Pyrolysis of municipal plastic wastes II: Influence of raw material composition under catalytic conditions

Recent advancements in the use of plastics as a carbon source for carbon nanotubes synthesis - A review

Plastics, which majorly consist of polypropylene (PP), polyethylene (linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE) and high-density polyethylene (HDPE)), polystyrene (PS), polyvinyl chloride (PVC), polyethylene terephthalate (PET), etc., are the most abundant municipal solid wastes (MSW). They have been utilized as a cheap carbon feedstock in the synthesis of carbon nanotubes (CNTs) because of their high hydrocarbon content, mainly carbon and hydrogen, especially for the polyolefins. In this review, the detailed progress made so far in the use of plastics (both waste and virgin) as cheap carbon feedstock in the synthesis of CNTs (only) over the years is studied. The primary aim of this work is to provide an expansive landscape made so far, especially in the areas of catalysts, catalyst supports, and the methods employed in their preparations and other operational growth conditions, as well as already explored applications of plastic-derived CNTs. This is to enable researchers to easily access, understand, and summarise previous works done in this area, forging ahead towards improving the yield and quality of plastic-derived CNTs, which could extend their market and use in other purity-sensitive applications.

Microwave co-pyrolysis for simultaneous disposal of environmentally hazardous hospital plastic waste, lignocellulosic, and triglyceride biowaste

Microwave co-pyrolysis was examined as an approach for simultaneous reduction and treatment of environmentally hazardous hospital plastic waste (HPW), lignocellulosic (palm kernel shell, PKS) and triglycerides (waste vegetable oil, WVO) biowaste as co-feedstock. The co-pyrolysis demonstrated faster heating rate (16-43 °C/min) compared to microwave pyrolysis of single feedstock (9-17 °C/min). Microwave co-pyrolysis of HPW/WVO performed at 1:1 ratio produced a higher yield (80.5 wt%) of hydrocarbon liquid fuel compared to HPW/PKS (78.2 wt%). The liquid oil possessed a low nitrogen content (< 4 wt%) and free of sulfur that could reduce the release of hazardous pollutants during its use as fuel in combustion. In particular, the liquid oil obtained from co-pyrolysis of HPW/WVO has low oxygenated compounds (< 16%) leading to reduction in generation of potentially hazardous sludge or problematic acidic tar during oil storage. Insignificant amount of benzene derivatives (< 1%) was also found in the liquid oil, indicating the desirable feature of this pyrolysis approach to suppress the formation of toxic polycyclic aromatic hydrocarbons (PAHs). Microwave co-pyrolysis of HPW/WVO improved the yield and properties of liquid oil for potential use as a cleaner fuel, whereas the liquid oil from co-pyrolysis of HPW/PKS is applicable in the synthesis of phenolic resin.

Oil Production by Pyrolysis of Real Plastic Waste

The aim of this paper is for the production of oils processed in refineries to come from the pyrolysis of real waste from the high plastic content rejected by the recycling industry of the Basque Country (Spain). Concretely, the rejected waste streams were collected from (1) a light packaging waste sorting plant, (2) the paper recycling industry, and (3) a waste treatment plant of electrical and electronic equipment (WEEE). The influence of pre-treatments (mechanical separation operations) and temperature on the yield and quality of the liquid fraction were evaluated. In order to study the pre-treatment effect, the samples were pyrolyzed at 460 °C for 1 h. As pre-treatments concentrate on the suitable fraction for pyrolysis and reduce the undesirable materials (metals, PVC, PET, inorganics, cellulosic materials), they improve the yield to liquid products and considerably reduce the halogen content. The sample with the highest polyolefin content achieved the highest liquid yield (70.6 wt.% at 460 °C) and the lowest chlorine content (160 ppm) among the investigated samples and, therefore, was the most suitable liquid to use as refinery feedstock. The effect of temperature on the pyrolysis of this sample was studied in the range of 430–490 °C. As the temperature increased the liquid yield increased and solid yield decreased, indicating that the conversion was maximized. At 490 °C, the pyrolysis oil with the highest calorific value (44.3 MJ kg⁻¹) and paraffinic content (65% area), the lowest chlorine content (128 ppm) and more than 50 wt.% of diesel was obtained.

