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Start Over Author "Ahmad Waqar" Publisher elsevier b.v.
130 results on '"Ahmad Waqar"'

37. Investigation of different configurations of alumina packed bed reactor for coke free conversion of benzene.

Author

Ahmad, Waqar, Lin, Leteng, and Strand, Michael

Subjects
*COKE (Coal product), *PACKED bed reactors, *BENZENE, *FLUIDIZED-bed combustion, *PEBBLE bed reactors, *COAL carbonization, *SURFACE reactions
Abstract

Conversion of producer gas tar without coke generation is a great challenge. This study investigates conversion of tar model benzene using different configurations of highly non-porous ɣ-Al 2 O 3 packed bed reactor at 1000–1100 0C. The configurations comprised of different positions (relative to top (P 1), center (P 2) and bottom (P 3) of reactor furnace), heights (5, 13 and 25 cm) and particles sizes (0.5, 3 and 5 mm) of alumina packed bed. Steam and CO 2 were used as reforming media for tested benzene concentrations (0.4–1.8 vol%). The results showed benzene conversions of 48–91% with negligible steady thin coke generation using a packed bed (height: 25 cm, particles size: 3 mm) at P 1. Whereas, relative high benzene conversions of 63–93 and 68–95% at P 2 and P 3 respectively with unsteady thick coke generation at benzene concentrations greater than 0.4 vol% increased differential upstream pressures (DUPs) of beds. Similar unsteady coke generation at benzene concentrations greater than 0.8 vol% and temperature of 1100 0C was observed with packed beds of heights of 5 and 13 cm, and particles size of 0.5 mm at P 1. Generation of unsteady coke with condensed structure as evidenced by its characterization was attributable to increased benzene polymerization and reduced bed surface gasification reactions due to improperly installed packed bed. Developed kinetic model predicted well the generated coke. As conclusion, properly installed alumina packed bed pertaining to tar concentration and other experimental conditions may inhibit coke generation during tar conversion. • Packed bed position influenced both benzene conversion and observed coke generation. • Packed bed height and particles size influenced coke generation only. • Increased polymerization and reduced gasification reactions lead coke generation. • Reduced concentrations of steam other than of CO2 generated coke. • Developed kinetic model estimated the generated coke well. [ABSTRACT FROM AUTHOR]

Published
2024
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49. Synergistic dual-additive regulated carbonate electrolyte stabilizes bidirectional interface for aggressive Ni-rich Li-metal full batteries.

Author

Wang, Kun, Wang, Xiangxiang, Ahmad, Waqar, Zhao, Jing, Li, Han, Wang, Liguang, Wan, Zhengwei, Jiang, Wei, Li, Siying, Yang, Fan, Ling, Min, Chen, Jun, Zhu, Weiwei, and Liang, Chengdu

Abstract

The escalating energy demands underscore the importance of Ni-rich Li-metal batteries (LMBs); however, their aggressive bidirectional electrode-electrolyte interfacial issues hinder the practical implementation. Overcoming the limited solubility (∼800 ppm) of lithium nitrate (LiNO 3) in commercially available carbonate electrolytes holds promise. Nevertheless, unintended effects caused by solubilizers raise emerging concerns. Herein, an additive solubilized additive strategy is introduced to synergistically stabilize the Ni-rich cathode and Li-metal anode (LMA) in carbonate electrolytes, where tris (2, 2, 2-trifluoroethyl) borate (TTFEB) as a solubilizer utilizes its electron-deficient B atom to snatch electron-rich NO 3 - anion of insoluble LiNO 3 and thus forms a unique TTFEB-LiNO 3 solvation structure in carbonate electrolytes. Valuably, the dual-additive electrolyte facilitates the formation of a robust LiF/Li 3 N-rich solid electrolyte interphase on LMA and a thin, uniform F, B, N-rich cathode electrolyte interphase on Ni-rich cathode, effectively suppressing the breeding of Li dendrites and mitigating the structure degradation of Ni-rich cathode. Consequently, the full cell, featuring a thin Li anode (50 µm) and a high-loading NCM811 cathode (4.04 mAh cm−2) in the dual-additive electrolyte, demonstrates a notable capacity retention of 81.5 % after 140 cycles. This work reveals the intricated LiNO 3 -carbonate solvation chemistry, inspiring further advancements in electrolyte engineering for practical LMBs. [Display omitted] • An additive solubilized additive strategy synergistically stabilizes aggressive Ni-rich LMBs in carbonate electrolytes. • TTFEB utilizes its electron-deficient B atom to snatch electron-rich NO 3 - anion of insoluble LiNO 3. • A robust LiF/Li 3 N-rich SEI is formed on LMA, effectively suppressing the breeding Li dendrites. • A thin, uniform F, B, N-rich CEI is generated on Ni-rich cathode, mitigating its structure degradation. • The full cell, featuring 50 μm Li and 4.04 mAh cm-2 NCM811, retains a high capacity retention of 81.5 % after 140 cycles. [ABSTRACT FROM AUTHOR]

Published
2024
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