Academic literature on the topic 'Crystallization by controlled cooling'

Made available in DSpace on 2016-06-02T19:56:34Z (GMT). No. of bitstreams: 1 2570.pdf: 2902537 bytes, checksum: 1256031839bb7982aebdbc96c5edf7bc (MD5) Previous issue date: 2009-06-29<br>Today, Brazil is the major producer and exporter of sugar in the world. In the last harvest 2008/2009, 31.5 millions tons were produced, of which 60% were exported providing a 40% of international market share. However, sugar is a product that has commercial difficulties, due to the hard restrictions, such as rates, subsidizes and technical barriers like the use of sulfur (input) in laundering. Because of this, the development of a technology for the production of sugar with superior quality, less cost and without sulfur for the laundering would be of great interest for the productive sector. The present work aims to study the process of crystallization of sucrose from sugar solutions of syrup and sugar cane by controlled cooling. A laboratory plant with production capacity of 1 kg of sugar per batch, installed in the laboratory of industrial development of the Sugarcane Technology Center (CTC) in Piracicaba was used for the present work. The results regarding the reduction of impurities initially present in sugar crystals through crystallization by controlled cooling were: 95% in color, 85% in starch and 80% in dextran. For the syrup classified as VVHP, reductions obtained in crystals through crystallization by controlled cooling were: 96% of the final color of the sugar (from 10,100 IU to 361 IU), 98% in the amount of ash conductivity, 84% in the amount of starch and 52% in the amount of dextran. Obtained the results led to the construction of a pilot plant by scaling the process that will be implemented in an industrial unit.<br>O Brasil, hoje, é o principal produtor e exportador de açúcar do mundo. Foram produzidas na última safra 2008/2009, 31,5 milhões de toneladas de açúcar, das quais cerca de 60% foram exportadas, gerando ao país um domínio de 40% do mercado internacional. No entanto, o açúcar é um produto de relativa dificuldade para comercialização internacional, em razão de fortes restrições, como cotas, subsídios e barreiras técnicas, como a utilização do enxofre (insumo), para o branqueamento. Por isso, o desenvolvimento de uma tecnologia de produção de açúcar de melhor qualidade, com redução de custos e que não necessite de enxofre para o branqueamento seriam de grande interesse para o setor produtivo. O presente trabalho tem por objetivo o estudo do processo de cristalização de sacarose a partir de soluções provenientes de açúcar e xarope de cana-de-açúcar por resfriamento controlado, através de uma planta laboratorial, com capacidade de produção de 1 kg de açúcar por batelada, instalada no laboratório de desenvolvimento industrial do Centro de Tecnologia Canavieira (CTC) em Piracicaba. Os resultados quanto à redução de impurezas presentes inicialmente nos cristais de açúcar através da cristalização por resfriamento controlado foram: de 95% de cor; 85% de amido e 80% de dextrana. Para o xarope classificado como VVHP, as reduções obtidas nos cristais através da cristalização por resfriamento controlado foram: de 96% na cor do açúcar final (de 10.100 UI para 361 UI), de 98% na quantidade de cinzas condutimétricas, de 84% na quantidade de amido e de 52% na quantidade de dextrana. A partir dos resultados obtidos, motivou-se a construção de uma unidade piloto através do scale-up do processo laboratorial, a ser implantada em uma unidade industrial.

