- Email: [email protected]
Al ratios for benzene reduction in gasoline with propylene
G Model
JIEC 2212 1–8 Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec 1 2 3 4 5
Comparison of synthesized H-Al-MCM-41 with different Si/Al ratios for benzene reduction in gasoline with propylene Q1 Jafar
Mahmoudi, Mohammad Nader Lotfollahi *, Ali Haghighi Asl
Faculty of Chemical, Gas and Petroleum Engineering, Semnan University, Semnan 35195-363, Iran
A R T I C L E I N F O
A B S T R A C T
Article history: Received 20 July 2014 Received in revised form 26 August 2014 Accepted 15 September 2014 Available online xxx
Benzene reduction in gasoline was investigated with propylene over synthesized mesoporous H-AlMCM-41 with Si/Al = 15, 29 and 42 as catalysts in order to produce more environmental friendly gasoline. The resulting catalysts were characterized by XRF, XRD, FTIR, TGA, BET and TPD-NH3 techniques. The results of alkylation of C6-cut obtained from gasoline indicated that the synthesized mesoporous H-AL-MCM-41 with Si/Al = 15 is the most active catalyst among the synthesized catalysts due to high crystallinity, favorable textural properties and large bronsted acidity. The higher conversion of benzene (47.88%) was observed over H-Al-MCM-41 with Si/Al = 15 at B/P = 1 and T = 200 8C. ß 2014 Published by Elsevier B.V. on behalf of The Korean Society of Industrial and Engineering Chemistry.
Keywords: H-Al-MCM-41 Synthesis Gasoline Benzene reduction Propylene
6 7
Introduction
8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
Benzene exists naturally in crude oil; so it passes into refined products such as gasoline that is one of the most applicable transportation fuels. Based on new environmental regulations, the amount of benzene in gasoline should be less than 0.62% [1,2] because of its carcinogenic properties. Therefore, the amount of benzene in gasoline should be controlled to reduce the human exposure of it. One of the methods to reduce the benzene in gasoline is catalytic alkylation of benzene with light olefins such as propylene. In these processes, catalyst plays an important role in the product distribution. In many petrochemical plants these alkylation reactions are performed with homogeneous catalysts such as mineral acids having many drawbacks [3–5]. In order to avoid the drawbacks of mentioned catalysts, many efforts have been done for developing alternative solid acid catalysts [6–9]. Different zeolites with acidic properties applied as a solid acid catalyst and were extensively evaluated in benzene alkylation with light olefins such as ethylene and propylene: alkylation of pure benzene with propylene was performed over HY zeolites [10]; Ga-modified H-ZSM-5 [11]; MCM-36 and MCM-22 [12]; series of b zeolites [13] and Hb zeolite [14–16] in different conditions on vapor phase. The main objective of many researches was the
* Corresponding author. Tel.: +98 23 33654120; fax: +98 23 33654120. E-mail addresses: [email protected], [email protected] (M.N. Lotfollahi).
alkylation of pure benzene to produce cumene and little works have been performed for alkylation of benzene in gasoline cut. In order to produce more environmental friendly gasoline, Laredo et al. [17–19] studied the alkylation of benzene in a C6 reformate heart-cut. Recently the interest in silica-alumina with controlled porosity in the mesoporous region as catalysts has been increased [20]. Purely siliceous MCM-41 does not have acidic properties. It was found that the incorporation of metals such as aluminum into the MCM-41 improves the acidity of it [21–23]. Recently, the alkylation of aromatic compounds in the presence of mesoporous Al-MCM-41 have been studied by many investigators including: alkylation of toluene with isopropanol on a MCM-41/g-A1203 catalyst [24,25]; comparison of mesoporous Al-MCM-41 molecular sieves in the production of p-cymene for vapor phase isopropylation of toluene at various reaction conditions [26]; vapor phase isopropylation of toluene with isopropyl-acetate over mesoporous MCM-41 materials and micro-porous zeolite catalysts [27]; vapor phase reaction of tert-butyl benzene with isopropyl acetate over mesoporous Al-MCM-41 molecular sieves [28]; gas phase alkylation of toluene with propylene over pure mesoporous molecular sieve Al-MCM-41 and micro/mesoporous composites [29]; vapor phase reaction of toluene with ethyl-acetate overAl-MCM-41 molecular sieves [30]. In this work, the mesoporous Al-MCM-41 with different Si/Al ratios was synthesized by sol–gel method using cetyltrimethylammonium bromide as a template. In order to improve the acidity of synthesized sample, ion exchange with ammonium nitrate was
http://dx.doi.org/10.1016/j.jiec.2014.09.017 1226-086X/ß 2014 Published by Elsevier B.V. on behalf of The Korean Society of Industrial and Engineering Chemistry.
Please cite this article in press as: J. Mahmoudi, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.09.017
29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56
G Model
JIEC 2212 1–8 J. Mahmoudi et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
2
57 58 59 60 61 62 63 64 65 66
performed. The physicochemical properties of synthesized catalysts were characterized by XRF, XRD, FTIR, TGA, BET, titration of surface acidic protons and TPD-NH3 techniques. In the next step, benzene reduction in gasoline produced by one of the Iranian refineries was investigated by alkylation process in liquid phase with propylene as an alkylating agent over the synthesized samples as catalyst. In addition, the alkylation of a benzene-cut over synthesized catalysts was performed for comparing the obtained results with the results of benzene alkylation in gasoline.
67
Experimental
68
Materials
69 70 71 72 73 74
Benzene (Merck Co. 99.5%), Propylene (Air product Co., 99%), sodium silicate solution (Merck Co. 27 wt.% SiO2), sodium aluminate (Aldrich, anhydrous technical, 50–56 wt.% Al2O3) and cetyltrimethylammonium bromide (CTAB, Merck Co, 99 wt.%) were used as raw materials. The composition of used benzene-cut was shown in Table 1.
75
Synthesis of Al-MCM-41
76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98
The synthesis of MCM support was described earlier in detail in the literature [8,9,22,31]. In this research, Al-MCM-41 has been synthesized using sodium silicate solution as a silica source, sodium aluminate as an aluminum source and cetyltrimethylammonium bromide (CTAB) as a template. The synthesis of Al-MCM41 was carried out by sol–gel method using a gel composition of 4SiO2: (0.05, 0.08 and 0.2) Al2O3: 1CTAB: 250H2O with Si/Al = 10, 25, 40 molar ratios. In a typical synthesis, the sodium silicate solution was added dropwise into a mixture of cetyltrimethylammonium bromide and deionized water with vigorous stirring at room temperature. At the end, certain amount of sodium aluminate was added dropwise into the mixture by varying the Si/Al ratio from 10 to 40. The gel mixture was heated to 100 8C for 1 day in an oil bath with vigorous stirring. After cooling to room temperature, the pH of the resulting gel was adjusted to around 10 by addition of acetic acid solution (25 wt.%). The pH adjustment and subsequent heating for 1 day was repeated three or four times until the pH of resulting gel was constant. The solid product was recovered by filtering the solution and then washed with 4 L of doubly distilled water. Finally, the products were dried at 100 8C in a day period. After that, the sample was calcined from room temperature to 550 8C with a heating rate of 1 8C/min and maintained at 550 8C for 3 h.
99
Preparation of H-Al-MCM-41
100 101 102 103 104 105 106
Al-MCM-41 samples were subjected to ammonium exchange treatment. For this, 1 g of each calcined Al-MCM-41 samples was ion exchanged with 50 ml of 1 M ammonium nitrate solution with vigorous stirring at 90 8C for 8 h and the procedure was repeated three times to complete ammonium exchange treatment for each samples. H-Al-MCM-41 samples were obtained by calcination of NH4-Al-MCM-41 samples at 550 8C for 2 h.
Table 1 Chemical composition of benzene-cut and C6-cut obtained from gasoline. Feed
Benzene cut C6-cut
Chemical Hexane
Benzene
Toluene
Xylene
Other
4.78 70.79
94.16 20.03
0 4.81
0 2.47
1.06 1.90
Catalyst characterization
107
The low-angle XRD patterns of the samples were recorded using a Bruker (model, D8 Advance, USA) X-ray diffractometer using Ni filtered CuKa radiation (l = 1.5406 A´˚ , kV = 40, mA = 30). The samples were scanned from 2u = 1–108 angle in steps of 0.018 with a count time of 1 s at each point. The elemental analysis of calcined samples was determined by X-ray fluorescence (XRF, Bruker AXS – S4 EXPLORER). The flat sample disks were analyzed with a voltage of 40 kV and current of 30 mA. The infrared spectra of samples were recorded in the range of 4000–400 cm1 wave numbers with resolution of 4 cm1 using a Shidmadzu Fourier-Transform Infrared FT-IR 8400 Spectrometer. The solid samples were mixed with KBr powder and compressed into pellet for analysis. The mmol of H+ per gram of catalyst (Bronsted acid sites in samples) was determined by the simple titration methodology described in the literature [32]. Temperature-programmed desorption (TPD) experiments of NH3 was carried out by using Micromeritics TPD/TPR 2900 apparatus. 212.5 mg of sample was activated by flowing 40 ml/min helium at 500 8C for 60 min, and then cooled to 25 8C and saturated with pure NH3 for 60 min. Subsequently, helium (40 ml/min) was passed for 40 min at 150 8C to remove physically adsorbed NH3. The NH3-TPD measurement was performed from 150 8C to 750 8C at a rate of 10 8C/min. A thermal conductivity cell was used for recording the desorbed amount of NH3. The thermogravimetric analysis (TGA) of the sample was carried out by using Mettler TGA/SDTA851 thermal analyzer under a nitrogen flow of 60 ml/min. The heating rate was 10 8C/min in temperature ranging from 30 up to 1000 8C. Surface area and pore size of the H-Al-MCM-41 samples were measured using the nitrogen adsorption–desorption method at liquid nitrogen temperature (76.03 K) by ASAP 2010 instrument. Prior to the measurements, the sample was degassed at 573 K under vacuum for 5 h.
108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142
C6-cut obtained from gasoline
143
In order to decrease the side reactions in the alkylation of benzene content in gasoline with propylene, the C6-cut was obtained by batch distillation of the gasoline at temperature ranging from 45 to 80 8C. The composition of the obtained C6-cut was shown in Table 1.
