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）通过基于 Fe 或 Co 的非均相催化剂转化为高级烃。在所谓的低温 FTS（T < 250 °C）中，到目前为止，人们普遍认为催化剂的孔在反应初始阶段的几天内就完全充满了液体反应产物（蜡），这导致了不希望的但不可避免的下降。最重要的是，如果使用 mm 颗粒作为技术固定床反应器（压降），则可以提高孔隙效率因子，并获得较低的活性和较高的甲烷选择性。在 DFG 项目的过程中，这将于 2020 年秋季完成，我们可以表明催化剂（钴）的孔隙并不总是完全填充，填充时间甚至可能持续几个月，最重要的是，如果链增长概率很高（> 0.9）。过程取决于 H2/CO 比率、压力和温度。所有实验均在磁悬浮天平中使用单个催化剂颗粒进行。在所申请的新研究项目（申请继续资助）内，应继续该研究并转移到。此外，基于实验和理论研究（建模），应研究一种基于 FTS 孔隙填充和氢解孔隙排水的有前途的新型瞬态过程，应回答以下两个主要问题： 1。 ）固定床反应器中CO转化率和气相组成的局部（轴向）差异是否对FTS初始阶段的局部孔隙填充程度有影响，这如何影响催化剂的有效活性和选择性（此处基于钴）？ 2) 固定床反应器的瞬态操作，即从孔隙填充 (FTS) 到孔隙排水（在不含 CO 的原料气的情况下进行氢解）的定期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？旨在进行以下检查： 固定床反应器的颗粒部分/完全填充有不同程度的 CO 转化率（高达 40%）的高级烃。一定时间后停止，对不同轴向位置的颗粒进行采样和分析（即填充程度、孔内液相的组成），进行氢解实验将获得快速反应的最佳反应条件。孔隙排水过程也应通过固定床反应器（强制流）的磁悬浮液中的原位测量直接研究，以及 FT 固定床反应器中高级烃的积累。应根据所提出的瞬态过程的优化对交替瞬态过程（孔隙的填充/排水）进行建模。