Waste to energy: Trending key challenges and current technologies in waste plastic management.

Due to the 'forever' degrading nature of plastic waste, plastic waste management is often complicated. The applications of plastic are ubiquitous and inevitable in many scenarios. Current global waste plastics production is ca. 3.5 MMT per year, and with the current trend, plastic waste production will reach 25,000 MMT by 2040. However, the rapid growth in plastic manufacture and the material's inherent nature resulted in the accumulation of a vast amount of plastic garbage. The current recycling rate is <10 %, while the large volumes of discarded plastic waste cause environmental and ecological problems. Recycling rates for plastic vary widely by region and type of plastic. In some developed countries, the recycling rate for plastics is around 20-30 %, while in many developing nations, it is much lower. These statistics highlight the magnitude of the plastic waste problem and the urgent need for comprehensive strategies to manage plastic waste more effectively and reduce its impact on the environment. This review critically analyses past studies on the essential and efficient techniques for turning plastic trash into treasure. Additionally, an attempt has been made to provide a comprehensive understanding of the plastic upcycling process, the 3Rs policy, and the life-cycle assessment (LCA) of plastic conversion. The review advocates pyrolysis as one of the most promising methods of turning plastic trash into valuable chemicals. In addition, plastic waste management can be severely impacted due to uncontrollable events, such as Covid 19 pandemic. Recycling and chemical upcycling can certainly bring value to the end-of-life plastic. However, the LCA analysis indicated there is still a huge scope for innovation in chemical upcycling area compared to mechanical recycling. The formulation of policies and heightened public participation could play a pivotal role in reducing the environmental repercussions of plastic waste and facilitating a shift towards a more sustainable future.

Effective utilization of discarded reverse osmosis post-carbon for adsorption of dyes from wastewater.

In this study, the deployment of post Reverse Osmosis (RO)-carbon as a adsorbent for dye removal from water has been investigated. The post RO-carbon was thermally activated (RO900), and the material thus obtained exhibited high surface area viz. 753 m2/g. In the batch system, the efficient Methylene Blue (MB) and Methyl Orange (MO) removal was obtained by using 0.08 g and 0.13 g/50 mL adsorbent dosage respectively. Moreover, 420 min was the optimized equilibration time for both the dyes. The maximum adsorption capacities of RO900 for MB and MO dyes were 223.29 and 158.14 mg/g, respectively. The comparatively higher MB adsorption was attributed to the electrostatic attraction between adsorbent and MB. The thermodynamic findings revealed the process as spontaneous, endothermic, and accompanied by entropy increment. Additionally, simulated effluent was treated, and >99% dye removal efficiency was achieved. To mimic an industrial perspective, MB adsorption onto RO900 was also carried out in continuous mode. The initial dye concentration and effluent flow rate were among the process parameters that were optimized using the continuous mode of operation. Further, the experimental data of continuous mode was fitted with Clark, Yan, and Yoon-Nelson models. Py-GC/MS investigation revealed that dye-loaded adsorbents could be pyrolyzed to produce valuable chemicals. The cost and low toxicity associated benefits of discarded RO-carbon over other adsorbents reveal the significance of the present study.

Bio-oil and biochar from the pyrolytic conversion of biomass: A current and future perspective on the trade-off between economic, environmental, and technical indicators.

Over the years, the transformation of biomass into a plethora of renewable value-added products has been identified as a promising strategy to fulfil high energy demands, lower greenhouse gas emissions, and exploit under-utilized resources. Techno-economic analysis (TEA) and life-cycle assessment (LCA) are essential to scale up this process while lowering the conversion cost. In this study, trade-offs are made between economic, environmental, and technical indicators produced from these methodologies to better evaluate the commercialization potential of biomass pyrolysis. This research emphasizes the necessity of combining LCA and TEA variables to assess the performance of the early-stage technology and associated constraints. The important findings based on the LCA analysis imply that most of the studies reported in literature focussed on the global warming potentials (GWP) under environmental category by considering greenhouse gases (GHGs) as evaluation parameter, neglecting many other important environmental indices. In addition, the upstream and downstream processes play an important role in understanding the life cycle impacts of a biomass based biorefinery. Under upstream conditions, the use of a specific type of feedstock may influence the LCA conclusions and technical priority. Under downstream conditions, the product utilization as fuels in different energy backgrounds is crucial to the overall impact potentials of the pyrolysis systems. In view of the TEA analysis, investigations towards maximizing the yield of valuable co-products would play an important role in the commercialization of pyrolysis process. However, comprehensive research to compare the conventional, advanced, and emerging approaches of biomass pyrolysis from the economic perspective is currently not available in the literature.

