Semi-batch reactors are widely spread in the fine chemicals and specialties industry. The reason is that, compared to the
pure batch operation, the feed of at least one of the reactants provides an additional way of controlling the reaction course,
which represents a safety factor and increases the constancy of the product quality. Process temperature and feed rate can
be optimized to satisfy safety constraints, i.e. cooling capacity and allowable accumulation. An economically better way of
operating a semi-batch reactor is to adapt the feed rate to the allowed accumulation of reactants. An experimental method
based on calorimetry will be presented and illustrated by an example.
Authors:K. Ishikiriyama, A. Boller, and B. Wunderlich
The melting and crystallization of a sharply melting standard has been explored for the calibration of temperature-modulated
differential scanning calorimetry, TMDSC. Modulated temperature and heat flow have been followed during melting and crystallization
of indium. It is observed that indium does not supercool as long as crystal nuclei remain in the sample when analyzing quasi-isothermally
with a small modulation amplitude. For standard differential scanning calorimetry, DSC, the melting and crystallization temperatures
of indium are sufficiently different not to permit its use for calibration on cooling, unless special analysis modes are applied.
For TMDSC with an underlying heating rate of 0.2 K min−1 and a modulation amplitude of 0.5–1.5 K at periods of 30–90 s, the extrapolated onsets of melting and freezing were within
0.1 K of the known melting temperature of indium. Further work is needed to separate the effects originating from loss of
steady state between sample and sensor on the one hand and from supercooling on the other.
The quality of measurement of heat capacity by differential scanning calorimetry (DSC) is based on strict symmetry of the
twin calorimeter. This symmetry is of particular importance for temperature-modulated DSC (TMDSC) since positive and negative
deviations from symmetry cannot be distinguished in the most popular analysis methods. The heat capacities for sapphire-filled
and empty aluminum calorimeters (pans) under designed cell imbalance caused by different pan-masses were measured. In addition,
the positive and negative signs of asymmetry have been explored by analyzing the phase-shift between temperature and heat
flow for sapphire and empty runs. The phase shifts change by more than 180° depending on the sign of the asymmetry. Once the
sign of asymmetry is determined, the asymmetry correction for temperature-modulated DSC can be made.
Authors:Elena Boldyreva, V. Drebushchak, I. Paukov, Yulia Kovalevskaya, and Tatiana Drebushchak
Monoclinic (I) and orthorhombic (II) polymorphs of paracetamol were studied by DSC and adiabatic calorimetry in the temperature
range 5 - 450 K. At all the stages of the study, the samples (single crystals and powders) were characterized using X-ray
diffraction. A single crystal → polycrystal II→ I transformation was observed on heating polymorph II, after which polymorph
I melted at 442 K. The previously reported fact that the two polymorphs melt at different temperatures could not be confirmed.
The temperature of the II→I transformation varied from crystal to crystal. On cooling the crystals of paracetamol II from
ambient temperature to 5 K, a II→ I transformation was also observed, if the 'cooling-heating' cycles were repeated several
times. Inclusions of solvent (water) into the starting crystals were shown to be important for this transformation. The values
of the low-temperature heat-capacity of the I and II polymorphs of paracetamol were compared, and the thermodynamic functions
calculated for the two polymorphs.
This study examines the polymerization of dental monomers catalyzed by synthesized acylphosphine oxides in a differential
scanning calorimetry (DSC) cell. This research focuses on establishing a relationship between radicals generated by the acylphosphine
oxide photoinitiators and the kinetic reaction rates of methyl methacrylate (MMA) and acrylamide (ACM), a model monomer. The
thermal stability of mono- and di-acylphosphine oxides was examined by DSC. Endothermic melting and exothermic polymerization
reactions initiated with the two initiators were recorded. The acrylamide model system laid the ground work for the critical
evaluation of the synthesized new initiators of mono (2,4,6-trimethylbenzoyl) diphenylphosphine oxide, and bis(2,4,6-trimethylbenzoyl)
phenylphosphine oxide. The bis(acyl) phosphine oxide photoinitiator was more reactive than the mono-(acyl) phosphine oxide
with methyl methacrylates under laboratory conditions. In exothermic reactions, temperatures rose higher and more rapidly
for bis(acyl) phosphine oxide initiated reactions than mono-(acyl) phosphine oxide initiated reactions.
