| 1. |
|
|
| 2. |
|
|
| 3. |
- O'Mahony, M. A., et al.
(författare)
-
Investigation into the mechanism of solution-mediated transformation from FI to FIII carbamazepine : The role of dissolution and the interaction between polymorph surfaces
- 2013
-
Ingår i: Crystal Growth and Design. - : American Chemical Society (ACS). - 1528-7505 .- 1528-7483. ; 13:5, s. 1861-1871
-
Tidskriftsartikel (refereegranskat)abstract
- The solution mediated polymorphic transformation (SMPT) of the pharmaceutical compound carbamazepine was investigated in ethanol. Bulk transformation experiments were performed by monitoring the solution concentration and polymorphic composition over time during the transformation from the metastable FI polymorph to the stable FIII polymorph for a variety of initial conditions. Microscopic techniques, single-crystal X-ray diffraction, and computational methods were used to analyze the transformation. The nucleating behavior of the stable FIII polymorph was a significant factor affecting the transformation time across the range of experiments. The surfaces of the metastable FI particles were responsible for the nucleation of FIII during the transformation. However, no specific lattice matching or epitaxy was conclusively identified. A modest amount of dissolution of the FI particles was found to favor the nucleation of FIII but where extensive dissolution or no significant dissolution occurred this had a negative effect on the nucleation of FIII.
|
|
| 4. |
- O'Mahony, M., et al.
(författare)
-
Investigating the dissolution of the metastable triclinic polymorph of carbamazepine using in situ microscopy
- 2014
-
Ingår i: CrystEngComm. - Royal Society of Chemistry (RSC)) : Royal Society of Chemistry (RSC). - 1466-8033. ; 16:20, s. 4133-4141
-
Tidskriftsartikel (refereegranskat)abstract
- Despite a tendency to undergo solution-mediated polymorphic transformation, the dissolution behaviour of the metastable FI (triclinic) polymorph of the pharmaceutical compound carbamazepine (CBZ) was investigated using in situ optical microscopy. Experiments were performed at an undersaturation where single crystals of the metastable FI polymorph dissolved. Dissolution in different solvents was investigated at a constant undersaturation. Separately the sublimation of FI was examined and additionally the dissolution was observed at undersaturations where the more stable FIII polymorph crystallized. The results show that both the dissolution and sublimation of FI occur primarily in the direction of the a-axis of the FI crystal structure where the CBZ molecules are found to stack in this direction. The order for the dissolution rate of FI was acetonitrile ≥ methanol > ethanol. The order of the dissolution rates in each of the solvents is inversely correlated to the viscosity and the binding energy of the solvents with the (100) surface of FI in each of the solvents. This suggests that the rate determining step for the dissolution may be either the diffusion or the detachment of CBZ molecules from the surface of FI. A notable difference in dissolution behaviour is also observed at undersaturations where the more stable FIII polymorph nucleates and grows.
|
|
| 5. |
- Croker, D. M., et al.
(författare)
-
Nucleation in the p-toluenesulfonamide/triphenylphosphine oxide co-crystal system
- 2013
-
Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 13:8, s. 3754-3762
-
Tidskriftsartikel (refereegranskat)abstract
- Nucleation has been studied in pure co-crystal and mixed co-crystal phase regions of the ternary phase diagram (TPD) in acetonitrile at 20 C using cooling crystallization experiments. Direct nucleation of each of the co-crystal phases in this system was independently observed in regions of the TPD where each is stable. In mixed regions, regions where either a co-crystal and a coformer, or both co-crystals, are stable, the phase that initially nucleated was a function of the mass composition in that region. The relative amount of each phase nucleating could be controlled by adjusting the relative mass fraction of each component. The kinetic return to equilibrium was also observed as the systems were held over time, with the selected mass fractions always returning to the equilibrium dictated by the TPD after 24 h
|
|
| 6. |
- Croker, D. M., et al.
(författare)
-
Solution mediated phase transformations between co-crystals
- 2013
-
Ingår i: CrystEngComm. - : Royal Society of Chemistry. - 1466-8033. ; 15:11, s. 2044-2047
-
Tidskriftsartikel (refereegranskat)abstract
- A solution mediated transformation between two co-crystal phases has been observed for the p-toluensulfonamide-triphenylphosphine oxide co-crystal system. This system has two known co-crystals with 1 : 1 and 3 : 2 stoichiometry respectively, and the ternary phase diagram (TPD) for the system has been determined in acetonitrile previously. By manipulating the solution composition in this solvent to a region of the TPD where the 1 : 1 co-crystal is stable, the 3 : 2 co-crystal could be observed to convert to the 1 : 1 co-crystal. The corresponding transformation was true for the 1 : 1 co-crystal in a region of the TPD where the 3 : 2 co-crystal is stable; the 1 : 1 co-crystal converted to the 3 : 2 co-crystal.
|
|
| 7. |
- Granberg, R. A., et al.
(författare)
-
Primary nucleation of paracetamol in acetone-water mixtures
- 2001
-
Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509 .- 1873-4405. ; 56:7, s. 2305-2313
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of solvent composition on primary nucleation of 4-hydroxyacetanilide (paracetamol) in acetone-water mixtures is investigated. The induction time for primary nucleation is determined, at various degrees of supersaturation and at different temperatures, in different solvent mixture compositions. Supersaturation is generated by the addition of water. and the homogeneous, agitated, isothermal solution is allowed to nucleate. The supersaturation driving force is calculated as the difference in the chemical potential. At equal thermodynamic driving force, the induction time depends on the composition of the solvent mixture. The interfacial energy is in the range 1-3 mJ/m(2) and tends to increase with decreasing solubility, i.e. increasing water content. The interfacial energy is slightly lower than a value calculated from a contact angle measurement (5 mJ/m(2)) in pure water and is significantly lower than values predicted by equations derived From simplified theories.
|
|
| 8. |
- Heffernan, C., et al.
(författare)
-
Effects of structurally - related impurities on the crystal growth of curcumin spherulites
- 2022
-
Ingår i: CrystEngComm. - : Royal Society of Chemistry (RSC). - 1466-8033. ; 24:28, s. 5156-5169
-
Tidskriftsartikel (refereegranskat)abstract
- The crystal growth of curcumin in pure propan-2-ol and in this solvent containing two structurally related impurities, demethoxycurcumin (DMC) and bisdemethoxycurcumin (BDMC), has been investigated by seeded isothermal desupersaturation experiments at 283, 293 and 308 K. In situ attenuated total reflectance UV-visible spectroscopy and focused beam reflectance measurement were used as process analytical technologies to monitor the solution concentration over time and to track the particle counts. Both impurities are found to slow down the growth of curcumin spherulites. The product particles collected after growth in the presence of the impurities present a rougher and more porous surface appearance in comparison to curcumin crystalline material grown in pure solutions. A detailed analysis of the powder X-ray diffraction patterns along with compositional analysis by high performance liquid chromatography of grown crystals reveals that impurities are not incorporated into the solid phase except at the highest impurity concentrations explored. By molecular modelling it is shown that the influence of impurities on the diffractograms of the material grown at high impurity concentrations is consistent with the formation of a solid solution. By fitting the Birth and Spread theory to the experimental growth data it is found that the interfacial energy for growth in the presence of the impurities is higher than that for growth of curcumin in the absence of impurities. Two scenarios are envisaged explaining the results. The first is that 3-D nucleation occurs on the impurity encumbered CUR crystallite generating new crystalline material on which crystal growth may continue. The second scenario envisages that a molecular cluster from the solution attaches to the impurity-encumbered surface and condenses into a crystalline surface nucleus without perfect lattice matching.
|
|
| 9. |
- Maher, Anthony, et al.
