Softwood Hydrolysis in a Shrinking Bed Flow-through Reactor

The advantages of countercurrent operation in dilute-acid hydrolysis of biomass have been shown in both mathematical simulations and in proof-of-concept experiments. This led to the installation of a pilot-scale countercurrent reactor at the National Renewable Energy Laboratory (NREL) in 2000. During the 6 months it was operated, not all technical problems were overcome. Especially, themechanical transport of the solid material upwards proved difficult to achieve at high temperature and/or high conversion, as the material became too mud-like. The material used in all these experiments was yellow poplar, a hardwood species that loses much of its lignin already in the prehydrolysis stage. In the following countercurrent stage, even more lignin is solubilized, and the materialbecomes mud-like. Softwood on the other hand, only loses about 10% of its lignin during hydrolysis, and seems to retain its structure. The result of this difference is that softwood is less muddy, and therefore probably easier to operate in a countercurrent reactor. To investigate this difference further, and to predict the mechanical behaviour of softwood in a countercurrent reactor, we haveused the shrinking bed flow-through reactor developed at NREL.