Multiscale molecular modeling can be an effective tool to aid the development of biomass conversion technology: A perspective

New Mechanistic Insights into the Lignin β-O-4 Linkage Acidolysis with Ethylene Glycol Stabilization Aided by Multilevel Computational Chemistry

Acidolysis in conjunction with stabilization of reactive intermediates has emerged as one of the most powerful methods of lignin depolymerization that leads to high aromatic monomer yields. In particular, stabilization of reactive aldehydes using ethylene glycol results in the selective formation of the corresponding cyclic acetals (1,3-dioxolane derivatives) from model compounds, lignin, and even from softwood lignocellulose. Given the high practical utility of this method for future biorefineries, a deeper understanding of the method is desired. Here, we aim to elucidate key mechanistic questions utilizing a combination of experimental and multilevel computational approaches. The multiscale computational protocol used, based on ReaxFF molecular dynamics, represents a realistic scenario, where a typical experimental setup can be reproduced confidently given the explicit molecules of the solute, catalyst, and reagent. The nudged elastic band (NEB) approach allowed us to characterize the key intermolecular interactions involved in the reaction paths leading to crucial intermediates and products. The high level of detail obtained clearly revealed for the first time the unique role of sulfuric acid as a proton donor and acceptor in lignin β-O-4 acidolysis as well as the reaction pathways for ethylene glycol stabilization, and the difference in reactivity between compounds with different methoxy substituents.

Catalytic liquefaction of sewage sludge to small molecular weight chemicals

The catalytic hydrotreatment of sewage sludge, the wet solid byproducts from wastewater treatment plants, using supported Ir, Pt, Pd, Ru catalysts had been investigated with different solvent conditions. Reactions were carried out in a batch set-up at elevated temperatures (400 °C) using a hydrogen donor (formic acid (FA) in isopropanol (IPA) or hydrogen gas), with sewage sludge obtained from different sampling places. Sewage sludge conversions of up to 83.72% were achieved using Pt/C, whereas the performance for the others catalysts is different and solvent had a strong effect on the conversion rate and product constitution. The sewage sludge oils were characterised using a range of analytical techniques (GC, GC-MS, GCxGC, GPC) and were shown to consist of monomers, mainly alkanes and higher oligomers.

Origins of complex solvent effects on chemical reactivity and computational tools to investigate them: a review

Origins of solvent-induced enhancement in catalytic reactivity and product selectivity are discussed with computational methods to study them.

Unravelling the catalytic influence of naturally occurring salts on biomass pyrolysis chemistry using glucose as a model compound: a combined experimental and DFT study

Alkali and alkaline-earth metal loaded biomass pyrolysis highlights that different metal ions have different effects on bio-oil composition.

Molecular Dynamics Simulations of Furfural and 5-Hydroxymethylfurfural at Ambient and Hydrothermal Conditions

In this work, we present results from molecular dynamics simulations of aqueous solutions of furfural and 5-hydroxymethylfurfural, which are important intermediates in the hydrothermal carbonization processes of biomass conversion. The computations were performed both at ambient and hydrothermal conditions using a two-level factorial design varying concentration, temperature, and pressure. A number of equilibrium and dynamic properties have been computed including enthalpies and free energies of vaporization, free energies of solvation, diffusion coefficients, and rotational/reorientational correlation times. Structural properties of solutions were analyzed using radial and spatial distribution functions. It was shown that the formation of hydrogen bonds among 5-hydroxymethylfurfural molecules is preferred compared to hydrogen bonding between 5-hydroxymethylfurfural and water. In addition, our results suggest that the oxygen atoms in the furan rings of furfural and 5-hydroxymethylfurfural do not participate in hydrogen bonding to the same extent as the oxygen atoms in the hydroxyl and carbonyl groups. It is also observed that furfural molecules aggregate under certain conditions, and we show how this is affected by changes in temperature, pressure, and concentration in agreement with experimental solubility data. The analysis of the computational results provides useful insight into the structure and dynamics of the considered molecules at conditions of hydrothermal carbonization, as well as at ambient conditions.

Molecular Modelling for Reactor Design

Chemical reactor modelling based on insights and data on a molecular level has become reality over the last few years. Multiscale models describing elementary reaction steps and full microkinetic schemes, pore structures, multicomponent adsorption and diffusion inside pores, and entire reactors have been presented. Quantum mechanical (QM) approaches, molecular simulations (Monte Carlo and molecular dynamics), and continuum equations have been employed for this purpose. Some recent developments in these approaches are presented, in particular time-dependent QM methods, calculation of van der Waals forces, new approaches for force field generation, automatic setup of reaction schemes, and pore modelling. Multiscale simulations are discussed. Applications of these approaches to heterogeneous catalysis are demonstrated for examples that have found growing interest over the last few years, such as metal-support interactions, influence of pore geometry on reactions, noncovalent bonding, reaction dynamics, dynamic changes in catalyst nanoparticle structure, electrocatalysis, solvent effects in catalysis, and multiscale modelling.

Progress in the production of biomass-to-liquid biofuels to decarbonize the transport sector – prospects and challenges

Annually the transport sector consumes a quarter of global primary energy and is responsible for related greenhouse gas emissions.

Mechanistic insights into the catalytic elimination of tar and the promotional effect of boron on it: first-principles study using toluene as a model compound

The incorporation of a monolayer subsurface B into the Ni catalyst results in a corrugated Ni top surface and the activation of toluene is significantly promoted on B–Ni.

Insights into the solvation of glucose in water, dimethyl sulfoxide (DMSO), tetrahydrofuran (THF) and N,N-dimethylformamide (DMF) and its possible implications on the conversion of glucose to platform chemicals

The presence of co-solvents, like DMSO, DMF and THF, significantly alters (i) the interaction of glucose with water, (ii) the mobility of glucose and (iii) its bonding with the solvent environment. This may have implications on glucose conversion reactions.

Solvation dynamics and energetics of intramolecular hydride transfer reactions in biomass conversion

Solvent dynamics and non-equilibrium solvation alter the energetics of the hydride transfer step and thus, can significantly affect reaction kinetics.