144 145 146 147 148
Experimental procedure in alkylation reaction
149
Alkylation of benzene with propylene was performed in a stainless steel batch reactor that schematic view of this experimental setup is shown in Fig. 1. The experimental setup shown in Fig. 1 was constructed by Paya Fanavar Mashin Company (Iran) including a 400 cm3 stainless steel agitation reactor with magnetic drive and explosion proof motor. The thermocouple is placed into a well in the reactor for the precise detection of reaction temperature. The reaction temperature was controlled by a temperature controller, accurate to 2 8C. In each experiment, appropriate amounts of components were weighed on an analytical balance and then were charged in the reactor. At first, the catalyst was activated at 500 8C in furnace for 2 h and then cooled to ambient temperature and added to the mixture in the reactor. The reactor was pressurized with nitrogen to reach the appropriate pressure (40–50 bar). The temperature controller allows the reactor to be heated by an electric heater to the required temperature. After 2 h agitation of mixture in the reactor under stirring (800 rpm), the agitation was stopped and the products were
150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167
Please cite this article in press as: J. Mahmoudi, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.09.017
G Model
JIEC 2212 1–8 J. Mahmoudi et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
3
Fig. 1. Schematic flow diagram of experimental setup for alkylation of benzene content in benzene-cut and C6-cut obtained from gasoline.
168 169 170 171 172
withdrawn from the reactor. Then the products were cooled down to 2 8C by flowing through a coil immersed in water-ice bath in order to condense the organic compounds completely. The liquid products were filtered for separation of catalyst and finally were analyzed by GC.
173
GC analysis
174 175 176 177 178 179 180 181 182 183 184
The gas chromatographic (GC) analysis of products was carried out using ACME 6100GC from Youngling instrument Co., LTD. (South Korea). This GC equipped with a helium ionization detector (HID) and TRB-WAX capillary column (60 m long and 0.32 mm OD, coated with a 0.5 mm thick film of polyethylene glycol as stationary phase). In order to identify the products and to measure the concentration of components in the mixture, the GC was calibrated by an external standard calibration method. Helium was used as carrier gas at the rate of 1 ml/min. Software supplied by Chrompack (detailed hydrocarbon analyzer) was used to handle the data generated by GC.
185
Conversion and selectivity calculations
186 187 188
Two important parameters, the conversion and the selectivity, reveal the catalytic activity of synthesized catalysts for alkylation of benzene. The conversion is obtained by the following equation: Conversion ð%Þ ¼
190 189 191 192
C0 Cp C0
100
(1)
where C0 is the concentration of benzene, toluene or xylene at time zero (feed) and Cp is the concentration of mentioned components in the product. The concentration values are in weight. The
selectivity of each component is calculated by the following equation: Selectivity ð%Þ ¼
Ci 100 Ct
193 194
(2)
where Ci is the concentration by weight for cumene, n-propylbenzene (PB), 1,3-diisopropylbenzene (1,3-DIPB), 1,2-diisopropylbenzene (1,2-DIPB), 1,4-diisopropylbenzene (1,4-DIPB) or other by-products produced in alkylation of benzene. Ct is the summation of the concentrations by weight for mentioned components.
196 195 197 198 199 200
Results and discussion
201
Characterization of the synthesized catalysts
202
XRF analysis The aluminum content in Al-MCM-41with various Si/Al ratios was measured using X-ray fluorescence (XRF) technique. The results of this analysis were listed in Table 2. It can be pointed out that the synthesis samples’ Si/Al ratio (Si/Al = 15, 29, 42) is greater than the hydrogels’ Si/Al ratio (Si/Al = 10, 25, 40). These observations are similar to those reported in the literature by Udayakumar et al. [28].
203 204 205 206 207 208 209
Table 2 Physicochemical properties of the synthesis catalysts. Catalyst
Al-MCM-41 (15) Al-MCM-41 (29) Al-MCM-41 (42)
Si/Al ratio
Calcined sample
Hydrogel
XRF
d100 (A˚)
a0 (A˚)
10 25 40
15 29 42
36 39.44 41.08
41.57 45.54 47.43
Please cite this article in press as: J. Mahmoudi, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.09.017
mmol of H+/g
0.338 0.286 0.204
G Model
JIEC 2212 1–8 J. Mahmoudi et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
4
210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229
XRD Fig. 2 shows the XRD pattern of the calcined Al-MCM-41 samples with various Si/Al ratios ranging from 15 to 42. These patterns show a sharp d100 reflection line in 2u = 2.58 and broad peaks in 2u = 4.338 (1 1 0) and 2u = 4.928 (2 0 0) for Al-MCM-41(15) (Si/Al = 15) which corresponds to well-ordered mesoporous materials with hexagonal symmetry [28]. For Al-MCM-41(29) (Si/Al = 29) and Al-MCM-41(42) (Si/Al = 42) sharp d100 reflection line were observed in 2u = 2.328 and 2.188, respectively. These patterns for recently mentioned samples also contain broad peaks in 2u = 4.058 (1 1 0) and 2u = 4.668 (2 0 0) for Al-MCM-41(29) and in 2u = 3.958 (1 1 0) and 2u = 4.698 (2 0 0) for Al-MCM-41(42). The d-spacing and unit cell parameters (a0) for the synthesis samples are listed in Table 2. The unit pffiffiffi cell parameters of samples calculated using the formula: 2d100 3 that d100 was calculated by Bragg’s equation (l = 2d sin u). As results in Table 2, by increasing the Al content in synthesis samples, the unit cell parameter is decreased. Similar results were reported by Selvaraj et al. [26] and Savidha and Pandurangan [27] for the isopropylation of toluene using ‘Al-MCM-41 molecular sieves.
230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249
FT-IR spectroscopy The FTIR spectra of the calcined H-Al-MCM-41 samples with various Si/Al ratios in the wave number region of 400–4000 cm1 are shown in Fig. 3. Based on the spectrum of calcined samples, there is a broad peak located around 3500 cm1 which are assigned to the O–H stretching of adsorbed water molecules and surface silanol groups (Si–OH group). Another peak in 1620–1640 cm1 is attributed to the adsorbed molecules deformation mode [33]. Also based on the spectrum of samples shown in Fig. 3, there are two intense peaks at the range 1000–1300 cm1 which are attributed to the asymmetric stretching vibration of T–O–T (T= Si or Al) [22]. The two peaks around 800 cm1 and around 460 cm1 are assigned to the symmetric T–O–T stretching and to the TO4 bending mode, respectively. The peak at around 960 cm1 is attributed to the presence of defective Si–OH groups [28]. Based on Fig. 3, this pick is more sensitive in the H-form of Al-MCM-41 (15) toward Al-MCM-41 (15) sample. As results, increasing of the Al content in H-Al-MCM-41 samples causes a shift of the lattice vibration band to a higher wave number. These may be due to increase of the mean T–O distances in the wall, by increasing the
Intensity
Fig. 3. FTIR spectra of H-Al-MCM-41 samples with various Si/Al: (—) Si/Al = 15, ( ) Si/Al = 29, and ( ) Si/Al = 42 and Al-MCM-41 with Si/ Al = 15 ( ).
0
2
4
6
8
10
2θ (degrees) Fig. 2. XRD patterns of Al-MCM-41samples with various Si/Al: (—) Si/Al = 15, ( ) Si/Al = 29, and ( ) Si/Al = 42.
incorporation of Al atom in the framework. These results are in good agreement with those reported in the literature [26].
250 251
Acidity of samples
252
Surface acidic protons. The mmol of H+ (Bronsted acidity) per gram of the catalyst was found similar to the methodology as reported by Saadatjoo et al. [32]. For this purpose, 0.1 g of H-Al-MCM-41 sample was ion exchanged with 10 ml saturated solution of NaCl by sonication. The ion exchange was repeated twice. The obtained solution was then titrated by sodium hydroxide solution 0.1 M to determine the loading of acid sites on the synthesized sample. The results of this analysis are summarized in Table 2. The result demonstrates that the amount of acid sites slightly decrease with increasing Si/Al ratios. Meanwhile, by this methodology the mmol of H+ per gram of the Al-MCM-41 (15) was determined 0.07. This result indicated that the loading of acid sites are found to be higher for H-form of Al-MCM-41 than for Al-MCM-41 implying an
253 254 255 256 257 258 259 260 261 262 263 264 265
Please cite this article in press as: J. Mahmoudi, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.09.017
G Model
JIEC 2212 1–8 J. Mahmoudi et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
5
Table 3 Surface area, pore size and TPD of NH3 results of the synthesis catalysts. Pore diameter (A˚)
BET-surface area (m2 g1)
Catalyst
H-Al-MCM-41 (15) H-Al-MCM-41 (42)
719.312 792.897
24.342 35.097
266 267
increase in Bronsted acidity by ion exchanging of zeolite with ammonium.
268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283
Temperature programmed desorption of ammonia (TPD-NH3). The acidic properties of H-Al-MCM-41 (15) and H-Al-MCM-41 (42) samples were evaluated by temperature programmed desorption (TPD) measurement of ammonia. The amount of desorbed ammonia which attributed to the total number of acid sites of catalyst was given in Table 3. It is observed two major regions according to the acid strength; a low temperature (LT) region (200–250 8C) and a high temperature (HT) region (380–450 8C) that occurred due to desorption of ammonia adsorbed on weak and strong acid sites, respectively [34]. Based on the data, lower temperature range exhibited higher amount of ammonia desorption. Meanwhile, as can be seen in Table 3 the amount of ammonia desorbed on weak and strong acid sites were increased from 0.313 to 0.43 mmol/g with increasing of Al content in mesoporous. The observed results agreed with published results by Savidha and Pandurangan [27].
