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Miscibility, Viscosity, Density, and Formation of Polymers in High-Pressure Dense FluidsLiu, Kun 18 January 2008 (has links)
This thesis is an experimental investigation of the phase behavior, volumetric properties, and viscosity of poly (methyl methacrylate) (PMMA), poly (ε-caprolactone) (PCL) and their blends. Homopolymerization and copolymerizations of methyl methacrylate (MMA) and 2-methylene-1,3-dioxepane (MDO) in mixtures of acetone + CO2 have also been explored.
The viscosities and densities of acetone + CO2 mixtures were measured in the temperature range 323-398 K at pressures up to 35 MPa. This is the first study in which viscosity of acetone + CO2 mixtures have been measured and the mixtures have been evaluated as solvents for PCL. It is shown that PCL can be readily dissolved in these fluid mixtures at modest pressures even at high carbon dioxide levels. Investigations have been conducted over a temperature range from 323 to 398 K at pressures up to 50 MPa for polymer concentrations up to 20 wt %, and CO2 concentrations up to 60 wt %. It is shown that in these mixtures PCL is dissolved at pressures that are much lower than the pressures reported for miscibility in the mixtures of carbon dioxide with other organic solvents. It is shown that PMMA also readily dissolves at modest pressures. Blends of PMMA and PCL require higher pressures than for the individual polymers for complete miscibility.
Free-radical polymerizations of MMA in acetone at 343 K were followed using in-situ measurements of viscosity and density at different pressures from 7- 42 MPa. This is the first time viscosity has been used as a real-time probe of high pressure polymerizations. Two distinct kinetic regimes were identified. Homopolymerizations of MDO were conducted in carbon dioxide at 323 and 343 K at pressures up to 42 MPa. For the first time it is shown that high molecular weight PCL can be produced from MDO in high pressure CO2. Ring-opening free-radical copolymerizations of MDO with MMA, styrene and acrylonitrile were conducted for the first time in carbon dioxide and have been shown to lead to polymers with high molecular weights. / Ph. D.
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The separation of detergent range alkanes and alcohol isomers with supercritical carbon dioxideZamudio, Michelle 04 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Data on the process performance at different operating conditions are required to determine the
feasibility of a separation process. Such data can be experimentally measured, but due to the time and
costs associated with pilot plant scale experiments, the use of predictive process models are often
preferred. The main aim of this project is to establish a working process model in Aspen Plus® that
can be used to predict the separation performance of a supercritical fluid fractionation process aimed
at the separation of mixtures of detergent range alkanes and alcohol isomers where similar boiling
points or low relative volatilities can occur.
Currently, an azeotropic distillation process is employed for the separation of detergent range
alkanes and alcohols. Although this process shows good separation performance, some concerns
regarding the operating conditions are raised: the preferred entrainer, diethylene glycol, is toxic to
humans; very low operating pressures of 0.016 – 0.031 MPa and high temperatures of 473 K are
required; additional processing units and materials are required to remove the entrainer from the
product streams. An alternative process, supercritical fluid fractionation, is proposed in this work
after previous studies have reported that this process have potential for the separation of alkanes and
alcohols. The supercritical fluid fractionation process addresses the concerns of the azeotropic
distillation process in the following ways: a non-toxic solvent, CO2, is used as the separating agent;
mild temperatures of 344 K is proposed, but at the cost of the low operating pressures of the
azeotropic process; and a single process unit and no additional material is required to separate the
solvent from the product streams. A process model was developed in Aspen Plus® to evaluate the separation performance of the
newly proposed supercritical fluid fractionation process and compare it to the current azeotropic
distillation process. The development of the process model included the development of an accurate
thermodynamic model in Aspen Plus®. After thorough evaluation of a number of cubic equations of
state, the RK-ASPEN model was found to be superior in its representation and prediction of phase
transition pressures for multi-component mixtures of detergent range alkanes and alcohols in the
temperature range 318 – 348 K. Phase transition pressures could be predicted with an error of less
than 6 % with the inclusion of regressed polar parameters and binary solute-solvent interaction
parameters for two multi-component mixtures: CO2 + (20 % n-dodecane + 70 % 1-decanol + 10 % 3,7-dimethyl-1-octanol) and CO2 + (25 % n-decane + 25 % 1-decanol + 25 % 3,7-dimethyl-1-octanol
+ 25 % 2,6-dimethyl-2-octanol).