(författare)
-
Investigation of the Solid-State Polymorphic Transformations of Piracetam
- 2012
-
Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 12:12, s. 6223-6233
-
Tidskriftsartikel (refereegranskat)abstract
- The solid-state polymorphic transformations of 2-oxo-1-pyrrolidine acetamide (piracetam) were investigated using a combination of off-line and online techniques: differential scanning calorimetry (DSC), high temperature X-ray diffraction (HT-XRD), thermal analysis, and hot-stage optical microscopy. Form II and Form III were each observed to transform directly to Form I upon heating, with Form II transforming at a slightly lower temperature. The transformation of both polymorphs to Form I was observed to cause physical cracking of the crystals as well as changing the optical properties. Form I consistently transformed to Form II when cooled. The molecular rearrangements required for the transformation from Form I to Form II were found to be more energetically favorable than those required for the transformation to Form III. The transformation from the metastable Form II to the stable Form III was not observed in the solid-state, while the Form II-Form III transition temperature was found to be higher than the transition temperature of both polymorphs to Form I.
|
|
| 10. |
- Maher, Anthony, et al.
(författare)
-
Solution-mediated polymorphic transformation : Form II to Form III piracetam in organic solvents
- 2014
-
Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 14:8, s. 3967-3974
-
Tidskriftsartikel (refereegranskat)abstract
- The solution-mediated polymorphic transformation from Form II to Form III 2-oxo-1-pyrrolidine acetamide (piracetam) was investigated in seven organic solvents over the temperature range of 5–50 °C. The transformation rate increased as a function of temperature, agitation, and the solubility of piracetam in the host solvent. However, this trend was reversed in 2-propanol. Molecular modeling demonstrated that 2-propanol forms interactions with piracetam molecules in solution stronger than those formed by other solvents, thereby retarding the nucleation and growth of FIII(6.525) during the transformation in this solvent.
|
|
| 11. |
|
|
| 12. |
|
|
| 13. |
- Zeglinski, Jacek, et al.
(författare)
-
Crystal Nucleation of Tolbutamide in Solution : Relationship to Solvent, Solute Conformation, and Solution Structure
- 2018
-
Ingår i: Chemistry - A European Journal. - : Wiley-VCH Verlagsgesellschaft. - 0947-6539 .- 1521-3765. ; 24:19, s. 4916-4926
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of the solvent in nucleation of tolbutamide, a medium-sized, flexible and polymorphic organic molecule, has been explored by measuring nucleation induction times, estimating solvent-solute interaction enthalpies using molecular modelling and calorimetric data, probing interactions and clustering with spectroscopy, and modelling solvent-dependence of molecular conformation in solution. The nucleation driving force required to reach the same induction time is strongly solvent-dependent, increasing in the order: acetonitrile < ethyl acetate < n-propanol < toluene. The combined DFT and MD modelling results show that in acetonitrile, ethyl acetate and n-propanol the nucleation difficulty is a function of the strength of solvent-solute interaction, with emphasis on the interaction with specific H-bonding polar sites of importance in the crystal structure. A clear exception from this rule is the most difficult nucleation in toluene despite the weakest solvent-solute interactions. However molecular dynamics modelling predicts that tolbutamide assumes an intramolecularly H-bonded conformation in toluene, substantially different from and more stable than the conformation in the crystal structure, and thus presenting an additional barrier to nucleation. This explains why nucleation in toluene is the most difficult and why the relatively higher propensity for aggregation of tolbutamide molecules in toluene solution, as observed with FTIR spectroscopy, does not translate into easier nucleation. Thus, our combined experimental and molecular modelling study suggests that the solvent can influence on the nucleation not only via differences in the desolvation but also through the influence on molecular conformation.
|
|
| 14. |
- Zeglinski, Jacek, et al.
(författare)
-
Probing Crystal Nucleation of Fenoxycarb from Solution through the Effect of Solvent
- 2019
-
Ingår i: Crystal Growth & Design. - : AMER CHEMICAL SOC. - 1528-7483 .- 1528-7505. ; 19:4, s. 2037-2049
-
Tidskriftsartikel (refereegranskat)abstract
- Induction time experiments, spectroscopic and calorimetric analysis, and molecular modeling were used to probe the influence of solvent on the crystal nucleation of fenoxycarb (FC), a medium-sized, flexible organic molecule. A total of 800 induction times covering a range of supersaturations and crystallization temperatures in four different solvents were measured to elucidate the relative ease of nucleation. To achieve similar induction times, the required thermodynamic driving force, RT In S, increases in the order: ethyl acetate < toluene < ethanol < isopropanol. This is roughly matched by the order of interfacial energies calculated using the classical nucleation theory. Solvent solute interaction strengths were estimated using three methods: solvent-solute enthalpies derived from calorimetric solution enthalpies, solvent-solute interactions from molecular dynamics simulations, and the FTIR shifts in the carbonyl stretching corresponding to the solvent solute interaction. The three methods gave an overall order of solvent solute interactions increasing in the order toluene < ethyl acetate < alcohols. Thus, with the exception of FC in toluene, it is found that the nucleation difficulty increases with stronger binding of the solvent to the solute.
|
|
| 15. |
- Ahuja, Dipali, et al.
(författare)
-
Investigation of solid-liquid phase diagrams of the sulfamethazine-salicylic acid co-crystal
- 2019
-
Ingår i: CrystEngComm. - : ROYAL SOC CHEMISTRY. - 1466-8033. ; 21:18, s. 2863-2874
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of temperature and solvent on the solid-liquid phase diagram of the 1 : 1 sulfamethazinesalicylic acid co-crystal has been investigated. Ternary phase diagrams of this co-crystal system have been constructed in three solvents: methanol, acetonitrile and a 7 : 3 (v/v) dimethylsulfoxide-methanol mixture, at three temperatures. The system exhibits congruent dissolution in acetonitrile and the co-crystal solubility has been determined by a gravimetric technique. The Gibbs energy of co-crystal formation from the respective solid components has been estimated from solubility data, together with the corresponding enthalpic and entropic component terms. The Gibbs energy of formation ranges from -5.7 to -7.7 kJ mol -1, with the stability increasing with temperature. In methanol and the DMSO-methanol mixture, the co-crystal dissolves incongruently. It is shown that the solubility ratio of the pure components cannot be used to predict with confidence whether the co-crystal will dissolve congruently or incongruently. The size of the region where the co-crystal is the only stable solid phase is inversely related to the pure component solubility ratio of salicylic acid and sulfamethazine.
|
|
| 16. |
- Ahuja, Dipali, et al.
