The effect of metal salts on the decomposition of sweet sorghum bagasse in flow-through liquid hot water

The impact of the metal salts NaCl, KCl, CaCl2, MgCl2, FeCl3, FeCl2, and CuCl2, particularly the latter, on the decomposition of hemicellulose and lignin from sweet sorghum bagasse in liquid hot water pretreatment processing was studied in an attempt to enhance the recovery of sugars. Transition metal chlorides significantly enhanced the hemicellulose removal compared to the alkaline earth metal chlorides and alkaline metal chlorides, contributing to the formation of a saccharide-metal cation intermediate complex. FeCl2 greatly increased xylose degradation and about 60% xylan was converted into non-saccharide products. In contrast, an excellent total and monomeric xylose recovery was obtained after the CuCl2 pretreatment. Most of the lignin was deposited on the surface of the residual solid with droplet morphologies after this pretreatment, and about 20% was degraded into monomeric products. The total recovery of sugars from sweet sorghum bagasse with 0.1% CuCl2 solution pretreatment and 48 h enzymatic digestibility, reached 90.4%, which is superior to the recovery using hot water pretreatment only.