Article pubs.acs.org/IECR
Graft Copolymerization of Glycidyl Methacrylate and Ethylene Glycol Dimethacrylate on Alumina for the Removal of Nitrogen and Sulfur Compounds from Gas Oil Ali Abedi,† Jackson M. Chitanda,† Ajay K. Dalai,*,† and John Adjaye‡ †
Department of Chemical and Biological Engineering, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5A9, Canada Syncrude Edmonton Research Centre, Edmonton, Alberta T6N 1H4, Canada
‡
S Supporting Information *
ABSTRACT: Functionalized polymers were synthesized and applied in removing nitrogen and sulfur compounds from gas oils. In this work, the polyglycidyl methacrylate-co-ethylene glycol dimethacrylate polymer incorporated with tetranitrofluorenone, PGMA-DAP-TENF, was synthesized with and without alumina support. Different techniques were used to characterize the synthesized polymers including Fourier transform infrared spectroscopy, Brunauer−Emmett−Teller method, dynamic light scattering, thermogravimetry/differenial thermal analyzer, carbon hydrogen nitrogen sulfur elemental analysis, and field emission scanning electron microscopy. The performance of the polymer with alumina, Al-PGMA-DAP-TENF, was compared to that without alumina using light gas oil. In addition, heavy gas oil feed was used to confirm the adsorption behavior of both polymers in a higher nitrogen and sulfur environment. The effect of adsorption time and temperature was tested using a 1:5, by weight, polymer to feed ratio. Results have shown that alumina particles enhanced the nitrogen removal efficiency of PGMA-DAP-TENF polymer while sulfur removal efficiency was not affected. The nitrogen removal efficiency of Al-PGMA-DAP-TENF polymer was more than twice that of PGMA-DAP-TENF polymer in LGO feed, and twice that in HGO feed. This was due to the higher surface area of Al-PGMA-DAP-TENF polymer, 202 m2/g, compared to that of PGMA-DAP-TENF polymer, 27 m2/g. In addition, Al-PGMA-DAP-TENF polymer removed more basic nitrogen compounds than PGMA-DAP-TENF polymer. This was attributed to the acidic nature of alumina particles that enhance the adsorption of basic nitrogen compounds present in gas oil feeds.
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INTRODUCTION
removing nitrogen compounds has a positive effect achieving ultradeep HDS.12,17−19 Different materials have been proposed to remove nitrogen compounds including silica gel, alumina, active carbon, and ion exchange polymers.6 However, using functionalized polymers by immobilization of π-acceptors on polymer supports has shown promising results on removing nitrogen and sulfur species from gas oil.20−24 The functionalized polymer method is based on the formation of charge transfer complexes (CTC) between π-acceptors in the polymer and π-donor nitrogen compounds in gas oil. The oil feed is pretreated with functionalized polymers prior to the HDS process to selectively remove nitrogen and sulfur compounds. Different combinations of polymer supports and π-acceptors have been proposed in which polyglycidy methacrylate-co-ethylene glycol dimethacrylate (PGMA-co-EGDMA) as a polymer support, and tetranitrofluorenone (TENF) as π-acceptor have successfully removed 11−19% of nitrogen content from light gas oil,21,23,24
The removal of refractory sulfur compounds using the standard hydrodesulfurization (HDS) processes is a great challenge facing oil sand derived fuels today, due to the high sulfur and nitrogen contents in oil sands derived gas oils (4% and 0.4%, respectively) and the strict environmental regulations to produce ultralow sulfur gasoline and diesel fuels.1 Nitrogen compounds in gas oil have been identified as severe inhibitors for the HDS catalyst,2−11 even when they are present at low concentrations.2−7 Nitrogen compounds inhibit HDS reactions by poisoning the catalyst and competing with sulfur compounds over active sites.12 Nitrogen compounds found in gas oil are divided into two types: basic and nonbasic compounds. Studies have shown that both types retard HDS reactions.2−4,13 Basic nitrogen compounds hinder HDS reactions by interactions with acidic sites of the catalyst.14 Nonbasic nitrogen, which accounts for approximately 70% of the total nitrogen content of heavy gas oil,3,15 inhibits HDS reactions by either adsorption over the support surface or conversion to basic nitrogen compounds via hydrogenation.4,16 Laredo et al. found that the inhibition effect of basic nitrogen and nonbasic nitrogen were similar.2−4 Studies have shown that © XXXX American Chemical Society
Received: June 15, 2016 Revised: August 20, 2016 Accepted: August 21, 2016
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DOI: 10.1021/acs.iecr.6b02319 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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Figure 1. Synthesis of Al-PGMA-DAP-TENF polymer.
