Gel time meter

In connection with bulk polymerization experiments of diallyl o-phthalate, it should be pointed out that this monomer behaves quite differently from vinyl-type monomers in that its rate of polymerization increases linearly with initiator concentration. This phenomenon is conveniently studied by use of a gel-time meter [100]. This instrument also is used to demonstrate that hydroquinone is a more effective inhibitor of the polymerization of a 1% solution of dibenzoyl peroxide in diallyl o-phthalate at 100°C than r-butyl catechol [100]. 

Commercially available mechanical gel time meters or gel timers can be used in place of manual stirring to determine gel time. There are various types of gel time meters available in the market. One such version measures a liquid s gel point by... 

Figure 7-31. Gel time meter. (Courtesy of Shyodu Instrument INC.)...

The metering pumps continuously deliver the components into mixing devices. There are many designs for mixing devices, and the choice depends on the properties of the system being processed, e.g., viscosity, gel formation time, temperature, etc. 

Before using the pH electrode, it should be calibrated using two (or more) buffers of known pH. Many standard buffers are commercially available, with an accuracy of 0.01 pH unit. Calibration must be performed at the same temperature at which the measurement will be made care must be taken to match the temperature of samples and standards. The exact procedure depends on the model of pH meter used. Modern pH meters, such as the one shown in Figure 5.8, are microcomputer-controlled, and allow double-point calibration, slope calculation, temperature adjustment, and accuracy to +0.001 pH unit, all with few basic steps. The electrode must be stored in an aqueous solution when not in use, so that the hydrated gel layer of the glass does not dry out. A highly stable response can thus be obtained over long time periods. As with other ion-selective electrodes, the operator should consult the manufacturer s instructions for proper use. Commercial glass electrodes are remarkably... 

This completely automatic installation operates well, but seems much too expensive to run. The specific electrical consumption is 210 watt-hours per cubic meter of air, which brings the consumption for the ozonated air at a concentration of 10 grams per cubic meter, to 21 watt-hours per gram of ozone. This electrical consumption is much higher than that necessary for the production of ozone itself, and five to six times higher than that required for a drying system using activated alumina or silica gel. 

The calculation of the specific activities, of formation of formaldehyde and CO, from yield versus contact time data provided the results presented in table 4. It is seen that the activity per square meter of surface are for both products, exhibited by sol-gel catalyst is lower than the specific activity of coprecipitated catalyst. Such differences of activity are attributable to the lower Mo contents of sol-gel catalysts (table 1). 

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