Distillation columns are primary equipment in petrochemical, gas plants and refineries. Distillation columns energy consumption is estimated to be 40% of the total plant energy consumption. Optimization of distillation columns has potential for saving large amount of energy and contributes to plant wide optimization. Currently rigorous tray to tray models are used to describe columns separation with high accuracy. Rigorous distillation models are being used as part of design, optimization and as a part of on-line real-time optimization applications. Due to large number of nonlinear equations, rigorous distillation models are not suitable for inclusion in optimization models of complex plants (e.g. refineries), since they would make the model too large. For this reason, current practice in plant-wide optimization for planning or for scheduling is to include simplified model. Accuracy of these simplified models is significantly lower than the accuracy of the rigorous models, thereby causing discrepancy between production planning and RTO decisions. This work describes reduced size hybrid model of distillation columns, suitable for use as stand-alone tool for individual column or as part of a complete plant model, either for RTO or for production planning. Hybrid models are comprised of first principles material and energy balances and empirical models describing separation in the column. Hybrid models can be used for production planning, scheduling and optimization. In addition this work describes inferential model development for estimating streams purity using real time data. Inferential model eliminates the need for Gas Chromatography GC analyzers and can be used for monitoring and control purposes. Predictions from the models are sufficiently accurate and small size of the models enable significant reduction in size of the total plant models. / Thesis / Master of Applied Science (MASc)

Membrane distillation (MD) is an emerging thermal separation technology which proved its efficiency in desalination of highly saline waters, including seawater, brines and impaired process waters. In a long-term prospective, MD can reinforce sustainability of the clean water production and mitigate the water-energy stress caused by lacking suitable freshwater recourses. However, just like in any other membrane separation process, MD membrane is susceptible to biofouling which presents a significant challenge by substantially reducing its performance and deteriorating permeate quality. This study evaluated different cleaning methods aimed at controlling biofilm development on a surface of hydrophobic MD membrane in a direct contact MD (DCMD) process fed by the Red Sea water. This was achieved by applying physical (hydraulic) cleaning and chemical cleanings with a range of chemicals utilized in membrane separation processes including citric acid (mineral acid), ethylenediaminetetraacetic acid (EDTA, metal-chelating agent) and sodium hypochlorite (NaOCl, oxidant). Flux recovery and changes in biofilm morphology, including its thickness and structure as well as microbial and extracellular polymeric substances (EPS) contents before and after cleanings have been analyzed to elucidate cleaning mechanisms and suggest effective strategies of biofilm removal. The results showed that 0.3% EDTA exhibited the best cleaning performance resulting in the highest permeate flux recovery (93%), followed by 0.3% NaOCl (89%), 3% citric acid (76%), and hydraulic (66%) cleanings. Application of EDTA and NaOCl has also resulted in the lowest number of bacterial cells and substantial reduction of the peak intensities caused by protein-like compounds and tyrosine-containing proteins present on the membrane surface after its treamtent. The observed trends are in a good correlation with the optical coherence tomography (OCT) observations which revealed substation changes in biofilm morphology leading to a significant reduction of biofilm thickness which followed the order of hydraulic cleaning < citric acid cleaning < NaOCl cleaning < EDTA cleaning. This study suggests that selection of an appropriate cleaning type and formulation is critical for achieving sustainable MD plant operations, both technically and economically.

The production of 7-tetradecene was examined. Properties for this compound were estimated using group contribution methods and compared to experimental data. Process simulation was used as a tool to identify competitive processing strategies. For reactive distillation, three different models were compared to determine the model complexity needed to describe the process: Model A, with the assumption of physical and chemical equilibrium; Model B, with kinetics described by a second order reaction and physical equilibrium; and Model C, a non-equilibrium stage model that accounts for mass transfer. A conceptual design was obtained with Model B and was checked with Model C, which described the process more accurately but was more difficult to converge. Since, Model A was easier to converge, it was used to predict process conversions at different pressures. Predictions favor working at 1 bar, due to the lower heat duty and the minimum stages required.

No description available.

Ph. D.

