Cellulose, hemicellulose and lignin slow steam pyrolysis: Thermal decomposition of biomass components mixtures

Biomass thermochemical decomposition products have been extensively studied as renewable substitutes of fossil fuel. The approach proposed in this work considers vegetal waste as a source of both energy and matter through the production of a vapor phase fuel, highly diluted in steam, suitable to be burned in non-conventional combustion systems and a char with soil amending and fertilizing properties.To demonstrate the feasibility of such a process an experimental set-up has been designed with the aim to investigate the effect of pressure, heating rate and final temperature in proper variation ranges (P = 1–5 × 105 Pa, HR = 5–40 K/min, T = 473–973 K) on the yields and on the chemical and physical properties of gaseous and solid products. In this paper the effect of temperature at constant pressure (P = 5 × 105 Pa) and heating rate (HR = 5 K/min) has been investigated in order to explore all the stages of the thermochemical degradation from torrefaction to mild gasification passing through devolatilization. For real biomasses a basic study on characterization of biomass components is needed.Knowledge of dependences on feedstock nature and process conditions is crucial for the comprehension of phenomena occurring during steam pyrolysis of real complex biomasses and for the optimization of the process operating variables. This study characterizes steam pyrolysis up to 873 K (at pressure P = 5 × 105 Pa and heating rate HR = 5 K/min) both of three single biomasses constituents (cellulose, hemicellulose and lignin) and of three binary mixtures in order to evaluate possible interactions between the biomass components. The results obtained highlight the importance of the interactions between components, mainly cellulose and lignin, on the yield and characteristics of solid and gaseous products. In particular, strong components interactions have been detected on the specific surface area of the solid product.

► Mechanisms involved in steam pyrolysis of biomass components have been studied.
► Char porosity, vapor phase yield and HHV increase with process final temperature.
► Cellulose with respect to xylan and lignin gives a char with a higher surface area.
► Lignin is fundamental for the production of a vapor phase with a higher HHV.
► Interactions between biomass components affect char surface area.