catalysts Article
Oligomerization of Butene Mixture over NiO/Mesoporous Aluminosilicate Catalyst Donggun Lee 1 , Hyeona Kim 1 , Young-Kwon Park 2 and Jong-Ki Jeon 1, * 1 2
*
Department of Chemical Engineering, Kongju National University, Cheonan 31080, Korea;
[email protected] (D.L.);
[email protected] (H.K.) School of Environmental Engineering, University of Seoul, Seoul 02504, Korea;
[email protected] Correspondence:
[email protected]; Tel.: +82-41-521-9363
Received: 29 August 2018; Accepted: 11 October 2018; Published: 16 October 2018
Abstract: This study is aimed at preparing C8 –C16 alkene through oligomerization of a butene mixture using nickel oxide supported on mesoporous aluminosilicate. Mesoporous aluminosilicate with an ordered structure was successfully synthesized from HZSM-5 zeolite by combining a top-down and a bottom-up method. MMZZSM-5 catalyst showed much higher butene conversion and C8 –C16 yield in the butene oligomerization reaction than those with HZSM-5. This is attributed to the pore geometry of MMZZSM-5 , which is more beneficial for internal diffusion of reactants, reaction intermediates, and products. The ordered channel-like mesopores were maintained after the nickel-loading on MMZZSM-5 . The yield for C8 –C16 hydrocarbons over NiO/MMZZSM-5 was higher than that of MMZZSM-5 catalyst, which seemed to be due to higher acid strength from a higher ratio of Lewis acid to Brønsted acid. The present study reveals that a mesoporous NiO/MMZZSM-5 catalyst with a large amount of Lewis acid sites is one of the potential catalysts for efficient generation of aviation fuel through the butene oligomerization. Keywords: butene; oligomerization; aviation fuel; mesoporous aluminosilicate; nickel
1. Introduction The greenhouse gas (GHG) emitted when an aircraft is in operation has negative impacts on the environment, including global warming [1]. To resolve such problems, the International Civil Aviation Organization announced a policy intended to reduce GHG emission by aircraft using biomass-derived fuels for aircraft [2]. Consequently, research about synthesis of aviation fuel from biomass is drawing attention. The Alcohol to Jet (ATJ) process for making alcohol from biomass as feedstock and for making aviation fuel from alcohol has recently attracted attention [3]. This process involves the production of butene through the dehydration of butanol, the synthesis of higher olefins by oligomerization of the newly produced butene, and hydrogenation of the higher olefins [4–6]. Studies on the synthesis of butenes through butanol dehydration in the first step are already under way [7–11]. We have previously reported that silica-based, solid acid catalysts with mesopores and highly dispersed metal oxide catalysts are effective in the production of butene by butanol dehydration [12,13]. Because the demand for aviation fuel is increasing steadily, maximizing the production of aviation fuel is of great interest to oil refining companies [14]. Because butene is an excess in the refineries (FCC), the use of oligomerization to convert butene into aviation fuel is a promising method for the generation of aviation fuel. The butene oligomerization reaction has been studied mainly using zeolites or heterogeneous catalysts [14–19]. Yoon et al. found that ferrierite, zeolite beta, and Amberlyst-35 exhibited high catalytic performance for the trimerization of isobutene [20–22]. It is also known that a catalyst loaded with nickel on Y zeolite or ZSM-5 is effective for trimerization of linear butene [23–26]. Catalysts 2018, 8, 456; doi:10.3390/catal8100456
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catalytic performance for the trimerization of isobutene [20–22]. It is also known that a catalyst loaded 2 of 13 zeolite or ZSM-5 is effective for trimerization of linear butene [23–26]. We have been studying the application of mesoporous aluminosilicate with zeolite framework for catalytic In particular, we haveofpublished research results in which a framework was We havereaction. been studying the application mesoporous aluminosilicate with zeolite framework constructed using commercial zeolite. From this, mesoporous aluminosilicate with a well-ordered for catalytic reaction. In particular, we have published research results in which a framework was structure was produced by combining top-down method and aluminosilicate a bottom-up method constructed using commercial zeolite. aFrom this, mesoporous with a[13,27]. well-ordered The purpose of this study was to prepare a particular fraction (C 8–C16; corresponding to aviation structure was produced by combining a top-down method and a bottom-up method [13,27]. fuel)The through oligomerization butene usinganickel oxidefraction supported on mesoporous aluminosilicate purpose of this study of was to prepare particular (C8 –C 16 ; corresponding to aviation with through a well-ordered structure.of We used ausing butene mixture the same compositionaluminosilicate as the product fuel) oligomerization butene nickel oxidehaving supported on mesoporous obtained from dehydration of butanol as raw material for the oligomerization. High-pressure with a well-ordered structure. We used a butene mixture having the same composition as the oligomerization the dehydration butene mixture was investigated in a fixed-bed continuous-flow reactor. product obtainedof from of butanol as raw material for the oligomerization. High-pressure Catalysts 2018, 8,on 456 with nickel Y
