A review on thermal and catalytic pyrolysis of plastic solid waste (PSW)

Insights into Thermal Degradation Behaviors and Reaction Kinetics of Medical Waste Infusion Bag and Nasal Oxygen Cannula

The thermal degradation behaviors and reaction kinetics of medical waste infusion bag (IB) and nasal oxygen cannula (NOC) were investigated under inert atmosphere with the heating rates of 5, 10, 15, and 25 K·min−1. Ozawa–Flynn–Wall (OFW), Kissinger–Akahira–Sunose (KAS), and Friedman were employed to estimate the activation energy. Coats–Redfern and Kennedy–Clark methods were adopted to predict the possible reaction mechanism. The results suggested that the reaction mechanism of IB pyrolysis was zero-order, and that of NOC pyrolysis was concluded that zero-order for the first stage and three-dimensional diffusion Jander equation for the second stage. Based on the kinetic compensation effect, the reconstructed reaction models for IB and NOC pyrolysis were elaborated by introducing adjustment functions. The results indicated that the reconstructed model fitted well with the experimental data. The results are helpful as a reference and provide guidance for the determination of IB and NOC degradation behaviors and the simulation of parameters.

Characteristics of Plastic Waste Processing in the Modern Recycling Plant Operating in Poland

Although Poland is one of the leading recipients of the waste stream in the European Union (EU), it is at the same time below the average in terms of efficiency of their use/utilization. The adopted technological solutions cause waste processing rates to be relatively low in Poland. As a result, the report of the Early Warning and Response System (EWRS) of the EU indicated Poland as one of the 14 countries of the EU which are at risk in terms of possibility of achieving 50% recycling of waste. This article discusses the implemented technological solutions, and shows the profitability of the investment and the values of the process heat demand both for extractor and reactor. The experimental part analyzed the composition of the input and output of the process and compared it to the required fuel specifications. Attention was drawn to the need to improve the recycling process in order to increase the quality of manufactured fuel components. As potential ways of solving the problem of low fuel quality, cleaning the sorted reaction mass from solid particles and extending the technological line with a distillation column have been proposed. The recommended direction of improvement of the technology is also the optimization of the process of the reactor’s purification and removal of contaminants.

Synthesis and characterization of starch based bioplatics using varying plant-based ingredients, plasticizers and natural fillers

With the ever-increasing demand of plastics in the world and their consequent disastrous effects on environment, a suitable environmental-friendly substitute like bioplastics/biodegradable plastics is the need time. This study centers on green-production of a variety of bioplastic samples from (1) banana peel starch (BPP) and (2) a composite of banana peel starch, cornstarch and rice starch (COM) with varying amounts of potato peel powder and wood dust powder as fillers, respectively. Two different plasticizers - Glycerol and Sorbitol - have been utilized separately and in a 1:1 combination. A total of 12 samples of each of two types of bioplastics were made using multiple amounts and combinations of the fillers and plasticizers, to test the differences in the physical and chemical characteristics (moisture content, absorption of water, solubility in water, solubility in alcohol, biodegradation in soil, tensile strength, Young's modulus and FT-IR) of the produced samples due to their different compositions. The differences in the properties of the bioplastic samples produced make them suitable for usage in many different applications. All 24 of the samples produced were synthesized using natural and environmentally safe raw material and showed biodegradation, thus proving to be a good alternative to the conventional plastics.

Chemical recycling of plastic waste: Bitumen, solvents, and polystyrene from pyrolysis oil

As an alternative to conventional plastic-waste treatments, herein, we report a pyrolytic plastic-recovery process in which diverse compounds and materials are recovered from the pyrolysis oil obtained from the plastic waste. Distillation of the pyrolysis oil led to a bitumen and a distilled fraction. The composition of the bitumen, as determined by saturate, aromatic, resin, and asphaltene (S.A.R.A.) analysis and corroborated by Fourier-transform infrared (FTIR) spectroscopy, was found to principally contain aromatics (55.05 wt%) and saturates (33.41 wt%), and has great potential as a modifier for bitumen mixtures by decreasing the viscosities or softening points of final products. The distilled fraction was characterised and compared to pyrolysis oil in terms of its physicochemical properties and composition. Analysis by gas-chromatography/mass-spectrometry (GC-MS) revealed high levels of aromatics, namely styrene, benzene, toluene, ethylbenzene, and α-methylstyrene, which are potentially recoverable base compounds for industrial use. With this in mind, the distillate was subjected to various processes, including aromatic extraction with sulfolane and subsequent fractional distillation to recover the principal compounds in the various GC-MS fractions. Fraction 1 was found to be rich in ethylbenzene and toluene, while fraction 2 contained 73.26 wt% styrene and was used to synthesise recycled polystyrene (PS), whose yield and molecular weight (M_w) were optimised by adjusting the initiator concentration, temperature, and time. The optimised recycled PS was characterised to provide a yield of 77.64% and a M_w higher than 53,000 g/mol; this recycled PS exhibited similar thermal properties to those of conventional PS prepared using petrochemical sources.

