Detection of acetylene impurities in ethylene and polyethylene manufacturing processes using tunable diode laser spectroscopy in the 3-μm range

Using recently developed GaInAsSb/AlGaInAsSb DFB lasers, tunable diode laser spectroscopy (TDLS) has been extended into the 3-μm wavelength region for the detection of acetylene impurities in hydrocarbon compounds encountered in ethylene manufacturing. Measurements of acetylene in pure polymer grade ethylene and in a gas mixture of ethylene and ethane typical of the process stream around a hydrogenation reactor have been performed. Using a procedure incorporating subtraction of a hydrocarbon background spectrum a detection limit of 5 ppbm was achieved under ordinary laboratory conditions. Under forced temperature cycling conditions, the detection limit deteriorated to 180 ppb m, due to temperature drift caused by optical interferences generated by reflections in the laser TO8 can.