Polar parameters were regressed from pure component vapour pressure data predicted with
correlations available in Aspen Plus®. Binary interaction parameters were regressed from
experimental bubble and dew point data. Binary bubble and dew point data were measured for a
number of systems containing ethane or CO2 and a C10-alkane or C10-alcohol isomer at temperatures
between 308 K and 353 K, and compositions ranging between 0.01 and 0.7 mass fraction solute. A
comparison between the phase equilibrium data measured for these systems revealed that the structure
of the molecule, and not only the molecular weight, influences its solubility in the supercritical
solvent. The phase transition pressures of n-decane, 2-methylnonane, 3-methylnonane and
4-methylnonane did not differ significantly in CO2 or ethane, and these compounds will in all
likelihood not be separated in a supercritical fluid fractionation process. The phase transition
pressures measured for the C10-alcohol isomers decreased in both CO2 and ethane in the following
order: 1-decanol, 3,7-dimethyl-1-octanol, 2-decanol, 2,6-dimethyl-2-octanol and
3,7-dimethyl-3-octanol. The position of the hydroxyl group and the number, length and position of
the side branches, all influence the solubility behaviour and phase transition pressures of the isomeric
alcohols in the supercritical solvent. Since the use of ethane did not show any significant benefits
with regard to selectivity, the use of the less harmful and less expensive solvent, CO2, in further
investigations was justified. The RK-ASPEN thermodynamic model, with the inclusion of the regressed polar and binary
solute-solvent interaction parameters, was implemented in the process model and the separation
performance of the process was simulated at different operating conditions for the CO2 +
(25 % n-decane + 25 % 1-decanol + 25 % 3,7-dimethyl-1-octanol + 25 % 2,6-dimethyl-2-octanol)
mixture. A comparison to experimental pilot plant data revealed that the model cannot be used to
predict the separation performance at low fractionation temperatures (316 K) due to shortcomings in
the thermodynamic model. However, the performance of the process at high fractionation
temperatures (344 K) could be predicted well, with an error of 10 – 36 %. Simulations for the CO2 +
(25 % n-decane + 25 % 1-decanol + 25 % 3,7-dimethyl-1-octanol + 25 % 2,6-dimethyl-2-octanol) and
CO2 + (20 % n-dodecane + 70 % 1-decanol + 10 % 3,7-dimethyl-1-octanol) mixtures showed that the
composition of the feed mixture have a significant effect on the location and size of the operating
window and optimum operating conditions. The optimum operating conditions were defined as the
conditions where an acceptable selectivity ratio and alcohol recovery occurred simultaneously. Since the selectivity ratio and alcohol recovery have opposing optimization approaches, a number of
possible optimum operating conditions exist, based on the product specifications. When an alcohol
and an alkane with similar phase behaviour exist in a mixture, a distinct minimum selectivity ratio
will occur at a point within the extract-to-feed ratio limits of the process. When the alkanes and
alcohols present in a mixture do not have similar or overlapping phase transition pressures, the
minimum selectivity ratio will typically cover a small range of extract-to-feed ratios at the high end
limit of the extract-to-feed ratio range.
To summarize: A process model was established in Aspen Plus® that can be used to determine
the feasibility and separation performance of a supercritical fractionation process for a feed mixture of
detergent range alkane and alcohol isomers. The model was used to prove that an SFF process is a
feasible alternative process to consider for the removal of alkanes from mixtures of detergent range
alcohol isomers, even where overlapping boiling points or low relative volatilities occur. During the
development of the process model, the following significant novel contributions were made:
· New phase equilibrium data were measured for C10-alkane and C10-alcohol isomers in
supercritical ethane, as published in The Journal of Supercritical Fluids 58 (2011) 330 –
342.
· New phase equilibrium data were measured for C10-alkane and C10-alcohol isomers in
supercritical CO2, as published in The Journal of Supercritical Fluids 59 (2011) 14 – 26.
· A thermodynamic model was developed in Aspen Plus® that can accurately predict the
phase transition pressures of binary, ternary and multi-component mixtures of detergent
range alkanes and alcohols in supercritical CO2, as published in The Journal of
Supercritical Fluids 84 (2013) 132 – 145.
· A process model was developed in Aspen Plus® that can be used to predict the separation
performance of a supercritical fluid fractionation process for the separation of mixtures of
detergent range alkanes and alcohols.
· Experimental and simulated results indicated that a supercritical fluid fractionation process
can be implemented successfully to separate an alkane from a mixture of alcohol isomers,
as was shown for two mixtures: CO2 + (25 % n-decane + 25 % 1-decanol + 25 %
3,7-dimethyl-1-octanol + 25 % 2,6-dimethyl-2-octanol) and CO2 + (20 % n-dodecane +
70 % 1-decanol + 10 % 3,7-dimethyl-1-octanol). / AFRIKAANSE OPSOMMING: Data oor die omvang van skeiding by verskillende bedryfstoestande word benodig om die
lewensvatbaarheid van ’n skeidingsproses te bepaal. Sulke data kan eksperimenteel gemeet word,
maar as gevolg van die tyd en kostes geassosieer met eksperimente op loodsaanlegskaal, word die
gebruik van prosesmodelle verkies. Die hoofdoel van hierdie projek is om ’n werkende prosesmodel,
wat daarop gemik is om C8 – C20 alkane en alkohol isomere te skei, in Aspen Plus® tot stand te bring
om die omvang van die skeiding van ’n superkritiese fraksioneringsproses te meet.
Tans word azeotropiese distillasie gebruik vir die skeiding van C8 – C20 alkane en alkoholisomere.
Alhoewel goeie skeiding met hierdie proses bewerkstellig word, is daar sekere eienskappe
van die proses wat aandag vereis: die voorgestelde skeidingsagent, dietileen glikol, is giftig vir mense;
baie lae bedryfsdrukke van 0.016 – 0.031 MPa en hoë temperature van 473 K word benodig;
addisionele proseseenhede en materiaal is nodig om die skeidingsagent van die produkte te verwyder.
Die gebruik van ’n alternatiewe proses - superkritiese fraksionering - word in hierdie werk voorgestel
nadat vorige studies getoon het dat hierdie proses die potensiaal het om alkane en alkohole te skei.