284 285 286 287 288 289 290 291 292 293 294 295 296 297 298
Thermogravimetric analysis (TGA) The thermal properties of the as-synthesized sample were investigated by TGA. The data of the percentage of weight loss in various ranges of temperatures for Al-MCM-41 (15) are presented in Table 3. Representative curves, the thermograms of the assynthesized sample, are shown in Fig. 4 (Table 4). The weight loss observed at temperature slower than 150 8C is attributed to desorption of physically adsorbed water in the voids formed by crystal agglomeration [35,36]. The main weight loss which is between 150 8C and 350 8C is due to the decomposition and combustion of the templating organic molecules [26,35]. The next weight loss which is between 350 8C and 550 8C corresponds to removal of organic residues. In this case, Boveri et al. have reported that the weight loss between 350 8C and 550 8C could be attributed to water loss from the silanol group condensation
100
Weight loss (%)
90 80 70 60 50 0
200
400
600
800
1000
Total acidity (mmol/g)
LT-peak
HT-peak
0.278 0.182
0.152 0.131
0.430 0.313
[37]. There was almost no change in weight loss after 550 8C, which indicated the completely removal of the organic template at 550 8C. The total weight loss percentage at 1000 8C for the AlMCM-41 (15) sample is equal to 44.114%.
299 300 301 302
Nitrogen adsorption isotherm For H-Al-MCM-41 (15) and H-Al-MCM-41 (42) samples, nitrogen adsorption isotherms were investigated at 76.03 K. The specific surface area was determined using the BET equation and pore size distribution was estimated by Barrett–Joyner–Halenda (BJH) method. The nitrogen adsorption isotherms of the H-AlMCM-41 (15) and H-Al-MCM-41 (42) samples are given in Fig. 5(a) and (b), respectively. Based on Fig. 5 the samples show a characteristic step around the P/P0 0.4–0.5 indicating the mesoporous nature of the catalysts [38]. Table 3 shows the specific surface area and pore size of the H-Al-MCM-41 samples. Based on Table 3 the high BET surface area of the H-Al-MCM-41 samples (719.312–792.897 m2 g1) coincided with the high surface area of mesoporous materials. Also as can be seen in Table 3, the pore diameter of samples was obtained in the range of 24.342–35.097 A˚ that agreed with the range of pore diameter for mesoporous materials [8]. Also the pore diameter was decreased with increasing aluminum content in samples. The results observed are in good agreement with the reported values [27,28].
303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322
Alkylation of benzene content in benzene-cut and C6-cut with propylene
323 324
In order to study the catalytic performance of synthesized catalysts, H-Al-MCM-41 prepared with various Si/Al ratios (Si/ Al = 15, 29, 42) were tested in the alkylation of benzene content in benzene-cut (Table 1) and C6-cut obtained from gasoline with propylene. These series of experiments were carried out at 200 8C, benzene/propylene (B/P) molar ratio = 1 over 1 g of catalyst. The chemical composition of the products in alkylation of the C6-cut obtained from gasoline and benzene-cut are presented in Tables 5 and 7, respectively. The selectivity of products and conversion of benzene for both mentioned feedstocks are listed in Tables 6 and 8, respectively. In alkylation of benzene-cut over three types of synthesized catalysts, the sample with Si/Al ratio of 15 gives the highest benzene conversion and cumene selectivity, which are 48.92% and 57.73%, respectively. Meanwhile, the same trend also was observed for alkylation of benzene content in C6-cut obtained from gasoline. In the alkylation of C6-cut using H-Al-MCM-41 (15) as catalyst, the maximum benzene conversion and cumene selectivity are 47.88% and 52.23%, respectively. As shown in
325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343
Table 4 TGA results for the as-synthesized sample. Catalyst
Temparature (˚C) Fig. 4. TGA curve of as-synthesized Al-MCM-41 (15) sample.
TPD of NH3
H-AL-MCM-41 (15)
Weight loss (wt.%) 50–150 8C
150–350 8C
350–550 8C
Total
2.865
26.049
15.20
44.114
Please cite this article in press as: J. Mahmoudi, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.09.017
G Model
JIEC 2212 1–8 J. Mahmoudi et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
6
a
Table 5 Chemical composition of the products in alkylation of the C6-cut obtained from gasoline with propylene over synthesized catalysts.
550 500
adsorpon
450
desorpon
Experimental condition
H-AL-MCM-41 (15)
400
Chemical composition (wt%) Benzene 10.44 Toluene 2.31 Xylene 1.27 Cumene 22.76 PB 0.03 1,3-DIPB 5.12 1,2-DIPB 3.24 1,4-DIPB 5.26 Hexane 42.41 7.16 Heavier polyalkylates + oligomer
Volume (cc/g)
350 300 250 200 150 100 50 0
0.1
0.2
0.3
0.4 0.5 0.6 0.7 Relave Pressure (P/P0)
0.8
0.9
H-AL-MCM-41 (42)
12.28 2.76 1.38 14.13 0.05 3.06 2.06 3.15 54.82 6.31
13.59 3.05 1.51 7.53 0.06 1.91 1.21 1.83 62.03 5.13
1
450 adsorpon
400
desorpon 350 300 Volume (cc/g)
H-AL-MCM-41 (29)
Catalyst weight = 1 g, (benzene/propylene) = 1, reaction temperature = 200 8C and reaction time = 2 h.
0
b
Catalysts:
250 200 150 100 50 0 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Figs. 8 and 9 show the selectivity of DIPB isomers in alkylation of benzene-cut and C6-cut, respectively. It seems that by increasing the aluminum content in synthesized samples, the DIPB isomers production increases slightly. In fact the access of reactants to acidic sites on catalyst will be increased with increasing the aluminum content in synthesized samples that produces more alkylated product, especially DIPB. Distribution of DIPB isomers are shown in Figs. 8 and 9. For HAl-MCM-41 (15) as catalyst in alkylation of benzene in C6-cut, the 1,2-DIPB, 1,3-DIPB and 1,4-DIPB isomer distributions were 23.8%, 37.59% and 38.61%, similar to the trend of distribution reported by Cejka et al. [29]. It was not considerable change in distribution of DIPB isomers with different Si/Al ratios. It seems that, the alkylation and isomerization rates play important role in distribution of DIPB isomers. 1,2-DIPB, 1,3-DIPB and 1,4-DIPB can be produced by alkylation directly and can be converted together with isomerization reaction. Based on the experimental data, due to the smaller steric hindrance of the propyl groups, the 1,4-DIPB was produced more than the other isomers. Also considerable concentration of the 1,2-DIPB isomer indicated that these isomers produced by alkylation directly and little isomerization was occurred.
Relave Pressure (P/P0) Fig. 5. Nitrogen adsorption isotherms of (a) H-Al-MCM-41 (15) and (b) H-Al-MCM41 (42).
344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359
Figs. 6 and 7, the benzene conversion and selectivity of cumene increase with increasing framework aluminum content for both benzene-cut and C6-cut alkylation. Based on the literature report, addition of excess Al atom (when the Si/Al ratio is lower than Si/Al = 10) into the MCM-41 might lead to the collapse of pores and channels of synthesized samples that produces catalyst with relatively weak activity [39–42]. Therefore in our experiments, H-Al-MCM-41 samples were synthesized with various Si/Al ratios higher than Si/Al = 10 to prevent the collapse of the structure. Also these results are in a similar order of acidic properties of samples as the effect of framework aluminum content. In the alkylation of C6-cut obtained from gasoline, enhancement of the cumene selectivity in product is favorable because the cumene can be used as a blending agent for enhancement of the octane number of gasoline [6]. The catalytic activity of synthesized samples is in good agreement with the results of Pandurangan et al. [27].
Table 6 Conversion and selectivity achieved after alkylation of the C6-cut obtained from gasoline with propylene over synthesized catalysts. Experimental condition
Conversion (%) Benzene Toluene Xylene Selectivity (%) Cumene PB 1,3-DIPB 1,2-DIPB 1,4-DIPB Heavier polyalkylates + oligomer
Catalysts: H-AL-MCM-41 (15)
H-AL-MCM-41 (29)
H-AL-MCM-41 (42)
47.88 51.97 48.58
38.69 42.62 44.13
32.15 36.59 38.87
52.23 0.07 11.75 7.44 12.07 16.43
49.13 0.17 10.64 7.16 10.95 21.94
42.61 0.34 10.81 6.85 10.36 29.03
Catalyst weight = 1 g, (benzene/propylene) = 1, reaction temperature = 200 8C and reaction time = 2 h.
Please cite this article in press as: J. Mahmoudi, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.09.017
360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381
G Model
JIEC 2212 1–8 J. Mahmoudi et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
7
Table 7 Chemical composition of the products in alkylation of the benzene-cut with propylene over synthesized catalysts. Experimental condition
Chemical composition Benzene Cumene PB 1,3-DIPB 1,2-DIPB 1,4-DIPB Hexane Heavier polyalkylates + oligomer
Catalysts: H-AL-MCM-41 (15)
H-AL-MCM-41 (29)
H-AL-MCM-41 (42)
(wt%) 48.09 27.16 0.29 4.33 3.94 6.27 4.86 5.06
56.93 19.58 0.47 3.05 2.63 4.08 7.89 5.37
65.86 12.79 0.58 1.86 1.73 2.55 8.47 5.89
Catalyst weight = 1 g, (benzene/propylene) = 1, reaction temperature = 200 8C and reaction time = 2 h.
382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406
On the other hand the alkylation of benzene in C6-cut over three type of catalysts H-Al-MCM-41, led to formation of undesired products mainly polyalkylbenzene and oligomers as shown in Tables 6 and 8. As mentioned in the literature [12,13], these byproducts, especially oligomers, ultimately decrease the catalyst life by deactivation of it. Between three types of H-AL-MCM-41, with increasing the framework aluminum content and therefore increasing acidity, the formation of these by-products was decreased. These may be attributed to the increasing in the ability of H-Al-MCM-41 (15) for alkylation reaction by suppressing the side reaction. Based on the data reported by Pergo et al. [20], the lower amount of oligomer was formed with MCM-41 mesoporus. The low formation of olefin oligomers is very important advantage of synthesized catalyst because presence of these compounds will affect catalyst life by pore blocking and coke deactivation [19]. Reusability of the catalyst was checked by recovering H-AlMCM-41 (15) in alkylation of C6-cut obtained from gasoline. For this purpose the H-Al-MCM-41 (15) was reused four times in consecutive alkylation reactions. The results given in Table 9 indicated that the benzene conversion range (47.51–40.69%) and the selectivity of cumene range (52.51–47.68%) were retained with a slight decrease. Therefore, there is not significant loss in the activity of catalyst on the recycling experiments. The results indicated that the catalyst is stable and provides a suitable regenerability.