Yes / In this work, for the first time, the synthesis of benzyl acetate via the esterification of acetic acid and benzyl alcohol is investigated in the reactive distillation system using a middle vessel (MVD), inverted (IBD), and conventional batch reactive distillation columns. The measurement of the performance of these column schemes is determined in terms of profitability through minimization of the batch time for a defined separation task. The control variables (reboil ratio for MVD, IBD columns) and (reflux ratio in case of CBD column) are considered as piecewise constants over batch time. The optimization results obviously indicate that the CBD system is a more attractive process in terms of batch time reduction, and maximum achievable yearly profit as compared to the MVD, and IBD operations.

Although distillation studies have been made for many types of rectifying columns under various conditions of operation, no systematic study has ever been made of the process that is the basis of rectification, e.g., flash distillation. It was the purpose of this investigation to study the action of the system methanol-water under-going flash distillation under various conditions of temperature, agitation, and rate of feed at a total pressure of 500 millimeters of mercury, absolute. The distillation took place in a nine inch diameter, electrically-heated, controlled temperature and pressure, cylindrical still 14 inches high. The liquid phase was agitated by the rotation of an externally driven 1-1/2-inch square paddle. An aqueous 25 weight per cent methanol solution was fed to the still in which the solution was subjected to flash distillation under conditions of a liquid hold-up of 445 cubic inches; vaporizing temperatures of 172 °F, 166 °F, and 162 °F; stirrer speeds of zero, 500, 1000, 1500, and 2000 revolutions per minute; and feed rates varying from 0.01 to 0.50 pounds per minute. From the results obtained it was concluded that the fraction vaporized was a function of the feed rate as follows: Z K₁(R₁ - R₂)^-b) Where: Z fraction vaporized K₁ fraction vaporized when the term (R₁ - R₂) was equal to one R₁ feed rate, pounds per minute R₂ feed rate when residue rate was equal to zero, pounds per minute B a constant for a given temperature and stirrer speed. The fraction vaporized was directly proportional to the stirrer speed and the vaporizing temperature. The vale of the fraction vaporized varied from 1.0 to 0.04. The composition of the distillate was an exponential function of the feed rate as follows: x_d K₂(R₁ - R₂)^a where: x_d distillate composition, weight per cent methanol K₂ distillate composition when the term (R₁ - R₂) was equal to one, weight per cent methanol. R₁ feed rate, pounds per minute R₂ feed rate when the residue rate was equal to one, pounds per minute a a constant for a given temperature and stirrer speed. The greatest degree of separation, as measured by the difference in distillate and residue compositions, occurred at stirrer speeds of zero, 1000, and 500 revolutions per minute at vaporizing temperatures of 162 °F, 166 °F, and 172 °F respectively. Some dynamic values of the distillate composition exceeded the static or thermodynamic values, for example, the theoretical value of the distillate composition of 68.5 weight per cent methanol at 162 °F was exceeded at zero and 500 revolutions per minute for feed rates in excess of 0.12 and 0.16 pounds per minute respectively. At 172 °F and 166 °F, the heat input as Btu per pound of distillate increased with increasing feed rates for feed rates from 0.022 to 0.122 pounds per minute and decreased with increasing feed rate for feed rates from 0.122 to 0.450 pounds per minute all at constant stirrer speed. An average value of the heat input of 1500 Btu per pound of distillate was obtained at 172 °F for stirrer speeds from zero to 1000 revolutions per minute and at 166 °F for stirrer speeds from zero to 2000 revolutions per minute. At 162 °F the heat input as Btu per pound of distillate increased with feed rate at all feed rates from 0.01 to 0.50 pounds per minute with an average value of 2000 Btu per pound of distillate being obtained. The dynamic equilibrium ratio was related to the product of the stirrer speed and the hold-up time as follows: N x_D/x_s K₃(n t_h)^d where: N dynamic equilibrium ratio x_D distillate composition, weight per cent methanol x_s composition of the liquid in the still at equilibrium, weight per cent methanol n stirrer speed, revolutions per minute t_h hold-up time, minutes K₃ a constant for a given temperature d a constant for a given temperature / Ph. D.

