Evidence of a low-temperature dynamical transition in concentrated microgels

A low-temperature dynamical transition has been reported in several proteins. We provide the first observation of a `protein-like' dynamical transition in nonbiological aqueous environments. To this aim we exploit the popular colloidal system of poly-N-isopropylacrylamide (PNIPAM) microgels, extending their investigation to unprecedentedly high concentrations. Owing to the heterogeneous architecture of the microgels, water crystallization is avoided in concentrated samples, allowing us to monitor atomic dynamics at low temperatures. By elastic incoherent neutron scattering and molecular dynamics simulations, we find that a dynamical transition occurs at a temperature $T_d\sim250$~K, independently from PNIPAM mass fraction. However, the transition is smeared out on approaching dry conditions. The quantitative agreement between experiments and simulations provides evidence that the transition occurs simultaneously for PNIPAM and water dynamics. The similarity of these results with hydrated protein powders suggests that the dynamical transition is a generic feature in complex macromolecular systems, independently from their biological function

Water-polymer coupling induces a dynamical transition in microgels

The long debated protein dynamical transition was recently found also in non-biological macromolecules, such as poly-N-isopropylacrylamide (PNIPAM) microgels. Here, by using atomistic molecular dynamics simulations, we report a description of the molecular origin of the dynamical transition in these systems. We show that PNIPAM and water dynamics below the dynamical transition temperature Td are dominated by methyl group rotations and hydrogen bonding, respectively. By comparing with bulk water, we unambiguously identify PNIPAM-water hydrogen bonding as the main responsible for the occurrence of the transition. The observed phenomenology thus crucially depends on the water-macromolecule coupling, being relevant to a wide class of hydrated systems, independently from the biological function

Vibrational dynamics changes of protein hydration water across the dynamic transition

The vibrational dynamics of protein hydration water has been studied by incoherent neutron scattering. Experiments on a sample of fully deuterated maltose binding protein allowed us to single out the hydration water susceptibility. The main inelastic features, corresponding to hydrogen-bond bending, hydrogen-bond stretching and librational excitations, have been followed over a temperature range extending from 50 to 300 K. It turns out that the temperature dependence of the hydrogen-bond stretching contribution is quite similar to that of the mean square displacements deduced by the quasielastic signal, thus suggesting a close relationship between the anharmonicity of longitudinal phonon-like motions and the onset of diffusive molecular dynamics. On the other hand, both hydrogen-bond bending and librational excitations show a temperature dependence consistent with a harmonic character over the whole temperature range

Process simulation of a neutral emission plant using chestnut’s coppice gasification and Molten Carbonated Fuel Cell

The problem of CO2 emissions and the need to find new energy sources are pushing scientific research toward the use of high efficiency technologies for electric power generation that can exploit renewable energy sources—potentially neutral for the environment in terms of greenhouse gas emissions. Process simulations of advanced plants fed by biomass are a key step to develop renewable resources based high temperature fuel cell applications. The aim of this work is to predict the component behavior of a specific power plant mainly composed of a gasifier, a molten carbonate fuel cell (MCFC), and a micro-gas-turbine (mGT) and fed by chestnut coppice, waste available in great quantity in Central Italy, as well as in several other European regions. The gasifier produces a gas with a high content of hydrogen and low content of char and tar. This syngas is exploited by the MCFC-mGT plant. The mGT, using the MCFC cathode outlet gases, shows through simulation to be able to operate the air compressor and produce further electrical power. Particular models for the MCFC and gasifier have been developed in FORTRAN by the authors and then interfaced to commercial software (CHEMCAD©) to simulate the plant's thermodynamic behavior. The results show the possibility of an extremely interesting “carbon neutral” plant configuration with high electrical and global efficiency (respectively, 41% and 86%), exclusively based on the use of renewable resources (biomass)