(författare)
-
Solution and calorimetric thermodynamic study of a new 1:1 sulfamethazine-3-methylsalicylic acid co-crystal
- 2020
-
Ingår i: CrystEngComm. - : Royal Society of Chemistry (RSC). - 1466-8033. ; 22:20, s. 3463-3473
-
Tidskriftsartikel (refereegranskat)abstract
- A new 1:1 co-crystal of sulfamethazine (API, SMT) and 3-methylsalicylic acid (coformer, 3mSA) has been synthesized and its crystal structure solved by single crystal X-ray diffraction (XRD). The co-crystal has been thoroughly characterized by powder XRD, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The pure co-crystal could be synthesized by solvent drop grinding, cooling crystallization and slurry conversion co-crystallization. Ternary phase diagrams have been constructed in methanol and acetonitrile at 30 degrees C. The co-crystal exhibits incongruent dissolution in both solvents. The thermodynamics of co-crystal formation have been estimated from solubility data and calorimetric data, respectively, showing that formation of the SMT-3mSA co-crystal from its solid components is spontaneous and entropy-driven. The co-crystal formation is associated with a 5% increase in molecular volume. A relationship between the size of the region where the co-crystal is the most stable solid phase and the relative solubility of the co-crystal components has been uncovered. The co-crystal region becomes smaller as the solubility ratio increases.
|
|
| 17. |
- Aisling, Lynch, et al.
(författare)
-
Crystal Growth of Single Salicylamide Crystals
- 2019
-
Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 19:12, s. 7230-7239
-
Tidskriftsartikel (refereegranskat)abstract
- Growth of single salicylamide crystals was investigated in a nonstirred growth cuvette and on a rotating disk. In the growth cuvette the crystal growth rates were measured for both primary nucleated crystals and seed crystals manually inserted into the cuvette. In the rotating disk experiments multiple seed crystals were attached to a disk that was rotated in a supersaturated solution. The crystal growth rates in the length and width direction were precisely measured in situ for each individual crystal, and growth rates were also extracted for a specific crystal facet, that is, (200). In all cases, the growth rate was considerably faster in the rotating disk experiments, shown to be governed by surface integration. Solvent was found to impact the growth rates of the crystal facets in part by creating different surface features. The influence of the supersaturation on the crystal growth rate depended on the solvent; in general, an increasing trend was observed. At relatively low supersaturations, it was discovered that the growth process will focus on repairing morphological defects. Within the range of experimental conditions, the growth kinetics were strongly affected by the temperature as was further indicated by the relatively high activation energy values obtained. The crystal seed quality was found to have a substantial impact on the growth rate, with rougher crystals leading to quicker growth. A wide growth rate dispersion was obtained for both crystal growth methods, found to be reduced by using seed crystals with high quality, lower supersaturations, and also within certain solvents.
|
|
| 18. |
- Alander, Eva M., et al.
(författare)
-
Agglomeration and adhesion free energy of paracetamol crystals in organic solvents
- 2007
-
Ingår i: AIChE Journal. - : Wiley. - 0001-1541 .- 1547-5905. ; 53:10, s. 2590-2605
-
Tidskriftsartikel (refereegranskat)abstract
- The agglomeration of paracetamol during crystallization in different pure solvents has been investigated. Narrowly sieved crystals were suspended as seeds and allowed to grow and agglomerate at constant supersaturation and temperature. Particles from each experiment were examined by image analysis and multivariate data evaluation, for the number of crystals per particle. From the resulting number distribution, parameters defining the degree of agglomeration were extracted. The degree of agglomeration among the product particles is fairly low in water, methanol, and ethanol, while it is substantial in acetone particularly, but also in acetonitrile and methyl ethyl ketone. Surfaces of large, well-grown paracetamol crystals have been characterized by contact angle measurements. The surface free energy components of different crystal faces have been estimated using Lifshitz-van der Waals acid-base theory. The data are used for estimation of the solid-liquid interfacial free energy of each face in the solvents of the agglomeration experiments and the corresponding crystal-crystal adhesion free energy of pairs of faces. The degree of agglomeration in different solvents does correlate to the free energies of adhesion. This supports the hypothesis that the influence of the solvent on the crystal agglomeration relates to physico-chemical adhesion forces between crystal faces in the solution.
|
|
| 19. |
- Alander, E. M., et al.
(författare)
-
Characterization of paracetamol agglomerates by image analysis and strength measurement
- 2003
-
Ingår i: Powder Technology. - : Elsevier BV. - 0032-5910 .- 1873-328X. ; 130:1-3, s. 298-306
-
Tidskriftsartikel (refereegranskat)abstract
- Paracetamol is crystallized in different solvents and techniques are developed and used to characterize the product. The product particles from three different solvent compositions: ethylene glycol, acetone and an acetone-water mixture (30-70 wt.%) have been examined. Product properties visually observed are quantified by image analysis and evaluation of measured image descriptors with Principal Component Analysis (PCA). The agglomerate strength has been determined by crushing single agglomerates. Depending on the solvent, the content of single crystals and agglomerates differ. Agglomerates differ by the number and size of crystals grown together, as well as by the strength.
|
|
| 20. |
- Alander, E. M., et al.
(författare)
-
Mechanisms of crystal agglomeration of paracetamol in acetone-water mixtures
- 2005
-
Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 44:15, s. 5788-5794
-
Tidskriftsartikel (refereegranskat)abstract
- The mechanisms governing the influence of the solvent composition on the agglomeration in a crystallization process have been investigated. Narrowly sieved paracetamol crystals were suspended in supersaturated acetone-water solutions, and were allowed to grow at isothermal conditions, after which the agglomeration was recorded. In all experiments the same sieve size fraction was used as well as the same magma density. In each experiment the supersaturation was kept constant. Experiments were performed in different solvent compositions at different supersaturation, crystal growth rate, solution viscosity, and agitation rate. For a statistically sufficient number of particles from each experiment, the number of crystals in each product particle was determined by image analysis and multivariate data evaluation. From the resulting number distributions of crystals per product particle, parameters defining the degree of agglomeration were extracted. The experimental results clearly establish that there is an influence of the solvent composition on the degree of agglomeration, which cannot be explained by differences in crystal growth rate, or differences in solution viscosity. The degree of agglomeration is found to decrease with increasing solvent polarity. It is, suggested that the mechanism by which the solvent influence relates to the crystal-solvent interaction and the physicochemical. adhesion forces between crystals in the solution.
|
|
| 21. |
- Alemrajabi, Mahmood, 1989-, et al.
(författare)
-
Isolation of rare earth element phosphate precipitate in the nitrophosphate process for manufacturing of fertilizer
- 2016
-
Ingår i: IMPC 2016 - 28th International Mineral Processing Congress. - : Canadian Institute of Mining, Metallurgy and Petroleum. - 9781926872292
-
Konferensbidrag (refereegranskat)abstract
- In the present study, the recovery of rare earth elements (REE) in the nitrophosphate process of fertilizer production is investigated. The apatite has been recovered from iron ore tailings by flotation. After digestion of apatite in concentrated nitric acid, Ca(NO3)2.4H2O is first separated by cooling crystallization and then the REEs are recovered by precipitation. Optimum conditions in these steps have been determined in a previous study. The precipitate mainly consists of CaHPO4.2H2O and REE phosphates. In the present study, selective dissolution and re-precipitation have been studied in order to obtain a precipitate that is more concentrated in REEs. The precipitate was selectively dissolved in nitric and phosphoric acid at different acidities (pH 6 to 0) with the liquid /solid ratio of 100 mL/g. It is shown that most of the CaHPO4.2H2O and other calcium containing compounds will be dissolved at pH 2 while the REE phosphates are not dissolved above a pH of approximately 2. Thus, by partial dissolution of the REE precipitate at pH 2.5 most of the solid calcium phosphates will be dissolved and the remaining solid phase, which is more concentrated in REEs, can be filtered off as a fairly concentrated REE solid mass and the liquor can be recycled back to recover more P nutrients. Alternatively, the REE enriched precipitate was dissolved completely in nitric acid and re-precipitated again by addition of ammonium hydroxide to pH 1.2. A chemical equilibrium software, MEDUSA (Puigdomenech, 2013) has been used to evaluate the experimental results and to estimate the optimum conditions for selectively dissolving the precipitate.
|
|
| 22. |
- Alemrajabi, Mahmood, 1989-, et al.
