1 Introduction
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In the previous LCA studies on PET recycling, the effect of multiple-recycling trips has not been discussed. The industry has grown fast and is likely to continue in the future (Glenz 2007). It is expected that the quantity of recycled PET will increase and the recycled polymer can be further recycled. We therefore formulate as our first research question: what is the effect of multiple-recycling trips on the overall environmental impact of PET recycling?
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The second parameter is related to the market demand of recycled PET pellets. Currently, about seven times more recycled PET pellets are used for recycled fibre than for recycled bottles (Thiele 2009). If more recycled PET pellets are available for B2B recycling, less of them would be available for fibres. The optimisation of B2B and B2F recycling should be studied to understand how the environmental impact can be minimised. The second research question of this study is: how does the overall environmental impact change when the share of recycled PET pellets used for B2F and for B2B recycling changes?
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Worldwide, in 2005, approximately 65% of the PET polymer was used to produce fibre and 30% was used to produce bottles (Glenz 2007).1 In contrast, in Europe, only about 35% of PET went into the fibre sector (Glenz 2007). It is interesting to investigate whether the share of the market demand of bottle and fibre influences the overall environmental impact of the recycling system. This leads to the third research question: how does the overall environmental impact change when the market demands of PET bottle and fibre change?
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The fourth parameter is related to bio-based feedstock. Bio-based plastics have attracted much attention in the past decades due to the concerns of limited fossil resources and climate change. Several studies have shown that bio-based materials have lower environmental impacts than their petrochemical counterparts (Crank et al. 2005; Hermann et al. 2007; Patel et al. 2003; Shen and Patel 2008; Patel et al. 2005). Bio-based PET and petrochemical PET are chemically identical. A comparative LCA of recycled PET, bio-based virgin PET and bio-based recycled PET has not been conducted so far. Our fourth research question is raised: how does recycled PET compare to bio-based virgin PET and bio-based recycled PET?
2 Methodology
2.1 Functional unit and system boundary
2.2 Life cycle inventory modelling
Changing parameters | Baseline | Scenario 1 | Scenario 2 | Scenario 3 | Scenario 4 |
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Baseline (current situation) | Multiple-recycling loops | Change of the share of R-PET pellets used for B2B recycling | Change of PET fibre and bottle demands | Bio-based PET, and recycled bio-based PET | |
n (number of recycling trips) | 1 | >1 | >1 | >1 | 1 |
b (share of R-PET pellets used for B2B recycling) | 12% | 12% | 0–100% | 0–100% | 12% |
Functional unit: Bottles/fibre (kg) | 350/650 | 350/650 | 350/650 | 650/350 | 350/650 |
PET polymer | Petrochem. | Petrochem. | Petrochem. | Petrochem. | Bio-based ethylene and petrochem. PTA |
Parameters | Value | Unit | Source |
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Virgin PET amorphous grade | Based on PlasticsEurope (Liebich and Giegrich 2010), the NREU and GHG emissions (100 years) of PET bottle-grade are 68.6 MJ/kg and 2.15 kg CO2 eq./kg. Based on Boustead (2005a; 2005b), the NREU and Global warming (100 years) of the SSP step (solid state polymerisation) are 1.96 MJ/kg and 0.10 kg CO2 eq./kg. The NREU and Global warming impact of PET amorphous are calculated: 68.60-1.96 = 66.64 MJ/t and 2.15-0.10 = 2.05 kg CO2 eq./kg. | ||
NREU (non-renewable energy use) | 66.64 | MJ/kg | |
Global warming (100 years) | 2.05 | kg CO2 eq./kg | |
Transportation distance, bottle waste collection (d1) | 400 | km | Assumed; to be checked in the sensitivity analysis. |
Energy use for bottle sorting, compacting and baling | Negligible | – | |
PET bottle-to-flake production: | |||
Baled PET bottle waste | 1,316 | kg/t flake | Arena et al. (2003) |
Electricity | 278 | kWh/t flake | Arena et al. (2003) |
Heat (from natural gas) | 2,500 | MJ/t flake | Arena et al. (2003) |
NaOH (30%) | 10 | kg/t flake | Arena et al. (2003) |
Sulphuric acid (30%) | 20 | kg/t flake | |
By-products (e.g. PE) | 88 | kg/t flake | Arena et al. (2003) |
Allocation factor of by-products | 5% | – | |
Solid waste a
| 222 | kg/t flake | Arena et al. (2003) |
Transportation distance, flake to pellet production (d2) | 400 | km | Assumed; to be checked in the sensitivity analysis |
Pellet production | |||
