High-temperature decomposition of the cellulose molecule: a stochastic molecular dynamics study

Abstract

The kinetics and products of cellulose pyrolysis can be studied using large-scale molecular dynamics simulations at high temperatures, where the reaction rates are high enough to make the simulation times practical. We carried out molecular dynamics simulations employing the ReaxFF reactive force field to study the initial step of the thermal decomposition process. We gathered statistics of simulated reactive events at temperatures ranging from 1400 to 2200 K, considering cellulose molecules with different molecular weights and initial conformations. Our simulations suggest that, in gas-phase conditions at these high temperatures, the decomposition occurs primarily through random cleavage of the b(1 ? 4)-glycosidic bonds, for which we obtained an activation energy of (171 ± 2) kJ mol -1 and a frequency factor of 1:07 AE 0:12 ð ÞÂ10 15 s -1 . We did not observe dependency of the kinetic parameters on the molecular weight or initial conformation. Some of the decomposition reactions involved the release of low-molecular-weight products. Excluding radicals, the most commonly observed species were glycolaldehyde, water, formaldehyde and formic acid. Many of our observations are supported by the existing experimental and theoretical knowledge. We did not, however, observe the formation of levoglucosan, which is the dominant product in conventional pyrolysis experiments at much lower temperatures. This is understandable, since the high temperatures can force the dominance of radical reactions over pericyclic reactions. Nevertheless, our results support further use of ReaxFF-based molecular dynamics simulations in the study of cellulose pyrolysis.

Chirality and bound water in the hierarchical cellulose structure

“…This includes studies on the crystal structure of cellulose microfibrils (Matthews et al 2006;Wada et al 2011;Oehme et al 2015bOehme et al , 2018, and, as mentioned before, various aspects of the microfibril twist (Yui et al 2006;Matthews et al 2006;Yui and Hayashi 2007;Paavilainen et al 2011;Hadden et al 2013;Bu et al 2015;Conley et al 2016;Kannam et al 2017). Other studies have looked at the interactions of microfibrils with water (Yui et al 2006;Bergenstråhle et al 2008;Maurer et al 2013;Kulasinski et al 2015Kulasinski et al , 2017Lindh et al 2016;O'Neill et al 2017), their response to elevated temperatures (Matthews et al 2011(Matthews et al , 2012bZhang et al 2011); their mechanical properties (Paavilainen et al 2012;Saitoh et al 2013;Molnár et al 2018), aggregation and disintegration (Oehme et al 2015a;Paajanen et al 2016;Silveira et al 2016), chemical modification (Wada et al 2011;Paajanen et al 2016), enzymatic degradation (Beckham et al 2011;Orłowski et al 2015), and dissolution in ionic liquids (Gross et al 2011;Uto et al 2018); the pyrolytic degradation of cellulose (Zheng et al 2016;Paajanen and Vaari 2017); and radiation-induced defects (Polvi et al 2012;…”

Design of ultrathin hybrid membranes with improved retention efficiency of molecular dyes

“…Before creating the complete systems with cellulose, dyes and solvent molecules, the substrate model was optimized and equilibrated in solution by means of short atomistic molecular dynamics (MD) simulations based on a reactive force eld (ReaxFF approach) appropriately parametrized to describe these kinds of system. [51][52][53][54][55][56] Preequilibration was performed in the NPT ensemble, at 300 K and 1 atm, to prepare the supports for subsequent simulations in crowded environments.…”

Selection of Optimal Polymerization Degree and Force Field in the Molecular Dynamics Simulation of Insulating Paper Cellulose

“…To determine the variation of the mechanical properties and solubility of the cellulose chain, models of 19 groups of single cellulose chains in the amorphous region with the polymerization degrees of 2,4,6,8,9,10,12,16,20,25,30,35,40,50,60,70,80,90, and 100 were constructed using COMPASS and PCFF force fields. The model density obtained by W. Chen [21] was about 1.385 g/cm 3 , while K. Mazeau and L. Heux [11] achieved a model with four different densities of 1.34-1.3927 g/cm 3 by modeling with the same method and standpoint, and proposed that the density of cellulose in the amorphous region is 1.28-1.44 g/cm 3 .…”