Die superkritiese fraksioneringsproses spreek al die kommerwekkende eienskappe van azeotropiese
distillasie aan soos volg: ’n veilige oplosmiddel, CO2, word as die skeidingsagent gebruik;
gemiddelde temperature van 344 K word voorgestel, maar ten koste van lae bedryfsdrukke; ’n enkele
proseseenheid en geen addisionele materiaal word benodig om die oplosmiddel van die produkte te
skei nie. ’n Prosesmodel is in Aspen Plus® ontwikkel om die omvang van die skeiding wat deur die
voorgestelde superkritiese fraksioneringsproses teweeggebring is, te evalueer en te vergelyk met die
azeotropiese distillasieproses wat tans in gebruik is. Die ontwikkeling van die prosesmodel sluit die
ontwikkeling van ’n akkurate termodinamiese model in Aspen Plus® in. Na deeglike evaluasie van ’n
aantal kubiese toestandsvergelykings is gevind dat die RK-ASPEN-model die faseoorgangsdrukke
van multi-komponentmengsels van C8 – C20 alkane en alkohole die beste voorspel binne die
temperatuurbereik van 318 – 348 K. Faseoorgangsdrukke kon voorspel word met ’n fout van minder
as 6 % met die insluiting van voorafbepaalde polêre parameters en binêre interaksie-parameters vir
twee multi-komponentmengsels: CO2 + (20 % n-dodekaan + 70 % 1-dekanol + 10 % 3,7-dimetiel-1-oktanol) and CO2 + (25 % n-dekaan + 25 % 1-dekanol + 25 %
3,7-dimetiel-1-oktanol + 25 % 2,6-dimetiel-2-oktanol).
Polêre parameters is bepaal met dampdruk data, wat voorspel is met korrelasies in Aspen Plus®.
Binêre interaksieparameters is van eksperimentele faseoorgangsdata bepaal. Binêre faseoorgangsdata
is vir ’n aantal sisteme wat uit etaan of CO2 en ’n C10-alkaan- of C10-alkohol-isomeer bestaan, gemeet
by temperature tussen 308 K en 353 K en samestellings van tussen 0.01 en 0.7 massafraksie van die
opgeloste stof. ’n Vergelyking tussen die gemete fase-ewewigsdata het onthul dat die struktuur van
die molekuul, en nie net die molekulêre massa nie, die oplosbaarheid van die stof in die superkritiese
oplosmiddel beïnvloed. Die faseoorgangsdrukke van n-dekaan, 2-metielnonaan, 3-metielnonaan en
4-metielnonaan het geen skynbare verskille getoon in etaan of CO2 nie en dus sal hierdie stowwe in
alle waarkynlikheid nie met ’n superkritiese fraksioneringsproses geskei kan word nie. Die
faseoorgangsdrukke wat vir die C10-alkohol gemeet is, het in beide etaan en CO2 afgeneem in die
volgende volgorde: 1-dekanol, 3,7-dimetiel-1-oktanol, 2-dekanol, 2,6-dimetiel-2-oktanol en
3,7-dimetiel-3-oktanol. Die posisie van die hidroksielgroep en die aantal, lengte en posisie van die
sytakke beïnvloed die oplosbaarheidsgedrag van die alkohol-isomere in die superkritiese oplosmiddel.
Aangesien die gebruik van etaan nie enige voordele ten opsigte van selektiwiteit inhou nie, is die
gebruik van die minder skadelike en goedkoper oplosmiddel, CO2, vir verdere ondersoeke
geregverdig. Die ontwikkelde termodinamiese model, met die insluiting van die polêre parameters en binêre
interaksieparameters, is in die prosesmodel ingesluit en die omvang van die skeiding van die proses is
gesimuleer by verskillende bedryfstoestande vir die CO2 + (25 % n-dekaan + 25 % 1-dekanol + 25 %
3,7-dimetiel-1-oktanol + 25 % 2,6-dimetiel-2-oktanol) mengsel. ’n Vergelyking tussen die
gesimuleerde data en die eksperimentele loodsaanlegdata het onthul dat die model nie die omvang van
die skeiding kan voorspel by lae fraksioneringstemperature (316 K) nie as gevolg van die
tekortkominge in die termodinamiese model. Die omvang van die skeiding by hoë temperature
(344 K) kon egter goed voorspel word met ’n fout van 10 – 36 %. Simulasies van die CO2 + (25 %
n-dekaan + 25 % 1-dekanol + 25 % 3,7-dimetiel-1-oktanol + 25 % 2,6-dimetiel-2-oktanol) en CO2 +
(20 % n-dodekaan + 70 % 1-dekanol + 10 % 3,7-dimetiel-1-oktanol) mengsels het getoon dat die
samestelling van die voermengsel ’n beduidende effek op die grootte van die bedryfsvenster en
optimum bedryfstoestande het. Die optimum bedryfstoestande word gedefinieer as die toestande waar
’n aanvaarbare selektiwiteitsverhouding en alkoholherwinning terselfdertyd voorkom. Aangesien die
selektiwiteitsverhouding en alkoholherwinning teenstrydige optimeringsbenaderings het, bestaan daar ’n aantal optimum bedryfstoestande gebaseer op die produkspesifikasies. Wanneer ’n alkohol en ’n
alkaan met ooreenstemmende fasegedrag saam in ’n mengsel voorkom, bestaan daar ’n duidelike
minimum selektiwiteitsverhouding by ’n punt binne die ekstrak-tot-voer-verhoudingslimiete van die
proses. Wanneer die alkane en alkohole in ’n mengsel nie ooreenstemmende fasegedrag toon nie, sal
die minimum selektiwiteitsverhouding oor ’n reeks ekstrak-tot-voer-verhoudings voorkom, tipies by
die hoë limiet van die ekstrak-tot-voer-verhoudingsreeks.