(författare)
-
Processing of a rare earth phosphate concentrate obtained in the nitrophosphate process of fertilizer production
- 2019
-
Ingår i: Hydrometallurgy. - : Elsevier. - 0304-386X .- 1879-1158. ; 189
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, different processes have been developed and applied to treat a rare earth phosphate concentrate obtained within the nitrophosphate process of fertilizer production. Methods to remove impurities such as Fe and Ca have been investigated as well as to separate the phosphorous and thereby facilitate dissolution of the rare earth elements (REE). These methods include thermal treatment with sodium hydroxide and sodium double sulphate precipitation with and without alkaline conversion, followed by selective dissolution in different acids. The proposed processes were compared and analyzed from the perspective of introducing an appropriate intermediate product for further individual REE separation. The results have shown that after thermal treatment with NaOH at 400 °C, the phosphorous can be removed from the rare earth phosphate concentrate by water leaching. Investigation of different REE phosphate concentrates demonstrated that mixed Ca and REE phases, e.g. REEmCan(PO4)3m+2n/3 and CaHPO4 are less likely to dephosphorize than REE(PO4).nH2O and FePO4.H2O under these conditions. The recovery of REE to a mild acidic solution is limited by the presence of remaining phosphate ions and by the formation of REE oxide phases during the thermal treatment. The results also show that a solution containing 40 g/L REE; free of phosphorous, calcium and iron can be obtained after reprecipitation of the rare earth phosphate concentrate as sodium rare earth double sulphates followed by alkaline conversion with sodium hydroxide and dissolution in nitric acid.
|
|
| 23. |
|
|
| 24. |
- Alemrajabi, Mahmood, 1989-
(författare)
-
Recovery of Rare Earth Elements from an Apatite Concentrate
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Rare earth elements (REE) are a group of 17 elements including lanthanides, yttrium and scandium; which are found in a variety of classes of minerals worldwide. The criticality of the application, lack of high grade and economically feasible REE resources and a monopolistic supply situation has raised significant attention in recovery of these metals from low grade ores and waste materials. In this thesis, the recovery of REE from an apatite concentrate, containing 0.5 mass% of REE, within the nitrophosphate route of fertilizer production has been investigated. Most of the REE (≥ 95%) content can be recovered into a phosphate precipitate with almost 30 mass% REE. Different processes have been developed to convert the REE phosphate precipitate into a more soluble form to obtain a solution suitable for further REE purification and individual separation. It has been shown that after reprecipitation of the REE phosphate concentrate as REE sodium double sulphate and then transformation into a REE hydroxide concentrate, a solution containing 45g/L REE free of Ca, Fe and P can be obtained. The results suggest that the apatite waste after processing of iron ore have the potential to be a very important source for REE in Europe and that the economy is strongly supported by the simultaneous extraction of phosphorous.The potential of using hollow fiber supported liquid membrane (HFSLM) extraction in individual and group separation of REE has been investigated. A hollow fiber supported liquid membrane plant in pilot scale has been operated according to the three main configurations: standard hollow fiber supported liquid membrane technology (HFSLM); hollow fiber renewal liquid membrane technology (HFRSLM) and emulsion pertraction technology (EPT). The standard HFSLM operation is more selective than HFRSLM and EPT, while higher metal transport rate is observed in EPT followed by HFRSLM and HFSLM. The HFRLM configuration helps to maintain the performance of the liquid membrane.
|
|
| 25. |
- Alemrajabi, Mahmood, et al.
(författare)
-
Recovery of rare earth elements from nitrophosphoric acid solutions
- 2017
-
Ingår i: Hydrometallurgy. - : Elsevier. - 0304-386X .- 1879-1158. ; 169, s. 253-262
-
Tidskriftsartikel (refereegranskat)abstract
- In the present study, the recovery of rare earth elements (REEs) from an apatite concentrate in the nitrophosphate process of fertilizer production has been studied. The apatite concentrate has been recovered from iron ore tailings in Sweden by flotation. In the first step, the apatite is digested in concentrated nitric acid, after which Ca(NO3)2.4H2O is separated by cooling crystallization. The solution is then neutralized using ammonia whereby the REEs precipitate mainly as phosphates (REEPO4.nH2O) and together with calcium as REEn Cam (PO4)(3n + 2m) / 3. In this work, the degree of rare earth coprecipitation during seeded cooling crystallization of Ca(NO3)2.4H2O has been studied. The solubility of calcium nitrate tetrahydrate (Ca(NO3)2.4H2O) in acidic nitrophosphoric acid solutions in the temperature range of − 2 °C to 20 °C has been determined. For the neutralization step, it is shown that the calcium concentration and the final pH play an important role in determining the concentration of REEs in the precipitate. It is found that reaching maximum recovery of REE with minimum simultaneous precipitation of calcium requires careful control of the final pH to about 1.8. It is further observed that the precipitation yield of REEs and iron is favored by a longer residence time and higher temperature. Finally, the effect of seeding with synthesized REE phosphate crystals as well as a mixture of REE and Ca phosphates on the precipitation rate and the composition of the precipitate was studied.
|
|
| 26. |
- Alemrajabi, Mahmood, 1989-, et al.
(författare)
-
Separation of Rare-Earth Elements Using Supported Liquid Membrane Extraction in Pilot Scale
- 2022
-
Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045.
-
Tidskriftsartikel (refereegranskat)abstract
- The use of supported liquid membrane extraction for recovery and separation of rare-earth elements (REEs) has been investigated. Experiments have been carried out using the different configurations: (1) standard hollow fiber supported liquid membrane operation (HFSLM), (2) renewal liquid membrane operation (HFRLM), and (3) emulsion pertraction technology (EPT). The experiments were performed in pilot scale using a hollow fiber module with a mass transfer surface area of 8 m2. Synthetic feed solution was used with compositions based on a process for recovery of REE from an apatite concentrate. The total concentration of REE in the feed was varied from 1 to 22 mM REE and the pH was varied in the range 1.5–3.2. Di(2-ethylhexyl) phosphoric acid (D2HEPA) diluted in kerosene, 10% (v/v), was used as the organic membrane solution, and 3 M HCl was used as stripping solution. In supported liquid membrane extraction, the extraction performance is governed by both the kinetics of REE transport through the membrane and by thermodynamics. The effect of feed composition on the selectivity and transport of REE through the liquid membrane have been investigated. The results show that the liquid membrane is more selective toward the heavy REE at lower pH values and higher REE concentration. HFRLM shows a higher transport rate than HFSLM, while the HFSLM configuration gives a higher selectivity toward individual REE. The membrane performance in HFSLM configuration rapidly decays with time, while in the HFRLM and EPT configurations, the performance is much more stable. Possible mechanisms for decaying membrane performance are discussed, and gel formation is identified as being of significant importance. Gel formation is observed at an organic loading above ∼46% for Nd, 38% for Y, 46% for Dy, and 65% for Er. The work performed in this study serves as an initial step to demonstrate that HFRLM and EPT can provide stable operation and be feasible options for processing of REE liquors. A process flow diagram for the recovery of the REE, present in the apatite concentrate, in three fractions is proposed based on the results from this study.
|
|
| 27. |
- Ashour, Radwa, et al.
