Enzyme hydrolysis of lignocellulosic material is a heterogeneous process and so it behaves

Significance 

Biofuel is a collective term for any fuel that is derived from biomass, that is, plant, algae material or animal waste. These types of fuels have been around longer than cars, but cheap gasoline and diesel have long kept them on the fringe. As such, much research has been centered around the simplification of the processes used for biofuel production. Technically, traditional approaches are mainly focused on the enzymatic hydrolysis of lignocellulosic materials through depolymerization into fermentable sugars, particularly using herbaceous crops.

Herbaceous crops are renewable and abundant. However, they consume large tract of land and demand intense labor; even most of them are considered agro-industrial residues or byproducts. There is a concern regarding their composition, given that they form very complex structures. A factor that plays an important role in the efficiency of the hydrolysis process and, consequently, affecting the cost of the process. For this reason, in many cases, a pretreatment stage is needed prior the enzyme hydrolysis. All these factors lead to a financially punitive production that is not sustainable nor competitive.

A review of existing literature shows that, currently, there is not an adequate kinetic model to predict the digestion process of all different types of substrates and conditions. Fortunately, it has already been established that the reasons for the aforementioned shortfalls can be attributed to the complexity of the enzymes action and the structural characteristics of the heterogeneous lignocellulosic biomass. Even worst, no model has considered certain typical effects of the heterogeneous nature of the process, such as the influence of the particle size on the hydrolysis rate.

Therefore, to address the aforementioned drawbacks, a team of researchers from the Department of Chemical Engineering and Food Technology at University of Cádiz (South of Spain) has developed a mathematical model to predict the kinetic behavior of the enzymatic conversion of different types of lignocellulosic biomass into fermentable sugars. The scientific squad is made up of Professor Ildefonso Caro, Professor Ana Blandino, Dr. Ana Belén Díaz and the PhD student Cristina Marzo. The group has vast knowledge in Chemistry and in Chemical Engineering and their research has been focused during the last years in the valorization of agro-food residues and byproducts. This includes grape and tomato pomace, orange peels, rice and wheat husk or exhausted sugar beet pulp, among others, to produce different value-added bioproducts.

In their last work, the aim was to develop a kinetic model based on the fundamentals of the heterogeneous reaction systems, to predict the enzymatic digestion of lignocellulosic biomass into monosaccharides. The results are currently published in the research journal, Biofuel, Bioproducts & Biorefining. In the proposed approach, digestion of the cellulosic polymers was carried out using enzymatic hydrolysis under different conditions. To assess the suitability of the model to any situation, the researchers analyzed the experimental data obtained during the hydrolysis of three different lignocellulosic residues. Specifically, the hydrolysis data of wheat straw, rice husks and exhausted sugar beet pellets were compared with the theoretical values calculated by the model.

The authors mainly observed that their model was able to predict the enzyme hydrolysis of lignocellulosic substrates under different conditions very accurately. Furthermore, the model could therefore be used efficiently in the optimization of the hydrolysis processes implemented in the bio-refinery industry.

In summary, the study investigated the influence of particle size on the kinetic process. Overall, strong robustness of the predictions was demonstrated by the effective simulation of hydrolysis of several lignocellulosic materials under different conditions. In a statement to Advances in Engineering, Professor Ildefonso Caro mentioned that “based on the demonstrated predictive efficient of the model, it could be successfully used to optimize the hydrolysis processes in the biorefinery industry”.

Reference

Ildefonso Caro, Ana Blandino, Ana Belén Díaz and Cristina Marzo. A kinetic model considering the heterogeneous nature of the enzyme hydrolysis of lignocellulosic materials. Biofuel, Bioproducts & Biorefining, volume 13, page 1044-1056.

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