Effect of Methanol on Catalytic Performance of HY Zeolite for

Article pubs.acs.org/IECR

Effect of Methanol on Catalytic Performance of HY Zeolite for Desulfurization of FCC Gasoline by Alkylation Rong Wang,†,‡ Yonghong Li,*,† Benshuai Guo,† and Hongwei Sun§ †

Key Laboratory for Green Chemical Technology, School of Chemical Engineering &Technology, Tianjin University, Tianjin 300072, P. R. China ‡ School of Environmental and Chemistry Engineering, Nanchang University, Nanchang 330031, China § Department of Chemistry, Nankai University, Tianjin 300071, P. R. China ABSTRACT: Desulfurization of FCC gasoline by alkylation over a solid acid catalyst is considered to be a viable and less costly path to meet environmental regulations of sulfur emissions. However, side reactions in this process lead to significant levels of coke which greatly reduce the catalyst lifetime. In this paper, experiments were designed in both real and simulated gasoline to investigate the effect of different concentrations of methanol on the catalytic behavior of HY zeolite in the alkylation process for desulfurization. The result showed that the presence of an appropriate amount of methanol in FCC gasoline (about 5 wt % of the feed) appeared to improve the catalyst selectivity for the alkylation of thiophenic compounds by decreasing the conversion of olefins to oligomers, which was favorable for prolonging the catalyst lifetime. Moreover, a deep investigation was also carried out by a theoretical calculation method of DFT to explain the reason for the advantageous effect of methanol on the catalyst performance in the desulfurization process.

1. INTRODUCTION Deep desulfurization of gasoline is receiving increased attention in the research community as a result of the increasingly stringent environmental requirements on fuel specifications. Consequently, many approaches to deep desulfurization for ultraclean gasoline have been proposed. Olefinic alkylation of thiophenic sulfur (OATS), as one of these approaches, can be handled under relatively mild conditions with a minimal loss of octane number and without any hydrogen consumption. It can be seen as a good alternative to the conventional catalytic hydro-desulfurization process.1,2 However, the published literature has proved that competitive reactions such as aromatic alkylation and alkene oligomerization in the OATS process can produce undesired side products, which can cause the deactivation of solid acid catalyst by adsorbing on the active sites and plugging the catalyst pores.3−9 To realize the large-scale industrialization of FCC gasoline desulfurization by alkylation technology, the selectivity of solid acid catalyst must be improved. Therefore, how to limit subsidiary reactions and prolong the catalyst life by adjusting the acidic catalyst nature and alkylation conditions is the first and foremost problem. Considering that the content of olefins in FCC gasoline is substantial (more than 30 wt %) and the reaction mechanism of olefins oligomerization is similar to that of thiophenic sulfurs alkylation, the side reactions are difficult to be avoided in the OATS process just by adjusting the catalyst nature. However, it is well-known that alcohol is widely used in the synthesis of ether compounds with olefins. Some literatures have studied the influence of etherification on olefins dimerization and found that the presence of alcohol appeared to improve the selectivity for isopentenes dimerization.10,11 Furthermore, both the etherification and alkylation can be catalyzed by acidic catalysts. Therefore it may be promising to add methanol into the OATS © 2012 American Chemical Society

process, as there may be competitive reactions between the etherification and oligomerization of olefins. This would probably lead to the high selectivity for alkylation of thiophenic sulfurs and the increase in the octane number of the products. As a result, experiments were designed to evaluate the influence of the addition of different amounts of methanol on the catalytic behavior of HY zeolite in the OATS process. A deep investigation on adsorption properties of the catalyst was also carried out by the density functional theory (DFT) method of quantum chemistry to explain the experimental results feasibly.

2. EXPERIMENTAL SECTION 2.1. Catalyst and Materials. The HY zeolite (Si/Al = 8, specific area, 620 m2/g) used in the experiments was obtained from Catalyst Company of Nankai University. It needed to be pretreated at 550 °C for 5 h under an air atmosphere to remove the impurities such as water and template agents. The compositions of real and simulated gasoline were listed in Table 1. The methanol (99.9 wt %) added in the gasoline material as well as the reagents for simulating gasoline were all purchased from Kewei Reagent Company of Tianjin University. 2.2. Experiments To Investigate the Effect of Methanol on Catalytic Behavior of HY. The alkylation activity test for the HY zeolite was carried out in a 100 mL closed batch reactor charged with 4.0 g of HY zeolite and 80 mL of gasoline material. Time zero was taken arbitrarily when the optimum reaction temperature of 120 °C was reached. The system pressure increased with the rising temperature. The Received: Revised: Accepted: Published: 6320

