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Quantitative comparison of iron and cobalt based catalysts for the Fischer-Tropsch synthesis under clean and poisoning conditions
Catalysis Today ( IF 5.3 ) Pub Date : 2019-04-07 , DOI: 10.1016/j.cattod.2019.04.011
Wenping Ma , Gary Jacobs , Dennis E. Sparks , Branislav Todic , Dragomir B. Bukur , Burtron H. Davis

Quantitative data comparing iron and cobalt based catalysts for the Fischer-Tropsch synthesis (FTS) are scarce due to the fact that these two kinds of catalysts typically utilize different process conditions. This paper focuses on studying the catalytic behavior of two highly active iron and cobalt based research catalysts at clean conditions and during poisoning with common syngas contaminants. The catalyst activity and selectivity at identical conditions, the CO conversion effect, and the effect of poisons on iron and cobalt catalysts were systematically explored in a quantitative manner. At a set of identical FTS conditions, the cobalt catalyst was 2.5 times as active as the iron catalyst with higher CH4 and C5+ selectivities but much less olefins and lower CO2 selectivity. Cobalt based catalysts are more susceptible to deactivation by oxidation at high CO conversions (e.g. > 80%) due to the high partial pressure of water (PH2O) in the reactor, while the iron catalyst can be stabilized at a high conversion level. Under clean FTS conditions, the cobalt catalysts displayed a more pronounced CO conversion effect on stability and selectivity; on the other hand, a combination of effects (i.e. from CO conversion and the nature of the catalyst) were observed for the iron catalysts. The sensitivities of the Fe and Co catalysts to the typical contaminants (i.e., H2S and NH3) present in the syngas derived from coal, natural gas or biomass were compared. Iron and cobalt catalysts exhibited similar resistance to the H2S poison (i.e. threshold levels 25–50 ppb), but the iron catalyst was found to be much more resistant to ammonia than the cobalt catalyst (i.e., threshold levels of 80 ppm and 45 ppb, respectively). Co-feeding 150–200 ppm ammonia lowered CH4 selectivity and 2-olefin content (suppressing secondary reactions of 1-olefin) on both types of catalysts. In contrast, co-feeding up to 1 ppm H2S significantly increased CH4 formation only on cobalt catalysts but had a minor effect on CH4 selectivity with iron catalysts. It increased 2-olefin content (enhanced secondary reactions of 1-olefin) regardless of catalyst type. H2S and NH3 have different impacts on H2, CO adsorption, and the formation of sulfur and nitride compounds have been proposed to explain these dissimilar effects.



中文翻译:

清洁和中毒条件下费托合成中铁和钴基催化剂的定量比较

由于这两种催化剂通常利用不同的工艺条件,因此比较用于费-托合成(FTS)的铁和钴基催化剂的定量数据很少。本文着重研究两种高活性铁和钴基研究催化剂在清洁条件下以及在常见合成气污染物中毒过程中的催化行为。在定量条件下,系统地研究了在相同条件下的催化剂活性和选择性,CO转化率以及毒物对铁和钴催化剂的影响。在相同的FTS条件下,钴催化剂的活性是铁催化剂的2.5倍,具有更高的CH 4和C 5 +选择性,但烯烃少得多,CO 2少选择性。钴基催化剂由于反应器中水的高分压(P H2O),在高CO转化率(例如> 80%)下更容易因氧化而失活,而铁催化剂则可以稳定在高转化率水平。在清洁的FTS条件下,钴催化剂对稳定性和选择性表现出更明显的CO转化效应。另一方面,对于铁催化剂,观察到了多种效果的组合(即,来自CO转化率和催化剂的性质)。比较了Fe和Co催化剂对源自煤,天然气或生物质的合成气中存在的典型污染物(即H 2 S和NH 3)的敏感性。铁和钴催化剂对H的抵抗力相似2 S毒气(即阈值水平25–50 ppb),但是发现铁催化剂比钴催化剂对氨的耐受性高得多(即,阈值水平分别为80 ppm和45 ppb)。在两种类型的催化剂上共同进料150-200 ppm的氨会降低CH 4的选择性和2-烯烃的含量(抑制1-烯烃的二次反应)。相反,共同进料至1 ppm H 2 S仅在钴催化剂上显着增加了CH 4的形成,但对铁催化剂对CH 4选择性的影响较小。无论催化剂类型如何,它都会增加2-烯烃含量(增强的1-烯烃二次反应)。H 2 S和NH 3对H 2的影响不同已经提出了CO,CO的吸附以及硫和氮化物化合物的形成来解释这些不同的影响。

更新日期:2020-03-12
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