合成气一步法制烯烃“积炭环”形成原因分析  

Formation of"carbon deposited rings"during direct conversion of syngas to olefins

作　　者：尚蕴山 冯波 袁德林 刘华 张凡 邢爱华 SHANG Yun-shan;FENG Bo;YUAN De-lin;LIU Hua;ZHANG Fan;XING Ai-hua(National Institute of Low Carbon and Clean Energy,Beijing 102209,China)

机构地区：[1]北京低碳清洁能源研究院,北京102209

出　　处：《天然气化工—C1化学与化工》2021年第1期50-54,共5页Natural Gas Chemical Industry

摘　　要：针对合成气一步法制烯烃反应过程中催化剂床层上部产生的"积炭环"现象,结合积炭层沉积物EDS元素分析与XRD分析、空管条件下CO转化率与产物选择性分析探究了"积炭环"形成原因。积炭层沉积物元素分析表明,实验条件下,沉积物主要含Fe、C;XRD分析显示,该"积炭环"区域的Fe元素主要以Fe3O4和Fe5C2形式存在,其基本形成过程为:久置钢瓶存储合成气中CO与钢瓶壁的铁反应生成羰基铁,反应过程中羰基铁随着合成气进入反应管,在593~603 K区域分解形成氧化铁,其部分碳化形成碳化铁,这些含铁物质催化合成气发生积炭和歧化反应形成积炭。空白反应结果显示,上述铁物种催化合成气反应生成CO2、CH4、C2~C4等轻质烃类。对比ZnCr2O4反应前/后XRF表征结果显示,Fe浓度并未增加,表明羰基铁在到达催化剂床层之前已彻底分解。通过增加活性炭吸附罐可脱除钢瓶合成气中的羰基铁等杂质,避免了"积炭环"的生成。Aiming at the phenomenon of"carbon deposition ring"in the upper part of catalyst bed in the process of one-step synthesis of olefins from syngas,the formation reason of"carbon deposition ring"was explored by combining EDS element analysis with XRD analysis and CO conversion and product selectivity analysis under empty tube conditions.EDS results showed that the deposit mainly contained Fe and C under the experimental conditions.XRD results indicated that the Fe element in the"carbon deposition ring"area mainly existed in the form of Fe3O4 and Fe5C2,and its basic formation process was as follows:CO in the syngas stored in steel cylinder for a long-time reacted with iron in the cylinder wall to form carbonyl iron,which entered the reaction tube with the syngas during the reaction,then was decomposed to form iron oxide in the temperature range of 593-603 K.Partial iron oxide specie was carbonized to form iron carbide.These iron containing species catalyzed the carbon deposition and disproportionation reactions of syngas to produce carbon deposition.The blank reaction results indicated that the formed iron species catalyzed the syngas reaction to produce CO2,CH4 and C2-C4 light hydrocarbons.Comparing the XRF results of fresh and used ZnCr2O4,the Fe concentration did not increase,indicating that the carbonyl iron was completely decomposed before reaching the catalyst bed.By equipping an activated carbon adsorption tank,the carbonyl iron and other impurities in the cylinder syngas could be removed,and the formation of"carbon deposition ring"could be avoided.

关 键 词：合成气 一步法制烯烃 羰基铁 积炭 

分 类 号：TQ241[化学工程—有机化工] O643.36[理学—物理化学]