# A Critical Review of SCWG in the Context of Available Gasification Technologies for Plastic Waste
## 6 Gasification of Plastic Waste: An Overview
### Co-Gasification
In 2013, [PERSON] and [PERSON] [110] investigated co-gasification of biomass and plastics in a fluidized bed pilot plant using four types of plastic material of different origins (plastics from MSW, plastics from automotive shredder residues, PE regrind, and virgin PE) and soft wood pellets. During the experiments, the quantity of wood was kept constant while the mixing ratios between the plastics were varied. Gasification was carried out at 850 \({}^{\circ}\)C. The composition of syngas as well as the tar content were influenced by the simultaneous presence of biomass with plastics. More CO and CO\({}_{2}\) were measured than expected for pure substances, while the amount of H\({}_{2}\) was underestimated or overestimated depending on the plastic material. It has been observed that the presence of wood charcoal with plastics favors polymers decomposition and significantly reduces tar formation. In 2015, [PERSON] et al. [152] studied steam gasification of PP/biomass mixtures and of their constituents using a two-stage process, in a dual-bed microreactor. The mixes consist of 70% plastic and 30% biomass. The experiments were carried out at 700 \({}^{\circ}\)C in the absence or presence of Fe\({}_{2}\)O\({}_{3}\)/CeO\({}_{2}\) catalyst. The presence of the catalyst favors the formation of gaseous products. Furthermore, confirming previous studies, also in this case a synergistic effect is observed by combining biomass with plastic, as the production of H\({}_{2}\) is greater compared to the added contribution of production of H\({}_{2}\) from the individual components. In 2016, [PERSON] et al. [87] studied co-gasification in a fluidized bed as a strategy for energetic valorization of rice processing wastes (rice husk, straw, and plastics, mainly PE from bags for rice packaging). During the process, different types of gasifying agents were tested. Good results were obtained with steam and oxygen, because the gas was not diluted in N\({}_{2}\) and it had a higher heating value. Moreover, CO\({}_{2}\) proved to be a good gasifying agent as it leads to a decrease in tar content and an increase in the yield of gas. In the same year, [PERSON] et al. [153] studied co-gasification in a bench scale plant of ternary blends of rice straw (RS), PE, and PVC using steam as a gasifying agent. Different operating parameters such as temperature, the type of plastics, and their mixtures were examined. It has been shown that the increasing temperature, increases the gas yield, its H\({}_{2}\) content, and its LHV. Similar results are also obtained by increasing the PE and PVC content. This work confirmed that the synergistic interactive effect takes place during the co-gasification of ternary blends of PE, PVC, and RS due to volatile-char interaction and mineral catalytic effects. In 2018, [PERSON] and [PERSON] [154] studied steam gasification of biomass and plastics in a semi-batch reactor at 1173 K. The waste plastics used in the process were recycled black polycarbonate (BPC) pellets, PP pellets, and PET. Mixtures with different biomass/plastic ratios were examined. Moreover, in this case there were synergistic effects that led to obtaining greater quantities of syngas than the weighted sum of single components gasification for all the plastics examined. [PERSON] et al. [155] in 2019 investigated co-pyrolysis and co-gasification of some types of biomass (eucalyptus wood (EW) and rice straw (RS)) with PE. The studies were conducted through a complex instrumentation consisting of a thermogravimetric analyzer coupled with a Fourier transform infrared spectrometer and a scanning electron microscope coupled with energy dispersion spectroscopy. They observed that the process can be divided into three stages: Two during pyrolysis (decomposition of biomass material; degradation of PE) and one during gasification (reaction of pyrolysis products with CO\({}_{2}\)). The experimental results showed that the addition of PE promotes the decomposition of EW and RS. [PERSON] et al.