(191e) Investigation of Rare Earths Exchanged on Zeolite Y for Adsorptive Desulfurization of Model Fuels in the Presence of Aromatics

Investigation
of Rare Earths Exchanged on Zeolite Y for Adsorptive Desulfurization of Model
Fuels In the Presence of Aromatics

Tyler
B. Crowl, Kevin X. Lee, and Julia A. Valla

Department of Chemical
& Biomolecular Engineering, University of
Connecticut, 191 Auditorium Road, Unit 3222, Storrs, CT 06269-3222, USA,

Phone: +1-860-486 2508, e-mail: ioulia.valla@.uconn.edu

            Sulfur compounds are found in hydrocarbon
transportation fuels and when combusted pose a threat to the environment. The traditional
Hydrodesulphurization (HDS) process requires high operating costs and excess
hydrogen to deeply desulfurize the fuel and the severity of the operating
conditions may degrade the quality of the fuel. Adsorptive desulfurization (ADS)
using bimetallic ion exchanged zeolite Y is an attractive alternative to HDS
which can be effective at even ambient conditions.¹ Cerium, a rare earth, has been shown to
exhibit excellent capacity and selectivity for the removal of benzothiophene through the formation of π-complexation and direct σ-bond, when ion-exchanged into zeolite Y.²
Copper has been shown to have a synergistic relationship with Ce on zeolite Y that
enhances the adsorption capacity and the overall desulfurization performance.³
This study investigates other Rare Earths (RE) such as La, Sm, Nd, Pr, and bimetallic Cu-RE
combinations to understand the effect of RE on ADS of benzothiophene.

            Y Zeolite was ion-exchanged with
different RE to 5wt% and materials were characterized by several techniques to
verify successful loading of the metals. Mesoporous materials were synthesized
using a top-down approach prior to ion-exchange with Cu-RE.⁴ Surface
acidity was determined by using pyridine diffuse reflectance infrared
spectroscopy (DRIFTS-FTIR). Metal loadings on the zeolite were quantified
using inductively couple plasma mass spectrometry (ICP-MS). The crystalline
structure was determined by X-ray diffractometer (XRD) measurements.

            Adsorption
experiments were conducted in a fixed-bed column to study the continuous
adsorption of sulfur compounds in model fuels. The mass of sorbent was varied
between 0.2 and 0.3 grams to achieve a constant bed height of 3cm. The model
fuels were prepared by combining 100 ppm sulfur of benzothiophene
(BT) in octane and 20% benzene and 100ppm sulfur of dibenzothiophene
(DBT) in octane with 1% naphthalene. The effluent was collected periodically
and analyzed using a gas chromatograph sulfur chemiluminescence
detector (GC-SCD). Figure 1a shows that PrY performed
the best out of the new RE tested, but still did not outperform CeY. Thus, the order from highest capacity to lowest was
found to be Ce>Pr>La>Nd>Sm.
Figure 1b shows the BT breakthrough curves on bimetallic Cu-RE materials. The
best performing bimetallic RE was CuCeY, with a capacity
of 1.756 mg S g^-1, and the order from highest capacity to lowest was
Ce>Nd>Sm>Pr>La.
The addition of Cu enhances the BT adsorptive capacity for all of the RE
tested, but did not show a significant increase for La and Pr. BT
adsorption results show that Ce is the best performing RE and has the most
synergistic performance.

Figure 1: Breakthrough curves of BT on (a) REY and
(b) Bimetallic RE Y with 20% benzene in octane.

            In the presentation, corresponding RE exchanged with
mesoporous zeolite Y will be discussed showing the results of the DBT
adsorption. Overall trends between BT and DBT adsorption on RE will be also
discussed.

References

1.
Lee KX, Valla JA. Applied Catalysis B : Environmental Investigation of
metal-exchanged mesoporous Y zeolites for the adsorptive desulfurization of
liquid fuels. "Applied Catal B, Environ. 2017;201:359-369.
doi:10.1016/j.apcatb.2016.08.018

2.
Velu S, Ma X, Song C. Selective Adsorption for
Removing Sulfur from Jet Fuel over Zeolite-Based Adsorbents. 2003:5293-5304.
doi:10.1021/ie020995p

3.
Lee KX, Tsilomelekis G, Valla JA. Applied Catalysis
B : Environmental Removal of benzothiophene and
dibenzothiophene from hydrocarbon fuels using CuCe mesoporous Y zeolites in the presence of aromatics. Appl Catal B Environ. 2018;234(April):130-142. doi:10.1016/j.apcatb.2018.04.022

4.
García-Martínez J, Johnson M, Valla J, Li K, Ying JY.
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