Title : Techno-economic and life-cycle assessment of biobased plastic production
Abstract:
The production of biobased plastics has gained considerable interest in recent years as society moves toward a more biobased economy. The economic viability of bioplastics production is dependent on the implementation of effective bio- and chemical catalytic processing. Polyethylene (PE) and polyethylene terephthalate (PET) are two of the most widely used fossil-based plastics. The production of bio-PE has been commercialized, through the catalytic dehydration of biobased ethanol to ethylene. PET is produced through the polycondensation of terephthalic acid (TPA) and monoethylene glycol (MEG). Bio-based MEG has been commercialized using bioethanol as feedstock, but commercial production of bio-p-xylene (precursor to TPA) has not yet been realized. A proposed pathway towards p-xylene is through 5-hydroxymethyl furfural (HMF) as intermediate. HMF is produced through the acid-catalyzed dehydration of sugars, and can be catalytically converted to p-xylene in two steps. Alternatively, HMF can be oxidized to 2,5-furandicarboxylic acid (FDCA), a chemical analogue to TPA, which can be polymerized with MEG to produce polyethylene furanoate (PEF) to replace PET.
This study aimed to identify the most viable biorefinery scenario for production of bioplastic from molasses. Process simulations were developed in AspenPlus® for bioplastics and their monomers/intermediates, and techno-economic analyses (TEAs) and life-cycle assessments (LCAs) were performed based on simulated mass and energy balances. PEF was the most profitable bioplastic, requiring a green premium (GP) price that is 44.4 % higher than the current market selling price of fossil-PET, mainly due to the efficient production of FDCA, which had the second highest production rate (59.0 ktpa) and the lowest energy demand (heat: 20.7 MW, power: 3.74 MW) of all scenarios. Advantages of the FDCA process includes the use of a single solvent system for all reactions, ease of solvent and product recovery, and the use of unrecovered FDCA as the dehydration catalyst. The platinum catalyst (Pt/C) used for HMF oxidation was responsible for 43.1% and 25.7% of the equipment operating cost, respectively. FDCA (GP:17.3%) was more profitable than PEF, due to the high cost of MEG (GP: 79.1%) production, which involves four conversion steps. Compared to FDCA, MEG had a lower yield (47.7 ktpa), higher energy demand (heat: 34.1 MW; power: 7.1 MW) and higher capital investment ($145.2 MM vs $78.5 MM). Ethylene had the second lowest energy demand (heat: 26.6 MW; power: 3.64 MW), and benefited from a relatively inexpensive catalyst, compared to other monomers and intermediates. Ethylene had the lowest capital investment ($59.7 MM) and operating cost ($33.3 MM), but was not economically viable (GP:84.7%), due to a low mass yield (27.3 ktpa) associated with dehydration products. PE (GP of 56.1 %) was preferable to ethylene, due to its’ higher market price and difficulties related to the transportation and storage of ethylene. PET required a GP of 128.1 %, due to the complex pathway of MEG, and especially p-xylene production from sugars, which involved many catalytic reactions and large volumes of organic solvents, resulting in extremely high energy demands and capital and operating costs. More work could be done to improve the catalytic activity and reaction selectivities, but other emerging technologies, which produce p-xylene and MEG from sugars in one or two steps, will likely be the key to cost-competitive bio-PET in the future. Life-cycle assessments were performed for each bioplastic, which determined that PE was the most environmentally sustainable, due to the minimal inventory requirement, compared to PET and PEF, which required large volumes of solvents, precious metals, and other raw materials.
Audience Takeaway Notes:
- Viable routes towards the production of bioplastics will be identified, with specific focus on chemical-catalytic processing.
- The results of the study will show which biobased plastics and monomers/intermediates are the most profitable as annexed to a sugar mill and highlight any shortcomings/ bottlenecks towards their future commercialization.
- The research will highlight areas of biobased, catalytic process technologies that require improvement/ further research.
- The research is an early phase design/pre-feasibility study of bioplastic production, which can provide readers with direction towards the development of their own biorefinery designs.
