碳热还原SO_2反应选择性的热力学分析及实验探究
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摘要
针对燃煤烟气SO_2脱除技术面临的可持续发展困境,以固体碳材料为还原剂的碳热SO_2还原制硫磺技术具有重要发展前景,其中抑制非目标副产物的伴生是实现SO_2定向还原的关键。基于吉布斯自由能最小原理对碳热还原SO_2反应进行平衡产物量的计算,并通过固定床-FTIR实验分析反应的气相产物,探究了硫产率、副产物CO、COS和CS_2的生成规律。基于温度对反应热力学平衡的影响,结合副反应,来推断出合理的反应机理。在摩尔比n(C)∶n(SO_2)≤1.0时体系中主要发生反应C+SO_2→S+CO_2,副产物CS_2生成量级仅为10~(-4),理论硫产率可维持在0.9以上。过量的碳会促进COS由主反应物一步生成,高温、碳过量会促进COS向CS_2的转化反应。相关研究结果对实际应用时最佳工况的选取以及单质硫选择性的提高具有重要指导意义。
In view of the sustainable development predicament faced by SO_2 removal technology from coal-fired flue gas, the technology of preparing sulfur through the Carbothermal reduction of SO_2 with solid carbon materials as reducing agenthas an important prospect.And the inhibition of the by-products is the key to realize SO_2 directional reduction. Based on the principle of minimum Gibbs free energy, the equilibrium product of the carbon thermal reduction of SO_2 was calculated, and the gaseous products of the reaction was analyzed by fixed bed-FTIR experiment to explore the sulfur yield and the law of CO, COS and CS_2 formation. Based on the effect of temperature on the thermodynamic equilibrium, a reasonable reaction mechanism was deduced, combined with the side reactions proposed by previous researchers. The reaction of C+SO_2→S+CO_2 mainly took place at n(C)∶n(SO_2)≤1.0, the magnitude of the by product CS_2 was only 10~(-4) mol, and the theoretical sulfur yield was above 0.9. Excess carbon would promote COS generated by the main reactants in one step, and high temperature and carbon excess would promote the conversion reaction of COS to CS_2. The results are of important to the selection of the best working conditions and the improvement of the elemental sulfur′s selectivity.
In view of the sustainable development predicament faced by SO_2 removal technology from coal-fired flue gas, the technology of preparing sulfur through the Carbothermal reduction of SO_2 with solid carbon materials as reducing agenthas an important prospect.And the inhibition of the by-products is the key to realize SO_2 directional reduction. Based on the principle of minimum Gibbs free energy, the equilibrium product of the carbon thermal reduction of SO_2 was calculated, and the gaseous products of the reaction was analyzed by fixed bed-FTIR experiment to explore the sulfur yield and the law of CO, COS and CS_2 formation. Based on the effect of temperature on the thermodynamic equilibrium, a reasonable reaction mechanism was deduced, combined with the side reactions proposed by previous researchers. The reaction of C+SO_2→S+CO_2 mainly took place at n(C)∶n(SO_2)≤1.0, the magnitude of the by product CS_2 was only 10~(-4) mol, and the theoretical sulfur yield was above 0.9. Excess carbon would promote COS generated by the main reactants in one step, and high temperature and carbon excess would promote the conversion reaction of COS to CS_2. The results are of important to the selection of the best working conditions and the improvement of the elemental sulfur′s selectivity.
引文
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[16] 王树森, 凌爱莲. SO2还原为元素硫的条件研究[J]. 北京工业大学学报, 1992, 18(1):56-61. WANG Shu-sen, LING Ai-lian. Studies of experiment conditions on reduction of SO2 to elemental sulfur [J]. Journal of Beijing Polytechnic University, 1992, 18(1):56-61.
[17] PANAGIOTIDIS T, RICHTER E, JüNTGEN H. Structural changes of an anthracite char during the reaction with sulphur dioxide [J]. Carbon, 1988, 26(1):89-95.
[18] BLACKWOOD J D, McCARTHY D J. The kinetically effective stoichiometry of reactions in the carbon-sulphur dioxide system [J]. Australian Journal of Chemistry, 1973, 26(4):723-731.