oligomerization of the butene mixture was investigated in a fixed-bed continuous-flow reactor. 2. Results and Discussion 2. Results and Discussion 2.1. Textural Properties of Catalysts 2.1. Textural Properties of Catalysts The N2 adsorption–desorption isotherm of MMZZSM-5 (Figure 1) showed a type IV(a) The N2 adsorption–desorption isotherm of MMZ (Figure 1) showed type IV(a) physisorption isotherm in the IUPAC classification [28,29]. the N2a adsorption– ZSM-5 Furthermore, physisorption isothermofin MMZ the IUPAC classification Furthermore, the N desorption isotherm ZSM-5 exhibited the[28,29]. H4 type of hysteresis loop, which is typical of 2 adsorption–desorption isotherm of MMZ exhibited the H4 type of hysteresis loop, which is typical of mesoporous zeolites mesoporous zeolites and micro-mesoporous materials [29,30]. In the case of NiO/MMZ ZSM-5 catalyst, ZSM-5 and [29,30].isotherm In the case of NiO/MMZ catalyst, of the micro-mesoporous characteristics of Nmaterials 2 physisorption were not much ZSM-5 different fromthe thecharacteristics N2 adsorption– N isotherm were not muchindicates differentthat fromthe thegeometry N2 adsorption–desorption isotherm of desorption isotherm of MMZ ZSM-5 . This of the ordered mesopores of 2 physisorption MMZ . Thisnot indicates that geometry MMZZSM-5 ZSM-5 was changed bythe NiO loading.of the ordered mesopores of MMZZSM-5 was not changed by NiO Theloading. pore size distribution curves of the three catalysts were compared in Figure 2. As expected size adsorption distributionisotherm, curves ofitthe three catalysts were compared in Figure 2. As expected fromThe the pore nitrogen was difficult to observe the mesopores of HZSM-5, while a from the nitrogen adsorption isotherm, it was difficult to observe the mesopores of HZSM-5, while a mesopore peak of about 3.0 nm could be observed on MMZZSM-5. Moreover, the pore size somewhat mesopore nm could on MMZ Moreover, thepore-size pore sizedistribution somewhat decreasedpeak after of theabout nickel3.0 loading of 9 be wt observed %. However, the overall ZSM-5 . characteristic decreased after the nickel of 9after wt %.NiO However, the overall characteristic pore-size distribution curve of the material did loading not change loading. curveThe of the material notofchange afterand NiOHZSM-5 loading.were 745 and 448 m2/g, respectively (Table 1). BET surfacedid areas MMZZSM-5 2 /g, respectively The BET surface MMZZSM-5 andZSM-5 HZSM-5 were 745were and 0.47 448 m (Table 1). Furthermore, the totalareas poreof volumes of MMZ and HZSM-5 and 0.19 cm3/g, respectively. 3 /g, respectively. Furthermore, the total MMZarea and HZSM-5 were 0.47 and 0.19 cm Therefore, it was clearpore thatvolumes the BET of surface and pore size of MMZ ZSM-5 catalyst were much larger ZSM-5 Therefore, was clear that the BETMeanwhile, surface areathe andBET poresurface size of MMZ catalyst were of much larger than thoseit of HZSM-5 catalyst. area and volume MMZ ZSM-5 ZSM-5pore than those slightly of HZSM-5 Meanwhile, the BET surface areathat andthe pore volume MMZ decreased after catalyst. the NiO loading, which was due to the fact nickel oxideofwas attached ZSM-5 decreased NiO loading, due to the fact that the nickel oxide was attached to the poreslightly surfaceafter and the partially blockedwhich a porewas mouth. to the pore surface and partially blocked a pore mouth.
Adsorption Desorption
Va/cm3(STP) g-1
NiO/MMZZSM-5
MMZZSM-5
HZSM-5
0.0
0.2
0.4
0.6
0.8
1.0
P/P0
Figure Figure1.1. N N22 adsorption–desorption adsorption–desorption isotherms isotherms of of various various catalysts. catalysts.
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dVp/dlogdp
NiO/MMZZSM-5
MMZZSM-5
HZSM-5 1
10
100
dp/nm
Figure 2. Pore size distribution of various catalysts. Table 1. Textural properties of the catalysts. Table 1. Textural properties of the catalysts. 2 −1 3 −1 ) a Zeolite Type Type SBET DPb (nm) b P (cm 3 g−1g Zeolite SBET(m(mg2 g−1) )VPV(cm ) aDP (nm)
HZSM-5 HZSM-5 MMZZSM-5 MMZZSM-5 NiO/MMZZSM-5 a a
NiO/MMZZSM-5
448 448 745 745 726
Total pore volume measured at p/p0 = 0.99.
726 b
0.190.19 0.470.47 0.43 0.43
2.7 2.7
2.7 2.7
Average pore diameter determined by the BJH method.
Total pore volume measured at p/p0 = 0.99. b Average pore diameter determined by the BJH method.
Low-angle XRD patterns of the MMZZSM-5 and NiO/MMZZSM-5 catalysts are presented in Figure 3. Low-angle XRD patterns of the MMZZSM-5 and NiO/MMZZSM-5 catalysts are presented in Figure 3. MMZZSM-5 has three diffraction peaks corresponding to 100, 110, and 200 Bragg reflections, respectively. MMZZSM-5 has three diffraction peaks corresponding to 100, 110, and 200 Bragg reflections, In particular, the peak at 2θ of 2.3◦ is the characteristic peak of the 2-D hexagonal structure, and the respectively. In particular, the peak at 2θ of 2.3° is the characteristic peak of the 2-D hexagonal two weak peaks at 3.9◦ and 4.5◦ show the inherent characteristics of the mesoporous material [27]. structure, and the two weak peaks at 3.9° and 4.5° show the inherent characteristics of the The NiO/MMZZSM-5 sample represents the characteristic peaks of MMZZSM-5 with three intense mesoporous material [27]. The NiO/MMZZSM-5 sample represents the characteristic peaks of MMZZSMpeaks at 2θ = 2.3◦ , 3.9◦ , and 4.5◦ , respectively. After nickel loading, the XRD patterns of the material 5 with three intense peaks at 2θ = 2.3°, 3.9°, and 4.5°, respectively. After nickel loading, the XRD showed a slight reduction in peak intensity but maintained the same patterns as those of MMZZSM-5 . patterns of the material showed a slight reduction in peak intensity but maintained the same patterns This suggests that the ordered mesoporous structures of the MMZZSM-5 are well retained after the as those of MMZZSM-5. This suggests that the ordered mesoporous structures of the MMZZSM-5 are well nickel loading. The XRD patterns of MMZZSM-5 and NiO/MMZZSM-5 material in the high-angle region retained after the nickel loading. The XRD patterns of MMZZSM-5 and NiO/MMZZSM-5 material in the (Figure 4) give a broad line centered at 2θ ≈ 23◦ , which indicates that the framework of MMZZSM-5 was high-angle region (Figure 4) give a broad line centered at 2θ ≈ 23°, which indicates that the framework not atomically ordered and the starting source, HZSM-5, was not present in the MMZZSM-5 material. of MMZZSM-5 was not atomically ordered and the starting source, HZSM-5, was not present in the A TEM image is presented in Figure 5 to determine whether MMZZSM-5 and NiO/MMZZSM-5 MMZZSM-5 material. have hexagonal structures. MMZZSM-5 has a well-ordered structure with mesopores that are hexagonal A TEM image is presented in Figure 5 to determine whether MMZZSM-5 and NiO/MMZZSM-5 have 1-D channels [31]. The NiO/MMZZSM-5 sample maintained the structural features of MMZZSM-5 after hexagonal structures. MMZZSM-5 has a well-ordered structure with mesopores that are hexagonal 1-D the nickel loading. channels [31]. The NiO/MMZZSM-5 sample maintained the structural features of MMZZSM-5 after the nickel loading.
