[No abstract submitted] / Science, Faculty of / Chemistry, Department of / Graduate

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Vita. Includes bibliographical references.

A large number of distillation sequences can be generated to separate a multicomponent azeotropic mixture. However, there is no systematic and efficient method for synthesising promising sequences, which also consider recycle connections and flowrates. In this work, a systematic procedure is developed for synthesising economically promising distillation sequences separating multicomponent homogeneous azeotropic mixtures. The procedure uses spherically approximated distillation boundaries, a shortcut column design method, and allows recycle and sequence alternatives to be screened. Both feasibility and design are addressed. Approximation of a distillation boundary as a spherical surface is a simple nonlinear, yet more accurate representation of the actual boundary than a linear approximation. For shortcut column design, azeotropes are treated as pseudocomponents and the relative volatilities of all singular points of the system are characterised, based on the transformation of vapour-liquid equilibrium behaviour in terms of pure components into that in terms of singular points. Once the relative volatilities of singular points are obtained, the classical Fenske-Underwood-Gilliland method can be used to design columns separating azeotropic mixtures. This method is extremely computationally efficient and can be applied to homogeneous azeotropic mixtures with any number of components; the results are useful for initialising rigorous simulations using commercial software and for assessing feasibility of proposed splits. Together with the spherical approximation of distillation boundaries, this shortcut method provides a basis for evaluating distillation sequences with recycles. Analysis of feasibility requirements of splits, component recovery requirements and the effects of recycles on the performance of proposed splits allows rules and procedures for selecting recycles to be proposed. Recycles with compositions of either singular points or mixtures of singular points are identified that are beneficial to the feasibility of sequences and the recovery of components. The principles are applicable to azeotropic mixtures with any number of components; using these procedures, recycle structures can be generated and are much simpler than the superstructures of recycle alternatives. The sequence synthesis procedure of Thong and Jobson (2001c) allows all potentially feasible sequences to be generated. To screen among these sequences, a split feasibility test and a two-step screening procedure are proposed. In the first step, feasibility of splits is tested efficiently and sequences containing either infeasible or sloppy splits are eliminated. In the second step, sequences containing sloppy splits are generated, based on the evaluation of sequences containing only feasible sharp splits. Using this procedure, the number of distillation sequences identified using the procedure of Thong and Jobson (2001c) can be significantly reduced. A systematic methodology is proposed for the synthesis and evaluation of multicomponent homogeneous azeotropic distillation sequences. The methodology is computationally efficient. It is demonstrated through a case study, the synthesis of distillation sequences separating a five-component mixture, in which two homogeneous azeotropes are formed, and for which over 5000 sequences producing pure component products can be generated. Using this methodology, only ten sequences are evaluated to identify three promising sequences. The evaluation of each sequence using the shortcut column design method is extremely efficient compared with that using the boundary value method.

