ENVIRONMENTALLY ACCEPTABLE DRAG-REDUCING SURFACTANTS FOR DISTRICT-HEATING AND COOLING

The aim of this work was to find drag-reducing surfactants for both di strict heating and cooling that are environmentally more acceptable th an the organic salts of quaternary ammonium compounds that so far have dominated this application. Vortex inhibition of test solutions in gl ass beakers has been used to screen a large number of surfactant mixtu res, various electrolytes, and temperatures. For the most interesting products, the pressure drop in a test loop was measured at various flo w rates and temperatures. N-cetyl sarcosinate and N-stearyl betaine, t he latter together with Na-dodecylbenzene sulfonate, give good drag re duction (DR) properties at 65-100 and 45-85 degrees C, respectively. T he sarcosinate is sensitive to pH changes, whereas the betaine-sulfona te complex is more robust. Ethoxylates of oleic acid monoethanolamide show good DR properties at 0-25 degrees C. At an increased salt concen tration, a mixture of this surfactant with an ethoxylated oleyl alcoho l worked well. At a still higher salt concentration, e.g., sea water, a combination of N-cetyl betaine and alkylbenzene sulfonate showed DR.