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近年来全球气候变暖问题愈发严重,有研究指出,在所有与高温有关的死亡中,有三分之一以上(37%)可归因于人为导致的全球变暖 [1]。目前普遍认为温室气体的大量排放是导致全球变暖的主要原因[2]。氢氟碳化合物(HFCs)作为第三代制冷剂,由于其不含氯元素,不会对臭氧层产生破坏,所以被广泛用于冰箱、空调中,用来替代第一代制冷剂氯氟烃(CFCs)、第二代制冷剂氢氯氟烃(HCFCs)。但是,研究发现大多数HFCs具有极高的全球变暖潜力值(GWP),且在大气中具有较长的寿命,其中,典型HFCs如1,1-二氟乙烷(HFC-152a)的GWP值为142,大气寿命是1.5 a。因此早在1997年《京都议定书》已将HFCs列为非CO2类温室气体,并且《蒙特利尔议定书(基加利修正案)》对HFCs的使用提出了更严格的要求。中国于2021年4月16日正式加入此议定书,决定加强对HFCs生产和消费方面的管控[3]。目前,中国致力于2030年达到“碳达峰”,2060年实现“碳中和”[4],所以对于HFCs的减排处理刻不容缓。
目前HFCs常用的处理方法主要有两种,消除处理法和资源化转化法[5-6]。消除处理法不能有效利用宝贵的氟资源,能耗高,同时会释放CO2加剧全球温室效应,不符合碳减排的大环境。而资源化转化法将HFCs转化为具有更高附加值的产品,是目前处理HFCs最有效的手段。其中,通过HFCs脱HF制备氢氟烯烃(HFOs)是最有价值的转化路线。
研究发现HFCs脱HF反应催化剂的活性位点为Lewis酸位点[7-11]。常用的Lewis酸催化剂主要包括氟化的Cr基、Mg基和Al基催化剂。Lim等[12]采用溶胶-凝胶法制备了Cr2O3催化剂,在1,1,1,2,3-五氟丙烷(HFC-245eb)脱HF生成2,3,3,3-四氟丙烯(HFO-1234yf)反应中,初始HFC-245eb转化率达到了80.1%,但由于其表面酸性太强导致催化剂快速积碳失活;加之Cr属于重金属元素,过度使用对环境会造成破环,逐渐被限制使用;Tang等[13]采用硬模板法制备了MgF2催化剂并对其HFC-152a脱HF反应进行研究,在反应600 h后转化率仍保持在45%以上;Mg基催化剂的酸性较弱导致活性低,且在温度高于300 ℃时容易出现烧结等问题,通常需要加入一些助剂来增加其酸性和比表面积;Al基催化剂兼具高活性和高性价比等优点,是目前HFCs气相脱HF制备HFOs反应最常用的催化剂[14-15]。Al基催化剂主要为AlF3催化剂。Yang等[16]制备了立方型AlF3催化剂,在350 ℃下1,1,1,3,3-五氟丙烷(HFC-245fa)脱HF反应中转化率为17.5%,对1,3,3,3-四氟丙烯(反式)(HFC-1234ze(E))的选择性保持在80%。但与Cr基催化剂相似,过强的Lewis酸容易引发积碳,从而导致催化剂失活[17]。因此,亟需寻找一种新型催化剂来缓解目前脱HF反应催化剂存在的活性与稳定性间的制约关系。
本文选用几种固体硫酸盐催化剂研究其对HFC-152a脱HF的反应性能,结果表明Al2(SO4)3催化剂表现出良好的催化性能。进一步研究发现结晶水含量与Al2(SO4)3催化剂的催化性能呈负相关。最后结合系列表征探讨了催化剂表面性能以及酸性对反应活性的影响,对Al2(SO4)3催化剂在HFC-152a脱HF反应中的催化机理做出假设。
硫酸铝催化剂在强温室气体1, 1-二氟乙烷气相催化裂解脱HF反应中的性能研究
Application of aluminum sulphate catalysts in the gas-phase catalytic cracking of potent greenhouse gas 1, 1-difluoroethane
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摘要: 通过评价系列硫酸盐催化剂对1,1-二氟乙烷(HFC-152a)气相催化裂解脱HF反应的催化活性,筛选出活性最优的硫酸铝催化剂,并采用热失重分析(TG-DTG)、X射线衍射(XRD)、扫描电镜(SEM)、N2物理吸附-脱附(BET)、吡啶红外(Py-IR)等手段对不同焙烧温度处理硫酸铝催化剂进行表征。结果表明,通过对比不同焙烧温度的硫酸铝催化剂发现结晶水含量对催化活性有抑制作用。反应后的催化剂具有更高的Lewis酸量,一方面是由于脱出结晶水有助于增加Al物种不饱和配位点,而其中部分不饱和位点被F物种占据,进而有助于增强Lewis酸性;另一方面,催化剂表面Brønsted酸位点同样易被F物种取代,具有一定的刻蚀作用,所以在增加Lewis酸量的同时,也增加了催化剂的比表面积,提高反应分子与活性位点的接触机率。最后通过采用原位红外表征(In-situ DRIFTS)研究硫酸铝催化剂在HFC-152a气相催化裂解中的催化机理。Abstract: The catalytic activity of series sulfate catalysts for the gas-phase catalytic cracking of 1,1-difluoroethane (HFC-152a) was evaluated, and the aluminum sulfate catalysts exhibited the optimal activity. The catalytic properties of aluminum sulfate catalysts were characterized by thermal weight loss analysis (TG-DTG), X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption-desorption, pyridine infrared (Py-IR). Comparation the catalytic activity of series aluminum sulfate treated with different calcination