Effects of reduction conditions on fused iron catalyst for high temperature Fischer-Tropsch synthesis

doi:10.16085/j.issn.1000-6613.2021-2571

Abstract

Abstract:

In order to investigate the phase change of fused iron catalyst during the reduction process and its effect on the performance in high temperature Fischer-Tropsch reaction, the catalyst was characterized by SEM, EDS, BET and in-situ XRD. The performance of Fischer-Tropsch reaction was evaluated in a fixed-bed reactor under 340℃, 2.4MPa, and H₂/CO=3.8, similar to industrial conditions. The effects of different heating processes, hydrogen partial pressure, reduction space velocity and reduction time on the phase structure, crystal size and reduction degree of the fused iron catalysts were analyzed. The results showed that the initial heating rate was quite significant. When the initial heating rate was over 2.4℃/min, reduction rate was too fast, and the α-Fe grains grown and agglomerated rapidly. The influence of hydrogen partial pressure on the reduction degree was not monotonical, and the change trend of reduction degree is the same when it is >70%.α-Fe was more stable at low hydrogen partial pressure, which, under 40%H₂/Ar, increased only by 1nm within 40h. The high reduction space velocity of 10000h^-1 made the catalyst surface pore distribution and pore size more uniform, and the reduction efficiency and limit reduction degree higher. The low reduction space velocity 1000—2000h^-1 gave the reduction catalyst stable surface/bulk structure, more stable crystal size and higher reaction activity. After reduced at 420℃ to the limiting reduction degree, the α-Fe continued to grow slowly with the increase of reduction time. The suitable reduction conditions were obtained as: reduction heating rate in between 0.4℃/min(200—350℃)—0.8℃/min(<200℃), space speed of 5000h^-1, and reduction time less than 30h.

Key words: Fischer-Tropsch synthesis, catalytic, reduction, reaction, stability, reactivity

摘要：

为了探索熔铁催化剂还原过程中物相变化及对高温费托反应性能的影响，采用SEM（扫描电子显微镜）、EDS（X射线能谱仪）、BET和原位XRD（X射线衍射）对催化剂进行了表征。并在类似工业条件（340℃、2.4MPa、H₂/CO比例为3.8）下，于固定床反应器上评价了费托反应性能。分析了不同升温过程、氢气分压、还原空速和还原时间对高温费托熔铁催化剂物相结构、晶粒尺寸、还原度等的影响。结果表明：起始升温速率影响显著，＞2.4℃/min时容易使催化剂局部温度过高进而还原速率过快，导致α-Fe晶粒快速长大并团聚。氢气分压影响还原度有转折点，＞70%时还原度变化趋势相同；对α-Fe晶粒尺寸的影响表现在低氢分压时更稳定，40h内40%H₂/Ar条件仅增加1nm。高还原空速（10000h^-1）使得还原催化剂表面孔道分布、孔径尺寸更均匀，还原效率及极限还原度更高；而低还原空速（1000~2000h^-1）则使得还原催化剂表/体相结构稳定，晶粒尺寸更稳定，费托合成反应活性高。还原时间在其他条件固定下有最佳值，420℃恒温还原到极限还原度后，α-Fe晶粒尺寸随还原时间延长继续缓慢增长。通过研究获得了适宜的还原条件为：还原升温速率0.4℃/min（200~350℃）~0.8℃/min（＜200℃），空速5000h^-1，还原时间＜30h。

关键词: 费托合成, 催化剂, 还原, 反应, 稳定性, 活性

CLC Number:

TQ519

ZHANG Qi, WANG Tao, ZHANG Xuebing, MENG Xiangkun, LYU Yijun, MEN Zhuowu. Effects of reduction conditions on fused iron catalyst for high temperature Fischer-Tropsch synthesis[J]. Chemical Industry and Engineering Progress, 2022, 41(S1): 239-246.

张琪, 王涛, 张雪冰, 孟祥堃, 吕毅军, 门卓武. 还原条件对高温费托合成熔铁催化剂性能的影响[J]. 化工进展, 2022, 41(S1): 239-246.