Flakes input | 1,031 | kg/t pellet | Shen et al. (2010) |
Heat (from natural gas) | 252 | MJ/t pellet | Bhatt (2008) |
Pellet extrusion | 447 | kWh/t pellet | Kent (2008) |
Material efficiency of PET (PET bottle-to-pellet, PET flow, η) | 95% | ||
Fraction of R-PET pellet (φ) | 35% | Assumed based on Van der Velden (2010); to be checked in the sensitivity analysis | |
MSWI plant with energy recovery: | |||
Gross calorific value of PET | 23 | MJ/kg in primary energy terms | Ecoinvent Database Version 2.0 (Doka 2007) |
Energy recovery from MSWI in Western Europe | 60% b
| Reimann (2006) and Personal communication with Dr. Reimann; to be checked in the sensitivity analysis. | |
Bio-based PET | |||
- Bio-based EG | Chen and Patel (Forthcoming): no land use change is assumed for maize and sugarcane production in the US and Brazil. Values reported in this table are based on 50% maize and 50% sugarcane as the feedstock. | ||
NREU | 17 | MJ/kg EG | |
Global warming (100 years) | −0.55 c
| kg CO2 eq./kg EG | |
- Petrochemical PTA | PlasticsEurope (Liebich and Giegrich 2010) | ||
NREU | 53 | MJ/kg PTA | |
Global warming (100 years) | 1.33 | kg CO2 eq./kg PTA | |
- Polymerization | Patel et al. (1999) | ||
Natural gas | 2.29 | GJ/t PET | |
Electricity | 101 | kWh/t PET | |
Steam | 240 | kg/t PET | |
PTA | 867 | kg/t PET | |
EG | 334 | kg/t PET | |
Data obtained from the Ecoinvent database version 2.0 | Process names in the Ecoinvent database | ||
Transportation by road | “Transportation, >32 t lorry, EURO3/RER” | ||
Heat from natural gas | “Heat, natural gas, at industrial furnace low-NOx >100 kW/RER” | ||
EU grid electricity mix d
| “Electricity, low voltage, production [grid name], at grid/[grid name]” | ||
NaOH | “Sodium hydroxide, 50% in water, Production mix, at plant/RER” | ||
Sulfuric acid | “Sulphuric acid, liquid, at plant/RER” | ||
Nitrogen | “Nitrogen, liquid, at plant/RER” | ||
MSWI of PET | “Disposal, polyethylene, 0.4% water, to municipal incineration/CH” |
2.3 Input data
2.4 Environmental impact categories: NREU and global warming
3 Results
3.1 The baseline case
3.2 Scenario 1: multiple-recycling trips—effect of n
3.3 Scenario 2: change the share of R-PET pellets used for B2B recycling—effect of b
(kg per functional unit) | Share of bottle waste going to B2B recycling (b) | Reference | |||||||
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0% | 6% | 12% (baseline) | 30% | 37% | 50% | 100% | |||
A | V-PET (first-life bottle) | 350 | 301 | 263 | 193 | 175 | 148 | 94 | 350 |
B | V-PET (added to R-bottle) | 0 | 32 | 57 | 102 | 114 | 131 | 166 | 0 |
C | V-PET fibre (make up) | 318 | 382 | 431 | 522 | 545 | 579 | 650 | 650 |
D | R-PET (used for r-bottle) | 0 | 17 | 30 | 55 | 61 | 71 | 90 | 0 |
E | R-PET (used for r-fibre) | 333 | 268 | 219 | 128 | 105 | 71 | 0 | 0 |
F | Total PC MSWI with ER | 650 | 700 | 737 | 807 | 825 | 852 | 906 | 1,000 |
V-PET total (A+B+C) | 67% | 71% | 75% | 82% | 83% | 86% | 91% | 100% | |
R-PET total (D + E) | 33% | 29% | 25% | 18% | 17% | 14% | 9% | 0% |
3.4 Scenario 3: change the demand of PET fibre and bottle (functional unit = 650 kg bottle and 350 kg fibre)
(kg per functional unit) | Share of bottle waste goes to B2B recycling (b) | Reference | |||||||
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0% | 5% | 10% | 12% (default) | 17% (minimal) | 50% | 100% | |||
A | V-PET (first-life bottle) | 368 | 388 | 409 | 420 | 444 | 276 | 175 | 650 |
B | V-PET (added to R-bottle) | 0 | 34 | 72 | 90 | 134 | 243 | 309 | 0 |
C | V-PET fibre (make up) | 0 | 0 | 0 | 0 | 0 | 219 | 350 | 350 |
D | V-PET bottle (make up) | 282 | 210 | 130 | 92 | 0 | 0 | 0 | 0 |
E | R-PET (used for r-bottle) | 0 | 18 | 39 | 49 | 72 | 131 | 166 | 0 |
F | R-PET (used for r-fibre) | 350 | 350 | 350 | 350 | 350 | 131 | 0 | 0 |
G | Total PC MSWI with ER | 632 | 612 | 591 | 580 | 556 | 724 | 825 | 1000 |
V-PET total (A+B+C+D) | 65% | 63% | 61% | 60% | 58% | 74% | 83% | 100% | |
R-PET total (E+F) | 35% | 37% | 39% | 40% | 42% | 26% | 17% | 0 |
3.5 Scenario 4: renewably sourced PET
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The system “Recycled bio-based PET” has the lowest impact among all four product systems; it offers at least 35% of the impact reductions (for both NREU and GHG emissions) compared to the reference system and at least 20% of impact reductions compared to the baseline recycling system.
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The product system of (virgin) bio-based PET, i.e., without recycling, saves NREU and GHG emissions by 21% and 25%, respectively, compared to the reference system where petrochemical PET is used (also without recycling).
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The (virgin) bio-based PET system is comparable to the recycled, petrochemical PET system (i.e. the baseline recycling system).