| 1. |
- Nordberg, Åke, et al.
(författare)
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Selective desorption of carbon dioxide from sewage sludge for in-situ methane enrichment : Enrichment experiments in pilot scale
- 2012
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Ingår i: Biomass and Bioenergy. - : Elsevier BV. - 0961-9534 .- 1873-2909. ; 37, s. 196-204
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Tidskriftsartikel (refereegranskat)abstract
- The application of in-situ methane enrichment for upgrading the biogas from anaerobic digestion to vehicle fuel or natural gas quality, has been studied in pilot scale and by computer simulation of the desorption step. Pilot plant experiments have been performed using a 19 m(3) and 15 m(3) continuously stirred tank reactor operating with municipal sewage sludge at mesophilic conditions connected respectively to a 90 dm(3) and 140 dm(3) external bubble column for selective desorption of CO2. The results show that the CH4 yield is unchanged during the experiments, and accordingly there is no evidence that the oxygen in the air used in the desorption of CO2 has a negative impact on the CH4 producing activity. The sludge recirculation system must be designed to avoid leakage of air into the digester, in order to maintain a low N-2 concentration in the biogas. At best, a biogas with a volume fraction of 87% CH4 and (p N-2 = 2% was obtained. The CH4 loss however amounted to 8%, which is unsatisfactory. The experimental results are compared with previous data in the literature and explanations are deducted for the difference in the performance. Computer simulations reveal that the sludge flow rate recirculated through the desorption column should be as low as possible to minimize the loss of CH4. An increased air flow rate through the desorption column and an increased desorption column volume will promote the desorption of CO2 and improve the ratio of CO2 to CH4 desorption.
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| 2. |
- Ahuja, Dipali, et al.
(författare)
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Investigation of solid-liquid phase diagrams of the sulfamethazine-salicylic acid co-crystal
- 2019
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Ingår i: CrystEngComm. - : ROYAL SOC CHEMISTRY. - 1466-8033. ; 21:18, s. 2863-2874
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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.
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| 3. |
- Ahuja, Dipali, et al.
(författare)
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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
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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.
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| 4. |
- Ahuja, D., et al.
(författare)
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Study of three solvates of sulfamethazine
- 2017
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Ingår i: CrystEngComm. - Cambridge, England : Royal Society of Chemistry (RSC). - 1466-8033. ; 19:43, s. 6481-6488
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Tidskriftsartikel (refereegranskat)abstract
- Three novel solvates of sulfamethazine (SMT), an anti-microbial and anti-infective sulfonamide drug with the solvents-dimethylacetamide, dimethylformamide and dimethyl sulfoxide have been identified and characterized by analytical techniques including differential scanning calorimetry, thermogravimetric analysis, X-ray diffraction and Raman spectroscopy. All three are 1:1 solvates. Crystal structure analysis revealed N-H-O type intermolecular hydrogen bonding interactions between SMT and the solvent imparting stability to the solvate structure. Thermal analysis measurements for the stoichiometry of the solvates were in good agreement with the single crystal data. The solubility of the solvates in their respective solvents at 25 °C has been determined.
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| 5. |
- Aisling, Lynch, et al.
(författare)
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Crystal Growth of Single Salicylamide Crystals
- 2019
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 19:12, s. 7230-7239
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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.
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| 6. |
- Alander, Eva M., et al.
(författare)
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Agglomeration and adhesion free energy of paracetamol crystals in organic solvents
- 2007
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Ingår i: AIChE Journal. - : Wiley. - 0001-1541 .- 1547-5905. ; 53:10, s. 2590-2605
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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.
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| 7. |
- Alander, E. M., et al.
(författare)
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Characterization of paracetamol agglomerates by image analysis and strength measurement
- 2003
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Ingår i: Powder Technology. - : Elsevier BV. - 0032-5910 .- 1873-328X. ; 130:1-3, s. 298-306
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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.
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| 8. |
- Alander, E. M., et al.
(författare)
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Mechanisms of crystal agglomeration of paracetamol in acetone-water mixtures
- 2005
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 44:15, s. 5788-5794
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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.
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| 9. |
- Albero Caro, Jesus, et al.
