Microbubble Plasma Processing for N‐Fertigation via Plasma Catalysis
Changping Zhuang, Nguyen Van Duc Long, Nam Nghiep Tran, Tianqi Zhang, Patrick J. Cullen, G. Akay, Volker Hessel
Abstract
Abstract Plasma can use intermittent renewable energy and abundant use of air to produce N‐fertilizers, with option of decentralized production “at‐farm”. Plasma can generate both nitrate and ammonia (NH 3 ) as key platform molecules toward all N‐fertilizers, including urea and ammonium nitrate. The most convenient way is to produce a “performance chemical” at the farm site. This is a fertigation solution that is ready to be pumped to the farm fields. This study reports about using a nonthermal plasma to generate nitrate and NH 3 in presence of water, in which these are immediately absorbed; creating a fertigation solution, termed in literature “plasma activated water (PAW)”. Both air and nitrogen plasmas have been used. The N‐content has been optimized by a process‐parametric study, yielding the second‐best result reported in literature and the best when concerning scale‐up ability. Strategic catalyst studies have been conducted, in terms of plasma‐catalysis synergy, varying the type of catalyst and the location of catalyst. Silica‐supported single/binary metal catalysts and γ‐alumina powder catalysts were used. Distinct catalyst placements inside the plasma electrode zone (glow or spark) and outside in the gas–liquid reactor were tested; with the aid of supports and without. We used proprietary NH 3 and N‐fixation catalysts besides specific commercial catalysts. Increasing the N‐fixation performance by about 70% as compared to noncatalytic processing, the study used a recycling loop to further boost the N‐fertilizer concentration. A plasma‐catalyst synergy was determined by structural changes of the catalyst transiently (during plasma operation). This laboratory study achieved a result that has potential for commercial N‐fertigation at farm, when multiplied by a factor of 10 via further process intensification, a factor of 10 by increase of plasma reactor scale, and a factor of 10 by reactor parallelization (“numbering‐up”). Admittedly, this is ambitious and needs considerable process development, yet is a possible way to go without a road blocker.