temperatures, the results showed that crystalline water had an opposite impact on the activity. Moreover, the spent catalysts had higher Lewis acid sites compared with fresh catalysts. On the one hand, the removal of crystalline water helped to increase the unsaturated coordination sites of aluminum species, then some of these unsaturated sites were occupied by fluorine species, which in turn helped to enhance the Lewis acidity of Al species; on the other hand, the Brønsted acid sites on the surface of catalyst were also susceptible to replace by fluorine species, which had a certain etching effect. Accordingly, the amount of Lewis acid sites as well as the specific surface area of the catalyst were improved, increasing the chance of contact between the reacting molecules and the active sites. Lastly, the catalytic mechanism of HFC-152a gas-phase catalytic cracking over aluminum sulfate catalyst was revealed by in-situ infrared characterization (In-situ DRIFTS).
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Key words:
- 1-difluoroethane /
- dehydrofluorination /
- Lewis acid catalysis /
- aluminum sulfate /
- greenhouse gases
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表 1 反应前后ASO-air-400催化剂的织构性质
Table 1. Texture properties of ASO-air-400 catalyst before and after the reaction
ASO-air-400 比表面积/(m2·g−1)
Surface area孔容/(cm3·g−1)
Pore volume平均孔径/nm
Average pore diameterFresh 1.60 0.01 38.97 Used 17.90 0.08 17.50 表 2 Py-IR测定的反应前后ASO-air-400催化剂的酸量
Table 2. Acid content of fresh and Used ASO-air-400 catalyst determined by pyridine Fourier infrared absorption spectroscopy
ASO-air-400 布朗斯特酸量/(μmol·g−1)
Brønsted acid content路易斯酸量/(μmol·g−1)
Lewis acid content总酸量/(μmol·g−1)
Total acid contentFresh 15.83 15.83 31.66 Used 8.60 35.05 43.65 -
[1] VICEDO-CABRERA A M, SCOVRONICK N, SERA F, et al. The burden of heat-related mortality attributable to recent human-induced climate change [J]. Nature Climate Change, 2021, 11(6): 492-500. doi: 10.1038/s41558-021-01058-x [2] 李晟. 高质量发展视角下产业结构升级对我国碳减排的影响 [J]. 可持续发展, 2021, 11(1): 149-159. doi: 10.12677/SD.2021.111018 LI S. The impact of industrial structure upgrading on my country’s carbon emission reduction from the perspective of high-quality development [J]. Sustainable Development, 2021, 11(1): 149-159(in Chinese). doi: 10.12677/SD.2021.111018
[3] 张朝晖, 陈敬良, 高钰, 等. 《蒙特利尔议定书》基加利修正案对制冷空调行业的影响分析 [J]. 制冷与空调, 2017, 17(1): 1-7,15. ZHANG Z H, CHEN J L, GAO Y, et al. Analysis on the influence of Kigali Amendment to Montreal Protocol to refrigeration and air-conditioning industry [J]. Refrigeration and Air-Conditioning, 2017, 17(1): 1-7,15(in Chinese).
