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 num bers of glucosidic units if suitable reaction conditions are chosen. Experi ments were carried out in a stream of nitrogen in a downflow cocurrent tubu lar 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 8 50 to 1200 degrees C and residence times from 35 to 75 ms. From the solid r esidue of the reaction, a water soluble fraction was recovered which contai ned anhydrosugars. Yields of soluble solids of up to 44% of the cellulose f ed were obtained in a small diameter tube, and up to 34% in a larger diamet er reactor, only a narrow window of reaction conditions exists which is opt imal for maximum yields. Carbohydrate analyses showed significant yields or anhydro-oligosaccharides from G(2) to G(7), the limit of resolution for th e 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 t he probable high unit value of anhydro-ologosaccharides, it would appear th at this method of flash pyrolysis may be worth further exploitation. (C) 20 00 Elsevier Science B.V. All rights reserved.