November 21, 2011 April 10, 2012 April 22, 2012 April 23, 2012 dx.doi.org/10.1021/ie202697w | Ind. Eng. Chem. Res. 2012, 51, 6320−6326

Industrial & Engineering Chemistry Research

Article

Vibrational frequencies were calculated at the same level of optimization to identify the nature of stationary points and obtain zero-point-energy (ZPE) corrections. The reaction trajectory was determined by the intrinsic reaction coordinate (IRC) method to verify the correctness of the obtained theoretical structure of transition state. Gaussian 03 programs were applied to all the calculations and all the calculation results were held for zero Kelvin.14

Table 1. Compositions of Real and Simulated FCC Gasoline in Experiments compositions

contents (wt %)

Real FCC Gasoline aromatics olefins saturated hydrocarbons organic sulfides

15.3 37.4 47.3 0.034

3. RESULTS AND DISCUSSION 3.1. Effect of Methanol on Catalytic Behavior of HY in the Alkylation Reaction. As shown in Figure 1, the major sulfur compounds in real gasoline are thiophene (T), 2methylthiophene (2MT), 3-methylthiophene (3MT), C2thiophenes (C2-T), and C3-thiophenes (C3-T). Regardless of whether MeOH was present or not in the system, most of thiophenic sulfides in the feed (with the boiling points lower than 185 °C) were transformed into much heavier molecules (with the boiling points higher than 185 °C) after the alkylation activity test. However, the content of T in the product was increased visibly with the increment of MeOH added in the reaction, revealing that too much methanol was not beneficial to the alkylation conversion of thiophenic compounds. Considering that the boiling point of 2,3,5-trimethylthiophene (C3-T) is very close to the final boiling point of the feed used in experiments (185 °C), the sulfides with boiling points heavier than 185 °C can be removed from gasoline by distillation. Hence, the total conversion of thiophenic sulfur compounds with boiling points lower than that of the C3-T can be used to represent the catalytic activity of HY zeolite for the alkylation desulfurization. The detailed comparison for the effect of different amounts of MeOH on the catalytic performance of HY zeolite is displayed in Figure 2, indicating that the addition of a suitable amount of MeOH (5 wt % of gasoline feed) had a little inhibition effect on the catalyst activity for thiophenic compounds alkylation and possessed an ability to decrease the olefins conversion. This was especially true for C5-olefins. The addition of MeOH had little impact on aromatics conversion, for there was no product of aromatics alkylation to be found.

Simulated Gasoline toluene (>99 wt %) isopentene (>99 wt %, containing 7.2 wt % 2-methyl-1-butene and 92.8 wt % 2-methyl-2-butene) n-octane (>99 wt %) thiophene (>99 wt %)

15.3 37.4 47.3 0.034

stirring speed was kept at 400 rpm. After 1 h the product was analyzed to ascertain the catalyst activity. Under the same conditions, a series concentration of absolute methanol was added in proportion to the quality of gasoline feed (tagged as 2 wt % MeOH, 5 wt % MeOH, and 10 wt % MeOH) to investigate the effect of different amounts of methanol on the catalytic performance of HY zeolite. Sample analysis was performed on a FULI9790 gas chromatograph (Zhejiang, China) that was equipped with two detectors (FID, OV-101 column, 30 m × 0.25 mm × 0.50 μm; FPD, OV-101 column, 60 m × 0.25 mm × 0.50 μm). Meanwhile, the different species of sulfur compounds and hydrocarbons in the samples were identified by the analysis of a GC-SCD (sulfur compound detector) with a HP-1 column (30 m × 0.32 mm × 0.25 μm) and a GC−MS (mass spectrometer) with a HP5-MS column (30 m × 0.25 mm × 0.25 μm), respectively. 2.3. Computational Details of DFT. All the geometric structures studied in this work were optimized at the B3LYP/631+G (d, p) level then the single point energies of the optimized geometries were calculated with the MP2/6-311+G (d, p) level of theory to obtain more realistic values.12,13

Figure 1. GC chromatograms of real FCC gasoline feed and products catalyzed by HY zeolite with addition of different concentrations of methanol. 6321

dx.doi.org/10.1021/ie202697w | Ind. Eng. Chem. Res. 2012, 51, 6320−6326


Article

Figure 2. Effect of methanol on the catalytic performance of HY zeolite for the alkylation of thiophene in real gasoline.