Not available / text

No description available.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Distillation is the most widely used separation technique in the chemical process industry and typically accounts for approximately one-third of the total capital cost and more than half of the total energy consumption of a typical petrochemical-chemical plant. Therefore, the design and optimization of the distillation sequence are of critical importance to the economics of the entire process. Azeotropic mixtures cannot be separated into their pure components via normal distillation. Enhanced distillation techniques such as heterogeneous azeotropic distillation should be considered for these mixtures. Isobaric vapour-liquid-liquid equilibrium (VLLE) data are highly important for the design and analysis of heterogeneous distillation columns. However, limited VLLE data are available in literature due to the difficulties involved with measuring such data. The objective of this work was to systematically evaluate and compare the performance of selected entrainers (including benzene, DIPE and cyclohexane) for the dehydration of C2 and C3 alcohols. To meet this objective, phase equilibrium data had to be measured. Isobaric VLLE at standard atmospheric conditions were measured with a dynamic Guillespie unit equipped with an ultrasonic homogenizer, which prevented liquid-liquid separation. Vapour-liquid equilibrium (VLE) and VLLE data were measured for ethanol/water/di-isopropyl ether (DIPE), n-propanol/water/DIPE and n-propanol/water/isooctane. The VLE data were found to be thermodynamically consistent according to the L-W (Wisniak 1993) and McDermott-Ellis consistency tests. No thermodynamic consistency test, specifically for VLLE data, could be found in literature, but the LLE part of the data followed a regular profile according to the Othmer-Tobias correlation. The binary DIPE/water and isooctane/water azeotropes, as well as ternary ethanol/DIPE/water and n-propanol/isooctane/water azeotropes, as measured in this work, agree well with those found in literature. Regressed parameters for the NRTL, UNIQUAC, and UNIFAC models, generally improved the model predictions compared with built-in Aspen parameters. This confirmed the importance of having actual measured VLLE data available for evaluation and improvement of estimations by thermodynamic models. NRTL predicted the ethanol/DIPE/water and n-propanol/DIPE/water VLLE most accurately. Despite the improved regressed parameters for n-propanol/isooctane/water predictions, the models are still considered unsuitable for accurate prediction of the VLLE behaviour of this system. Separation sequences were simulated in Aspen with built-in and regressed parameters, respectively, to illustrate the significant effect such inaccurate parameters have on these simulations. Phase diagram (VLLE data) evaluation of ethanol and isopropanol (IPA) with various entrainers, as found in literature, indicated that DIPE might be a good entrainer for the dehydration of these alcohols. Benzene and cyclohexane are generally used as entrainers in industry for these processes. Benzene is however carcinogenic and therefore an alternative has to be found (United States Department of Labour - Occupational Safety & Health Administration 2011). Separation sequences were simulated for ethanol dehydration with benzene and DIPE as entrainers, respectively. Taking cost and safety into account, DIPE can be considered an acceptable replacement for benzene as entrainer for ethanol dehydration. A separation sequence was also simulated for the dehydration of IPA with DIPE as entrainer and compared to a simulation with cyclohexane (Arifin, Chien 2007) as entrainer. DIPE was found to be a reasonable alternative to cyclohexane as entrainer for IPA dehydration. Two other separation sequences were simulated as practical examples where DIPE could be used as entrainer for the recovery of ethanol or n-propanol from aqueous Fischer Tropsch waste streams. DIPE is therefore found to be a feasible alternative entrainer to benzene and cyclohexane for the dehydration of ethanol and IPA via heterogeneous azeotropic distillation, based on pre-liminary cost considerations, separation ability and safety. Better entrainers than DIPE may exist, but from the data available in literature and the measurements made in this