Fig. 6. Effect of catalyst on benzene conversion and cumene selectivity in alkylation of benzene cut; H-AL-MCM-41 (42): 1; H-AL-MCM-41 (29): 2; H-AL-MCM-41 (15): 3.
Fig. 7. Effect of catalyst on benzene conversion and cumene selectivity in alkylation of C6-cut obtained from gasoline; H-AL-MCM-41 (42): 1; H-AL-MCM-41 (29): 2; HAL-MCM-41 (15): 3.
Table 8 Conversion and selectivity achieved after alkylation of the benzene-cut with propylene over synthesized catalysts. Experimental condition
Conversion (%) Benzene Selectivity (%) Cumene PB 1,3-DIPB 1,2-DIPB 1,4-DIPB Heavier polyalkylates + oligomer
Catalysts: H-AL-MCM-41 (15)
H-AL-MCM-41 (29)
H-AL-MCM-41 (42)
48.92
39.54
30.05
57.73 0.62 9.2 8.37 13.33 10.75
55.66 1.34 8.67 7.48 11.6 15.26
50.34 2.28 7.32 6.81 10.04 23.19
Catalyst weight = 1 g, (benzene/propylene) = 1, reaction temperature = 200 8C and reaction time = 2 h.
Fig. 8. Distribution of DIPB isomers over different catalysts in alkylation of benzene cut, H-AL-MCM-41 (42): 1; H-AL-MCM-41 (29): 2; H-AL-MCM-41 (15): 3.
Please cite this article in press as: J. Mahmoudi, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.09.017
G Model
JIEC 2212 1–8 J. Mahmoudi et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
8
Fig. 9. Distribution of DIPB isomers over different catalysts in alkylation of C6-cut obtained from gasoline; H-AL-MCM-41 (42): 1; H-AL-MCM-41 (29): 2; H-AL-MCM41 (15): 3.
Table 9 Reusability of H-Al-MCM-41 (15) in alkylation of C6-cut obtained from gasoline. Time run
Benzene conversion (%)
Cumene selectivity (%)
1 2 3 4
47.51 46.13 43.78 40.69
52.51 51.29 49.13 47.68
Catalyst weight = 1 g, (benzene/propylene) = 1, reaction temperature = 200 8C and reaction time = 2 h.
407 408 409 410 411 412 413 414
As results, in the benzene reduction in gasoline over H-AlMCM-41 (15) as catalyst, the DIPB isomers and others higher molecular weight aromatics should be separated from product by distillation to prevent the change of gasoline range. Based on the obtained data, the same trend also was observed for alkylation of benzene-cut in the case of DIPB and polyalkylbenzene production that for pure cumene producing, separation of these compounds by distillation is necessary.
415
Conclusion
416 417 418 419 420 421 422 423 424 425 426 427 428 429 430
In this study, mesoporous H-Al-MCM-41 with Si/Al = 15, 29 and 42 were synthesized by using cetyltrimethylammonium bromide as the template. The physicochemical properties of synthesized samples were characterized by XRF, XRD, FTIR, TGA, BET, titration of surface acidic protons and TPD-NH3 techniques. The results showed that the synthesized catalysts have good crystallinity and favorable textural properties (high surface and suitable pore size) and the acidity of synthesized catalysts were increased by decreasing the Si/Al ratios. The behavior of the synthesized catalysts in the liquid-phase alkylation of benzene in C6-cut obtained from gasoline and benzene-cut with propylene were investigated. Among the synthesized catalysts, It could be inferred that in C6-cut alkylation, there were high selectivity of cumene (52.23%) and benzene conversion (47.88%) for H-Al-MCM-41 (15) at B/P = 1, weight of catalyst = 1 g and T = 200 8C. In addition to
C6-cut, the alkylation of a benzene-cut was also performed and the results were compared with alkylation of the C6-cut obtained from gasoline. For the benzene-cut, the maximum benzene conversion (48.92%) was achieved over H-Al-MCM-41 with Si/Al = 15 as catalyst at same conditions. The results also showed that the H-AlMCM-41 (15) is reusable catalyst in alkylation of C6-cut obtained from gasoline.
431 432 433 434 435 436 437
Acknowledgement
438
The authors tend to appreciate for the partial financial support Q2 from the Science & Technology Park of Semnan University. Q3
439 440
References
441
[1] Regulatory announcement: direct final rule making revising mobile source air toxics early credit technology requirement, EPA420-F-08-007, February 2008 http://www.epa.gov/oms/regs/toxics/420f08007.htm. [2] Rules and Regulations, Federal Register, vol. 73 (49), March 2008. [3] K.S. Wong, Ph.D. thesis, University of Bath, United Kingdom, 2009. [4] B. Jacob, Ph.D. thesis, Cochin University of Science and Technology, India, 1998. [5] J.J. Chiu, D.J. Pine, S.T. Bishop, B.F. Chmelka, J. Catal. 221 (2004) 400. [6] C. Perego, P. Ingallina, Catal. Today 73 (2002) 3. [7] U. Sridevi, N.C. Pradhan, B.K.B. Rao, C.V. Satyanarayana, B.S. Rao, Catal. Lett. 79 (2002) 69. [8] A.B. Mohamed, Ph.D. thesis, Universiti Teknologi Malaysia, Malaysia, 2005. [9] F.B. AbuBakar, Ph.D. thesis, Universiti Teknologi Malaysia, Malaysia, 2010. [10] F. Cavani, G. Girotti, G. Terzoni, Appl. Catal. A: Gen. 97 (1993) 177. [11] I.I. Ivanova, N. Blom, E.G. Derouane, J. Mol. Catal. A: Chem. 109 (1996) 157. [12] Y. Zhang, H. Xing, P. Yang, P. Wu, M. Jia, J. Sun, T. Wu, React. Kinet. Catal. Lett. 90 (1) (2007) 45. [13] S. Siffert, L. Gaillard, B.L. Su, J. Mol. Catal. A: Chem. 153 (2000) 267. [14] M. Han, S. Lin, E. Roduner, Appl. Catal. A: Gen. 243 (2003) 175. [15] Z. Tian, Z. Qin, M. Dong, G. Wang, J. Wang, Catal. Commun. 6 (2005) 385. [16] Z. Tian, Z. Qin, G. Wang, M. Dong, J. Wang, J. Supercrit. Fluid. 44 (2008) 325. [17] G.C. Laredo, J.O. Marroquin, J. Castillo, P. Perez-Romo, J. Navarrete-Bolannos, Appl. Catal. A: Gen. 363 (2009) 19. [18] G.C. Laredo, J. Castillo, H. Armendariz-Herrera, Appl. Catal. A: Gen. 384 (2010) 115. [19] G.C. Laredo, R. Quintana-Solo´rzano, J. Castillo, H. Armendariz-Herrera, J.L. GarciaGutierrez, Appl. Catal. A: Gen. 454 (2013) 37. [20] C. Perego, S. Amarilli, A. Carati, C. Flego, G. Pazzuconi, C. Rizzo, G. Bellussi, Microporous. Mesoporous. Mater. 27 (1999) 345. [21] S.H. Park, B.Y. Song, T.G. Lee, J. Ind. Eng. Chem. 14 (2008) 261. [22] B. Lindlar, A. Kogelbauer, R. Prins, Microporous Mesoporous Mater. 38 (2000) 167. [23] Q. Zhao, Q. Wang, D. Wu, X. Fu, T. Jiang, H. Yin, J. Ind. Eng. Chem. 18 (2012) 1326. [24] J. Medina-Valtierra, M.A. Sfinchez, J.A. Montoya, J. Navarrete, J.A. de los Reyes, Appl. Catal. A: Gen. 158 (1997) LI. [25] J. Medina-Valtierra, O. Zaldivar, M.A. Sanchez, J.A. Montoya, J. Navarrete, J.A. de los Reyes, Appl. Catal. A: Gen. 166 (1998) 387. [26] M. Selvaraj, A. Pandurangan, K.S. Seshadri, P.K. Sinha, V. Krishnasamy, K.B. Lal, J. Mol. Catal. A: Chem. 186 (2002) 173. [27] R. Savidha, A. Pandurangan, Appl. Catal. A: Gen. 276 (2004) 39. [28] S. Udayakumar, A. Pandurangan, P.K. Sinha, J. Mol. Catal. A: Chem. 216 (2004) 75. [29] P. Prokesova, N. Zilkova, S. Mintova, T. Bein, J. Cejka, Appl. Catal. A: Gen. 281 (2005) 85. [30] K. Shanmugapriya, M. Palanichamy, V. Murugesan, Catal. Commun. 7 (2006) 47. [31] H.R. Emamian, A. Honarbakhsh-raouf, A. Ataie, A. Yourdkhani, J. Alloy Compd. 480 (2009) 681. [32] N. Saadatjoo, M. Golshekan, S. Shariati, H. Kefayati, P. Azizi, J. Mol. Catal. A: Chem. 377 (2013) 173. [33] R. Al-Oweini, H. El-Rassy, J. Mol. Struct. 919 (2009) 140. [34] S. Wang, X. Ma, J. Gong, X. Yang, H. Guo, G. Xu, Ind. Eng. Chem. Res. 43 (2004) 4027. [35] K.M. Parida, D. Rath, J. Mol. Catal. A: Chem. 258 (2006) 381. [36] B.R. Jermy, A. Pandurangan, Appl. Catal. A: Gen. 288 (2005) 25. [37] M. Boveri, J. Aguilar-Pliego, J. Perez-Pariente, E. Sastre, Catal. Today 107–108 (2005) 868. [38] P.J. Branton, P.G. Hall, S.W. Sing, J. Chem. Soc. Faraday Trans. 90 (19) (1994) 2965. [39] M. Busio, J. Janchen, J.H.C. van Hooff, Microporous Mater. 5 (1995) 211. [40] J.-H. Kin, M. Tanabe, M. Niwa, Microporous Mater. 10 (1997) 85. [41] A. Corma, V. Fornes, M.T. Navarro, J. Perezpariente, J. Catal. 148 (1994) 569. [42] K. Suzuki, Y. Aoyagi, N. Katada, M. Choi, R. Ryoo, M. Niwa, Catal. Today 132 (1) (2008) 38.