Previous researches have proven that the decrement in olefins conversion was favorable for prolonging the solid acid catalyst lifetime in the OATS process.7,8 The results showed that too many oligomers produced by side reactions of olefins in the process could cover the active sites and form coke, which would lead to catalyst deactivation. Given that there are four kinds of olefins in the feed and the weight percents of C4, C5, C6, and C7-olefins in total olefins are 9.7%, 51.8%, 27.3%, and 11.2%, respectively, it seems that the addition of the appropriate amount of MeOH in the alkylation process catalyzed by the HY zeolite was very promising to prolong the catalyst life. This is due to the conversion of major olefins in the feed, for example C5 and C6-olefins, obviously decreasing while the catalyst activity remained intact. The experiments were also carried out in simulated gasoline for further study by avoiding the complexity of components in real gasoline. The simulated gasoline was designed based on the compositions of real gasoline. According to the component analysis, thiophene, C5-olefins with branch chain, and toluene are the most representative of sulfides, olefins, and aromatics, respectively. So thiophene (T), isopentene (ISP) and toluene (PhMe) were selected to simulate gasoline (Table 1). The result obtained from the simulated system is shown in Table 2 and is similar to the outcome of real gasoline. The HY zeolite possessed a high activity for the alkylation of T in the system without MeOH, but its selectivity for the alkylation reaction was so low that the conversion of ISP was higher than 95%. It was not conducive to maintain the catalyst stability, because the content of thiophenic sulfides in the feed was so tiny that the olefins consumed in sulfides alkylation could be neglected. The conversion of olefins was considered as the consumption in side reactions. However, with the increase in the content of MeOH, the conversion of ISP obviously decreased while there was a little suppression of the alkylation of T and an increase in the proportion of monoalkylated thiophene (C5-T) in the product. The presence of MeOH appeared to improve the catalyst selectivity for sulfides alkylation. The proportion of ISP dimers increased with the MeOH content and no significant amounts of other oligomers were obtained when the MeOH content was higher than 5 wt

Table 2. Effect of Methanol on the Catalytic Performance of HY Zeolite for the Alkylation of Thiophene in Simulated Gasoline weight percents of methanol in the feed conversion/product yield (%)

0%

2%

Thiophenic Compounds thiophene conversion 100 100 C5-thiophene yield 0.8 2.2 C10-thiophene yield 99.2 97.8 Hydrocarbons methanol conversion 79.8 isopentene conversion 95.2 84.7 toluene conversion 5.3 3.1 dimer of isopentene yield 31.7 32.9 etherification product yielda 85.9 a

5%

10%

98.3 2.6 95.2

94.0 3.6 87.6

54.8 34.2 0.9 48.3 89.1

35.6 17.6 0 77.8 96.8

Ether product of methanol and isopentene.

% of the feed. Additionally, the etherification product of ISP and MeOH was also detected and its yield increased with the increment in the MeOH content. According to the results obtained from the two gasoline systems, aromatics alkylation had little influence on the catalyst behavior, especially in real gasoline. The major side reaction in the OATS process catalyzed by the HY zeolite was alkenes oligomerization. The addition of an appropriate amount of methanol could provide a great improvement on the catalyst performance in the process by sustaining the activity for sulfides alkylation and increasing the selectivity for olefins dimerization. 3.2. DFT Studies on the Adsorption Property of HY Zeolite. An improved understanding of how reactants interact with acid sites of the OATS catalysts is necessary to develop a rational approach to employing these catalysts and the computational chemistry is a good choice to solve this problem.5−8 Moreover, the explanation for experimental results needs more evidence. Therefore, DFT calculations were used to analyze general features of the interaction between reactants and the HY zeolite. The related energies during the adsorption process of different reactants were also calculated by the DFT method. 6322



Article

Figure 3. Optimized geometries of the cluster 5T of HY zeolite and different reactants on the cluster 5T of HY zeolite by physical adsorption: (a) cluster 5T of HY zeolite, (b) π-complexes of 2M2B on cluster 5T of HY zeolite, (c) π-complexes of T on cluster 5T of HY zeolite, (d) MeOH adsorbed on cluster 5T of HY zeolite.

