| 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. |
- 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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| 3. |
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| 4. |
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| 5. |
- Gracin, Sandra, et al.
(författare)
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Controlling polymorphism of p-aminobenzoic acid by sonication
- 2005
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Ingår i: the 16th International Symposium on Industrial Crystallization. - : VDI verlag Dusseldorf. ; , s. 677-682
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Konferensbidrag (refereegranskat)abstract
- The influence of ultrasound on the nucleation of p-aminobenzoic acid in supersaturated aqueous solutions has been investigated. The induction time and the solid phase structure has been determined in experiments with and without ultrasound. Different sonication schemes and intensities have been evaluated. It is found that sonication leads to a much shorter and reproducible induction time. In addition, it has been found that sonication preferentially favor the formation of one of the polymorphs.
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| 6. |
- Hammer-Olsson, Roy, et al.
(författare)
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Method of purifying potassium hydroxide
- 2007
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Patent (populärvet., debatt m.m.)abstract
- Method of purifying potassium hydroxide comprising (a) providing a solution of saturated potassium hydroxide solution having a temperature in the range from about -25 to about 60 0C (b) controling the temperature of the solution in such a way that the variation in temperature is in a range from about 0 to about 5 °C/h to form crystals of potassium hydroxide (c) separating the crystals from the solution.
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| 7. |
- Maher, Anthony, et al.
(författare)
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Solubility of form III piracetam in a range of solvents
- 2010
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Ingår i: Journal of Chemical and Engineering Data. - : American Chemical Society (ACS). - 0021-9568 .- 1520-5134. ; 55:11, s. 5314-5318
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Tidskriftsartikel (refereegranskat)abstract
- The polymorph known as Form III of 2-oxo-1-pyrrolidine acetamide (piracetam) was isolated by cooling crystallization from methanol and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). Form III is the thermodynamically stable polymorph of piracetam in the range of this solubility study. The solubility of Form III was determined by gravimetrically measuring the amount of Form III which was contained in a volume of saturated solution over the temperature range (278 to 323) K, following evaporation of the solvent. Five solvents were examined: methanol, ethanol, 2-propanol, acetone, and 1,4-dioxane. The results showed that the solubility values correlated positively with solvent polar characteristics from a qualitative point of view; an increase in solubility of Form 111 was observed with increasing solvent polarity and solvent acidity. As the number of carbons in the n-alcohols increases, the polarity of the solvent and its hydrogen donation ability decreases and so does the solubility of Form III in the solvent. 1,4-Dioxane and acetone are relatively nonpolar and non-hydrogen bond donating solvents compared to the n-alcohols, and accordingly Form III is much less soluble in these.
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| 8. |
- Munroe, Aina, et al.
(författare)
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Analysis of FII crystals of Sulphathiazole : Epitaxial growth of FII on FIV
- 2011
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Ingår i: CrystEngComm. - : Royal Society of Chemistry (RSC). - 1466-8033. ; 13:3, s. 831-834
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Tidskriftsartikel (refereegranskat)abstract
- This work describes the phenomenon of a less stable polymorph wedged as a middle layer in a more stable polymorph of sulfathiazole. Isolation of the pure FII polymorph of sulfathiazole consistently yielded crystals with a distinctive middle layer. Raman spectroscopy and X-ray diffraction have identified this middle layer as another polymorph of sulfathiazole, namely FIV. The solubilities of FII and FIV sulfathiazole are almost identical, with FIV slightly more soluble. It is thought that this causes FIV to nucleate first, followed by the epitaxial growth of FII. A morphological examination of the crystals demonstrated that the (100) face of the FII crystal matches the (101) face of the FIV crystal. It is proposed that the similarity of these faces supports the epitaxial growth of the FII polymorph on the surface of the FIV polymorph.
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| 9. |
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| 10. |
- Nordström, Fredrik, et al.
(författare)
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Phase equilibria and thermodynamics of hydroxybenzoic acid isomers
- 2005
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Ingår i: 16th International Symposium on Industrial Crystallization, Volym 3. - : V D I Verlag GmbH. ; , s. 35-40
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Konferensbidrag (refereegranskat)abstract
- Thermodynamics of ortho-, meta- and para-hydroxybenzoic acid have been investigated. Thermodynamic data were acquired through determination of solubility, enthalpy of fusion and melting temperature. The solubility of polymorphic and solvated modifications of the isomers have been determined by comprehensive measurements between 10 and 50°C in acetonitrile, acetic acid and acetone. For each isomer and modification a strong correlation was obtained between solubility and the van't Hoff enthalpy of solution. These trends were attributed to both solution and solid-state properties. The observed correlations could also be used to differentiate between solid phases.
