Magnesium Oxide-Catalyzed Conversion of Chitin to Lactic Acid

Abstract

Although chitin, an N-acetyl-D-glucosamine polysaccharide, can be converted to valuable products by means of homogeneous catalysis, most of the chitin generated by food processing is treated as industrial waste. Thus, a method for converting this abundant source of biomass to useful chemicals, such as lactic acid, would be beneficial. In this study, we determined the catalytic activities of various metal oxides for chitin conversion at 533 K and found that MgO showed the highest activity for lactic acid production. X-ray diffraction analysis and thermogravimetry-differential thermal analysis showed that the MgO was transformed to Mg(OH)₂ during chitin conversion. The highest yield of lactic acid (10.8 %) was obtained when the reaction was carried out for 6 h with 0.5 g of the MgO catalyst. The catalyst could be recovered as a solid residue after the reaction and reused twice with no decrease in the lactic acid yield.

Keywords: biomass; chitin conversion; heterogeneous catalysis; lactic acid; magnesium oxide.

Figure 1

XRD patterns of chitin (a) before and (b) after ball milling for 48 h.

Figure 2

XRD patterns of (a) MgO‐1 before the chitin conversion reaction, (b) solid residue recovered after the chitin conversion reaction under the conditions shown in Table 2, and (c) Mg(OH)₂ as a reference.

Figure 3

(Upper panel) TG‐DTA curves of the solid residue obtained after MgO‐1‐catalyzed chitin conversion reaction under the conditions shown in Table 2 and (lower panels) images of samples during TG analysis. The images in panels (a) to (f) were recorded at the points indicated on the TG curve.

Figure 4

Reaction‐time dependence of yield of (circles) lactic acid and (triangles) acetic acid from conversion of chitin (0.5 g in 50 g of water) catalyzed by MgO‐1 (0.5 g) at 533 K.

Figure 5

Proposed mechanism for chitin conversion into lactic acid.

Figure 6

Photographs of tubes used to detect (a) NH₃ and (b) NO_x before (upper tube) and after (lower tube) injection of gas in the reactor. The NH₃ detecting tube was pink before use and changed to yellow when NH₃ was detected. The NO_x detecting tube was white before use and would have changed to orange‐yellow if NO_x had been detected.