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Keywords:

  • absorption;
  • biomass;
  • heterogeneous catalysis;
  • hydrogen;
  • renewable resources

Abstract

Concerning energy and environmental sustainability, it is appealing to produce hydrogen from sugars or sugar alcohols that are readily obtained from the hydrolysis of cellulosic biomass. Nevertheless, the conversion of such compounds for hydrogen production poses great technical challenges. In this paper, we report that hydrogen purity and yield can be significantly improved by integrating in situ CO2 capture into the steam reforming reaction of the model compounds—glucose and sorbitol. The experimental assessment was conducted at a steam-to-carbon ratio of 1.8 for sorbitol and 6 for glucose from 450–625 °C. As predicted by thermodynamic analysis, combining CO2 capture and reforming reactions at favorable operating conditions yielded very high purity hydrogen, for instance, 98.8 mol % from sorbitol and 99.9 mol % from glucose. However, there are trade-offs between hydrogen purity and yield in practice. The lower operating temperatures in the examined range helped to increase the hydrogen purity and reduce the CO content in the gas product, whereas a high hydrogen yield was more likely to be obtained at higher temperatures. Coupling CO2 capture lowered the risk of coke formation during the steam reforming of glucose. Coke accumulated in the reactor for the sorption-enhanced steam reforming of glucose was mostly from the slow pyrolysis of glucose before it came into contact with the catalyst–acceptor bed. This problem may be solved by improving heat transfer or reconstructing the reactor, for instance, by using a fluidized-bed reactor.