[4] 倪吉, 杨奇. 实现碳中和, 对化工意味着什么 [J]. 中国石油和化工, 2020(11): 26-31. doi: 10.3969/j.issn.1008-1852.2020.11.006 NI J, YANG Q. What carbon neutrality means for the chemical industry [J]. China Petroleum and Chemical Industry, 2020(11): 26-31(in Chinese). doi: 10.3969/j.issn.1008-1852.2020.11.006
[5] 贾文志, 刘聪, 刘行, 等. 温室气体氢氟烃的处理与利用 [J]. 化工生产与技术, 2016, 23(4): 1-6, 8. doi: 10.3969/j.issn.1006-6829.2016.04.001 JIA W Z, LIU C, LIU X, et al. Treatment and utilization of greenhouse gases-HFCs [J]. Chemical Production and Technology, 2016, 23(4): 1-6, 8(in Chinese). doi: 10.3969/j.issn.1006-6829.2016.04.001
[6] 韩文锋, 靳碧波, 周强, 等. 三氟甲烷(HFC-23)的资源化转化利用 [J]. 化工进展, 2014, 33(2): 483-492. HAN W F, JIN B B, ZHOU Q, et al. Conversion and resource utilization of waste CHF3 gas [J]. Chemical Industry and Engineering Progress, 2014, 33(2): 483-492(in Chinese).
[7] PATIL P T, DIMITROV A, KIRMSE H, et al. Non-aqueous Sol-gel synthesis, characterization and catalytic properties of metal fluoride supported palladium nanoparticles [J]. Applied Catalysis B:Environmental, 2008, 78(1/2): 80-91. [8] LI G L, NISHIGUCHI H, ISHIHARA T, et al. Catalytic dehydrofluorination of CF3CH3(HFC143a) into CF2CH2(HFC1132a) [J]. Applied Catalysis B:Environmental, 1998, 16(4): 309-317. doi: 10.1016/S0926-3373(97)00087-8 [9] GANDLER J R, YOKOYAMA T. The E2 transition state: Elimination reactions of 2-(2, 4-dinitrophenyl)ethyl halides [J]. Journal of the American Chemical Society, 1984, 106(1): 130-135. doi: 10.1021/ja00313a027 [10] SONG T Y, DONG Z X, SONG J D, et al. Dehydrochlorination of 1, 1, 2-trichloroethane over SiO2-supported alkali and transition metal catalysts: Tunable selectivity controlled by the acid - base properties of the catalysts [J]. Applied Catalysis B:Environmental, 2018, 236: 368-376. doi: 10.1016/j.apcatb.2018.04.018 [11] MALLIKARJUNA R V N, SUBRAMANIAN M A. Fluoroolefin manufacturing process: US6031141[P]. [2000-02-29]. [12] LIM S, KIM M S, CHOI J W, et al. Catalytic dehydrofluorination of 1, 1, 1, 2, 3-pentafluoropropane (HFC-245eb) to 2, 3, 3, 3-tetrafluoropropene (HFO-1234yf) using in situ fluorinated chromium oxyfluoride catalyst [J]. Catalysis Today, 2017, 293/294: 42-48. doi: 10.1016/j.cattod.2016.11.017 [13] TANG H D, DANG M M, LI Y Z, et al. Rational design of MgF2 catalysts with long-term stability for the dehydrofluorination of 1, 1-difluoroethane (HFC-152a) [J]. RSC Advances, 2019, 9(41): 23744-23751. doi: 10.1039/C9RA04250D [14] RÜDIGER S, ELTANANY G, GROß U, et al. Real Sol-gel synthesis of catalytically active aluminium fluoride [J]. Journal of Sol-Gel Science and Technology, 2007, 41(3): 299-311. doi: 10.1007/s10971-006-9008-0 [15] CHRISTE K O, DIXON D A, MCLEMORE D, et al. On a quantitative scale for Lewis acidity and recent progress in polynitrogen chemistry [J]. Journal of Fluorine Chemistry, 2000, 101(2): 151-153. doi: 10.1016/S0022-1139(99)00151-7 [16] YANG H, WU S, CHEN Z F, et al. Catalytic performance for the conversion of potent fluorinated greenhouse gases by aluminium fluorides with different morphology [J]. Catalysis Letters, 2021, 151(7): 2065-2074. doi: 10.1007/s10562-020-03446-y [17] JIA W Z, WU Q, LANG X W, et al. Influence of lewis acidity on catalytic activity of the