Methanol to propylene reaction performance and trapped carbonaceous species over zeolites with different topologies
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摘要: 采用TEAOH溶液处理MFI结构ZSM-5分子筛、MWW结构MCM-22分子筛，NaOH溶液处理TON结构ZSM-22分子筛、CHA结构SSZ-13分子筛得到四种结构的扩孔分子筛。在反应温度480℃、反应压力0.1 MPa、甲醇与水质量比1：1、甲醇质量空速1.5 h-1的条件下，考察了四种扩孔分子筛的甲醇制丙烯（MTP）催化性能，并采用XRD、N2吸附-脱附、NH3-TPD、TG、UV-Raman和GC-MS等方法表征催化剂的物化性质及MTP反应2 h后的分子筛积炭性质。结果表明，四种分子筛扩孔改性后均出现介孔，其中，T-ZSM-5分子筛在MTP反应中寿命最长；T-MCM-22分子筛寿命次之且失活速率慢；而一维孔道结构N-ZSM-22分子筛和八元环尺寸较小的N-SSZ-13分子筛均失活迅速。受拓扑结构和孔道扩散的影响，MTP反应2 h后，分子筛积炭量增加的顺序为T-ZSM-5＜N-ZSM-22＜T-MCM-22＜N-SSZ-13且可溶焦分子质量随积炭量增加而增重，即从五甲基苯增重到菲、芘等多环芳烃。Abstract: Mesoporous ZSM-5 (MFI), MCM-22 (MWW), ZSM-22 (TON) and SSZ-13 (CHA) zeolites were obtained by TEAOH and NaOH solution treatment. Under the following operating conditions:t=480℃, p=0.1 MPa, m(methanol):m(H2O)=1:1 and WHSV (methanol)=1.5 h-1, the catalytic properties of four mesoporous zeolites with different topologies were investigated in the methanol to propylene (MTP) reaction. The fresh and spent samples after 2 h were characterized with XRD, nitrogen adsorption experiments, NH3-TPD, TG, UV-Rama and GC-MS techniques. It demonstrated that both zeolites exist mesopores after treated by alkali. The mesoporous T-ZSM-5 zeolite had the highest lifetime; the lifetime of T-MCM-22 zeolite with was secondary and deactivation rate was slow; The N-ZSM-22 with one-dimensional channel structure and N-SSZ-13 zeolite with 8-member ring channels both deactivated rapidly. Due to the difference of topology structure and diffusion performance, their coke contents after 2 h increased in the order:T-ZSM-5 < N-ZSM-22 < T-MCM-22 < N-SSZ-13. Moreover, the molecular weight of soluble coke increased with the increasing of coke contents, changed from pentamethylbenzene to polycyclic aromatic hydrocarbons, such as phenanthrene and pyrene.
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Key words:
- methanol to propylene (MTP) /
- mesoporous /
- zeolite topology /
- deactivation behavior
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图 1 甲醇制丙烯(MTP)反应评价装置示意图
Figure 1 Schematic layout of the experimental setup of methanol to propylene (MTP)
图 2 不同拓扑结构分子筛的XRD谱图
a: T-ZSM-5; b: T-MCM-22; c: N-ZSM-22; d: N-SSZ-13
Figure 2 XRD patterns of zeolites with different topologies
图 3 不同拓扑结构分子筛的TEM照片
(a): T-ZSM-5; (b): T-MCM-22; (c): N-ZSM-22; (d): N-SSZ-13
Figure 3 TEM images of zeolites with different topologies
图 4 不同拓扑结构分子筛对应的N2吸附-脱附等温曲线
□：T-ZSM-5；△：T-MCM-22；○：N-ZSM-22；▽：N-SSZ-13
Figure 4 N2 adsorption-desorption isotherms and pore distribution of zeolites with different topologies
图 5 不同拓扑结构分子筛对应的NH3-TPD谱图
a：T-ZSM-5；b：T-MCM-22；c：N-ZSM-22；d：N-SSZ-13
Figure 5 NH3-TPD profiles of zeolites with different topologies
图 6 不同拓扑结构分子筛催化MTP反应对应甲醇转化率随反应时间的变化
□：T-ZSM-5；△：T-MCM-22；○：N-ZSM-22；▽：N-SSZ-13
Figure 6 Relationship between methanol conversion and reaction time of MTP reaction of zeolites with different topologies
图 7 四种拓扑结构分子筛对应丙烯、乙烯碳基收率、P/E比及氢转移系数随反应时间的变化
□：T-ZSM-5；△：T-MCM-22；○：N-ZSM-22；▽：N-SSZ-13
Figure 7 Product yields ((a): propylene, (b): ethylene), P/E ratio (c) and C3 hydrogen transfer index (d) with TOS over zeolites with different topologies
