H2 is a key raw material in chemical and petrochemical industries, with further increasing interest as promising energy vector. The water gas shift (WGS) reaction is an industrially relevant reaction, which takes place in large scale plants and represents a key upgrading step allowing to adjust different syngas (CO + H2 ) compositions. The WGS is an exothermic reaction, thermodynamically favored at low temperature, while higher reaction rates are favored at higher temperature, which is why it is currently carried out in 2 steps: i) immediately after the steam reforming reactor (SRr) operating at about 350°C with Cr-rich Fe-based catalysts (HTS); ii) in the subsequent converter at about 220 °C using highly active Cu-based catalysts (LTS). Although on account of its high industrial relevance, the WGS reaction has been widely investigated, in the last years new subjects arose, with an increasing interest for new formulations able to operate in one step at middle temperature (MTS) or to replace the Cr-rich catalysts for HTS step. The former formulations operate at about 300°C with high activity, selectivity and stability with time-on-stream (TOS) reducing capital and operational expenditures (CAPEX and OPEX, respectively). The CO conversion may be increased expanding the PROX step, already present when the application of the H2 stream is low temperature fuel cells. In the second case, the main drawbacks of current Cr-promoted Fe-based HTS catalysts are the toxicity of Cr (VI) ions and the requirement to use high inlet steam flow to avoid the formation of metallic Fe, able to catalyze hydrocarbons formation. Thus, new formulations have to be Cr- and Fe-free and to operate with low steam/dry gas ratios, allowing to work more efficiently in the previous SR step, with catalytic performances better than those of commercial catalysts. In this contribution, the R&D from the laboratory to the pilot plant of new formulations for MTS and HTS applications are presented, to evidence how also widely investigated reactions such as the WGS may offer interesting opportunities of new research lines and applications of both academic and industrial interest. To obtain active catalysts and avoid interferences due to structure dishomogeneity or phase segregation, hydrotalcite-type (HT) anionic clays were selected as catalyst precursors, which are characterized by homogeneous cation distribution and are simple and relatively inexpensive to prepare on laboratory or industrial scale. The catalysts were fully characterized before and after reaction and the activity determined as a function of the reaction parameters, allowing to determine best compositions for each temperature range. Tests performed in a lab-scale pilot plant for more than 450 h of time-on-stream do not evidence any significant deactivation both in MTS and HTS conditions. These novel catalysts have been jointly patented by the University of Bologna and Air Liquide.
Audience Take Away:
- Also in well-known industrial processes there are margins for significant improvements.
- Key role of the literature to design further improvements.
- In MTS economic advantages of one step process, with reduction of capital and operative costs.
- In HTS removal of the main drawbacks of the current commercial catalysts.
- Advantages of the catalyst preparation from hydrotalcite-type precursors.