(744f) Coupled CO2 Capture and Conversion to Methanol Using Solid Sorbents with a Homogeneous Catalyst

The level of CO₂ in the atmosphere is increasing due to the burning of fossil fuels, with detrimental effects on the environment. To slow the rate of global warming, it is imperative that CO₂ emissions are captured before becoming atmospheric, and that the amount of CO₂ already in the atmosphere is reduced. As an alternative to solely capturing and storing CO₂, the possibility of utilization has brought on a new wave of CO₂ capture and conversion research. Currently, large-scale capture of CO₂ comes with two major energy sinks: CO₂ desorption from the capture agent, and the pressurization of the gas necessary for transportation. In recent reports, the coupling of amine-based CO₂ capture with catalytic hydrogenation of CO₂ to methanol has been successful^1,2. However, the homogeneous amines used in these systems are unstable under high temperature conditions and complicate product separation¹. Amine polymers, like polyethyleneimine (PEI), are both thermally stable and active for CO₂ capture agent when supported on silica³. This work improves upon purely homogeneous capture and conversion systems by implementing heterogeneous silica-supported amines in place of liquid amines, combined with a homogeneous catalyst in dioxane solvent. In this tandem system, higher methanol production is seen compared to the homogeneous amine and homogeneous catalyst system.

Ru[MACHO]BH was selected as the homogeneous catalyst, and pentaethylenehexamine (PEHA) was used as a baseline capture agent, with a loading of 20:1 Amine:Ru for each experiment in this study. Amines PEI (800 and 750,000 MW), PEHA, and propylethylenediamine (PED) were selected for comparison in this study. Two different silica supports have been tested. SBA-15 has been selected as it has one of the highest CO₂ uptakes among silica-supported amines. Fumed silica (FS) was also selected to determine the feasibility of an inexpensive support for this purpose. Two different methods of attaching amines to the silica surface have been tested in this system. The first is through a physical binding process, in which the amine physisorbs to the silica surface. In the cases of the smaller chain amines, as much as 10x more methanol is produced using silica-supported amines compared to their homogeneous counterparts per mole nitrogen. When FS was used as the support: 40% more methanol was produced when PED was chemically attached to FS than when it was physisorbed to FS. Even with these differences, all silica-supported PED materials outperformed homogeneous PED.