Fabrication of biobased heterogeneous solid Brønsted acid catalysts and their application on the synthesis of liquid biofuel 5-ethoxymethylfurfural from fructose

A series of biobased heterogeneous solid Brønsted acid catalysts with perfect spherical microstructures are successfully fabricated directly from waste Camellia oleifera shells by a simple hydrothermal carbonization-annealing-sulfonation process. 350 °C low temperature annealing process helps to increase the activity of the catalyst due to the simultaneous maintenance of the spherical microstructure and aromatic carbon framework. As a renewable catalyst with low cost, the as-prepared materials are successfully applied on the synthesis of green renewable liquid biofuel 5-ethoxymethylfurfural (EMF) directly from fructose. In the catalytic test, the influences of reaction time and temperature, fructose concentration, and adding amount of the catalyst on the yield of EMF are investigated systematically. As a result, the optimal reaction temperature is 100 °C, the EMF yield monotonically increases with prolonging the reaction time from 3 to 24 h, the optimal fructose concentration is 0.5 mmol, and the EMF yield gradually increases with increasing the adding amount of the catalyst from 50 to 150 mg. In addition, the as-prepared catalysts exhibit considerably high stability in the current EMF synthesis system, and they can maintain a similar level of reactivity after four catalytic cycles.