Experimental evaluation of black liquor carbonation for carbon dioxide capture

Abstract

Carbon dioxide is one of the main if not the most potent greenhouse gases responsible for climate change. Scientists put great efforts to tackle this problem and carbon dioxide capture seems to be a promising solution. The present study proposes a novel method of carbon dioxide capture using black liquor, a side stream from the paper and pulp industry. Its content in sodium hydroxide makes it an attractive candidate for carbon dioxide capture via carbonation. The black liquor was prepared from oat husks, a non-woody biomass, using the soda-pulping process. To estimate its carbon dioxide absorption capacity, a mixture of nitrogen and carbon dioxide (70:30%) was sparged into a bubble column reactor and computational fluid dynamics simulations of this setup were used to evaluate the mixing process. The formation of carbonate and bicarbonate ions throughout the carbonation process was followed using a Fourier-Transform Infrared (FTIR) probe and a pH meter. The absorption capacity was measured from the weight increase of the reactor. It was found to be around 30 g of carbon dioxide/L of black liquor. The carbonate and bicarbonate species in black liquor before and after carbonation were further characterized with 13C Nuclear Magnetic Resonance (NMR), X-ray Diffraction (XRD), Scanning Electron Microscope (SEM) and optical microscopy. Using industrial side-streams might enable an economically feasible process without the need for production of virgin absorbents or their recovery. Furthermore, this capturing process, which is performed at atmospheric conditions might reduce the overall energy consumption. The results demonstrated that black liquor could be an attractive absorbent for carbon dioxide, paving the way for a circular and resource-efficient economy.