(477c) The Formation Mechanism of the Tarry Material in Supercritical Water Gasification Process: a Study of Model Compounds

Tarry material (i.e., tar and char) is an undesirable product in the supercritical water gasification of biomass. It is composed of complex and high-molecular-weight compounds, which is difficult to gasify. The formation of tarry material, hence, reduces the carbon gasification efficiency of the process. 5-HMF (5-hydroxymethylfurfural) is believed to be an intermediate in the tarry material formation pathway. In the present work, the kinetic rates of formation of the char particles from glucose (a biomass model compound), 5-HMF and a mixture of them were compared. The experiments were conducted in a temperature range of 300 ? 450°C, at 25 MPa and up to a residence time of 3,000 s. The initial concentration of glucose was varied from 1.5 to 3 wt% (i.e., 0.42 to 0.83 M). The mixed feedstock was 1.5 wt% glucose and 0.01-M 5-HMF. Glucose was found to produce char particles much faster than 5-HMF feedstock. At 350ºC, the char particles emerged in as fast as 5 s from glucose while it took around 80 s for the 5-HMF experiment. While 0.01-M 5-HMF alone did not produce any particles (Chuntanapum et al., 2008), 0.01-M 5-HMF in the mixed feedstock with glucose gave char product, probably due to the catalytic effect of acidic products from glucose decomposition. High concentration of 5-HMF enhanced the formation of char particles, with the order of reaction of 4.29. The FT-IR and CHO elementary analysis of the solid products were carried out.

Reference:

Chuntanapum, A.; Yong, K. T. L.; Miyake, S.; Matsumura, Y. Behavior of 5-HMF in Subcritical and Supercritical Water. Ind. Eng. Chem. Res. 2008, 47, 2956-2962.