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

Abstract

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 a 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, 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 % N2). It was found that ETS-4 can easily upgrade the CH4 content of the gas mixture to 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 post-combustion.

On the Design of a Dual Reflux Pressure Swing Adsorption Process

“…Consequently, reliable simplified approaches to the design of DRPSA processes are not available. As a matter of fact, most contributions from the literature, involving either experiments − or mathematical models, − designed DRPSA processes through either trial-and-error approaches or using many oversimplifying assumptions. Among the latter approaches, it is worth mentioning the so-called equilibrium theory. ,,,,, Even if this approach can predict the effect of changing the main design parameters, the results are reliable provided the fulfillment of major assumptions, such as instantaneous equilibrium conditions, linear equilibrium isotherms, ideal gas behavior, ideal plug flow conditions in the fixed-bed, isothermal operation, negligible pressure drop, and complete separation of the two components of the mixture.…”

Separation of Methane and Nitrogen Using Heavy Reflux Pressure Swing Adsorption: Experiments and Modeling

“…One method is to develop better adsorbent materials that have increased selectivity for either CH 4 or N 2 . A range of commercially available adsorbents have been widely deployed to separate CH 4 from N 2 such as activated carbon, ETS-4, carbon molecular sieves, and zeolites. − Recently, Li et al , developed a new adsorbent named ionic liquidic zeolite (ILZ), which has shown better separation performance than activated carbon and ETS-4 in separating CH 4 and N 2 under similar operating conditions. ,− In our previous publication, we demonstrated through a combination of pilot-scale tests and process simulations how conventional PSA cycles using ILZs could be optimized to enrich dilute methane-in-nitrogen mixtures from CH 4 concentrations of 5–16 to 12–45% . However, a more concentrated CH 4 product is needed for utilization, either for power generation or household purposes.…”

“…Dual-reflux and triple-reflux PSA cycles, demonstrated at a laboratory scale and via numerical simulations, utilize continuous heavy reflux flows and have been shown to achieve substantial enrichments of dilute methane-in-nitrogen mixtures. ,,− However, these more complex PSA processes have high capital and operational costs, which could limit their large-scale application. Heavy reflux, also known as heavy product displacement or heavy purge, is one cycle modification that introduces a substream from the heavy product to purge the adsorption column after the adsorption steps.…”

Separation of methane and nitrogen using ionic liquidic zeolites by pressure vacuum swing adsorption

“…14 A range of chemical separation technologies have been explored to overcome the N 2 /CH 4 separation challenge such as solvent absorption, 15 adsorption, [16][17][18] membrane separation, 19 and cryogenics. 20 Among these technologies, adsorption has been widely used to process gas flows at scales from 10 to 100,000 Sm 3 Áh À1 (20 C and 1.01 bar), using pressure-vacuum swing adsorption (PVSA) processes with various adsorbents such as carbon molecular sieve (CMS), 21,22 Engelhard titanosilicate type 4 (ETS-4) 23,24 and activated carbon. 25,26 The separation of CH 4 /N 2 using CMS is often achieved by exploiting differences in adsorption kinetics, 27 while ETS-4 is a N 2 selective adsorbent that can be favorably applied to treat in gas sources with low N 2 concentrations.…”