work DIPE appears to be superior to benzene, cyclohexane and isooctane. / AFRIKAANSE OPSOMMING: Distillasie is die mees algemeen-gebruikte skeidingstegniek in die chemiese proses-industrie. Dit is tipies verantwoordelik vir ʼn derde van die totale kapitaalkoste en meer as die helfte van die totale energie verbruik op ʼn tipiese petrochemiese chemiese aanleg. Daarom is die ontwerp en optimering van ʼn distillasie trein van kardinale belang vir die winsgewendheid van die proses. Azeotropiese mengsels kan nie slegs deur normale distillasie in suiwer komponente geskei word nie. Gevorderde distillasie tegnieke soos heterogene azeotropiese distillasie moet dus oorweeg word vir sulke mengsels. Isobariese damp-vloeistof-vloeistof ewewigsdata is een van die belangrikste fisiese eienskappe vir die ontwerp van heterogene distillasie kolomme. Die hoeveelheid damp-vloeistof-vloeistof ewewigsdata wat beskikbaar is in die literatuur is egter baie beperk omdat dit moeilik is om die data te meet. In hierdie werk is isobariese damp-vloeistof-vloeistof ewewigsdata met ʼn dinamiese Guillespie eenheid, by standaard atmosferiese druk gemeet. Die eenheid is toegerus met ʼn ultrasoniese homogeniseerder om vloeistof-vloeistof skeiding te voorkom. Temperatuur is gemeet met ʼn akkuraatheid van 0.03oC by 0oC. Die sisteem se druk is konstant gehou op 101.3 kPa met ʼn akkuraatheid van 0.35 % VSU (Vol Skaal Uitset). Die ewewigsamestellings is met ʼn relatiewe akkuraatheid van 2 % gemeet. Daar is damp-vloeistof en damp-vloeistof-vloeistof ewewigsdata van etanol/water/di-isopropiel eter (DIPE), npropanol/ water/ DIPE en n-propanol/water/iso-oktaan gemeet. Die damp-vloeistof ewewigsdata is deur die LW (Wisniak 1993) en McDermott-Ellis termodinamiese konsistensie toetse getoets en konsistent bevind. Geen termodinamiese konsistensie toets spesifiek vir damp-vloeistof-vloeistof ewewigsdata kon gevind word nie. Die Othmer-Tobias korrelasie dui egter aan dat die vloeistof-vloeistof ewewig gedeelte van die data ʼn reëlmatige gang volg. Die binêre DIPE/water en iso-oktaan/water azeotrope en ternêre etanol/DIPE/water en n-propanol/iso-oktaan/water fase-ewewigte wat in hierdie werk gemeet is, stem ooreen met die wat in die literatuur te vind is. Die parameters vir die modelle (NRTL, UNIQUAC en UNIFAC) wat in hierdie werk bestudeer is, is in die algemeen verbeter deur regressie van die eksperimentele data. Dit dui daarop dat dit belangrik is om eksperimentele damp-vloeistof-vloeistof ewewigsdata te hê om die voorspellings van termodinamiese modelle mee te evalueer en te verbeter. Die etanol/water/ DIPE en n-propanol/water/DIPE damp-vloeistof-vloeistof ewewigsdata is die akkuraatste deur NRTL voorspel. Ten spyte van die verbeteringe wat deur regressie behaal is met die NRTL en UNIQUAC parameters vir n-propanol/water/isooktaan, word hierdie modelle steeds nie as gepas vir die voorspelling van hierdie datastel beskou nie. Skeidingsreekse is gesimuleer met die ingeboude Aspen parameters en regressie parameters, onderskeidelik, om te illustreer dat onakkurate parameters ʼn beduidende effek op sulke simulasies het. Die evaluasie van fase diagramme van etanol en IPA met verskeie skeidingsagente, wat in die literatuur te vind is, dui aan dat DIPE ʼn goeie skeidingsagent kan wees vir die dehidrasie van hierdie alkohole. Skeidingsreekse vir die dehidrasie van etanol met benseen en DIPE, onderskeidelik, is gesimuleer. Met koste en veiligheid in ag geneem, is daar gevind dat DIPE ʼn aanvaarbare plaasvervanger vir benseen as skeidingsagent vir etanol dehidrasie kan wees. Daar is ook ʼn skeidingsreeks vir die dehidrasie van IPA met DIPE as skeidingsagent gesimuleer en met ʼn simulasie (Arifin, Chien 2007) wat sikloheksaan as skeidingsagent gebruik, vergelyk. Daar is bevind dat DIPE ʼn redelike alternatief vir sikloheksaan kan wees as skeidingsagent vir IPA dehidrasie. Nog twee skeidingsreekse is gesimuleer om as praktiese voorbeelde te dien van die gebruik van DIPE as skeidingsagent om etanol of n-propanol vanaf waterige Fischer-Tropsch afvalstrome te herwin. Daarom is daar bevind dat DIPE ʼn geldige alternatiewe skeidingsagent vir benseen en sikloheksaan is, gebaseer op koste, skeidingsvermoë en veiligheid. Daar kan beter skeidingsagente as DIPE bestaan, maar vanuit die data beskikbaar in literatuur en die metings geneem in hierdie werk, is DIPE die beste.

