Real-Gas Effects and Phase Separation in Underexpanded Jets at Engine-Relevant Conditions

A numerical framework implemented in the open-source tool OpenFOAM is presented in this work combining a hybrid, pressure-based solver with a vapor-liquid equilibrium model based on the cubic equation of state. This framework is used in the present work to investigate underexpanded jets at engine-relevant conditions where real-gas effects and mixture induced phase separation are probable to occur. A thorough validation and discussion of the applied vapor-liquid equilibrium model is conducted by means of general thermodynamic relations and measurement data available in the literature. Engine-relevant simulation cases for two different fuels were defined. Analyses of the flow field show that the used fuel has a first order effect on the occurrence of phase separation. In the case of phase separation two different effects could be revealed causing the single-phase instability, namely the strong expansion and the mixing of the fuel with the chamber gas. A comparison of single-phase and two-phase jets disclosed that the phase separation leads to a completely different penetration depth in contrast to single-phase injection and therefore commonly used analytical approaches fail to predict the penetration depth.Comment: Preprint submitted to AIAA Scitech 2018, Kissimmee, Florid

Catalytic membrane reactor for Suzuki-Miyaura C-C cross-coupling: Explanation for its high efficiency via modeling

A polymeric catalytic membrane was previously prepared that showed remarkable efficiency for Suzuki-Miyaura C-C cross-coupling in a flow-through configuration. A mathematic model was developed and fitted to the experimental data to understand the significant apparent reaction rate increase exhibited by the catalytic membrane reactor compared to the catalytic system under batch reaction conditions. It appears that the high palladium nanoparticles concentration inside the membrane is mainly responsible for the high apparent reaction rate achieved. In addition the best performance of the catalytic membrane could be achieved only in the forced flow-through configuration, that, conditions permitting to the reactants be brought to the catalytic membrane by convection

Experimental and Numerical Investigation of Phase Separation due to Multi-Component Mixing at High-Pressure Conditions

[EN] Experiments and numerical simulations were carried out in order to contribute to a better understanding and prediction of high-pressure injection into a gaseous environment. Specifically, the focus was put on the phase separation processes of an initially supercritical fluid due to the interaction with its surrounding. N-hexane was injected into a chamber filled with pure nitrogen at 5 MPa and 293 K and three different test cases were selected such that they cover regimes in which the thermodynamic non-idealities, in particular the effects that stem from the potential phase separation, are significant. Simultaneous shadowgraphy and elastic light scattering experiments were conducted to capture both the flow structure as well as the phase separation. In addition, large-eddy simulations with a vaporliquid equilibrium model were performed. Both experimental and numerical results show phase formation for the cases, where the a-priori calculation predicts two-phase flow. Moreover, qualitative characteristics of the formation process agree well between experiments and numerical simulations and the transition behaviour from a dense-gas to a spray-like jet was captured by bothThe authors gratefully acknowledge the German Research Foundation (Deutsche Forschungsgemeinschaft) for providing financial support in the framework of SFB/TRR 40. Financial support was also provided by Munich Aerospace (www.munich-aerospace.de). Furthermore, the authors thank the Gauss Centre for Supercomputing e.V. (GCS) (www.gauss-centre.eu) for supporting this project by providing computing time on the GCS Supercomputer SuperMUC at Leibniz Supercomputing Centre (www.lrz.de).Traxinger, C.; Müller, H.; Pfitzner, M.; Baab, S.; Lamanna, G.; Weigand, B.; Matheis, J.... (2018). Experimental and Numerical Investigation of Phase Separation due to Multi-Component Mixing at High-Pressure Conditions. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 130-137. https://doi.org/10.4995/ILASS2017.2017.4756OCS13013

Challenges and progresses made on the microkinetic description of lignin liquefaction: Application of group contribution methods