The Use of Heterogeneous Catalysis in the Chemical Valorization of Plastic Waste

Plastic solid waste (PSW) is an ever-growing environmental challenge for our society, as it not only ends up in landfills but also in waterways and oceans and is consequently entering the food chain. A key strategy to overcome this problem while also preserving carbon resources is to use PSW as a feedstock, evolving towards a circular economy. To implement this, mechanical as well as chemical recycling technologies must be developed. Indeed, owing to the high volume of PSW generated each year, mechanical recycling alone is not adequate for addressing this global challenge. Because of this, chemical recycling via thermal and heterogeneous catalytic conversion has received growing attention. This process has the potential to take PSW and convert it into usable monomers, fuels, synthesis gas, and adsorbents under more sustainable conditions than thermal degradation. This Review highlights the recent research advances in catalytic technologies for PSW conversion and valorization.

Py-FTIR-GC/MS Analysis of Volatile Products of Automobile Shredder Residue Pyrolysis

Automobile shredder residue (ASR) pyrolysis produces solid, liquid, and gaseous products, particularly pyrolysis oil and gas, which could be used as renewable alternative energy resources. Due to the primary pyrolysis reaction not being complete, the yield of gaseous product is low. The pyrolysis tar comprises chemically unstable volatiles before condensing into liquid. Understanding the characteristics of volatile products will aid the design and improvement of subsequent processes. In order to accurately analyze the chemical characteristics and yields of volatile products of ASR primary pyrolysis, TG–FTIR–GC/MS analysis technology was used. According to the analysis results of the Gram–Schmidt profiles, the 3D stack plots, and GC/MS chromatograms of MixASR, ASR, and its main components, the major pyrolytic products of ASR included alkanes, olefins, and alcohols, and both had dense and indistinguishable weak peaks in the wavenumber range of 1900–1400 cm⁻¹. Many of these products have unstable or weaker chemical bonds, such as =CH–, =CH2, –C=C–, and –C=CH2. Hence, more syngas with higher heating values can be obtained with further catalytic pyrolysis gasification, steam gasification, or higher temperature pyrolysis.

Different reaction behaviours of light or heavy density polyethylene during the pyrolysis with biochar as the catalyst

Polyethylene is a major contributor of plastic waste, which can be converted into liquid fuel via catalytic pyrolysis. In this study, the pyrolysis of light or heavy density polyethylene (LDPE and HDPE) and their mixture with the biochar produced from gasification of poplar wood as catalyst was investigated. The results showed that, during the co-pyrolysis of LDPE and HDPE in absence or presence of biochar catalyst, cross-interaction of reaction intermediates originated from the degradation of LDPE and HDPE substantially promoted the formation of gaseous products and the evolution of heavy organics with π-conjugated structures in the tar. During the pyrolysis of HDPE, more heavy tar while less wax was produced, while it was contrary during the pyrolysis of LDPE. In the catalytic pyrolysis of LDPE, the volatiles could be effectively cracked over the biochar catalyst, forming more gases, while in the catalytic pyrolysis of HDPE, instead of catalyzing the cracking of the heavy components, the biochar catalyzed the polymerisation reactions. The properties of the biochar catalyst in terms of crystallinity, surface functionality, and internal structures also changed remarkably due to the transfer of oxygen-containing species from the polyethylene to biochar and the interaction of biochar with volatiles in the pyrolysis.

Valorization of waste polyethylene terephthalate plastic into N-doped microporous carbon for CO2 capture through a one-pot synthesis

Valorization of waste polyethylene terephthalate (PET) plastic into microporous carbon with N-doping treatment was successfully performed in a one-pot synthesis and the N-doped microporous carbon was used for CO₂ capture, which can mitigate plastic pollution and climate change simultaneously. The PET-derived microporous carbon developed by KOH activation and urea treatment in a one-pot synthesis at 700 °C exhibited the highest CO₂ adsorption uptake of 6.23 mmol g^-1 at 0 °C and 4.58 mmol g^-1 at 25 °C (1 atm). The Langmuir and pseudo second-order models displayed well-fitting relationships with equilibrium and kinetic experimental data obtained in this study. The N-doped microporous carbon showed high CO₂ selectivity over N₂, implying that it is feasible for treating flue gases (10% CO₂ and 90% N₂) at 50 °C. In addition, the CO₂ uptake was not only affected by micropores but also related with nitrogen and oxygen functional groups. Compared to the porous carbon prepared by two-pot synthesis where KOH activation and urea treatment were conducted separately, the porous carbon prepared by one-pot synthesis had higher oxygen contents and higher CO₂ adsorption uptake. All of findings implied that the N-doped microporous carbon was successfully developed from waste PET plastic for capturing CO₂ and can play a promising role in both sustainable waste management and environmental protection.