Figures/Tables 12

References 26

1	WANG Peng, CHEN Wei, CHIANG Fukuo, et al. Synthesis of stable and low-CO₂ selective ε-iron carbide Fischer-Tropsch catalysts[J]. Science Advances, 2018, 4(10).
2	DRY E M. The Fischer-Tropsch process: 1950—2000[J]. Catalysis Today, 2002, 71(3): 227-241.
3	DICTOR A R, BELL T A. Fischer-Tropsch synthesis over reduced and unreduced iron oxide catalysts[J]. Journal of Catalysis, 1986, 97(1): 121-136.
4	陈建刚, 相宏伟, 李永旺, 等. 费托法合成液体燃料关键技术研究进展[J]. 化工学报, 2003(4): 101-108.
	CHEN Jiangang, XIANG Hongwei, LI Yongwang, et al. Advance in key techniques of Fischer-Tropsch synthesis for liquid fuel production[J]. CIESC Journal, 2003(4): 101-108.
5	韩小雪, 陈妍希, 赵俏, 等. 碳限域铁基费托合成催化剂研究进展[J].化工进展, 2021, 40(4): 1917-1927.
	HAN Xiaoxue, CHEN Yanxi, ZHAO Qiao, et al. Advance in carbon-confined iron-based catalysts for Fischer-Tropsch catalysts[J]. Chemical Industry and engineering progress, 2021, 40(4): 1917-1927.
6	SANTOS P V, WEZENDONK A T, JAENJUAN J D, et al. Metal organic framework-mediated synthesis of highly active and stable Fischer-Tropsch catalysts[J]. Nature Communications, 2015, 6: 6451.
7	SMIT De E, WECKHUYSEN M B. The renaissance of iron-based Fischer-Tropsch synthesis: on the multifaceted catalyst deactivation behaviour[J]. Chemical Society Reviews, 2008, 37: 2758-2781.
8	NIELSEN R M, MOSS B A, BJORNLUND A S, et al. Reduction and carburization of iron oxides for Fischer-Tropsch synthesis[J]. Journal of Energy Chemistry, 2020, 51(12): 48-61.
9	刘化章. 氨合成催化剂: 实践与理论[M]. 北京: 化学工业出版社, 2007.
	LIU Huazhang. Ammonia synthesis catalysts[M]. Beijing: Chemical Industry Press, 2007.
10	郑遗凡, 刘化章, 李小年. 熔铁催化剂还原过程的原位XRD研究及活性相的形成机理[J]. 高等学校化学学报, 2009, 30(6): 1177-1182.
	ZHENG Yifan, LIU Huazhang, LI Xiaonian. In situ X-ray diffraction investigation on reduction process of ammonia-synthesis fused-iron catalysts and the formation mechanism of its active phase[J]. Chemical Journal of Chinese Universities, 2009, 30(6): 1177-1182.
11	杨霞珍, 张红, 霍超, 等. Fe-M(M=V、Cr、Mn)熔铁催化剂的费-托合成反应性能研究[J]. 高校化学工程学报, 2018, 32(6): 1359-1364.
	YANG Xiazhen, ZHANG Hong, HUO Chao, et al. Application of fused iron catalysts Fe-M (M=V, Cr, Mn) in Fischer-Tropsch synthesis[J]. Journal of Chemical Engineering of Chinese Universities, 2018, 32(6): 1359-1364.
12	CHENG K, ORDOMSKY V V, VIRGINIE M, et al. Support effects in high temperature Fischer-Tropsch synthesis on iron catalysts[J]. Applied Catalysis A General, 2014, 488: 66-77.
13	ADELEKE A A, GNANAMANIM K. Alumina-supported iron catalyst-long-term study of the light product distribution in Fischer-Tropsch synthesis[J]. Materials Today Chemistry, 2021, 21: 100490.
14	ZHANG Juan, ABBAS Mohamed, CHEN Jiangang. The evolution of Fe phases of a fused iron catalyst during reduction and Fischer-Tropsch synthesis[J]. Catalysis Science & Technology, 2017, 7(16): 3626-3636.
15	刘化章, 李小年. 氨合成催化剂母体相组成对还原性能的影响[J]. 化工学报, 1997, 48(3): 354-362.
	LIU Huazhang, LI Xiaonian. Effect of precursor phase composition of ammonia synthesis catalyst on reduction performance[J]. CIESC Journal, 1997, 48(3): 354-362.
16	LI Senzi, LI Anwu, KRISHNAMOORTHY Sundaram, et al. Effects of Zn, Cu, and K promoters on the structure and on the reduction, carburization, and catalytic behavior of iron-based Fischer-Tropsch synthesis catalysts[J]. Catalysis Letters, 2001, 77(4): 197-205.
17	HAO Qinglan, LIU Fuxia, WANG Hong, et al. Effect of reduction temperature on a spray-dried iron-based catalyst for slurry Fischer-Tropsch synthesis[J]. Journal of Molecular Catalysis A: Chemical, 2007, 261(1): 104-111.
18	SMIT De E, CINQUINI F, ANDREW M B, et al. Stability and reactivity of ε-χ-θ iron carbide catalyst phases in Fischer-Tropsch synthesis: controlling μ(C)[J]. Journal of the American Chemical Society, 2010, 132(42): 14928-14941.
19	龙永强, 刘平, 刘勇, 等. 相场法模拟球形和盘形第二相粒子对晶粒长大的影响[J]. 中国有色金属学报, 2009, 19(1): 84-89.
	LONG Yongqiang, LIU Ping, LIU Yong, et al. Phase field modeling for effects of spherical and discal second-phase particles on grain growth[J]. Chinese Journal of Nonferrous Metals, 2009, 19(1): 84-89.
20	ZHU Wenhui, WINTERSTEIN P J, YANG D W, et al. In situ atomic-scale probing of the reduction dynamics of two-dimensional Fe₂O₃ nanostructures[J]. Acs Nano, 2017,11: 656-664.
21	KARIMI A, POUR A N, TORABI F, et al. Fischer-Tropsch synthesis over ruthenium-promoted Co/Al₂O₃ catalyst with different reduction procedures[J]. Journal of Natural Gas Chemistry, 2010, 19(5): 503-508.
22	STEEN V E, PRINSLOO F F. Comparison of preparation methods for carbon nanotubes supported iron Fischer-Tropsch catalysts[J]. Catalysis Today, 2002, 71(3-4): 327-334.
23	DICTOR A R, BELL T A. Studies of Fischer-Tropsch synthesis over a fused iron catalyst[J]. Applied Catalysis, 1986, 20(1-2): 145-162.
24	李小年, 傅冠平, 刘化章. 助催化剂对Fe_1- _x O基氨合成催化剂活性的影响[J]. 催化学报, 1998, 19(1): 24-28.
	LI Xiaonian, FU Guanping, LIU Huazhang, et al. The effect of promoters on reduction performance of Fe_1- _x O based ammonia synthesis catalyst[J]. Chinese Journal of Catalysis, 1998, 19(1): 24-28.
25	ZHANG Juan, SUN Taomei, DING Jian, et al. Influences of melting method on fused iron catalysts for Fischer-Tropsch synthesis[J]. RSC Advances, 2016, 6(65): 1-16.
26	DUAN Xuezhi, WANG Di, QIAN Gang, et al. Fabrication of K-promoted iron/carbon nanotubes composite catalysts for the Fischer-Tropsch synthesis of lower olefins[J]. Journal of Energy Chemistry, 2016, 25(2): 311-317.

