# A Critical Review of SCWG in the Context of Available Gasification Technologies for Plastic Waste
## 6 Gasification of Plastic Waste: An Overview
### Polyolefin
#### 6.1.1 Polypropylene
Regarding olivine, using 100 wt% of this mineral in the gasifier bed they obtained: \(\sim\)2 g of tar/m\({}_{\text{N}}\)\({}^{3}\); net calorific value (LHV), \(\sim\)6 MJ/Nm\({}^{3}\); and gas yield, \(\sim\)5.5 Nm\({}^{3}\)/kg\({}_{\text{daf}}\). Instead, by varying the ER and the freeboard temperature they obtained a tar content of about 2 g of tar/Nm\({}^{3}\), an LHV of about 9 MJ/Nm\({}^{3}\), and a gas yield of about 3.5 Nm\({}^{3}\)/kg\({}_{\text{daf}}\). [PERSON] et al. [83] in 2013 studied the air gasification of post-consumer film waste and two reference polymers, PE and PP, in a bubbling fluidized bed. The experiments were conducted at a temperature of 750 \({}^{\circ}\)C and with different ER values (0.25-0.30-0.35). The experiments prove that film waste and analogue polymer derived wastes can be successfully gasified in a fluidized bed reactor, yielding net cold gas efficiency up to 61%, associated to gas heating values up to 5.7 MJ/m\({}^{3}\) and gas yields around 3.6 m\({}^{3}\)/kg. [PERSON] and [PERSON] [135] in 2014 investigated a screw kiln continuous reaction system for hydrogen production from the pyrolysis/steam gasification of virgin PP pellets. The pyrolysis was carried out at 500 \({}^{\circ}\)C, while the gasification temperature was varied in the tests (600, 700, 800, and 900 \({}^{\circ}\)C). The water injection rate was controlled at 14-23 g/h. Two catalysts (a laboratory-prepared Ni-Mg-Al catalyst and a commercial nickel catalyst) were used. The results show that an increase in the gasification temperature or in the water injection rate together with the presence of catalysts, favored the production of hydrogen. [PERSON] et al. (2018) in 2018 investigated the use of plastic waste from PP snack packaging as a carbon resources for steel carburization. By heating together some plastic waste from snack packaging and a steel sample to the carburizing temperature (1200 \({}^{\circ}\)C), carbon-rich reducing gases, such as CO and CH4, could be released from the plastic waste and absorbed by the steel sample such as carbon precursor for carburation. The resulting carburization effect on steel was investigated by optical microscopy, scanning electron microscopy, electron probe micro analyzer, and X-ray photoelectron spectrometer techniques. The results obtained showed that plastic waste from snack packaging could function effectively as a valuable carbon resource for carburizing steel, as it leads to an increase in the surface carbon content and in a corresponding evolution of the microstructure in steel. A summary view of the operating conditions used in the various works is shown in Table 3. As can be seen from the table, most of the experiments were carried out on a virgin polymer and not on a real waste polymer, using both fluidized and fixed bed reactors and air or steam as gasifying agents. Olivine or nickel-based catalysts are preferred over dolomite to reduce tar production. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Reactor** & **Feedstock** & **Bed Material** & \begin{tabular}{c} **Casification** \\ **Temperature** \\ \end{tabular}  & \begin{tabular}{c} **Tar Content** \\ **Agent** \\ \end{tabular}  & \ \begin{tabular}{c} **Casifying** \\ **Heating Value** \\ \end{tabular}  & \begin{tabular}{c} **Reference** \\ **Year** \\ \end{tabular}  \\ \hline Fluidized bed & Virgin PP & ash & 600-950 °C & 250 mg/Nm\({}^{3}\) & air & LHV: 52-11.4 M/Nm\({}^{3}\) & [PERSON] et al. [43] & 2006 \\ \hline \multirow{3}{*}{Image furnace} & \(\text{PP}+\text{AlO}(\text{H}_{0})\) & \multirow{3}{*}{-} & \multirow{3}{*}{1227 °C} & \multirow{3}{*}{-} & \multirow{3}{*}{air} & \multirow{3}{*}{-} & \multirow{3}{*}{-} & \multirow{3}{*}{-} & \multirow{3}{*}{-} & \multirow{3}{*}{1 abil} et al.