Este trabalho tem por objetivo comparar dois modos de operação de destilação em batelada: com refluxo constante e composição do destilado constante. Desenvolveuse um modelo matemático para a destilação em batelada de uma mistura binária (metanol-etanol) para operação com cada um destes modos. O modelo consiste basicamente dos balanços de massa e entalpia, relações e diagramas de equilíbrio líquido-vapor (composição de equilíbrio, temperaturas de bolha e orvalho da mistura), estimativa das propriedades físico-químicas da mistura (calor específico, calor latente de vaporização), determinação do número de estágios ideais necessários à separação (pelo método de McCabe-Thiele), cálculo de cargas térmicas no refervedor e condensador, consumo de utilidades (vapor de água e água de resfriamento), estimativa do tempo de destilação e alguns aspectos econômicos sobre o processo (custos de equipamentos e operacionais, capacidade de produção, lucro mensal). Implementou-se em uma planilha eletrônica este modelo para as simulações matemáticas e análise técnico-econômica do processo. Em escala de laboratório (foram realizados, ao todo, oito ensaios, quatro de refluxo constante e quatro de refluxo variável, utilizando uma coluna de pratos perfurados), constatou-se uma boa concordância entre estes resultados experimentais e os calculados a partir da modelagem. Em seguida, estudaram-se, isoladamente em cada modo de operação e de modo comparativo, as principais variáveis de processo (taxa de refluxo, composição do destilado, quantidade de carga, vazão de destilado, etc.) através de simulações matemáticas, tanto no cenário de uma unidade existente como no caso do projeto de uma instalação nova. Para uma instalação existente, verificou-se, que no modo de destilação com composição de destilado constante, mantendo-se a vazão do vapor de topo constante, o tempo de destilação é menor, a capacidade de destilação é maior, resultando em maior lucro mensal. Para uma instalação a ser projetada, de novo, o processo mais vantajoso é o de refluxo variável e vazão de vapor do topo constante, pois requer menores áreas dos trocadores de calor para uma dada separação num tempo fixo de processo. No entanto, para o processamento de uma dada quantidade num mesmo tempo, à medida que se adota, no projeto, um número maior de estágios de separação na coluna, a diferença de lucro mensal torna-se praticamente indistinta para os modos de destilação estudados. / The aim of this study is to compare two operational methods of batch distillation of a binary system (methanolethanol): constant reflux and constant distillate composition. A phenomenological modeling concerning each mode was developed. It was based on material and enthalpy balances, equilibrium relationships, estimation of physical properties (specific heat and latent vaporization heat of mixtures), determination of ideal stages number (using McCabe-Thiele method), calculation of rebolier and condenser thermal loads and areas, steam and cooling water requirement, distillation time and some economical aspects. The mathematical model was implemented into an electronic spreadsheet. The predicted values were compared to experimental results from eight tests carried out in a laboratory sieve tray column (four at constant reflux and four at constant distillate composition), and a good consistency was found. Then several case studies concerning each distillation mode as well as the comparative performance were accomplished through mathematical simulations. Evaluation of the basic process variables such as reflux rate, initial load, distillate composition and flow rate was done. Rating of an existing plant and design of a new installation were considered in this process analysis. For an existing installation, lower distillation time, as well as higher distillation capacity and monthly profit were observed when distilling with constant distillate composition, keeping constant the flow rate of vapor from the column top. This process is also the more advantageous one when designing a new plant since smaller heat exchanger areas are required. However, to process a quantity in a same time, in a design of a new plan, as number of separation stages increases, monthly profit becomes almost the same among the studied distillation modes.