[2] 梁勇,马智,潘志爽. 催化还原烟气中SO2到单质硫的研究进展[J]. 工业催化, 2007, 15(5) 55-59. LIANG Yong, MA Zhi, PAN Zhi-shuang. Researches in catalytic reduction of sulfur dioxide in flue gas to elemental sulfur [J]. Industrial Catalysis, 2007, 15(5) 55-59. (in Chinese)
[3] HUMERES E, MOREIRA R F P M, MARIA DA GLORIA B P. Reduction of SO2 on different carbons [J]. Carbon, 2002, 40(5):751-760.
[4] HUMERES E, PERUCH M G B, MOREIRA R F P M, et al. Reduction of sulfur dioxide on carbons catalyzed by salts [J]. International Journal of Molecular Sciences, 2005, 6(1):130-142.
[5] KLINZING G E, WALKER R J. Equilibrium studies of the direct reduction of sulphur dioxide by coal [J]. Fuel, 1984, 63(10):1450-1454.
[6] MORRIS E A, CHOI R, JIA C Q. Sulfur dioxide as an activating agent for sulfur-impregnated activated carbon produced from dense petroleum coke [J]. Journal of Sulfur Chemistry, 2013, 34(4):358-369.
[7] ABIáN M, MILLERA A, BILBAO R, et al. Interaction of soot — SO2: experimental and kinetic analysis [J]. Combustion Science and Technology, 2016, 188(4-5):482-491.
[8] HUMERES E, MOREIRA R D F P M. Kinetics and mechanisms in flow systems:reduction of SO2 on carbons [J]. Journal of Physical Organic Chemistry, 2012, 25(11):1012-1026.
[9] ABRAMOWITZ H, INSINGA R, RAO Y K. Kinetics of reaction of sulfur dioxide with carbon [J]. Carbon, 1976, 14(1):84-86.
[10] AND W F, JIA C Q. Influence of O2 and H2O on carbothermal reduction of SO2 by oil-sand fluid coke [J]. Environmental Science & Technology, 2005, 39(24):9710-4.
[11] MORRIS E A, JIA C Q, MORITA K. Effects of O2 on Characteristics of sulfur added to petroleum coke through reaction with SO2 [J]. Industrial & Engineering Chemistry Research, 2015, 49(24):12709-12717.
[12] 王智化,李谦,刘敬,等. 准东煤中碱金属的赋存形态及其在热解过程中的迁移规律[J]. 中国电机工程学报, 2014, 34(s1):130-135. WANG Zhi-hua, LI Qian, LIU Jing, et al. Occurrence of alkali metals in zhundong coal and its migration during pyrolysis process [J]. Proceedings of the CSEE, 2014, 34(s1):130-135. (in Chinese)
[13] LI K, LING L, LU C, et al. Catalytic removal of SO2, over ammonia-activated carbon fibers [J]. Carbon, 2001, 39(12):1803-1808.
[14] 王翠苹,巩建,姜旭. 基于HSC计算的煤焦油化学链热裂解反应优化[J]. 热科学与技术, 2016, 15(6):480-485. WANG Cui-ping, GONG Jian, JIANG Xu. Optimization of chemical looping reaction for thermal cracking of coal tar based on HSC calculation [J]. Journal of Thermal Science and Technology, 2016, 15(6):480-485. (in Chinese)
[15] JENKINS, BROOKE H D. Le Chatelier′s Principle [M]. Oxford OX4 2DQ, UK: Blackwell Publishing Ltd, 2008:160-163.
[16] 王树森, 凌爱莲. SO2还原为元素硫的条件研究[J]. 北京工业大学学报, 1992, 18(1):56-61. WANG Shu-sen, LING Ai-lian. Studies of experiment conditions on reduction of SO2 to elemental sulfur [J]. Journal of Beijing Polytechnic University, 1992, 18(1):56-61.
[17] PANAGIOTIDIS T, RICHTER E, JüNTGEN H. Structural changes of an anthracite char during the reaction with sulphur dioxide [J]. Carbon, 1988, 26(1):89-95.
[18] BLACKWOOD J D, McCARTHY D J. The kinetically effective stoichiometry of reactions in the carbon-sulphur dioxide system [J]. Australian Journal of Chemistry, 1973, 26(4):723-731.
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