Anisole hydrodeoxygenation over Ni-Co bimetallic catalyst: a combination of experimental, kinetic and DFT study.

Catalytic hydrodeoxygenation (HDO) of anisole was performed with a series of Ni and Co containing catalysts with different weight ratios on activated carbon (AC) for cyclohexanol production. The catalytic activities of various catalysts revealed that Ni5Co5-AC was the best catalytic system. Structural analysis obtained from XRD, TPR, XPS, and TEM evidently demonstrates that Ni5Co5-AC sample consists of a distorted metal alloy spinel structure and optimum particle size, enhancing its catalytic performance. Kinetics were investigated to identify cyclohexanol production rate, activation energy, and reaction pathway. Structural, experimental, kinetics and density functional simulations suggested that high amount of distorted metallic alloy in Ni5Co5-AC, presence of water, high adsorption efficiency of anisole, and low adsorption tendency of cyclohexanol on metallic alloy surface were the critical factors for HDO of anisole to cyclohexanol.

Biomass pyrolysis: A review on recent advancements and green hydrogen production.

Biomass pyrolysis has recently gained increasing attention as a thermochemical conversion process for obtaining value-added products, thanks to the development of cutting-edge, innovative and cost-effective pyrolysis processes. Over time, new and novel pyrolysis techniques have emerged, and these processes can be tuned to maximize the production of high-quality hydrogen. This review examines recent advancements in biomass pyrolysis by classifying them into conventional, advanced and emerging approaches. A comprehensive overview on the recent advancements in biomass pyrolysis, highlighting the current status for industrial applications is presented. Further, the impact of each technique under different approaches on conversion of biomass for hydrogen production is evaluated. Techniques, such as inline catalytic pyrolysis, microwave pyrolysis, etc., can be employed for the sustainable production of hydrogen. Finally, the techno-economic analysis is presented to understand the viability of pyrolysis at large scale. The outlook highlights discernments into future directions, aimed to overcome the current shortcomings.

Statistical evaluation of cow-dung derived activated biochar for phenol adsorption: Adsorption isotherms, kinetics, and thermodynamic studies.

Sustainable and economical wastewater treatment forms a vital step towards long-term sustainability of petrochemical refineries and industries. An affordable solution to this challenge is to employ biowaste as the key consumable active component. This paper describes the synthesis and characterization of activated biochar derived from cow-dung, a readily available raw material in low-resource settings, and its application for adsorption of phenol, one of the major pollutants in industrial wastewater. Adsorption parameters are optimized by using response surface methodology. Phenol adsorption equilibrium and kinetics data are well fitted to Freundlich isotherm (R2 = 0.97) and pseudo-second-order model (R2 = 0.99), respectively. The maximal adsorption capacity (518.89 mg/g) was attained using the Langmuir isotherm model at pH 6.0. Negative values of thermodynamic parameters confirmed the spontaneity, feasibility, and exothermic behaviour of adsorption reaction. The results demonstrate that synthesized activated biochar showed an excellent phenol adsorption capacity of 98.8 %.

Preparation and characterization of lignin-derived hard templated carbon(s): Statistical optimization and methyl orange adsorption isotherm studies.

In this study, lignin-derived zeolite templated carbon materials were fabricated to remove the organic contaminant, methyl orange. Response surface methodology with Box-Behnken design was used to optimize the adsorption parameters. Based on Box-Behnken design, a quadratic model was developed to correlate the adsorption variables with the response, removal efficiency. Analysis of variance revealed the adsorbent dosage as the most influential adsorption variable. Lignin derived ZSM-5 (PZ) and mordenite (PM) templated carbon materials exhibited high surface area; 476.0 and 716.0 m2/g respectively. The maximum theoretical adsorption capacity of PZ and PM for methyl orange was 514.0 and 225.0 mg/g, respectively. The experimental kinetic data best fitted to pseudo-second-order model for both the adsorbents. PZ adsorbent was also utilized to treat real wastewater containing dyes and achieved 40 % methyl orange removal efficiency. Adsorption thermodynamic study revealed the process as spontaneous, exothermic and also indicated the increment in entropy after adsorption.

Co-Hydrothermal Liquefaction of algal and lignocellulosic biomass: Status and perspectives.

