Adiabatic polymerizer

In a typical adiabatic polymerization, approximately 20 wt % aqueous acrylamide is charged into a stainless steel reactor equipped with agitation, condenser, and cooling jacket or coils. To initiate the polymerization, an aqueous solution of sodium bisulfite [7631-90-5] is added, followed by the addition of a solution of ammonium persulfate [7727-54-0] N2HgS20g. As the polymerization proceeds, the temperature rises to about 90°C, and then begins to fall at the end of the polymerization. The molecular weight obtained depends primarily on the initiator concentration employed. 

Temperature Profiles of Adiabatic Polymerizations. Experiments were conducted to characterize the adiabatic temperature profiles of photocured composites... 

L/mol, respectively. We have used these optimized values for comparing model predictions with experimental data obtained from adiabatic polymerization to study the effect of initial polymerization temperature and effects of initiator and catalyst concentrations [24]. 

This thermometric method, which consists of measuring the temperature of a reactive medium in an adiabatic polymerization process T(t), is quite close to the calorimetric method. If we assume that the product of specific heat and density, Cpp, does not depend on temperature and the degree of conversion (this assumption is quite realistic), then it is possible to relate changes in temperature dT to heat output dq ... 

Figure 2.4. Comparison of the kinetic function, calculated as f(P) = (I -P)(l + coP), and experimental data obtained by adiabatic polymerization at different initial temperatures 1510C(O) 159°C( ) 170°C ( ). Concentrations of the activator and catalyst are [A] = [C] = 4.45xl0 2 mol 1.

Figure 2.10. Temperature increase in adiabatic polymerization of polyurethane accompanied by the formation of interpenetrating networks in the polyurethane-unsaturated polyester system.

An approach based on measuring temperature changes in adiabatic polymerization or heat effects in an isothermal reaction gives us a clear picture of the process, although the overall estimate of the process characteristics of a chosen formulation has only limited validity. 

C. This figure is appropriate for adiabatic polymerization, which approximates reality in reactive processing of large articles with high volume-to-surface ratios. In this case, it is impossible to remove the heat effectively and to avoid intense local temperature jumps. Therefore, it is essential to know how to calculate temperature increase for reactions proceeding in non-isothermal conditions. The time dependence of viscosity in this situation can be written as... 

Figure 3. Styrene emulsion polymerization—variation of the propagation constant with temperature during adiabatic polymerization of 395-A latex particles (kp in...

Figure 7. Styrene emulsion polymerization—variation of the termination constant with free volume according to Equation 3 with molecular weight changes neglected during adiabatic polymerization of 1650-A latex particles over the conversion range, 0.7-0.911 ((A = 0.44 = 0.0708)...

A 3,500-gal reactor with styrene monomer undergoes adiabatic polymerization after being heated inadvertently to 70°C. The maximum allowable working pressure (MAWP) of the reactor is 5 bar absolute. Determine the relief vent diameter required. Assume a set pressure of 4.5 bara and a maximum pressure of 5.4 bara. Other data and physical properties are given as follows [12] ... 

The high speed of anionic polymerization as well as the low heat of polymerization of most lactams allows bulk polymerizations to be carried out under adiabatic conditions. Vice versa, the adiabatic polymerization is convenient for the estimation of the heat of polymerization [37, 38]. 

The kinetic treatment of the adiabatic polymerization is very complicated with respect to the variation with increasing temperature of rate coefficients and equilibrium constants. Equations derived with a series of simplifying assumptions (e.g. heat capacity of the monomer (Cp m ) = heat capacity of the amorphous polymer (Cp p) = constant = Cp) lead to [2]... 

In this study the researchers investigate theoretically and experimentally the adiabatic polymerization of styrene, methyl methacrylate, and butyl methacrylate at complex initiation, i.e., when a mixture of initiators with a differing activation energy is used. 

Heil et al. [38] employed a three-reactor CSTR. A latex seed was fed to the first reactor and monomer feeds of different compositions were fed to the first two reactors to produce a soft core, hard shell particle morphology. The three-reactor series would also have a narrower PSD than a single CSTR. Scott and Feast [31] used a single CSTR to carry out a high temperature (80-100 °C) adiabatic polymerization with cold feed streams. 

The solution of eqns [8] and [9] provides the conversion achieved in adiabatic polymerization. Figure 23 shows the results for methyl methacrylate with an initial temperature of 25 °C, using thermodynamic data from Odian." The conversion is 0.93, which means that independent of initiator burnout, complete conversion can never be achieved because of the high front temperature. This value is very sensitive to the exact values of the thermodynamic parameters so the calculated value may not correspond precisely to experiment. Nonetheless, thermodynamics must be considered when selecting candidates for FP. Similar monomers may exhibit very different conversions at the same temperature. For example, zero conversion will be obtained at 310 °C with styrene but a-methylstyrene will not react above 61 °C." ... 

For an adiabatic polymerization, the maximum conversion is uniquely determined by the AH and AS of polymerization. As the temperamre increases, the equilibrium conversion is reduced and can be related by... 

We expect that this approach will ultimately have three benefits over traditional methods of polymer synthesis 1) reduced energy costs, 2) reduced waste production, and 3) unique morphologies. A desirable feature of frontal polymerization is the rapid and uniform conversion of monomer to polymer. Performing an adiabatic polymerization of a neat monomer is difficult at best and dangerous at worst, but it can be advantageous because the heat of the reaction is used to increase the rate of reaction. Also, the absence of solvent eliminates the need to separate the polymer from the solvent and residual monomer, which requires energy and can have environmental ramifications. 

These rapid systems are used predominantly for (adiabatic) polymerizations below the melting point of PA 6. These cases allow one to prepare PA6 (97% conversion) with more than 40% crystaUtnity, often with both a and y phases. If difunctional NCL are used, for example, l,6-di(carbamoyl-e-caprolactam)hexane, HDICL18, the polymer product contains up to 80% of gel (insoluble in CF3CH2OH), which improves the mechanical properties [16, 17, 40]. 

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