Biochemical Engineering for Biomass Refinery
Lignocellulosic biomass is a kind of solid phase substrates with complex porous media.However, the traditional bioconversion technology of lignocelluloses focuses on improving the enzymatic hydrolysis efficiency, but knows little about its intrinsic porous characteristies.Indeed,from non-crystalliine region and crystalline regions of cellulose,filaments,pits,cell lumen,to vascular bundle,each level of lignocelluloses reflects the basic concept and theory of the porous medium,such as porosity,surface area,permeability,etc.The heat and mass transfer of porous medium are involved in many major pperation units of lignocelluloses bioconversion. We revealed that the intrinsically porous characteristics of lignocekllulose biomass,namely, porous media with pores of different aperture taking cell walls and intracellular materials as solid framework. These pores are used for the presence or transfer of fluids.
Based on the cognition of intrinsically porous characteristics of lignocellulosic biomass, we proposed the concept of seepage recalcitrance in terms of process engineering. Seepage recalcitrance is defined as the resistance of porous plant biomass to mass transfer.The resistance is determined by porous structure parameters including pore size distribution,specific surface area,tortuosity,fractal dimension and so on.Seepage recalcitrance and be characterized by threshold pressure,The higher the threshold pressure is ,the more the seepage recalcitrance is established in terms of the process engineering of mass transfer in porous media,used to be distinct form biomass recalcitrance,which is mainly proposed in terms of biology and botany.It is defined as the resistance of porous media into the process of plant cellulose bioconversion.Seepage recalcitrance cares about the whole plant structures including cell wall,various cells(pit in cell wall),and different tissues(lumen and intercellular,cell corner),and highlights the mass transfer in the whole enzymatic hydrolysis process,including the process of reaching and releasing substrate or active site both.
The proposal of biomass seepage recalcitrance would promote our understanding about the relationships between structure and enzymatic hydrolysis of lignocellulosic biomass.Moreover,for lignocellulosic biomass refining,pretreatment technology would be guided with an engineering index(threshold pressure) and enzymatic hydrolysis would be intensified by overcoming the threshold pressure.