This article explains how to find the right dataset for a chemical compound.
Sometimes chemical compounds cannot be found in databases, especially when they are more complex or less commonly used chemicals. How can you choose a fitting reference in this case?
Step 1. Check whether the use of the chemical contributes significantly to your composition or potential impacts (top 5 or top 10 chemicals).
If it has a tiny contribution compared to the entire product, a less accurate approximation is practical, whereas if it is a main component of the product, then a more precise approach is necessary.
Step 2. Check alternative chemical names.
Sometimes chemicals are present in ecoinvent with a different name, for example:
- 2-Aminoethanol = monoethanolamine
- Phenylethane = ethylbenzene
- Esterquats = Quaternary ammonium compounds
- Etc...
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 modelled as such:
- Non-ionic surfactant
- Ethoxylated alcohol
- Organic solvent
- Foaming agent
- Etc…
Step 4. Use a generic reference (chemical organic / chemical inorganic)
Use generic references for organic (carbon containing) or inorganic chemicals such as “market for chemical, organic | chemical, organic | Global” or “market for chemicals, inorganic | chemical, inorganic | Global” reference from ecoinvent.
Alternate option: Stoichiometric modelling
Model the production process of the chemical yourself. This means taking the components required to produce that chemical in the necessary ratio, and adding a production process (incl. % yield) or energy use to it.
See an example of producing pyrogenic silica (SiO2) from Silicium tetrachloride (SiCl4)
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 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 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 and put ' minus (-) in front of 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 easily be done in Mobius by simply putting a minus (-) in front of the property. This gives -1 kg mass.