Accumulation of liquid hydrocarbons during Fischer-Tropsch fixed-bed synthesis and process optimization based on periodical pore filling and pore draining

费托固定床合成过程中液态烃的积累及基于周期性孔隙充排的工艺优化

• 批准号: 318313257
• 负责人: Professor Dr.-Ing. Andreas Jess
• 金额: --
• 依托单位: Lehrstuhl für Chemische Verfahrenstechnik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/318313257?language=en
• 关键词: Accumulation; liquid; hydrocarbons; during; Fischer

In Fischer-Tropsch synthesis (FTS), syngas (CO and H2) is converted to higher hydrocarbons over heterogeneous catalysts based on Fe or Co. In case of the so-called low-temperature FTS (T < 250 °C), it was until now generally assumed that the pores of the catalyst are completely filled with liquid reaction products (wax) within a couple of days in the initial phase of the reaction. This leads to an unwanted but unavoidable decrease of the pore effectiveness factor and in return to a lower activity and a higher selectivity to methane, above all, if mm particle are used as in case of technical fixed-bed reactors (pressure drop).In the course of a DFG-project, which will be completed in autumn 2020, we could show that the pores of the catalyst (cobalt) are not always completely filled and the filling time may even last several months, above all, if the chain growth probability is high (> 0.9). The filling process depends on the H2/CO-ratio, pressure and temperature. All experiments were conducted with single catalyst particles in a magnetic suspension balance.Within the applied new research project (application for continuation of funding), this research should be continued and transfered to FTS in a fixed bed reactor. In addition, a promising new transient process based on pore filling by FTS and pore draining by hydrogenolysis should be investigated. Based on experimental and theoretical studies (modelling), the following two main questions should be answered: 1) Do local (axial) differences in CO conversion and gas phase composition, respectively, in a fixed bed reactor have an influence on the local pore filling degree during the initial phase of FTS, and how does this affect the effective activity and selectivity of the catalyst (here based on cobalt)? 2) Does a transient operation of a fixed-.bed reactor, i.e. a periodical switch from pore filling (FTS) to pore draining (hydrogenoloysis in case of a feedgas without CO) lead to a higher mean reaction rate and a higher rate of formation of liquid hydrocarbons?The following examinations are intended: The particles of a fixed-bed reactor are partly/completely filled with higher hydrocarbons at different degrees of CO conversion (up to 40%). The FTS is stopped after a certain time, and particles at different axial positions are sampled and analyzed (i.e. filling degree, composition of liquid phase in the pores). Experiments on the hydrogenolysis will gain the best reaction conditions with regard to a rapid pore draining process. The rate of pore filling should also be investigated directly by in situ measurements in a magnetic suspension balance with a fixed-bed reactor (forced flow). Finally, the accumulation of higher hydrocarbons in the FT fixed-bed reactor as well as the alternating transient process (filling/draining of pores) should be modelled with regard to an optimization of the proposed transient process.

在费托合成（FTS）中，合成气（CO和H2）在基于Fe或Co的非均相催化剂上转化为高级烃。在所谓的低温FTS（T < 250 °C）的情况下，直到现在通常认为催化剂的孔在反应的初始阶段在几天内被液体反应产物（蜡）完全填充。这导致不希望的但不可避免的孔效率因子的降低，并且返回到较低的活性和对甲烷的较高选择性，尤其是如果如在工业固定床反应器的情况下使用mm颗粒在将于2020年秋季完成的DFG项目的过程中，我们可以表明，催化剂（钴）的孔并不总是完全填充，并且填充时间甚至可能持续几个月，尤其是如果链增长概率高（> 0.9）的话。填充过程取决于H2/CO比、压力和温度。所有的实验都是在磁悬浮天平中用单个催化剂颗粒进行的。在应用新研究项目（申请继续资助）中，这项研究应该继续并转移到固定床反应器中的FTS。此外，一个有前途的新的瞬态过程的基础上的孔隙填充FTS和孔隙排水氢解应进行研究。 根据实验和理论研究（建模），应回答以下两个主要问题： 1)在固定床反应器中，CO转化率和气相组成的局部（轴向）差异是否分别对FTS初始阶段的局部孔隙填充度产生影响，以及这如何影响催化剂（此处基于钴）的有效活性和选择性？2)固定床反应器的瞬时操作，即从孔隙填充（FTS）到孔隙排出（在不含CO的原料气的情况下进行氢解）的周期性切换，是否会导致更高的平均反应速率和更高的液态烃形成速率？下面的检查是打算：固定床反应器的颗粒部分/完全填充有高级烃在不同程度的CO转化率（高达40%）。在一定时间后停止FTS，并且对不同轴向位置处的颗粒进行取样和分析（即，填充度、孔中液相的组成）。氢解实验将获得快速排孔过程的最佳反应条件。孔隙填充率也应该直接通过在带有固定床反应器（强制流动）的磁悬浮天平中进行原位测量来研究。最后，FT固定床反应器中的高级烃的积累以及交替的瞬态过程（孔隙的填充/排出）应针对所提出的瞬态过程的优化进行建模。