Accurate and reliable vapour-liquid equilibrium (VLE) and liquid-liquid equilibrium (LLE) data are the key to a successful design and simulation of most important industrial separation processes (traditional distillation, extractive and azeotropic distillation). This work focuses on measurement of new phase equilibrium data for systems comprising of propan-1-ol, water and diisopropyl ether which are of important use in the petrochemical industry. In addition, an investigation of phase equilibrium behavior for systems of interest constituted by solvents and high added-value oxygenated compounds deriving from lignocelluloses biomasses (bio-fuels) was conducted at the Ecole des Mines de Paris CEP/TEP laboratories (France).Various data bases such as Science Direct, ACS publications and Dortmund Data Bank (DDB, 2009) were used to confirm that no literature data is available for these systems. The VLE data measurements for the system of propan-1ol + water and propan-1ol + diisopropyl ether (DIPE) ( 333.15, 353.15 and 373.15 K ) were carried out using a dynamic still of Lilwanth (2011), with a test system (ethanol + cyclohexane at 40 kPa) undertaken prior measurements to confirm the accuracy of the method and apparatus.The phase equilibrium (VLE and LLE) behaviours for furan + n-hexane and furan + Methylbenzene, furfural + n-hexane and furan + water were determined at 101.3 kPa. The atmospheric dynamic ebulliometry was used to measure VLE systems at 101.3 kPa. A set of LLE data for furfural + n-hexane and furan + water systems were obtained using a static analytical method, with a newly commissioned LLE apparatus. Furfural + n-hexane system was compared used as test system, to verify the reliability of the new equipment. The NRTL model was used to correlate the LLE data, with Cox- Herington model used to predict the entire LLE curve for furfural+ n-hexane system. The experimental VLE data were correlated using the combined y − y method. The vapour phase non idealities were described using the methods from Nothnagel et al. (1973), Hayden and O’Connell (1975) and the Peng-Robinson (1976) model. The activity coefficients were correlated using the NRTL model of Renon and Prausnitz (1968) and the modified UNIQUAC model of Abrams and Prausnitz (1976). A propan-1-ol dehydration process was simulated using Aspen to illustrate the use and importance of thermodynamic models in industrial process design and simulation. The model used in the simulation was validated with measured VLE and literature LLE data. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.

O trabalho visa substituir processos comercialmente usados na indústria para purificação da glicerina obtida a partir de biodiesel. A purificação da glicerina até grau técnico ou P.A. (99,5 % em massa) implica em um grande consumo de energia nos processos de evaporação e destilação, pela necessidade de altos vácuos. Como alternativa, a desidratação da glicerina pode ser realizada por destilação azeotrópica heterogênea usando baixas temperaturas e a pressão atmosférica. O objetivo deste trabalho foi estudar a viabilidade técnica do processo de desidratação da glicerina por meio da destilação azeotrópica com tolueno e comparar o consumo de energia com os processos tradicionais. Para atingir o objetivo, avaliou-se a influencia das variáveis de processo: vazão de alimentação de glicerina (g/s) (X1 codificado), vazão de alimentação do vapor de tolueno (g/s) (X2 codificado), concentração inicial de glicerina (% em massa) (X3 codificado), temperatura de alimentação da glicerina (°C) (X4 codificado), na concentração final de glicerina. A construção do modelo foi feita a partir de um planejamento fatorial composto de segunda ordem, usando glicerina P.A. A concentração final foi estimada mediante o índice de refração e massa específica. Obteve-se o seguinte modelo: 2 1,96X2 13,18X3 6,42X1X3 2,24X2X3 1 %GLI = 79,42 8,88X1 + 4,72X + + + que mostrou que a temperatura de alimentação (X4 codificada) não exerceu influencia na concentração final de glicerina. Observou-se pelo modelo que é