(författare)
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Semibatch reaction crystallization of salicylic acid
- 2014
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Ingår i: Chemical engineering research & design. - : Elsevier BV. - 0263-8762 .- 1744-3563. ; 92:3, s. 522-533
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Tidskriftsartikel (refereegranskat)abstract
- Reaction crystallization of salicylic acid has been investigated by experiments and modeling. In the experimental work, dilute hydrochloric acid has been added to an agitated aqueous solution of sodium salicylate in 1 L scale, and product crystals have been characterized by image analysis. The results show that the product crystal number mean size at first increases with increasing agitation rate but then gradually decreases again at further increase in stirring rate. At lower stirring rate, larger crystals are obtained when the feeding point is located close to the agitator instead of being located out in the bulk solution. The mean crystal size increases with decreasing feeding rate and with decreasing reactant concentrations. There is a decrease in mean size with increasing feed pipe diameter. These trends in the experimental results show great similarity with previous results on benzoic acid. The experimental results have been examined by a population balance model accounting for meso and micro mixing, and crystal nucleation and growth rate dispersion. It is found that the crystallization kinetic parameter estimation is quite complex, and the objective function hyper surface contains many different minima. Hence, parameter estimation has to rely on a combination of mathematical optimization strategies and a scientific understanding of the physical meaning of the parameters and their relation to current theories. As opposed to our previous work on benzoic acid, it has not been possible to find a set of kinetic parameters that provides for a good description of all experimental data.
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| 10. |
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| 11. |
- Alemrajabi, Mahmood, 1989-, et al.
(författare)
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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.
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| 12. |
- Alemrajabi, Mahmood, 1989-, et al.
(författare)
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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.
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| 13. |
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| 14. |
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| 15. |
- Alemrajabi, Mahmood, 1989-
(författare)
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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.
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| 16. |
- 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.
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| 17. |
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| 18. |
- Alemrajabi, Mahmood, 1989-, et al.
(författare)
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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.
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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.
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| 19. |
- Alemrajabi, Mahmood, et al.
(författare)
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Upgrading of a rare earth phosphate concentrate within the nitrophosphate process
- 2018
-
Ingår i: Journal of Cleaner Production. - : Elsevier. - 0959-6526 .- 1879-1786. ; 198, s. 551-563
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Tidskriftsartikel (refereegranskat)abstract
- In the nitrophosphate process of fertilizer production, rare earth elements (REE) can be recovered as a REE phosphate concentrate. In this process, after digestion of apatite in concentrated nitric acid, Ca(NO3)2.4H2O is first separated by cooling crystallization and then the REE are precipitated in phosphate form by a partial neutralization step using ammonia. The obtained REE phosphate concentrate is contaminated by mainly calcium and iron, and the main solid phases are CaHPO4.2H2O, FePO4.2H2O and REEPO4.nH2O.In this study, a process to obtain a concentrate more enriched with REE with low concentration of calcium and iron and free of phosphorous is developed. In the developed process, enrichment and dephosphorization of the rare earth phosphate concentrate has been achieved by selective dissolution and re-precipitation of the REE as a sodium REE double sulfate salt. It is shown that by selective dissolution of the REE concentrate in nitric acid at a pH of 2.4, most of the calcium and phosphorus are dissolved, and a solid phase more enriched in REE is obtained. Thereafter, the REE phosphate concentrate is first dissolved in a mixture of sulfuric-phosphoric acid and then the REE are reprecipitated as NaREE(SO4)2.H2O by addition of a sodium salt. More than 95% of the Ca, Fe and P are removed and a REE concentrate containing almost 30 mass% total REE is obtained.
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| 20. |
- Ashour, Radwa, et al.
(författare)
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DTPA-Functionalized Silica Nano- and Microparticles for Adsorption and Chromatographic Separation of Rare Earth Elements
- 2018
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Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 6:5, s. 6889-6900
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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.
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| 21. |
- Bergillos-Ruiz, Marta, et al.
(författare)
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Impact of carrier particle surface properties on drug nanoparticle attachment
- 2024
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Ingår i: International Journal of Pharmaceutics. - : Elsevier BV. - 0378-5173 .- 1873-3476. ; 651
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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.
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| 22. |
- Bodnár, K., et al.
(författare)
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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
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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.
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| 23. |
- Bodnar, K., et al.
(författare)
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Stepwise use of additives for improved control over formation & stability of mefenamic acid nanocrystals produced by antisolvent precipitation
- 2017
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Ingår i: Crystal Growth and Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 17:2, s. 454-466
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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.
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| 24. |
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| 25. |
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| 26. |
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| 27. |
- Bäbler, Matthäus U., et al.
(författare)
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Isolation of Pharmaceutical Intermediates through Solid Supported Evaporation. Semicontinuous Operation Mode
- 2012
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 51:45, s. 14814-14823
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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.
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| 28. |
- Cheuk, Dominic, et al.
(författare)
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Influence of solvent on crystal nucleation of benzocaine
- 2020
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Ingår i: CrystEngComm. - : Royal Society of Chemistry (RSC). - 1466-8033. ; 22:48, s. 8330-8342
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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.
