Life Cycle Inventory (LCI): Data Collection, Mass Balance & Allocation Rules

Life Cycle Inventory (LCI) is the data-collection phase of a Life Cycle Assessment (LCA). It involves compiling and quantifying all inputs (raw materials, energy, water) and outputs (emissions to air, water, land) for a product system. For polymer processors, conducting an LCI is essential to generate Environmental Product Declarations (EPDs) and satisfy client requests for carbon footprint data. An engineer who can build a clean LCI sheet can help their company access green supply chains.

• Detail the steps of the LCI phase per ISO 14044 guidelines.
• Define unit processes and product system boundaries (cradle-to-gate).
• Construct mass and energy balances for a polymer processing line.
• Apply allocation rules (mass vs. economic) to split environmental loads in multi-product systems.
• Reference LCI database standards.

3.1 LCI Methodology (ISO 14040/44)

LCI is the second phase of LCA, occurring after Goal and Scope Definition. It requires mapping the flowchart of the product system and gathering quantitative data for each unit process (e.g., compounding, extrusion).

3.2 Mass and Energy Balances

For every unit process, inputs must balance outputs:

$$\sum \text{Mass In} = \sum \text{Mass Out} + \text{Accumulation}$$

For steady-state processing, accumulation is zero. Outputs include the primary product, coproducts, and emissions.

3.3 Allocation Rules in Co-production

When a unit process produces multiple products (e.g., a refinery cracking naphtha to yield ethylene, propylene, and butadiene), the environmental impacts must be allocated among them:

• Physical Allocation (Mass): Impacts split based on the mass ratio of the outputs.
• Economic Allocation: Impacts split based on the market value ratio of the outputs. ISO 14044 recommends avoiding allocation by dividing the process or expanding the system boundaries first, before resorting to physical or economic allocation.

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Problem: A compounding extrusion line produces two outputs: PP compound (90% mass fraction, market value = ₹150/kg) and low-grade purging scrap (10% mass fraction, market value = ₹30/kg). The process consumes $0.80$ kWh of electricity per kg of total output. The electricity grid emission factor is $0.90$ kg CO₂-eq/kWh. Calculate the carbon footprint allocation (in kg CO₂-eq/kg of product) for the PP compound using:

1. Mass allocation.
2. Economic allocation.

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Solution:

1. Calculate total emissions per kg of total output:

$$\text{Total Emissions} = 0.80 \text{ kWh/kg} \times 0.90 \text{ kg CO}_2\text{-eq/kWh} = \textbf{0.72 kg CO}_2\text{-eq/kg output}$$

1. Mass Allocation: Since PP compound represents 90% of the mass, it receives 90% of the emissions:

$$\text{Mass Allocated Emissions} = \frac{0.72 \text{ kg CO}_2\text{-eq} \times 0.90 \text{ mass ratio}}{0.90 \text{ kg of PP}} = \textbf{0.72 kg CO}_2\text{-eq/kg PP}$$

(Under mass allocation, both products receive the same emission rate per kg: 0.72 kg CO₂-eq/kg).

1. Economic Allocation: Calculate the economic value fractions for 1 kg of total output:

• Value of PP compound = $0.90 \text{ kg} \times 150 = \text{₹135.0}$
• Value of scrap = $0.10 \text{ kg} \times 30 = \text{₹3.0}$
• Total value = $135 + 3 = \text{₹138.0}$
• Value fraction for PP compound = $\frac{135}{138} = 0.97826$ (97.83% of value) Calculate economic allocated emissions for PP compound:

$$\text{Economic Allocated Emissions} = \frac{0.72 \text{ kg CO}_2\text{-eq} \times 0.97826}{0.90 \text{ kg of PP}} = \frac{0.70435}{0.90} = \textbf{0.7826 kg CO}_2\text{-eq/kg PP}$$

Interpretation: Mass allocation assigns 0.72 kg CO₂-eq/kg to the PP compound, while economic allocation assigns a higher value of 0.783 kg CO₂-eq/kg because the PP compound carries 97.8% of the economic benefit of the process. The choice of allocation rule significantly affects LCA results and must be declared under ISO 14044.

Indian automotive compounding units exporting to the EU compile LCIs using local grid emission factors (e.g., Central Electricity Authority of India data) to verify compliance with European green product standards.

• LCI: Life Cycle Inventory; compilation of inputs and outputs for a product system.
• Unit Process: The smallest element in the LCI system boundary for which data is collected.
• Mass Allocation: Splitting environmental loads based on product mass fractions.
• Economic Allocation: Splitting environmental loads based on product market values.
• ISO 14044: The international standard specifying requirements for LCA data collection.

1. ISO 14040 — Environmental management — Life cycle assessment — Principles and framework
2. ISO 14044 — Life cycle assessment — Requirements and guidelines

1. Detail the data collection steps required to establish an LCI for a plastic injection moulding facility, listing five input and five output parameters.
2. Explain why ISO 14044 recommends avoiding allocation by "system expansion". Give a packaging recycling example.
3. A chemical plant co-produces chlorine and caustic soda from salt brine electrolysis. Design a mass-balance worksheet allocating the electricity energy inputs.

Q1. Life Cycle Inventory (LCI) is which phase of a Life Cycle Assessment?

• B) Second phase (data collection)

Q2. Under ISO 14044, if allocation cannot be avoided, the first preference is given to:

• A) Physical allocation (e.g., mass fraction)

Q3. If a compounding line co-produces 95% plastic pellets and 5% scrap, mass allocation assigns what share of energy emissions to the pellets?

• B) 95%

Q4. The primary source for electricity grid emission factors in India is published by which agency?

• B) Central Electricity Authority (CEA)

Q5. Which ISO standard specifies guidelines and requirements for compiling a Life Cycle Inventory?

• C) ISO 14044