Application of a neural fuzzy model combined with simulated annealing algorithm to predict optimal conditions for polyethylene waste non-isothermal pyrolysis

In the present study, the waste polyethylene (PE) pyrolysis under different non-isothermal conditions was investigated to estimate the optimal conversions and pyrolysis rates. The pyrolysis study was carried out using Thermogravimetry (TG) of the virgin and the waste PE under different heating rates of 5, 10, 15 and 20 °C/min. The TG experiments indicated that the virgin and the waste PE pyrolysis processes mainly underwent in the temperature range of 390-510 °C. Subsequently, the adaptive neural fuzzy model was adopted to predict the conversions and the pyrolysis rates of the virgin and the waste PE. The optimal operating conditions in different temperature ranges were optimized by the simulated annealing algorithm (SA). Moreover, the R-squared values of the virgin PE conversions (~ 1) and pyrolysis rates (> 0.999), and the waste PE conversions (~ 1) and pyrolysis rates (> 0.999) revealed the high accuracy of the adaptive neural fuzzy model predicted results.

Catalytic Pyrolysis of a Residual Plastic Waste Using Zeolites Produced by Coal Fly Ash

The plastic film residue (PFR) of a plastic waste recycling process was selected as pyrolysis feed. Both thermal and catalytic pyrolysis experiments were performed and coal fly ash (CFA) and X zeolites synthesized from CFA (X/CFA) were used as pyrolysis catalysts. The main goal is to study the effect of low-cost catalysts on yields and quality of pyrolysis oils. NaX/CFA, obtained using the fusion/hydrothermal method, underwent ion exchange followed by calcination in order to produce HX/CFA. Firstly, thermogravimetry and differential scanning calorimetry (TG and DSC, respectively) analyses evaluated the effect of catalysts on the PFR degradation temperature and the process energy demand. Subsequently, pyrolysis was carried out in a bench scale reactor adopting the liquid-phase contact mode. HX/CFA and NaX/CFA reduced the degradation temperature of PFR from 753 to 680 and 744 K, respectively, while the degradation energy from 2.27 to 1.47 and 2.07 MJkg−1, respectively. Pyrolysis runs showed that the highest oil yield (44 wt %) was obtained by HX/CFA, while the main products obtained by thermal pyrolysis were wax and tar. Furthermore, up to 70% of HX/CFA oil was composed by gasoline range hydrocarbons. Finally, the produced gases showed a combustion energy up to 8 times higher than the pyrolysis energy needs.

Catalytic assessment of solid materials for the pyrolytic conversion of low-density polyethylene into fuels

Pyrolysis techniques provide an interesting way of recycling plastic wastes (PW) by transforming them into liquid fuels with high calorific values. Catalysts are employed in PW pyrolysis in order to favor cracking reactions; in that regard, cheap and abundant natural resources are being investigated as potential catalyst precursors. This article explores the pyrolysis of low-density polyethylene (LDPE) in a semibatch reactor under a reduced pressure of 300 torr and temperatures in the range of 370 °C-430 °C. Three different solid materials, an activated carbon (AC1), a commercial Fluid cracking catalyst (FCC) and an aluminum- pillared clay (Al-PILC), were tested as catalysts for the pyrolysis process. Thermogravimetric analyzes were previously performed to select the most catalytically active materials. AC1 displayed very low catalytic activity while FCC and Al-PILC displayed high activity and conversion to liquid products. Hydrocarbons ranging from C5 to C28 were identified in the liquid products as well as significant changes in their composition when FCC and Al-PILC catalyst were used. Differences in the catalytic activity of the 3 solid materials are ascribed mainly to differences in their acid properties.

Application of Artificial Neural Networks to Predict the Catalytic Pyrolysis of HDPE Using Non-Isothermal TGA Data

This paper presents a comprehensive kinetic study of the catalytic pyrolysis of high-density polyethylene (HDPE) utilizing thermogravimetric analysis (TGA) data. Nine runs with different catalyst (HZSM-5) to polymer mass ratios (0.5, 0.77, and 1.0) were performed at different heating rates (5, 10, and 15 K/min) under nitrogen over the temperature range 303–973 K. Thermograms showed clearly that there was only one main reaction region for the catalytic cracking of HDPE. In addition, while thermogravimetric analysis (TGA) data were shifted towards higher temperatures as the heating rate increased, they were shifted towards lower temperatures and polymer started to degrade at lower temperatures when the catalyst was used. Furthermore, the activation energy of the catalytic pyrolysis of HDPE was obtained using three isoconversional (model-free) models and two non-isoconversional (model-fitting) models. Moreover, a set of 900 input-output experimental TGA data has been predicted by a highly efficient developed artificial neural network (ANN) model. Results showed a very good agreement between the ANN-predicted and experimental values (R² > 0.999). Besides, A highly-efficient performance of the developed model has been reported for new input data as well.

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.

