Tin-containing β zeolite exhibits excellent catalytic performance in various biomass conversions to high-value chemicals due to its strong Lewis (L) acidity produced by framework Sn 4+ sites. However, it is difficult to incorporate Sn species into the framework of β zeolite due to that the ionic radius of Sn (0.69 Å) is larger than that of Si (0.40 Å). Herein, organic additives with carbonyl, hydroxyl , aldehyde or amine groups were used to stabilize Sn species in the gel and framework Sn 4+ in the zeolite. Among all additives, acetone (AC) has the best stabilizing effect on Sn species. The stabilization effect between AC and Sn 4+ sites was observed by FT-IR. The characterization results indicate that more tin species were incorporated into β framework and the L acid density increased due to the complexation between carbonyl group and Sn species. Compared to Sn-β-3d synthesized without additive, the L acid density of Sn-β-AC-3d increased by ∼50% (from 21 μmol g −1 to 34 μmol g −1 ). For the conversion of ethyl levulinate to γ-valerolactone, the reaction reached equilibrium faster over Sn-β-AC-3d than over Sn-β-3d at the investigated reaction temperatures. A yield of 98% was obtained over Sn-β-AC-3d at 110 °C. Besides, Sn-β-AC-3d exhibited good stability and reusability.
Min Pei,Xinwen Peng,Yuqing Shen,Yunlong Yang,Yuanlong Guo,Qiang Zheng,Haibo Xie,Hui Sun
Cellulose esters are important cellulose derivatives with good processing ability and material properties. The design and sustainable synthesis of cellulose esters are prime research topics. Herein, cellulose levulinate esters (CLEs) with degrees of substitution (DSs) ranging from 0.15 to 2.04 were simply prepared through an atom-economic reaction between cellulose dissolved in a newly developed 1.8-diazabicyclo[5.4.0]undec-7-ene/dimethyl sulfoxide/carbon dioxide solvent system and alpha-angelica lactone, a biomass-derived and commercially available platform chemical, without the addition of any external catalysts or condensation reagents. The optimized reaction conditions of 120 °C, 0.5 h, and a 5/1 molar ratio of alpha-angelica lactone to the hydroxyl groups in cellulose resulted in CLEs with appropriate DSs and satisfactory material properties. The structures and thermal properties of the CLEs were characterized by nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermal gravimetric analysis to develop an in-depth understanding of the correlations among the chemical structures, thermal properties, and mechanical properties. A study of solubility in conventional solvents indicated that the CLEs with appropriate DSs were soluble in water, providing a green processing strategy to prepare CLE films with tensile strengths of up to 72 MPa and elongation at break values of up to 26.7%. The morphologies of the films were characterized by scanning electron microscopy and atomic force microscopy. The cytotoxicity of the water-soluble CLEs was also evaluated in vaginal epithelial cells (VK2/E6E7) to identify the potential of the CLEs for biomedical applications.
As an important bio-based chemical, methyl levulinate (ML) can be produced via enzymatic esterification of levulinic acid with methanol. A kinetic model is developed in this work based on the law of mass action and reaction reversibility, to investigate the effect of enzyme loading, alcohol/acid ratio and temperature on ML yield. Data analysis shows that newly developed binary regression is apparently more persuasive than the commonly used unitary regression. Kinetic study reveals: (1) rate constants of esterification/hydrolysis increase with increasing enzyme loading, while their ratio (equilibrium constant) remains invariant. (2) Methanol has no toxicity towards lipase, and hence, neither the rate constants of esterification/hydrolysis nor the equilibrium constant are affected by alcohol/acid ratio. (3) Both rate constants of esterification/hydrolysis and the equilibrium constant increase with temperature elevation, and their relationships agree with Arrhenius equation and Van't Hoff equation, respectively. (4) The esterification is endothermic and spontaneous. In total, the application of binary regression analysis for the developed model to study the enzymatic esterification kinetics is quite successful.
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