Pyrolysis of Corncobs Catalyzed by Zinc Chloride for Furfural Production

The pyrolysis of corncobs impregnated with variable amounts of zinc chloride (ZnCl2) (up to 11%, on a dry sample mass basis) is investigated and compared with fir wood results. As expected, a continuous increase with the amount of impregnated catalyst in corncobs is observed of the formation rates of char and water (total yields from 46% up to 64%) associated with a decline in the yields of organic condensable products (from 38% to 18%) and gas (from 13% to 9%). Moderate ZnCl2 concentrations (2%−5%) favor the production of levoglucosenone (from trace amounts to 1%), acetic acid (from 4% to 6%), and furfural (from 0.65% to 6%). Moreover, low values, although causing the prompt decay in the yields of hydroxyacetaldehyde, hydroxypropanone, levoglucosan, minor carbohydrates, phenols, and guaiacols, enhance the formation rate of 5-hydroxy-methylfurfural, 4-hydroxy-5,6-dihydro-(2H)-pyran-2-one, 1-hydroxy-3,6-dioxabicyclo[3.2.1]octan-2-one, and 1,4:3,6-dianhydro-α-d-glucopyranose. Results support the speculation that dehydrated cellulose and galactoglucomannan hemicellulose produce levoglucosenone and 1,4:3,6-dianhydro-α-d-glucopyranose, instead of levoglucosan, which are then catalytically decomposed to other products, including furfural. ZnCl2 also catalyzes the primary paths of furfural formation via dehydration of pentosyl and glucosyl residues, with a stronger action on the former.