Advanced Process Design and Modeling Methods for Sustainable and Energy Efficient Processes

Abstract

Chemical engineering, as a discipline, uses knowledge of chemistry, thermodynamics, and transport to process and refine resources on a global scale. The chemical processing industry has an enormous impact on global energy consumption and contributes to climate change. Chemical engineers play a major role in the transition of the chemical industry away from fossil fuels and develop more sustainable and efficient methods to produce commodities. To achieve this goal, new chemical and processing technologies must be developed. It is critical in these early stages of development to identify chemical and processing pathways that are both practical and economically competitive to existing technologies. With the goal of increasing the speed of developing and implementing new chemical and processing technologies, screening and early stage evaluation is essential to guiding research towards the most promising new processes and chemical pathways. This work focuses on the investigation of new chemical processing technologies, which have received academic attention, but have not been evaluated in the context of practical implementation, process design, or energy consumption. We investigate the background of these new technologies and compare them to the conventional counterparts. We present chemical and operational insights gained from industrial patents to develop feasible process designs that inform the operation and demonstrate drastic improvements possible with established heat integration and process intensification techniques. One technology we investigate is aromatics separation from petroleum feedstocks using new ionic liquid (IL) solvents. ILs are very popular in literature to replace conventional organic solvents with their main novelty being non-volatility. A practically limitless number of ILs with different properties can be synthesized introducing the potential to develop IL solvents tailored to specific applications. We investigate the potential of ILs for aromatic extraction by first developing a methodology to model the process and capture molecular interactions between the solvent and typical hydrocarbons. We then developed an IL specific process design that overcomes the challenges related to the target feedstock. We finally determined the ideal IL solvent properties for the target application investigated. We simulate and optimize designs considering 16 different ILs and use the data to correlate solvent properties to key process variables and total process energy demand. We demonstrate that 11 of the 16 ILs require less energy compared to the conventional solvent with the best performing IL reduced energy demand by 43%. Another technology we investigate is chemical recycling of poly(ethylene terephthalate) (PET), commonly used in bottles, textiles, and packaging. Chemical recycling converts waste PET into monomers that can be reprocessed into PET polymer. The monomer products are easier to purify, and chemical recycling expands the scope of recyclable waste material. There are three PET chemical recycling pathways considered by industry and academia: glycolysis, methanolysis, and hydrolysis. We investigate the fundamental differences between these chemical pathways and highlight how differences in physical and chemical properties of reactants and products lead to processing differences. We use a combination of industrial literature review and design knowledge to develop the first complete process configurations for each depolymerization pathway. We demonstrate heat integration and process intensifications that drastically reduce energy demand. We use the combination of process design and literature to compare the designs and discuss uncertainties and advantages and disadvantages. Heat integrated continuous PET chemical recycling processes can be expected to consume between 6,000 – 10,000 kJ/kg PET regardless of the depolymerization route. Continuing the trend of investigating chemical recycling of polymers we consider nylon 6, the most widely produced polyamide used for electronics, automotive parts, and textiles. Nylon 6 polymer is readily converted to its monomer caprolactam with or without the use of water as a solvent. While the recycling of post-consumer nylon 6 waste has been limited, the recovery and recycling of nylon 6 scrap and oligomers is well known. We identify the three processing routes commonly used to produce caprolactam from nylon 6: liquid-phase hydrolysis, steam stripping, and solvent-free depolymerization. We identify decomposition reactions and use experimental data to develop a kinetic model for nylon 6 depolymerization. We incorporate the kinetic model into process models for the different processing routes and demonstrate novel process intensifications to drastically reduce energy demand. We compare and discuss potential applications for each process configuration processing different types of post-consumer waste. Concluding the topic of chemical recycling of polymers, we investigate nylon 66 depolymerization, which despite chemical similarities to nylon 6, is hardly considered for chemical recycling. We provide an overview of the different chemical recycling pathways proposed in literature including acid and alkaline hydrolysis, and ammonolysis. We use experimental data to develop a novel activity coefficient based kinetic model for nylon 66 hydrolysis and add degradation reactions to present the first alkaline hydrolysis process design for nylon 66. We investigate different sections of the process and operation sensitivity to design assumptions and provide a comparison to the similar PET alkaline hydrolysis process. We find the nylon 66 alkaline hydrolysis process has favorable energy demand and is deserving of further evaluation for commercial implementation. Overall, this work has advanced the aromatic extraction technology and chemical recycling of step growth polymers. We demonstrate broad and systematic methods of incorporating data from academic and industrial evaluations to produce practical and thermodynamically consistent process models. We use these models to describe the reactions, separations, and purifications of new technologies to quantify energy demands and where operational or data uncertainties exist to focus future research. We use the defined process flows and separations to demonstrate process intensifications that drastically reduce process energy demand by as much as 70%, which can alter conclusions and favorability of certain process configurations.