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固定床吸附装置广泛应用于大气污染防治、军事护学及核电等领域的有毒有害气体防护及净化,其可靠性和有效性决定了净化效果的好坏,以及系统效能的实现。由于吸附装置内的吸附材料 (通常为活性炭) 装填不密实、密封材料老化破裂、运输安装不当等因素造成的内部结构损坏,均会引起吸附装置发生机械泄露[1-4]。机械泄露的情况一旦发生,有毒气体将瞬时穿透防护层,导致吸附装置净化效能降低甚至失效[5-7]。因此,吸附装置机械泄露的非破坏性评价已引起国内外研究者重视。
机械泄露非破坏性评价的关键是根据吸附材料选择合适的示踪剂 (气体) 。利用示踪气体的吸附穿透时间与机械泄露的瞬时穿透之间的时间间隔可判断吸附装置是否存在机械泄露,并在测试结束后采用气流反向吹扫脱附的方法将残留在吸附装置内部的示踪剂完全脱除,从而不会对吸附装置的净化性能造成影响。氟利昂11的化学式为CCl3F,分子量137.37 g·mol−1,在1.01×105 Pa (1个标准大气压) 下沸点为23.7 ℃,水溶量为0.000 11 g·g−1。该化合物具有化学性质稳定、低浓度易检测、易脱附、无毒无害等特点,并且在吸附材料上具有一定的吸附容量,可作为机械泄露非破坏性检测的示踪气体。美国萨瓦那河实验室曾使用氟利昂11进行碘吸附器泄漏实验[8-9],发现氟利昂11可用于碘吸附器的出厂实验及现场测试。中国核辐射防护研究院对碘吸附器泄露试验中氟利昂11在活性炭床层的解吸行为进行了研究[10],提出了有利于氟利昂11在活性炭床层解吸的方法及条件。王坤俊等[11]开展了碘吸附器脉冲式氟利昂法泄露的检测技术研究,取得了与连续法进样一致的结果,并发现脉冲式进样更节省示踪剂用量。标准《M48A1过滤吸收器性能指标》(MIL-PRF-32137)[12]、《M98过滤吸收器性能指标》(MIL-PRF-51525B)[13]、《气相吸附过滤吸收器滤芯单元性能指标》(MIL-PRF-32016)[14]等均规定将氟利昂类物质作为此类吸附装置机械泄露非破坏性检测的示踪剂。目前,我国相关领域固定床吸附装置机械泄露的非破坏性检测方法尚未建立起来,相关的标准长期处于空白。
氟利昂类气体在吸附装置的吸脱附行为是建立机械泄露非破坏性评价的基础,目前鲜有研究报道[3]。本课题组基于前期研究成果[15-16],系统研究了低浓度氟利昂11气体在专用浸渍炭材料上的吸附穿透和脱附行为,并采用Wheeler方程、Yoon-Nelson方程、LDF方程以及Freundlich方程等动力学模型研究其吸脱附动力学,揭示氟利昂11在浸渍炭床层的吸脱附规律,以期为我国相关领域固定床吸附装置的研发及机械泄露非破坏性检验方法的建立提供参考。
氟利昂11在浸渍活性炭床层的吸脱附行为
The adsorption and desorption behavior of freon 11 on impregnated activated carbon bed
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摘要: 对低浓度氟利昂11气体在浸渍活性炭 (浸渍炭) 上的吸脱附行为进行了研究。考察了不同的气流比速和气流湿度条件对氟利昂11在浸渍炭床层吸附穿透的影响,利用Wheeler方程和Yoon-Nelson方程描述了吸附动力学过程。探讨了脱附温度、气流比速及床层含水率等影响因素对氟利昂11脱除效果的影响机制,运用LDF和Freundlich脱附动力学模型对脱附过程进行了描述。结果表明:氟利昂11在浸渍炭上的吸附动力学主要受外扩散控制,确定了其1%穿透时间与气流比速的定量关系;气流湿度对氟利昂11吸附行为的影响体现在与水分子发生竞争吸附,从而导致穿透曲线出现卷起现象;氟利昂11的脱附速率大小与脱附温度、气流比速和床层含水率呈正相关;当脱附温度为25~30 ℃,气流比速为0.8 L·min−1·cm−2时为最佳机械泄露测试脱附条件。本研究可为有毒有害气体净化用固定床吸附装置的设计,以及机械泄露非破坏性检验应用方法的建立参考。Abstract: The adsorption and desorption behavior of low concentration freon 11 gas on impregnated activated carbon was studied. The effects of air flow rate and air flow humidity on the adsorption penetration of freon 11 on impregnated carbon bed were investigated, and the adsorption kinetics was described by Wheeler equation and Yoon-Nelson equation. The influence mechanism of desorption temperature, air flow rate and bed water content on freon 11 removal was discussed. LDF and Freundlich desorption kinetics models were used to describe the desorption process. The results showed that the adsorption kinetics of freon 11 on impregnated carbon was mainly controlled by external diffusion. The quantitative relationship between 1% penetration time and air flow rate was determined. The influence of humidity effect on the adsorption behavior of freon 11 was reflected in the curl of the breakthrough curve caused by competition between freon 11 and water molecules. The desorption rate of freon 11 was positively correlated with the desorption temperature, air flow rate and bed water content. A desorption temperature at 25~30 ℃ and a air flow rate of 0.8 L·min−1·cm−2 were the best conditions for mechanical leakage test of desorption. The research results can provide important theoretical basis and technical support for the establishment of the application method of non-destructive inspection of mechanical leakage in fixed bed adsorption device for the purification of toxic and harmful gas .
