1 引言
2 甲醇制烯烃技术
2.1 工业化进程
2.2 分子筛
2.3 反应历程
2.3.1 诱导期
2.3.2 高效期
2.3.3 失活期
3 积炭的形成与演变
3.1 积炭的生成与分布
3.1.1 宏观生长规律
3.1.2 微观可视化分布
图4 HZSM-5和SAPO-34分子筛在660 K、不同MTH反应时间下的共聚焦荧光显微图像和切片示意图(a)[43]. SAPO-34分子筛中碳质物种的时空分布(b)[44]. 基于直接电子衍射技术对HZSM-5微孔积炭直接成像, 积炭物种富集于孔道交叉处并沿直孔道延伸(c)[48]. HZSM-5不同晶面的积炭HAADF-STEM图像, 直孔道(010)面的积炭更趋石墨化(d)[49]. 固定床反应器上积炭的TEM图(e)[42]Figure 4 Confocal fluorescence microscopy images and sectional diagrams of HZSM-5 and SAPO-34 crystals at 660 K and varying MTH reaction time (a)[43]. Spatial and temporal distribution of carbonaceous species in SAPO-34 molecular sieve (b)[44]. Direct imaging of carbon species accumulated inside HZSM-5 channel based on direct electron diffraction. Carbon accumulation signal is enriched at the channel intersection and extends along the straight channel (c)[48]. The HAADF-STEM images of carbon deposits on different crystal planes of HZSM-5, with the carbon deposits on the straight channel (010) plane being more graphite-like (d)[49].TEM diagram of carbon deposition in fixed bed reactor (e)[42] |
3.1.3 反应条件对积炭的调控
3.2 积炭的化学本质
3.2.1 结构解析
图5 673 K不同反应时间下新鲜和失活SAPO-34催化剂HP 129Xe核磁共振谱(a)[46]. 分离出的不溶性积炭的13C固态核磁共振光谱图(b)[2]. 300 ℃甲醇转化反应不同时间SAPO-34笼内留存的有机物的GC-MS谱图(c)[59]. 程序升温甲醇转化反应中SAPO-34催化剂上积炭物种的生成和随温度的演变(d)[58]. 不同温度下反应后SAPO-34笼内留存的有机物的GC-MS谱图(e)[57]Figure 5 Temperature-dependent HP 129Xe NMR spectra of fresh and spent SAPO-34 catalysts after MTO reaction at 673 K for various reaction times (a)[46]. 13C solid‑state NMR spectrum of the insoluble coke (b)[2]. GC-MS spectra of retained organics in SAPO-34 after methanol reaction at 300 ℃ for different times (c)[59]. Coke species evolution in the temperature-programmed methanol conversion over SAPO-34 (d)[58]. GC-MS analysis for the extracted species in SAPO-34 after different reaction temperatures (e)[57] |
图6 SAPO-34催化剂上提取的积炭物种的MALDI FT-ICR MS图(a)[2]. SAPO-34上MTO反应的积炭和水蒸气再生路径(b)[60]. HZSM-5上积炭物种的STM与nc-AFM图(c)和MALDI FT-ICR MS图(d)[3]Figure 6 MALDI FT-ICR MS spectrum of released carbonaceous deposits on SAPO-34 catalyst (a)[2]. The coking route of MTO reaction and the decoking route of steam regeneration of the spent SAPO-34 (b)[60]. Direct atomic-resolution imaging of carbon species on HZSM-5 by STM and nc-AFM (c) and MALDI FT-ICR MS spectrum analysis (d)[3] |
3.2.2 活性认知
3.3 积炭生长路径与失活机制
3.3.1 SAPO-34分子筛积炭生长路径
3.3.2 HZSM-5分子筛积炭生长路径
3.4 不同类型反应器积炭特征
3.4.1 流化床反应器
3.4.2 固定床反应器
3.4.3 反应装置之间的联系
图8 流化床反应器(a)[74]及DMTO放大装置(b)[73]示意图. 固定床反应器示意图(c). 流化床反应器中不同操作条件下积炭含量随时间的变化情况, 通过积炭沉积模型, 可模拟固定床反应器(d)[71]Figure 8 Diagram of fluidized bed reactor (a)[74] and DMTO amplifier (b)[73]. Fixed bed reactor (c). The variation of coke content over time under different operating conditions in a fluidized bed reactor can be simulated for a fixed bed reactor through a coke deposition model (d)[71] |
4 延缓积炭失活
4.1 催化剂改性
4.1.1 金属改性
4.1.2 结构优化
4.1.3 孔隙调控
4.2 反应气氛调节
4.3 积炭的调控与资源化利用
图9 SAPO-34晶体中活性烃池物种的定向构建示意图(a). 蒸气处理过程中生成的小分子气体含量(b). 698 K、WHSV为1.0 h−1的MTO转化过程中, 商用SA-34-Ⅰ催化剂在处理前后(即预积炭5 min, 随后水蒸气处理5 h的SAPO-34)甲醇转化率, 以及反应100 min时乙烯和丙烯的选择性(c)[98]Figure 9 Schematic diagrams of the directional construction of active hydrocarbon pool species within SAPO-34 crystals (a). The content of small molecular gases produced during vapor treatment (b). Time-dependent methanol conversion over the commercial SA-34-I catalyst before and after treatments (precoking for 5 min followed by steaming for 5 h) during the MTO conversion at 698 K with a WHSV of 1.0 h−1, and the selectivity of ethylene and propylene at TOS=100 min (c)[98] |
5 再生策略
5.1 空气再生
5.2 水蒸气再生
图10 积炭转化为特定中间体的示意图(a), 953 K氮气和蒸气裂解过程中分子质量小于200 Da的碳质中间体分布(b), 953 K氮气和蒸气裂解过程中分子量大于200 Da的碳质物质随时间演化的MALDI FT-ICR MS图(c), 923 K下用蒸气处理的失活分子筛的原位UV-Raman光谱(d), 953 K下失活分子筛蒸气裂解过程中分子筛微孔体积和积炭量的变化(e)[79]Figure 10 Schematic diagram of coke transformation into specific intermediates (a). Evolution of detailed distribution of carbonaceous intermediates with molecular mass smaller than 200 Da during nitrogen and steam cracking at 953 K, which is analyzed by GC-MS (b). Evolution of carbonaceous species with molecular mass larger than 200 Da during nitrogen and steam cracking at 953 K, which is analyzed by MALDI FT-ICR MS (c). Operando UV-Raman spectra of ZEOS-Coked samples treated by steam at 923 K with different time (d). Evolution of textual property and coke quantity of ZEOS-Coked samples during steam cracking at 953 K (e)[79] |