Hydrothermal liquefaction (HTL) effectively converts biomass to biofuels, thereby limiting the endless reliance on petroleum products derived from fossil fuels. However, the conversion is based on individual feedstock in the HTL process. In order to, further boost the conversion, HTL can be done by blending various feedstock, mainly algal and lignocellulosic biomass. Bibliometric analysis was carried out, and it was observed that there have been very few studies on Co-Hydrothermal Liquefaction (Co-HTL). There still exist several crucial gaps in process optimization when co-reactants are used due to their synergistic effects. The reaction kinetics and mechanism, catalyst screening and by-products application require further studies. Therefore, R&D is necessary to optimize the process to completely utilize the complementarity of the feedstocks under study resulting in better quality of products which require minor/ no upgradation steps.

Energy optimization from a binary mixture of non-edible oilseeds pyrolysis: Kinetic triplets analysis using Thermogravimetric Analyser and prediction modeling by Artificial Neural Network.

Pyrolysis kinetics and thermodynamic parameters of two non-edible seeds, Pongamia pinnata (PP) and Sapindus emarginatus (SE), and their blend in the ratio of 1:1 (PS) were studied using the thermogravimetric analyzer. Kinetic triplets were determined using both model-free [Starink (STR), Friedman (FRM), Iterative Kissinger-Akahira-Sunose (IT-KAS), Iterative Ozawa-Flynn-Wall (IT-OFW), Vyazovkin (VYZ), and Master plot (MP)] and model fitting Coats-Redfern (CR) methods at three different heating rates 10, 30 and 50 °C/min. Activation energies were 192.66, 179.44, and 163.25 kJ/mol for PP, SE, and PS, respectively. It was found that the blend of the two-biomass (PS) showed promising results with lower activation energy compared to the individual biomass. Thermodynamic parameters (ΔG, ΔS, and ΔH) were obtained using the model-free isoconversional method. The three hidden layers of complex neuron topology are well fitted to the experimental DTG curves by artificial neural network (ANN). The study confirmed that the heating rate had a significant impact on the kinetics and thermodynamic parameters. The reaction mechanism was also in consonance with the experimental data. The study suggests that the PP and SE seeds can be an appropriate feed for pyrolysis, and their blend (PS) can be a viable alternative in optimizing the entire process.

A detailed assessment of pyrolysis kinetics of invasive lignocellulosic biomasses (Prosopis juliflora and Lantana camara) by thermogravimetric analysis.

Thermogravimetric analysis of two invasive weeds Prosopis juliflora (PJ) and Lantana camara (LC) are carried out by pyrolysis under dynamic conditions (20 to 900 °C) at different heating rates 5, 10, 20 and 40 °C/min. Gross calorific values of PJ and LC are estimated to 18.2 and 18.92 MJ/kg respectively. Activation energy obtained by FRM, M-FRM, KAS, OFW, STR, NL-INT, NL-DIF methods are 157.56, 151.24, 140.86, 143.39, 140.74, 141.19, 157.59 kJ/mol for PJ and 169.98, 167.67, 149.39, 151.51, 149.23, 149.70, 169.98 kJ/mol for LC respectively. Kinetic compensation effects were well fitted with the experimental data, which provided the value of the pre-exponential factor. To identify the appropriate reaction mechanism, the Popescu and Master-plot methods are employed. Thermodynamic parameters (ΔG, ΔH, and ΔS) are also determined by NL-INT, NL-DIF, and M-FRM methods. Results of kinetic and thermodynamic parameters confirm the suitability of PJ and LC invasive weeds as potential biomasses for pyrolysis process.

Pyrolysis kinetics and synergistic effect in co-pyrolysis of Samanea saman seeds and polyethylene terephthalate using thermogravimetric analyser.

This work deals with co-pyrolysis of polyethylene terephthalate (PET) with Samanea saman seeds (SS) to understand the kinetics and synergistic effects between two different feedstocks. SS and PET were blended in different ratios (1:1, 3:1 and 5:1) and iso-conversional models such as Kissinger-Akahira-Sunose (KAS), Friedman method (FM), Starink (ST), Ozawa-Flynn-Wall method (OFW), and Coats-Redfern method (CR) were used to calculate the kinetic parameters. Results substantiate assumed hypothesis that blending of SS and PET at 3:1 provided higher synergistic effect and RMS value, which in turn indicated maximum formation of hot volatiles during pyrolysis. Kinetic analysis confirmed that individual SS and PET required higher activation energy while blended SS and PET at 3:1 ratio required lower activation energy to start the reaction. The thermodynamic and kinetic analysis confirmed that biomass had complex reaction kinetics which depends on reaction rate as well as its order.