H2SO4-Catalyzed Pyrolysis of Corncobs

The acid-catalyzed pyrolysis of corncobs is investigated for the production of chemicals (in particular furfural) and bioproducts. Particles, preimpregnated with H2SO4 concentrations up to about 4% (dry sample mass basis) and predried at 343 K, are exposed in the form of a packed-bed at a heating temperature of 800 K. The gas release rate remains approximately constant, at a value about half with respect to the maximum detected for acid-free samples, for a large part of the process transients. Conversion times are roughly increased by 50% while reaction temperatures, on the average, become lower by about 20-40 K. Dehydrating and charring reactions become successively more favored suppressing the formation of condensable organic compounds. A decay is observed in the yields of both some carbohydrates (hydroxyacetaldehyde, hydroxypropanone, furfuryl alcohol, etc.) and phenolics (phenol, guiacol, 4-methyguaicol, 4-ethylguaicol, syringol) although less steep for the latter. However, catalyst concentrations below 0.5% lead to maxima in the yields of levoglucosan, 5-hydroxymethylfurfural, and l,6-anhydro-beta-D-glucofuranose. Moreover, the production is significantly enhanced of levoglucosenone (from trace amounts up to 4.5%) and furfural (from 0.65% up to 5%) at catalyst concentrations around 1-2% and 2-3%, with 1,4:3,6-dianhydro-alpha-D-glucopyranose (maximum yield 0.65%) acting as a reaction intermediate. The yield of acetic acid remains constant at 4% up to catalyst concentration around 3%. Higher catalyst concentrations are associated with a rapid decline in the yields of all these organic compounds with the total amount of char, carbon dioxide, and water reaching 70%.