Kinetic Study on the Sulfuric Acid-Catalyzed Conversion of d -Galactose to Levulinic Acid in Water

Levulinic acid is an interesting building block for biofuel (additives) and biobased chemicals. It is accessible by an acid-catalyzed reaction of a wide variety of carbohydrates. We here report a kinetic study on the conversion of d-galactose to levulinic acid in aqueous solutions with sulfuric acid as the catalyst. The experiments were carried out in a broad range of temperatures (140-200 °C), initial concentrations of galactose (0.055-1.110 M), and concentrations of sulfuric acid (0.05-1 M). The experimental data were modeled using a power-law approach, and good agreement between the experimental data and the model was obtained. The maximum yield of levulinic acid (54 mol %) was achieved at 130-140 °C, low initial galactose concentrations (0.055 M), and high acid concentrations (1 M). With the kinetic information available, the most suitable reactor configuration was determined, and it is predicted that a continuously stirred-tank reactor is preferred over a plug-flow reactor. The findings presented here may also be applicable to the kinetic modeling of levulinic acid synthesis from more complex biomass sources such as lignocellulosic (woody) and aquatic (e.g., seaweed) biomass

Exploration of carbon based solid acid catalyst derived from corn starch for conversion of non-edible oil into biodiesel

To avoid the problems caused by free fatty acids in the conversion of low cost vegetable oils to biodiesel, the use of solid acid catalyst for (trans-) esterification reaction is considered. Such a catalyst could be produced eco-friendly by using renewable raw materials such as biomass. The use of starch for this purpose it still very limited. In this paper, various methods were explored to produce a solid acid catalyst from corn starch. We investigated two different carbonization methods: complete pyrolysis in an oxygen-free environment and hydrothermal carbonization at milder conditions. Starch was used either in the native form or as pregelatinized starch. After the carbonization, acidic sites were introduced by sulfonating the materials. To characterize the catalysts, Scanning Electron Microscopy (SEM) was applied while the sulfonic content was determined by Energy Dispersive X-ray Spectroscopy (EDS). To test the performance of the catalysts, the conversion of free fatty acids was determined using oleic acid as a representative component of biodiesel feedstock. By both of the carbonization methods, a catalyst can be obtained that shows up to 84 % conversion of oleic acid. The hydrothermal treatment may then be preferred since it can be done at milder conditions. Differences between the performances of the respective catalyst samples could be well explained by structural features seen in the SEM-pictures. These also have their effect on the amount of sulfonic groups that was found (from EDS). The general trend is logical: the catalysts with a higher sulfonic load give a higher conversion of oleic acid

Efficient Conversions of Macroalgae-Derived Anhydrosugars to 5‑Hydroxymethylfurfural and Levulinic Acid: The Remarkable Case of 3,6-Anhydro‑d‑galactose

Macroalgae or seaweed is considered a renewable and sustainable resource to produce biobased fuels, polymers, and chemicals due to its high content of polysaccharides. Various studies have reported the obtained 5-hydroxymethylfurfural (HMF) and levulinic acid (LA) from seaweeds. However, the source of the saccharides that is responsible for HMF formation, accurate yield data (often only HMF concentrations are given instead of yields on feed), and the reaction pathways (including byproducts) is not well understood. We here report a kinetic study on the conversion of 3,6-anhydro-d-galactose (D-AHG), one of the main building blocks of the polysaccharides in seaweed, to HMF and LA in water using sulfuric acid as a catalyst with the aim to rationalize and optimize the production of HMF and LA from seaweeds. The experiments were carried out in batch at temperatures between 160 and 200 °C using various initial concentrations of D-AHG (0.006–0.06 M) and sulfuric acid (0.0025–0.05 M) as the catalyst. The highest experimental yield of HMF within this range of experimental conditions was remarkably high (61 mol %) and obtained at 160 °C, with a low initial D-AHG concentration (0.006 M) and a low acid concentration (0.0025 M). These findings imply that D-AHG is a very good precursor for the HMF synthesis. Additional experiments outside the experimental window gave an even higher HMF yield of 67 mol %. The highest LA yields were 51 mol % [160 °C, low initial D-AHG concentration (0.006 M), and high acid concentration (0.05 M)]. The experimental data were modeled using a power law approach, and the kinetic model was used to determine reactor configurations giving the maximum yield of HMF and LA. The result showed that a plug flow reactor is favorable to achieve the highest yield of HMF, whereas a continuously ideally stirred tank reactor is the preferable reactor configuration to obtain the highest yield of LA