and 5−6% from heavy gas oil.22,23 In addition, PGMA-based particles can be separated from gas oil and regenerated using vacuum filtration and Soxhlet extractor, respectively.22,24 For example, PGMA-NN-TENF retained its nitrogen removal efficiency in heavy gas oil feed, around 6.5%, when it was washed with toluene.22 Polymer support can play a key role in increasing the efficiency and selectivity of the functionalized polymers. The higher is the surface area of the polymer, the more nitrogen compound it can remove.23 Further, studies have shown that using high surface area materials allows for selective removal of sulfur and nitrogen.12 Materials with high surface area, such as alumina, can be used with different polymers in order to increase the overall surface area of the material; and hence the adsorption efficiency. Studies have shown that grafting of polymers onto inorganic particles, such as SiO2, Al2O3, and TiO2, can enhance the mechanical and chemical properties of the polymers.25−30 For example, Jiao et al. observed increase in the strength of epoxy resin composites by grafting polyglycidyl methacrylate (PGMA) onto Al2O3 particles.28 To graft a polymer onto the alumina surface, first a silane coupling agent was used to modify the alumina surface; then a free-radical polymerization method was used to graft the polymer onto the alumina particles.27 Further, Guo et al. studied different methods and conditions to graft polystyrene onto the surface of silica gel surface.29,30 Our previous studies have shown that increasing the surface area of the polymer can enhance the efficiency of nitrogen removal from gas oil.23 The focus of all these studies was to change the selection of polymer support, linker, and π-acceptor without the addition of new compounds that could enhance the adsorption capacity of the functionalized polymer. Therefore, graft polymerization of (PGMA-co-EGDMA) polymer support onto alumina particles will be used to increase the surface area; and hence the
efficiency of nitrogen compounds removal from light and heavy gas oil feeds.
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EXPERIMENTAL PROCEDURES To study the effect of graft polymerization of polymer support onto alumina particles, two compounds were synthesized: the first compound consists of PGMA-co-EGDMA polymer grafted onto alumina particles (Al-PGMA-DAP-TENF), while the other was (PGMA-DAP-TENF) without alumina. For both polymers, polyglycidyl methacrylate-co-ethylene glycol dimethacrylate (PGMA), 1,3-diamnopropane (DAP), and 2,4,5,7tetranitro-9-fluorenone (TENF) were used as a polymer support, linker, and π-acceptor, respectively. The adsorption capacity was tested using different feeds including light gas oil (LGO) and heavy gas oil (HGO). In the first stage of this work, the polymers were synthesized and characterized, and then in the second stage the performance of both polymers was tested in a batch adsorption system, which consists of a 20 mL glass vial with a cap and a magnetic stirring bar; 1 g of dry polymer sample was mixed with 5 g of gas oil at 200 rpm. The removal efficiency R [%] was determined using the following equation: R [%] = (C i − Cf )/C i × 100
where Ci and Cf represent the concentration of nitrogen or sulfur compounds in untreated and treated feed, respectively. Materials. The starting materials were purchased from different sources. Sigma-Aldrich was the source for fuming nitric acid (>90%), glycidyl methacrylate (GMA), ethylene glycol dimethacrylate (EGDMA), poly[N-vinyl-2-pyrrolidone], PVP (average Mw 55 000 g/mol), 1-dodecanol (≥98.0%), cyclohexanol (99.0%), 1,3-diamnopropane (≥99%) (DAP), 3(trimethoxysilyl) propyl methacrylate (MPS), p-toluenesulfonic B
DOI: 10.1021/acs.iecr.6b02319 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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Industrial & Engineering Chemistry Research acid monohydrate (ACS reagent, ≥98.5%), and 1,4-dioxane (anhydrous, (99.8%). Fisher Scientific was the source for concentrated 95−98 w/w % sulfuric acid (certified ACS plus), acetone (cerified ACS), toluene (ACS reagent (≥99.5%)), acetic acid glacial (certified ACS), and ethanol (95%). Alfa Aesar was the source for 9-flourenone 98+%. Molekula Ltd. was the source for Azobis(isobutyronitrile) (AIBN), and Kaiser Chemicals provided substrate alumina. Polymer Synthesis. PGMA-DAP-TENF polymer was synthesized in three stages. First, PGMA-co-EGDMA polymer support, referred to as PGMA, was synthesized based on a method described by Svec et al.31 and modified by Abedi et al.23 First, PGMA polymer was synthesized by mixing GMA, EGDMA, and AIBN initiator in a 1000 mL three-neck round flask. Then two solutions, (1) PVP + DI water and (2) cyclohexanol + dodecanol, were added to the reactor. Then the reaction proceeded for 8 