Process development for reductive hydroformylation of renewable olefin-paraffin mixtures in multiphase systems

• Prozessentwicklung zur Reduktiven Hydroformylierung von regenerativen Olefin-Paraffin-Gemischen in Multiphasensystemen

Püschel, Sebastian; Leitner, Walter (Thesis advisor); Jupke, Andreas (Thesis advisor)

Aachen : RWTH Aachen University (2023)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2023

Abstract

This work covers the development of three different reaction systems to produce synthetic fuel alcohols from olefin paraffin mixtures, which are derived from Fischer Tropsch processes operating with bio syngas from the gasification of non edible biomass. These alcohols represent an interesting and important component of drop in capable synthetic fuels which are applicable in the fleet of existing vehicles. Beneficial influence on the density of the mixture as well as the combustion behavior represent the main advantages of higher alcohols in diesel type fuels. The pathway chosen to produce alcohols from olefins in this work is a hydroformylation and hydrogenation sequence, converting a C5 to C10 substrate mixture into C6 to C11 primary alcohols with aldehyde intermediates. These aldehydes, obtained in hydroformylation, already represent important platform chemicals in today’s chemical industry to produce a wide variety of products. The first reaction system investigated in this work is based on a major milestone in the development of industrial hydroformylation processes: the Ruhrchemie/Rhône-Poulenc process for the hydroformylation of propene in a water based liquid/liquid multiphase system and its efficient recycling of the precious rhodium/TPPTS catalyst. As this catalyst system exclusively produces aldehydes, a subsequent hydrogenation step is necessary, which leads to a two step process. This work further contributes to previous investigations of the application of this process concept to higher olefins with low water solubility. The focus of the investigation is to find reaction conditions for high once through conversion of the substrate to avoid energy intensive separation steps in the process. Batch reactions and continuous flow with a specially developed pilot plant setup led to high catalytic activity and stability. In a potential fuel production process leading towards alcohols, the aldehydes are not used as isolated intermediates. Hence, a tandem catalytic approach may increase the efficiency of the process by combining both the hydroformylation and hydrogenation reaction in a single process step. While tandem catalytic production of alcohols from olefins is known for cobalt based catalysts under harsh conditions, rhodium based processes have received comparably low attention. In combination with tertiary amines, molecular rhodium catalysts are capable of auto tandem reductive hydroformylation. In the second reaction system included in this work, this tandem catalytic approach is combined with a multiphasic catalyst recycling concept. By the introduction of alkanolamines to the reaction, a water based second phase for catalyst immobilization like in the two step process is investigated. By optimizing the reaction conditions for this biphasic system, namely the syngas pressure and composition, temperature as well as a Design of Experiment investigation of the reaction mixture composition, high selectivity towards the one step production of alcohols was achieved. The catalyst recycling concept was proven to be feasible in continuous flow. The most important parameter of this system was found to be the ratio between the alkanolamine and water in the aqueous catalyst phase, which significantly determines the catalytic activity as well as the phase behavior of the reaction. The third catalytic system in this work utilizes the strong dependence of the phase behavior on the water/amine ratio observed in the previously described multiphase system. When the amine is applied in excess to water, the formation of amphiphilic alcohols in combination with also amphiphilic alkanolamines leads to the formation of a single phase during the reaction. Since tertiary alkanolamines are CO2 responsive, the ionic strength of the amine can be influenced by the addition of carbon dioxide, resulting in a so called "switchable solvent system", where the reaction is carried out under monophasic conditions while the catalyst can be recycled by the formation of a biphasic mixture upon addition of CO2. As the monophasic behavior during the reaction eliminates liquid liquid mass transfer limitations, the reaction rate of the system was increased compared to the multiphase system. Furthermore, a high selectivity towards alcohols in combination with high yields of up to 99.6% were achieved. In summary, three different approaches to produce alcohols as fuel additives were successfully developed and compared regarding their catalytic activity and stability, while the latter is an important factor for the economic feasibility of a potential production process. During this work, various insights on a molecular as well as on a process level were gained and utilized.

Institutions

• Department of Chemistry [150000]
• Chair of Technical Chemistry and Petrochemistry [154110]