442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498
Please cite this article in press as: J. Mahmoudi, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.09.017
JIEC 2212 1–8 Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec 1 2 3 4 5
Comparison of synthesized H-Al-MCM-41 with different Si/Al ratios for benzene reduction in gasoline with propylene Q1 Jafar
Mahmoudi, Mohammad Nader Lotfollahi *, Ali Haghighi Asl
Faculty of Chemical, Gas and Petroleum Engineering, Semnan University, Semnan 35195-363, Iran
A R T I C L E I N F O
A B S T R A C T
Article history: Received 20 July 2014 Received in revised form 26 August 2014 Accepted 15 September 2014 Available online xxx
Benzene reduction in gasoline was investigated with propylene over synthesized mesoporous H-AlMCM-41 with Si/Al = 15, 29 and 42 as catalysts in order to produce more environmental friendly gasoline. The resulting catalysts were characterized by XRF, XRD, FTIR, TGA, BET and TPD-NH3 techniques. The results of alkylation of C6-cut obtained from gasoline indicated that the synthesized mesoporous H-AL-MCM-41 with Si/Al = 15 is the most active catalyst among the synthesized catalysts due to high crystallinity, favorable textural properties and large bronsted acidity. The higher conversion of benzene (47.88%) was observed over H-Al-MCM-41 with Si/Al = 15 at B/P = 1 and T = 200 8C. ß 2014 Published by Elsevier B.V. on behalf of The Korean Society of Industrial and Engineering Chemistry.
Keywords: H-Al-MCM-41 Synthesis Gasoline Benzene reduction Propylene
6 7
Introduction
8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
Benzene exists naturally in crude oil; so it passes into refined products such as gasoline that is one of the most applicable transportation fuels. Based on new environmental regulations, the amount of benzene in gasoline should be less than 0.62% [1,2] because of its carcinogenic properties. Therefore, the amount of benzene in gasoline should be controlled to reduce the human exposure of it. One of the methods to reduce the benzene in gasoline is catalytic alkylation of benzene with light olefins such as propylene. In these processes, catalyst plays an important role in the product distribution. In many petrochemical plants these alkylation reactions are performed with homogeneous catalysts such as mineral acids having many drawbacks [3–5]. In order to avoid the drawbacks of mentioned catalysts, many efforts have been done for developing alternative solid acid catalysts [6–9]. Different zeolites with acidic properties applied as a solid acid catalyst and were extensively evaluated in benzene alkylation with light olefins such as ethylene and propylene: alkylation of pure benzene with propylene was performed over HY zeolites [10]; Ga-modified H-ZSM-5 [11]; MCM-36 and MCM-22 [12]; series of b zeolites [13] and Hb zeolite [14–16] in different conditions on vapor phase. The main objective of many researches was the
* Corresponding author. Tel.: +98 23 33654120; fax: +98 23 33654120. E-mail addresses: [email protected], [email protected] (M.N. Lotfollahi).
alkylation of pure benzene to produce cumene and little works have been performed for alkylation of benzene in gasoline cut. In order to produce more environmental friendly gasoline, Laredo et al. [17–19] studied the alkylation of benzene in a C6 reformate heart-cut. Recently the interest in silica-alumina with controlled porosity in the mesoporous region as catalysts has been increased [20]. Purely siliceous MCM-41 does not have acidic properties. It was found that the incorporation of metals such as aluminum into the MCM-41 improves the acidity of it [21–23]. Recently, the alkylation of aromatic compounds in the presence of mesoporous Al-MCM-41 have been studied by many investigators including: alkylation of toluene with isopropanol on a MCM-41/g-A1203 catalyst [24,25]; comparison of mesoporous Al-MCM-41 molecular sieves in the production of p-cymene for vapor phase isopropylation of toluene at various reaction conditions [26]; vapor phase isopropylation of toluene with isopropyl-acetate over mesoporous MCM-41 materials and micro-porous zeolite catalysts [27]; vapor phase reaction of tert-butyl benzene with isopropyl acetate over mesoporous Al-MCM-41 molecular sieves [28]; gas phase alkylation of toluene with propylene over pure mesoporous molecular sieve Al-MCM-41 and micro/mesoporous composites [29]; vapor phase reaction of toluene with ethyl-acetate overAl-MCM-41 molecular sieves [30]. In this work, the mesoporous Al-MCM-41 with different Si/Al ratios was synthesized by sol–gel method using cetyltrimethylammonium bromide as a template. In order to improve the acidity of synthesized sample, ion exchange with ammonium nitrate was
http://dx.doi.org/10.1016/j.jiec.2014.09.017 1226-086X/ß 2014 Published by Elsevier B.V. on behalf of The Korean Society of Industrial and Engineering Chemistry.
Please cite this article in press as: J. Mahmoudi, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.09.017
29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56
G Model
JIEC 2212 1–8 J. Mahmoudi et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
2
57 58 59 60 61 62 63 64 65 66
performed. The physicochemical properties of synthesized catalysts were characterized by XRF, XRD, FTIR, TGA, BET, titration of surface acidic protons and TPD-NH3 techniques. In the next step, benzene reduction in gasoline produced by one of the Iranian refineries was investigated by alkylation process in liquid phase with propylene as an alkylating agent over the synthesized samples as catalyst. In addition, the alkylation of a benzene-cut over synthesized catalysts was performed for comparing the obtained results with the results of benzene alkylation in gasoline.
67
Experimental
68
Materials
69 70 71 72 73 74
Benzene (Merck Co. 99.5%), Propylene (Air product Co., 99%), sodium silicate solution (Merck Co. 27 wt.% SiO2), sodium aluminate (Aldrich, anhydrous technical, 50–56 wt.% Al2O3) and cetyltrimethylammonium bromide (CTAB, Merck Co, 99 wt.%) were used as raw materials. The composition of used benzene-cut was shown in Table 1.
75
Synthesis of Al-MCM-41
76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98
The synthesis of MCM support was described earlier in detail in the literature [8,9,22,31]. In this research, Al-MCM-41 has been synthesized using sodium silicate solution as a silica source, sodium aluminate as an aluminum source and cetyltrimethylammonium bromide (CTAB) as a template. The synthesis of Al-MCM41 was carried out by sol–gel method using a gel composition of 4SiO2: (0.05, 0.08 and 0.2) Al2O3: 1CTAB: 250H2O with Si/Al = 10, 25, 40 molar ratios. In a typical synthesis, the sodium silicate solution was added dropwise into a mixture of cetyltrimethylammonium bromide and deionized water with vigorous stirring at room temperature. At the end, certain amount of sodium aluminate was added dropwise into the mixture by varying the Si/Al ratio from 10 to 40. The gel mixture was heated to 100 8C for 1 day in an oil bath with vigorous stirring. After cooling to room temperature, the pH of the resulting gel was adjusted to around 10 by addition of acetic acid solution (25 wt.%). The pH adjustment and subsequent heating for 1 day was repeated three or four times until the pH of resulting gel was constant. The solid product was recovered by filtering the solution and then washed with 4 L of doubly distilled water. Finally, the products were dried at 100 8C in a day period. After that, the sample was calcined from room temperature to 550 8C with a heating rate of 1 8C/min and maintained at 550 8C for 3 h.
99
Preparation of H-Al-MCM-41
100 101 102 103 104 105 106
Al-MCM-41 samples were subjected to ammonium exchange treatment. For this, 1 g of each calcined Al-MCM-41 samples was ion exchanged with 50 ml of 1 M ammonium nitrate solution with vigorous stirring at 90 8C for 8 h and the procedure was repeated three times to complete ammonium exchange treatment for each samples. H-Al-MCM-41 samples were obtained by calcination of NH4-Al-MCM-41 samples at 550 8C for 2 h.
Table 1 Chemical composition of benzene-cut and C6-cut obtained from gasoline. Feed
Benzene cut C6-cut
Chemical Hexane
Benzene
Toluene
Xylene
Other
4.78 70.79
94.16 20.03
0 4.81
0 2.47
1.06 1.90
Catalyst characterization
107
The low-angle XRD patterns of the samples were recorded using a Bruker (model, D8 Advance, USA) X-ray diffractometer using Ni filtered CuKa radiation (l = 1.5406 A´˚ , kV = 40, mA = 30). The samples were scanned from 2u = 1–108 angle in steps of 0.018 with a count time of 1 s at each point. The elemental analysis of calcined samples was determined by X-ray fluorescence (XRF, Bruker AXS – S4 EXPLORER). The flat sample disks were analyzed with a voltage of 40 kV and current of 30 mA. The infrared spectra of samples were recorded in the range of 4000–400 cm1 wave numbers with resolution of 4 cm1 using a Shidmadzu Fourier-Transform Infrared FT-IR 8400 Spectrometer. The solid samples were mixed with KBr powder and compressed into pellet for analysis. The mmol of H+ per gram of catalyst (Bronsted acid sites in samples) was determined by the simple titration methodology described in the literature [32]. Temperature-programmed desorption (TPD) experiments of NH3 was carried out by using Micromeritics TPD/TPR 2900 apparatus. 212.5 mg of sample was activated by flowing 40 ml/min helium at 500 8C for 60 min, and then cooled to 25 8C and saturated with pure NH3 for 60 min. Subsequently, helium (40 ml/min) was passed for 40 min at 150 8C to remove physically adsorbed NH3. The NH3-TPD measurement was performed from 150 8C to 750 8C at a rate of 10 8C/min. A thermal conductivity cell was used for recording the desorbed amount of NH3. The thermogravimetric analysis (TGA) of the sample was carried out by using Mettler TGA/SDTA851 thermal analyzer under a nitrogen flow of 60 ml/min. The heating rate was 10 8C/min in temperature ranging from 30 up to 1000 8C. Surface area and pore size of the H-Al-MCM-41 samples were measured using the nitrogen adsorption–desorption method at liquid nitrogen temperature (76.03 K) by ASAP 2010 instrument. Prior to the measurements, the sample was degassed at 573 K under vacuum for 5 h.
108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142
C6-cut obtained from gasoline
143
In order to decrease the side reactions in the alkylation of benzene content in gasoline with propylene, the C6-cut was obtained by batch distillation of the gasoline at temperature ranging from 45 to 80 8C. The composition of the obtained C6-cut was shown in Table 1.
