Plastic recycling | EPFL Graph Search

Plastic recycling is the processing of plastic waste into other products. Recycling can reduce dependence on landfill, conserve resources and protect the environment from plastic pollution and greenhouse gas emissions. Recycling rates lag those of other recoverable materials, such as aluminium, glass and paper. Through 2015, the world produced some 6.3 billion tonnes of plastic waste, only 9% of which has been recycled, and only ~1% has been recycled more than once. Additionally, 12% was incinerated and the remaining 79% sent to landfill or to the environment including the ocean. Almost all plastic is not biodegradable and absent recycling, spreads across the environment where it can cause harm. For example, as of 2015 approximately 8 million tons of waste plastic enter the oceans annually, damaging the ecosystem and forming ocean garbage patches.Even the highest quality recycling processes lead to substantial plasti

Network design optimization of waste management systems: the case of plastics

François Maréchal

Failure in appropriately managing complex municipal solid waste systems in general and waste plastics in particular negatively affects public health and environment. A decision-making tool incorporating concepts of logistics and supply chain, considering different types of waste was developed. A multi-objective, multi-period mixed-integer linear programming (MILP) formulation, focusing on the plastic recycling network, incorporating features of multimodal transportation was implemented. The model aims at minimizing net present cost (NPC) and environmental impacts, illustrated by a case study of a Swiss waste treatment cluster. A reference situation was used for benchmarking and 7 new scenarios considered - corresponding to different plastics collection configurations. From the solutions space, designs arise that lead to a 2-fold decrease of NPC at the expense of increasing by 20 % current emissions, as well as solutions that provide small net gains in environmental aspects - close to 3 %, albeit a 4-fold increase in NPC due to large investments in recycling facilities and increased transportation costs. This work sheds light on the impact of supply chain and logistics aspects on the separate collection and treatment of waste plastics, in the context of a real municipal waste treatment policy, where a thermodynamic model to deal with the conversion processes is integrated into the general supply chain decision. As a result, important insights to guide decision-makers were obtained.

Elsevier2021

Sustainable polyesters via direct functionalization of lignocellulosic sugars

Adrien Julien Demongeot, Graham Reid Dick, Maxime Alexandre Clément Hedou, Harm-Anton Klok, Yves Leterrier, Jeremy Luterbacher, François Maréchal, Véronique Michaud, Thibault Rambert, Christèle Rayroud

The development of sustainable plastics from abundant renewable feedstocks has been limited by the complexity and efficiency of their production, as well as their lack of competitive material properties. Here we demonstrate the direct transformation of the hemicellulosic fraction of non-edible biomass into a tricyclic diester plastic precursor at 83% yield (95% from commercial xylose) during integrated plant fractionation with glyoxylic acid. Melt polycondensation of the resulting diester with a range of aliphatic diols led to amorphous polyesters (Mn = 30–60 kDa) with high glass transition temperatures (72–100 °C), tough mechanical properties (ultimate tensile strengths of 63–77 MPa, tensile moduli of 2,000–2,500 MPa and elongations at break of 50–80%) and strong gas barriers (oxygen transmission rates (100 µm) of 11–24 cc m−2 day−1 bar−1 and water vapour transmission rates (100 µm) of 25–36 g m−2 day−1) that could be processed by injection moulding, thermoforming, twin-screw extrusion and three-dimensional printing. Although standardized biodegradation studies still need to be performed, the inherently degradable nature of these materials facilitated their chemical recycling via methanolysis at 64 °C, and eventual depolymerization in room-temperature water.

2022

Flexibilisation of Biogas-Based Power-to-Gas Processes: A Techno-Economic and Experimental Assessment

Andreas Gantenbein

Biogas-based power-to-X technology allows storing renewable electricity, while producing CO2-neutral products.This work investigates the conversion and upgrading of digestion-derived gas mixtures with focus on increasing the operational flexibility of the overall process. Compensation of fluctuations in the feed gases enable a better economic predictability of the processes and increase the product gas output.A techno-economic evaluation was performed on bubbling fluidised bed (BFB) methanation and biological methanation for CO2 conversion in all-year operation. Each considered process was modelled and optimised to obtain grid-ready biomethane. Rate-based models were used for the main units (BFB reactor, H2-separation membrane). For the biological methanation, simulated performance data from literature were included. The analysis revealed a 17 - 19% lower production cost for BFB methanation, mainly due to lower investment cost for the main reactor vessel. Instead of using PEM electrolysis, high temperature electrolysis (SOE) would allow for heat integration with the BFB reactor, which increases the plant efficiency from 54% to 73% (LHV). A further production cost reduction can be achieved by direct methanation of biogas, omitting prior separation of CO2.Based on gas separation experiments with a commercial biogas upgrading module (Evonik Sepuran) performed in a TRL 5 plant, a flexible upgrading concept using a permeation model was developed. It allows to swiftly switch between conventional membrane-based CO2 separation by a 2-stage membrane unit and direct methanation of biogas and subsequent H2 recycling.A techno-economic analysis was performed on the flexible upgrading concept. The operation hours of the electrolyser were determined by applying a threshold to the electricity price distribution of the past years. The sensitivity on electricity cost (i.e. PtG operation hours) is clearly reduced with the flexible processes, resulting in a better economic predictability of the overall process, compared to a pure PtG installation. System analysis shows the need to allow part load operation of the methanation.Symmetric part load operation (reduced availability of CO2 and H2) was tested in a field experiment by direct methanation of biogas with subsequent H2 recycling in the TRL 5 methanation pilot plant. Stable operation of the methanation plant could be achieved at part load levels from 45% to 100% with closed recycle loop. The BFB reactor alone was tested in a load range of 20 to 100%. A dynamic experiment demonstrated fast, successive load changes while still producing grid-ready biomethane.Asymmetric part load (only H2 limiting) operation was investigated by process simulations and field experiments. Since CO2 is present in the system in an over-stoichiometric amount, H2 recycle and CO2 separation have to be performed simultaneously. Process simulations showed that selecting a most ideal PtG configuration based on technical feasibility is difficult, as further constraints, such as overall economics and operation scheduling have to be considered in process design and evaluation. In all cases, the CO2 separation from the integrated processes leads to a loss of H2 and CH4 from the process. The introduction of an additional membrane stage with a sweep stream is proposed to reduce the loss of reactive gases via the off gas stream.

EPFL2022

Flexibilisation of Biogas-Based Power-to-Gas Processes: A Techno-Economic and Experimental Assessment

Andreas Gantenbein

EPFL2022