Chemical Recycling Methods Research Articles

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.

Engineering terephthalic acid product from recycling of PET bottles waste for downstream operations

Since global oil prices have declined, the price of virgin PET has dropped dramatically, and caused the recycling of PET more challenging. To make the situation worse, the rapid precipitation of terephthalic acid (TPA) from alkaline hydrolysis of PET resulted in very small particles of TPA with unfavorable filtration and drying behaviors. The aim of this work was to engineer product properties of TPA for downstream operations with the existing processing steps. The size effects of TPA crystals/precipitates on filtration, and on drying behaviors, were conducted in terms of specific cake resistance and drying-rate curve, respectively. The whole operating windows was determined for a process optimization by varying operating temperature, feeding strategy, the proportion of water to dimethyl sulfoxide, and the introduction of a cooling operation. Our whole process could be achieved within 8 h at the optimal conditions. As compared to the literature method for chemical recycling of PET, the optimal case exhibited much improved specific cake resistance of ~4.8 × 106 m/g by two orders, and shortened the drying time to 3 h by three times. The TPA crystalline products were also characterized by FTIR for identification, NMR for purity, PXRD for crystallinity, and SEM for particle morphology.

Environment and plastics : A review on greener routes for plastic bottle (PET) waste management through recycling processes

Many research papers have been contributed by several authors for making polyethylene terephthalate (PET) waste recycling economically and ecologically more viable as it creates environmental hazards when disposed off after its short term use. Recycling of PET waste was started in last two decades. Most of the authors are devoting their time in getting economically viable solution for development of methods based on either mechanical or chemical recycling. Some success has been obtained in development of chemical recycling methods which provides value added products from PET waste. In this study the operating conditions and mechanism of various recycling processes available for the recycling of polyethylene terephthalate (PET) waste are reported and described.

Tertiary recycling of plastics waste: an analysis of feedstock, chemical and biological degradation methods

Globally, there is rising awareness of the severity of the plastic waste problem, and the implications of plastics accumulation in the environment. Current methods of waste management are anticipated to be insufficient in mitigating the long-term negative impact on society and the environment. Plastics recycling is one of many solutions that have been proposed, one of the most ecologically-friendly, as well as holding great economic potential by its realization into a circular economy. The technological know-how already exists for a number of different methods for plastic recycling; however, they are broadly uneven in their implementation due to feasibility and cost issues. Here, we review and compare methods of tertiary recycling—that is, complete breakdown of plastics into its chemical component materials—and offer an analysis of the potential obstacles that have to be addressed to increase waste plastic recycling rates. While chemical recycling methods are simpler and are already pilot tested at an industrial level, biological recycling either via microorganisms or biological-derived enzymes are as yet unproven but highly promising technologies. Looking forward, trend shifts towards more ecologically-friendly processes will drive initiatives to close the loop on commercial plastic production.

Chemical recycling ofPET: A stepping‐stone toward sustainability

AbstractThis paper focuses explicitly on the chemical approaches involved in the recycling of polyethylene terephthalate (PET). Due to the high rate of consumption as well as nonbiodegradability, PET plays a crucial role as one of the most significant sources of accumulated waste in the landfill which jeopardizes our planet. To address this issue as well as increased environmentally conscious, running out of landfill space, natural resource, and energy conservation, and producing value‐added chemicals to use as building block or co‐products, the chemical recycling methods have been evolved. Therefore, there has been an attempt to have a comprehensive review of the five types of conventional recycling methods namely hydrolysis, methanolysis, glycolysis, aminolysis, and ammonolysis studied by researchers over the last two decades. In this regard, the influence of diverse depolymerization reaction variables for instance, traditional catalyst, temperature profile, ionic liquid catalysts, phase transfer catalyst, microwave assistance, etc was reported. Moreover, the upsides and downsides of each technique were considered.

Tandem Catalysts for Polyethylene Upcycling: A Simple Kinetic Model.