图 8 不同拓扑结构分子筛反应2 h的TG曲线
Figure 8 TG profiles of partial deactivated zeolites with different topologies after 2 h
图 9 不同拓扑结构分子筛的内外部积炭量对比柱状图
Figure 9 Amounts of internal and external coke of partial deactivated zeolites with different topologies
图 10 不同拓扑结构分子筛反应2 h的UV-Raman谱图
a：D-T-ZSM-5；b：D-T-MCM-22；c：D-N-ZSM-22；d：D-N-SSZ-13
Figure 10 UV-Raman (k=244 nm) spectra of partial deactivated zeolites with different topologies after 2 h
图 11 不同拓扑结构分子筛反应2 h对应可溶性积炭的GC-MS谱图
Figure 11 GC-MS analyses of retained hydrocarbons of partial deactivated zeolites with different topologies after 2 h chromatograms from the dissolution-extraction experiments for deactivated samples
表 1 不同拓扑结构分子筛的比表面积和孔结构
Table 1 Specific surface areas and pore properties of zeolites with different topologies
Sample SBET a/(m2·g-1) Sext/(m2·g-1) Smicrob/(m2·g-1) vtotalc/(cm3·g-1) vmicrob/(cm3·g-1) vmesod/(cm3·g-1) T-ZSM-5 375 27 348 0.204 0.160 0.044 T-MCM-22 458 71 387 0.582 0.182 0.400 N-ZSM-22 225 45 181 0.420 0.060 0.320 N-SSZ-13 516 46 470 0.313 0.217 0.096 SBET: specific surface area; Sext: external surface area; Smicro=micropore specific area, a: BET method; b: t-plot method; c: volume adsorbed at p/p0 =0.99; d: mesopore volumes were calculated by vtotal-vmicro 
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表 2 不同拓扑结构分子筛反应2 h的产物分布
Table 2 Products yields of zeolites with different topologies measured at 2 h
Sample Gaseous product yields w/% x/%(methanol) P/E ratio C3 HTI C1 C2= C2 C3= C3 C4= C4 C5+ T-ZSM-5 4.56 8.59 1.49 9.74 16.43 4.45 16.39 38.35 100 1.13 1.695 T-MCM-22 1.04 11.36 0.80 15.98 6.34 6.53 19.45 38.50 100 1.41 0.397 N-ZSM-22 3.67 12.54 0.47 26.63 4.83 15.53 1.83 34.50 79 2.12 0.181 N-SSZ-13 0.76 42.63 0.78 21.85 0.96 6.80 0.14 26.08 84 0.51 0.044 reaction conditions: t=480 ℃, WHSV=1.5 h-1, p=0.1 MPa, m(H2O):m(CH3OH) = 1:1，2 h, C3 HTI = C3 alkanes/ C3 alkenes
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表 3 不同拓扑结构分子筛反应2 h的比表面积和孔结构
Table 3 Specific surface areas and pore properties of zeolites with different topologies after 2 h
Sample SBETa
/(m2·g-1)Sext
/(m2·g-1)Smicrob
/(m2·g-1)vtotalc
/(cm3·g-1)vmicrob
/(cm3·g-1)vmesod
/(cm3·g-1)D-T-ZSM-5 320 31 288 0.182 0.134 0.048 D-T-MCM-22 196 52 144 0.470 0.070 0.400 D-N-ZSM-22 81 44 37 0.379 0.084 0.295 D-N-SSZ-13 161 4 156 0.088 0.073 0.015 SBET: specific surface area; Sext: external surface area; Smicro= micropore specific area, a: BET method; b: t-plot method; c: volume adsorbed at p/p0 =0.99; d: mesopore volumes were calculated by vtotal-vmicro
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表 4 不同拓扑结构分子筛反应2 h对应可溶性积炭组成及相对含量
Table 4 Contents of soluble coke species on partial deactivated zeolites with different topologies after 2 h
Species Sample Relative content w/% D-T-ZSM-5 D-T-MCM-22 D-N-ZSM-22 D-N-SSZ-13 1 
0.02 - - - 2 
0.04 - - - 3 
0.05 - - - 4 
0.02 - - - 5 
12.86 - - 2.33 6 
81.27 - - - 7 
5.73 69.44 - - 8 
- 5.55 5.36 9.88 9 
- 17.10 8.14 7.10 10 
- - 12.35 6.07 11 
- 2.43 3.34 - 12 
- 1.40 6.68 22.92 13 
- - 8.02 1.41 14 
- - 30.06 - 15 
- 4.08 22.12 36.89 16 
- - 3.93 - 17 
- - - 7.21 18 
- - - 6.18
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