Fast Pyrolysis of Tea Waste under a Hydrogen-Rich Atmosphere: A Study on Nitrogen Evolution and Green Ammonia Production

Abstract

Nitrogen-rich biomass pyrolysis has been explored as a green, distributed, and simple alternative for sustainable ammonia production at atmospheric pressure. In this paper, tea waste was selected as a promising feedstock, and H 2 was employed as an enhancer to increase the yield of NH 3 . The nitrogen distribution among three-phase pyrolytic products affected by various temperatures and different atmospheres was compared and discussed. The evolution pathways for fuel−N during tea waste pyrolysis under a H 2 -rich atmosphere were concluded. Results indicated that the introduction of H 2 was favorable for the increase of the gas− N yield but decreased the yields of char−N and tar−N. At lower temperatures, the bond cleavage of amide−N (N−A) in fuels was enhanced by H 2 , which then yielded more NH 3 −N through deamination. Subsequently, H 2 improved the production of nitrile−N in tar, as well as NH 3 −N and HCN−N, by accelerating the secondary cracking of amine−N (tar−N) generated from the decomposition of amide−N. However, the formation of heterocyclic−N in tar through the polymerization of amine−N was restrained under a H 2 -rich atmosphere. Pyrolysis in the presence of H 2 generated a large amount of H radicals. When the temperature continued to increase, sufficient H radicals impressively advanced the ring rupture (into HCN−N) and full hydrogenation (into NH 3 −N) of pyridinic−N/pyrrolic−N (N-6/N-5) in char. Meanwhile, H radicals also intensified the thermal cracking of nitrile−N and ring opening of heterocyclic−N to form more HCN−N and NH 3 −N. Overall, more nitrogen evolved into NH 3 −N and HCN−N during pyrolysis in a H 2 -rich atmosphere, especially at high temperatures. The highest NH 3 yield of 43.33 wt % was achieved at 800 °C under a 25% H 2 + 75% Ar atmosphere.

Exploring the Green Production of Ammonia from Nitrogen-Enriched Biowaste Gasification: Nitrogen Conversion from Tea Waste and Theanine

“…A detailed description of the setup can be found elsewhere. 26 Prior to each trial, the quartz basket (length = 60 mm, inner diameter = 20 mm) carrying the sample (0.5 g) was placed on the top of the outer tube and purged in a high purity Ar flow of 400 mL/min. Once the target temperature (700, 800, and 900 °C) was attained, the quartz basket was rapidly moved into the reaction center.…”

“…In brief, the experimental setup comprises a fixed bed reactor (length = 700 mm and inner diameter = 32 mm), a steam generator, a feeding device, a condensing device, and a gas detection/collection unit. A detailed description of the setup can be found elsewhere …”

“…The feasibility of ammonia production from tea waste pyrolysis under a H 2enriched atmosphere was investigated in our previous work, and the results indicated that tea waste had great potential for sustainable ammonia production. 26 However, besides NH 3 , a portion of nitrogen was released as char-N, tar-N, and HCN during the tea waste pyrolysis process, which reduced the NH 3 production. 27,28 It is therefore imperative to adjust the transformation and migration of N-containing compounds into NH 3 .…”

“…The issue of tea waste disposal has been brought to attention due to the escalating utilization of tea, with over 90% of the tea being left after consumption. , Notably, tea waste is abundant in nitrogen functionalities, such as caffeine and amino acids, exhibiting a high nitrogen content of 5 wt %, rendering it a renewable source of hydrogen and nitrogen. The feasibility of ammonia production from tea waste pyrolysis under a H 2 -enriched atmosphere was investigated in our previous work, and the results indicated that tea waste had great potential for sustainable ammonia production . However, besides NH 3 , a portion of nitrogen was released as char-N, tar-N, and HCN during the tea waste pyrolysis process, which reduced the NH 3 production. , It is therefore imperative to adjust the transformation and migration of N-containing compounds into NH 3 .…”

Reactive Force Field Molecular Dynamics Investigation of NH3 Generation Mechanism during Protein Pyrolysis Process

“…At a high temperature of 2000 K, the NH 3 maximum conversion rates for the constituent amino acids and actual proteins reached 44% and 22%, respectively, indicating a high conversion efficiency. This disparity may have stemmed from the relatively simple amino structure of the constituent amino acids, which generally facilitates the deamination process [35]. In contrast, the nitrogen atoms in actual proteins are often embedded in complex networks, requiring the overcoming of higher energy barriers and decomposition into smaller molecules before the outermost nitrogen can be exposed and converted into NH 3 .…”