h at 80 °C under a nitrogen environment. For PGMA synthesis details refer to Rizwan et al.22 Second, DAP linker was attached to PGMA polymer support by mixing both compounds in ethanol solvent at 80 °C for 24 h. Third, the polymer support was incorporated with TENF π-acceptor by dissolving TENF in toluene and acetic acid solution, then adding PGMA. The reaction continued for 48 h at 90 °C. After each step the product was washed with the appropriate solvent and dried for 24 h under vacuum. TENF πacceptor was also synthesized in the laboratory using concentrated sulfuric and nitric acids with flourenone as described by Newman et al.,32 and modified by Abedi et al.23 For the Al-PGMA-DAP-TENF polymer, Al2O3 particles were first activated by using p-toluenesulfonic acid and dioxane as a solvent. p-Toluenesulfonic acid powder was dissolved in dioxane, then Al2O3 powder was added, and the temperature was increased to 100 °C. After 3 h, the product was filtered, washed with distilled water, and then dried under vacuum for 24 h. The MPS was attached to Al2O3 by adding activated Al2O3 powder, MPS, and ethanol in a three-neck round-bottom flask. The mixture was heated to 70 °C, and the reaction continued, under nitrogen, for 24 h. Once the reaction was over, the product, Al-MPS, was filtered and washed with ethanol and distilled water to remove unattached MPS. The product was allowed to dry under vacuum overnight. The next step was grafting PGMA into Al-MPS. Under nitrogen flow, in a 1000 mL three-neck round-bottom flask, equipped with a condenser, Al-MPS was dissolved in an ethanol and distilled water mixture. Then GMA, EGDMA, and AIBN initiator were added to the mixture. The temperature was increased to 70 °C, and the reaction was carried out for 24 h. The white product, Al-PGMA, was filtered and washed with ethanol and distilled water to remove unattached monomers, filtered, and dried in vacuum oven at 90 °C for 24 h. DAP and TENF were attached to Al-PGMA polymer respectively using similar procedures that were described earlier for PGMA-DAP-TENF polymer. Figure 1 illustrates the summary of Al-PGMA-DAP-TENF polymer synthesis. Polymer Characterization. Al-PGMA-DAP-TENF particles were characterized at different stages of synthesis using Fourier transform infrared (FT-IR) spectroscopy, Brunauer− Emmett−Teller (BET) method, dynamic light scattering (DLS), thermo gravimetry/differenial thermal analyzer (TGA/DTA), carbon hydrogen nitrogen sulfur (CHNS) elemental analysis, field emission scanning electron microscopy (FE-SEM), nitrogen and sulfur analyzer, and potentiometric titrator. FT-IR spectra were recorded using PerkinElmer
Spectrum GX instrument to identify the characteristic peaks of different functional groups at each stage of polymer synthesis. The sample was prepared for FT-IR analysis by mixing a few milligrams of the powder sample with KBr, and then the mixture was ground and pelletized. Prior to analysis, a blank sample of KBr only was run to calibrate the FT-IR instrument. All spectra were acquired with 16 scans, at the range of 400−2000 cm−1. For pyridine-FTIR analysis, pyridine adsorption was performed at room temperature overnight, and then the sample was kept in an oven for 1 h at 100 °C. After cooling to room temperature, the FTIR spectrum was recorded. For the dynamic light scattering (DLS) analysis, a Malvern Zetasizer Nano ZS instrument (Malvern Instruments Ltd., Westborough, MA, USA) was used to determine polydispersity index (PDI) of the polymers. The PDI was obtained in aqueous solution by suspending the polymer in 1 mL of water. Based on nitrogen adsorption and desorption at 77 K, surface area, pore size, and pore volume of the polymer were determined using Micromeritics 2000 ASAP analyzer. Before analysis, 0.1−0.2 g of the sample was degassed for 90 min at 150 °C under a vacuum of 10 μmHg. TGA/DTA analysis was performed using TGA Q500 model instrument. Under N2 atmosphere, 10−15 mg of the sample was heated to 600 °C at 10 °C/min, and data were recorded at 20 s intervals. Vario EL III CHNS element analyzer was used to determine carbon, hydrogen, nitrogen, and sulfur content in the polymer sample. A 4−6 mg portion of the sample was weighed in a tin boat and placed in the CHNS analyzer for combustion. Before the samples were analyzed, sulfanilic acid was used as a standard to calibrate the CHNS peaks. The surface morphology of the polymer at different synthesis stages was determined using the (FE-SEM) SU6600 machine. The polymer sample was sputter-coated with gold before analysis. The total nitrogen and sulfur contents of the oil samples were determined using an Antek-model 9000 N/S analyzer using a pyrofluorescence technique, following the ASTM D5453 method, and pyrochemiluminescence techniques, following the D4629 method, respectively.