Om op te som: ’n Prosesmodel is in Aspen Plus® tot stand gebring wat die lewensvatbaarheid
en omvang van die moontlike skeiding van ’n superkritiese fraksioneringsproses vir voermengsels van
C8 – C20 alkane en alkohol-isomere kan voorspel. Die model is gebruik om te bewys dat ’n
superkritiese proses ’n lewensvatbare alternatiewe proses is om te oorweeg vir die verwydering van
alkane uit mengsels van alkohol-isomere, self waar ooreenstemmende kookpunte of lae relatiewe
vlugtigheid tussen komponente voorkom. Tydens die ontwikkeling van die prosesmodel is die
volgende beduidende nuwe bydraes gemaak:
· Nuwe fase-ewewigsdata is gemeet vir C10-alkaan- en C10-alkohol-isomere in superkritiese
etaan, soos gepubliseer in The Journal of Supercritical Fluids 58 (2011) 330 – 342.
· Nuwe fase-ewewigsdata is gemeet vir C10-alkaan and C10-alkohol isomere in superkritiese
CO2, soos gepubliseer in The Journal of Supercritical Fluids 59 (2011) 14 – 26.
· ’n Termodinamiese model is ontwikkel in Aspen Plus® wat die faseoorgangsdrukke van
binêre, ternêre en multi-komponent mengsels van C8 – C20 alkane en alkohol-isomere in
superkritiese CO2 akkuraat kan voorspel, soos gepubliseer in The Journal of Supercritical
Fluids 84 (2013) 132 – 145.
· ’n Prosesmodel is ontwikkel in Aspen Plus® wat die omvang van die moontlike skeiding
van ’n superkritiese fraksioneringsproses, gemik op die skeiding van mengsels van C8 –
C20 alkane en alkohol-isomere, kan voorspel.
· Eksperimentele en gesimuleerde resultate toon aan dat ’n superkritiese
fraksioneringsproses suksesvol geïmplementeer kan word vir die skeiding van ’n alkaan
vanuit ’n mengsel van alkohol-isomere, soos bewys vir twee mengsels: CO2 + (25 %
n-dekaan + 25 % 1-dekanol + 25 % 3,7-dimetiel-1-oktanol + 25 % 2,6-dimetiel-2-oktanol)
en CO2 + (20 % n-dodekaan + 70 % 1-dekanol + 10 % 3,7-dimetiel-1-oktanol).
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Preparação de blocos quirais contendo selênio e telúrio via resolução cinética enzimática em CO2 supercrítico e determinação de excessos enantioméricos por RMN de 125Te e calcogenação de olefinas ativadas / Preparation of chiral building blocks containing S, Se and Te via kinetic enzymatic resolution in supercritical CO2, enantiomeric excess determinations by 125Te NMR, and chalcogenation of activated olefinesGariani, Rogério Aparecido 22 February 2011 (has links)
Esta tese esta dividida em três capítulos: Primeiro capítulo - Resolução cinética enzimática de sulfetos, selenetos e teluretos em CO2 supercrítico. Inicialmente, a estabilidade dos β-hidróxi organocalcogenetos foi avaliada em CO2 supercrítico. Como a variação da pressão e temperatura afeta a densidade do fluído de forma não linear, um estudo sistemático foi realizado para avaliação desses parâmetros, visando altos excessos enantioméricos para os β-hidróxi- sulfetos e -selenetos, os quais foram determinados por cromatografia líquida de alta eficiência (CLAE). Os β-hidróxi-teluretos não se apresentaram estáveis sob as mesmas condições. Desta maneira, um novo método para determinar o excesso enantiomérico dos β-hidróxi-teluretos foi desenvolvido, utilizando RMN de 125Te. Capítulo 2 - Utilização de teluroferrocenos quirais como sondas quirais para a determinação de excessos enantioméricos usando RMN de 125Te. Teluroferrocenos quirais, substituídos por grupos amidas, oxazolinas e aminas foram preparados. Tais moléculas contendo telúrio interagem com amostras quirais, formando complexos diastereoisoméricos, nos quais os átomos de telúrio são submetidos a diferentes ambientes químicos, o que resulta em diferentes deslocamentos químicos para cada complexo diastereoisomérico. A integração dos sinais de 125Te permite a determinação do excesso enantiomérico de amostras quirais. Terceiro capítulo - Calcogenação de olefinas ativadas. Organocalcogenolatos de lítio gerados in situ reagiram com olefinas ativadas. Na presença de uma fonte de prótons, foram formados os calcogenetos β-funcionalizados. Em meio anidro, o enolato intermediário pode ser capturado com compostos carbonílicos em reações tandem tri- componentes, gerando precursores de Morita-Baylis-Hillman, quando Y = S, Se. / This thesis contains three chapters: 1st chapter - Kinetic enzymatic resolution of sulfides, selenides and tellurides in supercritical CO2. Initialy, the stability of the β-hydroxy organochalcogenides in suprecritical CO2 was evaluated. As the variation in the pressure and temperature affect the fluid density in a non-linear way, a systematic study on the influence of these parameters was performed, aiming a high enantiomeric excess for the products. The enantiomeric excesses of the β-hydroxy sulfides and selenides were determined by high performance chiral liquid chromatography (HPLC). The β-hydroxy tellurides were not stable under the same conditions. In view of this fact, a new method to determine the enantiomeric excess of the β-hydroxy tellurides was developed, using 125Te NMR spectroscopy for this end. 2nd chapter - Use of chiral telluroferrocenes as chiral probes for the enantiomeric excess determination using 125Te NMR spectroscopy. Chiral telluroferrocenes, substituted by amides, oxazolines and amines were prepared. These chiral tellurium containing molecules interact with chiral samples, forming diastereomeric transient complexes in which the tellurium atoms are submitted to different chemical environments, what leads to different 125Te chemical shifts for each diastereomeric complex integration of the 125Te NMR spectra allowing the determination of the enantiomeric excess of the chiral samples. 3rd chapter - Chalcogenation of activated olefines. In situ gererated lithium organochalcogenolates were reacted with activated olefines. In the presence of a proton source, the β-functionalized chalcogenides were formed. Under anhydrous conditions, the intermediate enolate can be trapped with carbonyl compounds in a three components process to give precursors of Morita-Baylis-Hillman adducts when Y = S, Se.
