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  • 1.
    Bazooyar, Faranak
    University of Borås, School of Engineering.
    Molecular-level Simulations of Cellulose Dissolution by Steam and SC-CO2 Explosion2014Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Dissolution of cellulose is an important but complicated step in biofuel production from lignocellulosic materials. Steam and supercritical carbon dioxide (SC-CO2) explosion are two effective methods for dissolution of some lignocellulosic materials. Loading and explosion are the major processes of these methods. Studies of these processes were performed using grand canonical Monte Carlo and molecular dynamics simulations at different pressure/ temperature conditions on the crystalline structure of cellulose. The COMPASS force field was used for both methods. The validity of the COMPASS force field for these calculations was confirmed by comparing the energies and structures obtained from this force field with first principles calculations. The structures that were studied are cellobiose (the repeat unit of cellulose), water–cellobiose, water-cellobiose pair and CO2-cellobiose pair systems. The first principles methods were preliminary based on B3LYP density functional theory with and without dispersion correction. A larger disruption of the cellulose crystal structure was seen during loading than that during the explosion process. This was seen by an increased separation of the cellulose chains from the centre of mass of the crystal during the initial stages of the loading, especially for chains in the outer shell of the crystalline structure. The ends of the cellulose crystal showed larger disruption than the central core; this leads to increasing susceptibility to enzymatic attack in these end regions. There was also change from the syn to the anti torsion angle conformations during steam explosion, especially for chains in the outer cellulose shell. Increasing the temperature increased the disruption of the crystalline structure during loading and explosion.

  • 2.
    Bazooyar, Faranak
    et al.
    University of Borås, School of Engineering.
    Bolton, Kim
    University of Borås, School of Engineering.
    Molecular-level Simulations of Cellulose Dissolution by Steam and SC-CO2 Explosion2014Conference paper (Refereed)
    Abstract [en]

    Dissolution of cellulose is an important but tough step in biofuel production from lignocellulosic materials. Steam and supercritical carbon dioxide (SC-CO2) explosion are two effective methods for dissolution of some lignocellulosic materials. Loading and explosion are the major processes of these methods. Studies of these processes were performed using grand canonical Monte Carlo and molecular dynamics simulations at different pressure/ temperature conditions on the crystalline structure of cellulose. The COMPASS force field was used for both methods. The validity of the COMPASS force field for the calculations was confirmed by comparing the energy and structures obtained from molecular mechanics simulations of cellobiose (the repeat unit of cellulose), water–cellobiose, water-cellobiose pair and CO2-cellobiose pair systems with those obtained from first principle calculations with and without dispersion correction. A larger disruption of the cellulose crystal structure was seen during loading than that during the explosion process. This is seen by an increased separation of the cellulose chains from the centre of mass of the crystal during the initial stages of the loading, especially for chains in the outer shell of the crystalline structure. Reducing and non-reducing ends of the cellulose crystal show larger disruption than the central core; this leads to increasing susceptibility to enzymatic attack in these end regions. There was also change from the syn to the anti torsion angle conformations, especially for chains in the outer cellulose shell. Increasing the temperature increases the disruption of the crystalline structure during loading and explosion.

  • 3.
    Bazooyar, Faranak
    et al.
    University of Borås, School of Engineering.
    Momany, Frank A.
    Bolton, Kim
    University of Borås, School of Engineering.
    Validating Empirical Force Fields for Molecular-level Simulation of Cellulose Dissolution2012In: Computational and Theoretical Chemistry, ISSN 2210-271X, E-ISSN 2210-2728, Vol. 984, p. 119-127Article in journal (Refereed)
    Abstract [en]

    The calculations presented here, which include dynamics simulations using molecular mechanics forcefields and first principles studies, indicate that the COMPASS forcefield is preferred over the Dreiding and Universal forcefields for studying dissolution of large cellulose structures. The validity of these forcefields was assessed by comparing structures and energies of cellobiose, which is the shortest cellulose chain, obtained from the forcefields with those obtained from MP2 and DFT methods. In agreement with the first principles methods, COMPASS is the only forcefield of the three studied here that favors the anti form of cellobiose in the vacuum. This forcefield was also used to compare changes in energies when hydrating cellobiose with 1–4 water molecules. Although the COMPASS forcefield does not yield the change from anti to syn minimum energy structure when hydrating with more than two water molecules – as predicted by DFT – it does predict that the syn conformer is preferred when simulating cellobiose in bulk liquid water and at temperatures relevant to cellulosedissolution. This indicates that the COMPASS forcefield yields valid structures of cellulose under these conditions. Simulations based on the COMPASS forcefield show that, due to entropic effects, the syn form of cellobiose is energetically preferred at elevated temperature, both in vacuum and in bulk water. This is also in agreement with DFT calculations.

  • 4.
    Björk, Hans
    et al.
    University of Borås, School of Engineering.
    Lindecrantz, Kaj
    University of Borås, School of Engineering.
    Ericsson, Dag
    University of Borås, School of Engineering.
    Sarv, Hans
    University of Borås, School of Engineering.
    Bolton, Kim
    University of Borås, School of Engineering.
    Börjesson, Anders
    University of Borås, School of Engineering.
    Bazooyar, Faranak
    University of Borås, School of Engineering.
    Ahlström, Peter
    University of Borås, School of Engineering.
    Taherzadeh, Mohammad
    University of Borås, School of Engineering.
    Andersson, Bengt-Åke
    University of Borås, School of Engineering.
    Johansson, Andreas
    University of Borås, School of Engineering.
    Skrifvars, Mikael
    University of Borås, School of Engineering.
    20 år med Institutionen Ingenjörshögskolan: historik, nuläge och framtid2009Report (Other academic)
  • 5.
    Bolton, Kim
    et al.
    University of Borås, School of Engineering.
    Börjesson, Anders
    University of Borås, School of Engineering.
    Ahlström, Peter
    University of Borås, School of Engineering.
    Bazooyar, Faranak
    University of Borås, School of Engineering.
    Beräkningsteknik2009In: Vetenskap för profession, ISSN 1654-6520, no 10, p. 63-68Article in journal (Other academic)
  • 6. Samadikhah, Kaveh
    et al.
    Larsson, Ragnar
    Bazooyar, Faranak
    University of Borås, School of Engineering.
    Bolton, Kim
    University of Borås, School of Engineering.
    Continuum-molecular modelling of graphene2012In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 53, no 1, p. 37-43Article in journal (Refereed)
    Abstract [en]

    membranes using a hierarchical modeling strategy to bridge the scales required to describe and understand the material. Quantum Mechanical (QM) and optimized Molecular Mechanical (MM) models are used to describe details on the nanoscale, while a multiscale continuum mechanical method is used to model the graphene response at the device or micrometer scale. The complete method is obtained on the basis of the Cauchy Born Rule (CBR), where the continuum model is coupled to the atomic field via the CBR and a local discrete fluctuation field. The MM method, often used to model carbon structures, involves the Tersoff--Brenner (TB) potential; however, when applying this potential to graphene with standard parameters one obtains material stress behavior much weaker than experiments. On the other hand, the more fundamental Hartree Fock and Density Functional Theory (DFT) methods are computationally too expensive and very limited in terms of their applicability to model the geometric scale at the device level. In this contribution a simple calibration of some of the TB parameters is proposed in order to reproduce the results obtained from QM calculations. Subsequently, the fine-tuned TB--potential is used for the multiscale modeling of a nano indentation sample, where experimental data are available. Effects of the mechanical response due the calibration are demonstrated.

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