Piotr Majerski

A second look at fast pyrolysis of biomass—the RTI process

Abstract Over the past two decades a great deal of experimental work as been carried out on the development of fast pyrolysis processes, particularly for biomass and for lignocellulosic waste materials. High yields of an organic liquid product (50–70%) are typical of atmospheric pressure short contact time pyrolysis of such feedstocks. This liquid product has been shown to be usable both as an alternative liquid fuel, and as a chemical feedstock because of its content of significant concentrations of potentially useful organic chemicals. The characteristics of the more important fast pyrolysis processes are reviewed, and the advantages and problems existing with present pyrolysis reactors are discussed, with the emphasis on bubbling fluidized bed systems. Experience with the process has led us to a somewhat different view of the optimal conditions for fast pyrolysis, and has resulted in the recent development of a new fluid bed process—the RTI Process. Characteristics of the RTI process are described and its advantages over existing fast pyrolysis technologies summarized.

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°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 of anhydro-oligosaccharides from G2 to G7, the limit of resolution for the HPLC column used. Normally, these compounds made up ∼50% of the soluble solids fraction. Substantial amounts of material >G7 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.

Fast pyrolysis of sweet sorghum and sweet sorghum bagasse

Abstract The Waterloo Fast Pyrolysis methodology which employs a bed of fluidized sand at atmospheric pressure was used to evaluate the yields of pyrolytic liquids from Italian sweet sorghum and sweet sorghum bagasse. Reaction temperatures were varied from 400°C to 560°C, and apparent volatiles residence times from 222 to 703 ms. The sorghum bagasse gave results typical of similar grasses. A maximum liquid yield (dry basis) of 69.4% by weight was achieved at 510°C when the volatiles apparent residence time was held constant at 500 ms. However, at shorter residence times (255 ms), liquid yields were slightly higher at a constant temperature of 525°C. Because of the high ash content of the bagasse, the char obtained (about 13%) had an ash content of nearly 50%. The liquid product composition was similar to that obtained from fast pyrolysis of other grasses. Tests were also done with bagasse which had been deionized. A much higher conversion of the cellulose and hemicellulose content to anhydrosugars resulted, with a corresponding reduction in low molecular weight carbonyl compounds. Whole (raw) sweet sorghum was pyrolyzed similarly. The high sugar content (36%) of this biomass resulted in a more unusual pyrolysis behaviour. High yields of carbon dioxide were obtained, and liquid yields were somewhat lower (63%) than those from the bagasse, and were obtained at a lower temperature (450°C). Volatiles residence time in the range used had little effect on liquid yield amounts. Both raw sweet sorghum and sweet sorghum bagasse appear to be suitable feedstocks for the production of organic liquids by fast pyrolysis. However, better yields and a better quality liquid (for fuel purposes) are obtained from the bagasse.