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Organocatálise em CO2 supercrítico: reatividade e otimização de processo / Organocatalysis in supercritical CO2: reactivity and process optimization.Cassaro, Rafael Frascino 14 May 2015 (has links)
O dióxido de carbono no estado supercrítico (CO2-SC) tem despertado considerável interesse nos últimos anos como um novo solvente para reações orgânicas. Nesta tese foi investigada a influência do uso de CO2 supercrítico, associado ou não a líquidos iônicos ou cossolventes, como solvente em reações químicas visando à obtenção de precursores quirais. Foram estudadas as reações de condensação Aldólica, de Morita-Baylis-Hillman (MBH) e do tipo adição de Michael, empregando Organocatálise quando conveniente, isto é, catalisadores provenientes de aminoácidos e ácidos carboxílicos. As reações de MBH foram otimizadas através de um planejamento experimental e sua condição ótima se deu a 70°C, 110 bar, com 6 equivalentes de H2O, tempo reacional de 2h30 min e sem a presença de liquido iônico, tendo um rendimento de 84,6%. Para as condensações aldólicas os melhores resultados com acetona e p-nitrobenzaldeido como materiais de partida foram obtidos a 150 bar e 40°C, com a presença de liquido iônico, em 2 horas de tempo reacional com um rendimento de 54,0% e um excesso enantiomérico de 79,0% utilizando o catalisador (2S,4R)-4-(terc-butildimetilsililoxi)pirrolidina-2-ácido carboxílico. Com ciclohexanona como material de partida foram obtidos a 150 bar e 40°C com a presença de um doador de prótons (resina de troca iônica) em 2 horas de tempo reacional com um rendimento de 70,9% e um excesso enantiomérico de 91,2%, utilizando o catalisador (2S,4R)-4-(terc-butildimetilsililoxi)pirrolidina-2-ácido carboxílico. Outros aldeídos e cetonas utilizados como materiais de partida apresentaram rendimentos menores. Estudos de comportamento de fases foram feitos para os materiais de partida, catalisadores e produtos da reação de condensação Aldólica. Os melhores rendimentos foram obtidos em situações em que os materiais de partida e os catalisadores eram solúveis na fase supercrítica, mas os produtos não, formando uma segunda fase. / Supercritical carbon dioxide (sc-CO2) has attracted considerable interest in the last years as a new solvent for organic reactions. In this thesis, the influence of supercritical CO2 use, associated or not to ionic liquids or cosolvents, as a solvent for chemical reactions aiming at the synthesis of chiral precursors was studied. Aldol condensation, Morita-Baylis-Hillman (MBH) and Michael addition reactions were studied, employing organocatalysis when it was convenient, i.e., catalysts derived from aminoacids or carboxylic acids. MBH reactions were optimized through experimental design, resulting in a maximum yield of 84.6% for the optimal condition at 70°C, 110 bar, and 6 equivalents of H2O, reaction time of 2h30 min and the absence of ionic liquids. For the Aldol condensation reactions employing acetone and p-nitrobenzaldehyde, a maximum yield of 54.0%, with an enantiomeric excess of 79.0% was obtained at 150 bar, 40°C, 2h reaction time, in the presence of ionic liquid, using the catalyst (2S,4R)-4-(terc-butyldimethylsililoxy)pirrolidine-2-carboxylic acid. The yields were significantly lower for other aldehydes and ketones. Yields for Michael addition reactions were very low and their study was discontinued. Phase behavior studies were performed with starting materials, catalysts and products for the Aldol condensation reactions. The best yields were obtained for situations where the starting materials and catalysts were soluble in the supercritical phase and the products were not, forming a second phase.
