Recent Advances in Mechanochemical Pretreatment of Lignocellulosic Biomass

Abstract

Biorefineries are industrial facilities where biomass is converted into chemicals, fuels and energy. The use of lignocellulose as raw material implies the development of pretreatments to reduce its recalcitrant character prior to the processes that lead to the synthesis of the products of interest. These treatments are based on physico-chemical processes where it is necessary to use acids, bases, oxidants, and high pressure and temperature conditions that lead to the depolymerization of lignocellulose at the expense of generating a series of streams that must be treated later or to the production of by-products. In recent years, mechanochemistry is becoming relevant in the design of processes that help in the depolymerization of lignocellulose. These mechanochemical processes are being used in combination with chemicals and/or enzymes, allowing the use of minor loads of reagents or enzymes. In this review, the advances achieved in the use of mechanochemistry for treating lignocellulosic biomass or cellulose will be presented, with special emphasis on how these mechanochemical processes modify the structure of lignocellulose and help subsequent treatments. It will focus on using ball milling or extrusion, ending with a section dedicated to future work needed to implement these technologies at the industrial level.

Recrystallization of Cellulose, Chitin and Starch in Their Individual and Native Forms

“…Mechanical treatment associated with comminution, particle deformation, and accumulation of defects in the crystal lattice is an efficient method for changing the physicochemical properties of semi-crystalline polymers in the individual and native forms [1][2][3]. Thus, mechanochemical methods have shown good results for the modification and processing of lignocellulose materials [4][5][6], fabrication of nanosized and nano-structured cellulose particles, starch, and chitosan [7][8][9], amorphization and deacetylation of chitin [3,[10][11][12], and other mechanochemical reactions (oxidation and etherification) [13,14]. Amorphization (AM) of the crystalline regions of biopolymers (most typically, cellulose, starch, chitin, chitosan, and β-glucan) is largely responsible for the enhanced reactivity of mechanically pretreated materials.…”