Hydrogen/methane and hydrogen/nitrogen sensor based on the permselectivity of polymeric membranes

Abstract

A new gas sensor for measuring the concentration of binary gas mixtures in the 0-100% range based on the permselectivity of polymeric membranes has recently been developed by the authors. This sensor is not expensive and aimed at the low/medium precision market. This paper describes the use of this sensor for a hydrogen/methane binary gas mixture. Preliminary results are also provided for a hydrogen/nitrogen gas mixture. The membranes used are poly(etherimide) (PEI), Teflon-AF and poly(dimethylsiloxane) (PDMS) hollow fibers. The sensor has been subjected to a series of experiments to evaluate its response in terms of stability, repeatability and accuracy as well as to the effects of temperature. The permeate flow rate of the sensor relates to the gas mixture composition at a given temperature; a needle valve at the permeate side leads to a pressure build up, which can be related to the permeate flow rate and then to the feed composition. The sensor allows quantitative hydrogen analysis in binary mixtures with methane, showing a second-order polynomial response. The response of the sensor is fast, continuous, reversible, reproducible and long-term stable over a period of 1.5 x 10(7) s. The relative sensitivity of the sensor depends on the hydrogen feed concentration, ranging from 0.20 to 0.70. The sensitivity, temperature dependency and response time of the sensor are related to the membrane permeability and selectivity. A mathematical model has recently been described whose results are in agreement with our experimental results for PEI and Teflon-AF membranes.