Use of ozone in ECF bleaching of tropical hardwood (Eucalyptus camaldulensis and Acacia mangium) kraft pulps | |
| Author | Karim, Md. Rezaul |
| Call Number | AIT Diss. no. PP-06-01 |
| Subject(s) | Kraft paper Eucalyptus camaldulensis Acacia |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Technical Science in Pulp and Paper Technology |
| Publisher | Asian Institute of Technology |
| Abstract | The main objective of this research work was to investigate the partial replacement of chlorine dioxide with ozone in the prebleaching of kraft pulps from the most potential wood species, Eucalyptus camaldulensis and Acacia 'mangium, grown in Thailand and Indonesia, respectively. Chips of both wood species were cooked to two different kappa numbers, ca 20 and 15, called high kappa (HK) and low kappa (LK), respectively. After oxygen delignification the kappa numbers of these pulps were about 12 and 8, respectively. In the combined use of chlorine dioxide and ozone two different modes of application, (DZ) and (ZD), were evaluated for both eucalyptus and acacia pulps; (DZ) indicates that chlorine dioxide was charged first and then ozone without washing in between and (ZD) stands for the opposite sequence of chemicals application. Both modes of application were run with 15, 25, 40, 50, 60, 75 and 100% replacements. In all partial replacements the mode (DZ) was found superior to (ZD) in all respects. In the (DZ) mode, 40-50% replacements gave the best results in terms of kappa reduction, hexenuronic acids (Hex A) removal and brightness gain. The bleaching sequence (DZ)EopD₁ where 40% chlorine dioxide was replaced with ozone in prebleaching gave very similar result as reference sequence D₀EopD₁. In the case of both wood species, HK pulps showed better bleachability compared to LK pulps in term of oxygen equivalent (OXE) consumption in bleaching per lignin kappa number. In addition to the combined use of chlorine dioxide and ozone, other related prebleaching options such as a chelation Q stage before Z in the combined use of chlorine dioxide and ozone (DQZ), hot acid treatment before prebleaching, (AhotD₀ or Ahot(DZ)), hot chlorine dioxide treatment (DHT) and hot acid treatment followed by hot chlorine dioxide treatment without washing in between (AhotDHT) were also compared. The overall benefits of these options were not considerable compared to D₀ and (DZ). From the chlorine dioxide consumption point of view, the option Ahot(DZ) was the best among all other options. This option could save more than 40% of total chlorine dioxide consumed by D₀. The options (AhotDHT) and DHT were able to reduce chlorine dioxide consumption only marginally. The replacement of the chlorine dioxide stage in final bleaching with pressurized hydrogen peroxide (PO) was also studied. Brightening with (PO) instead of D₁ produced pulp with higher brightness stability and inferior strength properties. (DZ)EopQ(PO) sequence can save more than 60% of total chlorine dioxide consumed in the reference ECF sequence, D₀EopD₁. A marginal environmental benefit was achieved from the replacement of chlorine dioxide with ozone in (DZ) mode compared to D₀. The COD load was unchanged but a considerable reduction in AOX is assumed because of reduced chlorine dioxide charge in prebleaching. The replacement might be economical in cases where the chlorine dioxide capacity of a mill is a bottleneck and the use of residual oxygen is efficient. If the AOX limit is very low, the (DZ) mode also might be a cost effective option. Eucalyptus pulp with a certain kappa number was found easier to bleach compared to corresponding acacia pulp in term of total chemical consumption per ODt pulp to achieve targeted final brightness |
| Year | 2006 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Pulp and Paper Technology (PP) |
| Chairperson(s) | Malinen, Raimo 0. |
| Examination Committee(s) | Annachhatre, Ajit P.;Vilpponen, Aki;Alen, Raimo |
| Scholarship Donor(s) | Government of Finland |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2006 |