Conversion of plastic waste into fuel oil using zeolite catalysts in a bench-scale pyrolysis reactor

Conversion of Polypropylene into Light Hydrocarbons and Aromatics by Metal Exchanged Zeolite Catalysts

Polyolefins can be converted into C2-C5 hydrocarbons and benzene-toluene-xylene (BTX) aromatics as high-demand petrochemical feedstocks via catalytic pyrolysis on acidic zeolites. Bro̷nsted and Lewis acid sites are responsible for cracking polyolefins into olefins and subsequent aromatic formation. In this study, we have subjected the parent HZSM-5 zeolite to postsynthetic partial metal exchange with Fe, Co, Ni, Cu, and Ce cations to perturb Bro̷nsted/Lewis acidity. We have investigated these metal-modified HZSM-5 on the catalytic pyrolysis of polypropylene (PP) in a micropyrolyzer connected to a two-dimensional gas chromatograph coupled to a time-of-flight mass spectrometer and flame ionization detector (Tandem Pyrolyzer-GC × GC-TOF-MS/FID setup). Whereas Fe-, Co-, Cu-, and Ce-exchanged zeolites (with 2.5, 2.3, 1.9, and 0.8 wt % metal, respectively) had comparable product yields with the parent zeolite, Ni-exchanged zeolites with Ni content of 0.5 to 2 wt % were associated with enhanced BTX formation (28-38 wt %) compared to that of the parent zeolite (22 wt %). Pyridine-FTIR indicated that the Bro̷nsted/Lewis acid ratio of the parent zeolite decreased upon metal ion exchange. According to Pyridine-TPD, the parent zeolite's medium-strength acid sites were redistributed into weak and strong acid sites in Ni-exchanged zeolites. The higher amount of carbon deposits on Ni-exchanged zeolites compared to the parent and other metal ion exchanged zeolites was attributed to the enhanced aromatization activity by the simultaneous decrease in the Bro̷nsted/Lewis acid ratio and emergence of strong acid sites.

Chemical catalytic upgrading of polyethylene terephthalate plastic waste into value-added materials, fuels and chemicals

The substantial production of polyethylene terephthalate (PET) products, coupled with high abandonment rates, results in significant environmental pollution and resource wastage. This has prompted global attention to the development of rational strategies for PET waste treatment. In the context of renewability and sustainability, catalytic chemical technology provides an effective means to recycle and upcycle PET waste into valuable resources. In this review, we initially provide an overview of strategies employed in the thermocatalytic process to recycle PET waste into valuable carbon materials, fuels and typical refined chemicals. The effect of catalysts on the quality and quantity of specific products is highlighted. Next, we introduce the development of renewable-energy-driven electrocatalytic and photocatalytic systems for sustainable PET waste upcycling, focusing on rational catalysts, innovative catalytic system design, and corresponding underlying catalytic mechanisms. Moreover, we discuss advantages and disadvantages of three chemical catalytic strategies. Finally, existing limitations and outlook toward controllable selectivity and yield enhancement of value-added products and PET upvaluing technology for scale-up applications are proposed. This review aims to inspire the exploration of waste-to-treasure technologies for renewable-energy-driven waste management toward a circular economy.

Catalytic pyrolysis of waste polypropylene using low-cost natural catalysts

The objective of this research is to produce oil from the catalytic pyrolysis of waste polypropylene (WPP) using a low-cost natural catalyst. Three natural catalysts were examined, i.e. Kaolin, Hematite, and white sand. Different catalyst-to-plastic ratios were examined, i.e. 1:1, 1:2, 1:4, 1:6, and 1:8. The utilized catalysts were elementally analyzed using the XRF analysis and the surface area was analyzed by the BET multi-point method. The WPP thermal degradation behavior was investigated by the thermogravimetric analysis (TGA), then the generated liquid oil was analyzed using the gas chromatography-mass spectrometry (GC-MS) and the differential scanning calorimetry (DSC). Thermal cracking without a catalyst produced a yield of 70 wt% of liquid oil, and the maximum oil yield in case of using Hematite and white sand as a catalysts were 70 wt% and 68 wt%, respectively. However, the ratio of 1:2 of the Kaolin to the WPP produced the highest oil yield of 80.75 wt%, and the ratio of 1:8 of the white sand to the WPP produced the highest gas yield, i.e. 44 wt%. Using Kaolin in the catalytic pyrolysis of WPP produced oil with the lowest percentage of heavy oils, i.e. 25.98%, and the highest percentage of light oils, which is 25.37%, when compared to other catalysts such as Hematite and white sand. Kaolin has the lowest cost of oil production compared to Hematite and white sand, which is 0.28 $/kg of oil. Kaolin is an economical catalyst that improves the quality, as well as the quantity of the produced oil in comparison to Hematite, white sand and the non-catalytic case.