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Intensity (a.u.) Intensity Intensity (a.u.)(a.u.)
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6 6
2θ 2θ (degree) (degree) 6
8 8
10 10
8
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Intensity (a.u.) Intensity Intensity (a.u.)(a.u.)
Figure and NiO/MMZZSM-5. Figure 3. 3. Low-angle Low-angle XRD XRD patterns patterns of of MMZ MMZZSM-5 ZSM-5 and NiO/MMZZSM-5. Figure 3. Low-angle XRD patterns of MMZZSM-5 and NiO/MMZZSM-5. Figure 3. Low-angle XRD patterns of MMZZSM-5 and NiO/MMZZSM-5.
HZSM-5 HZSM-5 HZSM-5 MMZ MMZZSM-5 ZSM-5 MMZZSM-5 NiO/MMZ NiO/MMZZSM-5 ZSM-5 20 20 20
40 40
60 60
22 θθ (degree) 40 (degree) 60
NiO/MMZ 80 ZSM-5 80 80
Figure High angle XRD patterns MMZ ZSM-5, and NiO/MMZZSM-5. 2HZSM-5, θHZSM-5, (degree)MMZ Figure 4.High Highangle angleXRD XRD patterns of HZSM-5, MMZ ZSM-5,,and andNiO/MMZ NiO/MMZZSM-5. Figure 4.4. patterns ofof ZSM-5 ZSM-5. Figure 4. High angle XRD patterns of HZSM-5, MMZZSM-5, and NiO/MMZZSM-5.
(a) (a) (a)
(b) (b) (b)
Figure TEM image MMZ ZSM-5 and and (b) NiO/MMZ .. . Figure 5.5. ZSM-5 ZSM-5 Figure 5.TEM TEMimage imageofof of(a)(a) (a)MMZ MMZ ZSM-5 and (b) (b)NiO/MMZ NiO/MMZZSM-5 ZSM-5 Figure 5. TEM image of (a) MMZZSM-5 and (b) NiO/MMZZSM-5. 2.2. Acid Properties of Catalysts
The acidic characteristics of HZSM-5, MMZZSM-5 , and NiO/MMZZSM-5 were analyzed using NH3 -TPD (Figure 6). HZSM-5 exhibits two peaks at the desorption temperature of ammonia near
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2.2. Acid Properties of Catalysts The acidic characteristics of HZSM-5, MMZZSM-5, and NiO/MMZZSM-5 were analyzed using NH35 of 13 TPD (Figure 6). HZSM-5 exhibits two peaks at the desorption temperature of ammonia near 180 and 380 °C, indicating that weak strength acid sites and medium strength acid sites are widely distributed. ◦ C,curve Theand NH380 3-TPD of MMZ shows thatacid the sites peakand intensity is greatly compared to 180 indicating thatZSM-5 weak strength medium strengthreduced acid sites are widely HZSM-5. ThisThe indicates that MMZ has both the weak acid sites near 170 °C and medium strength distributed. NH3 -TPD curveZSM-5 of MMZ ZSM-5 shows that the peak intensity is greatly reduced acid near 340 °C, but the total amount of acid sites over is greatly to compared to HZSM-5. This indicates that MMZZSM-5 hasMMZ both ZSM-5 the weak acid reduced sites nearcompared 170 ◦ C and ◦ HZSM-5. strength The reason could that C, aluminum relatively less to over the amorphous medium acid nearbe340 but the is total amount of exposed acid sites MMZZSM-5framework is greatly that constructs the pore walls ofThe MMZ ZSM-5. could On thebeother hand, in theiscase of the less MMZ ZSM-5 catalyst, reduced compared to HZSM-5. reason that aluminum relatively exposed to the the peak temperature of NH 3 -TPD shifted to a lower temperature than that of HZSM-5, which means amorphous framework that constructs the pore walls of MMZZSM-5 . On the other hand, in the case of thatMMZ the acid strength was also weakened. the ZSM-5 catalyst, the peak temperature of NH3 -TPD shifted to a lower temperature than that of For the NiO/MMZ ZSM-5the catalyst, the desorption peak at a low temperature shifted to high HZSM-5, which means that acid strength was also weakened. temperature (210 °C), indicating that the acid strength of NiO/MMZ ZSM-5 is higher than to that of For the NiO/MMZZSM-5 catalyst, the desorption peak at a low temperature shifted high ◦ MMZZSM-5 catalyst. is indicating noticeable that high-temperature (540 °C) peak appeared on the temperature (210 It C), that an theadditional acid strength of NiO/MMZ ZSM-5 is higher than that of NH 3 -TPD profile of the NiO/MMZ ZSM-5 catalyst, which means that nickel oxide generates a new MMZZSM-5 catalyst. It is noticeable that an additional high-temperature (540 ◦ C) peak appeared ontype the of acid site. This high-temperature peak is known to be attributable to Lewis acid sites from nickel NH -TPD profile of the NiO/MMZ catalyst, which means that nickel oxide generates a new type 3 ZSM-5 oxide of acid[32]. site. This high-temperature peak is known to be attributable to Lewis acid sites from nickel Catalysts 2018, 8, 456
oxide [32].