Table 3. Changes on Geometric Parameters for Different Reactants before and after Adsorbed onto the Cluster 5T of HY Zeolite and the Corresponding Adsorption Energy material and status

ΔEads (kJ/mol)

distance of the two atoms (Å) O1Al 1.946 1.922

O1Si 1.739 1.728

C2C3 1.344 1.352

H1C3

H1C2

2M2B + HY adsorbed 2M2B

O1H1 0.966 0.990

2M2B −52

2.261

C3H2 1.091 1.092

2.136

T + HY adsorbed T

O1H1 0.966 0.980

O1Al 1.946 1.928

O1Si 1.739 1.729

C6C7 1.370 1.376

H1C6

H1C7

H1S

T −46

2.286

2.305

3.263

Me+HY adsorbed Me

O1H1 0.966 1.029

O1Al 1.946 1.904

O1Si 1.739 1.713

C10O5 1.425 1.436

O5H7 0.965 0.986

H1O5

H7O2

1.519

1.828

Me −75

and was not big enough to calculate the accurate adsorption energies, it was particularly suited to describing local phenomena such as the interaction of organic molecules with active sites and the formation and break of bonds by high quality theoretical methods.12,15,16 Moreover, the purpose was to study the interaction between reactants and active sites of catalysts as well as the order of adsorption strengths to explain the effect of methanol on the catalytic performance of HY zeolite. The cluster model could describe the forms of

The catalytically active center and a portion of the HY zeolite framework were represented by an isolated cluster 5T (Figure 3a), which consisted of four [SiH4] tetrahedrons and one [AlO4] tetrahedron. In this zeolite model, the terminal Si−O bond was replaced by the Si−H bond oriented in the direction of the former Si−O bond. When the T5 cluster was used, the resulting coordinates for the terminal SiH3 groups were held fixed throughout all the subsequent calculations while all the other coordinates were allowed to relax.15 Although the cluster model did not accurately represent the environment of zeolite 6323



Article

Figure 4. Energy profile and geometries of 2M2B from phys- to chem-adsorption on the cluster 5T of HY zeolite.

interaction and make reasonable comparisons for adsorption strengths of different reactants. According to the experimental results, T, 2-methyl-2-butene (2M2B) and MeOH were selected as model reactants for the calculation. Figure 3 displays the optimized geometries of different reactants adsorbed on the cluster 5T of HY zeolite. Table 3 and Figure 3 revealed that both 2M2B and T could be physically adsorbed on the catalyst, as the adsorption had little effect on their geometry structures. Most bond lengths, bond angles as well as the flat structure of the two reactants were unperturbed, except that the double bonds C2−C3 and C6−C7 (Figure 3b,c) were stretched slightly. The physisorption was accompanied by structural changes in the active sites of HY zeolite. The bond length between the zeolite proton H1 and the adjacent oxygen atom O1 (O1−H1) was obviously stretched while the bonds connected with O1 (O1−Si and O1−Al) were both shortened (Table 3). The adsorption had more impact on 2M2B, as the extension of O1−H1 on the πcomplex of 2M2B was longer than that on π-complex of T 0.01 Å. MeOH was adsorbed on the catalyst by forming two hydrogen bonds, one between the methanol oxygen atom O5 and the zeolite proton H1 and one between the methanol proton H7 and the adjacent oxygen atom O2 from the Al tetrahedron (Figure 3d). So two hydroxyl bonds (O1−H1 and O5−H7) were obviously lengthened (Table 3), which was consistent with the result obtained by Mihaleva.17 The physisorption energies of 2M2B and T are built up from a sum of weak van der Waals forces acting between the adsorbate and zeolite. Our calculation is relying mainly on DFT methods which will underestimate and poorly predict the strengths of weak interactions. However, the MP2 method can describe weak interactions exactly, as it takes into account the electronic correlation. Therefore, all geometric structures were optimized at B3LYP/6-31+G (d, p) level, then the single point energies of the optimized geometries were calculated with MP2/6-311+G (d, p) level to obtain more realistic values.12,16

