Novel One‐Step Process for the Production of Levulinic Acid from Furfural over Hierarchical Zeolites in a Microwave Reactor

Abstract

Here, a novel one‐step process is reported for the production of levulinic acid (LA) from furfural over hierarchical zeolites in a microwave reactor. The furfural conversion and product distribution are determined as a function of formalin concentration (CF) in water, catalyst properties, and heating mode. 20 wt% formalin is found to be the critical concentration, above and below which the 5‐hydroxymethylfurfrual and the LA are formed, respectively. The conversion and LA yield over H‐zeolite are higher by 2.3 and 17 times, respectively, as compared to those over Na‐zeolite. The Brønsted to Lewis acid sites ratio is found to be a crucial catalytic parameter to obtain the best activity and LA yield. Under optimal reaction conditions and with the best catalyst, 42% LA yield is obtained at 90% furfural conversion. The humins formed during the process are characterized using Fourier transformed infrared spectroscopy and thermogravimetric analysis. The humins yield, functionality, and decomposition temperatures are varied with both CF and catalyst properties. The reaction pathways and intermediates are also postulated. The integration of the developed process/route with the existing C6 routes allows the utilization of the entire carbohydrate content of the lignocellulosic biomass to produce LA, and consequently, the overall process becomes more economical.

Levulinic acid production from furfural: process development and techno-economics

“…The procedure used for the conversion of FF to LA and product analysis was similar to those reported in our earlier studies. 22,23 In brief, for a typical experiment, 2.5 g of solvent (formalin + water) was taken in a 10 mL Pyrex glass reactor vial. 0.25 g of furfural (furfural concentration, C FF ) (10 wt% with respect to solvent) was added to the solvent mixture, maintaining a 2 : 1 w/w formalin to furfural ratio (i.e., a 2.4 : 1 mol/mol formaldehyde to furfural ratio, while the stoichiometric requirement is 1 : 1 mol/mol).…”

“…The reaction temperature, time, maximum power (300 W) and stirring speed were programmed and set in the reactor. The optimal reaction conditions (170 °C and 1 h) obtained in our previous study, 22 over the synthesized HZSM-5 catalyst, were used here to test the initial parameter (i.e., the effect of the catalyst to furfural ratio). The MW power and heating ramp were auto-tuned to attain and maintain the set temperature.…”

“…In our earlier study, we reported a microwave (MW) heating based process for HMF/LA production from furfural over hierarchical HZSM-5 zeolites. 22,23 Here, we report the direct and rapid transformation of high wt% xylose and bio-derived furfural to levulinic acid in an energy-efficient microwave reactor without high-pressure hydrogen and expensive metal catalysts. The effects of the catalyst : formalin : furfural weight ratio, reaction temperature and time, furfural concentration, different organic solvents, and source of heating on the feed conversion and product distribution were studied.…”

Microwave-Assisted Conversion of Carbohydrates

“…Numerous literature data show that, under microwave activation conditions, higher reaction rates are achievable than under thermal activation [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 ]. This is the way to enhance the yields of final products.…”

“…A novel one-step process for the synthesis of levulinic acid from furfural produced from natural carbohydrates over hierarchical zeolites in a microwave reactor has been reported [ 27 ]. Brønsted acid sites play a role in the catalytic activity and their high concentration and properly chosen strength are beneficial for the high yield of levulinic acid reaching 42% at 90% furfural conversion.…”