Plastic waste as pyrolysis feedstock for plastic oil production: A review

Turning plastic waste into plastic oil by pyrolysis is one of the promising techniques to eradicate plastic waste pollution and accelerate the circular economy of plastic materials. Plastic waste is an attractive pyrolysis feedstock for plastic oil production owing to its favorable chemical properties of proximate analysis, ultimate analysis, and heating value other than its abundant availability. Despite the exponential growth of scientific output from 2015 to 2022, a vast majority of the current review articles cover the pyrolysis of plastic waste into a series of fuels and value-added products, and up-to-date reviews exclusively on plastic oil production from pyrolysis are relatively scarce. In light of this void in the current review articles, this review attempts to provide an up-to-date overview of plastic waste as pyrolysis feedstock for plastic oil production. A particular emphasis is placed on the common types of plastic as primary sources of plastic pollution, the characteristics (proximate analysis, ultimate analysis, hydrogen/carbon ratio, heating value, and degradation temperature) of various plastic wastes and their potential as pyrolysis feedstock, and the pyrolysis systems (reactor type and heating method) and conditions (temperature, heating rate, residence time, pressure, particle size, reaction atmosphere, catalyst and its operation modes, and single and mixed plastic wastes) used in plastic waste pyrolysis for plastic oil production. The characteristics of plastic oil from pyrolysis in terms of physical properties and chemical composition are also outlined and discussed. The major challenges and future prospects for the large-scale production of plastic oil from pyrolysis are also addressed.

Thermal degradation model of used surgical masks based on machine learning methodology

Background

The COVID-19 pandemic has leveraged facial masks to be one of the most effective measures to prevent the spread of the virus, which thereby has exponentially increased the usage of facial masks that lead to medical waste mismanagements which pose a serious threat to life. Thermal degradation or pyrolysis is an effective treatment method for the used facial mask wastes and this study aims to investigate the thermal degradation of the same.

Methods

Predicted the TGA experimental curves of the mask components using a Machine Learning model known as Artificial Neural Network (ANN).

Significant findings

Three different parts of the mask namely- ribbon, body, and corner were separated and used for the analysis. The thermal degradation behavior is studied using Thermogravimetric Analysis (TGA) and this is crucial for determining the reactivity of the individual mask components as they are subjected to a range of temperatures. Using the curves obtained from TGA, kinetic parameters such as Activation energy (E) and Pre-exponential factor (A) were estimated using the Coats-Redfern model-fitting method. Using the determined kinetic parameters, thermodynamic quantities such as a change in Enthalpy (ΔH), Entropy (ΔS), and Gibbs-Free energy (ΔG) were also calculated. Since TGA is a costly and time-consuming process, this study attempted to predict the TGA experimental curves of the mask components using a Machine Learning model known as Artificial Neural Network (ANN). The dataset obtained at a heating rate of 10°C/min was used to train the 3 different neural networks corresponding to the mask components and it showed an excellent agreement with experimental data (R² > 0.99). Through this study, a complex chemical process such as thermal degradation was modelled using Machine Learning based on available experimental parameters without delving into the intricacies and complexities of the process.

Progress and perspective for conversion of plastic wastes into valuable chemicals

Today, discarded plastics in nature have caused serious "white pollution", however these plastic wastes contain abundant carbon resources that could serve as the feedstock to produce commodities. Because of this, it is requisite to convert these plastic wastes into valuable chemicals. Herein, the state-of-the-art techniques for plastic conversion are divided into two categories, those performed under violent conditions and mild conditions, in which the conversion mechanisms are discussed. The strategies under violent conditions are closer to practical application thanks to their excellent conversion efficiencies, while the strategies under mild conditions are more environmentally friendly, showing enormous development potential in the future. We summarize in detail the pyrolysis, hydropyrolysis, solvolysis and microwave-initiated catalysis for bond cleavage in plastic wastes at temperatures ranging from 448 to 973 K. Also, we overview the photocatalysis, electrocatalysis and biocatalysis for bond cleavage in plastic wastes at near and even normal temperature and pressure. Finally, we present some suggestions and outlooks concerning the improvement of current techniques and in-depth mechanisms of investigation for conversion of plastics into valuable chemicals.