In this presentation a comprehensive microkinetic modelling framework and experimental tools are used to describe product yield and composition of direct lignin liquefaction processes with and without solvents (See Figure 1). With the framework proposed we aim to develop a unified theory and models capable of describing both dry (pyrolysis) and wet (hydrothermal and solvolysis) lignin liquefaction processes. An important phenomenon that has been shown to occur during lignin pyrolysis (as well as cellulose) is the formation of a liquid intermediate phase, and subsequent ejection of heavy products (\u3e~250 Da) as aerosols from this intermediate. In our presentation we will focus on the nature of lignin pyrolysis liquid intermediate through analysis of phase change equilibria temperatures for relevant lignin fragments, using group contribution methods. Specifically, estimation of boiling (Tb) and melting (Tm) points of lignin fragments was done using ARTIST software (Dortmund Data Bank Software & Separation Technology, GmbH). In total, 50 different lignin fragments were drawn, and their boiling and melting temperatures were calculated. The 50 fragments include monomers, dimers, trimers and tetrameters, with a variety of H, G and S units and inter-unit linkages. Figure 2 shows the calculated phase-change equilibria temperatures plotted against the number of aromatic units in a given lignin fragment. The dotted line at 400 °C is included as the approximate temperature at which both rupture of aliphatic linkages and conversion of short aromatic ring substituents occurs, but is less than the temperature for rearrangement of polycyclic structures. The collection of lignin fragments, such that Tm \u3c 400 \u3c Tb, make up the set of molecules that can exist as a liquid intermediate during pyrolysis, and are therefore the ones that have potential to be ejected as aerosols. The average lignin fragment in this range has 2.50 (± 0.11, standard error) aromatic units, molecular weight of 414 (± 20) Da, melting point of 292 (± 13) °C, and boiling point of 573 (± 19) °C. Relying solely on this analysis, one would expect these to be characteristics of an average molecule ejected as a liquid-phase aerosol during pyrolysis of lignin. Based on the quantification of phase equilibria temperatures, this liquid state can contain dimers and trimers, but typically not tetrameters or larger (they will preferentially depolymerize), or monomers (they will vaporize). It is these dimer and trimer products that should make up the majority of the heavy liquid products collected as aerosols. In order to validate this model, comparison was made with previously published work from Pecha, et al. (Ind. Eng. Chem. Res., 56, 2017, 9079-9089) and Bai, et al. (Fuel, 128, 2014, 170-179), who analyzed lignin pyrolysis oil with FT-ICR-MS. There is good agreement between the weights of species detected experimentally in these studies and those determined in this work based on group contribution calculations. Please click Additional Files below to see the full abstract

The design of two apparati to measure solid-liquid and liquid-liquid equilibria data.

Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2010.Two new apparati have been developed to measure solid-liquid and liquid-liquid equilibria via a synthetic visual method by determination of thermal signatures. One apparatus adopts a technique of using Peltier modules for cooling, and the other is a well-known design that uses a cryogenic fluid in a thermostatted glass cell for cooling of the sample. The Peltier design is for small sample volumes, with a 10 cm3 aluminium equilibrium cell and has a minimum operating temperature of 253.15 K. The glass design is developed to complement the Peltier and has a larger volume of 140 cm3 and a minimum operating temperature of 223.15 K. Both apparati have been semi-automated in order to increase the accuracy and improve the efficiency of data measurements. Therefore the experimenter no longer has to wait for many hours for the determination of equilibrium. This was done by incorporating software, which was specially designed for the apparati using Labview8TM, for controlling the cooling and heating rates. The uncertainty of the temperature measurements was found to be ±0.03 K for the Peltier apparatus and ±0.02 K for the Glass apparatus. Liquid-liquid equilibria data has also been measured on the Peltier apparatus, to demonstrate its versatility. This was done using a digital camera, controlled through the Labview software to identify cloud points. The results have been found to be comparable with literature values. For solid-liquid equilibria new systems of n-alkyl carboxylic acid binary mixtures have also been measured: heptanoic acid + butyric acid and heptanoic acid + hexanoic acid. These systems were measured using both apparati and both systems exhibited eutectic behaviour. All eutectic temperatures were measured on the Glass apparatus. Experimental data for these systems was modelled using the local composition models: Wilson, NRTL and UNIQUAC models. The NRTL model was found to give the best results for both systems with root mean square deviations (RMSD) of 2.16 K and 1.27 K and absolute average deviations (AAD) of 0.61 K and 0.49 K, between temperature measurements of this work and those calculated from the models, for the heptanoic acid + butyric acid and heptanoic acid + hexanoic acid systems, respectively