Valorization of the plastic residue from a WEEE treatment plant by pyrolysis

The possibility of a pyrolysis process as a mean of recycling the residual plastic rich fraction (WEEE residue) derived from of a material recovery facility has been evaluated. The unknown product composition of WEEE residue has been supposed through coupled thermal - infrared analysis and ultimate analysis and resulted as PP 3 wt%, PBT 3 wt%, PVC 4 wt%, styrene-based polymers (principally ABS) 50 wt%, thermosetting resins (principally, epoxy/phenolic resins) 24 wt%, inorganic fraction (principally fiber glass) 16 wt%. DSC experiments showed that the overall energy, defined as the degradation heat, needed in order to completely degrade WEEE residue was about 4% of the exploitable energy of the input material. The effect of temperature and different zeolite catalysts were investigated, in particular in terms of yield and quality of the produced oils during the pyrolysis process. Produced oils were potentially exploitable as fuels and almost all catalysts improved their quality. The best performance was reached by NaUSY(5.7) with the second highest production of light oil and the greatest total monoaromatics yield, plus 12 wt% in comparison to thermal pyrolysis experiments. Furthermore, light oil produced by NaUSY(5.7) has one of the best LHV (36 MJ/kg) and no halogenated compounds were detected by GC-MS analysis. Char or pyrolytic gas combustion could supply the energy required for the thermal degradation of WEEE Residue.

Impervious and influence in the liquid fuel production from municipal plastic waste through thermo-chemical biomass conversion technologies - A review

Plastic waste is an environmental burden substance, which poses a high threat to the society during disposal. Rather than disposal, recycling of this waste to liquid fuel gains importance owing to its high utility. Among various techniques, thermo-chemical recycling techniques hold more benefits in generating high value added liquid fuels. In this review, the details of municipal plastic waste generation are provided with a brief description of the plastic waste management option and importance of recycling is explained. The overview of the thermo-chemical treatment focusing on the pyrolysis, gasification and hydrocracking process was elaborated. Catalysts mediated pyrolysis have wide-open their prospective for the generation of bio-oil, hydrocarbons, syngas and deterioration of undesired substances. Generally, advance development of enthusiastic catalysts for the synthesis of bio-oil would be vital for scaling up the pyrolysis process to succeed in commercial manufacture of biofuels from waste plastics. Overall rate treatment depends on operating parameter which determines the process efficiency and product yield. Hence, critical assessment of various parameter that has remarkable effect in the thermo-chemical treatment process was documented in detail. Moreover, endorsements of liquid fuel production, economic viability, and energy requirement of the treatment process, were delivered to attain effectual plastic wastes management.

Technical description and performance evaluation of different packaging plastic waste management's systems in a circular economy perspective

The plastic waste disposal strongly raised in importance in the recent past and it is approaching a critical situation worldwide, so requiring putting in practice the criteria of circular economy by avoiding meaningless policy responses against the plastic materials. The world of plastic materials includes a wide range of goods in all the sectors of our life: packaging, construction, biomedicals, etc. The answer to the plastic waste disposal is build an industrial network characterized by reliability, flexibility, sustainability, utility in the industrial cycle and ability to provide useful products to the market. The traditional processes including recycling and energy recovery fulfil only a part of these conditions and need to be assessed in correlation to their real effect on the circular economy such as the uses of the obtained products in the anthroposphere's life cycle, the burdens generated by the processes itself, etc. Among the possible processes that can be more sustainable if compared with the traditional ones, in a real circular economy perspective, those based on thermochemical exploitation of products obtained by plastics are discussed and assessed. The results show that it is possible to transform an expensive and non-resolving plastic waste management system in an industrial network having an intrinsic economic sustainability and, overall, a well-defined role in the economic chain of plastics. The results show that an integration between the present system with the production of petrochemical products, including oil/gasoline/syngas/…, strongly improve the economic performance of the overall waste system, allowing a larger savings of not-renewable resources, a limited greenhouse burden, a release in the market of valuable products instead of poor quality materials and the minimization of waste destined to be landfilled.

Bimetallic carbon nanotube encapsulated Fe-Ni catalysts from fast pyrolysis of waste plastics and their oxygen reduction properties

Carbon-based bimetallic electrocatalysts were obtained by catalytic pyrolysis of waste plastics with Fe-Ni-based catalysts and were used as efficient oxygen reduction reaction (ORR) catalysts in this study. The prepared iron-nickel alloy nanoparticles encapsulated in oxidized carbon nanotubes (FeNi-OCNTs) are solid products with a unique structure. Moreover, the chemical composition and structural features of FeNi-OCNTs were determined. The iron-nickel alloy nanoparticles were wrapped in carbon layers, and the carbon nanotubes had an outer diameter of 20-50 nm and micron-scale lengths. FeNi-OCNT with a Fe/Ni ratio of 1:2 (FeNi-OCNT12) exhibited remarkable electrochemical performance as an ORR catalyst with a positive onset potential of 1.01 V (vs. RHE) and a half-wave potential of 0.87 V (vs. RHE), which were comparable to those of a commercial 20% Pt/C catalyst. Furthermore, FeNi-OCNT12 exhibited promising long-term stability and higher tolerance to methanol than the commercial 20% Pt/C catalyst in an alkaline medium. These properties were attributable to the protective OCNT coating of the iron-nickel alloy nanoparticles.

