(677f) Concentrated Phosphoric Acid for Enhanced Conversion of Cellulose to HMF

Achieving high yields of HMF requires effective hydrolysis, isomerization, and dehydration of glucose from cellulose. We report the use of a cellulose solvent (85% w/w phosphoric acid) to remove and then recover cellulose from several plant biomasses (corn stover, switchgrass, and poplar) and microcrystalline cellulose (Avicel). The resultant amorphous cellulose is subjected to a conversion process where maleic acid hydrolyzes the cellulose to glucose, AlCl₃ isomerizes the resultant glucose to fructose, and both acid catalysts dehydrate the fructose to HMF in a single reactor bi-phasic reactor where HMF is continuously extracted into MTHF.

The results confirm yields of HMF (35 to 40%) can be increased by cellulose dissolution in concentrated phosphoric acid followed by hydrolysis of the re-precipitated amorphous cellulose. The increase in HMF yields is dependent upon the type of biomass.  The total sugar conversion (C5 and C6 sugars) from the whole intact lignocellulosic starting biomass reaches >90% in the best case.