Download Adsorption of complex gases in clathrate hydrates.

Master projects in the group of physical chemistry, Department of chemistry, for students
in the Nanotechnology program, students interested in computational chemistry and
others.
Adsorption of complex gases in clathrate hydrates.
Introduction.
Ice represents a phase of water in which
molecules are organized in a crystalline structure.
The structure is sustained due to hydrogen bonds,
which connect different water molecules between
themselves. The variety of possible bond
orientations produces a variety of ice types: there
are known 15 different crystalline phases of
water.
There exist a number of structures, which form
large cavities and therefore are fragile. These
structures are unstable and are not observer in a
pure form. However if there exists a guest
molecule, which can fit into a cavity, it can
stabilize the structure because of additional
interactions of the water molecules with guests.
Such materials, in which the gas molecules are
trapped in water cavities that are composed of
hydrogen-bonded water molecules, are called gas
hydrates. In contrast to common ice, hydrates form at the temperatures above 0 Celsius.
Gas hydrates are interesting object for industry from two opposite perspectives. On the one hand,
they are formed in the gas and oil pipes in the deep sea, blocking the flow. It is therefore
important to understand how to “melt” them to prevent the blockage. On the other hand, they are
good adsorbents for climate gases, in particular carbon dioxide. It is therefore important to
understand how to capture the desired gases
Objectives.
The project is devoted to study the adsorption of complex gas molecules into clathrate hydrates.
The goal is to obtain the adsorption isotherms and use them in order to predict different
equilibrium properties.
Tools.
The study is performed using Monte Carlo simulations. MC is a powerful tool to obtain the
average macroscopic properties of a system by sampling different positions of the microscopic
phase space.
Requirements.
Familiarity with statistical mechanics and molecular interactions.
Supervision.
Postdoc fellow Kirill Glavatskiy, Professor Signe Kjelstrup.
Effect of composition on the heat and mass resistance
of the liquid-vapor interface.
Introduction.
Evaporation and condensation are typical examples of phenomena, where heat and mass transfer
happens. During this process, one phase transforms to the other and the most of interesting
phenomena happen at the boundary between two phases, the interface. In equilibrium, a typical
characteristic of the interface is the surface tension.
12
10
σ [J/(K m3)]
8
αqq = 0
α
=1
α
= 10
qq
qq
6
s
Heat and mass transfer are irreversible processes, which
can be described by so-called entropy production – the
quantity, which shows how fast the entropy changes in
time. The drastic changes of physical properties over a very
short region in space make the interface to be a special
region. In particular, the entropy production has a high
peak in that region. As in the bulk phase, heat and mass
transfer through the interface are characterized by the
resistances. Experiments and simulations show that,
comparing to the bulk region, surface puts up an additional
resistance to heat and mass transfer. This is closely related
to the rise of the entropy production in that region.
4
2
0
−40
−20
0
x [nm]
20
Like the surface tension, the interfacial resistance may change if one adds an additional
component to the fluid. Increasing or decreasing the interfacial resistance may be relevant for a
number of industrial applications such as distillation, osmotic phenomena, biological transport in
cells.
Objectives.
The project is devoted to study the effect of adding a solvate to a fluid on the interfacial
resistance. The goal of the project is to obtain an empirical expression for the resistance for
dilute mixtures.
Tools.
The study is performed using the square gradient model and the theory of non-equilibrium
thermodynamics. The square gradient model assumes that physical properties in the interfacial
region are described by introducing the gradients of densities as variables, in addition to the
densities themselves. The theory of non-equilibrium thermodynamics represents a systematic
way to describe such phenomena as heat conduction and diffusion.
Requirements.
Familiarity with fluid dynamics and thermodynamics of mixtures.
Supervision.
Postdoc fellow Kirill Glavatskiy, Professor II Dick Bedeaux.
40
Nanodesign of the electrocatalytic layer in a polymer electrolyte fuel cell
Introduction.
The performance of the fuel cell at high current densities is now severely hampered by masstransfer limitations. This means that the reacting gases do not have free access to the catalyst
surface in the nanoporous layer where the catalyst particles are buried. Product water is also
clogging the pores, preventing gas access, and return of water to the outside.
We have therefore proposed a new fuel cell design, inspired by fractal networks in nature and by
results obtained in the group on energy efficient design, see the figure. Heat, mass and charge
transfer are irreversible processes, which can be described by the entropy production – the
quantity, which shows how fast the entropy changes in time. This quantity should be small for
good fuel cell performance. In collaboration with SINTEF, we would now like to test the
theoretical prediction and check if we can improve energy efficiency and lower the amount of
catalyst in the system.
