In‐Situ Upgrading of Coal Pyrolysis Tar with Steam Catalytic Cracking over Ni/Al₂O₃ Catalysts

Abstract

In-situ upgrading of coal pyrolysis tar with steam catalytic cracking (SCC) is a promising technique to improve tar quality. In this study, Ni/Al 2 O 3 catalysts with different Ni contents were used for in-situ SCC of coal pyrolysis tar at 650°C. The results showed that Ni/Al 2 O 3 catalysts can enhance the water conversion and light tar yield. Both SCC and tar catalytic cracking can occur simultaneously over Ni/Al 2 O 3 , and the free radicals produced by tar catalytic cracking can be stabilized by active species generated from SCC to avoid excessive cracking of tar and improve light tar yield. 4Ni/Al 2 O 3 (4 wt. % Ni) exhibits the best performance, contributing to the highest water conversion of 4.74 wt. % and light tar yield of 11.90 wt. %, respectively.Correspondingly, the content of light fraction (boiling point less than 360°C) in tar sample increases from 48.0 wt. % to 67.0 wt. %, and the average molecular weight decreases from 353 amu to 253 amu over 4Ni/Al 2 O 3 . This is consistent with the increase of benzenes, phenols and naphthalenes and the decrease of long-chain aliphatic hydrocarbons, 3-and 4-ring aromatics in upgraded tar. In addition, the higher ratio of uncondensed aromatic protons to condensed aromatic protons in upgraded tar reveals the fact that 4Ni/Al 2 O 3 can promote ring-opening reaction of PAHs, which can well interpret the tar upgrading process.

A Comprehensive Review on Recent Advancements in Thermochemical Processes for Clean Hydrogen Production to Decarbonize the Energy Sector

“…Heterogenous catalysts show high catalytic activity, longer durability, greater thermal stability, greater chemical stability, nontoxicity, an easy recovery process, and greater tolerance whereas homogenous catalysts are toxic, flammable, corrosive, and produce by-products and wastewater which require complex and expensive disposal procedures [105]. Siqian Cao et al studied the in-situ steam catalytic cracking of coal pyrolysis in the presence of a Ni/Al 2 O 3 catalyst with different Ni contents at 650 • C [106]. They analyzed the effects of the catalyst and found that when using the Ni/Al 2 O 3 catalyst, water conversion increased and tar production decreased.…”

Catalytic Pyrolysis of Naomaohu Coal Using Combined CaO and Ni/Olivine Catalysts for Simultaneously Improving the Tar and Gas Quality

“…The objective of this process is to achieve clean and efficient usage of low-rank coal [1][2][3]. However, the conventional pyrolysis process often generates a notable quantity of heavy tars with boiling points exceeding 360 • C and also produces CO 2 as a by-product [4,5]. Over 50% of the total tar consists of heavy components characterized as highly viscous and corrosive [6].…”