Figure Figure 6. 6. NH33 -TPD profiles of various catalysts.
Figure showsthe the results of the pyridine-FTIR forNiO/MMZ the NiO/MMZ sample. As the ZSM-5 As Figure 77shows results of the pyridine-FTIR for the ZSM-5 sample. the desorption ◦ − 1 desorption increased 300 band C, theintensity band intensity at 1596 diminished drastically temperaturetemperature increased to 300 °C,tothe at 1596 cm−1 cm diminished drastically and ◦ C, indicating a very weak H acid site [33,34]. Four and disappeared at temperatures higher than 150 disappeared at temperatures higher than 150 °C, indicating a very weak H acid site [33,34]. Four well−1 at higher than 150 ◦ C. −1 atcm well-resolved can be observed at (1450, 1491, and 1542,1610) and cm 1610) resolved bandsbands can be observed at (1450, 1491, 1542, higher than 150 °C. Two of −1 while the band at 1542 cm−−1 1 −1), ), Two these bands are attributed to Lewis (1450 and 1610cm cm theseofbands are attributed to Lewis sitessites (1450 and 1610 while the band at 1542 cm − 1 corresponds is associated associated with corresponds to to the the Brönsted Brönsted sites sites[33,34]. [33,34]. Additional Additionalband bandnear near1491 1491cm cm−1 is with aa Lewis Lewis site and Brönsted site simultaneously. site and Brönsted site simultaneously. The catalysts are are shown shown in ZSM-5 The pyridine-FTIR pyridine-FTIR results resultsofofHZSM-5, HZSM-5,MMZ MMZ ZSM-5,, and andNiO/MMZ NiO/MMZZSM-5 ZSM-5 catalysts in −1−1) and also has Lewis sites (1450 cm−1−1, 1610 cm−−11 ). Figure 8. HZSM-5 is rich in Brönsted sites (1542 cm Figure 8. HZSM-5 is rich in Brönsted sites (1542 cm ) and also has Lewis sites (1450 cm , 1610 cm ). In also,both bothBrönsted Brönstedand andLewis Lewisacidity acidity can can be be observed. observed. It It should should also also be be noted noted that In MMZ MMZZSM-5 ZSM-5 also, that for for −1 ) was much −1 the NiO/MMZ catalyst, the band corresponding to the Lewis acid site (1450 cm ZSM-5 the NiO/MMZZSM-5 catalyst, the band corresponding to the Lewis acid site (1450 cm ) was much larger larger than that associated with the Brönsted site (1542 cm−1 ). That is, the NiO loading shows that the Lewis site is relatively increased. The pyridine-FTIR and NH3 -TPD results suggest that a new acid site is generated by loading of NiO over MMZZSM-5 , which is attributable to the Lewis site.
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than that associated with the Brönsted site (1542 cm−1). That is, the NiO loading shows that the Lewis −1). 3That site is that relatively increased. The pyridine-FTIR and -TPDis,results suggest that a new acid is than associated with the Brönsted site (1542 cmNH the NiO loading shows that thesite Lewis generated by loading of NiOThe overpyridine-FTIR MMZZSM-5, which attributable to the Lewisthat site. a new acid site is site is relatively increased. and is NH 3-TPD results suggest generated by loading of NiO over MMZZSM-5, which is attributable to the Lewis site.
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1450 1450 1596
1491
Absorbance Absorbance
1610 1596 a b
a b
1610
1650 1650
c d ec fd e f 1600
1542
1491
1542
1550
1500
a b ca db ec fd e f
1450 -1
number1500 (cm 1600 Wave 1550
)
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1400
1450
1400
-1
Wave number (cm ) Figure 7. Pyridine-FTIR spectra over NiO/MMZ ZSM-5 under a vacuum (a: room temperature, b: 100 °C, ◦ C, c: 150 °C, d: 200 °C, e: 250 °C, and f: 300 °C). Figure 7. Pyridine-FTIR spectra over NiO/MMZ under aa vacuum vacuum (a: Figure 7. Pyridine-FTIR spectra over NiO/MMZZSM-5 ZSM-5 under (a: room room temperature, temperature,b:b:100 100 °C, ◦ C, d: 200 ◦ C, e: 250 ◦ C, and f: 300 ◦ C). c:c: 150 150 °C, d: 200 °C, e: 250 °C, and f: 300 °C).
1451 1542 1610
1542
1491
1451
1491
1610
Absorbance Absorbance (a.u.)(a.u.)
NiO/MMZZSM-5 NiO/MMZZSM-5
MMZZSM-5 MMZZSM-5
HZSM-5 HZSM-5
1650 1650
1600
1550
1500
1450 -1
number1500 (cm ) 1600 Wave 1550
1450
1400 1400
-1
) Figure 8. Pyridine-FTIR spectra atWave 200 ◦number C under(cm a vacuum over various catalysts.
Figure 8. Pyridine-FTIR spectra at 200 °C under a vacuum over various catalysts.
2.3. Oligomerization Figureof8.Mixed-Butene Pyridine-FTIR spectra at 200 °C under a vacuum over various catalysts. 2.3. Oligomerization of Mixed-Butene The HZSM-5 catalyst showed good stability for butene oligomerization (Figure 9). In previous 2.3. Oligomerization of Mixed-Butene The HZSM-5 catalyst gooditstability for butene (Figure 9). of Insolid previous studies on trimerization ofshowed iso-butene, was proposed thatoligomerization the catalytic performance acid studies onand trimerization of showed iso-butene, it was that the catalytic acid catalysts zeolites could be altered by theirproposed pore [21,22]. Theperformance most common finding is The HZSM-5 catalyst good stability forgeometry butene oligomerization (Figure 9).ofInsolid previous catalysts andtrimerization zeolites could altered by pore geometry [21,22]. most common finding is that medium-pore molecular sieves, such zeolite MFI and zeolite beta,The were shown to beofsuitable for studies on of be iso-butene, itastheir was proposed that the catalytic performance solid acid that medium-pore sieves, such zeolite zeolite beta, were to befinding suitableis oligomerization ofmolecular iso-butene oraltered n-butene into diesel andand gasoline fuels due to shown their shape-selective catalysts and zeolites could be byas their poreMFI geometry [21,22]. The most common for of iso-butene orzeolite n-butene into MFI diesel and gasoline fuels due to to their shapeproperties [20,35]. Besides that,sieves, these were proved to have due to thatoligomerization medium-pore molecular such ascatalysts zeolite and zeolite beta,high werecoke-resistance shown be suitable limited polyaromaticof generation in or their pore structure. Based similar fuels analogies, thetheir stability of for oligomerization iso-butene n-butene into diesel andongasoline due to shapeHZSM-5 catalyst during the conversion of the butene mixture into C8 –C16 hydrocarbon could be due to the coke-resistance resulting from the pore geometry.
selective properties [20,35]. Besides that, these zeolite catalysts were proved to have high cokeresistance due to limited polyaromatic generation in their pore structure. Based on similar analogies, the stability of HZSM-5 catalyst during the conversion of the butene mixture into C8–C16 hydrocarbon could be due to the coke-resistance resulting from the pore geometry.
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Conversion of butene (%)
100 80 60 40 HZSM-5 MMZZSM-5 NiO/MMZZSM-5
20 0 1
2
3
4
5
6
Time on stream (h)
Figure Figure9.9.Conversion Conversionof ofbutene butenethrough throughthe theoligomerization oligomerizationofofaabutene butenemixture mixtureover overvarious variouscatalysts catalysts ◦ C, WHSV 10 h−−1 1 ). (Reaction condition: pressure 1.5 MPa, temperature 350 (Reaction condition: pressure 1.5 MPa, temperature 350 °C, WHSV 10 h ).
After catalyst showed much higher ZSM-5 Afterthe thereaction reactionhad hadprogressed progressedfor forsix sixhours, hours,the theMMZ MMZ ZSM-5 catalyst showed much higher butene conversion and C –C yield than those with HZSM-5 (Figures butene conversion and C8 8–C1616 yield than those with HZSM-5 (Figures99and and10). 10).From Fromthe theNH NH3 -TPD 3-TPD and was found to have fewer and weaker acidities than HZSM-5 andPyridine-FTIR Pyridine-FTIRresults, results,MMZ MMZZSM-5 ZSM-5 was found to have fewer and weaker acidities than HZSM-5 catalyst. catalyst is beneficial for butene ZSM-5 catalyst. Thus, Thus, itit isispresumed presumedthat thatthe thereason reasonwhy whythe theMMZ MMZ ZSM-5 catalyst is beneficial for butene oligomerization, is inferior to HZSM-5, is its pore ZSM-5 oligomerization, despite despite the the fact factthat thatthe theacidity acidityofofMMZ MMZ ZSM-5 is inferior to HZSM-5, is its pore geometry. MMZ has an average pore size of 2.7 nm, which is much larger the pore ZSM-5 geometry. MMZZSM-5 has an average pore size of 2.7 nm, which is much larger thanthan the pore size size (0.5– (0.5–0.6 nm) of HZSM-5. Consequently, it can be suggested that the mesoporous structure of MMZ ZSM-5 0.6 nm) of HZSM-5. Consequently, it can be suggested that the mesoporous structure of MMZ ZSM-5 plays an important role in overcoming the internal pore diffusion of the molecules participating plays an important role in overcoming the internal pore diffusion of the molecules participatinginin the thereaction. reaction. Moreover, was higher than that over the 1616hydrocarbons ZSM-5 Moreover,the theyield yieldfor forC8C–C 8–C hydrocarbonsover overNiO/MMZ NiO/MMZ ZSM-5 was higher than that over the MMZ (Figures 9 and 10). The pore size distributions of the two catalysts were not significantly MMZZSM-5 ZSM-5 (Figures 9 and 10). The pore size distributions of the two catalysts were not significantly different. On thethe other hand, according to theto NHthe pyridine-FTIR analysis, it can be confirmed 3 -TPD different. On other hand, according NHand 3-TPD and pyridine-FTIR analysis, it can be that when NiO loaded the Lewis acid sites become more abundant and the acid ZSM-5 confirmed that is when NiOonisMMZ loaded on ,MMZ ZSM-5, the Lewis acid sites become more abundant and strength becomes stronger. Therefore, the higher butene conversion over NiO/MMZ catalysts the acid strength becomes stronger. Therefore, the higher butene conversion over ZSM-5 NiO/MMZ ZSM-5 seemed to be due to higher acid strength resulting from a higher Lewis site-to-Brønsted site ratio. catalysts seemed to be due to higher acid strength resulting from a higher Lewis site-to-Brønsted site Consequently, it may be summarized that mesoporous structures, as well as the high ratio of Lewis ratio. Consequently, it may be summarized that mesoporous structures, as well as the high ratiotoof Brønsted were beneficial for beneficial productionfor of C butene oligomerization. 8 –C16 hydrocarbons Lewis toacid, Brønsted acid, were production of C8–C16through hydrocarbons through butene The carbon number distribution in the aviation fuel range (C –C hydrocarbons) was not 8 16 oligomerization. significantly influenced by the catalysts (Figure 11). In our previous study, it was found that dimers The carbon number distribution in the aviation fuel range (C8–C16 hydrocarbons) was not were the main reaction products at a low butane conversion over the zeolite catalysts [26]. In this study, significantly influenced by the catalysts (Figure 11). In our previous study, it was found that dimers because the butene conversion wasathigh over three conversion catalysts, the carbon number distribution were the main reaction products a low butane over the zeolite catalysts [26]. in In the this range of C –C hydrocarbon became broader, which is ascribed to the contribution of consecutive 8 16 study, because the butene conversion was high over three catalysts, the carbon number distribution cracking and subsequent pathways. in the range of C8–C16 oligomerization hydrocarbon became broader, which is ascribed to the contribution of
consecutive cracking and subsequent oligomerization pathways.