Of all plastics, the most abundantly produced is polyethylene, most of which is destined for landfills, shipping ports, and natural environments. The limited degradability and recyclability of this synthetic polymer motivates the development of chemical recycling methods. One possible approach consists of selective depolymerization to propylene with tandem olefin metathesis and double bond isomerization catalysts. In this paper, we transform thousands of coupled rate equations, pseudo-steady-state approximations, and local density approximations into one simple and analytically solvable Fokker-Planck type equation. The Fokker-Planck equation gives concise expressions for the rate of propylene production and polymer molecular weight evolution as functions of catalyst concentrations, rate constants, and ethylene concentrations.

Pyrolysis of plastic waste: Opportunities and challenges

With current low recycling rates and exponentially increasing production of plastics there is an increase in plastic material wastage, and thus new technologies are needed for waste refining. Presently in Europe, only about 10% of plastic waste is recycled, most of which is achieved through mechanical recycling. Chemical recycling methods like pyrolysis could significantly increase these recycling rates, as it can utilize mixtures of waste plastics unlike mechanical recycling. It can also be used to treat waste of many novel materials, such as composites, especially in the emerging phase when the volumes of the new materials in markets are low making separate collection of waste not a cost-efficient option. Pyrolysis offers an environmentally sound alternative to incineration and inefficient landfilling. Currently, main challenges for pyrolysis of plastic waste are unavailability and inconsistent quality of feedstock, inefficient and hence costly sorting, non-existent markets citing lack for standardized products, and unclear regulations around plastic waste management. Possible solutions could include tight cooperation between feedstock providers and converters for securing steady quantity and quality of feedstock. Advanced pre-treatment would provide the basis for cost-effective recycling. The classification of pyrolysis liquid as a product instead of waste is needed, and the REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) registration should be carried out to standardise the liquid oil as a product. In addition, sustainability impacts need to be clearly positive.

Chemical Recycling of Plastics by Microwave-Assisted High-Temperature Pyrolysis.

Use of plastics faces much criticism because of its shocking and increasing impact on the environment. But banning plastic will not help the environment. Only appropriate recycling of plastic waste can give satisfying solution. A lab‐scale chemical recycling method, in which a mixture of plastic wastes and plant oil is continuously cracked into ethylene, propylene, and other useful chemicals by using microwave‐assisted high‐temperature pyrolysis, is developed. The method has delivered interesting leads that provide the basis for setting up a new process. Based on the encouraging results, a “drop‐in” method for a renewable and circular polymer industry is also proposed. If it is commercially realized, plastic waste and plant oils will be the feedstock for the polymer industry and this industry will become renewable and circular.

Mono- and dimeric zinc(ii) complexes for PLA production and degradation into methyl lactate – a chemical recycling method

A series of well-defined mono- and dimeric Zn(ii)-complexes were prepared and fully characterised by X-ray crystallography and NMR spectroscopy.

A useful method for thorough dehydrochlorination of Poly(vinylidene chloride-co-vinyl chloride) using Zinc(II) oxide

A poly(vinylidene chloride)-based polymer is a good material for food packaging as a barrier for oxygen and steam; however, there are problems related to chemical recycling due to low temperature degradation. To aid in developing a chemical recycling method without the evolution of harmful hydrochloric acid (HCl) and organochlorines, we have proposed a dehydrochlorination process at a low temperature (around 423 K) using zinc(II) oxide (ZnO). ZnO particles dispersed into the polymer matrix were found to be effective for thorough dehydrochlorination because the reaction promoters (zinc chloride [ZnCl2] and water) spontaneously penetrated the polymer via exothermic reactions. As a result, only a small percentage of chlorine atoms remained with a low amount of HCl. The efficiency of dehydrochlorination was a result of increasing the contact area with ZnO particles using a heat-kneading apparatus. The catalyst ZnCl2 was involved in the cross-linking reaction to form C–C single bond. Due to exothermic reaction, the scission or isomerization to polyene and aromatics also proceeded over a short period, leading to a microporous carbonaceous solid with a surface area of 5 × 102 m2/g.