Equilíbrio líquido vapor na indústria de óleos vegetais

Orientadores: Antonio José de Almeida Meirelles, Jürgen GmehlingTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de AlimentosResumo: Propriedades termodinâmicas são úteis para a realização de projetos confiáveis, otimização e modelagem de processos que envolvam separação térmica e para a seleção de solventes usados em processos de extração. Tais propriedades são também necessárias no desenvolvimento de novos modelos termodinâmicos e no ajuste de parâmetros de modelos preditivos. Este trabalho de tese teve como objetivo principal ampliar o banco de dados de propriedades termodinâmicas para compostos graxos através da determinação sistemática do coeficiente de atividade à diluição infinita ( ), entalpia de excesso ( ) e dados de equilíbrio líquido-vapor (ELV) de sistemas contendo ácidos graxos e óleos vegetais. A primeira parte deste trabalho apresenta os dados de para vários solutos orgânicos diluídos em ácidos graxos saturados e insaturados, medidos pelo método de cromatografia gás-líquido na faixa de temperatura entre 303,13 K e 368,19 K. Através dos resultados obtidos, puderam ser identificadas diferentes tendências para compostos polares e não polares, tanto na série de ácidos graxos como também em relação à temperatura. Foi verificado que tanto a presença quanto o número de insaturações na cadeia carbônica do ácido graxo têm influência nas interações solvente-soluto e, consequentemente, nos valores de . A segunda parte deste trabalho tratou de medidas realizadas em sistemas contendo óleos vegetais refinados. Os óleos de soja, girassol e canola foram submetidos a determinações de , e ELV. As medidas de para n-hexano, metanol e etanol diluídos nos óleos vegetais foram determinadas pela técnica do Dilutor na faixa de temperatura entre 313,15 K e 353,15 K. Os dados experimentais obtidos foram comparados com os resultados gerados pelos métodos UNIFAC original e modificado (Dortmund) e para este último modelo, foi proposta uma extensão para os triacilgliceróis. Os dados de foram medidos para 11 misturas contendo solventes e os óleos vegetais relacionados anteriormente na faixa de temperatura de 298,15 K a 383,15 K. Todos os sistemas investigados apresentaram desvio em relação ao comportamento ideal e os valores de apresentaram-se, na maioria, positivos. Dados isotérmicos de ELV foram medidos para misturas entre os mesmos óleos vegetais e metanol, etanol e n-hexano a 348,15 K e 373,15 K através de um método estático. Para misturas com n-hexano, foi observado desvio negativo da lei de Raoult e um comportamento homogêneo, enquanto que as misturas com álcool apresentaram desvio positivo da idealidade e imiscibilidade. Os dados experimentais de ELV foram representados satisfatoriamente pelo modelo UNIQUAC, enquanto que os modelos UNIFAC modificado (Dortmund) e sua extensão proposta para triacilgliceróis foram capazes de predizer os sistemas apenas de forma qualitativa. Finalmente, dados isobáricos de ELV foram medidos para misturas com etanol + óleo de soja a 101,3 kPa e n-hexano + óleo de algodão a 41,3 kPa utilizando o ebuliômetro de Othmer modificado. Os resultados da correlação UNIQUAC também apresentaram boa concordância com os dados experimentais. Este trabalho resultou em um total de 1829 novos dados que irão expandir o banco de dados disponível para compostos graxos, permitindo uma descrição mais precisa do comportamento real de sistemas contendo tais substânciasAbstract: Thermodynamic properties are useful for the reliable design, optimization and modelling of thermal separation processes as well as for the selection of solvents used in extraction processes. They are also required for the development of new thermodynamic models and for the adjustment of reliable model parameters. In order to improve the thermodynamic properties data bank of fatty compounds, the systematic determination of activity Coefficients at infinite dilution ( ), excess enthalpies ( ) and vapor-liquid equilibria (VLE) data of systems containing fatty acids and vegetable oils was performed. The first part of this work presents data for several organic solutes dissolved in saturated and unsaturated fatty acids measured by gas-liquid chromatography at temperatures from 303.13 K to 368.19 K and the comparison to available literature data. Different trends for polar and non-polar compounds could be identified both in the series of fatty acids and as function of temperature. It appears that both the presence and the number of cis double bonds in the fatty acid alkyl chain have influence on the solvent-solute interactions and hence on the values of . The second part of this work deals with measurements performed on systems with refined vegetable oils. Soybean, sunflower and rapeseed oils were submitted to measures of , , and VLE. The measurements of for n-hexane, methanol and ethanol dissolved in these vegetable oils were determined by gas stripping method (dilutor technique) in the temperature range of 313.15 K to 353.15 K. The experimental data were compared with the results of the group contribution methods original UNIFAC and modified UNIFAC (Dortmund) and an extension of the latter method to triacylglycerols was proposed. The data were measured for eleven mixtures containing solvents (organic and water) and the prior mentioned vegetable oils in the temperature range from 298.15 K to 383.15 K. All systems investigated showed deviation from the ideal behavior and their experimental data are mostly positive. Isothermal VLE data have been measured for methanol, ethanol, and n-hexane with the same vegetable oils at 348.15 K and 373.15 K using a computer-driven static apparatus. For mixtures with n-hexane it was observed a negative deviation from Raoult¿s law and a homogeneous behavior, while mixtures with alcohols had a positive deviation from ideal behavior and, in some cases, with miscibility gap. The experimental VLE data were satisfactorily represented by the UNIQUAC model, while the mod. UNIFAC (Dortmund) method and its proposed extension for triacylglicerols were capable of predicting the experimental data only in a qualitative way. Finally, isobaric VLE data were measured for mixtures of ethanol with refined soybean oil at 101.3 kPa and for n-hexane and cottonseed oil at 41.3 kPa using a modified Othmer-type ebulliometer. The results of the UNIQUAC correlation also showed good agreement with the experimental results. This work resulted in a total of 1829 new data that will expand the available fatty compounds data base, allowing a more accurate description of the real behavior of fatty systemsDoutoradoEngenharia de AlimentosDoutora em Engenharia de Alimento