Production and utilization of pyrolysis oil from solidplastic wastes: A review on pyrolysis process and influence of reactors design

This paper reviews the new progress, challenges and barriers on production of pyrolysis oil from the plastic waste. Among the different processes thermal and catalytic are the potential methods to produce oil. Since the global plastic production increased over years the accumulation of plastic waste increases. Thus, converting the waste plastics into useful energy is very essential to avoid the environmental concerns. Initially the thermal pyrolysis process and its advantage on production of pyrolysis oil were discussed. During the thermal decomposition the waste plastic had been converted into the products such as gas, crude oil and solid residues. Secondly, the catalytic process and its recent trends were discussed. In addition, the factors affecting the catalytic pyrolysis process had been evaluated. Furthermore, the optimized concentration of catalyst subjected to the higher yield of fuel with low hydrocarbon content was found. The pyrolysis oil produced from the catalytic process has higher heating values, lower density and lower viscosity compared to thermal process. In addition, the application of pyrolysis oil on the diesel engines had been discussed. The effects of pyrolysis oil on combustion and emission characteristics were observed. This review summarizes the potential advantages and barriers of both thermal and catalytic process. Further, the optimized solutions and applications of pyrolysis oil are suggested for sustainability of the process. Besides the introduction of the pyrolysis oil were viable without making major modification to the existing engine design.

Recent Trends in the Pyrolysis of Non-Degradable Waste Plastics

Waste plastics are non-degradable constituents that can stay in the environment for centuries. Their large land space consumption is unsafe to humans and animals. Concomitantly, the continuous engineering of plastics, which causes depletion of petroleum, poses another problem since they are petroleum-based materials. Therefore, energy recovering trough pyrolysis is an innovative and sustainable solution since it can be practiced without liberating toxic gases into the atmosphere. The most commonly used plastics, such as HDPE, LDPE (high- and low-density polyethylene), PP (polypropylene), PS (polystyrene), and, to some extent, PC (polycarbonate), PVC (polyvinyl chloride), and PET (polyethylene terephthalate), are used for fuel oil recovery through this process. The oils which are generated from the wastes showed caloric values almost comparable with conventional fuels. The main aim of the present review is to highlight and summarize the trends of thermal and catalytic pyrolysis of waste plastic into valuable fuel products through manipulating the operational parameters that influence the quality or quantity of the recovered results. The properties and product distribution of the pyrolytic fuels and the depolymerization reaction mechanisms of each plastic and their byproduct composition are also discussed.

Characterization and Use of Char Produced from Pyrolysis of Post-Consumer Mixed Plastic Waste

In this work, the pyrolysis of post-consumer mixed plastic waste (polypropylene (PP), polystyrene (PS) and polyethylene film (PE)) is carried out. The solid product of the pyrolysis is characterized and tested for its use as adsorbent of lead present in aqueous media. The pyrolysis temperature has a great influence on the solid product yield, decreasing when the temperature increases. The highest yield to solid product obtained is from the pyrolysis of film at lower temperature (450 °C), reaching almost 14%. The results of product solid characterization reveal that the carbon, hydrogen and nitrogen content decreases with increasing pyrolysis temperature. Furthermore, both the ash and the volatile content are related to the pyrolysis temperature. The ash content is higher when the pyrolysis temperature is higher, while when the temperature increases, a solid product with lower volatile content is obtained. In respect to specific surface area, a higher pyrolysis temperature improves the properties of the solid product as an adsorbent. The adsorption capacity increases as the pyrolysis temperature increases, with the highest value of 7.91 mg/g for the solid obtained in the pyrolysis at 550 °C. In addition, adsorption capacity increases as the initial concentration of lead rises, reaching a maximum value close to 26 mg/g for an initial concentration of 40 mg/L. The Sips model is the one that best reproduces the experimental results of the adsorption process equilibrium study.

