Catalytic Valorization of Malic Acid with Alternative Solvents

• Autor(a) principal: Faria, Marta Pastor Fernandes Arraios
• Data de Publicação: 2017
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/26837
• topic: Malic Acid; Ionic Liquids; Supercritical CO2; Hydrogenation; Green Chemistry; Ácido Málico; Líquidos Iónicos; CO2 Supercrítico; Hidrogenação; Química Verde; Domínio/Área Científica::Engenharia e Tecnologia

The main focus of this research project consisted on the catalytic hydrogenation of malic acid, using ionic liquids as solvents and in presence of supercritical CO2. The catalysts used in this project were ruthenium and palladium heterogeneous catalysts. Using the catalyst ruthenium (II) bis(2-methylallyl)(1,5-ciclooctadiene) in the presence of ionic liquids containing the NTf2 anion, at 120 bar of hydrogen and a final pressure of 180 bar (after the addition of supercritical CO2), gamma-butyrolactone, 4-ethoxy-4-oxobutanoic acid, diethyl succinate and diethyl 2-hydroxysuccinate were mainly formed and were identified by gas chromatography coupled with mass spectrometry (GC-MS). When the ionic liquid [Bmim]NTf2 was used it was possible to obtain the compounds gamma-butyrolactone with a selectivity of 23.4%. However, increasing the aliphatic chain of the IL cation to [C6mim] it was possible to increase selectivity of this compound up to 41.4%. Nevertheless, using a completely different IL like [Emim]OAc, the formation of such compound did not occur. The referred compound has a significant importance in biodiesel field, and it is generally used as a building block in the synthesis of polymers and plastics, and therefore it is a target of this project. Changing the catalyst to palladium 5% on alumina and using ionic liquids with the [Emim] cation and different anions, new reaction conditions were studied to understand the influence of IL and catalyst in the type of products. Hence, using only 60 bar of hydrogen and around 60 bar of supercritical CO2, compounds butane-1,4-diol, diethyl succinate and diethyl 2-hydroxysuccinate were mainly obtained. Interestingly, the ionic liquid [Emim]OAc favored the formation of 1-methylpyrrolidine-2,5-dione and 1-ethylpyrrolidine-2,5-dione with high selectivity (30-60%). Catalysts used in these reactions were recovered by filtration, and analyzed by transmission electronic microscopy (TEM) which allowed the measurement of particles diameters. With ruthenium catalyst, nanoparticles were formed with 1.5-2.5 nm diameter. Ionic liquids used in the hydrogenation of malic acid were recovered by liquid-liquid extraction with an immiscible solvent. Their purity was assessed by NMR experiments, and compared with spectra from original ILs. Generally, it is possible to conclude that recovered ionic liquids were effectively recovered in high level of purity. In summary, the goals of this project were successfully accomplished, proving the usefulness of supercritical fluids and ionic liquids in carboxylic acid hydrogenation.