(173f) Study on the Competitiveness of Homogeneous Molecular Catalysis for the Continuous Valorization of CO2 in Organic Solvents

Study on the competitiveness of homogeneous molecular catalysis for the continuous valorization of CO₂ in organic solvents.

J.-K. Schnoor ^a, Prof. M. A. Liauw ^a

^a ITMC, RWTH Aachen University, Aachen-Germany

Introduction

As part of the Carbon2Chem project [1], the aim of the SynAlk subproject is the production of C₂₊-alcohols from steel mill furnace gases. Their use is important to reduce carbon emissions and close the carbon cycle. So far, heterogeneous catalysts have dominated the field of CO₂ utilization and are well established in many large scale chemical processes. Homogeneous catalysis has made great progress, however, and can easily be compared to its heterogeneous counterpart.

Overview

In this context, a continuous esterification is investigated in a PFTR setup. Continuous flow reactions have known advantages when it comes to reaction engineering as well as scale-up. [2] With organic solvent nanofiltration (OSN) the homogeneous molecular catalyst is recycled and its performance is compared to other catalysts. OSN allows a low temperature, and therefore low energy, catalyst recycle with very high recovery rates which makes it especially interesting for high-priced catalysts. [3]

Objective

The aim is to transfer the reaction from lab scale to pilot plant. Furthermore a homogeneously catalyzed process for the valorization of furnace gas derived CO₂ is being developed. In this context the potential of homogeneous and heterogeneous catalysis is compared. To increase the efficiency of the homogeneous molecular catalyst, OSN as well as layer-by-layer membranes are tested for the catalyst recycling. Different triflates are tested as homogeneous molecular catalysts which have so far been used as co-catalysts in homogeneous hydrogenation with sophisticated noble metal, or transition metal, catalysts.

Experimental setup

In a PFTR setup, the kinetics is determined for different homogeneous catalysts in organic solvents. The reactor is automatically fed with HPLC pumps with the corresponding reactants. The conversion and product yield are measured using GC analysis, NMR spectroscopy and inline mid-IR spectroscopy. With the Evonik METcell [4] and different layer-by-layer membranes [5] the catalyst is recycled using OSN. Permeation and retention of the different solvents and the catalyst are studied for varying solvent compositions and pressures. Catalyst leaching is quantified via ¹⁹F-NMR spectroscopy.

Results

With the kinetics, a reliable prediction of the reactor system can be made and the reactor size can reliably be increased over several orders of magnitude. With the identification of excellent downstream processing operation points, the upstream process can be adequately adapted to design a homogeneously catalyzed process which can competitively be used for the valorization of CO₂. So far, several operation points of the downstream process have been identified which allow a catalyst recovery rate of 99% and kinetic studies are being undertaken for these conditions. [6] With permeation and catalyst retention rates being determined for additional catalysts, the reactant, solvent and catalyst ratios can be adapted to meet the optimal recycle and downstream purification conditions.

Acknowledgements

We gratefully appreciate the support received from the Federal Ministry of Education and Research (Bundesministerium für Bildung und Forschung, BMBF, 03EK3041D, Verbundvorhaben Carbon2Chem-L4: SynAlk – Teilprojekt ‘Herstellung von C2+-Alkoholen auf Basis von H2, CO und CO2 aus Kuppelgasen').

[1] – M. Oles et al., Chemie Ingenieur Technik, 2018, 90, 169-178.

[2] – D. Dallinger & C. O. Kappe, Current Opinion in Green and Sustainable Chemistry, 2017, 7, 6-12.

[3] – R. P. Lively & D. S. Sholl, Nature Materials, 2017, 16, 276.

[4] – E. M. Rundquist et al., Green Chemistry, 2012, 14, 2197-2205.

[5] – S. Ilyas et al., Journal of Membrane Science, 2016, 514, 322-331.

[6] – J.-K. Schnoor et al., Manuscript in preparation