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Conversion, selectivity, and yield Conversion, selectivity, and yield (%) (%)
100
conversion of butene selectivity to C8-C16 conversion yield of C -Cof butene selectivity8 to 16 C8-C16 yield of C8-C16
100 90 90 80 80 70 70 60 60 50 50 40 40
HZSM-5
MMZZSM-5
NiO/MMZZSM-5
HZSM-5
MMZ Catalyst ZSM-5
NiO/MMZZSM-5
Catalyst
Selectivity Selectivity (%) (%)
Figure 10. Conversion of butene, selectivity to C8–C16 fraction, and yield of C8–C16 fraction over Figure 10.catalysts Conversion of condition: butene, selectivity to MPa, C8 –Ctemperature yield of C10 fraction T-O-S various (reaction pressure 1.5 350 °C, WHSV h−116, and 16 fraction, and 8 –C Figure 10. Conversion of butene, selectivity to C8–C 16 fraction, and yield of C8–C16 fraction over ◦ over 10 h−1 , 6 h).various catalysts (reaction condition: pressure 1.5 MPa, temperature 350 C, WHSV various catalysts (reaction condition: pressure 1.5 MPa, temperature 350 °C, WHSV 10 h−1, and T-O-S and T-O-S 6 h). 6 h). 25 20 25 15 20 10 15 5 10 0 255 200 25 15 20 10 15 5 10 0 255 200 25 15 20 10 15 5 10 0 5 0
NiO/MMZZSM-5 NiO/MMZZSM-5
MMZZSM-5 MMZZSM-5
HZSM-5 HZSM-5
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9
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Carbon 10 11 Number 12 13 14
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Figure 11. Product distribution of the C8 –C16 range Carbonthrough Number the oligomerization of a butene mixture Figure 11. Product distribution of the C8–C16 range through the oligomerization of a butene mixture over various catalysts (reaction condition: pressure 1.5 MPa, temperature 350 ◦ C, WHSV 10−1 h−1 , over various catalysts (reaction condition: pressure 1.5 MPa, temperature 350 °C, WHSV 10 h , T-OFigure 11. Product distribution of the C8–C16 range through the oligomerization of a butene mixture T-O-S 6 h). S 6 h). over various catalysts (reaction condition: pressure 1.5 MPa, temperature 350 °C, WHSV 10 h−1, T-OCatalytic S 6 h). stability of the NiO/MMZZSM-5 catalyst was evaluated under 1.5 MPa at 350 ◦ C for 30 h
Catalytic stability of the NiO/MMZZSM-5 catalyst was evaluated under 1.5 MPa at 350 °C for 30 h on stream (Figure 12). The conversion of butene was more than 80% and did not decrease significantly on stream (Figure 12). The conversion of butene was more than 80% and did 1.5 notMPa decrease significantly Catalytic stability of the NiO/MMZ ZSM-5 catalyst was exhibited evaluated at 350 °C for 30 h for 18 h on stream. However, the NiO/MMZ aunder decrease in butene conversion ZSM-5 catalyst for 18 h on stream. However, the NiO/MMZ ZSM-5 catalyst exhibited a decrease in butene conversion on stream 12). The conversion of having butene was more thandrop 80% and did not decrease after 18 h of(Figure time-on-stream (TOS) while no significant in selectivity to C8 –Csignificantly 16 fraction after 18 h of time-on-stream (TOS) while having no significant drop in selectivity to C 8–C16 fraction for 18 h on However, ZSM-5 catalystremained exhibited above a decrease conversion with TOS. Asstream. a result, the yieldthe ofNiO/MMZ C8 –C16 hydrocarbon 63% in forbutene 18 h TOS, then with a result, the yield of C8–Chaving 16 hydrocarbon remained above 63% for 18 h TOS, then after TOS. 18 hdecreased ofAstime-on-stream (TOS) no significant drop in selectivity to C8–C16 fraction gradually to 48.0% after 30while h TOS. gradually decreased to 48.0%yield after 30Ch8–C TOS. with As athe result, remained above 63% 18 h TOS, ToTOS. quantify cokethe deposits of formed 16onhydrocarbon the NiO/MMZ after for reaction for 30then h, ZSM-5 catalyst To quantify the coke deposits formed on the NiO/MMZ ZSM-5 catalyst after reaction for 30 h, the gradually decreased to 48.0% after 30 h TOS. the weight contents of these deposits were determined by TGA. According to Figure 13, two ranges of weight contents of these were determined by TGA. ZSM-5 According toafter Figure 13, two of quantify the cokedeposits deposits formed on the region NiO/MMZ reaction forranges 30 h, the weightTo losses can be recognized: a low-temperature at 400 °C, which could be attributed to volatile organic compounds and coke deposits, respectively. weight losses itcan befound recognized: a low-temperature at 400 °C, which could be attributed volatile organic and coke deposits, respectively. after TOS of 30 h. TOS of 30 h. it was found that about 4 wt % of coke was formed on the NiO/MMZZSM-5 catalyst after Consequently, TOS of 30 h.