Plant Design for Regeneration of Spent Bleaching Clay by Boil-Off Method and Acid Treatment

There are significant economic and environmental benefits to the recycling of the waste generated by edible oil refineries, spent bleaching clay is one of the major ones. These spent bleaching clays are disposed into landfills which causes environmental pollution in addition to odors and fire hazards. The amount of fresh clay used in edible oil refineries in Saudi Arabia is estimated to be 6000 tons per year. Thus, boil-off method followed by acid activation is explored in this paper as a chemical recycling method for spent bleaching clay. This treatment can remove the adsorbed oil content and reactivate the clay to recover the bleaching ability where it can be sold again with a reasonable price. The proposed process handles a feed of 26 tons per day of spent bleaching clay, the suggested design achieves a deoiled and activated clay with bleaching ability as fresh one. The plant includes batch reactors to carry out the oil removal by boil-off method then followed by acid activation. After both reactors, filter presses combined with washing process to separate the filtrate and neutralize the products. Heat exchangers, dryers and storage equipment are also included in the design. The suggested design requires a capital investment of $2.079 MM and the cash flows of this plant suggests that it will break even by around 5.2 years.

PVC concrete composites: comparative study with other polymer concrete in terms of mechanical, thermal and electrical properties

Recycling PVC wastes with conventional chemical recycling methods such as pyrolysis, gasification is not feasible due to the carbon dioxide and dioxin emmissions generated with these methods. PVC wastes can be disposed using in ready-mixed concrete which is the most commonly used building material. In this study, effects of waste PVC instead of fine aggregate and the effects of waste PVC on the concrete properties were analyzed using 0%, 30%, 35%, 40% and 45% (w/w) in the experiments. Effects of waste PVC in concrete were compared with the other waste polymer concrete in terms of mechanical, thermal and electrical properties. All waste polymers have reduced the mechanical strength of concrete as expected. Improvement rates for the splitting tensile strength for 28 days are found to be 54.46%, 48.52% and 6.93% for PP, PET and rubberized concrete, respectively, in comparison with reference concrete. For thermal conductivity, improvement rates for 40% PC, 40% PP and 40% PVC concrete are found to be 52.56%, 44.87% and 42.31%, respectively. For electrical resistivity, the highest improvement rate was determined as 136.03%, 132.38% and 105.92% for PC, PVC and rubberized concrete, respectively.

Chemical Recycling of Bio-based Poly(3-hydroxybutyrate) Wastes Under Methanolysis Condition Catalyzed by Fe-Containing Magnetic Ionic Liquid

An efficient method for chemical recycling of bio-based polymers Poly(3-hydroxybutyrate) (PHB) wastes was established from the perspective of biorefinery. This methanolysis reaction archived successfully transformation PHB into corresponding monomer catalyzed by imidazolium-based Fe-containing ionic liquid, 1-butyl-3-methylimidazolium tetrachloroferrate ([Bmim]FeCl4). Compared with FeCl3 or ionic liquid [Bmim]Cl, this ionic liquid showed excellent catalytic performance. The obtained product methyl 3-hydroxybutyrate (M3HB) with high purity, as a chemical raw material, can be used in various fields. Investigation also indicated that the thermal stability of catalyst played an important role in this reaction, this ionic liquid could be reused for six times without apparent decrease in the conversion of PHB or yield of M3HB. Furthermore, the effects of experimental factors, such as temperature, time, catalyst dosage and methanol dosage on the methanolysis results of PHB were examined. Kinetic study indicated that this reaction was first-order kinetic reaction with activation energy of 27.44 kJ/mol. Additionally, a possible mechanism of PHB methanolysis was proposed.

Titanate Nanotubes Modified With Zinc and Its Application in Post‐Consumer PET Depolymerization

The development of nanostructures has received notoriety due to the properties that the nanometric scale provides to the material. Among these properties, the increase in the catalytic activity due to the high specific surface area of nanostructures has been the focus of several studies. Among the nanometric catalysts that have been studied, titanate nanotubes present versatility of applications since they can be modified through the functionalization or ion exchange adding the structure metals that increase the catalytic efficiency. For the depolymerization of post‐consumer polyethylene terephthalate (PET) bottles by glycolysis, a chemical recycling method that is in accordance with the principles of sustainable development, which aims to obtain the bis(2‐hydroxyethyl) terephthalate (BHET) monomer, sodium titanate nanotubes (NaTNT) and zinc titanate nanotubes (ZnTNT) were used as catalysts. The nanostructures were efficient in the PET depolymerization reaction for 2, 3, and 4 h, converting PET into BHET with yield higher than 65% (w/w).

