Theses & Dissertations

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https://hdl.handle.net/20.500.11801/5
This collection is exclusively made up of theses, dissertations, and project reports submitted as a requirement for completing a graduate degree at UPR-Mayagüez. If you are a UPRM graduate student and you are looking for information related to the deposit process, please refer to https://libguides.uprm.edu/repositorioUPRM/tesis

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Browsing Theses & Dissertations by Subject "5-(Hydroxymethyl)furfural"
  • Publication
    Effect of protic and aprotic polar solvents on the heterogeneous catalytic conversion of hexoses
    ( 2018-12-12) Rivera-Goyco, Christian ; Cardona-Martínez, Nelson ; College of Engineering ; Hernández Maldonado, Arturo ; Martínez Iñesta, María ; Curet Arana, María ; Department of Chemical Engineering ; González Cruz, Michael
    We studied the synthesis, the characterization and the solvent effect on the catalytic performance of materials with Brønsted or Lewis acidity on the hexose conversion towards value-added molecules such as 5-(hydroxymethyl)furfural (HMF) and -hydroxy acids (AHAs). Sn-beta zeolites with different Si/Al and Si/Sn ratios were successfully synthesized using a fluorine-free post-synthesis procedure. We show that the utilization of Sn-beta in combination with high relative amounts of –valerolactone (GVL) as co-solvent with water increases the rate of glucose conversion by 4.5 times and the rate of fructose conversion by 4 times when compared to using only pure water. As we increased the GVL content we found that the rates for isomerization and retro-aldol condensation increased. For a ratio of GVL-water (9:1) we observed a 2.5 and 8-fold increase for fructose isomerization and fragmentation reaction rates, respectively, compared with the values obtained in water. To the best of our knowledge, this is the first time that the effect of GVL as co-solvent has been assessed for Lewis acid mediated reactions. We also found that addition of small amounts of potassium carbonate (K2CO3) in the GVL-water mixtures inhibits dehydration reaction promoted by Brønsted acids and increases the lactic acid (LA) and 2-hydroxybut-3-noic-acid (HBA) yields. Additionally, we obtained similar product distributions for glucose and fructose conversion for temperatures between 403 and 433 K in GVL-water mixtures. Glucose is more abundant and inexpensive than fructose and our results indicate that it may be used for AHAs production. Finally, we propose that the catalytic conversion of hexoses in GVL-water mixtures with a fluorine-free Sn-beta catalyst may offer a viable pathway for producing AHAs. This process may be coupled downstream with biomass-derived sugars obtained from lignocellulosic biomass deconstruction using GVL-water as solvent. We also showed that the utilization of polar aprotic solvents such as GVL and tetrahydrofuran (THF) as co-solvents with water increases the activity of CMK-3 functionalized with sulfonic acid (SA) groups towards the dehydration of fructose to HMF. We also evidenced that higher enhancements on fructose consumption and HMF production rates were observed for GVL than for THF. In contrast, higher HMF selectivities were obtained in THF. Increasing the water content, in both GVL-water and THF-water mixtures, decreased the activity towards fructose conversion. However, no differences in HMF selectivities were found for the solvent ratios of polar aprotic solvents and water studied. Differences in activity toward fructose consumption and HMF production were observed for CMK-3 materials grafted with different SA groups. Overall, aromatic SA groups were more active than aliphatic ones. CMK-3 Phenyl Sulfonic Acid (PhSA) was the material with highest activity. In contrast, ethyl Sulfonic Acid (ESA) was the least active material. In general, the stronger the acidity of the SA (lower pKa) the higher the activity, with the exception of Naphthalene Sulfonic Acid (NpSA). The PhSA, NpSA and Methyl Sulfonic Acid (MSA) groups had similar HMF selectivities (ca. 70%) but ESA had lower selectivities. The highest HMF yield achieved in our studies was 72% for an almost complete fructose conversion. It was obtained in THF-water (9:1) mixture and using CMK-3 MSA as catalyst. To our knowledge, this is the first time that carbon materials grafted with MSA or ESA had been used or assessed on the fructose dehydration towards HMF.