Made available in DSpace on 2016-06-02T19:55:41Z (GMT). No. of bitstreams: 1 6385.pdf: 11264050 bytes, checksum: cd77b4a424829bd8ae1b48ccd53f5616 (MD5) Previous issue date: 2014-10-08<br>Introduced during the colonial period in Brazil, nowadays sugar cane is one of the main crops of the country's economy, generating more than 2 billion dollars per year in the Brazilian trade balance. Despite the benefits of expanding the sugarcane sector every year, the environmental impacts caused by burning straw cane sugar made the State of São Paulo Government create the Protocol of Agro-Environmental Cooperation in 2007, which aims the total elimination of cane burning by 2017. However, when the sugar cane stops being burned, some components of the plant, which remained in the field due to the burning, will start being in larger quantities in the process, and the effects of this future reality in sugar quality have not been studied In this doctoral thesis, the two components of great impact on the specifications or quality of the sugar were chosen: starch and dextran which were studied in the crystallization unit operation (by controlled cooling and vacuum evaporation), so that the impact on the final product (sugar) were evaluated. This current study used a reponse surface methodology, with 2 levels (309 and 1062 ppm), two factors (dextran and starch), 3 center points (one central point in triplicate) and 4 axial points, totaling 11 trials per type of crystallization. The experiments were conducted with sugar Type 2 solutions contaminated with starch and dextran, in an agitated and jacketed crystallizer (8 liters) in the laboratory. When the crystallization was performed, the matters were centrifuged, the sugars were separated from the honeys, and forwarded to the physico-chemical, textural and optical microscopy analyzes. In relation to the physicochemical analyzes of sugar, starch and dextran contamination interfered directly in the responses: starch, dextran, color, turbidity and alcoholic floc in both crystallization techniques, however, the controlled cooling under the same conditions of contamination (0-2000 ppm), presented sugars to lower rates, which kept the product according to the market specifications. The results of grain size analysis showed frequency curves with accumulation of smaller crystals at the opening of 0.5 mm, according to the increase of dextran in the tests. And the optical microscopy analysis identified the existence of a relationship between the amount of contaminants, and the appearance of agglomerated crystals, besides "needle-like" crystals were not observed. The experimental chosen design collaborated in the identification of starch and dextran agents, in the increase or decrease of the analyzed responses, besides suggesting the collaboration of the combined effect on the quality of sugar. Concerning the product quality, the use of crystallization technique by controlled cooling proved to be the most suitable in the reduction of contaminants in the sugar, particularly in solutions containing 2,000 ppm of dextran and starch. Given the crop of sugarcane in the coming years, and that the contamination of dextran and starch may be higher than those found in syrups of industrial processes currently, this work may contribute to the knowledge of the contaminants and their combined actions in the crystallization and in understanding of the differences in the product quality.<br>Introduzida no período colonial no Brasil, a cana-de-açúcar é hoje uma das principais culturas da economia do país, gerando mais de 2 bilhões de dólares por ano na balança comercial brasileira. Apesar dos benefícios da expansão do setor sucroalcooleiro a cada ano, os impactos ambientais causados pelas queimadas da palha de cana-de-açúcar, levaram o Governo Estadual Paulista a criar em 2007, o Protocolo de Cooperação Agroambiental, que visa a eliminação total da queima de cana até 2017. No entanto, quando a cana-de-açúcar deixar de ser queimada, alguns componentes da planta que ficavam no campo com a queima passarão a entrar no processo em maiores quantidades, e os efeitos dessa futura realidade na qualidade do açúcar ainda não foram estudados. Nesse trabalho de doutorado, foram escolhidos dois componentes de grande impacto nas especificações ou qualidade do açúcar: o amido e a dextrana, os quais foram estudados na operação unitária de cristalização (por resfriamento controlado e por evaporação a vácuo), para que o impacto no produto final (açúcar) fosse avaliado. O presente trabalho utilizou um delineamento composto rotacional, com 2 níveis (309 e 1062 ppm), dois fatores (dextrana e amido), 3 pontos centrais (1 ponto central em triplicata) e 4 axiais, totalizando 11 experimentos por tipo de cristalização. Os experimentos foram realizados com soluções de açúcar Tipo 2, contaminadas com amido e dextrana, em um cristalizador agitado e encamisado (8 litros), em laboratório. Realizadas as cristalizações, as massas foram centrifugadas, e os açúcares separados dos méis, e encaminhados para as análises físico-químicas, granulométricas e de microscopia óptica. Em relação às análises físico-químicas do açúcar, as contaminações de dextrana e amido interferiram diretamente nas respostas: amido, dextrana, cor, floco alcoólico e turbidez, nas duas técnicas de cristalização, no entanto, o resfriamento controlado, nas mesmas condições de contaminação (0 a 2000 ppm), apresentou açúcares com os menores índices, o que manteve o produto nas especificações do mercado. Os resultados das análises granulométricas demonstraram curvas de frequência com acúmulo de cristais menores na abertura de 0,5 mm, conforme o aumento de dextrana nos testes. E as análises de microscopia óptica identificaram a existência de uma relação entre a quantidade de contaminantes, e o aparecimento dos cristais aglomerados, além de não serem observados cristais tipo agulha . O planejamento experimental adotado colaborou na identificação dos agentes amido e dextrana, no aumento ou na diminuição das respostas analisadas, além de sugerir a colaboração do efeito combinado desses na qualidade do açúcar. Em termos de qualidade do produto, a aplicação da técnica de cristalização por resfriamento controlado mostrou-se mais indicada na redução dos contaminantes no açúcar, principalmente em soluções com 2000 ppm de dextrana e amido. Tendo em vista a colheita de cana crua nos próximos anos, e que as contaminações de dextrana e amido poderão ser superiores as encontradas nos xaropes dos processos industriais hoje, o presente trabalho pode contribuir no conhecimento dos contaminantes e de suas ações combinadas na cristalização, e no entendimento das diferenças na qualidade do produto.