porous alumina for dehydrofluorination of 1, 1, 1, 2-tetrafluoroethane to trifluoroethylene [J]. Catalysis Letters, 2015, 145(2): 654-661. doi: 10.1007/s10562-014-1409-z [18] ÇıLGı G K, CETIŞLI H. Thermal decomposition kinetics of aluminum sulfate hydrate [J]. Journal of Thermal Analysis and Calorimetry, 2009, 98(3): 855-861. doi: 10.1007/s10973-009-0389-5 [19] CHOU K S, SOONG C S. Kinetics of the multistage dehydration of aluminum sulfate hydrate [J]. Thermochimica Acta, 1984, 81: 305-310. doi: 10.1016/0040-6031(84)85135-7 [20] CHOU K S, SOONG C S. Kinetics of the thermal decomposition of aluminum sulfate [J]. Thermochimica Acta, 1984, 78(1/2/3): 285-295. [21] BARTHOLOMEW C H, RAHMATI M, REYNOLDS M A. Optimizing preparations of Co Fischer-Tropsch catalysts for stability against sintering [J]. Applied Catalysis A:General, 2020, 602: 117609. doi: 10.1016/j.apcata.2020.117609 [22] ZARUBINA V, MELIÁN-CABRERA I. On the geometric trajectories of pores during the thermal sintering of relevant catalyst supports [J]. Scripta Materialia, 2021, 194: 113679. doi: 10.1016/j.scriptamat.2020.113679 [23] PAN C, GUO Z L, DAI H, et al. Anti-sintering mesoporous Ni-Pd bimetallic catalysts for hydrogen production via dry reforming of methane [J]. International Journal of Hydrogen Energy, 2020, 45(32): 16133-16143. doi: 10.1016/j.ijhydene.2020.04.066 [24] WANG Z K, HAN W F, TANG H D, et al. CaBaFx composite as robust catalyst for the pyrolysis of 1-chloro-1, 1-difluoroethane to vinylidene fluoride [J]. Catalysis Communications, 2019, 120: 42-45. doi: 10.1016/j.catcom.2018.11.011 [25] WANG J C, HAN W F, WANG S C, et al. Synergistic catalysis of carbon-partitioned LaF3–BaF2 composites for the coupling of CH4 with CHF3 to VDF [J]. Catalysis Science & Technology, 2019, 9(6): 1338-1348. [26] LI H R, LIU C L, WANG Y, et al. Synthesis, characterization and n-hexane hydroisomerization performances of Pt supported on alkali treated ZSM-22 and ZSM-48 [J]. RSC Advances, 2018, 8(51): 28909-28917. doi: 10.1039/C8RA04858D [27] MAITY J, JACOB C, DAS C K, et al. Direct fluorination of Twaron fiber and investigation of mechanical thermal and morphological properties of high density polyethylene and Twaron fiber composites [J]. Journal of Applied Polymer Science, 2008, 107(6): 3739-3749. doi: 10.1002/app.27510 [28] PENG T, CAI R Q, CHEN C F, et al. Surface modification of Para-aramid fiber by direct fluorination and its effect on the interface of aramid/epoxy composites [J]. Journal of Macromolecular Science, Part B, 2012, 51(3): 538-550. doi: 10.1080/00222348.2011.609777 [29] OU Y P, JIAO Q J, LI N, et al. Pyrolysis of ammonium perfluorooctanoate (APFO) and its interaction with nano-aluminum [J]. Chemical Engineering Journal, 2021, 403: 126367. doi: 10.1016/j.cej.2020.126367 [30] LIANG J, ROSELIUS M. FTIR study of a perfluoroacyl fluoride chemisorption onto alumina [J]. Journal of Fluorine Chemistry, 1994, 67(2): 113-117. doi: 10.1016/0022-1139(93)02958-H [31] LIMCHAROEN A, LIMSUWAN P, PAKPUM C, et al. Characterisation of C—F polymer film formation on the air-bearing surface etched sidewall of fluorine-based plasma interacting with Al2O3–TiC substrate [J]. Journal of Nanomaterials, 2013, 2013: 1-6.