Process simulation of bis (2- hydroxyethyl) terephthalate and its recovery using two stage evaporation systems

To preserve the petroleum feedstock and eliminate the environmental problems peculiar to polyethene terephthalate (PET) bottles littering the environment. Chemical recycling method was adopted to convert PET into useful products of prosperous sizeable industrial application. This work employed ASPEN PLUS V8.8 to simulate chemical glycolysis depolymerisation process of PET plastic wastes, using plug flow reactor for commercial production of pure bis (2- hydroxyethyl) terephthalate (BHET). The data for modelling were gotten from the experimental PET glycolysis depolymerisation work. Excess ethylene glycol (EG) was used to degrade PET waste with zinc acetate (Zn(Ac)2) as the active catalyst. The optimum operating conditions of the reaction were mean particle size PET of 127.5 μm, EG:PET (w/w) ratio of 5:1,469 K temperature, 101325 N/m 2 pressure and 3 h residence time. Reaction results were 100 % depolymerisation of PET, 85.24 % yield of BHET and 14.76 % Oligomer. Purification of the BHET was done with two stages evaporation processes using flash columns and crystallizer. Higher temperature and lower pressure were observed to increase the efficiency of the evaporators, but the heat duties increased and momentarily reduced the BHET recovery. BHET recovery was observed to decrease with increase in temperature in the case of crystallisation operation. This work achieved a higher yield and purity of BHET, a higher EG removal for re-use and less heat duties demanded in comparison to previous works. The processes with its operating conditions can be used for future scaling up of commercial processes.

Perancangan Sistem Daur Ulang Pasir Pada Industri Pengecoran Logam Skala Kecil Untuk Peningkatan Efisiensi Biaya Dan Pengurangan Limbah

Metal casting is a part of the manufacturing process to produce products that generally have intricate shapes or materials that can not be processed by ordinary machining. The complexity of the product can be achieved with the use of sand molds and the use of cores that are also made of sand. The process of recycling sand can be done by mechanical, thermal and chemical recycling methods. The sand system that has been used to produce waste in the form of waste sand, dust and other contaminants. This waste can be used for several purposes, among others: reused as metal casting sand, road construction, brick material etc. So far, recycling has been done on large scale metal casting. For medium and small scale this is not done. Used sand is treated as waste that is discarded and not utilized. The manufacture of a sand recycling system for metal casting allows the reuse of waste sand for print sand with the technical properties of sand that meet the desired quality. It will also be able to reduce waste disposed by metal casting. The study began with a literature study to find out the characteristics of used sand. Next is to plan the recycling process of the former sand, which then continued with manual sand recycling experiment. Against the recycled sand is then tested to determine its properties. The results of recycling experiments and test results are then analyzed to serve as a basis for designing and manufacturing sand recycling machines for small scale metal casting. The type of sand to be recycled is the CO2 process sand with a base of quartz sand. Based on the research that has been done, the following conclusions are obtained: CO2 process recycling sand technology produced is in the form of recycling system and analysis / study on the quality of recycling; design prototype sand recycling machine CO2 process produced is a design engine jaw crusher and hammer mill machine design.