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.

Thermal Pyrolysis of Polystyrene Aided by a Nitroxide End-Functionality. Experiments and Modeling

The thermal pyrolysis of polystyrene (PS) is gaining importance as the social pressure for achieving a circular economy is growing; moreover, the recovery of styrene monomer in such a process is especially relevant. In this study, a simple thermal pyrolysis process in the temperature range of 390–450 °C is developed. A working hypothesis is that by using a nitroxide-end functionalized PS (PS-T or dormant polymer), the initiation process for the production of monomer (unzipping) during the PS pyrolysis could be enhanced due to the tendency of the PS-T to activate at the nitroxide end. Two types of PS were used in this work, the first one was synthesized by free-radical polymerization (FRP-dead polymer) and the second by nitroxide-mediated polymerization (NMP) using three levels of nitroxide to initiator ratio: 1.3, 1.1, and 0.9. Analysis of the recovered products of the pyrolysis by gas-mass spectroscopy shows that the yield of styrene increases from ∼33% in the case of dead polymer to ∼38.5% for PS-T. A kinetic and mathematical model for the pyrolysis of dead and dormant polymer is proposed and solved by the method of moments. After a parameter sensitivity study and data fitting, the model is capable of explaining the main experimental trends observed.

Processing of flexible plastic packaging waste into pyrolysis oil and multi-walled carbon nanotubes for electrocatalytic oxygen reduction

Flexible plastic packaging waste causes serious environmental issues due to challenges in recycling. This study investigated the conversion of flexible plastic packaging waste with 11.8 and 27.5 wt.% polyethylene terephthalate (PET) (denoted as PET-12 and PET-28, respectively) into oil and multi-walled carbon nanotubes (MWCNTs). The mixtures were initially pyrolyzed and the produced volatiles were processed over 9.0 wt.% Fe₂O₃ supported on ZSM-5 (400 °C) to remove oxygenated hydrocarbons (catalytic cracking of terephthalic and benzoic acids) that deteriorate oil quality. The contents of oxygenated hydrocarbons were decreased in oil from 4.6 and 9.4 wt.% per mass of PET-12 and PET-28, respectively, to undetectable levels. After catalytic cracking, the oil samples had similar contents of gasoline, diesel and heavy oil/wax fractions. The non-condensable gas was converted into MWCNTs over 0.9 wt.% Ni supported on CaCO₃ (700 °C). The type of plastic packaging influenced the yields (2.4 and 1.5 wt.% per mass of PET-12 and PET-28, respectively) and the properties of MWCNTs due to the differences in gas composition. Regarding the electrocatalytic application, both MWCNTs from PET-12 and PET-28 outperformed commercial MWCNTs and Pt-based electrodes during oxygen evolution reaction, suggesting that MWCNTs from flexible plastic packaging can potentially replace conventional electrode materials.

Effective deoxygenation for the production of liquid biofuels via microwave assisted co-pyrolysis of agro residues and waste plastics combined with catalytic upgradation

Rice straw and sugarcane bagasse were co-pyrolyzed with polypropylene and polystyrene using microwaves, and the pyrolysis vapors were catalytically upgraded using HZSM-5 catalyst. The product yields, composition and properties of bio-oil from pyrolysis of individual feedstocks and equal composition mixtures before and after catalytic upgradation were thoroughly investigated. The pyrolysis oil yields from polypropylene (82 wt%) and polystyrene (98 wt%) were high compared to that from rice straw (26 wt%) and bagasse (29 wt%). Catalytic upgradation at weight hourly space velocity of 11 h^-1 resulted in higher selectivity to unsaturated aliphatics and aromatic hydrocarbons. Properties of upgraded bio-oil from biomass-polypropylene mixtures were similar to that of light fuel oil with high calorific value (43 MJ/kg), low viscosity (1 cP), optimum density (0.850 g/cm³) and flash point (70 °C). Oxygen content in catalytically upgraded co-pyrolysis bio-oil was low (<5%) as compared to upgraded pyrolysis bio-oil (14-18%), and pyrolysis bio-oil without upgradation (20-24%).

