Isomerization of Glucose to Fructose in Hydrolyzates

The isomerization of glucose-containing hydrolyzates to fructose is a key step in the 12 process from lignocellulosic biomass to the platform chemical hydroxymethylfurfural. We 13 investigate the isomerization reaction of glucose to fructose in water catalyzed by hydrotalcite. 14 Catalyst characterization is performed via IR, XRD and SEM. Firstly, glucose solutions at pH-neutral 15 conditions are converted under variation of temperature, residence time and catalyst loading 16 whereby a maximum of 25 wt.% fructose yield is obtained at 38 wt.% glucose conversion. Secondly, 17 isomerization is performed at pH = 2 using glucose solutions as well as glucose-containing 18 hydrolyzates from lignocellulosic biomass. Under acidic conditions, the hydrotalcite loses its 19 activity for isomerization. In consequence, it is unavoidable to neutralize the acidic hydrolyzate 20 before the isomerization step with an inexpensive base. As a neutralizing agent NaOH is preferred 21 over Ba(OH)2, since higher fructose yields are achieved with NaOH. Last, a pH-neutral hydrolyzate 22 from lignocellulose is subjected to isomerization, yielding 16 wt.% fructose at 32 wt.% glucose 23 conversion. This work targets the application of catalytic systems on real biomass-derived samples. 24