Catalytic methods for chemical recycling or upcycling of commercial polymers

Polymers (plastics) have transformed our lives by providing access to inexpensive and versatile materials with a variety of useful properties. While polymers have improved our lives in many ways, their longevity has created some unintended consequences. The extreme stability and durability of most commercial polymers, combined with the lack of equivalent degradable alternatives and ineffective collection and recycling policies, have led to an accumulation of polymers in landfills and oceans. This problem is reaching a critical threat to the environment, creating a demand for immediate action. Chemical recycling and upcycling involve the conversion of polymer materials into their original monomers, fuels or chemical precursors for value-added products. These approaches are the most promising for value-recovery of post-consumer polymer products; however, they are often cost-prohibitive in comparison to current recycling and disposal methods. Catalysts can be used to accelerate and improve product selectivity for chemical recycling and upcycling of polymers. This review aims to not only highlight and describe the tremendous efforts towards the development of improved catalysts for well-known chemical recycling processes, but also identify new promising methods for catalytic recycling or upcycling of the most abundant commercial polymers.

Current plastics pollution threats due to COVID-19 and its possible mitigation techniques: a waste-to-energy conversion via Pyrolysis

BACKGROUND

The extensive use and production of PPE, and disposal in the COVID-19 pandemic increases the plastic wastes arise environmental threats. Roughly, 129 billion face masks and 65 billion plastic gloves every month are used and disposed of on the globe. The study aims to identify the polymer type of face masks and gloves and sustainable plastic waste management options.

RESULTS

The identification of polymers, which can help for fuel conversion alternatives, was confirmed by FTIR and TGA/DTA analysis and confirms that the polymeric categories fit for the intended purpose. Moreover, the handling technique for upcycling and the environmental impacts of the medical face mask and glove were discussed. The FTIR result revealed that face masks and gloves are polypropylene and PVC thermoplastic polymer, respectively and they can be easily transformed to fuel energy via pyrolysis. The endothermic peaks around 431 ℃ for medical glove and 175 ℃ for surgical is observed tells that the melting point of the PVC and polypropylene of plastic polymers, respectively. The pyrolysis of the face mask and glove was carried out in a closed reactor at 400 ℃ for 1 h. Conferring to lab-scale processes, liquid, and wax fuel rate of 75%, char of 10%, and the rest non-condensable gases were estimated at the end.

CONCLUSIONS

It can be concluded that the medical plastics can be recycled into oil due to their thermoplastics nature having high oil content and the waste to energy conversion can potentially reduce the volume of PPE plastic wastes.

Performance of Different Catalysts for the In Situ Cracking of the Oil-Waxes Obtained by the Pyrolysis of Polyethylene Film Waste

Currently, society is facing a great environmental problem, due to the large amount of plastic waste generated, most of which is not subjected to any type of treatment. In this work, polyethylene film waste from the non-selectively collected fraction was catalytically pyrolyzed at 500 °C, 20 °C/min for 2 h, in a discontinuous reactor using nitrogen as an inert gas stream. The main objective of this paper is to find catalysts that decrease the viscosity of the liquid fraction, since this property is quite meaningful in thermal pyrolysis. For this purpose, the three products of catalytic pyrolysis, the gaseous fraction, the solid fraction and the liquid fraction, were separated, obtaining the yield values. After that, the aspect of the liquid fraction was studied, differentiating which catalysts produced a larger quantity of waxy fraction and which ones did not. The viscosity of these samples was measured in order to confirm the catalysts that helped to obtain a less waxy fraction. The results showed that the zeolites Y and the zeolites β used in this study favor the obtaining of a compound with a smaller amount of waxes than for example catalysts such as FCC, ZSM-5 or SnCl2.