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Nucleobases in supercritical fluidsSarfraz, Adnan 02 March 2010 (has links)
Diese Arbeit zeigt die Verwendung ueberkritischer Fluide als analytisches Werkzeug fuer den Transport einer Gruppe nichtfluechtiger Molekuele, naemlich Nucleobasen, in die Gasphase. Das am haeufigsten verwendete ueberkritische Fluid ist Kohlendioxid, welches sich jedoch als zu ineffizient bei der Aufloesung von Nucleobasen herausstellte. Deshalb wurde ein Gemisch aus Ethylen mit Ethanol als Cosolvens als ueberkritisches Loesungsmittel verwendet. Für die Erkennung des kritischen Punktes reiner Fluide oder verduennter Fluidmischungen wurde eine neue Methode entwickelt. Die Verschiebung des kritischen Punktes von Ethylen durch Zugabe von Ethanol wurde experimentell ermittelt und mit der Zustandsgleichung von Soave Redlich Kwong in Beziehung gesetzt. Fuer einen Molenbruch des Cosolvens Ethanol von 0.054 erhoeht sich die kritische Temperatur nur um 5,5 C, wohingegen die Theorie eine Erhoehung um 10 C vorhersagt. Fuenf biologisch relevante Nucleobasen wurden mit Hilfe von 3% Ethanol als Cosolvens in ueberkritischem Ethylen geloest. Die Zusammensetzung des Ueberschall-Molekularstrahles der expandierten Loesung wurde mit einem Quadrupol-Massenspektrometer quantitativ analysiert. Das Signalverhaeltnis der Nucleobasen zu Ethylen lag in der Groessenordnung von 10^-4 bis 10^-5. Diese Nucleobasen wurden auch auf Oberflaechen abgeschieden, sowohl durch Hochdruckexpansion der ueberkritischen Loesungen, als auch durch Verdampfung von alkoholischen Loesungen (nach der ’Drop Casting’ Methode). Die dabei entstehenden Morphologien wurden ex-situ mittels Rasterkraftmikroskopie untersucht. Die Ursachen dieser Unterschiede werden anhand der relevanten Nukleationsmechanismen diskutiert. / This work highlights the use of supercritical fluids (SCF) as an analytical tool for the transfer of a group of non-volatile molecules, namely nucleobases, into the gas phase. The most commonly used SCF carbon dioxide was found inefficient in dissolving the nucleobases. Therefore, a mixture of ethylene (p_c = 50.6 bar and T_c = 9.35 C) with a cosolvent was used as the SC solvent. A new bracketing method was developed for detecting the critical point (CP) of pure fluids and diluted mixtures of fluids. The shift in CP of ethylene on addition of ethanol was determined and related to theoretical calculations by using the Soave Redlich Kwong equation of state. Comparing the experimental results to theoretical methods for calculating the CP showed large deviations. The critical temperature shifted by only 5.5 C when the mole fraction of the cosolvent i.e. ethanol was 0.054. Five biologically relevant were dissolved in SC ethylene using 3% of ethanol as cosolvent. The supersonic molecular beam composition of the expanded solution was analyzed quantitatively using a quadrupole mass spectrometer and the ratio of the nucleobases to ethylene in the beam was found to be of the order of 10^-4 to 10^-5. Surface deposition of the nucleobases through SCF solutions was carried out and the morphology was recorded using Atomic Force Microscopy. Remarkable differences were observed while comparing the morphology obtained after deposition using rapid expansion of supercritical solutions (RESS) and drop casting method. These differences are discussed in terms of diffusion, rate of evaporation of the solvent, degree of supersaturation, and the nucleation process.
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Organocatálise em CO2 supercrítico: reatividade e otimização de processo / Organocatalysis in supercritical CO2: reactivity and process optimization.Rafael Frascino Cassaro 14 May 2015 (has links)
O dióxido de carbono no estado supercrítico (CO2-SC) tem despertado considerável interesse nos últimos anos como um novo solvente para reações orgânicas. Nesta tese foi investigada a influência do uso de CO2 supercrítico, associado ou não a líquidos iônicos ou cossolventes, como solvente em reações químicas visando à obtenção de precursores quirais. Foram estudadas as reações de condensação Aldólica, de Morita-Baylis-Hillman (MBH) e do tipo adição de Michael, empregando Organocatálise quando conveniente, isto é, catalisadores provenientes de aminoácidos e ácidos carboxílicos. As reações de MBH foram otimizadas através de um planejamento experimental e sua condição ótima se deu a 70°C, 110 bar, com 6 equivalentes de H2O, tempo reacional de 2h30 min e sem a presença de liquido iônico, tendo um rendimento de 84,6%. Para as condensações aldólicas os melhores resultados com acetona e p-nitrobenzaldeido como materiais de partida foram obtidos a 150 bar e 40°C, com a presença de liquido iônico, em 2 horas de tempo reacional com um rendimento de 54,0% e um excesso enantiomérico de 79,0% utilizando o catalisador (2S,4R)-4-(terc-butildimetilsililoxi)pirrolidina-2-ácido carboxílico. Com ciclohexanona como material de partida foram obtidos a 150 bar e 40°C com a presença de um doador de prótons (resina de troca iônica) em 2 horas de tempo reacional com um rendimento de 70,9% e um excesso enantiomérico de 91,2%, utilizando o catalisador (2S,4R)-4-(terc-butildimetilsililoxi)pirrolidina-2-ácido carboxílico. Outros aldeídos e cetonas utilizados como materiais de partida apresentaram rendimentos menores. Estudos de comportamento de fases foram feitos para os materiais de partida, catalisadores e produtos da reação de condensação Aldólica. Os melhores rendimentos foram obtidos em situações em que os materiais de partida e os catalisadores eram solúveis na fase supercrítica, mas os produtos não, formando uma segunda fase. / Supercritical carbon dioxide (sc-CO2) has attracted considerable interest in the last years as a new solvent for organic reactions. In this thesis, the influence of supercritical CO2 use, associated or not to ionic liquids or cosolvents, as a solvent for chemical reactions aiming at the synthesis of chiral precursors was studied. Aldol condensation, Morita-Baylis-Hillman (MBH) and Michael addition reactions were studied, employing organocatalysis when it was convenient, i.e., catalysts derived from aminoacids or carboxylic acids. MBH reactions were optimized through experimental design, resulting in a maximum yield of 84.6% for the optimal condition at 70°C, 110 bar, and 6 equivalents of H2O, reaction time of 2h30 min and the absence of ionic liquids. For the Aldol condensation reactions employing acetone and p-nitrobenzaldehyde, a maximum yield of 54.0%, with an enantiomeric excess of 79.0% was obtained at 150 bar, 40°C, 2h reaction time, in the presence of ionic liquid, using the catalyst (2S,4R)-4-(terc-butyldimethylsililoxy)pirrolidine-2-carboxylic acid. The yields were significantly lower for other aldehydes and ketones. Yields for Michael addition reactions were very low and their study was discontinued. Phase behavior studies were performed with starting materials, catalysts and products for the Aldol condensation reactions. The best yields were obtained for situations where the starting materials and catalysts were soluble in the supercritical phase and the products were not, forming a second phase.