织构参数	还原前	1000h^-1	2000h^-1	5000h^-1	10000h^-1
比表面积/m²·g^-1	1.3	15.7	15.3	20.1	16.3
孔容/cm³·g^-1	0.008	0.107	0.108	0.114	0.107
平均孔径/nm	3.157	20.232	20.569	18.258	20.117

织构参数	还原前	1000h^-1	2000h^-1	5000h^-1	10000h^-1
比表面积/m²·g^-1	1.3	15.7	15.3	20.1	16.3
孔容/cm³·g^-1	0.008	0.107	0.108	0.114	0.107
平均孔径/nm	3.157	20.232	20.569	18.258	20.117

元素分布	还原前	1000h^-1	2000h^-1	5000h^-1	10000h^-1
m(Al)/m(Fe)	0.020	0.012	0.016	0.023	0.007
m(K)/m(Fe)	0.010	0.010	0.007	0.006	0.005
还原度/%	0	75.15	85.83	93.82	96.24

元素分布	还原前	1000h^-1	2000h^-1	5000h^-1	10000h^-1
m(Al)/m(Fe)	0.020	0.012	0.016	0.023	0.007
m(K)/m(Fe)	0.010	0.010	0.007	0.006	0.005
还原度/%	0	75.15	85.83	93.82	96.24

项目	1000h^-1	2000h^-1	5000h^-1	10000h^-1
X（CO）/%	92.8	92.7	90.5	91.4
CH₄（摩尔分数）/%	34.1	37.4	32.5	27.3
C₂~C₄（摩尔分数）/%	42.3	44.8	45.3	42.0
C₅₊（摩尔分数）/%	23.6	17.8	22.2	30.7
C₂~C₄烯/烷比	0.4	1.4	1.1	1.4