Determination of effective moisture diffusivity and thermodynamic properties variation of regional wastes under different atmospheres

During the thermal process to transform lignocellulosic wastes in energy, the drying process is an important stage because it requires energy and decreases overall process yield. Considering this process, moisture diffusivity is an important factor that is considered essential to understand for design, analysis, and its optimization. In this work, this parameter was analyzed at non-isothermal condition and considering the process under inert and oxidative atmospheres. Lower diffusivities were obtained under low heating rates, due to the disfavoring the moisture diffusion in the particles. Higher effective diffusivity (Deff) values were obtained when the drying is carried out under the atmosphere oxidative. Moreover, the thermodynamic parameters and DTA curves were determined. ΔH values are positive in all cases, showing that the drying process is endothermic. ΔG are positive and ΔS negative, indicating that the process is non-spontaneous. DTA curves show that the drying process is endothermic, according with the calculated ΔH.Fil: Fernandez Brizuela, Anabel Alejandra. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Ingeniería Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Román Barón, María Celia. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Ingeniería Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Mazza, German Delfor. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; ArgentinaFil: Rodriguez, Rosa Ana. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Ingeniería Química; Argentin

Predicting Surface Diffusivities of Gas Molecules in Shale

Carbon dioxide injection can be utilised as a means of both enhancing gas recovery from shales and sequestering carbon, and thereby simultaneously addressing the growing worldwide gas demand, as well as the challenge of greenhouse gas emissions. Greater mobility of CO2 within the shale improves the displacement efficiency of the originally present CH4, as well as, increasing the CO2 penetration of the shale formation. Previous investigations have indicated that surface diffusion is much more significant than the bulk gas transport in shale gas reservoirs because of the larger fraction of adsorbed phase found in the nanopores of shales. The surface diffusivities of CO2 on different shales, at various temperatures, have been measured. A fractal theory for predicting the Arrhenius parameters of the surface diffusivity of molecules on heterogeneous surfaces has been applied to the surface diffusion of CO2 in shales. In line with the theory, it was found that both the pre-exponential factor and the activation energy are functions of the surface fractal dimension. Hence, the surface diffusivity, at a monolayer coverage, on shales could be established from an equilibrium gas adsorption isotherm, once the Arrhenius parameters have been calibrated for the specific chemical species. To the best of our knowledge this study is the first to apply the fractal theory and effectively predict, a priori, surface diffusivity parameters for such structurally and chemically heterogeneous natural samples as shales. This theory now enables the optimization of the designs of CO2 injection in field applications since surface diffusion is of major importance in the apparent permeability, and, thus, in the gas flow mechanisms

Catalytic and Sorption Measurements Using Flux Response Technology

Advancements in characterisation techniques in the field of heterogeneous catalysis have been explored, in particular the powerful in situ perturbation method, Flux Response Technology (FRT). The adaptation of FRT as a novel in situ perturbation technique in gas sorption measurements continues to yield consistent results with literature values. This is made possible because FRT measures miniscule changes in transient flows in the order of 10-2 μl/min for gaseous processes involving a change in volume (dV/dt). These changes are measured directly by a very sensitive differential pressure transducer (DPT) in a pneumatic system analogous to an electrical Wheatstone bridge assembly, whereby gas molecules replace electrons and capillaries function as resistors. By showing the successful incorporation of the measurements of adsorption capacities and diffusivity coefficients in the same experimental window, FRT’s use as a bolt-on technology for the rapid screening of catalyst material has been highlighted. The technique possesses a distinct advantage in requiring no prior calibrations to the system, enabling the analysis of a broad spectrum of materials and gases. The FRT technique also features a unique ability in being able to act as a dual flowrate and composition detector through the use of carefully calculated delay lines to separate changes in flowrate caused by perturbations of concentration and changes in composition. The FRT technique provides a quick, simple, accurate, and inexpensive method of characterising material properties in situ in heterogeneous catalysis. Several studies into the dynamics of gas sorption processes utilising FRT measurements on adsorbents were undertaken in the completion of this PhD. The diffusivity parameters of propane in varying alumina/CeZrOx washcoats of Cordierite monoliths were investigated under isothermal conditions. A novel method of analysing FRT derived response profiles with the Zero Length Column (ZLC) model was established and reported on. The diffusion coefficients obtained were consistent with previously reported macroscopic data and compared well when evaluating the structural differences of the washcoats of each sample (Granato et al., 2010). The dynamics of ammonia sorption on commercially available zeolites with varying SiO2/Al2O3 ratios was analysed to investigate the total acidity of these zeolites. The dynamics of carbon dioxide sorption were also investigated to analyse the total basicity of the same zeolite samples. Process optimisations were conducted to obtain an ultra fast isotherm measurement technique for the analysis of nitrogen sorption on aluminium oxides with varying surface areas at 77 K. Finally, insights into the development of a dynamic parallel performance testing (DPPT) FRT setup were undertaken to directly compare the activities of catalytic material operating side by side.Open Acces

