Toward Water-Based Recycling Techniques: Methodologies for Homogeneous Catalyst Recycling in Liquid/Liquid Multiphase Media and Their Implementation in Continuous Processes

Abstract

Biphasic water-based solvent systems offer the opportunity of efficient recycling of homogeneous catalysts. Water separates well from most organic solvents; therefore, water-soluble catalysts can be immobilized in this phase. Furthermore, water can substitute hazardous and environmentally unfriendly organic solvents in these systems. Within industry only the Ruhrchemie/Rhône-Poulenc process uses plain water to immobilize the homogeneous catalyst for the hydroformylation of propene. Yet for more hydrophobic substrates, no water-based system has been commercialized. This review will summarize recent developments in the field of water-based recycling strategies. Topics in this field are the intensification of the mixing process, the use of thermomorphic solvent systems, and the employment of several additives, like alcohols and surfactants. Continuously operated processes for these recycling strategies will be presented and discussed.

Thermomorphic Multiphase Systems: Switchable Solvent Mixtures for the Recovery of Homogeneous Catalysts in Batch and Flow Processes

“…The horizontal lines determine graphically the composition of the coexisting phases, which is commonly known as the distribution coefficient[ Eq. (6)].…”

“…The two liquid phases in equilibrium are connected by tie lines, as shown in Figure 5. From the end points of the tie lines, the distribution coefficient, K i ,b etween two phases, a and b,c an be calculated by using Equation (6).…”

“…The concentration and temperature dependence of LLE are described through the activity coefficients. However,t he occurrence of two liquid phases cannot be understood by Equation (6) alone. Looking at the concentrationd ependence of the Gibbs energy,t he formation of real two liquid phases can be explained in combination with the excessG ibbs energy,ass hown in Equations 7and( 8).…”

“…[4] In contrast, liquid multiphase systems are highly promising for the recovery of homogeneous transition-metal catalysts because both phases are selected in such aw ay that products are (only) present in one phase and the catalysti s( only) present in the other. [5,6] Unfortunately,l imitations evoked by the liquidliquid interface may limit the reactionperformance.…”

Facile catalyst recycling by thermomorphic behaviour avoiding organic solvents: a reactive ionic liquid in the homogeneous Pd-catalysed telomerisation of the renewable β-myrcene

“…Currently, research is carried out in many areas of organometallic catalysis on the use of novel solvent systems for the immobilization of catalysts, such as deep eutectic solvents, supported ionic liquid phases and other novel biphasic systems based on more sustainable solvents. [16][17][18] Our group recently developed a method to combine the introduction of a dimethylamine moiety by telomerisation with the recovery of the catalyst in an ionic liquid phase. 19 N, N-Dimethyl-ammonium-N,N-dimethyl carbamate (dimcarb) was used as a reactive ionic liquid (RIL) to immobilize the homogeneous transition metal catalyst and simultaneously react as a dimethylamine precursor.…”