Environmental impact assessment of converting flexible packaging plastic waste to pyrolysis oil and multi-walled carbon nanotubes

A solution to low recycling rates of plastic waste is the conversion into multi-walled carbon nanotubes (MWCNTs) that have high value and can create additional revenue for plant operators. The purpose of this study was to perform a life cycle assessment (LCA) of an integrated system that involves flexible packaging plastic waste (FPPW) pyrolysis, oil upgrading, and MWCNTs production. The objectives were to determine the environmental impact of MWCNTs synthesis from non-condensable pyrolysis gases, and to assess the environmental impact of MWCNTs synthesis from different plastic fractions. Integrating MWCNTs synthesis to the plastic pyrolysis process provides various environmental benefits including, reduction of contribution towards climate change, fossil depletion, human toxicity (cancer), and ionizing radiation potentials. Sensitivity analysis of MWCNTs yields provided the range of impacts on the environment and a critical yield of >2% for most impact categories was determined. Comparison of different plastic fractions indicated that using low PET content feedstock had lesser impact on the environment, and demonstrated comparable performance to mixed virgin plastics for most impact categories. The results highlighted the versatility of the integrated pyrolysis process for treating diverse plastic waste fractions with negligible effects from the impurities present in the actual FPPW during thermal processing.

A combined two-stage process of pyrolysis and catalytic cracking of municipal solid waste for the production of syngas and solid refuse-derived fuels

Pyrolysis combined to either thermal cracking or catalytic cracking of municipal solid waste was performed in a laboratory-scale facility consisting of a fixed-bed reactor followed by a tubular cracking reactor. The results showed great potential for the production of syngas. The incorporation of inexpensive and widely available dolomite in the cracking reactor (with a constant feedstock to calcined dolomite ratio of 5:1) favoured the catalytic cracking of the primary pyrolysis products towards H₂ and CO in a temperature range of 800-900 °C. More particularly, it was possible at 900 °C to achieve a syngas consisting of more than 80 vol% CO and H₂ with a heating value of 16 MJ/Nm³. Additionally, a homogeneous solid fuel was obtained as a solid residue, which can be used to provide additional energy to support the process or as a refuse-derived fuel. Thus, the great potential of this process was demonstrated for turning municipal solid waste into a valuable gas fraction that can be used directly as a fuel or as a source of different value-added products.

Non-biodegradable polymeric waste pyrolysis for energy recovery

Nowadays, increasing population, widespread urbanization, rise in living standards together with versatile use of polymers have caused non-biodegradable polymeric wastes affecting the environment a chronic global problem, simultaneously, the existing high energy demand in our society is a matter of great concern. Hence forth, this review article provides an insight into the technological approach of pyrolysis emphasizing catalytic pyrolysis for conversion of polymeric wastes into energy products and presents an alternative waste management technique which is a leap towards developing sustainable environment. Pyrolysis of waste non-biodegradable polymer materials involves controlled thermal decomposition in the absence of oxygen, cracking their macromolecules into lower molecular weight ones, resulting into the formation of a wide range of products from hydrogen, hydrocarbons to coke. Nanocatalyzed pyrolysis is a recommended solution to the low thermal conductivity of polymers, promoting faster reactions in breaking the C-C bonds at lower temperatures, denoting less energy consumption and enabling enhancement in the process selectivity, whereby higher value added products are generated with increased yield. Nanotechnology plays an indispensable role in academic research as well as in industrial applications. Existing reviews illustrate that one of the oldest application field of nanotechnology is in the arena of nanocatalysis. Nanocatalysis closes the gap between homo and heterogeneous catalyses while combines their advantageous characteristics and positive aspects, reducing the respective drawbacks. During the current nanohype, nanostructured catalysts are esteemed materials and their exploration provide promising solutions for challenges from the perspective of cost and factors influencing catalytic activity, due to their featured high surface area to volume ratio which render enhanced properties with respect to the bulk catalyst.

Influence of Chemical Surface Characteristics of Ammonium-Modified Chilean Zeolite on Oak Catalytic Pyrolysis