Made available in DSpace on 2015-05-08T15:00:02Z (GMT). No. of bitstreams: 1 parte1.pdf: 2575179 bytes, checksum: 8796ecfea1de6030d7f2f9efa941e491 (MD5) Previous issue date: 2010-12-01<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES<br>This work presents theoretical and experimental study of a system of control for a steam generator. This system was developed to control the crystallization of a cooling system for absorption. The control system maintains the pressure generator above the zone of crystallization of diagram temperature pressure-saturated solution concentration of LiBr-water. The control is accomplished through simultaneous use of the relay and the frequency converter. The frequency converter acts in engine speed of pump firing of condenser cooling tower, while the relay operates directly into the burner of the generator, consecutively in thermal power of combustion. The control system can act in any pressure reference values above the zone of crystallization of absorption cooling system. In the control flow control techniques were used and fuzzy Modeling and control power thermal combustion, on-off control. Ten different experiments were conducted, which proved the efficiency of the system of control.<br>Neste trabalho apresenta-se o estudo teórico e experimental de um sistema de controle para um gerador de vapor. Este sistema foi desenvolvido para controlar a cristalização de um sistema de refrigeração por absorção. O sistema de controle mantém a pressão do gerador acima da zona de cristalização do diagrama temperatura-pressãoconcentração de solução saturadas do LiBr-água. O controle é realizado por meio do uso simultâneo do relé e o conversor de freqüência. O conversor de freqüência atua na velocidade do motor de acionamento da bomba da torre de resfriamento do condensador, enquanto o relé opera no queimador do gerador, consecutivamente na potência térmica de combustão. O sistema de controle pode atuar em quaisquer valores de referência de pressão acima da zona de cristalização do sistema de refrigeração por absorção. No controle da vazão foram utilizados técnicas de controle e modelagem Fuzzy e para controlar a potência térmica combustão, o controle on-off. Foram realizados dez experimentos diferentes, que comprovam a eficiência do sistema de controle.