144 145 146 147 148
Experimental procedure in alkylation reaction
149
Alkylation of benzene with propylene was performed in a stainless steel batch reactor that schematic view of this experimental setup is shown in Fig. 1. The experimental setup shown in Fig. 1 was constructed by Paya Fanavar Mashin Company (Iran) including a 400 cm3 stainless steel agitation reactor with magnetic drive and explosion proof motor. The thermocouple is placed into a well in the reactor for the precise detection of reaction temperature. The reaction temperature was controlled by a temperature controller, accurate to 2 8C. In each experiment, appropriate amounts of components were weighed on an analytical balance and then were charged in the reactor. At first, the catalyst was activated at 500 8C in furnace for 2 h and then cooled to ambient temperature and added to the mixture in the reactor. The reactor was pressurized with nitrogen to reach the appropriate pressure (40–50 bar). The temperature controller allows the reactor to be heated by an electric heater to the required temperature. After 2 h agitation of mixture in the reactor under stirring (800 rpm), the agitation was stopped and the products were
150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167
Please cite this article in press as: J. Mahmoudi, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.09.017
G Model
JIEC 2212 1–8 J. Mahmoudi et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
3
Fig. 1. Schematic flow diagram of experimental setup for alkylation of benzene content in benzene-cut and C6-cut obtained from gasoline.
168 169 170 171 172
withdrawn from the reactor. Then the products were cooled down to 2 8C by flowing through a coil immersed in water-ice bath in order to condense the organic compounds completely. The liquid products were filtered for separation of catalyst and finally were analyzed by GC.
173
GC analysis
174 175 176 177 178 179 180 181 182 183 184
The gas chromatographic (GC) analysis of products was carried out using ACME 6100GC from Youngling instrument Co., LTD. (South Korea). This GC equipped with a helium ionization detector (HID) and TRB-WAX capillary column (60 m long and 0.32 mm OD, coated with a 0.5 mm thick film of polyethylene glycol as stationary phase). In order to identify the products and to measure the concentration of components in the mixture, the GC was calibrated by an external standard calibration method. Helium was used as carrier gas at the rate of 1 ml/min. Software supplied by Chrompack (detailed hydrocarbon analyzer) was used to handle the data generated by GC.
185
Conversion and selectivity calculations
186 187 188
Two important parameters, the conversion and the selectivity, reveal the catalytic activity of synthesized catalysts for alkylation of benzene. The conversion is obtained by the following equation: Conversion ð%Þ ¼
190 189 191 192
C0 Cp C0
100
(1)
where C0 is the concentration of benzene, toluene or xylene at time zero (feed) and Cp is the concentration of mentioned components in the product. The concentration values are in weight. The
selectivity of each component is calculated by the following equation: Selectivity ð%Þ ¼
Ci 100 Ct
193 194
(2)
where Ci is the concentration by weight for cumene, n-propylbenzene (PB), 1,3-diisopropylbenzene (1,3-DIPB), 1,2-diisopropylbenzene (1,2-DIPB), 1,4-diisopropylbenzene (1,4-DIPB) or other by-products produced in alkylation of benzene. Ct is the summation of the concentrations by weight for mentioned components.
196 195 197 198 199 200
Results and discussion
201
Characterization of the synthesized catalysts
202
XRF analysis The aluminum content in Al-MCM-41with various Si/Al ratios was measured using X-ray fluorescence (XRF) technique. The results of this analysis were listed in Table 2. It can be pointed out that the synthesis samples’ Si/Al ratio (Si/Al = 15, 29, 42) is greater than the hydrogels’ Si/Al ratio (Si/Al = 10, 25, 40). These observations are similar to those reported in the literature by Udayakumar et al. [28].
203 204 205 206 207 208 209
Table 2 Physicochemical properties of the synthesis catalysts. Catalyst
Al-MCM-41 (15) Al-MCM-41 (29) Al-MCM-41 (42)
Si/Al ratio
Calcined sample
Hydrogel
XRF
d100 (A˚)
a0 (A˚)
10 25 40
15 29 42
36 39.44 41.08
41.57 45.54 47.43
Please cite this article in press as: J. Mahmoudi, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.09.017
mmol of H+/g
0.338 0.286 0.204
G Model
JIEC 2212 1–8 J. Mahmoudi et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
4
210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229
XRD Fig. 2 shows the XRD pattern of the calcined Al-MCM-41 samples with various Si/Al ratios ranging from 15 to 42. These patterns show a sharp d100 reflection line in 2u = 2.58 and broad peaks in 2u = 4.338 (1 1 0) and 2u = 4.928 (2 0 0) for Al-MCM-41(15) (Si/Al = 15) which corresponds to well-ordered mesoporous materials with hexagonal symmetry [28]. For Al-MCM-41(29) (Si/Al = 29) and Al-MCM-41(42) (Si/Al = 42) sharp d100 reflection line were observed in 2u = 2.328 and 2.188, respectively. These patterns for recently mentioned samples also contain broad peaks in 2u = 4.058 (1 1 0) and 2u = 4.668 (2 0 0) for Al-MCM-41(29) and in 2u = 3.958 (1 1 0) and 2u = 4.698 (2 0 0) for Al-MCM-41(42). The d-spacing and unit cell parameters (a0) for the synthesis samples are listed in Table 2. The unit pffiffiffi cell parameters of samples calculated using the formula: 2d100 3 that d100 was calculated by Bragg’s equation (l = 2d sin u). As results in Table 2, by increasing the Al content in synthesis samples, the unit cell parameter is decreased. Similar results were reported by Selvaraj et al. [26] and Savidha and Pandurangan [27] for the isopropylation of toluene using ‘Al-MCM-41 molecular sieves.
230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249
FT-IR spectroscopy The FTIR spectra of the calcined H-Al-MCM-41 samples with various Si/Al ratios in the wave number region of 400–4000 cm1 are shown in Fig. 3. Based on the spectrum of calcined samples, there is a broad peak located around 3500 cm1 which are assigned to the O–H stretching of adsorbed water molecules and surface silanol groups (Si–OH group). Another peak in 1620–1640 cm1 is attributed to the adsorbed molecules deformation mode [33]. Also based on the spectrum of samples shown in Fig. 3, there are two intense peaks at the range 1000–1300 cm1 which are attributed to the asymmetric stretching vibration of T–O–T (T= Si or Al) [22]. The two peaks around 800 cm1 and around 460 cm1 are assigned to the symmetric T–O–T stretching and to the TO4 bending mode, respectively. The peak at around 960 cm1 is attributed to the presence of defective Si–OH groups [28]. Based on Fig. 3, this pick is more sensitive in the H-form of Al-MCM-41 (15) toward Al-MCM-41 (15) sample. As results, increasing of the Al content in H-Al-MCM-41 samples causes a shift of the lattice vibration band to a higher wave number. These may be due to increase of the mean T–O distances in the wall, by increasing the
Intensity
Fig. 3. FTIR spectra of H-Al-MCM-41 samples with various Si/Al: (—) Si/Al = 15, ( ) Si/Al = 29, and ( ) Si/Al = 42 and Al-MCM-41 with Si/ Al = 15 ( ).
0
2
4
6
8
10
2θ (degrees) Fig. 2. XRD patterns of Al-MCM-41samples with various Si/Al: (—) Si/Al = 15, ( ) Si/Al = 29, and ( ) Si/Al = 42.
incorporation of Al atom in the framework. These results are in good agreement with those reported in the literature [26].
250 251
Acidity of samples
252
Surface acidic protons. The mmol of H+ (Bronsted acidity) per gram of the catalyst was found similar to the methodology as reported by Saadatjoo et al. [32]. For this purpose, 0.1 g of H-Al-MCM-41 sample was ion exchanged with 10 ml saturated solution of NaCl by sonication. The ion exchange was repeated twice. The obtained solution was then titrated by sodium hydroxide solution 0.1 M to determine the loading of acid sites on the synthesized sample. The results of this analysis are summarized in Table 2. The result demonstrates that the amount of acid sites slightly decrease with increasing Si/Al ratios. Meanwhile, by this methodology the mmol of H+ per gram of the Al-MCM-41 (15) was determined 0.07. This result indicated that the loading of acid sites are found to be higher for H-form of Al-MCM-41 than for Al-MCM-41 implying an
253 254 255 256 257 258 259 260 261 262 263 264 265
Please cite this article in press as: J. Mahmoudi, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.09.017
G Model
JIEC 2212 1–8 J. Mahmoudi et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
5
Table 3 Surface area, pore size and TPD of NH3 results of the synthesis catalysts. Pore diameter (A˚)
BET-surface area (m2 g1)
Catalyst
H-Al-MCM-41 (15) H-Al-MCM-41 (42)
719.312 792.897
24.342 35.097
266 267
increase in Bronsted acidity by ion exchanging of zeolite with ammonium.
268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283
Temperature programmed desorption of ammonia (TPD-NH3). The acidic properties of H-Al-MCM-41 (15) and H-Al-MCM-41 (42) samples were evaluated by temperature programmed desorption (TPD) measurement of ammonia. The amount of desorbed ammonia which attributed to the total number of acid sites of catalyst was given in Table 3. It is observed two major regions according to the acid strength; a low temperature (LT) region (200–250 8C) and a high temperature (HT) region (380–450 8C) that occurred due to desorption of ammonia adsorbed on weak and strong acid sites, respectively [34]. Based on the data, lower temperature range exhibited higher amount of ammonia desorption. Meanwhile, as can be seen in Table 3 the amount of ammonia desorbed on weak and strong acid sites were increased from 0.313 to 0.43 mmol/g with increasing of Al content in mesoporous. The observed results agreed with published results by Savidha and Pandurangan [27].
