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Cellulose Hydrolysis in Acidified LiBr Molten Salt Hydrate Media

Deng, Weihua, Kennedy, James R., Tsilomelekis, George, Zheng, Weiqing, Nikolakis, Vladimiros
Industrial & Engineering Chemistry Research 2015 v.54 no.19 pp. 5226-5236
Fourier transform infrared spectroscopy, X-ray diffraction, acidity, activation energy, cations, cellulose, crystal structure, engineering, glucose, glycosidic linkages, hydrolysis, organic acids and salts, scanning electron microscopy, sulfuric acid, synergism, temperature
We screened nine acidified molten salt hydrates (solutions with water to salt molar ratio equal or less than the coordination number of the cation) as reaction media for cellulose hydrolysis, and we found that cellulose can be efficiently hydrolyzed in LiBr acidified MSH under mild conditions (>90% yield to water-soluble products in 0.05 M H₂SO₄ at 85 °C for 30 min). The effect of various factors (temperature as well as acid and initial cellulose concentrations) on the kinetics of hydrolysis reaction was also investigated. At the lowest temperatures examined (70 and 85 °C) low amounts of degradation products have been observed, and glucose appears to be in equilibrium with its dimers and possibly other oligomers. Higher temperatures (100–115 °C) enhanced the formation of degradation products (organic acids and humins). Analysis of the kinetic data indicate that hydrolysis rates are first order in cellulose and in H₂SO₄ concentration, and the initial hydrolysis rates have an apparent activation energy ∼123 kJ/mol. X-ray diffraction, SEM, and FTIR were also used to study cellulose’s structural/morphological changes upon treatment in the LiBr MSH media, in an attempt to understand the effects of the cellulose–salt interaction. Analysis of the data indicates that the enhancement of the hydrolysis rates can be attributed to the enhancement of the acidity of reaction media through synergistic effect of dilute acid and MSH, the breaking of crystalline structure through swelling, and the interaction of the salt with cellulose chains affecting the conformation and flexibility of the glycosidic bonds.