Direct production of ethyl levulinate from carbohydrates and biomass waste catalyzed by modified porous silica with multiple acid sites

Three modified porous silica solid acid catalysts with multiple acid sites (SO3H-Al/Silica, SO3H-Al-Zr/Silica, and SO3H-Zr/Silica) were prepared and characterized. The Pyridine-infrared spectra showed that both Bronsted (B) and Lewis (L) acid sites were present in all three catalysts. Catalytic acid sites with different acid strengths were also found, including strong sulfonic acids and several weak acids. The prepared solid acid catalysts were used to catalyze the ethanolysis of glucose, glucosyl-based carbohydrates, and starchy food waste to produce ethyl levulinate (EL). The formation of EL was promoted by the synergistic effect between multiple acid sites on the catalysts. A higher B/L ratio and -SO3H amount promoted the production of EL. The catalytic activity was positively correlated to the specific surface area of the catalysts. Promising results were obtained for SO3H-Al/ Silica: the maximum EL yield from glucose was 47.9%, and a small amount of 5-ethoxymethylfurfural was detected as a byproduct. Cellobiose, cellulose, expired wheat flour, and kitchen waste were also used as raw materials to produce EL, affording EL yields in the range of 1.6-38.9%. Finally, the stability of the prepared catalysts was explored after reuse and hot filtration.