|Schematic diagram of the two-stage pyrolysis-gasification experimental system. Credit: ACS, Elbaba et al.Click to enlarge.|
A team at the University of Leeds (UK) is investigating hydrogen production from waste tires using a two-stage pyrolysis-gasification reactor and Ni-Mg-Al (1:1:1) catalyst. A paper describing their work was published online 10 June in the ACS journal Energy & Fuels.
The generation rate of waste tires is increasing, especially with the continued increase in production of cars and trucks, the authors note. In 2007, the amount of waste tires was about 4.6 million tonnes within the US; nearly 3.4 million tonnes in Europe; more than 1 million tonnes in Japan; and about 1 million tonnes in China.
Regional and national governments use a wide variety of methods to deal with waste tires. In Europe, the main methods for waste tire management are materials recovery (38.7%), energy recovery (32.3%), and retreading (11.3%). In the US, the main methods for waste tire management are tire-derived fuel (52.8%), ground rubber (16.8%), and civil engineering applications (11.9%).
The pyrolysis and gasification of waste tires for the production of liquid fuels, chemical feedstocks, activated carbons, and gases has been extensively researched. Recently, it has been suggested that the thermal decomposition of waste tire at high temperature might be an alternative for production of hydrogen in future energy systems.
Catalysts play an important role in pyrolysis-gasification processes for maximizing hydrogen production. Nickel-based catalysts have been reported as promising catalysts for tar removal and hydrogen production in steam gasification processes due to their good catalytic effect and comparatively low cost.
—Elbaba et al.
The pyrolysis-gasification was carried out in a two-stage fixed bed reactor, with a laboratory-prepared Ni-Mg-Al (1:1:1) used as a catalyst. The tire rubber sample was pyrolyzed in the first reactor, and the pyrolysis products were passed directly to the second reactor where steam catalytic gasification of the pyrolysis gases was carried out.
In addition, the team also investigated the elastomer constituents most commonly used in tires: natural rubber (NR), styrene-butadiene rubber (SBR), and butadiene rubber (BR).
Experiments were conducted at a pyrolysis temperature of 500 °C and gasification temperature of 800 °C. The results showed that the gas and hydrogen yield were greatly increased for the tire and elastomer constituents during pyrolysis-gasification with the introduction of steam and/or catalyst.
For example, without steam and catalyst (sand), only 24.4 wt % gas yield in relation to the mass of BR was obtained. The gas yield in relation to the mass of BR was increased to 32.9 wt % with the introduction of water at the gasification temperature of 800 °C without the catalyst. The gas yield in relation to the mass of BR was further increased to 153.4 wt % in the presence of the Ni-Mg-Al catalyst and steam.
There was a significant increase in H2 and CO concentrations as well as a consequent decrease in CH4 and C2-C4 concentrations when the Ni-Mg-Al catalyst was applied to the pyrolysis-gasification process.
Hydrogen production increased from 0.68 to 5.43 wt % for the catalytic steam pyrolysis-gasification of waste tire in the presence of Ni-Mg-Al catalyst. The highest hydrogen production (15.26 wt %) was obtained for the BR feedstock.
Ibrahim F. Elbaba, Chunfei Wu and Paul T. Williams (2010) Catalytic Pyrolysis-Gasification of Waste Tire and Tire Elastomers for Hydrogen Production. Energy Fuels, Article ASAP doi: 10.1021/ef100317b