Assessment of limestone treatment with organic acids for CO₂ capture in Ca-looping cycles

The main challenge for CO₂ capture in calcium looping cycles is the decay of CO₂ carrying capacity of the CaO-based sorbents with increasing number of cycles. In this work, limestone was treated with organic acids and tested for CO₂ capture in calcium looping cycles to understand how practical and reliable the treatment is for CO₂ looping capture. The results showed that after 20 cycles the carbonation conversions of limestone treated with acetic acid, vinegar, formic acid, and oxalic acid were 33.1%, 21.1%, 31%, and 35.2%, respectively, compared to 18.9% for untreated limestone. The treatment with organic acids clearly improves the sintering-resistance properties of the modified sorbent. However, the activity of these sorbents was found to decline in similar fashion to that of untreated limestone. It was concluded that although limestone treatment with organic acids enhances CO₂ capture capacity, the enhancement is marginal in most cases while the treatment increases the cost of CO₂ capture significantly. Accordingly, the treatment may not be an adequate approach if the goal is to maintain low-cost capture of CO₂; moreover, treated sorbents which perform well for CO₂ capture do also perform well for SO₂ capture, causing their capacity to decline at least as rapidly as a natural untreated sorbent and often more so.