The adsorption energy of different reactants on the catalyst ΔEads was calculated by eq 1, where Eadsorbate/HY5T represents the calculated total energy of the adsorbate on HY5T cluster. EHY5T and Eadsorbate represent the energies of the separated HY5T cluster and the adsorbate, respectively. As listed in Table 3, all the values of ΔEads for the three reactants were negative, indicating that the lower the value is, the stronger the adsorption strength will be and the easier the adsorption of reactants will be. So MeOH was the most easily adsorbed on the catalyst among the three reactants. ΔEads = Eadsorbate/HY5T − E HY5T − Eadsorbate

(1)

The further calculation showed that 2M2B was initially adsorbed on the cluster in the form of a π-complex. Subsequently, an alkoxide species (σ-complex of 2M2B) was formed by protonation, which was similar to the previous research on the adsorption of linear alkenes on the zeolite.12 The reaction path in Figure 4 showed that in the transition state (image frequency, −127 cm−1) for the alkoxide complex formation, the acidic proton H1 was about halfway between the zeolite oxygen atom O1 and the alkene carbon atom C3. Simultaneously, the other carbon atom of the double bond C2 was moving close to the zeolite oxygen atom O2 and forming the covalent bond. The calculated activation energy (Eact) was 128 kJ/mol. The adsorption strength of the σ-complex of 2M2B was stronger than that of π-complex, as the ΔEads of the former with a covalent bond to the framework oxygen was lower than the latter, 13 kJ/mol. On the basis of the calculated adsorption energies in Table 3 and Figure 4, the order of adsorption strengths was MeOH with two hydrogen bonds > σ-complex of 2M2B > π-complex of 2M2B > π-complex of T. Although ΔEads for the σ-complex of 2M2B was lower than that for π-complex of T, 19 kJ/mol, the conversion of 2M2B from π- to σ-complex needed time and energy, the difference in adsorption strengths of T and 2M2B was relatively small in the initial stage of the adsorption, as 6324



■

ΔEads for π-complex of 2M2B was only lower than that for πcomplex of T, 6 kJ/mol. So MeOH adsorbed on the catalyst more strongly than T or 2M2B. And the physical adsorption of 2M2B seemed to occur a little more easily than that of T on acid sites of catalysts under the same reaction condition. Considering that the content of olefins was enormously higher than the tiny content of sulfides in the investigated gasoline feed (Table 1), the amount of activated olefins on the HY zeolite was greatly higher than the need for thiophenic sulfurs alkylation. The redundant activated olefins that stayed on the catalyst should cause side reactions and decrease the catalyst stability. However, methanol with the lowest adsorption energy could compete with olefins and thiophenic sulfurs for acid sites on the catalyst. When the concentration of methanol added in the system was moderate, only a part of the active sites were occupied. Although the competition of methanol could reduce the adsorbed olefins, it did not impact the amount of adsorbed olefins for thiophenic compounds alkylation. If the amount of methanol was excessive, most of active sites were covered by methanol which would inhibit the adsorption of other reactants and decrease the catalyst activity for thiophenic compounds alkylation. Therefore, the addition of a suitable amount of methanol appeared to have a beneficial effect on the catalytic performance of HY zeolite for the OATS process. The theoretical investigation could be used to explain the experimental results excellently.

Article

AUTHOR INFORMATION

Corresponding Author

*Tel.: 86-22-27406795. Fax: 86-22-27403389. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors gratefully acknowledge the financial support provided by the National Natural Science Foundation (No. 20976129) and the Program of Universities’ Innovative Research Terms (No. IRT0936).