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conversion of butenes selectivity to C8-C16 conversion butenes yield of C8-Cof 16 selectivity to C8-C16 6yield9 of C 12-C 15 18 21
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(h) and yield of C8–C16 fraction over Figure 12. Conversion of butene, selectivity Time to C8on –Cstream 16 fraction, NiO/MMZ ZSM-5 catalyst for TOS up to 30 h (reaction condition: pressure 1.5 MPa, temperature 350 °C, Figure 12. Conversion of butene, selectivity to C8 –C16 fraction, and yield of C8 –C16 fraction over Figure 12. Conversion of butene, selectivity to C8–C16 fraction, and yield of C8–C16 fraction over ). and WHSV 10 h−1catalyst NiO/MMZ for TOS up to 30 h (reaction condition: pressure 1.5 MPa, temperature 350 ◦ C, NiO/MMZZSM-5 ZSM-5 catalyst for TOS up to 30 h (reaction condition: pressure 1.5 MPa, temperature 350 °C, − 1 and WHSV 10 h −1 ). and WHSV 10 h ).
0100 60 0
50
60
Figure catalyst. Figure13. 13.Degradation Degradationtemperature temperaturemeasurement measurement thespent spentNiO/MMZ NiO/MMZZSM-5 ZSM-5 catalyst. Time (minute)ofofthe
3. MaterialsFigure and Methods 13. Degradation temperature measurement of the spent NiO/MMZZSM-5 catalyst. 3. Materials and Methods 3.1. Preparation of Catalysts 3. Materials and 3.1. Preparation of Methods Catalysts The procedure of the catalyst preparation consists of the top–down and bottom–up approaches [13,27]. The procedure of the catalyst preparation consists of the top–down and bottom–up approaches 3.1. Preparation of Catalysts A cationic surfactant and HZSM-5 zeolite were used as the template and the framework sources, [13,27]. A cationic surfactant and HZSM-5 zeolite were used as the template and the framework respectively. At first, HZSM-5 is rent into nano-unit in alkali (top–down approach). NaOH The procedure of the catalyst preparation consists of thesolution top–down and bottom–up approaches sources, respectively. At first, HZSM-5 is rent into nano-unit in alkali solution (top–down approach). (0.375 mol) was dissolved in 76.5 of deionized prepare NaOH aqueous (4.9 M, [13,27]. A cationic surfactant andmL HZSM-5 zeolitewater weretoused as the template and solution the framework NaOH (0.375 mol) was dissolved in 76.5 mL of deionized water to prepare NaOH aqueous solution 80.0 mL), and then 33.75 g of HZSM-5 (Zeolyst, SiO /Al O mole ratio = 50) was mixed into the NaOH 2 2 3 sources, respectively. At first, HZSM-5 is rent into nano-unit in alkali solution (top–down approach). (4.9 M, 80.0 mL), and then 33.75 g of HZSM-5 (Zeolyst, SiO2/Al2O3 mole ratio = 50) was mixed into aqueous solution and stirred for 1 h. Subsequently, this zeolitic nano-unit is assembled into ordered NaOH (0.375 mol) was dissolved in 76.5 mL of deionized water to prepare NaOH aqueous solution the NaOH aqueous solution and stirred for 1 h. Subsequently, this zeolitic nano-unit is assembled mesoporous material the template (bottom–up (4.9 M, 80.0 mL), and using then 33.75 g of HZSM-5 (Zeolyst,approach). SiO2/Al2O3 Hexadecyltrimethylammonium mole ratio = 50) was mixed into into ordered mesoporous material using the template (bottom–up approach). bromide (0.189 mol) was dissolved into 1050 mL of deionized water, and thenano-unit HZSM-5 solution was the NaOH aqueous solution and stirred for 1 h. Subsequently, this zeolitic is assembled Hexadecyltrimethylammonium bromide (0.189 mol) was dissolved into 1050 mL of deionized water, added drop-by-drop. This mixture was stirred for 24 h, and the pH was controlled to 10 using into ordered mesoporous material using the template (bottom–up approach). and the HZSM-5 solution was added drop-by-drop. This mixture was stirred for 24 h, and the pH CH COOH solution (50%). After pH adjustment and mixing were repeated three times, a water, white 3 Hexadecyltrimethylammonium bromide (0.189 mol) was dissolved into 1050 mL of deionized was controlled to 10 using CH3COOH solution (50%). After pH adjustment and mixing were repeated ◦ C overnight ◦C precipitate was obtained. The resulting products were dried at 110 and calcined at 550 and the HZSM-5 solution was added drop-by-drop. This mixture was stirred for 24 h, and the pH three times, a white precipitate was obtained. The resulting products were dried at 110 °C overnight for h in an airto atmosphere to3COOH obtain solution a mesoporous material. Subsequently, it was was4 controlled 10 using CH (50%). aluminosilicate After pH adjustment and mixing were repeated and calcined at 550 °C for 4 h in an air atmosphere to obtain a mesoporous aluminosilicate material. + form ion-exchanged using NH Cl aqueous solution (1 M) to convert to the NH and again converted 4 4 three times, a white precipitate was obtained. The resulting products were dried at 110 °C overnight Subsequently, it was ion-exchanged using NH4Cl aqueous solution (1 M) to convert to the NH4+ form ◦ C for to H+calcined form byatcalcination an air atmosphere at 550 h. The newlyaluminosilicate prepared material was and 550 °C for in 4 h in an air atmosphere to obtain a3 mesoporous material. and again converted to H+ form by calcination in an air atmosphere at 550 °C for 3 h. The newly named MMZZSM-5 , meaning mesoporous from ZSM-5. Subsequently, it was ion-exchanged usingmaterial NH4Cl aqueous solution (1 M) to convert to the NH4+ form prepared material was named MMZZSM-5, meaning mesoporous material from ZSM-5. + and again converted to H form by calcination in an air atmosphere at 550 °C for 3 h. The newly prepared material was named MMZZSM-5, meaning mesoporous material from ZSM-5.
