# Where does the CO2 come from when styrene monomer is made?

Canonical: https://senseible.earth/answers/styrene-monomer-co2-per-tonne

Most styrene is made by dehydrogenating ethylbenzene with superheated steam, so the main source is fuel burned in the steam superheater and boilers. Off-gas burned as fuel adds to it. Count fuel CO2 in Scope 1 and purchased benzene and ethylene in Scope 3.

## Scope 1 sources

- Fuel for the steam superheater, the largest single use.
- Hydrogen-rich off-gas burned as fuel.
- Flaring during start up and upsets.

## Scope 3 sources

- Benzene and ethylene, or bought ethylbenzene.
- Catalyst and chemicals.
- Transport of feedstock.

## Co-products

Toluene and off-gas leave the unit alongside styrene. If you split emissions between them, write down the method and use it every year.

## What Senseible does here

Senseible reads bills, fuel invoices and production records into dated, fingerprinted records, so the figure you send a buyer can be traced to its documents.

- [Steam cracker CO2](https://senseible.earth/answers/steam-cracker-co2-per-tonne-ethylene)
- [Polymer resin factors](https://senseible.earth/answers/polymer-resin-emission-factors-pp-hdpe-pvc)
- [Epoxy resin footprint](https://senseible.earth/answers/epoxy-resin-carbon-footprint-per-kg)

Sources: [IPCC 2006 Guidelines, Volume 2 Energy (fuel defaults)](https://www.ipcc-nggip.iges.or.jp/public/2006gl/vol2.html), [GHG Protocol Corporate Standard](https://ghgprotocol.org/corporate-standard), [GHG Protocol Corporate Value Chain (Scope 3) Standard](https://ghgprotocol.org/corporate-value-chain-scope-3-standard)

Last reviewed 2026-10-22.