Development of a Micropyrolyzer for Enhanced Isotope Ratio Measurement

Abstract

This paper presents design, fabrication, and testing of a microscale ceramic reactor for the pyrolysis of organic compounds. One application for this pyrolysis reactor is to convert the oxygen and hydrogen atoms in organic compounds to CO and H 2 for isotope ratio measurements in a continuous flow mode. Existing commercial pyrolyzers use high carrier gas flow rates (typically 80-100 mL/min) such that >95% of the CO and H 2 produced from a given sample is vented before introduction into the mass spectrometer. We describe here the fabrication and testing of a microscale pyrolysis reactor designed to be compatible with existing isotope ratio mass spectrometers. The microreactor uses carrier gas flow rates of 3-5 mL/min, decreasing the proportion of the CO and H 2 lost in venting and permitting analysis of samples 20-50 times smaller than can be analyzed with conventional pyrolysis reactors. Results have shown that organic compounds, such as 1-butanol, ethanol, and ethanolamine, can be fully decomposed to desired products CO and H 2 , at a temperature of 1200 °C, which is 200 °C lower than conventionally reported. Furthermore, we are able to eliminate undesired products such as methane and CO 2 in the pyrolysis process. The proof-of-concept experimental results clearly demonstrate that the micropyrolyzer quantitatively converts organic compounds to gases suitable for isotope ratio analysis.

Minimization of sample requirement for δ18O in benzoic acid

“…However, alternative approaches may lower this blank signal, such as the use of a molybdenum foil liner to block interaction between C and Al 2 O 3 within the reduction furnace of the HTC system 39. Another approach would be to operate the system at a lower temperature (e.g., 1080°C), thus reducing diffusion of atmospheric oxygen through the Al 2 O 3 reactor tube, and also decreasing the rate at which C reacts with the Al 2 O 3 reactor tube 43. However, this other approach must be applied with caution, due to the potential for incomplete reduction of sample O to CO at lower reaction temperatures 44…”