A multi-scale approach to process development: laboratory to pilot scaling of methanol synthesis from CO$_{2}$-rich synthesis gas with promoted carrier catalysts

RWTH Publications (RWTH Aachen)

Abstract

Methanol (MeOH) is set to become a major player in the defossilization of heavily carbon-reliant industries such as the chemistry sector and hard-to-abate parts of the transportation sectors. This can mostly be attributed to the fact, that it can be readily produced from different regenerative sources through adaptation of existing fossil resources based synthesis gas (SynGas) processes. However, many of the renewable sources that MeOHcan be produced from are prone to yield carbon dioxide (CO2)-rich SynGas process streams for further conversion to MeOH, which current commercial catalysts are not always well equipped for.In this context, some development has to be done to improve current copper oxide (CuO)/zinc oxide(ZnO)/aluminum oxide (Al2O3) (CZA) formulas by promoting the catalyst with metal oxides that provide more stable CO2 adsorption and deliver greater operational resilience against water (H2O) co-produced inMeOH synthesis based upon CO2-rich SynGas streams. Building on this, the present thesis addresses the extent to which the targeted addition of promoters to impregnated, CZA-based catalysts can enhance carbon conversion compared to commercial reference systems. Furthermore, it investigates how such improvements in CO2 conversion can be explained from a physio-chemical perspective, and how the synthesized catalysts perform in a multiscale context, scaling from laboratory to pilot scale, thereby assessing the transferability of laboratory findings to pilot-scale operation. A series of catalyst formulas was developed by promoting the popular CZA-complex with different promising catalyst additives. Differently promoted and chemically activated catalyst samples were produced through incipient wetness impregnation (IWI) of gamma alumina(γ-Al2O3) carrier spheres. Herein, a quinary formula was identified that promises to show good conversion ofCO2 to, and high selectivity for, MeOH. Based upon this quinary catalyst formulation, a further small batch of differently promoted catalyst samples was developed – each adding different metal oxides in promotional steps towards the quinary catalyst formulation containing 20% CuO, ZnO, CeO2, ZrO2, and CaO on a γ-Al2O3carrier.The produced samples underwent extensive physio-chemical characterization, catalyst testing, and deployment in a pilot-scale setup. The respective results are presented in three different contributions to international journals. The samples are characterized extensively by applying scanning electron microscopy (SEM), transmission electron microscopy (TEM) , nitrogen (N2)-adsorption and -desorption experiments with Brunauer-Emmett-Teller (BET) analysis, X-ray diffraction (XRD) spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), hydrogen (H2) temperature-programmed reduction and desorption, CO2 temperature programmed desorption and ammonia (NH3) temperature-programmed desorption. The catalysts all exhibited large mesoporous surface structures, very high specific surface areas, good metal oxide dispersion on the supports, and high loading-specific reducibility. The hydrogen uptake capacity was lower compared to the reference precipitated catalyst. However, this did not play an essential role relative to the measured conversions. In contrast, a clear positive correlation between the CO2 uptake capacity and the carbon conversion was observed. In a laboratory reactor setup, the samples were tested for their conversion efficiencies in both CO2-only SynGas streams as well as mixed carbon oxide SynGas streams extensively, which are more common in regenerative synthesis gas applications, even when using pure CO2 as carbon source. Reaction equilibria of CO2 and CO towards MeOH and water (H2O) were determined for investigation of industrially relevant SynGas compositions and their influence on catalyst conversion performance. Based upon these studies and the previously obtained, extensive performance data set a series of kinetic studies was applied. Through this a simple, robust kinetic model with good numerical fit was developed for all four promotional steps of the catalyst samples, which is able to accurately predict the reaction pathways of CO andCO2 on the catalyst surfaces as well as predicting catalyst performance in industrial process setups. For transfer of the laboratory test results to pilot and demonstration scale application and in addition to catalystdevelopment, this thesis also focuses on the design and realization of a renewable process for MeOH synthesisfrom biogas. In this process, biogas is first autothermally reformed to produce a CO2-rich SynGas, which is then catalytically converted to raw MeOH in isothermal reactors. The high CO2 content of the reformed gas poses a significant challenge for MeOH synthesis over commercially available catalysts, as it limits conversion and selectivity under standard operating conditions. Therefore, the CuO/ZnO-based catalysts developed and optimized in the laboratory, promoted with CeO2, ZrO2, and CaO, were scaled up to pilot format and implemented in the dedicated demonstration plant. This pilot-scale facility was designed, constructed, and commissioned to reform biogas into CO2-richsynthesis gas and subsequently convert it catalytically into raw MeOH. The pilot operation was carried out at the wastewater treatment plant in Dinslaken, Germany, using digester gas as a renewable feedstock under mild pressures and realistic operating conditions. The study focused on the influence of different synthesis gas compositions and reaction temperatures on the production performance and efficiency of the prototype catalyst, as well as on the assessment of operational factors relevant for future industrial-scale implementation of the biogas-to-methanol (B2M) process. This thesis thus represents the complete development chain in heterogeneous catalysis, demonstrating the importance of multi-scale methods in modern process design and providing the scientific foundation for the economic and sustainable integration of MeOH synthesis from biogas into a renewable carbon economy based on efficient supported catalysts.

Authors 1

1. Friedrich Carl Fritsch corresponding Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen