Methanol Usage in Toluene Methylation over Pt Modified ZSM-5 Catalyst: Effect of. Total Pressure and Carrier Gas. Supporting Information

Transcription

1 Methanol Usage in Toluene Methylation over Pt Modified ZSM-5 Catalyst: Effect of Total Pressure and Carrier Gas Supporting Information Yiren Wang, a Min Liu, a Anfeng Zhang, a Yi Zuo, a Fanshu Ding, a Yang Chang, a Chunshan Song, a,b* and Xinwen Guo a* a State Key Laboratory of Fine Chemicals, PSU-DUT Joint Center for Energy Research, School of Chemical Engineering, Dalian University of Technology, Dalian , P. R. China b EMS Energy Institute, PSU-DUT Joint Center for Energy Research, Department of Energy and Mineral Engineering, and Department of Chemical Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, United States *Corresponding Authors Xinwen Guo, Tel: ; guoxw@dlut.edu.cn Chunshan Song, Tel: ; csong@psu.edu S1

2 V ads (cm 3 /g) Figure S1. NH 3 -TPD profiles of H-ZSM-5 ( ), mzsm-5 ( ), and Pt/mZSM-5( ) catalysts a) b) HZSM c) mzsm Pt/mZSM P/P 0 Figure S2. N 2 adsorption (solid symbols) and desorption (open symbols) isotherm at 77K of HZSM-5, mzsm-5 and Pt/mZSM-5. S2

3 Adsorption amount (μmol/g) Adsorption amount (μmol/g) 1000 a) HZSM-5 mzsm-5 Pt/mZSM Time (min) Figure S3. n-hexane adsorption of HZSM-5, mzsm-5 and Pt/mZSM b) Time (min) HZSM-5 mzsm-5 Pt/mZSM-5 Figure S4. Cyclohexane adsorption of HZSM-5, mzsm-5 and Pt/mZSM-5. Table S1. Textural properties of HZSM-5, mzsm-5 and Pt/mZSM-5 Catalyst S BET a S micro b S meso b V micro b V total c (m 2 /g) (m 2 /g) (m 2 /g) (cm 3 /g) (cm 3 /g) n-hexane/cyclo-hexa ne ratio d HZSM mzsm Pt/mZSM a BET surface area calculated from the adsorption branch; b Micropore surface area, mesopore surface area and micropore volume calculated using the t-plot method; c Pore volume estimated from the single-point amount adsorbed at P/P 0 = 0.95; d The ratio of the saturation adsorption amount of n-hexane to cyclohexane. A few characterization methods (n-hexane/cyclohexane adsorption and N 2 physisorption analysis, Figure S2-S4 and Table S1) were applied to prove the reduction in effective dimensions of the catalyst pore openings. The apparent decrease in the surface area and pore volume could be attributed to the partially blocked pores by oxides. The decreased mesopore surface area could be S3

4 attributed to coverage of external surface (mesopore surface) by oxides. The extent of pore openings reduction was evaluated by using n-hexane and cyclohexane adsorption. n-hexane can enter a ten-member ring channel of zeolite readily while the diffusion of cyclohexane in a ten-member ring channel is limited. Therefore, the ratio of the saturation adsorption amount of n-hexane to cyclohexane over samples shows the reduction extent of the pore openings. The higher ratio means the larger reduction extent. Figure S5. Toluene conversion (solid) and para-selectivity (open) as a function of time on stream over Pt/mZSM-5. Reaction conditions: 460 o C, 0.2 MPa gauge pressure, WHSV=6h -1, nt/nm=6, nh 2 /n(t+m)=2, nh 2 O/n(T+M)=2. Figure S6. Toluene conversion and para-selectivity over Pt/mZSM-5 under H 2 atmosphere as a function of reaction pressure at 460 o C, WHSV=6h -1, nt/nm=2, nh 2 /n(t+m)=2, nh 2 O/n(T+M)=2. S4

5 Figure S7. a) Para-selectivity over Pt/mZSM-5 as a function of contact time of catalyst and reactant stream under H 2 ( ) or N 2 ( ) atmosphere. b) Ternary xylene isomer plot illustrating the effect on para-xylene selectivity by changing contact time under H 2 ( ) and N 2 ( ) atmosphere. S5

6 Figure S8. TG curves of Pt/mZSM-5 after toluene alkylation with methanol using N 2 or H 2 as carrier at MPa gauge reaction pressure (conditions: 460 o C, WHSV=2.5 h -1, nt/nm=4, n(h 2 or N 2 )/n(t+m)=2, nh 2 O/n(T+M)=2). TG analysis was first conducted under N 2 (a) to monitor the adsorbed aromatic molecules and coke precursor and then the same sample was conducted again under synthetic air (b) to evaluate the real coke deposits on the samples. S6

