Influence of process conditions on syngas production from the thermal processing of waste high density polyethylene

A range of process conditions, including the type of reactor, the reacting atmosphere and the presence of catalyst, and their influence on the production of syngas, i.e. hydrogen and carbon monoxide, from the thermal processing of waste high density polyethylene (HDPE) has been investigated. Pyrolysis in the presence of nitrogen and in the presence of carbon dioxide, two-stage pyrolysis-steam reforming and carbon dioxide/catalysis process conditions were investigated in relation to gas composition and particularly hydrogen and carbon monoxide yield. The influence of addition of a Ni-Mg-Al catalyst in the second reactor was also investigated. It was found that a two-stage pyrolysis at 500 °C, followed by second stage reaction at 800 °C resulted in a significant increase in hydrogen production. With the addition of carbon dioxide, the two stage process also increased carbon monoxide yield in addition to hydrogen. Addition of steam into the second stage reactor with the carbon dioxide produced a further increase in hydrogen production. Also, the presence of a Ni-Mg-Al catalyst in the second reactor increased the amount of hydrogen and carbon monoxide produced.