284 285 286 287 288 289 290 291 292 293 294 295 296 297 298
Thermogravimetric analysis (TGA) The thermal properties of the as-synthesized sample were investigated by TGA. The data of the percentage of weight loss in various ranges of temperatures for Al-MCM-41 (15) are presented in Table 3. Representative curves, the thermograms of the assynthesized sample, are shown in Fig. 4 (Table 4). The weight loss observed at temperature slower than 150 8C is attributed to desorption of physically adsorbed water in the voids formed by crystal agglomeration [35,36]. The main weight loss which is between 150 8C and 350 8C is due to the decomposition and combustion of the templating organic molecules [26,35]. The next weight loss which is between 350 8C and 550 8C corresponds to removal of organic residues. In this case, Boveri et al. have reported that the weight loss between 350 8C and 550 8C could be attributed to water loss from the silanol group condensation
100
Weight loss (%)
90 80 70 60 50 0
200
400
600
800
1000
Total acidity (mmol/g)
LT-peak
HT-peak
0.278 0.182
0.152 0.131
0.430 0.313
[37]. There was almost no change in weight loss after 550 8C, which indicated the completely removal of the organic template at 550 8C. The total weight loss percentage at 1000 8C for the AlMCM-41 (15) sample is equal to 44.114%.
299 300 301 302
Nitrogen adsorption isotherm For H-Al-MCM-41 (15) and H-Al-MCM-41 (42) samples, nitrogen adsorption isotherms were investigated at 76.03 K. The specific surface area was determined using the BET equation and pore size distribution was estimated by Barrett–Joyner–Halenda (BJH) method. The nitrogen adsorption isotherms of the H-AlMCM-41 (15) and H-Al-MCM-41 (42) samples are given in Fig. 5(a) and (b), respectively. Based on Fig. 5 the samples show a characteristic step around the P/P0 0.4–0.5 indicating the mesoporous nature of the catalysts [38]. Table 3 shows the specific surface area and pore size of the H-Al-MCM-41 samples. Based on Table 3 the high BET surface area of the H-Al-MCM-41 samples (719.312–792.897 m2 g1) coincided with the high surface area of mesoporous materials. Also as can be seen in Table 3, the pore diameter of samples was obtained in the range of 24.342–35.097 A˚ that agreed with the range of pore diameter for mesoporous materials [8]. Also the pore diameter was decreased with increasing aluminum content in samples. The results observed are in good agreement with the reported values [27,28].
303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322
Alkylation of benzene content in benzene-cut and C6-cut with propylene
323 324
In order to study the catalytic performance of synthesized catalysts, H-Al-MCM-41 prepared with various Si/Al ratios (Si/ Al = 15, 29, 42) were tested in the alkylation of benzene content in benzene-cut (Table 1) and C6-cut obtained from gasoline with propylene. These series of experiments were carried out at 200 8C, benzene/propylene (B/P) molar ratio = 1 over 1 g of catalyst. The chemical composition of the products in alkylation of the C6-cut obtained from gasoline and benzene-cut are presented in Tables 5 and 7, respectively. The selectivity of products and conversion of benzene for both mentioned feedstocks are listed in Tables 6 and 8, respectively. In alkylation of benzene-cut over three types of synthesized catalysts, the sample with Si/Al ratio of 15 gives the highest benzene conversion and cumene selectivity, which are 48.92% and 57.73%, respectively. Meanwhile, the same trend also was observed for alkylation of benzene content in C6-cut obtained from gasoline. In the alkylation of C6-cut using H-Al-MCM-41 (15) as catalyst, the maximum benzene conversion and cumene selectivity are 47.88% and 52.23%, respectively. As shown in
325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343
Table 4 TGA results for the as-synthesized sample. Catalyst
Temparature (˚C) Fig. 4. TGA curve of as-synthesized Al-MCM-41 (15) sample.
TPD of NH3
H-AL-MCM-41 (15)
Weight loss (wt.%) 50–150 8C
150–350 8C
350–550 8C
Total
2.865
26.049
15.20
44.114
Please cite this article in press as: J. Mahmoudi, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.09.017
G Model
JIEC 2212 1–8 J. Mahmoudi et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
6
a
Table 5 Chemical composition of the products in alkylation of the C6-cut obtained from gasoline with propylene over synthesized catalysts.
550 500
adsorpon
450
desorpon
Experimental condition
H-AL-MCM-41 (15)
400
Chemical composition (wt%) Benzene 10.44 Toluene 2.31 Xylene 1.27 Cumene 22.76 PB 0.03 1,3-DIPB 5.12 1,2-DIPB 3.24 1,4-DIPB 5.26 Hexane 42.41 7.16 Heavier polyalkylates + oligomer
Volume (cc/g)
350 300 250 200 150 100 50 0
0.1
0.2
0.3
0.4 0.5 0.6 0.7 Relave Pressure (P/P0)
0.8
0.9
H-AL-MCM-41 (42)
12.28 2.76 1.38 14.13 0.05 3.06 2.06 3.15 54.82 6.31
13.59 3.05 1.51 7.53 0.06 1.91 1.21 1.83 62.03 5.13
1
450 adsorpon
400
desorpon 350 300 Volume (cc/g)
H-AL-MCM-41 (29)
Catalyst weight = 1 g, (benzene/propylene) = 1, reaction temperature = 200 8C and reaction time = 2 h.
0
b
Catalysts:
250 200 150 100 50 0 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Figs. 8 and 9 show the selectivity of DIPB isomers in alkylation of benzene-cut and C6-cut, respectively. It seems that by increasing the aluminum content in synthesized samples, the DIPB isomers production increases slightly. In fact the access of reactants to acidic sites on catalyst will be increased with increasing the aluminum content in synthesized samples that produces more alkylated product, especially DIPB. Distribution of DIPB isomers are shown in Figs. 8 and 9. For HAl-MCM-41 (15) as catalyst in alkylation of benzene in C6-cut, the 1,2-DIPB, 1,3-DIPB and 1,4-DIPB isomer distributions were 23.8%, 37.59% and 38.61%, similar to the trend of distribution reported by Cejka et al. [29]. It was not considerable change in distribution of DIPB isomers with different Si/Al ratios. It seems that, the alkylation and isomerization rates play important role in distribution of DIPB isomers. 1,2-DIPB, 1,3-DIPB and 1,4-DIPB can be produced by alkylation directly and can be converted together with isomerization reaction. Based on the experimental data, due to the smaller steric hindrance of the propyl groups, the 1,4-DIPB was produced more than the other isomers. Also considerable concentration of the 1,2-DIPB isomer indicated that these isomers produced by alkylation directly and little isomerization was occurred.
Relave Pressure (P/P0) Fig. 5. Nitrogen adsorption isotherms of (a) H-Al-MCM-41 (15) and (b) H-Al-MCM41 (42).
344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359
Figs. 6 and 7, the benzene conversion and selectivity of cumene increase with increasing framework aluminum content for both benzene-cut and C6-cut alkylation. Based on the literature report, addition of excess Al atom (when the Si/Al ratio is lower than Si/Al = 10) into the MCM-41 might lead to the collapse of pores and channels of synthesized samples that produces catalyst with relatively weak activity [39–42]. Therefore in our experiments, H-Al-MCM-41 samples were synthesized with various Si/Al ratios higher than Si/Al = 10 to prevent the collapse of the structure. Also these results are in a similar order of acidic properties of samples as the effect of framework aluminum content. In the alkylation of C6-cut obtained from gasoline, enhancement of the cumene selectivity in product is favorable because the cumene can be used as a blending agent for enhancement of the octane number of gasoline [6]. The catalytic activity of synthesized samples is in good agreement with the results of Pandurangan et al. [27].
Table 6 Conversion and selectivity achieved after alkylation of the C6-cut obtained from gasoline with propylene over synthesized catalysts. Experimental condition
Conversion (%) Benzene Toluene Xylene Selectivity (%) Cumene PB 1,3-DIPB 1,2-DIPB 1,4-DIPB Heavier polyalkylates + oligomer
Catalysts: H-AL-MCM-41 (15)
H-AL-MCM-41 (29)
H-AL-MCM-41 (42)
47.88 51.97 48.58
38.69 42.62 44.13
32.15 36.59 38.87
52.23 0.07 11.75 7.44 12.07 16.43
49.13 0.17 10.64 7.16 10.95 21.94
42.61 0.34 10.81 6.85 10.36 29.03
Catalyst weight = 1 g, (benzene/propylene) = 1, reaction temperature = 200 8C and reaction time = 2 h.
Please cite this article in press as: J. Mahmoudi, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.09.017
360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381
G Model
JIEC 2212 1–8 J. Mahmoudi et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
7
Table 7 Chemical composition of the products in alkylation of the benzene-cut with propylene over synthesized catalysts. Experimental condition
Chemical composition Benzene Cumene PB 1,3-DIPB 1,2-DIPB 1,4-DIPB Hexane Heavier polyalkylates + oligomer
Catalysts: H-AL-MCM-41 (15)
H-AL-MCM-41 (29)
H-AL-MCM-41 (42)
(wt%) 48.09 27.16 0.29 4.33 3.94 6.27 4.86 5.06
56.93 19.58 0.47 3.05 2.63 4.08 7.89 5.37
65.86 12.79 0.58 1.86 1.73 2.55 8.47 5.89
Catalyst weight = 1 g, (benzene/propylene) = 1, reaction temperature = 200 8C and reaction time = 2 h.
382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406
On the other hand the alkylation of benzene in C6-cut over three type of catalysts H-Al-MCM-41, led to formation of undesired products mainly polyalkylbenzene and oligomers as shown in Tables 6 and 8. As mentioned in the literature [12,13], these byproducts, especially oligomers, ultimately decrease the catalyst life by deactivation of it. Between three types of H-AL-MCM-41, with increasing the framework aluminum content and therefore increasing acidity, the formation of these by-products was decreased. These may be attributed to the increasing in the ability of H-Al-MCM-41 (15) for alkylation reaction by suppressing the side reaction. Based on the data reported by Pergo et al. [20], the lower amount of oligomer was formed with MCM-41 mesoporus. The low formation of olefin oligomers is very important advantage of synthesized catalyst because presence of these compounds will affect catalyst life by pore blocking and coke deactivation [19]. Reusability of the catalyst was checked by recovering H-AlMCM-41 (15) in alkylation of C6-cut obtained from gasoline. For this purpose the H-Al-MCM-41 (15) was reused four times in consecutive alkylation reactions. The results given in Table 9 indicated that the benzene conversion range (47.51–40.69%) and the selectivity of cumene range (52.51–47.68%) were retained with a slight decrease. Therefore, there is not significant loss in the activity of catalyst on the recycling experiments. The results indicated that the catalyst is stable and provides a suitable regenerability.
