Pyrolytic Liquid Fuel – An Alternative for Producing Electrical Energy in Mexico

Millions of tons of urban solid waste are discarded yearly in Mexico. The rapid population growth, urbanization, and social development, together with a more significant number of inhabitants, resulted in a massive amount of municipal solid waste (MSW) that is increasing yearly. Most of these end up in landfills without being used for energy, causing severe social and environmental problems. Municipal solid waste (MSW) is the most significant main waste stream (representing 9.21% of the waste that can be used), including plastic bottles, food dishes, cans, bags, and containers. The recycling and sustainable disposal of plastic waste is a significant activity with a high rate of complexity due to various effects that occur during its processes, such as obstructions in mechanisms and pipes, prolonged degradation and biodegradation rates, and the presence of additives, and highly toxic dyes. Pyrolysis is one of the promising tech-nologies for converting waste into sound energy capable of being used in various applications such as power generation, transportation fuel, and multiple thermal purposes. According to the Ministry of Energy (SENER), Mexico has an installed generation capacity of 86,034 MW, of which almost 65% is based on fossil-based technologies.


INTRODUCTION
According to the Secretary of the Environment (Naturales secretería de Medio Ambiente y Recursos, 2020), plastic waste is solid waste generated in homes or the industrial sector, which results in the elimination of materials used in its various activities such as containers, packaging, and packaging, among others.
Pyrolysis is a thermal process in which carbon-based compounds, including municipal solid waste (MSW), can be converted into combustible liquids at temperatures ranging from 300 to 600 °C or even higher. The process must be carried out in the total or partial absence of oxygen (O 2 ) (Rehan et al., 2016). The literary review shows various municipal wastes, such as high-density polyethylene (HDPE), low-density polyethylene (LDPE), polystyrene (PS), and polypropylene (PP), which have been treated by thermal and catalytic pyrolysis to obtain fuel liquid (Ali et

METHODS
Different types of plastic waste are found in municipal landfills (MPW), such as polystyrene, high-density polyethylene (HDPE), low-density polyethylene, polypropylene (PP), and mixtures, which have been successfully treated in recycling processes. Catalytic and non-catalytic pyrolysis. The operating conditions such as temperature, residence time, raw material, type of reactor, and composition have been reported and published by various authors.  (Sharma et al., 2014), with this, the potential for the generation of electrical energy for the next 20 years (2042) was estimated. Table 1 shows the heating values of some of the everyday plastics that can be commonly found in landfills.
According to the Ministry of the Environment and Natural Resources (SEMARNAT), the generation of municipal solid waste (MSW) in Mexico for the year 2022 was estimated at approximately 120,128 tons/day, which translates into an average of 0.944 kg /inhabitant/day within which 31.56% corresponds to waste that can be used, and of these, 7.66% refers to plastics and 1.55% to expanded polystyrene, that is, approximately 11,051 tons per day (Naturales secretería de Medio Ambiente y Recursos, 2020). On the other hand, according to data obtained from the same SEMARNAT (Residuos Sólidos Urbanos (RSU) | Secretaría de Medio Ambiente y Recursos Naturales | Gobierno | Gob. Mx, n.d.) 83.93% is collected, and of this 78.54% ends up in final disposal sites, and only 9.63% of the total waste is recycled, it is expected that year after year the waste disposal will increase by an average of 2% ( Figure 1). The municipal solid wastes (MSW) were projected annually from 2022 to 2042, and according to this projection, they amount to more than 67 million tons ( Figure 1). The benefi ts of landfi ll savings and electricity generation from liquid fuel and coal are considered. Landfi ll savings were calculated using a basic landfi ll cost of MXN 121.58 per ton of waste (Residuos Sólidos Urbanos (RSU) | Secretaría de Medio Ambiente y Recursos Naturales | Gobierno | Gob.Mx, n.d.). Electricity savings were calculated based on the typical price of MXN 0.75 per kWh and GHG emissions were calculated using the method proposed by the Intergovernmental Panel on Climate Change (IPPC). The method is described by Equation 1.
where: Q -the total CH 4 emissions (ton/year); MSW T -the total MSW generated per year (ton/year); MSW F -the fraction of solids disposed of in landfi lls; MCF -a correction factor for methane; DOC -the degradable carbon fraction; DOC F -the dissimilated organic fraction; F -the gaseous fraction of CH4 in landfi lls; 16/12 -the molecular weight ratio of methane to carbon; OX -an oxidation factor.
The details of Equation 1 estimate the emission profi les for methane (CH4) and Mt.CO2 eq. Global warming potential (GWP) has been studied previously and can be consulted in the IPCC guidelines (Reay et al., 2007). The value of carbon is 23. 20 US$ per ton of CO2 equivalent is considered for GHC emission savings (Rehan et al., 2016).
The electrical energy potential was calculated using Equation 2, where PMSW is the electrical potential that can be generated through the pyrolysis of urban plastic waste (GW), MSW is the total urban solid waste generated annually (kg/year), FMSW is a factor that indicates the percentage of solid waste that can be recovered energetically, HHV is the higher calorifi c power that the plastics that can be recovered contain on average (MJ/kg), FLF is a factor that indicates the fuel liquid yield that can be can recover, tA is the annual time (s).

RESULTS AND DISCUSSIONS
According to the projection of municipal solid waste that can be used, by the year 2022, there would be an estimated 45.6 million tons of plastic, which means a potential of 36.48 million tons of liquid fuel, increasing to 54.48 MT in 2042. with a high calorifi c value of 40 MJ/kg, which translates into a tremendous electrical energy potential of approximately 46.25 GW, with an increase of 2% each year (Figure 2), that is, a Figure 2. Electricity generation capacity through pyrolytic technology using all the plastic waste generated in Mexico potential of 126.71 MW/day, which can be used to power about 23,038 homes on average (average consumption of 5.5 kW/day). The economic benefi ts for savings in fun landfi lls, electricity generation, and carbon credits tend to be approximately 1,574,622,866.63 US$ with an annual increase of 2%, generating signifi cant economic savings (Figure 3). The Table 2 describes the technical details, economic evaluation, and implementation technique of a pyrolytic technology plant.
The liquid produced from the pyrolysis of plastic waste also off ers the opportunity to be refi ned and distilled through refi ning plants, creating alternative fuels for electricity generation or transportation, fuel applications (Demirbas, 2004). In addition, the carbon produced through some chemical modifi cations can be used in water treatment plants or air purifi ers, creating benefi cial environmental impacts.
The most signifi cant benefi t is the reduction of GHG emissions, contributing to the reduction of greenhouse gases and benefi ting society and the environment since this would help reduce the high rates of climate change. In addition, the savings generated from the pyrolysis of MSW can help develop underdeveloped communities by creating direct jobs for the surrounding area and, in turn, increasing the quality of life in these areas.
On the other hand, it should be emphasized that some areas used for waste disposal can be recovered, benefi ting the surrounding fauna, and creating green spaces for the diff erent species.  (Figure 3).

CONCLUSIONS
The potential of recycling MSW through pyrolysis as an alternative technology in Mexico has been analyzed. The pyrolytic liquid generated from the thermochemical degradation of the waste shows a high energy potential, on average, an HHV of 40 MJ/kg. On the other hand, the liquid fuel shows similar properties to diesel, such as density (0.8 kg/m 3  The most crucial part that should be emphasized is the economic savings for landfill diversion, revenue for carbon credits, and electricity generation, which amount to 1,574,622,866.6 US$ with an annual increase of 2%. As observed, the pyrolysis of MSW offers excellent economic, social, and environmental benefits. However, before opting for the implementation of plants, environmental impact studies must be carried out.