Development of heterogenized catalyst systems for the synthesis of acrylic acid derivatives from carbon dioxide and ethylene (2015)

Use of CO2 as chemical feedstock represents one of the most sustainable ways for carbon recycling, generating high value products. Current industrial practices include the manufacture of urea, organic (poly)carbonates, and salicylic acid. CO2 can also be used to produce CO-rich syngas, which can be further processed to olefins, aldehydes, alcohols, or synthetic fuel via the Fischer-Tropsch process. Direct carboxylation with CO2 yielding carbonates, carbamates, carboxylates, or lactones is of great importance from the industrial point of view. The route has a high atom efficiency and avoids a complex process with significant amounts of waste, which is common in multi-step conventional processes. The synthesis of sodium acrylate from ethylene and CO2 represents one of the most attractive carboxylations. Contrary to the current acrylate production process via propene oxidation, the process utilizing ethylene and CO2 discussed in this work utilizes the cheap and abundantly available CO2 as C1 building block. Current state of the art of sodium acrylate catalytic reaction from ethylene and CO2 utilizes a molecular nickel complex to form a nickelalactone intermediate and a non-nucleophilic base to cleave nickelalactone, yielding sodium acrylate product. This reaction requires a complex process, with separate nickelalactone formation and cleavage with subsequent sophisticated product separation and base recycling processes. In addition, the alkoxide base may form inactive semicarbonate with CO2 as well as form conjugate acid which deactivates the nickel complex catalyst. In this work, three different metal catalyst - base combinations are proposed to overcome these limitations. A combination of molecular nickel complex with CO2-stable tertiary amine - NaH base system allows the one-pot process reaction with all reactants present during catalytic reaction. The tertiary amine is not consumed during the catalytic reaction and does not react with the metal complex. Some examples include the combination of triethylamine, phosphazene base, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) with NaH, LiH, or KH. The application of hydrophobic tertiary amine simplifies the base recycling step further. Trioctylamine, N,N-dimethylaniline, and N,N-diethylaniline combined with NaH have been identified as highly effective hydrophobic amine base suitable for this process. Turn Over Number (TON) of up to 16.91 (Turn Over Frequency (TOF) 6.52.10−5 s−1) was achieved with molecular nickel complex as catalyst and trioctylamine-NaH base combination. The second system utilizes a combination of immobilized nickel complex with amine-NaH base system. The immobilized complex was prepared via anchoring of the 1,2-bis(dicyclohexylphosphino)ethane (dcpe) ligand on functionalized silica and polystyrene support. Catalysts with metal complex loading as high as 0.1566 mmol/g and 0.134 mmol/g with silica gel and polystyrene support respectively have been successfully synthesized. MAS NMR investigations also confirmed the presence of covalently anchored active dcpe ligand. The catalytic test of the immobilized metal complex with triethylamine-NaH base system delivered a TON of up to 1.42 (Turn Over Frequency (TOF) 5.48.10−6 s−1), confirming the catalytic nature of the heterogeneously catalyzed reaction. The application of immobilized ligand catalyst system would allow a continuous one-pot process. The process can be designed so that the catalyst remains in the reactor during the whole catalytic reaction, thus minimizing the contact with oxidant or other impurities and improving its lifetime. The third system employs a combination of a molecular nickel complex with an immobilized base. Four different commercially available immobilized bases of the alkoxide and tertiary amine types have been identified as effective in the one-pot sodium acrylate reaction. Furthermore, two CO2-atmosphere tolerant immobilized bases were prepared via direct anchoring on polystyrene support and via copolymerization reaction. A high TON of up to 30.94 (TOF 4.30.10−4 s−1) could be achieved with the combination of (dcpe)-nickelalactone catalyst and immobilized sodium 2-fluorophenolate. In addition, successful recycling experiments of the immobilized base confirmed the versatility and suitability of the immobilized base for the catalytic reaction. A continuous process with two steps-filtration to recycle the immobilized base and isolate the sodium acrylate product is proposed as the most promising concept for an industrial application.