| 1. |
- Albers, E, et al.
(författare)
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Continuous estimation of product concentration with calorimetry and gas analysis during anaerobic fermentations of Saccharomyces cerevisiae
- 2002
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Ingår i: Thermochimica Acta. - 0040-6031. ; 394:1-2, s. 185-190
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Tidskriftsartikel (refereegranskat)abstract
- Product concentrations may be estimated from gas analysis or calorimetric measurements. These techniques of analysis are fast, simple, and provide a continuous output. To check the accuracy of these estimations, the anaerobic ethanol formation of an industrial strain of the yeast Saccharomyces cerevisiae was selected as a test system. Cultivations were carried out as batch cultures with different nitrogen sources (ammonium, glutamate and a mixture of amino acids) and 20 g/l of glucose as the carbon and energy source. The results showed that there was a good agreement between measured and calculated ethanol values. However, especially when using heat data the results are very sensitive to small changes in the stoichiometry of the catabolic reaction, i.e. ethanol is not the only product but there are also minor amounts of glycerol and acetate. The problems generated by these products when using heat data to calculate ethanol concentrations are discussed in detail. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 2. |
- Bastos, M, et al.
(författare)
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A new dissolution microcalorimeter: calibration and test
- 2003
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Ingår i: Thermochimica Acta. - 0040-6031. ; 405:1, s. 21-30
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Tidskriftsartikel (refereegranskat)abstract
- A new batch microcalorimetric vessel for the determination of enthalpies of dissolution of small amounts of easily or slightly soluble solids was developed at University of Lund, Sweden and was tested at University of Porto, Portugal. The vessel forms part of a series of twin heat conduction microcalorimeters. In a series of consecutive dissolution steps up to four samples, each 0.1-3 mg, can be injected into a solvent chamber of the vessel, volume 20 ml. The high stability of the baseline allows solution experiments to be extended over several hours.All measurements reported were conducted at 298.15 K and with water as the solven . The calorimeter was calibrated chemically by dissolution of potassium chloride. The performance of the instrument was further tested by measurements of the enthalpies of dissolution of acetanilide and adenine, 18.25 +/- 0.56 and 31.78 +/- 0.64 kJ mol(-1), respectively. No concentration dependence was found. The results are in good agreement with values in the literature. (C) 2003 Elsevier Science B.V. All rights reserved.
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| 3. |
- Markova, N, et al.
(författare)
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On application of an isothermal sorption microcalorimeter
- 2001
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Ingår i: Thermochimica Acta. - 0040-6031. ; 374:2, s. 93-104
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Tidskriftsartikel (refereegranskat)abstract
- A wide scope of application of a novel isothermal sorption microcalorimeter is presented. With the technique, it is possible to simultaneously and independently in one experiment obtain the sorption isotherm of a sample along with the corresponding differential enthalpies of sorption. The method is suited for measurements with water vapor as well as organic vapors and has been tested at temperatures between 25 and 40°C. The technique is suitable for the thermodynamic characterization of the sorption process. It is demonstrated that the method can be applied to the study of a wide range of physico-chemical phenomena associated with the uptake of vapor by a substance/material including capillary condensation, crystallization, lyotropic phase transitions and hydrate/solvate formation. The calorimetric data are reproducible and agree well with the results of well-established techniques such as solution calorimetry, differential scanning calorimetry, sorption microbalance and osmotic stress measurements.
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| 4. |
- Marques, Eduardo, et al.
(författare)
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A calorimetric study of the gel-to-liquid crystal transition in catanionic surfactant vesicles
- 2002
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Ingår i: Thermochimica Acta. - 0040-6031. ; 394:1-2, s. 31-37
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Tidskriftsartikel (refereegranskat)abstract
- Dilute solutions of catanionic vesicles formed by the mixed single-chained (sodium dodecylsulphate, SDS) and double-chained (didodecyldimethylammonium bromide, DDAB) surfactants have been investigated by differential scanning calorimetry. It is for the first time reported a gel-to-liquid crystal phase transition temperature, T-m, in this type of mixed vesicles. The SDS-rich vesicles (at X-SDS = 0.71) show a concentration-dependent T-m in the range 9-16 degreesC. Addition of salt is seen to have an effect on T-m similar to that observed with increasing surfactant concentration, both inducing a decrease in T-m. These results differ from those obtained for neat DDAB vesicles. The observed effects in the two types of vesicles are rationalised in terms of headgroup electrostatic interactions which may have influence on the chain packing and phase transition temperature.
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| 5. |
- Mattisson, Tobias, 1970, et al.
(författare)
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The reaction between limestone and SO2 under periodically changing oxidizing and reducing conditions - Effect of temperature and limestone type
- 1999
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Ingår i: Thermochimica Acta. - 0040-6031. ; 325:1, s. 59-67
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Tidskriftsartikel (refereegranskat)abstract
- The reaction between limestone and SO2 was investigated under both oxidizing and periodically changing oxidizing and reducing conditions at atmospheric pressure in a fixed-bed quartz reactor. Three limestones of different reactivities were sulfated at temperatures between 800 degrees and 875 degrees C with a gas mixture of 1500 ppm SO2, 10% CO2 and alternating O-2 and CO (0% or 4%). The experimental data found that periodically changing oxidizing and reducing conditions could have either a positive or a negative effect on the degree of conversion of CaO to CaSO4 compared to limestone samples sulfated under constant oxidizing conditions. In the temperature range 825-875 degrees C the conversion was relatively constant for all three limestones under oxidizing conditions. However, when the limestone samples were sulfated with periodically changing oxidizing and reducing gas mixtures a wide range of conversions were found. The highest degree of conversion was found at 825 degrees C for all three limestones and the lowest degree of conversion was found at 875 degrees C. The rapid decrease in conversion at high temperatures was due to the rapid release of SO2 due to both the decomposition of CaSO4 as well as a high rate of CaS oxidation. A comparison of the sulfation rates of several experiments performed with Koping limestone under alternating conditions showed a wide range of rates, indicating the difficulties in using laboratory rate data in sulfur capture modelling for fluidized-bed boilers.
