Economic and Environmental Benefits of Modular Microwave-Assisted Polyethylene Terephthalate Depolymerization
The growing amount of plastic waste endangers the environment. Polyethylene terephthalate (PET) is among the most widespread plastics due to its extensive use in fibers and packaging. Recently, chemical recycling and upcycling approaches have been proposed to produce valuable products from bale PET feedstocks. This work performs techno-economic analysis and life cycle assessment to evaluate the environmental and economic performances of various technologies, including electrification via microwaves over a heterogeneous catalyst. We demonstrate that using a microwave-assisted heterogeneous glycolysis process to produce bis(2-hydroxyethyl) terephthalate (BHET) could have lower production costs and emissions than the traditional dimethyl terephthalate (DMT) route due to the high reactivity and excellent reusability of the catalyst. The fast reaction rate and high selectivity render this process ideal for handling spatially distributed PET waste effectively.
Multifeedstock and Multiproduct Process Design Using Neural Network Surrogate Flexibility Constraints
Biorefineries are designed to utilize a combination of various technologies to transform biomass derived raw materials into different value-added products. This strategy has been highlighted in the literature for reducing waste, increasing profitability, and improving the process resilience to uncertain biomass feedstocks. In this work, a two-stage stochastic programming (TSSP) model is developed to maximize profit and minimize emissions under different sources of uncertainties. Data-driven surrogate models are built for biorefinery’s flexibility index (FI) to quantify and improve its operational flexibility. The neural network with rectified linear unit (ReLU) activation function is established as the appropriate surrogate model because it closely approximates the flexibility index while retaining the mixed-integer linear characteristics of the overall design formulation. Moreover, the stochastic programming demonstrates the magnitude of environmental impact uncertainty quantitatively in each scenario using empirical price/demand/supply uncertainty information, which cannot be addressed by the traditional Pedigree-based life cycle assessment (LCA) uncertainty analysis.
Mathematical Programming Approach to Optimize Tactical and Operational Supply Chain Decisions under Disruptions
Supply chain (SC) networks have become more prominent, complex, and challenging to manage, especially considering the multitude of risks and uncertainty that may manifest. Studies have shown two basic approaches to hedge against the negative impact of SC disruptions: proactive and reactive. While the former methods suggest different approaches to generating robust and resilient structures, the latter approach ensures that the SC recovers effectively. A general shortcoming of existing work is not considering SC dynamics. Consequently, disruptions are considered static events without including the durations and recovery policies. In this work, we develop a SC model that aids decision-making in addressing disruptions by considering proactive and reactive strategies. We adopted a discrete time-expanded model to solve the SC problem and consider the disruption dynamics using the rolling horizon framework. In the proposed SC model, a graph network represents the SC, where the nodes consisting of suppliers, manufacturing sites, warehouses, and customers interact using the arcs. The arcs determine the flow of materials between nodes. Independent disruptions can occur at the nodes and/or arcs, and the time of disruption is quantified using the geometric distribution. In the advent of disruption, we have adopted adjusting routing plans, inventory levels, capacity flexibility, and other tactical and operational decisions to hedge against disruption. To illustrate the proposed approach, we used a small problem to illustrate the effect of arcs and node disruption in decision-making and a realistic case study to demonstrate the proposed framework’s computational complexity. The results suggested that the effect of node disruption is more predominant because the initial network configuration limits the flexibility at the nodes. Furthermore, it was shown that the SC operated efficiently, as the solution offers a balance between the service level and the total cost of operating the SC.
Coupling Process Intensification and Systems Flowsheeting for Economic and Environmental Analysis of 5-Hydroxymethyl Furfural Modular Microreactor Plants
This work evaluates process intensification technologies, microreactors, and adsorption beds, in the production of HMF. The study is performed by developing a flowsheeting capability that accounts for heat and mass transfer in the reactor to allow for comparison of different scales at the design stage. The framework helps provide a detailed description of the reactor across scales and obtain more reliable economic and environmental results. These results show that scaling up the process by means of microreactor modules reduces the minimum selling price by at least 10% and the emissions by at least 5% compared to conventional reactors. The recovery of HMF by adsorption beds instead of vacuum distillation reduces the minimum selling price between 10 and 50% and the CO2 emissions up to 40%.
Comparison of 4,4′-Dimethylbiphenyl from Biomass-Derived Furfural and Oil-Based Resource: Technoeconomic Analysis and Life-Cycle Assessment
Replacing oil-based toluene with biomass-derived furfural for 4,4′-dimethylbiphenyl (DMBP) production can pave the way for sustainable polyester manufacture. This work compared the economic and environmental performances of two conceptual designs of 4,4′-DMBP production. The first toluene-based route consists of toluene alkylation to (methylcyclohexyl)toluene (MCHT), MCHT dehydrogenation to DMBP, and isomerization of lower-valued 3,3′-DMBP. The renewable furfural-based route includes hydrogenation of furfural to 2-methylfuran (MF), oxidative coupling of MF to 5,5′-dimethylfuran (DMBF), and tandem Diels–Alder dehydration of 5,5′-DMBF to 4,4′-DMBP. The reaction conditions are optimized to achieve a more economically feasible process using furfural feedstock. At a scale of 83 kmol/h feedstock, the 4,4′-DMBP minimum selling price of the furfural-based route is $3044/t, while that of the toluene-based route is $2488/t. The feedstock and 3,4′-DMBP isomer prices are identified as critical parameters for the economic evaluation by sensitivity analysis. A “cradle-to-gate” life-cycle assessment confirms that furfural-based DMBP production emits significantly fewer greenhouse gas (5.00 kg CO2 equiv/kg DMBP) as compared to the toluene-based counterpart (8.28 kg CO2 equiv/kg DMBP).