Hidrogenação livre de solvente do ácido succínico e da butirolactona: uma abordagem sustentável para obtenção de produtos de alto valor agregado

Abstract

γ-butyrolactone (GBL) and succinic acid (SUC) are platform molecules widely used in the production of high-value compounds. For this reason, the present study aimed to evaluate the hydrogenation of these compounds in sustainable, solvent-free media, employing supercritical carbon dioxide (scCO₂) conditions, with the use of both micro and macroscale (pellet) catalytic forms of PdRe/SiO₂. The study was divided into three articles. The first article primarily aimed to evaluate the effect of solvent-free reactions with the addition of scCO₂ as a reaction medium in the hydrogenation of GBL in batch processes. These same conditions were tested for the hydrogenation of SUC in batch, including an evaluation of the effects of temperature, H₂ pressure, catalyst mass, and the Re content in the catalyst. The third article focused on the development of technical catalysts in the form of PdRe/SiO₂ pellets for the study of solvent-free hydrogenation of GBL in continuous-flow systems. For this purpose, pellets with different thermal treatments (uncalcined and calcined at 300 and 500 °C) were evaluated and compared with powdered catalysts in batch systems. In fixed-bed reactors, the effects of temperature, pressure, GBL and H₂ flow rates, and bed height were assessed. The results demonstrated that the reaction medium had a significant impact on the selectivity of GBL hydrogenation, acting as a modulating factor for selectivity. Under solvent-free conditions, 93% selectivity for tetrahydrofuran (THF) was achieved. With the addition of scCO₂ (80 bar), selectivity was completely shifted to 1,4-butanediol (BDO), reaching 100%. For SUC, the most severe conditions of temperature (280 °C), pressure (90 bar), and catalyst mass (50 mg) resulted in 75.3% selectivity for THF. In the continuous-flow reactions of GBL, excellent results were obtained with the pellets calcined at 300 °C due to their high surface area. Under the conditions of 175 °C, 50 bar of H₂, a GBL flow rate of 0.1 mL/min, an H₂ flow rate of 0.7 mL/min, and a bed height of 7 cm, 52% GBL conversion and 86% selectivity for BDO were achieved. Overall, the results obtained in this work highlight the effectiveness of solvent-free approaches and the versatility of scCO₂ as a selectivity regulator, reinforcing the potential of these systems in green and sustainable processes with unprecedented selectivities for THF and BDO. Furthermore, the study suggested the development of technical catalysts for large-scale applications.