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| 6. |
- Wadsö, Ingemar, et al.
(författare)
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A new general-purpose isothermal microcalorimeter for use at temperatures up to 200 degrees C
- 2003
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Ingår i: Thermochimica Acta. - 0040-6031. ; 405:1, s. 15-20
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Tidskriftsartikel (refereegranskat)abstract
- The design and some properties of a new general-purpose isothermal microcalorimeter are reported. The instrument is a twin thermopile heat conduction calorimeter, which is designed for use up to 200 degreesC. The calorimetric units and surrounding heat sink are suspended inside a hollow aluminium construction, which is thermostated. Above that unit a second thermostated block is positioned and the whole assembly is suspended inside a Dewar vessel. When the instrument is used at room temperature and below, the thermostated units are cooled by use f an insertion Peltier effect cooler. The instrument can be used with a wide range of different reaction vessels (diameter 14 mm). Baseline experiments have been conducted in the temperature range 15-200 degreesC. Typical values obtained during 10 h periods at 200 degreesC are +/-3 and +/-10 nW for the baseline drift and baseline fluctuations, respectively. The heat detection limit, determined by release of electrical energy, is about 2 muJ. Preliminary stability measurements have been conducted at 100 degreesC on samples of stabilised and non-stabilised polyamide film. (C) 2003 Elsevier Science B.V. All rights reserved.
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| 7. |
- Wadsö, Ingemar, et al.
(författare)
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A new method for determination of vapour sorption isotherms using a twin double microcalorimeter
- 1996
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Ingår i: Thermochimica Acta. - : Elsevier BV. - 0040-6031. ; 271, s. 179-187
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Tidskriftsartikel (refereegranskat)abstract
- A new twin heat conduction microcalorimeter for the study of vapour sorption isotherms, sorption enthalpies and the kinetics of sorption has been developed. Each calorimeter has two calorimetric vessels which are connected by a steel tube. The upper vessel (a vaporization chamber) is charged with a vapour forming liquid and the lower vessel (a sorption chamber) contains the sorbent sample. An identical double calorimeter serves as a reference. During a measurement, the liquid in the upper vessel will vaporize and is allowed to diffuse to the sorption vessel. Thermal powers of vaporization and sorption are measured separately. The rate of vapour flow is obtained from a known value for the enthalpy of vaporization. Assuming equilibrium conditions and applying Fick's law of diffusion makes it possible to calculate the sorption isotherm. Results from test measurements of water vapour sorption on samples of crystalline NaCl and KCl in saturated aqueous solution and on cotton wool are presented.
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| 8. |
- Wadsö, Ingemar
(författare)
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Isothermal microcalorimetry in applied biology
- 2002
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Ingår i: Thermochimica Acta. - 0040-6031. ; 394:1-2, s. 305-311
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Tidskriftsartikel (refereegranskat)abstract
- Techniques of isothermal microcalorimetry have been much improved during the past two decades. In addition to their use in fundamental research, applications of practical importance have been established in some areas. However, no significant use of isothermal microcalorimetry has yet been seen in practical applications of biology, despite many methodological studies reported from that area. The main problem appears to be that the sample throughput of isothermal microcalorimeters is low compared to other techniques used in that field. Further, the non-specificity of calorimetric signals is in some cases a serious limitation. Significant progress has recently been made in the design of multi-channel isothermal microcalorimeters and in techniques where specific analytical methods have been combined with isothermal microcalorimeters. Some conclusions will be drawn with respect to the use of these techniques in applied work on living materials.
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| 9. |
- Wadsö, Lars, et al.
(författare)
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A double twin isothermal microcalorimeter
- 2000
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Ingår i: Thermochimica Acta. - 0040-6031. ; 360:2, s. 101-107
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Tidskriftsartikel (refereegranskat)abstract
- The design and properties of a double twin heat conduction microcalorimeter are described. In this instrument two twin microcalorimeters are placed close together, one on top of the other. The size of the instrument is the same as that of a commercial single twin microcalorimeter and each of the twin parts has similar properties as one normal twin microcalorimeter. The cross-talk between the calorimeters can be made low; we measured <0.1% of the signal generated in one calorimeter in the other calorimeter. This figure is, however, dependent on how well the two sides of the instrument are thermally balanced. The paper also contains a general discussion of the use of a reference in reducing the effect of temperature changes in the heat sink. The advantage with a double calorimeter is that one may easily perform two related calorimetric experiments at the same time and in close proximity to each other, e.g. both sorption isotherms and sorption enthalpies may be measured simultaneously, or the heat production rate of a biological process may be monitored at the same time as the CO2 production is measured.
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| 10. |
- Wadsö, Lars
(författare)
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Temperature changes within samples in heat conduction calorimeters
- 2000
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Ingår i: Thermochimica Acta. - 0040-6031. ; 366:2, s. 121-127
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Tidskriftsartikel (refereegranskat)abstract
- So-called isothermal calorimeters are often built on the heat conduction principle. This may sound as a contradiction, as heat conduction is a result of non-isothermal conditions, but most measurements with microcalorimeters and other such instruments are essentially isothermal as the temperature differences within the instruments are in the order of 10 mK. This paper presents simple methods to estimate the temperature changes within a sample in a heat conduction calorimeter during a measurement. It also shows that the determination of activation energy is normally not disturbed by these small temperature changes. In addition to the heat production rate in the sample, the thermal properties of the sample and the calorimeter are needed as input to the calculations.
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