(författare)
-
DTPA-Functionalized Silica Nano- and Microparticles for Adsorption and Chromatographic Separation of Rare Earth Elements
- 2018
-
Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 6:5, s. 6889-6900
-
Tidskriftsartikel (refereegranskat)abstract
- Silica nanoparticles and porous microparticles have been successfully functionalized with a monolayer of DTPA-derived ligands. The ligand grafting is chemically robust and does not appreciably influence the morphology or the structure of the material. The produced particles exhibit quick kinetics and high capacity for REE adsorption. The feasibility of using the DTPA-functionalized microparticles for chromatographic separation of rare earth elements has been investigated for different sample concentrations, elution modes, eluent concentrations, eluent flow rates, and column temperatures. Good separation of the La(III), Ce(III), Pr(III), Nd(III), and Dy(III) ions was achieved using HNO3 as eluent using a linear concentration gradient from 0 to 0.15 M over 55 min. The long-term performance of the functionalized column has been verified, with very little deterioration recorded over more than 50 experiments. The results of this study demonstrate the potential for using DTPA-functionalized silica particles in a chromatographic process for separating these valuable elements from waste sources, as an environmentally preferable alternative to standard solvent-intensive processes.
|
|
| 28. |
- Bergillos-Ruiz, Marta, et al.
(författare)
-
Impact of carrier particle surface properties on drug nanoparticle attachment
- 2024
-
Ingår i: International Journal of Pharmaceutics. - : Elsevier BV. - 0378-5173 .- 1873-3476. ; 651
-
Tidskriftsartikel (refereegranskat)abstract
- Hypothesis: The stabilization and isolation to dryness of drug nanoparticles has always been a challenge for nano-medicine production. In the past, the use of montmorillonite (MMT) clay carrier particles to adsorb drug nanoparticles and maintain their high surface area to volume ratio after isolation to dryness has proven to be effective. We hypothesise that the distribution of hydrophilic and hydrophobic patches on the clay's surface as well as its porosity/roughness, hinder the agglomeration of the drug nanoparticles to the extent that they retain their high surface area to volume ratio and display fast dissolution profiles. Experiments: In this work, the distribution of hydrophobicity and hydrophilicity, and the porosity/roughness, of the surface of selected silica carrier particles were varied and the impact of these variations on drug nanoparticle attachment to the carrier particle and subsequent dissolution profiles was studied. Findings: The fastest dissolution profiles at the highest drug nanoparticle loadings were obtained with a periodic mesoporous organosilane carrier particle which had a homogeneous distribution of hydrophobic and hydrophilic surface properties. Carrier particles with rough/porous surfaces and a combination of hydrophobic and hydrophilic patches resulted in nanocomposite powders with faster dissolution behaviour than carrier particles with predominantly either a hydrophobic or hydrophilic surface, or with non-porous/smoother surfaces.
|
|
| 29. |
- Bodnár, K., et al.
(författare)
-
Promotion of Mefenamic Acid Nucleation by a Surfactant Additive, Docusate Sodium
- 2019
-
Ingår i: Crystal Growth and Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 19:2, s. 591-603
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of docusate sodium (DOSS) on the nucleation of mefenamic acid (MEF) has been studied in different dimethylacetamide (DMA)-water mixtures. A series of induction time experiments were conducted under moderate supersaturations, varying the solvent composition and the concentration of DOSS. In 40% DMA-60% water, the presence of 0.1 and 0.2 mg/mL DOSS increased the nucleation rate. Evaluating the results by the classical nucleation theory reveals that the pre-exponential factor (A) increases by approximately 50% while the interfacial energy is essentially uninfluenced. It is also found that the crystal growth rate becomes higher in the presence of DOSS. It is thus hypothesized that transport and desolvation of MEF molecules are facilitated in the presence of DOSS. With increasing amount of DMA in the binary solvent mixture, the influence of DOSS appears to decrease.
|
|
| 30. |
- Bodnar, K., et al.
(författare)
-
Stepwise use of additives for improved control over formation & stability of mefenamic acid nanocrystals produced by antisolvent precipitation
- 2017
-
Ingår i: Crystal Growth and Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 17:2, s. 454-466
-
Tidskriftsartikel (refereegranskat)abstract
- A method of introducing different additives at different times during the process, i.e., stepwise addition of additives, has been developed to produce stable nanoparticles of mefenamic acid (MEF) by antisolvent precipitation. In the absence of additives, at optimized conditions, MEF crystals were prepared in the size range of 0.25-3.05 μm; however, these crystals formed large agglomerates in suspension (∼12.1 μm). In the presence of all additives evaluated, with the exception of hydroxypropylmethylcellulose (HPMC), smaller particles were produced in suspension, the most effective additive being sodium docusate (DOSS), generating nanoparticles, ∼312 nm in size. However, the particle size was not stable but increased to ∼788 nm after 80 min in suspension associated with a polymorphic transformation. Combining the initial use of DOSS with the subsequent addition of HPMC or poly(vinyl alcohol) (PVA) allowed for the production of a stable suspension of MEF nanocrystals (∼317 and ∼311 nm, respectively). The interaction of HPMC and PVA with MEF particles delayed polymorphic transformation by inhibiting nucleation and/or growth of the stable MEF polymorph. The results show that using stepwise addition of additives, separately targeting nucleation and crystal growth/phase transformation, can improve the manufacturing and stabilization of nanocrystal suspensions.
|
|
| 31. |
- Bäbler, Matthäus U., et al.
(författare)
-
Isolation of Pharmaceutical Intermediates through Solid Supported Evaporation. Semicontinuous Operation Mode
- 2012
-
Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 51:45, s. 14814-14823
-
Tidskriftsartikel (refereegranskat)abstract
- Solid supported evaporation (SSE) is a simple, nonselective method for isolating nonvolatile compounds from a solution. The solution is put in contact with porous polymer beads onto which the compound deposits upon evaporation of the solvent. This brings some advantages over direct evaporation to dryness in terms of safety, thermal decomposition, and solid handling, as the loaded beads form a free flowing granular material that is easily recovered. In this paper, SSE in a semicontinuous operating mode is investigated where the solution is continuously fed to (respectively sprayed over) an agitated bed of dry beads put under vacuum. It is found that under conditions where the solvent evaporation fate is high with respect to the feed rate, high bead loadings can be achieved before extensive sticking of beads and compound to the vessel walls occurs. The type of compound and solvent had little influence on the process performance, and, in cases where this was explored, the bead loading was found to be homogeneous. Based on a balance equation for the solvent fed to the system, a model is developed that results in a simple scale up criterion. The latter was successfully applied for transferring SSE from lab to the kilo lab scale.
|
|
| 32. |
- Cheuk, Dominic, et al.
