Levulinic acid (LA), accessible by the acid catalyzed degradation of biomass, is potentially a very versatile green intermediate chemical for the synthesis of various (bulk) chemicals for applications like fuel additives, polymers, and resin precursors. We report here a kinetic study on one of the key steps in the conversion of biomass to levulinic acid, i.e. the reaction of 5-hydroxymethylfurfural (HMF) to levulinic acid. The kinetic experiments were performed in a temperature window of 98-181 uC, acid concentrations between 0.05-1 M, and initial HMF concentrations between 0.1 and 1 M. The highest LA yield was 94% (mol/mol), obtained at an initial HMF concentration of 0.1 M and a sulfuric acid concentration of 1 M. The yield at full HMF conversion is independent of the temperature. An empirical rate expression for the main reaction as well as the side reaction to undesired humins was developed using the power law approach. Agreement between experimental and model data is good. The rate expressions were applied to gain insights into optimum process conditions for batch processing.
A variety of interesting bulk chemicals is accessible by the acid-catalyzed hydrolysis of cellulose. An interesting example is levulinic acid, a versatile precursor for fuel additives, polymers, and resins. A detailed kinetic study on the acid-catalyzed hydrolysis of cellulose to levulinic acid is reported in this paper. The kinetic experiments were performed in a temperature window of 150-200°C, sulfuric acid concentrations between 0.05 and 1 M, and initial cellulose intakes between 1.7 and 14 wt %. The highest yield of levulinic was 60 mol %, obtained at a temperature of 150°C, an initial cellulose intake of 1.7 wt %, and a sulfuric acid concentration of 1 M. A full kinetic model covering a broad range of reaction conditions was developed using the power-law approach. Agreement between the experimental data and the kinetic model is good. The kinetic expressions were used to gain insights into the optimum process conditions for the conversion of cellulose to levulinic acid in continuous-reactor configurations. The model predicts that the highest obtainable levulinic acid yield in continuous-reactor configurations is about 76 mol %, which was obtained when using reactors with a large extent of backmixing.
Supercritical carbon dioxide (CO 2) is well established for use as a processing solvent in polymer applications such as polymer modification, formation of polymer composites, polymer blending, microcellular foaming, particle production and polymerization. Its gas-like diffusivity and liquid-like density in the supercritical phase allow replacing conventional, often noxious, solvents with supercritical CO 2. Though only a few polymers are soluble in supercritical CO 2 , it is quite soluble in many molten polymers. CO 2 dissolution in a polymer has been interpreted physically but FT-IR studies lead to an explanation in terms of weak interactions between basic and acidic sites. Various experimental methods and equations of state are available to measure or predict the solubility of CO 2. Dissolved CO 2 causes a considerable reduction in the viscosity of molten polymer, a very important property for the applications stated above. CO 2 mainly acts as a plasticizer or solvent when contacted with a polymer. Gas solubility and viscosity reduction can be predicted theoretically from purecomponent properties. In this review, experimental and theoretical studies of solubility and viscosity of several polymer melts are discussed in detail. Detailed attention is also given to recently reported applications along with aspects related to polymer processing.
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