The influence of chemical surface characteristics of Chilean natural and modified zeolites on Chilean Oak catalytic pyrolysis was investigated in this study. Chilean zeolite samples were characterised by nitrogen absorption at 77 K, X-ray powder diffraction (XRD), and X-ray fluorescence (XRF). The nature and strength of zeolite acid sites were studied by diffuse reflectance infrared Fourier transform (DRIFT), using pyridine as a probe molecule. Experimental pyrolysis was conducted in a quartz cylindrical reactor and bio-oils were obtained by condensation of vapours in a closed container. Chemical species in bio-oil samples were identified by a gas chromatography/mass spectrophotometry (GC/MS) analytical procedure. Results indicate that after the ionic exchange treatment, an increase of the Brønsted acid site density and strength was observed in ammonium-modified zeolites. Brønsted acids sites were associated with an increment of the composition of ketones, aldehydes, and hydrocarbons and to a decrease in the composition of the following families (esters; ethers; and acids) in obtained bio-oil samples. The Brønsted acid sites on ammonium-modified zeolite samples are responsible for the upgraded bio-oil and value-added chemicals, obtained in this research. Bio-oil chemical composition was modified when the pyrolysis-derived compounds were upgraded over a 2NHZ zeolite sample, leading to a lower quantity of oxygenated compounds and a higher composition of value-added chemicals.

An Investigation of the Feasibility of the Organic Municipal Solid Waste Processing by Coking

In the context of transition to a circular economy, one of the strategic priorities is the development of technological innovations aimed at waste processing. In this study, the foundations have been developed for a low-temperature, environmentally safe method for efficient processing of organic municipal solid waste, which may be further applied for processing both municipal and industrial waste organics in order to obtain liquid products. The maximum yield of liquid products is ensured when conducting the coking of a mixture of organic waste with long residuum in the temperature range of 400–420 °C, with a heating rate of 5–70 °C/min, and with an optimal heating time to the coking temperature of 80 min. Recommendations on the use of the waste recycling products are given. The proposed process is consistent with the principles of circular economy and does not require external energy costs because the energy needed for the process is generated by burning the gas produced during the waste coking. The process does not produce emissions into the environment and, in combination with standard refining processes, can be used to obtain commercial petroleum products.

Production of benzene/toluene/ethyl benzene/xylene (BTEX) via multiphase catalytic pyrolysis of hazardous waste polyethylene using low cost fly ash synthesized natural catalyst

The valuable aromatics benzene, toluene, ethyl benzene and xylene (BTEX) were effectively produced from waste polyethylene (PE) using fly ash synthesized catalyst. The BTEX yield was enhanced significantly using multiphase catalytic pyrolysis of polyethylene. Low cost natural catalyst was synthesized from fly ash (FA) in 5 different synthesized form i.e., fly ash in natural form (FAN), fly ash calcined at 600 °C (FA-600), 700 °C (FA-700), 800 °C (FA-800) and 900 °C (FA-900). The thermal and catalytic pyrolysis both were conducted in a specially designed semi-batch reactor at the temperature range of 500-800 °C. Catalytic pyrolysis were performed in two different phases within the reactor batch by batch systematically, keeping the catalyst in a liquid phase (A-Type) and liquid and vapor phase/multiphase (B-Type), respectively. The maximum liquid yield of 78.20 wt% was obtained at a temperature of 700 °C using FA-800 catalyst in A-type arrangement. Total aromatics (BTEX) of 10.92 wt% was obtained for thermal pyrolysis at a temperature of 700 °C. In contrary, the aromatic (BTEX) contents were significantly increased for the catalytic pyrolysis in both reactor arrangement A and B types, nearly doubled from 10.92 wt% (thermal pyrolysis) to 21.34 wt% for A-type and 22.12 wt% for B type/multiphase. The pyrolysis oil was characterized using GC-FID, carbon residue test and other fuel testing methods to evaluate the suitability of its end use and aromatic content.

Property of filler-loaded magnetic ferrite from plastic waste bottle used to treat municipal domestic sewage

