液化残渣气化过程钠/铁协同催化作用及对焦结构演化的影响规律

Synergistic catalytic behaviors of sodium/iron during gasification of direct coal liquefaction residue and its effects on evolution of coal char

高钠煤直接液化后碱金属钠富集于液化残渣中,相比原煤,残渣的钠含量升高4~10倍,利用残渣固有钠及残留的铁基液化催化剂对液化残渣进行催化气化提质,是其资源化高效利用的理想方案。通过煤直接液化实验制取了钠含量较高的高碱液化残渣,研究了高碱液化残渣在气化过程中钠/铁协同催化的反应性,并建立适宜的动力学模型,考察了协同催化反应的动力学过程。围绕钠/铁间高温相互作用规律,通过联合FTIR,XRD,ICP-AES等技术,详细分析了气化焦有机结构、矿物质组成及钠高温释放率等。结果表明:钠/铁协同催化过程的活化能为66 kJ/mol~69 kJ/mol,与高碱液化残渣单独气化相比均有所降低,残渣最高气化反应性指数超过0.45°/min,相同温度下液化残渣最大反应速率分别增大了1.17倍(900℃)、1.33倍(1000℃)和1.14倍(1100℃);双金属间表现出明显的协同催化效应,n(Na)/n(Fe)对液化残渣气化反应性有一定影响,铁含量较高时易形成弱催化活性的铁/碱金属化合物K-Fe,Na-Fe和Li-Fe等,从而降低协同催化活性,且气化温度升高有利于强化铁与碱金属间结合作用;XRD分析同样证实,适量的铁基催化剂能够阻止钠与Si,Al反应生成无催化活性的矿物质,更好维持钠催化活性;钠/铁除具有协同催化效应外,含铁矿物对气化过程钠的高温释放过程还有显著抑制作用,相比高碱液化残渣单独气化,添加铁基催化剂后钠挥发量减少了9.6%~26.7%。

After the direct coal liquefaction process,sodium species become enriched in the direct coal liquefaction residue(DCLR).The sodium content in the DCLR further increases by 4-10 times compared to the raw coal.A promising strategy to efficiently utilize sodium-rich DCLR is to gasify it,leveraging the inherent sodium and residual iron-based catalyst.Sodiumrich DCLR was prepared in the experiment of direct coal liquefaction.The synergistic catalytic behaviors of sodium/iron during gasification process of sodium-rich DCLR were investigated and a suitable kinetic model was established to explore migration path of the gas-solid reaction interface.Using a combination of FTIR,XRD,ICP-AES and other techniques,the organic structure,mineral composition,and high-temperature release patterns of sodium species were analyzed meticulously based on the high-temperature interaction between sodium and iron.The results show that the activation energy of the sodium/iron synergistic catalytic process is 66 kJ/mol-69 kJ/mol,lower than that of the gasification process without adding iron-based catalyst.The peak gasification reactivity index surpassed 0.45°/min,and the maximum reaction rate increases by 1.17 times at 900℃,1.33 times at 1000℃,and 1.14 times at 1100℃,respectively,for identical temperature benchmarks.There exists a significant synergistic catalytic effect between bimetallic compounds.The molar ratio of sodium to iron has a certain influence on the gasification reactivity of DCLR.A higher iron content easily leads to the formation of weakly catalytic iron/alkali metal compounds,such as K-Fe,Na-Fe,Li-Fe,etc.,thereby reducing the synergistic catalytic activity.Moreover,the increase in gasification temperature augments the synergistic interaction between iron and alkali metals.XRD analysis also affirms that an appropriate content of iron-based catalysts can inhibit sodium from reacting with Si and Al,preventing the creation of non-catalytic minerals,thereby preserving sodium catalytic activity.Besides the synergistic catalytic effect,iron-containing minerals also have a significant inhibitory effect on the high-temperature release of sodium during the gasification process.Compared with gasification of sodium-rich DCLR,incorporating iron-based catalysts can reduce sodium volatilization by 9.6%-26.7%.