Objectives.
The overall objective is to find an improved fuel cell design, to help commercialisation of this
cell in the transport sector. The short term aim is to test the theory leading to the new design.
Tools.
The project is an experimental project where the student shall prepare and test single polymer
electrolyte fuel cells. The test shall be performed in a test station at Dept. of chemistry. The layer
production shall be performed with the assistance of SINTEF.
Requirements.
Familiarity with thermodynamics and experimental experience.
Supervision.
Postdoc fellow Odne Burheim, Dr. Magnus Thomassen, Professor Signe Kjelstrup.
A fundamental study of the interplay between biomass derived compounds
and the surface sites of nanoporous materials
Introduction
Biomass is presently the only renewable source of carbon that can be used for liquid fuels
production. Today, biofuels production technologies are commonly classified as 1st and 2nd
generation depending on the raw material used. 1st generation biofuels are typically made from
fertilizer intensive feedstocks (e.g. vegetable oils) that also rely heavily on agricultural areas
otherwise used for food crops. It now seems clear that such biofuels hardly can replace fossil
fuels in a sustainable manner in our future energy scheme. On the other hand, 2nd generation
biofuels (derived from non-food crops such as woods) presents opportunities for a sustainable
fuel supply for a large number of nations. 2nd generation wood derived biomass is, however,
difficult to convert into fermentable
sugars in an efficient manner, but
pyrolysis offers conversion of this
biomass to bio-oils in reasonable yields
at relatively low costs. Yet, the pyrolysis
bio-oil characteristics have to be
substantially improved before further
applications as transportation fuels and
catalytic processes involving nanoporous
solid catalysts represent feasible
upgrading routes. Due to a rapid catalyst
deactivation and non-optimal product
selectivity, further improvements of the
catalysts are desired. This project will
focus on the interactions between representative bio-oil model compounds and the acidic surface
sites of various nanoporous materials.
Objectives
The main objective is to obtain a deeper fundamental understanding of the aspects that govern
product selectivity and catalyst deactivation for systems relevant for bio-oil upgrading. Such
insights may in turn give valuable information regarding design of catalysts with improved
properties.
Tools
The primary tool will be infrared spectroscopy performed in transmission mode using a high
pressure, high temperature in-situ cell. Also diffuse reflectance Uv/Vis/NIR spectroscopy will be
employed.
Requirements
Background in physical chemistry.
Supervision
Associate professor Morten Bjørgen
Predicting cellular automata rules that model 2D chemical phenomena
Cellular automata (CA) is a class of discrete models which consist of
a regular grid of cells (in 1D, 2D, 3D, ...) where each cell can be in
a finite number of states. A set of rules change the cell state from one
iteration to the next depending on its previous state(s) and the states
of the cells in its nearest neighbourhood. CAs have been used for many
years to model a wide range of natural phenomena (travelling chemical
waves, biological pattern formation, forest fires, etc). Typically it
is being used to generate patterns which have properties similar to a
phenomenon under study.
However there is problem: How can we find CA rules which will generate
the oberved patterns? A proposed solution to this is to use
chemometric and machine learning methods to infer CA rules from
observed data. From a time series of observed patterns, data are
recorded in a grid and modelling is performed around various local
points. The time series of these local points and their neighbourhoods
form the basis for the chemometric or machine learning analysis that
will produce the derived CA rules. By running the CA using the learned
rules, hopefully the generated patterns will resemble the observed
patterns.
This MSc project will involve the following tasks: 1) setting up a
general CA system in Matlab or Mathematica, 2) testing of which
chemometric/machine learning methods are best for CA rule generation,
3) creating calibration data sets with different grid resolutions of
the observed time series and 4) making a method for evaluating the
quality of the generated CA patterns compared to the observed data.
Supervisor: Prof. Bjørn Alsberg
Hydrogen storage in carbon nanotubes
Introduction
Hydrogen is an important candidate for our future use of clean energy. For instance Denmark has
recently developed a full scale wind-hydrogen energy plant. Where excess wind power is used to
produce hydrogen by electrolyze water to hydrogen and oxygen. However the use of hydrogen
will depend on our ability to find convenient ways store and retrieve the hydrogen. In this project
we explore the possibilities to use carbon nanotubes as storage medium and especially boron
substituted carbon nanotubes that have been shown to provide more storage capacity. The
interaction of the hydrogen with the nanotubes is dominated by dispersion interactions and this
makes the theoretical description of these systems very demanding.