The present work investigates the properties of self-made magnetic filler from plastic waste bottle and explores a new technology approach of waste plastic resource utilization. The magnetic filler was prepared by air plasma modification and loading magnetic ferrite on the plastic strip from waste plastic bottle. The surface properties of magnetic filler were characterized by Atomic Force Microscope (AFM), contact angle system and Fourier Transform Infrared (FTIR). AFM images of original and modified plastic strip showed that low-temperature plasma treatment markedly increased the surface roughness of plastic strip. The mean roughness (Ra) of plastic strip rose from 1.116 to 5.024 nm. FTIR spectra indicated that a lot of polar oxygenic groups were introduced onto the surface of plastic by plasma modification. Modification by low-temperature plasma increased the hydrophilicity of plastic strip surface. When treatment time is 40 s, water contact angle of plastic strip surface reduced from 78.2° of original plastic strip to 25.3°. When used in bioreactor, magnetic filler had very favorable microenvironment for microorganism growth. Magnetic filler was more efficient for removing chemical oxygen demand (COD) and [Formula: see text] in sewage than nonmagnetic filler. The resource utilization of plastic wastes will become reality if the magnetic filler is applied widely.

A novel approach of solid waste management via aromatization using multiphase catalytic pyrolysis of waste polyethylene

A new and innovative approach was adopted to increase the yield of aromatics like, benzene, toluene and xylene (BTX) in the catalytic pyrolysis of waste polyethylene (PE). The BTX content was significantly increased due to effective interaction between catalystZSM-5 and target molecules i.e., lower paraffins within the reactor. The thermal and catalytic pyrolysis both were performed in a specially designed semi-batch reactor at the temperature range of 500 °C-800 °C. Catalytic pyrolysis were performed in three different phases within the reactor batch by batch systematically, keeping the catalyst in A type- vapor phase, B type- liquid phase and C type- vapor and liquid phase (multiphase), respectively. Total aromatics (BTX) of 6.54 wt% was obtained for thermal pyrolysis at a temperature of 700 °C. In contrary, for the catalytic pyrolysis A, B and C types reactor arrangement, the aromatic (BTX) contents were progressively increased, nearly 6 times from 6.54 wt% (thermal pyrolysis) to 35.06 wt% for C-type/multiphase (liquid and vapor phase). The pyrolysis oil were characterized using GC-FID, FT-IR, ASTM distillation and carbon residue test to evaluate its end use and aromatic content.

Processing real-world waste plastics by pyrolysis-reforming for hydrogen and high-value carbon nanotubes

Producing both hydrogen and high-value carbon nanotubes (CNTs) derived from waste plastics is reported here using a pyrolysis-reforming technology comprising a two-stage reaction system, in the presence of steam and a Ni-Mn-Al catalyst. The waste plastics consisted of plastics from a motor oil container (MOC), commercial waste high density polyethylene (HDPE) and regranulated HDPE waste containing polyvinyl chloride (PVC). The results show that hydrogen can be produced from the pyrolysis-reforming process, but also carbon nanotubes are formed on the catalyst. However, the content of 0.3 wt.% polyvinyl chloride in the waste HDPE (HDPE/PVC) has been shown to poison the catalyst and significantly reduce the quantity and purity of CNTs. The presence of sulfur has shown less influence on the production of CNTs in terms of quantity and CNT morphologies. Around 94.4 mmol H2 g(-1) plastic was obtained for the pyrolysis-reforming of HDPE waste in the presence of the Ni-Mn-Al catalyst and steam at a reforming temperature of 800 °C. The addition of steam in the process results in an increase of hydrogen production and reduction of carbon yield; in addition, the defects of CNTs, for example, edge dislocations were found to be increased with the introduction of steam (from Raman analysis).

Comparison of real waste (MSW and MPW) pyrolysis in batch reactor over different catalysts. Part II: contaminants, char and pyrolysis oil properties

Pyrolysis of real wastes (MPW and MSW) has been investigated at 500°C, 550°C and 600°C using Y-zeolite, β-zeolite, equilibrium FCC, MoO3, Ni-Mo-catalyst, HZSM-5 and Al(OH)3 as catalysts. The viscosity of pyrolysis oils could be decreased by the using of catalysts, especially by β-zeolite and MoO3. Both carbon frame and double bound isomerization was found in case of thermo-catalytic pyrolysis. Char morphology and texture analysis showed more coke deposits on the catalyst surface using MSW raw material. Pyrolysis oils had K, S, P Cl, Ca, Zn, Fe, Cr, Br and Sb as contaminants; and the concentrations of K, S, P, Cl and Br could be decreased by the using of catalysts.