(456c) High-Pressure Phase Behavior of Synthesis Gas in Hydroformylation Systems: Experimental Data and Prediction

Synthesis gas (CO/H₂) is one of the key components in the hydroformylation process where it reacts with olefins to form aldehydes. Classical production approaches such as the Ruhrchemie/Rhone-Poulenc process are well understood, but fail for the processing of long-chain olefins. The arising challenge is the homogeneously-catalyzed hydroformylation of these long-chain olefins which is currently investigated both in academia and industry.

One promising approach for the hydroformylation of long-chain olefins to aldehydes is the application of thermomorphic multicomponent solvent (TMS) systems, which consist of at least a polar and an apolar solvent [1]. For kinetic studies as well as for process design and optimization the gas-liquid phase-behavior is of high interest. To be able to describe the gas solubility in these complex systems, the gas solubility in all applied solvents as well as the hydroformylation educt (olefin) and product (aldehyde) have to be taken into account.

The aim of this work is to predict the influence of temperature, pressure, as well as of the composition of the multicomponent solvent system, on the synthesis gas solubility using the PC-SAFT equation of state [2]. Therefore the solubility of synthesis gas in the pure solvents as well as in binary and quaternary solvent systems containing components of the TMS and the hydroformylation educt / product was taken into account. Measurements were performed at different temperatures and solvent compositions.

Experimental high-pressure gas-solubility data was gained in a high-pressure variable-volume view cell applying both, the visual synthetic method for gas solubility in homogeneous systems and a newly developed and validated non-visual synthetic method for solubility measurements in immiscible solvents like PC/n-decane. Synthesis gas as well as CO solubilities were determined in pure components like n-decane, PC, DMF, 1-dodecene, n-dodecanal, as well as in binary and quaternary mixtures of the liquids for a temperature range of 303 to 363 K and at pressures up to 15 MPa. Binary gas solubilities and pure-component data were used to fit pure-component parameters and the binary interaction parameter for the PC-SAFT. The experimental data of ternary and higher gas-liquid systems was used to validate the prediction by PC-SAFT without fitting any parameters to this data.

It could be shown, that the temperature as well as the composition of the solvent system has a decisive influence on the high-pressure gas solubility. For all systems investigated, an increase in the gas solubility with increasing temperature was observed. Additionally, higher amounts of the polar solvent (DMF or PC) led to lower solubility of synthesis gas and CO. It could be shown that PC-SAFT is able to predict the synthesis-gas solubility in complex systems (hydroformylation educt, product and TMS) with very good accuracy. Besides the gas solubility itself, also the temperature dependency of the gas solubility is predicted correctly without the need of temperature dependent binary interaction parameters.

The results now enable a further specification of the process window and optimization of the reaction performance for hydroformylation reaction in TMS systems.

[1] Y. Brunsch, A. Behr, Angew. Chem. 125 (2013) 1627.

[2] J. Gross, G. Sadowski, Ind. & Eng. Chem. Res., 40 (2001) 1244-1260.