Formic acid synthesis using CO₂ as raw material: Techno-economic and environmental evaluation and market potential

The future of carbon dioxide utilisation (CDU) processes, depend on (i) the future demand of synthesised products with CO₂, (ii) the availability of captured and anthropogenic CO₂, (iii) the overall CO₂ not emitted because of the use of the CDU process, and (iv) the economics of the plant. The current work analyses the mentioned statements through different technological, economic and environmental key performance indicators to produce formic acid from CO₂, along with their potential use and penetration in the European context. Formic acid is a well-known chemical that has potential as hydrogen carrier and as fuel for fuel cells. This work utilises process flow modelling, with simulations developed in CHEMCAD, to obtain the energy and mass balances, and the purchase equipment cost of the formic acid plant. Through a financial analysis, with the net present value as selected metric, the price of the tonne of formic acid and of CO₂ are varied to make the CDU project financially feasible. According to our research, the process saves CO₂ emissions when compared to its corresponding conventional process, under specific conditions. The success or effectiveness of the CDU process will also depend on other technologies and/or developments, like the availability of renewable electricity and steam

Graphite exfoliation by supercritical carbon dioxide extraction

Supercritical carbon dioxide is used to exfoliate graphite, producing a small, several-layer graphitic flake. The supercritical conditions of 2000, 2500, and 3000 psi and temperatures of 40°, 50°, and 60°C, have been used to study the effect of critical density on the sizes and zeta potentials of the treated flakes. Photon Correlation Spectroscopy (PCS), Brunauer-Emmett-Teller (BET) surface area measurement, field emission scanning electron microscopy (FE-SEM), and atomic force microscopy (AFM) are used to observe the features of the flakes. N-methyl-2-pyrrolidinone (NMP), dimethylformamide (DMF), and isopropanol are used as co-solvents to enhance the supercritical carbon dioxide treatment. As a result, the PCS results show that the flakes obtained from high critical density treatment (low temperature and high pressure) are more stable due to more negative charges of zeta potential, but have smaller sizes than those from low critical density (high temperature and low pressure). However, when an additional 1-hour sonication is applied, the size of the flakes from low critical density treatment becomes smaller than those from high critical density treatment. This is probably due to more CO2 molecules stacked between the layers of the graphitic flakes. The zeta potentials of the sonicated samples were slightly more negative than nonsonicated samples. NMP and DMF co-solvents maintain stability and prevented reaggregation of the flakes better than isopropanol. The flakes tend to be larger and more stable as the treatment time increases since larger flat area of graphite is exfoliated. In these experiments, the temperature has more impact on the flakes than pressure. The BET surface area resultsshow that CO2 penetrates the graphite layers more than N2. Moreover, the negative surface area of the treated graphite indicates that the CO2 molecules may be adsorbed between the graphite layers during supercritical treatment. The FE-SEM and AFM images show that the flakes have various shapes and sizes. The effects of surfactants can be observed on the FE-SEM images of the samples in one percent by weight solution of SDBS in water since the sodium dodecylbenzene sulfonate (SDBS) residue covers all of the remaining flakes. The AFM images show that the vertical thickness of the graphitic flakes can ranges from several nanometers (less than ten layers thick), to more than a hundred nanometers. In conclusion, supercritical carbon dioxide treatment is a promising step compared to mechanical and chemical exfoliation techniques in the large scale production of thin graphitic flake, breaking down the graphite flakes into flakes only a fewer graphene layers thick