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RESULTS AND DISCUSSION Different characterization methods were used at different stages of the synthesis to confirm the grafting of PGMA polymer support onto alumina particles. The performance of the grafted polymer onto alumina particles, Al-PGMA-DAP-TENF, toward nitrogen and sulfur removal from light and heavy gas oil samples was compared to the nonalumina containing polymer, PGMA-DAP-TENF. Polymer Synthesis and Characterization. To confirm the synthesis of the grafted polymer, the FT-IR spectra of untreated alumina (Al), PGMA grafted alumina (Al-PGMA), and final functionalized polymer with TENF π-acceptor attached (Al-PGMA-DAP-TENF) were recorded as shown in Figure 2. Comparing the FT-IR spectra of untreated alumina, Figure 2a, with that after grafting the PGMA polymer, Figure 2b, the grafting of PGMA polymer on alumina surface was evident by the characteristic peaks of PGMA polymer on the alumina surface at 906 cm−1, assigned to stretching of the C−O bond in the epoxy group, and 1732 cm−1, attributed to stretching frequency of the carbonyl group (CO). These results were consistent with characteristic peaks of the PGMA polymer that were reported in the literature by Rizwan et al. and others.21−24 Finally, in Figure 2c the attachment of TENF π-acceptor on the polymer support was confirmed by the appearance of the stretching frequencies at 1361 cm−1, C
DOI: 10.1021/acs.iecr.6b02319 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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Figure 2. FT-IR spectra of (a) alumina, (b) Al-PGMA, (c) Al-PGMADAP-TENF, and (d) PGMA-DAP-TENF.
Figure 3. TGA/DTA thermogram of (a) alumina, (b) Al-PGMA, and (c) Al-PGMA-DAP-TENF.
representing the symmetric stretching vibration of nitro groups, 1475 and 1581 cm−1, attributed to C−C stretch in the aromatic ring, and the disappearance of the epoxy group peak at 906 cm−1. The FT-IR spectra of PGMA-DAP-TENF polymer without alumina can be found in Figure S1 in the Supporting Information section of this paper. FT-IR spectra of the PGMADAP-TENF polymer were consistent with that reported in the literature by Chitanda et al.24 Elemental analysis was performed to determine carbon, hydrogen, nitrogen, oxygen, and sulfur (CHNOS) contents of the polymer at different stages of synthesis and to confirm the synthesis of the final Al-PGMA-DAP-TENF polymer. Table 1
400 °C as seen by a small peak in DWC; less than 0.1 [%/C], could be due to some impurities present in the alumina particles. After grafting the PGMA polymer onto the alumina surface, the compound was decomposed in two stages: the first occurred at 390 °C, where 27% of the weight was lost, and the second occurred at 497 °C, where 0.09% of the weight was lost as shown in Figure 3b. In the first stage the polymer surface decomposed, and in the second stage the PGMA-cross-linking and random chain scission occurred. At 800 °C, Al-PGMA particles retained 57% of their initial weight. Comparing the maximum weight loss and residue at 600 °C, it was observed that the Al-PGMA particles decomposed at higher temperature and the residue was higher than that of PGMA, which decomposed at two stages: 323 and 397 °C, with residue of 16% at 600 as reported by Chitanda et al.24 Finally, Al-PGMADAP-TENF, Figure 3c, polymer retained only 40% of its initial weight at 800 °C, with maximum weight lost occurring at 291 °C, corresponding to 0.85 [%/C], and 381 °C, corresponding to 0.18 [%/ C]. Al-PGMA-DAP-TENF particles were decomposed at lower temperature and the residue at 800 °C was lower than that of Al-PGMA, which indicates a successful grafting and the formation of new compound. Even though the thermal stability of the