Exothermic processes solution process

Solution Process. With the exception of fibrous triacetate, practically all cellulose acetate is manufactured by a solution process using sulfuric acid catalyst with acetic anhydride in an acetic acid solvent. An excellent description of this process is given (85). In the process (Fig. 8), cellulose (ca 400 kg) is treated with ca 1200 kg acetic anhydride in 1600 kg acetic acid solvent and 28—40 kg sulfuric acid (7—10% based on cellulose) as catalyst. During the exothermic reaction, the temperature is controlled at 40—45°C to minimize cellulose degradation. After the reaction solution becomes clear and fiber-free and the desired viscosity has been achieved, sufficient aqueous acetic acid (60—70% acid) is added to destroy the excess anhydride and provide 10—15% free water for hydrolysis. At this point, the sulfuric acid catalyst may be partially neutralized with calcium, magnesium, or sodium salts for better control of product molecular weight. 

Reality Check Notice that qieacu0n is negative, so the solution process is exothermic. That is reasonable since the temperature of the water increases. 

The effect of a temperature change on solubility equilibria such as these can be predicted by applying a simple principle. An increase in temperature always shifts the position of an equilibrium to favor an endothermic process. This means that if the solution process absorbs heat (AHsoin. > 0), an increase in temperature increases the solubility. Conversely, if the solution process is exothermic (AH < 0), an increase in temperature decreases the solubility. 

Solution polymerizafion. Highly exothermic reactions can be handled by this process. The reaction is carried out in an excess of solvent that absorbs and disperses the heat of reaction. The excess solvent also prevents the formation of slush or sludge, which sometimes happens in the bulk process when the polymer volume overtakes the monomer. The solution process is particularly useful when the polymer is to be used in the solvent, say like a coating. Some of the snags with this process its difficult to remove residual traces of solvent, if that s necessary the same is true of catalyst if any is used. This process is used in one version of a low-pressure process for high-density polyethylene and for polypropylene. 

The explanation for the apparent correlation between catalytic activity and electron affinity of metals cannot be as simple as that which has been advanced for the homogeneous catalysts. This is because chemisorption on metals (unlike the splitting of hydrogen by metal ions in solution ) is an exothermic process and, hence, as shown earlier, catalytic activity depends not only on a low activation energy of adsorption but also on a low heat of adsorption. The interpretation applied earlier to homogeneous catalysts can account for an inverse dependence of Ea on the work function, but does not suggest any obvious reason why Q should show a similar dependence. 

We now consider the dependence of the stationary-state solution on the parameter d. To represent a given stationary-state solution we can take the dimensionless temperature excess at the middle of the slab, 0ss(p = 0) or 60,ss-With the above boundary conditions, two different qualitative forms for the stationary-state locus 0O,SS — <5 are possible. If y and a are sufficiently small (generally both significantly less than i), multiplicity is a feature of the system, with ignition on increasing <5 and extinction at low <5. For larger values of a or y, corresponding to weakly exothermic processes or those with low temperature sensitivity, the hysteresis loop becomes unfolded to provide... 

Solution-based polymerization is the most common process used today for SAP manufacture. This process is efficient and generally has a lower capital cost base. The solution process uses a water-based monomer solution to produce a mass of reactant polymerized gel. The polymerization s own reaction energy (exothermic) is used to drive much of the process, helping reduce manufacturing cost. The reactant polymer gel is then chopped, dried, and ground to its final granule size. Any treatment to enhance performance characteristics of the SAP is usually accomplished after the final granule size is created. 

Recall that, if y > 1, increase in T results in decrease in yt. Thus the left-hand side of the above equation becomes negative and hence Hf is positive - endothermic. In a similar way one may find that, if y, < 1, then the solution process is exothermic. If the solution process in an i-j binary system is endothermic, the i-i and j-j attractions are greater than the i-j attraction, i atoms attempt to have only i atoms as nearest neighbours - tendency toward phase separation or clustering. 

If the solution process is exothermic, the i-i and j-j attractions are smaller than the i-j attraction, i atoms attempt to have only j atoms as nearest neighbours, and j atoms attempt to have only i atoms as nearest neighbours - tendency toward compound formation. 

The nitration of aromatics is often a rapid and exothermic process which frequently requires dropwise addition of the nitrating solution in order to prevent rapid evolution of heat, which can lead to undesirable... 

The adsorption of surfactant on a mineral surface is generally an exothermic process and at a constant surfactant concentration in the solution its adsorbed amount decreases with increasing temperature. Using the partial derivation 31n c/3T for a constant number of CH2 groups n of an hydrocarbon chain of a surfactant and constant values of the surface coverage a, we arrive to an equation for calculation of the total adsorption energy E. From the relation E = Ep + Ea, Richter and Schneider74 derived an equation which is valid for all isotherms ... 

Solubility will decrease with increasing temperature for an exothermic solution process. This is the case for cerium(lll) sulfate—Ce2(S04)3—in water. 

The solution of the ester is an exothermic process. No attempt should be made to heat the mixture to reflux temperature until the ester has been dissolved. 

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