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Key words:
- adsorption /
- desorption /
- impregnated carbon /
- freon 11 /
- filter leakage
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表 1 浸渍炭比表面积和孔结构参数
Table 1. Specific surface area and pore structure parameters of impregnated carbon
吸附剂 比表面积/(m2·g−1) 总孔容/(cm3·g−1) 微孔孔容/(cm3·g−1) 中孔孔容/(cm3·g−1) 微孔百分比(%) 浸渍炭 541.5 0.276 0.232 0.044 84.06% 表 2 不同气流比速下浸渍炭床层对氟利昂11的吸附动力学参数
Table 2. Adsorption kinetic parameters of freon 11 by impregnated carbon bed at different air flow rates
比速/
(L·min−1·cm−2)饱和吸附容量/
(mg·g−1)1%穿透时间/min Wheeler方程吸附速率
常数kv/(min−1)Yoon-Nelson方程吸附速率
常数k’/(min−1)0.5 29.87 120.5 2 170.39 0.041 7 0.8 30.26 63.0 2 940.35 0.061 0 1.0 28.94 41.0 3 096.80 0.061 5 1.2 30.47 34.0 3 452.43 0.064 0 表 3 不同气流湿度下浸渍炭床层对氟利昂11的吸附动力学参数
Table 3. Adsorption kinetic parameters of freon 11 on impregnated carbon at different air humidity
相对湿度 饱和吸附容量/
(mg·g−1)1%穿透时间/min Wheeler方程吸附速率
常数kv/(min−1)Yoon-Nelson方程吸附速率
常数k’/(min−1)<1% 24.91 28.5 2480.67 0.061 2 30% 24.71 24.8 2506.84 0.064 4 44% 15.28 18.4 2609.11 0.091 9 60% 5.80 14.8 2997.95 0.160 3 74% 1.95 13.5 3165.32 0.389 0 表 4 不同气流比速下拟合方程参数和实验值
Table 4. Parameters of the fitting equation and experimental values at different air flow rates
比速/
(L·min−1·cm−2)实验结果 LDF拟合结果 Freundlich拟合结果 Qexp/(mg·g−1) texp/min ηe/% k/h−1 Qe/(mg·g−1) R2 拟合方程 R2 0.6 0.333 140.6 80.74 1.73 0.340 0.989 9 lnc=−0.55lnt+1.70 0.953 0 0.8 0.344 98.3 83.49 2.46 0.345 0.996 9 lnc=−0.43lnt+3.73 0.926 8 1.0 0.327 88.3 79.26 2.61 0.330 0.995 6 lnc=−0.52lnt+3.51 0.972 9 1.2 0.328 70.7 79.41 3.24 0.328 0.989 5 lnc=−0.52lnt+3.39 0.964 9 注:texp为氟利昂11气体质量浓度降到0.588 7 mg·m−3时对应的时间;ηe为达到脱附平衡时的脱附率;Qexp为实验条件下平衡脱附量;Qe为LDF方程拟合得到的平衡脱附量。 表 5 不同温度下拟合方程参数和实验值
Table 5. Parameters of the fitting equation and experimental values of the fitting equation at different temperatures
温度/ ℃ 实验结果 LDF拟合结果 Freundlich拟合结果 Qexp/(mg·g-1) texp/min ηe/% k/h-1 Qe/(mg·g-1) R2 拟合方程 R2 20 0.347 116.0 84.00 2.06 0.338 0.989 7 lnc=−0.53lnt+3.70 0.960 9 25 0.346 101.0 83.98 2.44 0.338 0.994 4 lnc=−0.54lnt+3.84 0.952 3 30 0.344 98.3 83.49 2.46 0.345 0.996 9 lnc=−0.43lnt+3.73 0.926 8 35 0.341 81.0 82.69 3.73 0.336 0.996 9 nc=−0.56lnt+4.03 0.951 9 40 0.379 71.0 91.84 5.49 0.373 0.9897 lnc=−0.66lnt+4.20 0.982 5 表 6 不同床层含水率下拟合方程参数和实验值
Table 6. Parameters of fitting equation and experimental values under different bed water content
床层含水率 实验结果 LDF拟合结果 Freundlich拟合结果 Qexp/(mg·g−1) texp/min ηe/% k/h−1 Qe/(mg·g−1) R2 拟合方程 R2 0 0.344 98.3 83.49 2.46 0.345 0.996 9 lnc=−0.43lnt+3.73 0.926 8 5% 0.366 92.7 93.04 4.48 0.355 0.981 3 lnc=−1.41lnt+5.29 0.926 9 10% 0.344 87.7 91.60 5.18 0.330 0.966 6 lnc=−1.42lnt+5.52 0.949 0 22% 0.324 75.2 95.86 10.27 0.308 0.936 5 lnc=−1.46lnt+5.61 0.984 6 -
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