Nitrogen Rejection by Dual Reflux Pressure Swing Adsorption Using Engelhard Titanosilicate Type 4

The need for cost-efficient technologies for natural gas processing coupled with low environmental impact is becoming increasingly important due to the growing production of natural gas from subquality gas wells. The removal of nitrogen from such gas sources is especially challenging because of the similar properties of nitrogen and methane. This work studies the separation of an 85 mol % CH4 + 15 mol % N2 gas mixture by dual reflux pressure swing adsorption (DR PSA) using N2-selective Engelhard titanosilicate type 4, ETS-4, as adsorbent via numerical simulations. Key DR PSA process parameters, such as the heavy product to feed flow ratio, the light reflux flow rate, and the feed step duration, were investigated to maximize the separation performance. In addition, productivity and energy requirements of the four DR PSA cycle configurations, namely, PL-A, PH-A, PL-B, and PH-B (PL, low pressure; PH, high pressure; A, heavy gas; B, light gas), were determined. The goal was to evaluate the capabilities of the nitrogen-selective ETS-4 in conjunction with the DR PSA process aiming to produce two useful product streams meeting pipeline specifications (>93 mol % CH4) and environmental regulations (>99 mol % N2). It was found that ETS-4 can easily upgrade the CH4 content of the gas mixture to the pipeline specifications at high recovery but cannot meet the environmental regulations. The gas enriched in N2 needs to be further processed or can be used for electricity production via combustion.