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Use of the supercritical fluid technology for the preparation of nanostructured hybrid materials and design of the interfaceGarcía González, Carlos A. 11 December 2009 (has links)
Los materiales compuestos nanoestructurados son considerados una opción prometedora
para la concepción de materiales multifuncionales. Sin embargo, la falta habitual de interacción
entre los componentes orgánicos e inorgánicos en los materiales híbridos nanoestructurados
comporta unas propiedades macroscópicas anisotrópicas que limitan su uso. Por ello, se hace
necesario el diseño de la interfase formada entre los componentes mencionados a fin de mejorar
sus prestaciones. En esta Tesis Doctoral se ha optado por el uso de dióxido de carbono supercrítico
(scCO2) para la modificación superficial de nanopartículas inorgánicas y para la preparación de
materiales híbridos nanoestructurados. Estos procesos supercríticos, diseñados como sostenibles,
se proponen como sustitutos de técnicas convencionales que empleen disolventes orgánicos.
El tratamiento superficial de nanopartículas de dióxido de titanio (TiO2) con
octiltrietoxisilano se ha empleado como sistema de estudio para evaluar el uso de recubrimientos
de alcoxisilanos bifuncionales como promotores de adhesión de partículas inorgánicas
nanométricas. El scCO2 se emplea como disolvente del alcoxisilano para la silanización del TiO2.
También se han llevado a cabo estudios fundamentales de solubilidad de octiltrietoxisilano en
CO2 y de la cinética del proceso de silanización del TiO2. La modulación de las propiedades
fisicoquímicas del scCO2 con la presión y la temperatura permite el control de las características
del recubrimiento con silano. El proceso de silanización supercrítico se ha extendido a diferentes
sistemas alcoxisilano-nanopartículas inorgánicas.
Asimismo, se ha evaluado la tecnología de scCO2 para la preparación de materiales
híbridos nanoestructurados que contengan nanopartículas inorgánicas silanizadas. El tratamiento
superficial de las nanopartículas favorece la distribución homogénea de éstas en el material
híbrido y mejora la interacción relleno-matriz orgánica. Se han procesado matrices
biopoliméricas de interés en ingeniería tisular, compuestas de ácido poliláctico o la mezcla
iv
polimetilmetacrilato/policaprolactona, con adiciones de nanopartículas de TiO2 o hidroxiapatita,
respectivamente. Para su procesado, se ha empleado scCO2 como no-disolvente utilizando la
técnica Particles from a Compressed Anti-Solvent (PCA). Además, se han preparado partículas
híbridas formadas por una mezcla lipídica de aceite de ricino hidrogenado y glicerilmonoestearato
con adiciones de TiO2 y cafeína, con posibles aplicaciones en cremas para uso tópico. Estas
partículas sólidas lipídicas se han obtenido usando la técnica Particles from Gas Saturated
Solutions (PGSS) que emplea scCO2 como soluto.
Por último, el proceso de silanización supercrítico se ha ensayado para materiales híbridos
complejos multiescalados. Se han procesado materiales de base cemento empleando un proceso
supercrítico de carbonatación-silanización en dos etapas. Primero, el cemento se carbonata de
manera acelerada usando scCO2 como agente de carbonatación. Este cemento, ya carbonatado, se
somete, finalmente, a un tratamiento hidrofóbico mediante silanización supercrítica, para su
posible aplicación en confinamiento de residuos peligrosos en ambientes húmedos o como
material de construcción duradero. / Nowadays, society is asking for a global changing in the way of manufacturing goods in a
more sustainable manner. Indeed, the weight of the classical factors (cost, quality, appearance)
influencing the acceptance of a certain good in the market have currently changed.
Manufacturing requirements and regulations concerning environment protection (e.g., resource
consumption, sustainability, toxicity, CO2 footprint, recycling potential) and quality features (e.g.,
product guarantees, durability against aggressive environments, corporate vision) are aspects of
increasing concern. The competitive position of a company is influenced by seizing the
opportunities and challenges and by managing the risks that the changeable market has. As a
consequence, the industry is continuously looking for smart and innovative solutions for the
design and manufacturing of materials with novel properties and increased added value, and for
the production of materials already existing in the market in a more efficient manner.
Nanostructured hybrid composites have emerged as a promising class of innovative
materials for many industrial sectors (e.g., energy, optoelectronics, biomedicine, cosmetics). The
multicomponent composition of these materials provides them with unique properties arising
from the synergistic combination of the characteristics of their individual components structured
at the nanolevel. Nevertheless, in numerous hybrid materials, the lack of coupling or bonding
between the components often leads to anisotropic macroscopic properties, limiting their use.
Hence, the interaction at the interphase between hybrid components must be properly
engineered to enhance materials properties. In this PhD Thesis, the quest for sustainable and
environmentally friendly processes led to the use of supercritical carbon dioxide (scCO2) for both
the surface modification of nanometric inorganic particles and the preparation of nanostructured
hybrid materials. These processes are designed for the replacement of conventional methods
using organic solvents.
vi
Bifunctional alkoxysilane molecules, acting as adhesion promoters, are, herein,
investigated for the surface modification of nanometric inorganic particles. The surface treatment
of titanium dioxide (TiO2) nanoparticles with octyltriethoxysilane is taken as the model system
for study. In terms of processing, scCO2 is used as the solvent of choice for alkoxysilanes for the
surface modification of TiO2. Fundamental studies on the solubility of the used silane in CO2 in
the pressure range 8-18 MPa at two different temperatures (318 and 348 K) and on the kinetics of
the TiO2 silanization process are performed. For the scCO2-aided silanization process, studies are
conducted to ascertain the effects and interactions of the operating variables on the properties of
the final material. Results show that the tunable physicochemical properties of scCO2 with
pressure and temperature (e.g., density, solvation power) allows the engineering control of the
characteristics of the silane coating. Examples of the extension of the application of the
supercritical silanization process to other sets of alkoxysilanes and inorganic nanoparticles are
also presented.