polymer decreases after grafting PGMADAP-TENF polymer on alumina, the polymer is thermally stable and can be safely used at temperatures below 200 °C. Figure S2, in Supporting Information section, shows the TGA/ DTA thermgram of PGMA-DAP-TENF polymer. The maximum weight loss occurred at 295 and 406 °C, which were similar, with 3−4% error, to the values reported for PGMA-DAP-TENF polymer by Chitanda et al.24 Table 2 presents surface area, pore diameter, and pore volume of AlPGMA-DAP-TENF particles at different stages. The BET method was used to determine the surface area, whereas the BJH method was used to obtain pore diameter and pore volume. As expected, Al particles showed the highest BET surface area, 373 m2/g. After grafting PGMA polymer onto Al
Table 1. Elemental CHNOS Analysis of Al-PGMA-DAPTENF Polymer at Various Stages sample/ element alumina Al activated Al-MPS Al-PGMA Al-PGMADAP Al-PGMADAP-TENF a
carbon [wt %]
hydrogen [wt %]
nitrogen [wt %]
oxygena [wt %]
sulfur [wt %]
0.0 5.4 14.9 19.8 18.2
2.7 2.9 3.5 4.0 4.3
0.0 0.0 0.0 0.0 0.9
97.3 89.9 81.3 76.0 76.5
0.0 1.9 0.3 0.2 0.0
30.7
4.8
1.0
63.5
0.1
Calculated by difference.
shows the elemental CHNOS composition of the Al-PGMADAP-TENF polymer. The elemental CHNOS analysis of PGMA- DAP-TENF polymer can be found in Table S1 in the Supporting Information section. From Table 1, it was observed that carbon and sulfur contents increased after activating Al particles by adding toluenesulfonic acid. When MPS was added to alumina particles, sulfur content decreased while carbon content increased. Grafting PGMA-co-EGDMA polymer on alumina surface further increased carbon content. Adding DAP linker and TENF π-acceptor were evident by the increase in nitrogen content of the polymer. Furthermore, CHNOS elemental analysis of PGMA-DAP-TENF polymer, shown in Table S1 in the Supporting Information section, was similar to that reported by Chitanda et al.24 Thermal stability of the Al-PGMA-DAP-TENF polymer was determined using the TGA/DTA analyzer. Figure 3 shows the dynamic weight lost, dashed vertical axis, and its corresponding derivative weight change (DWC), solid vertical axis, of AlPGMA-DAP-TENF at different stages of synthesis. As expected alumina particles, as shown in Figure 3a, were fairly stable between 30 to 800 °C. A small weight loss, occurred around
Table 2. Texture Properties of Al-PGMA-DAP-TENF Polymer at Different Stages of Synthesis sample alumina Al-PGMA Al-PGMA-DAPTENF PGMA-DAPTENF D
BET surface area, [m2/g]
pore diameter, [nm]
pore volume, [cm3/g]
373 195 202
21 9 9
1.07 0.42 0.46
27
19
0.13
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nm to 95 ± 7 nm after grafting the polymer support on the alumina surface. This observation was consistent with results of the BET analysis in Table 2 and similar to the images of Al and Al-PGMA particles reported by Jiao et al.28 Figure 6 shows
surface, the surface area decreased to 195 m2/g. Similarly, pore diameter and pore volume decreased to 9 nm and 1.07 cm3/g, respectively. The BET surface area of Al-PGMA was 3−5 times higher than that for PGMA-based particles reported in the literature.21,22,24 Finally, after attaching the DAP linker and TENF π-accpetor, Al-PGMA-DAP-TENF polymer texture properties changed slightly as the surface area increased to 202 m2/g, and pore volume to 1.46 cm3/g. Even though grafting PGMA-DAP-TENF decreased the surface area of alumina, the total surface area of Al-PGMA-DAP-TENF was higher than that of PGMA-DAP-TENF without alumina. In addition, the adsorption−desorption isotherms for Al, AlPGMA, and Al-PGMA-DAP-TENF, as shown in Figure 4,
Figure 6. FTIR spectra for adsorbed pyridine on (dotted line) PGMADAP-TENF and (solid line) Al-PGMA-DAP-TENF.
