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The biofuels of the future: understanding and modeling enzymatic hydrolysis

Décember 2016

Ethanol production using lignocellulosic resources, known as 2nd generation (or 2G) bioethanol, is one of the avenues being explored today to diversify the supply of sustainable fuels over the coming years. As part of this process IFPEN is studying enzymatic hydrolysis, one of the key aspects in the development of associated industrial processes.

Among the various component operations involved in the 2G biobased ethanol production process, the conversion of cellulose into glucose via enzymatic hydrolysis remain a bottleneck due to its complexity of implementation and the economic impact of this part in the overall cost of the process. This complexity is related to the enzyme cocktail used: it must contain at least 3 families of enzymes, each with a specific function (see figure 1):

  • endoglucanases, adsorbed along cellulose chains and able to attack them in a random manner. They thus create new, smaller cellulose chains that can be hydrolyzed by cellobiohydrolases,
  • cellobiohydrolases, which depolymerize cellulose chains in a processive manner by producing a soluble glucose dimer, cellobiose from the extremities of the cellulose chains,
  • β-glucosidases which, in the liquid phase, convert cellobiose into glucose.

Enzymatic hydrolysis is impacted by the compositional and structural characteristics of the lignocellulosic resource. The quality of the hydrolysis is depending on the origin of the biomass and the pre-treatment applied. The mechanism that influence the recalcitrance of the pretreated biomass is not fully understood at present due to a lack of description of this enzymatic substrate.

It is for this reason that, in the 2000s, IFPEN launched modeling research aimed at gaining new data to better describe the activity of the cellulases on lignocellulosic substrates [1-2] :

  • A first Ph.D was focused on a comprehensive kinetic study of a cellulose substrate model using purifed enzymes or a reconstituted cocktail. The results obtained made it possible to determine the elementary reaction mechanisms, the synergistic effects and the associated kinetic parameters for the different enzyme families in the cocktail (see example in figure 2).
  • This work was then supplemented by a second Ph.D aimed at incorporating the main characteristics of a pre-treated lignocellulosic substrate (particle size, distribution of the degree of polymerization of the cellulose chains, etc.) to move on industrial substrate.

The body of knowledge obtained was incorporated into a model, taking into account the composition of the enzyme cocktail as well as the characteristics of the pre-treated lignocellulose [3]. This model makes it possible to study the impact of the composition of cocktails on their hydrolysis performance, as illustrated in figure 3.

Ultimately, this type of approach will be used to guide the development of more effective enzymatic cocktails, optimize their implementation and predict the reactivity of various lignocellulosic substrates.

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  1. M. Chauve, Modélisation cinétique de l'hydrolyse enzymatique des substrats cellulosiques, Thèse de l’Université de Grenoble, 2011.
  2. M. Huron, Modélisation cinétique de l’hydrolyse enzymatique de biomasse lignocellulosique, Thèse de l’Université de Grenoble, 2014.
  3. M. Huron, D. Hudebine, N. Lopes Ferreira, D. Lachenal, Mechanistic modeling of enzymatic hydrolysis integrating substrate morphology and cocktail composition, Biotechnology and Bioengineering, 113(5), p.1011-1023, 2016.

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