Fuel cell and electrolyzer using plastic waste directly as fuel

The effective utilization of plastic waste, including its use as an energy or chemical resource, has attracted much attention. Nevertheless, energy recovery from plastics via incineration generates air pollutants and toxic compounds, while chemical conversion requires significant energy inputs, especially in the case of gasification. Herein, we report the electrochemical conversion of plastics into electricity or hydrogen without the use of special procedures. When a mixture of plastic solid combined with an acidic solution was fed into an electrochemical cell, the solid was found to dissolve in the solution at 100 °C or higher, followed by the release of protons from the anode to the cathode according to a multi-electron oxidation reaction. This oxidation reaction required an anode that was sufficiently porous so as to allow transport of the reactants. Taking the sponge sample as an example, the dissolved polyurethane had a molecular weight of 2000 or higher, the transport of which was facilitated using a carbon support with a pore diameter of approximately 10 nm. In addition, carbon black having an ordered porous structure exhibited better reagent transport compared to a disordered porous carbon black with similar pore diameters. As a consequence, this cell continuously provided power densities on the order of mW cm^-2 in the fuel cell mode and generated hydrogen at a low cell voltage of 0.55 V in the electrolyzer mode, using plastics as fuels at an operational temperature of 200 °C.

High-Precision Monitoring of Average Molecular Weight of Polyethylene Wax from Waste High-Density Polyethylene

High-density polyethylene (HDPE) is a major component of polyethylene waste, yet only under 29.9% of waste HDPE is recycled. As an important additive, polyethylene wax (PEW) is increasingly used in many industries such as plastics, dyes, and paints. The preparation of PEW has received considerable interest because recycling and precisely controllable production can bring huge economic benefits. In this study, to recycle waste HDPE, a single screw extruder was innovatively combined with a connecting pipe to prepare PEW from the pyrolysis of waste HDPE. Using a test platform, PEWs were prepared under different pyrolysis temperatures and screw speeds, and corresponding number-average molecular weights (NAMWs) of PEWs were measured. To precisely monitor NAMW of PEW, a program was developed in MATLAB. First, the relationship between NAMW and pyrolysis ratio was obtained, and a measure-point-independence verification was conducted. Then, modified Arrhenius equations and time-dependent pyrolysis temperature were for the first time introduced into the HDPE pyrolysis model. Furthermore, the screw-speed-dependent inverse method was proposed and validated for high-precision monitoring of NAMW of PEW from the pyrolysis of waste HDPE by extrusion. PEW of desired molecular weight was able to be precisely obtained from waste HDPE.

Regeneration and Recovery of Plastics

Plastics are the most essential commodities in the world and are replacing the metals, wood, glass, cements and other materials in some application areas. Plastics are easy handling, resource-saving, non-toxic with esthetically attractive. Oil and gas are the major feedstocks for plastics, besides sugar and corn as renewable feedstocks. Plastics represent a serious waste-handling problem, with only 10%–12% of the plastic waste generated worldwide being regenerated/recycled. After disposal, plastic waste takes very long time to decompose naturally and impact the environment during the degradation process. The above situation has necessitated the invention of efficient technologies for regeneration and recovery of plastics all over the world.

Insights into the evaluation of the abiotic and biotic degradation rate of commercial pro-oxidant filled polyethylene (PE) thin films

In this study, commercial products formulated from polyethylene (PE) with pro-oxidant additives, were subjected to abiotic and biotic environments. The materials were presumed to be oxo-biodegradable plastics with thicknesses varying between 30 and 70 μm, and calcium carbonate (CaCO₃) filler content reaching up to 11 wt%. Accelerated (aging) weathering tests conducted revealed that UV radiation triggered the biodegradation mechanism. Weight loss reached 50% after exposure to weathering which was attributed to triggering the fragmentation of the plastic films. Furthermore, some 83% of weight loss was estimated after 12 months of soil burial. Fluctuation of weight in mid exposure time spans was related to the cross-linking reaction within the polymeric matrix. The mechanical properties investigated along with the thermal stability profile determined for the materials showed that weathering was more severe than soil burial. Thermogravimetry revealed that onset temperature (T_os) was lower than conventional PO products by 25 °C. This could be attributed to the thermal response of the materials due to presence of ion salts and sterates within their composition. The claims by the manufacturing companies which provided the original specimens under an environmentally friendly pretence is disputed due to the fact that none of the products actually showed evidence of major fragmentation or deterioration after exposure to harsh environments. The work also paves the way in standardising assessment methodology for examining biodegradable plastics.

A review of the valorization and management of industrial spent catalyst waste in the context of sustainable practice: The case of the State of Kuwait in parallel to European industry

Industrial solid waste management encompasses a vital part of developed and developing countries strategies alike. It manages waste generated from vital industries and governs the hazardous waste generated as a major component of integrated waste management strategies. This article reviews the practices that govern the management approaches utilized in the developed world for industrial spent catalysts. It critically assesses the current situation of waste management within the developing world region focusing on the industrial waste component, in a novel attempt to crucially develop a strategy for a way forward based on best practices and future directions with major European industries. The review also draws parallels with European countries to compare their practices with those of the State of Kuwait, which rely solely on landfilling for the management of its industrial waste. Spent catalysts recovery methods are discussed at length covering conventional methods of valuable metals and chemicals recovery (e.g., hydrometallurgical, solid-liquid and liquid-liquid extraction) as well as biological recovery methods. A major gap exists within regulations that govern the practice of managing industrial waste in Kuwait, where it is essential to start regulating industries that generate spent catalysts in-view of encouraging the establishment of valorization industries for metal and chemical recovery. This will also create a sustainable practice within state borders, and can reduce the environmental impact of landfilling such waste in Kuwait.