FTIR spectra of adsorbed pyridine on (dotted line) PGMADAP-TENF and (solid line) Al-PGMA-DAP-TENF. The acidic surface of Al-PGMA-DAP-TENF polymer was evident by the band at 1577 cm−1, attributed to pyridine adsorption on Bronsted acid sites, and at 1475 cm−1, attributed to pyridine adsorption on Lewis acid sites. On contrast, no peaks were observed in the PGMA-DAP-TENF spectrum between 1400 and 1600 cm−1. Adsorption Studies. To compare the adsorption performance of Al-PGMA-DAP-TENF to that of PGMA-DAP-TENF, the polymers were tested using light gas oil (LGO) and heavy gas oil (HGO) feeds. In the first stage, the effect of adsorption time was examined by mixing the polymers at different time intervals, between 1 and 24 h, using LGO feed. Figure 7 shows
Figure 4. Adsorption−desorption isotherms of (a) alumina, (b) AlPGMA, and (c) Al-PGMA-DAP- TENF.
exhibited type IV isotherm with weak hysteresis loop, which indicates mesoporous materials. This result was in agreement with the pore diameters values shown in Table 2. Comparing the texture properties of Al-PGMA-DAP-TENF polymer with PGMA-DAP-TENF, it was noticed that alumina particles had significantly increased the surface area and pore volume of the polymer support, while the pore diameter decreased. In addition, the dispersity of the polymers were determined using DLS. The polydispersity index of PGMA-DAP-TENF and Al-PGMA-DAP-TENF were 0.56 and 0.46, respectively. These results indicate that both polymers have a broad size distribution. SEM images, at 35 000 magnification, were used to look at the morphology of the untreated alumina and the grafted particles as shown in Figure 5 panels a and b, respectively. It
Figure 7. Effect of adsorption time on the removal of nitrogen [N] and sulfur [S] compounds from light gas oil.
the effect of adsorption time on the removal efficiency of nitrogen (N) and sulfur (S) from LGO feed. It was observed that both polymers removed most of the nitrogen and sulfur compounds after 1 h, and then the removal efficiency became stable as the time prolonged. In the case of nitrogen compounds removal, it was observed that the removal efficiency of Al-PGMA-DAP-TENF was superior to that of PGMA-DAPTENF. The maximum removal efficiency of Al-PGMA-DAPTENF, 20.7%, was reached after 24 h, and was about three times as much as that of PGMA-DAP-TENF. Similarly, the removal efficiency of sulfur compounds for Al-PGMA-DAPTENF polymer was higher than that for PGMA-DAP-TENF polymer. The maximum sulfur removal efficiency of Al-PGMADAP-TENF was 3.4%, while that of PGMA-DAP-TENF was around 1.5%. However, both polymers were selective toward nitrogen compounds as the removal efficiency of nitrogen
Figure 5. SEM images of (a) alumina and (b) Al-PGMA at 35 000 magnification.
was observed that the untreated alumina particles, Figure 5a, were in a form of agglomerated spherical beads with some pores as shown by the arrows. After grafting the polymer support on the alumina surface, the alumina particles retained their structure; however, the agglomerated particles became fluffy and the pores decreased in size or disappeared as shown in Figure 5b. The average particle size increased from 43 ± 5 E
DOI: 10.1021/acs.iecr.6b02319 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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Industrial & Engineering Chemistry Research compounds was higher than that of sulfur compounds. The better performance of Al-PGMA-DAP-TENF compared to PGMA-DAP-TENF could be contributed to the high surface area of the polymer, 202 m2/g, compared to 27 m2/g for PGMA-DAP-TENF. Studies have shown that polymer surface area plays a major role in the adsorption capacity of the functionalized polymers.23,33 In addition, the interaction between the acidic sites of alumina particles and basic nitrogen compounds can also contribute to the superior performance of Al-PGMA-DAP-TENF. In their study of acid−base characterization of Pt/Al2O3 catalyst, Brean and Zhang observed an interaction between the acidic sites of alumina support and pyridine, basic nitrogen compounds.34 The effect of temperature on the removal efficiency of both polymers was investigated at different temperatures using 1:5 (by weight) polymer-to-oil ratio and 24 h adsorption time. Figure 8 shows