Despite their $\sim$2710 Ma age, thin komatiite lava flows in Munro township, NE Ontario have sufficiently well-preserved primary structures, textures, mineralogy, and whole-rock geochemistry to constrain the physical processes of cooling and crystal growth. Seawater convection drove a cooling and fracturing front through the upper surface and was the dominant mechanism of heat loss, leading to pronounced textural asymmetry within flows. Large plate-like crystals of olivine in the upper layers of flows grew by constrained crystallization arising from strong thermal pradients and the high lattice thermal conductivity and near-infrared transparency of olivine (3-5 times greater than that of the surrounding melt). Such crystals exhibit a very strong preferred orientation with the a crystallographic axis perpendicular to flow surfaces. Major and minor-element zoning within olivine crystals is closely modeled by fractional crystallization from the bulk liquid, and whole-rock geochemical variations within flows by crystal fractionation of highly magnesian olivine. The high chromium content of olivine is of mineralogical and technological interest, and is due to two substitutional mechanisms: $\sp{\lbrack 6\rbrack}$Cr$\sp{3+} + \sp{\lbrack 4\rbrack}$Al$\sp{3+} \rightleftharpoons\ \sp{\lbrack 6\rbrack}$Mg$\sp{2+} + \sp{\lbrack 4\rbrack}$Si$\sp{4+}$ and 2 $\sp{\lbrack 6\rbrack}$Cr$\sp{3+} + \sp{\lbrack 6\rbrack}\square \rightleftharpoons 3 \sp{\lbrack 6\rbrack}$Mg$\sp{2+}.$ Dendritic chromian spinel crystals nucleated heteroepitaxially on olivine substrates; the crystallographic relationship between the phases is (111) $\sb{\rm sp} \parallel$ (100) $\sb{\rm ol}$, (110) $\sb{\rm sp}\ \parallel$ (001) $\sb{\rm ol}\ \parallel$, and (211) $\sb{\rm sp}\ \parallel$ (010) $\sb{\rm ol}$. The Cr-spinel crystals have features typical of metallic, ionic, and organic crystal dendrites, but rarely found in minerals. Immobility of Mg and Si and a systematic loss of Ca in these altered rocks is due to a serpentinization reaction buffered by the desilication of glass or fine-grained plagioclase in the groundmass. Serpentinization occurred under conditions of low confining pressure, caused up to 30% expansion of the basal portions of flows, and predated tectonism at $\sim$2700 Ma.

This thesis describes the development of an empirical model of focus beam reflectance measurements (FBRM) and the application of the model to monitoring batch cooling crystallization and extracting information on crystallization kinetics. Batch crystallization is widely used in the fine chemical and pharmaceutical industries to purify and separate solid products. The crystal size distribution (CSD) of the final product greatly influences the product characteristics, such as purity, stability, and bioavailability. It also has a great effect on downstream processing. To achieve a desired CSD of the final product, batch crystallization processes need to be monitored, understood, and controlled. FBRM is a promising technique for in situ determination of the CSD. It is based on scattering of laser light and provides a chord-length distribution (CLD), which is a complex function of crystal geometry. In this thesis, an empirical correlation between CSDs and CLDs is established and applied in place of existing first-principles FBRM models. Built from experimental data, the empirical mapping of CSD and CLD is advantageous in representing some effects that are difficult to quantify by mathematical and physical expressions. The developed model enables computation of the CSD from measured CLDs, which can be followed during the evolution of the crystal population during batch cooling crystallization processes. Paracetamol, a common drug product also known as acetaminophen, is selected as the model compound in this thesis study. The empirical model was first established and verified in a paracetamol-nonsolvent (toluene) slurry, and later applied to the paracetamol-ethanol crystallization system. Complementary to the FBRM measurements, solute concentrations in the liquid phase were determined by in situ infrared spectra, and they were jointly implemented to monitor the crystallization process. The framework of measuring the CSD and the solute concentration allows the estimation of crystallization kinetics, including those for primary nucleation, secondary nucleation, and crystal growth. These parameters were determined simultaneously by fitting the full population balance model to process measurements obtained from multiple unseeded paracetamol-ethanol crystallization runs. The major contributions of this thesis study are (1) providing a novel methodology for using FBRM measurements to estimate CSD; (2) development of an experimental protocol that provided data sets rich in information on crystal growth and primary and secondary nucleation; (3) interpretation of kinetics so that appropriate model parameters could be extracted from fitting population balances to experimental data; (4) identification of the potential importance of secondary nucleation relative to primary nucleation. The protocol and methods developed in this study can be applied to other systems for evaluating and improving batch crystallization processes.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2012.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 171-175).