Isothermal titration calorimetry (ITC) has been used to develop a method to construct the solid-liquid equilibrium line in
ternary systems containing the solute to precipitate and an aqueous mixed solvent. The method consists in measuring the heat
of dissolution of a solid component (the solute) during successive additions of the liquid solvent. The cumulated heat, resulting
from the successive heat peaks obtained for the different injections of known volumes of solvent, plotted vs. the ratio of the numbers of moles nsolvent/nsolute is represented by two nearly straight lines. The intercept of the two lines gives the solubility limit and the corresponding
enthalpy of dissolution of the solute in the solvent.
Solubility diagrams have been established at 303.15 K in binary mixed solvents ethanol-water over the whole concentration
range for seven compounds of pharmaceutical interest, namely: urea, phenylurea, l-valine, dl-valine, l-valine ethyl ester hydrochloride, tris(hydroxymethyl)amino methane.
Heat divided by ligand concentration vs. heat, similar to the Scatchard plot, was introduced to obtain the equilibrium constant
(K) and the enthalpy of binding (DH) using isothermal titration calorimetry data. Values of K and DH obtained by this linear
pseudo-Scatchard plot for a system with a set of independent binding sites (such as binding fluoride ions on urease and monosaccharide
methyl a-D-mannopyranoside on concavalin A) were remarkably like that obtained from a normal fitting Wiseman method and other
our technical methods. On applying this graphical method to study the binding of copper ion on myelin basic protein (MBP),
a concave downward curve obtained was consistent with the positive cooperativity in the binding. A graphical fitting by simple
method for determination of thermodynamic parameters was also introduced. This method is general, without any assumption and
restriction made in previous method. This general method was applied to the product inhibition study of adenosine deaminase.
of polyurethane formation between several polyols and isocyanates with dibutyltin
dilaurate (DBTDL) as the curing catalyst, were studied in the bulk state by
differential scanning calorimetry (DSC) using an improved method of interpretation.
The molar enthalpy of urethane formation from secondary hydroxyl groups and
aliphatic isocyanates is 723 kJ mol-1
and for aromatic isocyanates it is 552 kJ mol-1
. In the case of a single second order reaction for aliphatic isocyanates
reaction, activation energy is 705 kJ mol-1
with oxypropylated polyols and 503 kJ mol-1
with Castor oil. For aromatic isocyanates and oxypropylated polyols the activation
energy is higher around 77 kJ mol-1 .
In the case of two
parallel reactions (situation for IPDI and TDI 2-4) best fits are observed
considering two different activation energies.
Authors:D. Živković, Ž. Živković, L. Yonghua, and K. Chou
Results of the comparative thermodynamic analysis of the Pb-BixMgySbz section (x:y:z=8:1:1, in mole ratio) in the Pb-Bi-Mg-Sb system, obtained experimentally by Oelsen calorimetry and predicted by general solution
model in the temperature range 600–1100 K, are given in this paper.
The thermal polymerization of inhibited styrene monomer is investigated by Accelerating Rate Calorimetry (ARC). The time-temperature-pressure data generated by this technique are utilized in evaluating the thermal hazards associated with the industrial processing of styrene monomer. Several examples are given on the interpretation and application of ARC data to environments ranging from lab to plant-scale conditions including discussions concerning the similarities and dissimilarities between the ARC and large-scale equipment. The polymerization of styrene monomer is also used to evaluate the performance of the ARC over a broad temperature range, 80–300°C. The data indicate that removal of the radiant heater assembly yields better agreement between the heat of polymerization of styrene as measured by the ARC and corresponding values from the literature. This effect is believed to be observable only under conditions of low reaction rates for long periods of time such as in the case of styrene monomer.