Construction material monitoring with "optical hair" hygrometers

Moisture is an essential parameter in the behaviour of capillary-porous construction materials such as timber and concrete. It affects liquid and gas transport phenomena, chemical and biological degradation processes, mechanical properties and, in the case of concrete, hydration. From a scientific point of view, moisture monitoring is essential in order to improve the understanding of material behaviour. Moisture measurements may increase the predictive accuracy of established material behaviour models. In practice, the increased knowledge of material behaviour improves structural maintenance planning. The main objective of this work is to propose a measurement method for non-destructive, in-depth moisture monitoring of construction materials. In this context, an intrinsic point and an averaging fibre optic relative humidity sensor have been developed and tested. The sensors are based on optical fibres that are coated with a hygroscopically swelling transducer polymer. When wet, the swelling of the coating strains the fibre (analogy with the hair hygrometer). The induced strain is assessed with conventional fibre optic strain sensing techniques such as fibre Bragg gratings and Michelson interferometry. Theoretical and experimental studies lead to a detailed understanding of the influence of humidity and temperature on the steady and transient state sensor behaviour. The sensors have an accurate, linear, reversible and reproducible response to relative humidity between 5 and 95 %RH and between 13 and 60 °C, at least. The sensor response time is in the order of 20 minutes. However, when packaged, the sensor responds slower. The temperature cross-sensitivity of the fibre Bragg grating sensor may be compensated with an additional non-hygroscopic grating, while the Michelson interferometric sensor provides an auto-compensation of temperature effects. Tests in mortar and timber samples demonstrate that the sensors preserve their sensing ability when embedded. These tests have also clarified the multiplexing potential of fibre Bragg gratings for forming a multi-point RH sensor. Multi-point sensors are particularly useful for profile measurements

Thermodynamic stability and kinetic analysis of pharmaceutical channel hydrate during dehydration process

This thesis presents a detailed study into the thermodynamic stability and dehydration kinetics of a model pharmaceutical channel hydrate: carbamazepine dihydrate. The model compound of different crystal habits and particle size distributions was prepared via solventmediated crystallisation technique and agitated hydration method. The causal relationship between key drying process parameters (i.e. temperature, pressure, relative humidity and organic solvent partial pressure) and dehydration behaviour of this model compound was established using Dynamic Vapour Sorption instruments. Solid state phase transformation mechanisms under these drying conditions were elucidated through the evolution of crystal structural determined by X-ray Powder Diffraction technique. Dehydration kinetics of carbamazepine dihydrate were found to be markedly influenced by increasing temperature, reducing pressure, low humidity and higher organic solvent partial pressure, providing that the drying environment stays below the critical humidity and partial pressure for the dihydrate and acetone solvate formations. Activation energy determined from the kinetic study allows differentiation between the physically bound water in the bulk and water of crystallisation. Agglomerated dihydrate however possessed a high free water retention capacity when it exceeded a certain particle size distribution. This type of agglomerate exhibited distinct closed structure characteristics, leading to a relatively more stable form of carbamazepine dihydrate, than those without inclusion of unbound water. The agglomeration effect can thus be potentially controlled and exploited to expand the environmental stability envelope of the desired hydrated forms during manufacturing processes. Subtle changes in the drying environment were able to induce polymorphic anhydrates of different stabilities. The solid state phase transformation pathway of carbamazepine dihydrate to the four polymorphic anhydrates and an amorphous form was strongly correlated to types of dehydration mechanism, and specifically to the accessibility of and interaction with surrounding solvent vapours (i.e. hydrogen bonding propensity). Alkanol solvent vapourmediated dehydration process was found to facilitate the formation of the thermodynamically stable anhydrate, without any loss in product crystallinity. Dipolar aprotic solvents however induced the (intermediate) formation of least metastable anhydrate, depending on the local chemical environment of solute-solvent system. In conclusion, the surrounding solvent vapour plays a crucial role in drying strategies for a channel type hydrate, as it provides potential to predict and tailor the polymorphism of the desired forms which could have profound implications on the quality and performance of the final product

