Theoretical Study of Moisture-Pretreated Lithium as Potential Material for Natural Gas Upgrading

Abstract

For efficient natural gas upgrading at near ambient temperatures, moisture-pretreated lithium is proposed as a reactive adsorbent, and its separation performance was examined for selected gas mixtures (involving combination of CH 4 , CO 2 , O 2 , N 2 , and/or H 2 ) by theoretical studies. For evaluating the proposed adsorbent, we used density functional theory calculations as well as temperature-programmed kinetic Monte Carlo calculations. Contributions of different mechanisms for the gas capture were examined, including diffusion, adsorption, and reaction. Among these mechanisms, reaction was found to be the dominant factor during the gas-capture process. In contrast to the conventional reactive adsorbents where gases directly react with adsorbents and thus are captured, the gas-capture mechanism herein follows the reaction between gases and species generated upon pre-exposure of lithium to moisture. The proposed separation process is thermodynamically favorable and would progress spontaneously. It is shown that for several gas mixtures containing methane, a perfect selectivity can be achieved in which a high-purity methane gas stream is the final gas product while the other gaseous components are transformed to corresponding solid products.

A critical review on the practical use of lithium cycle as an upfront nitrogen removal technology from natural gas

“…The feasibility of this process was recently highlighted through both experimental and theoretical testing. 16 The thermodynamic favorability of the reaction was also confirmed by Gu et al 14 Moreover, patents for the usage of lithium for the chemical sorption of nitrogen from NG were issued. 38,39 Nitrogen removal from NG using lithium solid chemisorption is a promising and novel process.…”

“…32 The reaction with moisture has two benefits: the creation of a lithium hydroxide layer that promotes a more active edge site for the nitridation reaction to occur, 16 and the release of energy (375 kJ/mol) that is used as the activation energy for the nitridation reaction. 14 Based on the existing research literature, there is conflictual evidence on the likelihood of lithium reacting to nitrogen in dry conditions. For instance, Mcfarlane and Tompkins 31 argues that it is possible for the reaction to occur, while Markowitz and Boryta 45 assert that lithium will remain stable for days.…”

“…Wayne Ronald Irvine 46 confirmed that the moisture pretreatment significantly enhances the reaction rate While Reaction (1) describes the primary reaction that occurs when lithium is exposed to nitrogen, when thinking about NG, lithium can be helpful to imagine other relevant species besides nitrogen (i.e., impurities), such as H 2 , CO 2 , and O 2 . For example, Gu et al 14 summarized 21 reactions, including lithium, lithium hydride, and lithium hydroxide with the aforementioned gases and calculated the activation energy for each reaction. Some of these reactions are highlighted with their Gibbs-free activation energies, reactions (2)(3)(4).…”

Prospective of Upfront Nitrogen (N2) Removal in LNG Plants: Technical Communication

“…Aside from the former absorption process, lithium-based adsorption was found to be promising, reducing the N 2 content in the gas to low levels, less than 2% [66,69]. This process consists of different steps (Figure 6), including the electrolysis of lithium chloride to obtain lithium.…”

“…A reaction of lithium nitride hydrolysis can be applied as a part of the proposed cycle (Reaction 2) and an additional step of treating lithium hydroxide with hydrochloric acid to obtain lithium (Reaction 3). In a numerical simulation analysis, Gu et al [69] concluded that the N 2 content of the gas could be reduced at ambient temperature and 1-80 bar pressure from 10% or 4% to 0.5% N 2 , achieving LNG specifications where moisture-pretreated lithium is used as an adsorbent, not dry. The advantage of using moisture-pretreated lithium instead of dry lithium was emphasized by Li [66] as water produces active edge sites on lithium and initiates the reactions with nitrogen.…”