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| 29. |
- Cheuk, Dominic, et al.
(författare)
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Investigation into solid and solution properties of quinizarin
- 2015
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Ingår i: CrystEngComm. - : Royal Society of Chemistry. - 1466-8033. ; 17:21, s. 3985-3997
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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.
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| 30. |
- Cheuk, D., et al.
(författare)
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Solid Forms, Crystal Habits, and Solubility of Danthron
- 2015
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Ingår i: Journal of Chemical and Engineering Data. - : American Chemical Society (ACS). - 0021-9568 .- 1520-5134. ; 60:7, s. 2110-2118
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Tidskriftsartikel (refereegranskat)abstract
- The polymorphism, crystal habits, and solubility of 1,8-dihydroxyanthraquinone (danthron) were investigated in acetic acid, acetone, acetonitrile, n-butanol, and toluene. The solubility was determined for the commercially available form (FI) from 293.15 K to 318.15 K. by the gravimetric method. The influence of solvents on crystal habit and polymorphic form has been investigated. Three different crystal habits of danthron were obtained from slow evaporation and cooling experiments. By evaporation, thin squares of FI were obtained from n-butanol and toluene solutions while both FT and fine needles of FIT were obtained from acetone and acetonitrile solutions. In addition, needle-shaped solvate crystals were obtained from acetic acid solutions and the structure of the solvate was solved by single crystal X-ray diffraction. From cooling crystallization experiments, mixtures of FI and FIT were often obtained from various solvents, but FT and FIT possess distinct habits which can be easily distinguished by visual comparison. Slurry conversion experiments have established that FT is the thermodynamically stable polymorph of danthron at ambient conditions. Differntial scanning calorimetry (DSC) and high-temperature powder X-ray diffraction (PXRD) have shown that both FI and FII will transform into a high-temperature form (FIV) around 435 K to 439 K before this form melts at 468.5 K. FI, FIT, and FIV have been characterized by transmission and high-temperature PXRD, scanning electron microscopy, infrared spectrometry, Raman spectrometry, thermogravimetric analysis, and DSC. The solubility of danthron FI in the pure organic solvents of the present work and in the temperature range investigated is below 4.3 % by weight and decreases in the order toluene, acetone, acetonitrile, and n-butanol.
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| 31. |
- Cheuk, Dominic, et al.
(författare)
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Thermodynamics of the Enantiotropic Pharmaceutical Compound Benzocaine and Solubility in Pure Organic Solvents
- 2020
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Ingår i: Journal of Pharmaceutical Sciences. - : Elsevier BV. - 0022-3549 .- 1520-6017. ; 109:11, s. 3370-3377
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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.
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| 32. |
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| 33. |
- Croker, D. M., et al.
(författare)
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Demonstrating the Influence of Solvent Choice and Crystallization Conditions on Phenacetin Crystal Habit and Particle Size Distribution
- 2015
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Ingår i: Organic Process Research & Development. - Washinhton, USA : American Chemical Society (ACS). - 1083-6160 .- 1520-586X. ; 19:12, s. 1826-1836
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Tidskriftsartikel (refereegranskat)abstract
- Phenacetin was used as a model pharmaceutical compound to investigate the impact of solvent choice and crystallization conditions on the crystal habit and size distribution of the final crystallized product. The crystal habit of phenacetin was explored using crash-cooling crystallization (kinetically controlled) and slow evaporative crystallization (thermodynamically controlled) in a wide range of organic solvents. In general, a variety of needle-type shapes (needles, rods, or blades) were recovered from fast-cooling crystallizations, in contrast to hexagonal blocks obtained from slow evaporative crystallizations. The solubility of phenacetin was measured in five solvents from 10-70 degrees C to allow for the design of larger-scale crystallization experiments. Supersaturation and the nucleation temperature were independently controlled in isothermal desupersaturation experiments to investigate the impact of each on crystal habit and size. The crystal size (needle cross-sectional area) decreased with increasing supersaturation because of higher nucleation rates at higher supersaturation, and elongated needles were recovered: Increasing the nucleation temperature resulted in the production of larger crystals with decreased needle aspect ratios. Antisolvent phenacetin crystallizations were developed for three solvent/antisolvent systems using four different antisolvent addition rates to simultaneously probe the crystal habit and size of the final product. In general, increasing the antisolvent addition rate, associated with increased rate of generation of supersaturation, resulted in the production of shorter needle crystals.
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| 34. |
- Croker, D. M., et al.
