Breakthrough Assessment and Kinetic Study of The Upfront Nitrogen Removal Using Lithium Cycle

Abstract

As Qatar continues to rely on the exportation of liquefied natural gas (LNG) as its primary source of economic growth, new technologies must be investigated to improve the economic appeal and production capacity of traditional LNG plants. This research work aims to investigate the feasibility of a proposed lithium cycle (Li-Cy) that partially removes nitrogen from the natural gas (NG) stream via chemi-sorption using lithium (Li) metal. Nitridation experiments conducted at 60, 80 and 100 oC showed the middle temperature to be the optimal condition for operation, yielding lithium conversion and nitrogen uptake rate of up to 80% and 19 mmol/g, respectively, after 30 minutes of moisture treatment and 2 hours of reaction time (F: 0.1 L/min, P: 1 atm). Meanwhile, hydrolysis trials proved using steam as a water source to react with lithium nitride (Li3N) could quickly convert almost all (98%+ conversion) solid particles into lithium hydroxide (LiOH) after 2 hours of reaction time. Experimental results were fit into kinetic models with the obtained areic reactivity of growth being 0.202 and 125 mol/m2.min, respectively. Preliminary economic evaluation of the proposed Li-Cy showed that given the current prices of ammonia and electricity, NH3 production would return 0.654 and 0.515 USD/kg Li under ideal (100% conversion) and real scenarios, respectively, both of which are higher than the estimated electrolysis cost of 0.468 USD/kg Li, translating to an annual net profit of approximately 6, 10, 16, 21 and 26 MM USD for a plant capacity of 1, 2, 3, 4 and 5 MTPA, respectively, from the ammonia production alone.