Table 3. Total Nitrogen and Sulfur Removal of Different Functionalized Polymersa polymer PGMA-ONTENF21 PGMA-NNTENF22 PGMA-NNTENF23 PGMA-NNTENF23 PAM-NNTENF23 PAM-NNTENF23 PS-NNTENF23 PS-NNTENF23 PGMA-DAPTENF* PGMA-DAPTENF* Al-PGMADAPTENF* Al-PGMADAPTENF*
nitrogen removal [%]
sulfur removal [%]
feed
process conditions
11.2
1.5
LGO
6.7
0.0
HGO
11.4
0.4
LGO
5.3
2.0
HGO
0.0
0.6
LGO
0.0
2.9
HGO
0.8
2.1
LGO
1.2
3.1
HGO
6.3
1.5
LGO
5.7
6.7
HGO
20.7
2.3
LGO
P/O = 0.25, T = 22 °C, t = 24 h P/O = 0.15, T = 110 °C, t = 1 h P/O = 0.2, T = 20 °C, t = 48 h P/O = 0.2, T = 20 °C, t = 48 h P/O = 0.2, T = 20 °C, t = 48 h P/O = 0.2, T = 20 °C, t = 48 h P/O = 0.2, T = 20 °C, t = 48 h P/O = 0.2, T = 20 °C, t = 48 h P/O = 0.2, T = 23 °C, t = 24 h P/O = 0.2, T = 23 °C, t = 24 h P/O = 0.2, T = 23 °C, t = 24 h
11.3
6.0
HGO
P/O = 0.2, T = 23 °C, t = 24 h
a
Notation: PGMA= polyglycidyl methacrylate and ethylene glycol dimethacrylate, NN = hydrazine, ON = hydroxylamine, DAP = diaminopropane, TENF = tetranitrofluorenone, PAM = polyacrylamide, PS = polystyrene, Al = alumina, P/O = polymer to oil ratio, (∗) current work.
Figure 8. Effect of adsorption temperature on the removal of nitrogen [N] and sulfur [S] compounds from light gas oil.
the removal efficiency of nitrogen and sulfur by both polymers at different temperatures. For the PGMA-DAP-TENF polymer, the maximum removal efficiency of nitrogen and sulfur was achieved at 30 °C. However, the nitrogen removal efficiency of Al-PGMA-DAP-TENF polymer was stable, around 21%, and slightly decreased to 20% at 60 °C. The slight change of nitrogen removal efficiency of Al-PGMA-DAP-TENF polymer was within the error range of the nitrogen removal efficiency. Thus, the nitrogen removal efficiency of Al-PGMA-DAP-TENF seemed to reach adsorption equilibrium between 23 and 60 °C. It is observed that the sulfur removal of PGMA-DAP-TENF was higher than that of Al-PGMA-DAP-TENF at 30 °C. This could be attributed to the exothermic nature of the adsorption process. At 30 °C PGMA-DAP-TENF showed the maximum removal efficiency of sulfur and nitrogen, whereas Al-PGMADAP-TENF performed at the same level in the tested temperature range. Furthermore, at all temperatures the nitrogen removal efficiency of Al-PGMA-DAP-TENF polymer was more than twice as much as the removal efficiency of PGMA-DAP-TENF polymer. On the other hand, the sulfur removal efficiency of sulfur was similar, except at 30 °C, at which the removal efficiency of PGMA-DAP-TENF was higher than that of Al-PGMA-DAP-TENF. Table 3 compares the total nitrogen and sulfur removal efficiencies of Al-PGMA-DAPTENF and PGMA-DAP-TENF to that of similar polymers reported in the literature.21−23 The performance of Al-PGMADAP-TENF was found to be superior to that of PGMA-DAPTENF and other polymers as it removed about twice as much nitrogen compounds as other polymers did in LGO and HGO feeds. For example in LGO feed, Al-PGMA-DAP-TENT removed 20.7% of the nitrogen content, whereas PGMA-
DAP-TENF removed 6.3%, and other polymers, such as PGMA-ON-TENF and PGMA-NN-TENF, removed 11.2% and 11.4%.21,22 Similarly in HGO feed, Al-PGMA-DAP-TENF removed 11.3% of the nitrogen content, while PGMA-DAPTENF removed 5.7%, and PGMA-NN-TENF removed 6.7− 5.3% as reported by Rizwan et al.22 and Abedi et al.23 In terms of sulfur content, Al-PGMA-DAP-TENF removal efficiency was higher than that of other polymers in LGO. However, the sulfur removal efficiency of Al-PGMA-DAP-TENF polymer was similar to that of PGMA-DAP-TENF in HGO. Both polymers removed more sulfur compounds in HGO feed than in LGO feed. This is due to the high sulfur content of HGO compared to that of LGO feed. Grafting PGMA-co-EGDMA polymers onto alumina enhanced the adsorption capacity of the polymer toward nitrogen and sulfur compounds. In addition, nitrogen and sulfur removal efficiencies of the PGMA-DAP-TENF polymer in a model fuel containing nitrogen and sulfur species showed higher nitrogen removal, 8.6%, compared to that of LGO, and no sulfur removal. The reason for the higher nitrogen removal and lower sulfur removal in model fuel compared to LGO feed is that the model fuel does not contain too many types of different compounds that compete with nitrogen and sulfur species over adsorption sites. Furthermore, the lower sulfur removal in the model fuel is attributed to the lower sulfur content of the model compounds and the selectivity of the PGMA-DAP-TENF polymer toward sulfur compounds. To investigate the removal efficiency of basic and nonbasic nitrogen compounds in LGO, a potentiometric titrator was used to analyze LGO feed before and after treatment. Figure 9 F