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| 11. |
- Nordström, Fredrik, et al.
(författare)
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Primary nucleation of salicylamide
- 2008
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Ingår i: Proc. 17’th International Symposium on Industrial Crystallization. ; , s. 713-720
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 12. |
- O'Mahony, Marcus, et al.
(författare)
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Examining Solution and Solid State Composition for the Solution Mediated Polymorphic Transformation of Carbamazepine and Piracetam
- 2012
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505.
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Tidskriftsartikel (refereegranskat)abstract
- Solution-mediated polymorphic transformations (SMPT) of the pharmaceutical compounds carbamazepine and piracetam have been investigated. Seeded transformation experiments were performed, and the solution concentration was monitored by in situ infrared spectroscopy using a calibration free method. Solid samples were also taken over time, and the percentage of metastable and stable polymorphic phases were determined using off line quantitative powder X-ray diffraction analysis. Solution and solid state data were compared for each compound. In the case of carbamazepine, the SMPT from FI to FIII was identified as being controlled by the growth of the stable FIII polymorph. For piracetam, the SMPT was also identified as being controlled by growth of the stable polymorph, but with a more considerable induction time for nucleation of the stable phase. This paper demonstrates how the rate determining steps of the SMPT can be identified if both solution and solid phase data are recorded. The results are compared with other studies reported in the literature and rationalized into four principal scenarios.
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| 13. |
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| 14. |
- Thati, Jyothi, et al.
(författare)
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Particle engineering of benzoic acid by spherical agglomeration
- 2012
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Ingår i: European Journal of Pharmaceutical Sciences. - : Elsevier BV. - 0928-0987 .- 1879-0720. ; 45:5, s. 657-667
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Tidskriftsartikel (refereegranskat)abstract
- The influence of process conditions on the properties of benzoic acid spherical agglomerates, are investigated. Agglomerates are produced in a fed-batch agitated tank process. Benzoic acid is dissolved in ethanol and the solution is mixed with the bridging liquid, before being fed into an agitated aqueous solution. A broader investigation has been performed using heptane as the bridging liquid, and in further experiments different bridging liquids are compared. The results show that the bridging liquid has an influence on the product properties, with diethyl ether and ethyl acetate being at the extreme end with no agglomerates formed at all. Using any of the other five solvents (chloroform, toluene, heptane, pentane, or cyclohexane) spherical agglomerates are formed, as long as a sufficient amount of the bridging liquid is used. The results show that the particle size and strength increase with increasing amount of bridging liquid, and with decreasing temperature. At amount of bridging liquid producing optimum particle shape, the largest agglomerates are produced when using either cyclohexane operating at 5 degrees C, or using toluene in a process at 20 degrees C. The highest particle fracture stress is obtained using toluene as the bridging liquid regardless of temperature. The particle shape depends on the bridging liquid, and becomes completely spherical when toluene or pentane is used. For four of the solvents the particle morphology improves with decreasing temperature, but for cyclohexane the result is the opposite. By continued agitation beyond the completion of the feeding, particle size and strength gradually increases and also the shape gradually becomes more spherical. High compressibility and low elastic recovery suggest that the particles are favorable for direct tabletting. The results are analyzed and discussed against capillary theory and granulation mechanisms.
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| 15. |
- Yang, Huaiyu, et al.
(författare)
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Thermodynamics of molecular solids in organic solvents
- 2012
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Ingår i: Journal of Chemical Thermodynamics. - : Elsevier BV. - 0021-9614 .- 1096-3626. ; 48, s. 150-159
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Tidskriftsartikel (refereegranskat)abstract
- The thermodynamics of solid-solution solubility are examined using data for two different compounds: butyl paraben and benzoic acid. Solubility data in different solvents are used to estimate melting properties of the pure solid solutes, and are used to estimate the solid state Gibbs free energy relative to the super cooled melt. The relation to melting data experimentally determined is analysed, and solution activity coefficients are calculated. The work shows that there is a strong relation between solid-liquid solubility data and thermodynamic data of the pure solute. For these compounds, the melting temperature of the pure solute can be fairly accurately estimated by extrapolation of solid-liquid solubility data up to mole fraction equal unity. The estimation of the melting enthalpy is less successful showing deviations in the order of 20% to 30% from the experimental values determined by differential scanning calorimetry. For butyl paraben and benzoic acid, the best estimation of the solid state Gibbs free energy is obtained if DSC determination of melting properties is combined with an estimation of the melt-solid heat capacity difference versus temperature relation by correlation to solubility data.
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