Identification of the Soluble Byproducts Formed during the Hydrothermal Conversion of Cellulose Catalyzed by Solid Tungstated Alumina

The soluble byproducts formed during the hydrothermal conversion of cellulose catalyzed by solid tungstated alumina (AlW) were analyzed by LC–MS and LC–MS2 to determine their formulas and possible structures. These identified soluble compounds could be roughly divided into four species of carboxylic acids, α-carbonyl aldehydes, carbocyclic compounds, and furanic compounds with molecular mass in the range of 90–220 Da. Compared with the noncatalytic condition, the addition of AlW could increase the selectivity of carboxylic acids (especially α-hydroxy acid) from cellulose and suppress the formation of furanic compounds, carbocyclic compounds, and hydrochar. Based on the product distribution, the hydrothermal conversion route of glucose was proposed by regarding the formed α-carbonyl aldehydes as the key intermediates for formation of carboxylic acids, carbocyclic compounds, and furanic compounds.