Fabrication of effective desulfurization species active sites in the CeY zeolites and the adsorption desulfurization mechanisms
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摘要: 以不同焙烧温度和Ce负载量的CeY分子筛为研究对象，运用XRD及N2吸附表征其织构性质；运用吡啶吸附红外光谱法剖析了分子筛中活性位的化学属性；采用固定床评价其对噻吩模拟油的吸附脱硫性能及芳烃和烯烃对噻吩脱除的影响；并结合红外光谱和GC-SCD技术分析了其脱硫机制。结果表明，CeY样品经150 ℃焙烧后，其超笼中具备高含量的B酸和Ce羟基化物种活性位，两者协同增强了噻吩低聚反应能力，进而提高了其吸附穿透硫容量（18.45 mg（S）/g）；而提升焙烧温度和Ce负载量会严重降低其有效活性位的数量，削弱了噻吩低聚反应能力，其吸附穿透硫容量显著减小（4.03 mg（S）/g）。当加入烯烃和芳烃后，CeY-12.3-150吸附剂对含低浓度（质量分数）1-己烯（< 1.0%）和苯（< 0.1%）的噻吩模拟油依旧保持较高吸附穿透硫容量；但随两者含量的持续增加，其硫容量急剧下降。其主要分别归因于噻吩烷基化反应的发生及"S-H"键的作用模式。Abstract: A series of CeY zeolites with different cerium loadings and calcined at different temperatures were prepared and used as the adsorbent for the desulfurization of thiophene containing model oil. The CeY zeolites were characterized by XRD, N2 sorption, FT-IR spectroscopy and GC-SCD and GC-MSD techniques. The effects of aromatics and olefins on the adsorption desulfurization performance were investigated and the active species and reaction mechanism for the adsorption desulfurization on CeY zeolites were probed. The results indicate that the CeY zeolite calcined at 150 ℃ is provided with a large number of Brönsted acid sites and hydroxylated cerium species in the supercages, which can synergistically promote the thiophene oligomerization and then enhance the sulfur breakthrough adsorption capacity (18.45 mg (S)/g). However, a further increase in the calcination temperature and cerium loading may greatly reduce the number of active sites for the adsorption desulfurization and suppress the thiophene oligomerization reaction, leading to a significant decrease in the sulfur breakthrough adsorption capacity (4.03 mg (S)/g). For the thiophene model oils containing low concentration of 1-hexene (< 1.0%) or benzene (< 0.1%), the CeY-12.3-150 zeolite (with a cerium loading of 12.3% and calcined at 150 ℃) also exhibits a relatively high sulfur breakthrough adsorption capacity. However, a further increase in the content of 1-hexene or benzene in the feed may lead to a sharp decrease in the sulfur breakthrough adsorption capacity, due to the alkylation of thiophene and the adsorption mode of "S-H" bonding.
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图 2 NaY和CeY分子筛的N2吸附-脱附等温线
Figure 2 N2 adsorption-desorption isotherms of the NaY and CeY zeolites
图 3 CeY分子筛吡啶吸附后在150 ℃脱附温度下的原位红外光谱谱图
Figure 3 Py-IR spectra of the CeY zeolites collected at 150 ℃ a: CeY-12.3-150; b: CeY-12.3-550; c: CeY-17.4-550
图 4 噻吩模拟油在CeY分子筛上的吸附穿透曲线(a)及穿透吸附硫容量(b)
Figure 4 Breakthrough curves of thiophene adsorption in a fixed-bed reactor on various CeY zeolites with a liquid feed containing 300 mg (S)/kg sulfur in n-octane at room temperature (a) and a comparison of various CeY zeolites in their sulfur breakthrough adsorption capacity (b)
图 5 NaY和三种不同Ce改性Y分子筛吸附噻吩后在不同脱附温度下的原位红外光谱谱图
Figure 5 FT-IR spectra of thiophene adsorbed on various CeY zeolites and degassed at different temperatures
a: background; b: 30 ℃; c: 100 ℃; d: 200 ℃; e: 300 ℃
图 6 噻吩在CeY分子筛上吸附后, 吸附剂表面上硫化物物种的GC-SCD(a)和GC-MSD(b)谱图
Figure 6 GC-SCD (a) and GC-MSD (b) chromatograms of the sulfur compounds trapped on various CeY zeolites after interaction with thiophene molecules
a: CeY-12.3-150; b: CeY-12.3-550; c: CeY-17.4-550
图 7 噻吩在CeY-12.3-150(左)和CeY-17.4-550(右)分子筛有效活性位上的低聚反应机制
Figure 7 Oligomerization reaction mechanism of thiophene adsorbed on the active sites of CeY-12.3-150 (left) and CeY-17.4-550 (right) zeolites
图 8 含不同苯质量分数的噻吩模拟油在CeY-12.3-150分子筛上的噻吩吸附穿透曲线(a), 苯吸附穿透曲线(b)及穿透吸附硫容量(c)
Figure 8 Breakthrough curves of thiophene (a) and benzene (b) adsorption in a fixed-bed reactor on the CeY-12.3-150 zeolite adsorbent with a liquid feed containing 300 mg (S)/kg sulfur thiophene and different benzene concentrations in n-octane at room temperature and the corresponding sulfur breakthrough adsorption capacities (c)
图 9 含不同1-己烯质量分数的噻吩模拟油在CeY-12.3-150分子筛上的噻吩吸附穿透曲线(a), 1-己烯吸附穿透曲线(b)及其穿透吸附硫容量(c)
Figure 9 Breakthrough curves of thiophene (a) and 1-hexene (b) adsorption in a fixed-bed reactor on the CeY-12.3-150 zeolite adsorbent with a liquid feed containing 300 mg (S)/kg sulfur thiophene and different 1-hexene concentrations in n-octane at room temperature and the corresponding sulfur breakthrough adsorption capacities (c)
图 10 含0.01%(a)和20.0%(b)1-己烯的噻吩模拟油在CeY-12.3-150分子筛上吸附脱硫过程中不同吸附时间段液相产物的GC-SCD谱图
Figure 10 GC-SCD chromatograms of the sulfur compounds in liquid products during the adsorption desulfurization process in a fixed-bed reactor on the CeY-12.3-150 zeolite with a liquid feed containing 300 mg (S)/kg sulfur thiophene and 0.01% (a) and 20.0% (b) 1-hexene in n-octane
图 11 C6噻吩在CeY-12.3-150分子筛上的形成机理
Figure 11 Formation mechanism of C6 thiophene on the CeY-12.3-150 zeolite
表 1 NaY和CeY分子筛的结构参数
Table 1 Textural properties of the NaY and CeY zeolites
Sample Ce loading w/% I12.5/I11.9 Surface area A /(m2·g-1) Pore volume v /(cm3·g-1) ABET Amicro Ameso vtotal vmicro vmeso NaY - 0 585.6 551.2 34.4 0.34 0.29 0.05 CeY-12.3-150 12.3 3.86 436.0 389.9 46.1 0.24 0.20 0.04 CeY-12.3-550 12.3 0.65 575.7 518.1 57.6 0.33 0.26 0.07 CeY-17.4-550 17.4 0.83 556.5 476.1 80.4 0.31 0.24 0.07 
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