Ethanolic crystallization kinetics

Hurley, M.A., Jones, A.G. and Drummond, J.N., 1995. Crystallization kinetics of cyanazine precipitated from aqueous ethanol solutions. Chemical Engineering Research and Design, 73B, 52-57. 

Recently, Edye et al, (4) described a fermentation process which used a mutant strain of Zymomonas mobilis to produce high concentrations of fructose and ethanol when grown on a concentrated sucrose medium. Johns and Greenfield (5) proposed ethanolIc crystallization as a means of recovering the fructose from the broth. The kinetic behaviour of fructose crystallization from ethanolIc solution has not been previously reported, and this work Investigates these crystallization kinetics. 

Fig 3 Crystallization kinetics of coexisting zeolites ZSM-20 (O) and Beta (O) formed in presence of ethanol (EtOH not completely eliminated) compared with that of pure ZSM-20 formed under the same conditions in complete absence of EtOH. 

The oxidation of N, A-dimethylaniline by aerated, ethanolic cupric chloride to give a mixture of products including methyl and crystal violets is simple second-order when an excess of amine is used Presumably Cu(I) is re-oxidised by dissolved oxygen, for otherwise the observed linearity of log [residual amine] versus time plots would not be found as Cu(II) disappears. Under nitrogen the kinetics are complex, but a new optical absorption (472 and 1007 nm) appears immediately on mixing the reactants. This absorption decays whilst a new one at 740 nm develops. The latter absorption originates from a 1 1 complex formulated... 

In this chapter, we have summarized (recent) progress in the mechanistic understanding of the oxidation of carbon monoxide, formic acid, methanol, and ethanol on transition metal (primarily Pt) electrodes. We have emphasized the surface science approach employing well-defined electrode surfaces, i.e., single crystals, in combination with surface-sensitive techniques (FTIR and online OEMS), kinetic modeling and first-principles DFT calculations. 

It is clear that kinetic effects must be utilized in the design of a process to make the commercially available Form A, because it is never the most thermodynamically stable form. Information from the literature and patents in reference [14] indicates that Form A can be successfully isolated from Acetonitrile, Acetone, Methyl isobutyl ketone, Toluene, the C2 to C4 alkenols, Ethanol, Methanol and Propan-2-ol. In these solvents it is likely that solvation is favourable to the nucleation rate of Form A or detrimental to crystal growth of the other forms, or both. For a new development compound there should be similar solvent interaction data available from polymorph screening experiments. 

The kinetic behaviour of fructose crystallization from aqueous ethanolIc solutions, typical in composition to those operated on an industrial scale, is strongly dependent on supersaturation, solvent composition and temperature. Provided the supersaturation is kept below 35 C of subcooling, nucleation does not occur. 

When the goal is the production of fine particles it is important to save the primary size of the crystals as they appear first in the solution, i.e. the nucleation has to be promoted over the growth and aggregation steps. In the case of undersaturated, weak initial solutions the precipitation takes place near the metastable region where the kinetic processes are rather slow. For example, the induction time which was necessary for crystallization in the weakest NaCl solutions approaches to 60 min. Repeating the precipitation (where the ethanol content was the same 99.6%) with saturated aqueous solution there was no measurable induction time and the particle size changed considerably within the applied 60 min operational time the d was 4.41 p,m after 10 min, 8.86 pm at 20 min and finally 16.27 pm at 60 min. It is obvious that in the latter case not the smallest available size was measured after 60 min, but for the sake of comparison the same operational time had to be applied. 

Berman et al. (1968) noted that mannitol is unusual among carbohydrates in that exists in several polymorphic forms , indicating that a number of these are often obtained simultaneously. They describe the preparation of a number of these modifications. The a form is obtained by slow crystallization from 96 per cent ethanol, the a form by evaporation from 100 per cent ethanol and the p form from aqueous ethanolic solutions, all apparently under thermodynamic conditions. On the other hand the y form is obtained kinetically by rapid cooling of a 1 1 water-ethanol solution. An additional k form was obtained (unexpectedly) upon evaporation of a boric acid/methanol solution (Kim et al. 1968). 

Sodium bicarbonate Sodium bicarbonate (NaHCOs) is an odorless, white crystalline powder with a saline, slightly alkaline taste. A variety of particle-size grades of powders and granules are available. The carbon dioxide yield is approximately 52% by weight. At RH below approximately 80% (at room temperature), the moisture content is less than 1%. Above 85% RH, it rapidly absorbs an excessive amount of water and may start to decompose. Its solubility in water is 1 part in 11 parts at 20°C, and it is practically insoluble in 95% ethanol at 20°C. When heated to 250-300°C, NaHCOs decomposes and is converted into anhydrous sodium carbonate. However, thisprocess is both time-and temperature-dependent, commencing at about 50°C. The reaction proceeds via surface-controlled kinetics, and when NaHCOs crystals are heated for a short period of time, very fine needle-shaped crystals of anhydrous sodium carbonate appear on the surface. ... 

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