The valuation of plant biomass from agricultural or forestry plants is part of a sustainable development approach. Research currently focuses on the development of new technologies to convert lignocellulosic biomass, the most abundant source of renewable carbon on the planet. So called second generation biochemical or thermochemical conversion techniques can transform biomass into biofuels and chemicals that can replace those obtained from petrochemical sources. The reactive extrusion using twin screw extrusion technology is very effective in the pretreatment of ligno-cellulosic biomass for second generation biofuels.
Lignocellulosic biomass may be extracted from the forest (wood chips, sawdust, bark …) or constituted from agricultural wastes (straw, stalks, bagasse, corn cobs …). Some high performance plants such as miscanthus and eucalyptus can be used as well as grass. The main advantage of this type of ligno-cellulosic biomass is that it does not compete with food production compared to the first generation which used agricultural resources.
Second generation biorefineries convert ligno-cellulosic biomass which is composed of the main following components:
- Cellulose, a linear polymer composed of hundreds of glucose units,
- Hemicellulose, a branched polymer composed of various sugars with 5 to 6 carbon atoms
- Lignin, a complex aromatic polymer more resistant to biological degradation than cellulose.
The twin screw extrusion process in the conversion of biomass
Twin-screw extruders perform the following functions in a continuous process:
- Thermomechanical defibration
- Chemical impregnation (intense solid-liquid mixing)
- Chemical reaction
- Micro / macro mixing
- Solid-liquid separation
The benefits of twin screw applied to the treatment of biomass are:
- Continuous Process
- Flexibility: ability to perform multiple functions in a single processing unit
- Reduction of characteristic times: faster reaction under the action of temperature and / or pressure, intense mixing of the reactants, more efficient heat transfer…