MCFC and microturbine power plant simulation

The consistent problem of the CO2 emissions and the necessity to find new energy sources, are motivating the scientific research to use high efficiency electric energy production's technologies that could exploit renewable energy sources too. The molten carbonate fuel cell (MCFC) due to its high efficiencies and low emissions seems a valid alternative to the traditional plant. Moreover, the high operating temperature and pressure give the possibility to use a turbine at the bottom of the cells to produce further energy, increasing therefore the plant's efficiencies. The basic idea using this two kind of technologies (MCFC and microturbine), is to recover, via the microturbine, the necessary power for the compressor, that otherwise would remove a consistent part of the MCFC power generated. The purpose of this work is to develop the necessary models to analyze different plant configurations. In particular, it was studied a plant composed of a MCFC 500kW Ansaldo at the top of a microturbine 100kW Turbec. To study this plant it was necessary to develop: (i) MCFC mathematical model, that starting from the geometrical and thermofluidodynamic parameter of the cell, analyze the electrochemical reaction and shift reaction that take part in it; (ii) plate reformer model, a particular compact reformer that exploit the heat obtained by a catalytic combustion of the anode and part of cathode exhausts to reform methane and steam; and (iii) microturbine-compressor model that describe the efficiency and pressure ratio of the two machines as a function of the mass flow and rotational regime. The models developed was developed in Fortran language and interfaced in Chemcad((c)) to analyze the power plant thermodynamic behavior. The results show a possible plant configuration with high electrical and global efficiency (over 50 and 74%). (c) 2006 Elsevier B.V. All rights reserved

Hydrogen recovery from On Site Electro Chlorination system.

The production of hypochlorite can occur through the process of electrolysis of a saline solution with a hydrogen production that is usually discarded. The main objective of the study was to assess, in practice, whether it is possible to recover the hydrogen produced during the electrolysis of a saline solution in order to use one or more fuel cells. The energy produced by such cells can be used to reduce the energy consumption of the production of sodium hypochlorite or other purposes. We first made an evaluation of the producibility of hydrogen from the electrolysis process for a OSEC (On Site Electro Chlorination) system, called MK4, working in batch mode. We then verified experimentally the ability to collect hydrogen and to use it in one or more fuel cells. The methodology involved the following steps: • Change of the original system to collect the gas, • Whatever purification of chlorine gas, • Measure of the flow of gas produced, • Analysis of the purity of the gas produced by gas chromatograph. Once purified from chlorine, the gas has been placed in different configurations of fuel cells stacks. The power obtained from the fuel cell was assumed to be about 24 W, so the efficiency is about 25 %, that is not very high for a fuel cell. It was evaluated that energy recovery is around 8-10%, considering the input power of the OSEC and the output power from the fuel cell. But the gas produced contains about 85% hydrogen and 15% oxygen. The presence of oxygen could reduce the proportion of hydrogen involved in the electrochemical reaction, lowering the efficiency of the fuel cell. If the presence of oxygen in the anode gas is limited, we may obtain an efficiency of the fuel cell of about 40%. So the energy recovery would be 14%

Energy optimisation and layout of a membrane-free OSEC system for the hypochlorite self-production in Developing Countries

The production of hypochlorite in an OSEC (On Site Electrochemical Chlorination) system occurs through electrolysis of a saline solution, with a hydrogen production that is usually discarded. The OSEC system described in this work - presently used in Gaza - has been optimised for use in Tanzania. The first approach focused on the possibility to use the OSEC System in Tanzania, by feeding it through a suitably designed photovoltaic generator allowing the energy independence of the entire process. The aim was to prove how an accurate sizing represents the basis for a good OSEC-feeding without MPPT and DC/DC converter devices, as well as how the electrolytic solution concentration is crucial. The second approach aimed at proving the possibility to exploit hydrogen in a fuel cell by recovering the hydrogen produced during the electrolysis of a saline solution in a membrane-free OSEC system, working in batch mode. Furthermore, an accurate analysis highlighted how and to what extent the presence of oxygen produced during the electrolysis process may limit the efficiency of the fuel cell (in our case, by 25%). More specifically, it was observed that if the percentage of oxygen volume is kept under 11-12%, a limited power loss is registered in the fuel cell; consequently, fuel cell efficiency may reach 40%, and the ensuing energy recovery may almost reach 13%. Finally, an indication of how to possibly limit the presence of oxygen is also provided. (C) 2013 Elsevier Ltd. All rights reserved