preferível utilizar valores máximos de X2.e mínimos de X1. Com estes ensaios foi possível obter uma glicerina 99% pura, porém apresentava um ligeiro cheiro de tolueno, que foi eliminado mediante arraste com ar (stripping). Para verificar o modelo empregou-se glicerina bruta oriunda do biodiesel previamente tratada. O processo prévio consistiu de: acidificação, neutralização, salting out com isopropanol, evaporação do álcool e troca iônica. A glicerina obtida após o processo de troca iônica, aparentemente só água e glicerina com 38,6 % em massa, foi usada para a verificação do modelo. Obteve-se por destilação azeotrópica uma glicerina com 92 % em massa, quando o valor predito pelo modelo foi 99 %. Esta glicerina tratada apresentou um desvio do modelo devido a presença de resíduos de sabões, porém ficou demonstrado a possibilidade de desidratação de glicerina por este processo necessitando apenas de melhorias nas etapas de purificação até a troca iônica. Também, avaliou-se a eficiência da coluna comparando a separação dada pela coluna com a dada por um único estágio de equilíbrio nas mesmas condições de vazão e concentração, concluindo-se que era da ordem de 10 %. Finalmente, este processo consome cerca de 57,72 % de energia em relação aos processos de evaporação e destilação a vácuo tradicionalmente usados. / This study aims to replace commercially processes used in industry for glycerine purification obtained from biodiesel. The purification of glycerine up to technical degree or PA (99.5% by weight) involves a large consumption of energy in the evaporation and distillation processes due to need operate at high vacuum. Alternatively, dehydration of glycerine can be achieved by heterogeneous azeotropic distillation using low temperature and atmospheric pressure. The objective of this work was to study the technical feasibility of the dehydration process of glycerine through azeotropic distillation with toluene and compare the energy consumption with traditional processes. To reach this objective, the influence of process variables: feed flow rate of glycerine (g/s) (X1 coded), feed flow rate of steam toluene (g/s) (X2 coded), initial concentration of glycerine (% by weight) (X3 coded), the temperature of food glycerine (°C) (X4 coded) has been studied in the final concentration of glycerine. The empirical model was built through fitting of data obtained from a factorial second order design, using glycerine PA. The final concentration was estimated by refractive index and density. The fitted model was: 2 1,96X2 13,18X3 6,42X1X3 2,24X2X3 1 %GLI = 79,42 8,88X1 + 4,72X + + + The model appoints that the feed (inlet glycerine solution) temperature (X4 coded) had no influence in the outlet concentration of glycerine. Moreover, it has been observed that is better to use maximum X2.and minimum X1. From these tests were possible to obtain a glycerine 99% purely, but it had a light smell of toluene, which was removed by stripping with air. In order to verify the empirical model, it has been used raw glycerine from biodiesel production. This glycerine was previously treated following the steps: acidification, neutralization, salting out with isopropanol, evaporation of isopropanol and ion exchange. The obtained glycerine after the process of ion exchange, presented 38.6% in weight, apparently only glycerine in water, has been used to check the model. Content of glycerine by this distillation was 92% in weight, when the predict value by the model was 99%. The deviation from the model was due to the presence of soap residues, but it has been demonstrated the possibility of dehydration of glycerine by this process requiring only some improvements in purification steps up to the ion exchange. In addition, it has been estimated the column efficiency by comparison of the separation in both column and single stage at the same flow rate and concentration conditions, concluding that it was 10 %. Finally, this process consumes approximately 57.72% of energy in relation to the processes of evaporation and vacuum distillation traditionally used.

