Kinetics of melt crystallization of organic eutectic forming binary mixtures in non-flow systems
TL;DR: In this paper, the effect of subcooling, superheating and the initial concentration of the melt on the crystallization kinetics of binary eutectic forming organic mixtures in non-flow systems with cooling from below for the preferential crystallization of one component alone was studied experimentally.
Abstract: The kinetics of melt crystallization of binary eutectic forming organic mixtures in non-flow systems with cooling from below for the preferential crystallization of one component alone have been studied experimentally. The effect of subcooling, superheating and the initial concentration of the melt on the crystallization kinetics have been studied. Based on the experimental data, a correlation for the instantaneous height of the crystal (volume fraction of the solidified mass) has been proposed. The experimental results were also analyzed based on a model from the literature, which considered simultaneous heat and mass transport. The analysis shows that in the present experiments, the melt crystal interface was very close to the initial melt composition, i.e. concentration equilibrium was maintained. This is attributed to the very low cooling rates used, even though the thermal diffusivity is much greater than the mass diffusivity of the melt.
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TL;DR: For the first time, the molecular mechanism and structure of liquid crystalline materials as a function of concentration, temperature, and frequency is explained.
Abstract: Broadband dielectric spectroscopy has been used to analyze the temperature, frequency, and concentration dependences of the molecular dynamics of a nematic liquid crystal (5CB) mixed with the nonpolar solvent benzene. Differential scanning calorimetry measurement has been also performed to confirm the phase transitions of 5CB/benzene mixtures. The phase transition temperatures (crystalline to isotropic phases) thus obtained have been described very accurately from the temperature-dependent relaxation strength, the relaxation time, and the symmetric shape parameter of the relaxation function obtained from the fitting procedure. Two relaxation processes reflecting overall rotations around the short and long molecular axes are observed in both the nematic and isotropic phases. In the crystalline phase, the former process with the longer relaxation time disappeared, and latter process with shorter relaxation time shows a discontinuity at the freezing temperature. The relaxation process with shorter relaxation time obtained in the crystalline phase is larger than that obtained in the nematic phase because of the large restrictions in the crystalline phase. For the first time, we have precisely explained the molecular mechanism and structure of liquid crystalline materials as a function of concentration, temperature, and frequency.
19 citations
TL;DR: In this article, a melt crystallization was carried out to explore the separation and purification process of chlorobromobenzene, and the influences of the cooling rate, final crystallization temperature, and crystal growth time were examined systemically based on the following criteria: the distribution coefficient, crystallization yield and purity.
7 citations
TL;DR: Surprisingly, the abnormal behavior of the isotropic phase was observed in LC/benzene mixtures that suggested the presence of local structure in the mixture, which set off the dipole moments along the long axis.
Abstract: Differential scanning calorimetry and broadband dielectric spectroscopy measurements were performed to investigate the phase transitions in nematic liquid crystal (LC)/benzene mixtures. Noticeable changes of the crystal-isotropic phase transition and the phase transition enthalpy were observed. We also estimated the number of unfreezable benzene molecules from the LC/benzene mixtures. The crystal-isotropic phase transition temperature was described very accurately from the temperature-dependent relaxation strength, the relaxation time, and the symmetric shape parameter obtained from the fitting procedure. Surprisingly, the abnormal behavior of the isotropic phase was observed in LC/benzene mixtures that suggested the presence of local structure in the mixture, which set off the dipole moments along the long axis. The interaction between the LC molecules was also discussed from the tau-beta diagram.
7 citations
TL;DR: In this article, a simulated moving-bed reactor (SMBR) for the production of p-xylene is studied as part of a proposal to modify an existing aromatics complex in order to increase the output of benzene and xylene.
Abstract: A simulated moving-bed reactor (SMBR) for the production of p-xylene is studied as part of a proposal to modify an existing aromatics complex in order to increase the production of benzene and p-xylene. The proposed complex includes a single-stage crystallization unit to further purify high p-xylene streams from a selective toluene disproportionation and said SMBR units. Mass balances for two cases are estimated, namely, the current flow of reformate fed to the complex and a twofold flow. Results show significant increases of benzene and p-xylene for both cases compared to the current production of the complex.