<br>It is essential to control crystallization in many areas of science and technology, such as the production of pharmaceuticals, pigments, concrete, semiconductors, as well as the formation of biominerals. In most practical circumstances, crystallization starts with heterogeneous nucleation at a foreign surface. Despite its widespread occurrence, mechanistic understanding of the role of a surface in heterogeneous nucleation is limited, especially in a solution environment. My thesis aims at elucidating the roles of surface chemistry and nanostructure on nucleation to enable rational design of surfaces for controlling crystallization from solution. To this end, I systematically investigated the role of surface chemistry, morphology, in particular porous structures of various polymeric materials on heterogeneous nucleation using small organic molecules as model compounds. I have demonstrated quantitatively the significance of surface chemistry to nucleation kinetics using a variety of polymer surfaces. By tuning the surface composition of the polymers, aspirin nucleation was promoted by up to an order of magnitude compared to the bulk. Further mechanistic investigations revealed that, macroscopically, it is through interfacial free energies that the surfaces influence the surface nucleation activity. Equipped with nucleation induction time statistics as a powerful tool, I found that nanoscopic pores of 50-100 nm accelerated nucleation by up to two orders of magnitude compared with surfaces without pores. Moreover, I demonstrated for the first time that the shape of surface nanopores is essential in determining the nucleation behavior, using lithographic methods for nanopatterning the polymer films. A molecular mechanism was further proposed based on additional mechanistic investigations. Furthermore, the nanoconfinement effect on nucleation was studied using polymeric microgels with tunable nanostructures and chemistry, whose mesh sizes range from 0.7-2 nm. We presented the first experimental evidence for the existence of an optimum confinement size at which the rate of nucleation was dramatically enhanced by up to four orders of magnitude. The degree of nucleation enhancement depends on the extent of polymer-solute interactions, whose role was elucidated from the perspective of adsorptive partitioning and nucleation-templating effect. In addition, the microgel nanostructure was also shown to play an important role in determining the crystal polymorphism of pharmaceutical compounds.<br>by Ying Diao.<br>Ph.D.

The work presented in this thesis is aimed to design efficient reactive crystallization operations that could potentially be implemented in the manufacture of enantiomerically pure compounds and β-lactam antibiotics. Multiple aspects of solution thermodynamics, reaction engineering and crystallization from complex solutions are involved and will be discussed in detail through the following chapters. The first piece of this work utilizes reactive crystallization for the manufacture of enantiomerically pure amino acids. Chemo-enzymatic stereoiversion reactions are used to enrich saturated or supersaturated solutions to favor the selection of a desired enantiomer. L-Methionine and L-Phenylalanine were resolve successfully from racemic mixtures by cyclic stereoinversion. r D-amino acids were oxidized by D-amino acid oxidase (D-AAO) and the resulting ketoacid was subsequently reduced by ammonia borane producing a racemic-mixture After the necessary enantiomeric enrichment was reached, system conditions were changed to induce supersaturation and promote crystal formation. In each case crystals with chemical and enantiomeric purities greater than 99% wt. were recovered. experimental information about reaction and crystallization kinetics was used to developed models. Such models were used to design model-based optimizations in which the productivity of the operation was enhanced by selecting an optimal temperature profile. The second example is a reactive crystallization towards the manufacture of β-lactam antibiotics. One of the major drawbacks of the utilization of enzymes towards the manufacture of β-lactam antibiotics is the fact that the same enzyme that catalyzes the synthesis of the antibiotic also catalyzes its hydrolysis and thus, its degradation. The reaction scheme is a kinetically controlled synthesis in which the desired product is an intermediate within the network. Hence, the focus of this work is to design an efficient reactive crystallization in which the product is crystallized before it is consumed by hydrolysis. In order to accomplish this goal we have study solution equilibria, reaction kinetics, and crystallization kinetics. Even though crystallization kinetics of ampicillin has been previously reported; the reported models are not applicable to a reactive crystallization scheme for a variety of reasons. In this work, we have developed a robust model that can be applied to multiple crystallization protocols that are consistent with the conditions at which the enzymatic reaction can be performed. Finally, a reactive-crystallization scheme in which ampicillin was successfully recovered from solution was developed. In this work, crystal seeds were used to promote crystallization of the desired product from the complex media. The results indicated that is possible to perform the reaction and crystallization in parallel, and still recover crystals with high purity. This work is the first example in which ampicillin was produced and recovered with high purity in a single stage. Previous work on reaction crystallization of antibiotics reported ampicillin crystallization; however, this was accompanied by precipitation of by-products which greatly reduces the applicability of the operation as product purification is required after the reaction.