The preparation of hybrid materials including silanized inorganic nanoparticles and
organic matrices is further tested using scCO2 technology. Surface treated nanoparticles are used
to facilitate the homogeneous distribution of the nanoparticles within the matix and to improve
the inorganic filler-organic matrix interaction. Biopolymeric matrices of either poly(L-lactic acid)
(L-PLA) or the blend poly(methylmethacrylate)/poly(ε-caprolactone) (PMMA/PCL) loaded with
nanometric titanium dioxide or hydroxyapatite, respectively, are prepared. To obtain these
hybrid materials, scCO2 is employed as an anti-solvent, using the Particles from a Compressed
Anti-Solvent (PCA) technique. Studies are performed to pursue the effect of the processing
conditions on the morphology of the precipitated hybrid materials. The resulting material,
obtained in the form of fibers, has suitable properties for its potential application in tissue
engineering. In a different system, hybrid particles composed of a lipidic matrix (hydrogenated
castor oil/glyceryl monostearate) loaded with silanized titanium dioxide and caffeine are
prepared. The Particles from Gas Saturated Solutions (PGSS) technique, assisted by the use of
scCO2 as a solute, is employed for the production of these solid lipid particles. The obtained
hybrid material is evaluated concerning the drug carrier and release ability and the UV-shielding
capacity. The UV-light protection and photoaging prevention capacity of the lipid-based hybrid
material provide excellent properties for the use of these particles in the formulation of
sunscreens and pharmaceutical dermal products.
vii
Finally, the possibility of extending the supercritical silane treatment to multiscale
complex hybrid materials is assessed. The technology based on the use of scCO2 is presented for
the two-step carbonation-silanization process of cement-based materials. In the first step, the
carbonation of cement is accelerated using scCO2 as the carbonation agent. The effects of the
cement formulation and process operation conditions on the microstructure and physicochemical
properties of carbonated samples are evaluated. The carbonation process is followed by the
hydrophobic treatment of the carbonated samples using a supercritical silanization method. The
surface modification of carbonated cement with octyltriethoxysilane confers water repellence to
the material. The carbonation-silanization process is scheduled and integrated to mitigate the
consumption of raw materials and the use of facilities.
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Kinetics Of Polymerization And Degradation By Non-Conventional TechniquesKarmore, Vishal K 02 1900 (has links)
Non-conventional techniques for polymerization and depolymerization were investigated. The rates of polymerization were enhanced higher in ultrasonic, supercritical fluids and microwaves. However in these system under certain conditions, simultaneous degradation also occurred. Depolymerization was studied by various methods like thermal degradation in supercritical fluids and in presence of oxidizers, Lewis acid and other organic acids. Degradation by ultrasound and thermal degradation of polymer mixtures were also investigated. The scission of the polymer backbone is random for thermal degradation while the scission occurs at the midpoint for ultrasonic degradation. The degradation rates in all the investigated techniques were higher than the degradation rates observed for pyrolysis. Degradation was possible at low temperature (< 50°C) for oxidative and ultrasound degradation while the degradation rates were two orders of magnitude higher in supercritical conditions. The molecular weight distribution was obtained by GPC analysis and the continuous distribution models were used to obtain the rate coefficients. The activation energies were calculated from the temperature dependence of the rate coefficients.
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Oxidation of lipids in a supercritical-fluid mediumSparks, Darrell Lynn, January 2008 (has links)
Thesis (Ph.D.)--Mississippi State University. Dave C. Swalm School of Chemical Engineering. / Title from title screen. Includes bibliographical references.
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Hochdruckextraktion von Naturstoffen mit nahe-/ überkritischen Fluiden unter Einbindung eines MembranverfahrensHerdegen, Volker 08 October 2014 (has links) (PDF)
Die vorliegende Arbeit beschäftigt sich mit dem Einsatz eines Membranverfahrens zur Extraktabtrennung unter Hochdruckbedingungen. Die in einem zu koppelnden Prozess extrahierten Naturstoffsubstanzen sollen dabei ohne große Energieverluste, wie sie bei der herkömmlichen Methode der Druckentspannung entstehen, in nahezu isobarer und isothermer Fahrweise aus dem verdichteten Lösungsmittel gewonnen werden. Für den Einsatz oxid-keramischer, integral-asymmetrisch aufgebauter Einkanal-Rohrmembranen wurden vor allem grundlegende Daten zum Transportverhalten hinsichtlich der beiden eingesetzten Gase CO2 und dem Frigen Tetrafluorethan ermittelt. Dies geschah für zwei Nanofiltrationsmembranen mit trennaktiven Schichten aus TiO2 und SiO2. Die Filtrationsleistung der Membranen wurde für drei beispielhafte Wertstoffe (Koffein, Aescin, Inulin), deren Extraktionsverhalten im Vorfeld untersucht wurde, u.a. anhand von Rückhalt und Deckschichtbildung bewertet.
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