Biodegradation kinetic modeling of oxo-biodegradable polypropylene/polylactide/nanoclay blends and composites under controlled composting conditions

Polypropylene/polylactide/nanoclay blend/composite films with/without pro-oxidants/compatibilizer were prepared and aerobically degraded to measure the CO₂ evolution under controlled composting conditions as per ASTM D 5338. A first-order Komilis model in series with a flat lag phase was postulated involving two stages; hydrolysis of solid carbon followed by its rapid mineralization. The first, rate-limiting stage further comprised of three possible parallel paths: the solid hydrolysis of readily, moderately, and slowly hydrolyzable carbon fractions. The model parameters were computed after correlating with the experimental data using nonlinear regression analysis. The results of the model characteristic parameters, un-degraded/hydrolyzable/mineralisable-intermediate carbon kinetics, and degradation curves exhibit two distinct kinetic regimes. The first regime comprising of slowly and moderately hydrolyzable carbon is shown by the first four films without pro-oxidants. This causes low degradability and degradation rate. The second regime comprising of the readily and moderately hydrolyzable carbon is shown by another four films containing pro-oxidants. They exhibit relatively high degradability and degradation rate, which peaks at around 11-14th day in the range of 0.219-0.268% per day. The values of their moderately hydrolyzable carbon fractions and the corresponding hydrolysis rates are significantly higher than that of the first regime. For the first regime, the degradability and degradation rate decreases with increase in the slowly hydrolyzable carbon impervious to microbial attack. Their degradation rate profiles show an absence of growth phase due to the absence of readily hydrolyzable carbon. The rate decreases monotonously starting from the maximum value ranging from 0.043 to 0.180% per day. The approach presented can also be implemented to model and design equipment for other waste biodegradation systems.

Pyrolysis, morphology and microwave absorption properties of tobacco stem materials

The recent development of microwave radiation technology has increased the application possibilities of waste tobacco stems (WTSs). In this study, the morphology and microwave absorption properties of tobacco stem materials as well as the pyrolysis of the resultant biomass (BMTS) were studied via thermogravimetry-differential scanning calorimetry (TG-DSC), scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and a vector network analysis (VNA). The results show that the BMTS pyrolysis involves four stages in air: dehydration, heat transfer, pyrolysis, and carbonisation, and it involves three stages in N2: moisture evaporation, de-volatilization, and charring. The microwave-assisted expansion of WTSs can improve the pore diameter and total porosity of the expanded tobacco stems (ETSs) and BMTS. The latter is a macroporous material with a total porosity of 78.2% and a probable pore size of 29.5 μm. Its pore size distribution ranges from 10.7 nm to 227 μm. The microwave absorption properties of the WTSs are affected by the moisture content, bulk density, and grain size; the properties can be enhanced by decreasing the grain size and increasing the moisture content and bulk density within the experimental range. The 3 dB bandwidth and amplitude vary by 0.45 MHz and - 0.406 dB per 1% increase in the moisture content of the materials, respectively. Our results demonstrate that tobacco stem materials with different moisture contents and grain sizes should be classified before the expansion or re-drying steps to ensure heating uniformity and product quality during the microwave radiation treatment.

Evaluation of the environmental impact of plastic cap production, packaging, and disposal

This study analysed the impact of the production of high-density polyethylene (HDPE) caps on the environment. To determine the environmental impact of injection moulding production, a life-cycle assessment was performed. The life-cycle assessment results showed that, in the injection moulding tool manufacturing process, the largest amount of environmental loading is attributable to electricity and steel consumption. Additionally, the HDPE cap production phase had the largest environmental impact associated with electricity consumption. However, scenario analysis showed that the environmental impact from electricity consumption can be reduced by up to ten times if cleaner sources of electricity are used. Large differences related to electricity sourcing should help developing countries to better understand the need to increase the use of cleaner sources of electricity.

Dissolution of adhesive resins present in plastic waste to recover polyolefin by sink-float separation processes

This study investigated the dissolution of adhesive resins present in polyolefin films that cause plastic materials to adhere to each other. The process of dissolution was made by the use of ethyl acetate and followed by separation through the sink-float process. The objective was to separate and characterize polyolefin films from plastic solid waste derived from recycled post-consumer paper. Through these procedures, 6% polyethylene of high-density (HDPE), 14% polyethylene of low-density (LDPE) and 39% polypropylene (PP) were separated and recovered from plastic waste. Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analyzes (TGA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) were conducted to determine the chemical, thermal and mechanical properties of the recovered polymers and to establish a comparison with standard commercial polymers. It demonstrated that recovered material kept their chemical, thermal, and mechanical properties. This process indicates possible economic viability considering the demand, the market value of the PP, and the required investment to be implemented in the recycling process that could be amortized in a short period of time. Moreover, the organic solvent used in the dissolution process can be easily recovered by distillation.