Special techniques are used as a high level description of electron correlation is needed to
account for the interaction. As illustrated in the figure above we can select subsystems and use a
more accurate description for these regions of the molecular system. This will make possible
calculations on large systems without compromising the overall accuracy.
Objectives
The main objective is to explore different nano-structures and substitutions in order to maximize
hydrogen storage. The development of subsystem quantum chemistry methods is also one of the
possibilities as part of this project. This is an active research area in computational chemistry.
Tools
The primary tool is state of the art quantum chemistry programs, in particular DALTON and
GAUSSIAN.
Requirements
Background in physical chemistry,
Supervision
Professor Henrik Koch
Molecular materials as electrical insulators
Introduction
Electrical insulation materials are used to shield the surroundings from high electric fields for
example in cables and in transformer oils, but the electrical breakdown of molecular materials is
poorly understood at a molecular level.
Many processes may occur: ionization and
dissociation
of
molecules,
electron
attachment and recombination of molecular
fragments, the formation of small gas
bubbles (boiling) and local plasmas. In the
picture to the right, a photograph of the
prebreakdown process in liquid cyclohexane
is shown. The bush-like channels where the
breakdown occurs emit light which can be
characterized by spectroscopic techniques.
Failures are often attributed to impurities or
defects in the material. It is therefore important to understand on a molecular level the interaction
with high electric fields and secondly, if free electrons are created, how a molecule can capture
free electrons before they are accelerated by the electric field and causes further damage.
Objectives
The overall objective is to contribute to the design of improved electrical insulators (in
collaboration with SINTEF Energy and ABB) by providing an improved model at the molecular
level. Depending on the background and the interests of the student, a project may include
calculations on commonly used materials to characterize their electrical properties, or to
contribute to the development of new models for molecular polarization and molecular
conductivity that may be implemented in a locally developed software.
Tools
Quantum chemical software as ADF or Gaussian are used on the national infrastructure for highperformance computing. An own-developed software (written in Python) based on electrostatics
and force-field methods is also used or further developed.
Requirements
A background in molecular modeling corresponding to TKJ4205 Molecular Modeling is
reasonable.
Supervision
Professor Per-Olof Åstrand, Dr. Stian Ingebrigtsen (SINTEF Energy)
Modeling of catalysts based on metal particles deposited on carbon materials
Introduction
Nano-scale metal particles deposited on carbon materials as graphite and fish-bone structures
give an improved catalytic activity in for example the production of hydrogen. In collaboration
with the Catalysis group at the Department of Chemical Engineering where the experimental
activities are carried out, we contribute to an improved
design of these catalysts by an improved
understanding of the processes at a molecular scale by
using molecular dynamics simulations and reactive
force fields. In the figure to the right, a snapshot from
a molecular dynamics simulation is shown with a
platinum cluster at the arm-chair side of a graphene
platelet. The reactivity of the metal clusters is studied
for example as a function of the type of metal (alloy),
their shape and size, and the characteristics of the
carbon surface.
Taking the concept one step further, one may use for
example titanium oxide particles deposited on carbon
to improve the absorption of solar light and thereby construct a new generation of solar cells.
The absorbed energy can either be used to produce electricity or locally in a chemical reaction
(photo-catalysis).
Objectives
The overall objective is to contribute to the design of (photo)-catatlysts based on the concept of
depositing (metal) particles on carbon materials. Force fields for chemical reactions in
conjunction with molecular dynamics simulations are used to provide a molecular model of the
systems at a realistic temperature and pressure. Depending on the background and interests of the
student, a project may include simulations using existing software and force fields or a
contribution to the development of more sophisticated force fields including also absorption of
light.
Tools
Implementations of the Reax force field in molecular dynamics software like LAMMPS and
ReacMD are used at the national infrastructure for high-performance computing. An owndeveloped software (written in Python) is used for method development. Quantum chemical
software like ADF or Gaussian is used to obtain reference data for parametrization of force
fields.
Requirements
A background in molecular modeling corresponding to TKJ4205 Molecular Modeling is
reasonable.
Supervision
Professor Per-Olof Åstrand, Professor De Chen (Dep. of Chemical Engineering)