denotes activated carbon), were studied for desulfurization of a model jet fuel by selective adsorption of thiophenic molecules. The model jet fuel (150 ppmw-S BT and 250 ppmw-S MBT in 19.75 wt% benzene + 80 wt% n-octane containing 700 ppmw naphthalene) was formulated such that it represented all jet fuels well. In addition, a commercial jet fuel, JP-5 was included in the tests. Comparisons with γ-Al 2 O 3 support and desulfurization of a commercial jet fuel were also studied. The results showed that the selective sulfur adsorption capacity of PdCl 2 was higher than that of CuCl and Pd 0 , in agreement with molecular orbital results. It was also found that the activated carbon is the best support for π-complexation sorbents to remove sulfur-containing compounds, i.e. benzothiophene and methylbenzothiophene. Among all the adsorbents studied, PdCl 2 /AC had the highest capacity for desulfurization. A significant synergistic effect was 3 observed between the carbon substrate and the supported π-complexation sorbent, and this effect was explained by a geometric effect. The saturated sorbent was regenerated by desorption assisted by ultrasound with a solvent of 30 wt% benzene and 70 wt% noctane. The results showed that the amount of sulfur desorbed was higher with ultrasound, 65 wt% desorption vs. 45 wt% without ultrasound in a static system at 50 o C. Section 2: Selective Adsorption of Sulfur Compounds: Isotherms, Heats and Relationship between Adsorption from Vapor and Liquid SolutionThis was a basic study in order to understand and better design sorbents for desulfurization of jet fuels. Adsorption isotherms were measured for thiophenic sulfur compounds, thiophene (T), benzothiopnene (BT), 2-methyl benzothiophene (2-MBT) and dibenzothiophene (DBT), from their binary solutions in n-octane. Two sulfur-selective, π-complexation sorbents were studied: Cu(I)-Y zeolite and PdCl 2 impregnated on activated carbon (PdCl 2 /AC). Vapor-phase isotherms of n-octane and thiophene were also measured. The selectivity of adsorption from liquid solutions followed the order of: T < BT < 2-MBT < DBT for PdCl 2 /AC, and T < DBT < 2-MBT < BT for Cu(I)-Y zeolite. The adsorption bond energies, which approximate the heats of vapor-phase adsorption, followed the order: T < BT < 2-MBT < DBT. This order was not followed for adsorption from liquid solutions on Cu-Y zeolite...