D2.3: Report on process performance indicators of agro-waste based packaging production
UGent monitors key process performance indicators for the entire packaging process, from polyhydroxyalkanoates (PHA) production up to its conversion into packaging materials. Therefore, data of all input and output flows of materials and energy for each process step were collected in Milestone MS8. These data are used to calculate the environmental performance of the whole packaging production process, both at pilot and large scale, using IChemE indicators. These indicators, developed by the Institution of Chemical Engineers, give guidance to the industry towards more sustainable activities and processes.
Task 2.4 focuses on the environmental performance of the entire packaging process at process level, both at pilot and large.
Four objectives are distinguished:
- Identifying the key process performance factors throughout the packaging production process, both at pilot and large scale;
- Investigating the potential environmental benefit (i.e. resource saving and waste reduction) that occurs when scaling up the process;
- Exploring potential improvements of production at large scale;
- Comparing the environmental performance of the production of the GLOPACK packaging with that of the production of conventional plastic packaging
To evaluate the environmental performance of the whole production process of the GLOPACK packaging, first a clear description of the production process is needed. The entire packaging process is analysed both at pilot scale (i.e. small scale intended for experimental or exploratory purpose) and large scale (i.e. industrial scale intended for commercial purpose). The packaging process (at both scales) includes the following stages and steps:
Stage 1: PHBV-based compound production, consisting of three steps: poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) production, milled fibre production and compounding and cutting.
Stage 2: Conversion of PHBV-based compounds into packaging materials, for which three options can be distinguished:
- Conversion into films by extrusion;
- Conversion into trays by thermoforming;
- Conversion into cups by injection moulding.
IChemE indicators allow evaluating the sustainability performance of (large) activities at process level. The focus is on the environmental component, which covers an assessment of resource usage and environmental burdens related to emissions, effluents and waste.
Results & implications
To meet the first objective, hotspots are identified for the two stages ‘PHBV-based compound production’ and ‘conversion of compounds into packaging’, both at pilot and large scale. Regarding PHBV-based compound production at pilot scale, PHBV production is the only contributor to the environmental impact for most of the indicators considered and also uses high amounts of electricity, nutrients and chemicals. Only the milled fibre production generates non-hazardous solid waste while using insignificantly amounts of electricity and materials. The compounding and cutting contributes mainly to material use and global warming impact due to the usage of dry ice for cooling at pilot scale and the emission of fossil CO2 from this source. However, this step is not energy-intensive. At large scale, PHBV production is the main contributor to all steps of the PHBV-based compound production except non-hazardous solid waste disposal. However, the share of PHBV production to energy use decreases as thermostatic baths are assumed to be not required at large scale. At compounding and cutting, a closed-loop system for heat exchange replaces the consumption of dry ice for cooling, positively affecting material use and global warming. When focusing on the full packaging production (incl. conversion of compounds into films, trays and cups), PHBV-based compound production is in most cases the main contributor to the environmental burden. However, extrusion and thermoforming and injection moulding are energy-intensive processes at large scale. At pilot scale, often no losses were assumed for these processes. The fact that more losses occur in these processes at large scale explains the higher contribution of stage 2 than stage 1 to the non-hazardous solid waste category.
Regarding the second objective, i.e. identifying the environmental benefit of scaling up the packaging process, for most indicators, enormous savings (i.e. energy, materials and water) and reduction in the burdens on atmospheric and aquatic systems can be obtained when the entire PHBV packaging process is scaled up. Regarding PHBV-based compound production, the main savings are attributed to the PHBV production step. Avoiding the use of dry ice for cooling during compounding at large scale positively affects global warming impact and material use. Regarding the impacts on land, the PHBV packaging process generates no hazardous solid waste since agro-inputs (i.e. fruit pulp waste and wheat straw) are used as feedstock. More non-hazardous solid waste is disposed of at large scale than at pilot scale. However, this can be seen only for films and cups while upscaling the tray production (incl. stage 1 and 2TF) can gain a small benefit from disposing less such waste at large scale.
Throughout the entire packaging process of PHBV, stage 1 is the main contributor to most of the environmental indicators studied both at pilot and large scale. Therefore, attention should be paid to the optimisation of this stage (objective 3). A theoretical option based on the stoichiometric synthesis and assumptions for the PHBV production is introduced. This new scenario consumes less energy, materials and water. On the contrary, this scenario induces higher burdens in terms of global warming and photochemical ozone than the original scenario on large scale, which is explained by a higher amount of biogenic CH4 emitted during the ‘complete’ anaerobic fermentation in the PHBV production. However, in a broader perspective, i.e. at life cycle level, this emitted CH4 can serve as a substitute for e.g. biogas. Research on optimizing the balances between the resource use and the waste emission in stage 1, e.g. on the stoichiometric analysis, should be further investigated.
Compared to the well-established production of polypropylene (PP) and polylactic acid (PLA) pellets, the production of PHBV-based compounds is still an emerging technology (objective 4). This production induces higher burdens than the production of PP pellets for most of the environmental indicators (except for ecotoxicity and hazardous solid waste disposal). By optimizing the resource usage and the emissions of wastewater through the stoichiometric analysis (see objective 3), the PHBV-based compounds can obtain a slightly reduced burden and become environmentally competitive for water consumption and eutrophication in addition to the two above-mentioned categories. However, more biogenic CH4 will in this case be emitted, resulting in a considerably higher burden on the atmosphere when considering only the process level (see discussed above). On the other hand, the production of PHBV-based compounds causes lower burdens in terms of ecotoxicity and impacts on land (i.e. only non-hazardous solid waste generated) compared to the PP pellet production. Additionally, in comparison with PLA pellets, less energy is consumed and no hazardous solid waste is disposed of per kg of PHBV-based compounds. However, one should pay attention to the emission of CH4 during the PHBV-based compound production, which causes atmospheric impacts. These findings are valid for the two considered FU: one kg of compound or m3 of materials. Keep in mind that fossil-based materials (PP) have a lower density compared to agro-based materials: PHBV and PLA. Consequently, with the assumption that trays/cups made of these materials have the same dimensions or films have the same thickness, the weight of materials (compounds) required is 1.35 folds and 1.45 folds higher for PHBV and PLA packaging, respectively, than for PP packaging. The more materials are needed, the higher the burdens are. On the other hand, the production of PHBV-based compounds developed in GLOPACK can be environmentally more beneficial than the production of PHB-based compounds (studied in Harding et al., 2007) in terms of material and energy use.
To conclude, one should keep in mind that it is still an emerging technology and improvements can still be achieved. Furthermore, biogenic CH4 released from the PHBV production can induce higher burdens on atmosphere at process level, but may gain benefits at life cycle level. Other waste (e.g. fermented sludge) generated by the entire packaging process can be valorised (e.g. anaerobic digestion, agricultural fertilisers) or recycled. The benefits of such activities are not included in the evaluation at process level when using IChemE indicators. It highlights the benefits of analysing the environmental burdens of the entire packaging process at both process and life cycle levels. The latter is investigated in Task 4.5 and then presented in Deliverable D4.4.