CO2 capture performance of CaO-based sorbent modified with torrefaction condensate during calcium looping cycles

In this work, the organic acid-rich torrefaction condensate (TC) from biomass torrefaction process was attempted to replace commercial acetic acid (AC) for acidification treatment of CaO sorbent to improve its CO2 capture performance during calcium looping cycles. The results showed that TC-modified sorbents exhibited a much slower carbonation reactivity decay than the AC-modified one over the cycles. According to the results of characterizations (thermal decomposition, morphology, phase composition, and N2 adsorption), the enhanced cyclic stability was probably due to the presence of carbon deposition from the decomposition of heavy tar in TC, which might act as a spacer and protective overlay to slow down the sintering of CaO particles. In addition, more carbon deposition could be dispersed in-situ into the TC-modified sorbents by increasing torrefaction temperature and TC addition amount, resulting in more thorough carbon deposition overlay and better sintering resistance. However, excessive carbon deposition (>50 wt%) leaded to slightly lower carbonation conversions and rates in the first two or three cycles. But this deficiency would disappear in subsequent cycles, as some carbon deposition was consumed by the carbon dioxide released during calcination. And the carbonation conversion of TC-modified sorbent with a carbon deposition content of 69.1 wt% was still as high as 81.5% after 10 cycles.

Automated summary

This study sought to use organic acid-rich torrefaction condensate (TC) as a replacement for commercial acetic acid (AC) in the acidification treatment of CaO sorbent to enhance its CO2 capture performance. The modified sorbents with TC exhibited better cyclic stability compared to the AC-modified ones. The presence of carbon deposition from TC, which acted as a spacer and protective overlay to slow down the sintering of CaO particles, was believed to be the reason for the improved cyclic stability.