(författare)
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Isothermal suspension conversion as a route to cocrystal production : One-pot scalable synthesis
- 2014
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Ingår i: Organic Process Research & Development. - : American Chemical Society (ACS). - 1083-6160 .- 1520-586X. ; 18:8, s. 941-946
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Tidskriftsartikel (refereegranskat)abstract
- Isothermal suspension conversion is presented as a suitable method for the manufacture of pure cocrystal products once the ternary phase diagram (TPD) for the cocrystal system in the desired solvent is available. One:one and 3:2 cocrystals of p-toluenesulphonamide/triphenylphosphine oxide were produced in acetonitrile and dichloromethane using this method. Eight individual batches of product were prepared with complete conversion to pure product achieved in seven batches. Product recovery (77-99%), reaction conversion (17-89%), and volumetric productivity (0.03-0.63 g/cm(3)) were calculated for each product batch. These parameters are essentially determined by the batch operating mass fraction composition selected from the TPD, allowing for tailoring of processing conditions to suit process requirements and capabilities by careful selection of the optimum operating mass fraction composition.
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| 35. |
- Croker, D. M., et al.
(författare)
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Nucleation in the p-toluenesulfonamide/triphenylphosphine oxide co-crystal system
- 2013
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 13:8, s. 3754-3762
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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
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| 36. |
- Croker, D. M., et al.
(författare)
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Solution mediated phase transformations between co-crystals
- 2013
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Ingår i: CrystEngComm. - : Royal Society of Chemistry. - 1466-8033. ; 15:11, s. 2044-2047
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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.
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| 37. |
- Croker, Denise, et al.
(författare)
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Understanding the p-toluenesulfonamide / triphenylphosphine oxide crystal chemistry: a new 1:1 cocrystal and ternary phase diagram
- 2012
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 12:2, s. 869-875
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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.
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| 38. |
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| 39. |
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| 40. |
- Diniz, Mariana O., et al.
(författare)
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New Solid Forms of Griseofulvin : A Solvate and a Relict Polymorph Related to Reported Solvates
- 2023
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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.
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| 41. |
- Fichtner, Frauke, et al.
(författare)
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Effect of preparation method on compactability of paracetamol granules and agglomerates
- 2007
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Ingår i: International Journal of Pharmaceutics. - : Elsevier BV. - 0378-5173 .- 1873-3476. ; 336:1, s. 148-158
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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.
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| 42. |
- Fichtner, Frauke, 1975-
(författare)
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Identification and Variation of some Functionality Related Characteristics of Pharmaceutically Relevant Solid Materials and their Effect on Product Performance
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis was to identify some functionality related characteristics of pharmaceutically relevant solid materials and to study the effect of their variation on processing behaviour and product performance. For this purpose, particles with different characteristics were prepared under a variety of conditions by crystal agglomeration, wet granulation and spray drying. The effect of particle size distribution on the evolution of the tablet microstructure during and after compression was investigated. The compression behaviour of particles with different nominal strength and degrees of agglomeration was studied and the influence of the surfactant concentration of amorphous particles on the compression behaviour was examined. The response of the powders to compression was described with the help of various techniques characterising the microstructure and tensile strength of the tablets produced. Furthermore, a method suitable for observing drug release from single matrix granules was developed and used to study the effect of granule porosity and compaction pressure on the drug release process. The particle size distribution did not influence the evolution of the tablet porosity or the tensile strength during compression, but it could have an effect on the evolution of the tablet microstructure during short-term storage, depending on the instability mechanism. The compression behaviour of particles prepared by crystal agglomeration and wet granulation was dependent on their degree of agglomeration and their failure strength. For particles with similar solid state properties and compression behaviour, the surface energy appears to have an effect on the bonding strength of adsorption bonds acting at interparticulate junctions. Using the method developed to observe the drug release from single matrix granules, reproducible data was obtained enabling the drug release process to be characterised. Depending on the type of matrix and the compaction pressure, the drug release rate could be enhanced or retarded.
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| 43. |
- Fichtner, Frauke, et al.
(författare)
-
Particle size distribution and evolution in tablet structure during and after compaction
- 2005
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Ingår i: International Journal of Pharmaceutics. - : Elsevier BV. - 0378-5173 .- 1873-3476. ; 292:02-jan, s. 211-225
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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.
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| 44. |
- Forsberg, Kerstin, et al.
(författare)
-
Crystal growth kinetics of iron fluoride trihydrate
- 2006
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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). .
