CATALYTIC REACTIONS IN WASTE PLASTICS, HDPE AND COAL STUDIED BY HIGH-PRESSURE THERMOGRAVIMETRY WITH ONLINE GC MS/

High-pressure thermogravimetry (TG) with rapid on-line gas chromatogra phy/mass spectrometry (GC/MS) has been used to investigate the effects of different catalysts on decomposition reactions of commingled waste plastics (predominantly PE), high-density polyethylene (HDPE) and mix tures of DECS-6 coal with waste plastics in H-2 at 900 psig. This perm its direct evaluation of relative decomposition and residual char amou nts as well as yield and composition of the evolved products. Catalyst s evaluated for the conversion of waste plastics include solid superac ids such as Fe2O3/SO42-, Al2O3/SO42-, Al2O3/SO42- promoted by 0.5% Pt, and ZrO2/SO42- (all added at 10 wt%), as well as a conventional crack ing catalyst of SiO2Al2O3 in a 4:1 ratio, a hydrocracking catalyst of NiMo/Al2O3 mixed with SiO2/Al2O3 (both added at 50%), and an HZSM-5 ze olite catalyst (added at 10%). Under these conditions cracking activit y for waste plastics reveals the following order: SiO2/Al2O3, HZSM-5 > NiMo/Al2O3 mixed with SiO2Al2O3 > solid superacids. Of the solid supe racids studied, the ZrO2/SO42- catalyst possesses the highest cracking activity and the approximate order of cracking activity is ZrO2/SO42- > Al2O3/SO42- > Pt/Al2O3/SO42- > Fe2O3/SO42- > no catalyst. The stron ger the cracking catalyst, the lighter the aliphatic products and the more abundant the isomeric constituents. Similar results are found for HDPE with these catalysts. For co-processing of coal with commingled waste plastic the HZSM-5 zeolite catalyst shows the most promising res ults by increasing the rate of the decomposition reactions at 420 degr ees C nearly tenfold. Hydrocracking catalysts, such as NiMo/Al2O3 mixe d with SiO2/Al2O3, show potential promise for co-processing of coal wi th commingled waste plastic due to their combined hydrogenation and cr acking ability. By contrast, a superacid such as ZrO2/SO42- or a crack ing catalyst such as SiO2/Al2O3 appears to have little effect on the d ecomposition rate of the mixture. To what extent these findings are in fluenced by transport limitations (e.g. due to incomplete mixing or de gree of crystallinity) and/or catalyst pretreatments is being studied further.