O trabalho visa substituir processos comercialmente usados na indústria para purificação da glicerina obtida a partir de biodiesel. A purificação da glicerina até grau técnico ou P.A. (99,5 % em massa) implica em um grande consumo de energia nos processos de evaporação e destilação, pela necessidade de altos vácuos. Como alternativa, a desidratação da glicerina pode ser realizada por destilação azeotrópica heterogênea usando baixas temperaturas e a pressão atmosférica. O objetivo deste trabalho foi estudar a viabilidade técnica do processo de desidratação da glicerina por meio da destilação azeotrópica com tolueno e comparar o consumo de energia com os processos tradicionais. Para atingir o objetivo, avaliou-se a influencia das variáveis de processo: vazão de alimentação de glicerina (g/s) (X1 codificado), vazão de alimentação do vapor de tolueno (g/s) (X2 codificado), concentração inicial de glicerina (% em massa) (X3 codificado), temperatura de alimentação da glicerina (°C) (X4 codificado), na concentração final de glicerina. A construção do modelo foi feita a partir de um planejamento fatorial composto de segunda ordem, usando glicerina P.A. A concentração final foi estimada mediante o índice de refração e massa específica. Obteve-se o seguinte modelo: 2 1,96X2 13,18X3 6,42X1X3 2,24X2X3 1 %GLI = 79,42 8,88X1 + 4,72X + + + que mostrou que a temperatura de alimentação (X4 codificada) não exerceu influencia na concentração final de glicerina. Observou-se pelo modelo que é preferível utilizar valores máximos de X2.e mínimos de X1. Com estes ensaios foi possível obter uma glicerina 99% pura, porém apresentava um ligeiro cheiro de tolueno, que foi eliminado mediante arraste com ar (stripping). Para verificar o modelo empregou-se glicerina bruta oriunda do biodiesel previamente tratada. O processo prévio consistiu de: acidificação, neutralização, salting out com isopropanol, evaporação do álcool e troca iônica. A glicerina obtida após o processo de troca iônica, aparentemente só água e glicerina com 38,6 % em massa, foi usada para a verificação do modelo. Obteve-se por destilação azeotrópica uma glicerina com 92 % em massa, quando o valor predito pelo modelo foi 99 %. Esta glicerina tratada apresentou um desvio do modelo devido a presença de resíduos de sabões, porém ficou demonstrado a possibilidade de desidratação de glicerina por este processo necessitando apenas de melhorias nas etapas de purificação até a troca iônica. Também, avaliou-se a eficiência da coluna comparando a separação dada pela coluna com a dada por um único estágio de equilíbrio nas mesmas condições de vazão e concentração, concluindo-se que era da ordem de 10 %. Finalmente, este processo consome cerca de 57,72 % de energia em relação aos processos de evaporação e destilação a vácuo tradicionalmente usados. / This study aims to replace commercially processes used in industry for glycerine purification obtained from biodiesel. The purification of glycerine up to technical degree or PA (99.5% by weight) involves a large consumption of energy in the evaporation and distillation processes due to need operate at high vacuum. Alternatively, dehydration of glycerine can be achieved by heterogeneous azeotropic distillation using low temperature and atmospheric pressure. The objective of this work was to study the technical feasibility of the dehydration process of glycerine through azeotropic distillation with toluene and compare the energy consumption with traditional processes. To reach this objective, the influence of process variables: feed flow rate of glycerine (g/s) (X1 coded), feed flow rate of steam toluene (g/s) (X2 coded), initial concentration of glycerine (% by weight) (X3 coded), the temperature of food glycerine (°C) (X4 coded) has been studied in the final concentration of glycerine. The empirical model was built through fitting of data obtained from a factorial second order design, using glycerine PA. The final concentration was estimated by refractive index and density. The fitted model was: 2 1,96X2 13,18X3 6,42X1X3 2,24X2X3 1 %GLI = 79,42 8,88X1 + 4,72X + + + The model appoints that the feed (inlet glycerine solution) temperature (X4 coded) had no influence in the outlet concentration of glycerine. Moreover, it has been observed that is better to use maximum X2.and minimum X1. From these tests were possible to obtain a glycerine 99% purely, but it had a light smell of toluene, which was removed by stripping with air. In order to verify the empirical model, it has been used raw glycerine from biodiesel production. This glycerine was previously treated following the steps: acidification, neutralization, salting out with isopropanol, evaporation of isopropanol and ion exchange. The obtained glycerine after the process of ion exchange, presented 38.6% in weight, apparently only glycerine in water, has been used to check the model. Content of glycerine by this distillation was 92% in weight, when the predict value by the model was 99%. The deviation from the model was due to the presence of soap residues, but it has been demonstrated the possibility of dehydration of glycerine by this process requiring only some improvements in purification steps up to the ion exchange. In addition, it has been estimated the column efficiency by comparison of the separation in both column and single stage at the same flow rate and concentration conditions, concluding that it was 10 %. Finally, this process consumes approximately 57.72% of energy in relation to the processes of evaporation and vacuum distillation traditionally used.

No description available.