Simultaneous production of carbon nanotubes and hydrogen gas from the thermal treatment of waste plastics

In this work a two-stage reaction system was used for the simultaneous production of carbon nanotubes (CNTs) and hydrogen gas from plastic feedstocks. Initial pyrolysis was undertaken in the first stage heated at 600 C, before the evolved gases were passed to a second stage where a catalyst was held. Carbon deposition builds up on the surface of the catalyst, whilst hydrogen and other gases are then collected downstream. A series of analytical techniques were used to characterise the carbon deposition on the catalysts, as well as any oils or gases produced. Initially, a two stage pyrolysis-gasification process was undertaken with plastics from waste electrical and electronic equipment for investigation into hydrogen production. The introduction of a nickel catalyst led to increased hydrogen production, with small amounts of CNTs observed in the carbon deposits on the catalyst surface. In order to increase the yield of CNTs, different plastics including polyethylene, polypropylene and polystyrene were investigated. The rate of steam injection into the two stage pyrolysis-gasification process was also investigated, and proved significant to obtaining high yields of CNTs and hydrogen. All of the plastics produced CNTs, with the largest yield obtained from the pyrolysis gasification of polystyrene at a steam injection rate of 0.25 g h -1 . Additionally, the use of different catalysts was investigated, with iron, nickel, cobalt and copper catalysts all tested. CNTs were produced on the iron, nickel and cobalt catalysts, with the iron catalyst producing the largest yield. The calcination temperature and metal loading on the nickel catalyst was also studied, with catalyst support interactions of intermediate strength and a higher metal loading producing larger CNT yields. Finally, investigations into the temperature of the second stage where the catalyst was held were undertaken, along with using different ratios of catalyst: plastic sample. These too proved important in achieving large yields of both CNTs and hydrogen