Investigation of the combustion of methane using CuO for radiocarbon dating

Abstract For the combustion of methane (CH 4 ) gas to carbon dioxide (CO 2 ), we investigated the use of copper oxide (CuO) as the source of oxygen, using our type 2 Micro Conventional Furnaces (MCF-II), traditionally used for the reduction of CO 2 to graphite for AMS measurement Yang and Smith, 2017 [1]. Experiments showed that both graphite and CH 4 can be oxidised to CO 2 rapidly at a temperature at 780 °C. The reaction is complete within just a few minutes for graphite and within about one hour for CH 4 gas. However, this method is only suitable for combustion of CH 4 when the concentration >3% due to the small internal volume of MCF-II. To combust gases of lower CH 4 concentration, we installed a gas circulation loop with additional components including 1) a novel, newly designed MCF-III with a dual tube furnace for heating 6 mm OD quartz tubes up to 850 °C; 2) a gas circulating unit comprising a miniature diaphragm pump and flow meter along with a needle valve for adjusting gas flow rate; 3) differently sized gas storage tubes and bags, permitting optimisation of the carbon sample size; 4) a water trap and miniature CO 2 gas traps −65 °C and −150 °C respectively Yang et al., 2013 [2]. This system is also suitable for collecting CO 2 from air at atmospheric concentrations. It also has the flexibility to assemble a specific gas trapping/combustion system to suit the composition of individual gas samples. We report on the early performance with some samples and our evaluation of the cross contamination between CO 2 and CH 4 based AMS measurement of a set of mixing gas CO 2 /CH 4 /N 2 samples.