■

REFERENCES

(1) Song, C. S. An overview of new approaches to deep desulfurization for ultra-clean gasoline, diesel fuel and jet fuel. Catal. Today 2003, 86, 211. (2) Babich, I. V.; Moulijn, J. A. Science and technology of novel processes for deep desulfurization of oil refinery streams: A review. Fuel 2003, 82, 607. (3) Bellière, V.; Geantet, C.; Vrinat, M.; Ben-Taârit, Y.; Yoshimura, Y. Alkylation of 3-methylthiophene with 2-methyl-2-butene over a zeolite catalyst. Energy Fuels 2004, 18, 1806. (4) Bellière, V.; Lorentz, C.; Geantet, C.; Yoshimura, Y.; Laurenti, D.; Vrinat, M. Kinetics and mechanism of liquid-phase alkylation of 3methylthiophene with 2-methyl-2-butene over a solid phosphoric acid. Appl. Catal., B 2006, 64, 254. (5) Arias, M.; Laurenti, D.; Geantet, C.; Vrinat, M.; Hideyuki, I.; Yoshimura, Y. Gasoline desulfurization by catalytic alkylation over silica-supported heteropolyacids: From model reaction to real feed conversion. Catal. Today 2008, 130, 190. (6) Wang, R.; Li, Y. H. Preparation of MCM-41 supported phosphoric acid catalyst for thiophenic compounds alkylation in FCC gasoline. Catal. Commun. 2010, 11, 705. (7) Zhang, Z. K.; Guo, X. Y.; Liu, S. L.; Zhu, X. X.; Xu, L. Y. Olefins alkylation thiophenic sulfur of the real gasoline over the fluorinated Hβ zeolite catalyst. Fuel Process. Technol. 2008, 89, 1135. (8) Zheng, X. D.; Dong, H. J.; Wang, X.; Shi, L. Study on olefin alkylation of thiophenic sulfur in FCC gasoline using La2O3-modified HY zeolite. Catal. Lett. 2009, 127, 70. (9) Jaimes, L.; de Lasa, H. Catalytic conversion of thiophene under mild conditions over a ZSM-5 catalyst. A kinetic model. Ind. Eng. Chem. Res. 2009, 48, 7505. (10) Cruz, V. J.; Izquierdo, J. F.; Cunill, F.; Tejero, J.; Iborra, M.; Fité, C. Acid ion-exchange resins catalysts for the liquid-phase dimerization/etherification of isoamylenes in methanol or ethanol presence. React. Funct. Polym. 2005, 65, 149. (11) Di Girolamo, M.; Marchionna, M. Acidic and basic ion exchange resins for industrial applications. J. Mol. Catal. A-Chem. 2001, 177, 33. (12) Svelle, S.; Kolboe, S.; Swang, O. Theoretical investigation of the dimerization of linear alkenes catalyzed by acidic zeolites. J. Phys. Chem. B 2004, 108, 2953. (13) Sousa, S. F.; Fernandes, P. A.; Ramos, M. J. General performance of density functionals. J. Phys. Chem. A 2007, 111, 10439. (14) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A.; Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J.; Zakrzewski, J. V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu,

4. CONCLUSIONS The experiments were carried out in both real and simulated gasoline to evaluate the effect of different concentrations of methanol on the catalytic performance of HY zeolite in the alkylation process for gasoline desulfurization. The results showed that the addition of a suitable amount of methanol (about 5 wt % of the gasoline feed) had little influence on the excellent catalytic activity of HY zeolite for the alkylation of thiophenic compounds. Additionally, it could decrease the olefins conversion for oligomerization, especially reduce the C5olefins trimerization and multimerization, which was favorable for the improvement of catalyst selectivity for thiophenic sulfurs alkylation and the prolonging of the catalyst lifetime. A deep investigation on the surface property of HY zeolite was also carried out by DFT calculation of quantum chemistry to explain the reason for the advantageous effect of the methanol presence on the catalyst behavior in the OATS process. The results indicated that methanol could compete with olefins and thiophenic sulfurs for acidic active sites on the catalyst, depending on its strongest adsorption strength. The content of thiophenic sulfides in the feed was so tiny that the demand for activated olefins for alkylation was small. The competition of an appropriate amount of methanol could greatly reduce the adsorbed olefins on acid sites and have little impact on the adsorption amount of olefins for thiophenic sulfurs adsorption. The amount of activated alkenes on the catalyst was obviously decreased, and side reactions could be reduced in the alkylation process. The theoretical investigation could be used to explain the experimental results excellently. And the addition of a suitable amount of methanol appeared to have a beneficial effect on the further application of HY zeolite in the OATS process. 6325



Article

G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, revision C.01; Gaussian Inc.: Wallingford, CT, 2004. (15) Boronat, M.; Corma, A. Are carbenium and carbonium ions reaction intermediates in zeolite-catalyzed reactions. Appl. Catal., A 2008, 336, 2. (16) Hansen, N.; Brüggemann, T.; Bell, A. T.; Keil, F. J. Theoretical investigation of benzene alkylation with ethene over H-ZSM-5. J. Phys. Chem. C 2008, 112, 15402. (17) Mihaleva, V. V.; Van Santen, R. A.; Jansen, A. P. J. A DFT study of methanol adsorption in 8T rings of chabazite. J. Phys. Chem. B 2001, 103, 6874.

6326


Effect of Methanol on Catalytic Performance of HY Zeolite for

Recommend Documents