Computer Simulation of the Dissolution and Regeneration of Cellulose from Ionic Liquids

Project Information

DiReC-IL

Grant agreement ID: 708175

DOI

10.3030/708175

Project closed

EC signature date 10 February 2016

Start date 1 January 2017

End date 31 December 2018

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 166 156,80

EU contribution

€ 166 156,80

Coordinated by

UNIVERSITAT WIEN
Austria

Periodic Reporting for period 1 - DiReC-IL (Computer Simulation of the Dissolution and Regeneration of Cellulose from Ionic Liquids)

Reporting period: 2017-01-01 to 2018-12-31

Summary of the context and overall objectives of the project

"The problem being addressed:
Cellulose is the most abundant and also the most widely used organic material on Earth accounting for roughly 40 and 90% of the dry mass of wood and cotton, respectively.
The separation of cellulose fibers from other plant materials is often achieved by applying strong, derivatizing chemicals (e.g. NaOH) in order to dissolve cellulose fibers, while keeping the polymeric structure of cellulose molecules intact.
Cellulose-intensive industries (paper and textile) consume an ever-increasing amount of cellulose. In order to satisfy this increasing need in a sustainable way one needs to improve processing techniques allowing 1) to employ resources (e.g. wood waste) not yet used and 2) to develop new, green and less hazardous chemicals which also ensure the application of less hostile processing conditions, and thus reducing related costs.

The recalcitrance of cellulose (its extraordinary resistance to mechanical and chemical impact) is rooted in its highly ordered pattern of H-bonds that hold cellulose fibers together.
Ionic liquids (ILs) were found to be very efficient solvents for dissolving cellulose, presumably because of their efficacy in breaking those strong H-bonds and their somewhat amphiphilic character providing a particular solvation environment.
The aim of this project is to provide new insight into the dissolution mechanism and to contribute in an indirect way to the development of better IL solvents.

Importance for society:
The development of more benign, potentially less dangerous solvents which, at the same time, also ensure better energy efficiency, and consequently more economical operation with lower carbon footprint are of crucial importance to improve sustainability of modern societies.
These better, greener technologies would allow for the development of industries (in line with one of the major objectives of the European Union) based on more carbon-neutral, bio-degradable resources, such as cellulose.

Overall objectives:
The main objective of this project is to provide new insight into the dissolution mechanism of cellulose in the BMIM Cl ionic liquid by applying a bottom-up approach starting with understanding the dissolution mechanism of glucose, the monomer of cellulose in this ionic liquid (in comparison to the dissolution in water), and then gradually increasing the complexity of considered sugars. This would eventually allow us to extrapolate to the case of cellulose.

Conclusions:
-The ideal set of force fields for the dissolution study consists of the force field by Mondal et al (J. Phys. Chem. B, 2015, 119, 11041–11051), CHARMM36 for sugars, and TIP4P/2005 for water.
-Cl ions form very strong H-bonds with the OH groups of sugars, sometimes even ""bidentate"" complexes. The breaking up of of H-bond between sugar molecules due to Cl ions happens on a much faster timescale than in water.
-The number of still intact H-bonds to other sugar molecules together with the number of already formed ones with the solvent is a good measure for the study of the evolution of the dissolution process
-In the case of larger sugar molecules, the change in conformation of glycosidic bonds is also an important indicator of the progress of the dissolution.
-The cation acts as a H-donor to form H-bonds with the OH groups of sugars (though much weaker than Cl ions). They can effectively shield the hydrophobic side of the sugar molecules (in the axial directions)."

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

"In the first phase, the optimization of a set of force field parameters was carried out.
Due to large number of available force fields we omitted any force field refinements. Instead, we set another alternative goal to assess available force fields and name three computer models (one for the sugars, the ionic liquid, and water) that work reliably well in combination.
Due to the abundance of force fields, and the scarcity of available (useful) experimental data this part took longer than expected. In fact, some experimental data was of little use, and in the end, we were left with a limited range of data. This data was completed with high precision (quantum) DFT calculations. This part was done in collaboration with Dr. Elixabete Rezabal (University of the Basque Country, Spain) who is an expert in conducting DFT calculations on solutions.

In second phase, the dissolution of crystalline β-D-glucose in IL and water was studied.
We performed simulations where we applied position restraint to all glucose molecules except for one, either at the middle or at the corner of an edge (those that we found to be most prone to get dissolved). We tested different potential collective variables as order parameter describing the dissolution and found that the number of H-bonds both with the other sugars and solvent molecules works best. Based on the generated dissolution trajectories further “reactive” trajectories were generated using the PyRETIS python library to carry out Transition Path Sampling calculations.
The analysis of the results is still being carried out, and we expect to finish this analysis and proposing a dissolution mechanism by Spring.

The dissolution of cellobiose, in a very similar manner is still being studied. We found that attacks on the glycosidic bond and breaking its stabilizing H-bonds (leading to conformational changes) is crucial for increasing the molecule's flexibility and hence also the probability of being exposed to further ""dissolution attacks"". In the case of both sugar molecules (glucose and cellobiose) we observed that the CH2OH group is the most likely to lose its H-bonds with other sugar molecules.

During the execution of the project we concluded that a restructuring of the tasks was sensible in order to reach a more complete picture.
Accordingly, we decided to first understand the dissolution mechanisms and to tackle the recrystallization in a later stage.

I took part in the following dissemination activities:
-Scientific conferences:
-Liquid matter conference 2017, Ljubljana, Slovenia
-European molecular liquids group (EMLG/JMLG) conference 2017, Vienna, Austria
-11th Conference on Colloid Chemistry, Eger, Hungary
-10th Liblice Conference on Statistical Mechanics, Srní, Czech Republic
-EMLG/JMLG Conference 2018, Nagoya, Japan
-Dissemination to the general public:
-“Lange Nacht der Forschung”, long night of the research: Nation-wide science night2028program series in Austria for the general public, especially kids
-“Apáczai Napok” Week of external presentations’ series at the Apáczai high school2028 (my former high school in Budapest, Hungary)"

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

We expect that other scientists will use this force field set for their cellulose dissolution studies in the BMIM Cl ionic liquid. Or in case of studying different ionic liquid, they will follow a similar rigorous approach to find the best force field.

The expected socio-economic impact of the project is that eventually it will contribute (by paving the way for similar, larger studies) to better understanding the dissolution mechanism of cellulose in ionic liquids which will allow to design better, more efficient solvents. Such innovations will spur further technological development of industrial processes based on cellulose, which will promote a more sustainable, green economy and will create further working opportunities.

Cellobiose solvated in BMIMCl