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| 45. |
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| 46. |
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| 47. |
- Forsberg, Kerstin, 1979-
(författare)
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Crystallization of Metal Fluoride Hydrates from Mixed Acid Solutions
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this work crystal growth and nucleation of b-FeF3×3H2O and crystallization of chromium (III), iron (III) and nickel (II) fluoride hydrates from mixed acid (1-3 mol/kg HNO3 and 1-6 mol/kg free HF) have been investigated. The solubility of b-FeF3×3H2O has been determined in solutions of different hydrofluoric acid (1-7mol/ kg) and nitric acid (0-7mol/ kg) concentrations at 30, 40 and 50°C. The total iron concentration at equilibrium ranges from about 1 to 35 g/kg solution. In the range of investigated conditions the solubility in terms of total iron content increases with increasing temperature and decreases with increasing concentration of hydrofluoric acid and nitric acid. The results are analysed by examining the chemical speciation in the solutions. The crystal growth kinetics of b-FeF3×3H2O crystals have been studied by performing seeded isothermal desupersaturation experiments in solutions of 1.5-3.0 mol/ kg nitric acid and 1.4- 5.6 mol/ kg free hydrofluoric acid at 30, 40 and 50°C. The results show that the crystal growth is surface integration controlled. When the driving force is based on a proper speciation no clear correlation of the growth rate with hydrofluoric acid or nitric acid concentration is found. The rate is about the same in industrial pickle liquor as in pure acid solutions. The growth rate at a supersaturation ratio (c(FeF3)free/cs(FeF3)free) of 2 was found to be 5.2×10-12m/s at 30°C, 7.9×10-12m/s at 40°C and 20×10-12m/s at 50°C. Thus, the crystal growth rate at 50°C is about four times higher than at 30°C. The temperature dependence of the rate constant corresponds to an activation energy of 55kJ/ mol. Crystallization from solutions supersaturated with both Cr(III) and Fe(III) has been investigated and it has been observed that Fe(III) and Cr(III) crystallizes in the form of Cr(Fe)F3×3H2O which is isostructural with CrF3×3H2O. Iron(III) and nickel(II) crystallizes into an unidentified fluoride hydrate crystal. The crystal growth rate of CrF3×3H2O at 50°C is about the same as the growth rate of b-FeF3×3H2O crystals.
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| 48. |
- Forsberg, Kerstin, et al.
(författare)
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Crystallization of metal fluoride hydrates from mixed hydrofluoric and nitric acid solutions, Part I : Iron (III) and Chromium (III)
- 2010
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 312:16-17, s. 2351-2357
-
Tidskriftsartikel (refereegranskat)abstract
- Crystallization from hydrofluoric acid/nitric acid solutions supersaturated with Fe(III) and Cr(III) has been investigated. Iron and chromium crystallizes into a solid solution in the form of Cr(Fe)F-3 center dot 3H(2)O, which is isostructural with CrF3 center dot 3H(2)O and alpha-FeF3 center dot 3H(2)O. By seeded isothermal desupersaturation experiments, the growth rate of beta-FeF3 center dot 3H(2)O crystals at 50 degrees C has been studied in hydrofluoric acid and nitric acid solutions containing Cr(III). It is found that the growth rate of beta-FeF3 center dot 3H(2)O is essentially uninfluenced by the presence of 5 g/kg Cr(III). At 50 degrees C and a supersaturation ratio of 2 (c(FeF3)(free)/c(s)(FeF3)(free)), the growth rate is (0.8-2.2) x 10(-11) m/s in 3 mol/(kg solution) HFfree and 3 mol/(kg solution) HNO3.
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| 49. |
- Forsberg, Kerstin, et al.
(författare)
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Crystallization of metal fluoride hydrates from mixed hydrofluoric and nitric acid solutions, part II : Iron (III) and nickel (II)
- 2010
-
Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 312:16-17, s. 2358-2362
-
Tidskriftsartikel (refereegranskat)abstract
- Crystallization of nickel fluoride hydrate from mixed pickle acid and the influence of Ni(II) on growth rate of beta-FeF3 center dot 3H(2)O have been studied. Iron and nickel crystallize into an unidentified Fe/Ni fluoride hydrate crystal having the overall mol ratio of Ni, Fe, and F equal to 1:2:8, which is in accordance with the number of fluoride ions needed to balance the positive charges of Ni and Fe. The most probable empirical formula of this material is (FeF3)(2)NiF2(H2O)(6-10). By seeded isothermal desupersaturation experiments, growth rate of beta-FeF3 center dot 3H(2)O crystals at 50 degrees C has been studied in a hydrofluoric acid and nitric acid solution containing Ni(II). It is found that the growth rate of beta-FeF3 center dot 3H(2)O is essentially uninfluenced by the presence of 4 g/kg Ni(II).
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| 50. |
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