(författare)
-
Influence of solvent on crystal nucleation of benzocaine
- 2020
-
Ingår i: CrystEngComm. - : Royal Society of Chemistry (RSC). - 1466-8033. ; 22:48, s. 8330-8342
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of the solvent in nucleation of a polymorphic organic molecule, benzocaine, has been explored by measuring nucleation induction times, probing solvent-solute interactions in solution with spectroscopy and modelling the strength of solvent-solute intermolecular interactions using density functional theory (DFT). Over 2640 induction time experiments were conducted to study the crystal nucleation of benzocaine FII in six different organic solvents. The nucleation driving force required to reach the same induction time is strongly solvent-dependent, increasing in the order: ethyl acetate < 1,4-dioxane < acetonitrile < methanol < n-butanol. Nucleation in toluene is reasonably easy but the exact position varies with the induction time. The order between the solvents overall corresponds to the order of increasing interfacial energy as determined within the classical nucleation theory. The shift of the FTIR carbonyl frequency reflecting the strength in the solvent-solute interaction decreases in the same order as the interfacial energy of benzocaine FII increases. This shift is corroborated by DFT calculated energies of binding one solvent molecule to the carboxyl group of benzocaine. An even better correlation of the influence of the solvent on the nucleation is provided by DFT calculated energy of binding the complete first solvation shell to the benzocaine molecule. The different methods reveal a consistent picture and suggest that the stronger the solvent binds to the benzocaine molecule in solution, the slower the nucleation becomes.
|
|
| 33. |
- Cheuk, Dominic, et al.
(författare)
-
Investigation into solid and solution properties of quinizarin
- 2015
-
Ingår i: CrystEngComm. - : Royal Society of Chemistry. - 1466-8033. ; 17:21, s. 3985-3997
-
Tidskriftsartikel (refereegranskat)abstract
- Polymorphism, crystal shape and solubility of 1,4-dihydroxyanthraquinone (quinizarin) have been investigated in acetic acid, acetone, acetonitrile, n-butanol and toluene. The solubility of FI and FII from 20 degrees C to 45 degrees C has been determined by a gravimetric method. By slow evaporation, pure FI was obtained from n-butanol and toluene, pure FII was obtained from acetone, while either a mixture of the two forms or pure FI was obtained from acetic acid and acetonitrile. Slurry conversion experiments have established an enantiotropic relationship between the two polymorphs and that the commercially available FI is actually a metastable polymorph of quinizarin under ambient conditions. However, in the absence of FII, FI is kinetically stable for many days over the temperature range and in the solvents investigated. FI and FII have been characterized by infrared spectroscopy (IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), transmission and ordinary powder X-ray diffraction (PXRD) at different temperatures. The crystal structure of FII has been determined by single-crystal XRD. DSC and high-temperature PXRD have shown that both FI and FII will transform into a not previously reported hightemperature form (FIII) around 185 degrees C before this form melts at 200-202 degrees C. By indexing FIII PXRD data, a triclinic P (1) over bar cell was assigned to FIII. The solubility of quinizarin FI and FII in the pure organic solvents used in the present work is below 2.5% by weight and decreases in the order: toluene, acetone, acetic acid, acetonitrile and n-butanol. The crystal shapes obtained in different solvents range from thin rods to flat plates or very flat leaves, with no clear principal difference observed between FI and FII.
|
|
| 34. |
- Cheuk, Dominic, et al.
(författare)
-
Thermodynamics of the Enantiotropic Pharmaceutical Compound Benzocaine and Solubility in Pure Organic Solvents
- 2020
-
Ingår i: Journal of Pharmaceutical Sciences. - : Elsevier BV. - 0022-3549 .- 1520-6017. ; 109:11, s. 3370-3377
-
Tidskriftsartikel (refereegranskat)abstract
- The thermodynamic relationship between FI and FII of ethyl 4-aminobenzoate (benzocaine) has been investigated. Slurry conversion experiments show that the transition temperature below which FI is stable is located between 302 K-303 K (29 degrees C-30 degrees C). The polymorphs FI and FII have been characterised by infrared spectroscopy (IR), Raman spectroscopy, transmission powder X-ray diffraction (XRPD) and differential scanning calorimetry (DSC). The isobaric solid state heat capacities have been measured by DSC. The quantitative thermodynamic stability relationship has been determined in a comprehensive thermodynamic analysis of the calorimetric data. The solubility of both polymorphs has been determined in eight pure organic solvents over the temperature range 278 K-323 K by a gravimetric method. The mole fraction solubility of benzocaine decreases in the order: 1,4-dioxane, acetone, ethyl acetate, chloroform, acetonitrile, methanol, n-butanol and toluene. Comparison with the determined activity of solid benzocaine forms shows that negative deviation from Raoult's law ideality is found in dioxane, acetone and ethyl acetate solutions, and positive deviation in solutions of the other investigated solvents.
|
|
| 35. |
- Croker, Denise, et al.
(författare)
-
Understanding the p-toluenesulfonamide / triphenylphosphine oxide crystal chemistry: a new 1:1 cocrystal and ternary phase diagram
- 2012
-
Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 12:2, s. 869-875
-
Tidskriftsartikel (refereegranskat)abstract
- A novel 1:1 cocrystal between p-toluenesulfonamide and triphenylphosphine oxide has been prepared and structurally characterized. This 1:1 cocrystal was observed to form during solid state grinding experiments, with subsequent formation of a known 3:2 cocrystal in the presence of excess sulfonamide. Both cocrystals are stable in the solid state. The ternary phase diagram for the two coformers was constructed in two different solvents: acetonitrile and dichloromethane. Examination of these diagrams clarified solution crystallization of both the newly discovered 1:1 cocrystal and the previously reported 3:2 cocrystal, and identified regions of stability for each cocrystal in each solvent. The choice of solvent was found to have a significant effect on the position of the solid state regions within a cocrystal system.
|
|
| 36. |
|
|
| 37. |
|
|
| 38. |
- Diniz, Mariana O., et al.
(författare)
-
New Solid Forms of Griseofulvin : A Solvate and a Relict Polymorph Related to Reported Solvates
- 2023
-
Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 23:12, s. 8953-8961
-
Tidskriftsartikel (refereegranskat)abstract
- This work presents two new solid forms, a polymorph and a solvate, of the antifungal active pharmaceutical ingredient griseofulvin (GSF). The novel forms were characterized by powder X-ray diffraction, differential scanning calorimetry, and thermogravimetric analysis, and their crystal structures were determined by single-crystal X-ray diffraction. The new polymorphic form (GSF Form VI) was obtained upon drying at room temperature the GSF-acetonitrile solvate. GSF Form VI is a relict structure related to reported solvates of GSF. Thermal stability studies show that Form VI is metastable and monotropically related to the stable GSF Form I. The new GSF-n-butyl acetate solvate was obtained by crystallization from an n-butyl acetate solution. The stoichiometry of the n-butyl acetate solvate is 1:0.5. The solvate loses the solvent from the crystal lattice at a temperature between 363.15 and 374.15 K.
|
|
| 39. |
- Fichtner, Frauke, et al.
