Aqueous Biphasic Systems for the Synthesis of Formates by Catalytic CO₂ Hydrogenation: Integrated Reaction and Catalyst Separation for CO₂‐Scrubbing Solutions

Abstract

Aqueous biphasic systems were investigated for the production of formate–amine adducts by metal‐catalyzed CO2 hydrogenation, including typical scrubbing solutions as feedstocks. Different hydrophobic organic solvents and ionic liquids could be employed as the stationary phase for cis‐[Ru(dppm)2Cl2] (dppm=bis‐diphenylphosphinomethane) as prototypical catalyst without any modification or tagging of the complex. The amines were found to partition between the two phases depending on their structure, whereas the formate–amine adducts were nearly quantitatively extracted into the aqueous phase, providing a favorable phase behavior for the envisaged integrated reaction/separation sequence. The solvent pair of methyl isobutyl carbinol (MIBC) and water led to the most practical and productive system and repeated use of the catalyst phase was demonstrated. The highest single batch activity with a TOFav of approximately 35 000 h−1 and an initial TOF of approximately 180 000 h−1 was achieved in the presence of NEt3. Owing to higher stability, the highest productivities were obtained with methyl diethanolamine (Aminosol CST 115) and monoethanolamine (MEA), which are used in commercial scale CO2‐scrubbing processes. Saturated aqueous solutions (CO2 overpressure 5–10 bar) of MEA could be converted into the corresponding formate adducts with average turnover frequencies up to 14×103 h−1 with an overall yield of 70 % based on the amine, corresponding to a total turnover number of 150 000 over eleven recycling experiments. This opens the possibility for integrated approaches to carbon capture and utilization.

Methylformate from CO2: an integrated process combining catalytic hydrogenation and reactive distillation

“…To achieve preferential partitioning of the catalyst in the n-decane phase, the solubility properties of the catalyst must be adjusted accordingly. The complex cis-[Ru (dppm) 2 Cl 2 ] 37 (dppm = Ph 2 P-CH 2 -PPh 2 ) is a powerful catalyst for CO 2 hydrogenation to FA 38,39 and thus was selected as lead structure for tagging with long alkyl chains at the aryl groups. The ligand synthesis starts from commercially available bromo aryl compounds bearing an octyl or a dodecyl chain in para-position.…”

“…2). Initially, methyl diethanolamine (MDEA), successfully used in biphasic organic/water systems for stabilizing FA, 38,39 was chosen to validate the approach. Catalytic hydrogenation of CO 2 using complex 1 was carried out under a standard set of reaction conditions and the stability of the catalyst system was tested by repetitive batch recycling of the alkane phase ( Table 1).…”

Carbon2Polymer – Chemical Utilization of CO2 in the Production of Isocyanates

“…With MEA as the amine, the catalytic system was reused ten times (eleven runs in total) reaching a total TON = 150 000 with an average TOF = 10 000 h −1 in the first seven cycles with a FA‐amine ratio ranging from 0.6 – 0.8. The catalyst leaching per cycle in the aqueous phase was found to be ≤ 0.26 % for Ru and ≤ 1.0 % for P of the initial catalyst loading, providing excellent catalyst retention in the selected solvent system .…”

Recent Advances Utilized in the Recycling of Homogeneous Catalysis

“…Scott et al . investigated aqueous biphasic system using cis ‐[Ru(dppm) 2 Cl 2 ] (dppm=bis‐diphenylphosphinomethane) as a catalyst for CO 2 hydrogenation to obtain formate‐amine adducts . High productivity was obtained with saturated aqueous solutions of CO 2 and monoethanolamine (MEA) was converted to formate amine adduct with 70 % yield and achieved a turnover number of 150000 over eleven recycling runs.…”