Some chemicals can be modeled directly using an existing dataset in the database. For example, the processes of producing urea in any part of China can be accounted for using a dataset “Urea Production|Urea|cut off, U-CN.” This dataset captures the foreground and background data associated with urea production.
Sometimes however, chemical compounds cannot be found in databases, especially when they are more complex or less commonly used chemicals. How can you choose a fitting dataset in this case?
This article outlines the steps to model chemical compounds that aren't found in databases offered in Ecochain software.
Feel like you're missing information? This article builds upon the following articles, check them out if you want to learn more:
On adding impact in Mobius: Mobius - How to: Add impact to your model using datasets
On adding impact in Helix: Helix- How to: Company level inputs
On environmental databases: Explained: Environmental databases in Helix and Mobius
On ecoinvent datasets: Explained: Ecoinvent datasets
Dataset workarounds
Step 1: Estimate the contribution of the impact of the chemicals in the process.
A less accurate approximation is practical if the chemical at hand contributes a tiny amount to the product's total impact. It will take less time to model a less accurate approximation without significantly affecting the result. By contrast, if the chemical is one of the key components of the product, then a more precise approach is necessary.
Step 2: Check for the chemical
Sometimes chemicals are present in ecoinvent with a different name, for example:
2-Aminoethanol = monoethanolamine
Phenylethane = ethylbenzene
Esterquats = Quaternary ammonium compounds
A helpful website we often use at Ecochain to find chemical synonyms is PubChem.
Step 3. Check whether the chemical belongs to a more generic category
Check whether the chemical belongs to a more generic category and can be modeled as such:
Non-ionic surfactant
Ethoxylated alcohol
Organic solvent
Foaming agent
For example, Tween 80, broadly categorized as a Polysorbate, can be modeled as a non-ionic surfactant.
Step 4. Use a generic dataset (chemical organic/chemical inorganic)
Use generic datasets for organic (carbon-containing) or inorganic chemicals such as the “market for chemical, organic | chemical, organic | Global” or “market for chemicals, inorganic | chemical, inorganic | Global” dataset from ecoinvent.
Stoichiometry workarounds
If adopting the abovementioned options is infeasible, the chemicals can be modeled using stoichiometry. For better understanding, an example of pyrogenic silica (SiO2) produced from Silicium tetrachloride (SiCl4) is described in detail.
Step 1: Atom weights of common elements.
Chemical element | Atom weight | Unit |
C | 12,011 | g·mol−1 |
H | 1,008 | g·mol−1 |
O | 15,999 | g·mol−1 |
Cl | 35,453 | g·mol−1 |
Si | 28,086 | g·mol−1 |
Step 2: Determine atom weights (molar masses) of the chemical reaction.
Chemical element | Atom weight | Unit |
Input | - | - |
SiCl4 | 169,898 | g·mol−1 |
2H2 | 4,032 | g·mol−1 |
O2 | 31,999 | g·mol−1 |
Sub-total | 205,928 | g·mol−1 |
Output | - | - |
SiO2 | 60,084 | g·mol−1 |
4HCl | 145,844 | g·mol−1 |
Sub-total | 205,928 | g·mol−1 |
Step 3: Relate atom weights (molar masses) of the chemical reaction to the reference chemical.
Chemical element | Atom weight | Unit | Calculation | Kg chemical /kg pyrogenic silica (SiO2) |
Input | - | - | - | - |
SiCl4 | 169,898 | g·mol−1 | 169,898/60,084 | 2,828 |
2H2 | 4,032 | g·mol−1 | 4,032/60,084 | 0,067 |
O2 | 31,999 | g·mol−1 | 31,999/60,084 | 0,533 |
Output | - | - | - | - |
SiO2 | 60,084 | g·mol−1 | 60,084/60,084 | 1,000 |
4HCl | 145,844 | g·mol−1 | 145,844/60,084 | 2,427 |
Step 4: Correction for yield Assumed yield = 90%.
Chemical element | Atom weight | Unit | Calculation | Kg chemical /kg pyrogenic silica (SiO2) |
Input | - | - | - | - |
SiCl4 | 169,898 | g·mol−1 | 2,828/0,9 | 3,142 |
2H2 | 4,032 | g·mol−1 | 0,067/0,9 | 0,075 |
O2 | 31,999 | g·mol−1 | 0,533/0,9 | 0,592 |
Output | - | - | - | - |
SiO2 | 60,084 | g·mol−1 | - | 1,000 |
4HCl | 145,844 | g·mol−1 | - | 2,427 |
Step 5: Find correct ecoinvent datasets.
SiCl4 = silicon tetrachloride production | silicon tetrachloride | Global
2H2 = chichibabin amination | hydrogen, liquid | Europe
O2 = -
4HCl = market for hydrochloric acid, without water, in 30% solution state | hydrochloric acid, without water, in 30% solution state | Europe
Step 6: Add chemical reaction to Mobius/Helix and put ' minus (-) in front of the property for 4HCl.
This should be done because the system is multifunctional. No allocation should be applied. Instead, the impact of 4HCl should be corrected. This can quickly be done in Mobius or Helix by simply putting a minus (-) in front of the property. This gives -1 kg mass.
A point to note when applying this approach is that the process energy requirement needs to be considered while considering the stoichiometric calculations.
Note: When applying this approach, the process energy requirement must be considered while considering the stoichiometric calculations.
Next Steps
This article provides a systematic approach to help you navigate the process modeling chemicals in LCA. For further assistance, consider exploring additional resources on our help center or contacting us directly. Good luck with your LCA endeavors!
Can’t find a specific plastic, or plastic process? Let us know, by reaching out to the Ecochain Helpdesk!