(författare)
-
Effect of preparation method on compactability of paracetamol granules and agglomerates
- 2007
-
Ingår i: International Journal of Pharmaceutics. - : Elsevier BV. - 0378-5173 .- 1873-3476. ; 336:1, s. 148-158
-
Tidskriftsartikel (refereegranskat)abstract
- The objective of this study was to investigate the effect of fracture strength of paracetamol particles on their compactability. For this purpose two series of paracetamol particles were prepared by crystal agglomeration and by granulation using different solvents. A free flowing particle size fraction of all types of particles was characterized with respect to their shape, degree of agglomeration and single fracture strength. The powders were compressed to tablets and the compression mechanism of the particles and the evolution in tablet micro-structure were assessed by compression parameters derived from the Heckel and Kawakita equations and by a tablet permeabililty coefficient. Tablet tensile strength and porosity were determined. The degree of deformation and fragmentation during compression varied between agglomerates and granules and was dependent on their failure strength. The granules varied in compactability with particle failure strength while the agglomerates showed limited variation. It is proposed that, the dominant mechanism of compression for the granules was permanent deformation while for the agglomerates it was fragmentation. It was thus found that the compression mechanism of the particles was dependent on both the degree of agglomeration and the particle failure strength.
|
|
| 40. |
- Fichtner, Frauke, et al.
(författare)
-
Particle size distribution and evolution in tablet structure during and after compaction
- 2005
-
Ingår i: International Journal of Pharmaceutics. - : Elsevier BV. - 0378-5173 .- 1873-3476. ; 292:02-jan, s. 211-225
-
Tidskriftsartikel (refereegranskat)abstract
- The objective of this study was to investigate the effect of the distribution in size of free-flowing particles for the evolution in tablet structure and tablet strength. For sucrose and sodium chloride, three powders of different size distributions were prepared by mixing predetermined quantities of particle size fractions. For paracetamol, three batches with varying particle size distributions were prepared by crystallisation. The powders were formed into tablets. Tablet porosity and tensile strength were determined directly after compaction and after short-term storage at two different relative humidities. Tablets were also formed after admixture of a lubricant (magnesium stearate) and the tablet tensile strength was determined. For the test materials used in this study, the spread in particle size had no influence on the evolution in tablet porosity and tensile strength during compression. However, the spread in particle size had a significant and complex influence on the short-term post-compaction increase in tablet tensile strength. The effect of the spread was related to the instability mechanism and the presence of lubricant. It is concluded that the distribution in size of free-flowing particles is not critical for the tablet porosity but may give significant effects on tablet tensile strength due to a post-compaction reaction.
|
|
| 41. |
- Forsberg, Kerstin, et al.
(författare)
-
Crystal growth kinetics of iron fluoride trihydrate
- 2006
-
Ingår i: Journal of Crystal Growth. - Royal Inst Technol, Dept Chem Engn & Technol, KTH, S-10044 Stockholm, Sweden. : Elsevier BV. - 0022-0248 .- 1873-5002. ; 296:2, s. 213-220
-
Tidskriftsartikel (refereegranskat)abstract
- Crystal growth of beta-FeF3 • 3H(2)O has been investigated in mixtures of 3 mol kg(-1) hydrofluoric acid and 3 mol kg(-1) nitric acid at 30, 40 and 50 degrees C. Seeded isothermal desupersaturation experiments have been performed in the range: 1.3 < S < 3.6. Solution samples were analysed for total iron concentration with inductively coupled plasma atomic emission spectroscopy. The true supersaturation driving force was estimated by a proper speciation using the software SSPEC using appropriate stability constants. Growth rate parameters of the BCF surface diffusion growth rate equation and the empirical power-law equation have been estimated by fitting the supersaturation balance equation using a nonlinear optimization procedure. The results show that the growth rate is surface integration controlled. The growth rate at a supersaturation ratio of 2 was found to be 3.5 x 10(-12) m s(-1) at 30 degrees C, 7.4 x 10(-12) m s(-1) at 40 degrees C and 16 x 10(-12) m s(-1) at 50 degrees C. The activation energy of the rate constant of crystal growth was found to be 61 kJ mol(-1). .
|
|
| 42. |
- Forsberg, Kerstin M., et al.
(författare)
-
The influence of hydrofluoric acid and nitric acid on the growth kinetics of iron(III) fluoride trihydrate
- 2015
-
Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 423, s. 16-21
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of hydrofluoric acid and nitric acid concentration on the growth rate of beta-FeF3 center dot 3H(2)O crystals has been studied in different hydrofluoric acid (4.7-10.7 mol/(kg H2O)) and nitric acid (2.1-4.6 mol/(kg H2O)) mixtures at 50 degrees C. Seeded desupersaturation experiments were performed and the results were evaluated by considering the chemical speciation using two different speciation programs. The growth rate at 50 degrees C at a supersaturation ratio of 2, expressed in terms of free FeF3, was found to be in the range of (0.4-3.8) x 10(-11) m/s. The growth rate order was found to be two or higher in all experiments. The low growth rate and high growth rate order indicate that the growth rate is governed by the surface integration step. The growth rate was found to be independent of variations in acid concentrations: this is in accordance with the assumption of a surface integration controlled growth rate.
|
|
| 43. |
|
|
| 44. |
- Forsberg, Kerstin, et al.
(författare)
-
Recycling of waste pickle acid by precipitation of metal fluoride hydrates
- 2007
-
Ingår i: Minerals Engineering. - : Elsevier BV. - 0892-6875 .- 1872-9444. ; 20:9, s. 950-955
-
Tidskriftsartikel (refereegranskat)abstract
- Stainless steel is pickled in mixed acid solutions (1-3 M HNO3 and 0.5-4 M HF). The spent solution is usually neutralized with lime, and in Sweden about 18,000 tons/yr of metal hydroxide sludge is disposed as landfill waste. We are developing a cost-saving and environmentally friendly process, involving crystallization of beta-FeF3 . 3H(2)O, where the metal content is recovered and the acid is recycled. Iron has been successfully separated from spent pickle bath solutions by precipitation of beta-FeF3 . 3H(2)O in a continuous crystallizer (10 L scale) where the solution is concentrated by nanofiltration. The crystal growth rate of beta-FeF3 . 3H(2)O has been determined in industrial pickle bath solutions at 50 degrees C and the results have been compared to previous measurements in pure HF/HNO3 solutions prepared in the laboratory. The growth rate of beta-beta eF(3) . 3H(2)O crystals at 50 degrees C is in the order of 10(-11) m/s in both industrial and pure acid mixtures.
|
|
| 45. |
- Ghosh, Peuli, et al.
(författare)
-
Impact of Additives on Drug Particles during Liquid Antisolvent Crystallization and Subsequent Freeze-Drying
- 2023
-
Ingår i: Organic Process Research & Development. - : American Chemical Society (ACS). - 1083-6160 .- 1520-586X. ; 27:11, s. 2020-2034
-
Tidskriftsartikel (refereegranskat)abstract
- The impact of single or combinations of additives on the generation of nanosuspensions of two poorly water-soluble active pharmaceutical ingredients (APIs), fenofibrate (FF) and dalcetrapib (DCP), and their isolation to the dry state via antisolvent (AS) crystallization followed by freeze-drying was explored in this work. Combinations of polymeric and surfactant additives such as poly(vinyl alcohol) or hydroxypropyl methyl cellulose and sodium docusate were required to stabilize nanoparticles (∼200-300 nm) of both APIs in suspension before isolation to dryness. For both FF and DCP, multiple additives generated the narrowest, most-stable particle size distribution, with the smallest particles in suspension, compared with using a single additive. An industrially recognized freeze-drying process was used for the isolation of these nanoparticles to dryness. When processed by the liquid AS crystallization followed by freeze-drying in the presence of multiple additives, a purer monomorphic powder for FF resulted than when processed in the absence of any additive or in the presence of a single additive. It was noted that all nanoparticles freeze-dried in the presence of additives had a flat, flaky habit resulting in large surface areas. Agglomeration occurred during freeze-drying, resulting in micron-size particles. However, after freeze-drying, powders produced with single or multiple additives showed similar dissolution profiles, irrespective of aging time before drying, thus attenuating the advantage of multiple additives in terms of size observed before the freeze-drying process.
|
|
| 46. |
- Gracin, Sandra, et al.
