(349d) Changes in Zeolite Structures Induced by Aqueous Biomass Solutions

Technology for the production of fuels and chemicals from alternative resources is needed to complement diminishing oil reserves. Biomass is a particularly interesting because it is renewable and CO₂-neutral. However, the considerable oxygen content and low vapor pressure of many biomass compounds present new challenges for processing technology. Specifically liquid phase processes will play a key role in future biorefineries. As water readily dissolves a considerable amount of polar oxygenates from biomass, it will likely be the solvent of choice in various processes. Unfortunately, many heterogeneous catalysts used in conventional oil refining have limited hydrothermal stability. Therefore, the development of heterogeneous catalysts with a sufficient stability for aqueous phase biomass conversion is one of the key challenges for implementing a biomass based infrastructure [1]. Numerous publications have reported modifications of zeolites by steaming [2]. However, relatively little is known about how the structure of zeolites is affected by water in liquid phase.

Different zeolites were treated with liquid hot water at 150 and 200 °C. Only very small changes were observed for the porosity, acidity and framework structure of ZSM-5 type zeolites. In contrast, much more pronounced modifications were observed for zeolite Y with different Si/Al ratios. The framework of these materials appears to disintegrate and form an amorphous silica-alumina phase with greatly reduced crystallinity and micropore volume. Structural changes were confirmed by ²⁷Al and ²⁹Si MAS NMR spectroscopy. In addition to pure water, different biomass solutions were used for treating zeolites. Increased dealumination of the zeolites was observed when molecules with multiple functional groups (e.g. glycerol, glucose) were present. It is suggested that this effect is due to the formation chelate complexes between the biomass molecules and aluminum cations.

References

1. Bell, A.T., Gates, B.C., and Ray, D. Catalysis for Energy. Washington, D.C., DOE BES report (2008).

2. C.S. Triantafillidis, A.G. Vlessidis, N.P. Evmiridis, Ind. Eng. Chem. Res. 39 (2000) 307.