Carbon capture using industrial side-streams as absorbents

Licentiate thesis, 2023

Recent predictions about climate change underscore the need to take drastic measures toward more sustainable and environmentally friendly practices. Reducing the emission of greenhouse gases and improving waste management are pertinent to this goal. A resourceful approach for carbon capture is to use industrial alkaline side-streams as absorbents of CO2 which could offer environmental and economic benefits.
Alkaline side-streams are present in many industries, such as paper and pulp manufacturing, iron and steel production and others. Their alkalinity comes from their content in metal oxides or hydroxides. These compounds can react with CO2 towards the formation of carbonates. Carbonation occurs naturally between atmospheric CO2 and earth minerals, at very slow rates. To accelerate this process water can be used as a medium to dissolve the metal oxides and facilitate the interaction between dissolved compounds coming from the industrial side-streams and CO2 from flue gas.
There are many pathways for exploration in this topic, such as the potential of different side-streams to capture CO2 based on their availability and carbon capture capacity, the prospects of utilization for the carbonated products, etc. This work focuses on answering some of these questions for five industrial side-streams. Firstly, an experimental setup was established using aqueous solutions of NaOH as a CO2 absorbent. Following that two side-streams of the paper and pulp industry and three of the steelmaking process were examined. The paper and pulp side-streams were black liquor and green liquor dregs. Black liquor has a high content of NaOH and it exhibited an absorption capacity of 30.8 g of CO2 / L. Green liquor dregs are a solid material rich in CaO and MgO. They were mixed with water at different concentrations and the maximum capture capacity obtained was 18 g of CO2 / L of mixture. Steelmaking slags contain CaO along with other metal complexes. The best-performing steel slag mixture had a maximum capacity of 38.7 g of CO2 / L of mixture.
This work paves the way to study the absorption capacity of more side-streams and offers a solid background upon which the carbonation process could be optimized and tailored to each type of side-stream for the purpose of industrial application.