(författare)
-
Influence of ultrasound on the nucleation of polymorphs of p-aminobenzoic acid
- 2005
-
Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 5:5, s. 1787-1794
-
Tidskriftsartikel (refereegranskat)abstract
- p-Aminobenzoic acid crystallizes in two different polymorphic forms: the alpha-form and the beta-form. The alpha-form crystals are needle-shaped, while the beta-form crystals have a more favorable prismatic shape. The system is enantiotropic with the transition temperature at approximately 25 degrees C. Below the transition temperature, the beta-form is the thermodynamically stable polymorph but can only be produced at very slow supersaturation generation either in water or in ethyl acetate. In the present work, the influence of ultrasound on the nucleation of p-aminobenzoic acid polymorphs has been investigated by use of several different sonication intensities and schemes. It is shown that sonication significantly reduces the induction time for nucleation. By using controlled sonication, we were able to more reproducibly crystallize the beta-form at more reasonable cooling rates. In addition, sonication is found to quite selectively favor the appearance of the beta-polymorph. It is even possible to produce the pure beta-form above the transition temperature where it is the metastable form and impossible to produce without sonication. The alpha-form structure is based on centro symmetric dimers formed by the association of carboxylic acid groups, while the beta-form contains four-membered hydrogen-bonded rings of alternating amino and carboxylic acid groups. It is suggested that ultrasound disturbs the building up of the dimers in the solution and thus favors the crystallization of the beta-polymorph.
|
|
| 47. |
- Gracin, Sandra, et al.
(författare)
-
Polymorphism and Crystallization of p-Aminobenzoic Acid
- 2004
-
Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 4:5, s. 1013-1023
-
Tidskriftsartikel (refereegranskat)abstract
- p-Aminobenzoic acid (PABA) crystallizes in two different polymorphic forms: the alpha-polymorph, which is the commercially available form and appears as long, fibrous needles, and the beta-polymorph, which appears in the form of prisms. The thermodynamic stability and crystallization from different solvents have been studied experimentally. The system is found to be enantiotropic with a transition temperature of 25degreesC, below which the beta-form is the stable polymorph. The compound has been crystallized from 13 different solvents, either by slow cooling after which the product is allowed to mature in suspension, or by rapid cooling followed by immediate isolation. Needles were obtained from all solvents by both methods. In water and in ethyl acetate, at slow cooling below 20degreesC, the prismatic beta-form is obtained, however, often together with the needles. The beta-form crystals usually needed hours or days to grow at the very slow cooling used, while needles usually appeared in seconds. By careful control of supersaturation and temperature, cooling crystallization can be performed to produce the pure beta-form in water and in ethyl acetate. The influence of the solvent is explained by analysis of the crystal structures versus the possible interaction of the solvent molecules with the solute in solution. The alpha-form structure is governed by carboxylic acid dimers and is kinetically favored since it is believed that the corresponding dimers easily form in the solution, especially in less polar solvents.
|
|
| 48. |
- Gracin, Sandra, et al.
(författare)
-
Prediction of Solubility of Solid Organic Compounds in Solvents by UNIFAC
- 2002
-
Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 41:20, s. 5114-5124
-
Tidskriftsartikel (refereegranskat)abstract
- Predictions of solubility of nine different solid organic fine chemical compounds in water and organic solvents of relevance to industrial processing are examined. UNIFAC interaction parameters are taken from standard reference literature, extracted from liquid-vapor equilibria. For most systems, predicted solubilities deviate more than 15% from experimental values. Deviations are due to uncertainties in the estimation of the activity of the pure solid as well as to deficiencies in the estimation of activity coefficients in the solution. By comparison with results from ab initio quantum chemical calculations of the elecrostatic potential on the molecular surface of the solutes, it can be shown that a key assumption of the UNIFAC approach is not necessarily fulfilled. The properties of a functional group may depend significantly on the properties of the rest of the molecule.
|
|
| 49. |
- Gracin, Sandra, 1968-
(författare)
-
Solubility and polymorphism of molecular compounds
- 2005
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with the controlled crystallization of small organic molecules and is focused on solubility and polymorphism. The solubility was determined for phenylacetic acid, p-hydroxyphenylacetic acid, p-aminophenylacetic acid, p-hydroxybenzoic acid and ibuprofen in both water and in a range of organic solvents. Data is discussed from the standpoint of molecular aspects of solute – solvent interactions and by estimated solid phase activity. It was shown that better understanding could be acquired by making a qualitative analysis of the molecular interactions in the solution and the crystal structure of the compounds in question. Solubility predictions that are carried out by the UNIFAC method are not sufficiently accurate to serve as a basis for a reliable design of a crystallization process or selection of a suitable solvent since they deviate more than 15% from experimental values. The reason for the discrepancies are related to uncertainties in the prediction of activity coefficients by UNIFAC, as well as, difficulties in the estimation of the activity of the solid state. p-Aminobenzoic acid (PABA) has been crystallized from thirteen different solvents either by slow cooling, after which the product is allowed to mature in suspension, or by rapid cooling followed by immediate isolation. Two different polymorphs have been crystallized. The system is found to be enantiotropic with the transition temperature of 25 °C, below which the β-form is the stable polymorph. The α-form was obtained from all solvents by both methods. The β-form is obtained only in carefully controlled conditions from water and ethyl acetate, well below the transition temperature. Often the α-form appears concomitantly. It is shown in this work that sonication significantly reduces the induction time for nucleation. The β-form crystallizes more reproducibly and at higher cooling rates when controlled sonication is used. In addition sonication is found to selectively favor the appearance of one of the polymorphs. Producing the pure β-form was possible even above the transition temperature where other crystallization techniques were only capable of producing the stable α-form. The α-form structure is based on centro symmetric dimers formed by association of carboxylic acid groups. It is suggested that the preference for nucleation of the α-polymorph is related to the formation of dimers in the supersaturated solution. Only at the condition where the formation of dimers is reduced sufficiently, (i.e. in the polar solvents or when sonication is applied) the nucleation of the β-form is favored.
|
|
| 50. |
- Gracin, Sandra, et al.
(författare)
-
Solubility of Phenylacetic Acid, p-Hydroxyphenylacetic Acid, p-Aminophenylacetic Acid, p-Hydroxybenzoic Acid, and Ibuprofen in Pure Solvents
- 2002
-
Ingår i: Journal of Chemical and Engineering Data. - : American Chemical Society (ACS). - 0021-9568 .- 1520-5134. ; 47:6, s. 1379-1383
-
Tidskriftsartikel (refereegranskat)abstract
- The solubility of phenyl acetic acid, p-hydroxyphenylacetic acid, p-aminophenylacetic acid, p-hydroxybenzoic acid, and ibuprofen in water and in a range of organic solvents of relevance to industrial processing is reported. The solvents used are water, methanol, ethanol, 2-propanol, acetone, 4-methyl-2-pentanone, ethyl acetate, chloroform, and toluene. Solubility data are discussed from the standpoint of molecular aspects of solute-solvent interactions and by estimated solid-phase activity.
|
|