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Nickel nitrate hexahydrate (98.0%) was impregnated on MMZZSM-5 catalyst by the dry impregnation method. The loading amount of nickel metal was 3 wt %. After calcination in an air atmosphere at 550 ◦ C for 3 h, the NiO/MMZZSM-5 catalyst was obtained. 3.2. Characterization of Catalysts The nitrogen physisorption isotherms of the catalysts were obtained using a BELSORP-mini II device (BEL Japan Inc., Toyonaka, Japan) at −196 ◦ C. XRD patterns of the catalysts were collected at 40 kV and 40 mA using a D/MAX-2200V Diffractometer (Rigaku Co., The Woodlands, TX, USA), and data were reduced using the JADE program. TEM images were collected using a JEM-3010 (JEOL, Tokyo, Japan) operated at 300 kV. The NH3 -TPD was performed using BEL-CAT-B device (BEL Japan Inc., Toyonaka, Japan). The sample was outgassed at 550 ◦ C in a He gas flow (50 mL/min) for an hour. The ammonia (5% in He) was adsorbed on the sample, and then the physically adsorbed ammonia was desorbed in a He gas flow (50 mL/min) for 2 h. Subsequently, the amount of ammonia desorbed was detected by a thermal conductivity detector while increasing the temperature of sample holder from 100 to 550 ◦ C at a heating rate of 10 ◦ C/min. FTIR spectra of adsorbed-pyridine were attained with a Spectrum GX device (Perkin Elmer Co., Waltham, MA, USA) equipped with an HgCdTe detector and a custom-made cell. FTIR spectra of pyridine adsorbed on the catalyst disk were measured while the temperature of the cell was increased to 300 ◦ C [12,13]. In order to determine the amount of the coke over the spent catalyst, a TGA analysis was carried out using a SDT Q600 device (TA Instruments, New Castle, DE, USA). N2 was injected through a mass flow controller (model 5850E from Brooks, Hatfield, PA, USA) operated using a flow pressure controller (ATOVAC, GMC 1200, Yongin, Korea). The sample was loaded onto a Pt holder, and the volume changes and energy flow were recorded while running N2 (60 mL/min) and increasing the temperature up to 600 ◦ C at a heating rate of 10 ◦ C/min. 3.3. Oligomerization of Butene Mixture The oligomerization reaction of the butene mixture was conducted in a fixed-bed continuous-flow reactor [26]. The reactor set-up and the experimental procedures for butene oligomerization were described in detail in the literature [26]. In our previous research on dehydration reaction of butanol, a mixture of butene (butene-1:butene-2 = 1.0:1.3) could be generated through dehydration of 2-butanol over a solid acid catalyst [13]. Accordingly, a mixture composed of 43.5% of butene-1 (99%, Rigas Korea Co., Daejeon, Korea) and 56.5% of butene-2 (11.8% of cis-2-butene and 87.5% of trans-2-butene, Rigas Korea Co., Daejeon, Korea) was used as a model reactant. The particle size of the catalyst was 25 µm or less. The reaction pressure and temperature were 15 bar and 350 ◦ C, respectively, unless otherwise specified. In this study, most of the reaction products were alkene compounds. Needless to say, in order to use this product as a fuel, it must be converted to a paraffin compound via a hydrogenation reaction. The selectivity to C8 –C16 hydrocarbons was calculated based on the alkenes in the range of C8 –C16 . The formulae for the conversion of butene, the selectivity to C8 –C16 hydrocarbons, and the yield of C8 –C16 hydrocarbons are as follows: Conversion of butene (wt %) = (consumed butene/fed butene) ∗ 100
(1)
Selectivity of C8 -C16 (wt %) = (C8 -C16 product/consumed butene) ∗ 100
(2)
Yield of C8 -C16 (wt %) = (C8 -C16 product/fed butene) ∗ 100
(3)
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4. Conclusions Mesoporous aluminosilicate with a well-ordered structure was successfully prepared from HZSM-5 by combining a top-down method and a bottom-up method. The ordered channel-like mesopores were maintained after the nickel-loading on MMZZSM-5 catalyst. The NH3 -TPD and pyridine-FTIR results revealed that a new kind of acid site (Lewis acid sites) was generated by NiO loading on MMZZSM-5 . The MMZZSM-5 catalyst showed much higher butene conversion and C8 –C16 yield in the butene oligomerization reaction than those with HZSM-5. This is attributed to the pore geometry of MMZZSM-5 , which is more beneficial for internal diffusion of reactants, reaction intermediates, and products. Moreover, the yield for C8 –C16 hydrocarbons over NiO/MMZZSM-5 was higher than that over the MMZZSM-5 , which seemed to be due to higher acid strength resulting from a higher ratio of Lewis sites to Brønsted sites. The present study reveals that mesoporous NiO/MMZZSM-5 catalyst with high concentration of Lewis acid sites is a potential catalyst for production of C8 –C16 hydrocarbons through the oligomerization of a butene mixture. Author Contributions: D.L. and H.K. performed experiments; D.L., H.K., Y.-K.P., and J.-K.J. collected and analyzed data; and D.L. and J.-K.J. wrote the manuscript. Funding: This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2015R 1D 1A 1A01058354). This work was also supported by “Human Resources Program in Energy Technology” of the Korea Institute of Energy Technology Evaluation and Planning (KETEP), granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea (No. 20174010201560). Conflicts of Interest: The authors declare no conflict of interest.
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