For many chemical products the contribution from raw materials is significant. As described earlier, raw materials (upstream production) have to be tracked up to natural resources. All natural resources themselves have a considered carbon footprint of zero. However, emissions from exploration, mining, and processing need to be taken into account.
For the production of chemicals the most important natural resource is crude oil. It is obvious that products further down the production chain like chemical specialties and active ingredients carry a larger fraction of raw material contribution as these have undergone more intensive processing. Even polymers and many crude oil based chemical intermediates typically have fractions of more than 50% originating from raw materials in their cradle- to - gate carbon footprint.
As in energy generation we have again different options to retrieve carbon footprints for raw materials:
• A detailed model of the individual upstream production steps. Basically each step is analyzed like the actual production step including its logistics (next sections). This can become very tedious and almost impossible as many intermediates which serve as raw materials are purchased from spot markets, where it is not possible to trace back production processes and origin.
• Sometimes a supplier can deliver the carbon footprint of his own products. This is a preferable way but consistency with the selected methodologies must be verified and potentially adjusted.
• Many bulk chemicals are listed in databases with their carbon footprints. A list of databases available can be found in . Data can be outdated as it is often based on older public information. Special care needs to be taken when using this data with respect to consistency with the selected methodology, the dependency on the region, site (see Section 188.8.131.52 for energies) and the respective manufacturing process. These parameters are usually documented in the database. Purity can also be of major relevance. The carbon footprint of highly purified substances can be two or three times higher than standard grades.
• Carbon footprint of precursors can also be approximated. This is recommended if data is not available via reliable other sources and tracing back of production processes is impossible or the effort cannot be justified. There are different methods for generating proxies available. Two alternatives are described below:
- Selection of an alternative substance that has a similar carbon footprint and where data is already available. Where necessary corrections can be made.
- Anticipation of a chemical synthesis route to build up the component from substances where data is available. The carbon footprint will then be made up of the footprint of theses substances and an estimation of the energies required for production.
The use of such proxies is usually very inaccurate and also difficult to reproduce. Application should only be done with critical expert judgment and under careful consideration of the conclusions.
Treating bio-based raw materials can become complex and there are again different options available. The topic has been intensively investigated in various studies of the climate footprint of biofuels. The options differ fundamentally in the way, plant growth is handled:
• C02 sequestrated for the growth of the plant can be taken into consideration and credited to the raw material. Meanwhile, technical processes associated with cultivation (e.g., fertilization and release of nitrous oxides) and transportation, as well as the chemical or biochemical processing is regarded as a 'debt' with emissions, similar to exploration and processing of crude oil. The carbon footprint calculated using this approach will mostly result in a negative number for total carbon.
• The CO2 sequestrated in the growth phase is not taken into consideration and the plant's footprint is set to zero. Cultivation and processing are again included. The carbon footprint will result in a positive number as only fossil carbon is accounted for.
Plant growth is a very sensitive issue as it depends highly on the comparison case for the land use. If waste land is used the first option is applicable. If a rainforest is cut down to cultivate plants, the impact on climate change might be debateable. If the origin of the raw material is not exactly known or verified, we recommend a conservative standpoint and assume a carbon footprint of zero for bio-based raw materials. Please also refer to Chapter 12 for a more intensive digression on bio-based materials.
In our example the handling of raw materials is simple as rock salt is a primary resource. Contributions originate from mining which are small. The data for rock salt, sodium carbonate and hydrochloric acid are taken from the GaBi database. The fractions of calcium chloride and sulfuric acid are very small and we use a substitution proxy for illustration purposes (Na2SO4 as another inorganic salt). Climate impact of the raw materials (CML 96 value):
Rock salt: 0.095 kg CO2e/kg rock salt
Sodium carbonate 2 kg CO2e/kg sodium carbonate Hydrochloric acid: 0.082 kg CO2e/kg HCl (30%)
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