DOI: 10.1021/acs.iecr.6b02319 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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Industrial & Engineering Chemistry Research
nitrogen, basic and nonbasic, and sulfur were tested using LGO and HGO feed. The effect of adsorption time and temperature revealed that the performance of Al-PGMA-DAP-TENF polymer was superior to that of PGMA-DAP-TENF. The nitrogen removal efficiency of Al-PGMA-DAP-TENF polymer was twice as much as that of PGMA-DAP-TENF in HGO, and the difference in performance was even greater in the LGO feed. The reason for that is attributed to the high surface area and the interaction of alumina particles of Al-PGMA-DAPTENF compared to those of PGMA-DAP-TENF polymer.
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Figure 9. Adsorption removal efficiency of both polymers on the removal of basic and nonbasic nitrogen compounds from light gas oil.
ASSOCIATED CONTENT
S Supporting Information *
illustrates the adsorption removal efficiency of both polymers toward basic and nonbasic nitrogen compounds using a 1:5 polymer-to-oil ratio (P/O), room temperature, and 24 h adsorption time. Both polymers removed more nonbasic nitrogen compounds than basic nitrogen compounds from light gas oil. Similar results were obtained by Rizwan et al., who found that PGMA incorporated with TENF increased the selectivity of TENF toward nonbasic nitrogen compounds.22 Al-PGMA-DAP-TENF polymer removed more basic nitrogen compound than PGMA-DAP-TENF polymer. Al-PGMA-DAPTENF removed 8.3% of the basic nitrogen, whereas PGMADAP-TENF removed only 1.7% of the basic nitrogen compounds. In addition to the higher surface area of AlPGMA-DAP-TENF compared to PGMA-DAP-TENF, the acidic nature of Al-PGMA-DAP-TENF polymer, as shown earlier in Figure 6, enhanced the adsorption capacity of AlPGMA-DAP-TENF toward basic nitrogen compounds. Similar analysis was done using heavy gas oil feed. Figure 10 shows the removal efficiency of both polymers toward basic
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.6b02319. FT-IR spectrum of PGMA-DAP-TENF; TGA/DTA thermogram of PGMA-DAP-TENF polymer; elemental CHNOS analysis of PGMA-DAP-TENF polymer at various stages (PDF)
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AUTHOR INFORMATION
Corresponding Author
*Tel: +1 (306) 966-4771. Fax: +1 (306) 966-4777. E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors gratefully acknowledge the financial support from MITACS and Syncrude Canada Ltd. REFERENCES
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Figure 10. Adsorption removal efficiency of both polymers on the removal of basic and nonbasic nitrogen compounds from heavy gas oil.
nitrogen and nonbasic nitrogen compounds in HGO feed. The removal efficiency of nitrogen compounds in HGO feed was lower than that with LGO feed, but the trend was similar as AlPGMA-DAP-TENF polymer removed twice as much nitrogen compounds as PGMA-DAP-TENF polymer. With HGO feed, as with LGO feed, Al-PGMA-DAP-TENF polymer removed more basic nitrogen compounds than PGMA-DAP-TENF.
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CONCLUSION The effect of alumina support on the performance of functionalized polymers was investigated by comparing the removal efficiency of PGMA-DAP-TENF polymer without alumina particles to that of the same polymer grafted on alumina, Al-PGMA-DAP-TENF. In the first stage both compounds were synthesized and characterized, then in the second stage the removal efficiency of both polymers toward G
DOI: 10.1021/acs.iecr.6b02319 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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