Flash pyrolysis of cellulose for production of anhydro-oligomers

Evidence is presented showing that it should be possible to depolymerize a purified cellulose to produce anhydro-oligosaccharides containing small numbers of glucosidic units if suitable reaction conditions are chosen. Experiments were carried out in a stream of nitrogen in a downflow cocurrent tubular reactor with a high temperature wall, Two sizes of particles of Avicel pH102 were used and two sizes of reactor tube with wall temperatures from 850 to 1200 degrees C and residence times from 35 to 75 ms. From the solid residue of the reaction, a water soluble fraction was recovered which contained anhydrosugars. Yields of soluble solids of up to 44% of the cellulose fed were obtained in a small diameter tube, and up to 34% in a larger diameter reactor, only a narrow window of reaction conditions exists which is optimal for maximum yields. Carbohydrate analyses showed significant yields or anhydro-oligosaccharides from G(2) to G(7), the limit of resolution for the HPLC column used, Normally, these compounds made up similar to 50% of the soluble solids fraction. Substantial amounts of material > G(7) were also produced but could not be identified, Tests were also done with pretreated Avicel, but only one method gave improved results (slow preheating) Given the probable high unit value of anhydro-ologosaccharides, it would appear that this method of flash pyrolysis may be worth further exploitation. (C) 2000 Elsevier Science B.V. All rights reserved.