Acid temperature control commercial systems

High-temperature/low-pressure inorganic digestions are an area of application that has benefited from recent advances in vessel and sensor design. The inert properties of Teflon and its resistance to acid attack make it the material of choice for microwave pressure-vessel construction. Improved commercial systems offer additional safety precautions and improved facilities for pressure and/or temperature control. Also, the distribution of microwave radiation inside the oven cavity is fairly homogeneous. Low-pressure systems allow decomposition temperatures of about 180 °C. However, for many matrices, such temperatures are not sufficient to guarantee the complete ashing of thermoresistant sample components. 

There are numerous modified conditions of the acetic acid acetylation system practiced commercially. But the basic principles are the same. The objective in all of the commercial processes is to produce a clear, gel-free, acid dope having target viscosity. Some of the main processing factors are catalyst level, acetic acid to anhydride ratio, initial temperature of the A mix (A mix refers to a mixture of acetic acid and acetic anhydride.), amount of excess acetic anhydride, the equipment used to agitate the reaction medium, the extent of jacket cooling to control the exotherm, peak temperature (the maximum temperature reached during the acetylation), and the temperature-time profile for the acetylation. 

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