Process Wednesday: foaming -- not just for beer

Apropos of nothing, here's our mentor-by-literature, Neal Anderson, in his book Practical Process Research and Development, on foaming issues in scale-up reactors:

To prepare for a run, it is essential to review a process and examine the detail of exactly how the operations will be carried out. Vessels must be selected so that the reactions can be stirred at the minimum volume of the reaction (V_min) and so that the reaction can be contamined (and usually stirred) at the maximum batch volume (V_max). 

Gases evolved during processing, for instance during decarboxylation or neutralization of an acidic stream with NaHCO₃, may form foams; such reaction mixtures take up a larger portion of the vessel volume. A defoaming agent was added to a Lossen rearrangement to address these problems (Figure 14.7); however, assays may be needed to detect the presence of any defoaming agent in the product. For the safety of operators and to minimize risk of contamination, any key volumes should be measured without opening the vessels. If the addition of key reagents is to be controlled by temperature, a sensitive temperature probe must be positioned so that the temperature can be monitored at the start and the end of the addition. 

Incidentally, Anderson's figure shows the relevant defoamer to be Dow's Antifoam 2210, which is apparently a "10 percent active silicone-glycol emulsion". (Boy, you don't need much of it -- Dow suggests that you start at 50 ppm, or 66 ounces in a 1000 gallon reaction.)