Fig. 6. Effect of catalyst on benzene conversion and cumene selectivity in alkylation of benzene cut; H-AL-MCM-41 (42): 1; H-AL-MCM-41 (29): 2; H-AL-MCM-41 (15): 3.
Fig. 7. Effect of catalyst on benzene conversion and cumene selectivity in alkylation of C6-cut obtained from gasoline; H-AL-MCM-41 (42): 1; H-AL-MCM-41 (29): 2; HAL-MCM-41 (15): 3.
Table 8 Conversion and selectivity achieved after alkylation of the benzene-cut with propylene over synthesized catalysts. Experimental condition
Conversion (%) Benzene Selectivity (%) Cumene PB 1,3-DIPB 1,2-DIPB 1,4-DIPB Heavier polyalkylates + oligomer
Catalysts: H-AL-MCM-41 (15)
H-AL-MCM-41 (29)
H-AL-MCM-41 (42)
48.92
39.54
30.05
57.73 0.62 9.2 8.37 13.33 10.75
55.66 1.34 8.67 7.48 11.6 15.26
50.34 2.28 7.32 6.81 10.04 23.19
Catalyst weight = 1 g, (benzene/propylene) = 1, reaction temperature = 200 8C and reaction time = 2 h.
Fig. 8. Distribution of DIPB isomers over different catalysts in alkylation of benzene cut, H-AL-MCM-41 (42): 1; H-AL-MCM-41 (29): 2; H-AL-MCM-41 (15): 3.
Please cite this article in press as: J. Mahmoudi, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.09.017
G Model
JIEC 2212 1–8 J. Mahmoudi et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
8
Fig. 9. Distribution of DIPB isomers over different catalysts in alkylation of C6-cut obtained from gasoline; H-AL-MCM-41 (42): 1; H-AL-MCM-41 (29): 2; H-AL-MCM41 (15): 3.
Table 9 Reusability of H-Al-MCM-41 (15) in alkylation of C6-cut obtained from gasoline. Time run
Benzene conversion (%)
Cumene selectivity (%)
1 2 3 4
47.51 46.13 43.78 40.69
52.51 51.29 49.13 47.68
Catalyst weight = 1 g, (benzene/propylene) = 1, reaction temperature = 200 8C and reaction time = 2 h.
407 408 409 410 411 412 413 414
As results, in the benzene reduction in gasoline over H-AlMCM-41 (15) as catalyst, the DIPB isomers and others higher molecular weight aromatics should be separated from product by distillation to prevent the change of gasoline range. Based on the obtained data, the same trend also was observed for alkylation of benzene-cut in the case of DIPB and polyalkylbenzene production that for pure cumene producing, separation of these compounds by distillation is necessary.
415
Conclusion
416 417 418 419 420 421 422 423 424 425 426 427 428 429 430
In this study, mesoporous H-Al-MCM-41 with Si/Al = 15, 29 and 42 were synthesized by using cetyltrimethylammonium bromide as the template. The physicochemical properties of synthesized samples were characterized by XRF, XRD, FTIR, TGA, BET, titration of surface acidic protons and TPD-NH3 techniques. The results showed that the synthesized catalysts have good crystallinity and favorable textural properties (high surface and suitable pore size) and the acidity of synthesized catalysts were increased by decreasing the Si/Al ratios. The behavior of the synthesized catalysts in the liquid-phase alkylation of benzene in C6-cut obtained from gasoline and benzene-cut with propylene were investigated. Among the synthesized catalysts, It could be inferred that in C6-cut alkylation, there were high selectivity of cumene (52.23%) and benzene conversion (47.88%) for H-Al-MCM-41 (15) at B/P = 1, weight of catalyst = 1 g and T = 200 8C. In addition to
C6-cut, the alkylation of a benzene-cut was also performed and the results were compared with alkylation of the C6-cut obtained from gasoline. For the benzene-cut, the maximum benzene conversion (48.92%) was achieved over H-Al-MCM-41 with Si/Al = 15 as catalyst at same conditions. The results also showed that the H-AlMCM-41 (15) is reusable catalyst in alkylation of C6-cut obtained from gasoline.
431 432 433 434 435 436 437
Acknowledgement
438
The authors tend to appreciate for the partial financial support Q2 from the Science & Technology Park of Semnan University. Q3
439 440
References
441
[1] Regulatory announcement: direct final rule making revising mobile source air toxics early credit technology requirement, EPA420-F-08-007, February 2008 http://www.epa.gov/oms/regs/toxics/420f08007.htm. [2] Rules and Regulations, Federal Register, vol. 73 (49), March 2008. [3] K.S. Wong, Ph.D. thesis, University of Bath, United Kingdom, 2009. [4] B. Jacob, Ph.D. thesis, Cochin University of Science and Technology, India, 1998. [5] J.J. Chiu, D.J. Pine, S.T. Bishop, B.F. Chmelka, J. Catal. 221 (2004) 400. [6] C. Perego, P. Ingallina, Catal. Today 73 (2002) 3. [7] U. Sridevi, N.C. Pradhan, B.K.B. Rao, C.V. Satyanarayana, B.S. Rao, Catal. Lett. 79 (2002) 69. [8] A.B. Mohamed, Ph.D. thesis, Universiti Teknologi Malaysia, Malaysia, 2005. [9] F.B. AbuBakar, Ph.D. thesis, Universiti Teknologi Malaysia, Malaysia, 2010. [10] F. Cavani, G. Girotti, G. Terzoni, Appl. Catal. A: Gen. 97 (1993) 177. [11] I.I. Ivanova, N. Blom, E.G. Derouane, J. Mol. Catal. A: Chem. 109 (1996) 157. [12] Y. Zhang, H. Xing, P. Yang, P. Wu, M. Jia, J. Sun, T. Wu, React. Kinet. Catal. Lett. 90 (1) (2007) 45. [13] S. Siffert, L. Gaillard, B.L. Su, J. Mol. Catal. A: Chem. 153 (2000) 267. [14] M. Han, S. Lin, E. Roduner, Appl. Catal. A: Gen. 243 (2003) 175. [15] Z. Tian, Z. Qin, M. Dong, G. Wang, J. Wang, Catal. Commun. 6 (2005) 385. [16] Z. Tian, Z. Qin, G. Wang, M. Dong, J. Wang, J. Supercrit. Fluid. 44 (2008) 325. [17] G.C. Laredo, J.O. Marroquin, J. Castillo, P. Perez-Romo, J. Navarrete-Bolannos, Appl. Catal. A: Gen. 363 (2009) 19. [18] G.C. Laredo, J. Castillo, H. Armendariz-Herrera, Appl. Catal. A: Gen. 384 (2010) 115. [19] G.C. Laredo, R. Quintana-Solo´rzano, J. Castillo, H. Armendariz-Herrera, J.L. GarciaGutierrez, Appl. Catal. A: Gen. 454 (2013) 37. [20] C. Perego, S. Amarilli, A. Carati, C. Flego, G. Pazzuconi, C. Rizzo, G. Bellussi, Microporous. Mesoporous. Mater. 27 (1999) 345. [21] S.H. Park, B.Y. Song, T.G. Lee, J. Ind. Eng. Chem. 14 (2008) 261. [22] B. Lindlar, A. Kogelbauer, R. Prins, Microporous Mesoporous Mater. 38 (2000) 167. [23] Q. Zhao, Q. Wang, D. Wu, X. Fu, T. Jiang, H. Yin, J. Ind. Eng. Chem. 18 (2012) 1326. [24] J. Medina-Valtierra, M.A. Sfinchez, J.A. Montoya, J. Navarrete, J.A. de los Reyes, Appl. Catal. A: Gen. 158 (1997) LI. [25] J. Medina-Valtierra, O. Zaldivar, M.A. Sanchez, J.A. Montoya, J. Navarrete, J.A. de los Reyes, Appl. Catal. A: Gen. 166 (1998) 387. [26] M. Selvaraj, A. Pandurangan, K.S. Seshadri, P.K. Sinha, V. Krishnasamy, K.B. Lal, J. Mol. Catal. A: Chem. 186 (2002) 173. [27] R. Savidha, A. Pandurangan, Appl. Catal. A: Gen. 276 (2004) 39. [28] S. Udayakumar, A. Pandurangan, P.K. Sinha, J. Mol. Catal. A: Chem. 216 (2004) 75. [29] P. Prokesova, N. Zilkova, S. Mintova, T. Bein, J. Cejka, Appl. Catal. A: Gen. 281 (2005) 85. [30] K. Shanmugapriya, M. Palanichamy, V. Murugesan, Catal. Commun. 7 (2006) 47. [31] H.R. Emamian, A. Honarbakhsh-raouf, A. Ataie, A. Yourdkhani, J. Alloy Compd. 480 (2009) 681. [32] N. Saadatjoo, M. Golshekan, S. Shariati, H. Kefayati, P. Azizi, J. Mol. Catal. A: Chem. 377 (2013) 173. [33] R. Al-Oweini, H. El-Rassy, J. Mol. Struct. 919 (2009) 140. [34] S. Wang, X. Ma, J. Gong, X. Yang, H. Guo, G. Xu, Ind. Eng. Chem. Res. 43 (2004) 4027. [35] K.M. Parida, D. Rath, J. Mol. Catal. A: Chem. 258 (2006) 381. [36] B.R. Jermy, A. Pandurangan, Appl. Catal. A: Gen. 288 (2005) 25. [37] M. Boveri, J. Aguilar-Pliego, J. Perez-Pariente, E. Sastre, Catal. Today 107–108 (2005) 868. [38] P.J. Branton, P.G. Hall, S.W. Sing, J. Chem. Soc. Faraday Trans. 90 (19) (1994) 2965. [39] M. Busio, J. Janchen, J.H.C. van Hooff, Microporous Mater. 5 (1995) 211. [40] J.-H. Kin, M. Tanabe, M. Niwa, Microporous Mater. 10 (1997) 85. [41] A. Corma, V. Fornes, M.T. Navarro, J. Perezpariente, J. Catal. 148 (1994) 569. [42] K. Suzuki, Y. Aoyagi, N. Katada, M. Choi, R. Ryoo, M. Niwa, Catal. Today 132 (1) (2008) 38.
442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498
Please cite this article in press as: J. Mahmoudi, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.09.017