Este trabalho tem por objetivo comparar dois modos de operação de destilação em batelada: com refluxo constante e composição do destilado constante. Desenvolveuse um modelo matemático para a destilação em batelada de uma mistura binária (metanol-etanol) para operação com cada um destes modos. O modelo consiste basicamente dos balanços de massa e entalpia, relações e diagramas de equilíbrio líquido-vapor (composição de equilíbrio, temperaturas de bolha e orvalho da mistura), estimativa das propriedades físico-químicas da mistura (calor específico, calor latente de vaporização), determinação do número de estágios ideais necessários à separação (pelo método de McCabe-Thiele), cálculo de cargas térmicas no refervedor e condensador, consumo de utilidades (vapor de água e água de resfriamento), estimativa do tempo de destilação e alguns aspectos econômicos sobre o processo (custos de equipamentos e operacionais, capacidade de produção, lucro mensal). Implementou-se em uma planilha eletrônica este modelo para as simulações matemáticas e análise técnico-econômica do processo. Em escala de laboratório (foram realizados, ao todo, oito ensaios, quatro de refluxo constante e quatro de refluxo variável, utilizando uma coluna de pratos perfurados), constatou-se uma boa concordância entre estes resultados experimentais e os calculados a partir da modelagem. Em seguida, estudaram-se, isoladamente em cada modo de operação e de modo comparativo, as principais variáveis de processo (taxa de refluxo, composição do destilado, quantidade de carga, vazão de destilado, etc.) através de simulações matemáticas, tanto no cenário de uma unidade existente como no caso do projeto de uma instalação nova. Para uma instalação existente, verificou-se, que no modo de destilação com composição de destilado constante, mantendo-se a vazão do vapor de topo constante, o tempo de destilação é menor, a capacidade de destilação é maior, resultando em maior lucro mensal. Para uma instalação a ser projetada, de novo, o processo mais vantajoso é o de refluxo variável e vazão de vapor do topo constante, pois requer menores áreas dos trocadores de calor para uma dada separação num tempo fixo de processo. No entanto, para o processamento de uma dada quantidade num mesmo tempo, à medida que se adota, no projeto, um número maior de estágios de separação na coluna, a diferença de lucro mensal torna-se praticamente indistinta para os modos de destilação estudados. / The aim of this study is to compare two operational methods of batch distillation of a binary system (methanolethanol): constant reflux and constant distillate composition. A phenomenological modeling concerning each mode was developed. It was based on material and enthalpy balances, equilibrium relationships, estimation of physical properties (specific heat and latent vaporization heat of mixtures), determination of ideal stages number (using McCabe-Thiele method), calculation of rebolier and condenser thermal loads and areas, steam and cooling water requirement, distillation time and some economical aspects. The mathematical model was implemented into an electronic spreadsheet. The predicted values were compared to experimental results from eight tests carried out in a laboratory sieve tray column (four at constant reflux and four at constant distillate composition), and a good consistency was found. Then several case studies concerning each distillation mode as well as the comparative performance were accomplished through mathematical simulations. Evaluation of the basic process variables such as reflux rate, initial load, distillate composition and flow rate was done. Rating of an existing plant and design of a new installation were considered in this process analysis. For an existing installation, lower distillation time, as well as higher distillation capacity and monthly profit were observed when distilling with constant distillate composition, keeping constant the flow rate of vapor from the column top. This process is also the more advantageous one when designing a new plant since smaller heat exchanger areas are required. However, to process a quantity in a same time, in a design of a new plan, as number of separation stages increases, monthly profit becomes almost the same among the studied distillation modes.

Membrane distillation (MD) is an emerging technology capable of treating high-saline feeds and operating with low-grade heat energy. However, commercial implementation of MD is limited by so-called temperature polarization, which is the deviation in the temperature at the feed-membrane interface with respect to the bulk fluid. This work presents solutions to alleviate temperature polarization in MD by employing a localized heating concept to deliver heat at the vicinity of the feed-membrane interface. This can be realized in multiple ways, including Joule heating, photothermal heating, electromagnetic induction heating, and nanofluid heating. In the first experiment, a Joule heating concept was implemented and tested, and the results showed a 45% increase in permeate flux and a 57% decrease in specific energy consumption. This concept was further improved by implementing a new dead-end MD configuration, which led to a 132% increase in the gained output ratio. In addition, the accumulation of foulants on the membrane surface could be successfully controlled by intermittent flushing of feedwater. Three-dimensional CFD calculations of conjugate heat transfer revealed a more uniform heat transfer and temperature gradient across the membrane due to the increased feedwater temperature over a larger membrane area. In another approach, a photothermal MD concept was used to heat the feed water locally. A 2-D photothermal material, MXene, recently known for its photothermal property, was used to coat commercial MD membranes. The coated membranes were evaluated under one-sun illumination to yield a permeate flux of 0.77 kg.m$^{−2}$h$^{−1}$ with a photothermal efficiency of 65.3% for a feed concentration of 0.36 g.L$^{−1}$. The system can produce around 6 liters of water per day per square meter of membrane. An energy analysis was also performed to compare the efficiency of various energy sources. Considering the sun as a primary energy source, the performance of different heating modes was compared in terms of performance and scale-up opportunities. Overall this work demonstrates that the application of localized heating will enable the scale-up and the use of renewable energy sources to make the MD process more efficient and sustainable. / The illustrative figure was produced by Ana Bigio, scientific illustrator, KAUST.