2 citations
TL;DR: In this article, the authors investigated the behavior of ice crystal growth at two different operating parameters (coolant temperature and circulation time) for progressive freeze concentration (PFC) of glucose solution through a vertical finned crystallizer (VFC).
Abstract: Behaviours of ice crystal growth at two different operating parameters namely coolant temperature and circulation time were investigated for progressive freeze concentration (PFC) of glucose solution through a vertical finned crystallizer (VFC). Two determinant parameters which are ice production rate (mu), and water recovery (WR) were used to illustrate the behaviours of ice crystal growth in this study. From the result, higher ice production rate (mu) and water recovery (WR) were achieved at lower coolant temperature. On the other hand, longer circulation time resulted in lower ice production rate (mu), but at the same time increased the water recovery (WR). The maximum ice production rate (mu) and water recovery (WR) attained through this study were 1.522 gm-2s-1 and 51.131 %, respectively.
2 citations
Cites background from "Kinetics of melt crystallization of..."
...According to Radhakrishnan and Balakrishnan [3], the basic characteristic of PFC process is normally described by the rate of crystal growth, in which this rate is mainly determined by heat and mass transfer at solid-liquid interface....
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Journal Article•
33 citations
Additional excerpts
...Wynn [1] has classified melt crystallization processes into two categories — suspension processes and progressive freezing....
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TL;DR: In this article, the authors review the physico-chemical fundamentals, various process fundamentals, large scale application examples and the possibilities of combination of melt crystallization with other separation processes and a consideration of advantages and disadvantages of this particular separation process should indicate possibilities for new fields of application.
Abstract: Melt crystallization of organic substances and its large scale application. In the separation and purification of organic substances, water- and solvent free melt crystallization is gaining importance as an independent thermal unit operation. This contribution reviews the physico-chemical fundamentals, the various process fundamentals, large scale application examples and advantageous possibilities of combination of melt crystallization with other separation processes. A consideration of advantages and disadvantages of this particular separation process should indicate possibilities for new fields of application.
32 citations
TL;DR: In this article, an approximate analysis of the growth of, and the temperature within, a deposit which may occur in a cold surface in a gas stream is developed with the convective heat transfer to the surface of the deposit taken into account.
29 citations
"Kinetics of melt crystallization of..." refers background in this paper
...Similar dependency of the average crystal growth rate on subcooling was noticed by Libby and Chen [13] while studying the condensation of a gas stream on a cold surface....
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TL;DR: In this paper, experiments of purification by isothermal sweating were carried out with naphthalene-benzothiophene solid solution mixtures, and the results showed that the purification rate coefficient for the layer type was always lower than those for the suspension type, while the amount of impurities unable to be removed by sweating from the layer was larger than that for suspension crystals.
Abstract: In order to provide a quantitative basis to discuss the efficiency of purification of organic mixtures achieved by layer or suspension type melt crystallization operations, experiments of purification by sweating were carried out with naphthalene-benzothiophene solid solution mixtures. The rate and the degree of composition changes were analyzed for crude crystals prepared either as a layer on a cold surface or as a suspension in a supercooled melt. The purification by sweating was conducted at constant temperatures (isothermal sweating) and the rate of composition change was evaluated by the purification rate coefficient kp, which was defined as the ratio of the purification rate to the excess amount of the impurity in the crude crystal phase. The values of the purification rate coefficient for the layer type were found to be always lower than those for the suspension type, while the amount of impurities unable to be removed by sweating from the layer was larger than that for the suspension crystals. Consequently, it is concluded that purification by isothermal sweating in terms of the rate and the attainable purity was higher for the suspension type than the layer one in the present experiments. These results and the significance of the purification rate coefficient were discussed quantitatively.
18 citations
"Kinetics of melt crystallization of..." refers background in this paper
...[12] observed a square root dependence while studying solidification rates....
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01 Jan 1937
15 citations
"Kinetics of melt crystallization of..." refers methods in this paper
...The boundary layer thickness d is determined using the approach of Zief and Wilcox [11], who analyzed the free convection mixing during zone melting of organics in vertical glass tubes and this is given by...
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...The boundary layer thick- ness d is determined using the approach of Zief and Wilcox [11], who analyzed the free convection mixing during zone melting of organics in vertical glass tubes and this is given by d= aR F (R/l)0.44(Vcrl/D)0.26 (8) where, a=66 when the interface density\bulk density of the melt....
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