Chemical recycling of poly(lactic acid) by water-ethanol solutions

The chemical recycling of PLA by hydrolysis in water-ethanol solutions at moderate temperatures was investigated and the kinetic parameters of the hydrolysis, rate constant and activation energy (Ea) were assessed. Hydrolysis experiments of PLA in 50% ethanol at 40, 60, 70 and 80 °C were performed. Analyses of the molecular weight distribution (MWD) of PLA were performed by conducting a deconvolution of the MWD distribution since the MWD at the latter stages of the hydrolysis experiments was not normally distributed. Conducting this analysis allowed us to identify the more likely possible hydrolysis reactions and to estimate the prevalent rate of hydrolysis. A reparameterization of the Arrhenius equation was conducted for a better estimation of the Ea with a low correlation coefficient between the parameters. No dependence of the hydrolysis rate with the change in pH for 50% ethanol was detected. For a better understanding of the effect of temperature on the hydrolytic degradation of PLA in water, hydrolysis experiments were also performed at 60, 70, 80 and 90 °C. The final Ea values for the hydrolytic degradation of PLA in 50% ethanol and in water were 9.627 × 104 and 10.474 × 104 J/mol, respectively, that are within the same range of values reported in literature. The Ea was 9% higher when PLA was hydrolyzed in water than in 50% ethanol. This study presents an alternative method for PLA chemical recycling using 50% ethanol.

Routes to greener plastics

Polymer Chemistry Plastics are mostly produced from fossil fuel resources and are often discarded after short-term use (see the Editorial by MacArthur). In a Perspective, Hillmyer discusses two routes toward more sustainable plastics: (i) production of the monomer building blocks of commodity polymers from plant resources and (ii) creation of new plant-based polymers that can compete with existing fossil fuel–based products. In a related Perspective, Garcia and Robertson look at why only a small percentage of mixed plastic waste is recycled. They highlight three main steps to more recycling: advances in mixed-plastics recycling, reducing the energy requirements for chemical recycling methods, and exploding the range of plastics that can be recycled. In a third Perspective, Albertsson and Hakkarainen look at the possible roles of degradable polymers in reducing plastic waste. Science , this issue p. [868][1], p. [870][2], p. [872][3]; see also p. [843][4] [1]: /lookup/doi/10.1126/science.aao6711 [2]: /lookup/doi/10.1126/science.aaq0324 [3]: /lookup/doi/10.1126/science.aap8115 [4]: /lookup/doi/10.1126/science.aao6749

Eco-friendly technology for recycling of cutting fluids and metal chips: A review

Recently, as environment regulations have been strengthened around the world, new policies that take the environment into consideration have been introduced in various industries. As a result, to protect against environmental pollution and save resources, eco-friendly technologies have been studied. Especially in the machining and machinery industries, interest in how to handle the recycling of cutting fluids and metal chips has increased because these materials are highly toxic. Cutting fluids increase tool life and productivity by cooling and lubricating during processing. However, cutting fluids and metal chips result in environmental pollution and are harmful to the human body. In order to solve the problems associated with these materials, eco-friendly technologies for the recycling of cutting fluids and metal chips have been proposed by researchers and industrial workers. In this paper, a review of physical, chemical and biological recycling methods for cutting fluids is performed, and research and development in relation to the recycling of metal chips are reviewed. Moreover, companies involved in the recycling metal chips are summarized based on the country of origin. The final part of this paper provides a technical summary of cutting fluids and metal chips according to associated the methods used to recycle these materials.

Carbon Footprint Analysis of Fibre Reinforced Composite Recycling Processes

Global rise of composite material demand has led to major legacy problems of manufacturing and end of life waste. The heterogeneous nature of composite material is the main challenge for recycling. In the European Union, tighter legislation on landfill, increasing landfill tax and loss of valuable material are driving the need for development of composite recycling technology. However, the recycling environmental benefits may not be optimised due to lack of high integrity environmental datasets. This study considered mechanical, high voltage fragmentation (HVF) and chemical recycling methods. New carbon footprint models were developed for each process. Experimental modelling was used to provide detailed process data associated with the processes. The Environmental Product Declaration (EPD) of the processes were evaluated through life cycle assessment studies. This work identifies that the electrical energy demand dominates the overall resource footprint in mechanical and HVF recycling methods. For both processes, extended tool life and optimised processing rate could significantly reduce the carbon footprint per unit of weight of waste processed. Environmental impact of the chemical recycling method was highly dominated by acetone used as the solvent. The refined datasets generated in this study enable better resource analysis to minimise carbon footprint of composite recycling processes. This is hoped to help increase market value of the recyclates by highlighting the environmental benefits gained through potential reuse applications.