Experimental analysis of waste polyurethane from household appliances and its utilization possibilities

Polyurethane has a good insulation characteristic, and it is widely used as an insulation and lining material for refrigerators. Nevertheless, at the end of a product's lifetime, serious problems arise related to waste management. Recently, energy recovery has been marked as a promising solution, especially, waste-to-energy applications. To find an appropriate application for such waste, a thermal analysis was performed. An experimental analysis of polyurethane (PU) waste material was performed by the method of pyrolysis gas chromatography with mass spectrometric detection (Py-GC/MS) at various pyrolytic temperatures, namely, at 500, 600 and 700 °C. Waste polyurethane foam was conducted to investigations in the form of a bulk sample and sorted grain-size samples with a goal to detect the chemical composition of the pyrolysate. The investigation revealed various groups of organic compounds such as heterocyclic compounds of nitrogen and simple and polycyclic aromatic hydrocarbons, while notable concentrations of compounds containing chlorine were detected as well. The experimental analysis found differences in the composition of amines and other compounds and in the dependence on grain size composition. Bulk samples produced the highest concentration of amines (˃ 40%) at a temperature of 500 °C. The sample homogenization led to a significant increase in amines production. Polyurethane waste of grain size from 0.125 to 0.25 mm contained approximately 80% amines. The pyrolysis of the bulk sample at 600 °C yielded only 24% nitrogen heterocyclic compounds, while from the sorted grain-size <0.045 mm and 0.045-0.063 mm, yields were increased to 47.4 and 45.7%, respectively.

Plastic Solid Waste (PSW) in the Context of Life Cycle Assessment (LCA) and Sustainable Management

Over the past few decades, life cycle assessment (LCA) has been established as a critical tool for the evaluation of the environmental burdens of chemical processes and materials cycles. The increasing amount of plastic solid waste (PSW) in landfills has raised serious concern worldwide for the most effective treatment. Thermochemical post-treatment processes, such as pyrolysis, seem to be the most appropriate method to treat this type of waste in an effective manner. This is because such processes lead to the production of useful chemicals, or hydrocarbon oil of high calorific value (i.e. bio-oil in the case of pyrolysis). LCA appears to be the most appropriate tool for the process design from an environmental context. However, addressed limitations including initial assumptions, functional unit and system boundaries, as well as lack of regional database and exclusion of socio-economic aspects, may hinder the final decision. This review aims to address the benefits of pyrolysis as a method for PSW treatment and raise the limitations and gaps of conducted research via an environmental standpoint.

Production of biohydrogen from gasification of waste fuels: Pilot plant results and deployment prospects

Hydrogen is seen as a key element of the future energy mix because it does not generate greenhouse gas emissions at the point of use. Understanding the technologies that can generate low carbon hydrogen is essential in planning the development of future gas networks and energy generation via fuel cells. One promising approach is hydrogen production by gasification of waste, referred to as biohydrogen. This paper summarises work undertaken to design a commercial Waste-to-Hydrogen (WtH₂) plant, which includes an assessment of future markets for hydrogen, the identification of an appropriate scale for the plants, and development of specifications for process design and output streams. An experimental programme was undertaken to demonstrate bioH₂ production from refuse derived fuel (RDF) at pilot scale and provided experimental data to underpin commercial designs. On this basis, a reference design for small commercial plants was developed for bioH₂ production for heating and transport utilisation. A preliminary carbon assessment shows that carbon savings for biohydrogen in a commercial scale are more than four times greater than alternative technologies.

Fuel production by cracking of polyolefins pyrolysis waxes under fluid catalytic cracking (FCC) operating conditions

The catalytic cracking of high-density polyethylene pyrolysis waxes under fluidized catalytic cracking conditions has been investigated with the aim of producing fuels at large-scale from waxes obtained in pyrolysis plants located nearby collection and segregation points. Additionally, preliminary information about the capacity of these units to valorize waste polyolefins has been obtained. The catalytic cracking runs have been performed in a riser simulator reactor under industrial conditions: 500-560 °C; catalyst to oil mass ratio, 3, 5 and 7 g_cat g_oil^-1; and, contact time, 6 s. The product distribution has been quantified determining the yields of different fractions, which have been defined according to their boiling point range: dry gas, liquefied petroleum gas, naphtha, light cycle oil, heavy cycle oil and coke. The concentration of the families of compounds has been also determined, which are n-paraffins, iso-paraffins, olefins, naphthenes and aromatics. For the shake of comparison, the results of catalytic cracking of a common stream fed to the industrial units, i.e., vacuum gasoil, have been included. Globally, promising results have been obtained in the valorization of waste polyolefins by means of this combination of pyrolysis-cracking stages that expose, at the same time, the capacity of this unit to manage waste plastics.