Highly concentrated solution

A typical flow diagram for pentaerythritol production is shown in Figure 2. The main concern in mixing is to avoid loss of temperature control in this exothermic reaction, which can lead to excessive by-product formation and/or reduced yields of pentaerythritol (55,58,59). The reaction time depends on the reaction temperature and may vary from about 0.5 to 4 h at final temperatures of about 65 and 35°C, respectively. The reactor product, neutralized with acetic or formic acid, is then stripped of excess formaldehyde and water to produce a highly concentrated solution of pentaerythritol reaction products. This is then cooled under carefully controlled crystallization conditions so that the crystals can be readily separated from the Hquors by subsequent filtration. 

Formaldehyde is produced and sold as water solutions containing variable amounts of methanol. These solutions are complex equiUbrium mixtures of methylene glycol, CH2(OH)2, poly(oxymethylene glycols), and hemiformals of these glycols. Ultraviolet spectroscopic studies (13—15) iadicate that even ia highly concentrated solutions the content of unhydrated HCHO is <0.04 wt%. 

Larch gum is readily soluble in water. The viscosity of these solutions is lower than that of most other natural gums and solutions of over 40% soHds are easily prepared. These highly concentrated solutions are also unusual because of their Newtonian flow properties. Larch gum reduces the surface tension of water solutions and the interfacial tension existing in water and oil mixtures, and thus is an effective emulsifying agent. As a result of these properties, larch gum has been used in foods and can serve as a gum arabic substitute. 

The only clearly defined crystalline compositions are three forms of phosphoric acid and hemihydrate, pyrophosphoric acid, and crystalline P O q. The phosphoric acids obtained in highly concentrated solutions or by mixing phosphoric acid with phosphoms pentoxide are members of a continuous series of amorphous (excluding [Y OO]) condensed phosphoric acid mixtures. Mixtures having more than 86% P2O5 contain some cyclic metaphosphoric... 

In order to hilfill the processing requirements, bismaleimide building blocks have to be formulated into products that enable their use as highly concentrated solutions, powders, or hot melts. 

In this lecture we will be concerned by exocytosis of neurotransmitters by chromaffin cells. These cells, located above kidneys, produce the adrenaline burst which induces fast body reactions they are used in neurosciences as standard models for the study of exocytosis by catecholaminergic neurons. Prior to exocytosis, adrenaline is contained at highly concentrated solutions into a polyelectrolyte gel matrix packed into small vesicles present in the cell cytoplasm and brought by the cytoskeleton near the cell outer membrane. Stimulation of the cell by divalent ions induces the fusion of the vesicles membrane with that of the cell and hence the release of the intravesicular content into the outer-cytoplasmic region. 

In this study we examined the influence of concentration conditions, acidity of solutions, and electrolytes inclusions on the liophilic properties of the surfactant-rich phases of polyethoxylated alkylphenols OP-7 and OP-10 at the cloud point temperature. The liophilic properties of micellar phases formed under different conditions were determined by the estimation of effective hydration values and solvatation free energy of methylene and carboxyl groups at cloud-point extraction of aliphatic acids. It was demonstrated that micellar phases formed from the low concentrated aqueous solutions of the surfactant have more hydrophobic properties than the phases resulting from highly concentrated solutions. The influence of media acidity on the liophilic properties of the surfactant phases was also exposed. 

Baum has reviewed the theory and the laboratory, rig, and plant experience which has led to the current views on concentration mechanisms. Essentially, interpretation is based on the difference between heat transfer at certain localised sites of the tube and that at the free surface. In normal boiling, the removal of steam from the surface leads to its direct replacement by liquid, so that accumulation of solutes does not occur to any appreciable extent. However, in certain cases, principally those three listed above, where there is an inadequate supply of water to the surface for boiling to be maintained, steam preferentially forms. Consequently, solute is deposited and accumulates with the formation of highly concentrated solution (lO -lO that in the bulk). 

Radiocontrast media (RCM) are highly concentrated solutions of triiodinated benzene derivatives used for performing diagnosis and treatment of vascular disease and enhancement of radiographic contrast [1,2]. However, adverse reactions after RCM administration are common [3]. The frequency and mechanisms of hypersensitivity reactions differ between monomeric and dimeric as well as between ionic and non-ionic types of RCM. Mild immediate reactions have been reported to occur in 3.8-12.7% of patients receiving ionic monomeric RCM and in 0.7-3.1% of patients receiving non-ionic RCM [4-6]. Severe immediate adverse reactions to ionic RCM have been reported in 0.1-0.4% of intravenous procedures, while reactions to nonionic iodinated RCM are less frequent (0.02-0.04%) [4-7]. Fatal hypersensitivity... 

A higher-MHz NMR spectrometer is always a better choice, since the sensitivity of the experiment is proportional to the frequency of measurement. Moreover, with highly concentrated solutions, the presence of some solid particles can cause an increase in T) (FID will be short) and line broadening of the NMR signals will result. Therefore, an optimum concentration (say, 25-50 millimolar solution) is recommended. Of course, H-NMR spectra can be readily measured at much lower concentrations, though higher concentrations are necessary for recording - C-NMR spectra. 

Moreover, such solutions can also canse the sample to crystallize out in the syringe. In this case it is recommended to dilnte the sample and apply larger volumes. Of course, a further possibility is the application of highly concentrated solutions manually with a pipette or, if the sample does not crystallize out in the syringe, semiautomated by the Alltech TLC sample streaker. 

FIGURE 5.3 Sparkling spots over the sorbent area near the application area caused by highly concentrated solutions (in this case 1.5% solution). 

A comparison of the solution behaviour of PS in both solvents, toluene and frans-decalin, reveals that the limiting power of the molar mass dependence of r 0 (3.35 and 3.28, respectively) is very close to the value of 3.4 observed in highly concentrated solutions and melts. The concentration dependence of r 0, however, is clearly different in each of the solvents ... 

For highly concentrated solutions, Eq. (20) can be simplified, due to the fact that in such a case the plateau modulus G p is Mw independent. Under these conditions it is clear that E is solely a function of... 

Thermochromism of spiroindolinonaphthooxazine is observed only in high-concentration solution.77 A high concentration ( 10 3 M) of 33 in ethanol produces a bluish solution, and its color intensity increases as the temperature of such concentrated solution increases. This thermal equilibrium is also affected by substituent groups. Donor substituent groups promote the formation of the colored form. 

Electrodialysis has advantages and disadvantages. For instance, the process requires very little energy and can recover highly concentrated solutions. On the other hand, similarly to other membrane processes, electrodialysis membranes are susceptible to fouling and must be regularly replaced. 

Platzman (1967) has emphasized that most direct ionizations in molecules leave the positive ions in an excited state. Based on crude DOSD, he estimated that in water the average positive ion will have about 8 eV excitation energy. Later, the less approximate calculation of Pimblott and Mozumder (1991) reduced that figure to about 4 eV The chemical role of this excitation energy is unknown, although it may have some effect in the radiolysis of highly concentrated solutions. 

T. Ookoshi and M. Onaka, Zeolite-catalyzed macrolactonization of m-hydro-xyalkanoic acids in a highly concentrated solution, Tetrahedron Lett., 39 (1998) 293-296. 

The fact that a certain amount of water cannot crystallize in a high concentrated solution, and that the molecules cannot move any more to the existing crystals, is important during the freezing of biological substances. Table 1.1 shows this for some food products. 

Chemical action between the highly concentrated solute and the adsorbent may occur. This explanation cannot be rejected h prion even in cases where it appears extremely improbable. Thus... 

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