## 1 Introduction  
Today, humans depend on plastic materials because of their uses and advantages. A total of 368 Mt of plastic were produced worldwide in 2019, with 58 Mt being produced in Europe. This led to a large production of plastic waste. In 2018, 29.1 Mt of post-consumer plastic waste was collected in Europe, and about 25% of plastic waste ended up in landfills (in Spain, this value increased to 39%) [1]. Spain has two collection systems: the selective collection of municipal waste in homogeneous fractions, which are normally recycled in their great majority, and the collection of non-segregated waste (the fraction of municipal waste not collected selectively), which includes a great amount of organic fraction mixed with other types of municipal waste. This second flow of municipal waste has more disadvantages than recycling due to the high heterogeneity and variety of materials it contains. Unfortunately, the non-selective collection system is the most popular among Spanish citizens, with 86% of municipal waste collected in this system for provinces such as Granada [2]. This organic-rest fraction comprises 12.6% of plastics [3] that could be recovered and used through a recycling or valorization process. Among valorization techniques, the conversion of plastics into valuable hydrocarbon fuels has attracted attention [4]. There are numerous techniques for plastic waste, mainly mechanical and chemical recycling. [PERSON] et al. [5] made a comprehensive compilation of the ways to recycle different plastic waste and found that chemical recycling, and in particular pyrolysis, is a promising complementary model to support a circular economy for all plastics since it is specially focused on the plastic waste that cannot be mechanically recycled for technical or economic reasons, such as mixed polymers (including multilayers, multi-materials, very dirty plastics, etc.). In addition, [PERSON] et al. [6] reviewed the potential of pyrolysis for the recovery of plastic waste. Their work discussed the different types of pyrolysis, operating conditions, use of catalysts, etc., and their effect on the characteristics of the pyrolysis products obtained. [PERSON] et al. [7] studied the most influential factors in the pyrolysis process, the products that can be obtained, and the differences when using catalysts. [PERSON] et al. [8] reviewed the plastic waste pyrolysis process, analyzing the parameters that most influence the characteristics of the final products, such as temperature, residence time, pressure, catalyst, and the type of reactor. Additionally, in a recent study, [PERSON] et al. [9] extensively reviewed the current state of converting plastic waste to fuels. The authors reviewed traditional technologies, such as thermal pyrolysis, and new technologies, including catalytic pyrolysis, hydrothermal liquefaction, and advanced oxidation processes, such as photocatalytic oxidation, Fenton oxidation, and electrocatalytic oxidation. The authors indicate that it is possible to convert plastic waste to fuel through catalysts efficiently. However, problems such as the deactivation of the catalyst and its cost must be taken into account. In this sense, the authors included a line of research in the future: a greater study on the use of catalysts, emphasizing the development of catalysts that have good adaptability, high activity and recyclability. Therefore, pyrolysis can be considered an interesting recycling technology for municipal mixed plastic waste such as mixed polyethylene (PE) (high-density (HDPE) and low-density (LDPE)) or polyolefin mixtures (PE, polypropylene (PP) and polystyrene (PS)) that are currently not mechanically recycled but incinerated and/or dumped to landfill. Thermal or non-catalytic pyrolysis involves heating municipal mixed plastic waste at moderate temperatures in an inert atmosphere to produce three main products: gas, liquid ( oils), and solid (char).