7 C T, S PX & Y PX C T, S PX & Y PX a) b) C T S PX Y PX C T S PX Y PX MPa 0.2 MPa 0.4 MPa Reaction Pressure (gauge) WHSV (h -1 ) Contact time s s s s s s Figure S9. Toluene conversion, para-selectivity and yield of para-xylene over Pt/mZSM-5 under H 2 atmosphere as a function of a) reaction pressure when WHSV=2.5 h -1, b) WHSV at atmospheric pressure. Reaction conditions: 460 o C, nt/nm= 4, nh 2 /n(t+m)= 2, nh 2 O/n(T+M)= 2. Contact time = active catalyst volume/ reactant feed rate. Experiments results comparing the effect of WHSV and pressure are shown in Figure S9. If reaction pressure and reactant composition were maintained, altering WHSV only changes contact time (Figure S9 b). For para-selectivity, the effects of reaction pressure and WHSV are same. For yield of para-xylene, reaction pressure is the more important factor. Figure S10. TG curves of mzsm-5 after toluene alkylation with methanol using N 2 or H 2 as carrier at atmospheric pressure (reaction conditions: 460 o C, WHSV=2.5 h -1, nt/nm=4, n(h 2 or N 2 )/n(t+m)=2, nh 2 O/n(T+M)=2). TG analysis was first conducted under N 2 (a) to monitor the adsorbed aromatic molecules and coke precursor and then the same sample was conducted again under synthetic air (b) to evaluate the real coke deposits on the samples. S7

8 C T S PX Figure S11. Toluene conversion (solid) and para-selectivity (open) as a function of time on stream over mzsm-5 under H 2 atmosphere. Reaction conditions: 460 o C, WHSV=6h -1, nt/nm=6, nh 2 /n(t+m)=2, nh 2 O/n(T+M)=2. Methanol interacts with H-ZSM-5 surface stronger than aromatics such as toluene and methyl naphthalene (Nie et al., J. Phys. Chem. C, 2012, 116, 4071). Water could be a competitive adsorbate that modulate toluene to methanol ratio accumulated on the catalyst surface. Toluene conversion increased in the presence of water, which indicate water inhibited invalid conversion of methanol to byproduct (e.g. light hydrocarbons) H Time on stream (h) N 2 80 Figure S12. Toluene conversion (solid) and para-selectivity (open) as a function of time on stream over Pt/mZSM-5 under N 2 ( ) and H 2 ( ) atmosphere. Reaction conditions: 460 o C, WHSV= 2.5 h -1, total pressure= 0.2 MPa (gauge), p-toluene= 16 kpa, p-methanol= 4 kpa, p-water= 40 kpa. Shown in Figure S12, there is no significant induction periods observed over Pt/mZSM-5 under N 2 atmosphere. S8

9 S PX B C D 93.0 A C T Figure S13. Toluene conversion vs. para-selectivity over Pt/mZSM-5 under H 2 atmosphere. A) catalyst pre-treated in H 2, TOS = 1 h; B) catalyst pre-treated in N 2, TOS = 1h; C) catalyst pre-treated in H 2 and toluene, TOS =1 h; D) catalyst pre-treated in H 2 and toluene, TOS=2 h. Reaction conditions: 460 o C, WHSV= 2.5 h -1, total pressure= 0.2 MPa (gauge), p-toluene= 16 kpa, p-methanol= 4 kpa, p-water= 40 kpa. A) The reaction condition discussed in the total pressure effect section (induction period exist). B) Using N 2 as the pretreat carrier, therefore no hydrogen spillover would happen prior to the introduction of reactants. C, D) After pretreated with H 2, toluene was introduced to the reaction system first. After 1h (toluene conversion < 0.5 %), reactants (toluene and methanol mixtures) were introduced. Product collected 1 h and 2 h after toluene and methanol introduction was analyzed, results shown in Figure S13, C and D. The toluene conversion of experiment B was 5.3%, indicating hydrogen spillover in the pretreatment period is not the reason for induction period. The toluene conversions of experiment C, D were 10.8% (TOS= 1 h) and 11.5% (TOS= 2 h), close to toluene conversion obtained at the stable period (11.8%). Results of C and D support the assumption that hydrogenation of methoxonium ions is quick and the formation of methanol-toluene co-adsorption complex is relatively slow. The pre-adsorbed toluene on Pt/mZSM-5 facilitates the formation of toluene methanol co-adsorption complex, resulting the higher toluene conversion. S9

10 Methanol usage for toluene alkylation with methanol to produce para-xylene (denoted as U m-px ): 1 para-xylene U m-px = 100% methanol R (methanol 2 DME) P Table S2 The influence of atmosphere on effluent molar distribution of toluene methylation over Pt/mZSM-5 and mzsm-5. Pt/mZSM-5 mzsm-5 Carrier gas N 2 H 2 N 2 H 2 U m-px Methanol Methane Ethylene Ethane Propylene Propane Butylene Butane Benzene Toluene EB p-xylene m-xylene o-xylene MEB TriMB TetraMB Table S3 Benzene content (mol %) in products: Effect of total pressure a Pt/mZSM-5 mzsm-5 Total pressure (gauge) N2 H2 N2 H2 0 MPa MPa MPa a Reaction conditions : 460 o C, WHSV=2.5h -1, p-toluene = 16 kpa, p-methanol = 4 kpa, p-water = 40 kpa. Results were obtained from the product in 4-6h on stream. S10