Abstract
Eucalyptus sp. is the most important planted crop for the production of chemical pulp. This pulp is mostly bleached with chlorine dioxide, which produces hypochlorous acid in situ when reacting with lignin. However, applying hypochlorus acid directly is not practiced, even though it contributes significantly to the bleaching reactions. Therefore, this article presents hypochlorous acid as the main bleaching chemical for oxygen delignified Eucalyptus sp. kraft pulp. The results showed that hypochlorous acid solely decreased the kappa number of the pulp more efficiently than chlorine dioxide did, without increasing the content of adsorbable organic halogens (AOX) in the effluent. The bleaching sequence with hypochlorous acid, ozone and hydrogen peroxide produced fully bleached pulps, with low organically bound halogens (OX) and aerobically digestible effluents. The bleached pulps and digested effluents complied with international standards for the pulp industry. The hypochlorous acid bleaching sequence is appealing because it is short, uses mild conditions and requires less or similar energy to produce the bleaching chemicals than comparable ECF bleaching sequences from literature.
Highlights
Eucalyptus sp. is the most relevant planted crop for the pulp industry
The results showed that hypochlorous acid solely decreased the kappa number of the pulp more efficiently than chlorine dioxide did, without increasing the content of adsorbable organic halogens (AOX) in the effluent
D stage oxidizes lignin structures, which are later solubilized during alkaline extraction (E) (Suess, 2010), and the residual chromophores are removed by a final peroxide bleaching stage (P) giving the pulp good brightness stability. (Suess, 2010) (Dence et al, 1996)
Summary
Eucalyptus sp. is the most relevant planted crop for the pulp industry. It is a highly productive crop, reaching maturity in 10 years (De los Santos, 2016)(Toyssy and UPM Kymmene, 2016). The chloroammonium cation is a stronger oxidant than HOCl (Chenna et al, 2013) This catalytic stage was used in the bleaching sequence HcatZP which provided fully bleached pulp with good viscosity, mechanical properties, and acceptable OX levels of 150 mg OX/ODT pulp, (Afsahi et al, 2019a, 2019b). The reagents for ClO2 production, often including sodium chlorate (NaClO3) (OxyChem, 2018), are transported to the mill There, they react in an acidic environment consuming energy produced by the pulp mill (OxyChem, 2018)(WHO et al, 2002) (Suhr et al, 2015). Industrial Crops & Products 172 (2021) 114004 are aerobically digested and characterized by their Adsorbable Organi cally bound Halogens (AOX), Chemical Oxygen Demand (COD), Total Organic Carbon (TOC) and Biological Oxygen Demand (BOD7)
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