Production of Sustainable Hydrogen from Lignocellulosic Biomass: Towards Integrated Biorefinery

According to the Net Zero Emissions by 2050 (NZE2050) scenario of the International Energy Agency (IEA), the global CO2 emissions need to be reduced by around 45% from 2010 levels by 2030 and reach net zero by 2050. In such a scenario, hydrogen is projected as a fascinating energy carrier among the environmentally friendly solutions by using sustainable resources for its production. However, the production of hydrogen from renewable resources towards a sustainable circular bioeconomy is rare to date. In this framework, the production of H₂-rich syngas from an organosolv cellulose pulp is presented.

In the first step, the softwood sawdust is fractionated on a laboratory scale into its main components (cellulose, lignin, and hemicellulose) using a mild-conditions formic acid organosolv process. The fractionation was subsequently upscaled from lab scale to pilot scale. Silicon (Si) was the main inherent mineral element in the resulting cellulose pulp while alkali metals were dissolved.

Next, different experimental conditions were applied to carry out steam gasification of the cellulose pulp in a lab-scale semi-continuous reactor using a in a multi-stage process approach: a slow pyrolysis followed by the steam gasification of biochar. At temperatures below 950°C, the steam gasification of cellulose pulp biochar was significantly hindered by the inhibitory effect of Si.

At 950°C, the results showed a great potential hydrogen production up to 56.3 vol.% and 40 g_H2/kg_{cellulose pulp}. The process was modeled to examine the overall performance and evaluate the heat integration. When integrating organosolv treatment to steam gasification, hydrogen production efficiency dropped from 41.5 to 26.2% while the energy requirement raised from 77 to 111 kWh/kg (H₂).

Further assessment in terms of solvent and by-products recovery is necessary to improve process efficiency. Thus, hydrogen from integrated biorefineries could potentially complement electrolysis (51%, 50-65 kWh/_kgH2).

The ability to generate hydrogen (H2) through cellulose pulp and create value-added products using lignin and hemicellulose opens up fresh possibilities for the establishment of environmentally friendly biorefineries that operate on a closed carbon cycle. These biorefineries can be developed using biomass sources unrelated to food production, contributing to sustainable and renewable energy solutions.