# A Critical Review of SCWG in the Context of Available Gasification Technologies for Plastic Waste
## 6 Gasification of Plastic Waste: An Overview
### Plastics Mix  
Very often the gasification of plastic material does not concern a single type of feedstock but a mix of different plastic materials, for example, those coming from municipal solid waste (MSW). Among these materials we find not only PP and PE but also PS, PVC, polymethylmethacrylate (PMMA), and PET. In particular, PS is used for protective packaging containers, lids, bottles, trays, tumblers, and disposable cutlery. PVC is used for tamper-resistant over-the-counter medications and shrink wrap for consumer products. The PVC rigid vinyl film is used in blister and clamshell packaging to protect medicines, personal care products, and other household goods. PET is widely used for packaging foods and beverages, especially convenience-sized soft drinks, juices, and water. Finally, PMMA is known for its applications in various markets such as car, windows, smartphone, screens and aquariums. A research group that has been interested in the problem of gasification of plastic mixes is that of [PERSON] et al. (Department of Energy and Environmental System Engineering, University of Seoul). In 2013, this research group has published two papers about this topic. In the first one [89], they studied air gasification of a mix of recycled polymers (PP, PE, PS, PVC, PMMA, and PET) in a two-stage gasifier, using olivine as a bed material and activated carbon (AC) as a tar-cracking additive. In all experiments, the reaction temperatures of the lower and upper reactors were maintained at 800 \({}^{\circ}\)C. With 1500 g of AC, a 30% by volume of H\({}_{2}\) was obtained and the tar removal efficiency reached 98% using steam as a gasifying agent. With the combined use of olivine and activated carbon and an ER of about 0.31, LHVs in the range of 5.3-6.2 MJ/Nm\({}^{3}\) were obtained. In the second one [138], they investigated again air gasification of a mix of recycled polymers (PP, PE, PS, PVC, PMMA, and PET) using a two-stage gasifier. Instead of olivine, calcined dolomite was used as a bed material together with activated carbon as a tar-cracking additive. Moreover, in this case, various operational parameters were examined. When the amount of activated carbon increased from 0 to 900 g using calcined dolomite as the bed material, the concentrations of H\({}_{2}\) and CO in the producer gas increased considerably (H\({}_{2}\): From 14.9 to 26.1 vol%; CO: From 9.4 to 16.8 vol%). Using 900 g of AC, the total amount of tar was reduced by 96%. The maximum LHV of the producing gas was approximately 13.4 MJ/Nm\({}^{3}\). In 2013, [PERSON] and [PERSON] [115] studied steam gasification of plastic wastes in a dual fluidized bed gasification pilot plant (DFB) using olivine as a bed material. Several types of common plastics (both recycled and virgin) were studied: PE, PP and blends of PE + PS, PE + PET, and PE + PP. This experimental work demonstrates that the tested polymers are suitable feedstock for the DFB gasifier. The study showed how polymer mixes behave differently than pure polymers. In particular, the polymer mixtures PE + PP and PE + PS generated more H\({}_{2}\) and CO than pure polymers. The mixture of PE + PET gave rise to a high amount of CO\({}_{2}\) due to the high oxygen content of PET. The most recent study on plastic mix gasification is that of [PERSON] et al. [139] in 2020. They evaluated the catalytic steam gasification of different polymers and their mixtures (LDPE, HDPE, PP, and PS) with a dolomite supported Ni catalyst in a drop-tube fixed-bed reactor. \"A 5 wt% NiO/dolomite catalyst gave the highest degree of carbon conversion for all evaluated plastics and mixtures\". The study revealed synergistic interactions between different plastics mixed together. These interactions can lead to an increase or decrease in the amount of gas produced. For example, mixtures containing PE show a reduced production of gas, while those containing polystyrene give rise to a very high production of H\({}_{2}\), CO, and CO\({}_{2}\).