Analysis of Fuel Alternative Products Obtained by the Pyrolysis of Diverse Types of Plastic Materials Isolated from a Dumpsite Origin in Pakistan

The current energy crisis and waste management problems have compelled people to find alternatives to conventional non-renewable fuels and utilize waste to recover energy. Pyrolysis of plastics, which make up a considerable portion of municipal and industrial waste, has emerged as a feasible resolution to both satisfy our energy needs and mitigate the issue of plastic waste. This study was therefore conducted to find a solution for plastic waste management problems, as well as to find an alternative to mitigate the current energy crisis. Pyrolysis of five of the most commonly used plastics, polyethylene terephthalate (PET), high- and low-density polyethylene (HDPE, LDPE), polypropylene (PP), and polystyrene (PS), was executed in a pyrolytic reactor designed utilizing a cylindrical shaped stainless steel container with pressure and temperature gauges and a condenser to cool down the hydrocarbons produced. The liquid products collected were highly flammable and their chemical properties revealed them as fuel alternatives. Among them, the highest yield of fuel conversion (82%) was observed for HDPE followed by PP, PS, LDPE, PS, and PET (61.8%, 58.0%, 50.0%, and 11.0%, respectively). The calorific values of the products, 46.2, 46.2, 45.9, 42.8 and 42.4 MJ/kg for LPDE, PP, HPDE, PS, and PET, respectively, were comparable to those of diesel and gasoline. Spectroscopic and chromatographic analysis proved the presence of alkanes and alkenes with carbon number ranges of C₉-C₁₅, C₉-C₂₄, C₁₀-C₂₁, C₁₀-C₂₈, and C₉-C₁₇ for PP, PET, HDPE, LDPE, and PS, respectively. If implemented, the study will prove to be beneficial and contribute to mitigating the major energy and environmental issues of developing countries, as well as enhance entrepreneurship opportunities by replicating the process at small-scale and industrial levels.

Step-By-Step Modeling and Demetallation Experimental Study on the Porous Structure in Zeolites

The organization of microporous space in zeolites is discussed. A new step-by-step model is proposed that explains the principles of organizing the hierarchy of microporous space at the stage of assembling zeolites from elements of minimal size: a primary building unit, secondary building units, tertiary building units or building polyhedra, a sodalite cage, and a supercage. To illustrate the stepwise hierarchical porous structure of nanomaterials, the following zeolites with small and large micropores have been selected as the model objects: sodalite (SOD, the maximum diameter of a sphere that can enter the pores is 0.3 nm) and zeolites of type A (LTA, the maximum diameter of a sphere that can enter the pores is 0.41 nm), type X, Y (FAU, the maximum diameter of a sphere that can enter the pores is 0.75 nm), and type BETA (the maximum diameter of a sphere that can enter the pores is 0.67 nm). Two-dimensional and three-dimensional modeling in 3Ds Max software was used. We believe that such an approach will be useful for developing ways to create complex zeolite compositions for specific applications, such as catalysis, where the geometry of the pores determines the size of the molecules entering the voids and computer modeling can play an important predictive role. This work takes a look at specific aspects of using the heat desorption method to study mesoporous materials with a BETA zeolite as an example and presents the results of experimental research into the characteristics of the porous structure of hierarchically structured zeolite materials (specific surface area 180-380 m²/g, external surface area 120-200 m²/g, micropore volume 0.001-0.1 mL/g).

Recent Advances in Catalytic Pyrolysis of Municipal Plastic Waste for the Production of Hydrocarbon Fuels

Currently, the resources of fossil fuels, such as crude oil, natural gas, and coal, are depleting day by day due to increasing energy demands. Nowadays, plastic items have witnessed a substantial surge in manufacturing due to their wide range of applications and low cost. Therefore, the amount of plastic waste is increasing rapidly. Hence, the proper management of plastic wastes for sustainable technologies is the need of the hour. Chemical recycling technologies based on pyrolysis are emerging as the best waste management approaches due to their robustness and better economics. However, research on converting plastic waste into fuels and other value-added goods has yet to be undertaken, and more R&D is required to make waste-plastic-based fuels economically viable. In this review article, the current status of the plastic waste pyrolysis process is discussed in detail. Process-controlling parameters such as temperature, pressure, residence time, reactor type, and catalyst dose are also investigated in this review paper. In addition, the application of reaction products is also described in brief. For example, plasto-oil obtained by catalytic pyrolysis may be utilized in various sectors, e.g., transportation, industrial boilers, and power generation. On the other hand, byproducts, such as solid residue (plasto-char), could be used as a road construction material or to make activated carbon or graphenes, while the non-condensable gases have a good potential to be utilized as heating/energy source.