NMR Techniques for Measuring Transport Phenomena in Microporous Materials

The primary aim of this thesis is to investigate and quantify the self-diffusion processes of gaseous molecules adsorbed in industrially relevant microporous zeolite materials using Pulsed Field Gradient Nuclear Magnetic Resonance (PFG NMR). The main body of this work involves the use of weakly adsorbing hydrocarbon gases (CH4, C2H6 and C3H¬8) adsorbed in a large pore β-zeolite structure. This thesis describes the development of a solely PFG NMR based technique for measuring the molecular displacements of these species at varying length-scales. This enabled the characterisation of self-diffusion regimes across zeolite beds and within individual zeolite crystallites. The characterisation of self-diffusion processes within single zeolite crystallites was critical with respect to accounting for quantitative discrepancies reported in the literature between PFG NMR and alternative measurement techniques. This approach also revealed that the transitions in the Gaussian probability distributions of the molecular displacements in the aforementioned self-diffusion regimes could be recorded by varying the experimental time-scale for observing molecular motion. This technique was extended to characterise the self-diffusion processes of the aforementioned hydrocarbons in small (≤ 1 µm) and large (≥ 15 µm) zeolite crystallites to investigate the dependence of this technique on zeolite geometry. It was found that the self-diffusion coefficients within single crystallites were in good agreement with one another, despite their differing crystallite geometries. This technique was subsequently used to study the self-diffusion behaviour of two-component hydrocarbon gaseous mixtures with differing sorption properties co-adsorbed in β-zeolite. Excellent chemical shift resolution was obtained for chemically similar species using NMR spectroscopy, relaxometry and diffusometry without the use of Magic Angle Spinning (MAS). This connoted that conventional PFG NMR is capable of precisely characterising individual species in real world multi-component systems. This thesis also describes the self-diffusion of ammonia in small pore chabazite structures, which are typically used in Selective Catalytic Reduction (SCR) processes. It was found that the self-diffusion coefficient of this strongly adsorbing species increased with molecular loading up to a certain point. This peculiar behaviour implied a strong concentration and inter-molecular dependence within the zeolite structure. Lastly, the techniques which were developed at high magnetic field strengths (300 MHz) were transferred to a lower field strength (43 MHz) benchtop spectrometer at the Johnson Matthey Technology Centre (JMTC). This describes the first characterisation of mass transport behaviour of weakly interacting sorbates in zeolites using a portable spectrometer. This presents an excellent opportunity for future off-line molecular displacement measurements to be made for complex and real-world systems in a matter of minutes

Dehydrogenation of isobutane using a structured adsorptive reactor

Imperial Users onl

Carbon molecular sieves for air separation

PhD ThesisCarbon is one of the naturally occurring elements and has an atomic weight 12.01 atomic mass units (amu) and atomic number 6. It has six electrons and has an electronic configuration of: ls2 2S2 1p2 in the ground state. This element exists in different crystalline forms-diamond, graphite, buckminsterfullerene1 and carbyne2. Carbon also has the ability of catenation via formation of σ and π bonds.Air Products and Chemicals Inc.: SERC

Processing of thick section epoxy powder composite structures

The use of epoxy powder as the primary matrix in thick fibre-reinforced composite parts is investigated. The characteristics of three epoxy powders are assessed using several experimental techniques, focusing on their curing behaviour. At least one epoxy powder is shown to have advantageous characteristics for manufacturing thick-section composites. Material models are developed which can describe the processing behaviour (cure kinetics, viscosity change, etc.) of an epoxy powder. The cure kinetics model makes use of an additional rate constant to better describe the rate of cure at both high and low temperatures. The chemorheological model is based on an existing model for toughened epoxies. A one-dimensional simulation tool for manufacturing thick-section composite laminates is developed in MATLAB. The simulation tool employs a resin flow model for vacuum-bag-only prepregs to describe the infusion process and subsequent thickness change. This thickness change is coupled to a model for through-thickness heat transfer which can be solved numerically for various thermal boundary conditions. The model is used to explore the suitability of epoxy powders for the manufacturing thick-section composite structures. The aforementioned simulation tool is validated against experimental results for thick-section composite laminates. The experiments are carried out using a modified heated tool and test apparatus which apply known thermal boundary conditions. A linear variable differential transformer is used to measure the thickness change of each laminate during testing, while thermocouples are used to measure the temperatures at various positions within each laminate. The results of the tests show good agreement with the one-dimensional simulation tool. Additional simulations are performed to investigate the influence of material format, thickness change, and heating methods. Methods for reducing thermal and cure gradients are explored also. A method is outlined for implementing the process models within commercial finite element software, Abaqus FEA. User subroutines for heat transfer and thermal expansion are used to define the various process models. One-dimensional simulations are validated, and a convergence study is performed on time step size and element size. Simulations show the effect of in-plane heating for glass-fibre and carbon-fibre laminates, and the processing of a wind turbine blade root section is investigated. Overall, it is shown that thick-section composite structures can be manufactured using a low-cost commodity epoxy powder from the coating industry, and that these structures do not suffer from the risk of uncontrolable thermal events